Academic literature on the topic 'Fischer-Tropsch reaction water'

This review summarizes recent development relating to 2D materials and their derivatives for solar-driven CO₂ reduction by H₂O or H₂, as well as CO hydrogenation (via the water gas shift reaction or Fischer–Tropsch synthesis) to produce valuable products (especially hydrocarbons, alcohols and aromatics).

The effects of metallic cobalt crystal phase on catalytic activity of cobalt catalysts in the Fischer–Tropsch synthesis were investigated in a continuous spinning basket reactor. The cobalt catalysts were prepared by impregnation of the cobalt active phase in a microemulsion system on multiwall carbon nanotube supports. A series of cobalt catalysts with different Co particle sizes was prepared by variation of the water-to-surfactant molar ratio from 2 to 12 in the microemulsion system. The X-ray diffraction results validate a complex composition of cobalt phases containing cobalt oxides and metallic cobalt with hexagonal close-packed and face-centered cubic phases. The results show that larger cobalt particles exhibit more face-centered cubic and less hexagonal close-packed metallic cobalt. The experimental results show that the catalysts with higher fractions of hexagonal close-packed phase exhibited higher conversion in the Fischer–Tropsch reaction.

Background: The Fischer-Tropsch Synthesis (FTS) remains an important process for motor fuel production from CO and H2. The composition of the FTS products (hydrocarbon mixtures) depends on the properties of a catalyst and on the process conditions. Summary: The introduction of zeolites into catalytic systems can alter the molecular weight distribution paving the way to tailor-made fuels, as was revealed by recent research results produced in the laboratories worldwide. The AlO4 and SiO4 tetrahedrons, which constitute the zeolites, are able to transfer electrons and ions in a way, which makes water-zeolite interfaces capable of initiating active carbonium ions. It was shown in a number of works that the water-zeolite interface plays a key role in diverting the FTS from the classical route. Conclusion: This review gives a critical analysis of literature data on the role of water-zeolite interfaces on FTS cobalt catalysts and on the interactions of hydrophobic and hydrophilic zeolites with water.

This work analyzes different gasification processes affect on WGS process with Excel-Aspen Plus based models.in large scale production. Results show that Shell gasifier can obtain higher (CO + H2)/syngas ratio and higher thermal efficiency but lower H2/CO ratio than Texaco gasifier. However, both of H2/CO ratios are below 1.0 and WGS reaction has to carry out to prepare for the Fischer-Tropsch synthesis. The simulation shows Shell syngas does not offer adequate H2O molecules for WGS shift reaction and it can be supplied by the 5.2MPa steam generated from the boiler of the Shell gasification process. Texaco syngas has sufficient H2O molecules to meet the need of this reaction. The overall thermal efficiency of the Texaco-WGS is lower than that of the Shell-WGS.

Nearly a century ago, Fischer and Tropsch discovered a means of synthesizing organic compounds ranging from C1 to C70 by reacting carbon monoxide and hydrogen on a catalyst. Fischer–Tropsch synthesis (FTS) is now known as a pseudo-polymerization process taking a mixture of CO as H2 (also known as syngas) to produce a vast array of hydrocarbons, along with various small amounts of oxygenated materials. Despite the decades spent studying this process, it is still considered a black-box reaction with a mechanism that is still under debate. This investigation sought to improve our understanding by taking data from a series of experimental Fischer–Tropsch synthesis runs to build a computational model. The experimental runs were completed in an isothermal continuous stirred-tank reactor, allowing for comparison across a series of completed catalyst tests. Similar catalytic recipes were chosen so that conditional comparisons of pressure, temperature, SV, and CO/H2 could be made. Further, results from the output of the reactor that included the deviations in product selectivity, especially that of methane and CO2, were considered. Cobalt was chosen for these exams for its industrial relevance and respectfully clean process as it does not intrinsically undergo the water–gas shift (WGS). The primary focus of this manuscript was to compare runs using cobalt-based catalysts that varied in two oxide catalyst supports. The results were obtained by creating two differential equations, one for H2 and one for CO, in terms of products or groups of products. These were analyzed using sensitivity analysis (SA) to determine the products or groups that impact the model the most. The results revealed a significant difference in sensitivity between the two catalyst–support combinations. When the model equations for H2 and CO were split, the results indicated that the CO equation was significantly more sensitive to CO2 production than the H2 equation.

In the Fischer–Tropsch (FT) synthesis, a mixture of CO and H2 is converted into hydrocarbons and water with diluted organics. This water fraction with oxygenated hydrocarbons can be processed through aqueous-phase reforming (APR) to produce H2. Therefore, the APR of FT water may decrease the environmental impact of organic waters and improve the efficiency of the FT process. This work aimed at developing a kinetic model for the APR of FT water. APR experiments were conducted with real FT water in a continuous packed-bed reactor at different operating conditions of temperature (210–240 °C), pressure (3.2–4.5 MPa) and weight hourly space velocity (WHSV) (40–200 h−1) over a nickel-copper catalyst supported on ceria-zirconia. The kinetic model considered C1-C4 alcohols as reactants, H2, CO, CO2 and CH4 as the gaseous products, and acetic acid as the only liquid product. The kinetic model included seven reactions, the reaction rates of which were expressed with power law equations. The kinetic parameters were estimated with variances and confidence intervals that explain the accuracy of the model to estimate the outlet liquid composition resulting from the APR of FT water. The kinetic model developed in this work may facilitate the development of APR to be integrated in a FT synthesis process.

Aqueous-phase reforming of 5 wt% ethylene glycol was studied at temperature of 498 K over Pt supported on Al2O3, SiO2, TiO2, CeO2. High selectivity about 90% for generation of hydrogen was observed over the supported Pt catalysts, suggesting that the methanation or the Fischer-Tropsch reactions involving CO/CO2 and H2 does not appear to be important over these catalysts under the present conditions. Compared with Pt/SiO2 and Pt/CeO2, Pt supported on Al2O3 and TiO2 produced measurable amounts of gaseous alkane that may be due to the acidity of the supports. To verify this suppose, the water-gas shift reaction was carried out over the catalysts under the same reaction conditions, and no CH4 was observed over these Pt catalysts. Relatively higher generation rates of hydrogen and carbon dioxide were achieved over Pt/Al2O3 and Pt/SiO2 catalysts.

