Sorption-enhanced Water-gas Shift Process Research Articles

CO2 capture and H2 production performance of calcium-based sorbent doped with iron and cerium during calcium looping cycle

As the interest in environmentally-friendly energy processes increases, many studies have been focused on producing hydrogen as an alternative energy carrier via catalytic reaction processes. Sorption enhanced water gas shift (SEWGS) that combines WGS and in situ CO2 removal is a promising technology for high-purity H2 production and CO2 capture. In this study, Fe/Ce-modified CaO-Ca12Al14O33 bi-functional porous nanotubes were synthesized in one step by template method and applied for H2 production from SEWGS process. The unique porous nanotube structure fully exposes the catalytic active sites and facilitates the gas-solid transport, resulting in the excellent H2 production and CO2 capture performance in SEWGS/regeneration cycles. The introduction of Ce enhances the basicity of the nanotube material, thereby increasing the affinity for CO2. The interaction of Fe-Ce improves the redox capability of Fe2+ and Fe3+, which is beneficial to the conversion of CO. In addition, the formed Ca2Fe2O5 and Ca2CeO4 both increase the concentration of oxygen vacancies, further enhancing the SEWGS reactivity of the material. The optimal molar ratio of Fe/Ce/Al/Ca is 10/3/10/100, and the CO conversion, H2 concentration, CO2 capture capacity of the Fe/Ce-modified bi-functional material were 76.9 %, 70.1 % and 83.2 % after 20 cycles. The effect of Fe/Ce doping on CaO-based materials was investigated at the molecular level using density functional theory (DFT). The results demonstrate that the addition of Ce can effectively maintain the stable structure of Fe-CaO-based materials. The modification of Fe/Ce is expected to promote efficient H2 generation from CaO-based materials through the SEWGS process.

Revealing the Role of MgO in Sorption‐Enhanced Water Gas Shift Reaction for H2 Production: A DFT Study

AbstractThe sorption‐enhanced water gas shift (SEWGS) process has emerged as a promising technology for high‐purity H2 production. MgO serves as a competitive sorbent in SEWGS, removing CO2 in situ. Yet the reaction mechanism of SEWGS employing MgO is not well understood. In this work, the reaction mechanism of SEWGS on the MgO surface is revealed by density functional theory (DFT) analysis. The MgO(110) surface shows a remarkable enhancement for SEWGS. Spontaneous dissociation of H2O is observed whether in the presence of CO or CO2, leading to the enrichment of hydroxyl groups for subsequent reactions. CO2 generated is captured by surface basic sites, resulting in the formation of MgCO3. The presence of the generated hydroxyl group enhances the dehydrogenation reaction on the surface, facilitating hydrogen production. The reaction pathway is described as follows. First, spontaneous dissociation of H2O occurs when co‐adsorbed with CO on the MgO surface. Then, two hydroxyl groups interact, yielding atomic O for CO oxidization and atomic H for H2 generation. Ultimately, CO2 is captured by the surface while H2 desorbs from the surface. The rate‐limiting step is H2 generation with an energy barrier of 0.68 eV. The calculation results elucidate the enhancement mechanism of MgO on the SEWGS process.

Sorption-enhanced water gas shift reaction by in situ CO2 capture on an alkali metal salt-promoted MgO-CaCO3 sorbent

CO2 capture and sequestration is one of the viable solutions to reduce the CO2 emissions from fossil fuel combustion, and sorption-enhanced water gas shift (SEWGS) is a promising technology for pre-combustion CO2 capture. In this study, a novel alkali metal salt (AMS)-promoted MgO-CaCO3 sorbent was applied to the SEWGS process, and this sorbent exhibited fast sorption rate, high capacity and good stability in 30 CO2 capture cycles. Catalyst and sorbent particles were arranged in a layer-by-layer alternating configuration in the reactor. The effects of operating conditions such as temperature, pressure and initial H2O/CO molar ratio were investigated, and the thermodynamic equilibrium analyses of the CO2 sorption on AMS-promoted MgO-CaCO3 and the SEWGS process in the layered configuration were carried out, based on which the optimization of the reactor configuration was performed. A high-purity H2 (99.4% in dry basis) was experimentally achieved in the SEWGS process at 573 K, 12 atm and an initial H2O/CO molar ratio of 1.5 with a three catalyst/sorbent layered configuration, and the cyclic stability was demonstrated over 10 consecutive SEWGS cycles.

Ultrafast and Stable CO2 Capture Using Alkali Metal Salt-Promoted MgO-CaCO3 Sorbents.

As a potential candidate for precombustion CO2 capture at intermediate temperatures (200-400 °C), MgO-based sorbents usually suffer from low kinetics and poor cyclic stability. Herein, a general and facile approach is proposed for the fabrication of high-performance MgO-based sorbents via incorporation of CaCO3 into MgO followed by deposition of a mixed alkali metal salt (AMS). The AMS-promoted MgO-CaCO3 sorbents are capable of adsorbing CO2 at an ultrafast rate, high capacity, and good stability. The CO2 uptake of sorbent can reach as high as above 0.5 gCO2 gsorbent-1 after only 5 min of sorption at 350 °C, accounting for vast majority of the total uptake. In addition, the sorbents are very stable even under severe but more realistic conditions (desorption in CO2 at 500 °C), where the CO2 uptake of the best sorbent is stabilized at 0.58 gCO2 gsorbent-1 in 20 consecutive cycles. The excellent CO2 capture performance of the sorbent is mainly due to the promoting effect of molten AMS, the rapid formation of CaMg(CO3)2, and the plate-like structure of sorbent. The exceptional ultrafast rate and the good stability of the AMS-promoted MgO-CaCO3 sorbents promise high potential for practical applications, such as precombustion CO2 capture from integrated gasification combined cycle plants and sorption-enhanced water gas shift process.

