High-pressure CO2 Research Articles

Influence of oxygen partial pressure on the passivation and depassivation of super 13Cr stainless steel in high temperature and CO2 rich environment.

The passivation and depassivation characteristics of Super 13Cr stainless steel were examined under a range of oxygen partial pressures within a high-temperature (120 ℃) and high-pressure (3MPa) CO2 atmosphere. We performed comprehensive electrochemical assessments, encompassing open-circuit potential monitoring, electrochemical impedance spectroscopy, and linear polarization resistance analysis, to evaluate the corrosion resistance and passive film stability. The results demonstrate that the addition of low O2 partial pressures enhanced the stability of the passive film, while higher O2 levels led to the loss of the passivation properties of Super 13Cr stainless steel. The study elucidates the pivotal role of oxygen in the corrosion mechanisms affecting Super 13Cr stainless steel, presenting valuable data to enhance for integrity management in severe environmental conditions.

Investigation into Enhancing Methane Recovery and Sequestration Mechanism in Deep Coal Seams by CO2 Injection

Injecting CO2 into coal seams to enhance coal bed methane (ECBM) recovery has been identified as a viable method for increasing methane extraction. This process also has significant potential for sequestering large volumes of CO2, thereby reducing the concentration of greenhouse gases in the atmosphere. However, for deep coal seams where formation pressure is relatively high, there is limited research on CO2 injection into systems with higher methane adsorption equilibrium pressure. Existing studies, mostly confined to the low-pressure stage, fail to effectively reveal the impact of factors such as temperature, high-pressure CO2 injection, and coal types on enhancing the recovery and sequestration of CO2-displaced methane. Thus, this study aims to investigate the influence of temperature, pressure, and coal types on ECBM recovery and CO2 sequestration in deep coal seams. A series of CO2 core flooding tests were conducted on various coal cores, with CO2 injection pressures ranging from 8 to 18 MPa. The CO2 and methane adsorption rates, as well as methane displacement efficiency, were calculated and recorded to facilitate result interpretation. Based on the results of these physical experiments, numerical simulation was conducted to study multi-component competitive adsorption, desorption, and seepage flow under high temperature and high pressure in a deep coal seam’s horizontal well. Finally, the optimization of the total injection amount (0.7 PV) and injection pressure (approximately 15.0 MPa) was carried out for the plan of CO2 displacement of methane in a single well in the later stage.

High-pressure supercritical CO2-assisted fabrication of two-dimensional LaAlO3 and its room temperature ferromagnetism

Abstract Spintronics applications in two-dimensional (2D) magnetic materials can significantly contribute to the miniaturization and energy efficiency of semiconductor devices. However, current 2D ferromagnetic materials face challenges such as ferromagnetic instability and low Curie temperature (Tc), which limit their broader application. In this study, 2D room-temperature ferromagnetic LaAlO3 was successfully prepared with supercritical carbon dioxide (SC CO2). With the enhanced stress effect of CO2 molecules, the contents of oxygen vacancies OV, aluminium vacancies AlV, and AlO4 in the 2D structure are elevated, and then the ferromagnetic properties of LaAlO3 appeared to be significantly enhanced due to defects and spatial symmetry breaking of the octahedron. Notably, the 2D intrinsic ferromagnetic LaAlO3 exhibited a Tc above 350 K. Therefore, this work supplies a new means for SC CO2 to modulate the microstructure and ferromagnetic properties of 2D LaAlO3, which is conducive to expanding the applications of LaAlO3.

Experimental comparison of cycle modifications and ejector control methods using variable geometry and CO2 pump in a multi-evaporator transcritical CO2 refrigeration system

