CO2 Capture System Research Articles

Post-combustion slipstream CO2-capture test facility at Jiangyou Power Plant, Sichuan, China: performance of a membrane separation module under dynamic power-plant operations

Abstract Membrane-based separation technologies have the potential to lower the cost of post-combustion CO2 capture from power-plant flue gases through reduced energy and capital costs relative to conventional solvent approaches. Studies have shown promise under controlled conditions, but there is a need for data on performance and reliability under field conditions. Coal-fired power plants in China operate in a dynamic manner, with increases and decreases in output causing changes in flue-gas composition. In this paper, we describe the first field test of a membrane-based post-combustion CO2-capture system connected to a dynamically operating power plant in China. We report the performance of a Membrane Technology Research, Inc. (MTR) PolarisTM membrane-based capture system over a range of plant operating loads ranging from 54% to 84% and conducted an operational stability test over a 168-h period during which the power plant was operating at an average load of 55%, but ramped as high as 79% and as low as 55%. Our results confirm the ability of a membrane capture system to operate effectively over a wide range of host-plant operating conditions, but also identity several issues related to plant integration, system control and resilience in the face of host-plant upsets that require attention as membrane separation systems move towards commercial use.

Evaluation of Calcium Looping Cycle as a Time-flexible CO2 Capture and Thermo-Chemical Energy Storage System

Currently, the time flexibility of energy conversion systems is an issue of great operational importance considering the high integration of time-irregular renewable energy sources (e.g., solar, wind) which put an additional pressure on the conventional fossil-based systems. In addition, the reduction of fossil CO2 emissions from various energy-intensive industrial sectors needs to be addressed considering the issues of global warming and climate change. This paper evaluates the innovative Calcium Looping (CaL) cycle both as an energy-efficient post-combustion CO2 capture option and as a time-flexible thermo-chemical energy storage system. As illustrative energy conversion system to which the calcium looping cycle will be applied, a natural gas-based combined cycle power plant was considered. The net power output was about 400 - 500 MW with a 90 % CO2 capture rate. Corresponded non-decarbonized case was also considered to calculate the CO2 capture penalty. In-depth modelling, simulation and thermal integration evaluations were done to cover the following relevant operational elements: characterization of decarbonized combined cycle power plants with CaL cycle with / without solid sorbent storage; mass and energy integration issues; detailed techno-economic and environmental calculations of main performance indicators; flexible part load operation of the power plant to take advantages of CaL thermo-chemical energy storage characteristics etc. As the results show, the flexible time-operation of the decarbonized power plant integrated with CaL cycle using sorbent storage option improves the overall performances e.g., capital cost reduction up to 10 %, lower electricity production cost up to 5 % etc.

Energy consumption, environmental performance, and techno-economic feasibility analysis of the biomass-to-hydrogen process with and without carbon capture and storage

Owing to the negative environmental impact and safety problems of fossil fuel resources, chemical processes based on renewable energy have been extensively studied for further development. In this study, the thermodynamic, economic, and environmental performances of biomass-to-hydrogen (BTH) conversion were assessed using corn straw as a raw material. Further, the process used to achieve BTH conversion with/without carbon capture and storage (CCS) was evaluated and analyzed in this study. According to the simulation results, the economic and environmental properties of BTH processes using different CO2 capture rates were evaluated via thermodynamics and life cycle assessment. Compared with the biomass hydrogen production process without CCS, the EC of the BTH process with CCS decreased by 17%. However, the total investment and production cost of biomass hydrogen production with CCS increased by 1.3% and 14.6–19.4%, respectively. The energy efficiency of BTH conversion with CCS was 17% lower than that of BTH conversion without CCS. Further, the payback period of the BTH process performed with CCS was approximately 5–6 years. According to the energy consumption and the economic and environmental performances, BTH conversion with a CO2 capture rate of 80% is a appropriate CCS system for CO2 capture. The life cycle assessment of BTH conversion demonstrates that the BTH system with CCS can result in negative greenhouse gas emissions. The development of the BTH process using CCS is thus of great significance for achieving carbon neutralization.

Computational Investigation of the Thermochemistry of the CO2 Capture Reaction by Ethylamine, Propylamine, and Butylamine in Aqueous Solution Considering the Full Conformational Space via Boltzmann Statistics.

