Dissertations / Theses on the topic 'Industrial Chemistry/Chemical Engineering'

Environmental and industrial systems have been investigated using vibrational spectroscopy. These applications were chosen to demonstrate the potential of vibrational spectroscopy as a means of obtaining molecular information from either in-situ or model environments in a rapid, convenient manner requiring minimal sample handling. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) has been used to investigated two systems in the area of environmental chemistry. Using the characteristic CO stretching bands of the Mn(CO)$ sb3$ fragment, methylcyclopentadienyl manganese tricarbonyl (MMT), an additive to Canadian gasoline, was detected on soils treated with gasoline up to twelve months after exposure. Its longevity on and its interaction with different soils and various substrates was studied. A breakdown of the local symmetry of the manganese tricarbonly moiety suggests a Bronsted-type interaction between the soil and the carbonyl ligands of MMT. The uptake by harbour sediments of two tributyltin species used as marine antifouling agents, was also studied using DRIFTS. Water/sediments ratios and salinity were investigated as factors affecting adsorption. A novel infrared cell for probing the gas-phase infrared spectroscopy (HAGIS) cell was used to study the thermal decomposition products of ethylxanthanate-treated sulphide minerals and those of the related ethylxanthate metal complexes. The gas-phase decomposition products from sulphide minerals treated with ethylxante include $ rm CS sb2, COS, CO sb2, CH sb4, SO sb2,$ ethanol and possibly metal xanthates. The relative amounts of the products depend on the type of mineral surface, the temperature and the atmosphere in the cell. Iron, zinc, lead, nickel and copper ethylxanthate complexes were synthesized, and their thermal decomposition products were also studied by HAGIS. The complexes were classified according to the generation of the primary gas-phase decomposition products. Schemes for the produ

The thesis presents an experimentally validated modelling study of the flow of combustion air in an industrial radiant tube burner (RTB). The RTB is used typically in industrial heat treating furnaces. The work has been initiated because of the need for improvements in burner lifetime and performance which are related to the fluid mechanics of the com busting flow, and a fundamental understanding of this is therefore necessary. To achieve this, a detailed three-dimensional Computational Fluid Dynamics (CFD) model has been used, validated with experimental air flow, temperature and flue gas measurements. Initially, the work programme is presented and the theory behind RTB design and operation in addition to the theory behind swirling flows and methane combustion. NOx reduction techniques are discussed and numerical modelling of combusting flows is detailed in this section. The importance of turbulence, radiation and combustion modelling is highlighted, as well as the numerical schemes that incorporate discretization, finite volume theory and convergence. The study first focuses on the combustion air flow and its delivery to the combustion zone. An isothermal computational model was developed to allow the examination of the flow characteristics as it enters the burner and progresses through the various sections prior to the discharge face in the combustion area. Important features identified include the air recuperator swirler coil, the step ring, the primary/secondary air splitting flame tube and the fuel nozzle. It was revealed that the effectiveness of the air recuperator swirler is significantly compromised by the need for a generous assembly tolerance. Also, there is a substantial circumferential flow maldistribution introduced by the swirier, but that this is effectively removed by the positioning of a ring constriction in the downstream passage. Computations using the k-ε turbulence model show good agreement with experimentally measured velocity profiles in the combustion zone and proved the use of the modelling strategy prior to the combustion study. Reasonable mesh independence was obtained with 200,000 nodes. Agreement was poorer with the RNG  k-ε and Reynolds Stress models. The study continues to address the combustion process itself and the heat transfer process internal to the RTB. A series of combustion and radiation model configurations were developed and the optimum combination of the Eddy Dissipation (ED) combustion model and the Discrete Transfer (DT) radiation model was used successfully to validate a burner experimental test. The previously cold flow validated k-ε turbulence model was used and reasonable mesh independence was obtained with 300,000 nodes. The combination showed good agreement with temperature measurements in the inner and outer walls of the burner, as well as with flue gas composition measured at the exhaust. The inner tube wall temperature predictions validated the experimental measurements in the largest portion of the thermocouple locations, highlighting a small flame bias to one side, although the model slightly over predicts the temperatures towards the downstream end of the inner tube. NOx emissions were initially over predicted, however, the use of a combustion flame temperature limiting subroutine allowed convergence to the experimental value of 451 ppmv. With the validated model, the effectiveness of certain RTB features identified previously is analysed, and an analysis of the energy transfers throughout the burner is presented, to identify the dominant mechanisms in each region. The optimum turbulence-combustion-radiation model selection was then the baseline for further model development. One of these models, an eccentrically positioned flame tube model highlights the failure mode of the RTB during long term operation. Other models were developed to address NOx reduction and improvement of the flame profile in the burner combustion zone. These included a modified fuel nozzle design, with 12 circular section fuel ports, which demonstrates a longer and more symmetric flame, although with limited success in NOx reduction. In addition, a zero bypass swirler coil model was developed that highlights the effect of the stronger swirling combustion flow. A reduced diameter and a 20 mm forward displaced flame tube model shows limited success in NOx reduction; although the latter demonstrated improvements in the discharge face heat distribution and improvements in the flame symmetry. Finally, Flue Gas Recirculation (FGR) modelling attempts indicate the difficulty of the application of this NOx reduction technique in the Wellman RTB. Recommendations for further work are made that include design mitigations for the fuel nozzle and further burner modelling is suggested to improve computational validation. The introduction of fuel staging is proposed, as well as a modification in the inner tube to enhance the effect of FGR.

