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The hydration of CO 2 suffers from kinetic inefficiencies that make its natural trapping impractically sluggish. However, CO 2 -fixing carbonic anhydrases (CAs) remarkably accelerate its equilibration by 6 orders of magnitude and are, therefore, "ideal" catalysts. Notably, CA has been detected in ureolytic bacteria, suggesting its potential involvement in microbially induced carbonate precipitation (MICP), yet the dynamics of the urease (Ur) and CA genes remain poorly understood. Here, through the use of the ureolytic bacterium Sporosarcina pasteurii , we investigate the differing role of Ur and CA in ureolysis, CO 2 hydration, and CaCO 3 precipitation with increasing CO 2(g) concentrations. We show that Ur gene up-regulation coincides with an increase in [HCO 3 - ] following the hydration of CO 2 to HCO 3 - by CA. Hence, CA physiologically promotes buffering, which enhances solubility trapping and affects the phase of the CaCO 3 mineral formed. Understanding the role of CO 2 hydration on the performance of ureolysis and CaCO 3 precipitation provides essential new insights, required for the development of next-generation biocatalyzed CO 2 trapping technologies.

The utilization of steel slag for CO 2 sequestration is an effective way to reduce carbon emissions. The reactivity of steel slag in CO 2 sequestration depends mainly on material and process parameters. However, there are many puzzles in regard to practical applications due to the different evaluations of process parameters and the lack of investigation of material parameters. In this study, 318 samples were collected to investigate the interactive influence of 12 factors on the carbonation reactivity of steel slag by machine learning with SHapley Additive exPlanations (SHAP). Multilayer perceptron (MLP), random forest, and support vector regression models were built to predict the slurry-phase CO 2 sequestration of steel slag. The MLP model performed well in terms of prediction ability and generalization with comprehensive interpretability. The SHAP results showed that the impact of the process parameters was greater than that of the material parameters. Interestingly, the iron ore phase of steel slag was revealed to have a positive effect on steel slag carbonation by SHAP analysis. Combined with previous literature, the carbonation mechanism of steel slag was proposed. Quantitative analysis based on SHAP indicated that steel slag had good carbonation reactivity when the mass fractions of "CaO + MgO", "SiO 2 + Al 2 O 3 ", "Fe 2 O 3 ", and "MnO" varied from 50-55%, 10-15%, 30-35%, and <5%, respectively.

This paper reports for the first time the use and application of a novel technique in the characterization of mineral carbonation reaction and CO 2 sequestration in soil stabilization using flow meters. Soils based on SiO 2 with two different sizes were tested. Lime (Ca(OH) 2 ) was used as the reactant. Instant CO 2 flow rate (L/min), total CO 2 volume (L), temperature (°C), and absolute pressure (kPa) were monitored and recorded for 1 h by flow meters connected to the mold inlet and outlet. It was determined that the mineral carbonation reaction started in the first seconds and ended before the 5th minute. The mineral carbonation is a short-term and potential reaction, and it is not a time-dependent reaction. It is separated from other carbonation reactions with these characteristics. The highest CO 2 captured value was obtained in the soil mixed with 5% lime, where fines were not used. The second highest CO 2 captured value was obtained in soil mixed with 1% lime, where fines were not used. CO 2 captured with 1% lime is more than CO 2 captured with 5% lime in the soil containing fines. Accordingly, 1-5% lime can be used in soil carbonation studies. According to the soil properties, the highest CO 2 captured and the CO 2 efficiency was achieved with the use of 6-7% water by weight., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

By-products from the non-ferrous industry are an environmental problem; however, their economic value is high if utilized elsewhere. For example, by-products that contain alkaline compounds can potentially sequestrate CO 2 through the mineral carbonation process. This review discusses the potential of these by-products for CO 2 reduction through mineral carbonation. The main by-products that are discussed are red mud from the alumina/aluminum industry and metallurgical slag from the copper, zinc, lead, and ferronickel industries. This review summarizes the CO 2 equivalent emissions generated by non-ferrous industries and various data about by-products from non-ferrous industries, such as their production quantities, mineralogy, and chemical composition. In terms of production quantities, by-products of non-ferrous industries are often more abundant than the main products (metals). In terms of mineralogy, by-products from the non-ferrous industry are silicate minerals. Nevertheless, non-ferrous industrial by-products have a relatively high content of alkaline compounds, which makes them potential feedstock for mineral carbonation. Theoretically, considering their maximum sequestration capacities (based on their oxide compositions and estimated masses), these by-products could be used in mineral carbonation to reduce CO 2 emissions. In addition, this review attempts to identify the difficulties encountered during the use of by-products from non-ferrous industries for mineral carbonation. This review estimated that the total CO 2 emissions from the non-ferrous industries could be reduced by up to 9-25%. This study will serve as an important reference, guiding future studies related to the mineral carbonation of by-products from non-ferrous industries., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Microalgae CO 2 sequestration has gained considerable attention in the last three decades as a promising technology to slow global warming caused by CO 2 emissions. To provide a comprehensive and objective analysis of the research status, hot spots, and frontiers of CO 2 fixation by microalgae, a bibliometric approach was recently chosen for review. In this study, 1561 articles (1991-2022) from the Web of Science (WOS) on microalgae CO 2 sequestration were screened. A knowledge map of the domain was presented using VOSviewer and CiteSpace. It visually demonstrates the most productive journals (Bioresource Technology), countries (China and USA), funding sources, and top contributors (Cheng J, Chang JS, and their team) in the field of CO 2 sequestration by microalgae. The analysis also revealed that research hotspots changed over time and that recent research has focused heavily on improving carbon sequestration efficiency. Finally, commercialization of carbon fixation by microalgae is a key hurdle, and supports from other disciplines could improve carbon sequestration efficiency., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Despite the consensus that keeping global temperature rise within 1.5 °C above pre-industrial level by 2100 reduces the chance for climate change to reach the point of no return, the newest Intergovernmental Panel on Climate Change (IPCC) report warns that the existing commitment of greenhouse gas emission reduction is only enough to contain the warming to 3-4 °C by 2100. The harsh reality not only calls for speedier deployment of existing CO 2 reduction technologies but demands development of more cost-efficient carbon removal strategies. Here we report an ocean alkalinity-based CO 2 sequestration scheme, taking advantage of proton consumption during nitrate assimilation by marine photosynthetic microbes, and the ensuing enhancement of seawater CO 2 absorption. Benchtop experiments using a native marine phytoplankton community confirmed pH elevation from ~8.2 to ~10.2 in seawater, within 3-5 days of microbial culture in nitrate-containing media. The alkaline condition was able to sustain at continued nutrient supply but reverted to normalcy (pH ~8.2-8.4) once the biomass was removed. Measurements of δ 13 C in the dissolved inorganic carbon revealed a significant atmospheric CO 2 contribution to the carbonate alkalinity in the experimental seawater, confirming the occurrence of direct carbon dioxide capture from the air. Thermodynamic calculation shows a theoretical carbon removal rate of ~0.13 mol CO 2 /L seawater, if the seawater pH is allowed to decrease from 10.2 to 8.2. A cost analysis (using a standard bioreactor wastewater treatment plant as a template for CO 2 trapping, and a modified moving-bed biofilm reactor for nitrate recycling) indicated that a 1 Mt CO 2 /year operation is able to perform at a cost of ~$40/tCO 2 , 2.5-5.5 times cheaper than that offered by any of the currently available direct air capture technologies, and more in line with the price of $25-30/tCO 2 suggested for rapid deployment of large-scale CCS systems.

