四氫呋喃-乙醇變壓精餾分離

第42卷第10期化學(xué)工程Vol 42 No 102014年10月CHEMICAL ENGINEERING( CHINAOct.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(yáng)化工大學(xué)遼寧省化工分離技術(shù)重點(diǎn)實(shí)驗室,遼寧沈陽(yáng)110142)摘要:共沸混合物分離是化工過(guò)程中常見(jiàn)的分離難題。變壓精餾是根據物系壓力改變而使液體混合物共沸點(diǎn)組成發(fā)生變化,進(jìn)而使共沸物系得以分離的一種有效分離方法。在熱力學(xué)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(guò)程進(jìn)行分析及模擬,并對工藝參數進(jìn)行優(yōu)化。研究結果表明: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(jìn)行較好的分離。關(guān)鍵詞:汽液平衡;共沸物;變壓精餾;模擬中圖分類(lèi)號:TQ028.3文獻標識碼:A文章編號:10059954(2014)10002005DOI: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(diǎn)712于化工、制藥、染料等領(lǐng)域。工業(yè)生產(chǎn)中產(chǎn)生的四氫應用 Aspen Plus模擬軟件,依據四氫呋喃呋喃和乙醇液體混合物具有最低共沸點(diǎn),采用普通乙醇體系汽液平衡數據研究了其變壓精餾分離精餾無(wú)法對其實(shí)現有效分離。具有最低共沸點(diǎn)的難過(guò)程特性,并對過(guò)程工藝參數進(jìn)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(gè)具有較高分離效率的四氫呋喃-乙醇雙塔變壓精餾等6特殊精餾方法。但與之相比,變壓精餾更餾分離路線(xiàn)。研究結果將有助于指導該類(lèi)共沸體系具有工藝簡(jiǎn)單、不引入雜質(zhì)以及節約能耗等獨特分離過(guò)程的工業(yè)設計。收稿日期:201401406作者簡(jiǎn)介:紀智玲(1962—),女,副教授,主要研究傳質(zhì)過(guò)程及新型分離技術(shù),電話(huà):18602419780,E-mal:yizhiling@163.com。紀智玲等四氫呋喃-乙醇變壓精餾分離1四氫呋喃-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(xiàn)2返回到常壓塔DOW生偏差的特點(diǎn),改變體系壓力可以移動(dòng)常壓下形成繼續精餾。的二元物系共沸點(diǎn)或改變其共沸組成,通過(guò)不同操作壓力的精餾過(guò)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HFEEDH LOW從圖1和表1可以看出,隨著(zhù)壓力的增加四氫呋喃-乙醇的共沸點(diǎn)沿參考線(xiàn)向左移動(dòng),四氫呋喃在共沸物中的摩爾分數減少。常壓以下,壓力的減小FED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Fig2 PSD Flowchart塔。在加壓條件下,隨著(zhù)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(shí),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,模擬計算依據見(jiàn)表2家0.8表2變壓精餾模擬計算依據Table 2 basic facts for PSd simulation0.6( kmol. h-1)醇摩爾分數進(jìn)料溫度分離要求乙參數名稱(chēng)進(jìn)料量/進(jìn)料組成乙醇摩爾分數b60,325kPac 100 kP數值1000.7常溫0.995以上0.2d506.625kPae 810.6kPf 1 000 k Pa2.2模擬過(guò)程分析與優(yōu)化液相四氫呋喃摩爾分數對分離過(guò)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(mǎn)足生產(chǎn)工藝條件下投Fig. 1 Pressure effect on system vapor-liquid equilibrium人較小能耗的操作條件表1壓力對共沸組成的影響2.2.1常壓塔總塔板數對乙醇產(chǎn)品純度(摩爾分Table 1 Effect of pressure on azeotrope composition數)與再沸器熱負荷Q的影響60.795kPa100kPa506.625kPa810.6kPa1000kPa常壓塔總塔板數對塔底乙醇產(chǎn)品純度(摩爾分乙醇摩數)及再沸器熱負荷Q影響見(jiàn)圖30.0250.09350.6360.902爾分數l.000共沸溫2280度51.0465.35141.97150.830999}嘆2270摩爾分數器熱負葡22609961.2變壓精餾常規工藝流程依據1.1節的分析可設計變壓精餾流程如圖20.9942230所示。在圖2中,循環(huán)高壓共沸組成混合物2引入0.993C.coco2220常壓塔LOW循環(huán)進(jìn)料,塔頂物流1為常壓條件下的1416182022242628303塔板數共沸物,塔底物流3可以得到高純度的乙醇產(chǎn)品;常圖3總塔板數的影響壓塔塔頂的共沸物即物流1進(jìn)入高壓塔HGH進(jìn)行Fig 3 Effects of total number of trays化學(xué)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)隨由圖5可知,隨循環(huán)物流進(jìn)料位置的下移,乙醇著(zhù)總塔板數的增加而增大,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,其隨塔板數增加的幅度趨緩,之后保持由圖6可知,原料的進(jìn)料位置過(guò)低或過(guò)高時(shí),乙定值。