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Subject: search.filters.subject.Membrane reactors

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    Optimization of biodiesel production using heterogenous catalyst in a packed bed reactor
    (2018) Ayodeji, Olagunju Olusegun; Musonge, Paul
    Industrial development is associated with an increase in pollution levels and rising fuel prices. Research on clean energy contributes to reduction of fossil fuel dependency, decrease in ozone layer depletion and reduction in emission of toxic gases. The development of renewable energies increases the energy independence and reduces the impact of environmental pollution from fossil fuels. The biodiesel market is among the fastest growing renewable energy markets and its demand in the energy sector has tremendously increased over the last decade due to its environmental friendly qualities. Biodiesel is considered as a promising diesel fuel substitute based on the similarities of its properties with that of petroleum based diesel fuel. However, the high cost of the feedstock, environmental pollution as a result of wastewater generated from a homogeneous process has limited its full implementation. In addition, other technical challenges encountered during the production such as the immiscibility of the reagents and the reversibility of the transesterification reaction calls for innovative technologies to be developed. One promising solution to these issues is the use of membrane technology to serve as a reaction and separating medium for the production of biodiesel. This study is aimed at optimizing biodiesel production from vegetable oils using heterogeneous catalysts in a ceramic membrane. The objectives were to evaluate the performance of calcium oxide (CaO) as a catalyst supported on activated carbon in a membrane reactor for biodiesel production. Further still, to evaluate the membrane performance regarding permeate quality and to optimize the process using design of experiment. The final objective was to investigate the influence of operating parameters such as temperature, methanol/oil ratio, catalyst amount and reaction time on biodiesel yield. The transesterification of soya bean oil with methanol in the presence of a supported catalyst was carried out on a laboratory scale. The membrane reactor was designed and assembled for this purpose. The membrane reactor integrated many procedures such as combining reaction and separation in a single unit, continuous mixing of raw materials and maintaining high mass transfer between the immiscible phases during the reaction. The effect of the process parameters on the biodiesel production and FAME (fatty acid methyl ester) yields were investigated. One factor at a time (OFAT) experiments were conducted to identify the optimum range of the yield. The membrane reactor produced a permeate stream which separated at room temperature into a FAME rich non-polar phase and a methanol polar phase. The optimum range was between 90% - 94% within a reaction time of 60 – 180 minutes, methanol to oil ratio 3:1 - 9:1 and temperature range of 60 0C - 70 0C. Methyl ester produced met the ASTM D6751 and SANS 1935 specifications. The response surface methodology (RSM) based on the central composite design (CCD) was used to optimize the process. The optimization experiments were conducted around the optimum range established by the OFAT method. The optimum condition for transesterification of soya bean oil to fatty acid methyl ester was obtained at 3 g/L catalyst concentration, 65 0C temperature, 4.5:1 methanol to oil molar ratio and 90 minutes reaction time. At these optimum conditions, the FAME yield was 96.9 %, which is well within the yield of 97.7 % as predicted by the model. In conclusion, this work presents a study of high quality biodiesel production using a ceramic membrane reactor with the advantage of selectively permeating FAME and methanol. This study therefore showed that the use of a membrane for biodiesel production conserved water for other purposes; eliminates the purification step and wastewater generation thereby reducing the cost of biodiesel production.