The increase in demand of fossil fuel uses for developmental activity and manufacturing of goods have resulted a huge emission of global warming gases (GWGs) in the atmosphere. Among all GWGs, CO 2 is the major contributor that inevitably causes global warming and climate change. Mitigation strategies like biological CO 2 capture through sequestration and their storage into biological organic form are used to minimize the concentration of atmospheric CO 2 with the goal to control climate change. Since increasing atmospheric CO 2 level supports microbial growth and productivity thus microbial-based CO 2 sequestration has remarkable advantages as compared to plant-based sequestration. This review focuses on CO 2 sequestration mechanism in bacteria through different carbon fixation pathways, involved enzymes, their role in calcite, and other environmentally friendly biomaterials such as biofuel, bioplastic, and biosurfactant., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Azolla is a group of aquatic floating plants that can achieve very high growth rates compared to other aquatic macrophytes, with a doubling time of 2-5 days under optimal growing conditions. The ability of Azolla to grow at such rapid rates allows for the opportunity of utilizing it as a method to sequester a significant amount of atmospheric CO 2 in the form of biomass, which can be locked away to completely remove the carbon from the active carbon cycle, or which can be used in various applications such as animal feeds, biofertilizers, and biofuel production, which in turn will contribute to reduction in the fossil CO 2 emissions. In this desktop study, the potential use of Azolla for mitigating the annual increase in the atmospheric CO 2 levels was addressed, which were estimated at 18.9 billion tons of CO 2 per year. A theoretical setup of 1-ha ponds was assessed to estimate the total Azolla growing area required for counterbalancing the annual atmospheric CO 2 increase. Each 1-ha pond was found capable of capturing 21,266 kg of CO 2 (C) per year. The calculated required total area to mitigate the total annual increase was estimated to be 1,018,023 km 2 (equivalent to around a fifth of the Amazon forest area). Sensitivity analysis, which was based on the variations in the productivity of Azolla due to growing conditions, indicated that the required area would range between 763,518 and 1,527,036 km 2 . This study provides a novel natural method for CO 2 sequestration that has lower environmental impacts compared to conventional sequestration technologies as an alternative green approach for mitigating the effects of fossil fuels., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The rapid acceleration in emissions of inevitably generated CO 2 due to numerous activities mainly anthropogenic have devastating environmental effects leading to climatic concerns. Hence, significant, sustainable approaches should be developed for reduction of CO 2 emission targets, balancing the existing needs of the current population. Biological carbon acquisition, storage and usage are considered crucial alternative strategies in assimilating inorganic carbon, manifested by diverse variety of microorganisms. Furthermore, central biochemical routes along with associated enzymes serve as considerable factors for understanding molecular microbial CO 2 assimilation. Microorganisms exhibit an impeccable capability to facilitate evolved mechanisms in sequestering inorganic carbon at higher pace to produce biomaterials like biofuels, bioplastics etc. This review endorses the importance of microorganisms in reducing the concomitant release of CO 2 by providing supervision in biotechnological applications (such as genetic engineering, microbial electrosynthesis, gas fermentation and protein engineering) to mitigate CO 2 at an industrial scale., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Strategies for depleting carbon dioxide (CO 2 ) from flue gases are urgently needed and carbonic anhydrases (CAs) can contribute to solving this problem. They catalyze the hydration of CO 2 in aqueous solutions and therefore capture the CO 2 . However, the harsh conditions due to varying process temperatures are limiting factors for the application of enzymes. The current study aims to examine four recombinantly produced CAs from different organisms, namely CAs from Acetobacterium woodii (AwCA or CynT), Persephonella marina (PmCA), Methanobacterium thermoautotrophicum (MtaCA or Cab) and Sulphurihydrogenibium yellowstonense (SspCA). The highest expression yields and activities were found for AwCA (1814 WAU mg -1 AwCA) and PmCA (1748 WAU mg -1 PmCA). AwCA was highly stable in a mesophilic temperature range, whereas PmCA proved to be exceptionally thermostable. Our results indicate the potential to utilize CAs from anaerobic microorganisms to develop CO 2 sequestration applications.

Mineral carbonation can simultaneously realize the effective treatment of CO 2 and iron and steel slag; thus, it is of great significance for the low carbon and sustainable development of iron and steel industry. In this article, the researches of mineral carbonation process using iron and steel slag as feedstock are reviewed, and the carbonation reaction mechanism and the parameters affecting the reaction rate and carbonation degree are analyzed. Furthermore, the effect of different enforcement approaches, such as ultrasonic enhancement, mixed calcination, microbial enhancement, and cyclic coprocessing on mineral carbonation reaction, is introduced. The additional effects of mineral carbonation, such as solving the problem of poor volume stability of steel slag, weakening the leaching of heavy metal ions, and reducing the pH of the leachate, are also illustrated. Moreover, issues related to mineral carbonation technology that should be emphasized upon soon, such as the production of valuable products, use of industrial wastewater, aqueous phase recycling use, multiparameter coupling analysis, and research on the properties of carbonation residues, are also discussed, which contribute some perspectives to the future development of mineral carbonation of iron and steel slag., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The increased CO 2 quantities in the environment have led to many harmful effects. Therefore, it is very important to decrease the CO 2 levels in the environment. CO 2 capture along with safe and permanent storage using mineral CO 2 sequestration method can play an important role to reduce carbon emissions into the environment. Mineral sequestration is a stable storage method that provides long-term storage and an appropriate substitute for the more popular geological storage method. The process is most suited for places where there is a lack of underground cavities for underground geological storage. Minerals rich in Ca and Mg are used predominantly in carbonation reactions. In addition, those alkaline wastes that are rich in Mg and Ca such as cement waste, steel slag and many process ashes can also be employed in CO 2 sequestration. Mineral carbonation could be used for the sequestration of billions of tonnes of CO 2 every year. However, various drawbacks related to mineral carbonation still need to be addressed, such as resolving the slow rate of reactions, necessity of large amounts of feedstock, decreasing the high overall cost of CO 2 sequestration and reducing the huge energy requirements to accelerate the carbonation reaction. This study explores a number of carbonation methods, parameters that control the process and future potential applications of carbonated products.

The degrees of mineral carbonation in (a) construction and demolition waste (C&DW) and (b) a mixture of cement and fly ash were studied through a dynamic experimental method to determine the variation in the rate and extent of CO 2 sequestration achievable under simulated outdoor conditions. A number of experiments were performed in a self-designed rotating batch reactor by churning the two samples together with CO 2 , which was passed through the mixtures by using water vapor as the medium of transfer. At an injection flow rate of 1 L/min for CO 2 , the theoretical extent of carbonation was observed to be 39.1% for the mixture of cement and fly ash and 25% for C&DW. It was further observed that upon increasing the CO 2 flow rate to 10 L/min, the carbonation in the mixture of cement and fly ash increased by 37.2% after 15 h of rotation at 60 rounds per hour (rph) for a temperature of 40 °C. Weighing, scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS) were performed for the samples before and after the batch reaction to study the quantitative, qualitative and morphological aspects of the process.

Carbon dioxide (CO 2 ) capture and storage (CCS) plays a crucial role in reducing carbon emissions to the atmosphere. However, gas leakage from deep storage reservoirs, which may flow back into near-surface and eventually to the atmosphere, is a major concern associated with this technology. Despite an increase in research focusing on potential CO 2 leakage into deep surface features and aquifers, a significant knowledge gap remains in the geochemical changes associated with near-surface. This study reviews the geochemical processes related to the intrusion of CO 2 into near-surface environments with an emphasis on metal mobilization and discusses about the geochemical research approaches, recent findings, and current knowledge gaps. It is found that the intrusion of CO 2 (g) into near-surface likely induces changes in pH, dissolution of minerals, and potential degradation of surrounding environments. The development of adequate geochemical research approaches for assessing CO 2 leakage in near-surface environments, using field studies, laboratory experiments, and/or geochemical modeling combined with isotopic tracers, has promoted extensive surveys of CO 2 -induced reactions. However, addressing knowledge gaps in geochemical changes in near-surface environments is fundamental to advance current knowledge on how CO 2 leaks from storage sites and the consequences of this process on soil and water chemistry. For reliable detection and risk management of the potential impact of CO 2 leakage from storage sites on the environmental chemistry, currently available geochemical research approaches should be either combined or used independently (albeit in a manner complementarily to one another), and the results should be jointly interpreted.

