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Flud Phase Equlbra 275 (2008) 33 38 Contents lsts avalable at ScenceDrect Flud Phase Equlbra journal homepage: www.elsever.

Unversty, Tape, Tawan, ROC artcle nfo abstract Artcle hstory: Receved 3 May 2008 Receved n revsed form 5 September 2008 Accepted 8 September 2008 Avalable onlne xxx Keywords: Sold solublty

1 Flud Phase Equlbra 275 (2008) Contents lsts avalable at ScenceDrect Flud Phase Equlbra journal homepage: Solubltes of cnnamc acd, phenoxyacetc acd and 4-methoxyphenylacetc acd n supercrtcal carbon doxde Yan-Png Chen, Yen-Mng Chen, Muo Tang Department of Chemcal Engneerng, Natonal Tawan Unversty, Tape, Tawan, ROC artcle nfo abstract Artcle hstory: Receved 3 May 2008 Receved n revsed form 5 September 2008 Accepted 8 September 2008 Avalable onlne xxx Keywords: Sold solublty Supercrtcal carbon doxde Correlaton The sold solubltes of cnnamc acd, phenoxyacetc acd and 4-methoxyphenylacetc acd n supercrtcal carbon doxde were measured usng a sem-flow apparatus. The experments were taken at 308.2, and K. The pressure range was from 11 to 24 MPa. These data were confrmed as equlbrum sold solubltes based on a plug flow mass transfer model. The sold solubltes were further correlated usng the equatons of state or sem-emprcal models. The correlaton results are satsfactory wth optmally ftted bnary nteracton parameters n the Peng Robnson equaton of state Elsever B.V. All rghts reserved. 1. Introducton Supercrtcal technology s wdely appled n extracton, chemcal reacton and materals processng [1,2] where sold compounds are usually nvolved n those processes. Sold solublty data n supercrtcal fluds, especally n carbon doxde, are essental to the development of the related ndustral processes. Sold solubltes n supercrtcal carbon doxde are revewed or collected n recent lterature [3,4]. It s notced that more expermental data for organc and pharmaceutcal compounds are stll needed. The motvaton of ths study was to measure novel solublty data of sold acd compounds n supercrtcal carbon doxde. We have measured the solubltes of organc and pharmaceutcal components n supercrtcal carbon doxde usng a sem-flow apparatus [5,6]. In ths study, we appled the same apparatus to measure the sold solubltes of three acdc organc compounds, cnnamc acd, phenoxyacetc acd and 4-methoxyphenylacetc acd, n supercrtcal carbon doxde. The expermental temperatures were 308.2, and K. The pressure range was from 11 to 24 MPa. Cnnamc acd and phenoxyacetc acd are used n agrculture and pharmaceutcal ndustres. 4-Methoxyphenylacetc acd s used n organc synthess and also n pharmaceutcal ndustres. These polar compounds all have the COOH functon group. As far as we know, no sold solublty data for these compounds n supercrtcal carbon doxde have been shown n lterature. In ths research, we report new expermental data that are useful n process development or theoretcal model correlaton. The measured results n ths study were frstly examned by a plug-flow mass transfer model to ensure that equlbrum solubltes were obtaned. The expermental data were then correlated usng ether the equaton of state or sem-emprcal models. The correlaton accuracy and the optmally ftted model parameters are presented n ths study. 2. Expermental 2.1. Chemcals Carbon doxde (component 1) was purchased from San-Fu Chemcal Co. (Tawan) wth a mnmum purty of 99.8 mass%. Cnnamc acd and phenoxyacetc acd were purchased from Merck Company, and 4-methoxyphenylacetc acd was purchased from Acros Company. All pure chemcals had a mnmum purty of 99 mass%, and were used wthout further purfcaton. The propertes of these pure components are lsted n Table 1. The crtcal temperatures and pressures of the three sold compounds were estmated from the Joback correlaton equaton [7]. The acentrc factors were estmated from the Ambrose method [8]. The structures of the three sold components are llustrated n Fg Expermental apparatus and procedures Correspondng author. E-mal address: ypchen@ntu.edu.tw (Y.-P. Chen). Ths study appled a sem-flow type apparatus to measure the sold solubltes of three organc compounds. The expermental /$ see front matter 2008 Elsever B.V. All rghts reserved. do: /j.flud FLUID-8022; No. of Pages 6

