第42卷第10期化學工程Vol 42 No 102014年10月CHEMICAL ENGINEERING( CHINA)Oct.2014四氫呋喃-乙醇變壓精餾分離紀智玲,王志恒,李文秀,于三三,張志剛,李雙明,范俊剛,張弢(沈陽化工大學遼寧省化工分離技術重點實驗室,遼寧沈陽110142)摘要:共沸混合物分離是化工過程中常見的分離難題。變壓精餾是根據(jù)物系壓力改變而使液體混合物共沸點組成發(fā)生變化,進而使共沸物系得以分離的一種有效分離方法。在熱力學分析基礎上,提出了四氫呋喃乙醇液體混合物變壓精餾分離雙塔工藝流程。以 NRTL-RK為物性計算方法,利用 Aspen Plus模擬軟件對變壓精餾分離工藝過程進行分析及模擬,并對工藝參數(shù)進行優(yōu)化。研究結(jié)果表明:在常壓塔和0.8MPa高壓塔組成的雙塔流程中變壓精餾可將四氫呋喃-乙醇最低共沸混合物進行較好的分離。關鍵詞:汽液平衡;共沸物;變壓精餾;模擬中圖分類號:TQ028.3文獻標識碼:A文章編號:10059954(2014)100020-05DOI:10.3969/j.isn.10059954.2014.10.005Pressure-swing distillation separation oftetrahydrofuran-ethanol azeotropeJI Zhi-ling, WANG Zhi-heng, LI Wen-xiu, YU San-san, ZHANG Zhi-gang, LI Shuang-mingFAN Jun-gang, ZHANG TaoKey Lab of Chemical Separation Technology of Liaoning Province, Shenyang University of Chemical TechnologyShenyang 110142, Liaoning Province, ChinaAbstract: Azeotrope separations are tough issues commonly confronted in chemical processes. Pressure-swingdistillation( PSD)is based on the fact that azeotropic composition varies with the operational pressure, by whichazeotrope is then separated effectively. The azeotrope of tetrahydrofuran-ethanol characters that azeotropic pointappears in the vapor-liquid equilibrium, which makes it hard to separate tetrahydrofuran-ethanol liquid mixtureexperimentally and industrially. PSD is expected to fix this kind of separations effectively. In the research a dualcolumn process flow of tetrahydrofuran-ethanol pressure-swing distillation was put forward based on thermodynamicsanalysis. Aspen Plus simulation of pressure-swing distillation process of tetrahydrofuran-ethanol azeotrope wascarried out via NRTL-RK method. The technological parameters were optimized based on the process analysis. Itshows that tetrahydrofuran-ethanol azeotrope can be well separated by means of a two-column pressure-swingdistillation process, which is composed of atmospheric tower and high pressure tower(0. 8 MPa). It is helpful inguiding the process design for separation of tetrahydrofuran-ethanol azeotropeKey words: vapor-liquid equilibria; azeotrope; pressure-swing distillation; simulation四氫呋喃與乙醇是重要的有機溶劑,廣泛應用優(yōu)點12。于化工、制藥、染料等領域。工業(yè)生產(chǎn)中產(chǎn)生的四氫應用 Aspen Plus模擬軟件,依據(jù)四氫呋喃呋喃和乙醇液體混合物具有最低共沸點,采用普通乙醇體系汽液平衡數(shù)據(jù)研究了其變壓精餾分離精餾無法對其實現(xiàn)有效分離。