Integrated CO2 Capture Research Articles

Selecting the approach for dynamic modelling of CO2 capture in biomass/waste fired CHP plants

Integrating CO2 capture with biomass/waste fired combined heat and power (CHP) plants is a promising method to achieve negative emissions. However, the use of versatile biomass/waste and the dynamic operation of CHP plants result in bigger fluctuations in the properties of flue gas (FG), e.g. CO2 concentration (CO2vol%) and flowrates, and the heat that can be used for CO2 capture, when comparing with coal fired power plants. To address such a challenge, dynamic modelling is essential to accurately estimate the amount of captured CO2 and optimize the operation of CO2 capture. This paper compares three dynamic approaches commonly used in literature, namely using the ideal static model (IST) and using dynamic models without control (Dw/oC) and with control (DwC), for MEA based chemical absorption CO2 capture. The performance of approaches is assessed under the variations of key factors, including the flowrate and CO2vol% of FG, and the available heat for CO2 capture. Simulation results show clear differences. For example, when the CO2vol% drops from 15.7 % to 9.7 % (about 38 %) within 4 hours, DwC gives the highest amount of captured CO2, which is 7.3 % and 22.3 % higher than IST and Dw/oC, respectively. It is also found that the time step size has a clear impact on the CO2 capture amount, especially for DwC. Based on the results, suggestions are also provided regarding the selection of dynamic modelling approaches for different purposes of simulations.

Chemical looping CO2 capture and in-situ conversion: Fundamentals, process configurations, bifunctional materials, and reaction mechanisms

As an emerging and promising technology to debate the energy and environment issues raised by anthropogenic CO2 emissions, chemical looping CO2 capture and in-situ conversion (CL-ICCC) exhibits the merit of high efficiency, low cost, and high safety to achieve integrated CO2 capture and conversion (ICCC) by eliminating the purification, compression, transportation, and storage procedures. However, the interpretation and state-of-the-art of CL-ICCC are still unclear, which contribute to a harmful effect on promoting this technology for industrial applications. Herein, this work presents a timely review on CL-ICCC by giving fundamental discussions on definition, process configuration, bifunctional material, reaction mechanism and thermo-economic behavior. Based on the product distributions (syngas, CO, CH4, C2H4/C3H6), CL-ICCC systems using abundant bifunctional materials with flexible combinations of sorbents and catalysts are classified to satisfy the demand of customers. Lots of moderating strategies are proposed to enhance the activity and stability of bifunctional material, meanwhile, reaction mechanism is revealed to explain the underlying reason for superior performance. The challenges and future prospectives from the aspects of microscopic reaction mechanism, bifunctional material rational design, reaction equipment development and system integration and optimization are discussed to provide possible suggestions. This review aims to illustrate CL-ICCC more clearly and accelerate its commercial demonstration.

Integrations of desulfurization, carbon capture, and methanation at an isothermal intermediate temperature

Integrated CO2 capture and conversion (iCCC) technology has been recognized as the most efficient technology for Carbon Capture, Utilization, and Storage (CCUS). However, its industrialization is hindered by some unsolved engineering problems. Typically, sulfur impurities in most industrial flue gas will have significant poisoning effects on the process. Herein, we report integrations of SO2 removal, CO2 capture and conversion (iSCCC) at an isothermal intermediate temperature in a two-fixed-bed column system. By rationally developing the SO2 adsorbent pellets of ZnO-CaO, the CO2 adsorbent pellets of AMS-MgO, and the methanation catalyst pellets of Ni-La/Al2O3, each individual unit is optimized. Specifically, the in-situ dynamic structure evolution observed by the atmospheric aberration-corrected scanning transmission electron microscopy as well as the theoretical dynamics calculation provide an in-depth understanding of the CO2 adsorption and desorption performance changing with the temperature on the AMS-MgO pellets, which builds a bridge for a successful 99.3 % CO2 methanation efficiency. As a result, the matched iSCCC process demonstrates exceptional performance from simulated flue gas containing 1000 ppm SO2 and 20 vol% CO2, with full desulfurization and decarbonation and a CO2 conversion efficiency of 93.6 % after 20 cycles isothermally at 400 °C, superior to all the reported performance so far as we know, providing a promising route to practical large-scale iSCCC towards carbon neutrality.

