VAPOR-LIQUID EQ.UI.LlBRIA OF TilE BINARY SYSTEMS! BEIZENE-ETHYLENE DIOHLORIDE ETHYL AC:Jb'TATE·BEHZENE ETHYL AOE'JATE-ETHYLE.NE DICHLORIDE by JAMES CARL JOHNS.ON A THESIS aubmitted to OREGON S~ATE COLLEGE in partial tul!illment of the ~equirement. a . tor the de.gree of MASTER OF SCIENCE June 1956 Redacted for Privacy fi**tst #S*rT rf, [Exlrrl F$frlrlnr re qhntr of rrJir Redacted for Privacy 'of Srnrnfrmt S ffi*l lfti{.t.rtF; Redacted for Privacy (trfrrll of llrrfrmf,,,lbldlfftt, hltt*; Redacted for Privacy DlrE af, S$rftnt* frubof H ttr*tr l* trfra'by f,Er*noll ftmfgil Ef Imrr Iohrcl* TABLE OF CONTENTS Historical Int~oduction. • • • • • • • • • • • • • • It l Introduction • • • • • • • • • • • • • • • • • • • • • 3 Theoretical Considerations • • • • • • • • • • • • • • 5 Experimental Eq~1pment • • • • • • • • • ~ • • • • • .14 Equilibrium Stills. • • • • • • • • • • • • • • .14 Pressure Control. • ...... • • • • .. .. • • .18 Temperature Measurement • • • • • • • • ..20 eaaurement of Refractive Irldex • • • • •• •• ••21 reasurement of Dens1 tv~~ • • 1 • • • .. •· • • • • • .21 I Sample Tubes. • • • • • • • ! • • • • .. • • • • .. .22 Chemicals and Pur1£1oation • • • • • • • • • • • • • .23 Experimental Procedure • • • • • . .. • • • • • • • .27 Operation of Stille • • • • • • • • • • • • • • .27 Calibration of Thermocouples......... ....31 Determination of Calibration Curves • • • •. • • • .32 Accuracy of Analysis • ., ...............33 Tbermod~namic Analysis ot Data • • • • • • • • • • • .35 Evaluation of Experimental Data. • • • • • • • • • • .38 Ethyl Acetate-Ethylene Dichloride • • • • • .. • .38 Ethyl Acetate-Benzene .• • • • • • • • • .. • • • .46 Benzene.-Ethylene Dichloride ••• • •••••• •53 Discussion of Expe~imental Results • • • • • • • • • .63 Summary •• . .. ,. • • • . .. • • .72 --------------~--------------- TABLE OF CONTENTS ( Cont• d.) Nomenclature • • • • • • • • • • .. • • • • • .. • • • ·74 Bibliography • • • • • • • ., • • • .. • • • • • • • • ·15 Appendix • • • • • • • • • • • • • • • • • • • • • • ·11 VAPOR·LI~UID EQUILIBRIA OF THE BINARY SYSTEMS; BENZENE-ETHYLENE DICHLORIDE ETHYL ACETATE·BENZENE ETHYL ACETATE-ETHYLENE DIOHLORIDE HISTORICAL INTRODUCTION Through the years much time and effort have been ex• pended 1n an effort to better understand the conditions of equilibrium between a liquid and its vapor. An early literature classic was •on the Distillation of Binary 1xturea" by Lord Rayleigh (11• pp.531-537). In this paper he described a atlll tor determining the equilibri• um ~elat1onsh1p and presented data tor several eyatema. ince thia time the experimental methods have been greatly improved with the result that his data have been super­ seded by more recent worka. Lord Rayleigh's still haa been replaced by more modern deaigna which have been developed to correct tor the errors inherent in that type ot apparatus. Paralleling the improvement in experimental methods haa been an effort to better correlate and uee the data Obtained trom equilibrium stills. The use ot fUgacity and activity coetf1c1ents to correct tar the non-ideal behavior ot the vapor and liquid haa permitted an ex­ tension of the data tar beJond the ideal relationshipa caloulated by a combination ot the lawa of Raoult and Dalton. By ua1ng these correction factors, data taken a under the most ideal conditiona in the laboratory may be uaed under the far different condition• of 1~duatry. Likewise, data from binarr systems may now be used to pre­ dict the equilibrium relat1onah1pa for multicomponent collection ot these coefficients p~ovidea the key to a more efficient and widespread uae ot equilibrium data 1n the tuture. '• 3 INTRODUCTIO The dat ot many investigators .for the equ1l1bl'1um ~ela.tionahip betweetn liquid ~d ita... vapot- may bo tound in the lit ratur • The collection of thia literature apans more than hal! a centuey ot work . Tlll-ough this period the quality ot the dat presented has been greatly improved . Many changes have been made in the type of equilibrium stills; new methods ot preparation have pro­ vided chemicals of greater purity; and the development of better analytical equipment have resulted in an increase in the accuracy of the data. A study or the d ta publish• ed on identical systems by different investigators often indicates large differences in the repo~ted values. The possible causes tor these differences are widespread. By using activity coefficients and the Duhem eque.tion, Red­ lich and Kister (12. pp . 341·34~) 13, PP•34~ - 348) have ~rovided a method of analysis which indicates the thermo­ dynamic consistency or inooneiatency ot the data and m y also point to the cause ot any inconsistencies present. A study has been made of two of the types ot equi• librium atilla used by previous investigators in an etfox-t to understand the inherent diacrepencies in the particular apparatus . These at1lla are basically ditt rent in their method of operation. The first, as designed by Otbmer (101 pp . 