New sulfonated carbon catalysts for esterification of free fatty acids for biodiesel production at lower costs
Researchers at Wake Forest University and Virginia Tech report on their development of sulfonated carbon catalysts for the conversion of low-quality fats and oils containing high concentrations of free fatty acids into biodiesel in a paper in the journal Bioresource Technology. The new technology could reduce costs by up to 15% for a small-scale biodiesel production facility.
Conventional biodiesel is made via a base catalyzed transesterification process that does not function particularly well in the presence of free fatty acids. While high-quality vegetable oil feedstock has low FFA content, it is expensive. Inexpensive feedstocks, such as waste grease and oil, has high FFA content.
It is generally accepted that a two-step process is required to treat oils with a high FFA content; in the first step an acid-catalyzed esterification of FFAs is accomplished, and in the second step the base catalyzed transesterification reaction is carried out...In principle a single acid catalyzed reaction is possible however the acid catalyzed transesterification reaction is kinetically slow and requires high temperatures. The homogeneously catalyzed reactions required for the treatment of oils with high FFA content generate significant quantities of corrosive aqueous waste. Thus there is a real need for effective solid catalysts for the esterification and transesterification reactions. Ideally a heterogeneous catalyst would perform both reaction under mild conditions, but in the absence of achieving that goal, separate solid catalysts for the two-step process are desirable.—Deshmane et al.
Current esterification processes use sulfuric acid, which has to be neutralized over a long period of time. In contrast the Wake Forest/Virginia Tech catalyst is a solid and can be separated relatively easily, noted Brian Hanson, a chemist at Virginia Tech who worked on the project.
From a commercial standpoint, this new catalyst could reduce costs by as much as 15% for a small-scale biodiesel production facility, according to a feasibility study conducted by Wake Forest University Schools of Business. While more research needs to be done to test the viability of the catalyst on a larger scale outside of the lab, it could one day help to make sewer waste and used oil waste affordable sources of fuel.
Chinmay A. Deshmane, Marcus W. Wright, Abdessadek Lachgar, Matthew Rohlfing, Zhening Liu, James Le, Brian E. Hanson (2013) “A comparative study of solid carbon acid catalysts for the esterification of free fatty acids for biodiesel production. Evidence for the leaching of colloidal carbon”, Volume 147, Pages 597-604 doi: 10.1016/j.biortech.2013.08.073