Supercritical Carbon Dioxide Research Articles

Graphene aerogels: part 2 - derived from commercial graphene and chemically reduced graphene oxide via supercritical carbon dioxide drying

Graphene aerogels: part 2 - derived from commercial graphene and chemically reduced graphene oxide via supercritical carbon dioxide drying

Numerical Investigation of Thermohydraulic Characteristics in Supercritical CO2 Natural Circulation Loop with Spatially Varying Temperature

Investigation of thermohydraulic characteristics is highly significant for any natural circulation loop (NCL) applications. The physical properties of supercritical fluids are highly sensitive to temperature when they cross pseudo-critical points. In the current study, steady state thermohydraulic characteristics of NCL with a spatially varying temperature distribution on the source along with different orientations of the source and sink are numerically investigated. A three-dimensional rectangular NCL with a uniform diameter and constant length of source and sink is modeled. The temperature of the sink is held constant, while the temperature of the source varies spatially with local maximum and minimum temperatures. The system performance is investigated for four different operating pressures ranging from 8 to 12 MPa. The mass flow rate is observed to increase with increasing operating pressure for all orientations and heat load distribution at the source. The results also indicate that heat transfer degrades when the fluid crosses the pseudo-critical point. It has been noticed that spatially varying temperature distribution has a maximum of 48% heat transfer variation compared to the constant temperature distribution. Furthermore, a source or sink located in the horizontal leg performs better than the vertical leg.

Flow synthesis of silver nanoparticles using water in supercritical CO2 emulsion

Rapid and continuous synthesis of metal nanoparticles using green solvent system is still a serious challenge for both fundamental and practical research. In this work, we report a new flow process using water in supercritical CO2 (w/scCO2) emulsion and applied it to the synthesis of silver nanoparticles (AgNPs). To investigate the performance of our system, AgNPs were synthesized by batch, flow and w/scCO2 emulsion flow system at 40 ºC while using AgNO3, NaBH(OAc)3, trisodium citrate and Aerosol-OT as precursor, reducer, stabilizer and emulsifier. As a result, we demonstrated that water droplets in w/scCO2 emulsion significantly contribute to a rise in the size controllability and productivity (product yield). Additionally, w/scCO2 emulsion flow process allowed the control of mean size from 4.0 to 36.6 nm and yield from 25% to 65% by changing the CO2 pressure and Aerosol-OT concentration. Furthermore, synthesized AgNPs successfully gave citrate-modified surface with high zeta potential of –54 mV and the transparent water dispersion with unimodal size distribution, showing promising potential to allow various practical applications.

Demonstration of a multi-channel fluidized bed particle–supercritical carbon dioxide heat exchanger for concentrating solar applications

High-temperature thermal energy storage in oxide particles at temperatures above 600°C can couple concentrated solar energy with high-efficiency thermal power cycles to provide dispatchable solar-driven electricity. Challenges remain in developing cost-effective primary heat exchangers, which require expensive alloys, to extract the high-temperature thermal energy from the particles to power cycle fluids, such as supercritical CO2 (sCO2) in recuperated Brayton cycles. To explore one pathway for cost-effective, high-temperature particle heat exchangers, the current study demonstrates a shell-and-plate, particle–sCO2 heat exchanger with narrow-channel fluidized beds coupled with micro-channel sCO2 flows in the heat exchanger walls. This study evaluates the feasibility of multiple parallel, narrow-channel fluidized beds in shell-and-plate particle–sCO2 HXs, to achieve high bed-wall heat fluxes at elevated temperatures. A reduced-order model simulates the narrow-channel, fluidized-bed particle–sCO2 heat exchanger to design the fluidized bed geometry, in terms of depth, height, and number of channels,for a nominal 40-kWth heat exchanger at particle and sCO2 inlet temperatures up to 600°C and 400°C respectively. The resulting shell-and-plate heat exchanger design operates with bubbling fluidization of the downward-flowing oxide particles to enhance bed-wall heat transfer. The heat exchanger core is fabricated with etched sCO2 micro-channels in thin wall plates that are diffusion bonded to spacer frames to form the shell-and-plate structure with 12 parallel, fluidized bed channels, 10.4 mm deep. The heat exchanger is tested at the National Solar Thermal Test Facility at Sandia National Laboratories with CARBOBEAD HSP particles at design particle flow rates of 0.20 kg s−1 and inlet temperatures up to 525°C. Results show that fluidization across multiple parallel channel beds can maintain uniform particle inventory with a common freeboard zone above the heat exchanger core. Bubbling fluidization improves particle–wall heat transfer coefficients but also increases axial dispersion of particle thermal energy, which lowers the log-mean temperature difference such that total heat transfer remains relatively constant to within ±10% over a broad range of fluidization gas velocities. The axial dispersion required particle and sCO2 flow rates to be increased by 25% over model-designed conditions to achieve the targeted 40 kWth, which indicates the importance of incorporating axial dispersion into heat exchanger design models and of deploying bed structures to suppress it. This study demonstrates the feasibility and preferred fluidizing gas conditions for particle heat exchangers for releasing high-temperature thermal energy storage systems.