Land cover change (LCC) and its impact on CO 2 sequestration and radiative forcing (RF) could dramatically affect climate change, but there has been little effort to address this issue in South and Southeast Asia over a long period of time using actual land cover information. In this study, annual land cover data from 1992 to 2015 were used to assess the CO 2 flux and corresponding RF due to LCC in South and Southeast Asia. The results showed that 553.2 × 10 3 km 2 of the region experienced LCC during this period, mostly due to land reclamation, urban expansion, and deforestation. These LCC caused a marked net decrease in net ecosystem productivity (NEP) as a composite of the various land cover categories during the whole study period, especially since 2001. The CO 2 sequestration was 2160 TgCO 2 during the early 1990s however cumulative sequestration decreased by 414.95 TgCO 2 by 2015. Correspondingly, the cooling effect of NEP, i.e. the total actual RF, was -0.366 W m -2 in South and Southeast Asia between 1992 and 2015. However, the potential RF of the cumulatively reduced NEP due to LCC relative to the 1990s resulted in a warming effect of 2.33 × 10 -3 W m -2 in 2015. Our study provides an applicable framework to accurately assess the potential effect of large-scale LCC on climate.

In this study, carbonic anhydrase (CA, EC 4.2.1.1) molecules were embedded into metal-organic frameworks (MOFs) via co-precipitation (CA@ZIF-8), and then these CA@ZIF-8 nanocomposites were encapsulated in the poly(vinyl alcohol) (PVA)-chitosan (CS) hydrogel networks to prepare CA@ZIF-8-PVA-CS composite hydrogels (PVA/CS/CA@ZIF-8) with high activity, stability, and reusability. The immobilization efficiency of CA was greater than 70%, suggesting the high immobilization efficiency. The prepared PVA/CS/CA@ZIF-8 composite membranes displayed excellent higher stability against a high temperature, denaturants, and acid than free CA and CA@ZIF-8. Furthermore, these membranes exhibited an excellent performance for CO 2 capture. The amount of calcium carbonate obtained by PVA/CS/CA@ZIF-8 hydrogel membranes was 20- and 1.63-fold than free CA and CA@ZIF-8 composites, respectively. Furthermore, the hydrogel membranes exhibited superior reusability and mechanical strength. The hydrogel membrane maitained 50% of its original activity after 11 cycles. However, CA@ZIF-8 completely lost activity. These results indicated that the PVA/CS/CA@ZIF-8 membranes can be efficiently applied to capture CO 2 sequestration.

Seaweed powder has been found to act as an effective catalyst for the fixation of CO₂ into epoxides to generate cyclic carbonates under solvent free conditions. Model background reactions were performed using metal halides and amino acids typically found in common seaweeds which showed potassium iodide (KI) to be the most active. The efficacy of the seaweed catalysts kelp ( Laminaria digitata ) and dulse ( Palmaria palmata ) was probed based on particle size, showing that kelp possessed greater catalytic ability, achieving a maximum conversion and selectivity of 63.7% to styrene carbonate using a kelp loading of 80% by weight with respect to epoxide, 40 bar of CO₂, 120 °C for 3 h. Maximizing selectivity was difficult due to the generation of diol side product from residual H₂O found in kelp, along with a chlorinated by-product thought to form due to a high quantity of chloride salts in the seaweeds. Data showed there was loss of organic matter upon use of the kelp catalyst, likely due to the breakdown of organic compounds and their subsequent removal during product extraction. This was highlighted as the likely cause of loss of catalytic activity upon reuse of the Kelp catalyst.

The Blue Lagoon is a geothermal aquifer with a diverse ecosystem located within the Reykjanes UNESCO Global Geopark on Iceland's Reykjanes Peninsula. Blue Lagoon Ltd., which exploits the aquifer, isolated a strain of coccoid cyanobacteria Cyanobacterium aponinum (C. aponinum) from the geothermal fluid of the Blue Lagoon more than two decades ago. Since then Blue Lagoon Ltd. has cultivated it in a photobioreactor, for use as an active ingredient in its skin care products. Until recently, the cultivation of C. aponinum was achieved by feeding it on 99.99% (4N) bottled carbon dioxide (CO 2 ). In this investigation, C. aponinum was cultivated using unmodified, non-condensable geothermal gas (geogas) emitted from a nearby geothermal powerplant as the feed-gas instead of the 4N-gas. The geogas contains roughly 90% vol CO 2 and 2% vol hydrogen sulfide (H 2 S). A comparison of both CO 2 sources was made. It was observed that the use of geogas did enhance the conversion efficiency. A 13 weeks' average CO 2 conversion efficiency of C. aponinum was 43% and 31% when fed on geogas and 4N-gas, respectively. Despite the high H 2 S concentration in the geogas, sulfur accumulation in the cultivated biomass was similar for both gas sources. Our results provide a model of a CO 2 sequestration by photosynthetic conversion of otherwise unused geothermal emission gas into biomass.

Growing industrialization and the desire for a better economy in countries has accelerated the emission of greenhouse gases (GHGs), by more than the buffering capacity of the earth's atmosphere. Among the various GHGs, carbon dioxide occupies the first position in the anthroposphere and has detrimental effects on the ecosystem. For decarbonization, several non-biological methods of carbon capture, utilization and storage (CCUS) have been in use for the past few decades, but they are suffering from narrow applicability. Recently, CO 2 emission and its disposal related problems have encouraged the implementation of bioprocessing to achieve a zero waste economy for a sustainable environment. Microbial carbonic anhydrase (CA) catalyses reversible CO 2 hydration and forms metal carbonates that mimic the natural phenomenon of weathering/carbonation and is gaining merit for CCUS. Thus, the diversity and specificity of CAs from different micro-organisms could be explored for CCUS. In the literature, more than 50 different microbial CAs have been explored for mineral carbonation. Further, microbial CAs can be engineered for the mineral carbonation process to develop new technology. CA driven carbonation is encouraging due to its large storage capacity and favourable chemistry, allowing site-specific sequestration and reusable product formation for other industries. Moreover, carbonation based CCUS holds five-fold more sequestration capacity over the next 100 years. Thus, it is an eco-friendly, feasible, viable option and believed to be the impending technology for CCUS. Here, we attempt to examine the distribution of various types of microbial CAs with their potential applications and future direction for carbon capture. Although there are few key challenges in bio-based technology, they need to be addressed in order to commercialize the technology., (© 2017 The Society for Applied Microbiology.)

The CO 2 mineralization process, accelerated by carbonic anhydrase (CA) was proposed for the efficient capture and storage of CO 2 , the accumulation of which in the atmosphere is the main cause of global warming. Here, we characterize a highly stable form of the cloned CA from the Gram-negative marine bacterium Aliivibrio salmonicida, named ASCA that can promote CO 2 absorption in an alkaline solvent required for efficient carbon capture. We designed a mature form of ASCA (mASCA) using a codon optimization of ASCA gene and removal of ASCA signal peptide. mASCA was highly expressed (255 mg/L) with a molecular weight of approximately 26 kDa. The mASCA enzyme exhibited stable esterase activity within a temperature range of 10-60 °C and a pH range of 6-11. mASCA activity remained stable for 48 h at pH 10. We also investigated its inhibition profiles using inorganic anions, such as acetazolamide, sulfanilamide, iodide, nitrate, and azide. We also demonstrate that mASCA is capable of catalyzing the conversion of CO 2 to CaCO 3 (calcite form) in the presence of Ca 2+ . It should be noted that mASCA enzyme exhibits high production yield and sufficient stabilities against relatively high temperature and alkaline pH, which are required conditions for the development of more efficient enzymatic CCS systems.