To reduce the direct global warming impact of refrigerants in HVAC&R applications, low-global warming potential (GWP) refrigerants, including natural refrigerants, have been extensively investigated as alternatives to hydrofluorocarbon (HFC) refrigerants. Among the natural refrigerants, Carbon Dioxide (CO2) offers several advantages, such as excellent transport and thermo-physical properties, being neither toxic nor flammable, and having a low price and high availability around the world. However, the high critical pressure and low critical temperature of CO2 often lead to transcritical operation, resulting in lower efficiency due to the additional compressor power necessary to achieve transcritical operation relative to subcritical HFC cycles. Therefore, a number of cycle modifications are used to enhance the coefficient of performance (COP) of transcritical CO2 cycles to meet or surpass those of HFC cycles. This paper provides a systematic experimental investigation of four such cycle architectures by employing the same multi-stage, two-evaporator CO2 refrigeration cycle test stand, 3 of these configurations in transcritical and 1 in subcritical conditions. The four cycles architectures included intercooling, open economization, an internal heat exchanger and two different ejector control approaches. Specifically, a variable-diameter motive nozzle and a variable-speed liquid CO2 pump located directly upstream of the ejector motive nozzle inlet were analyzed. Based on the experimental data, the maximum COP improvements are 4.64 % and 9.47 % when the ejector and the internal heat exchanger are used, respectively. The CO2 pump, once successfully stabilized, can control the ejector, increase its efficiency by up to 15 % and increase the cooling capacity to a maximum of 6.2 %. Nevertheless, a reduction in COP is measured when the pump is in use; however, unlike the other three different configurations, it was only analyzed under subcritical conditions.

CO2 hydrogenation over Fe-Mn-Zn spinel oxide nanohybrids precatalysts

Catalytic CO2 hydrogenation using green hydrogen is a promising approach for mitigating CO2 emissions and utilizing CO2 as a feedstock. While Fe-based catalysts produce long-chain hydrocarbons under high-pressure CO2 hydrogenation reactions, the C2+ hydrocarbon yield tends to be insufficient at low-pressure conditions over the catalyst. This study reports the enhancement of light olefin selectivity of CO2 hydrogenation over Fe-based catalysts at low pressure via nanoscale hybridization with manganese (Mn) and zinc (Zn) oxides. The resulting hybridized catalyst exhibited distinctive performance in terms of CO2 hydrogenation to light olefins at relatively low pressure (0.7 MPa) in terms of CO2 conversion rate and C2–C4 yield with high olefin rates. Mn and Zn incorporation in Fe oxide decreased the reduction temperature, forming more Fe carbide phase. CO2 adsorption capability at relevant temperatures seems to be improved when Mn and Zn are present. This mixed oxide precatalyst approach can be extended to other elements.

Tertiary-Amine-Functional Poly(arylene ether)s for Acid-Gas Separations.

Competitive sorption enables the emergent phenomenon of enhanced CO2-based selectivities for gas separation membranes when using microporous polymers with primary amines. However, strong secondary forces in these polymers through hydrogen bonding results in low solvent solubility, precluding standard solution processing approaches to form these polymers into membrane films. Herein, we circumvent these manufacturing constraints while maintaining competitive-sorption enhancements by synthesizing eight representative microporous poly(arylene ether)s (PAEs) with tertiary amines. High-pressure H2S, CO2, and CH4 sorption isotherms were collected for these samples to demonstrate enhanced affinity for acid gases relative to the unfunctional control polymer. Although competitive sorption was observed for all samples, improvements were less pronounced than for primary-amine-functional analogs. For H2S-based separations, the benefits of competitive sorption offset decreases in selectivity due to plasticization. This detailed study helps to elucidate the role of tertiary amines for acid gas separations in solution-processable microporous PAEs.

Investigation of clinical and paraclinical consequences of tramadol poisoning and related factors

Tramadol, is frequently misused and leading to an increase in cases of overdose and poisoning worldwide. This study aimed to investigate the clinical and paraclinical consequences of tramadol poisoning and related factors. This was a retrospective study performed on patients with acute tramadol poisoning who were referred to the Amir Al-Momenin Hospital Emergency Department, Zabol, during 2019-2020. Patients’ socio-demographic information and clinical and paraclinical manifestations were collected in a predesigned checklist. Overall, 71 subjects were included in this study. The mean dose of tramadol was 640.14 ± 521 mg. Seizures occurred in 17 subjects that were not dose-dependent. In patients who died or were in a coma, pH, bicarbonate (HCO3 ), and oxygen saturation (O2 sat) levels decreased, while PCO2 levels increased significantly (P < 0.05). The dose of tramadol used in the poisoning of this substance played no role in the course of the disease and the prognosis of patients, but low pH, HCO3 , O2 sat, and high CO2 pressure could be related to the outcome of these patients.

