Liquid CO2 Research Articles

Transport and Energetics of Carbon Dioxide in Ionic Liquids at Aqueous Interfaces.

A major hurdle in utilizing carbon dioxide (CO2) lies in separating it from industrial flue gas mixtures and finding suitable storage methods that enable its application in various industries. To address this issue, we utilized a combination of molecular dynamics simulations and experiments to investigate the behavior of CO2 in common room-temperature ionic liquids (RTIL) when in contact with aqueous interfaces. Our investigation of RTILs, [EMIM][TFSI] and [OMIM][TFSI], and their interaction with a pure water layer mimics the environment of a previously developed ultrathin enzymatic liquid membrane for CO2 separation. We analyzed diffusion constants and viscosity, which reveals that CO2 molecules exhibit faster mobility within the selected ILs compared to what would be predicted solely based on the viscosity of the liquids using the standard Einstein-Stokes relation. Moreover, we calculated the free energy of translocation for various species across the aqueous-IL interface, including CO2 and HCO3-. Free energy profiles demonstrate that CO2 exhibits a more favorable partitioning behavior in the RTILs compared to that in pure water, while a significant barrier hinders the movement of HCO3- from the aqueous layer. Experimental measurement of the CO2 transport in the RTILs corroborates the model. These findings strongly suggest that hydrophobic RTILs could serve as a promising option for selectively transporting CO2 from aqueous media and concentrating it as a preliminary step toward storage.

In Situ Measurement of Liquid and Gas CO2 with High Purity at Deep-Sea Hydrothermal Vents in the Mariana Arc Using Raman Spectroscopy

In Situ Measurement of Liquid and Gas CO₂ with High Purity at Deep-Sea Hydrothermal Vents in the Mariana Arc Using Raman Spectroscopy

CO2-philicity to CO2-phobicity Transition on Smooth and Stochastic Rough Cu-like Substrate Surfaces.

CO2 on metal substrates is essential to CO2 liquefaction and transportation of CO2, yet the manipulation of the wettability of the CO2 and the elucidation of its underlying mechanism have not been fully achieved. Here, using molecular dynamics simulations, we report CO2 wetting characteristics on both smooth and stochastic rough Cu-like substrate surfaces. The results indicate that the apparent contact angle (CA) of the CO2 droplet on the smooth surface decreases from 180° to 0° as the CO2-solid characteristic interaction energy increases from 0.002 to 0.016 eV. In addition, the CAs become greater with increasing the density of surface asperities, regardless of the intrinsic surface wettability. This is attributed to the capillary drying-out of liquid CO2 molecules in gaps between surface asperities at the three-phase contact line of the droplet, which is usually overlooked in previous theoretical studies. Notably, the intrinsically CO2-philic surface transforms to the CO2-phobic due to an increase in the density of surface rugosity. Moreover, we verify the range of applicability of the CA prediction models concerning the nanoscale asperities. This work is beneficial for fully understanding the influence of nanoscale surface topography on CO2 wettability and shedding light on the design of functionalized and patterned surfaces to manipulate CO2 wettability.

Performance of compressed CO2 energy storage systems with different liquefaction and storage scenarios

Energy storage technologies play a hard role in smoothening the fluctuations and improving penetrations of renewables. Compressed CO2 energy storage is a promising large-scale technology because of the excellent thermos-physical characteristics of CO2. As one of the primary constraints, the condensation of CO2 should be addressed to successfully develop compressed CO2 energy storage technology. In this paper, four compressed CO2 energy storage systems with different liquefication and storage scenarios are proposed and analyzed comparatively. The parametric analysis is conducted by establishing thermodynamic and economic modeling. Results indicate system A is advantageous with the highest round trip efficiency and the lowest levelized cost of electricity in comparison with other proposed systems in this paper. CO2 is liquefied by the two-tank cold storage subsystem and stored in the isovolumic tank in system A. It has 71.54 % of round trip efficiency and 40.61 kWh/m3 of energy density separately under designed conditions. With a mass flow rate of 37.86 kg/s, CO2 of 6.1*105 m3 in the gas holder is pressurized and stored in the liquid CO2 tank of 1970.03 m3. System A arrives at 0.1109 $/kWh for the levelized cost of electricity and 3.03 million$ for the net present value. The purchased cost of tanks takes the largest share over total system investment.