CO 2 -derived succinate production was enhanced by Actinobacillus succinogenes through polystyrene (PSt) microsphere materials for CO 2 adsorption in bioreactor, and the adhesion forces between A. succinogenes bacteria and PSt materials were characterized. Synthesized uniformly sized and highly cross-linked PSt microspheres had high specific surface areas. After modification with amine functional groups, the novel amine-functionalized PSt microspheres exhibited a high adsorption capacity of 25.3 mg CO 2 /g materials. After addition with the functionalized microspheres into the culture broth, CO 2 supply to the cells increased. Succinate production by A. succinogenes can be enhanced from 29.6 to 48.1 g L -1 . Moreover, the characterization of interaction forces between A. succinogenes cells and the microspheres indicated that the maximal adhesive force was about 250 pN. The amine-functionalized PSt microspheres can adsorb a large amount of CO 2 and be employed for A. succinogenes anaerobic cultivation in bioreactor for high-efficiency production of CO 2 -derived succinate.

This manuscript presents experimental data for 20 adsorption materials (metal-organic frameworks, porous polymer networks, and Zeolite-5A), including CO2 and N2 isotherms and heat capacities. With input from only experimental data, working capacities per energy for each material were calculated. Furthermore, by running seven different carbon-capture scenarios in which the initial flue-gas composition and process temperature was systematically changed, we present a range of performances for each material and quantify how sensitive each is to these varying parameters. The presented calculations provide researchers with a tool to investigate promising carbon-capture materials more easily and completely., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In this work, the potential of CO₂ mineral carbonation of brucite (Mg(OH)2) derived from the Mount Tawai peridotite (forsterite based (Mg)₂SiO4) to produce thermodynamically stable magnesium carbonate (MgCO3) was evaluated. The effect of three main factors (reaction temperature, particle size, and water vapor) were investigated in a sequence of experiments consisting of aqueous acid leaching, evaporation to dryness of the slurry mass, and then gas-solid carbonation under pressurized CO2. The maximum amount of Mg converted to MgCO₃ is ~99%, which occurred at temperatures between 150 and 175 °C. It was also found that the reduction of particle size range from >200 to <75 µm enhanced the leaching rate significantly. In addition, the results showed the essential role of water vapor in promoting effective carbonation. By increasing water vapor concentration from 5 to 10 vol %, the mineral carbonation rate increased by 30%. This work has also numerically modeled the process by which CO₂ gas may be sequestered, by reaction with forsterite in the presence of moisture. In both experimental analysis and geochemical modeling, the results showed that the reaction is favored and of high yield; going almost to completion (within about one year) with the bulk of the carbon partitioning into magnesite and that very little remains in solution.

The soaring increase of flue gas emission had caused global warming, environmental pollution as well as climate change. Widespread concern on reduction of flue gas released from industrial plants had considered the microalgae as excellent biological materials for recycling the carbon dioxide directly emitted from exhaust industries. Microalgae also have the potential to be the valuable feedback for renewable energy production due to their high growth rate and abilities to sequester inorganic carbon through photosynthetic process. In this review article, we will illustrate important relative mechanisms in the metabolic processes of biofixation by microalgae and their recent experimental researches and advances of sequestration of carbon dioxide by microalgae on actual industrial and stimulate flue gases, novel photobioreactor cultivation systems as well as the perspectives and limitations of microalgal cultivation in further development.

Biocatalytic CO2 sequestration to reduce greenhouse-gas emissions from industrial processes is an active area of research. Carbonic anhydrases (CAs) are attractive enzymes for this process. However, the most active CAs display limited thermal and pH stability, making them less than ideal. As a result, there is an ongoing effort to engineer and/or find a thermostable CA to fulfill these needs. Here, the kinetic and thermal characterization is presented of an α-CA recently discovered in the mesophilic hydrothermal vent-isolate extremophile Thiomicrospira crunogena XCL-2 (TcruCA), which has a significantly higher thermostability compared with human CA II (melting temperature of 71.9°C versus 59.5°C, respectively) but with a tenfold decrease in the catalytic efficiency. The X-ray crystallographic structure of the dimeric TcruCA shows that it has a highly conserved yet compact structure compared with other α-CAs. In addition, TcruCA contains an intramolecular disulfide bond that stabilizes the enzyme. These features are thought to contribute significantly to the thermostability and pH stability of the enzyme and may be exploited to engineer α-CAs for applications in industrial CO2 sequestration.

In this study, CO2 sequestration was investigated through the microbially-induced calcium carbonate precipitation (MICP) process with isolates obtained from a cave called 'Cave Without A Name' (Boerne, TX, USA) and the Pamukkale travertines (Denizli, Turkey). The majority of the bacterial isolates obtained from these habitats belonged to the genera Sporosarcina, Brevundimonas, Sphingobacterium and Acinetobacter. The isolates were investigated for their capability to precipitate calcium carbonate and sequester CO2. Biotic and abiotic effects of CO2 sequestration during MICP were also investigated. In the biotic effect, we observed that the rate and concentration of CO2 sequestered was dependent on the species or strains. The main abiotic factors affecting CO2 sequestration during MICP were the pH and medium components. The increase in pH led to enhanced CO2 sequestration by the growth medium. The growth medium components, on the other hand, were shown to affect both the urease activity and CO2 sequestration. Through the Plackett-Burman experimental design, the most important growth medium component involved in CO2 sequestration was determined to be urea. The optimized medium composition by the Plackett-Burman design for each isolate led to a statistically significant increase, of up to 148.9%, in CO2 uptake through calcification mechanisms., (© FEMS 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

This work explored several synthesis routes to obtain calcium silicates from different calcium-rich and silica-rich industrial residues. Larnite, wollastonite and calcium silicate chloride were successfully synthesised with moderate heat treatments below standard temperatures. These procedures help to not only conserve natural resources, but also to reduce the energy requirements and CO2 emissions. In addition, these silicates have been successfully tested as carbon dioxide sequesters, to enhance the viability of CO2 mineral sequestration technologies using calcium-rich industrial by-products as sequestration agents. Two different carbon sequestration experiments were performed under ambient conditions. Static experiments revealed carbonation efficiencies close to 100% and real-time resolved experiments characterised the dynamic behaviour and ability of these samples to reduce the CO2 concentration within a mixture of gases. The CO2 concentration was reduced up to 70%, with a carbon fixation dynamic ratio of 3.2 mg CO2 per g of sequestration agent and minute. Our results confirm the suitability of the proposed synthesis routes to synthesise different calcium silicates recycling industrial residues, being therefore energetically more efficient and environmentally friendly procedures for the cement industry., (© The Author(s) 2014.)

