乙酸乙酯-乙醇-离子液体等压汽液平衡数据的测定

第36卷第3期北京化工大学学报(自然科学版)Vol 36, No. 32009年Journal of Beijing University of Chemical Technology(Natural Science)2009乙酸乙酯-乙醇-离子液体等压汽液平衡数据的测定朱久娟张继国李群生”邢风英(北京化工大学化学工程学院,北京100029)摘要:在101.32kPa下,用改进的 Othmer釜测定了两种乙酸乙酯乙醇离子液体三元物系的等压汽液平衡数据,即乙酸乙酯乙醇-1-丁基3-甲基咪唑四氟硼酸盐([BMIM]BF4)与乙酸乙酯乙醇1-辛基3-甲基咪唑四氟硼酸盐([OMIM]BF4)。实验结果表明:加入[BMIM]BF4和[OMIM]BF4,汽液平衡线偏离乙酸乙酯乙醇物系的汽液平衡线;离子液体摩尔分数越大偏离程度越大;[BMIM]BF4与[OMM]BF4表现出明显盐效应使乙酸乙酯对乙醇的相对挥发度发生改变,均消除了乙酸乙酯乙醇物系的共沸点。离子液体对乙酸乙酯的盐析效应顺序为:[OMIM]BF4> [BMIM]BF4。因此,[BMIM]BF4和[OMM]BF4可以作为乙酸乙酯乙醇物系萃取精馏的溶剂汽液平衡数据的测定可为分离过程优化设计提供依据。关键词:汽液相平衡;乙酸乙酯;乙醇;1-丁基3甲基咪唑四氟硼酸盐;1-辛基-3-甲基咪唑四氟硼酸盐中图分类号;TQ013.1引言BF4/[OMIM]BF4)三组分物系等压汽液平衡数据,并讨论了离子液体对乙酸乙酯乙醇共沸物物系分乙酸乙酯是应用广泛的脂肪酸酯之一,因其具离的不同影响。有极好的溶解性,故被应用于涂料、水果香精等山目前,乙酸乙酯主要由乙酸和乙醇通过酯化反应生1实验部分产工业上采用乙醇过量的方法提高生产率,而乙酸1.1原料乙酯与乙醇的沸点只差1℃,常压下形成共沸物,乙酸乙酯、乙醇,分析纯,天津化学试剂公司;不能用一般的精馏方法分离因此国内外在乙酸乙[BMM]BF4、OMM]BF,质量分数大于98%,河酯与乙醇的分离方面做了大量的工作13北师范大学化学化工研究所。共沸体系不能通过简单蒸馏实现完全分离。离1.2实验装置子液体作为一种新型“绿色”溶剂因其温度范围宽、实验中所采用的汽液相平衡装置为北洋化工实蒸气压低热稳定性好、无污染等优点而被广泛应用验设备公司CE2型改进的 Othmer汽液平衡釜,如于萃取和对于共沸物或沸点相近物系的分离过图1所示。程4,发展与完善含有离子液体物系的热力学数据对更好地理解离子液体的分离规律及发展热力学模型很重要4。目前,已有文献报道了相关的研究成果612),如液液平衡、无限稀释时的活度系数等,但等压汽液平衡数据还很缺乏,同时也没有建立很好的理论预测模型。由文献[78]可知[BMM]BF4对共沸物的分离效果较好,但是[OMIM]BF4对共沸物物系的分离数据还没有报道,故有必要进行测定。本文测定乙酸乙酯乙醇离子液体([BMIM]1一加热棒;2-液相取样;3—平衡室;4-温度计;5—冷凝器;收稿日期:2008-08-28干燥器;7U型压力计;8气压球;9气相取样口第一作者:女,1983年生,硕士生图1 Othmer汽液平衡釜通讯联系人ig. 1 Othmer vapoE-mail:ligs@mail,buct.edu.cn北京化工大学学报(自然科学版)2009年13实验步骤表1乙酸乙酯(1)-乙醇(2)-[BMIM]BF4(3)[OMIM]BF4采用称重法配制试样。将50mL试样加入到平(3)三组分物系的汽液平衡数据(101.32kPa)衡釜中,加热至沸腾。平衡室温度恒定不变时达到Tabe1 Vle data for the termary systems of ethyl acetate平衡,保持约30min,然后采用微量进样器分别直接(1)-ethanol(2)with [BMIM]BF,(3)or [OMIM]从汽相、液相取样口取样分析,取样间隔约15mnBF,(3)at 101.32 kPa14分析方法r(LBMIMJBF4)/% T/K 51 yI y1汽、液相中乙酸乙酯与乙醇的含量分析采用气349.760.1120.2002.0151.0741.982相色谱法测定,液相中离子液体的含量通过称重法10.066346.950.3050.4121.6761.1311.597测定。气相色谱仪为北京东西电子生产的345.940.5220.5731.4091.2451.229GC4000A型气相色谱仪,操作条件: Porapak-Q填充345.940.6770.6791.2861.3831.009柱(3m×0.3mm),载气(氢气)流量30mL/min,柱9939346.350.7710.7441.2201.5290.86310.024346.700.8230.7881.1971.6170.799温383.15K,汽化室温度413.15K,TCD温度10.058350.850.9630.9511.0761.5120.746423.15K,采用面积归一化法定量。353.350.1830.3032.1361.1391.9412结果与讨论351.950.2670.3942.0071.1641.7852.1汽液平衡数据的校证29,865349.950.4920.5961.7341.2161.5用本实验装置所测定的乙酸乙酯乙醇二组分30.227349400.5890.6791.6981.2181.476物系的等压汽液平衡数据与文献值基本吻合(见30.109349.200.6460.7281.6691.2061.46图2),最大偏差为0.004,说明实验装置可靠。