Vapour-liquid equilibria in the ternary mixtures N2CH4C3H8 and CH4C2H6C3H8

Vapour-liquid equilibria in the ternary mixtures Nz-CH4-C3H8 and CH4-CzH6-C3H8 G. Trappehl and H. Knapp Institute of Thermodynamics and Plant Design, Technical University of Berlin-West, Strasse des 17. Juni 135, D-1000 Berlin 12, FRG

Received 21 August 1987 A systematic study has been performed with mixtures consisting of N 2, CH 4, C2H 6 and C3H 8 to investigate experimentally phase equilibria and caloric properties and to test the accuracy of thermodynamic correlations. This Paper reports more results of T-p-x-y measurements on ternary systems in the range 20 < p < 120 bar and T = 200 K. The results are compared with data calculated by generalized equations of state.

Keywords: phase equilibria; nitrogen; hydrocarbons

Computer program packages for process design or simulation often include generalized equations of state (GEQS) useful for the calculation of thermodynamic properties. Therefore, considerable effort is spent in the attempt to improve the accuracy of equations of state (EQS) describing the p - v - T - x behaviour of mixtures. Progress and test of the equations must be based on accurate experimental p-v-T-x, h - T - p - x or vapour-liquid equilibria (VLE) data. In the high pressure low temperature apparatus (described in Reference 1), T - p - x - y measurements were made on two ternary systems. A review of this experimental work and of published VLE data is given in Table 1.

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A series of isothermal and isobaric measurements is carried out beginning with the binary mixture (1 + 2). Then component 3 is added until binary (2+ 3) is approached or until the system becomes supercritical. For measurements beginning with the binary mixture (2 + 3) the apparatus must be evacuated and filled again.

Experimental results The results for ternary mixtures are illustrated in the triangular 3 component diagrams and in the K - x diagrams for three typical cases shown in Figures 1, 2 and 3. The results are listed completely in Tables A1 A6.

Comparison of experiment and correlation Figures 1 3 and the tables in the Appendix also present the results of calculations with GEQS. For high pressures and for mixtures containing supercritical components it is possible and practical to use p - v - T - x information 0011-2275/88/060398-08 $03.00 ~.'~ 1988 Butterworth & Co (Publishers) Ltd

398

Cryogenics 1988 Vol 28 June

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Figure 2 N 2 CH4-C3H 8 system at 200 K and 120 bar. (a) O, Vapour; V , liquid. (b) . Calculated by EQS LKP; experimental points: D, N2; [], CH4; [], C3H8

Figure 3 C H 4 C 2 H 6 - C 3 H 8 system at 2 0 0 K and 2 0 bar. (a) O , Vapour; V , liquid. (b) . Calculated by EQS RKS; experimental points: El, CH4; [~, C2H6; I], C3H8

presented by EQS for the calculation of the conditions in multicomponent-multiphase systems. In thermodynamic equilibrium, the fugacity, f~, of each component i is equal in all coexisting phases, for example, in both vapour, V, and liquid, L

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Table 1

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Experimental VLE data for systems containing N 2, CH 4, C2H 6 or C3H 8 (review of published data and this work)

System N 2 CH 4 C3H 8 CH 4 C2H 6 C3H 8

Tmin Tmax (K)

Pmin Pmax (bar)

Experimental points

Reference

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Poon etal. 2 This work a Price 3 Wichterle et al. 4 Parikh et al. 5 This work b

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aSee Figures 1 and 2 and Tables A I A 4 bSee Figure 3 and Tables A 5 and A 6

Cryogenics 1988 Vol 28 June

399

Vapour-liquid equilibria in ternary mixtures: G. Trappehl and H. Knapp Lee-Kesler-P1/Scker 1° (LKP). Therefore, the experimental data are compared with results calculated with these GEQS. The pure component parameters M, T~, Pc, vc and co and the binary K o values were taken from Reference 11.

work was done with the assistance of M. Behne (student helper), L. Kroll (mechanic) and C. Eichenauer (technician).

Summary

References

Experimental VLE data are presented in figures and tables for two ternary mixtures N 2 - C H 4 - C a H s and C H 4 - C 2 H 6 - C 3 H s . The experimental results are cornred with results obtained by thermodynamic calculations based on three recommended GEQS.

Acknowledgements The authors are grateful to Deutsche Forschungsgemeinschaft, (DFG) for financial support. The experimental

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Cryogenics 1988 Vol 28 June

1 Trappehl, G. and Knapp, H. Cryogenics (1987) 27 696--716 2 Pooh, D.P.L and Lu, B.C.-Y. Adv Cryog Eng (1974) 7 106 3 Price,A.R. Thesis Rice Institute, Houston, USA (1957) 4 Wiehterle, l. andKobayashi, R. JChemEngData(1972) 171,4,13 5 Parikh, J.S., Bukacek, R.F., Grahm, L. and Leipziger, S. J Chem Eng Data (1984) 29 301-303 6 Redlich,O. and Kwong,J.N.S. Chem Rev (1949) 44 233 7 Sonve,G. Chem Ing Sci (1972) 27 1197 8 Peng,D.Y. and Robinson, D.B. lnd Eng Chem Fundam 1976) 15 59 9 PI6cker, U., Knapp, H. and Pransnitz, J.M. lnd Eng Chem Process Des Dev (1978) 17 324

10 Knapp, H., D6ring, R., Oellrieh, L., Pliicker, U. and Prausnitz, J.M. Dechema Chem Data Ser Vol b, Part 1 {1982)

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