Liquid-liquid equilibria for ternary systems polyoxymethylene dimethyl ethers+water+n-hexane

doi:10.11949/j.issn.0438-1157.20160391

Abstract

Abstract:

Polyoxymethylene dimethyl ethers (PODE_n) are promising diesel additive which can be synthesized from aqueous formaldehyde solutions and methanol. Formaldehyde+methanol has been found as an economical and feasible way for the production of PODE_n due to the cheap raw materials. In this study the extraction process is chosen to obtain PODE_n from aqueous solution. A reliable thermodynamic model for a good system description is important for extraction equipment modeling, development and design. Liquid-liquid equilibria(LLE) data are valuable in studies of the applicability of thermodynamic model. In this work, LLE was analytically determined at 293.15 K for the following four systems:(PODE₁+water+n-hexane), (PODE₂+water+n-hexane), (PODE₃+water+n-hexane) and (PODE₄+water+n-hexane), respectively. Based on high selectivity of PODE₁-4 over water and the PODE_n mass fraction in the organic phase was much larger than that in aqueous phase, it was found that washing with n-hexane was an effective way of extracting PODE_n from the aqueous phase without losing any significant amount of PODE_n to the extract phase. The isothermal experimental data were shown a good linear fit in Hand plots with R² being approximately unity. The well-known NRTL and UNIQUAC thermodynamic models were applied to correlate the experimental data, and the results of root mean square deviation calculation (RMSD) and ternary phase diagram analysis indicated that NRTL and UNIQUAC models all shown good predictive capabilities.

Key words: extraction, n-hexane, polyoxymethylene dimethyl ether, aqueous solution, phase equilibria

摘要：

聚甲氧基二甲醚（PODE_n）是一种极具应用前景的清洁柴油调和组分。研究了293.15 K、常压下PODE₁+水+正己烷、PODE₂+水+正己烷、PODE₃+水+正己烷、PODE₄+水+正己烷这4组三元体系的液液相平衡。PODE₁-4组分的萃取选择性系数S远大于1，表明正己烷作为萃取剂从水溶液中萃取PODE_1-4是可行的；经Hand结线关联检验，各体系的相平衡数据具有较高的一致性；采用NRTL和UNIQUAC热力学模型对相平衡数据进行拟合，均方根差计算（RMSD）结果和三元相图分析结果表明NRTL和UNIQUAC都能较好地描述三元体系的液液相平衡。

关键词: 萃取, 正己烷, 聚甲氧基二甲醚, 水溶液, 相平衡

CLC Number:

TQ013.1

ZHUANG Zhihai, ZHANG Jianqiang, LIU Dianhua. Liquid-liquid equilibria for ternary systems polyoxymethylene dimethyl ethers+water+n-hexane[J]. CIESC Journal, 2016, 67(9): 3545-3551.

庄志海, 张建强, 刘殿华. 聚甲氧基二甲醚+水+正己烷三元体系的液液相平衡[J]. 化工学报, 2016, 67(9): 3545-3551.

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