Chemical Engineering Science, Vol. 42, No. 12, pp. 2935-2940, 1987. 0009-2509187 $3.00 + 0.00 Printed in Great Britain. Pergamon Journals Ltd. zyxwvu APPLICATION OF A NEW CUBIC EQUATION OF STATE TO HYDROGEN SULFIDE MIXTURES JOSE 0. VALDERRAMAT and S. OBAID-UR-REHMAN Chemical Engineering Department, King Fahd University of Petroleum &c Minerals, Dhahran 31261, Saudi Arabia and LUIS A. CISTERNAS Departamento de Ingenieria Quimica, Universidad de1 Norte, Casilla 1280 Antofagasta, Chile zyxwvutsrqponml (Received 19 October 1986, accepted zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIH for publication 8 April 1987) Abstract-A cubic equation of state (EOS) recently proposed by the authors has been applied to the calculation of VLE of H&containing systems. Mixtures of HIS + hydrocarbons have been systematically studied and correlations for the interaction parameter are proposed. Comparison with other four well known EOS has been done. Other miscellaneous HzS systems have been also analysed. It is concluded that the new equation performs better than other cubic equations for the systems considered here. INTRODUCTION Hydrogen sulfide is frequently found in many natural gases and crude oils. In the production and processing of these materials a detailed knowledge of the phase behavior of H,S with the various hydrocarbons be- comes necessary. Also, H2S is one of the most common nonhydro- carbon components found in fuel mixtures derived from heavy oils or coal. Therefore, good methods used for calculating properties or phase equilibria of these mixtures should be capable of representing the com- plex behavior caused by the presence of H,S. Whenever EOS or generalized methods are used to predict phase equilibria, interaction parameters are required. Of special need are the interactions between H2S and hydrocarbons. Many VLE data on H2P systems have been published, but no systematic analy- ses of H,S-hydrocarbon mixtures have been done. In a recent publication (referred to as I, hereafter) we have proposed a modified version of Pate1 and Teja’s equation of state (Teja and Patel, 1981; Pate1 and Teja, 1982) to be applied in generalized form to polar fluids and their mixtures. In the proposed equation, hereafter referred to as the VC equation, the force constant ‘a’ is expressed in terms of the reduced temperature and the critical compressibility factor. This instead of the acentric factor which other cubic equations of state use (such as the Patel-Teja equation itself). The modified EOS has been applied to predict PVT behavior of pure fluids and their mixtures. As stated in I, for non-polar fluids (mostly hydrocarbons) no major differences were found between the VC equation and the original of Pate1 and Teja (PT) or others such as Peng-Robinson (PR; Peng and Robinson, 1976), Soave-Redlich- Kwong (SRK; Soave, 1972) and Soave-van der Waals ‘Author to whom correspondence should be addressed. (SVDW; Soave, 1984). However, for polar fluids and mixtures containing polar fluids, great improvements were found using the VC equation. The study presented here is an application of the VC equation to H2S-containing mixtures. Also, the other cubic equations mentioned above (PR, SRK, SVDW and PT) have been applied to these mixtures for comparison and discussion. Binary interaction par- ameters have been calculated and correlations in terms of the reduced temperature are proposed for H,S-hydrocarbon systems. DEVELOPMENT OF EQUATIONS Valderrama and Cisternas’s equations are as fol1ows: Equation of state RT p=-- a V-b V( V+b)+c( V-b)’ (1) Force constant a = a( T,)a( T,, 2,) a( TC) = Q,R2Tz/PC (2) a( TR, 2,) = [I +F(l- ,/T,)l’ F = - 6.608 + 70.43 zC - 159.0 z,’ Q, = 0.69368 - 1.06344 z, + 0.68290 2,’ - 0.21044 zc3 + 0.003753 z,‘. Volume constants b = b( T,) = Q, RT,/P, c = c( T,) = S& RT, PC Q, = 0.025987 + 0.180755 z, + 0.061259 zf R, = 0.57750 - 1.89841 ZC. (3) 2935