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    Development and evaluation of woven fabric immersed membrane bioreactor for treatment of domestic waste water for re-use
    (2014) Cele, Mxolisi Norman; Rathilal, Sudesh; Pillay, Visvanathan Lingamurti
    Increased public concern over health and the environment, the need to expand existing wastewater treatment plants due to population increase, and increasingly stringent discharge requirements, have created a need for new innovative technologies that can generate high quality effluent at affordable cost for primary and secondary re-use. The membrane biological reactor (MBR) process is one of the innovative technologies that warrant consideration as a treatment alternative where high quality effluent and/or footprint limitations are a prime consideration. MBR processes have been applied for the treatment of industrial effluent for over ten years (Harrhoff, 1990). In this process, ultrafiltration or microfiltration membranes separate the treated water from the mixed liquor, replacing the secondary settling tanks of the conventional activated sludge process. Historically, energy costs associated with pumping the treated water through the membranes have limited widespread application for the treatment of high volumes of municipal wastewater. However, recent advancements and developments in membrane technology have led to reduced process energy costs and induced wider application for municipal wastewater treatment (Stephenson et al., 2000). This report describes a small and pilot scale demonstration study conducted to test a woven fabric microfiltration immersed membrane bioreactor (WFM-IMBR) process for use in domestic wastewater treatment. The study was conducted at Durban Metro Southern Wastewater Treatment Works, Veolia Plant, South Africa. The main objective of this project was to develop and evaluate the performance of an aerobic woven fabric microfiltration immersed membrane bioreactor (WFM-IMBR) for small scale domestic wastewater treatment. The experiments were oriented towards three sub objectives: to develop the membrane pack for immersed membrane bioreactor based on WF microfilters; to evaluate the hydrodynamics of WF membrane pack for bioreactor applications; and to evaluate the long-term performance and stability of WFM-IMBR in domestic waste water treatment. The literature was reviewed on membrane pack design for established commercial IMBR. The data collected from literature was then screened and used to design the WF membrane pack. Critical flux was used as the instrument to measure the WF membrane pack hydrodynamics. Long-term operation of the WFM-IMBR was in two folds: evaluating the performance and long term stability of WFM-IMBR. The membrane pack of 20 flat sheet rectangular modules (0.56 m by 0.355 m) was developed with the gap of 5 mm between the modules. The effects of parameters such as mixed liquor suspended solids or aeration on critical flux were examined. It was observed that the critical flux decreased with the increase of sludge concentration and it could be enhanced by improving the aeration intensity as expected and in agreement with the literature. Hence the operating point for long term subcritical operation was selected to be at a critical flux of 30 LMH and 7.5 L/min/module of aeration. Prior to the long term subcritical flux of WFM-IMBR, the operating point was chosen based on the hydrodynamic study of the WF membrane pack. The pilot scale WFM-IMBR demonstrated over a period of 30 days that it can operate for a prolonged period without a need for cleaning. Under subcritical operation, it was observed that there was no rise in TMP over the entire period of experimentation. Theoretically this was expected but it was never investigated before. Good permeate quality was achieved with 95% COD removal and 100% MLSS removal. The permeate turbidity was found to be less than 1 NTU and it decreased with an increase in time and eventually stabilized over a prolonged time. Woven fibre membranes have demonstrated great potential in wastewater treatment resulting in excellent COD and MLSS removal; low permeate turbidity and long term stability operation. From the literature surveyed, this is the first study which investigated the use of WF membranes in IMBRs. The study found that the small scale WFM-IMBR unit can be employed in fifty equivalence person and generate effluent that is free of suspended solids, having high levels of solid rejection and has acceptable discharge COD for recycle. Future work should be conducted on energy reduction strategies that can be implemented in WFM-IMBR for wastewater treatment since high energy requirements have been reported by commercial IMBRs.
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    Development and evaluation of silicone membrane as aerators for membrane bioreactors
    (2005) Mbulawa, Xolani Proffessor
    In bubble-less aeration oxygen diffuses through the membrane in a molecular form and dissolves in the liquid. Oxygen is fed through the lumen side of silicone rubber tube. On the outer surface of the membrane there is a boundary layer that is created by oxygen. This then gets transported to the bulk liquid by convective transport created by water circulation through the pump. The driving force of the convective transport is due to concentration difference between the dissolved oxygen in water and oxygen saturation concentration in water at a particular temperature and pressure. The design of a membrane aerated bioreactor needs an understanding of the factors that govern oxygen mass transfer. It is necessary to know the effects of operating conditions and design configurations. Although various methods of bubble-less aeration have been reported, there still exists a lack of knowledge on the immersed membrane systems. This study is aiming at contributing to the development of an immersed membrane bioreactor using silicone rubber tubular membrane as means of providing oxygen. The secondary objective was to investigate the influence that the operating conditions and module configuration have on the system behaviour. From the experimental study, the characteristic dissolved oxygen -time curve show that there is a saturation limit equivalent to the equilibrium dissolved oxygen concentration, after which there is no increase in dissolved oxygen with time. At ambient conditions the equilibrium dissolved oxygen is approximately 8 mg/L. This is when water is in contact with air at one atmospheric pressure. At the same conditions the equilibrium dissolved oxygen concentration when water is in contact with pure oxygen is approximately 40 mg/L. This is why all the experiments were conducted from 2mg/L dissolved oxygen concentration in water, to enable enough time to reach equilibrium so as to determine mass transfer coefficient. The most important parameters that were investigated to characterise the reactor were, oxygen supply pressure, crossflow velocity, temperature and module orientation. Observations from the experimental study indicated that when the system is controlled by pressure, crossflow does not have a significant effect on mass transfer. When the system is controlled by the convective transport from the membrane surface to the bulk liquid, pressure does not have a significant effect on mass transfer. All four effects that were investigated in the study are discussed.