CO2 Sequestration Process Research Articles

Use of CO2 curing to enhance the properties of cold bonded lightweight aggregates (CBLAs) produced with concrete slurry waste (CSW) and fine incineration bottom ash (IBA)

In this study, concrete slurry waste (CSW) obtained from ready-mixed concrete plants was recycled as a fresh cementitious binder and used together with municipal solid waste incineration (MSWI) fine bottom ash (IBA) from waste-to-energy plants to produce cold bonded lightweight aggregates (CBLAs) by using a pelletizing technique. The influence of different curing methods on the properties of the produced CBLAs were experimentally investigated, including moist curing, steam curing, and accelerated CO2 curing at 0.1 bar and flow-through CO2 curing under ambient pressure. The results showed that CBLAs obtained by steam curing at 60 °C had the highest pellet strength, and the CO2 cured samples had the lowest water absorption values. CO2 curing with a pressure of 0.1 bar promoted a better pellet strength. The CO2 curing method can sequestrate 3.5–4.1% (by mass of pellets) of CO2, which can serve as a sustainable CO2 sequestration process to produce CBLAs.

Carbon dioxide sequestration process for the cement industry

Due to the significant amount of CO2 released from the cement industry, a CO2 sequestration process suitable for cement-manufacturing plants is required to reduce greenhouse gas emission and to mitigate global warming. In the present study, a new overall process of CO2 treatment is proposed for the cement industry that includes the extraction of KCl and CaCl2 from the cement by-products, KCl membrane electrolysis for KOH formation, and CO2 capture-mineralization using the extracted KOH and CaCl2. For this three-step process, various experiments were conducted to determine how the results varied in relation to experimental conditions and to find the most suitable conditions for process operation. The KCl and CaCl2 were extracted using pure water and HCl solutions at various concentrations, respectively, from industrial cement kiln dust. KCl membrane electrolysis was carried out to measure the electrochemical performance in relation to the KCl or KOH concentration, temperature, and applied current density. The single process of CO2 capture-mineralization was tested by measurement of the CO2 removal efficiency in relation to variation of the Ca/CO2 ratio and gas retention time. In addition, the purity of the CaCO3 produced was evaluated in relation to the Ca/CO2 ratio, and the CO2 removal efficiency was examined over time on stream.

Coupling a sterically hindered amine-based absorption and coal fly ash triggered amine regeneration: A high energy-saving process for CO2 absorption and sequestration

Developing a promising process for CO2 sequestration with large capacities, fast kinetics and low energy requirements is still of great importance. Here, we developed a new CO2 sequestration process that integrates a sterically hindered amine based CO2 absorption and coal fly ash based amine regeneration. The present study investigated the technical feasibility of the new process and gained a detailed insight into the reaction mechanisms involved. We found that the CO2 rich 2-amino-2-methyl-1-propanol (AMP) solution can be chemically regenerated by CaO. The species analysis by FT-IR and 13C-NMR revealed that CaO was effective to regenerate AMP and combine with CO2 in the AMP solution to produce carbonate precipitates. The evaluation of the AMP regeneration using a CaO containing fly ash indicated that fly ash was also effective for AMP regeneration and CO2 mineralisation. The characterizations of the fly ash before and after mineralisation via SEM equipped with EDX and XRD confirmed that the CaO in fly ash played a decisive role in the process. The new approach developed in this work presents an alternative to the traditional thermal CO2 desorption process, which can save energy for amine regeneration significantly and has added benefit of direct CO2 mineralization.