Comparison of upward and downward flow in high-pressure bulk CO2 gas adsorption on NaY zeolite fixed bed

Adsorption is an appealing technology for the removing of CO2 from natural gas because it can handle high CO2 concentrations at high pressures. The determination of mono-component breakthrough curves provides heat and mass transfer parameters to assess separation effectiveness that can be used for simulation of swing adsorption separation processes (PSA, TSA etc.). However, in lab-scale fixed-bed adsorption, it may be challenging to perform this assessment due to low flow conditions that are usually employed, affecting the flow regimedepending on the operation conditions. In this sense, this work aimed to evaluate the effect of flow regime configurations and difference in gases densities by means of residence time distribution (RTD) analysis in the PSA of CO2 in a NaY zeolite fixed bed , in order to to collect information that satisfy pipeline specifications in industrial applications. A high-pressure lab-scale apparatus was used with NaY particles of 0.7250 mm mean diameter, a 10.5 cm bed height , and a tubular column of 2.0 cm internal diameter. The upward and downward flows were conducted under 528.82 ± 4.59 NmL min−1 inlet mass flow rate, 51 bar, and 30 °C. The RTD analysis was performed to verify the flow regime, and mass transfer zone (MTZ) length was estimated. It was observed that downward flow conditions promoted higher concentration spread than upward flow. RTD analysis showed that downward flow is dominated by laminar convection while the upward flow is dominated by dispersion. MTZ length increased from 0.64 cm in upward flow to 5.81 cm in downward flow. Therefore, assessing CO2 flow conditions and, additionally, the difference in gases densities, are important steps that should be taken when dealing with fluid adsorption under high pressure because different densities between fluid components severely changed and affected flow regime and, consequently, separation effectiveness.

Interfacial properties of CO2 and liquid sulfur in high-sulfur gas fields: Molecular simulations on carbonate mineral surfaces

As the global energy landscape transforms, the development of high-sulfur natural gas has become increasingly critical. However, sulfur deposition during these gas field developments significantly affects operational efficiency. This study employed molecular dynamics simulation to explore the effectiveness of CO2 in alleviating sulfur deposition on carbonate rock reservoirs. Specifically, it examined the interfacial tension between liquid sulfur and CO2, the wettability of sulfur on carbonate rock mineral surfaces, and the kinetics of CO2 displacing liquid sulfur. Results show that as CO2 pressure increases from 10 MPa to 60 MPa, the interfacial tension between liquid sulfur and CO2 decreases by 84 %, from 35.54 mN/m to 5.53 mN/m. The contact angles of sulfur droplets on calcite and dolomite surfaces stabilize at 41.82° ± 2.10° and 44.33° ± 3.27°, respectively, indicating greater sulfur spread on calcite surfaces. With higher CO2 pressures, sulfur deposition on mineral surfaces and interfacial tension both decrease significantly, while the wetting angle of liquid sulfur increases, particularly on dolomite. At 60 MPa CO2 pressure, the adsorption energy of dolomite for liquid sulfur drops from 364.56 kcal/mol to 25.46 kcal/mol, a 93 % reduction, suggesting CO2′s dual role in displacing sulfur and promoting its desorption from mineral surfaces. Furthermore, the efficiency of sulfur deposition alleviation in carbonate rock slit structures improves and stabilizes at around 40 MPa CO2 pressure. This study presents a potential environmentally friendly approach for efficiently developing high-sulfur gas fields, and its findings provide practical insights for optimizing CO2 injection strategies to mitigate sulfur deposition.