Metal oxide and nitrate-modified calcium gluconate-based sorbent with high stability for integrated carbon capture and utilization process

In this study, metal oxides (MgO, CeO2, and Al2O3) and metal nitrates (Mn(NO3)2, Al(NO3)3, Mg(NO3)2, and Fe(NO3)3) were used to modify calcium gluconate-based sorbents for the integrated CO2 capture and utilization (ICCU) process. We employed conventional thermogravimetric analysis (TGA) and microfluidized bed thermogravimetric analysis coupled with mass spectrometry (MFB-TGA-MS) to explore the cyclic CO2 capture behavior, physical and chemical properties, and morphology in detail. Our findings reveal that calcium gluconate modified with aluminum nitrate (CG-Al-N) exhibited superior CO2 capture capacity (9.81 mmol∙g−1 over 20 cycles), along with a high surface area (35.67 m2∙g−1) and pore volume (0.16 cm3∙g−1). In comparison, pure calcium gluconate displayed a capacity of 7.09 mmol∙g−1, a surface area of 27.66 m2∙g−1, and a pore volume of 0.06 cm3∙g−1, while commercial calcium oxide demonstrated 1.96 mmol∙g−1, 4.62 m2∙g−1, and 0.01 cm3∙g−1, respectively. Notably, after 100 cycles, CG-Al-N retained a CO2 capture capacity of 11.75 mmol∙g−1, achieving 66% of the capacity of the pure CaO sorbent. This observation strongly suggests that CG-Al-N has excellent anti-sintering properties. Furthermore, data was acquired under fluidized and isothermal conditions by utilizing MFB-TGA-MS. CG-Al-N consistently exhibited an average CO2 capture capacity (9.57 mmol∙g−1), CO yield (5.00 mmol∙g−1), and CO selectivity (∼100%) over 20 ICCU cycles, with the dominant route being the reverse water–gas shift (RWGS) reaction, highlighting the self-catalytic activity of gluconate-based sorbents. Morphological evolution also revealed finer pores and a skeleton structure of cycled CG-Al-N, which affirms the unobstructed gas entry and ensures a continuous gas–solid reaction.

Characteristics of coal slime pyrolysis with integrated CO2 capture

Faced with increasingly severe energy and environmental issues, the clean and efficient utilization of coal slime is an urgent problem to be solved. Due to the concerns about carbon reduction and the intention to produce high quality gaseous products, pyrolysis experiments of coal slime coupled with in-situ and ex-situ CO2 capture were carried out in a fixed-bed reactor. The effect of pyrolysis temperatures, mixing ratios of coal slime and CaO, and the CO2 capture ways were investigated. The gaseous products from coal slime pyrolysis mainly included H2, CO, CO2, CH4, etc. It was revealed that after adding CaO, the hydrogen content in the pyrolysis gas increased significantly, while the CO2 content decreased. When the temperature increased from 600 to 800 °C, the generation of gas products was enhanced. Due to the different interactions between the coal slime and CaO, the CO2 capture efficiency of in-situ capture was higher than that of ex-situ capture, but ex-situ capture presented a relatively higher hydrogen production. When the coal slime/CaO mixing ratio is 1:1 and the pyrolysis temperature is 600 °C, the in-situ CO2 capture ratio could reach 92.1%, and H2 content at this situation is 56.5%. For ex-situ CO2 capture, the capture efficiency of CO2 increased with the increasing proportion of CaO. When the coal slime/CaO mixing ratio was 1:1, the ex-situ capture efficiency of CaO for CO2 is 74% at 600 °C while the H2 content is 59.3%. After CO2 was captured by CaO, the diffraction peaks of CaCO3 appeared in XRD patterns, and the microscopic morphology of CaCO3 particles was clustered. Peaks corresponding to CaCO3 also appeared in the C 1s, Ca 2p, and O 1s regions of the XPS peak spectrum, and showed a trend of first increasing and then decreasing as the temperature gradually increased. This study will provide a theoretical guidance on the efficient and clean utilization of coal slime.

