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Lime enhanced gasification (LEGS) process based on calcium looping in which CaO is employed as CO2 sorbent is an emerging technology for hydrogen production and CO2 capture. In this work, carbide slag which was an industrial solid waste was utilized as CO2 sorbent in hydrogen production process. Modification of carbide slag by propionic acid was proposed to improve its reactivity. The CO2 capture behavior of raw and modified carbide slags was investigated in a dual fixed-bed reactor (DFR) and a thermo-gravimetric analyzer (TGA). The results show that modification of carbide slag by propionic acid enhances its CO2 capture capacity in the multiple calcination/carbonation cycles. The favorable carbonation temperature and calcination temperature for modified carbide slag are 680–700 °C and 850–950 °C, respectively. Prolonged carbonation treatment is beneficial to CO2 capture of raw and modified carbide slags. The prolonged carbonation for 9 h in the 21st cycle increases the conversions of raw and modified carbide slags in this cycle. And then the carbonation conversions of the two sorbents were also improved in the subsequent cycles. Calcined modified carbide slag shows more porous microstructure compared with calcined raw one for the same number of cycles. Modification of carbide slag by propionic acid increases the surface area, pore volume and pore area. In addition, the volume and area of the pores in 20–100 nm in diameter were improved, which had been proved to be more effective to capture CO2. The microstructure of calcined modified carbide slag favors its higher CO2 capture capacity in the multiple calcination/carbonation cycles. [ABSTRACT FROM AUTHOR]

• The adsorption of CO 2 and H 2 O by CaO/Ca 12 Al 14 O 33 was studied by DFT calculations. • The chemical adsorption of CO 2 and H 2 O on Ca 12 Al 14 O 33 -supported CaO is competitive. • The adsorption of CO 2 on Ca 12 Al 14 O 33 -supported CaO is stronger than that of H 2 O. • The adsorbed H 2 O activates adjacent O atoms of CaO, which benefits CO 2 adsorption. • The DFT can predict the CO 2 adsorption performance of different CaO-based sorbents. The synthetic CaO/Ca 12 Al 14 O 33 sorbent has been regarded as an efficient CO 2 sorbent during the calcium looping cycles. In this work, the CO 2 adsorption performance of the synthetic CaO/Ca 12 Al 14 O 33 sorbent in the presence of H 2 O was investigated by density functional theory (DFT) calculations. DFT was used to analyze the adsorption of CO 2 and H 2 O on the synthetic sorbent. Both structural parameters (atomic layout and electronic configuration) and the adsorption parameters (energy, bond lengths, angles, bond population and charge transfer) of CO 2 and H 2 O on the synthetic sorbent were determined. To confirm the feasibility of DFT analysis, the CO 2 capture performance of the synthetic sorbent in the presence of steam was examined in a dual fixed bed reactor. The results indicate strong interactions between the C atom and the O atom in CaO and interactions between the H atom and the O atom in CaO. The higher adsorption energy of CO 2 than H 2 O on pristine CaO and Ca 12 Al 14 O 33 -supported CaO suggests that the adsorptions of CO 2 and H 2 O are competitive and that the adsorption of CO 2 is stronger than that of H 2 O. The adsorption of H 2 O leads to the activation of adjacent O atoms of CaO and thus stronger CO 2 adsorption on the O atom with H 2 O adsorbed. The electrons in the p orbital of the O atom near the Fermi level play important roles in CO 2 adsorption by CaO. The presence of Ca 12 Al 14 O 33 hinders CO 2 adsorption by CaO. A low Ca 12 Al 14 O 33 content in synthetic sorbents should be maintained to ensure high CO 2 capture capacity and sintering resistance of synthetic sorbents. DFT calculations can predict the CO 2 adsorption performance of CaO-based sorbents with additives under different reaction atmospheres. [ABSTRACT FROM AUTHOR]