Influence of inner wall roughness of supersonic separator on non-equilibrium condensation of CO2 benefiting flue gas decarbonization

Supersonic separators are energy efficient and environmental separation device. Recent work has demonstrated the potential of supersonic separators to separate CO2 from flue gas. Because the supersonic flows in the separator is accompanied by shock waves and non-equilibrium condensation, the current cognition level on flow behavior in the separator is low. This work establishes a numerical model to describe the high-speed two-phase flows in the separator and the non-equilibrium condensation of CO2 during carbon capture process, and clarify the influence of inner wall roughness on carbon capture process. The results show that the rapid expansion of gas pushes the thermodynamic system to non-equilibrium state and promotes the spontaneous condensation of CO2. Wall roughness has obvious influence on normal shock wave position, non-equilibrium condensation and normal shock wave intensity. When the roughness height increases by 0.1 mm, the maximum droplet radius in the separator decreases by 17.4%, liquid CO2 fraction decreases by 49.1%, and radial range of liquid phase decreases by 46.3%.

Investigation of the smashing characteristics induced by energy distribution of CO2 BLEVE for coalbed methane recovery

Failure in the near field of coal by liquid CO2 phase transition blasting (LCO2-PB) is the major reason for fracturing performance and enhancing coalbed methane (ECBM) recovery. Features to clarify this failure are of significant importance for the field projects. Some studies have revealed that the energy of LCO2 releasing can determine the damage feature to some extent. This study was therefore initiated to investigate the effect of BLEVE energy on the fracturing performance of LCO2-PB in coal. A series of LCO2-PB fracturing tests was carried out on hard and soft coal to examine the effect of CO2 BLEVE energy on fracture morphology. It was obtained that, compared with fractal dimension of hard coal under lower import energy (623.48 kJ) is around 2.17, the higher import energy (831.36 kJ) provides a larger fractal dimension (2.32), especially for high rupture pressure (95 MPa), which make fragments smash into a smaller radial. Although higher input energy favours a large superfluous energy density for any coal types, soft coal represents a stronger tendency to fracture in the stress drop stage. Lower input energy in hard coal seam products a longer main fracture, and excellent fracturing in soft coal prefers the higher import energy.

Dissolution behavior of different lubricating oils in liquid and supercritical CO2

In deep drilling, lubrication and cooling tremendously affect drill life and machining quality. In this work, we investigate on the cryogenic Minimum Quantity Lubrication (cMQL) with oil and liquid or supercritical CO2. In the drilling process, both fluids are conducted through small flow channels inside the drill to the cutting edge. For a stable process, single-phase conditions are required. Systems of five different lubricants with carbon dioxide are investigated at 25 °C, 40 °C and 60 °C. Investigations are made optically in a view cell at pressures between 60 bar and 300 bar and quantitatively between 60 bar and 250 bar using the static-analytical method. For the application, information on the mixing kinetics of the oils and CO2 is further required. To get an insight into the flow behavior under pressure, an optically accessible flow duct is presented that resembles the conditions in the real drilling process.

Efficiency and energy balance for substitution of CH4 in clathrate hydrates with CO2 under multiple-phase coexisting conditions.

