Biodiesel production from waste frying oil in sub- and supercritical methanol on a zeolite Y solid acid catalyst

Waste frying oil (WFO) is a very important feedstock for obtaining biodiesel at low cost and using WFO in transesterification reactions to produce biodiesel helps eliminate local environmental problems. In this study biodiesel was produced from WFO in sub- and super-critical methanol on a zeolite Y solid acid catalyst. The procedure was optimized using a design of experiments by varying the methanol to WFO molar ratio, the reaction temperature, and the amount of catalyst. Typical biodiesel yields varied from 83 to nearly 100% with methyl esters content ranging from 1.41–1.66 mol·L^-1 and typical dynamic viscosities of 22.1-8.2 cP. Gas chromatography was used to determine the molecular composition of the biodiesel. The reaction products contained over 82 wt-% methyl esters, 4.2 wt-% free acids, 13.5 wt-% monoglycerides, and 0.3 wt-% diglycerides. The transesterification of WFO with methanol around its critical temperature combined with a zeolite Y as an acid catalyst is an efficient approach for the production of biodiesel with acceptable yields.