- Email: [email protected]
Activity coefficients at infinite dilution for hydrocarbons in furfuryl alcohol at T=(278.15 and 298.15) K, determined by g.l.c.
J. Chem. Thermodynamics 36 (2004) 561–565 www.elsevier.com/locate/jct
Activity coefficients at infinite dilution for hydrocarbons in furfuryl alcohol at T ¼ (278.15 and 298.15) K, determined by g.l.c. Marta K. Kozłowska a, Trevor M. Letcher a
b,*
ska , Urszula Doman
a
Physical Chemistry Division, Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, Warsaw 00-664, Poland b School of Pure and Applied Chemistry, Natal University-Durban, Private bag X10, Dalbridge 4041, Durban, South Africa Received 18 December 2003; accepted 4 March 2004 Available online 21 April 2004
Abstract The potential of the polar solvent, furfuryl alcohol, as a solvent in the separation of aromatics from aliphatics and other hydrocarbons, has been investigated by measuring activity coefficients at infinite dilution. The activity coefficients at infinite dilution for some alkanes, cycloalkanes, alkenes, alkynes and benzene in furfuryl alcohol have been determined by g.l.c. at T ¼ (278.15 and 298.15) K. The method used is we believe, a more controlled and reliable method than the alternative pre-saturation method. The results have been used to calculate the selectivity factor and hence predict the potential for furfuryl alcohol as a solvent in separating aromatic compounds from aliphatic compounds and other hydrocarbons using extractive distillation. The results have been compared to the recently published work on a related polar solvent – furfural. The excess enthalpies of mixing at infinite dilution have also been calculated. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Activity coefficients at infinite dilution; Furfuryl alcohol; Hydrocarbons; Selectivities; Excess enthalpies of mixing at infinite dilution
1. Introduction The separation of aromatic from aliphatic compounds is important in oil refineries involved in the production of transport fuels. Highly polar solvents such as sulfolane and N-methyl-pyrrolidinone, which also have low volatility, are used to effect such separation [1]. Furfuryl alcohol (C5 H6 O2 ) is a polar solvent with a high boiling point (443.2 K) and low vapour pressure, and as a result, has the potential of being a good solvent for separating aromatic and aliphatic compounds. It is a by-product of the sugar industry, where it is made by the acid hydrolysis of bagasse, followed by oxidation. In this work, the activity coefficients at infinite dilution were determined using a g.l.c. method for moderately volatile solvents, recently reported by one of the authors [2]. These activity coefficients were used to cal*
Corresponding author. Tel.: +27-31-260-3090; fax: +27-31-2603091. E-mail address: [email protected] (T.M. Letcher). 0021-9614/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2004.03.001
culate the selectivity at infinite dilution [3] for the separation of benzene from the alkanes, cycloalkanes, alkenes and alkynes used in this work. The activity coefficients were also used to determine the partial molar excess enthalpy of mixing at infinite dilution. This property gives an indication of the type and magnitude of the interaction between each of the hydrocarbons and furfuryl alcohol. The activity coefficient results are compared to recently reported data [4] on a related set of mixtures involving hydrocarbons in furfural.
2. Experimental 2.1. Chemicals The furfuryl alcohol was supplied by Illovo Sugar Company and was distilled before use. The mass fraction purity, as analysed by g.l.c. was found to be better than 0.99. The water content of the furfuryl alcohol was always better than 0.003 mole fraction, as determined by Karl Fisher titration. The solutes used were: pentane,
562
M.K. Kozłowska et al. / J. Chem. Thermodynamics 36 (2004) 561–565
