Fluid Phase Equilibria 320 (2012) 11–25 Contents lists available at SciVerse ScienceDirect Fluid Phase Equilibria j our na l ho me page: www.elsevier.com/locate/fluid Correlation to predict solubility of hydrogen and carbon monoxide in heavy paraffins Seethamraju Srinivas a , Randall P. Field a,∗ , Suphat Watanasiri b , Howard J. Herzog a a MIT Energy Initiative, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA b Aspen Technology Inc., 200 Wheeler Rd., Burlington, MA 01803, USA a r t i c l e i n f o Article history: Received 26 October 2011 Received in revised form 9 February 2012 Accepted 10 February 2012 Available online 18 February 2012 Keywords: Modeling Solubility Hydrocracker Fischer–Tropsch synthesis Peng–Robinson equation of state a b s t r a c t The Fischer–Tropsch (FT) reactor and hydrocracker, which are important elements of a synthetic liq- uid fuel process, are multi-phase reactors having gas–solid–liquid reactions involving H 2 and/or CO. To predict the reactor performance, it is therefore important for simulation models used in the techno- economic or feasibility studies of such processes to accurately capture the solubility of H 2 and CO in the reactant–product mixture. This poses challenges in terms of the asymmetric nature of the mixture and accurate characterization of the components involved. Using solubility experimental data and validated component characterization equations from literature, correlations to determine the Peng–Robinson binary interaction parameters and hence, predict the solubility of H 2 and CO are presented. These binary interaction parameter correlations are expressed as a function of the solvent carbon number and tem- perature. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Processes for conversion of low-value feed stocks like coal, biomass, residual oil, etc., into liquid fuels are gaining renewed interest in the current energy situation. The indirect liquefaction process involving Fischer–Tropsch (FT) synthesis converts these raw materials into synthetic liquid fuels via gasification. FT syn- thesis is a heterogeneous catalytic process that converts syngas (a mixture of CO and H 2 ) predominantly to n-paraffins as represented in (1). nCO + (2n + 1)H 2 → C n H 2n+2 + nH 2 O (1) This polymerization reaction can generate a product distribution with the carbon number (n) varying from 1 to 70, or more. The FT raw product mixture is quite asymmetric in nature with respect to the size and the nature of the components present with com- ponents ranging from light gas (H 2 , CO, etc.) to heavy paraffins. Such a mixture provides challenges in obtaining phase equilibrium experimental data and in predicting phase behavior from existing thermodynamic models. This motivates us to derive a correlation to predict the solubility of H 2 and CO in the heavy paraffin sol- vents with an extrapolative capability. After a short review on the importance of solubility, a discussion on the property methods con- sidered with some comments on water-handling is presented. It ∗ Corresponding author. Tel.: +1 617 324 2391. E-mail address: rpfield@mit.edu (R.P. Field). then addresses the issue of estimation of critical parameters and their role in solubility prediction. The methodology used in arriv- ing at the binary interaction parameters which in turn are used to develop the solubility correlation is described later. The final sections present the results and their validation. Investigations by different researchers on Fischer–Tropsch syn- thesis in slurry reactors led to the conclusion that solubility of syngas components (H 2 and CO) is needed in understanding the reaction rate and selectivity since solubility plays a role in the synthesis chemistry (e.g., Satterfield and Stenger [1]) as well as the hydrodynamics (e.g., Quicker and Deckwer [2]). The solubil- ity information is also valuable in the design and operation of the reactors. Caldwell and van Vuuren [3] noted the importance of vapor–liquid equilibria (VLE) in FT process, and derived a criterion for prediction of maximum operating temperature for slurry sys- tems, based on Anderson–Schulz–Flory product distribution. It is important to note that the solubility of H 2 and CO increases with increase in temperature, an unusual behavior as compared to other gases. This temperature dependence must be captured well by the chosen thermodynamic model. The solubility of H 2 and CO also increases with solvent molecular weight or carbon number. And, as expected, solubility increases with pressure. Further, there is no correlation between the solubility of these two gases. While CO is more soluble than H 2 , the sensitivity towards temperature is higher for H 2 [4]. In establishing a solubility correlation for H 2 and CO in the heavy paraffins, Wang et al. [5] point out the two major challenges. The first challenge is the inherent asymmetric nature of the components involved in these mixtures which makes 0378-3812/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2012.02.008