Solubility of Acenaphthene in Pure Non-Aqueous Solvents Between 298.15 and 333.15 K

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. In situated. this model, activity coefficient is expressed in terms 19 The group activity coefficient Γk is found using the of two types of contributions . expression,

C R ln γi = ln γi + ln γi …(3) ln Γk = Qk[1−ln∑θm ψmk −∑(θm ψkm/∑θn ψnm)] …(12)

The combinatorial part (superscript C), reflects the (i) Eq. (12) also holds for ln Γk . θm is the area fraction excess entropy of mixing due to differences in size of group m and the sums are over all different groups. and shape, and the residual part (subscript R), reflects θ is calculated as shown in Eq. (13). the excess enthalpy of mixing resulting from m interaction energies. θ = Q X /∑Q X …(13) m m m n n C γi = ln(Φi/xi)+(zqi /2)ln(θi /Φi)+li −(Φi/xi) ∑ xjjl …(4) j where Xm is the mole fraction of group m in the mixture. The group interaction parameter ψmn is given li = (z/2)( ri- qi )-(ri -1); z = 10 …(5) by,

θi = qi xi / Σ qj xj …(6)

Ψmn = exp –[(Umn −Unn)/ RT] = exp (−amn/ T) …(14) Φi = ri xi / Σ rj xj …(7) Umn is a measure of the energy of interaction Parameters ri and qi are measures of molecular van between groups m and n. The group interaction der Waals volumes and molecular surface areas parameters amn must be evaluated from experimental respectively. Parameters ri and qi are calculated as the phase equilibrium data. amn has units of Kelvin and sum of the group volume and area parameters Rk and amn # anm. Parameters amn and anm are obtained from Qk. databases using a wide range of experimental results.

i i ri = Σ νk Rk and qi = Σ νk Qk …(8) Solubility prediction using UNIFAC model The solubility of acenaphthene in the temperature i where νk , always an integer, is the number of groups range of 298.15 to 333.15 K was predicted using the of type k in molecule i. Group parameters Rk and Qk UNIFAC activity coefficient model along with are obtained from the van der Waals group volumes Eq. (2). The predicted solubility was compared with and surface areas Vwk and Awk experimental data by calculating percentage relative deviation. Activity coefficient calculations were done R k = Vwk /15.17 …(9) using a computer program written in C. This program 186 INDIAN J. CHEM. TECHNOL., MARCH 2007

uses the UNIFAC model and interaction parameters Table 2 — Comparison between experimental and predicted mole of Poling et al20. The saturation solubility for a fraction solubility of acenaphthene in pure solvents in the particular temperature is calculated iteratively using temperature range of 298.15 to 313.15 K

Eq. (2). For an initial guess of solubility, an arbitrary Solvent used Temp Xexp Xpred %RD fractional value between 0 and 1 is given. The K program calculates activity coefficient and solubility Benzene 298.15 0.1732 0.21728 −25.45 values using the above referred set of equations and 303.15 0.2015 0.24846 −23.31 the initial guess to arrive at a new solubility value 308.15 0.2371 0.28280 −19.27 which is compared to the original value. Iteration is 313.15 0.2746 0.32047 −18.02 continued until the difference between successive 318.15 0.3127 0.36166 −15.66 values is less than a set tolerance. The UNIFAC 323.15 0.3592 0.40656 −13.18 predicted values were compared with the 328.15 0.4133 0.45538 25.01 333.15 0.4734 0.50833 32.15 experimental values by calculating the percent relative deviation (%RD) as defined by Eq. (15). Methanol 298.15 0.0056 0.01050 −81.03 303.15 0.0071 0.01246 −70.68 ⎡⎤(Predicted value - Experimental value) 308.15 0.0092 0.01477 −57.13 %RD= ×100 ⎢⎥Experimental value 313.15 0.0118 0.01752 −48.47 ⎣⎦ 318.15 0.0149 0.02081 −39.66 …(15) 323.15 0.0177 0.02481 −38.60

Table 2 lists the predicted values and the 328.15 0.0204 0.02973 −40.23 corresponding percent relative deviations compared to 333.15 0.0234 0.03590 −47.13 the experimental data. 2-Propanol 298.15 0.0128 0.01622 −26.72 303.15 0.0204 0.01934 5.20 Discussion 308.15 0.0375 0.02302 38.61 Choi et al.13 have reported acenaphthene + benzene 313.15 0.0677 0.02741 59.51 solubilities at 306.55, 312.95, 319.85, 328.05, 335.95 318.15 0.0947 0.03625 61.72 323.15 0.1233 0.03897 68.39 and 345.75 K. The authors’ data in the case of 328.15 0.1491 0.04670 68.68 acenaphthene in benzene measured over the 333.15 0.1739 0.05631 67.62 temperature range of 298.15 to 333.15 K agree well with data reported by Choi et al13. Comparison of 2-Methyl-1-propanol 298.15 0.0167 0.02248 −34.61 plots of ln x versus 1/T of SLE data reported in this 303.15 0.0236 0.02683 −13.69 13 308.15 0.0356 0.03200 10.11 work and those of Choi et al. show linear variation 313.15 0.0564 0.03815 32.36 with slopes and intercepts varying only within 0.9% 318.15 0.0929 0.04553 50.99 and 0.02%. 323.15 0.1364 0.05449 60.05 Solid liquid equilibria of PAHs have been studied 328.15 0.1912 0.06550 65.74 in benzene over wide temperature ranges (303.8, 333.15 0.2484 0.07937 68.05