hexane, heptane, cyclopentane, cyclohexane, cycloheptane, hex-1-ene, hept-1-yne, hex-1-yne, hept-1-yne and benzene. They were all supplied by Aldrich. It was unnecessary to purify the solutes further, because of the nature of the g.l.c. experiment. 2.2. Apparatus and procedure
0 1 VN expðCÞ=n3 ¼RT =c1 13 p1 p3 =c13 p1 ðUo t=n3 Þ ¼ a bðUo t=n3 Þ;
ð1Þ
where the net solute retention volume VN is given by VN ¼ J32 Uo ðtR tG Þ;
ð2Þ
and
The g.l.c. apparatus has been described previously [4,5]. The columns used were stainless-steel tubing (4.2 mm bore; length 0.75 m to 1.5 m) with the support being silanized chromosorb (Supelco, Inc., 125 lm to 150 lm). A catharometer detector was used and the carrier gas was helium. The flow rate was maintained as constant as possible for each set of measurements on each column. This rate was measured using a calibrated soap bubble meter and the results were corrected for water vapour. The column temperature was controlled in a well-stirred waterbath, to within 0.005 K, using a Tronac controller. 3. Results The activity coefficients, c1 13 , were determined form the following equation [1]:
n o.n o 2 3 ðpi =po Þ 1 ; J32 ¼ ð3=2Þ ðpi =po Þ 1
ð3Þ
and 1
J23 ¼ ðJ32 Þ :
ð4Þ
Here, pi refers to the carrier gas inlet pressure, po the outlet pressure, J32 po the mean column pressure, n3 the amount of liquid solvent on the column, T the column temperature, p1 the saturated vapour pressure of the solute at temperature T , t is the time elapsed from the start of the carrier gas passing through the column, p30 the partial pressure of the solvent and Uo refers to the flow rate of the carrier gas as measured at the outlet of the chromatograph column. The vapour pressure correction term C is given by C ¼ ðB11 V1 Þp1 =RT þ ð2B12 V11 ÞJ23 po =RT ;
ð5Þ
TABLE 1 The values of properties: solute virial coefficients, B11 , solute-carrier gas mixed virial coefficients, B12 , solute molar volumes, V1 and solute vapour 0 pressures, p1 at T ¼ (278.15 or 298.15) K, used in the determination of the activity coefficient, c1 13 and the solvent vapour pressure p3 Solute
T /K
3
1
p1 /Pa
V1
B12
B11
3
1
3
1
(cm Æ mol )
(cm Æ mol )
(cm Æ mol )
Pentane
278.15 298.15
)1300 )1120
24 24
114.4 117.4
30557.0 68339.5
Hexane
278.15 298.15
)1900 )1600
28 29
128.3 131.6
7859.5 20175.4
Heptane
278.15 298.15
)2700 )2200
30 31
144.0 147.5
2049.7 6087.1
Cyclopentane
278.15 298.15
)1300 )1066
18 18
91.7 93.7
14214.2 42324.2
Cyclohexane
278.15 298.15
)1750 )1550
21 21
106.5 108.7
4895.1 13033.8
Cycloheptane
278.15 298.15
)2300 )2050
24 24
121.3 123.7
921.0 2899.4
Hex-1-ene
278.15 298.15
)2034 )1746
48 50
122.5 125.8
9912.3 24791.1
Hept-1-ene
278.15 298.15
)3123 )2643
53 55
137.8 141.6
2614.3 7517.2
Hex-1-yne
278.15 298.15
)2070 )1784
46 48
109.1 116.6
5271.1 17710.0
Hept-1-yne
278.15 298.15
)3183 )2693
48 50
125.4 132.8
1312.9 5560.0
Benzene
278.15 298.15
)1600 )1400
17 18
87.3 89.4
4641.0 12688.7
M.K. Kozłowska et al. / J. Chem. Thermodynamics 36 (2004) 561–565
563
TABLE 2 The retention time at T ¼ 298:15 K for nitrogen, tG , and for the solute, hexane in the solvent furfuryl alcohol, tR ; J32 ; flow rate, Uo ; time interval, t; loading mass fraction, L and the amount of solvent on the column, n3 tG /s
tR /s
J32
107 Uo /(m3 Æ s1 )
t/min
L
n3 /mmol
15.04 16.58 16.62 16.62 16.62 16.62
39.43 43.17 42.95 41.70 41.10 40.60
0.9609 0.9701 0.9751 0.9751 0.9751 0.9751
5.47 5.47 5.60 5.60 5.60 5.60
75 67 41 157 256 296
0.1686 0.1662 0.1701 0.1701 0.1701 0.1701
3.278 3.567 3.610 3.610 3.610 3.610
where B11 is the second virial coefficient of pure solute, V1 the molar volume of the solute as liquid, V11 the partial molar volume of the solute at infinite dilution in the solvent and B12 the mixed second virial coefficient of the solute and carrier gas. As the value of V11 is not known, it has been replaced by V1 . The effect is likely to be very small. 0 The values of c1 13 and p3 were determined from equation (1) from a plot of VN expðCÞ=n3 versus Uo t=n3 . Equation (1) is a modified form of the Everett and Cruickshank equation [1,2,6] and takes into account the volatility of the solvent. In this work, as in previous work, the solute, carrier gas and solvent (stationary phase) have been designated with subscripts 1, 2 and 3, respectively. Results were collected from four columns for the work at T ¼ 278:15 K and five columns for the work at
