Supercritical Carbon Dioxide Research Articles

Probing Supercritical CO2 to Improve the Susceptibility of Semicrystalline Polyethylene Terephthalate to Enzymatic Hydrolysis

Probing Supercritical CO₂ to Improve the Susceptibility of Semicrystalline Polyethylene Terephthalate to Enzymatic Hydrolysis

Development and optimization of general drying models for cod (Gadus spp.) using supercritical carbon dioxide

This study aimed to investigate the supercritical carbon dioxide (SC-CO2) drying of cod (Gadus spp.) by developing and optimizing a general mathematical drying model. We applied a central composite rotatable design (CCRD) considering the time (180–360 min), temperature (35–45 °C), and CO2 flow rate (15–25 kg/h) as independent factors, aiming at the reduction of moisture and water activity (aw) of Gadus morhua. Time and flow rate (FR) were the main factors affecting the moisture and aw responses. The mathematical models developed were validated with the accuracy and bias factors and generalized using Gadus chalcogrammus samples, resulting in the acceptable range of 1.003–1.121. The optimal parameter values for drying performance were 312.38 min, 45.38 °C, and 27.4 kg/h (R2 = 0.999). Our results suggest a promising application of SC-CO2 as a fish drying technology, describing a generalist-validated and optimized SC-CO2 drying model for Gadus spp. Industrial applicationThe present study collaborates with understanding supercritical carbon dioxide (SC-CO2) as an innovative fish drying technology at a laboratory scale. The optimal variables that were effective in reducing cod fillets water content were 312.38 min, 45.38 °C, and 27.4 kg/h, in which 26.4% moisture and 0.815 aw were predicted. Therefore, SC-CO2 is suggested to be a promising non-thermal food drying technology applied to fish products.

Thermochemical conversion of guaiacol with supercritical CO2: Experimental insights

The excessive CO2 in the environment resulting from the combustion of fossil fuels has posed a significant challenge in terms of its conversion and utilization. In this work, the thermochemical conversion of guaiacol under supercritical CO2 (scCO2) was proposed, which not only enabled the consumption of CO2 but also facilitated the conversion of biomass into valuable products. It was concluded that the carbon gasification efficiency (CE) and hydrogen gasification efficiency (HE) were 37.10 % and 51.77 %, respectively, when the CO reached the maximum of 8.72 ± 0.28 mol/kg at 700 °C for 20 min. The addition of catalyst promoted the production of H2 and increased CE, the H2 yield of guaiacol gasification under different catalysts was ordered as Al2O3 > KOH > without catalyst > KCl. As the reaction temperature increased, the unreacted guaiacol and phenol decreased and were gradually converted to liquid products such as pyrene and benzo[c]phenanthrene. With the increase in reaction temperature, the more fully guaiacol was reacted, the easier it was to carbonize and form more carbon microspheres. In addition, reaction pathways for free radicals were proposed, including cleavage of free radicals, isomerization of free radicals, secondary cleavage of free radicals and recombination of free radicals. In short, degrading guaiacol using scCO2 is a feasible approach, which provides a new direction for the disposal and energy recovery of biomass in the future.

Wettability of Different Mineral Surfaces in Supercritical CO2 Extraction: Interpretations from the Molecular Composition of Crude Oil

Wettability of Different Mineral Surfaces in Supercritical CO₂ Extraction: Interpretations from the Molecular Composition of Crude Oil

A new model to predict the small-hole decompression process of long CO2 pipeline

CO2 pipeline transportation is considered as an economical and safe way of moving large quantities of CO2 in Carbon Capture Utilization and Storage (CCUS) projects. However, design and planning of CO2 pipelines passing through populated areas require careful risk assessment of accidental pipeline failure scenarios leading to CO2 pipeline decompression. In this study, a new zero-dimensional multi-stage outflow model describing transient decompression of CO2 is developed. The model accounts for the experimentally observed liquid level variation along the pipeline and uses the liquid volume fraction threshold parameter (αt) to mark the end of the saturated liquid flow decompression stage. Besides, the Lee model is applied to describe the mass transfer in gas-liquid phases. The model was validated against experimental data obtained large-scale pipeline decompression tests and can be recommended for simulation of outflow of supercritical and liquid CO2 from pipelines longer than 258 m and the orifice-to-pipeline diameter ratios smaller than 0.21. The advantage of this model lies in its use of the relatively simple Vessel Blowdown Model (VBM) to accurately model the depressurization process. It addresses the inconvenience posed by the heavy computational burden of high-dimensional models when predicting long-duration leakages in large-capacity pipelines.