Calcium-looping coupling methane partial oxidation and dry reforming process for integrated CO2 capture and conversion: Regulable H2/CO molar ratio and excellent coke deposition-resistant

Calcium-looping coupling methane partial oxidation and dry reforming process for integrated CO2 capture and conversion: Regulable H2/CO molar ratio and excellent coke deposition-resistant

Ultrastable bifunctional multi-stage active metal catalysts for low concentration CO2 capture and in-situ conversion

Integrating CO2 capture and in-situ conversion is a promising means of processing low concentration CO2 in flue gas. The development of a low cost, highly stable catalyst to reduce the running cost is key to the development of this technology. The ultrastable bifunctional multi-stage active metal catalysts (Ca12Al14O33-y (Ca2Fe2O5)-CoxCaO) were synthesized by the solid phase synthesis method with low cost industrial powder raw materials. The catalyst was stabilized with calcium aluminate (Ca12Al14O33) and calcium ferrite (Ca2Fe2O5) as a substrate structural framework for CaO and enhanced the dispersion of CaO. It not only solved the problem of CaO deactivation due to sintering, pore collapse, and agglomeration in the continuous high-temperature reaction, but also showed excellent catalytic performance for reverse-water–gas-shift (RWGS) reaction. On the basis of calcium-looping and RWGS reaction, the high temperature CO2 capture and in-situ conversion process is realized in the same fixed-bed reactor for processing simulated flue gas with 16.7 vol% CO2. The results showed that at the optimum operating temperature of 610 °C, the catalyst still maintains a stable CO2 capture capacity, over 98% CO2 conversion rate and close to 100% CO selectivity after 100 cycles. The multi-stage active metal structure catalysts provided a unique construction idea for designing ultrastable catalysts for low concentration CO2 capture and in-situ conversion with great potential for industrial application.

Analysis of integrated CO2 capture and utilization via calcium-looping in-situ dry reforming of methane and Fischer-Tropsch for synthetic fuels production

Calcium-looping is an attractive approach for removing CO2 in flue gas from the coal-fired power plant to form CaCO3. The integration of CO2 capture via calcium-looping and in-situ dry reforming of methane with CaCO3 allows the simultaneous CaCO3 decomposition to regenerate CaO and syngas production. The produced syngas is expected for further utilization, e.g. Fischer-Tropsch synthesis to produce valuable fuels. In this work, an integrated process of calcium-looping in-situ dry reforming of methane and Fischer-Tropsch was developed using Aspen Plus. Moreover, two other processes were also simulated as the comparison, consisting of the serial process of calcium-looping CO2 capture, ex-situ dry reforming of methane with CO2 and Fischer-Tropsch and the standalone process of calcium-looping CO2 capture. The results indicate that the reduction in the demand for CaO sorbent and the enhancement in Fischer-Tropsch products yield and carbon conversion efficiency are achieved by integrating in-situ dry reforming of methane with CaCO3. Additionally, integrating CO2 capture and in-situ dry reforming of methane with CaCO3 in the case of the integrated process is efficient for enhancing the system efficiency and energy availability. Compared with the serial process, the integrated process shows a drop in the heat energy requirement of 28.08% and possesses the energy conversion efficiency of 43.74% and exergy efficiency of 41.81%. This work exhibits the prospect of the integrated process of calcium-looping in-situ dry reforming of methane and Fischer-Tropsch in the field of CO2 capture and utilization for Fischer-Tropsch fuels production.