29.919348.760.7451.2331.4390.7901.6251.2101,4349.440.8080.8561.5521.1631.41330.102350950.9280.9471.4261.0771.38I([OMIM]BF4)/% T/K I1 yI y1 y2 a110.085351.450.0920.1802.0841.0082.16610.107349650.1860.3151.9231.0082.0120210.160348.450.3040.4401.7101.0131.79910.081347.550.4030.5281.5951.0311.657040.60.81.010.263347.350.5270.6251,4551.0461.49610.186347.300.5810.6601.3941.0721.400图2101.32ka下乙酸乙酯(1)乙醇(2)物系x1y1曲线10.104347.540.6670.7291.3291.0641.343Fig 2 Vapor-liquid equilibrium(vle) diagram of the ethyl10.081347.840.7620.8021.2681.07acetate(1)-ethanol (2)system at 101.32 kPa000349060.9130.9291.1762.2汽液平衡数据9630.9701.1550.9921.242在10132kPa下,测定了乙酸乙酯乙醇离子30.740365.840.0870.2012.0550.735液体三元物系汽液相平衡的数据(见表1),其中液30.540363.650.14102961.9780.7422.56相组成是按脱离子液体的摩尔分数计算的。活度系数(%)的计算公式12如式(1),计算结357.650.4040.618果列于表1中。30218356560.5480.741X1=30244356.040.67008261.4660.6342.33830.435355.660.7710.8871.3880.6042.3y、x为组分i在汽、液相中的摩尔分数;p为平衡时的总压,即101.32kPa;p是纯物质i的饱和蒸0,409354.130.9120.9601.3320.5922.316气压,由 Antoine方程计算12;g是组分i在汽相中y为活度系数;an2为乙酸乙酯对乙醇的相对挥发度第3期朱久娟等:乙酸乙酯乙醇离子液体等压汽液平衡数据的测定17的逸度系数,g是纯组分i在饱和状态时的逸度系数。离子液体被认为不挥发,故把汽相看作为理想状态,式(1)可以简化为乙酸乙酯对乙醇的相对挥发度(a12)16计算结果列于表1中,定义式如式(3)u/(3)y2/x223离子液体浓度对汽液相平衡的影响随离子液体([BMIM]BF4和[OMIM]BF4)的●无离子液体;x(BMIM]BF4)=10%;加入,汽相组分中的乙酸乙酯含量增加。由图3可Ar([BMIM]BF4)=30%: Vr([OMIM]BF. )=10%:▲x([OMM]BF4=30%见汽液平衡曲线偏离乙酸乙酯乙醇二组分物系的图4离子液体对相对挥发度的影汽液平衡曲线;且随离子液体含量的增加,汽液线偏Fig 4 Effect of ionic liquid on relative volatility离程度增大,乙酸乙酯乙醇的共沸点消失,故[OMIM]BF4使y1的增加更大;综上可知离子液[ BMIMJBF4与[OMIM]BF4可作为乙酸乙酯乙醇体与乙醇的结合作用强于乙酸乙酯故离子液体对萃取精馏的溶剂。乙酸乙酯为盐析效应,且对于乙酸乙酯的盐析效应遵循如下规律:[OMIM]BF4>[BMIM]BF4这是因为在有机溶剂中,离子液体的“分子”特性占主导地位,当阴离子相同时,阳离子体积越大,离子液体“分子”与有机溶剂分子之间的色散作用力越强。“分子”体积较大的离子液体[OMM]BF4溶于乙酸乙酯乙醇体系中,通过化学亲和力、氢键力以及离P=10132kPa子的静电引力等作用与乙醇“绑定”,使得乙醇的活02040.60.81.0度系数减少,从而提高了乙酸乙酯的活度系数、对乙醇的相对挥发度。无离子液体;vx([BMM]BF4=10%;图5是乙酸乙酯(1)-乙醇(2)离子液体(3)三Ar([BMIM]BF4)=30%:Vr([OMIM]. )=10%:组分物系的Tx1-y1图。由图5可见,随离子液体▲x(OMIM]BF4)=30%含量的增加,平衡温度(T)均有所升高;当[BMIM]图3三组分物系的等压汽液平衡曲线Fig 3 Isobaric VLE diagram of the ternary systems离子液体的加入明显提高了乙酸乙酯-乙醇物系的相对挥发度。