Ind. Eng. Chem. Process Des. Dev. 1983,22,676-678
676
and may prove amenable to a group contribution approach. I t is accurate, simple to use, and, once the binary coefficients have been obtained, requires no iterations in the calculations. Acknowledgment Part of this work was carried out under grant number CpE 810 4201 from the National science Foundation. Literature Cited Chueh, P. L.; Prausnitz, J. M. A I C M J . 1987, 13, 1107. Cote. H. M.; Thodos, G. J . Chem. Eng. Data 1982, 7 , 82. Etter, D. 0.: Kay, W. B. J . Chem. Eng. Data 1981, 6, 409.
Grieves, R. 6.; Thodos. 0. AIChE J . 1982, 8 , 550.
~ ~ ~ , n " p : ; " ; ~ ~ J,&' ~ 5~9"~$;~~8g. , i i ~ . A ~ ~ ~ ~ ~ ,
Mehra, v. s.;T w o s , G. J . C h m . ~ n gDate . 1983, 8 . I. Mehra, V. S.;Thodos, G. J . Chem. €ng. Date 1988. 13, 155. Mlchelsen, M. L. F/uH Phase €9u//i6. 1980, 4, 1. Ng, H. J.; Robinson, D. 6. Leu, A. D. Paper presented at the 9Gth National A I C M Meeting, Houston, TX, April 1481. Peng, D.; Robinson, D. 6. AI(%€ J . 1977, 2 3 , 137. Rm, T. J.; Meson, D. F.; Thodos, G. J . €47.Data 1959, 4 , 201. Teja, A. S.;Rowlinson, J. S. Chem. €ng. Scl. 1979, 28, 529. Wllson, G. M. J . Am. Chem. SOC. 1884, 86, 127.
Received for review September 7, 1982 Accepted March 17, 1983
COMMUNICATIONS Vapor-Liquid Equttibria by UNIFAC Group Contribution. Revision and Extension. 3
Revised UNIFAC interaction parameters are presented for the alkene and chloro-alkene groups. Interaction parameters are ako given for a flexible ester group which, for example, may be used for acrylates and benzoates.
Introduction The UNIFAC group contribution method is applied to the prediction of liquid-phase activity coefficients in nonelectrolyte nonpolymeric mixtures at low to moderate pressures and temperatures between 300 and 425 K. The parameters needed for the use of UNIFAC are group volumes (Ilk),group surface areas ( Q k ) , and group interaction parameters (amnand anm).Extensive tables with revised and updated values for these parameters for 40 commonly applicable groups have recently been presented by Gmehling et al. (1982), and parameters for silicone groups have been published by Herskowitz and Gottlieb (1981). It is the aim of this short paper (1)to report on the revision of the interaction parameters for the alkene (M) and the chloro (ClCC) groups and (2) to extend the range of applicability of the UNIFAC method by introducing an extra ester group (COO). The paper will thus serve as a supplement and correction to the paper by Gmehling et al. (1982). Revision of C=C a n d ClCC Parameters Reliable vapopliquid equilibrium data for alkane-alkene mixtures are scarce. The interaction parameters between the alkane (CH2) and the alkene (C=C) groups have therefore been estimated by Gmehling et al. (1982) from a very small data base containing mixtures with monoolefins only. The estimated parameters have for some systems, e.g., those containing 1,3-butadiene with aliphatic hydrocarbons, given rise to quite erroneous predictions of activity coefficients. The activity coefficient of hexane at infinite dilution in lB-butadiene at 300 K is thus predicted as 2.59 X Many and reliable infinite dilution activity coefficients for alkane-alkene systems in the temperature range 305 to 354 K have been measured by Alessi et al. (1982). It was therefore decided to use these data for reestimating the alkane-alkene interaction parameters. The revised
parameters are shown in Table I, which also shows all other group interaction parameters involving the alkene group. All these parameters (except for CS2) have been revised since they are based on the alkane-alkene interaction parameters. It has also been necessary to reestimate interaction parameters for the ClCC group which is a chloro group connected to an alkene group. These parameters are also shown in Table I. It is strongly recommended to use the revised parameters in Table I instead of the parameters presented by Gmehling et al. (1982). Figures 1 and 2 show the predicted vapor-liquid equilibria for l-hexene-ethyl acetate at 333.15 K and for acetonitrile-trichloroethylene at 