VAPOR LIQUID EQUILIBRIUM DATA GENERATION FOR ACETIC ACID AND p-xylene AT ATMOSPHERIC PRESSURE

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1 Int. J. Chem. Sc.: 14(3), 2016, ISSN X VAPOR LIQUID EQUILIBRIUM DATA GENERATION FOR ACETIC ACID AND p-xylene AT ATMOSPHERIC PRESSURE PAWAN KIRAN MALI *,a and PRAKASH V. CHAVAN b a Department of Chemcal Technology, Bharat Vdyapeeth Deemed Unversty, College of Engneerng, PUNE (M.S.) INDIA b Department of Chemcal Engneerng, Bharat Vdyapeeth Deemed Unversty, College of Engneerng, PUNE (M.S.) INDIA ABSTRACT In the present study, vapor lqud equlbrum data (VLE) has been generated for bnary system: acetc acd and p-xylene, at atmospherc pressure (96.15 Kpa). The recrculaton type of apparatus was used for generatng the VLE data for a gven temperature and compostons 1. The actvty coeffcents were estmated usng Wlson and NRTL models at dfferent composton. It has been seen that expermental data fts well to the predcted data. Further, thermodynamc consstency of expermental data has been confrmed usng Redlch- Kster and pont to pont test methods. It has been found that expermental data s thermodynamcally consstent. Key words: VLE, WILSON, NRTL, Acetc acd, p-xylene, Bnary nteracton parameters, Thermodynamc consstency. INTRODUCTION Acetc acd and p-xylene are used for manufacturng of the terepethalc acd 1, whch s prmarly used as the raw materal for manufacturng of polyester, a polymer used to make the varety of household tems such as plastc bottles and other plastc tems used n day to day lfe. The lqud stream generated n the manufacturng of terepethalc acd usually contans acetc acd and p- xylene par. It s mperatve to separate acetc acd from p-xylene for reuse. Dstllaton s commonly exercsed for separaton. However, the ratonal desgn of the dstllaton column needs VLE data, whch determnes the extent of purty of compound to be dstlled. Therefore, n the present study, expermental VLE data pertanng to acetc acd and p-xylene par has been generated at atmospherc pressure. The devaton of the * Author for correspondence; E-mal: ms.pavanmal@gmal.com

2 1512 P. K. Mal and P. V. Chavan: Vapor Lqud Equlbrum Data. soluton from an dealty has been determned by estmatng actvty coeffcent usng Wlson and NRTL models. An attempt has also been made to confrm thermodynamc consstency of expermental VLE data. EXPERIMENTAL Acetc acd (99.8, W/V %) and para Xylene (99, W/V %) were purchased from Spectrochem and Loba Cheme, respectvely. The Chemcals purchased was of hghest purty avalable n the market and they were used wthout further processng. Analytcal method The mxtures were analyzed by the refractve ndex method, usng ATAGO RX dgtal refractometer. The calbraton curve was used for back calculaton of the mole fractons of the components usng the refractve ndex readngs, the refractve ndex measurements were carred out at constant temperature 20 o C. Fg. 1 shows the calbraton curve. Refractve ndx, nd Apparatus and expermental procedure X, Y Mole fracton 1 1 Fg. 1: Calbraton curve In ths study, the VLE experments were performed usng a glass dynamc recalculatng stll apparatus 3. The schematc representaton s shown n Fg. 2. The acetc acd and p-xylene par of known concentraton was ntroduced nto the bolng chamber and the mxture was heated to reach equlbrum. The bnary mxture n the bolng chamber starts to bol. After certan tme the lqud recrculaton starts. The lqud

3 Int. J. Chem. Sc.: 14(3), mxture passes from the pores provded at the base of the nnermost glass arrangement, as shown n the fgure at pont B. After gettng heated up to certan range lqud goes for the recrculaton. The lqud sample removal arrangement s provded at S1. Generaton of the vapors starts as heatng proceeds and the vapors are collected below the total condenser at pont S2 as shown n the Fg. 2. Arrangement of the total condenser helps to collect the condensed vapors wthout escapng vapors to surroundng and further rse n temperature starts the recrculaton of the vapors. After certan tme span, at certan bolng pont the temperature remans constant. Ths can be consdered as equlbrum temperature. The equlbrum temperature s recorded at pont rght above the Cottrell pump. The temperature was measured wth the help of Resstance Temperature Detector (RTD) thermometer. A B C D E F S1 S2 L G H I J K Fg. 2: Expermental setup (A) Glass bed (B) Pores for lqud passage (C) Temperature (RTD) (D) Vacuum jacket (E) Magnetc strrer (F) Spral col (G) Cottrell pump (H) Jacket arrangement for cottrell pump (I) Temperature measurement provson (K) Dran out (L) Total condenser arrangement, S1- Lqud sample removal, S2- Vapor sample removal The lqud phase sample s collected at pont S1 and the vapor phase sample s collected at pont S2. At the lqud sample collecton sde the col arrangement s done for proper mxng of the lqud. At the vapor sample collecton sde an arrangement of magnetc strrer s provded for proper mxng of the composton and good results.

