CO2 In Pure Water Research Articles

CO2 solubility in aqueous solution of salts: Experimental study and thermodynamic modelling

AbstractThere are many economic obstacles and complex engineering problems associated with CO2 capture and storage in saline aquifers that need to be addressed. Overcoming such challenges requires precise knowledge on the fluid phase equilibria of CO2‐brine systems. Having accurate CO2 solubility data over a wide range of temperature and pressure can greatly assist in resolving these obstacles by improving the performance and accuracy of the thermodynamic modeling and subsequent CCS engineering success.CO2 solubility in pure water and NaCl solutions has been widely studied in the literature, however, there is a lack of data on CO2 solubility at lower temperatures (below 298 K). Furthermore, limited phase equilibria data are available for CO2 solubility in CaCl2, MgCl2, and KCl solutions at elevated temperatures (i.e., T > 323.15 K).In this work, the phase equilibria of CO2 and brine systems are investigated experimentally and theoretically. In this study, solubilities of CO2 in pure water and various concentrations of NaCl (10, 15, 20, and 22 wt%), KCl (10, 15, and 22 wt%), CaCl2 (7.5, 10, 15.7, and 23.4 wt%), and MgCl2 (6.7, 11, 18, and 29 wt%) aqueous solutions are reported. All CO2 solubilities were measures at 323.15, 373.15, and 423.15 K and over various pressure ranges, while solubilities in 10 and 20 wt% NaCl aqueous solutions were also measured over the temperature range of 263 to 298 K and pressures up to the hydrate dissociation pressure of each system. Equation of state modelling using the PC‐SAFT and the Cubic Plus Association equations of state, is performed in the theoretical part of the study to validate the measured solubility data. © 2024 The Author(s). Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd.

Synergy of Photogenerated Electrons and Holes toward Efficient Photocatalytic Urea Synthesis from CO2 and N2

AbstractDirectly coupling N2 and CO2 to synthesize urea by photocatalysis paves a sustainable route for urea synthesis, but its performance is limited by the competition of photogenerated electrons between N2 and CO2, as well as the underutilized photogenerated holes. Herein, we report an efficient urea synthesis process involving photogenerated electrons and holes in respectively converting CO2 and N2 over a redox heterojunction consisting of WO3 and Ni single‐atom‐decorated CdS (Ni1‐CdS/WO3). For the photocatalytic urea synthesis from N2 and CO2 in pure water, Ni1‐CdS/WO3 attained a urea yield rate of 78 μM h−1 and an apparent quantum yield of 0.15 % at 385 nm, which ranked among the best photocatalytic urea synthesis performance reported. Mechanistic studies reveal that the N2 was converted into NO species by ⋅OH radicals generated from photogenerated holes over the WO3 component, meanwhile, the CO2 was transformed into *CO species over the Ni site by photogenerated electrons. The generated NO and *CO species were further coupled to form *OCNO intermediate, then gradually transformed into urea. This work emphasizes the importance of reasonably utilizing photogenerated holes in photocatalytic reduction reactions.

Synergy of Photogenerated Electrons and Holes toward Efficient Photocatalytic Urea Synthesis from CO2 and N2.

Directly coupling N2 and CO2 to synthesize urea by photocatalysis paves a sustainable route for urea synthesis, but its performance is limited by the competition of photogenerated electrons between N2 and CO2, as well as the underutilized photogenerated holes. Herein, we report an efficient urea synthesis process involving photogenerated electrons and holes in respectively converting CO2 and N2 over a redox heterojunction consisting of WO3 and Ni single-atom-decorated CdS (Ni1-CdS/WO3). For the photocatalytic urea synthesis from N2 and CO2 in pure water, Ni1-CdS/WO3 attained a urea yield rate of 78 μM h-1 and an apparent quantum yield of 0.15 % at 385 nm, which ranked among the best photocatalytic urea synthesis performance reported. Mechanistic studies reveal that the N2 was converted into NO species by ⋅OH radicals generated from photogenerated holes over the WO3 component, meanwhile, the CO2 was transformed into *CO species over the Ni site by photogenerated electrons. The generated NO and *CO species were further coupled to form *OCNO intermediate, then gradually transformed into urea. This work emphasizes the importance of reasonably utilizing photogenerated holes in photocatalytic reduction reactions.