Numerical study on heat transfer deterioration of supercritical CO2 in lattice structure array channel

This study numerically explores the fluid flow and heat transfer features of supercritical carbon dioxide (CO2) in lattice structure array channel. The mitigation mechanism of the miniature cylindrical lattice structure array on heat transfer deterioration (HTD) of supercritical CO2 in vertically upward heated channel is studied. This paper evaluates the effect of several key influential parameters (length, diameter, pitch and number) of cylindrical lattice structure array on fluid flow field involving vortex structures, heat transfer coefficient, buoyancy effect and accelerated effect. The results indicate that the lattice structure can effectively suppress the HTD by generating the vortex structure which promoting the turbulent mixing effect and enhancing the turbulent kinetic energy (TKE) of the fluid. Compared with the smooth channel, the peak wall temperature of the lattice structure channel is reduced by about 50 °C, with a corresponding increase in the heat transfer coefficient of about 140 %. The average heat transfer coefficient of the channel is increased by more than 1/3. Furthermore, by increasing lattice length can reduce flow layer stratification and by increasing lattice diameter can creating a composite vortex, which enhance flow mixing strength. The larger the lattice pitch, the worse the overall suppression effect. A denser lattice arrangement produces more temperature valleys, thereby increasing the heat transfer coefficient. The conclusions in this study could provide the main theory support for security and stability of supercritical CO2 heat exchangers in power system.

The investigation of thermo-economic performance for dry-cooled closed Brayton cycle coupled to nuclear microreactors using different coolants

Dry-cooled closed Brayton cycle (CBC) coupled to gas-cooled nuclear microreactors offers a compact structure and can be deployed in water-deficient areas. The gas-cooled reactor utilizes coolants including supercritical carbon dioxide (S–CO2), helium, and He–Xe mixture. The choice of working fluids for CBC strongly affects its size and performance, where smaller plant sizes, higher thermal efficiency, and lower investments are preferred. This study investigates the thermo-economic performances of dry-cooled CBC coupled to nuclear microreactors using different coolants. A design method for dry-cooled CBC is developed based on the integration of thermodynamic modeling and component preliminary design. Baseline designs are first established, followed by an analysis of the effects of key design parameters. Furthermore, a multi-object optimization is conducted to compare the Pareto frontiers of CBC using different working fluids. The results demonstrate that the helium simple cycle exhibits superior efficiency and precooler size due to its higher reactor outlet temperature, though with a larger capital cost. The Pareto frontier of the He–Xe cycle is worse than that of the helium cycle. The S–CO2 recompression cycle has a comparable efficiency with a smaller capital cost at mediate reactor outlet temperatures but suffers from large precooler sizes. The findings revealed that the S–CO2 recompression cycle is a more promising choice if the reactor outlet temperature can be further elevated.

