Lignin-derived Solid Catalyst for Biodiesel Production from High-Acid-Value Jatropha Oil

Biodiesel is essentially a mixture of compounds known as "methyl esters"and it is usually produced by the acid- or base-catalyzed reaction between methanol and plant oil. This reaction is often referred to as the "transesterification" reaction. "Homogeneous" acid or alkaline solutions which are conventionally used as catalysts in the transesterification reaction, are known to create problems, among which are: (1) difficulty in separation of the catalysts, (2) corrosion of the reactor, (3) sulfur contamination in the biodiesel, and (4) formation of soap.

The use of solid catalysis in a "heterogeneous" reaction system is said to offer the advantage of easier product separation compared to the use of homogeneous catalysts. Solid catalysts are also reported to have comparable catalytic performance with homogeneous catalysts, and produce lesser pollutants. Scientists from the Universiti Kebangsaan Malaysia, and the Chinese Academy of Sciences, report the use of a solid acid catalyst derived from lignin, for the transesterification of high-acid-value jatropha oil. High-acid-value plant oils contain large amounts of fatty acids, and this generally requires an acid esterification reaction for biodiesel production.

The solid catalyst was prepared by subjecting the lignin to phosphoric acid treatment, followed by pyrolysis (oxygen-free heating) at 400 ^oC to produce a solid char, and then sulfonation by concentrated sulfuric acid.

When the solid catalyst was tested for the transesterification of oleic acid, a 96.1% conversion efficiency was obtained. No deactivation was observed when the catalyst was reused three times. When tested on the one-step transesterification of crude jatropha oil with a high acid value, 96.3% biodiesel yield was obtained. The full study is published in the open access journal, Biotechnology for Biofuels (URL above).