Integration of a diamine solvent based absorption and coal fly ash based mineralisation for CO2 sequestration

Our previous studies have revealed that diamines containing one primary amine group exhibit a superior kinetics while retaining their intrinsic high capacities towards CO2 absorption when compared with monoethanolamine. However, these diamine absorbents typically suffer from high regeneration energy due to the inherent structural stability of the formed carbamate species. In an effort to overcome this challenge, we developed a new CO2 sequestration process that integrates the CO2 absorption by a diamine solvent and the diamine regeneration as well as CO2 mineralization by CaO-rich fly ash. Herein, we found that CO2 rich diamine solutions can be chemically regenerated by fly ash with the stable cyclic performance via the CO2 absorption - mineralization experiments, and the CO2 sequestration capacity of the fly ash used in this process dominated the amine regeneration performance. The FT-IR analysis of species in the solution along with the characterizations of fly ash via SEM, EDX and XRD revealed that fly ash was effective to regenerate a diamine - 1-(2-hydroxyethyl)-4-aminopiperidine (C4) by deprotonation of C4H+, meanwhile, the CaO component in fly ash can react with CO2 in the C4 solution to produce the calcium carbonate precipitate. This approach presents a significant energy saving alternative to the traditional CO2 desorption process.

Modification of a model for mixed hydrates to represent double cage occupancy

Gas hydrates are subject of current research work and are also important for several industrial applications. When transporting natural gases or oil through pipelines, the formation of gas hydrates and thus a blockage of the pipeline must be avoided. There is also a great interest to understand the thermophysical properties and the phase change behavior of hydrates during liquefaction processes of natural gases, for CO2 capture and sequestration (CCS) processes, and for CH4 and C2H6 hydrates, which can be found on the seabed or in permafrost soils as a potential energy source. In this work, the model for mixed gas hydrates (mixtures of water with more than one hydrate former), which has been introduced in a previous work [Fluid Phase Equilib. 459 (2018) 170–185] and is intended for the use in CCS relevant applications, is modified to take double cage occupancy into account. The three-phase equilibrium data can be reproduced up to high pressures at which N2, O2, and Ar are known to double occupy the hydrate cavities. The influence of double occupied hydrate cages and the improved reproduction of experimental phase equilibrium data at pressures at which double cage occupancy occurs are shown for pure hydrate and for mixed hydrate phase equilibrium and composition data. In case of mixed hydrates, comparisons are shown for synthetic air (N2+O2).

CO2 interaction induced mechanical characteristics alterations in coal: A review

Coal geo-mechanical alterations caused by CO2 interaction should be critically evaluated to enhance the efficiency of CO2-ECBM and CO2 sequestration processes, while mitigating associated hazards. We provide a detailed overview on the CO2 interaction induced mechanical alterations in coal, by comprehensively reviewing the influential parameters and causative factors. Although studies provide persuasive evidence to conclude the general fact that CO2 interaction causes severe mechanical degradation in coal, the degree of strength reduction is influenced by numerous parameters: 1) stress state - elevated in-situ stresses diminish the CO2-induced coal strength reduction, due to reduced CO2 adsorption potential and the hindered swelling effect, 2) CO2 adsorption pressure and phase - magnitude of strength reduction increases with increasing CO2 adsorption pressure and CO2 phase transition into supercritical state causes a noticeable strength reduction, because of the higher adsorption and polymerization capacities of supercritical CO2, 3) CO2 interaction time - due to rapid CO2 adsorption process, significant mechanical degradation occurs in the short-term, whereas additional CO2 exposure continuous to reduce the strength, but at a slower rate, 4) coal seam characteristics - high-rank coal with a well-formed cleat system exhibits greater strength reductions, compared to low-rank coal, because coal cleat system facilitates easy invasion of CO2 and acts as a locus for CO2 adsorption, expanding the coal matrix along the cleat walls. Moreover, we highlight that there are multiple factors that may contribute to the overall mechanical strength alteration: 1) CO2 adsorption induced surface energy reduction, 2) CO2-induced plasticization of coal polymer-structure, 3) formation of micro-cracks due to shrinkage, free- and differential-swelling, and 4) dissolution of cleat and pore filling minerals, causing bond energy reduction, influencing grain-to-grain contact and forming secondary porosity systems in coal. However, we infer that the mechanical degradation depends on the heterogeneity and anisotropy of the coal reservoir. Therefore, the degradation should be specifically assessed by considering the targeted reservoir characteristics, prior to the implementation of CO2-ECBM and CO2 sequestration field projects.