Enhancement of the CO2 adsorption and hydrogenation to CH4 capacity of Ru–Na–Ca/γ–Al2O3 dual function material by controlling the Ru calcination atmosphere

Integrated CO2 capture and utilization (ICCU) technology requires dual functional materials (DFMs) to carry out the process in a single reaction system. The influence of the calcination atmosphere on efficiency of 4% Ru-8% Na2CO3-8% CaO/γ-Al2O3 DFM is studied. The adsorbent precursors are first co-impregnated onto alumina and calcined in air. Then, Ru precursor is impregnated and four aliquotes are subjected to different calcination protocols: static air in muffle or under different mixtures (10% H2/N2, 50% H2/N2 and N2) streams. Samples are characterized by XRD, N2 adsorption-desorption, H2 chemisorption, TEM, XPS, H2-TPD, H2-TPR, CO2-TPD and TPSR. The catalytic behavior is evaluated, in cycles of CO2 adsorption and hydrogenation to CH4, and temporal evolution of reactants and products concentrations is analyzed. The calcination atmosphere influences the physicochemical properties and, ultimately, activity of DFMs. Characterization data and catalytic performance discover the acccomodation of Ru nanoparticles disposition and basic sites is mostly influencing the catalytic activity. DFM calcined under N2 flow (RuNaCa-N2) shows the highest CH4 production (449 µmol/g at 370°C), because a well-controlled decomposition of precursors which favors the better accomodation of adsorbent and Ru phases, maximizing the specific surface area, the Ru-basic sites interface and the participation of different basic sites in the CO2 methanation reaction. Thus, the calcination in a N2 flow is revealed as the optimal calcination protocol to achieve highly efficient DFM for integrated CO2 adsorption and hydrogenation applications.

Sulphur poisoning and regeneration of Li-Ru/Al2O3 dual function material for the integrated CO2 capture and methanation

Effective integration of the CO2 capture from flue gases and its subsequent methanation with renewable H2 to achieve a net-zero chemical looping process poses strong challenges in the development of highly performing Dual Function Materials (DFMs). Li-Ru/Al2O3 DFM has been shown to optimally operate the cyclic process at low temperature (260 – 280 °C) with stable performance upon ageing and outstanding tolerance to SOx impurities in the flue gas, which, however, slowly deteriorate its CO2 capture capacity. This work investigates the mechanisms behind the sulfur-poisoning and self-regeneration capability of the catalytic features of the Li-Ru DFM as well as the irreversible inhibition of CO2 adsorption. Eventually, we demonstrate the remarkable effectiveness of a simple ex-situ regeneration procedure for a heavily sulfur-aged DFM aiming to minimize the consumption of critical raw materials within a circular economy approach.

Integrating calcium-looping and reverse-water–gas-shift reaction for CO2 capture and conversion: Screening of optimum catalyst

Integrating calcium-looping cycle (CaL) with reverse-water–gas-shift (RWGS) reaction represents an effective path to realizing integrated CO2 capture and utilization (ICCU). Screening a suitable catalyst to construct highly efficient CaO-based dual function materials (DFMs) is essential for CaL-RWGS. In the current work, M@CaO (M = Ni, Co, Mn, and Fe) DFMs are prepared for CaL-RWGS, and the influence of catalyst component on the structure, CO2 capture and RWGS performance, and kinetic behaviors of the CaO-based DFMs is investigated. Results show that the interaction between CaO and catalyst affects the average grain size and dispersion of metallic catalyst, oxygen vacancy concentration, surface basicity, and reducibility of CaO-based DFMs. The desired Mn@CaO DFMs exhibit outstanding CaL-RWGS performance at 650 °C, 15%CO2 and 50%H2, with a great CO2 uptake (12.30 mmol CO2/g), a favorable CO yield (5.92 mmol CO/g), and an impressive CO2 conversion (53.53%), as well as a high CO selectivity (89.98%). Furthermore, Mn@CaO exhibits excellent carbonation and regeneration kinetics but inferior working stability for CO2 capture and CO production in multiple CaL-RWGS cycles. Overall, Mn could be a competitive and cost-effective catalyst candidate for high-performance CaO-based DFMs for CaL-RWGS applications, while further work is needed to improve cyclic stability.