Thesis (MScEng)--Stellenbosch University, 2002.
ENGLISH ABSTRACT: Can salts present in an aqueous industrial effluent be retained by the [me ash that is produced as a by-product of gasification or by power stations utilising coal as the raw material? In order to answer this question, the actual chemistry that occurs during the mixing and settling process, needs to be understood. At the Sasol Secunda petrochemical plants in South Africa, ash is produced as a byproduct from the gasification of coal, and by the coal-fired power stations (steam plants). The [me portion of the ash (± 50J.lm in diameter) is disposed of through the use of a closed loop wet ash disposal system. The ash is transported as a slurry to the disposal sites (ash darns). The industrial effluent used to transport the ash consists mainly of the recycled ash effluent, known as clear ash effluent (CAE), as well as a variety of process waste streams containing high concentrations of salts. This mixture of ash and water is pumped to ash dams, where the ash is allowed to settle and is therefore separated from the effluent. From the ash darns the effluent flows into evaporation dams, and finally into CAE dams before being returned to the ash plant in Sasol 2 and 3 to be mixed once again with the ash. During this contact time of the ash with the water certain chemical reactions may occur. If one understands what chemical reactions occur during this process, and under what conditions they occur, then it will be possible to utilise the ash disposal system to its full potential, possibly enhancing the salt retention ability. An investigation was thus conducted into what processes actually occurs during the entire ash water contact period. The overall aim of the project was to obtain an understanding of the functioning of the [me ash disposal system so that its efficiency can be improved upon, and furthermore, so that the ash darns can be utilised more effectively in retaining salts. This investigation focussed on the chemical reactions that occur when an industrial effluent is mixed with fine ash, and consisted of four main aspects: • A literature survey on related issues. • An analysis and evaluation of the changes that occur in the actual disposal system. • Laboratory column experiments to investigate, in more detail, the different chemical reactions, which occur during the different stages of the disposal process. • The drilling of boreholes into the ash dams to obtain core material at a variety of depths and locations for analysis purposes. From this investigation it was concluded that salts are retained in the ash dams; based on the results obtained from the laboratory column experiments and the production rate of the fine ash from Sasol 2 and Sasol 3, the potential amount of salts that can be removed from the system (either due to precipitation or water retention in the ash dams) is approximately 95 tons/day. The salts that were found to be most pertinent to the wet ash disposal system utilised at Sasol, Secunda, are Ca, S04, Na, and Cl. Of these, Ca, S04 and Na were identified in literature to be the components most commonly associated with fly ash leachate. The Ca chemistry, which occurs in the ash disposal system, was explored extensively. Is was found that Ca, which is initially present in the fresh fine ash as lime, is leached from the ash into the effluent, where it reacts with carbon dioxide in the atmosphere, and is therefore removed from the system due to the precipitation of calcite. Sodium, S04, and Cl were all found to be retained in the ash; the S04 appears to be retained in a stable form within the ash, not merely due to hydraulic retention, which suggests that the ash system has the potential to act as a salt sink for S04 ions. The mechanism of salt retention in the ash darns was found to be predominantly by means of hydraulic retention, and therefore the salts have the potential to be flushed out of the ash dams into the underlying soil material. However, results from the core drilling exercise revealed that there doesn't appear to be a significant seepage of elements from the ash fill material into the underlying vertisol material. Some components (AI, Fe, Na, K, Mg, Cr, P, Ti and V) from the older, and inactive ash dam, do appear to have percolated into the underlying material. However, a significant amount of water, and therefore salts, are still retained in the ash dam. In terms of the mineralogical composition of the ash dams, a significant difference was observed between the mineral phases present in the ash fill material of an active and an inactive ash dam. Ettringite was detected throughout the borehole drilled into the inactive ash darn, and was not evident at all in the core material from the two boreholes drilled into the active dam, which suggests that this mineral is formed in the ash darns over a long time period. The minerals quartz and mullite were found in the fresh [me ash as well as in most of the core material obtained from the drilling exercise. The mineralogical composition of the ash fill samples, from the boreholes drilled into the centre of the active and inactive ash darns, was found to be very consistent with depth. This finding, combined with the fact that the chemical composition of the core samples varied more significantly in the borehole located near the edge of the active fine ash darn, indicated that the lateral position of the ash in the ash dam influences the chemical reactions that occur. Overall, from this investigation it was concluded that although the chemistry, involved in the mixing of an industrial effluent with fine ash, is extremely complex and site-specific, it is possible to determine the most significant changes which occur within a wet ash disposal system. Besides providing one with a better understanding of the working of the Secunda ash disposal system, the results of this investigation have also provided the framework for future research on this topic and related issues, i.e. the construction of a pilot scale ash darn set-up; further column experiments to investigate the extent to which S04 ions can be removed from the system; the influence of the addition of CO2 to the system; and more extensive core drilling in the vicinity of the ash darns.
AFRIKAANSE OPSOMMING: Kan soute teenwoordig in 'n industriële uitvloeisel teruggehou word in fynas geproduseer as neweproduk van steenkoolkragsentrales? Om 'n antwoord op hierdie vraag te kry, moet die chemiese reaksies wat gebeur tydens die meng en wegdoening van die as en aswater verstaan word. By die Sasol petrochemiese aanlegte in Secunda, Suid Afrika, word fynas geproduseer as 'n neweproduk in die vergassing en die stoomopwekkingprosesse. Die fynas (50)lm diameter) word weggedoen deur 'n geslote nat asstelsel. Die industriële uitvloeisel wat gebruik word vir die vervoer van die as bestaan hoofsaaklik uit hergebruikte aswater (genoem CAE - clear ash effluent), asook 'n verskeidenheid ander prosesafvalstrome wat hoë konsentrasies soute bevat. Die mengsel van as en aswater word in 'n asflodder gepomp na die asdamme, waar die as besink en sodoende geskei word van die waterfase (aswater). Vanaf die asdamme vloei die aswater na verdampingsdamme, en daarna na die CAE damme, vanwaar die CAE weer na die Sasol aanleg teruggepomp word om weer met as gemeng te word. Gedurende die kontak tussen die CAE en as gebeur sekere chemiese reaksies. Indien hierdie reaksies verstaan word, en onder watter toestande dit plaasvind, kan die asdamstelsel tot volle kapasiteit benut word deur moontlik die soutretensie binne die asdam te verhoog. 'n Ondersoek is gedoen om te bepaal watter prosesse plaasvind gedurende kontak tussen die as en water. Die doel van die ondersoek was om 'n beter begrip te kry oor die funksionering van die fynas-wegdoeningstelsel en om te bepaal of die asdamme meer effektiefbedryfkan word om moontlik meer soute te akkommodeer. Die ondersoek het uit vier hoofaspekte bestaan: • Literatuuroorsig, • 'n Analise en evaluering van die veranderinge wat plaasvind oor die asdamstelsel, • Laboratoriumskaal kolomeksperimente om in meer besonderhede die chemiese reaksies wat 'n rol in die aswaterstelsel speel, te bepaal, en • Die boor van toetsgate op die bestaande asdamme om boorkerne te ontleed by bepaalde dieptes en liggings. Uit die ondersoek is bevind dat soute wel in die asdamme behou word. As die kolomtoetse as basis gebruik word, en die produksietempo van fynas vanaf Sasol 2 en 3, dan kan daar 'n potensiële 95 ton soute per dag deur die asstelsel verwyder word (deur hoofsaaklik waterretensie en presipitasie van soute). Die mees prominente soute wat in die Sasol asstelsel voorkom is Ca, S04, Na, en Cl. Vanhierdie soute, is Ca, S04, en Na deur die literatuur geïdentifiseer as komponente wat met vliegas loog geassosieer word. Die Ca chemie, wat in die asstelsel plaasvind, is in besonderhede ontleed. Dit is bevind dat Ca, teenwoordig in die vars fynas as kalk, vanuit die as in die aswater geloog word, waar dit dan met atmosferiese CO2 reageer en dan vanuit die stelselverwyder word deur die presipitasie van kalsiet. Natrium, S04 en Cl word in die as teruggehou. Dit wil voorkom asof die S04 in 'n stabiele vorm in die as teruugehou word, nie net deur die hidrouliese retensie nie en dat die asstelsel dalk as 'n potensiële sink vir S04 kan optree. Die meganisme van soutretensie in die asdamme is hoofsaaklik deur hidrouliese retensie, met die gevolg dat die soute potensieel in die onderliggende grond uitgewas kan word. Die resultate van die boorkernondersoek wys egter dat daar nie beduidende uitwassing van hierdie soute in die grond is nie. Dit wil voorkom of sekere komponente (Al, Fe, Na, K, Mg, Cr, P, Ti en V) van die ou en onaktiewe asdam in die grond geloog is. 'n Beduidende verskil was gevind tussen die minerale fases in die asmateriaal van die aktiewe en onaktiewe asdamme. Ettringiet was teenwoordig deur die hele diepte van die boorkern van die onaktiewe dam, maar was nie teenwoordig in beide boorkerns van die gate op die aktiewe asdam nie. Dit impliseer dat hierdie mineraaloor 'n langer tyd gevorm word. Kwarts en mulliet was deurentyd in al die boorkerne teenwoordig. Die mineralogie van die boorkern van die middel van die aktiewe asdam was baie konstant met diepte (in teenstelling met dié van die boorkern op die kant van die asdam) wat daarop dui dat die laterale posisie van die as in die asdam die chemiese reaksies wat mag plaasvind kan beïnvloed. Die ondersoek bevestig dat alhoewel die chemiese reaksies betrokke in die aswaterstelsel baie kompleks en liggingspesifiek is, die mees beduidende veranderinge wat in die asstelsel plaasvind, wel bepaal kan word. Die ondersoek het benewens 'n beter begrip van hoe die asdamme reageer, ook 'n raamwerk gegee vir verdere navorsing in hierdie veld, bv. die bou van 'n loodsskaal-asdam, verdere kolomtoetse om die vermoë van die asstelsel om S04 ione te verwyder te bepaal en die invloed van gemanipuleerde kalsiet presipitasie deur die byvoeging van CO2.

Les oxydes d'azote (NOx) sont responsables de la plupart des problèmes liés à l'environnement tels que le processus de formation de l'ozone troposphérique et le phénomène des pluies acides. Parmi les procédés de dénitrification mis en place par les industriels, les technologies de Recombustion et de Réduction Sélective Non Catalytique (RSNC), qui utilisent respectivement des hydrocarbures et des composés azotés (l'ammoniac, l'urée, ou l'acide cyanurique) comme agents réducteurs, présentent des avantages très attractifs. Ces techniques sont performantes, relativement simples à mettre en œuvre, et ne nécessitent qu'un faible coût d'investissement. L'objectif de ce travail consiste à étudier les influences des principaux paramètres de fonctionnement d'une installation sur la performance de réduction de NO des procédés de Recombustion et de RSNC en utilisant respectivement le méthane (CH4) et l'ammoniac (NH3) comme agent réducteur. Les études paramétriques de réduction de NO ont été réalisées sur un réacteur de type piston à l'échelle du laboratoire. Les effluents gazeux sont analysés par spectroscopie d'absorption Infrarouge à Transformée de Fourrier (IRTF). Les principaux paramètres de fonctionnement tels que la température des fumées, le temps de passage, la concentration initiale en NO dans les fumées et la quantité d'agent réducteur injecté ont été analysés. Le procédé de Recombustion par le méthane est une approche très efficace. Dans nos conditions expérimentales un taux de réduction maximal de NO proche de 90% a été obtenu. La performance du procédé est étroitement liée à la valeur des principaux paramètres de fonctionnement utilisés comme : la température de fumées, le facteur de richesse de la zone de Recombustion, le temps de passage moyen et la concentration initiale en NO. Selon les conditions expérimentales, une compétition entre deux processus chimiques peut se produire : la réduction de NO par Recombustion et la formation de NO via le mécanisme du NO-précoce. Les résultats expérimentaux obtenus ont été comparés à ceux issus de la modélisation par le code de calcul SENKIN-CHEMKIN II en utilisant quatre mécanismes de référence : GDF-Kin®3.0_NCN (El Bakali et col., 2006), Glarborg (Glarborg et col., 1998), GRI3.0 (Smith et col., 1999) et Konnov (Konnov et col., 2005). En utilisant l'ammoniac NH3 comme agent réducteur, un taux de réduction proche de 80% a été obtenu dans nos conditions optimales pour le procédé RSNC. L'étude de l'influence des paramètres de fonctionnement a montré que sous certaines conditions opératoires, une compétition entre le processus de formation de NO par l'oxydation de NH3 et la réduction de NO par RSNC pouvait se produire. Plusieurs composés chimiques tels que CH4, C2H2, C2H4, C2H6, CH3OH, C2H5OH, CO et H2 ont été évalués comme additifs au procédé RSNC. L'utilisation de ces additifs conduit à un décalage de l'ordre de 100 K de la fenêtre optimale de température pour le procédé de réduction. D'autre part, l'addition de ces composés permet également d'améliorer très sensiblement le taux de réduction de NO pour les températures de fumées les plus basses. Le mécanisme cinétique détaillé de Coda Zabetta et Hupa (2008) a été modifié et optimisé par rapport à nos conditions expérimentales. Il permet de prédire correctement l'effet des additifs étudiés sur la performance du procédé RSNC. Une analyse cinétique permet également d'expliquer l'effet de ces additifs sur la réduction de NO par l'ammoniac.

