Submitted to: Energy and Fuels
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/27/2007
Publication Date: 1/1/2008
Citation: Ngo, H., Zafiropoulos, N.A., Foglia, T., Samulski, E.T., Lin, W. 2008. Efficient two-step synthesis of biodiesel from greases. Energy and Fuels. 22(1):626-634. Interpretive Summary: Biodiesel (BD), a renewable and biodegradable diesel fuel, currently is made by a simple chemical process, the base-catalyzed transesterification of an oil or fat into its simple fatty esters (typically methyl esters). The cost of the oil or fat is the major factor in producing the fuel. Yellow and brown greases are lower-cost feedstocks and hence are attractive candidates for producing BD. The high free fatty acid (FFA) content of these feedstocks, however, makes it difficult to produce BD from these feedstocks using conventional methods. This paper addresses this need in that it describes the synthesis and use of immobilized acid catalysts that are highly efficient in esterifying the FFA in grease to esters suitable for biodiesel production. In this way greases with FFA content of > 50% are readily converted to biodiesel in a straight forward simplified two-step process. This novel technology should foster the use of these second use fats and oils as biodiesel feedstocks.
Technical Abstract: In this paper, we report the use of a series of diarylammonium catalysts that are highly effective in catalyzing the esterification of the FFA present in greases (12 – 50 wt% FFA). At a catalyst loading of 2-3 mol%, high conversions of FFA to esters (95 - 99%) were achieved by treating the greases with 5-20 equiv. of methanol at 95 deg C for 2 h. The treated greases had a final FFA content of 0.5 – 1 wt%. We also incorporated these diarylammonium catalysts into insoluble porous polymers prepared by radical-initiated polymerization. The polymer-immobilized catalysts were found to be equally effective as their homogeneous counterparts in esterifying FFA to esters, and were readily recycled and re-used for esterification reactions upon re-activation with triflic acid. The resulting ester-glyceride mixtures were then converted to total esters by base-catalyzed transesterification. This two-step protocol provides an efficient procedure for the production of biodiesel from greases.