Synergistic effects of in situ fibrillated polytetrafluoroethylene and polystyrene–butadiene block on the microcellular foaming behaviors of polyphenylene oxide modified by high‐impact polystyrene

AbstractMicrocellular foams of polyphenylene oxide/high‐impact polystyrene (PPO/HIPS) with high strength are prepared using supercritical CO2 foaming technology. The study focuses on examining the influence of polytetrafluoroethylene (PTFE) and polystyrene–butadiene block (SEBS) polymers in PPO/HIPS blends. Compared with the pure PPO/HIPS blend, the PPO/HIPS blend with 1 phr PTFE exhibits higher impact strength (7.62 kJ/m2), and the foam compressive strength is 5% larger. The PPO/HIPS foams with 1 phr PTFE (as a nucleating agent) and 5 phr SEBS (as a toughening agent) display a small cell diameter (13.73 μm) and the highest cell density (2.02 × 109 cells/cm3) compared to the pure PPO/HIPS blend. Moreover, the compressive strength of the PPO/HIPS/PTFE‐1/SEBS‐5 foam (1.63 MPa at a 5% strain) demonstrates a remarkable increase of 92% compared to that of the PPO/HIPS/PTFE‐1 foam.

Study on Surface Characteristics and Work Hardening of SiCp/Al Composites by SCCO2-MQL Combined with Ultrasonic Vibration Milling

This study investigated the milling of SiCp/Al composite materials using Polycrystalline Diamond (PCD) tools under various machining conditions, including dry cutting conditions, supercritical carbon dioxide (SCCO2) conditions, supercritical carbon dioxide cooling with minimum quantity lubrication (SCCO2-MQL) conditions, ultrasonic vibration conditions, and supercritical carbon dioxide cooling with minimum quantity lubrication combined with ultrasonic vibration conditions. The objective was to compare the surface roughness and morphology of the materials under different machining conditions. Furthermore, under dry cutting conditions and SCCO2-MQL combined with ultrasonic vibration, the effects of different milling parameters on the surface roughness and morphology of SiCp/Al composite materials were investigated through a univariate experiment. Microhardness tests were carried out on the machined workpieces to explore the influence of process conditions and milling parameters on work hardening. The experimental results indicate that among all the tested machining conditions, the SCCO2-MQL in combination with the ultrasonic vibration process significantly reduced the surface roughness of the material. When the milling speed was increased from 40 m/min to 120 m/min, both the surface roughness and the degree of work hardening first increased and then decreased. As the feed rate or cutting depth increased, the degree of work hardening also increased. Therefore, under SCCO2-MQL combined with ultrasonic vibration conditions, it is recommended to use a milling speed of more than 60 m/min and avoid using high feed rates and cutting depths in order to optimize the machining performance.

PdRu Bimetallic Nanoparticles/Metal-Organic Framework Composite through Supercritical CO2-Assisted Immobilization.

Metal-nanoparticle (NP)/metal-organic framework (MOF) composites have attracted considerable attention as heterogeneous catalysts. Compared with porous carbon, silica, and alumina, the charge-transfer interaction between the metal NPs and the MOF accelerated the catalytic activity. In this study, PdRu bimetallic NPs were successfully immobilized on MOFs such as MIL-101(Cr) by using supercritical carbon dioxide. The STEM-EDX images show a uniform 3D distribution of the PdRu bimetallic NPs on MIL-101(Cr). The resulting PdRu@MIL-101(Cr) catalyst exhibited higher CO oxidation than monometal/MOF composites such as Pd@MIL-101(Cr) and Ru@MIL-101(Cr). Furthermore, PdRu@MIL-101(Cr) exhibited higher catalytic activity than PdRu@SiO2. This is because the particle size of the PdRu bimetallic NPs in MIL-101(Cr) was within the range of 2-3 nm. The synergistic effects were based on the combination of two metals, Pd and Ru, small bimetal particle formation, and charge-transfer interactions between the bimetal NPs and the MOF. These factors enhance the catalytic activity of the bimetal/MOF composites.