Rubisco is the enzyme responsible for CO2 fixation in nature, and it is activated by CO2 addition to the amine group of its lysine 201 side chain. We are designing rubisco-based biomimetic systems for reversible CO2 capture from ambient air. The oligopeptide biomimetic capture systems are employed in aqueous solution. To provide a solid foundation for the experimental solution-phase studies of the CO2 capture reaction, we report here the results of computational studies of the thermodynamics of CO2 capture by small alkylamines in aqueous solution. We studied CO2 addition to methyl-, ethyl-, propyl-, and butylamine with the consideration of the full conformational space for the amine and the corresponding carbamic acids and with the application of an accurate solvation model for the potential energy surface analyses. The reaction energies of the carbamylation reactions were determined based on just the most stable structures (MSS) and based on the ensemble energies computed with the Boltzmann distribution (BD), and it is found that ΔGBD ≈ ΔGMSS. The effect of the proper accounting for the molecular translational entropies in solution with the Wertz approach are much more significant, and the free energy of the capture reactions ΔWGBD is more negative by 2.9 kcal/mol. Further accounting for volume effects in solution results in our best estimates for the reaction energies of the carbamylation reactions of ΔWABD = -5.4 kcal/mol. The overall difference is ΔGBD - ΔWABD = 2.4 kcal/mol for butylamine carbamylation. The full conformational space analyses inform about the conformational isomerizations of carbamic acids, and we determined the relevant rotational profiles and their transition-state structures. Our detailed studies emphasize that, more generally, solution-phase reaction energies should be evaluated with the Helmholtz free energy and can be affected substantially by solution effects on translational entropies.

Review on Carbon Capture in ICE Driven Transport

The transport sector powered by internal combustion engines (ICE) requires novel approaches to achieve near-zero CO2 emissions. In this direction, using CO2 capture and storage (CCS) systems onboard could be a good option. However, CO2 capture in mobile sources is currently challenging due to the operational and space requirements to install a CCS system onboard. This paper presents a systematic review of the CO2 capture in ICE driven transport to know the methods, techniques, and results of the different studies published so far. Subsequently, a case study of a CCS system working in an ICE is presented, where the energy and space needs are evaluated. The review reveals that the most suitable technique for CO2 capture is temperature swing adsorption (TSA). Moreover, the sorbents with better properties for this task are PPN-6-CH2-DETA and MOF-74-Mg. Finally, it shows that it is necessary to supply the energy demand of the CCS system and the option is to take advantage of the waste heat in the flue gas. The case study shows that it is possible to have a carbon capture rate above 68% without affecting engine performance. It was also found that the total volume required by the CCS system and fuel tank is 3.75 times smaller than buses operating with hydrogen fuel cells. According to the review and the case study, it is possible to run a CCS system in the maritime sector and road freight transport.

Evaluation on water balance and amine emission in CO2 capture

CO2 capture using amine-based solvent is now available for large scale deployment. Water balance and amine emission are drawing more and more attention as they have significant impacts on operation stability, economic cost and environmental pollution. However, experimentally investigating a new amine solvent in a demonstration test platform is time-consuming and costly. In this paper, a shortcut method was developed based on volatility data of a solvent to evaluate water balance and amine emission in CO2 capture system. Water balance can be achieved by employing a simple water wash after absorber and regulating water wash temperature according to flue gas temperature, CO2 concentration, and CO2 removal efficiency. Simple water wash reduces monoethanolamine (MEA) emission from absorber (215–425 mg/m3) to a level below 5 mg/m3. With constant water wash temperature, increasing absorber temperature condenses more water which is beneficial for reducing amine emission. Variable amines and configurations are also evaluated. Simple water wash is not efficient for those volatile solvents such as 40% 2-amino-2-methyl-1-propanol (AMP), piperazine (PZ)/1-(2-Hydroxyethyl)piperidine (HEPD), MEA/N-methylpyrrolidone (NMP) water-lean solvent, and 2-(diethylamino)ethanol (DEEA)/2-((2-aminoethyl) amino) ethanol (AEEA) biphasic solvent as their amine emissions after simple water wash are still higher than 100 mg/m3. For those solvents with moderate volatility, such as 30%MEA and 30–40%AMP, a second water wash is effective to reduce amine emission below 1 mg/m3. While for those highly volatile solvents, such as PZ/HEPD and DEEA blended biphasic solvents, acid wash for further amine emission reduction may be more competitive in view of capital cost and operation cost.