Modeling CO2 solubility in water using gradient boosting and light gradient boosting machine

The growing application of carbon dioxide (CO2) in various environmental and energy fields, including carbon capture and storage (CCS) and several CO2-based enhanced oil recovery (EOR) techniques, highlights the importance of studying the phase equilibria of this gas with water. Therefore, accurate prediction of CO2 solubility in water becomes an important thermodynamic property. This study focused on developing two powerful intelligent models, namely gradient boosting (GBoost) and light gradient boosting machine (LightGBM) that predict CO2 solubility in water with high accuracy. The results revealed the outperformance of the GBoost model with root mean square error (RMSE) and determination coefficient (R2) of 0.137 mol/kg and 0.9976, respectively. The trend analysis demonstrated that the developed models were highly capable of detecting the physical trend of CO2 solubility in water across various pressure and temperature ranges. Moreover, the Leverage technique was employed to identify suspected data points as well as the applicability domain of the proposed models. The results showed that less than 5% of the data points were detected as outliers representing the large applicability domain of intelligent models. The outcome of this research provided insight into the potential of intelligent models in predicting solubility of CO2 in pure water.

Visual experimental study of nanofluids application to promote CO2 absorption in a bubble column

The addition of dispersed-phase nanoparticles in the liquid phase can enhance the gas–liquid transfer process as the suspended nanoparticles affect the transfer process inside the fluid through micro-disturbance or micro-convection effects. In this paper, a high-speed digital camera was used to visualize the bubble behavior of CO2 in pure water and nanofluids to examine the effects of CO2 gas flow rate, nanoparticle solid content and type on the bubble behavior in the fluids. The CO2 absorption performance in three water-based nanofluids were compared in a bubbler. And the mass transfer characteristics during CO2 bubble absorption and the reasons for the enhanced gas–liquid mass transfer effect of nanoparticles were analyzed. The results showed that the presence of nanoparticles affected the formation process of bubbles in the fluid, shortened the bubble detachment time, reduced the detachment diameter, effectively increased the gas–liquid contact area, and improved the bubbles detachment frequency. The system with MCM-41 corresponded to a higher overall mass transfer coefficient. Uncalined MCM-41 contained surfactant which enhanced foaming behavior in water. This prevented the transfer of CO2 to some extent, and the CO2 absorption by uncalined MCM-41/H2O was 5.34% higher than that by pure water. Compared with SiO2 nanoparticles with the same particle size and the same composition, MCM-41 had a higher adsorption capacity and better hydrophilicity due to its larger specific surface area and rich porous structure, which was more favorable to accelerate the collision between nanoparticles and CO2 bubbles to cause micro-convection. Under the condition of 0.1% (mass) solid content, the enhancement of CO2 absorption process by MCM-41 nanoparticles was more significant and improved by 16.9% compared with pure water.

Equilibrium conditions of hydrate dissociation of CO2 + bromocyclohexane or tetrahydrothiophene + H2O

Hydrate can be used as an effective way to separate CO2. However, the formation of CO2 hydrate requires high pressure and low temperature conditions in pure water, it limits the hydrate method application for the separation of CO2. Thermodynamic prompters can be used to reduce the pressure of CO2 hydrate formation. In this work, the effect of tetrahydrothiophene and bromocyclohexane on CO2 hydrate dissociation conditions is first studied. The addition of tetrahydrothiophene can greatly reduce the equilibrium pressure of CO2 hydrate dissociation. Structure II hydrate forms in the system of CO2 + tetrahydrothiophene + H2O, while structure I hydrate forms in the system of CO2 + H2O. Hydrate equilibrium pressure increases with the increase of temperature. At any temperature, the hydrate equilibrium pressure of CO2 + tetrahydrothiophene + H2O reduces more than 2 MPa, compared the hydrate equilibrium pressure of CO2 in pure water in this work. Bromocyclohexane has almost no effect on the phase equilibrium conditions of CO2 hydrate. The experimental results also show that tetrahydrothiophene can be as a promoter for CO2 hydrate formation.

Modeling CO2 Solubility in Water at High Pressure and Temperature Conditions

CO2 dissolution in water at different temperature and pressure conditions is of essential interest for various environmental, geochemical, and thermodynamic related problems. The topic is of special interest in studies of CO2 geological sequestration in brine-bearing aquifers. In this Article, four powerful machine learning (ML) techniques—Radial Basis Function Neural Network (RBFNN), Multilayer Perceptron (MLP), Least-Squares Support Vector Machine (LSSVM), and Gene Expression Programming (GEP)—are implemented to develop economical, rapid, and reliable models to predict the solubility of CO2 in water. To expand the prediction capability of the ML approaches, their control parameters are optimized by various techniques. To this end, four back-propagation algorithms are applied in the MLP learning phase, while Particle Swarm Optimization (PSO), Differential Evolution (DE), Genetic Algorithm (GA), and Firefly Algorithm (FFA) are used to optimize the RBFNN and LSSVM control parameters. A wide-ranged database including temperature and pressure as inputs and CO2 solubility in pure water as output is utilized to develop the models, which are then compared with each other and also against existing models. The results demonstrate that the prediction performance of the proposed models is quite satisfactory. In addition, the comparison results reveal that the LSSVM-FFA is the best paradigm to estimate the solubility of CO2 in pure water, as it outperforms the other proposed ML techniques as well as prior models. The overall RMSE and R2 values for LSSVM-FFA are 0.3261 and 0.9930, respectively.

