In Situ CO2 Capture Using CaO/γ-Al2O3 Washcoated Monoliths for Sorption Enhanced Water Gas Shift Reaction

In situ capture of CO2 allows the thermodynamically constrained water gas shift (WGS) process to operate at higher temperatures (i.e., 350 °C) where reaction kinetics are more favorable. Dispersed CaO/γ-Al2O3 was investigated as a sorbent for in situ CO2 capture for an enhanced water gas shift application. The CO2 adsorbent (CaO/γ-Al2O3) and WGS catalyst (Pt/γ-Al2O3) were integrated as multiple layers of washcoats on a monolith structure. CO2 capture experiments were performed using thermal gravimetric analysis (TGA) and a bench scale flow through reactor. Enhancement of the water gas shift (EWGS) reaction was demonstrated using monoliths (400 cells/in.2) washcoated with separate layers of dispersed CaO/γ-Al2O3 and Pt/γ-Al2O3 in a flow reactor. Capture experiments in a reactor using monoliths coated with CaO/γ-Al2O3 indicated that increased concentrations of steam in the reactant mixture increase the capture capacity of the CO2 adsorbent as well as the extent of regeneration. A maximum capture capacity of 0.63 mol of CO2/kg of sorbent (for 8.4% CaO on γ-Al2O3 washcoated with a loading of 3.45 g/in.3 on monolith) was observed at 350 °C for a reactant mixture consisting of 10% CO2, 28% steam, and balance N2. Hydrogen production was enhanced in the presence of monoliths coated with a layer of 1% Pt/γ-Al2O3 and a separate layer of 9.4% CaO/γ-Al2O3. A greater volume of hydrogen compared to the baseline WGS case was produced over a fixed amount of time for multiple cycles of EWGS. The CO conversion was enhanced beyond equilibrium during the period of rapid CO2 capture by the nanodispersed adsorbent. Following saturation of the adsorbent, the monoliths were regenerated (CO2 was released) in situ, at temperatures far below the temperature required for decomposition of bulk CaCO3. It was demonstrated that the water gas shift reaction could be enhanced for at least nine cycles with in situ regeneration of adsorbent between cycles. Isothermal regeneration with only steam was shown to be a feasible method for developing a process.