Determination of the kinetics of biodiesel saponification in alcoholic hydroxide solutions
Determination of the kinetics of biodiesel saponification in alcoholic hydroxide solutions
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DOI：
10.1016/j.fuel.2014.10.001
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发表时间：
2015-01-15
期刊：
影响因子：
7.4
通讯作者：
Phan, Anh N.
中科院分区：
文献类型：
--
作者：
Eze, Valentine C.;Harvey, Adam P.;Phan, Anh N.
本研究主要集中在均相碱催化酯交换过程中发生的副反应的动力学，这是以前没有研究。在甲醇和乙醇（通常用于生物柴油生产）中，在40 ℃、50 ℃和60 ℃的温度下，研究了脂肪酸甲酯（FAME）与氢氧化钠和氢氧化钾的皂化速率。还研究了水对醇氢氧化物溶液中FAME皂化速率的影响（在60 ℃下）。醇的种类对FAME皂化反应的表观速率常数影响较大，而金属氢氧化物的种类对FAME皂化反应的表观速率常数影响较小。使用乙醇氢氧化物的FAME皂化的表观速率常数比甲醇氢氧化物高5-7倍。这是由于乙醇的酸度较低，导致乙醇-氢氧化物溶液中氢氧根离子的浓度较高。FAME皂化反应的速率常数随温度的升高而增大。例如，在甲醇-NaOH溶液中，在40 ℃下为1.31 L mol（1）min（1），但在50和60 ℃下为3.08和5.63 L mol（1）min（1）。醇类氢氧化物中FAME皂化反应的Arrhenius活化能在60.3-64.0 kJ mol（1）范围内。发现在水存在下，FAME在乙醇-氢氧化物中的皂化率比在甲醇-氢氧化物中的皂化率高3.5倍。这表明在碱催化的酯交换反应中，甲醇的使用应优于乙醇，因为通过甘油三酯和烷基酯的皂化产生的皂的量将较低。皇冠版权所有（C）2014由爱思唯尔有限公司出版。保留所有权利。
The research focused mainly on kinetics of the side reactions occurring during homogeneous basecatalysed transesterification processes, which were not studied previously. The rates of fatty acid methyl esters (FAME) saponification with sodium and potassium hydroxides were investigated in methanol and ethanol (commonly used in biodiesel production) at temperatures of 40, 50 and 60 degrees C. The effect of water on the rate of FAME saponification in the alcoholic hydroxide solutions was also studied (at 60 degrees C). The apparent rate constants of FAME saponification were strongly influenced by the types of alcohol, but little affected by variation of the metal hydroxides. The apparent rate constants for FAME saponification using the ethanol hydroxides were 5-7 times higher than for methanol hydroxides. This was due to the lower acidity of ethanol, leading to a higher concentration of hydroxide ions in the ethanol-hydroxide solutions. The rate constant of the FAME saponification increased with temperature. For example, it was 1.31 L mol (1) min (1) at 40 degrees C, but 3.08 and 5.63 L mol (1) min (1) at 50 and 60 degrees C in the methanol-NaOH solution. Arrhenius activation energies for the FAME saponification in the alcoholic hydroxides were in the range of 60.3-64.0 kJ mol (1). It was found that the FAME saponification rate in ethanol-hydroxides was 3.5 times higher than that in methanol-hydroxides in the presence of water. This indicates that use of methanol should be preferred over ethanol in alkali-catalysed transesterification, as the amount of soap produced by saponification of triglycerides and alkyl esters will be lower. Crown Copyright (C) 2014 Published by Elsevier Ltd. All rights reserved.