Effect of sedimentary heterogeneities in the sealing formation on predictive analysis of geological CO2 storage

Numerical models of geologic carbon sequestration (GCS) in saline aquifers use multiphase fluid flow-characteristic curves (relative permeability and capillary pressure) to represent the interactions of the non-wetting CO2 and the wetting brine. Relative permeability data for many sedimentary formations is very scarce, resulting in the utilisation of mathematical correlations to generate the fluid flow characteristics in these formations. The flow models are essential for the prediction of CO2 storage capacity and trapping mechanisms in the geological media. The observation of pressure dissipation across the storage and sealing formations is relevant for storage capacity and geomechanical analysis during CO2 injection.This paper evaluates the relevance of representing relative permeability variations in the sealing formation when modelling geological CO2 sequestration processes. Here we concentrate on gradational changes in the lower part of the caprock, particularly how they affect pressure evolution within the entire sealing formation when duly represented by relative permeability functions.The results demonstrate the importance of accounting for pore size variations in the mathematical model adopted to generate the characteristic curves for GCS analysis. Gradational changes at the base of the caprock influence the magnitude of pressure that propagates vertically into the caprock from the aquifer, especially at the critical zone (i.e. the region overlying the CO2 plume accumulating at the reservoir-seal interface). A higher degree of overpressure and CO2 storage capacity was observed at the base of caprocks that showed gradation. These results illustrate the need to obtain reliable relative permeability functions for GCS, beyond just permeability and porosity data. The study provides a formative principle for geomechanical simulations that study the possibility of pressure-induced caprock failure during CO2 sequestration.

Effects of supercritical CO2 on micropores in bituminous and anthracite coal

The effects of supercritical CO2 (ScCO2) on coal micropores play a critical role in determining the CO2 capacity of coalbeds. To investigate the effects of ScCO2 on micropores in coals of different ranks under a range of temperature and pressure conditions, CO2 sequestration processes are replicated using a ScCO2 geochemical reactor. Four samples of coal of different ranks are exposed to ScCO2 and water for 240 h at 62.5 °C and 15 MPa, and CO2 adsorption tests, Fourier transform infrared spectroscopy, and X-ray diffraction are performed to determine the volume and pore size distribution of the micropores, the types and contents of the organic groups, and the aromatic crystallite structures of the coal samples before and after the ScCO2-H2O treatment. The influence of the chemical structure and the organic groups of the coal on the coal micropores is then studied. Micropores with widths <0.46 nm are mainly associated with the inter-layer spacing of the aromatic layers. Swelling caused by ScCO2 detaches heterocycles and non-condensed polynuclear aromatics of high-volatile bituminous coal, resulting in slight increases in the volume of micropores with widths <0.46 nm. The falling off of cross-links with low bond energies caused by swelling and the formation of CArCAr cross-links between the aromatic layers caused by polyaddition reactions together cause a decrease in the volume of micropores with widths <0.46 nm in semi-anthracite and anthracite coal. Micropores with widths >0.46 nm are pores in the macromolecular structure of coal and are known as intermolecular pores, and their volumes are determined by the directional arrangement of aromatic crystallites and the aliphatic hydrocarbon chain length. The broken bonds caused by ScCO2 in high-volatile bituminous coal form new aliphatic or aromatic compounds via addition and polyaddition reactions. These processes increase the directional arrangement of aromatic crystallites, resulting in a decrease in the volume of micropores with widths >0.46 nm. As the coal rank increases, the aliphatic hydrocarbon chain length gives priority to the macromolecular structure of coal after the ScCO2 treatment, resulting in an increase in the volume of micropores with widths >0.46 nm in semi-anthracite and anthracite coal.