101.6 kPa. Extra Ester Group The usual ester group is defined as a rather large group (CCOO) consisting of a COO group plus a neighboring CHB or CH2 group. This means that the group is not very flexible. It is only possible to predict activity coefficients for mixtures containing esters of acetic, propanoic, and related acids or derivatives of these. The UNIFAC method fails, for example, for mixtures containing acrylates. Previous attempts (Maaloe, 1979) to define the ester group as a COO group alone showed that the attainable fit to experimental vapor-liquid equilibrium data was not as good as with the large CCOO group. The group volumes (Rk) and surface areas ( Q k ) are in the UNIFAC method normally calculated via a normalization of van der Waals volumes and surface areas. By treating Rcoo and QCm as parameters which are estimated simultaneously with the interaction parameters acoolx and axlcoO it has been possible to obtain acceptable results with a COO group. Table I1 shows the estimated parameters. The application of the COO group can only be recommended when it is impossible to use the CCOO group, for example for acrylates or benzoates. Figures 3 and 4 show predictions with the new COO group for methanol-methyl acrylate at 101.3 kPa and for acetone-
0196-4305/83/1 122-0676$01.50/0 0 1983 American Chemical Society
Ind. Eng. Chem. Process Des. Dev., Vol. 22, No. 4, 1983
Table I. Revised UNIFAC G r o w Interaction Parameters
X 1 2 3 3 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 a
CH, C=e ACH ACCH, OH CH,OH HlO ACOH CH,CO CHO
"c=c/x
UX/C=C
UX/ClCC
86.02
-35.36 -4.189 00.00 -66.46 00.00 38.81 -259.1 3.446 74.15 n.a. -113.6 457.0 524.1 225.8 33.47 -12.52 787.6 n.a. 270.6 496.1 526.1 n.a. 217.5 -34.57 182.6 42.92 n.a. n.a. n.a.a -83.30 37.85 ccoo 132.1 449.1 n.a. HCOO -62.55 214.5 240.2 CH,O 26.51 240.9 n.a. CNH, 1.163 163.9 n.a. CNH -28.70 61.11 n.a. -25.38 (C) 3N n.a. n.a. ACNH, n.a. n.a. n.a. pyridine n.a. CCN -40.62 336.9 3.509 COOH 318.9 -11.16 1264.0 204.6 cc1 -245.4 97.51 n.a. 5.892 CCl , 18.25 111.2 -13.99 51.06 CCl, 187.1 -109.7 CCl, 160.9 n.a. ACCl 393.1 -158.8 10.76 CNO, 357.5 -1.996 n.a. n.a. n.a. ACNO, -47.37 76.30 16.62 CS, n.a. n.a. n.a. CH,SH n.a. furfural n.a. n.a. n.a. n.a. n.a. DOH I n.a. n.a. n.a. n.a. n.a. Br n.a. n.a. 31.14 C& 41.38 n.a. -137.4 Me,SO 422.4 9.a. n.a. ACRY n.a. -66.46 ou.00 ClCC 124.2 n.a. n.a. n.a. ACF -70.45 n.a. DMF 249.0 n.a. n.a. n.a. CF, ma., not available.
aclcclx 47.41 124.2 395.8 n.a. 738.9 528.0 n.a. ma. -40.90 n.a. 16.99 n.a. -217.9 n.a. n.a. n.a. n.a. n.a. 304.0 898.2 428.5 n.a. -149.8 -134.2 n.a. 379.4 n.a. 167.9 n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. 00.00 n.a. n.a. n.a.
677
Table 11. UNIFAC Parameters for the Ester Group: COO; Rcoo = 1.38; Qcoo = 1.20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
18 19 20 21 22 23 24 25 26 27 28 29 30
X CH.
c=e
ACH ACCH, OH CH,OH H,O ACOH CH,CO CHO
ccoo
HCOO CH,O CNH, CNH (C)3N ACNH, pyridine CCN COOH CCl
cc1,
CCl, CCl, ACCl CNO, ACNO, CS, CH,SH furfural 31 DOH 32 I 3 3 Br 34 c-c 35 Me,SO 36 ACRY 37 ClCC 38 ACF 39 DMF 40 CF, 4 1 COO
ax/coo
%oo/x
387.1 48.33 103.5 69.26 190.3 165.7 -197.5 -494.2 -18.80 n.a. a 560.2 -70.24 417.0 n.a. -38.77 n.a. n.a. n.a. 120.3 -337.0 n.a. -96.87 255.8 256.5 -145.1 n.a. n.a. 469.8 n.a. n.a. ma. 68.55 n.a. n.a. 153.7 423.4 730.8 n.a. n.a. n.a. 0.0
529.0. 1397.0 317.6 615.8 88.63 171.0 284.4 -167.3 123.4 n.a. -234.9 65.37 -247.8 n.a. 284.5 n.a. n.a. n.a. -61.60 1179.0 n.a. 305.4 -193.0 335.7 1107.0 n.a. n.a. 885.5 n.a. n.a. n.a. 288.1 n.a. n.a. -29.34 -53.91 -198.0 n.a. n.a. n.a. 0.0 ~~
ma., not available.
00 00
02
OL
08
06
10
x1
Figure 1. Experimental and predicted x-y diagram for 1-hexene (1)-ethyl acetate (2) at 333.15 K.
X1
Figure 3. Experimental and predicted x-y diagram for acetone (1)-methyl methacrylate (2) at 101.3 kPa.
methyl methacrylate at 101.3 kPa. The agreement between the predicted and experimental values in Figures 3 and 4 is typical for predictions with the new COO group.
Figure. 2. Experimental and predicted x-y diagram for acetonitrile (1)-trichloroethylene (2) at 101.6 kPa.