Non-isothermal electrochemically mediated amine regeneration for CO2 capture: Performance evaluation and optimization

Carbon dioxide emission is the main environmental impact of energy systems fed by carbon-intensive fuels. Developing CO2 capture systems can be an effective solution towards mitigating such detrimental impacts causing global warming. This study proposes a non-isothermal electrochemical CO2 capture and storage system operating based on ethylenediamine and copper ions. Also, the system is parametrically analyzed and optimized from an energy perspective. To conduct the parametric analysis, a mathematical model is developed based on the activities and equilibrium constants of the involved reactions. The influence of design variables on the system’s performance is investigated. The optimization study aims at minimizing the total electrical work consumed by the system via genetic algorithm. In both parametric and optimization studies, the impact of CO2 concentration in exhaust gases, varying from 4 % to 15 %, on the system’s performance is evaluated to measure the system’s ability to work under low CO2 concentration conditions. The results reveal that for the CO2 concentrations of 15 %, 10 %, and 4 %, the system’s minimum attainable total electrical work is 32.53, 32.9, and 34.18 kJ.mol−1CO2, respectively. These optimized works, however, are achieved at the cost of extra heating loads demanded by the system within the range of 152−156 kJ.mol−1CO2 that must be supplied at temperatures below 90 ℃.

Invoking chemical principles to predict the anions of dihydrooxazole family as prospective carbon capture moieties

The present study investigates 17 under-explored isomers of dihydrooxazole family, including oxazoline, oxadiazoline and oxatriazoline and their proposed anions as potential azolate based CO2 capture systems, using quantum chemical calculations. The presence of a π bond and –NH in the five-membered heterocyclic ring renders the isomers of dihydrooxazole family suitable for carbon capture, when deprotonated at the –NH nitrogen in the ring. Relative energies (ΔErel) of the isomers supported by their gas phase enthalpies of formation (ΔfH° (298.15 K)) and natural bond orbital (NBO) analysis, aided in the screening of stable anions suitable for CO2 capture. The deprotonation energies (ΔH298) of the isomers could establish a relationship between stability and basicity of the anions. The CO2-anion interaction with the selected anions was found to be feasible resulting into stable carbamates. The proposed anions could be a new addition to the family of azolate based carbon capture moieties.

Unravelling CO2 capture performance of microalgae cultivation and other technologies via comparative carbon balance analysis

Microalgae cultivation, absorption, adsorption, and membrane separation are widely applauded as promising technologies to sequester CO2 from flue gas. Herein, comparative carbon balance was used to elucidate their CO2 capture performance in the aspects of CO2 emission rates (direct, indirect, total, and net), CO2 removal efficiencies (apparent and actual), and CO2 removal rate per power input ratio. Screening criteria for effective CO2 capture system rule out energy-intensive sorption processes, put forward low energy membrane separation, and disclose alterable competency of microalgae cultivation. For CO2 capture from flue gas, microalgae (Chlorella vulgaris) cultivation in open raceway ponds was only inferior to membrane separation. To improve microalgal CO2 capture, the sensitivity analysis was performed by replacing original microalgae species (C. vulgaris) or cultivation system (open raceway pond). The microalgal CO2 capture in open raceway ponds became worse following the substitution of C. vulgaris with alternatives (Botryococcus braunii, Chlorella kessleri, Chlorella pyrenoidosa, Scenedesmus obliquus, Spirulina sp., or Tetraselmis suecica). For microalgal (C. vulgaris) CO2 capture, the competent cultivation systems included open raceway pond and airlift photobioreactor, while the bubble column, flat panel, or tubular photobioreactors were classified as non-competent systems. In short, microalgal (C. vulgaris) CO2 capture was technically feasible in open raceway pond or airlift photobioreactor; further, the use of airlift photobioreactor was preferred for better CO2 capture and microalgae biomass production. Due to the necessity of a huge working volume, the low scalability of microalgae cultivation could hamper the industrial application of microalgal CO2 capture from flue gas.

An Experiment on Flashing-Spray Jet Characteristics of Supercritical CO2 from Various Orifice Geometries

Supercritical CO2 pipelines usually are used to link the CO2 capture system to the geological storage. There are severe hazards once the asphyxiating gas leaks from the long-distance pipeline. The uncertainty of near-field jet characteristics results in imprecise consequences assessment of accidental release of supercritical CO2. To improve the prediction of consequences of accidental release accuracy, the near-field mechanisms of flashing-spray jet was investigated. In this work, an experimental setup with multiple measurement instruments was developed to impose controllable CO2 release from a high-pressure vessel. The flashing-spray jet structures of supercritical CO2 from circular and rectangular orifices were recorded by a high-speed camera. Results indicate that the near-field structures of supercritical CO2 jet from circular and rectangular orifices are totally different, which causes the different dispersion consequences. The jet angle and shock waves were analyzed quantitatively. Lastly, the models of flashing-spray based on the two different phenomena from rectangular and circular orifices were discussed. The combination of macroscopic and microscopic data in the jet can help to understand the complex physics and improve discharge and dispersion model. This work provides a fundamental data to consequences assessment of accidental release of supercritical CO2.

