(144d) Thermodynamic Characterization of Heavy Paraffin Mixtures to Employ the Soave-Readlich-Kwong Equation of State

The Fischer-Tropsch process allows to obtain heavy hydrocarbons from synthesis gas. However owing to the intrinsic characteristics of the process and the nature of the products the FT wax need to be subjected to a catalytic hydroconversion stage in order to improve both yields and quality of middle distillate cuts. It was found that the performance of this process and the quality of products are strongly affected by the vapor-liquid equilibrium inside the catalytic reactor, so that it becomes very important to be able to accurately model this equilibrium. To do this, the Soave-Readlich-Kwong equation of state was chosen, for which reliable characterization procedures are available to describe the heavy normal paraffin behavior. In order to fully attain the objective, two more steps were necessary: (i) a way to estimate the binary interaction parameters between hydrogen and paraffins and (ii) a characterization procedure of iso-paraffins. For the first item, a literature relationship was adopted (Tsonopoulos et al., 1986), while a new characterization procedure was needed for iso-paraffins. In this paper, an original procedure is developed to estimate the critical properties of iso-paraffins on the basis of a gas-chromatographic trace of the stream. It is shown that the use of such a procedure leads to significantly improvement of the esteem the kinetic model.