One of the major economic drags on biodiesel is represented that most production processes are batch processes, batch processes almost always being more expensive than continuous processes.
Thus this report from Thai scientists of potentially of large commercial significance in the growing biodiesel market:
Biodiesel (fatty acid alkyl esters) is an alternative fuel for diesel engines. It is an alcohol ester product from the transesterification of triglycerides in vegetable oils or animal fats. This can be accomplished by reacting lower alcohols such as methanol or ethanol with triglycerides. The reaction proceeds well in the presence of some homogeneous catalysts such as sodium hydroxide and sulfuric acid, or heterogeneous catalysts such as metal oxides or carbonates or enzymes. Sodium hydroxide is very well accepted and widely used because of its low cost and high product yield, but the solubility of potassium hydroxide in methanol is higher than that of sodium hydroxide. Although the reaction system is simple, one drawback that prevents wider use of biodiesel is its high energy consumption and production cost, partly resulting from the complicated separation and purification of the product. Therefore, to perform the reaction without the presence of a catalyst is one effective way to reduce the biodiesel cost. Various biodiesel production processes employing homogeneous, heterogeneous catalytic, and noncatalytic supercritical methods as reported in the literature are summarized in Table 1.1-5 Recently, there have been some reports on the noncatalytic transesterification reaction employing supercritical methanol conditions.3,6,7
Unfortunately in Asia, where this work was undertaken, much of the biodiesel source material is palm oil, which has been environmentally controversial because of the implications of the destruction of forests. However, I can think of no reason that similar processes could not be successful with oils that are somewhat benign, such as rapeseed oil.
Biological diesel fuel is a promising technology that may represent a small, but significant contribution in the difficult fight against global climate change.
The article abstract, from the ASAP section of
Energy and Fuels, can be found here:
http://pubs.acs.org/cgi-bin/abstract.cgi/enfuem/asap/abs/ef050329b.htmlThe use of supercritical fluids, notably supercritical carbon dioxide and supercritical water, is a burgeoning and exciting area of chemistry, having become within technical viability owing to the grand advances in materials science in the last several decades.
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