2 34 Y.-P. Chen et al. / Flud Phase Equlbra 275 (2008) Table 1 Purtes and physcal propertes of the chemcals used n ths study. Compound Molecular weght (10 3 kg/mol) T m (K) V S (10 3 m 3 /mol) T c (K) P c (MPa) ω Purty (mass%) Carbon doxde (CO 2) [16] [16] [16] >99.8 Cnnamc acd (C 9H 8O 2) [14] [14] [7] [7] [8] >99.0 Phenoxyacetc acd (C 8H 8O 3) [14] [15] [7] [7] [8] > Methoxyphenylacetc acd (C 9H 10O 3) [14] [15] [7] [7] [8] >99.0 apparatus s smlar as that n our prevous research [5]. It s conssted of three sectons for the supply of supercrtcal CO 2, the equlbrum between the sold and the supercrtcal CO 2, and the analyses of the expermental results. Pure CO 2 was frstly lquefed to K and was then pressurzed to a desred pressure by a HPLC pump (Thermo Separaton Product). The ext pressure was controlled usng a back-pressure regulator (Tescom). The hgh pressure CO 2 passed through a preheatng col mmersed n a water bath. It reached a specfc supercrtcal state and was then charged nto the pre-equlbrum and equlbrum cells. The pre-equlbrum cell had a volume of 150 cm 3 where 25 g sold sample was dstrbuted n fve layers of glass beads. The volume of the equlbrum cell was 300 cm 3 n whch 50 g of sold sample was dstrbuted n 10 layers. At the ends of both cells, flters were equpped to prevent any entranment. The expermental temperature and pressure were detected n the equlbrum cell by calbrated thermocouple (Ins Co.) and pressure gauge (Hese Co.), respectvely. The accuraces for ther readngs were ±0.1 K and ±0.03 MPa, respectvely. The supercrtcal CO 2 flew through the equlbrum cell and then expanded to atmospherc pressure after a needle valve. The needle valve was wrapped wth a heatng tape to keep the temperature above the meltng pont of the sold by K n order to avod any precptaton n the lne. Sold was separated from the gas phase upon de-pressurzaton, and was dssolved nto a flask wth organc solvent of ethyl acetate. The flow rate of the gas was recorded by a wet test meter (Rtter TG1). The soluton n the collectng flask was soncated for more than 10 mn. Its composton was measured by a UV vs spectrometer (Jasco, UV-975). A sharp absorpton peak n the UV vs spectrometer was observed at the wavelength of 254 nm for cnnamc acd and phenoxyacetc acd, and was at 274 nm for 4-methoxyphenylacetc acd. Calbratons of the UV measurements were satsfactory wth a R 2 regresson coeffcent better than At least three sold solublty data were taken at each expermental temperature and pressure. The uncertanty of expermental measurements was better than ±5%. 3. Results and dscusson The expermental solublty data n supercrtcal CO 2 have been examned by applyng a flud sold mass transfer model [9]. The detal procedures have been presented n our prevous work [5]. The basc crteron of ths mass transfer model s to calculate the rato of the measured sold solublty relatve to ts saturated value, X = C/C sat, under varous expermental condtons (temperature, pressure, and flow rate). If the values of X are close to unty, the expermentally measured sold solubltes are accepted as equlbrum data. In our experments, the X values under varous expermental condtons were all greater than 0.999, and the mass transfer effect s confrmed to be neglgble n ths study. The measured sold solublty data n supercrtcal CO 2 for cnnamc acd, phenoxyacetc acd and 4-methoxyphenylacetc acd are presented n Tables 2 4, respectvely. The denstes of supercrtcal CO 2 at varous expermental condtons were calculated from the Peng Robnson equaton of state [10]. These values were most near to the expermental values from IUPAC, and are also ncluded n these tables. Generally, the solubltes for all three sold compounds ncreased wth pressure at a fxed temperature. At a constant temperature, phenoxyacetc acd showed the largest solublty n supercrtcal CO 2. Ths may be due to the relatvely hgher sold vapor pressure as ndcated n the followng correlaton results usng equaton of state (EOS). Cnnamc acd and 4-methoxyphenylacetc acd had smlar and compettve sold solubltes at each expermental temperature. These sold solublty data were further correlated usng the equaton of state, or sememprcal equaton approaches. Fg. 1. Structures of sold compounds n ths study.