具有最低共沸點的難過程特性,并對過程工藝參數(shù)進行優(yōu)化分析,提出分離混合物,可以采用恒沸精餾,萃取精餾,加鹽精個具有較高分窣效率的四氫呋喃-κ醇雙塔變壓精餾等6特殊精餾方法。但與之相比,變壓精餾更餾分離路中國煤化工錄該類共沸體系具有工藝簡單、不引入雜質(zhì)以及節(jié)約能耗等獨特分離過程CNMHG收稿日期:20140作者簡介:紀智玲(1962—),女,副教授,主要研究傳質(zhì)過程及新型分離技術,電話:1860419780,E-mail:yizhiling@163.com。紀智玲等四氫呋喃-乙醇變壓精餾分離211四氫呋喃-乙醇變壓精餾精餾,塔底物流4為所得到的高純度的四氫呋喃產(chǎn)變壓精餾是利用二元混合物系對拉烏爾定律產(chǎn)品,塔頂共沸物料經(jīng)物料路線2返回到常壓塔LOW生偏差的特點,改變體系壓力可以移動常壓下形成繼續(xù)精餾。的二元物系共沸點或改變其共沸組成,通過不同操作壓力的精餾過程組合可以在塔頂或者塔底得到高純度組分。1.1四氫呋喃-乙醇物系在不同壓力下汽液相平衡FEEDH LOWHIGH從圖1和表1可以看出,隨著壓力的增加四氫呋喃-乙醇的共沸點沿參考線向左移動,四氫呋喃在共沸物中的摩爾分數(shù)減少。常壓以下,壓力的減小EED原料;3-乙醇;4四氫呋喃;LOW常壓塔;HGH高壓塔;使四氫呋喃-乙醇的相對揮發(fā)度增大,但是對設備的B1-減壓閥;B2輸送泵氣密性要求增加,為了降低操作成本,選擇使用常壓圖2變壓精餾工藝流程Fig 2 PSD Flowchart塔。在加壓條件下,隨著壓力的增加,四氫呋喃-乙醇相對揮發(fā)度增加,但增加到一定程度時,壓力的增2模擬計算與優(yōu)化分析加對相對揮發(fā)度的影響明顯變小,為了降低設備的2.1模擬規(guī)定投資費用。高壓塔選擇操作壓力為810.6kPa。氣液平衡采用 NRTL-RK模型,模擬計算依據(jù)見表20.8表2變壓精餾模擬計算依據(jù)Table 2 basic facts for pSd simulation0.6參數(shù)名稱進料量/進料組成乙kmol·h-2)醇摩爾分數(shù)進料溫度分離要求乙麗0.4醇摩爾分數(shù)d506.625kPa數(shù)值0.7常溫0.995以上e 810.6kPaf 1 000 k Pa2.2模擬過程分析與優(yōu)化液相四氫呋喃摩爾分數(shù)對分離過程工藝而言,產(chǎn)品純度、產(chǎn)量與能耗之圖1壓力對物系汽液平衡的影響間互相制約。因此需要選擇滿足生產(chǎn)工藝條件下投Fig. 1 Pressure effect on system vapor-liquid equilibrium入較小能耗的操作條件。表1壓力對共沸組成的影響2.2.1常壓塔總塔板數(shù)對乙醇產(chǎn)品純度(摩爾分Table 1 Effect of pressure on azeotrope composition數(shù))與再沸器熱負荷Q的影響常壓塔總塔板數(shù)對塔底乙醇產(chǎn)品純度(摩爾分60.795kPa100kPa506.625kPa810.6kPa1000kPa乙醇摩數(shù))及再沸器熱負荷Q影響見圖30.0250.09350.6360.902爾分數(shù)共沸溫51.0465.35122.33141.97150.830.99922700.99乙醇摩爾再沸器熱貧萄1.2變壓精餾常規(guī)工藝流程0.992240依據(jù)1.1節(jié)的分析可設計變壓精餾流程如圖2所示。在圖2中,循環(huán)高壓共沸組成混合物2引入0.993中國煤化工3032220常壓塔IoW循環(huán)進料,塔頂物流1為常壓條件下的CNMHG共沸物,塔底物流3可以得到高純度的乙醇產(chǎn)品;常圖3總塔板數(shù)的影響壓塔塔頂?shù)墓卜形锛次锪?進入高壓塔HGH進行Fig 3 Effects of total number of trays化學工程2014年第42卷第10期由圖3可以看出,乙醇產(chǎn)品純度(摩爾分數(shù))隨由圖5可知,隨循環(huán)物流進料位置的下移,乙醇著總塔板數(shù)的増加而增大,但塔底乙醇產(chǎn)品純度達產(chǎn)品純度降低而所需的再沸器熱負荷増加。到一定程度,其隨塔板數(shù)增加的幅度趨緩,之后保持由圖6可知,原料的進料位置過低或過高時,乙定值。同樣隨著塔總板數(shù)的増加,再沸器熱負荷φα醇產(chǎn)品純度玓降低且再沸器熱負荷增加。降低。綜合考慮,常壓塔理論塔板數(shù)選擇為22塊,可避免塔板數(shù)增加導致的設備投資費用。1.012.2.2常壓塔回流比對乙醇產(chǎn)品純度與能耗Q的影響0.98乙醇摩爾分數(shù)沸器熱負荷在常壓塔理論塔板數(shù)為22的情況下,研究回流21400.96比對產(chǎn)品純度及再沸器熱負荷的影響見圖4。