Department of Physical Chemistry, Faculty of Chemistry, University of Bucharest, Bd. Regina Elisabeta 4-12, , Bucharest, Romania

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1 ISOTHERMAL LIQUID-VAOR EQUILIBRIUM IN ACETONITRILE-WATER SYSTEM Rodca Vlcu, Zoca Cenuse abstact: The study of ths system started from the mportance that acetontrle has as the component of some mxtures appearng n plastcs synthess or as a consequence of the extracte dstllaton n some ndustral processes. The paper presents a systematc and crtcal study of the sothermal equlbrum acetontrle-water system at 0, 30 and 40ºC. The systems present a maxmum n the total apour pressure dagram whch s mong wth temperature. The processng of the expermental data exstng n the lterature [-3] on acetontrle-water system as well as the authors expermental data obtaned under sothermal condtons at 40ºC n an nstallaton based on the statc prncple, p=f(x), were presented. The actty coeffcents were correlated and generalzed on the bass of seeral models of the lqud state,.e, by Margules, Wlson, NRTL and UNIFAC equatons. The analyss of the correlaton shows that the best generalzed equaton for ths system s UNIFAC wth a deaton n G E /RT of the order of 0 - and k j=0.0. Introducton Although separaton of multcomponent system s largely nestgated, deeper theoretcal and expermental researches are stll possble and necessary. The specalty lterature dealng wth separaton processes reeals that the challenge of the expermental technque s to obtan, by separaton, of seeral hgh purty components out of the multcomponent mxture wth numerous azeotropes or partal mscble components, sometmes under extreme pressure and temperature condtons. The most mportant nformatonal alue at present seems to be usng of the estmaton methods wth respect the structural parameters. Ths asserton s supported by the frequent use and perfecton of the equaton resulted from dfferent models of the lqud state as Margules, Wlson, NRTL, UNIFAC, ASOG and so on, equatons For a better pcture of acetontrle behaour n water, the data n the lterature [-3] refferng to the lqud apour equlbrum of acetontrle and water were completed by the sothermal study of ths system at 40ºC and a crtcal analyss on the bass of seeral models of the lqud state was performed. Department of hyscal Chemstry, Faculty of Chemstry, Unersty of Bucharest, Bd. Regna Elsabeta 4-, 03008, Bucharest, Romana Analele UnerstăŃ dn Bucureşt Chme, Anul XIV (sere nouă), ol. I-II, pg Copyrght 005 Analele UnerstăŃ dn Bucureşt

2 384 R. VILCU et al. Results and Dsscuson The measurements of the sothermal lqud-apour equlbrum were carred out n an nstallaton based on the prncple of the sotensoscopc method. The performance of the nstallaton was already analysed [4]. The propertes of the components of the system are presented n Table (a, b). Table a. hyscal propertes of the substances Subst. M (g/mol) urty (%) T m ( 0 C) T b ( 0 C) ρ (g/cm 3 ) η T C (K) C (atm) V C (cm 3 /mole) ω Aceto ntrle * Water * * at 0 0 C Table b. hyscal propertes of the substances Subst. Antones s parameters A B C Acetontrle [3] [3] [3] Water A determnaton of the saturaton pressure of acetontrle was carred out ntally and the A, B, C parameters of the Antone equatons were calculated (see Table b). The acetontrle was spectroscopc R.C.B-Bruxelles reagent and was used as receed, wth ndcated purty of at least 99.8%. The water was trple deonzed. Vapour pressure of the pure acetontrle was measured and an Antone equaton was ftted to the expermental data. The A, B, C parameters calculated from own expermental data together wth the relate deaton δ()=0.067 for acetontrle and for water. The expermental saturaton pressure for acetontrle are lsted n Table. The expermental saturaton pressure for acetontrle water system are lsted n Table 3. In Fgure are llustrated the expermental lqud apour equlbrum n bnary acetontrlewater system at 0, 30, 40 and 50ºC. Wth expermental or calculated alues of the equlbrum apour phase.

3 ISOTHERMAL LIQUID-VAOR EQUILIBRIUM 385 δ() Table. Saturaton pressures of acetontrle t ( 0 C) exp (mm Hg) calc (mm Hg) / (exp calc) = N f x ACN Table 3 Saturaton pressure (mm Hg) n acetontrle-water system 0 0 C [] 30 0 C [] 40 0 C 50 0 C [3] (mm Hg) y ACN x ACN (mm Hg) y ACN x ACN (mm Hg) y ACN x ACN (mm Hg) The actty coeffcents were calculated by equaton y lnγ = ln + 0 x l 0 ( B )( ) RT j + y δ The ntegraton of the general coexstance equaton allowed the calculaton of the apour phase composton n equlbrum wth lqud phase for the bnary system. j e + x + x KT l d= ( y x ) γ dln γ y y where apour excess olume, e, can be calculated by the equaton: e = y y x ( y ) dy

4 386 R. VILCU et al (mm Hg) x, y 0 0 C 30 0 C 40 0 C Fg. Lqud-apor equlbrum data n bnary system acetontrle-water The data from the Table 3 allowed the apprecaton of the actty coeffcents, the nondmensonal Gbbs excess free enthalpy and the Q functon for the thermodynamc consstency checkng up usng the Redlch-Kster crtera. The Rackett s parameters, Tsonopolous constants and UNIFAC parameters are lsted n Table 4. Table 4. Constants for actty coeffcents correlaton s Rackett s parameters Tsonopolous constants UNIFAC Ionsaton potental V ref X a b R Q (ev) [5].400 [5] The expermental data were correlated by Margules, Wlson, NRTL and UNIFAC equatons and the standard deatons by applyng these equatons to the expermental data are gen n Table 5.

5 ISOTHERMAL LIQUID-VAOR EQUILIBRIUM 387 Table 5. Correlatng parameters for acetontrle water system t ( 0 C) K j Model Redlch- Kster deaton arameters of the correlaton equaton Standard deaton n: A A a G E /RT γ γ Margules Wlson NRTL UNIFAC Margules Wlson NRTL UNIFAC Margules Wlson NRTL UNIFAC The best equaton whch correlates the 0ºC equlbrum data s Wlson equaton wth a k j =0.0. The Redlch-Kster deaton s the smallest one, equals On the other hand the best equaton whch correlates the 30ºC and 40ºC equlbrum data s UNIFAC equaton. The Redlch-Kster deaton s of the thrd order (3.8-9) 0-3, the deaton n G E /RT are of the order 0 - The best results were obtaned for UNIFAC equaton wth k j =0.0. Usng UNIFAC correlaton equaton alues of the actty coeffcents are n a good agreement wth the expermental data wthn the range of molar fracton: x ACN = REFERENCES. A. S. Verk, Anorg. Chem, 6, 8-3,950. D. S. Blackford and D. York, J. Eng. Data, 0, 33-35, S. R. Wlson,. B. atel, M. M. Abbott and H. Van Ness, 4, 30-3, R. Vlcu, Z. Cenuse, F. Gothard and V. Langshaw, Re. Roum. de Chm., 8, 89-90, 983.

6 388 R. VILCU et al. 5 S. J. Sandler, Models for Thermodynamc and hase Equlbra Calculatons, Marcel Dekker, Inc. New York- Basel-Hong Kong, 35, D. R. Lde, Handbook of Chemstry and hyscs, CRC ress, Boca Raton, Boston, NY, 8-85, 999.