T ¼ 298:15 K. The dead space volume was determined by injecting nitrogen into the carrier gas. The flow rates ranged from 0.50 cm3 Æ s1 to 0.57 cm3 Æ s1 and the injected volume ranged from 0.1 mm3 to 0.4 mm3 . The loading of the solvent on the chromosorb in the column, ranged from mass fraction 0.16 to mass fraction 0.18 and the amount of solvent on each column ranged from 3.2 mmol to 3.6 mmol. The values of B11 , B12 , V1 , p1 are given in table 1. A sample of the raw data obtained for one of the 22 sets of data, namely for heptane in furfuryl alcohol at T ¼ 298:15 K is given in table 2. The values of a and b together with their standard deviations, for each set of 0 results, together with the calculated values of c1 13 and p3 are given in table 3. Each set was determined from at least five points over a period of between 1 h and 5 h. The slope b was small in each set of results as a result of
TABLE 3 A summary of the results obtained for the solutes in furfuryl alcohol at T ¼ (278.15 and 298.15) K, where a is the intercept, b the slope, c1 13 the activity coefficient at infinite dilution and p30 the calculated partial pressure Solute
a/(m3 Æ mol1 )
Pentane Hexane Heptane Cyclopentane Cyclohexane Cycloheptane Hex-1-ene Hept-1-ene Hex-1-yne Hept-1-yne Benzene
2.48E ) 03 7.75E ) 03 2.22E ) 02 9.41E ) 03 2.29E ) 02 1.04E ) 01 1.19E ) 02 3.63E ) 02 4.44E ) 02 1.62E ) 01 1.38E ) 01
(9.1E ) 05) (2.7E ) 04) (2.9E ) 04) (2.0E ) 04) (3.4E ) 04) (2.5E ) 03) (3.4E ) 04) (5.1E ) 04) (9.4E ) 04) (5.1E ) 03) (3.7E ) 03)
Results measured at 278.15 K 5.92E ) 05 (5.7E ) 05) 1.45E ) 04 (1.7E ) 04) 1.77E ) 04 (1.9E ) 04) 1.10E ) 04 (1.3E ) 04) 1.42E ) 04 (2.0E ) 04) 8.13E ) 04 (1.4E ) 03) 1.69E ) 04 (2.1E ) 04) 1.74E ) 04 (2.7E ) 04) 2.82E ) 04 (5.2E ) 04) 1.46E ) 03 (2.6E ) 03) 1.16E ) 03 (2.0E ) 03)
30.5 38.0 50.9 17.3 20.7 24.1 19.5 24.3 9.88 10.9 3.62
55 43 19 27 14 18 33 11 15 21 19
Pentane Hexane Heptane Cyclopentane Cyclohexane Cycloheptane Hex-1-ene Hept-1-ene Hex-1-yne Hept-1-yne Benzene
1.46E ) 03 3.99E ) 03 1.09E ) 02 4.88E ) 03 1.24E ) 02 4.82E ) 02 6.03E ) 02 1.64E ) 02 2.31E ) 02 6.59E ) 02 6.18E ) 02
(1.0E ) 04) (2.2E ) 04) (6.7E ) 04) (2.6E ) 04) (1.1E ) 03) (5.0E ) 03) (2.3E ) 04) (1.6E ) 03) (2.7E ) 03) (3.5E ) 03) (5.8E ) 03)
Results mesured at 298.15 K 5.24E ) 05 (5.8E ) 05) 1.43E ) 04 (1.3E ) 04) 4.36E ) 04 (3.9E ) 04) 1.79E ) 04 (2.2E ) 04) 5.12E ) 04 (6.5E ) 04) 2.03E ) 03 (2.7E ) 03) 1.88E ) 04 (1.7E ) 04) 6.16E ) 04 (1.1E ) 04) 1.01E ) 03 (1.4E ) 03) 2.72E ) 03 (2.5E ) 03) 2.29E ) 03 (3.2E ) 03)
24.8 30.8 37.2 12.0 15.4 17.7 16.6 20.2 6.07 6.76 3.16
89 89 99 91 103 104 77 93 108 102 92
b
The standard deviations of the a and b values are given in brackets.
c1 13
p30 /Pa
564
M.K. Kozłowska et al. / J. Chem. Thermodynamics 36 (2004) 561–565
TABLE 4 The values of Sij1 , determined from equation (6) and H1E1 as determined from equation (7) at T ¼ 298:15 K Solute (i)
Sij1
H1E1 /(kJ Æ mol1 )
Pentane Hexane Heptane Cyclopentane Cyclohexane Cycloheptane Hex-1-ene Hept-1-ene Hex-1-yne Hept-1-yne Benzene
7.8 9.7 11.8 3.8 4.9 5.6 5.3 6.4 1.9 2.1 1.0
7.1 7.2 10.8 12.6 10.2 10.6 5.6 6.4 16.8 16.3 4.6
the low volatility of the solvent. The estimated error in c1 13 as calculated in previous work [1,4–6], is better than 4%. The activity coefficients, c1 13 , at T ¼ 298:15 K were used to calculate the selectivity factor, Sij1 [3] where 1 Sij1 ¼ c1 i3 =cj3 ;
ð6Þ
where i refers to an alkane, or an alkene, or an alkyne, or a cycloalkane and j refers to benzene. The activity coefficients were also used to determine the partial molar excess enthalpy at infinite dilution, H1E1 from 1 H1E1 ¼ R o ln c1 : 13 =oT
The results of
Sij1
and
ð7Þ H1E1
are given in table 4.