A Greener Way of Making Cellulose Clothing

Cotton is the world's most demanding non-food crop. Cotton grows in arid countries such as India and China. However, its production consumes an enormous 250 billion tons of water annually, amplifying water scarcity. Cellulose, found in plants like wood, bamboo, and mosses, offers a sustainable alternative for textiles. Traditionally, cellulose is processed into textiles using the viscose method, which involves carbon disulfide. This process releases hydrogen sulfide, harmful to aquatic life and human health, and carbon disulfide, a hazardous pollutant affecting the reproductive system and vision. Many research groups have proposed an alternative method, which involves dissolving cellulose in dimethyl sulfoxide (DMSO) and Diazabicyclo[5.4.0]undec-7-ene (DBU) under 1 atm of CO2. DBU, with a pKaH ~ 12, deprotonates cellulose’s hydroxyl groups forming a DMSO-soluble cellulose carbonate complex that can be spun into filaments. However, DBU is costly, hazardous, and prone to hydrolysis, leading to byproducts. The objective of the research was to find a more environmentally friendly, less toxic, and cost-effective base for cellulose dissolution. Two tertiary amines, triethylamine (pKaH~9) and tripropylamine (pKaH~10.7), were tested. Due to its low basicity triethylamine failed to dissolve cellulose even under high CO2 pressure (up to 50 bar), resulting in a cloudy solution. Tripropylamine is insoluble in DMSO, therefore resulting in a phase separation of a tripropylamine layer and cellulose/DMSO layer. Additionally, 2,2,6,6-tetramethyl-piperidine was also tested at high CO2 pressure (up to 50 bar), but a biphasic solution was formed at 10 bar . This indicates that the protonated form of the base does not dissolve in DMSO. Ultimately, no alternative base was found to be sufficiently basic to deprotonate the hydroxyl groups on cellulose and promote dissolution, even at high pressure.

Simulation Study on Rock Crack Expansion in CO2 Directional Fracturing

In underground construction projects, traversing hard rock layers demands concentrated CO2 fracturing energy and precise directional crack expansion. Due to the discontinuity of the rock mass at the tip of prefabricated directional fractures in CO2 fracturing, traditional simulations assuming continuous media are limited. It is challenging to set boundary conditions for high strain rate and large deformation processes. The dynamic expansion mechanism of the 3D fracture network in CO2 directional fracturing is not yet fully understood. By treating CO2 fracturing stress waves as hemispherical resonance waves and using a particle expansion loading method along with dynamic boundary condition processing, a 3D numerical model of CO2 fracturing is constructed. This model analyzes the dynamic propagation mechanism of 3D spatial fractures network in CO2 directional fracturing rock materials. The results show that in undirected fracturing, the fracture network relies on the weak structures near the rock borehole, whereas in directional fracturing, the crack propagation is guided, extending the fracture’s range. Additionally, the tip of the directional crack is vital for the re-expansion of the rock mass by high-pressure CO2 gas, leading to the formation of a symmetrical, umbrella-shaped structure with evenly developed fractures. The findings also demonstrate that the discrete element method (DEM) effectively reproduces the dynamic fracture network expansion at each stage of fracturing, providing a basis for studying the CO2 directional rock cracking mechanism.

Chirality hierarchical transfer in homochiral polymer crystallization under high-pressure CO2

Ordered phase transitions are commonly correlated to symmetry breaking, while disordered phase transitions are characterized by symmetry restoration. Nevertheless, this study demonstrates that these correlation relations are not always applicable in chiral polymers under high-pressure Carbon Dioxide. Without racemization, homochiral Poly (lactide acid) can generate two vortex-shaped dendritic crystals with opposite spiral chirality, and snowflake-shaped dendritic crystals without spiral chirality. The transition from homochiral molecules to achiral crystals signifies the chiral symmetry restoration during the ordering process. The primary elements responsible for the various hierarchical transfers of homochiral Poly (lactide acid) are related to chain tilt, surface stress, and frustrated structures of Poly (lactide acid) crystals. Here, we show the entropy impact of Carbon Dioxide can be utilized to programmatically regulate the morphological chirality of crystal superstructure and crystal form of homochiral Poly (lactide acid).