Assessment of CaO-based sorbent/spinel catalyst composites for the oxidative dehydrogenation of ethane in isothermal integrated CO2 capture and utilization

In this study, a comparative analysis of the isothermal integrated CO2 capture and utilization (ICCU) performance of MgB2O4 (B = Cr, Ga, Fe, Al)/CaCe15 was conducted. Results show that MgCr2O4/CaCe15 demonstrates exceptional performance, with CO2 uptake capacity, CO2 conversion, ethane conversion, ethylene selectivity, and ethylene yield after multiple cycles measuring at 0.22 g/g, 35.6 %, 19.6 %, 89 %, and 17.4 %, respectively. The dominant mechanism during the CO2 utilization stage was explored, and the coupling mechanism of catalytic dehydrogenation and reverse water–gas shift reaction is dominant. The reaction pathway during CO2 utilization was investigated, and results show that hydrogenation activation (CO2*+H* → HCOO* → CO*+OH*) is the primary pathway for CO2 dissociation, with the oxidative dehydrogenation of ethane mainly attributed to the activation of C–H on distinct C atoms, CH3CH3* → CH3CH2* → CH2CH2*. Meanwhile, the scission of the first C–H bond during CO2 utilization is the rate-determining step. Furthermore, we investigated the influencing factors and discovered that increasing the concentration of ethane and weight hourly space velocity both lead to a decrease in ethylene yield.

The Effect of Alkali Metals (Li, Na, and K) on Ni/CaO Dual-Functional Materials for Integrated CO2 Capture and Hydrogenation.

Ni/CaO, a low-cost dual-functional material (DFM), has been widely studied for integrated CO2 capture and hydrogenation. The core of this dual-functional material should possess both good CO2 capture-conversion performance and structural stability. Here, we synthesized Ni/CaO DFMs modified with alkali metals (Na, K, and Li) through a combination of precipitation and combustion methods. It was found that Na-modified Ni/CaO (Na-Ni/CaO) DFM offered stable CO2 capture-conversion activity over 20 cycles, with a high CO2 capture capacity of 10.8 mmol/g and a high CO2 conversion rate of 60.5% at the same temperature of 650 °C. The enhanced CO2 capture capacity was attributed to the improved surface basicity of Na-Ni/CaO. In addition, the incorporation of Na into DFMs had a favorable effect on the formation of double salts, which shorten the CO2 capture and release process and promoted DFM stability by hindering their aggregation and the sintering of DFMs.

Effect of the Ni-to-CaO Ratio on Integrated CO2 Capture and Direct Methanation

Direct methanation in an integrated CO2 capture and utilization system has recently gained considerable attention as a promising approach owing to its simplified process and lower requirement of total thermal energy as compared to conventional CO2 capture and utilization techniques. This study formulated macroporous structured Ni/CaO catal-sorbents by controlling the Ni-to-CaO ratio. The influence of this ratio on the CO2 capture (capacity and kinetics) and direct methanation performances (productivity and kinetics) was evaluated at 500 °C. CO2 capture combined with direct methanation experiments revealed that 10Ni/CaO exhibited the best CO2 capture capacity, kinetics, and CH4 productivity with the thermal stability of Ni and CaO species.