4. Discussion The large value of c1 13 for an alkane or a cycloalkane, or an alkene in furfuryl alcohol (table 3) is a reflection of the disparity in polarity between each of the solutes and the solvent. This disparity is also reflected in the large positive values of H1E1 in table 4. The large endothermic effect for those mixtures is due to the dissociation of the furfuryl alcohol on mixing. The smaller values of c1 13 for the alk-1-ynes or benzene in furfuryl alcohol reflects the competition between the attractive association of the dissimilar compounds and the dissociation of each of the polar or polarizable pure compounds. The dissociation effect is dominant and the activity coefficients are relatively small but larger than unity. These dissociation effects are also reflected in the large H1E1 values. The values of Sij1 in table 4, are relatively large and can be compared to the Sij1 value (of 12.5) for hexane and benzene in N-methyl-pyrrolidinone [1]. The latter compound is used commercially for the separation of aromatics from alkane compounds. The Sij1 values for the compounds reported in this work (table 4) indicate that furfuryl alcohol may be considered as a potential
solvent in the separation (using extractive distillation) of non-polar hydrocarbons from benzene and possibly other aromatic compounds. Activity coefficients for seven of the 11 mixtures reported here have been previously published [7,8]. A summary and a comparison of the results are reported in table 5. Our results compare favourably (within the combined experimental errors) with all the reported results, but in most cases our results are slightly lower. None of the previously reported results took account of solute vapour imperfections. These were taken into account in our work but were always less than 4% of the determined c1 13 value. The previously reported results were all measured using a pre-saturator technique. The higher results of these workers [7,8] are consistent with solvent loss from the column. We believe that our technique offers greater control over solvent loss by evaporation. The values of p30 reported in table 3 (apart from one value) are within 20 Pa of the values reported in the literature [9]: 23 Pa at T ¼ 278:15 K and 101 Pa at T ¼ 298:15 K. The method does appear capable of determining vapour pressures of low volatile organic liquids to within an order of magnitude. The activity coefficients at infinite dilution reported here are in every case, higher (by between 10% and 20%) than the results recently reported for the same solutes in furfural [4]. This is a reflection of the stronger association between the alcohol molecules (H-bonding) than between the aldehyde molecules (no H-bonding). The same explanation can be applied to the larger H1E1 values of the hydrocarbon solutes in furfuryl alcohol as compared to the values for the furfural mixtures. The Sij1 values for the mixtures reported here are of similar magnitude to the values reported for the furfural mixtures at the same temperature [4].
TABLE 5 A comparison of the c1 13 for hydrocarbon solutes in furfuryl alcohol reported here at T ¼ (278.15 and 298.15) K with the results at T ¼ (300 and 303) K taken from the literature Solute
Pentane Hexane Heptane Cyclopentane Cyclohexane Cycloheptane Hex-1-ene Hept-1-ene Hex-1-yne Hept-1-yne Benzene
c1 13 278.15 K
298.15 K
300 K [7]
303 K [8]
30.5 38.0 50.9 17.3 20.7 24.1 19.5 24.3 9.88 10.9 3.62
24.8 30.8 37.2 12.0 15.4 17.7 16.6 20.2 6.07 6.76 3.16
24 31.1 41.9
3.02 39.9
18
15.7 16.3 21.2
3.8
3.32
M.K. Kozłowska et al. / J. Chem. Thermodynamics 36 (2004) 561–565
Acknowledgements The authors thank the National Research Foundation (South Africa) and the Warsaw University of Technology for financial support including travel costs (for M.K. Kozłowska) from Poland to South Africa. The work was partly done under the auspices of a collaborative South Africa–Poland Research agreement. References [1] T.M. Letcher, P. Whitehead, J. Chem. Thermodyn. 32 (2000) 1121– 1130. [2] J.W. Bayles, T.M. Letcher, W.C. Moollan, J. Chem. Thermodyn. 25 (1993) 781–786.
565
[3] M. Krummen, T.M. Letcher, J. Gmehling, J. Chem. Eng. Data 47 (2002) 906–910. [4] T.M. Letcher, M.K. Kozłowska, U. Doma nska, J. Chem. Thermodyn. 36 (2004) 37–40. [5] T.M. Letcher, in: M.L. McGlashan (Ed.), Chemical Thermodynamics, Special Periodical Reports, vol. II, The Chemical Society, London, 1978, pp. 46–70. [6] A.J.B. Cruickshank, B.W. Gainey, C.P. Hicks, T.M. Letcher, R.W. Moody, C.L. Young, Trans. Faraday Soc. 65 (1969) 1014– 1024. [7] R.K. Kuchhal, K.L. Mallik, J. Chem. Eng. Data 17 (1972) 49–50. [8] M.N. Pultsin, A.A. Gaile, V.A. Proskuryakaw, Russ. J. Phys. Chem. (English Translation) 48 (1974) 1206–1208. [9] S. Budavari (Ed.), Merck Index Rahway, NJ, USA, 1989, p. 673.
