Solubility Of CO2 In Water Research Articles

Pore-scale phenomena in carbon geological storage (Saline aquifers—Mineralization—Depleted oil reservoirs)

The injection of CO2 into geological formations triggers inherently coupled thermo-hydro-chemo-mechanical processes. The reservoir pressure and temperature determine the CO2 density, the CO2-water interfacial tension, and the solubility of CO2 in water (hindered by salts and competing gases). The CO2-water interface experiences marked pinning onto mineral surfaces, and contact angles can range from the asymptotic advancing to receding values, in contrast to the single contact angle predicted by Young’s equation. CO2 dissolves in water to form carbonic acid and the acidified water dissolves minerals; mineral dissolution enhances porosity and permeability, triggers settlement, may couple with advection to form “wormholes”, produces stress changes and may cause block sliding and shear bands. Convective currents can emerge beneath the CO2 plume and sustain CO2 and mineral dissolution processes. On the other hand, mineralization is a self-homogenizing process in advective regimes. The crystallization pressure can exceed the tensile capacity of the host rock and create new surfaces or form grain-displacive lenses. Within the rock matrix, coupled reactive-diffusion-precipitation results in periodic precipitation bands. Adequate seal rocks for CO2 geological storage must be able to sustain the excess capillary pressure in the buoyant CO2 plume without experiencing open-mode discontinuities or weakening physico-chemical interactions. CO2 injection into depleted oil reservoirs benefits from time-proven seals; in addition, CO2 can mobilize residual oil to simultaneously recover additional oil through oil swelling, ganglia destabilization, the reduction in oil viscosity and even miscible displacement. Rapid CO2 depressurization near the injection well causes cooling under most anticipated reservoir conditions; cooling can trigger hydrate and ice formation, and reduce permeability. In some cases, effective stress changes associated with the injection pressure and cooling thermoelasticity can reactivate fractures. All forms of carbon geological storage will require large reservoir volumes to hold a meaningful fraction of the CO2 that will be emitted during the energy transition.

Hydrophobicity-aerophilicity effect boosting efficient CO2 photoreduction in graphitic carbon nitride modified with fluorine-containing groups

Inspired by the lotus leaf effect, constructing a hydrophobic surface to endow photocatalysts with underwater aerophilicity, is an effective measure to improve the accessibility of CO2 on the catalyst surface during CO2 photoreduction in the liquid phase. Unfortunately, the aerophilic advantages of the material cannot be fully exploited with the extremely low solubility of CO2 in water. Thus, applying the “hydrophobicity-aerophilicity effect” to gaseous CO2 atmosphere, that is, proving that the hydrophobic material has aerophilic effect in air, has become a challenge. Herein, a hydrophobic graphitic carbon nitride (g-C3N4) photocatalyst modified by CF2 groups (CF2-TCN) is developed to enhance the aerophilicity of the CF2-TCN in air. A theoretical model of the gas-phase “hydrophobicity-aerophilicity effect” and the corresponding theoretical support are presented. Experimental characterizations demonstrate that the grafted CF2 groups create a hydrophobic surface for CF2-TCN, acting as a gas transport layer and enhancing the aerophilicity of CF2-TCN. Theoretical calculations further explain that the strong electronegativity of F atoms in CF2 groups affects the electron cloud distribution of g-C3N4, facilitating the adsorption and activation of CO2 by CF2-TCN. Furthermore, the electron-withdrawing effect of F atoms efficiently extracts electrons, accelerating the intramolecular charge transfer. Benefiting from enhanced aerophilicity and improved electron transfer, the output of CO and CH4 by CF2-TCN are 30.94 and 7.39 μmol·h−1·g−1 without any sacrificial agents, far exceeding that of bulk g-C3N4 (BCN) by 5.54 and 18.95 times, respectively.

