Adsorption of hydrogen sulfide, carbon dioxide, methane, and their mixtures on activated carbon

Abstract

H2S and CO2 are acid contaminants of natural gas and biogas, which removal have been studied using adsorption data for monocomponent and binary mixtures. However, equilibrium adsorption data for H2S + CO2 + CH4 mixture has not been investigated yet. In this work, H2S and CO2 partition coefficients (K) and activated carbon (AC) selectivity (S) for H2S + CO2 + CH4 mixture separation at high-pressure and different temperatures were determined. To reach this goal, monocomponent isotherms for H2S, CO2 and CH4 on Brazilian babassu coconut hush AC were experimentally determined at different temperatures and pressures. Then, obtained data were correlated by Langmuir and Tóth models, and multicomponent adsorption was predicted using Extended Langmuir, Extended Tóth and Ideal Adsorption Solution Theory (IAST) methods. Results indicate AC captures approximately 26 wt% of H2S or CO2. K values for CO2 and H2S reached more than 3 and 26, respectively, depending on the predictive model utilized and were higher for diluted mixtures (high CH4 content in gas phase). S values for CO2 and H2S can reach values greater than 25 for Tóth + IAST. Furthermore, selectivity toward H2S is approximately 5.6 times greater than CO2. The effect of temperature on multicomponent results indicate K and S values decrease as temperature increases. Therefore, results obtained herein show that is possible to separate H2S and CO2 from mixture containing CH4 using this AC as adsorbent and better separation performance was observed for low H2S and CO2 concentrations and lower temperatures.