同樣隨著(zhù)塔總板數的增加,再沸器熱負荷φε醇產(chǎn)品純度均降低且再沸器熱負荷增加。降低。綜合考慮,常壓塔理論塔板數選擇為22塊,可避免塔板數增加導致的設備投資費用。1.0121802.2.2常壓塔回流比對乙醇產(chǎn)品純度與能耗Qa216的影響0.98乙醇摩爾分數兩沸器熱負荷在常壓塔理論塔板數為22的情況下,研究回流2140≥0.96比對產(chǎn)品純度及再沸器熱負荷的影響見(jiàn)圖4。21200.9421000.933000208009121516182022進(jìn)料位置2400圖6主進(jìn)料位置的影響0.98Fig 6 Effects of feed location0.97一乙醇摩爾分再沸器熱負0.96故常壓塔循環(huán)進(jìn)料最佳進(jìn)料位置在第3塊塔板,主進(jìn)料最佳進(jìn)料位置在第9塊塔板0.20.40.60.81.01回流比R22.2.4常壓塔循環(huán)進(jìn)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 ratioq/q表示常壓塔塔頂產(chǎn)品摩爾流量與主進(jìn)料摩爾流量之比,它也可反映循環(huán)進(jìn)料量對常壓塔操圖4可知隨著(zhù)回流比Rn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,研究循環(huán)進(jìn)料量對產(chǎn)品純度及再沸器熱負荷的影響。純度(摩爾分數)及再沸器熱負荷Q均顯著(zhù)增加,但乙醇產(chǎn)品純度達到一定值后趨于穩定,而再沸器熱負荷卻是線(xiàn)性增大。在滿(mǎn)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。2.2.3進(jìn)料位置的影響白0.971800選擇常壓塔理論塔板數為22,回流比為0.6,常乙醇摩爾分數再沸器熱負荷壓塔循環(huán)進(jìn)料1和主進(jìn)料FEED位置對產(chǎn)品純度及再沸器熱負荷Q的影響如圖5和圖6所示。0.91.1.31.51.71.92.1224圖7常壓塔循環(huán)進(jìn)料量的影響Fig 7 Effects of reflux feeding flow rate如圖7所示,隨常壓塔循環(huán)進(jìn)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(zhù)增加,但相乙醇摩爾分數應再沸器熱負荷也明顯增大。從圖7中可以得出,再沸器熱負付0.84合適的循環(huán)進(jìn)料量可取q/qp=1.5。0246810121516182022進(jìn)料位貿2.2.5高壓塔工藝條件優(yōu)化圖5循環(huán)進(jìn)料位置的影響繼續運用同樣方法對高壓塔進(jìn)行優(yōu)化分析,優(yōu)Fig 5 Effects of reflux feeding location化工藝條件總結果如表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Table 3 Optimization of operating parameters備名稱(chēng)參數名稱(chēng)參數值總塔板數四氫呋喃汽相一四氫呋喃液桕循環(huán)物流進(jìn)料位置3乙醇液相勤0.4乙醇汽相常壓塔LOW主進(jìn)料位置回流比操作壓力/kPa1012141618202224總塔板數24塔板數進(jìn)料位置高壓塔HGH圖8常壓塔汽液摩爾分數分布回流比Fig. 8 Mole fraction distribution of atmospheric column操作壓力/kPa810.63模擬結果與討論3.1變壓精餾流程模擬結果一四氫吠啪汽相采用表3所示優(yōu)化工藝參數,對圖2所示流程四氫呋喃液相0.5-乙醇汽相進(jìn)行模擬優(yōu)化,模擬結果如表4所示。乙醇液相0.3表4變壓精餾流程模擬結果Table 4 pSD simulation results0246810121416182022226流股FEED塔板數溫度℃2566.566.9478.98149.08圖9高壓塔汽液摩爾分數分布Fig9 Mole fraction distribution of high pressure colun壓力/kPa102.925811.8101.725104.2824.4爾流量/100150120(kmol h")4結論(1)由汽液相平衡數據分析可知,壓力改變可摩爾分數301300670009較大程度上移動(dòng)四氫呋喃,乙醇共沸點(diǎn),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。乙醇摩爾分數0.70.2670.3330.99880.003(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(jìn)行研究,得到優(yōu)化工藝操作參數。在此條件下,通過(guò)計算模擬由表4結果可知,變壓精留分離后,常壓塔底可該雙塔工藝流程,可得到純度為997%的四氫呋喃得到摩爾分數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。3.2塔內汽液摩爾分數分布(3)本研究提出的四氫呋喃-乙醇變壓精餾流常壓塔LOW和高壓塔HCH塔內汽液相摩爾程對共沸物系分離工藝優(yōu)化分析和對相應現有工藝裝置改造具有重要的指導意義。分數分布分別如圖8和圖9所示。由圖8和圖9可見(jiàn),常壓塔LOW和加壓塔參考文獻HGH塔頂區域汽液二相均接近共沸組成;而分別[1 BRUNNER E, SCHOLZ A G R. sobaric vapor-liqui在塔釜區域,汽液二相摩爾分數均趨近于1,反映該quilibria of the tetrahydrofuran-ethanol system at 25, 50變壓精餾流程可在常壓塔底得到高純乙醇和在高壓and 100 kPa[ J]. 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