Numerical modelling of H2 storage with cushion gas of CO2 in subsurface porous media: Filter effects of CO2 solubility

The central objective of this study is to improve the understanding of flow behaviour during hydrogen (H2) storage in subsurface porous media, with a cushion gas of carbon dioxide (CO2). In this study, we investigate the interactions between various factors driving the flow behaviour, including the underlying permeability heterogeneity, viscous instability, and the balance between the viscous and gravity forces. In particular, we study the impact of CO2 solubility in water on the level of H2 purity. This effect is demonstrated for the first time in the context of H2 storage. We have performed a range of 2D vertical cross-sectional simulations at the decametre scale with a very fine cell size (0.1 m) to capture the flow behaviour in detail. This is done since it is at this scale that much of the mixing between injected and native fluids occurs in physical porous media. It is found that CO2 solubility may have different (positive and negative) impacts on the H2 recovery performance (i.e., on the purity of the produced H2), depending on the flow regimes in the system. In the viscous dominated regime, the less viscous H2 may infiltrate and bypass the cushion gas of CO2 during the period of H2 injection. This leads to a quick and dramatic reduction in the H2 purity when back producing H2 due to the co-production of the previously bypassed CO2. Interestingly, the impurity levels in the H2 are much less severe in the case when CO2 solubility in water is considered. This is because the bypassed CO2 will redissolve into the water surrounding the bypassed zones, which greatly retards the movement of CO2 towards the producer. In the gravity dominated scenario, H2 accumulates at the top of the model and displaces the underlying cushion gas in an almost piston-like fashion. Approximately 58% of H2 can be recovered at a purity level above 98% (combustion requirements by ISO) in this gravity-dominated case. However, when CO2 solubility is considered, the H2 recovery performance is slightly degraded. This is because the dissolved CO2 is also gradually vaporised during H2 injection, which leads to an expansion of mixing zone of CO2 and H2. This in turn reduces the period of high H2 purity level (>98%) during back-production.

INVESTIGATIONS ON THE STORAGE EFFICIENCY OF CO2 IN CARBONATE AQUIFERS

The production of associated and nonassociated gas increases due to additional new oil and gas fields. Consequently, there will be an increase of CO2 released from associated gas, and especially, from nonassociated gas. Actually, CO2 may still be utilized in an attempt of increasing oil recovery through the methods of EOR (Enhanced Oil Recovery) or IOR (Improved Oil Recovery). In general, on the one hand, the CO2 availability in the atmosphere is still be needed for the photosynthesis process. But, on the other hand, this gas can stimulate the greenhouse effect that influences the global warming and weather changes. Prior being utilized, CO2 can be stored first in the depleted oil reservoirs or in the aquifers. The feasibility of these reservoirs or aquifers as a CO2 storage can be determined through the mechanisms of CO2 /water injection, or CO2 solubility in the water. For the purpose of several experiments, specific characters of the cores and formation water were decided taken from a representative carbonate reef formation in West Java region to substitute the samples from Natuna Field. The experiments were then continued on studying the CO2 solubility in the formation water not only at constant volume but also with varied volume, and also the CO2 storage efficiency in the carbonate rocks saturated with water.

Solubilities of CO2, O2 and N2 in rocket propellant 5 under low pressure

The static method of isochoric saturation was used to measure the solubilities of CO2, O2 and N2 in rocket propellant 5 (RP5) at temperatures ranging from 253.15 to 323.15 K in 10 K intervals and pressures ranging from 0 to 120 kPa. The measurement accuracy of the constructed experimental setup was verified by measuring the solubility of CO2 in water. The relative expanded uncertainty (k = 2) in the solubility data was less than 4.0%. The solubilities of CO2, O2 and N2 in RP5 increased with pressure. As the temperature increased, the solubility decreased for CO2 solubility and increased for O2 and N2. Henry's constants for the three gases in RP5 decreased over the experimental temperature and pressure ranges in the order of N2 > O2 > CO2. The measured solubilities of CO2, O2 and N2 could be fitted with a modified Krichevsky–Kasarnovsky equation, and the maximum deviation between the measured and calculated data was less than 8.04%, 7.03% and 6.18%, respectively.