Mobility of elements released from coal during CO&lt;SUB align="right"&gt;2 sequestration

A key greenhouse emission reduction strategy is to sequestrate CO2 in the subsurface by injecting it into coal seams. We investigated the injection of CO2 into coal seams using static batch experiments conducted under similar temperature and pressure conditions to that of the formation from which the coal samples were originally obtained, in an effort to understand the mobilisation of elements released from the coal. Anthracite and high volatile bituminous coal samples (4-8 mm in size) were exposed to a solution of supercritical CO2 (ScCO2) and water at a temperature of approximately 40°C and a pressure of 9.8 MPa. The results obtained indicate that elements show different mobilities after exposure to the ScCO2-H2O solution. Their mobilities are mainly influenced by the occurrence of the elements in the coal minerals. It was found that the mobilisation of elements associated with carbonate minerals was greater than that of elements associated with sulphide and sulphate minerals; which was in turn greater than that of elements associated with silicate minerals. The results also show that close attention should be paid to the potential environmental hazards that might arise if the elements are released into groundwater systems during the CO2 sequestration process. [Received: December 16, 2015; Accepted: June 18, 2017]

Mobility of elements released from coal during CO&lt;SUB align="right"&gt;2 sequestration

A key greenhouse emission reduction strategy is to sequestrate CO2 in the subsurface by injecting it into coal seams. We investigated the injection of CO2 into coal seams using static batch experiments conducted under similar temperature and pressure conditions to that of the formation from which the coal samples were originally obtained, in an effort to understand the mobilisation of elements released from the coal. Anthracite and high volatile bituminous coal samples (4-8 mm in size) were exposed to a solution of supercritical CO2 (ScCO2) and water at a temperature of approximately 40°C and a pressure of 9.8 MPa. The results obtained indicate that elements show different mobilities after exposure to the ScCO2-H2O solution. Their mobilities are mainly influenced by the occurrence of the elements in the coal minerals. It was found that the mobilisation of elements associated with carbonate minerals was greater than that of elements associated with sulphide and sulphate minerals; which was in turn greater than that of elements associated with silicate minerals. The results also show that close attention should be paid to the potential environmental hazards that might arise if the elements are released into groundwater systems during the CO2 sequestration process. [Received: December 16, 2015; Accepted: June 18, 2017]

Characterization of dynamic mechanical alterations of supercritical CO2-interacted coal through gamma-ray attenuation, ultrasonic and X-ray computed tomography techniques

Coal-Supercritical CO2 (S-CO2) interaction causes severe mechanical alterations in coal that can possibly affect the mechanical competency and the coal seam integrity. Conventional static mechanical testings often fail to conduct repetitive and temporal measurements on coal specimens in the process of coal-S-CO2 interaction, thus unable to attain at decisive and reliable conclusions. Moreover, the said techniques fail to capture the mechanical anisotropies of heterogeneous coal mass that arise due to complex spatial distribution of mineral/maceral phases and fracture network. We combine three non-destructive techniques, viz. gamma-ray attenuation, ultrasonic technique and micro computed tomography to evaluate the S-CO2 interaction induced localized and anisotropic micro-structural alterations and the consequent mechanical response of a heterogeneous coal core specimen. Dynamic moduli were computed at radial and axial directions at natural condition, after 14 days and 45 days of S-CO2 interaction, and the resultant mechanical alterations were elucidated with the 3D-reconstructed micro-CT data collected at the same stages. Visualization and quantification of coal micro-structure emphasize that S-CO2-interacted coal mass is subjected to severe micro-cracking due to differential and free swelling, drying induced shrinkage and surface energy reduction, which can possibly lead to mechanical degradation. Spatial distribution of minerals and fractures at specific orientations significantly affects the gamma and ultrasonic wave propagation, thus can be successfully utilized to reflect the mechanical anisotropies. For same interaction condition and period, coal mass exhibits mechanical anisotropies and strength alterations at different levels, in which more heterogeneous mineral/maceral distribution causes significant localized mechanical alterations in mineral-rich areas, compared to that of comparatively homogeneous coal-rich regions. Temporal evaluation of strength parameters suggests that regardless of the considered orientations, significant strength alterations occur at initial stage of the coal-S-CO2 interaction process and the longer interaction causes only a slight strength reduction. Overall results conclude that S-CO2 induced mechanical property alterations in heterogeneous coal are highly localized and anisotropic, thus should be carefully evaluated in CO2 sequestration and ECBM extraction processes.

