Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/19/2012
Publication Date: 1/20/2013
Citation: Ngo, H., Vanselous, H.N., Strahan, G.D., Haas, M.J. 2013. Esterification and Transesterification of greases to fatty acid methyl esters with highly active diphenylamine salts. Journal of the American Oil Chemists' Society. 90:563-570. Interpretive Summary: There is an increasing need of superior catalysts for the production of biodiesel, a renewable fuel composed of fatty acid methyl esters (FAME), from waste greases (i.e., used cooking oils). Currently sodium methoxide is the most common and efficient catalyst for FAME synthesis. This catalyst however is only compatible with refined oils (e.g., soybean oils). It will not work well with the waste greases because these typically contain impurities known as free fatty acids (FFA). The FFA can react with the catalyst to form soap, which lowers FAME yields and requires substantial efforts to clean up the FAME products. Our group has discovered two other catalysts (diphenylamine sulfate and diphenylamine hydrochloride) that are compatible with waste greases. These salts are easy to handle and will not react with the FFA to form soap. They can simultaneously esterify and transesterify waste greases in the presence of excess methanol at 125 deg C within 1 hour. The yields of the FAME products were as high as 95% depending on the greases used. The success of this work can potentially reduce the cost of biodiesel production, enhance development of the rural economy and improve the environmental and public health.
Technical Abstract: Diphenylamine sulfate (DPAS) and diphenylamine hydrochloride (DPACl) salts were found to be highly active catalysts for esterification and transesterification of inexpensive greases to fatty acid methyl esters (FAME). In the presence of catalytic amounts of DPAS or DPACl and excess methanol, the free fatty acids as well as the glycerides in the waste greases were converted to FAME at 125 deg C within 1 hour. The diphenylammonium salts are much easier to work with when compared to concentrated liquid acids such as sulfuric acid and hydrochloric acid. Interestingly, the DPACl catalyst gave much higher conversion (>99%) than the parent liquid hydrochloric acid.