The impact of using recycled culture medium to grow Chlorella vulgaris in a sequential flow system: Evaluation on growth, carbon removal, and biochemical compositions

Excessive of carbon dioxide (CO2) emission and water pollution have been identified as the two primary challenges to humans and environment. Hence, biological carbon sequestration by microalgae is recommended as an environmentally friendly approach to capture and convert this CO2 into value-added products. However, research related to the development of efficient system to concurrently overcome low CO2 solubility in water and reduction of water footprint in microalgae cultivation is still limited in the literature. In this study, the CO2 capture by Chlorella vulgaris in a recycled cultivation medium was exploited using a sequential flow photobioreactor system. The study revealed that nutrient replenished recycled medium did not significantly affect the growth performance and lipid content of C. vulgaris. It was also observed that the CO2 capture efficiency and protein content were gradually increased from the first (SFB-RWN1) to the third (SFB-RWN3) cycle of cultivation due to the increment of carbon and nitrogen content in the microalgae cell. Besides, the lipid profile of C. vulgaris cultivated in the recycled medium comprised of high concentration of saturated (up to 32.41%) and polyunsaturated (up to 43.21%) fatty acid methyl ester (FAME). The present study suggested that growing C. vulgaris in a recycled medium is a feasible solution to fix CO2 from the atmosphere and help to reduce water footprint in the microalgae cultivation system.

Experiments and modeling of CO2 solubility in water-based and oil-based drilling fluids

An experimental apparatus has been developed to measure the CO2 solubility in water, brines, polymer solutions, white oil and drilling fluids using the sample analysis method. The experimental results show that the electrolytes can significantly reduce the solubility of CO2 in water and the salting-out effect can be enhanced by increasing the molar concentration of salt ions. The influences of different polymers are similar, which can reduce the gas solubility to a certain extent. Furthermore, CO2 solubility in the oil-based drilling fluid is significantly larger than that in the water-based drilling fluid. Considering the complicated interactions between gas, electrolytes, polymers and base oil in the drilling fluid, a simple and reliable model for predicting the CO2 solubility is developed. Validation of the model calculations against the experimental measurements indicates that the simulation errors of CO2 solubility in the water-based and oil-based drilling fluids are 3.47% and 6.75%, respectively.

Effect of Metal Cocatalysts and Operating Conditions on the Product Distribution and the Productivity of the CO2 Photoreduction.

The CO2 photoreduction is a promising way to convert one of the most abundant greenhouse gases to valuable chemicals. The photoreduction in the liquid phase is limited by the low solubility of CO2 in water, but this point is overcome here by using an innovative photoreactor, which allows one to work up to pressures of 20 bar, improving the overall productivity. The photoreduction was performed in the presence of Na2SO3 and using in primis commercial titanium dioxide (P25) and a set of titania catalysts functionalized by surface deposition of either monometallic or bimetallic cocatalysts. The gaseous products were hydrogen and traces of CO, while, in the liquid phase, formic acid/formate, formaldehyde and methanol were quantitatively detected. The pH was observed to shift the products distribution. A neutral environment led mainly to hydrogen and methanol, while, at pH 14, formate was the most abundant compound. The trend for monometallic cocatalysts showed enhanced productivity when using noble metals (i.e., gold and platinum). In order to limit the cost of the catalytic material, bimetallic cocatalysts were explored, adding titania with Au+Ag or Au+Pt. This may open to the possibility of performing the reaction with a smaller amount of the most expensive metals. In the end, we have expressed some conclusions on the cost of the photocatalysts here employed, to support the overall feasibility assessment of the process.

Regenerable solvents mediate accelerated low temperature CO2 capture and carbon mineralization of ash and nano-scale calcium carbonate formation

The dual need to remove CO2 from our emissions and treat alkaline industrial residues such as ash materials motivate the design of innovative pathways to simultaneously capture and convert CO2 into mineralized carbonates. Direct carbon mineralization is one approach that addresses the need to simultaneously treat alkaline industrial residues and mineralize CO2 emissions. Low CO2 solubility in water and slow kinetics at ambient temperature have challenged the direct carbon mineralization of alkaline industrial residues. To address these challenges, the use of CO2 capture solvents that enhance CO2 solubility and facilitate accelerated carbon mineralization of fly ash at temperatures below 90 °C is investigated. Calcium carbonate formation results in the inherent regeneration of the solvent. The carbon mineralization extents of non-calcium carbonate content in fly ash were 50% and 51% and in waste ash were 58% and 62% in 2.5 M sodium glycinate and 30 wt% MEA solutions, respectively. The experiments were performed at 50 °C for 3 h with CO2 partial pressure of 1 atm in a continuously stirred slurry environment with 15 wt.% solid. Furthermore, nanoscale CaCO3 is successfully synthesized from dissolved calcium using CO2-loaded sodium glycinate and surfactants such as CTAB (Cetyl Trimethyl Ammonium Bromide). Surfactants such as CTAB bind to the calcium carbonate surface and regulate the growth of calcium carbonate particles. These innovative approaches demonstrate the feasibility of directly storing CO2 in fly ash and waste ash as calcium carbonate and producing nanoscale calcium carbonate using regenerable CO2 capture solvents.

