Phase equilibrium of transesterification reaction system between soybean oil and methanol

doi:10.11949/0438-1157.20211791

Abstract

Abstract:

Biodiesel is a clean and renewable liquid fuel that is readily made from vegetable oils. Transesterification of the refined vegetable oils with methanol is an important reaction for the production of biodiesel. In order to accurately calculate the multicomponent-phase equilibrium compositions in the transesterification reactions, the multicomponent-phase equilibria of the transesterification reaction between soybean oil and methanol at atmospheric pressure and 60℃ were studied. The transesterification of triolein with methanol was particularly taken as a model reaction, and the UNIFAC and modified UNIFAC activity coefficient models were used to predict the ternary and quaternary phase equilibrium compositions. The results showed that in the region that the overall composition deviates from the binary composition of methanol-methyl esters, the UNIFAC and modified UNIFAC models accurately provided the ternary and quaternary phase equilibrium compositions in the transesterification reaction system. At the glycerol contents greater than 2.2%(mass) or the conversions lower than 90%(mass), using the UNIFAC model, the phase equilibrium compositions for the reaction process were accurately calculated with a deviation of about 2% compared to the experimental values. Both the experimental and modeled values showed that the continuous countercurrent separation of glycerol can improve the methanol to oil ratios and facilitate the mass transfer and transesterification rates. These results provide a theoretical reference for biodiesel process simulation, equipment optimization and new technology development.

Key words: phase equilibrium, transesterification, biodiesel, soybean oil, methanol, fatty acid methyl esters, glycerol

摘要：

生物柴油是一类清洁的可再生液体燃料，精炼植物油与甲醇酯交换是制备生物柴油的重要反应。针对目前难以准确获得酯交换反应体系的多组分相平衡组成等方面存在的问题，研究了间歇反应和连续逆流分离甘油等不同反应方式下大豆油与甲醇酯交换反应体系的多组分相平衡行为，并以三油酸甘油酯与甲醇酯交换为模型反应，采用UNIFAC和Modified UNIFAC模型进行了模拟计算。结果表明，在常压、60^oC反应条件下，在总组成偏离甲醇-甲酯二元组成的区域，UNIFAC和Modified UNIFAC模型准确计算了生物柴油酯交换反应体系的三元和四元相平衡组成。在甘油含量大于2.2%(质量)或转化率小于90%(质量)的酯交换反应中，计算值与实验值的平均偏差约为2%。酯交换反应相平衡的实验值和模型计算值表明，采用连续逆流方式分离甘油可以提高酯相中的甲醇含量，有利于传质和酯交换反应。这些结果为生物柴油工艺过程模拟、设备优化以及新技术开发提供了理论参考。

关键词: 相平衡, 酯交换, 生物柴油, 大豆油, 甲醇, 脂肪酸甲酯, 甘油

CLC Number:

O 642.42

Jiaren ZHANG, Haichao LIU. Phase equilibrium of transesterification reaction system between soybean oil and methanol[J]. CIESC Journal, 2022, 73(5): 1920-1929.

张家仁, 刘海超. 大豆油与甲醇酯交换反应体系的相平衡研究[J]. 化工学报, 2022, 73(5): 1920-1929.

Figures/Tables 6

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序号	总组成（质量分数）				Conv./%	酯相组成（质量分数）				甘油相组成（质量分数）
序号	x₁	x₂	x₃	x₄	Conv./%	x₁	x₂	x₃	x₄	x₁	x₂	x₃	x₄
间歇反应
1	0.821	0.179			0	0.915	0.085			0.011	0.989
2	0.736	0.171	0.011	0.082	10.03	0.839	0.071	0	0.091	0.006	0.889	0.083	0.023
3	0.654	0.161	0.020	0.165	20.11	0.745	0.070	0	0.184	0.004	0.810	0.153	0.033
4	0.335	0.127	0.057	0.480	58.88	0.384	0.068	0.001	0.547	0.001	0.543	0.444	0.013
5	0.164	0.108	0.070	0.659	80.09	0.187	0.060	0.001	0.752	0	0.445	0.549	0.006
6	0.083	0.099	0.079	0.740	89.97	0.094	0.059	0.002	0.845	0	0.387	0.609	0.004
7		0.088	0.087	0.825	100.00		0.053	0.002	0.945		0.331	0.667	0.002
连续逆流分离甘油
1	0.900		0.100		0	1.000		0	0.005	0		1.000
2	0.874	0.034	0.092	0.000	0	0.980	0.015	0	0.188	0	0.183	0.817	0
3	0.622	0.149	0.072	0.157	20.13	0.767	0.044	0.001	0.384	0	0.591	0.402	0.007
4	0.512	0.088	0.059	0.342	40.05	0.577	0.039	0.001	0.574	0	0.456	0.540	0.004
5	0.352	0.071	0.040	0.537	60.37	0.375	0.050	0.001	0.723	0	0.384	0.612	0.004
6	0.173	0.113	0.020	0.695	80.08	0.180	0.094	0.003	0.805	0	0.579	0.390	0.031
7	0.088	0.106	0.022	0.784	89.88	0.092	0.099	0.004	0.005	0	0.528	0.455	0.017
8		0.098	0.005	0.898	100.00	完全互溶

序号	总组成（质量分数）				Conv./%	酯相组成（质量分数）				甘油相组成（质量分数）
序号	x₁	x₂	x₃	x₄	Conv./%	x₁	x₂	x₃	x₄	x₁	x₂	x₃	x₄
间歇反应
1	0.821	0.179			0	0.915	0.085			0.011	0.989
2	0.736	0.171	0.011	0.082	10.03	0.839	0.071	0	0.091	0.006	0.889	0.083	0.023
3	0.654	0.161	0.020	0.165	20.11	0.745	0.070	0	0.184	0.004	0.810	0.153	0.033
4	0.335	0.127	0.057	0.480	58.88	0.384	0.068	0.001	0.547	0.001	0.543	0.444	0.013
5	0.164	0.108	0.070	0.659	80.09	0.187	0.060	0.001	0.752	0	0.445	0.549	0.006
6	0.083	0.099	0.079	0.740	89.97	0.094	0.059	0.002	0.845	0	0.387	0.609	0.004
7		0.088	0.087	0.825	100.00		0.053	0.002	0.945		0.331	0.667	0.002
连续逆流分离甘油
1	0.900		0.100		0	1.000		0	0.005	0		1.000
2	0.874	0.034	0.092	0.000	0	0.980	0.015	0	0.188	0	0.183	0.817	0
3	0.622	0.149	0.072	0.157	20.13	0.767	0.044	0.001	0.384	0	0.591	0.402	0.007
4	0.512	0.088	0.059	0.342	40.05	0.577	0.039	0.001	0.574	0	0.456	0.540	0.004
5	0.352	0.071	0.040	0.537	60.37	0.375	0.050	0.001	0.723	0	0.384	0.612	0.004
6	0.173	0.113	0.020	0.695	80.08	0.180	0.094	0.003	0.805	0	0.579	0.390	0.031
7	0.088	0.106	0.022	0.784	89.88	0.092	0.099	0.004	0.005	0	0.528	0.455	0.017
8		0.098	0.005	0.898	100.00	完全互溶

方法	间歇反应		连续逆流分离甘油
方法	MAD	MSD	MAD	MSD
UNIFAC	0.020	0.001	0.019	0.002
Modified UNIFAC	0.022	0.001	0.026	0.002

方法	间歇反应		连续逆流分离甘油
方法	MAD	MSD	MAD	MSD
UNIFAC	0.020	0.001	0.019	0.002
Modified UNIFAC	0.022	0.001	0.026	0.002

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