Several chemical industries in Canada discharge untreated effluents containing substantial amounts of organic pollutants. Environmental concern regarding the pollution of water bodies has led the authorities to issue stringent regulations with respect to the quality and quantity of wastewater that can be discharged. Chemical characterization and biotreatability of some waste streams generated by a chemical industry in Quebec was therefore undertaken. The study showed that two highly concentrated effluents were amenable to biological treatment. The first effluent, "plastifiant", was generated from the production of plastics, while the second, "colonne", was the product of a resin distillation column. Batch assay tests, including biochemical methane potential (BMP) and anaerobic toxicity assay (ATA), showed a moderate degree of anaerobic treatability with soluble COD removals of 45 to 61% and 11 to 67% for the colonne and plastifiant, respectively. Percentage COD removal was found to vary depending on the source of seed sludge. A mixture of biomasses from different sources was shown to be preferable for the anaerobic degradation of both effluents. The colonne effluent did not exhibit any toxicity to methanogenic bacteria. Inhibition of anaerobic microorganisms from the plastifiant effluent was found to be directly proportional to the increase in concentration, indicating that this effluent should be diluted. Continuous flow studies revealed that the selected effluents could be treated by anaerobic, aerobic or sequential anaerobic-aerobic techniques with soluble COD removals of 58, 80 and 89%, respectively. A significant impact of the type of anaerobic sludge and operating parameters with respect to the extent of biological treatment was noted, suggesting that the treatment efficiencies can be further improved. The one-step anaerobic or aerobic process was found to be applicable as a pre-treatment, while for a full treatment and direct discharge into receiving water

Includes abstract.
Includes bibliographical references.
Industrial wastewater contains many soluble inorganic and organic components and solid particles. This study focused on inorganic industrial hypersaline brines. Chemical engineering presents a variety of mechanical, thermal, biological and chemical processes capable of treating hypersaline brines to the standard required by legislation. However, some of these technologies are inefficient, costly and outdated and are not applicable in solving modern brine accumulation problems.

Includes sysnopsis.
Includes bibliographical references (p.93-106).
This thesis aims to demonstrate the application of industrial ecology (IE) theory to understand environmental sustainability problems relating to the accumulation of saline wastes and to study the potential for integrated technology interventions which take multi-party engagements and effects into account.

South African industries are currently generating increasing quantities of hypersaline brine streams. These wastewater streams need to be processed in an ecologically friendly and economically favourable method to produce both purified water and salts.

Bibliography: leaves [95]-99.
Previous reports identified selective catalytic hydrogenation as a possible route to the purification of industrial 1-hexene streams. Even so, reported performance has been poor and, consequently, the principal aim of this study is to adjust operating conditions so as to improve process performance to an industrially interesting level. In particular, the influence of hydrogen excess and competitive adsorbates (CO and ethanol) on overall process performance is evaluated for representative (1,5-hexadiene and 1-hexyne) impurity removal from a 1-hexene stream over a bi-metallic Pd-Ag/titania catalyst.

Bibliography: leaves [95]-99.
Previous reports identified selective catalytic hydrogenation as a possible route to the purification of industrial 1-hexene streams. Even so, reported performance has been poor and, consequently, the principal aim of this study is to adjust operating conditions so as to improve process performance to an industrially interesting level. In particular, the influence of hydrogen excess and competitive adsorbates (CO and ethanol) on overall process performance is evaluated for representative (1,5-hexadiene and 1-hexyne) impurity removal from a 1-hexene stream over a bi-metallic Pd-Ag/titania catalyst.

The primary theme of this research was the characterisation of new and novel organo-tellurium complexes, using the technique of single crystal X-ray analysis to establish more firmly the various coordination modes of tellurium. In each study the unit cell dimensions and intensity data were collected using an Enraf-Nonius CAD-4, four circle diffractometer. The raw data collected in turn was transferred to the Birmingham University Honeywell Multics System and processed using the appropriate computer packages for the determination of crystal structures. The molecular and crystal structures of: bis[2-(2-pyridyl)phenyl]tritelluride, bis[2-(N-hydroxy)iminophenyl] ditelluride, 2-(2-pyridyl)phenyltellurium(IV) tribromide, (2-N,N-dimethylbenzylamine-C,N')tellurium(IV)tribromide, 2-dichloro(butyl)tellurobenzaldehyde, 2-dichlorobutotelluro-N-dimethylbenzyl ammonium chloride, dimethyldithiocarbamato[2-(2-pyridyl)phenyl]tellurium(II), dimethyldithiocarbamato[2-(2-quinolinyl)phenyl]tellurium(II) and para-ethoxypheny[2-(2-pyridyl)phenyl]telluride are described. In each structure, the Lewis acidity of tellurium appears to be satisfied by autocomplex formation, through short-range intramolecular secondary bonds between tellurium and an electron denoting species, (generally nitrogen in these structures) with long range weak inter molecular contacts forming in the majority of the tellurium(IV) structures. The order of Lewis acidity in each structure can be considered to be reflected by the length of the short range intramolecular secondary bond, identified, that is, when tellurium has a low Lewis acidity this interaction is long. Interestingly, no primary bonds are found trans to a Te-C covalent bond in any of the above structures, highlighting the strong trans effect of aromatic and aryl groups in tellurium complexes.

Includes abstract.
Includes bibliographical references (leaves 79-82).
Linear alpha-olefins, including 1-hexene, are used mainly as co-monomers in the production of polymers. The very low tolerance of the polymerisation catalyst to highly unsaturated impurities makes removal of these impurities from the olefin feedstock crucial. In South Africa, linear alpha-olefins are a major product of Fischer-Tropsch synthesis. A complex extractive distillation process is used to separate impurities from the product stream. A final polishing step by adsorption results in a significant loss of valuable alpha-olefin.

Bibliography: pages [201]-212.
Solids suspension and gas dispersion studies were performed on a total of 40 industrial flotation cells of various types, sizes and duties in a Platinum Group Metal (pgm) concentrator in the North West Province of South Africa. The wide variety of cells studied included a Bateman 3-m³ cell, Outokumpu 16-m³ conventional and 50-m³ TankCells, WEMCO 84, 120, 144 cells and WEMCO 144 with 164 mechanism and high-power motor. The gas phase properties of bubble size, superficial gas velocity, air holdup and bubble surface area flux were used in characterising these cells. The bubble size was measured at six different locations in the cells using the UCT Bubble Size Analyser. The superficial gas velocity and gas holdup were measured similarly with other special designed devices. The bubble surface area flux, a new parameter for characterising the hydrodynamics and gas dispersion in flotation cells, was calculated from the ratio of the superficial gas velocity to the Sauter mean bubble size. The results of these measurements were analysed in terms of key variables including air flowrate, impeller speed and location in the cell. The bubble size was found to increase with increasing air flowrate and decreasing impeller speed. Bubbles in the impeller zone were found to be smaller than bubbles in the quiescent zone due to significant bubble coalescence in this region. The bubble size was also found to be inversely related to the power consumption provided that this was expressed on an impeller-swept-volume basis. The superficial gas velocity was found to increase with increasing air flowrate and impeller speed and was significantly affected by location in the cell. Differences in superficial gas velocities were observed at constant air flowrates and at different impeller speeds. This unexpected finding was attributed to differences in flow patterns in the cells. Air holdup was found to be largely insensitive to changes in air flowrate and impeller speed in cells operating at their normal conditions. Differences in air holdup in the quiescent and turbulent zones were observed but these were more noticeable in smaller cells. The bubble surface area flux in industrial flotation cells was found to be in the range of 50-60 m²/m²/s irrespective of the type, size and duty of cell. However, it was observed that the bubble surface area flux could be varied by manipulating certain key cell variables such as the impeller speed and the air flowrate. The bubble surface area flux was found to increase with increasing air flowrate until reaching an optimum at sufficiently high air flowrates.

An investigation of biohydrogen production from glucose by Clostridium beijerinckii was conducted in a synthetic wastewater solution. A study examining the effect of initial pH (range 5.7 to 6.5) and COD loading (range 1 to 3 g/L) on the specific conversion and hydrogen production rate has shown interaction behaviour between the two independent variables. Highest conversion of 10.3 mL H2/(g COD/L) was achieved at pH of 6.1 and COD of 3 g/L, whereas the highest production rate of 71 mL H2/(h*L) was measured at pH 6.3 and substrate loading of 2.5 g COD/L. In general, there appears to be a strong trend of increasing hydrogen production rate with an increase in both substrate concentration and pH. Butyrate (14% to 63%), formate (10% to 45%) and ethanol (16% to 40%) were the main soluble products with other volatile fatty acids and alcohols present in smaller quantities. Absence of the key nutrients biotin, MgSO4.7H2O and FeSO4.7H2O caused a significant decrease in hydrogen yield when compared to the results obtained under standard synthetic wastewater conditions, though no significant difference was observed when concentrations of biotin, MgSO4.7H2O, K2HPO4, KH2PO4, were decreased partially. Preliminary experiments with wastewater effluent obtained from a yogurt manufacturer gave poor biohydrogen production.
Ce projet de recherche porte sur la production de biohydrogène par le Clostridium beijerinckii en utilisant comem subtrat le glucose contenu dans une eau usée synthétique. Une étude de l'effet du pH initial (intervalle de 5.7 à 6.5) et de la charge organique (intervalle de DCO de 1 à 3 g/L) sur la conversion spécifique et le taux de production d'hydrogène a démontré des interactions entre ces deux variables indépendantes. La conversion la plus élevée, 10.3 mL H2/(g COD/L), a été observée à un pH de 6.1 et une DCO de 3 g/L alors que le plus haut taux de production, 71 mL H2/(h*L), a été obtenu à un pH de 6.3 et une DCO de 2.5 g/L. La tendance globale indique que le taux de production d'hydrogène augmente lorsque la charge organique et le pH augmentent. Le butyrate (14% à 63%), le formate (10% à 45%) et l'éthanol (16% à 40%) formaient les principaux produits solubles. Des acides gras volatiles et des alcools ont également été observés en faibles quantités. L'absence de nutriments essentiels tels que biotine, le MgSO4.7H2O et le FeSO4.7H2O a causé une diminution significative de la production d'hydrogène comparativement aux résultats obtenus à l'aide des conditions de référence utilisées pour la solution d'eau usée synthétique. Aucun impact significatif n'a toutefois été observé lorsque la concentration de ces nutriments était diminuée que partiellement. Des essais préliminaires à partir d'eau usée provenant d'une usine de production de yogourt ont indiqué une faible production d'hydrogène à partir de ce substrat.