Effect of different salts on the kinetic parameters of the carbon dioxide hydrate formation

In this study, the effects of sodium chloride (NaCl), potassium chloride (KCl), magnesium chloride (MgCl2), and calcium chloride (CaCl2) on the kinetic parameters of carbon dioxide (CO2) hydrate formation including induction time, amount of gas consumption, rate of gas consumption and storage capacity were experimentally studied. Aqueous solutions with the ion concentration same as the Persian Gulf Seawater were prepared and all the experiments were conducted at a temperature of 274.15 K and pressure of 3.5 MPa. The results showed that salts have an inhibitory effect on the kinetic parameters of CO2 hydrate formation by reducing CO2 solubility in water and electrostatic interaction between water molecules and ions. The intensity of ion inhibition depends on the ion size, ion charge, ion concentration, and the kosmotropic and chaotropic properties of ions. Examination of the kinetic parameters of CO2 hydrate formation in saline solutions with a constant concentration of 1000 mg/L of each ion showed that the Mg2+ has the greatest inhibitory effect on the kinetic parameters by increasing the induction time by 110.71% and reducing gas consumption, rate of gas consumption, and storage capacity by 48.21%, 82.14%, and 68.75%, respectively compared to pure water. The results showed that the inhibition effect of salt ions on the CO2 hydrate formation is in the following order: Mg2+> Ca2+>Na+>K+.

Potensi Pemanfaatan Gas Karbon Dioksida (CO2) sebagai Density Agent untuk Larutan Pemisah Cangkang dan Kernel Sawit

In order to achieve the national target of decarbonization by 2030, Palm oil mills (POM) can contribute to reducing CO2 emissions generated from their production activities. The CO2 emitted from POM is currently discharged into the environment without further treatment. As a result, the amount of CO2 in the atmosphere will rise, increasing global warming. This study proposes an approach of utilizing CO2 as a density agent in separation fluid formulation. The formulated fluid is then used to separate palm shells and kernels in the claybath. The solubility of CO2 in water occurs physically and is dependent on temperature and partial CO2 gas in the air. Monoethanolamine (MEA) was used as an absorbent to ensure the full interaction of CO2 with water. The chemisorption method is selected to dissolution CO2 into aqueous MEA. The mass ratios of MEA were varied by 10, 20, 30, 40, 50 % w/w. The achieved appropriate densities of formulated fluid were 1,11, 1,14, dan 1,17 g/cm3 at mass ratios of MEA:H2O is 30, 40, dan 50% w/w, respectively. All achieved densities fall between palm shells and kernels densities. Furthermore, the formulated fluid can be used as separation fluid in claybath for separating palm shells and kernels. In addition to the proposed idea of utilizing CO2 and, at the same time, reducing CO2 emission from POM.

Failure analysis of gas pipeline in a gas collecting station

The gas collecting line of a gas collecting station failed and had obvious corrosion pits. The failure reasons of the pipeline in this section are studied by means of macroscopic morphology analysis, mechanical property analysis, hardness analysis and microstructure analysis. The results show that the main reason is the mechanical damage caused in the construction process for the damage of the anticorrosive coating on the outer surface of the pipe section. The main reason for the failure of “corrosion pit” inside the pipe section is that the wet gas transported contains CO2, which dissolves in water to generate H2CO3, and the pipe section is corroded in H2CO3 solution by electrochemical corrosion, which gradually develops into a more serious corrosion pit. In order to prevent the occurrence of such failure, 13Cr (martensite) material can be used to meet the corrosion resistance requirements, but also can appropriately increase the gas temperature in the tube to reduce the solubility of CO2 in water to prevent corrosion.

