1,2-dichloropropane(1) - 2-methoxyethanol(2)계의

과잉 몰 부피 및 과잉 몰 엔탈피의 측정

김문갑, 이영세

국립 상주대학교 화학공학과

Excess Molar Volumes and Enthalpies for 1,2-dichloropropane + 2-methoxyethanol at the Temperature 298.15K.

Moon-Gab Kim, Young-Sei Lee

Department of Chemical Engineering, Sangju National University

Introduction

The use of 1,2-dichloropropane is as a chemical intermediate in the production of carbon tetrachloride and perchloroethylene, lead scavenger for antiknock fluids. In addition, 1,2-dichloropropane is classified as pro-environmental material without environmental restrictions[VOCs(volatile organic compounds), ODS(ozone depletion substances), and toxic substances] for use metal degreasing agent and solvent. It has lead to an increased interest in the thermodynamic properties of mixtures of 1,2-dichloropropane with additives for the purpose of wide applications

This paper reports excess molar volumes VE  using a digital vibrating-tube densimeter and excess molar enthalpies HE by means of an isothermal microcalorimeter with a flow mixing cell for the binary mixture {1,2-dichloropropane + 2-methoxyethanol} at 298.15K under atmospheric pressure. The results of excess molar volumes and excess molar enthalpies were correlated by the model of Redlich-Kister polynomial by using  Nelder-Mead[1]'s simplex pattern search method.  A survey of the literature reveals no studies of VE and HE for this mixture.

Experimental Section

All the chemicals(1,2-dichloropropane and 2-methoxyethanol) in this present study were supplied by Fluka. The stated purity of all the chemicals exceeded 99.0%(Puriss grade) and 99.5%(Puriss, ACS grade) respectively. Since the impurities in chemicals were mostly water, it was dehydrated by molecular sieves(Aldrich, type 4Å, 1/8 in. pellets)and degassed by ultrasound(ultrasonic bath, Bransonic, Model 8210, U.S.A.). 1,2-Dichloropropane was further purified under reduced pressure by fractional distillation. The middle portion of distillate collected was used for the experimental investigation.  From gas chromatographic analysis we found the resulting purity 99.0 mass% for 1,2-dichloropropane and 99.7 mass% for 2-methoxyethanol. In order to check the purity of compounds, also density values, □ and refractive indices, [eqn: n_D^20] (measured by a refractometer, Kyoto Electronics, model RA-520, with an accuracy of ±0.00001) were determined and are listed in Table 1 in comparison with literature data[2,3].

Densities of the pure components and binary mixtures were determined using a vibrating-tube densimeter(model DMA 58, Anton Paar, Graz, Austria) equipped with an automatic sample changer(model SP3, Anton Paar, Graz, Austria) with a resolution ±5×10-6 g/cm3. The apparatus was calibrated with double-distilled and degassed water and dry air at atmospheric pressure. The temperature in the measuring cell was regulated to ±0.01K. The sample solutions of different composition were prepared by mass in a sealed vial(approximately 50cm3) using a Mettler balance(model AT-201, Switzerland) accurate to within ±0.01mg.  In order to prevent the error in composition, which may arise from evaporation during sampling procedure, more volatile component was directly charged into the bottle. The charged bottle was close and weighed. The second component was injected into the bottle through the vial cap by a digital buret(Walu Labortechnik, model Continuous RS), which can be fulfilled continuous pulse-free operation, for faster preparation to minimize the experimental error.

The excess molar enthalpies, HE, were determined using an isothermal microcalorimeter with a flow mixing cell(Calorimetry Sciences Corporation, CSC-4400, Utah, U.S.A). The measuring unit of the calorimeter is a large heat sink(approximately 66 liters) incorporating two test wells. The water bath of the calorimeter provided temperature control of ±0.0005K. Liquid components studied were pumped into the mixing cell of the calorimeter by means of digital HPLC pump(Acuflow Series Ⅱ, Fisher Scientific, U.S.A) operated in a steady-state(fixed composition) mode at atmospheric pressure.  The pumps were  calibrated by determining the volumetric flow rate of bi-distilled water and a empirical correction equation was fitted for each pump. And the excess molar enthalpies from an experiment were obtained by subtracting heat effect from baseline values. The total volumetric flow rate was 0.5□·min-1 depending on the magnitude of the measured heat signal. The performance of the calorimeter was examined by means of enthalpies of mixing for the systems cyclohexane+n-hexane (particularly for the endothermic processes) and water+ethanol(particularly for the exothermic processes) recommended as a reference mixture in isothermal microcalorimeter[5,6]. In all cases the smoothed results agreed within 1.6% of previously published values.

Results and Discussions

Experimental excess molar volumes VE and excess molar enthalpies HE at 298.15K for the binary mixture of 1,2-dichloropropane and 2-methoxyethanol are listed in Tables 2 and 3 and their dependences on mole fraction  were shown in Fig. 1 and 2 together with the results of model calculations. From Fig. 1, the mixture 1,2-dichloropropane + 2-methoxyethanol has positive VE over the entire composition range. These positive deviations from ideal behavior are coincident with loosening of intermolecular interaction of a component with weak self-association(2-methoxyethanol).  The maximum value of this mixture is found to be about 0.2 cm3·mol-1 at x1=0.724. The dependence of HE on compositions has an S-Shape form, being negative for poor and positive for rich component of 1,2-dichloropropane. This shows that a relatively high energy is needed to break hydrogen bonds of 2-methoxyethanol with an increase of  halogenated hydrocarbon molecular during mixing. For the binary mixture VE and HE values were fitted to the Redlich-Kister equation to correlate the composition dependence of both excess of properties by means of Redlich-Kister  equation.

