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

In situ capture of CO 2 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-Al 2 O 3 was investigated as a sorbent for in situ CO 2 capture for an enhanced water gas shift application. The CO 2 adsorbent (CaO/γ-Al 2 O 3 ) and WGS catalyst (Pt/γ-Al 2 O 3 ) were integrated as multiple layers of washcoats on a monolith structure. CO 2 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-Al 2 O 3 and Pt/γ-Al 2 O 3 in a flow reactor. Capture experiments in a reactor using monoliths coated with CaO/γ-Al 2 O 3 indicated that increased concentrations of steam in the reactant mixture increase the capture capacity of the CO 2 adsorbent as well as the extent of regeneration. A maximum capture capacity of 0.63 mol of CO 2 /kg of sorbent (for 8.4% CaO on γ-Al 2 O 3 washcoated with a loading of 3.45 g/in. 3 on monolith) was observed at 350 °C for a reactant mixture consisting of 10% CO 2, 28% steam, and balance N 2 . Hydrogen production was enhanced in the presence of monoliths coated with a layer of 1% Pt/γ-Al 2 O 3 and a separate layer of 9.4% CaO/γ-Al 2 O 3 . 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 CO 2 capture by the nanodispersed adsorbent. Following saturation of the adsorbent, the monoliths were regenerated (CO 2 was released) in situ, at temperatures far below the temperature required for decomposition of bulk CaCO 3 . 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.