Liquid “Syngas” Based on Supercritical Water and Graphite Oxide/TiO2 Composite as Catalyst for CO2 to Organic Conversion

The conversion of carbon monoxide into organic substances is one of the top topics of modern science due to the development of industry and the climate changes caused by it on the one hand, and the possibility of obtaining an economic effect on the other, as it could allow for partial recovery of fuels. A problem in this regard has always been the low solubility of CO2 in water, which eliminated the possibility of easy converting carbon dioxide into the liquid. The development of research on water critical states revealed the fact that water in a subcritical state has a much higher ability to dissolve gases. And this effect was used to obtain the "liquid synthesis gas" model presented in this paper. Equally important was the selection of an appropriate catalyst that would increase the efficiency of the conversion process by generating hydrogen in the system under the influence of cold plasma. In this work we present the studies of transformation of CO2 dissolved in supercritical water using partially reduced graphite oxide—nanometric titania composite (RGO-TiO2) as catalyst, due to the ability of RGO to generate hydrogen in the water environment (water splitting) under the influence of various physical factors, especially cold plasma. The RGO catalyst was stabilized with titanium oxide to obtain higher activity at lower RGO concentrations in the system. Therefore, research on conversions was preceded by a thorough analysis of CO2 solubility in supercritical water, as well as an analysis of the structural, morphological, and spectroscopic properties of the catalyst.Graphic General scheme of cold plasma reactor.

Electrolytic reduction of CO2 in KHCO3 and alkanolamine solutions with layered double hydroxides intercalated with gold or copper

The application of electrocatalytic reduction of CO2 is limited by the low solubility of CO2 in water, separation of products, energy conversion efficiency and insufficient catalyst performance. In this research, enhanced CO2 reduction was observed in alcohol amine solution by using layered double hydroxides (LDHs) intercalated with gold or copper. Copper was found to be distributed more evenly and thus had a larger electrochemical active surface area (ECSA) through the pre-intercalation of EDTA when compared with the direct ion-exchange of [AuCl4]− with LDHs. In 0.5 M KHCO3 solutions, CO and H2 was monitored for Au/MgAl-LDHs while additional products of CH4 and HCOOH was measured by using Cu/MgAl-LDHs. In 1.0 M alcohol amine solutions, CO and H2 were determined as the main products for both Au/MgAl-LDHs and Cu/MgAl-LDHs. Under all the test conditions hydrogen evolution reaction (HER) was enhanced towards negative potential, resulting in a higher Faraday's Efficiency (FE) for H2.

Kinetic and Thermodynamic Analysis of High-Pressure CO2 Capture Using Ethylenediamine: Experimental Study and Modeling

One of the alternatives to reduce CO2 emissions from industrial sources (mainly the oil and gas industry) is CO2 capture. Absorption with chemical solvents (alkanolamines in aqueous solutions) is the most widely used conventional technology for CO2 capture. Despite the competitive advantages of chemical solvents, the technological challenge in improving the absorption process is to apply alternative solvents, reducing energy demand and increasing the CO2 captured per unit of solvent mass. This work presents an experimental study related to the kinetic and thermodynamic analysis of high-pressure CO2 capture using ethylenediamine (EDA) as a chemical solvent. EDA has two amine groups that can increase the CO2 capture capacity per unit of solvent. A non-stirred experimental setup was installed and commissioned for CO2 capture testing. Tests of the solubility of CO2 in water were carried out to validate the experimental setup. CO2 capture testing was accomplished using EDA in aqueous solutions (0, 5, 10, and 20 wt.% in amine). Finally, a kinetic model involving two steps was proposed, including a rapid absorption step and a slow diffusion step. EDA accelerated the CO2 capture performance. Sudden temperature increases were observed during the initial minutes. The CO2 capture was triggered after the absorption of a minimal amount of CO2 (~10 mmol) into the liquid solutions, and could correspond to the “lean amine acid gas loading” in a typical sweetening process using alkanolamines. At equilibrium, there was a linear relationship between the CO2 loading and the EDA concentration. The CO2 capture behavior obtained adapts accurately (AAD < 1%) to the kinetic mechanism.