Field Assessment of Lamium album in Reducing Mycotoxin Biosynthesis in Winter Wheat Infected by Fusarium culmorum

Fungicides play a crucial role in conventional agriculture for disease control, but their prolonged use raises health and environmental concerns. Fusarium culmorum (F. culmorum), a major wheat pathogen causing Fusarium head blight (FHB) and Fusarium crown rot (FCR), poses significant mycotoxigenic threats. The application of natural plant extracts has been proven to fight against phytopathogenic fungi. This study aimed to a field experiment that was carried out at the Field Experimental Station of the Institute of Plant Protection—National Research Institute in Winna Góra, Poland, during the 2022/2023 season to evaluate the potential of Lamium album (L. album) flower extract as a foliar spray against mycotoxigenic fungi in two winter wheat varieties: Arkadia and Julius. The supercritical carbon dioxide extraction method (SC-CO2) was employed to obtain the L. album flower extract. Ergosterol (ERG) and mycotoxin accumulation in the harvested wheat grains were analyzed using chromatography-based methods. The results demonstrated a notable reduction in ERG content in the field plots treated with L. album flower extract, from 26.07 µg/g (control group) to 8.91 µg/g (extract-treated group) for Arkadia and from 70.02 µg/g (control group) to 30.20 µg/g (extract-treated group) for Julius. The treatment with L. album reduced mycotoxin biosynthesis in both varieties, with deoxynivalenol (DON) and zearalenone (ZEN) production significantly decreased. Additionally, Arkadia exhibited greater resistance to Fusarium infection, and the antifungal effect of L. album was more pronounced than in the Julius variety, which proved to be more sensitive. In conclusion, L. album flower extract exhibited promising antifungal effects in field experiments to fight against F. culmorum in winter wheat varieties, suggesting a potential alternative to synthetic fungicides. However, as complete prevention of mycotoxin contamination was not achieved, further research is warranted to optimize extract concentrations and conduct long-term analyses to consider this plant extract as a sustainable control agent.

Thermodynamic crossovers in supercritical fluids

Can liquid-like and gas-like states be distinguished beyond the critical point, where the liquid-gas phase transition no longer exists and conventionally only a single supercritical fluid phase is defined? Recent experiments and simulations report strong evidence of dynamical crossovers above the critical temperature and pressure. Despite using different criteria, many existing theoretical explanations consider a single crossover line separating liquid-like and gas-like states in the supercritical fluid phase. We argue that such a single-line scenario is inconsistent with the supercritical behavior of the Ising model, which has two crossover lines due to its symmetry, violating the universality principle of critical phenomena. To reconcile the inconsistency, we define two thermodynamic crossover lines in supercritical fluids as boundaries of liquid-like, indistinguishable, and gas-like states. Near the critical point, the two crossover lines follow critical scalings with exponents of the Ising universality class, supported by calculations of theoretical models and analyses of experimental data from the standard database. The upper line agrees with crossovers independently estimated from the inelastic X-ray scattering data of supercritical argon, and from the small-angle neutron scattering data of supercritical carbon dioxide. The lower line is verified by the equation of states for the compressibility factor. This work provides a fundamental framework for understanding supercritical physics in general phase transitions.

One-Step Synthesized Solid Acid Catalyst with High Zr Content for Efficient and Green PET Degradation in Supercritical CO2

One-Step Synthesized Solid Acid Catalyst with High Zr Content for Efficient and Green PET Degradation in Supercritical CO₂

Optimization of Well Placement in Carbon Capture and Storage (CCS): Bayesian Optimization Framework under Permutation Invariance

Carbon Capture and Storage (CCS) stands as a pivotal technological stride toward a sustainable future, with the practice of injecting supercritical CO2 into subsurface formations being already an established practice for enhanced oil recovery operations. The overarching objective of CCS is to protract the operational viability and sustainability of platforms and oilfields, thereby facilitating a seamless transition towards sustainable practices. This study introduces a comprehensive framework for optimizing well placement in CCS operations, employing a derivative-free method known as Bayesian Optimization. The development plan is tailored for scenarios featuring aquifers devoid of flow boundaries, incorporating production wells tasked with controlling pressure buildup and injection wells dedicated to CO2 sequestration. Notably, the wells operate under group control, signifying predefined injection and production targets and constraints that must be adhered to throughout the project’s lifespan. As a result, the objective function remains invariant under specific permutations of the well locations. Our investigation delves into the efficacy of Bayesian Optimization under the introduced permutation invariance. The results reveal that it demonstrates critical efficiency in handling the optimization task extremely fast. In essence, this study advocates for the efficacy of Bayesian Optimization in the context of optimizing well placement for CCS operations, emphasizing its potential as a preferred methodology for enhancing sustainability in the energy sector.

