A Study On The Effects Of Biodiesel Production Over Zeolite

In this thesis, oleic acid and ethanol were chosen as the model compounds for biodiesel production. The primary objectives of this study were to investigate the effects of pore sizes and surface hydrophobic property of zeolites on catalysis performance for biodiesel production. And on this basis, the zeolites were further modified to improve the catalysis performance for biodiesel production. In addition, different kinetic models were applied to describe the esterification over zeolites.At first, microporous zeolites(BEA type Beta zeolite and MFI type ZSM-5 zeolite) and micro-mesoporous zeolites(MFI type ZRP-5 zeolite) with various Si/A1 ratios were employed in the esterification of oleic acid with ethanol. The effect of pore sizes on the internal mass transfer limitation was investigated by Thiele modulus calculation. The results showed that the zeolites with high Si/Al ratios showed hightest catalytic performance. Among these three zeolites at the same Si/A1 ratios, ZRP-5 zeolite which has the lowest internal mass transfer limitations exhibited the worst catalyst performance. The Eley-Rideal model analysis demonstrated that on the surface of high hydrophobic zeolites, the adsorption of oleic acid molecules was more favorable than the adsorption of the polar ethanol molecules, resulting in higher coverage of oleic acid molecules on the surface of zeolites and higher conversion rate of esterification. Moreover, the water contact angle tests and the FTIR analysis were used to further validate the assumption of kinetic model. The highest conversion rate of 73.6% was achieved when the reaction was catalyzed by Beta(50) zeolites under optimized conditions of the molar ratio of oleic acid to ethanol of 1:20, catalyst loading of 0.167 meq/g(oleic acid), temperature of 78.0 °C, reaction time of 10.0 h and stirring speed of 600 rpm. The conversion rate of oleic acid remained above 70.0 % after five runs and there was no apparent loss of the active component(Al) from the zeolite.A surface graft/coating method was developed to prepare polystyrene sulphonic acid functionalized zeolite. The operational variables of this process were optimized by the response surface methodology. The results showed that the highest conversion 96.4% was achieved at the optimal experimental conditions, including reaction time 4.1, molar ratio of ethanol to oleic acid 15:1, catalyst dosage 47.8 wt%. In addition, the polystyrene sulphonic acid functionalized zeolites which were used up to five times, the organic sulfonic groups were still stable incorporation into the structure of zeolites, which was verified by the Fourier transform infrared spectroscopy. Compared with cation exchange resin and zeolites, the esterification catalyzed by polystyrene sulphonic acid functionalized zeolites have the highest oleic acid conversion and shortest reaction time.