Experimental analysis of temperature effects in supercritical-assisted atomization

Supercritical CO2 is proved as an excellent choice in supercritical-assisted atomization of nanoparticle suspensions for fabrication of micro/nano-powders. As the rheological properties of the supercritical fluids are strongly dependent on the temperature, the breakup mechanism of the CO2-liquid mixture upon injection is significantly affected by crossing the critical temperature of the binary mixture. In this study, we investigate the breakup of CO2-water mixture (CO2-A) at subcritical, critical, and supercritical states and compare it with the cases where N2 is utilized as the assisting fluid (N2-A) at the same injection conditions. High-speed imaging and laser diffraction systems are utilized to analyze the primary and secondary atomization of the injected CO2-water mixture (over 20 to 40 °C injection temperature range). In general, CO2-A showed smaller and more homogenous droplets compared to N2-A. Therefore, the use of CO2 as the atomization gas is superior to N2. The underlying mechanism in primary breakup of CO2-A involves the emergence, expansion, and burst of CO2 bubbles and formation of ligaments that break up into droplets. The core of the jet in CO2-A system expands up to 50% due to emergence of gas bubbles, while the expansion ratio remains unchanged in the N2-A jet. The finest and most homogenous droplet sizes are achieved by operating near the critical point at 31.5 °C and 7.5 MPa. High solubility of CO2 in water and low interfacial tension of the CO2-water mixture are the main contributors.

CO2 Solubility in Aqueous Electrolyte Solutions Confined in Calcite Nanopores

Geological carbon dioxide sequestration in deep saline aquifers can play a key role in the successful mitigation of greenhouse gas emissions. Several conditions have been identified that affect the solubility of CO2 in water, including temperature, pressure, pH, and salinity. At similar conditions, the solubility in bulk fluids differs from the solubility in confined porous media. We conducted equilibrium molecular dynamics (MD) simulations to investigate the solubility of CO2 in water confined in slit-shaped calcite pores. We studied the effects of brine (NaCl and MgCl2). Compared to bulk water/brine, the solubility of CO2 is lower in calcite pores and decreases as the pores narrow. Adsorption energy calculations were performed to compare our results to CO2 solubility in water-filled silica pores. These results indicate that narrower calcite pores are less attractive for the adsorption of CO2. In addition, the simulation results suggest that the difference in the positions where the ions adsorb also affects whether salts increase or decrease the solubility of CO2 in confined water. Confinement and ions also reduce the mobility of CO2 in water. These observations contribute to the design of long-term CO2 sequestration strategies as they provide boundary constraints for the amount of CO2 that can dissolve in hydrated pores, as well as the timing of CO2 transport in such systems.

Catalyst-Proximal Plastrons for Enhancing Electrocatalytic Reduction of CO2 on Copper in Aqueous-Phase Systems

