Study On Preparation Of Biodiesel Without Glycerol In Supercritical/Subcritical Conditions

Increasing depletion of oil resources makes people pay more and more attention to the research and development of new energy. Biodiesel is biodegradable, non-toxic and environmentally friendly. So biodiesel has been concerned about widespread. Preparation of biodiesel in supercritical/subcritical conditions has advantages of fast reaction rate, high yield, and adaptability of raw oil. The process of preparation of biodiesel in supercritical/subcritical conditions, palm oil as raw oil, MC as ester exchange reagent, has successfully solved the by-product glycerol problem, improved the utilization rate of raw oil and is a kind of green synthesis of new technology.This paper mainly investigated the process of MC and palm oil for transesterification reaction of biodiesel preparation in the supercritical/subcritical MC system. The quantitative analysis method of fatty acid methyl ester was established with the nonpolar high temperature capillary column DB-5ht. As total amount of fatty acid methyl ester ranging from0.5mg/ml to1.5mg/ml, the standard curves had wide linear range and high accuracy, and the RSD of total amount of fatty acid methyl ester was0.3%, and the precision and repeatability were good. The reaction product was characterized by GC-MS and the peak sequence of product component was as follows:glycerol carbonate (GC:4.31min and GDC:6.04min), fatty acid methyl ester (C12:6.86min, C14:8.49min, C16:9-11min, C18:11-12min, C20:13.70min), monoglyceride(14-17min), fatty acid glycerol carbonate(18-20min), diglyceride(23-26min) and triglyceride(27-34min). In order to improve the harsh reaction conditions, a spot of KOH was added in the supercritical MC system for the first time. The yield of fatty acid methyl ester could reach92.4%and the reaction conditions:reaction temperature is280℃, reaction pressure is9.1MPa, molar ratio of MC to palm oil is20:1, reaction time is20min, amount of KOH is0.1%. In addition, the transesterification kinetics of MC and palm oil in the condition of subcritical with the presence of KOH was studied. The activation energy and frequency factor were determined:Ea,43.0kJ/mol; A,6.92×102min-1.Finally, the physical properties, low temperature crystallization, low temperature rheological properties and combustion characteristics of the biodiesel blend oil were investigated. The results show that the addition of biodiesel delayed the crystallization speed of diesel oil paraffin, slowed down the increase of the diesel oil viscosity, and improved the cold flow property of0#diesel oil. Besides, DSC curve and low temperature viscosity-temperature characteristic curve in the characterization of oil low temperature characteristics had a certain correlation. When the volume fraction of biodiesel was not higher than5%, comparing with the0#diesel oil, blend oil basic combustion characteristic parameters had not changed very much, which would provide a theoretical basis for the use of biodiesel.