Includes bibliographical references (leaves 99-110).
The Fischer-Tropsch synthesis catalysed by iron is a well-established process for the production of synthetic fuels, waxes and many other chemicals, yet there are many aspects that are still not totally understood. Controversy still exists as to what the active phase(s) is of the iron Fischer-Tropsch catalyst. A big drawback of the iron based Fischer-Tropsch synthesis is that one of its primary products, wate, changes the structure and stability of the catalyst. Little is know about the effect that water partial pressure has on the phases present in the working catalyst.

The structural and functional roles of lanthana in unsupported iron-based catalysts for the high-temperature water-gas shift reaction and Fischer-Tropsch synthesis were investigated. The performance of the catalysts with varying lanthana contents was based on their activity, selectivity, and stability. With regard to the former reaction, extent of reduction of the iron in Fe2O3/Cr2O3/CuO/La2O3 water-gas shift catalysts is a key parameter that was characterized using UV-visible spectroscopy. Minor addition of lanthana (<0.5 wt%) produces more active and stable catalysts apparently because it stabilizes the iron-chromium spinel, increases the surface area of the reduced catalysts, enhances the reduction of hematite to the magnetite active phase, and facilitates the adsorption of CO on the surface of the catalyst modeled by an adsorptive Langmuir-Hinshelwood mechanism. Statistical 95% confidence contour plots of the adsorption equilibrium constants show that water adsorbs more strongly than CO, which inhibits the reaction rate. A calibration curve that correlates the oxidation state of surface iron domains to normalized absorbance of visible light was successfully generated and applied to the water-gas shift catalysts. UV-visible studies indicated higher extent of reduction for surface Fe domains for the catalysts promoted with 1 wt% of lanthana and showed potential to be a more convenient technique for surface chemistry studies than X-ray absorption near edge spectroscopy (XANES). Lanthana addition to iron-based Fischer-Tropsch catalysts enhances the olefin-to-paraffin ratio, but decreases their activity, stability, and selectivity to liquid hydrocarbons. Adding lanthana at the expense of potassium reduces the water-gas shift selectivity and enhances the activity and stability of the catalysts. Finally, a model that simulates heat and mass transfer limitations on the particle scale for the Fischer-Tropsch reaction applicable at lab-scale suggests optimal operating and design conditions of 256°C, 30 bar, and 80 mirons are recommended for higher selectivity to liquid hydrocarbons. The model considers pressure drop, deactivation, pore diffusion, film heat transfer, and internal heat transfer when solving for the optimal conditions, and maps them as functions of design variables. This model can be up-scaled to provide guidance for optimal design of commercial-size reactors.

