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염승호,고영욱 한국생물공학회 2018 Biotechnology and Bioprocess Engineering Vol.23 No.4
Waste cooking oil (WCO) has attracted attention as a non-edible feedstock for biodiesel. Although an alkali catalyst has several advantages over an acid catalyst in biodiesel production, biodiesel conversion from WCO is only 5.2% when using an alkali catalyst (NaOH), owing to its high free fatty acid (FFA) content of 4.2%. In this study, a novel two-step process in a single reactor, comprised of re-esterification of the FFAs with crude glycerol, using a Tin (II) chloride (SnCl2) catalyst, and subsequent transesterification with methanol, using an alkali catalyst, was adopted, and each step was optimized. This study revealed that the FFA content after re-esterification should be approximately 1.5%, not only to save glycerol and the catalyst involved in the re-esterification, but also to achieve high biodiesel conversion during the transesterification. An alkaline catalyst was successfully used to produce biodiesel in the second step, and a 92.8% conversion to biodiesel was achieved under the optimized conditions (0.6% catalyst relative to WCO, 0.2mL-methanol/WCO, 70ºC, 3 h). Overall, this novel two-step process achieved highly enhanced biodiesel conversion (4.0% to 92.8%) with significantly reduced reaction time (12 h to 4 h) and methanol requirements (15 mL/g-WCO to 0.2 mL/g-WCO).
염승호 한국생물공학회 2016 Biotechnology and Bioprocess Engineering Vol.21 No.2
In this study, several methods were devised and evaluated to enhance biodiesel production by whole cells immobilized onto the polyurethane foam coated with activated carbon. Biodiesel conversion was increased to 76.4% with the increase in the number of polyurethane foam until it occupied 18.0 or 2.4% of reaction mixture based on apparent or actual volume of supports, respectively. Stepwise methanol addition to prevent methanol inhibition on the immobilized whole cells was optimized in terms of number of aliquot and feeding interval. When 4.5 molar ratio of methanol to soybean oil was divided into 4 equal aliquots and each aliquot was fed to the reaction mixture every 24 h, the highest final biodiesel conversion of 82.4% was achieved. Chemical treatment of the immobilized cells with 0.1% of chloroform for 2 h enhanced biodiesel conversion to 90.5%. The initial addition of 5% glycerol in the fresh reaction mixture increased biodiesel conversion to 90.3% while the removal of glycerol during biodiesel production barely increased biodiesel conversion. The biodiesel conversion was increased with the increase of initial water content in the fresh reaction mixture and the highest value was 92.7% at 3.0% of water content, but decreased thereafter. The effects of co-addition of glycerol and water on biodiesel production were also investigated, and the co-addition of 3.125% of glycerol and 1.875% of water relative to soybean oil substantially increased biodiesel conversion to 95.0%. By these optimization of reaction conditions and co-adding glycerol and water, initial biodiesel production rate and final biodiesel conversion were remarkably enhanced by 26.8 and 24.1%, respectively.