Separation of greenhouse gases from gas mixtures using nanoporous polymeric membranes

Removal of greenhouse gases from gas streams using porous membranes was carried out in this work. Theoretical studies were performed in terms of mathematical modeling and numerical simulation of CO2 capture in a flat‐sheet membrane contactor. Numerical simulation was performed using computational fluid dynamics (CFD) of mass and momentum transfer in the membrane module for laminar flow conditions. Physical absorption was considered in the simulations for absorption of CO2 in pure water. CO2 concentration distribution in the membrane module was determined through numerical solution of continuity equation coupled with the Navier‐Stokes equations. The modeling predictions indicated that the CO2 concentration difference is not appreciable in the membrane direction. Moreover, velocity distribution was determined in the liquid side of membrane contactor. CFD also represents a design and optimization tool for membrane gas separation processes. POLYM. ENG. SCI., 55:975–980, 2015. © 2014 Society of Plastics Engineers

A Phase-Partitioning Model for CO2–Brine Mixtures at Elevated Temperatures and Pressures: Application to CO2-Enhanced Geothermal Systems

Correlations are presented to compute the mutual solubilities of CO2 and chloride brines at temperatures 12–300°C, pressures 1–600 bar (0.1–60 MPa), and salinities 0–6 m NaCl. The formulation is computationally efficient and primarily intended for numerical simulations of CO2-water flow in carbon sequestration and geothermal studies. The phase-partitioning model relies on experimental data from literature for phase partitioning between CO2 and NaCl brines, and extends the previously published correlations to higher temperatures. The model relies on activity coefficients for the H2O-rich (aqueous) phase and fugacity coefficients for the CO2-rich phase. Activity coefficients are treated using a Margules expression for CO2 in pure water, and a Pitzer expression for salting-out effects. Fugacity coefficients are computed using a modified Redlich–Kwong equation of state and mixing rules that incorporate asymmetric binary interaction parameters. Parameters for the calculation of activity and fugacity coefficients were fitted to published solubility data over the P–T range of interest. In doing so, mutual solubilities and gas-phase volumetric data are typically reproduced within the scatter of the available data. An example of multiphase flow simulation implementing the mutual solubility model is presented for the case of a hypothetical, enhanced geothermal system where CO2 is used as the heat extraction fluid. In this simulation, dry supercritical CO2 at 20°C is injected into a 200°C hot-water reservoir. Results show that the injected CO2 displaces the formation water relatively quickly, but that the produced CO2 contains significant water for long periods of time. The amount of water in the CO2 could have implications for reactivity with reservoir rocks and engineered materials.

Fundamental Seismic Parameters of Injected CO2

When CO2 is injected into a saline aquifer, its flow is controlled by the rock permeability, porosity, chemical composition and fluids, and its state-of-phase which is controlled by the reservoir pressure and temperature conditions. During the injection procedure, CO2 dissolves in the formation water and with time this increasing dissolution enhances trapping mechanism. While monitoring CO2 as a liquid or gas, it becomes equally important to quantify it both in its dissolved and gaseous states. We dissolved CO2 in pure water and passed it through a variable low pressure cell at room temperature. During this time, ultrasonic transmission tests were conducted to monitor the seismic response with CO2 in its dissolved and its gaseous phases. It was found that the signal amplitude was far more sensitive to the amount of dissolved CO2 than velocity, and it was observed that the transmission amplitudes were a function of the density of the dissolved CO2 in brine. These empirical relationships were based on seismic data recorded in a pressure cell containing a CO2:water mixture without a matrix, and a matrix consisting of glass beads saturated with a CO2:water mixture. These data provide reason to believe that while seismic reflectivity may be used successfully for fluid monitoring, the use of transmission seismic such as is found in vertical seismic profiling, may be useful for quantifying fluid in-place, for verification purposes.

