Solubilities at High Dilution of Toluene, Ethylbenzene, 1,2,4-Trimethylbenzene, and Hexane in Di-2-ethylhexyl, Diisoheptyl, and Diisononyl Phthalates Delphine Bourgois,* ,² Diane Thomas, ² Jean-Louis Fanlo, ‡ and Jacques Vanderschuren ² Chemical Engineering Department, Faculte ´ Polytechnique de Mons, Rue de l’Epargne, 56, 7000 Mons, Belgium, and Research Centre LGEI, Ecole des Mines d’Ales, 6 Avenue de Clavie `res, 30319 Ale `s Cedex, France Henry’s constants of toluene, ethylbenzene (EtB), 1,2,4-trimethylbenzene (TMB), and hexane in di-2-ethylhexyl phthalate (DEHP), diisoheptyl phthalate (DIHP), and diisononyl phthalate (DINP) were determined experimentally applying a dynamic method, at temperatures ranging from (293.15 to 373.15) K and at 1 atm. The logarithms of Henry’s constants were fitted as linear functions of the inverse of absolute temperature (thanks to equations similar to the van’t Hoff equation). These equilibrium data were predicted with a mean relative deviation of 11 % by the modified UNIFAC thermodynamic model of solution. Introduction This paper presents the first experimental part of a general study devoted to the design of a regenerative VOC (volatile organic compounds, involving vapor pressures greater than 10 Pa at 293.15 K) absorption process using heavy solvents as scrubbing agents. The knowledge of the solubilities of a gaseous compound in liquid solvents is essential as well for the solvent selection as for the design of gas-liquid contactors. The solubility data, at a given temperature, for different partial pressures of the solute in the gas phase are generally fitted by Henry’s law, applicable for very dilute solutions and near atmospheric pressure. Many techniques 1 have been investigated and developed to determine the Henry’s constants or the activity coefficients at infinite dilution. A quite simple direct and dynamic technique was chosen here consisting of the saturation of a known absorbent volume in continuous contact with a VOC-containing gas of constant concentration. Our literature review concerning the solubilities of hydro- carbons in phthalates highlighted that a lack of data still exists concerning the systems of VOC-phthalate and temperatures investigated. Alessi et al. 2 determined activity coefficients at infinite dilution for 14 hydrocarbons including toluene, EtB, and hexane in 8 phthalates including DEHP, by gas chroma- tography at (298.15, 323.15, 348.15, and 373.15) K. Weisweiler and Winterbauer 3 studied the solubility of toluene, EtB, and hexane in DEHP and DIHP at 308.15 K (for the three VOC) and 343.15 K (only for the two first) by headspace gas chromatography. Experimental Section Chemicals. All chemical products were of analytical grade and had purities of 99.5 %, 99.8 %, 98 %, and 99 % for toluene, EtB, TMB, and hexane, respectively, and 98 % for all phthalates. Volatile organic compounds were purchased from Acros Organ- ics. DIHP and DINP were obtained from Aldrich, whereas DEHP was provided by Acros Organics. Tables 1 and 2 give some important properties of VOC and phthalates used in our experiments. The vapor pressures of VOC were estimated using the Wagner equation. 4 The densities of the VOC were given by the manufacturers. The densities and viscosities of the phthalates were measured experimentally using a densimeter (VWR International) and a falling sphere visco- simeter (Gebru ¨der Haake K.G.), respectively. Apparatus and Procedure. The applied dynamic method was based on the saturation of a weighted quantity of phthalate brought continuously in contact with a polluted air, the VOC concentration of which was fixed to a constant value. The experimental apparatus is shown in Figure 1. It is rather similar to that already used by Cotte et al. 5 for the measurement of solubilities of odorous VOC in aqueous solutions of polyeth- ylene glycol. Experiments were carried out within a 0.25 L thermostatic cell where the carrying air, fed at 1 L‚min -1 with an inlet VOC concentration of 0.5‚10 -3 kg‚m -3 , was bubbled into a heavy solvent volume of 0.1 L, at different temperatures from (293.15 to 373.15) K. The bubbler, placed in a thermostatic bath, was equipped with a grade no. 1 sintered glass having a pore diameter of (100 to 160) μm. A precise rate of VOC was injected by a syringe dispenser in a dry air stream of 10 L‚min -1 , whose flow rate was measured * Corresponding author. E-mail: Delphine.Bourgois@fpms.ac.be. ² Faculte ´ Polytechnique de Mons. ‡ Ecole des Mines d’Ales. Table 1. CASRN, a Molecular Formula, Molar Mass M, Density G, and Vapor Pressure P sat at 293.15 K for the VOC M F P sat VOC CASRN molecular formula kg‚mol -1 kg‚m -3 kPa hexane 110-54-3 C6H14 0.08619 659 16.15 toluene 108-88-3 C7H8 0.09214 865 2.92 EtB 100-41-4 C8H10 0.10616 867 0.95 TMB 95-63-6 C9H12 0.12019 899 0.21 a CASRN, Chemical Abstracts Service Registry Number. Table 2. CASRN, Molecular Formula, Molar Mass M, Density G, and Viscosity η at 293.15 K for the Phthalates M F η phthalate CASRN molecular formula kg‚mol -1 kg‚m -3 Pa‚s DIHP 71888-89-6 C22H34O4 0.3625 990 0.045 DEHP 117-81-7 C24H38O4 0.3906 983 0.076 DINP 68515-48-0 C26H42O4 0.4206 972 0.097 1212 J. Chem. Eng. Data 2006, 51, 1212-1215 10.1021/je050529h CCC: $33.50 © 2006 American Chemical Society Published on Web 05/24/2006