CCGT unit with a carbonation system for CO2 capture

The paper considers the issues of creating energy-efficient and environmentally friendly resource-saving energy generation technologies based on fossil fuels, solid waste and materials. A natural gas CCGT with a MSW ash carbonation unit was chosen as the research object. The prototype of the CCGT unit is the CCGT “Akademicheskaya” with an installed capacity of 230 MW. For the carbonation of MSW ash, a direct semi-dry route is used. In the calculation of the CCGT, the power and efficiency of the cycle are determined, as well as the parameters of the flue gas, which are transferred to the calculation of carbonation. As a result of calculations, it was found that this specific CO2 emissions from the power plant using carbonation can be reduced by almost 20% from 403 to 329 g kWh-1, however, a large amount of required MSW (2.6-6.7 kg per kg of flue gases) causes certain difficulties for the implementation of the project.

Modular monolith adsorbent systems for CO2 capture and its parameterized optimization

A key challenge for power plant carbon capture systems is operating economically under varying load conditions. Daily variations may be handled through control systems with reduced economic performance, but longer term seasonal cycles will require different solutions to enable robust and economic operation. We propose to use modular monolith adsorbent (MMA) designs whose capacity and configuration can be altered to respond to variations in flue gas flow. The configuration of the blocks is defined by the pattern of their serial and parallel connection. The ability to present a shorter, but wider, bed at different flue gas flowrates can then be exploited to improve performance and continuing to meet constraints on product purity and recovery. This additional degree of freedom afforded by the modular nature of the design allows an active response to the flowrate conditions and increases the flexibility of the system over the space of flowrate and concentration. In order to compare the proposed MMA systems and the conventional passive design method, case studies with varying flue gas amounts in a power plant are carried out. Simulation results show that the proposed MMA systems have improved optimal solutions because of their design flexibility, compared to the conventional passive design approach. Lastly, the optimized solutions are presented as a parametric map with different CO2 capture fractions and flowrate of flue gas. These parametric off-line solutions can be a guideline for the process implementation and reduce the operating complexity even if the MMA systems are used.

Production of cooling water by Ti3C2Tx MXene interlayered forward osmosis membranes for post-combustion CO2 capture system

Forward osmosis (FO) technology has the potential to replace the trim cooler and to supply cooling water for a post-combustion CO2 capture system. Herein, a high-performance MXene (Ti3C2Tx) interlayered FO membrane was fabricated. Thanks to the ability of MXene to adjust the structures of substrate and polyamide, the MXene interlayered FO (MXene-FO) membrane showed improved permeability and selectivity in a monoethanolamine (MEA) draw solution. The performance of MXene-FO membrane was investigated at different membrane orientations and temperatures with amino acid/salt (AAS) solutions (taurine/KOH and β-alanine/KOH) as draw solutions. Because the osmotic pressures provided by AAS solutions (104.4 ± 0.3 bar for 3 mol/L taurine/KOH and 153.7 ± 0.2 bar for 5 mol/L β-alanine/KOH solutions) are higher than that of 5 mol/L MEA solution (93.0 ± 0.1 bar), the MXene-FO membrane exhibited higher water fluxes in AAS solutions. Besides, the good performance of the MXene-FO membrane was shown with the presence of small specific amino acid fluxes and specific KOH fluxes. To investigate the feasibility of using saline water as the feed solution, 3.5 wt% NaCl solution was applied and the results indicated that the MXene-FO membrane maintained stable water fluxes and small specific solute fluxes. This work demonstrates the potential of nanomaterials interlayered FO membranes for cooling water production in a post-combustion CO2 capture system.