This dissertation contains simulations of chemical catalysis in both biological and heterogeneous contexts. A mixture of classical, quantum, and hybrid techniques are applied to explore the energy profiles and compare possible chemical mechanisms both within the context of human and bacterial enzymes, as well as exploring surface reactions on a metal catalyst. A brief summary of each project follows.

Project 1 - Bacterial Enzyme SpvC

The newly discovered SpvC effector protein from Salmonella typhimurium interferes with the host immune response by dephosphorylating mitogen-activated protein kinases (MAPKs) with a β-elimination mechanism. The dynamics of the enzyme substrate complex of the SpvC effector is investigated with a 3.2 ns molecular dynamics simulation, which reveals that the phosphorylated peptide substrate is tightly held in the active site by a hydrogen bond network and the lysine general base is positioned for the abstraction of the alpha hydrogen. The catalysis is further modeled with density functional theory (DFT) in a truncated active-site model at the B3LYP/6-31 G(d,p) level of theory. The truncated model suggested the reaction proceeds via a single transition state. After including the enzyme environment in ab initio QM/MM studies, it was found to proceed via an E1cB-like pathway, in which the carbanion intermediate is stabilized by an enzyme oxyanion hole provided by Lys104 and Tyr158 of SpvC.

Project 2 - Human Enzyme CDK2

Phosphorylation reactions catalyzed by kinases and phosphatases play an indispensable role in cellular signaling, and their malfunctioning is implicated in many diseases. Ab initio quantum mechanical/molecular mechanical studies are reported for the phosphoryl transfer reaction catalyzed by a cyclin-dependent kinase, CDK2. Our results suggest that an active-site Asp residue, rather than ATP as previously proposed, serves as the general base to activate the Ser nucleophile. The corresponding transition state features a dissociative, metaphosphate-like structure, stabilized by the Mg(II) ion and several hydrogen bonds. The calculated free-energy barrier is consistent with experimental values.

Project 3 - Bacterial Enzyme Anthrax Lethal Factor

In this dissertation, we report a hybrid quantum mechanical and molecular mechanical study of the catalysis of anthrax lethal factor, an important first step in designing inhibitors to help treat this powerful bacterial toxin. The calculations suggest that the zinc peptidase uses the same general base-general acid mechanism as in thermolysin and carboxypeptidase A, in which a zinc-bound water is activated by Glu687 to nucleophilically attack the scissile carbonyl carbon in the substrate. The catalysis is aided by an oxyanion hole formed by the zinc ion and the side chain of Tyr728, which provide stabilization for the fractionally charged carbonyl oxygen.

Project 4 - Methanol Steam Reforming on PdZn alloy

Recent experiments suggested that PdZn alloy on ZnO support is a very active and selective catalyst for methanol steam reforming (MSR). Plane-wave density functional theory calculations were carried out on the initial steps of MSR on both PdZn and ZnO surfaces. Our calculations indicate that the dissociation of both methanol and water is highly activated on flat surfaces of PdZn such as (111) and (100), while the dissociation barriers can be lowered significantly by surface defects, represented here by the (221), (110), and (321) faces of PdZn. The corresponding processes on the polar Zn-terminated ZnO(0001) surfaces are found to have low or null barriers. Implications of these results for both MSR and low temperature mechanisms are discussed.

Thesis (M. Eng. in Logistics)--Massachusetts Institute of Technology, Engineering Systems Division, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 60-62).
The chemical industry is a highly competitive and low margin industry. Chemical transportation faces stringent safety regulations meaning that Cost-To-Serve (C2S), costs associated with products net flow from manufacturers to customers, consists of a big percentage of the delivered product cost. Supply chain practitioners in this industry need to make key logistics decisions to minimize C2S for profitability and business sustainability. In this thesis, we present a network optimization model to minimize the total C2S for SKU-1, a low volume and low margin industrial chemical with a customer base spread across North and South America. We use a mathematical linear program to investigate the effects on total C2S when available production capacities and sources are shifted. We develop the model as a minimum cost flow problem, and more specifically, as a production and transportation problem (PTP). We analyze the total C2S under three scenarios. In the baseline scenario there are three manufacturing facilities in the Midwest, South East, and Europe. In the second scenario, where the Midwest supplier is excluded from the network, the C2S increases by 3%. In the third scenario, where both the Midwest and South East facilities are excluded, the C2S increases by 13%. Under each scenario we calculate the C2S for each individual customer and identify the customers most impacted by the change in supply. Our results provide insight regarding the changes expected to the supply network under capacity constraints and how those changes may affect the profitability of individual customers.
by Fred Dacha and Li Jin.
M.Eng.in Logistics

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Desulfurization of fossil fuels with supercritical water (SCW) has been the topic of many studies over the past few decades. This process does not require the use of any catalyst, eliminates the need for a hydrogen feed, and minimizes coke formation. Previous research has shown that it has the potential to be a viable commercial process, and recent experimental studies have proven that water acts as one hydrogen source for sulfur removal in this process. However, the exact desulfurization mechanism is largely unknown, as are many other reaction mechanisms involving sulfur compounds. Recent work has greatly expanded our ability to build comprehensive reaction mechanisms automatically for the decomposition of organic sulfur compounds using the automated Reaction Mechanism Generator (RMG). This thesis presents the implementation of this and other tools to investigate chemical processes relevant to our use of fuel sources containing sulfur compounds, and it shows some steps that have been taken to improve our predictions for these mechanisms and those that will be generated in the future. Previous investigations had focused on the pyrolysis of small sulfur compounds containing less than six heavy atoms, so RMG is first used to study the pyrolysis of t-butyl sulfide. A detailed reaction mechanism is then presented for the SCW desulfurization of hexyl sulfide. Comprehensive kinetic mechanisms for these larger molecules are likely to include thousands of reactions, so RMG builds this model in a systematic and unbiased way using a database of ab initio data. This database is expanded with potentially relevant thermochemical and kinetic parameters using transition state theory and quantum chemical calculations at the CBS-QB3 and CCSD(T)-F12 levels of theory. With these data, as well as previously calculated rates for hydrocarbon and sulfur kinetics, RMG is used to build a reaction mechanism for the conversion of hexyl sulfide to hydrogen sulfide, pentane, and carbon monoxide in the presence of SCW. This mechanism is validated with results from batch and flow reactor experiments, and predictions are accurate within a factor of two for reactant and major product concentrations. Analysis of the proposed mechanism shows that the molecular addition of water to the carbonsulfur double-bond in hexanethial is a key step in the SCW process, as this not only leads to the desulfurization of the compound, but also prevents the thioaldehyde from undergoing addition reactions with other hydrocarbons in a process that could eventually form coke. Thus, this work not only has implications in the SCW desulfurization process, but in the overall crude oil upgrading process as well. The calculated kinetic and thermochemical parameters are used to generate predictive reaction mechanisms for other processes relevant in fuel chemistry, such as the geological formation of oil and gas from kerogen. This not only allows us to model experimental work investigating the effect sulfur compounds have on the oil-to-gas process, but we also explore how these effects differ at geological conditions and timescales. And as the possible applications of RMG grow, the need for accurate parameters in mechanism generation become even more critical. A thermochemical database is generated for a wide variety of sulfur compounds using the highaccuracy CCSD(T)-F12/cc-pVTZ-F12 method, and this provides a basis for the investigation of organosulfur chemistry with tighter uncertainty.
by Caleb Andrew Class.
Ph. D.

Various technical lignins, e.g. industrial Softwood Kraft lignin (SKL), are now largely available while they are generally underutilized due to their heterogeneous and complicated structures and/or the poor properties. SKL has here been modified by physical, chemical and biochemical methods for preparation of lignin microspheres, phenol substitution in phenol-formaldehyde (PF) resin preparation and preparation of highly efficient fertilizers. Physically, a brand-new slow and exhaustive solution evaporation process was developed for the highly efficient and productive preparation of microsphere structures. Highly homogenous SKL hollow microspheres were obtained and for the first time, urea encapsulating SKL microspheres were similarly prepared which could be an excellent controlled release urea fertilizer. Chemically, Mannich reaction (one type of amination) was deeply investigated by including for the first time an LC-MS study of vanillin reaction, resulting in the establishment of a fast and reliable lignin reactivity (for phenol substation in PF resin) quantification method. In addition, SKL was functionalized using the Mannich reaction or esterification, leading to an improved hydrophobicity and compatibility for blending with polylactic acid (PLA). Using dip-coating technique for the first time, PLA-functionalised SKL-coated urea pellets were prepared, leading expectedly to a highly efficient urea fertilizer with simultaneous controlled- and slow- release and biological stabilization effects. Biochemically, SKL was demethylated via incubation with different laccase-mediator combinations, which in principle will increase its reactivity in PF resin preparation. However, polymerization occurred which would decrease the reactivity.  The overall effects need to be further investigated. Conclusively, broader or larger scale SKL applications can expectedly be realized after the development of SKL modifications tailored towards the optimum desired structures and properties.