Study on the criterion of the onset of heat transfer deterioration for supercritical CO2 in upward flow

Supercritical fluid heat transfer deterioration (HTD) tends to lower the heat transfer capacity and should be avoided in designing and optimizing heat transfer equipment. It is essential to establish accurate criteria for predicting the onset of HTD. In this study, an experimental investigation of supercritical CO2 in a heated tube with diameters of 8 and 14.5 mm was conducted. By integrating the data obtained from this experiment with experimental data from the published literature, a large dataset covering a wide range of parameters was constructed. Eleven HTD criteria that are only applicable to other fluids and ten HTD criteria that can be applied to supercritical CO2 were compared and evaluated with the experimental dataset. Results show that most of the correlations established for other fluids cannot be directly adapted to CO2. The criteria that only consider mass flux are not accurate for predicting the onset of HTD. With a detailed analysis of the influence pattern of each system parameter on HTD, a new criterion incorporating multiple influencing factors was established. Excellent prediction accuracy of the new criterion was observed from the validation with the experimental dataset.

CO2-assisted rapid synthesis of porphyrin-based Bi-MOFs for photocatalytic CO2 reduction: An efficient strategy for carbon cycle

Exploring a facile, rapid and efficient route to produce metal-organic frameworks (MOFs) with highly accessible active sites is of great importance for catalysis. Here we demonstrate the CO2 coordination can drive low temperature rapid synthesis of porphyrin-based bismuth-MOFs (Bi-PMOFs) by utilizing synergistic physical and chemical properties of supercritical CO2 (SC-Bi-PMOFs). The molecular-level role of scCO2 in the synthesis of SC-Bi-PMOFs have been investigated through a series of characterizations including in-situ time-dependent infrared spectroscopy, wherein chemical coordination of CO2 promotes to fabricate 2D SC-Bi-PMOFs nanosheets. Moreover, the formation of Cu-PMOFs and Fe-PMOFs proves the universal scCO2 strategy for synthesizing PMOFs. Density functional theory (DFT) calculations together with experiments results confirm the SC-Bi-PMOFs with abundant active sites guarantee efficient ligand-to-metal charge transfer and reduction efficiency of CO2. The high-efficiency utilization of CO2 for synthesizing a series of MOFs and subsequent catalysis on photocatalytic CO2 reduction for valuable chemicals realize the carbon recycle.

Numerical simulation of CO2 storage by basalts in Xingouzui formation, Jianghan Basin, China

Sedimentary basins often develop large amounts of basalts, but there are few studies. The diagenetic history of basalts in sedimentary basins is different from that of continental flood basalts and deep-sea basalts. A large amount of basalt is developed in the Jianghan Basin. Minerals undergo varying degrees of alteration, such as the alteration of olivine into serpentine. Numerical simulations were used to study the interaction between basalt-CO2-formation water in the Xingouzui Formation. The effects of basalt alteration and CO2 injection mode (supercritical CO2, saturated CO2 water, co-injection of CO2 and water) on CO2 storage were investigated. The results show that the reactivity between unaltered basalt and CO2 is strong, and the maximum CO2 mineral trapping reaches 22–49 kg/m3 after CO2 injection for one month. However, the reactivity between the altered basalt and CO2 is obviously decreased. Compared with the unaltered basalt, the maximum CO2 mineral trapping for the altered basalt decreased by at least 15.4 % after CO2 injection for one year. For severely altered basalt with high serpentine content, the maximum CO2 mineral trapping even drops by more than 90 %. CO2 mineral trapping will be overestimated when the feedback of reservoir porosity and permeability changes on flow is not considered. The co-injection of CO2 and water can make full use of the advantages that water injection can promote CO2 dissolution and the resulting acidic environment is beneficial to mineral dissolution. This method could be an option after careful assessment of CO2 leakage risks and technical feasibility.