JCT 03/178
Activity coefficients at infinite dilution for hydrocarbons in furfuryl alcohol at T ¼ (278.15 and 298.15) K, determined by g.l.c. Marta K. Kozłowska a, Trevor M. Letcher a
b,*
ska , Urszula Doman
a
Physical Chemistry Division, Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, Warsaw 00-664, Poland b School of Pure and Applied Chemistry, Natal University-Durban, Private bag X10, Dalbridge 4041, Durban, South Africa Received 18 December 2003; accepted 4 March 2004 Available online 21 April 2004
Abstract The potential of the polar solvent, furfuryl alcohol, as a solvent in the separation of aromatics from aliphatics and other hydrocarbons, has been investigated by measuring activity coefficients at infinite dilution. The activity coefficients at infinite dilution for some alkanes, cycloalkanes, alkenes, alkynes and benzene in furfuryl alcohol have been determined by g.l.c. at T ¼ (278.15 and 298.15) K. The method used is we believe, a more controlled and reliable method than the alternative pre-saturation method. The results have been used to calculate the selectivity factor and hence predict the potential for furfuryl alcohol as a solvent in separating aromatic compounds from aliphatic compounds and other hydrocarbons using extractive distillation. The results have been compared to the recently published work on a related polar solvent – furfural. The excess enthalpies of mixing at infinite dilution have also been calculated. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Activity coefficients at infinite dilution; Furfuryl alcohol; Hydrocarbons; Selectivities; Excess enthalpies of mixing at infinite dilution
1. Introduction The separation of aromatic from aliphatic compounds is important in oil refineries involved in the production of transport fuels. Highly polar solvents such as sulfolane and N-methyl-pyrrolidinone, which also have low volatility, are used to effect such separation [1]. Furfuryl alcohol (C5 H6 O2 ) is a polar solvent with a high boiling point (443.2 K) and low vapour pressure, and as a result, has the potential of being a good solvent for separating aromatic and aliphatic compounds. It is a by-product of the sugar industry, where it is made by the acid hydrolysis of bagasse, followed by oxidation. In this work, the activity coefficients at infinite dilution were determined using a g.l.c. method for moderately volatile solvents, recently reported by one of the authors [2]. These activity coefficients were used to cal*
Corresponding author. Tel.: +27-31-260-3090; fax: +27-31-2603091. E-mail address: [email protected] (T.M. Letcher). 0021-9614/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2004.03.001
culate the selectivity at infinite dilution [3] for the separation of benzene from the alkanes, cycloalkanes, alkenes and alkynes used in this work. The activity coefficients were also used to determine the partial molar excess enthalpy of mixing at infinite dilution. This property gives an indication of the type and magnitude of the interaction between each of the hydrocarbons and furfuryl alcohol. The activity coefficient results are compared to recently reported data [4] on a related set of mixtures involving hydrocarbons in furfural.
2. Experimental 2.1. Chemicals The furfuryl alcohol was supplied by Illovo Sugar Company and was distilled before use. The mass fraction purity, as analysed by g.l.c. was found to be better than 0.99. The water content of the furfuryl alcohol was always better than 0.003 mole fraction, as determined by Karl Fisher titration. The solutes used were: pentane,
562
M.K. Kozłowska et al. / J. Chem. Thermodynamics 36 (2004) 561–565
hexane, heptane, cyclopentane, cyclohexane, cycloheptane, hex-1-ene, hept-1-yne, hex-1-yne, hept-1-yne and benzene. They were all supplied by Aldrich. It was unnecessary to purify the solutes further, because of the nature of the g.l.c. experiment. 2.2. Apparatus and procedure
