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

Abstract

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.

Structured Ni@NaA zeolite supported on silicon carbide foam catalysts for catalytic carbon dioxide methanation

“…To overcome the limitation of conventional packed beds, structured catalysts such as monoliths, 14,15 structured fibrous networks, 16‐18 and structured foams 13,19‐23 have been studied to mitigate the effect by heat/mass transfer on chemical transformation and separation processes, including catalysis such as catalytic CO 2 methanation. For example, Ni catalysts supported on ceria‐zirconia coated foams (including open‐cell silicon carbide (SiC), alumina and aluminium foams) and carbon felt were developed and assessed for promoting catalytic CO 2 methanation, and heat regulation 20,24 .…”

Catalyst-free ceramic-carbonate dual phase membrane reactor for hydrogen production from gasifier syngas

“…Besides the in-situ separation of H 2 , CO 2 removal has been confirmed as another promising route to promote the WGS reaction for H 2 production. Typically, CO 2 sorbents were used for in situ CO 2 removal to enhance the reaction performance [20][21][22]. It is also highly desirable to use a CO 2 -selective membrane for the WGS reaction because CO 2 -selective membrane reactors have the potential to achieve higher H 2 recovery [5].…”

Monitoring Solid Oxide CO2 Capture Sorbents in Action

“…[1,[12][13][14][15][16][17][18] These CaO-based chemisorbents appear to have similar working capacities, tolerance to steam, and cyclic working capacities, but poorer regeneration capabilities compared to their Na 2 O (periodic group I)-based counterparts. At the time of writing, only one study by Duyar et al has demonstrated that support CaO sorbents can be regenerated at temperatures as low as 350 8C.…”

“…At the time of writing, only one study by Duyar et al has demonstrated that support CaO sorbents can be regenerated at temperatures as low as 350 8C. [18] The separation, capture, and storage of CO 2 , the major greenhouse gas, from industrial gas streams has received considerable attention in recent years because of concerns about environmental effects of increasing CO 2 concentration in the atmosphere. An emerging area of research utilizes reversible CO 2 sorbents to increase conversion and rate of forward reactions for equilibrium-controlled reactions (sorption-enhanced reactions).…”