Enhancing CO2 capture of an aminoethylethanolamine-based non-aqueous absorbent by using tertiary amine as a proton-transfer mediator: From performance to mechanism

Non-aqueous absorbents (NAAs) have attracted increasing attention for CO2 capture because of their great energy-saving potential. Primary diamines which can provide high CO2 absorption loading are promising candidates for formulating NAAs but suffer disadvantages in regenerability. In this study, a promising strategy that using tertiary amines (TAs) as proton-transfer mediators was proposed to enhance the regenerability of an aminoethylethanolamine (AEEA, diamine)/dimethyl sulfoxide (DMSO) (A/D) NAA. Surprisingly, some employed TAs such as N,N-diethylaminoethanol (DEEA), N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDETA), 3-dimethylamino-1-propanol (3DMA1P), and N,N-dimethylethanolamine (DMEA) enhanced not only the regenerability of the A/D NAA but also the CO2 absorption performance. Specifically, the CO2 absorption loading and cyclic loading were increased by about 12.7% and 15.5%-22.7%, respectively. The TA-enhanced CO2 capture mechanism was comprehensively explored via nuclear magnetic resonance technique and quantum chemical calculations. During CO2 absorption, the TA acted as an ultimate proton acceptor for AEEA-zwitterion and enabled more AEEA to form carbamate species (AEEACOO-) to store CO2, thus enhancing CO2 absorption. For CO2 desorption, the TA first provided protons directly to AEEACOO- as a proton donor; moreover, it functioned as a proton carrier and facilitated the low-energy step-wise proton transfer from protonated AEEA to AEEACOO-. Consequently, the presence of TA made it easier for AEEACOO- to obtain protons to decompose, resulting in enhanced CO2 desorption. In a word, introducing the TA as a proton-transfer mediator into the A/D NAA enhanced both the CO2 absorption performance and the regenerability, which was an efficient way to "kill two birds with one stone".

Photoresponsive Covalent Organic Frameworks: Visible-Light Controlled Conversion of Porous Structures and Its Impacts

Covalent organic frameworks are a novel class of crystalline porous polymers that enable molecular design of extended polygonal skeletons to attain well-defined porous structures. However, construction of a framework that allows remote control of pores remains a challenge. Here we report a strategy that merges covalent, noncovalent, and photo chemistries to design photoresponsive frameworks with reversibly and remotely controllable pores. We developed a topology-guided multicomponent polycondensation system that integrates protruded tetrafluoroazobenzene units as photoresponsive sites on pore walls at predesigned densities, so that a series of crystalline porous frameworks with the same backbone can be constructed to develop a broad spectrum of pores ranging from mesopores to micropores. Distinct from conventional azobenzene-based systems, the tetrafluoroazobenzene frameworks are highly sensitive to visible lights to undergo high-rate isomerization. The photoisomerization exerts profound effects on pore size, shape, number, and environment, as well as molecular uptake and release, rendering the system able to convert and switch pores reversibly and remotely with visible lights. Our results open a way to a novel class of smart porous materials with pore structures and functions that are convertible and manageable with visible lights.

Low temperature and facile synthesis of nitrogen-doped hierarchical porous carbon derived from waste polyethylene terephthalate for efficient CO2 capture

Waste polyethylene terephthalate (PET) with high carbon content (>60 wt%) has shown great potential in the field of synthesizing carbon materials for CO2 capture, attracting increasing attention. Herein, an innovative strategy was proposed to synthesize nitrogen-doped hierarchical porous carbon (PC) for CO2 capture using PET as precursor and sodium amide (NaNH2) as both nitrogen dopant and low-temperature activator. As-synthesized N-doped PC exhibited a significantly high micropore volume of 0.755 cm3/g and a rich content of N- and O-containing functional groups, offering ample active sites for CO2 molecules. Further, the adsorbents demonstrated excellent CO2 capture capacity, achieving 5.7 mmol/g (0 °C) and 3.3 mmol/g (25 °C) at 1 bar, respectively. This was primarily attributed to the synergistic effect of narrow micropores filling and electrostatic interactions. Moreover, as-synthesized PC exhibited rapid CO2 adsorption capability, and its dynamic adsorption process was effectively described using a pseudo-second-order kinetic model. After five consecutive cycles, PET-derived PC still maintained ~100 % of adsorption capacity. They also possessed good CO2/N2 selectivity and reasonable isosteric heat of adsorption. Therefore, as-synthesized nitrogen-doped PC is a promising CO2 adsorbent through low-temperature activation of carbonized PET with NaNH2. Such findings have substantial implications for waste plastic recycling and mitigating the greenhouse effect.