0 1 VN expðCÞ=n3 ¼RT =c1 13 p1 p3 =c13 p1 ðUo t=n3 Þ ¼ a bðUo t=n3 Þ;
ð1Þ
where the net solute retention volume VN is given by VN ¼ J32 Uo ðtR tG Þ;
ð2Þ
and
The g.l.c. apparatus has been described previously [4,5]. The columns used were stainless-steel tubing (4.2 mm bore; length 0.75 m to 1.5 m) with the support being silanized chromosorb (Supelco, Inc., 125 lm to 150 lm). A catharometer detector was used and the carrier gas was helium. The flow rate was maintained as constant as possible for each set of measurements on each column. This rate was measured using a calibrated soap bubble meter and the results were corrected for water vapour. The column temperature was controlled in a well-stirred waterbath, to within 0.005 K, using a Tronac controller. 3. Results The activity coefficients, c1 13 , were determined form the following equation [1]:
n o.n o 2 3 ðpi =po Þ 1 ; J32 ¼ ð3=2Þ ðpi =po Þ 1
ð3Þ
and 1
J23 ¼ ðJ32 Þ :
ð4Þ
Here, pi refers to the carrier gas inlet pressure, po the outlet pressure, J32 po the mean column pressure, n3 the amount of liquid solvent on the column, T the column temperature, p1 the saturated vapour pressure of the solute at temperature T , t is the time elapsed from the start of the carrier gas passing through the column, p30 the partial pressure of the solvent and Uo refers to the flow rate of the carrier gas as measured at the outlet of the chromatograph column. The vapour pressure correction term C is given by C ¼ ðB11 V1 Þp1 =RT þ ð2B12 V11 ÞJ23 po =RT ;
ð5Þ
TABLE 1 The values of properties: solute virial coefficients, B11 , solute-carrier gas mixed virial coefficients, B12 , solute molar volumes, V1 and solute vapour 0 pressures, p1 at T ¼ (278.15 or 298.15) K, used in the determination of the activity coefficient, c1 13 and the solvent vapour pressure p3 Solute
T /K
3
1
p1 /Pa
V1
B12
B11
3
1
3
1
(cm Æ mol )
(cm Æ mol )
(cm Æ mol )
Pentane
278.15 298.15
)1300 )1120
24 24
114.4 117.4
30557.0 68339.5
Hexane
278.15 298.15
)1900 )1600
28 29
128.3 131.6
7859.5 20175.4
Heptane
278.15 298.15
)2700 )2200
30 31
144.0 147.5
2049.7 6087.1
Cyclopentane
278.15 298.15
)1300 )1066
18 18
91.7 93.7
14214.2 42324.2
Cyclohexane
278.15 298.15
)1750 )1550
21 21
106.5 108.7
4895.1 13033.8
Cycloheptane
278.15 298.15
)2300 )2050
24 24
121.3 123.7
921.0 2899.4
Hex-1-ene
278.15 298.15
)2034 )1746
48 50
122.5 125.8
9912.3 24791.1
Hept-1-ene
278.15 298.15
)3123 )2643
53 55
137.8 141.6
2614.3 7517.2
Hex-1-yne
278.15 298.15
)2070 )1784
46 48
109.1 116.6
5271.1 17710.0
Hept-1-yne
278.15 298.15
)3183 )2693
48 50
125.4 132.8
1312.9 5560.0
Benzene
278.15 298.15
)1600 )1400
17 18
87.3 89.4
4641.0 12688.7
M.K. Kozłowska et al. / J. Chem. Thermodynamics 36 (2004) 561–565
563
TABLE 2 The retention time at T ¼ 298:15 K for nitrogen, tG , and for the solute, hexane in the solvent furfuryl alcohol, tR ; J32 ; flow rate, Uo ; time interval, t; loading mass fraction, L and the amount of solvent on the column, n3 tG /s
tR /s
J32
107 Uo /(m3 Æ s1 )
t/min
L
n3 /mmol
15.04 16.58 16.62 16.62 16.62 16.62
39.43 43.17 42.95 41.70 41.10 40.60
0.9609 0.9701 0.9751 0.9751 0.9751 0.9751
5.47 5.47 5.60 5.60 5.60 5.60
75 67 41 157 256 296
0.1686 0.1662 0.1701 0.1701 0.1701 0.1701
3.278 3.567 3.610 3.610 3.610 3.610
where B11 is the second virial coefficient of pure solute, V1 the molar volume of the solute as liquid, V11 the partial molar volume of the solute at infinite dilution in the solvent and B12 the mixed second virial coefficient of the solute and carrier gas. As the value of V11 is not known, it has been replaced by V1 . The effect is likely to be very small. 0 The values of c1 13 and p3 were determined from equation (1) from a plot of VN expðCÞ=n3 versus Uo t=n3 . Equation (1) is a modified form of the Everett and Cruickshank equation [1,2,6] and takes into account the volatility of the solvent. In this work, as in previous work, the solute, carrier gas and solvent (stationary phase) have been designated with subscripts 1, 2 and 3, respectively. Results were collected from four columns for the work at T ¼ 278:15 K and five columns for the work at