Reaction water, a high-strength COD (chemical oxygen demand) petrochemical effluent, is generated during the Fischer-Tropsch reaction in the SASOL Synthol process at SASOL SynFuels, Secunda, South Africa. Distillation of the reaction water to remove non- and oxygenated hydrocarbons yields approximately 25 - 30 ML/d of an organic (carboxylic) acid-enriched stream (average COD of 16 000 mg/L) containing primarily C2 – C5 organic acids, light oils, aldehydes, ketones, cresols and phenols. Together with the Oily sewer water (API) and Stripped Gas Liquor (SGL) process streams, this process effluent is currently treated in ten dedicated activated sludge basins. However, the successful operation of these activated sludge systems has proven to be difficult with low organic loading rates (3.5 kg COD/m3.d) low COD removal efficiencies (<80 %) and high specific air requirements (60 - 75 m3 air/kg CODrem). It is hypothesised that these operational difficulties can be attributed to organic shock loadings, variation in volumetric and hydraulic loadings, as well as variations in the composition of the various process streams being treated. Due to the fact that the Fischer-Tropsch (Synthol) reaction water constitutes 70 % of the COD load on the activated sludge systems, alternative processes to improve the treatment cost and efficiency of the Fischer-Tropsch acid stream are being investigated. Various studies evaluating the aerobic and anaerobic treatment of Fischer-Tropsch reaction water alone in suspended growth wastewater treatment systems have proven unsuccessful. High rate fixed-film processes or biofilm reactors, of which the fluidised-bed reactors are considered to he one of the most effective and promising processes for the treatment of high-strength industrial wastewaters, could he a suitable alternative. The primary aim of this study was to evaluate the suitability of biological fluidised-bed reactors (BFBRs) for the treatment of Fischer-Tropsch reaction water. During this study, the use of aerobic and anaerobic biological fluidised-bed reactors (BFBR), using sand and granular activated carbon (GAC) as support matrices, were evaluated for the treatment of a synthetic effluent analogous to the Fischer-Tropsch reaction water stream. After inoculation, the reactors were operated in batch mode for 10 days at a bed height expansion of 30% and a temperature of 30 ºC to facilitate biofilm formation on the various support matrices. This was followed by continuous operation of the reactors at hydraulic retention times (HRTs) of 2 days. While the COD of the influent and subsequent organic loading rate (OLR) was incrementally increased from 1 600 mg/L to a maximum of 20 000 mg/L and 18 000 mg/L for the aerobic and anaerobic reactors, respectively. Once the maximum influent COD concentration had been achieved the OLR was further increased by decreasing the HRTs of the aerobic and anaerobic reactors to 24h and 8h, and 36h, 24h and 19h, respectively. The dissolved O2 concentration in the main reactor columns of the aerobic reactors was constantly maintained at 0.50 mg/L. Chemical Oxygen Demand (COD) removal efficiencies in excess of 80 % at OLR of up to 30 kg COD/m3.d were achieved in the aerobic BFBRs using both sand and GAC as support matrices. Specific air requirements were calculated to be approximately 35 and 41 m3 air/kg CODrem for the BFBRs using sand and GAC as support matrices, respectively. The oxygen transfer efficiency was calculated to be approximately 5.4 %. At high OLR (> 15 kg COD/m3.d) significant problems were experienced with plugging and subsequent channelling in the BFBR using GAC as support matrix and the reactor had to be backwashed frequently in order to remove excess biomass. Despite these backwash procedures, COD removal efficiencies recovered to previous levels within 24 hours. In contrast, no significant problems were encountered with plug formation and channelling in the BFBR using sand as support matrix. In general the overall reactor performance and COD removal efficiency of the aerobic BFBR using sand as support matrix was more stable and consistent than the BFBR using GAC as support matrix. This BFBR was also more resilient to variations in operational conditions, such as the lowering of the hydraulic retention times and changes in the influent pH. Both aerobic reactors displayed high resilience and COD removal efficiencies in excess of 80 % were achieved during shock loadings. However, both reactors were highly sensitive to changes in pH and any decrease in pH below the pKa values of the volatile fatty acids in the influent (pKa of acetic acid = 4.76) resulted in significant reductions in COD removal efficiencies. Maintenance of reactor pH above 5.0 was thus an essential facet of reactor operation. It has been reported that the VFA/alkalinity ratio can be used to assess the stability of biological reactors. The VFA/alkalinity ratios of the aerobic BFBRs containing sand and GAC as support matrices were stable (VFNalkalinity ratios of < 0.3 - 0.4) until the OLR increased above 10 kg/m3.d. At OLRs higher than 10 kg/m3.d the VFA/alkalinity ratios in the BFBR using sand support matrix increased to 4, above the failure limit value of 0.3 - 0.4. In contrast the VFA/alkalinity ratios of the BFBR using GAC support matrix remained stable until an OLR of 15 kg/m3.d was obtained, where the VFA/alkalinity ratios then increased to > 3. Towards the end of the study when an OLR of approximately 25 kg/m3.d was obtained the VFA/alkalinity ratios of both the BFBRs using sand and GAC as support matrices increased to 9 and 6 respectively, indicating the decrease in reactor stability and acidification of the process. Total solid (TS) and volatile solid (VS) concentrations in the aerobic BFBRs were initially high and decreased over time. While the total suspended solids (TSS) and volatile suspended solids (VSS) concentrations were initially low and increased over time as the OLR was increased, this is thought to be as a result of decreased HRT leading to biomass washout. The anaerobic BFBR using sand as support matrix never stabilised and COD removal efficiency remained very low (< 30 %), possibly due to the high levels of shear forces. Further studies concerning the use of sand as support matrix were subsequently terminated. An average COD removal efficiency of approximately 60 % was achieved in the anaerobic BFBR using GAC as a support matrix at organic loading rates lower than 10 kg COD/m3.d. The removal efficiency gradually decreased to 50 % as organic loading rates were increased to 20 kg COD/m3.d. At OLRs of 20 kg COD/m3.d, the biogas and methane yields of the anaerobic BFBR using GAC as support matrix were determined to be approximately 0.38 m3 biogas/kg CODrem (0.3 m3 biogas/m3reactor vol.d), and 0.20 m3 CH4/kg CODrem (0.23 m3 CH4/m3reactor vol.d), respectively. This value is 57 % of the theoretical maximum methane yield attainable (3.5 m3 CH4/kg CODrem). The methane yield increased as the OLR increased, however, when the OLR reached 8 kg/m3.d the methane yield levelled off and remained constant at approximately 2 m3 CH4/m3reactor vol.d. Although the methane content of the biogas was initially very low (< 30 %), the methane content gradually increased to 60 % at OLRs of 20 kg COD/m3.d. The anaerobic BFBR using GAC as support matrix determined that as the OLR increased (>12 kg/m3.d), the VFA/alkalinity ratio increased to approximately 5, this is indicative of the decrease in stability and acidification of the process. The anaerobic BFBR using GAC as support matrix experienced no problems with plug formation and channelling. This is due to the lower biomass production by anaerobic microorganisms than in the aerobic reactors. The TS and VS concentrations were lower than the aerobic concentrations but followed the same trend of decreasing over time, while the TSS and VSS concentrations increased due to decreased HRTs. The anaerobic BFBR was sensitive to dramatic variations in organic loading rates, pH and COD removal efficiencies decreased significantly after any shock loadings. Compared to the activated sludge systems currently being used for the biological treatment of Fischer-Tropsch reaction water at SASOL SynFuels, Secunda, South Africa, a seven-fold increase in OLR and a 55 % reduction in the specific air requirement was achieved using the aerobic BFBRs. The methane produced could also be used as an alternative source of energy. It is, however, evident that the support matrix has a significant influence on reactor performance. Excellent results were achieved using sand and GAC as support matrices in the aerobic and anaerobic BFBRs, respectively. It is thus recommended that future research be conducted on the optimisation of the use of aerobic and anaerobic BFBRs using these support matrices. Based on the results obtained from this study, it can be concluded that both aerobic and anaerobic treatment of a synthetic effluent analogous to the Fischer-Tropsch reaction water as generated by SASOL in the Fischer-Tropsch Synthol process were successful and that the application of fluidised-bed reactors (attached growth systems) could serve as a feasible alternative technology when compared to the current activated sludge treatment systems (suspended growth) currently used. Keywords: aerobic treatment, anaerobic treatment, biological fluidised-bed reactors, petrochemical effluent, Fischer-Tropsch reaction water, industrial wastewater.
Thesis (M. Omgewingswetenskappe)--North-West University, Potchefstroom Campus, 2004.