Effects of Na+, K+, Ca2+, and Mg2+ cations on CO2–brine interfacial tension under offshore storage conditions

AbstractThe laboratory determination of CO2‐brine interfacial tension is very important for estimating the storage capacity of saline aquifers during the CO2 sequestration process. In this paper, we measured CO2 and the brine interfacial tension using the pendant‐drop method at a temperature of 285–300 K and pressure of 3–9 MPa. The brine was composed of Na+, K+, Ca2+, and Mg2+ cations with different molalities. The experimental results indicate that interfacial tension increased with temperature and salinity but decreased with pressure until it reached a plateau. At the same temperature and pressure, the plateau value increased with increasing brine salinity for all types of brines used in this work. Moreover, the plateau exists whenever the CO2 is liquid. The interfacial tension between CO2 and brine with bivalent cations is larger than that between CO2 and monovalent brines. Finally, we established an empirical equation based on the relationship between interfacial tension and temperature, pressure, and salt molality grounded on experimental data, which allows the evaluation of CO2–brine interfacial tension values with a mean deviation of ±4 mN·m−1. © 2018 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

A Comprehensive Overview of CO2 Flow Behaviour in Deep Coal Seams

Although enhanced coal bed methane recovery (ECBM) and CO2 sequestration are effective approaches for achieving lower and safer CO2 levels in the atmosphere, the effectiveness of CO2 storage is greatly influenced by the flow ability of the injected CO2 through the coal seam. A precious understanding of CO2 flow behaviour is necessary due to various complexities generated in coal seams upon CO2 injection. This paper aims to provide a comprehensive overview on the CO2 flow behaviour in deep coal seams, specifically addressing the permeability alterations associated with different in situ conditions. The low permeability nature of natural coal seams has a significant impact on the CO2 sequestration process. One of the major causative factors for this low permeability nature is the high effective stresses applying on them, which reduces the pore space available for fluid movement with giving negative impact on the flow capability. Further, deep coal seams are often water saturated where, the moisture behave as barriers for fluid movement and thus reduce the seam permeability. Although the high temperatures existing at deep seams cause thermal expansion in the coal matrix, reducing their permeability, extremely high temperatures may create thermal cracks, resulting permeability enhancements. Deep coal seams preferable for CO2 sequestration generally are high-rank coal, as they have been subjected to greater pressure and temperature variations over a long period of time, which confirm the low permeability nature of such seams. The resulting extremely low CO2 permeability nature creates serious issues in large-scale CO2 sequestration/ECBM projects, as critically high injection pressures are required to achieve sufficient CO2 injection into the coal seam. The situation becomes worse when CO2 is injected into such coal seams, because CO2 movement in the coal seam creates a significant influence on the natural permeability of the seams through CO2 adsorption-induced swelling and hydrocarbon mobilisation. With regard to the temperature, the combined effects of the generation of thermal cracks, thermal expansion, adsorption behaviour alterations and the associated phase transition must be considered before coming to a final conclusion. A reduction in coal’s CO2 permeability with increasing CO2 pressure may occur due to swelling and slip-flow effects, both of which are influenced by the phase transition in CO2 from sub- to super-critical in deep seams. To date, many models have been proposed to simulate CO2 movement in coal considering various factors, including porosity, effective stress, and swelling/shrinkage. These models have been extremely useful to predict CO2 injectability into coal seams prior to field projects and have therefore assisted in implementing number of successful CO2 sequestration/ECBM projects.

