Study On The Preparation Of Biodiesel At The Catalysis Of Heterogeneous Catalysts

Biodiesel, as an environmental friendly, renewable and clean liquid fuel, is being greatly concerned and widely developed in the world with increasing of environmental pollution and the reduction of oil resources. Recently, biodiesel is produced by the transesterification of oil and lower alcohols at the catalysis of homogeneous catalysts. However, the separation of catalysts and the treatment of alkaline wastewater are not only difficult but also environment unfriendly. And the byproduct glycerol produced in the transesterification reaction needs to be separated and refined for further use. The green chemical raw material MC, which is very promising in substitution of methanol as acyl acceptor for biodiesel production, can solve the problem mentioned above. Further, the use of heterogeneous catalysts makes the separation easier without waste water. Therefore, studies on the transesterification of MC and palm oil at the catalysis of heterogeneous solid base and enzyme were carried out in order to explore the mechanism of catalytic reaction and provide the academic and experimental support for the green preparation of biodiesel. The research work was summarized as below:Firstly, the gas chromatography method for the analysis fatty acid methyl esters (FAMEs) in the biodiesel was established with high temperture column, which was also applicable to the determination of triglycerides (TG), diglycerides (DG), and monoglycerides (MG). Fatty acid glycerol carbonate monoesters (FAGC) as intermediate product, with glycerol dicarbonate (GDC) and glycerol carbonate (GC), was characterized by GC-MS and the structure and mechanism of key fragment ions were proposed. Biodiesel was composed of GDC, GC, FAMEs and FAGC. Finally, two-step process was proposed for the transesterificaition of triglycerides with MC. Secondly, several supported soild base catalysts were prepared withγ-Al2O3 (KOH/γ-Al2O3, KNO3/γ-Al2O3, K2CO3/γ-Al2O3) and molecular sieve (MgO/SBA-15) as carriers, respectively, the base strength of which were all characterized. Then, the performances of these base catalysts were evaluated in the transesterification of MC and palm oil. The solid base (NaOH,KOH) and immobilized lipase Novozyme 435 were proved to be very effective for this reaction under the same reaction conditions.After that, the transesterification of palm oil and MC at the catalysis of KOH was investigated. The effects of reaction conditions (molar ratio of MC and palm oil, catalyst amount, reaction temperature and time) on FAMEs yield were explored. The highest FAMEs yield could reach 96.2% at refluxing temperature for 8 h with molar ratio of MC and oil 9:1 and 8.5% KOH (based on oil weight). Further, the kinetics of this KOH-catalyzed transesterification of palm oil and MC was researched over a temperature range of 65-75℃. A pseudo first-order model was put forward and the simulated values could fit the experimental values quite well, indicating that the transesterification kinetics agreeed with the pseudo first-order model. The acticaion energy (Ea) obtained was 79.1 kJ mol-1 from Arrhenius equation. Finally, the mechanism of the KOH-catalyzed transesterification was proposed.The lipase-catalyzed transesterification for biodiesel production has drawn much attention due to its feasibility in mild conditions, easy separation and repeated use. Two commercial available immobilized-lipases Novozym 435 and Lipozyme RM IM were used in the transesterification reaction of palm oil and MC under identical conditions. Novozym 435 showed better activity than Lipozyme TL IM. The yield of FAMEs could reach 90.5% at 55℃for 24 h with the molar ratio of MC to oil 10:1 and the catalyst amount of 20% Novozym 435 (based on the oil weight). There was no obvious loss in FAMEs yield after Novozym 435 having been used for eight cycles. Based on the optimized reaction condition, the kinetics model and the mechanism were proposed. The kinetics agreed with the ordered bi-bi mechanism. The activation energy (Ea) was 26.0 kJ mol-Finally, the study on combustion, fuel economy and emission characteristics was conducted in a diesel engine fuelled with blends of palm oil methyl ester and diesel oil without any change in engine parameters. And the effect of the addition of MC and GC in the blend fuel on engine fuel consumption and emissions was also researched. The results showed that the blend fuel can be directly applied in diesel engine and the combustion process of the engine with MC and GC in the fuel was very similar to that of the engine fuelled with pure blend fuel. The blend fuel with MC and GC has a little effect on fuel economy of engine. Smoke, HC and CO emissions of the engine fuelled with blend fuel containing high oxygen MC and GC could be reduced effectively, meanwhile, the NOx emission increased slightly.