[eqn: {Q }^{E }= { x}_{1 } (1- { x}_{1 } ) SUM from { { j}=1} to n { A}_{ j}(1-2 { x}_{1 } ) ^{j-1 }]                                (1)

where QE = HE/J·mol-1 or VE/cm3·mol-1 and x1 is the mole fraction of 1,2-dichloropropane. The Redlich-Kister model gives an almost quantitative description of VE and HE for the system. Values of the coefficients Aj, determined by a Nelder-Mead simplex pattern search method, minimizing a function of n variables, are given in Table 4 along with standard deviations □ for the representation.

References

1. Nelder, J. A. and Mead, R. : A simplex method for function minimization.,     Comp. J., 7, 308-313, 1965

2. Lide, D. R., editor : CRC Handbook of Chemistry and Physics, 74th ed.,       CRC Press, 1993

3. Dean, J. A., : Lange's Handbook of Chemistry, 14th ed., McGraw-Hill, 1992

4.  Isothermal Microcalorimeter Use's Manual Revision 3.0, Calorimetry            Sciences Corp(1997)

5. Sabbah, R., Xu-wu, A, Chickos, J. S., Planas Leit□o, M. L., Roux, M. V.,        Torres, L. A., : Reference materials for calorimetry and differential thermal     analysis, Thermochimica Acta, 331, 93-204, 1999

6.  Wads, I. : Needs for standards in isothermal microcalorimeter,               Thermochimica Acta, 347, 73-77, 2000

7. Chand, A., Fenby, D. B. : J. Chem. Thermodyn., 10, 997-1001, 1978

8. Costigan, M. J., Hodges, L. J., Marsh, K. N., Stokes, R. H., Tuxford, C. W. :      The isothermal displacement calorimeter: design modifications for              measuring exothermic enthalpies of mixing, Aust. J. Chem., 33, 2103-2119, 1980

9.  Tanaka, R., D'arcy, P. J., Benson, G. C. : Application of a flow                 microcalorimeter to determine the excess enthalpies of binary mixtures of      non-electrolytes, Thermochimica Acta, 11, 163-175, 1975

10. Redlich, O., Kister, A. T. : . Algebraic representation of thermodynamic        properties and the classification of solutions, Ind. Eng. Chem., 40,              345-348, 1948

Table 1. Densities and refractive indices of pure components and comparison with literature values
	□/g·cm-3			[eqn: n_D^20]
component	exptl.	lit.		exptl.	lit.
1,2-dichloropropane	1.15458	1.1560		1.43856	1.4394[2]
		1.1558			1.4390[3]
2-methoxyethanol	0.96458	0.9647		1.40178	1.4024[2]
		0.9646			1.4021[3]

Table 4. Coefficients Ai and standard deviations □ for least-squares representations of VE/(cm3·mol-1) and HE/(J·mol-1) for binary mixture of {xCH3CHClCH2Cl+ (1-x)CH3OCH2CH2OH} at 298.15K by eqn. (1)
	VE	HE
	(cm3·mol-1)	(J·mol-1)
A1	0.63478	533.01458
A2	-0.44372	-2167.50029
A3	0.44428	814.77498
A4	-2.47732	-909.35213
A5	-1.01208	95.35616
A6	7.00296	704.65264
A7	1.77179	1284.09547
A8	-6.36789	-1592.50734
□	0.00597	1.63033

Table 2. Experimetal values of Densities □ and excess molar volume VE for the system of {xCH3CHClCH2Cl+ (1-x)CH3OCH2CH2OH} at 298.15K.
	□		VE
x	(g·cm3)		(cm3·mol-1)
0.000	0.95999		0.00000
0.056	0.97282		0.01253
0.112	0.98504		0.02720
0.174	0.99834		0.04452
0.226	1.00927		0.06065
0.293	1.02295		0.08304
0.343	1.03271		0.10142
0.409	1.04523		0.14001
0.474	1.05741		0.14870
0.544	1.07024		0.16963
0.615	1.08268		0.18859
0.688	1.09530		0.19828
0.724	1.10153		0.19987
0.762	1.10793		0.19783
0.801	1.11446		0.19164
0.836	1.12020		0.17972
0.877	1.12704		0.15811
0.918	1.13388		0.12708
0.960	1.14055		0.10969
1.000	1.14798		0.00000

Fig. 1. Excess molar volumes VE for binary mixture of {1,2-dichloropropane(1) and 2-methoxyethanol(2)} at 298.15K : □, this work; ―, Redlich-Kister model using parameters listed in Table 4.

Table 3. Experimetal values of Excess molar enthalpies HE for binary mixture of {xCH3CHClCH2Cl+ (1-x)CH3OCH2CH2OH} at 298.15K.
	HE		HE
x	(J·mol-1)	x	(J·mol-1)
0.017	-20.40474	0.466	97.05380
0.033	-33.91812	0.506	140.43762
0.066	-58.71698	0.547	185.74484
0.100	-79.48286	0.588	229.79842
0.134	-90.90786	0.631	271.85717
0.186	-94.98906	0.674	312.14149
0.221	-90.11456	0.718	346.78725
0.257	-76.98142	0.763	371.72856
0.293	-55.5185	0.808	383.51075
0.331	-30.09691	0.855	375.66895
0.349	-15.05974	0.902	329.13223
0.388	16.88956	0.950	234.98787
0.426	54.62745

Fig. 2. Excess molar enthalpies HE for the system of {1,2-dichloropropane(1) and 2-methoxyethanol(2)} at 298.15K : □, this work; ―, Redlich-Kister model using parameters listed in Table 4.