The effects of supercritical CO2 on mesopore and macropore structure in bituminous and anthracite coal

The effects of supercritical CO2 (scCO2) on coal pores play a critical role in CO2 geological storage-enhanced coalbed methane recovery (CO2-ECBM). To investigate the effects of scCO2 on the pore structure and connectivity in coals of different ranks, CO2 sequestration processes were replicated using a scCO2 geochemical reactor. Four coal samples with different ranks were exposed to scCO2 and water for 240 h under 80 °C and 20 MPa. Mercury intrusion porosimetry, nitrogen adsorption tests, and scanning electron microscopy analysis were used to identify the pore volume, pore size distribution, pore connectivity, and pore morphology of the coal samples before and after scCO2-H2O treatment. The increase in the macropore volume caused by the scCO2 is mainly controlled by the pores >30 μm, resulted from the dissolution of carbonate minerals with large grain size in organic matter. The coal rank has a positive influence on the volume and specific surface area of the pores >30 μm, whereas coal rank is more significant for macropore specific surface area in the high-volatile bituminous coal and macropore volume in the low-volatile bituminous, semi-anthracite, and anthracite coal. With an increase in the coal rank, the volume and specific surface area of the mesopores increase. The changes in the mesopore volume in the high-volatile bituminous coal are caused by changes in the pores 20–50 nm in diameter, while these changes in the low-volatile bituminous coal, semi-anthracite, and anthracite are caused by changes in the pores <20 nm, due to the formation of dissolution-created pores in minerals; additionally, many pores <3 nm are generated by the scCO2. At the macropore scale, the scCO2 increases the volume of the non-effectively interconnected pores more than that of the effectively interconnected pores, indicating that the scCO2 has a weak effect on the increase in macropore connectivity. The volume of the effectively interconnected pores increases more at the mesopore scale than at the macropore scale, and the scCO2 treatment increases the connectivity of the mesopores.

The effects of CO2 on organic groups in bituminous coal and high-rank coal via Fourier transform infrared spectroscopy

The interactions between supercritical CO2 and coal and their effects on changes in the coal pore structure and organic groups play a critical role in the CO2 geological storage-enhanced coalbed methane recovery. To investigate the effects of supercritical CO2 on organic groups in coals of different ranks and its mechanisms under different temperature and pressure conditions, CO2 sequestration processes in bituminous coals and high-rank coals were replicated using a high-pressure reactor. Four coal samples of different ranks were exposed to supercritical CO2 and water under three temperatures and pressures for 240 h. Fourier transform infrared spectroscopy was used to provide semiquantitative ratios and Fourier transform infrared spectra of coal samples before and after the supercritical CO2–H2O treatment. The results show that interactions between supercritical CO2 and coal were controlled by the coal macromolecular structure, and semianthracite is the inflection point of interaction characteristics for coal samples of different ranks. Bituminous coal, including high- and low-volatility bituminous coal, has a low degree of condensation of its aromatic structure, and its aromatic nuclei can facilitate addition reactions. Swellings primarily break cross-links between aromatic nuclei in the same aromatic layer. These characteristics favor the polymerization addition of aliphatic side chains of aromatic nuclei, causing an increase in the degree of condensation of the aromatic structures in bituminous coal. High-rank coals including semianthracite and anthracite have a high degree of condensation of their aromatic structures, and the aromatic nuclei favor substitution reactions. Swellings primarily break cross-links connecting different aromatic layers, and bond dissociation reactions and sulfuration reactions are more significant for high-rank coal. These characteristics cause a decrease in the degree of condensation of the aromatic structure in high-rank coal. Temperature and pressure have a great impact on interactions between supercritical CO2 and coal and are controlled by the reaction types of the organic groups. With the increase in experimental temperature and pressure, the changes in the organic group content can be classified as the descending type, the rising type, the lower opening parabola type, and the upper opening parabola type. 45.0°C and 10 MPa is the inflection point of the changes in the organic group content. Descending- and rising-type changes favor addition, bond dissociation, and sulfuration reactions, which are endothermic. The reaction rate of supercritical CO2 and the organic groups increases, and the effects caused by temperature and pressure decrease as the temperature and pressure increase. Lower opening parabola- and upper opening parabola-type changes favor substitution, oxidation, and addition polymerization reactions, which are exothermic. These changes were significantly affected by a variety of reactions and were suppressed by high temperature and pressure. When the temperature is ≤45.0°C and the pressure is ≤10 MPa, supercritical CO2 has remarkable effects on alkyl and hydroxy groups and has a stronger effect on bituminous coal. When the temperature is &gt;45.0°C and the pressure is &gt;10 MPa, supercritical CO2 has remarkable effects on oxygen- and sulfur-containing groups and has a greater effect on high-rank coals.