QC 170912

The Anglo Research Nickel (ArNi) process is a novel extractive metallurgical process that arose out of the need to develop a processing route for the recovery of nickel from lateritic ore deposits that is both economical and environmentally acceptable.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2019
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 131-138).
Due to the rise in demand of crude oil over the long term, technologies to upgrade crude oil need to be developed to ensure maximum use efficiency of future oil sources. In typical carbon rejection processes, coke formation is a common phenomenon that would lead to decreased yield of upgraded oil. As a result, the chemical behavior of coke formation is a potent area of research. Due to the high complexity of the composition of crude oil and coke, this work simplifies the study of supercritical water upgrading of crude oil to a hexylbenzene pyrolysis system. The pyrolysis of hexylbenzene at process conditions of 450°C and 75 creates several hundred products resolved by GCxGC, and the analysis is intractable if one considers only the experimental data, which does not reveal reactive intermediates or reaction paths.
However, introducing theoretical considerations using the Reaction Mechanism Generator (RMG) allows analysis of a vast number of species while retaining information of elementary reaction steps and reactive intermediates. Information on these steps and intermediates can be obtained from Quantum Chemistry Hexylbenzene pyrolysis was characterized using RMG with key steps computed using Quantum Chemistry. The results indicate that the retro-ene reaction, previously thought to carry an important role in hexylbenzene pyrolysis, is much slower than reported in literature. Furthermore, alkylaromatic chemistry at 450°C is extremely sensitive to species thermochemistry. Further investigation was done on the formation of 2-ring aromatic species in hexylbenzene pyrolysis, likely precursors of coke.
Thermochemistry and rate calculations were made for 2-ring species as a result of the intramolecular and intermolecular addition pathways, resulting in 27 thermochemistry group additivity values to allow for extrapolation of this work's calculations to analogous species. In addition, 25 training reactions were added to allow rate rules calculated in this work to be extrapolated to similar reactions. Finally, all this new chemical knowledge was incorporated into RMG, and a detailed kinetic model for hexylbenzene pyrolysis was constructed. The generated model was able to predict the total molar yield of bridged 2-ring aromatics, and fused 2-ring aromatics. However, many individual species had inaccurate molar yield predictions, and some key pathways to form 2-ring species were found to be missing. Additional quantum calculations were performed after the construction of this kinetic model to attempt to resolve these mispredictions.
by Lawrence Tin Chi Lai.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Chemical Engineering

Includes abstract.
Includes bibliographical references (leaves 128-133).
A feasibility study for the application of reset control to the temperature control loop of a pressurized exothermic batch leach reactor in the hydrometallurgical Precious Group Metals (PGM) industry is carried out. Keywords: Reset control; Clegg integrator; initial states; industrial batch reactor; temperature control; exothermic reactions; multiple reactions; dissolve; leach; hydrometallurgy; platinum; Precious Group Metals (PGMs).

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2016.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 79-85).
Flow chemistry is becoming an accepted method of continuous synthesis with its considerable advantages over batch chemistry, such as smaller infrastructure, faster production, and safer operation for aggressive reactions or extreme conditions. However, to realize the full benefits of flow chemistry in multi-step reactions, continuous work-up techniques are needed. They will eliminate intermediate batch work-up steps that are often inefficient and time-consuming. This thesis describes the development of continuous liquid-liquid extraction and evaporation techniques along with their integration in multistep reaction sequences and purification on the mL/min scale. Fully-integrated syntheses for active pharmaceutical ingredients (APIs), lidocaine and fluoxetine, were studied in detail. These two examples represent two different strategies for integrating multistep reactions. Sequential reactive steps in the lidocaine synthesis were designed to be compatible without any separation, while in-line purification, liquid-liquid extraction, was required for the fluoxetine synthesis. The key outcome of this work was the construction of a compact, reconfigurable system for manufacturing four different APIs, at throughput of hundreds to thousands dosages per day. The system represents a significant advance in continuous manufacturing by demonstrating feasibility of facility decentralization and on-demand production. Another significant accomplishment of this thesis is the development of multistage liquid-liquid extraction using liquid-liquid membrane-based separators that enable highly efficient continuous extraction. While previous efforts have demonstrated a single stage or, at most, a few stages in crosscurrent configuration, the objective was to build a countercurrent extraction setup in the context of laboratory scale (i.e. mL/min). The setup was made possible with an integrated pressure control element, allowing non-precise interstage pumping to be employed. This setup was found effective for a wide range of industrially-relevant applications, from multicomponent solvent recovery to in-line removal of phase transfer catalysts. The thesis provides opportunities for future directions. For example, improvement in unit operations, such as pumping, solid handling, evaporation, and process control, will be needed to reach the potential of flow synthesis. The countercurrent extraction setup can be automated for faster screening and optimization of extraction conditions as well as be applied to complex processes, such as reactive extraction and enantioseparation.
by Nopphon Weeranoppanant.
Ph. D.

Atmospheric aerosols have significant impact on the chemical balance of the atmosphere, biogeochemical cycles, the Earth's climate and human health. Although extensive studies have been performed to explore these effects, there is still considerable uncertainty regarding the global impacts of atmospheric aerosols. For example, understand heterogeneous photochemistry on aerosols may be crucial to accurately predict the impact of aerosol loadings on atmospheric chemistry, yet few studies have been conducted. In this dissertation research, laboratory studies were performed to investigate heterogeneous photoreactions of HNO3 and O3 on typical components of metal containing aerosols. Results indicate that the presence of irradiation has the potential to change the reaction mechanism, kinetics, reaction extent, products, and product partitioning. The presence of water at different relative humidity also plays a key role in the rates of these reactions and the product distribution. Increasing evidence has suggested that anthropogenic aerosols play a more important role in supplying soluble iron into open ocean water compared with mineral dust. Dissolution experiments to simulate atmospheric processing were performed to compare iron mobilization abilities of coal fly ash with Arizona test dust, a model for mineral dust aerosol. Results indicate that coal fly ash spheres, which is mainly composed of aluminosilicate glass, are unstable and disintegrate into irregular fragments during simulated cloud processing. The disintegration of spherical fly ash facilitates the release of iron and thus iron mobilization. In contrast, aluminosilicate mineral as the main component of Arizona test dust is relative stable and thus shows no significant change of morphology during simulated atmospheric processing. The iron solubility strongly depends on the source material, surface pH, types of acidic media, and the presence of solar irradiation. Heavy metals in the environment have a negative effect on human health. A study on Pb mobilization from PbO particles following exposure to NO2 shows interaction of PbO particles with NO2 leads to an increase in Pb dissolution. These results point to the potential importance and impact that heterogeneous chemistry with trace gases can have on increasing solubility and therefore the mobilization of heavy metals such as lead in the environment. Furthermore, as a transition metal, iron is capable of generating reactive oxygen species and contributing to oxidative stress. Collaboration work indicates that size and surface area of iron nanoparticles play a role in affecting bacteria growth, pathogenicity, and impairing the AMP activity. Nanoparticles, especially the smaller particles with large surface areas, may be harmful to human health as it relates to individuals susceptible to bacterial infections and/or colonization. This thesis summarizes the above studies in Chapter 3 to Chapter 7. The research described herein provides a number of important issues where further studies are warranted. The last chapter suggests future directions for laboratory studies that have the potential to make an important contribution on understand the global impacts of atmospheric aerosols and heterogeneous chemistry.

An increasing demand exists for the treatment of hypersaline industrial wastewaters such as those from the shale gas industry, seawater desalination plants, and thermoelectric power-generating facilities. Membrane distillation (MD) is an emerging thermal-based desalination process, which can potentially treat hypersaline industrial wastewaters by exploiting low-grade or waste heat. High performance MD membranes are the key to the advancement and further commercialization of this emerging desalination technology. This research aims at (i) developing novel MD membranes with special surface wettability using advanced materials and surface engineering techniques and (ii) gaining fundamental understanding of the scaling and fouling mechanisms of the newly developed MD membranes.

Engineering the wettability of materials and interfaces can effectively be leveraged to membrane fabrication. Omniphobic membranes that resist wetting from both water and oil can extend MD applications for desalination of emerging high-salinity wastewaters containing diverse low surface tension contaminants. Fundamental understanding of interfacial phenomena and relating such knowledge to membrane surface wettability are crucial to improving omniphobic MD membrane design and performance. This work elucidates the factors that determine surface omniphobicity of microporous membranes and evaluates the potential application of these membranes in desalination of low surface tension wastewaters by membrane distillation. Specifically, the effects of surface morphology and surface energy on membrane surface omniphobicity were systematically investigated by modifying a prototype glass fiber substrate with silica nanoparticles and fluoroalkylsilane. A re-entrant structure, defined as a nanoscale architecture with increased air to solid ratio, developed by the spherical silica nanoparticles was found to play a critical role in rendering the membrane surface omniphobic,

Electrospinning is a promising and versatile technique to fabricate omniphobic membranes, because electrospun nanofibers with cylindrical shape feature a re-entrant structure and could be further engineered for additional levels of re-entrant structures. This work presents a facile approach to fabricate a robust omniphobic membrane by exploiting the versatility of electrospinning, which allows the preparation of a nanofiber scaffold with targeted physical and chemical properties. The fabricated electrospun omniphobic MD membranes were evaluated in terms of wetting resistance to various low surface tension liquids and desalination performance with feed solutions of varying surface tensions.

Microporous polyvinylidene fluoride (PVDF) membranes have been widely used for MD applications because of their hydrophobic nature, excellent chemical compatibility, and facile processability. However, application of conventional hydrophobic PVDF membranes in MD is limited due to their susceptibility to wetting and fouling by low surface tension contaminants. This study presents scalable surface engineering of a conventional hydrophobic PVDF microporous substrate to produce an omniphobic membrane. Desalination performance of the fabricated omniphobic membrane was evaluated in direct contact membrane distillation with synthetic wastewaters containing low surface tension contaminants, including surfactants and mineral oil. The performance of the fabricated omniphobic membrane with produced water from the shale gas industry was further examined to highlight its potential application in desalinating complex, high salinity industrial wastewaters.

