Indian Journal of Chemical Technology Vol. 14, March 2007, pp. 183-188 Solubility of acenaphthene in pure non-aqueous solvents between 298.15 and 333.15 K M Thenmozhi*, S Parvin Banu & T Karunanithi Department of Chemical Engineering, Annamalai University, Annamalai Nagar 608 002, India Email: [email protected] Received 2 September 2005; revised received 7 November 2006; accepted 3 January 2007 Binary solid-liquid equilibria (SLE) for the systems acenaphthene +benzene, +methanol, +2-propanol, +2-methyl- propan-1-ol, +ethyl acetate, +methyl ethyl ketone, +acetone, +chloroform are reported in the temperature range of 298.15 K to 333.15 K. The predictive ability of UNIFAC model as applied to SLE data of these systems is evaluated by comparing with the experimental values using percent relative deviation (%RD). Scope for improvements in UNIFAC model is analyzed based on the application of this model to SLE involving polycyclic aromatic compounds. Keywords: SLE, Acenaphthene, UNIFAC, Polycyclic aromatic hydrocarbons (PAHs) IPC Code: C10H35/00 Acenaphthene, also known as 1,2-dihydroacenaph- by Acree et al9-12. Of the nine solvent + solute systems thylene or 1,8-ethylenenaphthalene, is a tricyclic studied in the present work, excepting benzene and aromatic hydrocarbon. Acenaphthene belongs to a chloroform, SLE data are available only at the larger group of compounds called polycylic aromatic reference temperature of 298.15 K. In the case of hydrocarbons (PAH’s). It is used as a dye acenaphthene in benzene or chloroform, SLE data are intermediate, in the manufacture of some plastics, and available. Both Choi et al.13 and McLaughlin and as an insecticide and fungicide. Acenaphthene is Zainal14 have reported SLE data for acenaphthene in regarded as an environmental pollutant since it is benzene over the temperature range of 306 K to 345.8 irritating to the skin and mucous membranes of K and 303.8 to 342 K respectively. These data when humans and animals1. interpolated to common temperatures differ by about Acenaphthene is present in industrial products from 8-10%. Kotula and Marciniak have reported petrochemical, coke, coal tar processing and wood solubilities of naphthalene and acenaphthene in six preservative factories. Acenaphthene enters the chloro derivative solvents, chloroform, tetrachloro- environment through cigarette smoke, automobile methane, 1,1-dichloroethane, 1,2-dichloroethane, exhausts, and through effluents from petrochemical trichloroethylene and tetrachloroethylene15. In the industry, pesticides and wood preservative industries. absence of reliable experimental data, mathematical PAHs being relatively insoluble in water associate models are used for SLE prediction. A number of with the particulate phase, in particular the organic correlations are available in literature for activity matter2. PAHs emitted to air are mainly bound to coefficient prediction which in turn is used to aerosols and hence able to travel long distances3. calculate solubility data. Many of these have been Deposition of PAHs in the environment through fog applied for a variety of non-polar, polar and particles has been studied4. The removal of PAHs electrolyte systems and their advantages and from the soil takes place from abiotic loss (e.g. limitations are known. Group contribution is one of leaching, hydrolysis, photodegradation), volatiliza- the widely used methods for SLE prediction. tion5-7 and microbial degradation8. As the As most industrial operations such as separation environmental impacts of PAHs are acknowledged, it and chemical reaction are carried out at higher is important to have their solid-liquid equilibrium temperatures, SLE data at higher temperatures are (SLE) data which would be useful in their processing needed for design and efficient operation of such and handling. Solid-liquid equilibrium of PAHs in processes. This work studies the solubility of different pure and mixed organic solvents has been acenaphthene in eight different solvents over the studied extensively by various researchers, especially temperature range of 298.15 and 333.15 K. The 184 INDIAN J. CHEM. TECHNOL., MARCH 2007 solvents studied were chosen so as to fill the gaps in methyl ethyl ketone, acetone and chloroform were acenaphthene SLE data available in literature. The measured over the temperature range of 298.15 K to experimental data are compared with UNIFAC 333.15 K. predicted values. The physical properties of acenaphthene are shown in Table 1. The experimental binary solid liquid Experimental Procedure equilibrium data of acenaphthene are listed in Table 2. Acenaphthene (99% pure) and solvents (HPLC grade) used in this study were supplied by s.d. fine Model used for prediction chem limited. Acenaphthene was recrystallized from Equating the fugacity of a pure solid to the fugacity methanol for a minimum of four times before use. of the solid in solution and utilizing equations arising The solubility apparatus consisted of a rectangular from appropriate thermodynamic cycle, yields the constant