Flowsheet modelling and techno-economic analysis of CO2 capture coupled pyro-hydrolysis of CaCl2 waste for HCl acid regeneration

Pyro-hydrolysis of CaCl2 waste for HCl regeneration, which entails high temperatures and substantial energy consumption, remains challenging due to concerns regarding cost and CO2 emissions. This study presents a low-emission process integrating CO2 capture with SiO2-assisted CaCl2 pyro-hydrolysis technology for HCl regeneration, with a comparative techno-economic feasibility evaluation using Aspen Plus. When employing the same process components as for FeCl2 pyro-hydrolysis, it is demonstrated that 18 wt% HCl acid, a similar concentration to that generated from FeCl2 pyro-hydrolysis, can be produced from SiO2-assisted CaCl2 pyro-hydrolysis with a higher energy consumption. The CaCl2 pyro-hydrolysis were further optimized with the integration of water recycling and exhaust heat recovery, reducing the water and energy consumption down to −1.1 kg/kg-HCl gas and 21,601 kJ/kg-HCl gas, respectively. The water consumption is lower than that of the FeCl2 process (+ 5.4 kg/kg-HCl gas) and the energy consumption is at a comparable level with the FeCl2 process (20,989 kJ/kg-HCl gas). Furthermore, with the integration of a two-stage CO2 capture unit, the CO2 emission was reduced down to 0.07 kg/kg-HCl gas with a CO2 capture efficiency of 91%. Economic analysis results reveal that the capital and annual operating cost for the CO2 capture coupled CaCl2 pyro-hydrolysis is 12.5 million A$, and 4.1 million A$, respectively. The NPV, IRR, and payback duration of 13 million A$, 12.04%, and 8.6 years, respectively, could be achieved for the optimized CaCl2 pyro-hydrolysis scenario. The sensitive analysis results suggest that the HCl market price and annual operating cost are the most influential parameters and should be especially considered in a future deployment.

Limestone hydrogenation combined with reverse water–gas shift reaction under fluidized and iso-thermal conditions using MFB-TGA-MS

The integrated CO2 capture and utilization (ICCU) in conjunction with the reverse water–gas shift (RWGS) reaction has emerged as a promising approach to achieve carbon neutrality. However, the scalability of CaCO3 hydrogenation in the context of large volumes of industrial flue gas is impeded by the limited understanding of its performance under fluidized and iso-thermal conditions. This study utilized micro-fluidized bed thermogravimetric analysis coupled with mass spectrometry (MFB-TGA-MS) and in-situ measurements to investigate limestone decomposition under H2 and Ar atmospheres. Results showed that H2 atmosphere increased the limestone decomposition rate by 5-fold (79.1% CO2 conversion and ∼100% CO selectivity at 710 °C) compared to Ar, with RWGS as the dominant route and self-catalytic activity of calcined CaO. Morphology evolution revealed finer pores and textures under H2 conditions. Meanwhile, apparent kinetic models analyzed experimental data and showed a reduction in activation energy from 178.5 kJ/mol (Ar) to 161.3 kJ/mol (H2). These findings support the effectiveness of ICCU-RWGS approaches for further commercialization.

Synthesis and evaluation of novel and efficient Ni-based dual functional materials (DFMs) for integrated CO2 capture and hydrogenation

We report on the synthesis and evaluation of novel, highly active and stable bimetallic DFMs for simultaneous CO2 adsorption and subsequent hydrogenation to value added products. The DFMs contain various combinations of Ni (5–15 wt%) and Cu (5–15 wt%) with Na2O (5–15 wt%) as adsorbent supported on alumina (γ-Al2O3). The DFMs were synthesized via sequential incipient wetness impregnation method and were thoroughly characterized by combination of various surface sensitive and bulk sensitive analytical tools such as XRD, XPS, BET surface area, HR-TEM and H2-TPR. The DFMs were evaluated for CO2 capture and subsequent hydrogenation in a fixed-bed quartz tubular reactor connected with an online gas analyzer. The results demonstrated that at an operating temperature of 320℃, the DFM with a composition of 10 wt%Ni5wt%Cu/10 wt%Na2O.Al2O3 resulted in exceptionally high CO2 adsorption (310.84 μmol/g) and subsequent hydrogenation to methane (249.2 μmol CH4/gDFM). The XPS analysis revealed that this DFM contains comparatively larger percentage of highly ionized and/or induced Ni2+ as well as Cu+1 species. The results of H2-TPR also clearly indicated improvement in its reducibility. Moreover, the TEM analysis results revealed the presence of well-dispersed and smaller metal oxide particles in the bimetallic 10 wt%Ni5wt%Cu/10 wt%Na2O.Al2O3 DFM. In this regards, the exceptional high performance of the 10 wt%Ni5wt%Cu/10 wt%Na2O.Al2O3 DFM was attributed to the synergistic effects of the bimetallic combination of Ni with Cu resulting in enhanced physicochemical properties and thus demonstrated exceptionally higher performance.