764•76$), provides for the recirculation of a 4 v•por formed from a boiling liquid; while the second, described by Jones, Schoenborn and Colburn (6, pp .666-669i reelrculates the vapor through the liquid until .a steady condition ia reached. Three binary systems have been studied in these stills. Th&ae systems are: benzene..etb.ylene dichloride, eteyl acetate-benzene an4 ethyl acetate-ethylene di.. chloride. The data obtained were eOrl'elated and examined by the methods or Redlich and Kister to provide a com• parison of the results to be expected from the operation Of theae two Stille. THEORETICAL CONSIDERATIONS •I Fo, the cases of ideal solutions and vapo:rs it is possible to calculate vapo:r•llqutd equilibl'i\.Ull data through the combination of the laws ot Raoult and Dalton­ Hence, (1) Howeve,, .the oases in wbieh th1s relationship ifJ obeyed are rare. For thi.s reason 1t 1s quite often nf3ceasaey to correct ro:r the dev1at1ona from ideal behavior. The deviations ot the \fapor from a per·t ·aot gaa may be corttectEJd by using the .f'tlgaoity of the plU'e vapor at the total pveasu.re in place ot the pressure on the vapol". Thus. Equation 1 would be written: (2) At atmospheric pressure the terms !'or the fugacity 1n Equation a and fop the total pressure 1n Equation 1 are nearly equal foP moat substances and the use ot either is· accep·table. A$ th& pre.asure .1n(freaaes it beoomea in­ creasingly n•aease~y to make the fugacity correction. '.t'h'$ causes ot the deviations 1n the l1qu!d phase are man,y fold. Unfortunately, even at low pressures few liqu1ds are t:ruly ideal and it is necessary to make eot'*­ rections tor their non•ideal behavio~ ln nearly all eases. All or the deviations or the 11quid phase are combined intQ one cot-reotlon tao'tor1 the activity coeff'ie1ent. The equation tor the equilibrium between a liquid and 1ta 6 vapor is then written as: Ylf'J:ii : ~ 1xlP~ • (3) The activity coefficients are different for each component, but in a binary system they are related by the Duhem equationt d ln 1(. .. d ln '6z. xl( d x1 >.:u ,t- x2( d x2 >...-,t <4> Several e.mp1:rioal and sem1theoret1cal solutions of the Duhem equation have been made . Best known of' these are the Margulea and Van Laar equatione. 'l'he Margulea equations are empirical expressions 1n series form, When rearranged in form as done by C~lson and Colburn (2, p.l89) they may be written aa: log ¥ l c• (2B•A)x22 + 2(A•B)xa.3 (5) log ~ 2 : (2A•B)x12 + 2(B- A}x1l • Van Laar attempted to follow a theoretical approach to the solution ·of the Dubem equation. He uaed the thermodynamic changes which oooured when pure liquids are mixed as his basis. Ce.rtain assumptions were made by Van Laar· which influence the reliability of the equations • .. He assumed that the change in entropy ~ is equal to that of an ideal solution, that no volume change· takes) p_l._ace upon mixing and that the van der Waals equation applies to each of the ·.components and to the. 1n;ixtures , both &ill liquids and aa vapors. One ot the fo~s of his equation& is: 7 A log'6 1 : ( l .. ~~~>a (6) B l.og ~ 2 = ( 1 t- !ii )2 As writte~, the eo~tanta A and B are identical in the two pairs of equations• Their values may be readily obtained t:rom experimental data by plotting the logarithm ot the activity ooetticient against the molar composition ot the liquid. On tbia graph the intersection of the curve log '6 1 • t(x) and x1 : 0 is A and ·similarly the intersection or log ~ 2 : g(x) and ~2 : 0 ia B. Alterna­ tivelr, the slope or the curve representing log ~ 1 : f(x) at x1 : 0 1a ·2A2/B and the slope of the c1.1rve log ~ 2 =g(x) at x2 =0 is •2B~/A. The a ement or the Margnlea and Van Laar equations with experimental data is dependent upon th agreemont ot the characteristics of the system with the aaaumpt1ona m de in the derivation ot the equations. As the ratio or the two constants used in the Van Laar and argulea eql;tat1ons approaohea l, the ()urves defined by the•• equationa become similar and the uae ot either is aat!a­ tactory. Carlson and Colburn (2. p.58~) have stated that in genttral t~e Van L ar equations have been found to 1'1t the data well. The7 have p~oposed the use or th argulea equations when the ratio or the molar volum e of thi components is approx~ately 1 and the constants A and B 8 differ considerably. The use of the Van Laar equations is recottm1$nded when the ratio ot the molar volumes i aomewhat larger the.n 1. Several methods have been proposed and used for the emoothing or experilru~ntal data" However, unless due care 1s given to the election ot the points through which the curve is drawn the result• are erroneous and the data . oar tully oollecttld in the laboratocy is not ut111~ed to its fullest possible degree~ One method of smoothing the data ia to plot the composition of the vapor against that or the liquid and to draw the best line through the experimental points.