Effect of Wettability Changes on Evaporation Rate and the Permeability Impairment due to Salt Deposition

Pore-scale visualization was employed to investigate evaporative drying of brine and associated salt deposition at different wetting conditions, using a 2.5D etched-silicon/glass micromodel based on a thin section image of a carbonate rock. We also compared air drying with CO2 drying, with the latter having important applications in CO2 sequestration processes. The resulting permeability impairment was also measured. For deionized water in a water-wet model, we observed the three classical periods of evaporation: the constant rate period (CRP), the falling rate period (FRP), and the receding front period (RFP). The length of the deionized water CRP was much shorter for a uniformly oil-wet model, but mixed wettability made little difference to the drying process. For brine systems at all wetting conditions, the dry area became linear with the square root of time after a short CRP. This is due to the deposited salt acting as a physical barrier to hydraulic connectivity, unlike the case of deionized water, w...

Experimental Investigation of the Geochemical Interactions between Supercritical CO2 and Shale: Implications for CO2 Storage in Gas-Bearing Shale Formations

Interactions between injected CO2 and shale formation during the process of CO2 sequestration with enhancing shale gas recovery (CS-EGR) may alter the physical and chemical properties of the rock, affecting the efficiency of CO2 storage as well as CH4 production. To better understand these interaction-induced changes in shale properties, two shale samples selected from a marine Longmaxi formation and terrestrial Chang-7 member of the Yanchang formation were first reacted with supercritical CO2 (scCO2) in a laboratory batch reactor at 80 °C and 15 MPa with different time intervals, and then characterization methods were designed to access the geochemical changes including optical microscope (OM), X-ray diffraction (XRD), element analysis (EA), low-pressure gas adsorption (LPGA), and Fourier transform infrared spectroscopy (FTIR). The results indicate that the nanopore structure system of the two shale samples was significantly changed after scCO2–shale interaction due to the scCO2-induced extraction of hyd...

Phase Equilibria of the CH4-CO2 Binary and the CH4-CO2-H2O Ternary Mixtures in the Presence of a CO2-Rich Liquid Phase

The knowledge of the phase behavior of carbon dioxide (CO2)-rich mixtures is a key factor to understand the chemistry and migration of natural volcanic CO2 seeps in the marine environment, as well as to develop engineering processes for CO2 sequestration coupled to methane (CH4) production from gas hydrate deposits. In both cases, it is important to gain insights into the interactions of the CO2-rich phase—liquid or gas—with the aqueous medium (H2O) in the pore space below the seafloor or in the ocean. Thus, the CH4-CO2 binary and CH4-CO2-H2O ternary mixtures were investigated at relevant pressure and temperature conditions. The solubility of CH4 in liquid CO2 (vapor-liquid equilibrium) was determined in laboratory experiments and then modelled with the Soave–Redlich–Kwong equation of state (EoS) consisting of an optimized binary interaction parameter kij(CH4-CO2) = 1.32 × 10−3 × T − 0.251 describing the non-ideality of the mixture. The hydrate-liquid-liquid equilibrium (HLLE) was measured in addition to the composition of the CO2-rich fluid phase in the presence of H2O. In contrast to the behavior in the presence of vapor, gas hydrates become more stable when increasing the CH4 content, and the relative proportion of CH4 to CO2 decreases in the CO2-rich phase after gas hydrate formation.