Anthropogenic activities have substantially increased the level of greenhouse gases (GHGs) in the atmosphere and are contributing significantly to the global warming. Carbon dioxide (CO2 ) is one of the major GHGs which plays a key role in the climate change. Various approaches and methodologies are under investigation to address CO2 capture and sequestration worldwide. Carbonic anhydrase (CA) mediated CO2 sequestration is one of the promising options. Therefore, the present review elaborates recent developments in CA, its immobilization and bioreactor methodologies towards CO2 sequestration using the CA enzyme. The promises and challenges associated with the efficient utilization of CA for CO2 sequestration and scale up from flask to lab-scale bioreactor are critically discussed. Finally, the current review also recommends the possible future needs and directions to utilize CA for CO2 sequestration., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Geological carbon dioxide (CO2) sequestration entails capturing and injecting CO2 into deep saline aquifers for long-term storage. The injected CO2 partially dissolves in groundwater to form a mixture that is denser than the initial groundwater. The local increase in density triggers a gravitational instability at the boundary layer that further develops into columnar plumes of CO2-rich brine, a process that greatly accelerates solubility trapping of the CO2. Here, we investigate the pattern-formation aspects of convective mixing during geological CO2 sequestration by means of high-resolution three-dimensional simulation. We find that the CO2 concentration field self-organizes as a cellular network structure in the diffusive boundary layer at the top boundary. By studying the statistics of the cellular network, we identify various regimes of finger coarsening over time, the existence of a non-equilibrium stationary state, and a universal scaling of three-dimensional convective mixing.

The urgent need to find mitigating pathways for limiting world CO2 emissions to net zero by 2050 has led to intense research on CO2 sequestration in deep saline reservoirs. This paper reviews key advancements in lab- and simulation-scale research on petrophysical, geochemical, and mineralogical changes during CO2–brine–rock interactions performed in the last 25 years. It delves into CO2 MPD (mineralization, precipitation, and dissolution) and explores alterations in petrophysical properties during core flooding and in static batch reactors. These properties include changes in wettability, CO2 and brine interfacial tension, diffusion, dispersion, CO2 storage capacity, and CO2 leakage in caprock and sedimentary rocks under reservoir conditions. The injection of supercritical CO2 into deep saline aquifers can lead to unforeseen geochemical and mineralogical changes, possibly jeopardizing the CCS (carbon capture and storage) process. There is a general lack of understanding of the reservoir's interaction with the CO2 phase at the pore/grain scale. This research addresses the gap in predicting the long-term changes of the CO2–brine–rock interaction using various geochemical reactive transport simulators. Péclet and Damköhler numbers can contribute to a better understanding of geochemical interactions and reactive transport processes. Additionally, the dielectric constant requires further investigation, particularly for pre- and post-CO2–brine–rock interactions. For comprehensive modeling of CO2 storage over various timescales, the geochemical modeling software called the Geochemist's Workbench was found to outperform others. Wettability alteration is another crucial aspect affecting CO2–brine–rock interactions under varying temperature, pressure, and salinity conditions, which is essential for ensuring long-term CO2 storage security and monitoring. Moreover, dual-energy CT scanning can provide deeper insights into geochemical interactions and their complexities. [ABSTRACT FROM AUTHOR]

The properties of amorphous calcium carbonate (ACC) and its transformations to crystalline polymorphs are frequently studied in aqueous systems and in small quantities. In this study, synthetic calcium carbonate stones are created from bulk ACC and crystalline polymorphs, which were precipitated from gaseous CO2, at a gradient of end pH. Some of the ACCs hardened into stones which are durable against an abrasion and impact test, while some of the ACCs create fragile, friable stones. When ACCs which transform to durable stones and those which transform into fragile stones were subject to calorimetry, significant differences were observed. These stones, synthesized from gaseous CO2, can be used as a storage reservoir for utilized CO2 in construction and other infrastructure applications. [ABSTRACT FROM AUTHOR]

Human survival is threatened by the rapid climate change due to global warming caused by the increase in CO2 emissions since the Second Industrial Revolution. This study developed a secondary cement product production technology by replacing cement, a conventional binder, with calcium silicate cement (CSC), i.e., CO2 reactive hardening cement, to reduce CO2 emissions and utilize CO2 from the cement industry, which emits CO2 in large quantities. Results showed that the carbonation depth, compressive strength increase rate, and CO2 sequestration rate increased as the CSC content increased, suggesting that CSC can be applied as a secondary cement product. [ABSTRACT FROM AUTHOR]

The dissolution of supercritical carbon dioxide (ScCO2) in water forms a ScCO2–H2O system, which exerts a transformative influence on the physicochemical characteristics of coal and significantly impacts the CO2-driven enhanced coalbed methane (CO2-ECBM) recovery process. Herein, the effect of ScCO2–H2O treatment on the physicochemical properties of coal was simulated in a high-pressure reactor. The migration of major elements, change in the pore structure, and change in the CH4 adsorption capacity of coal after the ScCO2–H2O treatment were detected using plasma emission spectroscopy, the low-temperature liquid nitrogen adsorption method, and the CH4 adsorption method, respectively. The results show that (1) the ScCO2–H2O treatment led to mineral reactions causing a significant migration of constant elements in the coal. The migration of Ca ions was the most significant, with an increase in their concentration in treated water from 0 to 16–970 mg·L−1, followed by Na, Mg, and K. Al migrated the least, from 0 to 0.004–2.555 mg·L−1. (2) The ScCO2–H2O treatment increased the pore volume and pore-specific surface area (SSA) of the coal via the dissolution and precipitation of minerals in the coal pores. The total pore volume increased from 0.000795–0.011543 to 0.001274–0.014644 cm3·g−1, and the total pore SSA increased from 0.084–3.332 to 0.400–6.061 m2·g−1. (3) Changes in the CH4 adsorption capacity were affected by the combined effects of a mineral reaction and pore structure change. The dissolved precipitates of the minerals in the coal pores after the ScCO2–H2O treatment caused elemental migration, which not only decreased the mineral content in the coal pores but also increased the total pore volume and total pore SSA, thus improving the CH4 adsorption capacity of the coal. This study provides theoretical support for CO2 sequestration and ECBM recovery. [ABSTRACT FROM AUTHOR]

Reactor temperature manipulation to increase product yields of chemical reactions is a known technique used in many industrial processes. In the case of exothermic chemical reactions, the well-known Le Chatelier's principle predicts that a decrease in temperature will displace the chemical reaction toward the formation of products by increasing the value of the equilibrium constant. The reverse is true for endothermic reactions. Reactor temperature manipulation in an industrial system, however, affects the values of many variables, including physical properties, transport parameters, reaction kinetic parameters, etc. In the case of reactive absorption, some variables change with increasing temperatures due to solute absorption, while others change in such a way that the solute absorption rate decreases. For example, temperature drop increases product formation for exothermic reactions but reduces the value of transport parameters, leading to decreasing interfacial concentrations and absorption rates. Therefore, temperature manipulation strategies must be designed carefully to achieve the process goals. In this work, we theoretically study the use of temperature as a tool to increase CO2 absorption by solvents in a semi-batch reactor. A computer code has been developed and validated using reported experimental data. Calculated results demonstrate an increase in absorbed CO2 of more than 28% with respect to the highest temperature used. Despite high agitation and high gas flow rate, the system is mass transfer controlled at short times, becoming kinetically controlled as time increases. An operating strategy to decrease cooling energy costs is also proposed. This study reveals that reactor temperature manipulation can be an effective process to improve CO2 absorption by solvents in two-phase semi-batch reactors. [ABSTRACT FROM AUTHOR]

Carbon capture utilization and storage technique (CCUS) is an effective way to mitigate climate change. Carbon dioxide (CO2) sequestration binders (CSB) composed of hydrated lime (CH) and cement has great application prospects in CCUS. Although CH in CSB can improve the carbon absorption capacity, it causes a significant decrease in flexural strength. This study focused on the effect of polyvinyl alcohol (PVA) on the CO2 absorption capacity and flexural strength of CSB. The results show that PVA is beneficial to enhancing the flexural strength of CSB either under natural carbonation or accelerated carbonation. This enhancement is more pronounced at an early age for CSB with high CH content. Furthermore, CO2 uptake experiments show that the PVA would not reduce the CO2 absorption of CSB and even has a slight improvement effect. Finally, thermodynamic modeling and price calculation were adopted for CSB to illustrate the chemical phase and economic cost changes. The outcomes of this study shed new light on PVA to optimize CSB. [ABSTRACT FROM AUTHOR]

