1、Separation of acetonitrile-ethyl acetate by extractive distillation with mixed solvent Li Chunli1, Zong Lili2and Fang Jing School of Chemical Engineering, Hebei University of Technology, Tianjin, 30013 E-mail:lichunli_, Tel: +86-022-60202246 Abstract Computer-aided molecular design (CAMD) approach w
2、as bring in this work for selectingextractivesolvents. The separation of acetonitrile-ethyl acetate Azeotropic system was carried out through a batchextractive distillation processes withN,N-dimethylformamide(DMF),glycol(EG) and DMF-EG mixture assolvents separately. The effects of different operatin
3、g conditions were studied, solvents, ratio of mixed solvent,solvent flow rate and reflux ratio were all included. It was found that the mixed solvent DMF-EG showed betterseparation effect than the single solvent. The best proportion of the mixed solvent was 3:7 ( the quality of DMF and EG )； when th
4、e solvent flow rate and reflux ratio increased, the separation effect of mixed solventimproved； under the conditions that solvent flow rate was 20 mL/min, reflux ratio was 2, quality fraction ofethyl acetate in the top product could reach 99.62%. Keywords Separation； Batch extractive distillation； M
5、ixed solvents； Acetonitrile； Ethyl acetate 1.Introduction Acetonitrile and ethyl acetate are widely used in chemical and pharmaceutical industries as chemical rawmaterials and good organic solvent1. But the two form azeotrope, ethyl acetate hold 77% and the other 23% isacetonitrile(mass fraction), c
6、ommon distillation method can not make any effect. Therefore, some companieshave to treat them as waste, this not only cause seriously waste of resources and economy, but also pollute theenvironment. At present, Di Jiandong2of Tianjin university has realized the separation of acetonitrile-ethylaceta
7、te by heterogeneous batch azeotropic distillation, but the product received in this way have lower purity,but high energy consumption. According to the difference of solubility that acetonitrile and ethyl acetate in thewater, Ma Wenchan3adopts the method of liquid-liquid extractive which use water a
8、s extractive agent toseparate acetonitrile-ethyl acetate ,the product of ethyl acetate can achieve 98.5%,but acetonitrile mixed withabundant water,so recovery of acetonitrile is very difficult.According to our knowledge, no authors have studiedthe separation of acetonitrile - ethyl acetate by extrac
9、tive distillation. In recent years, the application ofextractive distillation4-6for the separation of close-boiling mixture has been widely accepted and commercialized over the conventional distillation which may also be feasible but with substantial columninvestment. However, due to the problem of
10、selectivity and solubility are often inconsistent in single solvent,limit its application and development. Mixed solvents guarantee high selectivity,and improved solubility at thesame time through the combination of main solvent and vice solvent7. In recent years, mixed solvents areapplied more and
11、more in extractive distillation8-11 . This paper is devoted to the study of the separation of the mixture acetonitrile ethyl acetate by usingextractive batch distillation which extractive solvent is mixed solvents. First, the selection of an adequateextractive solvent is presented based on the compu
12、ter aided molecular design of solvents for separationprocesses combining group contribution methods with graph principle. Later, results of several laboratory batchtests are presented serving for determination of the most effective solvent. Finally, the main operatingparameters of extractive distill
13、ation process were optimized. 2. Entrainer selection for the separation of acetonitrile ethyl acetate mixture The extractive distillation is generally applied to the separation of close-boiling mixtures, which byconventional distillation is difficult to separate. The design and optimization of extra
14、ctive distillation is morecomplex than that of the conventional distillation when considering the selection of suitable solvent to enhancethe separation. In the extractive distillation, the selection of a suitable solvent is fundamental to ensure aneffective and economical design. Currently, the sol
15、vent selection can be effectively handled by the assistance ofthecomputer-aided molecular design (CAMD) approach.The candidates as extractive solvent were chosen by the graph principle and group contribution methodcombined with computer-aided molecular design. Firstly, based on Modfied UNIFAC method
16、, the functionalgroups systematically are classified and pre-selected according to some rules, and then the automaticcombination of groups is completed by using a graph algorithm. The group contribution methods are used to get the basic physical and thermal properties. The basic molecular library is
