Study Of The Coupling Of Heterogeneous Catalysis And Membrane Separation For Biodiesel Production

The dwindling petroleum reserves and increasingly serious environmental problems demand a substitute for petroleum oil. Among all the potential alternatives, biodiesel which commonly consists of fatty acid methyl ester (FAME) is a promising one. Recently, such reactive-separation processes as reactive distillation, reactive absorption, and membrane reactors based on esterification or transesterification reactions carried out in integrated units have been introduced to the biodiesel production. Among them, membrane reactor technology attracts much interest for its ability to obtain high quality biodiesel and remarkable biodiesel yield.In this work, solid alkali, soild acid and monolithic catalyst were used in a membrane reactor in order to obtain a process in which heterogeneous catalyzed transesterification and membrane separation processes were coupled. The effects of reaction temperature, catalyst amount and circulation velocity on the production of biodiesel were investigated. The membrane reaction system was simulated using Aspen Plus and a model was established for the biodiesel production in the membrane reactor. A KF/HT/CM catalytic membrane was prepared for the use in membrane reactor in the future.1. Transesterification of soybean oil to produce biodiesel was performed in a membrane reactor packed with shaped KF/Ca-Mg-Al hydrotalcite solid base. The micro-filtration ceramic membrane was used to retain the oil during the transesterification reaction. High quality biodiesel was produced by the coupling of heterogeneous alkali catalyzed transesterification and separation process in the fixed bed membrane reactor. The central composite design (CCD) of response surface methodology (RSM) was employed to investigate the effects of reaction temperature, catalyst amount and circulation velocity on the biodiesel production.70℃ reaction temperature,0.531 g/cm3 catalyst amount and 3.16 mL/min circulation velocity was found to be the optimum condition, achieving a 91% biodiesel yield within 3 h of circulation time. The biodiesel yield remained 85% when the catalyst was employed for the third time.2. Production of biodiesel from the transesterification between soybean oil and methanol was conducted in this study by a membrane reactor, in which ceramic membrane was packed with MCM-41 supported p-toluenesulfonic acid (PTSA). Box-Behnken design and RSM were used to investigate the effects of reaction temperature, catalyst amount and circulation velocity on the yield of biodiesel. A reduced cubic model was developed to navigate the design space. Reaction temperature was found to have most significant effect on the biodiesel yield while the interaction of catalyst amount and circulation velocity have minor effect on it.80℃ of reaction temperature,0.27 g/cm3 of catalyst amount and 4.15 mL/min of circulation velocity were proved to be the optimum conditions to achieve the highest biodiesel yield. The biodiesel yield remained 91.7% of the fresh catalyst when the PTSA/MCM-41 used for a third time.3. Ca-Mg-Al hydrotalcite was deposited on the inert honeycomb ceramic surface as a second carrier and KF was loaded on the support as an active component. The KF/Ca-Mg-Al hydrotalcite/honeycomb ceramic monolithic catalyst was packed in the membrane reactor for biodiesel production from the transesterification between soybean oil and methanol. The central composite design (CCD) of response surface methodology (RSM) was employed to investigate the effects of reaction temperature, catalyst amount and circulation velocity on the production of biodiesel. A quadratic model was developed to navigate the design space. Assisted by the software, reaction temperature of 70℃, catalyst amount of 1.5 g and circulation velocity of 4.9 mL/min is found to be the optimum condition. The highest biodiesel yield could achieve 91.6% and the catalyst showed a reasonable stability under the optimum conditions suggested by the software.4. The kinetics parameters, liquid-liquid equilibrium parameters and the filtration equation were obtained from the experiment. A model for the membrane system in Chapter 2 based on reaction, phase equilibrium and micro-filtration was developed. The membrane reaction was simulated with the assistance of Aspen Plus. The results of simulation and model showed that the reaction system maintained in two phase when the conversion of soybean oil blow 70% with an initial mass ratio of 0.4～0.6. When the oil conversion was lower than 60%, the oil content in the methanol rich phase was relatively low and can be treated as oil free. With the same reaction time, the biodiesel yield increased with the increase of reaction temperature. However, the increasing trends were almost the same. If adequate time was given, the final yields were also the same even with lower reaction temperature, indicating that the membrane reactor was particularly useful in removing unreacted oil from the FAME and shifting the reaction equilibrium to the product side.5. Ca-Mg-Al HT was coated on the surface of CM by in situ hydrothermal synthesis method. Such preparative parameters of HT/CM as crystallization time, crystallization temperature and molar ratio of raw materials were investigated and found to affect the crystallinity and the direct growth of HT on CM. KF was loaded on HT/CM prepared at proper conditions by impregnation and calcination. FAME yield of transesterification between palm oil and methanol was used to determine the catalytic activity of prepared KF/HT/CM. According to the XRD and SEM results of the HT/CM samples, crystallized at 150℃ for 6 h with urea to cations molar ratio of 3:1 was considered to be the proper condition of the in situ synthesis of HT on CM. The catalytic test showed that the KF/HT/CM with the KF load ratio of 92.1 and 110.9 wt.% had the best activity and reusability. With respect to pure powder KF/HT, the as-coated KF/HT on supports was observed a similar catalytic performance when the load ratio of KF was relatively high.