Carbon dioxide capture, utilization, and storage (CCUS) is one of the essential approaches to achieving permanent CO2 emission reduction. A new idea of absorbing and mineralizing CO2 with industrial wastewater and converting activated calcium into micron CaCO3 powder is proposed in this paper, which synchronizes water softening and CO2 fixation. Therefore, this paper investigated the characteristics of circulating water quality in the iron and steel industry and the transformation behaviors of CO2 capture by activated calcium to CaCO3 powder in the mild aqueous environment under different process parameters. The phase composition, morphology, and particle size distribution (PSD) of CaCO3 powder were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and (laser particle size analyzer) LPSA, respectively. In addition, a green integrated cycle system for industrial water capture of mineralized CO2 was preliminarily constructed, which provides a reference method for carbon reduction and economic utilization of carbon sources in an industrial system. [ABSTRACT FROM AUTHOR]

About one million tons of CO2 have been injected into the Farnsworth unit to date. The target reservoir for CO2 injection is the Morrow B Sandstone, which is primarily made of quartz with lesser amounts of albite, calcite, chlorite, and clay minerals. The impact of CO2 injection on the mineralogy, porosity, and pore water composition of the Morrow B Sandstone is a major concern. Although numerical modeling studies suggest that porosity changes will be minimal, significant alterations to mineralogy and pore water composition are expected. Given the implications for CO2 storage effectiveness and risk assessment, it is crucial to verify the accuracy of theoretical model predictions through laboratory experiments. To this end, batch reaction experiments were conducted to model conditions near an injection well in the Morrow B Sandstone and at locations further away, where the CO2 has been diluted by formation water. The laboratory experiments involved submerging thin sections of both coarse- and fine-grained facies of the Morrow B Sandstone in formation water samples with varying levels of CO2. The experiments were conducted at the reservoir temperature of 75 °C. Two experimental runs were conducted, one lasting for 61 days and the other for 72 days. The initial fluid composition used in the second run was the same as in the first. The mineralogy changes in the thin sections were analyzed using SEM and the Tescan Integrated Mineral Analyzer (TIMA), while changes in the composition of the formation water were determined using ICP-AES. During each experiment, a thin layer of white fine-grained particles consisting mainly of dolomite and silica formed on the surface of the thin sections, leading to significant reductions in Ca, Mg, and Sr in the formation water. This outcome is consistent with numerical model predictions that dolomite would be the primary mineral that would react with injected CO2 and that silica would be oversaturated in the formation water. Changes in mineral abundance in the thin sections themselves were much less systematic than in the theoretical modeling experiments, perhaps reflecting heterogeneities in the mineral grain size surface area to volume ratios and mineral distributions in the thin sections not considered in the numerical models. [ABSTRACT FROM AUTHOR]

The paper addresses the problem of geomechanical effects in the vicinity of production/injection wells and their impacts on the processes of enhanced oil recovery by CO2 injection and CO2 sequestration in a partially depleted oil reservoir. In particular, it focuses on natural fracture systems and their dynamics caused by variations in the rock geomechanical state due to reservoir pressure changes during production/injection processes. The comprehensive approach to the problem requires the combined modeling of both geomechanical and flow phenomena associated with effective coupling simulations of their evolution. The paper applies such an approach to a real, partially depleted oil reservoir in Poland. An effective method of coupled geomechanical and dynamic simulations was used together with the natural boundary and initial conditions for both simulation types. In addition, typical operating conditions were applied in analyzing the processes of enhanced oil recovery by CO2 injection and CO2 sequestration. The detailed results of relevant modeling and simulations are presented and discussed focusing on various scale consequences, including the reservoir, well, and completion ones. Both general conclusions as well as the ones specific to the analyzed geological structure are drawn; they confirm the significant dependence of well performance on geomechanical effects and point out several key factors for this dependence. The conclusions specific to the analyzed structure concern fracture reactivation in tensile/hybrid failure mode caused by pressure build-up during CO2 injection and the importance of the fracture-induced aperture changes resulting from the normal stress, while the shear stress is found to be negligible. [ABSTRACT FROM AUTHOR]

Injecting power plant flue gas into a goaf stores CO2 in the flue gas and effectively prevents the spontaneous combustion of the coal remaining in the goaf. Here, we investigated the adsorption behavior of three types of coal at normal temperature and pressure using a self-developed adsorption experimental device. We used a specific surface area and porosity analyzer to study the effects of pore structure, mineral content, and moisture content on CO2 adsorption in coal. Based on the experimental data, we designed a multifactor CO2 adsorption prediction model based on a backpropagation (BP) neural network. The results indicated that the pore size of most micropores in coal was in the range of 0.5–0.7 and 0.8–0.9 nm. The specific surface area and pore volume were positively correlated with the CO2-saturated adsorption capacity, whereas the mean pore diameter, mineral content, and moisture content were inversely associated with the CO2-saturated adsorption amount. The accuracy of the multifactor BP neural network prediction model was satisfactory: the determination coefficients (R2) of the training and test sets were both above 0.98, the root mean square error (RMSE) and mean absolute error (MAE) of the test set were both less than 0.1, and the prediction results satisfied the requirements. To optimize the prediction performance of the model, we used the random forest algorithm to calculate the importance of each factor. The sum of the importance weights of the specific surface area, moisture content, and pore volume was 91.6%, which was much higher than that of the other two factors. Therefore, we constructed an optimization model with specific surface area, moisture content, and pore volume as input variables. The R2 values of the training and test sets in the simplified model were improved compared with those of the multifactor model, the RMSE and MAE were reduced, and the fitting effect was ideal. The prediction model of CO2 adsorption in coal based on the BP neural network can predict the CO2 adsorption capacity of coal under different physical and chemical conditions, thereby providing theoretical support for the application of CO2 storage technology in goafs. [ABSTRACT FROM AUTHOR]

Recently there have been significant advances in the viscosification of CO2 using a low concentration of oligomers. The new engineered molecules do not adsorb onto rock. This paper studies the effects of different CO2-enhanced viscosity levels in subsurface aquifers and reservoirs. The study was conducted using numerical modeling and simulation tools in homogeneous, heterogenous, fractured, and unfractured media. The viscosity enhancement of CO2 varied from 2- to 20-fold. The simulations included homogeneous, layered, and fractured domains in 2D and in 3D for improved oil recovery. The results showed that in unfractured, homogenous, and layered media, a 10-fold viscosity increase leads to significant increases in oil recovery. In a fractured medium with a highly connected fracture network, a 20-fold viscosity enhancement may have a considerable effect in delaying breakthrough and improving oil recovery. Simulations were performed in a compositional three-phase flow based on higher-order discretization. The algorithm included Fickian diffusion, which may add to oil recovery performance when there is a sufficient surface area between the CO2-rich phase and the oil phase. In CO2 sequestration, an increase in the viscosity of CO2 and consequent mobility control promotes CO2 dissolution in the aqueous phase. Due to the increase in the density of the aqueous phase from CO2 dissolution, the CO2 is carried away from the cap rock to the bottom of the formation. This work is of particular importance in improved oil recovery and in safe CO2 sequestration due to solubility trapping and mitigation of pressure increase. The higher-order numerical scheme used in this simulation guarantees a level of accuracy not obtained in traditional simulators. [ABSTRACT FROM AUTHOR]