Short-term effects of CO2 leakage on the soil bacterial community in a simulated gas leakage scenario.

The technology of carbon dioxide (CO2) capture and storage (CCS) has provided a new option for mitigating global anthropogenic emissions with unique advantages. However, the potential risk of gas leakage from CO2 sequestration and utilization processes has attracted considerable attention. Moreover, leakage might threaten soil ecosystems and thus cannot be ignored. In this study, a simulation experiment of leakage from CO2 geological storage was designed to investigate the short-term effects of different CO2 leakage concentration (from 400 g m−2 day−1 to 2,000 g m−2 day−1) on soil bacterial communities. A shunt device and adjustable flow meter were used to control the amount of CO2 injected into the soil. Comparisons were made between soil physicochemical properties, soil enzyme activities, and microbial community diversity before and after injecting different CO2 concentrations. Increasing CO2 concentration decreased the soil pH, and the largest variation ranged from 8.15 to 7.29 (p < 0.05). Nitrate nitrogen content varied from 1.01 to 4.03 mg/Kg, while Olsen-phosphorus and total phosphorus demonstrated less regular downtrends. The fluorescein diacetate (FDA) hydrolytic enzyme activity was inhibited by the increasing CO2 flux, with the average content varying from 22.69 to 11.25 mg/(Kg h) (p < 0.05). However, the increasing activity amplitude of the polyphenol oxidase enzyme approached 230%, while the urease activity presented a similar rising trend. Alpha diversity results showed that the Shannon index decreased from 7.66 ± 0.13 to 5.23 ± 0.35 as the soil CO2 concentration increased. The dominant phylum in the soil samples was Proteobacteria, whose proportion rose rapidly from 28.85% to 67.93%. In addition, the proportion of Acidobacteria decreased from 19.64% to 9.29% (p < 0.01). Moreover, the abundances of genera Methylophilus, Methylobacillus, and Methylovorus increased, while GP4, GP6 and GP7 decreased. Canonical correlation analysis results suggested that there was a correlation between the abundance variation of Proteobacteria, Acidobacteria, and the increasing nitrate nitrogen, urease and polyphenol oxidase enzyme activities, as well as the decreasing FDA hydrolytic enzyme activity, Olsen-phosphorus and total phosphorus contents. These results might be useful for evaluating the risk of potential CO2 leakages on soil ecosystems.

Influence of Fluid Exposure on Surface Chemistry and Pore-Fracture Morphology of Various Rank Coals: Implications for Methane Recovery and CO2 Storage

The surface chemistry and pore-fracture morphology of coals are critical to the process of CO2 sequestration in coal seams with enhanced coalbed methane (CH4) recovery (CO2-ECBM). To assess the influence of deionized water–CO2 mixture (DH2O–CO2) exposure on these properties, the interaction of DH2O–CO2 with three rank coals, i.e., sub-bituminous coal (SBC), high volatile bituminous coal (HVBC), and anthracite, was conducted on a dynamic supercritical fluid extraction system with a temperature of 45 °C and an equilibrium pressure of 12 MPa. Characterization methods including proximate analysis (PA), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), probe molecule (N2/CO2) adsorption, and low-field nuclear magnetic resonance (NMR) were adopted to fully address the changes in surface functional groups and pore-fracture characteristics. The results indicate that the geochemical interaction occurs between the mineral matters and DH2O–CO2 as demonstrated by the change in th...