Synthesis of biodiesel from soybean oil by coupling catalysis with subcritical methanol
Synthesis of biodiesel from soybean oil by coupling catalysis with subcritical methanol
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DOI：
10.1016/j.enconman.2008.08.008
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发表时间：
2008-12
影响因子：
10.4
通讯作者：
Jianzhong Yin;Minhui Xiao;Aiqin Wang;Z. Xiu
中科院分区：
文献类型：
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作者：
Jianzhong Yin;Minhui Xiao;Aiqin Wang;Z. Xiu
以大豆油和甲醇为原料，在超临界和亚临界条件下合成生物柴油。在超临界条件下，当醇油摩尔比为42：1，反应温度为260 ~ 350°C时，甲酯产率最高可达98%以上。为了降低操作温度和压力，提高甲醇的转化率，提出了在反应混合物中加入助溶剂以改善反应过程，并将催化与超临界效应耦合的新思想。因此，在2.5wt%己烷、300°C的温度、甲醇与油之比为42的情况下，在30分钟内观察到85.5%的转化率，而在相同条件下在没有己烷的情况下观察到62.2%的转化率;在较少的二氧化碳、300°C的温度、42的甲醇与油比的情况下，在20分钟内观察到91.6%的转化率，在相同条件下，无CO2时转化率为51.4%，在反应温度为160°C、醇油摩尔比为24：1、催化剂用量为KOH/油=0.1wt%、反应时间为10 min的条件下，甲酯的产率可达98%。相比之下，在常规碱催化方法中需要大于lwt %的催化剂;而在260°C（对应于亚临界条件）下没有催化剂仅获得6%的甲酯产率。结果表明，将催化剂与亚临界操作耦合，可大大减少催化剂用量，提高甲醇利用率。因此，本方法提供了一些优于常规碱催化剂方法和昂贵的超临界方法的优点。
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°C to 350°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 2.5wt% hexane, temperature of 300°C, methanol to oil ratio of 42, a 85.5% conversion is observed in 30min, while a 62.2% conversion is observed without hexane in the same condition; with less carbon dioxide, temperature of 300°C, methanol to oil ratio of 42, a 91.6% conversion is observed in 20min, 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=0.1wt%), a 98% yield of methyl esters was obtained in 10min at a reaction temperature of 160°C and the molar ratio (methanol/oil) of 24:1. In contrast, above 1wt% of catalyst is required in the conventional alkali-catalyzed method; while only 6% yield of methyl ester was obtained at 260°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.