Title Two-step supercritical dimethyl carbonate method for biodiesel production from Jatropha curcas

This study reports on a novel two-step process for biodiesel production consisting of hydrolysis of oils in sub-critical water and subsequent supercritical dimethyl carbonate esterification. This process found to occur optimally at the subcritical water treatment (270°C/27MPa) for 25 min followed by a subsequent supercritical dimethyl carbonate treatment (300°C/9MPa) for 15 min to achieve a comparably high yield of fatty acid methyl esters, at more than 97wt%. In addition, the fatty acid methyl esters being produced satisfied the international standard specifications for use as biodiesel fuel. This new process for biodiesel production offers milder reaction condition (lower temperature and lower pressure), non-acidic, non-catalytic and applicable to feedstock with high amount of free fatty acids such as crude Jatropha curcas Oil. To date, biodiesel has been widely produced and used in many countries. Biodiesel, a clean fuel commonly derived by transesterification of either edible or non-edible oils with alcohol, is a comparable match to petroleum diesel. The current commercial biodiesel production method called the alkali-catalyzed method, transesterifies triglycerides in the presence of alkaline catalyst with methanol to produce fatty acid methyl esters (FAME). However, this method does not suit feedstock with high content of free fatty acids, which consume the catalyst to form saponified substance and reduce the yields of fatty acid methyl esters (Hawash et al., 2009). In order to overcome these problems, the one-step non-catalytic supercritical methanol process (Saka process) and two-step process (Saka-Dadan process) have been developed Furthermore, the increasing trend towards biodiesel production has also led to an extreme increase of glycerol as by-product. In Europe, glycerol price decreased tremendously due to extensive supply in the market and glycerol-producing chemical companies were extremely affected (Willke and Vorlop, 2004). Glycerol, accounts 10% of mass of the feedstock, is recovered together in mixture with methanol, water and residues of the alkaline catalyst after the transesterification process. Several complicated purification processes have to be conducted for this mixture to recover the pure glycerol, and this makes the price ten times higher than the unpurified one. By considering the complicated process and its cost, the pursuit to recover pure glycerol is not an economical one. To balance glycerol's availability and demand, attempts to utilize glycerol from biodiesel production in innovative new ways have been reported (Silva et al., 2009; Tang 4 et al., 2009). However, it is superior if biodiesel production could produce less or no glycerol at all. In accordance …