17、 formed by using several limited rules ofbasic physical properties. In the stage of solvent screening, the molecules in the basic molecular library are useddirectly. The candidate solvent molecules are obtained by using the solvent constraint and the appropriatesolvent molecules can be determined by
18、 using the refined calculation or checking property library. According to the above method, we got some candidate solvents through the graph principle and groupcontribution method combined with computer-aided molecular design. After cautiously selected we obtainedDMF and EG as solvents which are the
19、 most appropriate for the separation of acetonitrile ethyl acetate. 3.Experiment supplies of the extractive distillation 3.1Materials The component mass fraction of acetonitrile ethyl acetate raw material is 0.77/0.23 (ethyl acetate/acetonitrile). The purity of DMF is 0.995 (mass fraction).The purit
20、y of EG is 0.995 (mass fraction). 3.2Equipment Batch experiments were carried out in a small laboratory column to evaluate the feasibility of the newsolvent. The glass column has a total height of 1.8 m and an internal diameter of 30mm. It is packed withstainless steel -rings of 3 mm 3 mm. The total
21、 packed height is about 1.5m. The bottom is a 1500 ml flaskwith opening. The solvent is feed to the column from the top section. The flow rate is controlled by a rotameter.The reflux ratio is provided at the top of the column by a solenoid valve. The sketch map is showed in Fig. 1. 4.Results and dis
22、cussion In order to illustrate the effect of the new solvent to acetonitrile ethyl acetate ,we do some experience toinvestigate the technological parameters,and receive optimized operation conditions. 4.1Effects of different solvent The effects of different solvent on the concentration of ethyl acet
23、ate in the top product were showed inFig.2.To do this,some conditions were maintained:solvent flow rate was 15mL/min, solvent ratio(mass ratio ofsolvent to the product)was 4.0， reflux ratio was 1,n(DMF)： n(EG)=1:1 in the mixed solvent(DMF:N,N-dimethyformamide； EG: ethylene glycol).Fig.2 shows that t
24、he three solvents all has the function of increase theconcentration of ethyl acetate in the top product,Destroy the azeotropic composition. When the solvent is DMFor EG only,the concentration of ethyl acetate in the top product will be 90.4% and 93.9%,respectively.But whenuse n(DMF)： n(EG)=1:1 as so
25、lvent,the concentration will increase to 97.7678%,the effect obviously superior tothe single solvent.This due to combination of the strong solubility of DMF and the efficient selectivity ofEG.They complement and promote each other,so the mixed solvent reveals better effect on the concentration ofeth
26、yl acetate than single solvent.The relative volatility of acetonitrile ethyl acetate was changed in a largeextent ,so that the separation efficiency improved and the purity of product increased. 4.2Effects of mixed solvents with different ratio The effects of mixed solvent with different ratio on th
27、e concentration of ethyl acetate in the top product areshowed in Fig.3. Similarly,to do this, some conditions were maintained:solvent flow rate was 15mL/min, solvent ratio(massratio of solvent to the product)was 4.0， reflux ratio was 1.We can see from Fig.3 that while the the content ofDMF in mixed
28、solvent increase, the concentration of ethyl acetate in the top product increase first and thendecrease,and when the content of DMF was 30%,the ethyl acetate own the highest concentration that is98.3104%.When the content of DMF in mixed solvent lower than 30%,the main solvent EG ensure theselectivit
29、y of the mixed solvent, but added of DMF improved the solubility of the mixed solvent,so show bettereffect.When the content of DMF in mixed solvent higher than 30%, the selectivity of EG decreased gradually,so the effect of the mixed solvent was weakened.According to these data, we think the mixed s
30、olvent that DMF/EG= 3/7 was the best. 4.3Effects of solvent flow rate The effects of solvent flow rate on the concentration of ethyl acetate in the top product are showed in Fig.4. In the above conditions that be optimized, we investigated the effect on the reflux ratio on the concentration of ethyl
31、 acetate in the top product. From the line chart we find that the concentration of ethyl acetate in the topproduct increase with the increase of reflux ratio,while the reflux ratio exceed 2,the purity of the product willalmost constant.On the other hand, exceed reflux ratio will bring some problems,such as extend operation time,energy needed in the tower bottom increase, influence production efficiency and so on.So we should decreasethe reflux ratio