[ES] La presente tesis doctoral se centra en el desarrollo de nuevas membranas de separación de gases, así como su empleo in-situ en reactores catalíticos de membrana para la intensificación de procesos. Para este propósito, se han sintetizado varios materiales, como polímeros para la fabricación de membranas, catalizadores tanto para la metanación del CO2 como para la reacción de síntesis de Fischer-Tropsch, y diversas partículas inorgánicas nanométricas para su uso en membranas de matriz mixta. En lo referente a la fabricación de las membranas, la tesis aborda principalmente dos tipos: orgánicas e inorgánicas. Con respecto a las membranas orgánicas, se han considerado diferentes materiales poliméricos, tanto para la capa selectiva de la membrana, así como soporte de la misma. Se ha trabajado con poliimidas, puesto que son materiales con temperaturas de transición vítrea muy alta, para su posterior uso en reacciones industriales que tienen lugar entre 250-300 ºC. Para conseguir membranas muy permeables, manteniendo una buena selectividad, es necesario obtener capas selectivas de menos de una micra. Usando como material de soporte otro tipo de polímero, no es necesario estudiar la compatibilidad entre ellos, siendo menos compleja la obtención de capas finas. En cambio, si el soporte es de tipo inorgánico, un exhaustivo estudio de la relación entre la concentración y la viscosidad de la solución polimérica es altamente necesario. Diversas partículas inorgánicas nanométricas se estudiaron para favorecer la permeación de agua a través de los materiales poliméricos. En segundo lugar, en cuanto a membranas inorgánicas, se realizó la funcionalización de una membrana de paladio para favorecer la permeación de hidrógeno y evitar así la contaminación por monóxido de carbono. El motivo por el cual se dopó con otro metal la capa selectiva de la membrana metálica fue para poder emplearla en un reactor de Fischer-Tropsch. Con relación al diseño y fabricación de los reactores, durante esta tesis, se desarrolló el prototipo de un microreactor para la metanación de CO2, donde una membrana polimérica de capa fina selectiva al agua se integró para evitar la desactivación del catalizador, y a su vez desplazar el equilibrio y aumentar la conversión de CO2. Por otro lado, se rediseñó un reactor de Fischer-Tropsch para poder introducir una membrana metálica selectiva a hidrogeno y poder inyectarlo de manera controlada. De esta manera, y siguiendo estudios previos, el objetivo fue mejorar la selectividad a los productos deseados mediante el hidrocraqueo y la hidroisomerización de olefinas y parafinas con la ayuda de la alta presión parcial de hidrógeno.
[CAT] La present tesi doctoral es centra en el desenvolupament de noves membranes de separació de gasos, així com el seu ús in-situ en reactors catalítics de membrana per a la intensificació de processos. Per a aquest propòsit, s'han sintetitzat diversos materials, com a polímers per a la fabricació de membranes, catalitzadors tant per a la metanació del CO2 com per a la reacció de síntesi de Fischer-Tropsch, i diverses partícules inorgàniques nanomètriques per al seu ús en membranes de matriu mixta. Referent a la fabricació de les membranes, la tesi aborda principalment dos tipus: orgàniques i inorgàniques. Respecte a les membranes orgàniques, diferents materials polimèrics s'ha considerat com a candidats prometedors, tant per a la capa selectiva de la membrana, així com com a suport d'aquesta. S'ha treballat amb poliimides, ja que són materials amb temperatures de transició vítria molt alta, per al seu posterior ús en reaccions industrials que tenen lloc entre 250-300 °C. Per a aconseguir membranes molt permeables, mantenint una bona selectivitat, és necessari obtindre capes selectives de menys d'una micra. Emprant com a material de suport altre tipus de polímer, no és necessari estudiar la compatibilitat entre ells, sent menys complexa l'obtenció de capes fines. En canvi, si el suport és de tipus inorgànic, un exhaustiu estudi de la relació entre la concentració i la viscositat de la solució polimèrica és altament necessari. Diverses partícules inorgàniques nanomètriques es van estudiar per a afavorir la permeació d'aigua a través dels materials polimèrics. En segon lloc, quant a membranes inorgàniques, es va realitzar la funcionalització d'una membrana de pal¿ladi per a afavorir la permeació d'hidrogen i evitar la contaminació per monòxid de carboni. El motiu pel qual es va dopar amb un altre metall la capa selectiva de la membrana metàl¿lica va ser per a poder emprar-la en un reactor de Fischer-Tropsch. En relació amb el disseny i fabricació dels reactors, durant aquesta tesi, es va desenvolupar el prototip d'un microreactor per a la metanació de CO2, on una membrana polimèrica de capa fina selectiva a l'aigua es va integrar per a així evitar la desactivació del catalitzador i al seu torn desplaçar l'equilibri i augmentar la conversió de CO2. D'altra banda, un reactor de Fischer-Tropsch va ser redissenyat per a poder introduir una membrana metàl¿lica selectiva a l'hidrogen i poder injectar-lo de manera controlada. D'aquesta manera, i seguint estudis previs, el objectiu va ser millorar la selectivitat als productes desitjats mitjançant el hidrocraqueix i la hidroisomerització d'olefines i parafines amb l'ajuda de l'alta pressió parcial d'hidrogen.
[EN] The present thesis is focused on the development of new gas-separation membranes, as well as their in-situ integration on catalytic membrane reactors for process intensification. For this purpose, several materials have been synthesized such as polymers for membrane manufacture, catalysts for CO2 methanation and Fischer-Tropsch synthesis reaction, and inorganic materials in form of nanometer-sized particles for their use in mixed matrix membranes. Regarding membranes manufacture, this thesis deals mainly with two types: organic and inorganic. With regards to the organic membranes, different polymeric materials have been considered as promising candidates, both for the selective layer of the membrane, as well as a support thereof. Polyimides have been selected since they are materials with very high glass transition temperatures, in order to be used in industrial reactions which take place at temperatures around 250-300 ºC. To obtain highly permeable membranes, while maintaining a good selectivity, it is necessary to develop selective layers of less than one micron. Using another type of polymer as support material, it is not necessary to study the compatibility between membrane and support. On the other hand, if the support is inorganic, an exhaustive study of the relation between the concentration and the viscosity of the polymer solution is highly necessary. In addition, various inorganic particles were studied to favor the permeation of water through polymeric materials. Secondly, as regards to inorganic membranes, the functionalization of a palladium membrane to favor the permeation of hydrogen and avoid carbon monoxide contamination was carried out. The membrane selective layer was doped with another metal in order to be used in a Fischer-Tropsch reactor. Regarding the design and manufacture of the reactors used during this thesis, a prototype of a microreactor for CO2 methanation was carried out, where a thin-film polymer membrane selective to water was integrated to avoid the deactivation of the catalyst and to displace the equilibrium and increase the CO2 conversion. On the other hand, a Fischer-Tropsch reactor was redesigned to introduce a hydrogen-selective metal membrane and to be able to inject it in a controlled manner. In this way, and following previous studies, the aim is to enhance the selectivity to the target products by hydrocracking and hydroisomerization the olefins and paraffins assisted by the presence of an elevated partial pressure of hydrogen.
I would like to acknowledge the Spanish Government, for funding my research with the Severo Ochoa scholarship.
Escorihuela Roca, S. (2019). Novel gas-separation membranes for intensified catalytic reactors [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/121139
TESIS