Integrated capture and solar-driven utilization of CO2 from flue gas and air

Integrated capture and solar-driven utilization of CO2 from flue gas and air

An investigation of the Ni/carbonate interfaces on dual function materials in integrated CO2 capture and utilisation cycles

CO2 capture and utilisation (CCU) is a promising strategy to effectively mitigate the adverse greenhouse effects caused by CO2 emissions at an industrial scale. Through a process intensification strategy known as integrated CO2 capture and utilisation (ICCU), CO2 capture and catalytic CO2 conversion can be achieved in a single process with the use of dual function materials (DFMs), which are both CO2 sorbents and CO2 conversion catalysts. Given the significantly different operating conditions of ICCU from conventional catalytic CO2 hydrogenation, the catalytic mechanism of DFMs, especially during CO2 hydrogenation, needs to be thoroughly investigated. In this study, the relationship between the nature of the Ni/carbonate interfaces and the performance of Ni-based DFMs over ICCU cycles is systematically investigated. A series of Ni/alkaline earth carbonate DFMs were synthesised with varying Ca:Mg ratios to simulate different metal-carbonate model interfaces. At 400 °C, CH4 formation with nearly 100% CH4 selectivity was achieved on Ni/CaCO3 over 15 ICCU cycles. In general, Ni/CaCO3 interfaces correspond to higher CO2 conversion and higher CH4 selectivity than Ni/MgCO3 interfaces. Such trend may be attributed to the higher surface basicity of CaO and the higher thermal stability of CaCO3. As a consequence, the hydrogenation of the Ni/CaCO3 interface proceed via the formate pathway, in which carbonates are consecutively converted to surface formates, methoxyl, methyl species and eventually desorb as methane. This reaction model is applicable to the hydrogenation of both surface carbonate and bulk carbonates, although the former proceeds with much faster kinetics. On the weakly alkaline Ni/MgCO3 interface, MgCO3 preferentially decomposes to form gaseous CO2, which is subsequently hydrogenated via the reverse-water-gas-shift pathway, with CO as the key reaction intermediate. Interestingly, in situ infrared spectroscopy shows similar surface significant species during the direct hydrogenation of DFMs and during the conventional catalytic hydrogenation of molecular CO2, suggesting that the catalytic mechanisms during the two operating regimes are highly correlated.

Amino acid promoted single-step carbon dioxide capture and mineralization integrated with polymer-mediated crystallization of carbonates

Integrated CO2 capture and mineralization is a promising technology for cutting CO2 emissions and associated environmental impacts. Two major challenges in CO2 mineralization in aqueous media are (1) the lack of green and energy-efficient processes and (2) limited applications of the produced carbonates. Here, we present a very efficient, environmentally friendly, and convenient integrated CO2 capture and mineralization method to produce functional calcium carbonate (CaCO3) particles. We use a gas diffuser reaction setup to bubble CO2 in liquid media containing reagents such as amino acid as CO2 absorption promotor, water-soluble polymers as crystal growth modifiers, and Ca2+ ions. Different concentrations of amino acid L-arginine with a fixed CO2 bubbling rate were investigated for Ca2+ conversion. At the optimized conditions, more than 90% Ca2+ was converted to CaCO3 within 5 min of CO2 bubbling at a nominal rate. Additionally, functional carbonates that could be used as dye, heavy metals adsorbents, and functional composite fillers are produced using crystal growth modifiers. The method is simple, efficient, eco-friendly, and could be used for CO2/Ca2+-rich industrial waste valorization.