Closo-[B12 H12 ]2- Derivatives with Polar Groups As Promising Building Blocks in Metal-Organic Frameworks for Gas Separation

Engineering design of metal organic frameworks (MOFs) for gas separation applications is nowadays a thriving field of investigation. Based on the recent experimental studies of dodecaborate-hybrid MOFs as potential materials to separate industry-relevant gas mixtures, we herein present a systematic theoretical study on the derivatives of the closo-dodecaborate anion [B12 H12 ]2- , which can serve as building blocks for MOFs. We discover that amino functionalization can impart a greater ability to selectively capture carbon dioxide from its mixtures with other gases such as nitrogen, ethylene and acetylene. The main advantage lies in the polarization effect induced by amino group, which favors the localization of the negative charges on the boron-cluster anion and offers a nucleophilic anchoring site to accommodate the carbon atom in carbon dioxide. This work suggests an appealing strategy of polar functionalization to optimize the molecule discrimination ability via preferential adsorption.

Readily regenerable amine-free CO2 sorbent based on a solid-supported carboxylate ionic liquid

Accumulation of anthropogenic CO₂ is undoubtedly the major cause of global warming. In addition to reducing emissions, minimising the threatening effects of climate change in the near future might also require the capture of enormous amounts of CO₂ from point sources or from the atmosphere. In this regard, the development of novel affordable and energetically attainable capture technologies is greatly needed. In this work, we report rapid and greatly facilitated CO₂ desorption for amine-free carboxylate ionic liquid hydrates as compared to a benchmark amine-based sorbent. Complete regeneration was achieved at moderate temperature (60 °C) over short capture-release cycles using model flue gas on a silica-supported tetrabutylphosphonium acetate ionic liquid hydrate (IL/SiO₂), whereas the polyethyleneimine counterpart (PEI/SiO₂) only recovered half its capacity after the first cycle in a rather sluggish release process under the same conditions. The IL/SiO₂ sorbent achieved a slightly superior working CO₂ capacity than PEI/SiO₂. The easier regeneration of carboxylate ionic liquid hydrates, which behave as chemical CO₂ sorbents leading to bicarbonate in a 1:1 stoichiometry, is due to their relatively low sorption enthalpies (≈40 kJ mol^-1). The faster and more efficient desorption from IL/SiO₂ fits a first-order kinetic model (k = 0.73 min^-1), whereas a more complex process was observed for PEI/SiO₂ (pseudo-first order initially, k = 0.11 min^-1, pseudo-zero order at later stages). The remarkably low regeneration temperature, the absence of amines and the non-volatility of the IL sorbent are favourable assets to minimise gaseous stream contamination. Importantly, regeneration heats -a crucial parameter for practical application- are advantageous for IL/SiO₂ (4.3 kJ g (CO₂)^-1) vs. PEI/SiO₂, and fall within the range of typical amine sorbents indicating a remarkable performance at this proof-of-concept stage. Further structural design will enhance the viability of amine-free ionic liquid hydrates for carbon capture technologies.