Effect of Carbon Dioxide in Seawater on Desalination: A Comprehensive Review

The two main methods of removing salt from ocean water currently in use for large scale applications are: distillation using thermal desalination and membrane reverse osmosis separation. A detailed knowledge of the CO2 solubility in the seawater at the conditions prevailing in the system is required for the modeling of CO2 release in the multi‐stage flash distillers. The measurement of the solubility of CO2 in pure water has been extensively studied in the literature, whereas there is a lack of saline solutions studies. Several studies have investigated the solubility of CO2 in seawater under different temperatures and pressures without covering the conditions that prevailed in the desalination plants for example low pressures and high temperatures. The gas solubility can be theoretically estimated by considering the ionic strength and the salting‐out parameter in the low‐pressure regime, i.e., near atmospheric pressure. The measurements of gas solubility can be made as a function of the seawater temperature and salinity at low pressure where effect of pressure can be considered negligible. Alkaline scale formation causes fouling in the MSF plants and it is known that the rate of formation of calcium carbonate and magnesium hydroxide in seawater depends on a number of parameters such as temperature, pH, concentration of bicarbonate ions, rate of CO2 release, concentration of Ca2+ and Mg2+ ions, and total dissolved solids. This review shows an overview of the carbon dioxide solubility in the high concentrated saline water, carbonate equilibriums in the seawater and the various correlations used to characterize the CO2‐seawater system.

Physical Solubility and Diffusivity of N2O and CO2 in Aqueous Sodium Glycinate Solutions

Physical solubility and diffusivity of N2O and CO2 in pure water and of N2O in aqueous sodium glycinate solutions of mass fraction (0.1 to 0.5) were measured at T = (303.15 to 323.15) K. Since it was not possible to measure these properties for CO2 due to the chemical reaction between CO2 and the amine group of sodium glycinate, these were estimated using the well-known N2O analogy. While the physical solubility increases with a decrease in temperature and with a decrease in mass fraction, diffusivity decreases with a decrease in temperature as well as an increase in mass fraction except for concentrated solution (mass fraction 0.4 and 0.5) where it increases with a decrease in temperature.

The Effect on the CO2 Solubility into Water (Measurement of the CO2 Solubility by a Gas Expansion Method)

The solubility of CO2 in pure water was investigated at high-pressure conditions, from 7 to 12 MPa, and at temperatures between 2.5-20°C. CO2 clathrate hydrate film formed at temperatures below approximately 10°C. The CO2 solubility was estimated by expanding the dissolved gas. The solubility decreased with decreasing temperature and with decreasing pressure, although some researchers reported it decreased with increasing pressure at 7°C, in the presence of the hydrate. Many other researchers reported that the pressure conditions did not affect the solubility in the presence of the hydrate. Although this seemed to be mostly correct, we did confirm a small difference of the solubility at pressures ranging 7-12 MPa.

Carbonic anhydrase activity in leaves as measured in vivo by 18O exchange between carbon dioxide and water

Carbonic anhydrase activity of intact Commelina communis L. leaves was measured using mass spectrometry, by following the 18O-exchange kinetics between 18O-enriched carbon dioxide and water. A gas-diffusion model (Gerster, 1971, Planta 97, 155–172) was used to interpret the 18O-exchange kinetics and to determine two constants, one (k) related to the hydration of CO2 and the other (ke), related to the diffusion of CO2. Both constants were determined in Commelina communis L. leaves after stripping the lower epidermis to remove any stomatal influence. The hydration constant (k) was 17200 +2200 ·min−1 (mean±SD, 12 experiments), i.e., about 8 600 times the uncatalyzed hydration of CO2 in pure water, and was specifically inhibited by ethoxyzolamide, a powerful inhibitor of carbonic anhydrases, half-inhibition occurring around 10−5 Methoxyzolamide. The diffusion constant (ke) was 1.18±0.28·min−1 (mean±SD, 12 experiments) and was only slightly inhibited (about 20%) by ethoxyzolamide. Carbonic anhydrase activity of stripped leaves was not affected by the leaf water status (up to 50% relative water deficits), was strongly inhibited by monovalent anions such as Cl− or NO3−, and decreased by about 50% when the photon flux density during growth was increased from 100 to 500 μmol photons·m −2·s−1. By studying the effect of ethoxyzolamide (10−4 M) on photosynthetic O2 exchange, measured using 18O2 and mass spectrometry, we found that inhibition of carbonic anhydrase activity by 92–95% had little effect on the response curves of net O2 evolution to increased CO2 concentrations. Ethoxyzolamide had no effect on the photosynthetic electron-transport rate, measured as gross O2 photosynthesis at high CO2 concentration (>350 μl·−1), but was found to increase both gross O2 photosynthesis and O2 uptake at lower CO2 levels. The chloroplastic CO2 concentration calculated from O2-exchange data was not significantly modified by ethoxyzolamide. We conclude from these results that, under normal conditions of photosynthesis, most of the carbonic anhydrase activity is not involved in CO2 assimilation. Measurement of carbonic anhydrase activity using 18O-isotope exchange therefore provides a suitable model to study the in-vivo regulation of this chloroplastic enzyme in plants submitted to various environmental conditions.