3 Y.-P. Chen et al. / Flud Phase Equlbra 275 (2008) Table 2 Solublty of cnnamc acd (2) n supercrtcal CO 2 (1). T (K) P (MPa) 10 4 y 2 1 (kg/m 3 ) Equaton of state method At sold supercrtcal flud phase equlbrum, the equal fugacty crteron s appled and the sold solublty s expressed as: y = pvp S exp[ (p pvp ˆ SCF p )/RT] S where s the sold molar volume, P vp s the sold vapor pressure, and ˆ SCF s the fugacty coeffcent of sold n the supercrtcal flud phase. The sold vapor pressure was expressed by the conventonal equaton: ln p vp = A B T where A and B were two emprcal parameters. Two EOS were employed n ths study n data regresson: the Table 3 Solublty of phenoxyacetc acd (3) n supercrtcal CO 2 (1). T (K) P (MPa) 10 4 y 3 1 (kg/m 3 ) (1) (2) Table 4 Solublty of 4-methoxyphenylacetc acd (4) n supercrtcal CO 2 (1). T (K) P (MPa) 10 4 y 4 1 (kg/m 3 ) Soave Redlch Kwong EOS [11]: p = RT b a ( + b) and the Peng Robnson EOS [10]: p = RT b a (4) ( + b) + b( b) In these EOS, V was the molar volume and the EOS parameters (a and b) were determned from the crtcal constants of the pure compounds. The van der Waals mxng rules (VDW2) wth two bnary nteracton parameters (k j and l j ) were used n ths study: a m = x x j (a a j ) 0.5 (1 k j ) (5) j (b + b j ) b m = x x j (1 l 2 j ) (6) j If parameter l j was taken as zero and only a sngle parameter k j was used, t was denoted as the VDW1 mxng rules. The bnary nteracton parameters together wth the parameters n the sold vapor pressure equaton were optmally ftted to the expermental sold solublty data by mnmzng the followng objectve functon: obj = k y exp,k ycal,k y exp,k The summaton was over all expermental kth ponts. The superscrpts exp and cal represented the expermental and calculated values, respectvely. Table 5 presents the optmally ftted parameters from the EOS method. The bnary nteracton parameters were taken as temperature-ndependent and ther values are all n reasonable range. Both EOS wth the VDW2 mxng rules yelded satsfactory results where the absolute average devaton n sold solublty (AADY) s around 5% Sem-emprcal correlaton equaton method Two commonly used sem-emprcal equatons were appled n ths study for sold solublty data correlaton. The Chrastl equaton (3) (7)

4 36 Y.-P. Chen et al. / Flud Phase Equlbra 275 (2008) Table 5 Correlated results of solublty data n SCCO 2 usng varous EOS mxng rules. Mxng rules Peng Robnson EOS Soave Redlch Kwong EOS k 1j l 1j AADY (%) k 1j l 1j AADY (%) CO 2 (1) + Cnnamc acd (2) ln P vp 2 (10 6 MPa) = ( /T(K)) VDW VDW CO 2 (1) + Phenoxyacetc acd (3) ln P vp 3 (10 6 MPa) = ( /T(K)) VDW VDW CO 2 (1) + 4-Methoxyphenylacetc acd (4) ln P vp 4 (10 6 MPa) = ( /T(K)) VDW VDW n exp y AADY (%) = 100 j,k ycal j,k. n k=1 y exp j,k [12] expressed the sold solublty n a three-parameter form (n, C, and D): ln S (kg/m 3 ) = n ln 1 (kg/m 3 ) + C T + D (8) S = 1M y M 1 (1 y ) (9) Mendes Santago and Teja [13] also proposed the followng equaton that ftted the sold solublty usng three parameters (E, F, and G): T ln(y P(MPa)) = E + F 1 (kg/m 3 ) + GT (10) The parameters n the above two sem-emprcal equatons were optmally ftted to the expermental sold solublty data usng the same objectve functon n Eq. (7). Table 6 llustrates the correlaton results from the two sem-emprcal equatons. The grand AADY value over all expermental solublty data was around 8% that was larger than that from the EOS correlaton. Fgs. 2 4 present the expermental data and the calculated results from the Peng Robnson EOS for three sold compounds, respectvely. Satsfactory agreement between measured and correlated results s observed. The cross-over pressures are estmated as MPa for cnnamc acd, MPa for phenoxyacetc acd, and MPa for 4-methoxyphenylacetc acd, respectvely. Fg. 2. Solublty data of cnnamc acd (2) n SCCO 2 (1): ( ) K, ( ) K, ( ) K, and ( ) Peng Robnson equaton of state wth VDW2 mxng rule. Table 6 Correlated results of the solublty data n SCCO 2 usng varous emprcal models. Chrastl equaton Mendez Santago and Teja equaton n C D AADY (%) E F G AADY (%) CO 2 (1) + Cnnamc acd (2) CO 2 (1) + Phenoxyacetc acd (3) CO 2 (1) + 4-Methoxyphenylacetc acd (4) n exp y AADY (%) = 100 n k=1 j,k ycal j,k y exp j,k.