The performance of MD systems is hampered by fouling and inorganic scaling, particularly when a system treats hypersaline industrial wastewaters with high levels of total dissolved solids and organic matter. This dissertation research investigated fouling and scaling mechanisms of omniphobic membranes, focusing on the impact of surface chemistry. The omniphobic membranes were fouled by hydrophobic, low surface tension contaminants via attractive interactions, but further adsorption into the pores was prevented by a thermodynamic barrier created by a re-entrant structure, which sustains a metastable non-wetting condition. Also, the non-adhesive and slippery surface nature of the omniphobic membrane was shown to delay both homogeneous and heterogeneous nucleation, demonstrating its potential for a high recovery MD system to treat hypersaline industrial wastewaters.

This work presents pioneering advances in the development of novel MD membranes with special wettability for extended MD applications. The fundamental understanding of the interfacial phenomena, advanced materials, and surface engineering techniques as well as fouling and scaling mechanisms will shed light on the design parameters for high membrane performance and efficient process operation. These important insights can inform the realization of emerging membrane-based technologies for sustainable treatment of challenging industrial wastewaters. The implications of the results in this dissertation are potentially far-reaching; we anticipate that they will shape the discussion of next generation desalination technologies.

This thesis describes the design and implementation of an interactive dynamic simulator called DASPRII. The starting point of this research has been an existing dynamic simulation package, DASP. DASPII is written in standard FORTRAN 77 and is implemented on universally available IBM-PC or compatible machines. It provides a means for the analysis and design of chemical processes. Industrial interest in dynamic simulation has increased due to the recent increase in concern over plant operability, resiliency and safety. DASPII is an equation oriented simulation package which allows solution of dynamic and steady state equations. The steady state can be used to initialise the dynamic simulation. A robust non linear algebraic equation solver has been implemented for steady state solution. This has increased the general robustness of DASPII, compared to DASP. A graphical front end is used to generate the process flowsheet topology from a user constructed diagram of the process. A conversational interface is used to interrogate the user with the aid of a database, to complete the topological information. An original modelling strategy implemented in DASPII provides a simple mechanism for parameter switching which creates a more flexible simulation environment. The problem description generated is by a further conversational procedure using a data-base. The model format used allows the same model equations to be used for dynamic and steady state solution. All the useful features of DASPI are retained in DASPII. The program has been demonstrated and verified using a number of example problems, Significant improvements using the new NLAE solver have been shown. Topics requiring further research are described. The benefits of variable switching in models has been demonstrated with a literature problem.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, February 2002.
Includes bibliographical references (leaves 110-119).
Microchemical systems are sub-milliliter systems for chemical processes. They are constructed using microfabrication techniques originally developed for the fabrication of microelectronic circuits. The reduction in size, as compared to conventional systems, offers several advantages in improvement of heat and mass transfer and control of flow fields. In addition, microchemical systems are smaller, therefore inherently safer and capable of shorter thermal response times. The focus of this work has been a microchemical system with a multi-inlet contactor for liquid-liquid processes. The systems are fabricated using, primarily, silicon and glass in which feature sizes range from approximately 10 to 500 [mu]m. The multi-inlet contactor consists of 10 alternating inlets for two components. Fluids continuously enter the contactor, are focused by a converging channel, mix and react in a 50 m channel. The contactor is the central element in the microchemical system that also includes a parallel plate heat exchanger, infrared transmission detection capabilities and thin film metal temperature sensors. Quantitative data are obtained using on-chip optical detection methods, integrated thin film sensors, and off-chip pressure sensors. For microchemical systems, the length scales are short. Consequently, Reynolds numbers are small and the flow is laminar. When two or more streams are contacted in a homogeneous system, the flow is stable. The short length scales of the resulting lamellar stream enable rapid diffusion mixing for applications, such as kinetics studies or reaction-rate-limited operation of fast reactions.
(cont.) The mixing characteristics in the multi-inlet contactor are investigated through experiments and simulations. Without optimization, sub-second mixing times are achieved. By using experiments and simulations to gain a better understanding of diffusion mixing in the system, 99% mixing is achieved in less than 25 ms. Characterization of the microchemical system also includes determining the overall heat transfer coefficient for the parallel plate heat exchanger and demonstrating on-chip infrared transmission detection from 4000-1000 cm-1. Thus, these devices combine all the features necessary for kinetic studies, specifically control of residence time, control and monitoring of temperature, and concentration measurement by infrared spectroscopy. As a demonstration of microchemical systems as tools for kinetics studies, the microchemical mixer was used with in situ Fourier Transform infrared spectroscopy to monitor the alkaline hydrolysis of methyl formate. This reaction follows second order kinetics and is fast with a half life of 70 ms for the conditions used in this study. The rate constant that was extracted was in good agreement with the literature value. Moreover, in contrast to a previous study, no sample post processing was needed and the half-life of the reaction was reduced by an order of magnitude. Microchemical systems can also be useful tools in achieving and understanding heterogeneous fluid contacting. When an aqueous phase and organic phase are contacted in a 1:1 volumetric ratio, flow segregation can occur ...
by Tamara M. Floyd.
Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2005.
Includes bibliographical references.
(cont.) HCl-induced QLL formation at stratospheric conditions. It appears that the real part of the refractive index of the QLL formed via exposure to gas-phase HCl is closer. to that of liquid water or aqueous HCI solution than to that of ice. We estimate the thickness of the QLL in our experiments to be on the order of 100 nm. We found using the flow tube-CIMS technique that the presence of the QLL enhances the chlorine-activation reaction of HC1 with ClONO₂. The presence of the QLL also enhances CH₃COOH adsorption. We find that the solubilities of HC1 and CH₃COOH in the QLL are intermediate between the solubilities of each species in liquid H20 and those in ice. In a flow-tube CIMS study of HCI adsorption on different types of ice surface, we found that HCI adsorption on polycrystalline ice films typically used in laboratory studies consists of two modes: one relatively strong mode leading to irreversible adsorption, and one relatively weak binding mode leading to reversible adsorption. We have indirect experimental evidence that these two modes of adsorption correspond to adsorption to sites at crystal faces and those at grain boundaries, but there is not enough information to enable us to conclusively assign each adsorption mode to a type of site. We also found indirect evidence that HCI hexahydrate formation on ice at conditions relevant to the polar stratosphere is a process involving hydrate nucleation and propagation on the crystal surface, rather than one originating in grain boundaries, as has been suggested for ice formed at lower temperatures.
Characterization of the interaction of hydrogen chloride (HCl) with polar stratospheric cloud (PSC) ice particles is essential to understanding the processes responsible for ozone depletion. The interaction of HCI with ice was studied between -87⁰C and -30⁰C using the complementary approach of a) ellipsometry to monitor the ice surface with chemical ionization mass spectrometry (CIMS) detection of the gas phase, and b) flow tube experiments with CIMS detection. The flow tube-CIMS technique was also used to study the chlorine activation reaction of chlorine nitrate (ClONO₂) and HCl on ice, the co-adsorption of acetic acid (CH₃COOH) and HCI on ice, and the adsorption of CFC-12 (CC1₂F₂) on ice. CH₃COOH and CC1₂F₂ were employed as nonreactive probe molecules to provide information about the state of the ice surface in the HCl-ice system. The ellipsometer-CIMS studies were performed on single-crystalline ice samples, and the flow tube-CIMS studies were performed on smooth and vapor-deposited polycrystalline ice films and on zone-refined ice cylinders. A numerical modeling framework is presented for the interpretation of the flow tube-CIMS studies. A disordered surface region, or quasi-liquid layer (QLL), was detected on bare ice using ellipsometry down to -30 ⁰C. We also found using ellipsometry that trace amounts of HCl induce QLL formation on the ice surface in the vicinity of the solid-liquid equilibrium line on the HCl-ice phase diagram, including conditions encountered in the polar stratosphere during PSC events. These results are supported by the results of the flow tube-CIMS studies of the reaction of ClONO₂ and HCl on ice, CH₃COOH/HC1 co-adsorption on ice, and HCl adsorption on ice. This is the first report of direct experimental evidence of
by Vivian Faye McNeill.
Ph.D.

