VAPOR LIQUID EQUILIBRIUM AND RESIDUE CURVE MAP FOR ACETIC ACID-WATER-ETHYL ACETATE TERNARY SYSTEM

Transcription

1 VAPOR LIQUID EQUILIBRIUM AND RESIDUE CURVE MAP FOR ACETIC ACID-WATER-ETHYL ACETATE TERNARY SYSTEM Desai Sunita. S.,Sinhgad College of Engineering, Gadekar Shamla V.,BVDUCOE, Pune, P.L.V.N. Saichandra, Sinhgad College of Engineering, ABSTRACT Azeotropic behavior is relatively a common phenomenon, one of the most efficient methods of treating an azeotrope is the introduction of an entrainer (mass separation) through the process of heterogeneous azeotropic and/or extractive distillation. For the design of such a process the need of vapor liquid equilibrium (VLE) data remains of the fundamental importance. The number of ternary and quaternary VLE data available in the literature is very scarce in comparison with homogeneous binary VLE data. So the attempt is made to find experimental VLE data for the ternary system acetic acid-water-ethyl acetate at 301 K and 1 atm, by using modified form of Othmer's still apparatus and analyzed by refractive index method. The system becomes heteroazeotropic due to addition of ethyl acetate which acts as an entrainer. The obtained experimental VLE data was used to plot the residue curve map (RCM) which is a triangular diagram often used to describe the equilibrium relationships for ternary mixtures. Ternary diagrams makes an effective tool for the heuristic synthesis and shortcut design to separation processes. The RCM analysis is also used to estimate distillation parameters such as feed location, distillations regions etc. KEYWORDS: Experimental data; VLE; Ternary; Residue Curve Map

2 National Conference, CHEMCON 2010, Dee 2010 INTRODUCTION Azeotropic behavior is relatively a common phenomenon, one of the most efficient methods of treating an azeotrope is the introduction of an entrainer (mass separation) through the process of heterogeneous azeotropic and/or extractive distillation. For the design of such a process the need of vapor liquid equilibrium (VLE) data remains of the fundamental importance. The number of ternary and quaternary VLE data available in the literature is very scarce in comparison with homogeneous binary VLE data. So the attempt is made to find experimental VLE data for the ternary system acetic acid-water-ethyl acetate by using modified form of Othmer's still apparatus and analyzed by refractive index method. The system becomes heteroazeotropic due to addition of ethyl acetate which acts as an entrainer This type of ternary system have been investigated extensively because of their wide application in industrial processes such as purified terphthalic acid and acetic acid recovery. The phase behavior of the mixtures of this type plays an important role in the research of critical phenomenon and wetting transitions. The obtained VLE data for the acetic acid- water - ethyl acetate was used to plot the residue curve map (RCM), which is a triangular diagram often used to describe 'he equilibrium relationships for ternary mixture[i,2]. XPERIMENTAL Chemical An Iytical grade chemicals and a laboratory source of distilled water were used. The solvents and the acid were tested for purity by density as well as refractive index determination. The properties of chemicals at 30 C are given below [3]. Substai ce nd p (gm/crrr') B.P.oC Acetic a ~id I Water E~yl acetate l "

3 Experimental apparatus, procedure and analysis Equilibrium apparatus used for measuring vapor-liquid equilibrium data was developed by Othmer. The still is classed as a circulating still. Circulation method was used to find VLE data for acetic acid -water-ethyl acetate. The main features of the still are boiling chamber/ section, condensation section, reflux section, heating media. Heating coils are provided inside the boiling section. The schematic diagram of the apparatus assembly is shown in figurel. The feed mixture consisting of three components i.e. acetic acid, water and ethyl acetate were fed to the boiling section, heated continuously until thermal equilibrium was attained. The vapors will start to rise and are condensed in the receiver and again recirculated. After thermal equilibrium i.e. when the temperature of vapor and liquid were same, sample of vapor and liquid were withdrawn from the respective ports and analyzed by using refractometer [4]. Calibration chart The most important and first part of the experiment is preparation of the calibration chart. The LLE data for the system Acetic acid - Water - Ethyl acetate in reported DECHEMA series is as shown in table 1 & 2. [5,6]. Binodal curve and feed points are shown in figure 2. RE UL T AND DISCUSSION From obtained experimental results as in table 3 and VLE plot as shown in figure 3 fo lowing points are discussed. Nodes and Saddle points We find that there are two nodes present in the system. The highest boiling acetic acid (l18 0c) becomes a stable node and the minimum boiling azeotrope between water and ethyl acetate ( c) becomes unstable node. Ethyl acetate and water acts as saddle points. The continuous dark line shown in figure 4 is called as distillation line or distillation boundary line. Due to presence of distillation line ternary p.ot is divided in two separate regions i.e. region I and region II as shown

