Dissertations / Theses on the topic 'Hollow fiber reactor'

Protecting the quality and quantity of our water resources requires advanced treatment technologies capable of removing nutrients from wastewater. This research work investigated the capability of one such technology, a hollow-fiber membrane-aerated biofilm reactor (HFMBR), to achieve completely autotrophic nitrogen removal from a wastewater with high nitrogen content. Because the extent of oxygenation is a key parameter for controlling the metabolic processes that occur in a wastewater treatment system, the first part of the research investigated oxygen transfer characteristics of the HFMBR in clean water conditions and with actively growing biofilm. A mechanistic model for oxygen concentration and flux as a function of length along the non-porous membrane fibers that comprise the HFMBR was developed based on material properties and physical dimensions. This model reflects the diffusion mechanism of non-porous membranes; namely that oxygen follows a sorption-dissolution-diffusion mechanism. This is in contrast to microporous membranes in which oxygen is in the gas phase in the fiber pores up to the membrane surface, resulting in higher biofilm pore liquid dissolved oxygen concentrations. Compared to offgas oxygen analysis from the HFMBR while in operation with biofilm growing, the model overpredicted mass transfer by a factor of approximately 1.3. This was in contrast to empirical mass transfer coefficient-based methods, which were determined using either bulk aqueous phase dissolved oxygen (DO) concentration or the DO concentration at the membrane-liquid interface, measured with oxygen microsensors. The mass transfer coefficient determined with the DO measured at the interface was the best predictor of actual oxygen transfer under biofilm conditions, while the bulk liquid coefficient underpredicted by a factor of 3. The mechanistic model exhibited sensitivity to parameters such as the initial lumen oxygen concentration (at the entry to the fiber) and the diffusion coefficient and partitioning coefficients of oxygen in the silicone membrane material. The mechanistic model has several advantages over empirical-based methods. Namely, it does not require experimental determination of KL, it is relatively simple to solve without the use of advanced mathematical software, and it is based upon selection of the membrane-biofilm interfacial DO concentration. The last of these is of particular importance when designing and operating HFMBR systems with redox (aerobic/anoxic/anaerobic) stratification, because the DO concentration will determine the nature of the microenvironments, the microorganisms present, and the metabolisms that occur. During the second phase of the research, the coupling of two autotrophic metabolisms, partial nitrification to nitrite (nitritation) and anaerobic ammonium oxidation, was demonstrated in a single HFMBR. The system successfully treated a high-strength nitrogen wastewater intended to mimic a urine stream from such sources as extended space missions. For the last 250 days of operation, operating with an average oxygen to ammonia flux (JO2/JNH4+) of 3.0 resulted in an average nitrogen removal of 74%, with no external organic carbon added. Control of nitrite-oxidizing bacteria (NOB) presented a challenge that was addressed by maintaining the JO2/JNH4+ below the stoichiometric threshold for complete nitrification to nitrate (4.57 g O2 / g NH4 +). The DO-limiting condition resulted in formation of harmful gaseous emissions of nitrogen oxides (NO, N2O), which could not be prevented by short-term control strategies. Controlling JO2/JNH4+ prevented NOB proliferation long enough to allow an anaerobic ammoniaoxidizing bacteria (AnaerAOB) population to develop and be retained for >250 days. Addition of a supplemental nutrient solution may have contributed to the growth of AnaerAOB by overcoming a possible micronutrient deficiency. Disappearance of the gaseous nitrogen oxide emissions coincided with the onset of anaerobic ammonium oxidation, demonstrating a benefit of coupling these two autotrophic metabolisms in one reactor. Obvious differences in biofilm density were evident across the biofilm depth, with a region of low density in the middle of the biofilm, suggesting that low cell density or exocellular polymeric substances were primarily present in this region, Microbial community analysis using fluorescence in situ hybridization (FISH) did not reveal consistent trends with respect to length along the fibers, but radial stratification of aerobic ammonia-oxidizing bacteria (AerAOB), NOB, and AnaerAOB were visible in biofilm section samples. AerAOB were largely found in the first 25% of the biofilm near the membrane, AnaerAOB were found in the outer 30%, and NOB were found most often in the mid-depth region of the biofilm. This community structure demonstrates the importance of oxygen availability as a determinant of how microbial groups spatially distribute within an HFMBR biofilm. The combination of these two aspects of the research, predictive oxygen transfer capability and the effect of oxygen control on performance and populations, provides a foundation for future application of HFMBR technology to a broad range of wastewaters and treatment scenarios.
Ph. D.