4 1514 P. K. Mal and P. V. Chavan: Vapor Lqud Equlbrum Data. RESULTS AND DISCUSSION The bolng pont and refractve ndex n Table 1 shows the comparson between the expermental values and lterature values. The values of Antone constants are mentoned n Table 2. The data regresson was done to calculate bnary nteracton parameters and also for calculated actvty coeffcents. Table 1: Propertes of components S. No. Name of chemcal Bolng pont ( o C) at atmospherc pressure Densty (Lterature) g/cm 3 Refractve ndex at 20 o C Mole. weght (g/mol) Lterature Expt. Lterature Expt. 1 Acetc acd p-xylene by 4,5 The equlbrum relatonshp can be expressed by followng relatonshp s gven l sat s s V (P P ) y ϕ P = x ϕ ϕ exp (1) RT sat Where P s total pressure and T s temperature n equlbrum system, P s the saturaton vapor pressure of pure component I, whch can be obtaned from the Antone equaton; y s the mole fracton of component n the vapor phase; x s the mole fracton of component n the lqud phase, R s the unversal gas constant, V l s the lqud mole volume of pure lqud, calculated from the modfed Rackett equaton, and γ s the actvty coeffcent of component. At low pressure, the exponental term n equaton (1) s approxmately equal to one, thus equaton (1) can be smplfed to y ϕ P = x ϕ v ϕ s (2) The actvty coeffcent of component, γ, can be determned based on these equatons. γ was also calculated by the soluton models for the excess Gbbs energy, such as the Wlson, NRTL, and UNIQUAC models, and the relatonshp s ln γ = E ( δ ( ng ) δn RT (3)

5 Int. J. Chem. Sc.: 14(3), Table 2: Antone constants values for the two components consdered whle calculatons 4 S. No. Component A B C 1 Acetc acd p-xylene The equaton used for the calculaton s 5 ln P sat = A B (T C )...(4) Where, P sat s n (kpa), T s n ( o C) Table 3: Expermental Txy data and actvty coeffcents S. No. T(K) x 1 y 1 γ 1 (exp) γ 2 (exp) γ 1 (cal) γ 2 (cal) By the help of data regresson, we have found out the bnary nteracton parameters. Table 4 gves the detal about the bnary nteracton parameters.

6 1516 P. K. Mal and P. V. Chavan: Vapor Lqud Equlbrum Data. Table 4: Bnary nteracton parameters for Wlson and NRTL Models 2,6 S. No. Bnary parameters WILSON NRTL 1 u 12 -u u 12 -u α Δy Δy ΔP Fg. 3: Txy Dagram for acetc acd and p-xylene Wlson and NRTL model fttng Fg. 4: xy Dagram WILSON and NRTL model fttng

7 Int. J. Chem. Sc.: 14(3), Consstency of data Area test Expermental errors may cause devaton of the actvty coeffcents drawn from the expermental VLE data from the Gbbs Duhem equaton. Therefore, the Herngton method was used to check the thermodynamc consstency 7. The data found was consstent by both area test and pont to pont test. The detals of the consstency test are gven below. After rgorous procedure of model fttng, we have passed the data through the consstency test such as Herngton s area test, whch comes postve when the area above the curve equals the area below the curve. Followed by ths test, we have used the pont to pont consstency test n whch we have passed the crtera. Accordng to ths method the expermental data s thermodynamcally consstent f, from ln (γ 1 / γ 2 ) v/s x 1 plots the value of D J s less than 10 and the values of D and J can be calculated usng the equaton (5) and (6). Where, S 1 s area under curve above the x axs and S 2 s area below the x axs under the curve. ( S1 S2 ) ( S + S ) D = 100 (5) 1 2 Max Mn (T T ) J = 150 (6) Mn T Ln ( γ1/ γ 2) x n mole fracton Pont to pont test Fg. 5: Consstency by area test The vanness pont to pont test 4 calculates the average devaton between expermental

8 1518 P. K. Mal and P. V. Chavan: Vapor Lqud Equlbrum Data. and calculated gas phase solute concentraton (y ) of component and system pressure (P). The crtera for pont to pont test method are lsted table below n ths sutable actvty coeffcent model s used to calculate y and the total pressure P. Frst the actvty coeffcent model parameters are evaluated through regresson wth expermental VLE data. Sutable objectve functon s used to perform the regresson average devaton calculated between expermental and model based calculated value 7,8. A crteron for the data to be consstent s gven n Table 5 below. Table 5: Crtera of consstency test for pont to pont method S. No. Parameter Formula Crtera 1 Overall devaton n gas phase solute concentraton 2 Overall devaton n total n cal exp = [ Y Y ] 1 ΔY = j 1 ΔY 0.01 N 1 n cal exp = [ ] system pressure = P j 1 P ΔP ΔP 1.33 N In Table 5, J s the data number, N s the total number of the data ponts, y j cal and y j exp are the calculated and expermental vapor phase composton of speces and p cal and p exp are the calculated and expermental pressure of the system. CONCLUSION Vapor lqud equlbrum data for bnary mxture, acetc acd and p-xylene, s generated n ths work. The actvty coeffcent calculaton shows that the data s deal up to K temperature. The bnary mxture conforms to non-dealty beyond temperature K. It can be sad that data s consstent as data passes area test and pont to pont test of consstency. REFERENCES 1. M. A. Joshep, D. Ramjugernath and J. D. Raal, Phase Equlbrum Propertes of Bnary System wth Dacetyl from Computer Controlled Vapor Lqud Equlbrum Stll, Flud Phase Equlbra, 5, (1980). 2. N. A. M. Fadzl, M. H. Ab. Rahm and G. P. Manam, A Bref Revew of para Xylene Oxdaton to Terepethalc Acd as Model of Prmary C-H Bond Actvaton, Chnese J. Catal., 35, (2014).

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