| As the global population grows, the consumption of petroleum products has been increasing fast, which results in rising concerns for the decreased fossil fuel reserves and increased oil prices. Therefore, in many countries researches on developing alternative energies are conducted in the hope of finding new energy resources that are both environmentally friendly and renewable. Biodiesel was mainly produced from vegetable oils or animal fats by transesterification of triglycerides or esterification of free fatty acids(FFAs) with short-chain alcohols. Biodiesel is one of the promising substitutes because of its biodegradability and nontoxicity. In addition, its properties such as the viscosity and calorific value are similar to those of the petroleum diesel.In this thesis, the esterification of acidified oil was studied. Using acidified oil to produce biodiesel, it not only reduces the cost of biodiesel but also relieves environmental hazards. At first, the esterification of acidified oil with methanol was investigated using sulfonated cation exchange resin(SCER) in an isothermal batch reactor. The effects of different reaction parameters such as methanol to acidified oil mass ratio, reaction temperature, catalyst loading were studied to optimize the conditions for maximum conversion of FFAs. The results showed that the optimal conversion rate of FFAs was91.87 % after 8 h, at a methanol to acidified oil(20.0 g) molar ratio of 31.8:1.0, reaction temperature of 65.0 o C and catalyst loading of 5.0 g. The external and internal mass transfer resistances were negligible in the kinetic study on the basis of experimental results.A pseudo-homogeneous kinetic model for esterification of acidified oil with methanol by the SCER was set up. The activation energy and thermodynamic parameters including ?G,?S and ?H were determined. The conversions obtained from the established model are in good agreement with the experimental data.The esterification of acidified oil with ethanol catalyzed by SCER was further optimized using the response surface methodology(RSM). The effects of the molar ratio of ethanol to acidified oil, reaction time and catalyst loading on the conversion rate of FFAs were investigated at the temperature of the boiling point of ethanol. Results showed that the highest conversion rate of 75.24 % was obtained at the molar ratio of ethanol to acidified oil of 23.2, reaction time of 8.0 h and catalyst loading of 35.0 wt.%. Moreover,the conversion rate of FFAs was increased to 98.32 % by using a water adsorption apparatus under the RSM optimized conditions. Scanning electronic microscopic-energy dispersive spectrometric(SEM-EDS), X-ray diffractometric(XRD) andthermogravimetric-derivative thermogravimetric(TG-DTG) analyses confirmed that the morphology of catalysts did not change much and the mechanical and thermal stabilities were still good after the reaction. Furthermore, SCER exhibited a high catalytic activity and stability after being reused for five successive times. The fuel properties of the biodiesel were comparable to that of ASTM, EN and GB biodiesel standard.Furthermore, the esterification of acidified oil with ethanol under microwave radiation was modeled and optimized using RSM and artificial neural network(ANN). The impacts of mass ratio of ethanol to acidified oil, catalyst loading, microwave power and reaction time were evaluated by RSM and ANN. RSM showed the optimal conditions as catalyst loading of 5.85 g, molar ratio of ethanol to acidified oil of 3.2:1.0(20.0 g acidified oil),microwave power of 328.62 W and reaction time of 98.04 min with FFAs conversion rate of 78.57 %. Both of the models were fitted well with the experimental data, however, the ANN exhibited better prediction accuracy than the RSM based on the statistical analyses.Furthermore, membrane vapor permeation and in-situ molecular sieve dehydration were investigated to enhance the esterification under the optimized conditions. |
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