Utilizing poly(4‐hydroxybutyrate) as a reinforcing additive to produce high‐performance and biodegradable PBAT blends tailored for foaming applications

AbstractPoly(butylene‐adipate‐co‐terephthalate) (PBAT) is recognized for its advantages as a biodegradable thermoplastic polyester. However, its application is often limited due to low strength and poor processability. In contrast, poly(4‐hydroxybutyrate) (P4HB) emerges as a fully biodegradable polyester characterized by high strength, excellent toughness, and facile processing. In this study, P4HB was employed to reinforce PBAT, and glycidyl methacrylate grafted onto poly(4‐hydroxybutyrate) (P4HB‐g‐GMA) was introduced as an effective compatibilizer to address their inherent incompatibility. The study explored the influence of P4HB‐g‐GMA content on the mechanical, thermal, morphological, and rheological properties of the blends. The findings revealed that P4HB‐g‐GMA significantly enhanced the compatibility, mechanical properties, and melt strength of PBAT/P4HB blends. Furthermore, various PBAT/P4HB foams were prepared through a batch foaming process, employing supercritical CO2 as a physical foaming agent. The volume expansion ratio and cell size of PBAT/P4HB foams increased with higher levels of the compatibilizer.

Simulation of DME-O2 Combustion in a Hollow Cone Impinging Jet Combustor for Direct-Fired Supercritical CO2 Power Cycle

ABSTRACT Combustion is critical in the direct-fired supercritical CO2 power cycle. A hollow cone impinging jet combustor is designed. Instead of methane, dimethyl ether is used as the fuel for the direct-fired supercritical CO2 cycle, with a higher hydrocarbon ratio and oxygen. The dimethyl ether combustion process is simulated by Fluent, based on the k-ε turbulence model and Eddy-Dissipation Concept combustion model, combined with the dimethyl ether combustion mechanism. The effects of the CO2 recycling ratio, the excess oxygen coefficient, and in-combustor pressure are investigated to support improving combustion performance. The results indicate that the recycled CO2 intensifies the movement of the mixture in the combustor, reduces the peak temperature, and makes temperature distribution more uniform. As the excess oxygen coefficient increases, the peak temperature is enhanced, and the combustion is more sufficient. The effect of in-combustor pressure is complex. On the one hand, increasing in-combustor pressure reduces the jet penetration and inhibits the contact between dimethyl ether and O2, leading to a lower peak temperature. On the other hand, it prolongs the residence time of the high-temperature exhaust, making the reaction between dimethyl ether and O2 more sufficient. The optimal operating condition of the combustor is a CO2 recycling ratio of 0.95, an excess oxygen coefficient of 1.20, and an in-combustor pressure of 30 MPa. Moreover, the obtained combustion products parameters, such as temperature, component concentration, and mass flow rate, can guide the performance analysis for the direct-fired supercritical CO2 power cycle.

Numerical investigation of the overall thermal and thermodynamic performance of a high concentration ratio parabolic trough solar collector with a novel modified twisted tape insert using supercritical CO2 as the working fluid

Supercritical CO2 (sCO2) is favoured as the next-generation working fluid for advanced high-temperature and high-concentration ratio parabolic trough solar collectors (PTSC) due to the fluid’s low cost, availability and thermal stability at high temperatures. However, the lower thermal transport properties of sCO2 compared to conventional working fluids necessitate heat transfer enhancement of receivers using sCO2. In this study, a combined and extensively validated approach using Monte-Carlo ray tracing for optical analysis and computational fluid dynamics (CFD) for thermal and thermodynamic analysis were used to investigate the overall thermal and thermodynamic performance of a high concentration ratio sCO2-based PTSC with a modified twisted tape (MTT) inserts in the receiver. MTT inserts with twist ratios in the range of 2.0 to 4.0 and width ratios in the range of 0.75 to 0.95 were investigated. Results show enhancement of the heat transfer performance by up to 73% and thermal efficiency by 6%, and reduction of the receiver heat losses and circumferential temperature gradients when the MTT inserts are used. In addition to presenting results using the first law of thermodynamics, this study also considered the second law of thermodynamics by evaluating the entropy generation rates due to heat transfer and fluid friction irreversibilities. Results showed that the use of MTT inserts caused a reduction in the total entropy generation rates, with the lowest irreversibility occurring at a Reynolds number of 1,650,000 for a twist ratio of 2.0 and width ratio of 0.95.