Ti3C2Tx MXene-Based Three-Dimensional Architecture for Carbon Dioxide Capture

Dramatic increases in fossil fuel consumption inevitably led to the emission of huge amounts of CO2 gas, causing abnormalities in the climate system. Despite continuous efforts to resolve global atmospheric problems through CO2 capture and separation, success has been limited by poor CO2 selectivity in the CO2/N2 mixture. Herein, we demonstrate the fabrication of a three-dimensional (3D) nanostructure from two-dimensional transition metal carbides (Ti3C2Tx, MXene), and assess its utility as an adsorbent in a CO2 capture system. Through structural and textural analysis, we confirm that the as-prepared MXene possesses high size uniformity with a thickness of ~2.5 nm, and that an MXene aerogel interconnected by MXene nanosheets has a 3D porous architecture with micro/nano porosity (Barrett-Joyner-Halenda (BJH) pore size = 11.4 nm). Moreover, the MXene aerogel exhibits favorable adsorption behavior for CO2, due to the high-quality MXene nanosheets even with a low specific surface area. Our approach could lead to significant advances in CO2 capture by adsorbents and open up new opportunities for mass production.

Electrowinning-coupled CO2 capture with energy-efficient absorbent regeneration: Towards practical application

Continuous drop of renewable electricity price offers excellent opportunity to electrify the CO2 capture processes in a cost-effective and decentralized way. Electrochemical CO2 capture represents a promising technology for CO2 emission reduction, particularly in the industries where thermal energy is not available. However, existing electrochemical technologies are either energy-intensive or operated at impractically low current densities. Here, we report an electrowinning-coupled CO2 capture (ECC) system which mimics industrially available electro-refining process for an energy-efficient amine-based CO2 capture. In applying ammonia as CO2 capture solvent and zinc metal as electrowinning medium, we experimentally achieved a low power consumption of 14.7 kJe/mol CO2 for solvent regeneration at an industrially preferred current density of 100 A/m2. This energy performance is very competitive with other state-of-the-art electrochemical CO2 capture technologies (50–500 kJe/mol CO2), and also outperforms the commercial amine processes driven by thermal energy (100–150 kJth/mol CO2). The desirable energy performance is due to the single-step two-electrons Zn(NH3)42+/Zn(s) redox reactions occurred during electrochemical operation of ECC, which avoids the formation of stable intermediate species and thus brings a low energy consumption. We anticipate the energy competitiveness would pave the way for ECC to move towards practical application.

Assessment of Hybrid Solvent—Membrane Configurations for Post-Combustion CO2 Capture for Super-Critical Power Plants

The reduction of fossil CO2 emissions from key relevant industrial processes represents an important environmental challenge to be considered. To enable large-scale deployment of low carbon technologies, a significant research and development effort is required to optimize the CO2 capture systems. This work assesses various hybrid solvent-membrane configurations for post-combustion decarbonization of coal-based super-critical power plants. As an illustrative chemical solvent, Methyl-Di-Ethanol-Amine was assessed. Various membrane unit locations were assessed (e.g., top absorber, before absorber using either compressor or vacuum pump). All investigated designs have a 1000 MW net power output with a 90% decarbonization ratio. Benchmark concepts with and without carbon capture using either reactive gas-liquid absorption or membrane separation technology were also evaluated to have a comparative assessment. Relevant evaluation tools (e.g., modeling, simulation, validation, thermal integration, etc.) were employed to assess the plant performance indicators. The integrated evaluation shows that one hybrid solvent-membrane configuration (membrane unit located at the top of absorption column) performs better in terms of increasing the overall net plant efficiency than the membrane-only case (by about 1.8 net percentage points). In addition, the purity of captured CO2 stream is higher for hybrid concepts than for membranes (99.9% vs. 96.3%). On the other hand, the chemical scrubbing concept has superior net energy efficiency than investigated hybrid configurations (by about 1.5–3.7 net percentage points).

Hierarchical porous graphene oxide/carbon foam nanocomposites derived from larch for enhanced CO2 capture and energy storage performance

The development of biomass-based carbon foams with hierarchical pore structures could lead to practical applications in CO2 capture systems and supercapacitors. However, these materials typically exhibit inferior adsorption and electrochemical characteristics because their pore structures are damaged during processing. The present work synthesized hierarchical porous graphene oxide (GO)/biomass-based carbon foam (GCF) nanocomposites from liquefied larch sawdust using in situ polymerization, foaming and carbonization steps. The GO enhanced the thermal stability of the foam while preventing collapse of the pore structure. The resulting GCF nanocomposites possessed hierarchical pore structures with greater ultramicroporosity than the original CF, especially with regard to the number of pores with sizes from 0.50 to 0.80 nm. Micropores with diameters less than 0.60 and 0.80 nm were found to be the primary factors determining CO2 adsorption at 0.15 and 1 bar, respectively, such that the GCF-0.2 (the addition of 0.2 wt%) exhibited the highest CO2 capacity of 4.99 mmol g−1 at 0 °C and 1 bar. These materials also showed CO2/N2 selectivity values up to 100.21, moderate heats of adsorption between 10.27 and 18.77 kJ mol−1 and good stabilities. The GCF-0.2 displayed a specific capacitance of 173.20 F g−1 at a current density of 1A g−1 in a 6 M KOH electrolyte and demostrated superior capacitance retention that could lead to applications in supercapacitors.

