Efficient Two-Step Synthesis of Biodiesel from Greases

摘要

Biodiesel (BD) is an alternative diesel fuel derived from both vegetable oils and animal fats. Currently, most BD is made by alkali-catalyzed transesterification of a refined oil or fat, the cost of which is the major expenditure in producing BD. Yellow and brown greases are readily available renewable fats that are less expensive and hence represent attractive feedstocks for the production of BD. The high free fatty acid (FFA) content of these feedstocks, however, makes it difficult to produce BD using base-catalyzed transesterification. 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 (12-40 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 ℃ 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 via free 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 reused for esterification reactions upon reactivation with triflic acid. The resulting ester-glyceride mixtures were then readily converted to total esters by base-catalyzed transesterification. This two-step protocol provides an efficient procedure for the production of biodiesel from greases.