4 in figure 4. Each distillation region must contain one stable node, one unstable node and at least one saddle [8-10]. Region I The points in region I are in direction towards stable node acetic acid via ethyl acetate as a saddle point. There are three vertices in this region I- 1. Highest boiling point stable node, acetic acid. 2. Saddle point, ethyl acetate. 3. The point S unstable node, minimum boiling azeotrope on water ethyl acetate edge. The residue curve emerges from the unstable node and goes via saddle point towards the stable node. From figure 4 points 4,5,6,7,9,10 lie in this region, the residue curves for these points tends towards stable node acetic acid. Region II The points in this region II are also directing towards stable node acetic acid. There are three vertices in this region II - 1. Highest boiling point stable node, acetic acid 2. Saddle point, ethyl acetate. 3. The point S unstable node, minimum boiling azeotrope on water ethyl acetate edge. It has lowest boiling point. From figure 4 the residue curves for points 8,12,11,3,2 in region IIemerges from the unstable node and goes towards stable node acetic acid via saddle point water. From figure 4 i) B.P. of point 4 is C and B.P. of point 6 is 71 C ii) B.P. of point 10 is 84 C and B.P. of point 9 is 73 C iii) B.P. of point 14 is 97 C and B.P. of point 10 is 96 C which shows that temperature increases along the residue curve. Thus one important property of residue curve "The temperature must always increase along the residue curve", is verified from above points.

5 CONCLUSION The separation of non ideal mixtures are complex, the product purity can not be achieved due to presence of azeotropes in the system, residue curve map is found to be effective tool for such system. Vapor liquid equilibrium data is obtained for the ternary system acetic acid-water-ethyl acetate by experimentation and with this data residue curve map is plotted. The residue curve map gives correct visualization of physical and thermodynamic limits of the system which is used for proper design of distillation column. Distillation region I and II found to be the correct to operate the column Note" Teflon stopcccs.. Bmm All d,men$k)rls in mm "'.. Counler ) Figure 1: Vapor liquid equilibrium apparatus

6 Acetic Acid (118 C) (Stable node) o " 100 FIG.2 BINODAL CURVE & feed POINTS Figure 2: Binodal curve and feed points (Experimental tie lines in mole% at temperature = q Acetic Acid(IIBOC) (Stable node) Wiler -\."II CI> b_. v c_,..."oo. Figure 3: VLE for acetic acid-water-ethyl acetate ternary system at 301 K and 1 atm.

7 National Conference, CHEMCON 2010,27-29 Dec 2010 Acetic Acid (1 J 8"C) (Stable node) o. 100 Figure 4: Residue curve map for acetic acid-water-ethyl acetate ternary system. Table 1: Reported LLE data in mole% for acetic acid-water-ethyl acetate Left phase Right phase Sr.No. [ 1 ] [ 2 ] [ 1 ] [ 2 ] I [ 1] Water [ 2 ] Acetic ACId Table 2: Calibration chart for acetic acid - water - ethyl acetate Sr.No. Mole% Mole% Refractive [water] [acetic Index

8 acid] I Table 3: Experimental vapor liquid equilibrium data for acetic acid-water-ethyl acetate ternary system Liquid Liquid Vapor Temperature Composition Composition Point c Mole% Mole% No [water] [ acetic [water] [ acetic acid] acid]

9 ABBREVIATION & SYMBOLS VLE vapor liquid equilibrium LLE liquid liquid equilibrium RCM residue curve map B.P. boiling point nd refractive index p density REFERENCES [1] Andrea Colombo, Paolo Battilana, Vittorio Ragaini and Claudia L. Bianchi,"Liquid Equilibria of the Ternary systems Water + Acetic Acid + Ethyl acetate and Water + Acetic Acid + Isophorone", J. Chern. Eng. Data, 44, pp (1999). [2] Chemistry data Series, DECHEMA, Vol. V, part 2, pp ,(1980). [3] F.H. Garner, S. R. M. Ellis, " Extraction of acetic acid from water by ethyl acetate," Chemical Engineering Science,,Vol. 282, pp (1953). [4] Gert - Jan A. F. Fien and Y. A. Liu, "Heuristic Synthesis and shortcut Design of Separation Processes Using Residue Curve Map: A Review", Ind. Eng. Chern. Res., 33, pp (1994).

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