Study on windage loss characteristics of supercritical CO2 Taylor-Couette-Poiseuille flows

Taylor-Couette-Poiseuille (TCP) flow is prevalent in rotating machinery, occurring extensively between a high-speed rotating shaft and its static case. This study employed a numerical simulation method to investigate the flow characteristics and windage loss in supercritical carbon dioxide (sCO2) TCP flow. The findings revealed that increasing the rotational Reynolds number and aspect ratio and decreasing the axial Reynolds number and radius ratio reduced the friction coefficient (Cf). Ultimately, a Cf correlation for sCO2 TCP flow was derived through fitting simulation results, exhibiting an average relative error within ± 2 %. These results established a theoretical foundation for the structural design of sCO2 rotating machinery.

Revealing the effect of O2, SO2 and H2O in supercritical CO2 on the corrosion behavior of 316 L steel at elevated temperature

Closed supercritical CO2 (sCO2) power systems require steels that can resist corrosion in high temperature CO2 containing different impurities at ppm levels. However, potential impurity effects on Fe-16Cr steels are not well understood. Herein we evaluated the corrosion behavior of 316 L steel in sCO2 containing 100 ppm O2, SO2 or H2O at 600 °C and 20 MPa. All investigated impurities enhanced Fe-oxide nodule formation, leading to higher carburization in underlying substrate. Presence of O2 caused transition of chromia scale into Fe-Cr spinel, because Cr supply from underlying substrate could not meet the consumption. Spallation occurred when 316 L was exposed with SO2 impurity, attributed to the formation of sulfides within and beneath the oxide scales. H2O impurity showed relatively low damage to protective chromia layer with localized aggravation. Corrosion mechanisms related to impurities were unraveled based on experimental results and thermodynamic analysis.

Water Impact on Adsorbed Oil Detachment From Mineral Surfaces by Supercritical CO2: A Molecular Insight

AbstractGeochemical reactions are crucial for in situ CO2 mineralization underground associated with CO2‐enhanced oil recovery (CO2‐EOR) in a hydrocarbon reservoir. However, the presence of formation water and adsorbed oil on rocks generates physical barriers to CO2's access to mineral surfaces, which may yield impedance to CO2 mineral trapping that has yet to be accounted for. In this study, we mimic the dynamic oil detachment process using molecular dynamic (MD) simulation and analyze the influence of an adsorbed oil film on supercritical CO2 (scCO2) diffusion toward the mineral surface in the presence and absence of a water phase. Our results demonstrated a negative impact of water on oil film detachment by scCO2, which may weaken mineral reactions and is unfavorable for mineralized CO2 storage underground.

Waste-to-energy poly-generation scheme for hydrogen/freshwater/power/oxygen/heating capacity production; optimized by regression machine learning algorithms

Utilization of machine learning techniques in the analysis and enhancement of poly-generation energy systems improves their efficiency and sustainability. Also, waste-to-energy systems propose a hopeful answer for both waste management and sustainable energy and water production. The production of hydrogen and freshwater through these systems not only provides valuable resources but also contributes to environmental sustainability. This research utilizes artificial intelligence's machine learning algorithms to examine and enhance a waste-to-energy system within a poly-generation energy system that generates hydrogen, freshwater, power, oxygen, and hot air. The integrated system consists of a waste combustion chamber, a proton exchange membrane electrolyzer, a supercritical carbon dioxide Brayton cycle, and a desalination system. Based on the findings, the machine learning algorithms exhibiting R-squared values exceeding 99% are considered strong fits. Additionally, all algorithms with high predicted R-squared values have the capability to accurately forecast new data using the provided training data. The emissions of 669.7 g/kWh and an efficiency of 69.62% are achieved when the pressure ratio is 10.73 and the temperature is 863.6 °C under optimal conditions. The accuracy and validity of the machine learning techniques are further confirmed by the strong agreement with thermodynamic modeling.

Forefront Research of Foaming Strategies on Biodegradable Polymers and Their Composites by Thermal or Melt-Based Processing Technologies: Advances and Perspectives.