Light Triggered Pore Size Tuning in Photoswitching Covalent Triazine Frameworks for Low Energy CO2 Capture

Recently, photo switching porous materials have been widely reported for low energy costed CO2 capture and release via simply remoted light controlling method. However, most reported photo responsive CO2 adsorbents relied on metal organic framework (MOFs) functionalisation with photochromic moieties, and MOF adsorbents still suffered from chemically and thermally unstable issues. Thus, further metal free and highly stable organic photoresponsive adsorbents are necessary to be developed. Covalent triazine frameworks (CTFs), because of their high porosity and stability, have attracted great attention for CO2 capture. Considering the high CO2 uptake capacity and structural tunability of CTFs, it suggests high potential to fabricate the photoswitching CTF materials by the same functionalisation method as MOFs. Herein, the first series of photo switching CTFs were developed for low energy CO2 capture and release. Apart from that, the CO2 switching efficiency could be doubled either through the azobenzene numbers adjusting method or through the previously reported structural alleviation strategy. Furthermore, the pore size distribution of azobenzene functionalised PCTFs also could be tuned under UV exposure, which may contribute to the UV light induced decrease of CO2 uptake capacity. These photoswitching CTFs represented a new kind of porous polymers for low energy costed CO2 capture.

Carbon dioxide separation and capture by adsorption: a review

Rising adverse impact of climate change caused by anthropogenic activities is calling for advanced methods to reduce carbon dioxide emissions. Here, we review adsorption technologies for carbon dioxide capture with focus on materials, techniques, and processes, additive manufacturing, direct air capture, machine learning, life cycle assessment, commercialization and scale-up.

Post-combustion CO2 capture via a variety of temperature ranges and material adsorption process: A review

Carbon dioxide (CO₂) emissions from fossil fuel combustion have been linked to increased average global temperatures, a global challenge for many decades. Mitigating CO₂ concentration in the atmosphere is a priority for the protection of the environment. This is a comparison of the three main technological categories available for CO₂ capture and storage. They include: oxy-fuel combustion, pre-combustion, and post-combustion. Each capture technology has inherent benefits and disadvantages in cost, implementation, and flexibility, but post-combustion CO₂ capture has demonstrated the most promising results in typical power plant configurations. This paper presents a review of different post-combustion CO₂ capture materials; solvents, membranes, and adsorbents, focusing on economical and environmentally safe low to high temperature solid adsorbents. Furthermore, the authors summarize the advantages and limitations of the materials investigated to provide insight into the challenges and opportunities currently facing the development of post-combustion CO₂ capture technologies. The solid sorbents currently available for CO₂ capture are also reviewed in detail, including physical and chemical properties, reactions, and current research efforts on improvement.

The feasibility of CO2 emission reduction by adsorptive storage on Polish hard coals in the Upper Silesia Coal Basin: An experimental and modeling study of equilibrium, kinetics and thermodynamics

Carbon dioxide storage in unmineable coal seams is advantageous in the highly industrialized areas, such as the Upper Silesia Coal Basin (USCB), Poland, where heavy industry constitutes the source of huge CO₂ emissions and coal mines will be closed in the future, due to unprofitability. The paper presents the results of experimental and theoretical research of CO₂ capture on medium rank C and B bituminous coals coming from three mines located in the USCB. The porous texture of the investigated adsorbents was analyzed using SEM images and the N₂ and CO₂ isotherms at -196 °C and 0 °C, respectively. Qualitative studies using DRIFT spectroscopy showed that band intensity attributed to the functional groups of coals changed after CO₂ adsorption. The analyses encompassed the equilibrium, kinetics and thermodynamics of CO₂ adsorption on coals at 25, 50 and 75 °C (up to 2000 kPa). The adsorption isotherms were obtained by the static gravimetric method and described by means of the Langmuir, Freundlich, Dubinin-Radushkevich and Dubinin-Astakhov models. The highest CO₂ uptakes were obtained for medium rank C bituminous coals at 25 °C; the values were 1.600 mol/kg and 1.274 mol/kg. The adsorption kinetics was better characterized by the Avrami fractional-order model rather than by the pseudo-first and pseudo-second order models. The results reveal that the adsorption process is the fastest for medium rank C bituminous coals. The isosteric heats of adsorption were calculated in the following two ways: based on the multi-temperature Toth isotherm and the Clausius-Clapeyron equations. Depending on degree of coal metamorphism, the heat of adsorption ranged from 18 to 26 kJ/mol. The estimated maximum temperature increase due to heat accumulation in the insulated coalbed during CO₂ adsorption was 6 °C and did not reach the self-ignition temperature in any of the tested adsorption systems.