T ¼ 298:15 K. The dead space volume was determined by injecting nitrogen into the carrier gas. The flow rates ranged from 0.50 cm3 Æ s1 to 0.57 cm3 Æ s1 and the injected volume ranged from 0.1 mm3 to 0.4 mm3 . The loading of the solvent on the chromosorb in the column, ranged from mass fraction 0.16 to mass fraction 0.18 and the amount of solvent on each column ranged from 3.2 mmol to 3.6 mmol. The values of B11 , B12 , V1 , p1 are given in table 1. A sample of the raw data obtained for one of the 22 sets of data, namely for heptane in furfuryl alcohol at T ¼ 298:15 K is given in table 2. The values of a and b together with their standard deviations, for each set of 0 results, together with the calculated values of c1 13 and p3 are given in table 3. Each set was determined from at least five points over a period of between 1 h and 5 h. The slope b was small in each set of results as a result of
TABLE 3 A summary of the results obtained for the solutes in furfuryl alcohol at T ¼ (278.15 and 298.15) K, where a is the intercept, b the slope, c1 13 the activity coefficient at infinite dilution and p30 the calculated partial pressure Solute
a/(m3 Æ mol1 )
Pentane Hexane Heptane Cyclopentane Cyclohexane Cycloheptane Hex-1-ene Hept-1-ene Hex-1-yne Hept-1-yne Benzene
2.48E ) 03 7.75E ) 03 2.22E ) 02 9.41E ) 03 2.29E ) 02 1.04E ) 01 1.19E ) 02 3.63E ) 02 4.44E ) 02 1.62E ) 01 1.38E ) 01
(9.1E ) 05) (2.7E ) 04) (2.9E ) 04) (2.0E ) 04) (3.4E ) 04) (2.5E ) 03) (3.4E ) 04) (5.1E ) 04) (9.4E ) 04) (5.1E ) 03) (3.7E ) 03)
Results measured at 278.15 K 5.92E ) 05 (5.7E ) 05) 1.45E ) 04 (1.7E ) 04) 1.77E ) 04 (1.9E ) 04) 1.10E ) 04 (1.3E ) 04) 1.42E ) 04 (2.0E ) 04) 8.13E ) 04 (1.4E ) 03) 1.69E ) 04 (2.1E ) 04) 1.74E ) 04 (2.7E ) 04) 2.82E ) 04 (5.2E ) 04) 1.46E ) 03 (2.6E ) 03) 1.16E ) 03 (2.0E ) 03)
30.5 38.0 50.9 17.3 20.7 24.1 19.5 24.3 9.88 10.9 3.62
55 43 19 27 14 18 33 11 15 21 19
Pentane Hexane Heptane Cyclopentane Cyclohexane Cycloheptane Hex-1-ene Hept-1-ene Hex-1-yne Hept-1-yne Benzene
1.46E ) 03 3.99E ) 03 1.09E ) 02 4.88E ) 03 1.24E ) 02 4.82E ) 02 6.03E ) 02 1.64E ) 02 2.31E ) 02 6.59E ) 02 6.18E ) 02
(1.0E ) 04) (2.2E ) 04) (6.7E ) 04) (2.6E ) 04) (1.1E ) 03) (5.0E ) 03) (2.3E ) 04) (1.6E ) 03) (2.7E ) 03) (3.5E ) 03) (5.8E ) 03)
Results mesured at 298.15 K 5.24E ) 05 (5.8E ) 05) 1.43E ) 04 (1.3E ) 04) 4.36E ) 04 (3.9E ) 04) 1.79E ) 04 (2.2E ) 04) 5.12E ) 04 (6.5E ) 04) 2.03E ) 03 (2.7E ) 03) 1.88E ) 04 (1.7E ) 04) 6.16E ) 04 (1.1E ) 04) 1.01E ) 03 (1.4E ) 03) 2.72E ) 03 (2.5E ) 03) 2.29E ) 03 (3.2E ) 03)
24.8 30.8 37.2 12.0 15.4 17.7 16.6 20.2 6.07 6.76 3.16
89 89 99 91 103 104 77 93 108 102 92
b
The standard deviations of the a and b values are given in brackets.
c1 13
p30 /Pa
564
M.K. Kozłowska et al. / J. Chem. Thermodynamics 36 (2004) 561–565
TABLE 4 The values of Sij1 , determined from equation (6) and H1E1 as determined from equation (7) at T ¼ 298:15 K Solute (i)
Sij1
H1E1 /(kJ Æ mol1 )
Pentane Hexane Heptane Cyclopentane Cyclohexane Cycloheptane Hex-1-ene Hept-1-ene Hex-1-yne Hept-1-yne Benzene
7.8 9.7 11.8 3.8 4.9 5.6 5.3 6.4 1.9 2.1 1.0
7.1 7.2 10.8 12.6 10.2 10.6 5.6 6.4 16.8 16.3 4.6
the low volatility of the solvent. The estimated error in c1 13 as calculated in previous work [1,4–6], is better than 4%. The activity coefficients, c1 13 , at T ¼ 298:15 K were used to calculate the selectivity factor, Sij1 [3] where 1 Sij1 ¼ c1 i3 =cj3 ;
ð6Þ
where i refers to an alkane, or an alkene, or an alkyne, or a cycloalkane and j refers to benzene. The activity coefficients were also used to determine the partial molar excess enthalpy at infinite dilution, H1E1 from 1 H1E1 ¼ R o ln c1 : 13 =oT
The results of
Sij1
and
ð7Þ H1E1
are given in table 4.
