Noncatalytic Biodiesel Synthesis under Supercritical Conditions

Abstract

The constant increase in greenhouse gases in the environment is forcing people to look for different ways to reduce such pollution. One of these ways is the use of biodiesel for road transport. Conventional biodiesel production involves the catalytic triglyceride transesterification process. When using homogeneous two-stage catalysis, it is difficult to purify the resulting product from the by-products formed, and the catalysts cannot be reused. In the case of heterogeneous catalysis, the process costs are increased due to separation and regeneration of the catalysts. To solve these problems of catalytic synthesis, a noncatalytic process has been recently studied that which takes place under supercritical conditions for an alcohol or other acyl receptor. In such biodiesel production, fatty feedstocks and alcohols are used as raw materials, with the synthesis taking place at supercritical conditions for alcohol, i.e., high temperature and pressure, thus making the process quite simple. This paper reviews the results obtained from biodiesel synthesis using a noncatalytic supercritical process for transesterification using both alcohols and carboxylate esters of low molecular weight, evaluating the optimal conditions for these processes and biofuel stability at high temperatures.