Fischer-Tropsch Reaction Water (FTRW) is a high organic strength wastewater produced as a by-product in Sasol’s Fischer-Tropsch Reactors. Typically it has an organic load of 18000 mgCOD/L and is highly acidic with a pH of approximately 3.8. It is deficient in nutrients (N and P and other micronutrients). This dissertation deals with the biological and physico-chemical model development of a dynamic anaerobic digestion model, and explores two different approaches to representing the physico-chemical processes that complement and interact with the bioprocesses. The performances of the resultant two dynamic models (ADFTRW1 & AD-FTRW2) were compared in order to assess to what extent the more detailed and rigorous ionic speciation modeling in AD-FTRW2 addressed the shortcomings attributed to the simplified physicochemical modeling in AD-FTRW1. The ionic speciation model used in AD-FTRW2 uses a classic equilibrium formulation along the same lines as in the UCTADM2 model for anaerobic digestion of municipal wastewater sludges (Brouckaert et al., 2010), while AD-FTRW1 uses a simplification of the approach developed by Musvoto et al. (2000) in order to represent short chain fatty acid (SCFA) dissociation and the weak acid base chemistry of the inorganic carbon system. A 44 day extract from a 700 day laboratory-scale dataset (Van Zyl et al. 2008) was used as the basis for comparing the models. During this period the membrane bio-reactor was subjected to varying flow and load conditions. To validate the models, the experimentally measured and model predicted process variables of reactor alkalinity, reactor pH, biogas production and effluent SCFA concentration were compared. It was found that AD-FTRW2 provided superior agreement with pH data, but predictions of alkalinity, gas production rate and effluent short-chain fatty acids were not significantly improved in AD-FTRW2 relative to AD-FTRW1. This outcome was hypothesized since pH is strongly dependent on physico-chemical processes such as ionic interactions in solution and gas exchange which were the components to the models (AD-FTRW1 versus AD-FTRW2) which differed most significantly. Alkalinity, which is also highly influenced by physico-chemical model representations showed substantial improvement however statistical analysis could not show this improvement to be significant. The other two variables that were compared, biogas production and effluent SCFA concentration, displayed very similar agreement with experimental data. These variables depend more on mass balance effects and biological kinetics and were therefore not significantly altered by the more rigorous handling of aqueous chemistry in AD-FTRW2. It was concluded that AD-FTRW2 constitutes an improvement in model predictive power over AD-FTRW1 at a small cost in computing time.
Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2013.

The Fischer-Tropsch reaction technology is utilised in Sasol’s Coal-to-liquid plant to produce liquid fuels from low grade coal. There are several processes on the Coal-to-liquid plant that generate aqueous streams which contain a high organic load and require treatment. The main contributors to the wastewater are the Phenosolvan plant, producing stripped gas liquor (SGL), and the Synthol plant, producing Fischer-Tropsch reaction water (FTRW). Stripped gas liquor contains water, organic acids, ammonia, and potentially toxic phenols. Fischer-Tropsch reaction water contains volatile fatty acids and alcohol. Stripped gas liquor is therefore nitrogen-rich while FTRW is nitrogen-deficient and requires nutrient supplementation for anaerobic treatment. Therefore co-treatment of the two streams could reduce nitrogen supplementation requirements. This study is part of a larger project to determine the feasibility of anaerobically co-digesting FTRW and SGL. This study has looked at the influence of SGL on the methanogenic activity of FTRW-acclimated sludge and involved the development of a method which allows accurate recording of the methanogenic activity in batch assays. Other studies involving the anaerobic digestion of high phenolic wastewaters showed that the phenol had an inhibitory effect on the specific methanogenic activity of the sludge, which was not acclimated to the phenol. The objective of this work was to test the hypotheses that (1) anaerobic sludge acclimated to FTRW will be inhibited by high molecular weight organics in SGL and (2) FTRW-acclimated sludge will not degrade phenolic compounds in SGL. This information will be used for designing process configurations for simultaneous treatment of the two streams with minimum contamination of the effluent stream. The serum bottle was used as a small batch reactor and the biogas production was monitored as an indication of the state of the reaction. The biogas produced was collected and measured by the downward displacement of a sodium hydroxide solution, which absorbed the carbon dioxide and collected only the methane. A concentration of 1 g COD/ℓ FTRW was chosen as the reference test due to the reproducibility of the replicates within each experiment as well as its reproducibility across different batches of sludge. For the first inhibition test, the test units contained an additional 5% SGL (0.05 g COD/ℓ SGL) and an additional 15% SGL (0.15 g COD/ℓ SGL, i.e. 13% of the total COD load) respectively, added to 1 g COD/ℓ FTRW. The 5% SGL test unit showed no inhibition compared to the reference unit. There was a reduction in the specific methanogenic activity of the 15% SGL test units compared to the reference unit. Since the total COD load was not the same in each unit, it cannot be conclusively stated that the SGL was responsible for the reduction in SMA, but this seems a reasonable possibility in the light of results from the reference test selection experiments which showed higher SMA at higher organic loading rates. For the second inhibition test, the test units contained 85% FTRW (0.85 g COD/ℓ FTRW) and 15% SGL (0.15 g COD/ℓ SGL) to make up a total COD load of 1 g COD/ℓ. There was an increase in the specific methanogenic activity of the test unit compared to the reference unit. There was very little change in the phenol concentration. Therefore, it was concluded the addition of SGL potentially reduced the SMA and that this could be an inhibitory effect, but that any inhibition would be a function of the concentration of potentially inhibitory substances in SGL and that these concentrations vary from batch to batch. However, the degree of SMA reduction is fairly low and would not prevent co-digestion of the two streams at the concentrations tested. It has been shown that FTRW anaerobic digestion can proceed adequately in the presence of SGL. There was some evidence that phenolics were degraded but at a much slower rate than COD. The percentage reduction in SMA due to additional SGL at concentrations and SGL:FTRW ratios tested was between 0 and 51%. Ultimately, this work is a first step in the development of a co-digestion model relating organic loading rate, SGL:FTRW feed ratio to methane recovery and extent of biodegradation of phenol for use in the design and optimization of a co-digestion system.
M.Sc.Eng. University of KwaZulu-Natal, Durban 2014.