4. Discussion The large value of c1 13 for an alkane or a cycloalkane, or an alkene in furfuryl alcohol (table 3) is a reflection of the disparity in polarity between each of the solutes and the solvent. This disparity is also reflected in the large positive values of H1E1 in table 4. The large endothermic effect for those mixtures is due to the dissociation of the furfuryl alcohol on mixing. The smaller values of c1 13 for the alk-1-ynes or benzene in furfuryl alcohol reflects the competition between the attractive association of the dissimilar compounds and the dissociation of each of the polar or polarizable pure compounds. The dissociation effect is dominant and the activity coefficients are relatively small but larger than unity. These dissociation effects are also reflected in the large H1E1 values. The values of Sij1 in table 4, are relatively large and can be compared to the Sij1 value (of 12.5) for hexane and benzene in N-methyl-pyrrolidinone [1]. The latter compound is used commercially for the separation of aromatics from alkane compounds. The Sij1 values for the compounds reported in this work (table 4) indicate that furfuryl alcohol may be considered as a potential
solvent in the separation (using extractive distillation) of non-polar hydrocarbons from benzene and possibly other aromatic compounds. Activity coefficients for seven of the 11 mixtures reported here have been previously published [7,8]. A summary and a comparison of the results are reported in table 5. Our results compare favourably (within the combined experimental errors) with all the reported results, but in most cases our results are slightly lower. None of the previously reported results took account of solute vapour imperfections. These were taken into account in our work but were always less than 4% of the determined c1 13 value. The previously reported results were all measured using a pre-saturator technique. The higher results of these workers [7,8] are consistent with solvent loss from the column. We believe that our technique offers greater control over solvent loss by evaporation. The values of p30 reported in table 3 (apart from one value) are within 20 Pa of the values reported in the literature [9]: 23 Pa at T ¼ 278:15 K and 101 Pa at T ¼ 298:15 K. The method does appear capable of determining vapour pressures of low volatile organic liquids to within an order of magnitude. The activity coefficients at infinite dilution reported here are in every case, higher (by between 10% and 20%) than the results recently reported for the same solutes in furfural [4]. This is a reflection of the stronger association between the alcohol molecules (H-bonding) than between the aldehyde molecules (no H-bonding). The same explanation can be applied to the larger H1E1 values of the hydrocarbon solutes in furfuryl alcohol as compared to the values for the furfural mixtures. The Sij1 values for the mixtures reported here are of similar magnitude to the values reported for the furfural mixtures at the same temperature [4].
TABLE 5 A comparison of the c1 13 for hydrocarbon solutes in furfuryl alcohol reported here at T ¼ (278.15 and 298.15) K with the results at T ¼ (300 and 303) K taken from the literature Solute
Pentane Hexane Heptane Cyclopentane Cyclohexane Cycloheptane Hex-1-ene Hept-1-ene Hex-1-yne Hept-1-yne Benzene
c1 13 278.15 K
298.15 K
300 K [7]
303 K [8]
30.5 38.0 50.9 17.3 20.7 24.1 19.5 24.3 9.88 10.9 3.62
24.8 30.8 37.2 12.0 15.4 17.7 16.6 20.2 6.07 6.76 3.16
24 31.1 41.9
3.02 39.9
18
15.7 16.3 21.2
3.8
3.32
M.K. Kozłowska et al. / J. Chem. Thermodynamics 36 (2004) 561–565
Acknowledgements The authors thank the National Research Foundation (South Africa) and the Warsaw University of Technology for financial support including travel costs (for M.K. Kozłowska) from Poland to South Africa. The work was partly done under the auspices of a collaborative South Africa–Poland Research agreement. References [1] T.M. Letcher, P. Whitehead, J. Chem. Thermodyn. 32 (2000) 1121– 1130. [2] J.W. Bayles, T.M. Letcher, W.C. Moollan, J. Chem. Thermodyn. 25 (1993) 781–786.
565
[3] M. Krummen, T.M. Letcher, J. Gmehling, J. Chem. Eng. Data 47 (2002) 906–910. [4] T.M. Letcher, M.K. Kozłowska, U. Doma nska, J. Chem. Thermodyn. 36 (2004) 37–40. [5] T.M. Letcher, in: M.L. McGlashan (Ed.), Chemical Thermodynamics, Special Periodical Reports, vol. II, The Chemical Society, London, 1978, pp. 46–70. [6] A.J.B. Cruickshank, B.W. Gainey, C.P. Hicks, T.M. Letcher, R.W. Moody, C.L. Young, Trans. Faraday Soc. 65 (1969) 1014– 1024. [7] R.K. Kuchhal, K.L. Mallik, J. Chem. Eng. Data 17 (1972) 49–50. [8] M.N. Pultsin, A.A. Gaile, V.A. Proskuryakaw, Russ. J. Phys. Chem. (English Translation) 48 (1974) 1206–1208. [9] S. Budavari (Ed.), Merck Index Rahway, NJ, USA, 1989, p. 673.
JCT 03/178