Biofuel production via fermentation is produced primarily by fermentation of simple sugars. Besides the sugar fermentation route, there exists a promising alternative process that uses syngas (CO, H2, CO2) produced from biomass as building blocks for biofuels. Although syngas fermentation has many benefits, there are several challenges that still need to be addressed in order for syngas fermentation to become a viable process for producing biofuels on a large scale. One challenge is mass transfer limitations due to low solubilities of syngas species. The hollow fiber reactor (HFR) is one type of reactor that has the potential for achieving high mass transfer rates for biofuels production. However, a better understanding of mass transfer limitations in HFRs is still needed. In addition there have been relatively few studies performing actual fermentations in an HFR to assess whether high mass transfer rates equate to better fermentation results. Besides mass transfer, one other difficulty with syngas fermentation is understanding the role that CO and H2 play as electron donors and how different CO and H2 ratios effect syngas fermentation. In addition to electrons from CO and H2, electrodes can also be used to augment the supply of electrons or provide the only source of electrons for syngas fermentation. This work performed an in depth reactor comparison that compared mass transfer rates and fermentation abilities. The HFR achieved the highest oxygen mass transfer coefficient (1062 h-1) compared to other reactors. In fermentations, the HFR showed very high production rates (5.3 mMc/hr) and ethanol to acetic acid ratios (13) compared to other common reactors. This work also analyzed the use of electrons from H2 and CO by C. ragsdalei and to study the effects of these two different electron sources on product formation and cell growth. This study showed that cell growth is not largely effected by CO composition although there must be at least some minimum amount of CO present (between 5-20%). Interestingly, H2 composition has no effect on cell growth. Also, more electron equivalents will lead to higher product formation rates. Following Acetyl-CoA formation, H2 is only used for product formation but not cell growth. In addition to these studies on electrons from H2 and CO, this work also assessed the redox states of methyl viologen (MV) for use as an artificial electron carrier in applications such as syngas fermentation. A validated thermodynamic model was presented in order to illustrate the most likely redox state of MV depending on the system setup. Variable MV extinction coefficients and standard redox potentials reported in literature were assessed to provide recommended values for modeling and analysis. Model results showed that there are narrow potential ranges in which MV can change from one redox state to another, thus affecting the potential use as an artificial electron carrier.

Pre-combustion decarbonisation is one of the three main routes widely discussed for CO2 capture from fossil fuels. This thesis focuses on the development of a catalytic hollow fibre membrane reactor for the combined steam methane reforming (SMR) and water-gas shift (WGS) reaction, using a Ni-based catalyst, and at a temperature window suitable for harvesting pure H2, a clean energy carrier, from the reaction by a Pd membrane. Apart from developing the catalyst and the Pd-based composite membrane, which are normally considered as the two essential components of a membrane reactor involving hydrogen separation, this study introduces the concept of incorporating the catalyst into a micro-structured ceramic hollow fibre substrate to promote mass transfer efficiency. Meanwhile, the impact of each fabrication step, i.e. catalyst composition and preparation, ceramic hollow fibre fabrication, catalyst incorporation and electroless plating of Pd membranes, on the assembly and final performance of the catalytic hollow fibre membrane reactor was systematically evaluated. In contrast to previous studies involving micro-structured ceramic hollow fibres for catalytic reactions, the one developed in this study possesses a plurality of unique micro-channels, with significant openings on the inner surface of the ceramic hollow fibre. In addition to reduced mass transfer resistance for both catalytic reaction and hydrogen permeation, a microstructure of this type significantly facilitates catalyst incorporation and, as a results, enable the application of this hollow fibres for a wider spectrum of catalytic reactions.

An asymmetric ceramic hollow fibre is proposed as a substrate for the development of a catalytic hollow fibre microreactor (CHFMR) and a catalytic hollow fibre membrane microreactor (CHFMMR). The ceramic substrate that is prepared using the phase inversion and sintering technique has a finger-like structure and a sponge-like region in the inner region and the outer surface respectively. The finger-like structure consists of thousands of conical microchannels distributed perpendicularly to the lumen of ceramic hollow fibres onto which a catalyst is impregnated using the sol-gel Pechini method to improve a catalytic reaction. To further enhance the catalytic reaction, a membrane has been incorporated on the outer layer of ceramic hollow fibre. This study focuses on the use of palladium (Pd) and palladium/silver (Pd/Ag) membranes to separate hydrogen from reaction zones in the water-gas shift (WGS) reactions and the ethanol steam reforming (ESR) respectively. In the development of CHFMMR, the fabrication of Pd and Pd/Ag membranes is carried out prior to the catalyst impregnation process to avoid the dissolution of catalyst into the plating solution due to the presence of ammonia and ethylenediaminetetraacetic acid (EDTA). The catalytic activity tests show that the CHFMR, that does not have the Pd membrane on its outer surface, improves the carbon monoxide (CO) conversion compared with its fixed-bed counterpart. The presence of conical microchannels is expected to enhance the activities of the catalyst in the substrate. The incorporations of Pd and Pd/Ag membranes on the outer layer of ceramic hollow fibres enable pure hydrogen to be produced in the shell-side for both the WGS reaction and the ESR. The CHFMMR is used to remove one of the products enabling the WGS reaction to favour the formation of product. It also facilitates the small amount of catalyst to be used to produce significant amount of hydrogen in the ESR.