This chapter deals with magnetic colloids with catalytic properties for the treatment of polluted waters and the efficient production of fuel alternatives. This kind of materials presents great advantages such as high surface/volume ratio, reproducibility, selectivity, ability to be magnetic harvested, functionalizable surfaces (e.g. with tunable pores and selective chelators deposited on them), high efficiencies and reusability. In particular, this chapter will consider the case of magnetic iron oxide colloids, which can be easily synthesized at low cost, are biocompatible and presents a well-developed surface chemistry. The most common techniques for the synthesis and functionalization of these magnetic nanoparticles will be reviewed and summarized. The iron oxide nanoparticles present outstanding properties that can be exploited in different aspect of the wastewater treatment such as heavy metals and organic pollutants removal by ionic exchange or adsorption, and degradation of the contaminants by advanced oxidation processes, among others. In the field of alternative energies, they have also been used as catalysts for biofuels production from oil crops, in Fischer-Tropsch reactions for liquid hydrocarbons and many other processes with potential environmental impact.

A co-production system based on FT synthesis reactor and gas turbine was simulated and analyzed. Syngas from entrained bed coal gasification was used as feedstock of low temperature slurry phase Fischer-Tropsch reactor. Raw synthetic liquid produced was fractioned and upgraded to diesel, gasoline and LPG. Tail gas composed of unconverted syngas and F-T light component was fed to gas turbine. Supplemental fuel (NG, or refinery mine gas) might be necessary, which was dependent on gas turbine capacity, expander through flow capacity, etc. FT yield information was important to the simulation of this co-production system. A correlation model based on Mobil’s two step pilot plant was applied. This model proposed triple chain-length-dependent chain growth factors and set up correlations among reaction temperature with wax yield, methane yield, and C2-C22 paraffin and olefin yields. Oxygenates in hydrocarbon phase, water phase and vapor phase were also correlated with methane yield. It was suitable for syngas, iron catalyst and slurry bed. It can show the effect of temperature on products’ selectivity and distribution. Deviations of C5+ components yields and distributions with reference data were less than 3%. To light gas components were less than 2%. User models available to predict product yields, distributions, cooperate with other units and do sensitive studies were embedded into Aspen plus simulation. Performance prediction of syngas fired gas turbine was the other key of this system. The increase in mass flow through the turbine affects the match between compressor and turbine operating conditions. The calculation was carried out by GS software developed by Politecnico Di Milano and Princeton University. The simulated performance assumed that the expander operates under choked conditions and turbine inlet temperature equals to NG fired gas turbine. A “F” technology gas turbine was selected to generate power. Various cases were investigated so as to match FT synthesis island, power island and gasification island in co-production systems. Effects of CO2 removal/LPG recovery, co-firing, CH4 content variation were studied. Simulation results indicated that more than 50% of input energy was converted to electricity and FT products. Total yield of gasoline, diesel and LPG was 136g-155g/NM3(CO+H2). At coal feed 21.9kg/s, net electricity exported to grid was higher than 100MW. Total production of diesel and gasoline (and LPG) was 118,000 tons(134,000tons)/Year. Under economic analysis conditions assumed in this paper, co-production system was economic feasible. The after tax profits can research 17 million EURO. Payback times were ranged from 6-7 years.