Many experimental and theoretical studies on CH4-CO2 hydrates have been performed aiming at the extraction of CH4 as a relatively clean energy resource and concurrent sequestration of CO2. However, vague or insufficient characterization of the environmental conditions prevents us from a comprehensive understanding of even equilibrium properties of CH4-CO2 hydrates for this substitution. We propose possible reaction schemes for the substitution, paying special attention to the coexisting phases, the aqueous and/or the fluid, where CO2 is supplied from and CH4 is transferred to. We address the two schemes for the substitution operating in three-phase and two-phase coexistence. Advantages and efficiencies of extracting CH4 in the individual scheme are estimated from the chemical potentials of all the components in all the phases involved in the substitution on the basis of a statistical mechanical theory developed recently. It is found that although substitution is feasible in the three-phase coexistence, its working window in temperature-pressure space is much narrower compared to the two-phase coexistence condition. Despite that the substitution normally generates only a small amount of heat, a large endothermic substitution is suggested in the medium pressure range, caused by the vaporization of liquid CO2 due to mixing with a small amount of the released CH4. This study provides the first theoretical framework toward the practical use of hydrates replacing CH4 with CO2 and serves as a basis for quantitative planning.

Oxygen-Resistant CO2 Reduction Enabled by Electrolysis of Liquid Feedstocks.

Electrolytic CO2 reduction fails in the presence of O2. This failure occurs because the reduction of O2 is thermodynamically favored over the reduction of CO2. Consequently, O2 must be removed from the CO2 feed prior to entering an electrolyzer, which is expensive. Here, we show that the use of liquid bicarbonate feedstocks (e.g., aqueous 3.0 M KHCO3), rather than gaseous CO2 feedstocks, enables efficient and selective CO2 reduction without additional procedures for removing O2. This effect is made possible because liquid bicarbonate solutions, which serve as a liquid CO2 carrier, deliver high concentrations of captured CO2 to the cathode, while the low solubility of O2 in aqueous media maintains a low O2 concentration at the same cathode surface. Consequently, electrolyzers fed with liquid bicarbonate feedstocks create an environment at the cathode that favors the reduction of CO2 over O2. We validate this claim by electrochemically converting CO2 into CO with reaction selectivities of 65% at 100 mA cm-2 using a 3.0 M KHCO3 solution bubbled with 100% CO2 or 100% O2. Similar experiments performed with a gaseous CO2 feedstock showed that merely 0.5% of O2 in the feedstock reduced CO selectivity by >90% after 1 h of electrolysis. Our findings demonstrate that a liquid bicarbonate feedstock enables efficient CO2 reduction without the need for expensive O2 removal steps.

Evaluating liquid CO2 hydrate formation kinetics, morphology, and stability in oceanic sediments on a lab scale using top injection

Storing captured CO2 into the deep oceanic sediments as CO2 hydrates offers a potential approach to reducing atmospheric carbon emissions. However, two major challenges are slow CO2 hydrate formation kinetics and lack of an understanding of CO2 hydrate stability dynamics. To counter these challenges, the conversion of high-pressure liquid CO2 (LCO2) to CO2 hydrates has been experimentally explored [with and without a hydrate kinetic promoter L-tryptophan] in a lab-scale reactor embedded with an artificial seabed. The stability of these CO2 hydrates was also evaluated by submerging them in the aqueous phase (mimicking hydrostatic pressure of fluid) at thermodynamic conditions found at an oceanic depth of 1 km [3–4 °C, 10 MPa] for 14 days. In-situ high-pressure Raman spectroscopy was used to estimate the real-time solubility of CO2 in the aqueous medium, and an image processing thresholding technique was used for detecting CO2 hydrate formation/dissociation patterns in sediments during the stability testing.The lab-scale experimental results indicate that in comparison to gaseous CO2, the liquid CO2 forms hydrates much faster [60 times] in the sediments. These CO2 hydrates exhibited decent stability over 14 days when submerged in an aqueous medium [3–4 °C, 10 MPa]. At the end of the stability test, hydrates were dissociated by thermal stimulation to assess the CO2 hydrates inside the sediments qualitatively. A significant decrease in the height of the sand bed [6.0 cm to 5.5 cm] and the evolution of CO2 across the sediments confirmed the presence of a good number of hydrates inside the sediments.