314.6, 336.4 and 342.6 K) by McLaughlin and Ethyl acetate 298.15 0.1079 0.12625 14 −17.01 Zainal . These data have been correlated using 303.15 0.1447 0.15185 −4.94 21 different models including UNIFAC . 308.15 0.1853 0.18300 1.24 For the acenaphthene in benzene, 1-propanol, 313.15 0.2377 0.22073 7.14 2-methyl-1-propanol and ethyl acetate systems 318.15 0.2930 0.26597 9.23 323.15 0.3485 0.31871 8.55 studied in this work, at lower temperatures the 328.15 0.4112 0.37969 7.66 UNIFAC model over predicts the experimental data 333.15 0.4807 0.44669 7.07 and at higher temperatures, it under predicts. The Methyl ethyl ketone 298.15 0.1301 0.11677 10.25 solubility predictions for the systems acenaphthene + acetone and acenaphthene + chloroform show 303.15 0.1604 0.14146 11.81 308.15 0.2015 0.17130 14.99 decreasing deviations with increasing temperature. 313.15 0.2462 0.20729 15.80 The deviations in UNIFAC prediction for 318.15 0.3002 0.25036 16.60 acenaphthene in methanol and methyl ethyl ketone do 323.15 0.3626 0.30124 16.92 not show any particular trend. 328.15 0.4267 0.36015 15.60 333.15 0.4867 0.42669 12.33 Plots of logarithm of experimental mole fraction solubility of acenaphthene versus inverse of absolute Contn — THENMOZHI et al.: SOLUBILITY OF ACENAPHTHENE IN PURE NON-AQUEOUS SOLVENTS 187

Table 2 — Comparison between experimental and predicted mole temperature are shown in Fig. 1. Of the eight fraction solubility of acenaphthene in pure solvents in the acenaphthene + solvent systems studied in this work, temperature range of 298.15 to 313.15 K benzene, ethyl acetate, methyl ethyl ketone, acetone

and chloroform show a linear trend. The three Solvent used Temp Xexp Xpred %RD K alcohols show different types of nonlinear variations. The systems showing linear trend have been observed Acetone 298.15 0.1360 0.08535 37.24 to have activity coefficient values close to unity and 303.15 0.1655 0.10860 34.38 308.15 0.2008 0.13908 30.74 those showing non-linear trends have large activity 313.15 0.2412 0.17870 25.91 coefficient values (in the range of 7 to 19). 318.15 0.2902 0.22868 21.20 323.15 0.3478 0.28852 17.04 328.15 0.4153 0.35619 14.23 Conclusions SLE data for acenaphthene in the pure solvents Chloroform 298.15 0.1905 0.27013 −41.80 303.15 0.2193 0.29996 −36.78 benzene, chloroform, methanol, 2-propanol, 2- 308.15 0.2531 0.33221 −31.26 methyl-1-propanol, ethyl acetate, methyl ethyl ketone 313.15 0.2902 0.36708 −23.14 and acetone are reported over a temperature range of 318.15 0.3326 0.40478 −19.19 298.15 K to 333.15 K. Prediction of experimental data 323.15 0.3781 0.44555 −16.91 is done with UNIFAC method. Considering the wide 328.15 0.4317 0.48967 −16.12 range of applicability, the UNIFAC model is preferred to others. The greatest advantage in using UNIFAC method is that parameters are revised periodically and extended to new functional groups by various researchers22-25. Also modifications to UNIFAC are reported as it applies to specific types of systems. In the case of acenaphthene the UNIFAC prediction of SLE data are not satisfactory. This may be due to the inadequacies of group contribution concept in defining molecular behaviour. PAHs when split into functional groups as defined by the UNIFAC method, have only AcH, Ac and AcCH2. For example, solutions of naphthalene in benzene should show ideal behaviour since they have similar functional groups. Unifac predictions of this system is good, whereas SLE predictions of higher PAHs such as phenanthrene, pyrene, chrysene and triphenylene in benzene are very poor and unreliable even though they have same functional groups. Attempts are being made by the authors to correct such failures. Further research is being carried out on inclusion of this effect in terms of correction factors.

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