Highlights • Synthetic CaO-based CO 2 sorbent was prepared using paper fibre as a biotemplate. • Synthetic sorbent is mainly composed of CaO and Ca 12 Al 14 O 33. • Synthetic sorbents possess microtube-like structure with superior CO 2 uptake. • Synthetic sorbent has improved sintering resistance in severe calcination condition. Abstract Calcium looping is regarded as an effective and viable way to address CO 2 emissions. To overcome the loss-in-capacity problems of calcium-based sorbents with the number of calcium looping cycles, a novel CaO/Ca 12 Al 14 O 33 sorbent with a microtube-like structure was prepared from carbide slag and Al(NO 3) 3 ·9H 2 O using paper fibre as a biotemplate. The CO 2 capture performance and microstructure of the novel synthetic sorbent under calcium looping conditions were investigated. The results show that the utilization of the biotemplate is good to retain the high cyclic CO 2 capture reactivity of the synthetic sorbent. Due to the unique hollow porous structure, the CO 2 capture capacity of the synthetic sorbent containing 7.5 wt% Al 2 O 3 retains 0.56 and 0.33 g/g after 30 cycles under mild and severe calcination conditions, respectively, which are 2.56 and 2.11 times higher than those of carbide slag under the same respective calcination conditions. With the presence of 10% steam in the carbonation atmosphere, the CO 2 capture capacity of the synthetic sorbent retains 0.55 g/g under the severe calcination conditions after 10 cycles. The native hierarchical biostructure of paper fibre is preserved in the synthetic sorbent. CaO and Ca 12 Al 14 O 33 are uniformly distributed in the synthetic sorbent, resulting in a high sintering resistance during multiple CO 2 capture cycles. CO 2 can penetrate through the microtube-like structure of the synthetic sorbent from two directions, i.e., from the outer surface and inner surface. This phenomenon effectively enlarges the contact area between CO 2 and CaO. The CaO/Ca 12 Al 14 O 33 sorbent with a hollow porous structure by means of a biotemplate appears promising in the calcium looping technology for CO 2 capture. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A bifunctional system integrating with CO 2 capture and heat storage is proposed. • Original carbide slag can be used in CaO/Ca(OH) 2 thermochemical heat storage process. • High Cl content results in low cyclic CO 2 capture capacity of carbide slag. • Hydration performance of carbide slag with Cl is improved after CO 2 capture cycles. • CaO after CO 2 capture cycles is promising to be used for heat storage. Abstract Carbide slag is an industrial waste generated from ethylene gas production in chlor-alkali plants. Here, a novel system coupling calcium looping and CaO/Ca(OH) 2 thermochemical heat storage using carbide slag were proposed to simultaneously capture CO 2 and store heat. For CaO/Ca(OH) 2 thermochemical heat storage, the hydration/dehydration performance of original carbide slag and carbide slag that experienced calcium looping cycles for CO 2 capture was investigated. The performances of the two types of carbide slag with and without chlorine were compared. The dehydration conversions of carbide slag improved with the increase of dehydration temperature. The chlorine content has no apparent effect on the hydration/dehydration performance of original carbide slag. However, for CO 2 capture, carbide slag with high chlorine content shows lower carbonation conversion than that of carbide slag without chlorine. The hydration/dehydration conversions of carbide slag that experienced CO 2 capture cycles are lower than those of original carbide slag. For carbide slag with chlorine, the hydration conversion can be improved by more than one CO 2 capture cycle. Therefore, carbide slag that experienced various CO 2 capture cycles is still suitable to be used in CaO/Ca(OH) 2 thermochemical heat storage although calcium looping has an adverse effect on the hydration/dehydration performance of carbide slag. [ABSTRACT FROM AUTHOR]

Herein, a hollow microtubular Fe/Mn-promoted CaO-Ca 12 Al 14 O 33 bi-functional material was prepared by the bio-template method and used for H 2 production from sorption enhanced water gas shift (SEWGS). The microtubular Fe/Mn-promoted CaO-Ca 12 Al 14 O 33 exhibits excellent CO 2 capture and H 2 production performance in SEWGS/regeneration cycles. The stable hollow microtubular structure improves available adsorption and catalytic sites in Fe/Mn-promoted CaO-Ca 12 Al 14 O 33 for CO 2 capture and H 2 production. Mn addition improves CO 2 affinity capacity of the microtubular material. The Fe-Mn interaction increases redox ability of Fe3+/Fe3+, 2+, which promotes CO conversion. Moreover, the formed Ca 2 Fe 2 O 5 and Ca 2 MnO 4 both increase oxygen vacancies to promote catalytic activity of the microtubular material for WGS and its CO 2 capture capacity. The CO conversions for the microtubular material with the Fe/Mn/Al/Ca molar ratio= 10/2/10/100 are 98.7% and 94.0% after 20 cycles under the mild and severe calcination conditions, respectively. The hollow microtubular bi-functional material shows good prospect for efficient H 2 production from SEWGS. [Display omitted] • Microtubular Fe/Mn-promoted CaO-Ca 12 Al 14 O 33 bi-functional material was prepared. • Microtubular material is good for H 2 production by sorption enhanced water gas shift. • Porous and hollow microtubular structure of the material keeps stable in cycles. • Synergistic effect of Fe/Mn in the material promotes CO 2 capture and H 2 production. • High and stable H 2 production from SEWGS using microtubular material is achieved. [ABSTRACT FROM AUTHOR]