The cyclic injection of CO2, referred to as the huff-n-puff (HnP) method, is an attractive option to improve oil recovery from unconventional reservoirs. This study evaluates the optimization of the CO2 HnP method and provides insight into the aspects of CO2 sequestration for unconventional reservoirs. Furthermore, this study also examines the impact of nanopore confinement, fluid composition, injection solvent, diffusivity parameters, and fracture properties on the long-term recovery factor. The results from over 500 independent simulations showed that the optimal recovery is obtained for the puff-to-huff ratio of around 2.73 with a soak period of fewer than 2.7 days. After numerous HnP cycles, an optimized CO2 HnP process resulted in about 970-to-1067-ton CO2 storage per fracture and over 32% recovery, compared to 22% recovery for natural depletion over the 30 years. The optimized CO2 HnP process also showed higher effectiveness compared to the N2 HnP scenario. Additionally, for reservoirs with significant pore confinement (pore size ≤ 10 nm), the oil recovery improved by over 3% compared to the unconfined bulk phase properties. We also observed over 300% improvement in recovery factor for a fluid with a significant fraction of light hydrocarbons (C1–C6), compared to just a 50% improvement in recovery for a fluid with a substantial fraction of heavy hydrocarbons (C7+). Finally, the results also showed that fracture properties are much more important for CO2 HnP than natural depletion. This study provides critical insights to optimize and improve CO2 HnP operations for different fluid phases and fracture properties encountered in unconventional reservoirs. [ABSTRACT FROM AUTHOR]

Deep saline aquifers have been used for waste-fluid disposal for decades and are the proposed targets for large-scale CO2 storage to mitigate CO2 concentration in the atmosphere. Due to relatively limited experience with CO2 injection in deep saline formations and given that the injection targets for CO2 sometimes are the same as waste-fluid disposal formations, it could be beneficial to model and compare both practices and learn from the waste-fluid disposal industry. In this paper, we model CO2 injection in the Patterson Field, which has been proposed as a site for storage of 50 Mt of industrial CO2 over 25 years. We propose general models that quickly screen the reservoir properties and calculate pressure changes near and far from the injection wellbore, accounting for variable reservoir properties. The reservoir properties we investigated were rock compressibility, injection rate, vertical-to-horizontal permeability ratio, average reservoir permeability and porosity, reservoir temperature and pressure, and the injectant total dissolved solids (TDS) in cases of waste-fluid injection. We used experimental design to select and perform simulation runs, performed a sensitivity analysis to identify the important variables on pressure build-up, and then fit a regression model to the simulation runs to obtain simple proxy models for changes in average reservoir pressure and bottomhole pressure. The CO2 injection created more pressure compared to saline waste-fluids, when similar mass was injected. However, we found a more significant pressure buildup at the caprock-reservoir interface and lower pressure buildup at the bottom of the reservoir when injecting CO2 compared with waste-fluid injection. [ABSTRACT FROM AUTHOR]

CO 2 injection technology into coal seams to enhance CH 4 recovery (CO 2 -ECBM), therefore presenting the dual benefit of greenhouse gas emission reduction and clean fossil energy development. In order to gaze into the features of CO 2 injection's influence on reservoir pressure and permeability, the Thermal-Hydraulic-Mechanical coupling mechanism of CO 2 injection into the coal seam is considered for investigation. The competitive adsorption, diffusion, and seepage flowing of CO 2 and CH 4 as well as the dynamic evolution of fracture porosity of coal seams are considered. Fluid physical parameters are obtained by the fitting equation using MATLAB to call EOS software Refprop. Based on the Canadian CO 2 -ECBM project CSEMP, the numerical simulation targeting shallow low-rank coal is carried out, and the finite element method is used in the software COMSOL Multiphysics. Firstly, the direct recovery (CBM) and CO 2 -ECBM are compared, and it is confirmed that the injection of CO 2 has a significant improvement effect on methane production. Secondly, the influence of injection pressure and temperature is discussed. Increasing the injection pressure can increase the pressure difference in the reservoir in a short time, so as to improve the CH 4 production and CO 2 storage. However, the increase in gas injection pressure will also lead to the rapid attenuation of near-well reservoir permeability, resulting in the weakening of injection capacity. Also, when the injection temperature increases, the CO 2 concentration is relatively reduced, and the replacement effect on CH 4 is weakened, resulting in a slight decrease in CBM production and CO 2 storage. [ABSTRACT FROM AUTHOR]

Carbon-dioxide-enhanced shale gas recovery technology has significant potential for large-scale emissions reduction and can help achieve carbon neutrality targets. Previous theoretical studies mainly focused on gas adsorption in one-dimensional pores without considering the influence from the pore geometry. This study evaluates the effects of pore shape on shale gas adsorption. The pure and competitive gas adsorption processes of CO2 and CH4 in nanopores were investigated using molecular simulations to improve the prediction of shale gas recovery efficiency. Meanwhile, quantitative analysis was conducted on the effects of the pore shape on the CO2-EGR efficiency. The results indicate that the density of the adsorption layer in pores is equally distributed in the axial direction when the cone angle is zero; however, when the cone angle is greater than zero, the density of the adsorption layer decreases. Smaller cone-angle pores have stronger gas adsorption affinities, making it challenging to recover the adsorbed CH4 during the pressure drawdown process. Concurrently, this makes the CO2 injection method, based on competitive adsorption, efficient. For pores with larger cone angles, the volume occupied by the free gas is larger; thus, the pressure drawdown method displays relatively high recovery efficiency. [ABSTRACT FROM AUTHOR]

Coal maceral composition has a great effect on gas adsorption and diffusion. The interaction between maceral composition and supercritical CO2 (SCCO2) fluid will affect gas diffusion behavior in coals. Thus, the diffusivity derived from adsorption kinetics of CH4 and CO2 in vitrinite- and inertinite-rich coals with low-violate bituminous rank collected from the Hancheng mine of the Weibei coalfield pre- and post-SCCO2 fluid exposure (SFE) were tested at the conditions of 45 °C and 0.9 MPa. In combination with pore distribution and functional group content, the possible mechanism of the alterations in gas diffusion characteristics in coals with various maceral compositions was addressed. The results show that for vitrinite-rich coals, SFE increases the macropore apparent diffusion coefficient of CH4, while this treatment decreases the micropore apparent diffusion coefficient of CH4. However, the reverse trend is found for CO2 diffusion–adsorption rate. For inertinite-rich coals post-SFE, CH4 diffusion–adsorption rate increases, while an increase and a decrease in diffusivity CO2 occur for macropore and micropore, respectively. Generally, SFE shows a stronger impact on CO2 adsorption rate than CH4 in coals. The results suggest that the diffusion of CH4 and CO2 in coals with different maceral compositions show selectivity to SCCO2 fluid. The possible reason can be attributed to the changes in pore structure and surface functional group content. SFE causes an increase in macro/mesopore volume of all samples. However, SFE induces a reduction in oxygen-containing species content and micropore volume of inertinite-rich coals, while the opposite trend occurs in vitrinite-rich coals. Thus, the changes in pore volume and surface functional group account for the difference in gas diffusivity of coals with different maceral compositions. With regard to the micropore diffusion–adsorption behavior of CH4 and CO2, the impact of oxygen-containing species is superior to pore volume. The oxygen-containing species favor CO2 diffusion–adsorption but go against CH4 transport. This effect accounts for the reduction in the micropore diffusion–adsorption rate of CH4 and the increase in micropore diffusivity of CO2 in vitrinite-rich coals, respectively. However, the aforementioned effect is the opposite for inertinite-rich coals. Overall, the changes in gas diffusion in coals with different maceral composition during the CO2-ECBM process requires further attention. [ABSTRACT FROM AUTHOR]

