Phase equilibria of “syngas” components, aiming for separation by flash distillation

Abstract

Syngas is a mixture containing methane, hydrogen, carbon dioxide, and carbon monoxide, and it is generated in various processes, such as gasification or methane production via steam reforming. It is desired to separate the syngas to its components in order to create a reliable clean source of energy from methane and hydrogen and to reduce emissions by capturing carbon dioxide. As for today, there is no available data on phase equilibrium of syngas in the literature, which is essential for developing separation processes by distillation. The composition of the syngas depends on its source; therefore, the method for calculating the phase equilibrium shall support any initial composition of the syngas. In the current research, we perform phase stability analysis, using tangent plane distance function and minimizing Helmholtz free energy of the system using two mixing rules: van der Waals and Wong and Sandler. The main strength of the suggested method is its ability to predict any number of phases, avoiding the need for prior knowledge. The current manuscript presents an analysis of binary mixtures of the syngas components, CH4 + CO2, CH4 + CO, CH4 + H2, CO2 + CO, CO2 + H2, and CO + H2, in order to fit the model's parameters to experimental data from the literature, at various temperatures. The aim of this research is to determine which mixing rule shall be further used and to determine the temperature dependent parameters. The parameters fitting is done by minimizing the sum of square errors using “steepest decent” and Fibonacci search method.