Carbon oxides methanation in equilibrium; a thermodynamic approach

Abstract

Global warming and greenhouse gases as two main threat to human societies due to increasing carbon oxides, such as CO and CO2 and lack of energy storages results in challenges efforts to controlling these atmospheric pollutions in various ways and methods. Carbon oxides methanation was considered as chemical process to conversion carbon oxides to their products as syngas. Various parameters can be effective on this process such as temperature, pressure and equivalence ratio of feeding products specially H2/CO2 and H2/CO. In this study, three various equivalence ratio of feeding products were investigated against pressure and temperature in equilibrium condition to determine concentration of main products. Five various pressures applied to system of equilibrium, i.e. 1, 5, 10, 25, 50 atm beside temperature change from 200 K to 1500 K. Moreover, fugacity effects also were investigated in Soave–Redlich–Kwong equation of state in comparison with ideal gas. Results revealed that fugacity was completely changes the results especially for water production and hydrogen consumption. According to the results, carbon di and monoxides conversion were increased during pressure increasing where methane selectivity also increased. In maximum condition of coke formation there was 0.1 mol fraction of it in both CO and CO2 methanation. Although, higher equivalence ratio of each carbon oxides combination feeding products ascended CH4 selectivity and yield but in high equivalence ratio (ER = 6) CH4 yield decreased about 8% for both investigated methanation process. In lower equivalence ratio (lower than stoichiometric) condition, methane yield replaced with mainly carbon yield.