Biosorptive efficacy of granular activated carbon in pressure swing adsorption based model cooling system: performance assessment, isotherm modeling and cost evaluation

The notable environmental concerns of the halogen-containing obnoxious conventional refrigerants have grounded to devise the environmentally benign and efficient cooling system. In view of this alarming issue, an experimental model cooling system based on pressure swing adsorption-desorption (PSAD) mechanism has been contrived for its performance assessment and analysis of isotherm modeling. The physicochemical properties of the wood apple (Limonia acidissima) shell-derived carbonized char are enhanced by multi-stage activation to obtain two activated carbon granular adsorbents viz. PCACG and ACG towards their application in the proposed system. The performance indicative microporous characteristics of the adsorbents are investigated, and it is observed that the indigenously prepared activated carbon possesses high surface area, i.e., 1065 m² gm^-1 and 1023 m² gm ^-1 for PCACG and ACG, respectively. Carbon dioxide and bio-precursor-based adsorbents are used as adsorbent-adsorbate pair in the developed single-bed cooling system. The coefficient of performance (COP) of the cooling system are computed to be 4.93 and 2.79 utilizing PCACG and ACG, respectively while the cooling effects are quantified as 146.26 J s ^-1 and 128.48 J s^-1.Besides, the CO₂ gas adsorption mechanism onto solid adsorbent surfaces has been interpreted by Langmuir, Dubinin-Raduskevich (D-R), and Dubinin-Astakhov (D-A) isotherm models. Among them, D-A isotherm has accurately predicted the adsorption mechanism of carbon dioxide on to adsorbent. Importantly, the cost estimation of preparing PCACG and ACG exhibited the cost-effectiveness for their successful application. Based on their comparative characteristics, it is observed that the PCACG adsorbent is more energy efficient than ACG in the long run.

Investigating algae for CO2 capture and accumulation and simultaneous production of biomass for biodiesel production

Carbon capture and sequestration technologies are used to reduce carbon emissions. Membranes, solvents, and adsorbents are the three major methods of CO₂ capture. One of the promising methods is the use of algae to absorb CO₂ from flue gases and convert it into biomass. Algae have great potential as renewable fuel sources and CO₂ capture using photosynthesis for carbon fixation has also attracted much attention. This paper presents an extensive and in-depth report on the utilization of algae for carbon capture and accumulation. This is done in conjunction with cultivating the algae for the production of biomass for biodiesel production. Different systems are investigated for algae cultivation as well as carbon capture to effectively mitigate carbon emissions. The performance and productivity of these biosystems depend on various conditions including algae type, light sources, nutrients, pH, temperature, and mass transfer. Macroalgae and microalgae species were explored to determine their suitability for carbon capture and sequestration, along with the production of biodiesel. The steps for producing biodiesel were comprehensively reviewed, which are harvesting, dehydrating, oil extraction, oil refining, and transesterification. This technology combines active carbon capture with the potential of biodiesel production.

Review of post-combustion carbon dioxide capture technologies using activated carbon

Carbon dioxide (CO₂) is the largest anthropogenic greenhouse gas (GHG) on the planet contributing to the global warming. Currently, there are three capture technologies of trapping CO₂ from the flue gas and they are pre-combustion, post-combustion and oxy-fuel combustion. Among these, the post-combustion is widely popular as it can be retrofitted for a short to medium term without encountering any significant technology risks or changes. Activated carbon is widely used as a universal separation medium with series of advantages compared to the first generation capture processes based on amine-based scrubbing which are inherently energy intensive. The goal of this review is to elucidate the three CO₂ capture technologies with a focus on the use of activated carbon (AC) as an adsorbent for post-combustion anthropogenic CO₂ flue gas capture prior to emission to atmosphere. Furthermore, this coherent review summarizes the recent ongoing research on the preparation of activated carbon from various sources to provide a profound understanding on the current progress to highlight the challenges of the CO₂ mitigation efforts along with the mathematical modeling of CO₂ capture. AC is widely seen as a universal adsorbent due to its unique properties such as high surface area and porous texture. Other applications of AC in the removal of contaminants from flue gas, heavy metal and organic compounds, as a catalyst and catalyst support and in the electronics and electroplating industry are also discussed in this study.

