Japanese researchers have devised a low-cost, ecologically friendly solid catalyst for the production of biodiesel: a carbon catalyst produced from sugar, starch or cellulose.
The team from the Tokyo Institute of Technology, the National Institute of Advanced Industrial Science and Technology, and the University of Tokyo reported their results in the 10 November issue of Nature.
The production of biodiesel through the esterification of higher fatty acids requires an efficient catalyst. Commonly, that catalyst is a liquid acid such as sulphuric acid (H2SO4). However, the separation of the catalyst from the reaction mixture is costly and wasteful.
Other catalysts such as Nafion or sulphonated napthalene are either expensive or offer less or rapidly diminishing catalytic activity.
The researchers avoided all those issues by devising a mechanism to incompletely sulphonate (treat with sulfuric acid) carbonized natural organic material such as sugar, starch or cellulose to prepare a more robust solid catalyst.
Incomplete carbonization of these natural products results in a rigid carbon material. The team found that sulphonation of this material generates a stable solid with a high density of active sites, enabling the inexpensive preparation of a high-performance catalyst.
|Pyrolysis of the sugars causes their incomplete carbonization (middle; outlined in blue) and formation into polycyclic aromatic carbon sheets; sulphuric acid (concentrated or fuming) is used to sulphonate the aromatic rings to produce the catalyst.|
The team found that the activity of the solid sulphonated carbon catalyst is more than half that of a liquid sulphuric acid catalyst, and much higher than that achieved by conventional solid acid catalysts.
Although the report in Nature focused on sugar, they have also successfully prepared catalysts identical in function from carbonized starch and cellulose.
Saccharide molecules may therefore be generally suitable for preparing these catalysts, which can be used as a replacement for liquid sulphuric acid in esterification reactions.
In addition to biodiesel production, such environmentally benign alternative catalysts should find application in a wide range of other acid-catalyzed reactions.
Green chemistry: Biodiesel made with sugar catalyst, Nature 438, 178 (10 November 2005) | doi:10.1038/438178a
(A hat-tip to David Jamroga!)