On optimisation of N2 and CO2-selective hybrid membrane process systems for post-combustion CO2 capture from coal-fired power plants

A superstructure-based optimisation model for the CO2 capture process using an N2-selective and CO2-selective membranes is presented. The model automatically selects either of the membranes for each membrane stage to have a hybrid membrane CO2 capture process. The superstructure embeds numerous process routes and allows the collection of product streams and residue streams from either the retentate side or permeate side of the multi-membrane stages. This results in novel process flowsheets for post-combustion CO2 capture using membrane technology. In the study, the optimisation of carbon capture by an all N2-selective membrane process is also carried out. At 90% recovery and 95% product purity, the multi-stage optimisation of the N2–CO2 hybrid membrane process reduces the total membrane area by 46% and the cost of capture by 14% compared to the optimised CO2-selective membrane process.

Carbon Capture and Storage Energy Consumption and Performance Optimization Using Metamodels and Response Surface Methodology

Abstract Oil and gas industries have high carbon dioxide (CO2) emissions, which is a great environmental concern. Monoethanolamine (MEA) is widely used as a solvent in CO2 capture and storage (CCS) systems. The challenge is that MEA–CCS itself is an energy-intensive process that requires optimum configuration and operation, and numerous design parameters and heat demands must be considered. Thus, the current work evaluates the energy distributions and CO2 removal efficiency of a CCS installed in floating production storage and offloading units under different operating conditions of a power and heat generation hub. The optimization procedures are implemented using highly accurate surrogate models for the following responses: (1) overall power consumption of CCS, (2) CCS separation performance, and (3) CCS heating and cooling demands. The input variables considered in the present research include the following: (1) the exhaust gas compositions and mass flowrate, (2) the operating pressure and temperature parameters of CCS and the injection compression unit, (3) the structural parameters of absorber and stripper columns, and (4) MEA solution parameters. The optimum CCS configuration significantly reduces the total heating and cooling demands by 62.77% (7 × 106 kW) and the overall power consumption by 8.65% (1.8 MW), and it increases the CCS separation performance by 4.46% (97.46%) and mitigates the CO2 emissions of proper CCS by 1.02 t/h compared with conventional operating conditions.

Regeneration of Na2Q in an Electrochemical CO2 Capture System

The CO2 capture system based on the electrochemical desorption at room temperature and atmospheric pressure may solve the high regeneration energy consumption problem of the amine-based postcombustion CO2 capture technology. In our former work, 0.7 M Na2Q was used to absorb CO2, and the pH mediator, tiron (QH2), was used to adjust the pH of the solution during the redox process to desorb CO2 and regenerate the absorbent. However, the absorbent does not completely regenerate due to the poor reduction of Q. In this work, the regeneration of 0.05–0.7 M Na2Q and the modification of graphite felt (GF) electrodes were further investigated. The results show that the reproducibility and the cyclicality of the Na2Q solution with a lower concentration (0.1 M) are better than those of 0.7 M Na2Q under the same conditions. The GF electrodes after acid treatment, heat treatment, phosphorus-doped, or MnO2-modified improve their electrochemical activities under acidic and weakly alkaline conditions. Phosphorus-doped or MnO2-modified GF electrodes also significantly improve the redox reaction under strongly alkaline conditions. The process of CO2 capture combining the Na2Q regeneration with the CO2 absorption is proposed to improve the reducibility of Q. In addition, a possible electrochemical reaction process of the Na2Q system is proposed. QH2 is oxidized to produce Q, in which a 1,4-Michael reaction to produce sodium 1,2,4-trihydroxybenzene-3,5-disulfonate occurs. The byproduct tiron-o-quinone is also produced, which could further polymerize to form oligomers. During the reduction of high-concentration Na2Q, the oligomers precipitate out of the solution, resulting in inhibition of the reduction.