第36卷第3期北京化工大學學報(自然科學版)Vol 36, No. 32009年Journal of Beijing University of Chemical Technology(Natural Science)2009乙酸乙酯-乙醇-離子液體等壓汽液平衡數(shù)據(jù)的測定朱久娟張繼國李群生”邢風英(北京化工大學化學工程學院,北京100029)摘要:在101.32kPa下,用改進的 Othmer釜測定了兩種乙酸乙酯乙醇離子液體三元物系的等壓汽液平衡數(shù)據(jù),即乙酸乙酯乙醇-1-丁基3-甲基咪唑四氟硼酸鹽([BMIM]BF4)與乙酸乙酯乙醇1-辛基3-甲基咪唑四氟硼酸鹽([OMIM]BF4)。實驗結果表明:加入[BMIM]BF4和[OMIM]BF4,汽液平衡線偏離乙酸乙酯乙醇物系的汽液平衡線;離子液體摩爾分數(shù)越大偏離程度越大;[BMIM]BF4與[OMM]BF4表現(xiàn)出明顯鹽效應使乙酸乙酯對乙醇的相對揮發(fā)度發(fā)生改變,均消除了乙酸乙酯乙醇物系的共沸點。離子液體對乙酸乙酯的鹽析效應順序為:[OMIM]BF4> [BMIM]BF4。因此,[BMIM]BF4和[OMM]BF4可以作為乙酸乙酯乙醇物系萃取精餾的溶劑汽液平衡數(shù)據(jù)的測定可為分離過程優(yōu)化設計提供依據(jù)。關鍵詞:汽液相平衡;乙酸乙酯;乙醇;1-丁基3甲基咪唑四氟硼酸鹽;1-辛基-3-甲基咪唑四氟硼酸鹽中圖分類號;TQ013.1引言BF4/[OMIM]BF4)三組分物系等壓汽液平衡數(shù)據(jù),并討論了離子液體對乙酸乙酯乙醇共沸物物系分乙酸乙酯是應用廣泛的脂肪酸酯之一,因其具離的不同影響。有極好的溶解性,故被應用于涂料、水果香精等山目前,乙酸乙酯主要由乙酸和乙醇通過酯化反應生1實驗部分產(chǎn)工業(yè)上采用乙醇過量的方法提高生產(chǎn)率,而乙酸1.1原料乙酯與乙醇的沸點只差1℃,常壓下形成共沸物,乙酸乙酯、乙醇,分析純,天津化學試劑公司;不能用一般的精餾方法分離因此國內(nèi)外在乙酸乙[BMM]BF4、OMM]BF,質量分數(shù)大于98%,河酯與乙醇的分離方面做了大量的工作13北師范大學化學化工研究所。共沸體系不能通過簡單蒸餾實現(xiàn)完全分離。離1.2實驗裝置子液體作為一種新型“綠色”溶劑因其溫度范圍寬、實驗中所采用的汽液相平衡裝置為北洋化工實蒸氣壓低熱穩(wěn)定性好、無污染等優(yōu)點而被廣泛應用驗設備公司CE2型改進的 Othmer汽液平衡釜,如于萃取和對于共沸物或沸點相近物系的分離過圖1所示。程4,發(fā)展與完善含有離子液體物系的熱力學數(shù)據(jù)對更好地理解離子液體的分離規(guī)律及發(fā)展熱力學模型很重要4。目前,已有文獻報道了相關的研究成果612),如液液平衡、無限稀釋時的活度系數(shù)等,但等壓汽液平衡數(shù)據(jù)還很缺乏,同時也沒有建立很好的理論預測模型。由文獻[78]可知[BMM]BF4對共沸物的分離效果較好,但是[OMIM]BF4對共沸物物系的分離數(shù)據(jù)還沒有報道,故有必要進行測定。本文測定乙酸乙酯乙醇離子液體([BMIM]1一加熱棒;2-液相取樣;3—平衡室;4-溫度計;5—冷凝器;收稿日期:2008-08-28干燥器;7U型壓力計;8氣壓球;9氣相取樣口第一作者:女,1983年生,碩士生圖1 Othmer汽液平衡釜通訊聯(lián)系人ig. 1 Othmer vapoE-mail:ligs@mail,buct.edu.cn北京化工大學學報(自然科學版)2009年13實驗步驟表1乙酸乙酯(1)-乙醇(2)-[BMIM]BF4(3)[OMIM]BF4采用稱重法配制試樣。將50mL試樣加入到平(3)三組分物系的汽液平衡數(shù)據(jù)(101.32kPa)衡釜中,加熱至沸騰。平衡室溫度恒定不變時達到Tabe1 Vle data for the termary systems of ethyl acetate平衡,保持約30min,然后采用微量進樣器分別直接(1)-ethanol(2)with [BMIM]BF,(3)or [OMIM]從汽相、液相取樣口取樣分析,取樣間隔約15mnBF,(3)at 101.32 kPa14分析方法r(LBMIMJBF4)/% T/K 51 yI y1汽、液相中乙酸乙酯與乙醇的含量分析采用氣349.760.1120.2002.0151.0741.982相色譜法測定,液相中離子液體的含量通過稱重法10.066346.950.3050.4121.6761.1311.597測定。氣相色譜儀為北京東西電子生產(chǎn)的345.940.5220.5731.4091.2451.229GC4000A型氣相色譜儀,操作條件: Porapak-Q填充345.940.6770.6791.2861.3831.009柱(3m×0.3mm),載氣(氫氣)流量30mL/min,柱9939346.350.7710.7441.2201.5290.86310.024346.700.8230.7881.1971.6170.799溫383.15K,汽化室溫度413.15K,TCD溫度10.058350.850.9630.9511.0761.5120.746423.15K,采用面積歸一化法定量。353.350.1830.3032.1361.1391.9412結果與討論351.950.2670.3942.0071.1641.7852.1汽液平衡數(shù)據(jù)的校證29,865349.950.4920.5961.7341.2161.5用本實驗裝置所測定的乙酸乙酯乙醇二組分30.227349400.5890.6791.6981.2181.476物系的等壓汽液平衡數(shù)據(jù)與文獻值基本吻合(見30.109349.200.6460.7281.6691.2061.46圖2),最大偏差為0.004,說明實驗裝置可靠。