Gas Separation by Adsorption in Order to Increase CO2 Conversion to CO via Reverse Water Gas Shift (RWGS) Reaction

Abstract

In this research project, adsorption is considered in conjunction with the reverse water gas shift reaction in order to convert CO2 to CO for synthetic fuel production. If the CO2 for this process can be captured from high emitting industries it can be a very good alternative for reduced fossil fuel consumption and GHG emission mitigation. CO as an active gas could be used in Fischer-Tropsch process to produce conventional fuels. Literature review and process simulation were carried out in order to determine the best operating conditions for reverse water gas shift (RWGS) reaction. Increasing CO2 conversion to CO requires CO2/CO separation downstream of the reactor and recycling unreacted CO2 and H2 back into the reactor. Adsorption as a viable and cost effective process for gas separation was chosen for the CO2/CO separation. This was started by a series of adsorbent screening experiments to select the best adsorbent for the application. Screening study was performed by comparing pure gas isotherms for CO2 and CO at different temperatures and pressures. Then experimental isotherm data were modeled by the Temperature-Dependent Toth isotherm model which provided satisfactory fits for these isotherms. Henry law’s constant, isosteric heat of adsorption and binary mixture prediction were determined as well as selectivity for each adsorbent. Finally, the expected working capacity was calculated in order to find the best candidate in terms of adsorption and desorption. Zeolite NaY was selected as the best candidate for CO2/CO separation in adsorption process for this project. In the last step breakthrough experiments were performed to evaluate operating condition and adsorption capacity for real multi component mixture of CO2, CO, H2 in both cases of saturated with water and dry gas basis. In multi components experiments zeolite NaY has shown very good performance to separate CO2/CO at low adsorption pressure and ambient temperature. Also desorption experiment was carried out in order to evaluate the working capacity of the adsorbent for using in industrial scale and eventually temperature swing adsorption (TSA) process worked very well for the regeneration step. Integrated adsorption system downstream of RWGS reactor can enhance the conversion of CO2 to CO in this process significantly resulting to provide synthetic gas for synthetic fuel production as well as GHG emission mitigation.