• The WGS reaction mechanism in the presence of CaO was studied by DFT calculations. • The most possible pathway of WGS reaction on the CaO surface is the redox-a pathway. • As the rate-limiting step, H 2 O is dissociated spontaneously on the CaO surface. • The presence of CaO decreases energy barrier of WGS reaction along redox-a pathway. The water gas shift reaction is an important reaction for H 2 production in various industrial applications. The presence of CaO can promote the reactivity of the water gas shift reaction without any catalysts, but the enhancement mechanism of CaO in this reaction is difficult to determine just by the experiment. In this work, the water gas shift reaction along four possible pathways on the CaO surface were studied by density functional theory (DFT) analysis. The energy barriers along the pathways were analyzed to determine the most possible reaction pathway and role of the CaO surface. The DFT calculation results show that the WGS reaction is more prone to proceed along the redox-a pathway probably: H 2 O dissociates into hydroxyl and atomic H spontaneously when H 2 O and CO co-adsorb on the CaO surface, then the hydroxyl continues to dissociate and CO is oxidized by the generated atomic O. Afterwards, H 2 molecule generates from two atomic H, and then CO 2 adsorbs and H 2 desorbs simultaneously on the CaO surface. The CaO surface enables the spontaneous dissociation of H 2 O, which is the rate-limiting step of WGS reaction. The generation of CO 2 is facilitated, and the energy barrier is reduced from 2.304 to 0.757 eV on the CaO surface. Besides, the formation of CO 3 2− on the surface avoids the energy barrier for CO 2 desorption, while the CO 2 also occupies the active site and reduces the enhancement of CaO on WGS reaction. The calculation result reinforces the comprehension on the mechanism of CaO on WGS reaction. [ABSTRACT FROM AUTHOR]

A hollow nanostructured CaO-based material fabricated from calcined limestone and glucose by hydrothermal carbonization method was proposed to be used in the process coupled Ca-looping for CO 2 capture and CaO/Ca(OH) 2 heat storage. The effects of hydrothermal temperature and interval in the preparation process on CO 2 capture and heat storage capacities of the hollow CaO were studied. The interaction effect of Ca-looping and heat storage on the performance of the hollow CaO was determined. The hollow nanostructure of CaO decreases the diffusion resistance of CO 2 and steam in its inner. The CO 2 capture capacity of the hollow CaO reaches 0.45 g/g after 20 Ca-looping cycles, which is 1.7 times as high as that of limestone. The hollow CaO (hydrothermal temperature of 170 °C for 6 h) after 10 Ca-looping cycles achieves a heat storage capacity of 0.85 mol/mol during the subsequent heat storage cycles, which is 1.3 times as high as that of limestone. A few heat storage cycles improve pore structure of the sintered hollow CaO after Ca-looping cycles, so its CO 2 capture capacity in the following Ca-looping cycle is enhanced by 94%. Thus, the hollow nanostructured CaO seems promising in the process coupled Ca-looping and CaO/Ca(OH) 2 heat storage. • Hollow nanostructured CaO is prepared from limestone by the carbonaceous templating. • The hollow CaO is used in a process coupled Ca-looping and CaO/Ca(OH) 2 heat storage. • The hollow CaO simultaneously achieves high CO 2 capture and heat storage capacities. • The hollow CaO maintains porous structure during Ca-looping and heat storage cycles. • A few heat storage cycles alleviate the sintering of hollow CaO in Ca-looping cycles. [ABSTRACT FROM AUTHOR]

A novel CeO 2 -modified CaO/Ca 12 Al 14 O 33 bi-functional material fabricated by wet-mixing method was used in sorption-enhanced steam gasification of biomass for H 2 production. The CO 2 capture performance of the bi-functional material was investigated during the multiple carbonation/calcination cycles in a dual fixed-bed reactor. H 2 production from the sorption-enhanced steam gasification of bagasse char using CeO 2 -modified CaO/Ca 12 Al 14 O 33 was studied. When the mass ratio of CaO/Ca 12 Al 14 O 33 /CeO 2 is 75:10:15, CO 2 capture capacity of CeO 2 -modified CaO/Ca 12 Al 14 O 33 reaches 0.48 g/g after 20 cycles under the realistic calcination condition, which is 30% higher than that of CaO/Ca 12 Al 14 O 33. The average H 2 concentration and yield using CeO 2 -modified CaO/Ca 12 Al 14 O 33 during 10 cycles achieve 81.1 vol% and 0.124 L/g, which are 17.4% and 47.3% higher than those using CaO/Ca 12 Al 14 O 33 , respectively. CeO 2 in CeO 2 -modified CaO/Ca 12 Al 14 O 33 enhances water gas shift and steam methane reforming reactions. CeO 2 -modified CaO/Ca 12 Al 14 O 33 possesses stronger basicity, and Ce3+ in the surface creates oxygen vacancies and promotes the conductivity of lattice oxygen, which are favorable for CO 2 capture. CeO 2 improves the cyclic stability of CaO/Ca 12 Al 14 O 33 and stabilizes pores in 10–100 nm in diameter, which facilitates CO 2 capture and H 2 production. Thus, CeO 2 -modified CaO/Ca 12 Al 14 O 33 appears promising for H 2 production from the sorption-enhanced steam gasification of biomass. • CeO 2 -modified CaO/Ca 12 Al 14 O 33 bi-functional material is good in biomass gasification. • CeO 2 -modified CaO/Ca 12 Al 14 O 33 possesses high cyclic CO 2 capture capacity. • CeO 2 -modified CaO/Ca 12 Al 14 O 33 favors H 2 production in steam gasification of biomass. • CeO 2 -modified CaO/Ca 12 Al 14 O 33 obtains strong basicity due to the presence of CeO 2. • CeO 2 -modified CaO/Ca 12 Al 14 O 33 maintains stable porous structure in cycles. [ABSTRACT FROM AUTHOR]