Metallocene catalyzed linear low density polyethylene (m-LLDPE) is a new generation of olefin copolymer. Based on the more recently developed metallocene-type catalysts, m-LLDPE can be synthesized with exactly controlled short chain branches and stereo-regular microstructure. The unique properties of these polymers have led to their applications in many areas. As a result, it is important to have a good understanding of the oxidation mechanism of m-LLDPE during melt processing in order to develop more effective stabilisation systems and continue to increase the performance of the material. The primary objectives of this work were, firstly, to investigate the oxidative degradation mechanisms of m-LLDPE polymers having different comonomer (I-octene) content during melt processing. Secondly, to examine the effectiveness of some commercial antioxidants on the stabilisation of m-LLDPE melt. A Ziegler-polymerized LLDPE (z-LLDPE) based on the same comonomer was chosen and processed under the same conditions for comparison with the metallocene polymers. The LLDPE polymers were processed using an internal mixer (torque rheometer, TR) and a co-rotating twin-screw extruder (TSE). The effects of processing variables (time, temperature) on the rheological (MI, MWD, rheometry) and molecular (unsaturation type and content, carbonyl compounds, chain branching) characteristics of the processed polymers were examined. It was found that the catalyst type (metallocene or Ziegler) and comonomer content of the polymers have great impact on their oxidative degradation behavior (crosslinking or chain scission) during melt processing. The metallocene polymers mainly underwent chain scission at lower temperature (< 220°C) but crosslinking became predominant at higher temperature for both TR and TSE processed polymers. Generally, the more comonomers the m-LLDPE contains, a larger extent of chain scission can be expected. In contrast, crosslinking reactions were shown to be always dominant in the case of the Ziegler LLDPE. Furthermore, it is clear that the molecular weight distribution (MWD) of all LLDPE became broader after processing and tended generally to be broader at elevated temperatures and more extrusion passes. So, it can be concluded that crosslinking and chain scission are temperature dependent and occur simultaneously as competing reactions during melt processing. Vinyl is considered to be the most important unsaturated group leading to polymer crosslinking as its concentration in all the LLDPE decreased after processing. Carbonyl compounds were produced during LLDPE melt processing and ketones were shown to be the most imp0l1ant carbonyl-containing products in all processed polymers. The carbonyl concentration generally increased with temperature and extrusion passes, and the higher carbonyl content fonned in processed z-LLDPE and m-LLDPE polymers having higher comonomer content indicates their higher susceptibility of oxidative degradation. Hindered phenol and lactone antioxidants were shown to be effective in the stabilization of m-LLDPE melt when they were singly used in TSE extrusion. The combination of hindered phenol and phosphite has synergistic effect on m-LLDPE stabilization and the phenol-phosphite-Iactone mixture imparted the polymers with good stability during extrusion, especially for m-LLDPE with higher comonomer content.

A study of clay chemistry has been approached with three aims: - to modify the conducting properties by intercalation of tetrathiafulvalene, - to study the electrochemistry of redox-active coordination compounds immobilised on clay coated electrodes, and - to study the role of clays as reagents in inorganic glass forming reactions using mainly solid-state magic-angle-spinning NMR. TTF was intercalated by smectites containing different interlayer and lattice cations. Evidence from ESR and 57Fe Mossbauer indicated charge-transfer from TTF to structural iron in natural montmorillonite, and to interlayer Cu2+ in Cu2+ exchanged laponite. No charge transfer was observed for laponite (Na+ form) itself. Ion exchange of TTF3(BF4)2 with laponite was found to proceed quantitatively. The intercalated species were believed to be (TTF)2+ dimers. Conductivity data showed an order of magnitude increase for the intercalated clays. The mechanism is thought to be ionic rather than CT as Na+ laponite showed a similar enhancement in conductivity. Mechanically robust colloidal clay films were prepared on platinum electrodes. After immersion in solutions containing redox active complexes [Co(bpy)3]3+ and [Cr(bpy)3]3+, the films became electroactive when a potential was applied. Cyclic voltammograms obtained for both complexes were found to be of the diffusion controlled type. For [Co(bpy)3]3+ immobilised on clay coated electrodes, a one-step oxidation and four-step reduction wave was observed corresponding to a one electron stepwise reversible reduction of Co(III), through Co(II), Co(I), Co(O) to Co(I) oxidation state. For [Cr(bpy)3]3+ the electrochemistry was complicated by the presence of additional waves corresponding to the dissociation of [Cr(bpy)3]3+ into the diaquo complex. ESR and diffuse reflectance data supported such a mechanism. 29Si, 27Al and 23Na MAS NMR spectroscopy, supported by powder XRD and FTIR, was used to probe the role of clays as reagents in glass forming reactions. 29Si MAS NMR was found to be a very sensitive technique for identifying the presence and relative abundance of crystalline and non-crystalline phases. In thermal reactions of laponite formation of new mineral phases such as forsterite, akermanite, sillimanite and diopside were detected. The relative abundance of each phase was dependent on thermal history, chemical nature and concentration of the modifier oxide present. In continuing work, the effect of selected oxides on the glass forming reactions of a model feldspar composition was investigated using solid state NMR alone. Addition of network modifying oxides generally produced less negative 29Si chemical shifts and larger linewidths corresponding to a wider distribution of Si-O-Si bond angles and lengths, and a dominant aluminosilicate phase with a less polymerised structure than the starting material. 29Si linewidths and 27Al chemical shifts were respectively correlated with cationic potential and Lewis acidity of the oxide cations. Anomalous Al(4) chemical shifts were thought to be due to precipitation of aluminate phases rather than a breakdown in Lowenstein's aluminium avoidance principle.

Perturbations in the bismuth market resulted in Mining and Chemical Products Ltd., seeking further outlets in the market. Together with Manchem Ltd. they were anxious to evaluate the possibility of using bismuth compounds as a replacement for lead/calcium soaps in paint driers. A range of new organobismuth compounds were synthesised of the type RBiX2 and R3BiX2 (X= halogen, OOCR, dithiocarbamate). A variety of synthetic techniques were explored, including the use of mathematical reactions, phase-transfer catalysis and microwave energy. The preparation of a range of trivalent and pentavalent organobismuth carboxylates is reported and their infra-red , 13C, lH nmr spectra. The compounds were evaluated as paint driers and in cases found to enhance paint drying to a greater degree than the standard driers, to which they were being compared. The drying times of paint films containing the organobismuth compounds are reported, together with a comparison of the drying times with the addition of bismuth tris-diethyldithiocarbamate, which may promote the cross-linking reaction that occur in paint films during the drying process. Examples are reported to illustrate the great reductions in reaction times possible when using microwave energy. Reactions such as metallation of aromatic rings, ligand redistribution and synthesis were carried out in PTFE containers in a conventional domestic microwave oven. An X-ray diffraction study of (phenylazophenyl-C,N')mercury(II) chloride has shown it to be dimeric via long Hg-Cl bridging interactions of 3.367A. Its crystal structure is reported, together with its 13C nmr spectra and mass spectrum. The Lewis acidity of compounds of the type RBiX2 was investigated. The donor group being anchored to the organo group (R). The dithiocarbamates bis- (diethyldithiobarbamato)phenylbismuth(Ill) and [2-2-pyridyl)phenylbismuth(III) were synthesised, and their crystal structures, 14N, 13C nmr ar1d infra-red spectra are reported. Both compounds are pseudo-pentagonal bipyramidal in geometry, with two long Bi-S bonds and two short Bi-S bonds. The reaction of RBiBr2 (R= 2-(pyridyl) with various ligands is reported. The infra-red evidence suggesting that the coordination of extra ligands is accompanied by a reduction of the strength of the Bi-interaction.

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Dentre as diversas aplicações dos radioisótopos, a utilização dos radiotraçadores é considerada uma das mais importantes, no diagnóstico de funcionamento dos equipamentos de processos, em plantas de indústrias químicas e petroquímicas. Os radiotraçadores são utilizados em procedimentos analíticos para obtenção de dados qualitativos e quantitativos de sistemas, em estudos de transferências físicas e físico-químicas. Na produção de radioisótopos gasosos utilizados como traçadores em processos industriais, destacam-se o 41Ar e 79Kr, gases nobres (inertes) que possuem baixa reatividade com os demais elementos químicos. O 41Ar é um emissor gama de alta energia (1,29 MeV) e apresenta elevada porcentagem de transformações com essa energia, o que resulta em quantidades relativamente pequenas necessárias em relação a outras para uma detecção eficaz, mesmo em componentes com grandes espessuras. Atualmente, a produção de radioisótopos gasosos em reatores nucleares de pesquisa é realizada em pequenas quantidades (bateladas), por meio de ampolas de quartzo contendo o gás natural 40Ar ou 78Kr. Nesse sentido, o objetivo desse estudo é desenvolver um sistema de irradiação capaz de produzir em escala contínua, o radioisótopo gasoso 41Ar, dentre outros, com atividade de 7,4x1011 Bq (20 Ci) por ciclo de irradiação, por meio do Reator IEA-R1 de 4,5 MW, fluxo de nêutrons térmicos médio de 4,71 x 1013 ncm-2s-1, para suprir uma demanda existente em empresas de END e inspeções, e pelo próprio Centro de Tecnologia das Radiações, no IPEN/CNEN-SP. O sistema de irradiação (SI) é constituído por uma cápsula de irradiação em alumínio, linhas de transferência, válvulas agulhas, conexões anilhadas, conectores rápidos, manovacuômetro, sistema de vácuo, dewar de liquefação, blindagem em chumbo, cilindros de armazenamento e transporte (CAT), dentre outros. O SI foi aprovado nos testes de estanqueidade e estabilidade (testes de formação de bolhas, pressurização, evacuação e com equipamento leak detector SPECTRON 600 T). Na produção experimental para obtenção de 1,07x1011 Bq (2,9 Ci) de 41Ar, distribuíram-se dosímetros de alanina em diversos componentes e dispositivos do SI. Além disso, determinaram-se as taxas de exposição na parede da blindagem em chumbo, ao concentrar o gás radioativo liquefeito e no CAT, após a transferência do 41Ar, pelo medidor de radiação portátil Teletector ® Probe 6150 AD-t/H.
Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Today, speciality use organoclays are being developed for an increasingly large number of specific applications. Many of these, including use in cosmetics, polishes, greases and paints, require that the material be free from abrasive impurities so that the product retains a smooth `feel'. The traditional `wet' method preparation of organoclays inherently removes abrasives naturally present in the parent mineral clay, but it is time-consuming and expensive. The primary objective of this thesis was to explore the alternative `dry' method (which is both quicker and cheaper but which provides no refining of the parent clay) as a process, and to examine the nature of the organoclays produced, for the production of a wide range of commercially usable organophilic clays in a facile way. Natural Wyoming bentonite contains two quite different types of silicate surface (that of the clay mineral montmorillonite and that of a quartz impurity) that may interact with the cationic surfactant added in the `dry' process production of organoclays. However, it is oil shale, and not the quartz, that is chiefly responsible for the abrasive nature of the material, although air refinement in combination with the controlled milling of the bentonite as a pretreatment may offer a route to its removal. Ion exchange of Wyoming bentonite with a long chain quaternary ammonium salt using the `dry' process affords a partially exchanged, 69-78%, organoclay, with a monolayer formation of ammonium ions in the interlayer. Excess ion pairs are sorbed on the silicate surfaces of both the clay mineral and the quartz impurity phases. Such surface sorption is enhanced by the presence of very finely divided, super paramagnetic, Fe2O3 or Fe(O)(OH) contaminating the surfaces of the major mineral components. The sorbed material is labile to washing, and induces a measurable shielding of the 29Si nuclei in both clay and quartz phases in the MAS NMR experiment, due to an anisotropic magnetic susceptibility effect. XRD data for humidified samples reveal the interlamellar regions to be strongly hydrophobic, with the by-product sodium chloride being expelled to the external surfaces. Many organic cations will exchange onto a clay. The tetracationic cyclophane, and multipurpose receptor, cyclobis(paraquat-p-phenylene) undergoes ion exchange onto Wyoming bentonite to form a pillared clay with a very regular gallery height. The major plane of the cyclophane is normal to the silicate surfaces, thus allowing the cavity to remain available for complexation. A series of group VI substituted o-dimethoxybenzenes were introduced, and shown to participate in host/guest interactions with the cyclophane. Evidence is given which suggests that the binding of the host structure to a clay substrate offers advantages, not only of transportability and usability but of stability, to the charge-transfer complex which may prove useful in a variety of commercial applications.

