THE INDUSTRIAL PRODUCTION PROCESS OF METHYL ESTERS OF FATTY ACIDS BY CATALYST-FREE SUPERCRITICAL METHANOL

摘要

The process for producing methyl esters of fatty acids (bio diesel fuel) from vegetable oil such as soybean oil and rapeseed oil has been promoted commercially. Most of methods for bio diesel fuel production use the alkaline catalyst to promote transesterification of triglycerides. But, this process has a few disadvantages such as removal catalyst and saponified by-products, separation of the crude glycerol after reaction. Furthermore, free-fatty acids contained in oil are not esterified under alkaline-catalysed method. The fundamental studies of catalyst-free method have been curried out using super critical methanol. Generally, the condition of transesterification with supercritical methanol is required high temperature and pressure to obtain high conversion of transesterification from triglycerides. We have developed the industrial process for producing high quality bio diesel fuel by utilization of the transesterification from crude fatty acids. It is known that triglycerids are conversed to crude fatty acids by hydrolysis easily. After that, the crude fatty acids are smoothly esterified by catalyst-free supercritical methanol. The advantage of this method is that the operating condition of transesterification is reasonable (less than 573 K, 20 MPa). This operating condition is available for practical plants sufficiently. In fact, triglycerides as main ingredient of vegetable oil is required higher condition (more than 623 K, 45 MPa) in order to obtain complete transesterification. We have refined methyl esters of fatty acids produced using this method by distillation and mechanical separation methods and established the basic production process of methyl esters of fatty acids by catalyst - free supercritical methanol. As a result, approximately 90 wt% of crude fatty acids is converted and refined to methyl esters, and it was confirmed that the residue after refining were available for fuel of general-boiler. Therefore, the clean and zero-emission process can be realized for the industrial production of bio diesel fuel from vegetable oil.