由图4可知离子液体的加入量越多,乙酸乙酯乙醇的相对挥发度提高幅度越大,说明离子液体对乙酸乙酯乙醇物系表现出明显的盐效应,可以提高此物系的分离效果24离子液体种类对汽液相平衡的影响0204观察图3和图4可知[OMIM]BF4的分离效果摩尔分数强于[BMIM]BF4从表1中y1可知离子液体的加入对乙酸乙酯的活度系数有增大作用,对乙醇的活离子液体;●r(IBMM]BF4)=10%r([BMIM]BF)=30%: Ax([OMIM]BF4)=10%;度系数影响不大,但当[ OMIM]BF4的摩尔分数约-( OMIM JBF,)=30%空心点了-x1图:实心点:r-y图为30%时,乙醇的活度系数降低显著(y2<1.000图5三组分物系的Tx1y1图加入等摩尔分数的[OMIM]BF4与[BMIM]BF4时Fig 5 T-x1-yI diagram of the termary systems北京化工大学学报(自然科学版)2009年BF4摩尔分数为10%时,共沸点并未消失,但共沸the heat capacity of the ionic liquid [Emim]BFa and its物的组成改变(x1≈0680),当[BMIM]BF4摩尔分agueous solution [J]. 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Journal of Chemical engi130(1/2):243-252neering Data,2008,53(2):427-433[12] Orchille's A V, Miguel P J, Vercher E, et al.Isobaric[4]田涛,郑丹星,武向红,等.室温离子液体[Emm]BF4vapor-liquid equilibria for ethyl acetate ethanol +1及其水溶液体系的比热容测定[J].北京化工大学学ethyl-3-methylimidazolium trifluoromethanesulfonate at报:自然科学版,2008,35(3):27-30.100 kPa [J]. Jourmal of Chemical Engineering Data2007,52(6):2325-2330Tian T, Zheng DX, Wu X H, et al. Determination of第3期朱久娟等:乙酸乙酯乙醇离子液体等压汽液平衡数据的测定Isobaric vapor-liquid equilibria for ethyl acetate-ethanol-ionicliquid ternary systemsZHU JiuJuan ZHANG JiGuo LI Qun Sheng XING Feng YingCollege of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, China)Abstract: Isobaric vapor- liquid equilibrium data for ethyl acetate-ethanol-ionic liquid ternary systems were mea-sured in a modified Othmer still at 101. 32 kPa. The ionic liquids employed were 1-butyl-3-methylimidazoliumtetrafluoroborate([BMIM]BF4) and ethyl 1-octyl-3-methylimidazolium tetrafluoroborate([OMIm]BF4 ).Thevapor-liquid equilibrium curves of the ethyl acetate-ethanol-ionic liquid systems deviate from that of the IL-freesystem and the deviation increases with increasing amounts of IL. The Ils show a salting-out effect which in-creases the volatility of ethyl acetate relative to that of ethanol, and even leads to an elimination of the azeotropicpoint. The salting-out effect on ethyl acetate decreases in the order: [OMIM]BF4>[BMIM]BF4. As a resultit is concluded that [BMIM]BF4 and [OMIM]BF4 can be used as entrainers for the separation of ethyl acetateand ethanol, and the vle data obtained here can be used to optimize the processKey words: vapor-liquid equilibrium; ethyl acetate; ethanol; 1-butyl-3-methylimidazolium tetrafluoroborate; 1-octyl-3-methylimidazolium tetrafluoroborate