Oil agglomeration combined with bubble flotation has proven to be an effective means of upgrading and recovering waste fine coal when low-oil floc-type agglomerates are formed. Low-oil recovery is desirable, since less ash is incorporated into the agglomerates and the expense of using oil is reduced. In this state, the flocs are too small and weak for screen separation but can be successfully recovered by flotation as even a small amount of oil imparts a much improved surface character, and agglomerate strength is less important. Reduction of the amount of wetting phase used in the oil agglomeration process for advance coal cleaning and utilization technologies is important to the economics of the process. An analysis was made of the agglomerate surface properties and on the size enlargement characteristics and possible mechanisms of the process taking place when floc-type coal-oil agglomerates are formed at oil levels less than about 2% oil by weight. Since this product exists not as dense agglomerates but only as small aggregates of a few particles, the adhesion technique was used to determine the surface properties of agglomerates made from a high purity coal. The surface properties closely matched those of the oil at agglomerate oil-levels above 2% by weight. Particle-size measurements by laser diffraction were then correlated to the surface properties as a function of the oil-level and of agglomerate particle packing. Subsequently, the surface free energies of agglomerates made from coals of several different ranks were measured by the adhesion technique. Oil levels from 0 to 10% by weight were used. As was expected, it was found that higher-rank coals are more easily oil-wetted and that the surface properties of the agglomerates correlate with agglomeration recovery and ash removal data. It has been illustrated in pilot studies that oil-agglomeration together with flotation gives an enhanced combustibles recovery and ash separation. To corroborate successful flotation results for such agglomerates, a computational fluid dynamics simulation was formulated to model their recovery. This simulation employed the finite volume method, and featured three-phase flow as well as the collection of particles by bubbles. Additionally, a novel formulation of a boundary element method for unsteady full Navier-Stokes flow was undertaken to model the collisional aspects of micro-flotation. This method was successfully implemented, but problems with numerical instability in the required flow regimes prevented a more detailed micro-flotation study in the present work. The surface properties of coal-oil agglomerates were incorporated into a model based on the resolved hydrodynamics of the flotation process. The overall result was an integrated model where individual local mechanisms could be summed to determine recovery values which compared very well to a wide range of data. (Abstract shortened by UMI.)

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2006.
Includes bibliographical references (p. 251-257).
Many technologically important processes in the chemical and mechanical industries involve coupled interactions of heat and mass transfer with chemical reactions - e.g. commercial burners, gas turbines, internal combustion engines, etc. However, detailed computational studies of such processes remain difficult at best, particularly due to the large reaction mechanisms that describe the chemical kinetics over the relevant range of reaction conditions. As a result, reduced models that contain fewer reactions and/or species while still capturing the "important" kinetics are often used in place of the full comprehensive reaction model in modeling complex reacting flows. "Adaptive Chemistry" - a method that uses several smaller locally-accurate reduced reaction models rather than a single "catch-all" model - has been shown in the combustion literature to be a viable option for improving computational efficiency in such studies. However, several outstanding challenges have prevented the adoption of this method in mainstream studies, most notably the difficulty of determining the accuracy of a solution obtained using Adaptive Chemistry. The focus of this research was to develop methods to enable efficient and accurate implementation of Adaptive Chemistry for reacting flow simulations.
(cont.) A method was developed for determining how much error may be tolerated in each reduced model in order to achieve a desired accuracy in Adaptive Chemistry solutions at steady-state. A novel model reduction method was also developed to obtain automatically reduced models (based on reaction elimination) that are guaranteed to satisfy the imposed error tolerances at all conditions in a user-specified range. In order to enable point-validated reduced models to be used accurately over ranges, an iterative method was developed for identifying ranges of reaction conditions over which such reduced models are guaranteed to remain valid. An Adaptive Chemistry method that demonstrates the application of these methods is presented. Efficient implementations of construction, storage and retrieval of reduced models that are appropriate for the reaction conditions encountered during Adaptive Chemistry simulations are presented, including an algorithm that adapts the library of reduced models to the solution trajectory "on the fly".
(cont.) The error-controlled Adaptive Chemistry method developed here is the first method that enables rigorous control of the model reduction error in steady-state Adaptive Chemistry solutions, as demonstrated in 1-D and 2-D premixed and partially premixed flame simulations. Results of a collaborative effort to facilitate engine research by developing the necessary cyberinfrastructure to provide remote access to the model reduction tools developed here are also discussed. Finally, methods are described for extending the error control criteria developed and demonstrated for reduced reaction models to reduced-species models and suggestions are made for future research in Adaptive Chemistry.
by Oluwayemisi Oluwi Oluwole.
Ph.D.

Thesis (Ph. D.)--University of Sydney, 2009.
Includes graphs and tables. Title from title screen (viewed November 06, 2009). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Faculty of Engineering and Information Technologies. Degree awarded 2009; thesis submitted 2008. Includes bibliographical references. Also available in print form.

The secondary milling circuit at Waterval UG2 Concentrator had undergone a circuit change with the commissioning of the IsaMill, a horizontally stirred mill, in parallel with the secondary ball mill. The operation treats the PGM bearing UG2 ore type and produces a final concentrate enriched with PGM's. The concept was to treat the finer silicate rich fraction in the IsaMill and the coarser chromite rich fraction through the ball mill. This circuit is typical of a UG2 plant in which maximum silicate with minimal chromite breakage is targeted. As a result of the circuit change an opportunity for optimisation around the industrial scale ball mill was considered for this study. Of concern in this study were new operating conditions for the mill in the changed circuit at which improved performance could be obtained. Another objective was to investigate if a difference in breakage response for the silicate and chromite fractions could be identified for different operating conditions in the ball mill. The secondary mill at Waterval UG2 Concentrator was already fitted with an online ball and pulp load sensor, the Sensomag. The information obtained from the sensor is in the form of shoulder and toe positions for the ball and pulp filling in the rotating ball mill. The mill was surveyed at various ball filling and mill % solids conditions and information from the online sensor was used to understand the mill performance, particularly with regards to mill load behaviour. Hence a final objective was to demonstrate that the information obtained from the online sensor could be related to mill operating conditions. The sensor output was envisioned to eventually form part of the mill control philosophy. Samples were taken of the mill feed and discharge streams at the different operating conditions and analysed for grind as well as PGM and Cr₂O₃ content. The majority of the PGM's in the UG2 ore are in the silicates and thus the PGM distribution results would indicate the amount of breakage in the silicate fraction. Cr₂O₃ is used as an indicator of the chromite content in UG2 ore. In order to identify optimum mill performance the results were analysed using different measures which include general grind, particle and species distributions, reduction ratios, sieve efficiencies and specific energy. By comparing the results the differences and limitations of certain techniques were identified. It was found that the mill performance varied at different operating conditions. The optimum ball filling was found to be around 30%, which is similar to site operational target. The optimal % solids for this mill however seems to be higher than what the mill is typically operated at. No peak in % solids for mill performance was obtained. Scope exists to determine how far from the investigated maximum of 75% solids (by mass) does the optimum in-mill density lie for this mill. Thus new optimum conditions in terms of % solids do exist for the mill in the modified circuit. Results also showed that the size reduction of the silicates increased with an increase in mill % solids and ball filling degree. For chromite, the mill % solids did not appear to have any effect at low ball fillings, but a slight shift was observed at the higher ball fillings tested. The trend suggests that the size reduction of both silicates and chromite increased with an increase in ball filling, albeit at different rates. Finally, the test work has demonstrated that the online sensor outputs can be related to mill performance. Differences in shoulder and toe positions for the ball and pulp loads were distinct between operating conditions. Improved grind performance was observed at conditions that resulted in lower free pulp angles. Thus the sensor could be used as a control tool to identify and maintain optimum mill operational conditions. The Sensomag should be incorporated into a mill controller that looks at more than just mill ball filling. Conditions that result in optimum mill efficiency can be identified and the mill may be controlled using the sensor data. It is recommended that the mill continue to be run at 30% ball filling and at higher mill % solids than the maximum reached in this work.