Conclusion New UNIFAC parameters for interaction with C=C and ClCC groups have been presented. It is recommended that these parameters substitute the parameters published by Gmehling et al. (1982). Parameters for a flexible ester group (COO) are presented. The new COO group should only be used when it is not possible to use the CCOO group.
Ind. Eng. Chem. Process Des. D ~ v1083, . 22, 678-681
678
votan)-Lisboa, for support of the UNIFAC project. Literature Cited Alessi, P.; Klklc, I.; Fredenslund, Aa.; Rasmussen, P. Can. J . Chem . Eng . 1082, 60, 300. Gmehling, J.; Rasmussen, P.; Fredenslund, Aa. Ind. Ens. Chem. Process D e s . b e v . lg82, 27, 118. Herskowltz, M.; Gomleb, M. Ind. Eng. Chem. Process D e s . D e v . 1981, 20, 407.
Maahe, 8. MSc. Thesis, Instltuttet for Kemlteknik, The Technical University of Denmark, Lyngby, Denmark, 1979.
02
00
OL
06x
OB
Figure 4.
10
Experimental and predicted x-y diagram (1)-methyl acrylate (2) a t 101.3 kPa.
for methanol
Acknowledgment The authors thank Professors Aa. Fredenalund and U. Onken for their strong interest in this work. The authors are grateful to Arbeitsgemeinschaft Industrieller Forschungsvereinigungen (AIF), the Danish Statens teknisk videnskabelige Forshingsrad, NATO, and Junta Nacional De Investigacdo Cientifica e Tecnologica (Comissdo In-
Faculdade de Engenharia Universidade do Porto 4099 Porto, Portugal Lehrstuhl Technische Chemie B University of Dortmund 46 Dortmund 50, West Germany Instituttet for Kemiteknik The Technical University of Denmark DK-2800 Lyngby, Denmark
Eugenia Almeida Macedo Ulrich Weidlich Jurgen Gmehling*
Peter Rasmussen
Received for reuiew August 13, 1982 Accepted F e b r u a r y 18, 1983
An Explanatlon for Deviations of Flscher-Tropsch Products from a Schuiz-Flory Dlstrlbution An explanation is proposed for the deviations of Fischer-Tropsch products from a Schulz-Flory distribution. The analysis presented here is for a skny reactor configuration, but it can be extended to explain observations reported with fixed bed reactors as well. I t is shown that negative deviations from a Schulz-Flory distribution are due to transient holdup of higher molecular weight products in the oil phase Surrounding the catalyst. Guidelines are proposed for minimizing these deviations and for obtaining product distributions characteristic of the catalyst.
Introduction A number of studies have shown that the products obtained during Fischer-Tropsch synthesis follows a Schulz-Flory distribution (viz., Henrici-OlivB and OlivB, 1976; Madon, 1979; KeUner and Bell,1981; Satterfield and Huff, 1982). Two representations for this type of distribution are given by Wn - (1 + span-1 _
(1)
r n / r l = a"-l
(2)
n
Here, n is the number of carbon atoms in the product, w, is the weight fraction of products containing n carbon atoms, P , is the rate of production of products containing n carbon atoms, and ct is the probability of chain growth. When the logarithm of w,/n or rn/rl is plotted vs. n, a straight line is obtained. It has recently been noted by several authors that products containing ten or more carbon atoms are often present in amounts lower than would be predicted from a Schulz-Flory distribution determined on the basis of the observed distribution of C1 through Clo products. Henrici-0liv6 and Olive (1976) have suggested that such deviations are due to cracking of higher molecular weight products and/or to underestimation of the quantities of these products due to difficulties in their analysis by gas chromatography. The latter possibility has also been proposed by Satterfield and Huff (1982) to explain the 0196-43051a311 122-oe7a$oi .501o
negative deviations from a Schulz-Flory distribution observed during synthesis over an iron catalyst contained in a well-stirred slurry reactor. In a subsequent publication, Satterfield et al. (1982) suggested that the observed discrepancy might be due to the accumulation of the higher molecular weight products in the oil used to suspend the catalyst. Pannell et al. (1982) have also reported negative deviations from the Schulz-Flory distribution during Fischer-Tropsch synthesis over iron, cobalt, and ruthenium catalysts conducted in a Berty reactor. Quite interestingly, the magnitude of the deviation was found t o decrease with increasing time on stream but was still noticeable for Cm products even after 10 days of continuous operation. Similar observations have been made by the present authors in the course of their investigation of Fischer-Tropsch synthesis over a fused iron catalyst in a well-stirred slurry reactor. The purpose of the present note is to propose a quantitative interpretation for the deviations from the Schulz-Flory distribution noted above. This analysis has been carried out for a slurry reactor configuration but can be extended to explain the observations reported with fured bed reactors as well. The results of this study show that negative deviations from a Schulz-Flory distribution are due to a transient holdup of higher molecular weight products in the oil phase surrounding the catalyst. Guidelines are proposed for minimizing these deviations and for obtaining product distributions characteristic of the true performance of the catalyst studied. 0 1983 American Chemical Society