The last few decades have witnessed significant advances in the development of polymeric-based foam materials. These materials find several practical applications in our daily lives due to their characteristic properties such as low density, thermal insulation, and porosity, which are important in packaging, in building construction, and in biomedical applications, respectively. The first foams with practical applications used polymeric materials of petrochemical origin. However, due to growing environmental concerns, considerable efforts have been made to replace some of these materials with biodegradable polymers. Foam processing has evolved greatly in recent years due to improvements in existing techniques, such as the use of supercritical fluids in extrusion foaming and foam injection moulding, as well as the advent or adaptation of existing techniques to produce foams, as in the case of the combination between additive manufacturing and foam technology. The use of supercritical CO2 is especially advantageous in the production of porous structures for biomedical applications, as CO2 is chemically inert and non-toxic; in addition, it allows for an easy tailoring of the pore structure through processing conditions. Biodegradable polymeric materials, despite their enormous advantages over petroleum-based materials, present some difficulties regarding their potential use in foaming, such as poor melt strength, slow crystallization rate, poor processability, low service temperature, low toughness, and high brittleness, which limits their field of application. Several strategies were developed to improve the melt strength, including the change in monomer composition and the use of chemical modifiers and chain extenders to extend the chain length or create a branched molecular structure, to increase the molecular weight and the viscosity of the polymer. The use of additives or fillers is also commonly used, as fillers can improve crystallization kinetics by acting as crystal-nucleating agents. Alternatively, biodegradable polymers can be blended with other biodegradable polymers to combine certain properties and to counteract certain limitations. This work therefore aims to provide the latest advances regarding the foaming of biodegradable polymers. It covers the main foaming techniques and their advances and reviews the uses of biodegradable polymers in foaming, focusing on the chemical changes of polymers that improve their foaming ability. Finally, the challenges as well as the main opportunities presented reinforce the market potential of the biodegradable polymer foam materials.

Predicting the solubility of solids in supercritical carbon dioxide using the Chrastil equation with parameters estimated from a group contribution method

Predicting the solubility of a solid in supercritical carbon dioxide (scCO2) can be useful for many applications. However, an accurate prediction is extremely difficult since current methods require knowledge about the properties of the solid in question or lengthy computational calculations and often yield significant deviations. Here, a new approach is proposed that allows the solubility of any solid in supercritical carbon dioxide to be rapidly predicted based solely on the structural formula of the solute. This approach is based on the prediction of Chrastil’s parameters using group contribution methods (GCMs) followed by their use in Chrastil’s equation. For this purpose, group contribution methods to estimate Chrastil’s parameters were developed using more than 6000 experimental data points from 210 solids. These parameters were used to predict the solubility data of 30 solids (around 1300 experimental points) in pure scCO2 with Chrastil’s equation, obtaining a relatively accurate fit for 70 % of the experimental points. The average absolute relative deviation was 51.22 % (less than 8.31 · 10−4 in absolute deviation), while the logarithmic deviation was 10.83 %. The deviations obtained were substantially lower than other estimations proposed in the literature. This methodology is easily extended, faster, and more accurate than other methods and does not require the use of computational methods or the estimation of solid properties. Moreover, new ways to predict the solubility of solids in supercritical carbon dioxide can be developed in the future based on this methodology.

Study on geothermal energy self-recycling extraction and ScCO2 storage in the horizontal well annuli with fracture network system

With the extensive exploitation of fossil fuels, a substantial number of production and injection wells have been or are on the verge of being abandoned. However, many of these wells present viable opportunities for geothermal energy extraction, as they are situated in geothermal reservoirs with favourable temperatures. In alignment with carbon neutrality policies, supercritical CO2 (ScCO2) has emerged as the preferred working fluid for geothermal extraction, facilitating subsequent storage. This study has developed three transient models to characterize the heat and mass transfer processes of ScCO2 circulating within a horizontal wellbore and the reservoir's fracture network. Finite element method and Comsol Multiphysics 6.1 software are employed to solve these models. Results show that ScCO2 efficiently flows from the annuli into the hydraulic fracture network and then circulates back through the annuli completing a self-recycling heat extraction process. The findings reveal several key insights: (a) Lower injection mass flow rates and flow rates lead to more efficient extraction of thermal energy within horizontal wellbores. (b) Low-temperature ScCO2 enhance thermal energy recovery. (c) The larger the coverage area of the fracture network, the more effective the heat extraction. (d) The efficiency of heat extraction and ScCO2 storage in the horizontal well-fracture network self-circulation system is 3 to 5 times and 6 to 7 times higher than that of the horizontal well self-recycling and injection-production systems. (e) Periodic thermal extraction proves to be more efficient than continuous methods. (f) The cumulative heat production of the vertical dual well injection-production system is the highest, reaching 2.45 × 1011 kJ. But it's still lower than the self-circulating system. The heat extraction effect of the diagonal dual well injection-production system is the lowest, which is 1.83 × 1011 kJ. (g) Three developed transient models facilitate efficient heat extraction and ScCO2 storage reservoir screening and evaluation. In conclusion, the self-recycling system has achieved efficient heat extraction and carbon dioxide storage, providing a theoretical basis for future energy conversion and management.