Biological and chemical treatment technologies for waste amines from CO2 capture plants

Amine-based carbon dioxide capture is the most mature technology for reducing flue gas CO₂ emissions. It has been postulated and observed during commercialisation of this technology that significant quantities of waste amines are produced. Further industrial implementation of this technology requires adequate disposal or valorisation options for this waste. This review presents an analysis of seven biological and chemical technologies for waste amine amelioration or valorisation. Of these, the biological treatments are identified as being more mature for industrial application with the capacity for marketable product generation. Slow speed is the main drawback of the biological processes but this does not hinder their commercial viability. Using waste amine for NOx reduction in power stations is a secondary option, where it seems probable that the amount of waste amine generated in the CO₂ capture plant is sufficient to fulfil the DeNOx requirements of the flue gas. This route, however, requires investigation into the impact of waste amine impurities on the power station and the CO₂ capture plant operations.

Prospects and issues of integration of co-combustion of solid fuels (coal and biomass) in chemical looping technology

The utilization of fossil fuels leads to the emission of greenhouse gases into the environment. As a consequence, ozone layer depletion, global warming, acid rain, etc. are caused. Thus, alternate ways have to be planned to eradicate the detrimental effects of the usage of fossil fuels. As biomass is a renewable energy source, co-utilization of coal with biomass could significantly reduce carbon emission. In addition, chemical looping combustion (CLC) is a promising technology for the inherent capture of CO₂ without any post-treatment of flue gas. Hence, the integration of co-combustion of solid fuel with CLC technology can produce clean energy in the context of carbon negative system. The present study addresses the issues and prospects of the co-CLC process of solid fuels such as coal and biomass. Low-cost oxygen carriers, which are suitable for the solid-CLC process, are elucidated. The effect of solid fuel based inherent constituents such as ash, volatile matter and tar on the performance of the CLC process is discussed. Furthermore, the beneficial and inhibitory effects of the co-combustion of solid fuels are elaborated. The formation and reduction mechanism of NO_x and SO_x pollutants during the CLC process are investigated. In addition, the effect of gasifying medium (CO₂ and steam) during the co-CLC technology is also discussed. The performance of the CLC based thermal power plants is analyzed, and the results show a gain of 5-6% in net thermal efficiency, compared to a power system operating under conventional technology. The effect of the process parameters on gas conversion, char conversion, overall solid fuel conversion, combustion efficiency and CO₂ yield is investigated. The investigation shows that the co-combustion based CLC is a potential technology for the implementation of carbon capture and storage (CCS) with a low energy penalty.

CO2 utilization via a novel anaerobic bioprocess configuration with simulated gas mixture and real stack gas samples

CO₂, which is considered to be one of the major causes of climate change, has reached to critical levels in the atmosphere due to tremendous consumption of fossil fuels all over the world. In this study, anaerobic bioconversion of CO₂ into bio-methane using a novel bioprocess configuration (HYBRID bioreactor) was studied under mesophilic conditions. Varying ratios of H₂/CO₂ gas mixture and volumetric feeding rates were investigated and no additional organic matter and trace element were needed throughout the study. The maximum methane production of 19 m³ CH₄/m³ _reactor/d was achieved at a H₂/CO₂ ratio of 4:1 and feeding rate of 24 m³ gas/m³ _reactor/d. It was determined that H₂ conversion rate is about 96%. For demonstration purpose, real stack gas sample from a petrochemical industry was also tested under optimized operational conditions. No inhibitory effect from stack gas mixture was observed. This study provided an environmentally friendly and sustainable solution for industries such as petrochemical industry in order to produce extra energy while capturing their waste CO₂. Thereby, a sustainable and environmentally friendly model solution was presented for industries with high CO₂ emissions.