The most significant issue associated with the oxidative methane conversion processes is the use of pure oxygen, which is extremely expensive. By using a dense oxygen permeable membrane reactor, a possible decrease in the air separation cost can be expected due to the elimination of oxygen plants. Besides, higher reaction yields can be attained due to the selective dosing of oxygen into the reaction zone. This thesis focuses on the development and potential application of functional micro-structured catalytic ceramic hollow fibre membrane reactor (CHFMR) in oxidative methane conversion to syngas (known as partial oxidation of methane (POM)) and to ethane and ethylene (known as oxidative coupling of methane (OCM)). As the membrane reactor performance is crucially dependant on the oxygen permeation rate and good contact between oxygen and methane, two types of membrane reactor designs were proposed in this study. The first design involves the development of CHFMR that consists of two layers i.e.: an outer oxygen separation layer and an inner catalytic substrate layer, known as dual-layer catalytic hollow fibre membrane reactor (DL-CHFMR). The DL-CHFMR was fabricated via a novel single-step co-extrusion and co-sintering technique, in which the thickness and the composition of each functional layer can be controlled in order to improve reactor performance. The second design involves the development of CHFMR with an outer dense separation layer integrated with conical-shaped microchannels open at the inner surface, created via a viscous fingering induced phase inversion technique. Besides substantially reducing resistance across the membrane, the microchannels can also act as a structured substrate where catalyst can be deposited for the catalytic reaction to take place, forming a catalytic hollow fibre membrane microreactor (CHFMMR). Although the CHFMRs discussed in this study are designed particularly for POM and OCM, there are general advantages of such membrane structures and reactor designs for improving the overall reaction performance. Therefore, these reactor designs can be transferred to other important catalytic reactions.

In recent years ceramic membrane technology has advanced considerably and ceramic membranes are now being applied to a number of high temperature applications, in particular in the energy industry as membrane reactors. Due to the thermal stability of ceramic materials, development in this area is extremely promising as these applications cannot be realized using polymeric membrane technology. Although a wide range of ceramic materials have been developed and processing techniques have improved considerably, the high production cost and lack of control over membrane properties when fabrication processes are scaled up are prohibitive in the commercial application of ceramic membrane technology. However, by using a dry-wet spinning process and the combined phase inversion and sintering technique, novel asymmetric hollow fibre morphologies consisting of a porous sponge-like structure and finger-like macrovoids in which catalyst may be deposited can be prepared in a cost effective way. These asymmetric hollow fibres are prepared from raw materials and are suitable for use in catalytic membrane reactors. Fibre morphology is determined by the rheological properties of the ceramic spinning suspension as well as the parameters used during fibre spinning and the effect of sintering during heat treatment. A generic mechanism has been suggested for the formation of asymmetric structures and the parameters at each of these three stages have been varied systematically in order to predict and control hollow fibre structure. Hollow fibres prepared in this way have been characterized in terms of morphology, pore size distribution, porosity and mechanical strength in terms of their applicability to membrane reactor applications. The versatility of this preparation technique is demonstrated by the inclusion of a chapter describing a catalytic membrane reactor for hydrogen production by water-gas-shift as well as a reactor for the dehydrogenation of propane. It should also be noted that this reactor design could be applied to a number of other catalytic gas phase reactions.

碩士
國立臺灣科技大學
化學工程研究所
81
Denitrification is part of biological process for removing nitrogenous compounds from wastewater. It converts Nitrate, Nitrire into Nitrogen using carb on source as electron donor. In this study,we immobilized enriched denitrifica tion microorganism with hollow fiber and used acetic acid as carbon source to carry out the process of denitrification. Two process were employed to treat the wastewater as follows: (1).Microfiltration hollow fiber reactor with cr- oss flow is applied to treat high strength nitrate industrial wastewater. (2).Dialysis hollow fiber reactor is utilized to treat low strength nitrate domestic wastewater. In the case of cross- flow filtration,the volume- tric loading was 21.2 kgNitrate per cubic meter per day with inflow water at pH=8,nitrate loading 3000p pm,and C/N ratio1.5. The nitrate and T.O.C removal could reach 99% and 95% ,respectively. For the dialysis hollow fiber reactor operation, 100ppm nitrate loading,could be reduced below 10ppm with H.R.T=0.5 hr.

碩士
淡江大學
化學工程學系
88
The reaction of urea and urease is used to study the performance of the hollow-fiber membrane reactors with two different arrangement types. The transport of species through the membrane by diffusion and convection, and the inhibition effect on the enzyme were taken into account. In the theoretical analysis, both the reactor systems with different arrangements were divided into five well-mixed regions and two plug flow reactors. Considering diffusive and convective transports, reaction production and inhibition effect in each region, a set of ordinary differential equations for species was obtained and then solved by numerical method. Thus, the change of the concentrations of urea and ammonium carbonate under different operating conditions could be obtained. The experiments were carried out in a batch-type system under various operating conditions, such as inlet flow rate, inlet concentration of urea, and concentration of urease. The results show that the concentration of ammonium carbonate increases with the flow rate, inlet concentration of urea and concentration of urease. The hollow-fiber membrane reactor with type I arrangement is better than type II in production yield.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1999.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 525-540).

Thesis (M.S.)--University of Wisconsin--Madison, 1996.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 169-178).