Characterization and mechanism of multi-scale pore changes in scCO2-water injection into different porosity coal specimen

The process of supercritical CO2 (scCO2) injection into the coal body induces inhomogeneous changes in pore, which has a significant effect mechanical changes of the geological storage of CO2 coal seams. In this study, the effect of scCO2-water intrusion on coal samples with different porosity was investigated by NMR equipment and the change in the mechanical properties were tested by uniaxial compression and acoustic emission techniques after treatment. Results showed that during the treatment of scCO2-water, the pores of different scales showed an exponential change trend of y = a·xb, with the macropore of low-porosity coal samples continuously increasing and the macropore of high-porosity coal samples continuously decreasing. The pore changes after treatment mainly occurred in the micropore range, and the changes of low-porosity coal samples were more than 6%, while the changes of high-porosity coal samples were less than 2.3%. The changes in the fractal dimension of low-porosity coal samples exceeded those observed in high-porosity. The geochemical impact, effective stress of scCO2-water mixed fluid, and the adsorption and expansion mechanism of matrix macromolecules are influenced by varying porosity. This study helps to understand the internal multi-scale pore coupling mechanism and the effect on the coal mechanical properties after CO2 injection.

PBS melt strength improving for supercritical CO2 foaming molding by physical adsorption and crystallization

PBS melt strength improving for supercritical CO2 foaming molding by physical adsorption and crystallization

Characterization of Biodegradable Polymers for Porous Structure: Further Steps toward Sustainable Plastics.

Plastic pollution poses a significant environmental challenge, necessitating the investigation of bioplastics with reduced end-of-life impact. This study systematically characterizes four promising bioplastics-polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and polylactic acid (PLA). Through a comprehensive analysis of their chemical, thermal, and mechanical properties, we elucidate their structural intricacies, processing behaviors, and potential morphologies. Employing an environmentally friendly process utilizing supercritical carbon dioxide, we successfully produced porous materials with microcellular structures. PBAT, PBS, and PLA exhibit closed-cell morphologies, while PHBV presents open cells, reflecting their distinct overall properties. Notably, PBAT foam demonstrated an average porous area of 1030.86 μm2, PBS showed an average porous area of 673 μm2, PHBV displayed open pores with an average area of 116.6 μm2, and PLA exhibited an average porous area of 620 μm2. Despite the intricacies involved in correlating morphology with material properties, the observed variations in pore area sizes align with the findings from chemical, thermal, and mechanical characterization. This alignment enhances our understanding of the morphological characteristics of each sample. Therefore, here, we report an advancement and comprehensive research in bioplastics, offering deeper insights into their properties and potential morphologies with an easy sustainable foaming process. The alignment of the process with sustainability principles, coupled with the unique features of each polymer, positions them as environmentally conscious and versatile materials for a range of applications.

Performance and cost potential for direct-fired supercritical CO2 natural gas power plants

Direct-fired supercritical CO2 (sCO2) power cycles are being explored as an attractive alternative to natural gas combined cycle (NGCC) plants with carbon capture and storage (CCS). Therefore, understanding their performance and cost potential is important for the commercialization of the technology. This study presents detailed techno-economic optimization results of natural gas-fired, utility-scale power plants based on the direct sCO2 power cycle, which is lacking in public literature. The study considered multiple plant configurations with varying levels of thermal integration with the plant air separation unit (ASU) to shows the systematic impact of thermal integration on plant performance and economics. Several design variables for each power cycle configuration were identified and optimized to minimize the levelized cost of electricity (LCOE). The optimized direct sCO2 power plants achieved ∼48 % plant efficiency (HHV basis) which is similar or slightly higher plant efficiencies than state-of-the-art NGCC plants based on the F-class gas turbine with carbon capture and storage (CCS). The LCOE of the optimized direct sCO2 plants is 13–17 % higher than the reference NGCC plants with CCS due to high capital costs associated with the ASU and sCO2 power block, though there is significant room for improvement due to high uncertainty in component capital costs for these new plants. Based on the results, direct sCO2 power cycles have the potential to achieve >50 % efficiency (HHV basis) with >98 % CO2 capture rate which can lead to significant efficiency improvement and CO2 emissions reductions compared to NGCC plants with CCS.