Immobilized carbonic anhydrase: preparation, characteristics and biotechnological applications

Carbonic anhydrase (CA) is an essential metalloenzyme in living systems for accelerating the hydration and dehydration of carbon dioxide. CA-catalyzed reactions can be applied in vitro for capturing industrially emitted gaseous carbon dioxide in aqueous solutions. To facilitate this type of practical application, the immobilization of CA on or inside solid or soft support materials is of great importance because the immobilization of enzymes in general offers the opportunity for enzyme recycling or long-term use in bioreactors. Moreover, the thermal/storage stability and reactivity of immobilized CA can be modulated through the physicochemical nature and structural characteristics of the support material used. This review focuses on (i) immobilization methods which have been applied so far, (ii) some of the characteristic features of immobilized forms of CA, and (iii) biotechnological applications of immobilized CA. The applications described not only include the CA-assisted capturing and sequestration of carbon dioxide, but also the CA-supported bioelectrochemical conversion of CO₂ into organic molecules, and the detection of clinically important CA inhibitors. Furthermore, immobilized CA can be used in biomimetic materials synthesis involving cascade reactions, e.g. for bone regeneration based on calcium carbonate formation from urea with two consecutive reactions catalyzed by urease and CA.

A novel process for CO2 capture by using sodium metaborate. Part I: effects of calcination

This paper presents a comprehensive study on the carbonation of sodium metaborate (NaBO₂) and the synthesis of high added value chemicals via NaBO₂ and carbon dioxide (CO₂). Carbon dioxide (CO₂) is a greenhouse gas and NaBO₂ is a by-product of sodium borohydride (NaBH₄) hydrolysis reaction to produce H₂. Therefore their transformation into commercial chemicals is quite important in order to provide a mutual benefit to global warming issue and hydrogen economy. In the presented study, reaction parameters such as hydration factor, furnace type, calcination temperature, and environment are investigated at different levels and optimized. The effects of those key parameters on CO₂ fixation yield are discussed. It is found that 400 °C is a key temperature for dehydration and reaction steps. Both dehydrated NaBO₂ is obtained and maximum carbonation conversion is reached at 400 °C. Moreover, at relatively low temperatures (below 400 °C), a new reaction pathway is proposed and proved by thermodynamic calculations. Structural properties of NaBO₂ are exhibited differences regard to thermal exposure and the conversion is strictly related to the structural properties.

Utilization of waste bittern from saltern as a source for magnesium and an absorbent for carbon dioxide capture

During solar salt production, large quantities of bittern, a liquid by-product containing high inorganic substance concentrations, are produced. The purpose of this research was to examine the utilization of waste bittern generated from salterns as a source for Mg production and as an absorbent for carbon dioxide (CO₂) capture. The study was conducted in a sequential two-step process. At NaOH/Mg molar ratios of 2.70-2.75 and pH 9.5-10.0, > 99% Mg precipitation from the bittern was achieved. After washing with water, 100-120 g/L of precipitate containing 94% Mg(OH)₂ was recovered from the bittern. At the optimum NH₄OH concentration of 5%, 120 g of sodium bicarbonate precipitate per liter of bittern were recovered, which was equivalent to 63 g CO₂ captured per liter of bittern. These results can be used to support the use of bittern as a resource and reduce economic losses during solar salt production.