The effects of organic fertilisers on soybean plant photosynthesis

ABSTRACT The paper reports the effects of organic fertilisers on the photosynthetic characteristics and growth of soybean plants. The photosynthetic parameters were performed through gas exchange analysis by chlorophyll a fluorescence emission, in three phenological stages of culture. Photosynthetic activity, liquid CO₂ assimilation rates, stomatal conductance and water use efficiency were favoured by the addition of organic fertilisers to the soil. The addition of organic fertilisers reduced the initial chlorophyll a fluorescence, increased the electron transport rate, the internal CO₂ concentration, the potential efficiency of photosystem (II) and the effective quantum efficiency of photosystem (II) in soybean plants.

Formation temperature range expansion and energy storage properties of CO2 hydrates

A hybrid thermal cycle is developed by storing liquid CO2 using an intermittent heat pump cycle (IHP) and forming CO2 hydrates (CHRs) using a CHR thermal cycle (CHT) with a high charge/discharge efficiency at low temperatures. The proposed technology for physical batteries operates the IHP in summer, when outside temperatures are high, and the CHT in winter. The operating period of a CHT with a high charge/discharge efficiency can be extended and the annual efficiency of IHP/CHT hybrid systems can be improved by increasing the temperature of the low-temperature heat source of the CHT. Therefore, cyclopentane, the crystal structure of which differs from that of CHRs, is added to the host fluid in this study. Then, the CHR formation temperature range is expanded based on the results of the experiment. When the CHR formation temperature (outdoor air temperature as low-temperature heat source) is increased from the conventional 0 °C–15 °C, the amount of generated CHR slightly exceeds the amount generated by a conventional system. These findings show that a CHT system, which conventionally requires a low-temperature heat source (approximately 0 °C), can now be operated at a moderate temperature of 15 °C. When CHR are formed at 0 °C for 18 h and then dissociated at 25 °C, the prototype reactor produces a high-pressure dissociated gas of 20.5 MPa at an initial formation pressure of 5 MPa. When cyclopentane is added to water in a 3500 cm3 vessel at the appropriate concentration, CO2 hydrates large enough to be produced even at outdoor temperatures of about 15 °C or less. The proposed system can be operated at outdoor temperatures below 15 °C. These results represent the close realization of the proposed CHT.

Mechanism and destruction status of CO2 BLEVE during CO2 geological storage and enhanced oil recovery injection process

In CO2-oil recovery enhancement technology, the occurrence of a Boiling Liquid Expansion Vapor Explosion (BLEVE) can result in dangerous events that endanger the lives and health of workers, while also leading to significant economic losses. This happens when there is an excessive injection concentration and volume of CO2, coupled with container defects. To address the limited research on the mechanism and destruction of BLEVE, this study conducts experiments to explore these issues. The experimental results reveal that the bursting piece ruptures at a temperature of 36 °C, and the specimen explodes when the pressure intensity exceeds the residual strength of the specimen, reaching 69.97 MPa. The findings indicate that parameters, such as initial pressure, initial temperature, and failure pressure, can impact the risk of CO2 BLEVE occurrence and the propagation of explosion shock waves. The pressure inside the container during the BLEVE process fluctuates due to the joint action of the leakage rate and gasification rate of liquid CO2. This research provides a framework for evaluating the risk of CO2 BLEVE during CO2 geological storage and enhanced oil recovery injection processes, offering theoretical support for BLEVE prevention and control.