temperature bath with two sides made of following equation for the solubility of a solute in glass to facilitate viewing the presence of solid phase either pure or mixture of solvents. in the equilibrium mixture. Uniform temperature throughout the bath was achieved by continuous ΔhTf ΔC T T stirring. Three necked round bottomed (R.B) flasks, im⎛⎞p ⎛ mm⎞ ln(γ=iix )⎜⎟ 1 − − ⎜ln +− 1 ⎟ mounted on serial magnetic ports were used for RTTRTTm ⎝⎠ ⎝ ⎠ holding samples in the thermostat. To one mouth, ΔHSp Δ p water cooled condenser was fitted to avoid loss of −+ …(1) RTR solvents during equilibration. The second mouth was sealed with one-holed stopper to insert a thermometer. where γi -liquid phase activity coefficient of the The third one was used as a sampling port. solute, xi -mole fraction solubility of solute, f Solvent and excess solute taken in R.B. flasks were ∆hi - molar enthalpy of fusion of the solute at its triple heated to a higher temperature than the required one, point, ∆Cpi- difference between the solid and liquid and then were cooled to the required temperature to heat capacities of pure solute at its triple point, ensure saturation. The mixture is equilibrated at that Tt- triple point temperature of the solute, ∆Hp- molar temperature for a minimum of 2 h. The sample, drawn enthalpy change of the solid phase transition, using a preheated syringe to prevent crystallization, ∆Sp- molar entropy change of the solid phase was injected into preweighed sample bottle having transition. Teflon septum. Care was taken to ensure that no Acenaphthene does not undergo solid phase solids were drawn while sampling. The syringe also transitions and hence the terms involving enthalpy had Teflon septum to avoid escaping of volatile and entropy changes of phase transition do not appear. solvent vapours which may reduce the accuracy of The two ∆Cp terms are generally neglected and experimental measurement. The samples drawn were Eq. (1) is written in the following form without losing weighed immediately. Weight of each sample drawn much accuracy18. was always greater than 20 g (at least 22 mL in volume), so that, any error introduced because of f ΔhTi⎛m⎞ solvent evaporation would be as small as possible. ln(γ=iix )⎜ 1 −⎟ …(2) RTT⎝⎠ The septum was then removed and the sample dried m off the solvent in a vacuum dryer at 35ºC for 24 h. To use Eq. (2) to estimate solubility, γi should be This was cooled in a desiccator to room temperature known, which is dependent on among other and weighed. This procedure was repeated till the dry properties, the solubility also. Hence, an iterative sample weight reached a constant value. For most samples, drying was complete within five days. From Table 1 — Physical properties of acenaphthene these observations, mole fraction solubility was Property Value calculated. The sampling method adopted in this work is similar to the one described by Gracin and CAS No. 83-32-9 16 Molecular mass 154.21 Rasmuson . All the precautions indicated by Gracin Melting point 367.15 K and Rasmuson were followed in this work. Heat of fusion 20710 J/mol Using the above described procedure binary SLE Transition temperature No transition exists data for acenaphthene in benzene, methanol, The enthalpy of fusion and melting point were taken from 2-propanol, 2-methylpropan-1-ol, ethyl acetate, published data17 THENMOZHI et al.: SOLUBILITY OF ACENAPHTHENE IN PURE NON-AQUEOUS SOLVENTS 185 9 scheme is used to calculate solubility. Various models Qk = Awk/(2.5×10 ) …(10) are available in literature for γi estimation. Group contribution is one of the techniques for activity The normalization factors 15.17 and 2.5×109 are coefficient calculation. The concept is that each determined by the volume and external surface area of functional group contributes a part to the total system a CH2 unit in polyethylene. property. Group interaction parameter values are The residual part of the activity coefficient is based assigned to functional groups using a large data base on the solution of groups concept. of VLE, activity coefficients at infinite dilution, azeotropic and excess enthalpy data measured over R (i) (i) ln γi = ∑vk (ln Γk −ln Γk ) …(11) wide temperature ranges. These parameters are k applied to new solid-liquid systems which have the (i) same constituent functional groups, making SLE where Γk is group residual activity coefficient and Γk prediction possible in the absence of experimental is the residual activity coefficient of group k in a data. Multicomponent SLE data prediction with reference solution containing only molecules of (i) UNIFAC does not require higher mixture values than type i. The term ln Γk is necessary to attain the these binary interaction parameters, which is one of normalization that activity coefficient γi becomes the major advantages of this method. The UNIquac unity as xi 1. The activity coefficient for group k in Functional group Activity Coefficient model, molecule i depends on the molecule i in which k is UNIFAC is one of the group contribution methods.