5 Y.-P. Chen et al. / Flud Phase Equlbra 275 (2008) were also determned from expermental results. Fg. 3. Solublty data of phenoxyacetc acd (3) n SCCO 2 (1): ( ) K, ( ) K, ( ) K, and ( ) Peng Robnson equaton of state wth VDW2 mxng rule. Lst of symbols a, b parameters n the equaton of state A, B parameters n the sold vapor pressure equaton C parameter n the Chrastl model, or the sold solublty D parameter n the Chrastl model E, F, G parameters n the Mendez Santago and Teja equaton k, l bnary nteracton parameters M molecular weght n parameter n the Chrastl equaton obj objectve functon defned n Eq. (7) P pressure P c crtcal pressure R gas constant S sold solublty defned n Eq. (8) T temperature T c crtcal temperature T m meltng temperature V molar volume V s sold molar volume X relatve saturated concentraton of the sold solute y mole fracton Greek letters fugacty coeffcent densty ω acentrc factor Subscrpts 1 component 1, CO 2, j component or j k the kth expermental pont m mxture property sat saturated value Superscrpts cal calculated value exp expermental value vp vapor pressure Acknowledgements The authors are grateful to the support of ths research from the Natonal Scence Councl, Tawan, ROC. Expermental work of S.Y. Huang s apprecated. References Fg. 4. Solublty data of 4-methoxyphenylacetc acd (4) n SCCO 2 (1): ( ) K, ( ) K, ( ) K, and ( ) Peng Robnson equaton of state wth VDW2 mxng rule. 4. Concluson The sold solubltes n supercrtcal CO 2 were measured n ths study for cnnamc acd, phenoxyacetc acd and 4- methoxyphenylacetc acd. The expermental temperatures were 308.2, and K where the pressure ranged from 11 to 24 MPa. The mass transfer effect was confrmed to be neglgble n ths study. The measured data were satsfactorly correlated usng the Soave Redlch Kwong and Peng Robnson EOS wth VDW2 mxng rules where the absolute average devaton n sold solublty was 5%. The cross-over pressures for these sold compounds [1] E. Reverchon, R. Adam, Nanomaterals and supercrtcal fluds, J. Supercrt. Fluds 37 (2006) [2] M. Bahram, S. Ranjbaran, Producton of mcro- and nano-composte partcles by supercrtcal carbon doxde, J. Supercrt. Fluds 40 (2007) [3] F.P. Lucen, N.R. Foster, Solubltes of sold mxtures n supercrtcal carbon doxde: a revew, J. Supercrt. Fluds 17 (2000) [4] R.B. Gupta, J.-J. Shm, Solublty n Supercrtcal Carbon Doxde, CRC Press, New York, [5] S.-Y. Huang, M. Tang, S.L. Ho, Y.-P. Chen, Solubltes of N-phenylacetamde, 2- methyl-n-phenylacetamde and 4-methyl-N-phenylacetamde n supercrtcal carbon doxde, J. Supercrt. Fluds 42 (2007) [6] C.-S. Su, Y.-P. Chen, Measurement and correlaton for the solublty of nonsterodal ant-nflammatory drugs (NSAIDs) n supercrtcal carbon doxde, J. Supercrt. Fluds 43 (2007) [7] K.G. Joback, R.C. Red, Estmaton of pure-component propertes from group contrbutons, Chem. Eng. Commun. 57 (1987) [8] D. Ambrose, J. Walton, Vapor pressures up to ther crtcal temperatures of normal alkanes and 1-alkanols, Pure Appl. Chem. 61 (1989) [9] A. Abaroud, F. Trabels, F. Recasens, Quas-statc measurement of equlbrum solubltes n SC fluds: a mass transfer crteron, Flud Phase Equlb. 169 (2000)

6 38 Y.-P. Chen et al. / Flud Phase Equlbra 275 (2008) [10] D.Y. Peng, D.B. Robnson, A new two-constant equaton of state, Ind. Eng. Chem. Fundam. 15 (1976) [11] G. Soave, Equlbrum constants from a modfed Redlch Kwong equaton of state, Chem. Eng. Sc. 27 (1972) [12] J. Chrastl, Solublty of solds and lquds n supercrtcal gases, J. Phys. Chem. 86 (1982) [13] J. Mendez-Santago, A.S. Teja, The solublty of solds n supercrtcal fluds, Flud Phase Equlb (1999) [14] CRC Handbook of Chemstry and Physcs, 87th ed., CRC Press, Boca Raton, FL, (Secton 3). [15] A. Immrz, B. Perrn, Predcton of densty n organc crystals, Acta Crystallogr. A33(1977) [16] B.E. Polng, J.M. Prausntz, J.P. O Connell, The Propertes of Gases and Lquds, 5th ed., McGraw-Hll, New York, 2001 (Appendx A).

Energy, Entropy, and Availability Balances Phase Equilibria. Nonideal Thermodynamic Property Models. Selecting an Appropriate Model

Energy, Entropy, and Availability Balances Phase Equilibria. Nonideal Thermodynamic Property Models. Selecting an Appropriate Model Lecture 4. Thermodynamcs [Ch. 2] Energy, Entropy, and Avalablty Balances Phase Equlbra - Fugactes and actvty coeffcents -K-values Nondeal Thermodynamc Property Models - P-v-T equaton-of-state models -