Three major challenges — grid stability, domestic oil limitations, and climate change — could all be addressed simultaneously by using off-peak electrical energy to recycle CO2 into liquid fuels (such as gasoline, jet fuel, and diesel). Simulations have shown that recent innovations should make it practical to reduce CO2 to CO at over 66% of theoretical efficiency limits. When combined with other process advances, it would then be possible to synthesize most hydrocarbons and alcohols from point-source CO2 and clean off-peak grid energy (wind or nuclear) at system efficiencies in the range of 51–61%. Energy storage density in renewable, carbon-neutral kerosene is 44 MJ/kg, compared to ∼0.4 MJ/kg for Li-ion batteries. This process begins by electrolyzing water using clean energy to get the hydrogen required by the Reverse Water Gas Shift (RWGS) reactor and by a novel Renewable Fischer Tropsch Synthesis (RFTS) process. Off-peak grid energy averaged only $13/MWhr in the Minnesota hub in 2009. At such prices, the synthesized liquid fuels (“WindFuels”) should compete even when petroleum is only $50/bbl. Considerable effort over the past decade has been put into exploring high-temperature (HT) paths toward the production of renewable syngas (H2 + CO) that could lead to sustainable synthesis of liquid fuels; but competitive fuel production from these HT thermo-chemical routes still appears to be decades away. An alternative path — the RWGS reaction — utilizes much less aggressive conditions and should be much more practical. With low-cost hydrogen becoming available from off-peak wind and nuclear, efficient reduction of CO2 to CO becomes viable at moderate temperatures (750–1000 K) via the RWGS reaction. Challenges arise because of equilibrium limits imposed by the reaction thermodynamics below 800 K and because of competing methanation and coking reactions above 800 K to 1000 K, depending on the catalysts. Several promising sets of conditions and catalysts are being evaluated. To drive the reaction to the right, a multi-stage process is required with efficient separation processes. This in turn depends on advances in cost-effective gas-to-gas recuperators for relatively low pressures to limit parasitic methanation reactions. Another challenge may be passivation of the recuperator surfaces to minimize hydrogenation of the CO during the heat recovery. Preliminary simulations indicate reduction of CO2 to CO with about 2.2 MJ/kg-CO should be practical at commercial scale.

Abstract Biogas, a promising alternative fuel, a substitute for fossil fuels, is predominantly a mixture of methane and carbon dioxide. Both are major greenhouse gases. Methane has a long-term effect on the environment while carbon dioxide is recycled by the plants. Hence, capture and burning of biogas to consume methane as a fuel is desired both from energy and environmental outlook. The presence of a large amount of carbon dioxide in biogas, however, impairs combustion in engines resulting into slow burning and higher hydrocarbon and carbon monoxide emissions. Dry reforming, a conversion process of biogas to synthesis gas (syngas), a mixture of hydrogen and carbon monoxide, is a catalytic process that has the potential to greatly improve biogas combustion in engines. The researchers’ focus in dry reforming, however, has been for the generation of hydrogen for fuel cells and reactants for Fischer Tropsch process in industry — this approach aims towards maximum conversion of methane and carbon dioxide. The work presented here investigates the possibility of partial conversion of biogas to harness maximum energy and reduce emissions from I.C. Engines. The published research on dry reforming of biogas has examples of high concentrations of methane in the syngas with calorific values suitable for I.C. Engine application. For example, a 50:50 v/v CH4/CO2 composition biogas has calorific value of 13.33 MJ/kg which when converted to a syngas at 550°C results in a gas with 18:42:14:26 v/v CO2/CH4/H2/CO and a calorific value of 19.96 MJ/kg). Such compositions have moderate percentage of hydrogen to act as combustion enhancer and the carbon dioxide present helps to control NOx emissions. The major contributors of energy are methane and carbon monoxide in these cases. The dry reforming reaction is an endothermic reaction, which produces hydrogen. The side reactions that happen are the reverse water gas shift reaction, which reduces hydrogen yield and the Bouduard reaction which results in carbon deposition on the catalyst surface. The reactor conditions need to be chosen appropriately, especially the reactor temperature. Simulation of dry reforming reaction using a process simulation software (Aspen Plus) is carried out to find the extent of conversion and exit syngas composition for different biogas compositions. The endothermic heat for the reactor can be provided by the heat of the engine exhaust — therefore, an opportunity exists to use waste heat recovery from the engine exhaust. However, there is a tradeoff between the reactor temperature, syngas composition going to engine inlet and the engine exhaust heat — which is investigated in this study.

Doty Energy is developing advanced processes to permit the production of fully carbon-neutral gasoline, jet fuel, diesel, ethanol, and plastics from exhaust CO2 and off-peak clean energy (wind and nuclear) at prices that can compete with fossil-derived products. Converting CO2 into fuels will eliminate the need for CO2 sequestration, reduce global CO2 emissions by 40%, and provide a nearly insatiable market for off-peak wind. It has long been known that it is theoretically possible to convert CO2 and water into standard liquid hydrocarbon fuels at high efficiency. However, the early proposals for doing this conversion had efficiencies of only 25% to 35%. That is, the chemical energy in the liquid fuels produced (gasoline, ethanol, etc.) would be about the 30% of the input energy required. The combination of the eight major technical advances made over the past two years should permit this conversion to be done at up to 60% efficiency. Off-peak grid energy averaged only $16.4/MWhr in the Minnesota hub throughout all of 2009 (the cheapest 6 hours/day averaged only $7.1/MWh). At such prices, the synthesized standard liquid fuels (dubbed “WindFuels”) should compete even when petroleum is only $45/bbl. A more scalable alternative for transportation fuels is needed than biofuels. It is in our economic and security interests to produce transportation fuels domestically at the scale of hundreds of billions of gallons per year. WindFuels can scale to this level, and as they are fully carbon-neutral they will dramatically reduce global CO2 emissions at the same time. Switching 70% of global transportation fuels from petroleum to WindFuels should be possible over the next 30 years. WindFuels will insure extremely strong growth in wind energy for many decades by generating an enormous market for off-peak wind energy. WindFuels is based largely on the commercially proven technologies of wind energy, water electrolysis, and Fischer Tropsch (FT) chemistry. Off-peak low carbon energy is used to split water into hydrogen and oxygen. Some of the hydrogen is used to reduce CO2 into carbon monoxide (CO) and water via the Reverse Water Gas Shift (RWGS) reaction. The CO and the balance of the hydrogen are fed into an FT reactor similar to those used to produce fuels and chemicals from coal or natural gas. The processes have been simulated, and key experiments are being carried out to help optimize process conditions and validate the simulations.