Corrosion at Top-of-the-Line in High Pressure and Dense CO2 Environments

This study presents unique data on top-of-the-line corrosion (TLC) occurring in high-pressure environments where CO2 was in the gaseous, liquid, or supercritical state. While CO2 is traditionally in a gaseous phase, this form of degradation is referred to as TLC. In this study, similar phenomena with different mechanisms were observed in liquid CO2 and supercritical states all of which are referred to as TLC due to the location of specimens and ease of comprehension. Experiments were conducted to investigate the effect of CO2 partial pressure (ranging from 20 bar to 100 bar) with temperatures (30°C to 50°C) relating to different water condensation rates (0.001 mL/m2/s to 0.1 mL/m2/s). Uniform and localized TLC rates increased with a higher water condensation rate and surface temperature. As long as CO2 remained gaseous, its partial pressure (pCO2) showed a negligible influence on both uniform and localized TLC rates. At the highest gaseous CO2 content tested, the formation of a protective iron carbonate (FeCO3) layer decreased the TLC rate, with this effect being more pronounced at lower water condensation rates. The risk of localized corrosion for specimens exposed to this environment at high and medium water condensation rates remained an issue. In the dense phase CO2 environment, the difference in temperature between the bulk environment and the specimen’s surface caused a similar phenomenon to water condensation, termed water drop-out, which resulted in corrosion. The rate of water drop-out could not be measured experimentally or estimated theoretically but is a complex function of temperature, pCO2, and CO2 physical state. The interplay between high pCO2 and low pH of the dropped-out water led to elevated uniform and localized corrosion rates. The depth of localized corrosion, at the high and medium water drop-out conditions, reached its maximum at the surface temperature of ca. 45°C. At a lower surface temperature of ca. 25°C and a higher surface temperature of ca. 65°C, the maximum penetration rate was decreased due to slower kinetics of reactions and the formation of a more protective FeCO3 layer, respectively. The results presented in this study highlight the significant difference between corrosion rates, especially in the form of localized damage, in gaseous and dense-phase CO2 environments.

Unveiling the inhibition of high-pressure CO2 flow accelerated corrosion at gradual contraction and gradual expansion tubings

The different inhibition behavior of imidazoline quaternary ammonium salt for high-pressure CO2 flow accelerated corrosion of carbon steel gradual contraction and gradual expansion tubings was unveiled combing high pressure dynamic in situ electrochemical methods and microstructure characteristics analysis. It is manifested that there is no noticeable inhibition effect in high CO2 partial pressure environments at extremely low inhibitor concentration. At low inhibitor concentration, the polarization resistance and inhibition efficiency increase firstly and then decrease along the flowing direction of gradual contraction tubing. However, the polarization resistance generally drops along the gradual expansion tubing. As the inhibitor concentration of the corrosion inhibitor is further increased, the polarization resistance and inhibition efficiency are reduced in a whole along the gradual contraction tubing. Nevertheless, the polarization resistance is raised, followed by a fall along the flowing direction of gradual expansion tubing. The inhibition effect at the top and the bottom of gradual contraction tubing exhibits symmetry while it is asymmetrical at the top and the bottom of inclination section in gradual expansion tubing. The distinct inhibition effect at different inhibitor concentration is relevant to flow characteristics of fluid at gradual contraction tubing and gradual expansion tubing. The findings could provide valuable guidance for the protection of flow accelerated corrosion at gradual contraction tubing and gradual expansion tubing under high CO2 partial pressure conditions.

Dynamic characteristics of high-pressure and high-density carbon dioxide leakage process

The leakage of high-pressure and high-density carbon dioxide (CO2) during storage and transportation can result in the rapid release of a substantial amount of CO2, presenting significant risks to Carbon Capture and Storage (CCS) technology. Investigating the dynamic characteristics of high-pressure and high-density CO2 leakage in storage tank, as well as understanding the variations in CO2 pressure, temperature, density, and phase during the leakage process, is crucial for the design of tank and pipeline leakage prevention. Existing research mainly focuses on leakage at the top or side of storage tank, there is a lack of attention to leakage from the bottom of storage tank. To simulate the bottom leakage processes, a depressurized experimental system with a 0.065 m3 CO2 storage tank volume was constructed. The range of CO2 parameter conditions for filling density is 811 ∼ 998 kg/m3, with initial pressure ranging from 5.72 ∼ 16.50 MPa. According to the change in the slope of the pressure drop in the storage tank, the leakage can be divided into three processes. The closer to the top of the storage tank, the liquid–gas phase transition of CO2 occurs earlier. The pressure shows two inflection points (point I and point II) representing the upper and lower limits of CO2 saturation pressure, respectively. The lower filling density results in a higher saturation pressure, while the higher initial pressure also leads to a higher saturation pressure. The current work can help to better understand pressure, temperature, density, and phase state changes of CO2 during leakage.