Highlights: 1. What are the main findings? CO2–N2 mixture dissolution in brine is examined by considering the cross-diffusion effect for CO2 sequestration in a deep storage reservoir. Heterogeneity lowers the average dissolved CO2 and impedes the onset of convection. 2. What is the implication of the main finding? Correlations are developed to predict the transition time between the dissolution regimes. The possibility of impure carbon dioxide (CO2) sequestration can reduce the cost of these projects and facilitate their widespread adoption. Despite this, there are a limited number of studies that address impure CO2 sequestration aspects. In this study, we examine the convection–diffusion process of the CO2–nitrogen (N2) mixture dissolution in water-saturated porous media through numerical simulations. Cross-diffusion values, as the missing parameters in previous studies, are considered here to see the impact of N2 impurity on dissolution trapping in more realistic conditions. Homogeneous porous media are used to examine this impact without side effects from the heterogeneity, and then simulations are extended to heterogeneous porous media, which are a good representative of the real fields. Heterogeneity in the permeability field is generated with sequential Gaussian simulation. Using the averaged dissolved CO2 and dissolution fluxes for each case, we could determine the onset of different dissolution regimes and behaviors of dissolution fluxes in CO2–N2 mixture dissolution processes. The results show that there is a notable difference between the pure cases and impure cases. Additionally, a failure to recognize the changes in the diffusion matrix and cross-diffusion effects can result in significant errors in the dissolution process. At lower temperatures, the N2 impurity decreases the amount and flux of CO2 dissolution; however, at higher temperatures, sequestrating the CO2–N2 mixture would be a more reasonable choice due to enhancing the dissolution behavior and lowering the project costs. The results of the heterogeneous cases indicate that heterogeneity, in most cases, reduces the averaged dissolved CO2, and dissolution flux and impedes the onset of convection. We believe that the results of this study set a basis for future studies regarding the CO2–N2 mixture sequestration in saline aquifers. [ABSTRACT FROM AUTHOR]

The storage of carbon dioxide in secure underground sites has been identified as an important contributor to preventing climate change impacts of excessive CO2 in the atmosphere. Significant quantities of carbon dioxide must be collected and stored for this technology to make the required contribution to climate change abatement. The carbon dioxide can be stored as a gas, supercritical fluid or a solid by mineralization. Most attention has been on reservoirs which are depleted in oil or gas or in saline aquifers more generally. Trapping gas or supercritical fluid requires a setting similar to the natural trapping of gases in sub-surface sedimentary rock reservoirs. The most advanced high-volume projects focus on the trapping of supercritical fluids. Pumping carbon dioxide into basalt host rocks to promote carbonate mineralization is also being undertaken. In this paper another environment in which CO2 is naturally introduced into geological materials and stored below ground is reviewed. The environment is natural hydrothermal systems which are commonly found around magmatically active locations. In these areas it is common for the cool near-surface (meteoric) water to descend as a replacement (recharge) of the warm or hot magmatic water in the hydrothermal-magmatic system. The descending CO2 can react with existing rocks and minerals to form carbonates of calcium and other cations. It is proposed that introduction of CO2 into naturally descending meteoric water recharge in hydrothermal systems may be a mechanism for CO2 sequestration by mineral trapping. Further investigation of this process and its potential is proposed. [ABSTRACT FROM AUTHOR]

• The liquid CO 2 -seawater system in unsealed submarine sediments is simulated. • Liquid CO 2 hydrate conversion capacity is identified from driving force and contact ability. • "Comfort zone" for submarine CO 2 hydrate sequestration is identified. • The influences of sediment type and CO 2 -seawater ratio are revealed. CO 2 hydrate provides an important way for the long-term stable way for CO 2 sequestration, but the current understanding of CO 2 hydrate formation behavior from liquid CO 2 and seawater in submarine sediments is still unclear. In this work, we constructed the unsealed submarine sediments and examined the effects of multiple factors on CO 2 hydrate formation from two perspectives: driving force of hydrate formation and CO 2 -water contact ability. "T-p comfort zone" that CO 2 could be more sequestrated as hydrate was identified, and if CO 2 is injected in the appropriate area, the floating CO 2 from deep sediments could always flow in the relatively "comfort zones" and eventually be more solidified. The relations of CO 2 -water distribution and quantity in sediments further determined the hydration rate and capacity. Due to the better dispersibility, the maximum CO 2 storage density of 66.8 kg/m3 in hydrate form was obtained in silt system at 60 vol% CO 2 , which was 60 % higher than the sandy system. The addition of 25 wt% clay inhibited the hydrate quantity to 40 kg/m3. Our results present the friendly CO 2 sequestration conditions and optimized path in unsealed marine sediments. [ABSTRACT FROM AUTHOR]

Geological CO 2 sequestration (GCS) in shale reservoirs is considered an imperative approach to reducing CO 2 emissions and mitigating greenhouse gas effects, with the wettability of reservoir rocks playing a critical role in this process. In this study, we comparatively investigated the wetting characteristics of H 2 O on the organic matter (graphene) and inorganic matter (hydroxylated quartz) surfaces of shale in a CO 2 atmosphere utilizing molecular dynamics (MD) simulations and focused on elucidating the effects of CO 2 pressure, temperature, and salinity on wettability from the perspectives of the H 2 O droplet contact angle (CA), gas-water density distributions and interaction energy. The results demonstrate that the H 2 O droplet is gradually stripped from the graphene surface by CO 2 with increasing CO 2 pressure, inducing a wetting transition from intermediate-wet to strongly CO 2 -wet, while the hydroxylated quartz surface consistently exhibits a strongly H 2 O-wet state. This significant discrepancy in wetting behaviors can be attributed to the differential adsorption capabilities of CO 2. The hydrophilicity of graphene and quartz surfaces is enhanced with increasing temperature for the given CO 2 pressure condition, and the wettability alteration is more pronounced above the CO 2 critical temperature for graphene, while the opposite is observed for quartz. The H 2 O CA in the CO 2 -H 2 O-shale systems only slightly increases with increasing salinity, which is related to the spatial effect of ions in the brine. The results of this work indicate that the CO 2 -wet feature of shale organic matter during GCS is favorable for the adsorption trapping of CO 2 but unfavorable for capillary trapping, while the opposite is true for inorganic matter. This study sheds light on the phenomena and regularity of the wettability alterations of shale organic and inorganic matter by CO 2 injection, and the results gained are expected to furnish new insights into CO 2 sequestration-enhanced gas recovery (CS-EGR) and gas-water two-phase flow at the nanoscale. [Display omitted] [ABSTRACT FROM AUTHOR]

This study investigates the synergistic effects of CO 2 mixing and CO 2 curing on the CO 2 uptake capacity of Portland cement. After a normal mixing or ten minutes of CO 2 mixing, samples underwent 0.5, 1, or 3 days of CO 2 curing at a 10 % CO 2 concentration. Hydration and carbonation characteristics were assessed by means of a thermogravimetry analysis, reacted water and CO 2 uptake measurements, pore solution analysis, X-ray diffractometry, and Rietveld-refinement-based quantification. The CO 2 -mixed samples displayed an escalating trend in terms of CO 2 uptake with longer curing times and greater reaction degrees compared to normally mixed samples. In addition, extended CO 2 curing durations resulted in decreased levels of portlandite and increased amounts of crystalline carbonates, alongside a reduction in the ratio of amorphous to crystalline carbonates. Subsequently, improvements in the compressive strength were noted with longer CO 2 curing durations. • The effects of CO2 mixing and CO2 curing on Portland cement were investigated. • CO2 mixing resulted in increasing trends of CO2 uptake with curing age. • CO2 mixing facilitated the reaction of clinkers at early curing age. • CO2 curing exceeding 1 day strengthened microstructure by larger CO2 uptake. • CO2 mixing and CO2 curing can fix CO2 in cement during fresh and hardened states. [ABSTRACT FROM AUTHOR]