Real-time monitoring of coalbed methane production network following liquid CO2 injection in a low-efficiency well network: Response to gas and water production characteristics

Through real-time monitoring of gas composition, water ions, and productivity variations in multiple production wells after liquid CO2 injection, it reveals differences in reservoir response characteristics and geological control mechanisms between coalbed methane production wells. The results show that CO2 forms preferential migration channels along low ground stress and high-altitude directions. The production wells are divided into efficient stimulation wells, inefficiency stimulation wells, inhibition wells, and unaffected wells according to stimulation effect. The efficient stimulation wells show that the stimulation mode is CO2 displacement. The gas production increases significantly, with a maximum increase rate of 46.85 %. The N2 component in the produced gas and the HCO3− + CO32− ions in the produced increase during the continuous injection. The inefficient stimulation wells and inhibition wells show CO2 driven water production mode. The N2 and CO2 component, and the HCO3− + CO32− ions increase during the injection process. And the formation of water-abundant zones around the production wells inhibits the production of gas. The unaffected well is not affected by CO2 injection and shows a natural gas production mode of drainage depressurization and desorption. The results of the study provide technical support for the implementation and evaluation of the CO2-ECBM project.

Numerical study of the transient behaviors of vapour-liquid equilibrium state CO2 decompression

The vapor–liquid equilibrium (VLE) state of CO2 commonly appears in pipelines for its transport, refrigeration systems, and large-scale trans-critical cycle systems. However, the behavior of sudden leaks in such systems remains unclear, which poses a challenge in assessing the risk of leakage. This work is focused on the decompression behavior of VLE state CO2 with different volume fractions of vapor phases in high-pressure pipeline leakage, specifically with the development of a computational fluid dynamics (CFD) model with a nonequilibrium phase transition and the real gas model. The results suggest that the Peng-Robinson Equation of State (PR EoS) is more conservative in predicting the degree of superheat than that of Span-Wagner (S-W) EoS and GERG-2008 EoS. Moreover, it is found that the initial volume fraction of the vapor phase in VLE state CO2 plays a crucial role in determining the characteristics of sudden leakage, such as pressure, temperature, and decompression wave speed both inside and outside the pipe. However, the position of the Mach disk remains unaffected by the initial volume fraction of the vapor phase. The initial vapor volume fraction of 0.2 has the most significant impact on the transient behaviors of the leakage, that is, the speed of the initial decompression wave is approximately 1.46 times slower than that of pure liquid CO2, the pressure and temperature start to decrease approximately 0.46 ms after those of pure liquid CO2, which is about 5.1 times later. Additionally, the peak pressure of the near-field jet is 6.3% higher and the maximum velocity is 11.4% higher than that of pure liquid CO2. It hopes that this work will contribute to the improvement of research models that assess the consequences of potential high-pressure pipeline rupture scenarios.

Electrochemical acetate production from high-pressure gaseous and liquid CO2

Electrochemical acetate production from high-pressure gaseous and liquid CO2

Multi-variable study of a novel multigeneration system using biogas separation unit and LNG cold energy utilization, producing electricity, cooling, heat, fresh water, liquid CO2, biomethane, and methanol

Biogas fuel has gained recognition as a highly suitable alternative to fossil fuels, attributed to its renewable nature and remarkable energy density. Biogas fuel utilization facilitates the integration of combined energy systems equipped with multi-generational structures, rendering them suitable for long-term planning and management. Hence, this study presents a unique approach to using biogas for multigeneration, exhibiting enhanced thermodynamic efficiencies and negative carbon dioxide emissions. To achieve the stated objective, an innovative system is devised that involves the utilization of a biogas separation unit in integration with several other components, including a LNG cold energy utilization unit, an ammonia Rankine cycle, a desalination unit, a Kalina cycle, a solid oxide electrolyzer cell, a biomethane combined cycle, and a methanol synthesis unit. The newly devised configuration is simulated through the Aspen HYSYS software and assessed from energy, exergy, environmental, and economic considerations. Based on the research findings, the suggested methodology exhibits energy and exergy efficiencies of 91% and 83%, correspondingly. Furthermore, the evaluation of the entire unit cost of the product and the levelized energy cost reveals values of 4.81 $/GJ and 0.033 $/kWh, respectively. The carbon dioxide emission intensity of the newly implemented process is calculated to be − 0.1041 kg/kWh. The economic aspects reveal a favorable net present value of 1470.6 M$ and a payback period of 5.29 years.