Experimental and thermodynamic study of amyl acetate, amyl acetoacetate, and isoamyl acetoacetate in CO2 solvent

Acetate ester compounds find widespread use in various applications such as surface coatings, ink formulations, pharmaceuticals, and adhesives. It is essential to investigate the phase transition behavior of amyl acetate, amyl acetoacetate, and isoamyl acetoacetate in high-pressure supercritical CO2 (SC-CO2). The vapor-liquid equilibria (VLE) of the SC-CO2 + amyl acetate, SC-CO2 + amyl acetoacetate, and SC-CO2 + isoamyl acetoacetate systems were examined at different temperatures (313.2 ≤ T ≤ 393.2 K) and pressures (1.67 ≤ P ≤ 20.76 MPa). The solubility curve of these systems shows Type-I phase behavior, and the critical points of these binary mixtures were observed between the critical properties of the pure components involved in the systems. The solubility of amyl acetate, amyl acetoacetate, and isoamyl acetoacetate in the SC-CO2 + amyl acetate, SC-CO2 + amyl acetoacetate, and SC-CO2 + isoamyl acetoacetate systems increases with increasing temperature at constant pressure. The two-parameter model of Peng-Robinson equation of state along with a mixing rule, accurately correlated the phase transition behavior and critical mixtures curves for all three systems. The binary interaction parameters (BIPs) were adjusted, and the minimum root mean square deviation percentage was identified for all three systems. The calculated error% was found to be within reasonable limits, with values of 4.95 %, 3.93 %, and 4.18 % for SC-CO2 + amyl acetate, SC-CO2 + amyl acetoacetate, and SC-CO2 + isoamyl acetoacetate systems, respectively. Furthermore, the interaction parameters for the SC-CO2 + amyl acetoacetate mixture was found to be temperature-dependent, and the tested linear regression correlation coefficient for the BIPs parameters of (kij) and (ηij) are 0.98533 and 0.99083, respectively. This is the first research study on the phase behavior of acetate ester compounds in SC-CO2 solvents, and the results have a significant impact on industries at different operating conditions.

Powering the Future Green Buildings: Multifunctional Ultraviolet-Shielding Transparent Wood.

Indoor UV damage is a serious problem that is often ignored. Common glasses cannot filter UV rays well and have fragility and environmental issues. UV-shielding transparent wood (TW) holds promise, yet striking the right balance between blocking UV rays and allowing sufficient visible-light transmission poses a challenge. The pronounced capillary force, fueled by persistent moisture and extractives in wood, alongside the existence of multiphase interfaces, collectively hinder the uniform penetration of polymers and the effective dispersion of nanomaterials within the wood skeleton. Here, we incorporate high-pressure supercritical CO2 fluid-assisted impregnation (HSCFI) into fabricating UV-shielding TW. The supercritical CO2 pretreatment efficiently eliminates moisture and refines wood structure by extracting polar substances, resulting in a prominent 52.4% increase in average water permeability. Subsequently, this HSCFI method facilitates the infiltration of methyl methacrylate (MMA) monomer and Ce-ZnO nanorods (NRDs) into the refined anhydrous wood, leveraging the excellent solvency of supercritical CO2 for MMA. The impregnation rate of PMMA undergoes a substantial increase from 34.5 to 59.1%. With the robust UV-blocking capability of Ce-ZnO NRDs, thanks to dual-valence Ce doping widening the ZnO energy gap via the Burstein-Moss effect and their unique photoactive microstructure featuring a solid prism with a sharp hexahedral pyramidal tip, along with intrinsic physical scattering/reflection actions, Ce-ZnO NRDs@TW achieves an impressive 99.6% UVA radiation blockage (the highest for TW) and maintains high visible-light transmission (83.2%). Furthermore, Ce-ZnO NRDs@TW presents favorable energy-saving, sound absorption, and antifungal abilities, making it a promising candidate for future green buildings.

