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Indexed by:期刊论文

Date of Publication:2008-12-01

Journal:ENERGY CONVERSION AND MANAGEMENT

Included Journals:SCIE、EI、Scopus

Volume:49

Issue:12

Page Number:3512-3516

ISSN No.:0196-8904

Key Words:Biodiesel; Transesterification; Subcritical methanol; Supercritical methanol; Soybean oil

Abstract:Biodiesel synthesis from soybean oil and methanol was investigated under supercritical and subcritical conditions. Under the supercritical conditions, the maximum methyl ester yield exceeded 98% when the molar ratio of methanol to oil was 42:1 and the reaction temperature ranged from 260 degrees C to 350 degrees C. In order to decrease the operational temperature and pressures and to increase the conversion efficiency of methanol, first co-solvent was added to the reaction mixture to improve the reaction process, and then a novel idea was presented in which catalysis and supercritical effect were coupled together. Thus, with 2.5 wt% hexane, temperature of 300 degrees C, methanol to oil ratio of 42, a 85.5% conversion is observed in 30 min, while a 62.2% conversion is observed without hexane in the same condition; with less carbon dioxide, temperature of 300 degrees C, methanol to oil ratio of 42, a 91.6% conversion is observed in 20 min, while a 51.4% conversion is observed without carbon dioxide in the same condition; With only a little amount of potassium hydroxide as the catalyst (KOH/oil = 0.1 wt%), a 98% yield of methyl esters was obtained in 10 min at a reaction temperature of 160 degrees C and the molar ratio (methanol/oil) of 24:1. In contrast, above 1 wt% of catalyst is required in the conventional alkali-catalyzed method: while only 6% yield of methyl ester was obtained at 260 degrees C (corresponding to subcritical conditions) without the catalyst.
   This result demonstrated that by coupling the catalysis and subcritical operation, the amount of catalyst could be largely reduced and the methanol utilization could be significantly enhanced. Thus, the present method offers some advantages over both the conventional alkali-catalyst method and the expensive supercritical method. (c) 2008 Elsevier Ltd. All rights reserved.