Electrocatalytic reduction of CO2 (CO2RR) is an attractive method of converting CO2 to solar fuels. Much research in this field has been focused on developing novel catalysts to enhance the activity and product distribution (selectivity). Copper has been studied widely as it can produce both one carbon (C1) products such as methane and formate, and products with two or more carbons (C2+) such as ethylene, ethanol, and n-propanol1. Copper is not immune from the competing hydrogen evolution reaction: the poor solubility of CO2 in water (~34 mM at ambient conditions) limits the CO2RR current density, and hydrogen generation is favored if the aqueous CO2 concentration becomes locally undersaturated close to the catalyst during CO2RR2. This limitation is even more pronounced for nanotextured copper, because the increased active surface area leads to faster depletion of local CO2 thereby promoting hydrogen evolution over CO2RR. Hence, overcoming these CO2 availability limitations can enable higher CO2RR activity while reducing co-evolution of hydrogen.In this work, we develop a gasphilic CO2 trap that increases gas-liquid mass transfer and maintains supersaturated CO2 concentration around the catalyst during CO2RR. Gasphilic surfaces need a special combination of surface chemistry and texture to capture bubbles and form a sheet of gas underwater which is called a plastron3. By creating pyramidal textures, CO2 bubbles are efficiently captured within the textures and form a CO2 plastron. When this plastron is placed proximal to both smooth and nanostructured copper catalysts during CO2RR, the current density is enhanced and maintained throughout the reaction, when compared to two commonly used methods of CO2 delivery: headspace and bubbling in the bulk electrolyte. The plastron allows for quick replenishment of CO2 during the CO2RR reaction in the vicinity of the catalyst. As a result, the H2 Faradaic efficiency is reduced from 33% to 13% on smooth copper, and from 62% to 33% on nanostructured copper. This is accompanied by an increased production of C2+ products including ethylene, ethanol and propanol, as well as acetone and acetate at Faradaic efficiencies exceeding 1%. We highlight the importance of this catalyst-proximal plastron approach by comparing against recent aqueous-phase CO2RR studies, and discuss how this approach can inform optimal design of continuous CO2RR systems such as gas-diffusion electrodes.[1] Nitopi, S., Bertheussen, E., Scott, S. B., Liu, X., Engstfeld, A. K., Horch, S., Seger, B., Stephens, I. E. L., Chan, K., Hahn, C., Nørskov, J. K., Jaramillo, T. F. & Chorkendorff, I. Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte. Chem. Rev. 119, 7610–7672 (2019).[2] Lobaccaro, P., R. Singh, M., Lee Clark, E., Kwon, Y., T. Bell, A. & W. Ager, J. Effects of temperature and gas–liquid mass transfer on the operation of small electrochemical cells for the quantitative evaluation of CO2 reduction electrocatalysts. Physical Chemistry Chemical Physics 18, 26777–26785 (2016).[3] Panchanathan, D., Rajappan, A., Varanasi, K. K. & McKinley, G. H. Plastron Regeneration on Submerged Superhydrophobic Surfaces Using In Situ Gas Generation by Chemical Reaction. ACS Appl. Mater. Interfaces 10, 33684–33692 (2018).

Synthetic Formatotrophs for One-Carbon Biorefinery.

The use of CO2 as a carbon source in biorefinery is of great interest, but the low solubility of CO2 in water and the lack of efficient CO2 assimilation pathways are challenges to overcome. Formic acid (FA), which can be easily produced from CO2 and more conveniently stored and transported than CO2, is an attractive CO2‐equivalent carbon source as it can be assimilated more efficiently than CO2 by microorganisms and also provides reducing power. Although there are native formatotrophs, they grow slowly and are difficult to metabolically engineer due to the lack of genetic manipulation tools. Thus, much effort is exerted to develop efficient FA assimilation pathways and synthetic microorganisms capable of growing solely on FA (and CO2). Several innovative strategies are suggested to develop synthetic formatotrophs through rational metabolic engineering involving new enzymes and reconstructed FA assimilation pathways, and/or adaptive laboratory evolution (ALE). In this paper, recent advances in development of synthetic formatotrophs are reviewed, focusing on biological FA and CO2 utilization pathways, enzymes involved and newly developed, and metabolic engineering and ALE strategies employed. Also, future challenges in cultivating formatotrophs to higher cell densities and producing chemicals from FA and CO2 are discussed.

Experimental and theoretical study on water solubility of carbon dioxide in oil and gas displacement

The emission of greenhouse gas carbon dioxide causes the global temperature to rise year by year. A possible method for CO2 storage and emission reduction is to use it to displace oil and gas. Solubility of CO2 in water is key to replace oil and gas. The present study investigates the effects of the temperature, pressure, and addition of salt and methane on the water solubility of CO2 by high temperature and high pressure cell combined with chromatographic analysis. The results show that the phase state of CO2 in water with temperature and pressure greatly affects its solubility. Besides, its solubility in the supercritical and liquid state is significantly greater than that in the gaseous state. The solubility of CO2 gas in brine and water increases with an increase in pressure; however, this increasing tendency gradually decreases. At the same time, the addition of CH4 gas can boost the dissolution of CO2 gas, while the addition of NaCl can significantly reduce its solubility; as the salt content in the water increases, the solubility of CO2 gradually decreases. Given the influence of saturated vapor pressure of water at vapor-liquid equilibrium, a thermodynamic constitutive equation was established to calculate the water solubility of CO2. The results showed that the prediction error of CO2 solubility in water is within 8%, that of pure CO2 is less than 4%. A comparison of these results with those predicted using the artificial neural network model showed that the thermodynamic model is more suitable for predicting water solubility required for replacing oil and gas by carbon dioxide.