A robust drift-flux model for two-phase CO2 pipe flow

CO2 transportation via pipelines and injection wells serves as the interface between carbon sources and storage sinks and thus plays a vital role in large-scale CCUS. CO2 is generally designed to be transported as dense-phase or supercritical fluids, but liquid-gas two-phase CO2 flow may occur during various scenarios such as pipeline start-up, shut-in, depressurization, capacity change, and subsurface injections. Despite the widespread existence of multiphase CO2 pipe flow during CO2 transportation, multiphase CO2 flow models are relatively scarce in the body of publicly available literature and existing models are only moderately accurate. In this work, we developed a robust drift-flux model capable of predicting the liquid holdup and pressure drop in two-phase pure CO2 pipe flow. The system of constitutive equations was solved by the marching method. The thermodynamic properties of liquid and vapor CO2 phases were determined by the highly accurate Helmholtz-type equation of state (EOS) developed by Span and Wagner. Supercritical CO2 friction correlation was employed to estimate the frictional pressure gradient of two-phase pure CO2 flow. A comprehensive verification against available two-phase CO2 flow loop test data shows that the model has superior performance over existing models in both horizontal and downward two-phase CO2 flow, with a maximum of 5% error in liquid holdup prediction and a maximum of 10% error in pressure drop prediction. This model may serve as a valuable tool for the design and optimization of CO2 pipelines in ongoing and future CCUS efforts worldwide.

CO2 absorption and desorption performance by ChCl-MEA-PZ deep eutectic solvent aqueous solutions

With the increasingly serious climate problem, carbon dioxide capture has been paid more and more attention. Deep eutectic solvent (DES), which is environmentally friendly and simple to synthesize, has attracted considerable attention as a new type of carbon dioxide absorbent. Choline chloride (ChCl) - monoethanolamine (MEA) - piperazine (PZ) DESs were prepared. The chemical reaction between ChCl-MEA-PZ DES and CO2 was confirmed to be the zwitterionic mechanism by NMR spectrum analysis. The influences of molar ratio between ChCl, MEA and PZ, gas–liquid flow rates, water content and CO2 concentration on CO2 absorption character were studied by a microchannel reactor. Under appropriate conditions, CO2 absorption efficiency could reach 99.95 %. The addition of promoter PZ could significantly enhance CO2 absorption performance. Additionally, desorption energy consumption of DES solution after CO2 saturation is lower than that of the standard 30 wt% MEA solution, which proves process friendliness of the DES. This study not only provides technical support but also sheds light on the potential applications of DESs in CO2 capture.

Development and assessment of a solar-driven charging station integrated with liquid CO2 as an energy storage option

It is expected that there will soon be a substantial increase in the number of charging stations developed and built in the near future due to a drastic increase in the number of electric vehicles. Charging stations pose a major concern for the grid because of the additional load they will generate. The development of self-sufficient and renewable-powered charging stations is therefore essential. This study develops a novel solar-powered charging station that integrates liquid CO2 as an energy storage option for dedicated off-grid conditions. Solar energy is captured and stored by converting gaseous CO2 into liquid to operate the system without requiring grid power. The stored liquid CO2 is then expanded via turbine for power generation when solar power is unavailable or insufficient to meet demand. We investigate the effects of utilizing yearly dynamic solar data and yearly average solar data on estimating off-grid conditions and system performance. Based on the results, it appears that using yearly averages can lead to an error of 37 % in estimating the solar PV area to be allocated for off-grid conditions. The total area of PV panels is found to be 100,723 m2, and it results in 63,938 m2 for the cases when yearly dynamic and yearly average solar data are used. The overall energy and exergy efficiencies of the developed systems are further calculated to be 0.062 and 0.066, respectively.