21200.9421000.931.0020802800246810121516182022進料位置圖6主進料位置的影響0.98Fig 6 Effects of feed location乙醇摩爾分數(shù)0-再沸器熱負何0.96故常壓塔循環(huán)進料最佳進料位置在第3塊塔0.95板,主進料最佳進料位置在第9塊塔板00.20.40.60.81.01.2回流比R2常壓塔循環(huán)進料量對乙醇產(chǎn)品純度及再沸圖4回流比的影響器熱負荷的影響Fig 4 Effects of reflux ratioqb/q表示常壓塔塔頂產(chǎn)品摩爾流量與主進料摩爾流量之比,它也可反映循環(huán)進料量對常壓塔操圖4可知隨著回流比R1的增加,塔底乙醇產(chǎn)品作的影響。選用前述適宜的操作參數(shù),研究循環(huán)進料量對產(chǎn)品純度及再沸器熱負荷的影響。純度(摩爾分數(shù))及再沸器熱負荷Qε均顯著增加,但乙醇產(chǎn)品純度達到一定值后趨于穩(wěn)定,而再沸器熱負荷卻是線性增大。在滿足分離要求前提下盡可能選擇較小的回流比,故常壓塔選擇回流比為0.6。20002.2.3進料位置的影響1800選擇常壓塔理論塔板數(shù)為22,回流比為0.6,常0.96乙醇摩0-再沸器1600壓塔循環(huán)進料1和主進料FEED位置對產(chǎn)品純度及1400再沸器熱負荷Q的影響如圖5和圖6所示。0.91.1131.51.71.92.12240qq圖7常壓塔循環(huán)進料量的影響Fig. 7 Effects of reflux feeding flow rate21800.94長如圖7所示,隨常壓塔循環(huán)進料量增大,即常壓2140塔塔頂采出量增大,乙醇產(chǎn)品純度高顯著增加,但相一乙醉摩爾分數(shù)再沸器熱負荷2100應再沸器熱負荷也明顯增大。從圖7中可以得出,0.84合適的循環(huán)02468101215161820中國煤化工2.2.5高CNMHG圖5循環(huán)進料位置的影響繼續(xù)這力同陽行優(yōu)化分析,優(yōu)Fig 5 Effects of reflux feeding location化工藝條件總結(jié)果如表3所示。紀智玲等四氫呋喃-乙醇變壓精餾分離表3工藝流程優(yōu)化操作參數(shù)Table 3 Optimization of operating parameters設備名稱參數(shù)名稱參數(shù)值平四氫呋喃汽相總塔板數(shù)四氫呋喃液相循環(huán)物流進料位置2390000乙醇液相乙醇汽相常壓塔LOW主進料位置回流比0.6操作壓力/kPa0246810121416182022總塔板數(shù)塔板數(shù)進料位置高壓塔HGH圖8常壓塔汽液摩爾分數(shù)分布回流比8 Mole fraction distribution of atmospheric column操作壓力/kPa810.63模擬結(jié)果與討論0.93.1變壓精餾流程模擬結(jié)果采用表3所示優(yōu)化工藝參數(shù),對圖2所示流程0-四氫呋喃液相0.5乙醇汽相進行模擬優(yōu)化,模擬結(jié)果如表4所示。勤0.4一乙醇液相表4變壓精餾流程模擬結(jié)果0.2Table 4 PSD simulation results468101214161820222426流股FEED塔板數(shù)圖9高壓塔汽液摩爾分數(shù)分布溫度/566.9478.98Fig9 Mole fraction distribution of high pressure column壓力/kPa102.925811.8101.725104.24摩爾流量100150120kmol h)4結(jié)論四氫呋喃0.30.7330.670.00120.997(1)由汽液相平衡數(shù)據(jù)分析可知,壓力改變可摩爾分數(shù)以較大程度上移動四氫呋喃-乙醇共沸點,使得變壓精餾可以較好地分離四氫呋喃-乙醇二元共沸物系。乙醇摩0.70.2670.3330.99880.003爾分數(shù)(2)應用 Aspen Plus模擬軟件對變壓精餾分離四氫呋喃-乙醇共沸物系雙塔工藝流程進行研究,得由表4結(jié)果可知,變壓精餾分離后,常壓塔底可該雙塔工藝流程,可得到純度為99.7%的四氫呋喃得到摩爾分數(shù)99.88%的乙醇,高壓塔底可得到與99.5%的乙醇產(chǎn)品99.7%的四氫呋喃。(3)本研究提出的四氫呋喃-乙醇變壓精餾流3.2塔內(nèi)汽液摩爾分數(shù)分布程對共沸物系分離工藝優(yōu)化分析和對相應現(xiàn)有工藝常壓塔LOW和高壓塔HCH塔內(nèi)汽液相摩爾裝置改造具有重要的指導意義。分數(shù)分布分別如圖8和圖9所示。由圖8和圖9可見,常壓塔DOW和加壓塔參考文獻:HlH塔頂區(qū)域汽液二相均接近共沸組成;而分別(1 BRUNNER E, SCHOLZ A G R.orir在塔釜區(qū)域,汽液二相摩爾分數(shù)均趨近于1,反映該中國煤化工 system at25,50變壓精餾流程可在常壓塔底得到高純乙醇和在高壓塔底得到高純四氫呋喃,該結(jié)論與變壓精餾流程模2]YOSHCNMHG4,29:2831.AAGI A. 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