Layered Double Hydroxides/Multiwalled Carbon Nanotubes-Based Composite for High-Temperature CO2 Adsorption

Layered double hydroxides (LDH)-derived mixed metal oxides (MMO) are considered as promising solid sorbents for CO2 capture in the temperature range of 350–500 °C. Accordingly, they find potential applications in the sorption enhanced water–gas shift process and in removal of CO2 from hot flue gas/syngas. Numerous strategies have been explored to improve the CO2 capture property of LDH-derived MMO under the conditions of intended applications. These strategies include novel sorbents by replacement of cations and intercalation of organic anions on Mg–Al LDH, development of LDH-based hybrid/composite materials, optimization of synthesis conditions to control particle size, and method development for different types of alkali impregnation. The present work involves synthesis of a Mg–Al LDH/multiwalled carbon nanotubes (MWNTs) composite and explores its applicability for CO2 capture under dry conditions. Additionally, K2CO3 is impregnated onto the composite to study the effect of alkali promotion. The K2CO3-promoted Mg–Al LDH/MWNT composite exhibited a fresh adsorption capacity of 1.12 mmol g–1 at 300 °C under a total pressure of 1 bar. The enhanced CO2 sorption capacity of composites in comparison with their pristine counterparts can be attributed to improved particle dispersion. Further, the K2CO3-promoted Mg–Al LDH/MWNT composite shows an average working capacity of 0.81 mmol g–1 over 10 cycles in the temperature range of 300–400 °C. The deactivation model provides excellent predictions of the experimental CO2 breakthrough curves obtained with various sorbents. The values of model parameters are comparable with those reported in the literature.

Production of fuel-cell grade hydrogen by sorption enhanced water gas shift reaction using Pd/Ni–Co catalysts

It has been demonstrated both thermodynamically and experimentally that fuel-cell grade hydrogen can be produced by a one-step sorption enhanced water gas shift (SEWGS) process at about 500°C, where the water gas shift (WGS) catalyst and the CO2 sorbent are highly integrated. A synthetic CaO-based mixed oxide sorbent was also assessed, which showed a good CO2 capture capacity and stability in the cyclic operation of the SEWGS reaction. Catalysts play a significant role in CO conversion via WGS, methanation and methane steam reforming reactions. A Pd promoted Ni–Co catalyst (1%Pd/20%Ni–20%Co) derived from hydrotalcite-like material (HT) showed a high activity for WGS and methane steam reforming. The methanation activity was further reduced on 30%Ni–10%Co. There exists an optimum temperature (500°C) for hydrogen production by the SEWGS process, where it is kinetically limited by the WGS reaction at lower temperatures (425–475°C) and it is thermodynamically unfavorable at higher temperatures (475–550°C). The challenges for hydrogen production by SEWGS at high CO pressures were also demonstrated, where CO pressure has shown a negative influence on WGS activity. An induction period was observed, which can be reduced by improving catalyst activity and by adding hydrogen to the reactant mixture.

Performance of Water–Gas Shift Catalysts under Sorption-Enhanced Water–Gas Shift Conditions

Abstract The second pre-combustion decarbonisation technology Sorption Enhanced Water-Gas Shift (SEWGS) combines the WGS reaction with simultaneous CO 2 capture by using a mixture of WGS catalyst and CO 2 sorbent. Accordingly, the WGS catalyst is exposed to all conditions encountered in the cyclic SEWGS process, such as exposure to steam in the regeneration step. This paper shows that commercial precious metal, FeCr, and CoMo WGS catalysts are robust towards periodic exposure to these atypical conditions. Catalyst behavior is reported to periodic exposure to these atypical conditions at a temperature of 400 ∘ C, pressures up to 5 bara and H 2 S contents from 1 ppm to 2,000 ppm. Although additional experiments need to be performed at increased pressure, it appears that all catalysts can potentially be used in the SEWGS process.

Reduction in the cost of pre-combustion CO2 capture through advancements in sorption-enhanced water-gas-shift

Abstract Sorption-enhanced water-gas-shift (SEWGS) is a pre-combustion decarbonisation technology combining adsorption of CO2 with the water-gas-shift reaction. This process maximises the production of hydrogen from syngas whilst simultaneously capturing and separating CO2. Simulations have been completed to evaluate the use of SEWGS for power generation from natural gas with carbon capture. The modelling results show that using the SEWGS process could significantly reduce the cost of capturing CO2 versus a reference design that uses amine absorption. Work has also been completed to show that using a counter-current steam-rinse step may be an improvement over a co-current CO2-rinse cycle proposed previously.

99/03641 High-temperature coal gas desulfurization using CuMnO based sorbent. I. Sulfidation of CuMnO based sorbent: Wan., C. et al. Ranliao Huaxue Xuebao, 1998, 26, (5), 400–405. (In Chinese)

Sorption-enhanced water-gas-shift (SEWGS) is a pre-combustion decarbonisation technology combining adsorption of CO2 with the water-gas-shift reaction. This process maximises the production of hydrogen from syngas whilst simultaneously capturing and separating CO2.Simulations have been completed to evaluate the use of SEWGS for power generation from natural gas with carbon capture. The modelling results show that using the SEWGS process could significantly reduce the cost of capturing CO2 versus a reference design that uses amine absorption. Work has also been completed to show that using a counter-current steam-rinse step may be an improvement over a co-current CO2-rinse cycle proposed previously.