Experimental Study And System Optimization Of Biodiesel Production By Subcritical/Supercritical Heterogeneous Catalysis

Environmental problems and energy crisis have become one of the biggest threats to China’s development,which hinders the process of building a resource-saving society.The production of biodiesel from edible waste oil can solve a series of problems such as energy shortage and alleviate the impact of various waste oil on the environment.In this paper,the best performance catalyst was selected through the stability experiments of five catalysts.The experimental study on the catalytic performance of subrcritical/supercritical ethanol was carried out with oleic acid as the research object.The kinetic model of heterogeneous catalytic esterification was established,and the kinetic parameters were obtained.The influence of impurities(water)and reaction pressure on the conversion rate of biodiesel was studied.Based on the experimental results,two supercritical preparation systems of biodiesel were designed,which comprehensively evaluated the construction investment and operating costs,clarified the best heat exchange scheme,and further optimized the parameters of the heat exchange network.The research results can provide theoretical basis for supercritical technology of biodiesel.The main conclusions are as follows:(1)The experimental study of catalyst screening was carried out in batch reactor.The stability of five solid oxide catalysts(MgO/ZnO/SiO2/TiO2/ZrO2)was tested under supercritical conditions,and the catalyst characterization before and after the reaction was completed.The results show that ZrO2 has the best stability.(2)The subcritical/supercritical heterogeneous esterification of oleic acid and ethanol over ZrO2 was studied.The results show that ZrO2 has excellent catalytic performance in subcritical and supercritical conditions,and the complete conversion of oleic acid can be guaranteed at 18MPa,325℃ and 7min.The one-dimensional quasi homogeneous model was used to simulate heterogeneous catalytic process,and the kinetics followed one-step reversible reaction model.Based on the eley-ripple mechanism,the mechanism and kinetics model of catalytic reaction was further constructed.Under supercritical conditions,the presence of water will have adverse effects on esterification and catalyst,thus reducing the conversion of biodiesel.However,the pressure change of 8-18MPa will not affect the homogeneous state of the reaction system,so the conversion rate of reaction varies very little with the pressure.(3)Two supercritical preparation systems of biodiesel were designed.Through comprehensive evaluation of construction investment and maintenance during operation,the medium heat exchange scheme was determined.The heat exchange network was optimized to reduce the pressure of the intermediate medium to 12MPa,which can make the system run stably.