Olivine dissolution from Indian dunite in saline water

The rate and mechanism of olivine dissolution was studied using naturally weathered dunite FO_98.21(Mg_1.884Fe_0.391SiO₄) from an Indian source, that also contains serpentine mineral lizardite. A series of batch dissolution experiments were carried out to check the influence of temperature (30-75 ^∘C), initial dunite concentration (0.5 and 20 g/L), and salinity (0-35 g/L NaCl) under fixed head space CO₂ pressure (P[Formula: see text] = 1 barg) on dunite dissolution. Dissolved Mg, Si, and Fe concentrations were determined by inductive coupled plasma atomic emission spectroscopy. End-product solids were characterized by scanning electron microscopy and X-ray diffraction. Initially, rates of dissolution of Si and Mg were observed to be in stoichiometric proportion. After 8 h, the dissolution rate was observed to decline. At the end of the experiment (504 h), an amorphous silica-rich layer was observed over the dunite surface. This results in decay of the dissolution rate. The operating conditions (i.e., salinity, temperature, and mineral loading) affect the dissolution kinetics in a very complex manner because of which the observed experimental trends do not exhibit a direct trend.

Carbon dioxide capture strategies from flue gas using microalgae: a review

Global warming and pollution are the twin crises experienced globally. Biological offset of these crises are gaining importance because of its zero waste production and the ability of the organisms to thrive under extreme or polluted condition. In this context, this review highlights the recent developments in carbon dioxide (CO2) capture from flue gas using microalgae and finding the best microalgal remediation strategy through contrast and comparison of different strategies. Different flue gas microalgal remediation strategies discussed are as follows: (i) Flue gas to CO2 gas segregation using adsorbents for microalgal mitigation, (ii) CO2 separation from flue gas using absorbents and later regeneration for microalgal mitigation, (iii) Flue gas to liquid conversion for direct microalgal mitigation, and (iv) direct flue gas mitigation using microalgae. This work also studies the economic feasibility of microalgal production. The study discloses that the direct convening of flue gas with high carbon dioxide content, into microalgal system is cost-effective.

The O2-assisted Al/CO2 electrochemical cell: A system for CO2 capture/conversion and electric power generation

Economical and efficient carbon capture, utilization, and sequestration technologies are a requirement for successful implementation of global action plans to reduce carbon emissions and to mitigate climate change. These technologies are also essential for longer-term use of fossil fuels while reducing the associated carbon footprint. We demonstrate an O2-assisted Al/CO2 electrochemical cell as a new approach to sequester CO2 emissions and, at the same time, to generate substantial amounts of electrical energy. We report on the fundamental principles that guide operations of these cells using multiple intrusive electrochemical and physical analytical methods, including chronopotentiometry, cyclic voltammetry, direct analysis in real-time mass spectrometry, energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, and coupled thermogravimetric analysis-Fourier transform infrared spectroscopy. On this basis, we demonstrate that an electrochemical cell that uses metallic aluminum as anode and a carbon dioxide/oxygen gas mixture as the active material in the cathode provides a path toward electrochemical generation of a valuable (C2) species and electrical energy. Specifically, we show that the cell first reduces O2 at the cathode to form superoxide intermediates. Chemical reaction of the superoxide with CO2 sequesters the CO2 in the form of aluminum oxalate, Al2(C2O4)3, as the dominant product. On the basis of an analysis of the overall CO2 footprint, which considers emissions associated with the production of the aluminum anode and the CO2 captured/abated by the Al/CO2-O2 electrochemical cell, we conclude that the proposed process offers an important strategy for net reduction of CO2 emissions.

Amine reclaiming technologies in post-combustion carbon dioxide capture

Amine scrubbing is the most developed technology for carbon dioxide (CO2) capture. Degradation of amine solvents due to the presence of high levels of oxygen and other impurities in flue gas causes increasing costs and deterioration in long term performance, and therefore purification of the solvents is needed to overcome these problems. This review presents the reclaiming of amine solvents used for post combustion CO2 capture (PCC). Thermal reclaiming, ion exchange, and electrodialysis, although principally developed for sour gas sweetening, have also been tested for CO2 capture from flue gas. The three technologies all have their strengths and weaknesses, and further development is needed to reduce energy usage and costs. An expected future trend for amine reclamation is to focus on process integration of the current reclaiming technologies into the PCC process in order to drive down costs.