Simulations have shown that it should be possible (within a relatively short time frame) to profitably synthesize high-purity carbon-neutral ethanol, gasoline, jet fuel, propylene, and many other hydrocarbons, in volumes that cannot be matched by any other renewable avenue, from captured CO2, water, and cheap off-peak low-carbon energy, notably form wind farms. The process, dubbed WindFuels, requires no biomass, and it is expected to solve the grid stability and energy storage challenges of wind energy. The process is based largely on the commercially proven technologies of wind energy, water electrolysis, and Fischer Tropsch Synthesis (FTS) chemistry. Wind energy is used to electrolyze water into hydrogen and oxygen. Some of the hydrogen is used in a process, the so-called reverse water gas shift (RWGS) reaction, that reduces CO2 to carbon monoxide (CO) and water. The CO and the balance of the hydrogen are fed into an FT reactor, similar to that commonly used to produce fuels and chemicals from coal or natural gas. Improved sub-processes have been simulated in detail, and key experiments will soon be carried out to help optimize process conditions. Conversion efficiencies (from input electrical to output chemical) are expected to approach 60%. Putting renewable hydrogen into liquid fuels solves the distribution and storage problems that have beset utilization of hydrogen in vehicles. Converting CO2 into fuels can eliminate the need for CO2 sequestration and reduce global CO2 emissions by 40% by mid-century. The amount of water needed for the renewable FTS (RFTS) process is an order of magnitude less than needed for biofuels. The atmosphere will eventually provide an unlimited source for CO2, though initially the CO2 would come from ammonia plants, biofuel refineries, cement factories, fossil power plants, and ore refineries. When the input energy is from off-peak wind and reasonable monetary credit is included for climate benefit, WindFuels could compete when petroleum is as low as $45/bbl.

The rapidly increasing cost of petroleum products and uncertainty of long-term supply have prompted the U.S. military to aggressively pursue production of alternative fuels (synfuels) such as coal-to-liquids (CTL). U.S. Air Force is particularly active in this effort while the entire military is involved in simultaneously developing fuel specifications for alternative fuels that enable a single fuel for the entire battle space; all ground vehicles, aircraft and fuel cells. By limiting its focus on coal, tar sands and oil shale resources, the military risks violating federal law which requires the use of synfuels that have lifecycle greenhouse gas emissions less than or equal to emissions from conventional petroleum fuels. A climate-friendly option would use a high temperature nuclear reactor to split water. The hydrogen (H2) would be used in the reverse water gas shift (RWGS) to react with carbon dioxide (CO2) to produce carbon monoxide (CO) and water. The oxygen (O2) would be fed into a supercritical (SC) coal furnace. The flue gas CO2 emissions would be stripped of impurities before reacting with H2 in a RWGS process. Resultant carbon monoxide (CO) is fed, with additional H2, (extra H2 needed to adjust the stoichiometry: 2 moles H2 to one mole CO) into a conventional Fischer-Tropsch synthesis (FTS) to produce a heavy wax which is cracked and isomerized and refined to Jet Propulsion 8 (JP-8) and Jet Propulsion 5 (JP-5) fuels. The entire process offers valuable carbon-offsets and multiple products that contribute to lower synfuel costs and to comply with the federal limitation imposed on synfuel purchases. While the entire process is not commercially available, component parts are being researched; their physical and chemical properties understood and some are state-of-the-art technologies. An international consortium should complete physical, chemical and economic flow sheets to determine the feasibility of this concept that, if pursued, has broad applications to military and civilian aviation fleets and freight-hauling diesel engines.

This review paper describes techniques proposed for applying microwave-induced plasma gasification (MIPG) for cleaning rivers, lakes and oceans of synthetic and organic waste pollutants by converting the waste materials into energy and useful raw materials. Rivers close to urban centers tend to get filled with man-made waste materials, such as plastics and paper, gradually forming floating masses that further trap biological materials and animals. In addition, sewage from residences and industries, as well as rainwater runoff pour into rivers and lakes carrying solid wastes into the water bodies. As a result, the water surfaces get covered with a stagnant, thick layer of synthetic and biological refuse which kill the fish, harm animals and birds, and breed disease-carrying vectors. Such destruction of water bodies is especially common in developing countries which lack the technology or the means to clean up the rivers. A terrible consequence of plastic and synthetic waste being dumped irresponsibly into the oceans is the presence of several large floating masses of garbage in the worlds’ oceans, formed by the action of gyres, or circulating ocean currents. In the Pacific Ocean, there are numerous debris fields that have been labeled the Great Pacific Garbage Patch. These patches contain whole plastic litters as well as smaller pieces of plastic, called microplastics, which are tiny fragments that were broken down by the action of waves. These waste products are ingested by animals, birds and fishes, causing death or harm. Some of the waste get washed ashore on beaches along with dead marine life. The best solution for eliminating all of the above waste management problems is by the application of MIPG systems to convert solid waste materials and contaminated water into syngas, organic fuels and raw materials. MIPG is the most efficient form of plasma gasification, which is able to process the most widest range of waste materials, while consuming only about a quarter of the energy released from the feedstock. MIPG systems can be scaled in size, power rating and waste-treatment capacity to match financial needs and waste processing requirements. MIPG systems can be set up in urban locations and on the shores of the waterbody, to filter and remove debris and contaminants and clean the water, while generating electric power to feed into the grid, and fuel or raw materials for industrial use. For eliminating the pelagic debris fields, the proposed design is to have ships fitted with waste collector and filtration systems that feeds the collected waste materials into a MIPG reactor, which converts the carbonaceous materials into syngas (H2 + CO). Some of the syngas made will be used to produce the electric power needed for running the plasma generator and onboard systems, while the remainder can be converted into methanol and other useful products through the Fischer-Tropsch process. This paper qualitatively describes the implementation schemes for the above processes, wherein MIPG technology will be used to clean up major waste problems affecting the earth’s water bodies and to convert the waste into energy and raw materials in a sustainable and environmentally friendly manner, while reducing the dependence on fossil fuels and the release of carbon dioxide and methane into the atmosphere.