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圖2101.32ka下乙酸乙酯(1)乙醇(2)物系x1y1曲線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汽液平衡數(shù)據(jù)9630.9701.1550.9921.242在10132kPa下,測定了乙酸乙酯乙醇離子30.740365.840.0870.2012.0550.735液體三元物系汽液相平衡的數(shù)據(jù)(見表1),其中液30.540363.650.14102961.9780.7422.56相組成是按脫離子液體的摩爾分數(shù)計算的?；疃认禂?shù)(%)的計算公式12如式(1),計算結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為組分i在汽、液相中的摩爾分數(shù);p為平衡時的總壓,即101.32kPa;p是純物質i的飽和蒸0,409354.130.9120.9601.3320.5922.316氣壓,由 Antoine方程計算12;g是組分i在汽相中y為活度系數(shù);an2為乙酸乙酯對乙醇的相對揮發(fā)度第3期朱久娟等:乙酸乙酯乙醇離子液體等壓汽液平衡數(shù)據(jù)的測定17的逸度系數(shù),g是純組分i在飽和狀態(tài)時的逸度系數(shù)。離子液體被認為不揮發(fā),故把汽相看作為理想狀態(tài),式(1)可以簡化為乙酸乙酯對乙醇的相對揮發(fā)度(a12)16計算結果列于表1中,定義式如式(3)u/(3)y2/x223離子液體濃度對汽液相平衡的影響隨離子液體([BMIM]BF4和[OMIM]BF4)的●無離子液體;x(BMIM]BF4)=10%;加入,汽相組分中的乙酸乙酯含量增加。由圖3可Ar([BMIM]BF4)=30%: Vr([OMIM]BF. )=10%:▲x([OMM]BF4=30%見汽液平衡曲線偏離乙酸乙酯乙醇二組分物系的圖4離子液體對相對揮發(fā)度的影汽液平衡曲線;且隨離子液體含量的增加,汽液線偏Fig 4 Effect of ionic liquid on relative volatility離程度增大,乙酸乙酯乙醇的共沸點消失,故[OMIM]BF4使y1的增加更大;綜上可知離子液[ BMIMJBF4與[OMIM]BF4可作為乙酸乙酯乙醇體與乙醇的結合作用強于乙酸乙酯故離子液體對萃取精餾的溶劑。乙酸乙酯為鹽析效應,且對于乙酸乙酯的鹽析效應遵循如下規(guī)律:[OMIM]BF4>[BMIM]BF4這是因為在有機溶劑中,離子液體的“分子”特性占主導地位,當陰離子相同時,陽離子體積越大,離子液體“分子”與有機溶劑分子之間的色散作用力越強?！胺肿印斌w積較大的離子液體[OMM]BF4溶于乙酸乙酯乙醇體系中,通過化學親和力、氫鍵力以及離P=10132kPa子的靜電引力等作用與乙醇“綁定”,使得乙醇的活02040.60.81.0度系數(shù)減少,從而提高了乙酸乙酯的活度系數(shù)、對乙醇的相對揮發(fā)度。無離子液體;vx([BMM]BF4=10%;圖5是乙酸乙酯(1)-乙醇(2)離子液體(3)三Ar([BMIM]BF4)=30%:Vr([OMIM]. )=10%:組分物系的Tx1-y1圖。由圖5可見,隨離子液體▲x(OMIM]BF4)=30%含量的增加,平衡溫度(T)均有所升高;當[BMIM]圖3三組分物系的等壓汽液平衡曲線Fig 3 Isobaric VLE diagram of the ternary systems離子液體的加入明顯提高了乙酸乙酯-乙醇物系的相對揮發(fā)度。由圖4可知離子液體的加入量越多,乙酸乙酯乙醇的相對揮發(fā)度提高幅度越大,說明離子液體對乙酸乙酯乙醇物系表現(xiàn)出明顯的鹽效應,可以提高此物系的分離效果24離子液體種類對汽液相平衡的影響0204觀察圖3和圖4可知[OMIM]BF4的分離效果摩爾分數(shù)強于[BMIM]BF4從表1中y1可知離子液體的加入對乙酸乙酯的活度系數(shù)有增大作用,對乙醇的活離子液體;●r(IBMM]BF4)=10%r([BMIM]BF)=30%: Ax([OMIM]BF4)=10%;度系數(shù)影響不大,但當[ OMIM]BF4的摩爾分數(shù)約-( OMIM JBF,)=30%空心點了-x1圖:實心點:r-y圖為30%時,乙醇的活度系數(shù)降低顯著(y2<1.000圖5三組分物系的Tx1y1圖加入等摩爾分數(shù)的[OMIM]BF4與[BMIM]BF4時Fig 5 T-x1-yI diagram of the termary systems北京化工大學學報(自然科學版)2009年BF4摩爾分數(shù)為10%時,共沸點并未消失,但共沸the heat capacity of the ionic liquid [Emim]BFa and its物的組成改變(x1≈0680),當[BMIM]BF4摩爾分agueous solution [J]. 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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