Thermodynamic and Exergoeconomic Analysis of a Novel Compressed Carbon Dioxide Phase-Change Energy Storage System

As an advanced energy storage technology, the compressed CO2 energy storage system (CCES) has been widely studied for its advantages of high efficiency and low investment cost. However, the current literature has been mainly focused on the TC-CCES and SC-CCES, which operate in high-pressure conditions, increasing investment costs and bringing operation risks. Meanwhile, some studies based on the phase-change CO2 energy storage system also have had the disadvantages of low efficiency and the extra necessity of heat or cooling sources. To overcome the above problems, this paper proposes an innovative compressed CO2 phase-change energy storage system. During the energy charge process, molten salt and water are used to store heat with a smaller temperature difference in heat exchangers, and high-pressure CO2 is reserved in liquid form. During the energy discharge process, throttle expansion is applied to realize the evaporation at room temperature, and CO2 absorbs the reserved heat to improve the power capacity in the turbine and the system energy storage efficiency. The thermodynamic and exergoeconomic studies are performed firstly by using MATLAB. Then, the parametric study based on energy storage efficiency, system unit product cost, and exergy destruction is analyzed. The results show that energy storage efficiency can be improved by lifting liquid CO2 pressure as well as compressor and turbine isentropic efficiencies, and CO2 evaporation pressure has the optimal pressure point. The system unit product cost can be reduced by decreasing liquid CO2 pressure and compressor isentropic efficiency, while CO2 evaporation pressure and turbine isentropic efficiency both have optimal points. Finally, the optimization of two performances is performed by NSGA-II, and they can reach 75.30% and 41.17 $/GJ, respectively. Moreover, the optimal energy storage efficiency is obviously higher than that of other energy storage technologies, indicating the great advantage of the proposed system. This study provides an innovative research method for a new type of large-scale energy storage system.

Molecular dynamics simulations of the interfacial tension and the solubility of brine/H2/CO2 systems: Implications for underground hydrogen storage

The interfacial tension (IFT) between the reservoir fluids and the solubilities of the injected hydrogen and cushion gas in the underground brine plays a critical role in the security and efficiency of the trapping mechanisms associated with underground hydrogen storage (UHS), but its behavior at the molecular level is still poorly understood. This study utilizes molecular dynamics simulations to provide insights into the prevailing interactions associated with the interfacial characteristics and the solubilities of hydrogen and CO2 (used as a cushion gas) in brine at high-pressure, high-temperature, and various salt and CO2 concentrations. The study reports the solubilities of H2 and CO2 in the ternary brine/H2/CO2 systems for the first time and correlates the findings with UHS implementations. Results show that the increase in the CO2 concentration reduces the IFT due to the CO2-brine alike interactions. Besides, H2 and CO2 molecules trapped by brine hydrogen bonds were quantified to evaluate the solubility of the injected fluids in brine during UHS schemes.

Synthesis of ethylene urea using carbon-dioxide-adsorbed titanium–zirconium mixed oxides

To address the increasing global levels of CO2 emissions, it is necessary to develop efficient strategies that can convert CO2 into useful chemicals such as carbonates, ureas, and carbamates. Hybrid systems that combine direct capture and subsequent utilization of CO2 offer a unique emission-controlling pathway for achieving a carbon-neutral society. Ti-Zr mixed oxides could be ideal candidates for CO2 adsorption owing to the high specific surface areas pore sizes. Therefore, in this study, metal oxides with desirable acid-base sites that is, TixZr(1−x)O2 with different Ti/Zr ratios were synthesized using combined sol-gel and solvothermal methods and then utilized to adsorb and synthesize ethylene urea (EU), an important precursor of pharmaceuticals and agricultural products. The results indicated that the CO2 adsorption capacity of TiO2-ZrO2 mixed oxides were higher than that of TiO2 alone at 100 kPa and 25 °C, corresponding to their higher specific surface areas and pore volumes compared to their individual oxide counterparts. CO2-adsorbed TixZr(1−x)O2 was subsequently used as a CO2 source to generate EU through a reaction with ethylenediamine (EDA) and 2-propanol. Notably, samples containing higher proportions of Zr-Ti0.3Zr0.7O2 and ZrO2 produced EU in significant amounts, owing to their acid-base bifunctionality. Overall, EU was synthesized using CO2-adsorbed TixZr(1−x)O2 as a CO2 source and as an accelerator for reacting with EDA, without requiring high-pressure or high-purity CO2.