Prediction and modeling of tie-dye polyester fabric's texture and color feature in supercritical carbon dioxide

To mitigate the water-intensive challenges of tie-dye clothing production and address the absence of objective evaluation for finished products, we have explored the correlation between tie-dye techniques in supercritical carbon dioxide (SC-CO2) and image patterns. Employing digital image processing, we extracted the average HSV three-component value of the valid tie-dye area, the proportion of incompletely dyed area in the HSV color space, and the initial three texture features of the digital tie-dye image using the Tamura method. We scrutinized five factors in the supercritical CO2 dyeing process: rotational speed, dyeing temperature, dyeing pressure, dye concentration, and dyeing time. The single-factor climbing test revealed that temperature and pressure are the predominant factors influencing tie-dyeing performance. We propose a correlation between the texture parameters of tie-dyeing and the swelling effect of polyester fabric in a supercritical CO2 environment. Subsequently, we conducted two-factor tests on temperature and pressure to investigate their specific effects on the parameters of supercritical polyester tie-dyeing. The results indicated significant changes in regularity, saturation, and the proportion of undyed area with variations in dyeing temperature and pressure. Building upon these findings, we developed an artificial neural network for predicting tie-dye dyeing temperature and pressure in supercritical CO2, utilizing features regularity, saturation, and proportion of undyed area as inputs. In the 105st round, experimental results demonstrated an accuracy of 0.99445, substantiating the efficacy of tie-dye pattern features in supercritical CO2 for technique forecasting.

Pseudo-transient flow path optimization of a solar tower receiver operating with supercritical carbon dioxide

Aiming to further promote the decarbonization of energy production processes, this article simulates and optimizes the pseudo-transient behavior of a cylindrical solar receiver subjected to a spatially varying concentrated heat flux. The model employed, which accounts for its thermal–hydraulic behavior, uses supercritical carbon dioxide (s-CO2) as the heat transfer fluid and is based on a literature-validated hybrid formulation that axially discretizes the tube of the receiver and simultaneously solves the 2-D temperature distribution within the cross-section of each node. The operational conditions imposed on the receiver were determined such that it can produce 10 MW in a recompression Brayton cycle. Also, the receiver’s surface was exposed to a spatially variable concentrated solar boundary condition based on the direct normal irradiance (DNI) of a representative day for each month of the year, which was selected from the typical meteorological year (TMY) in Seville (Spain). The results showed that the combined thermal–hydraulic efficiency of the receiver increases with the number of panels and that the mass flow flowing through each symmetrical side of the receiver should not necessarily be identical for achieving maximal efficiency. More importantly, the results showed that by simply changing the location of the s-CO2 inlet and outlet ports, one can increase the efficiency of the receiver by about 3 % while considering the exact same concentrated solar irradiation.

In-situ laboratory study on influencing factors of pre-SC-CO2 hybrid fracturing effect in shale oil reservoirs

Supercritical CO2 (SC-CO2) fracturing, being a waterless fracturing technology, has garnered increasing attention in the shale oil reservoir exploitation industry. Recently, a novel pre-SC-CO2 hybrid fracturing method has been proposed, which combines the advantages of SC-CO2 fracturing and hydraulic fracturing. However, the specific impacts of different pre-SC-CO2 injection conditions on the physical parameters, mechanical properties, and crack propagation behavior of shale reservoirs remain unclear. In this study, we utilize a newly developed "pre-SC-CO2 injection → water-based fracturing" integrated experimental device. Through experimentation under in-situ conditions, the impact of pre-SC-CO2 injection displacement and volume on the shale mineral composition, mechanical parameters, and fracture propagation behavior are investigated. The findings of the study demonstrate that the pre-injection SC-CO2 leads to a reduction in clay and carbonate mineral content, while increasing the quartz content. The correlation between quartz content and SC-CO2 injection volume is positive, while a negative correlation is observed with injection displacement. The elastic modulus and compressive strength exhibit a declining trend, while Poisson's ratio shows an increasing trend. The weakening of shale mechanics caused by pre-injection of SC-CO2 is positively correlated with the injection displacement and volume. Additionally, pre-injection of SC-CO2 enhances the plastic deformation behavior of shale, and its breakdown pressure is 16.6% lower than that of hydraulic fracturing. The breakdown pressure demonstrates a non-linear downward trend with the gradual increase of pre-SC-CO2 injection parameters. Unlike hydraulic fracturing, which typically generates primary fractures along the direction of the maximum principal stress, pre-SC-CO2 hybrid fracturing leads to a more complex fracture network. With increasing pre-SC-CO2 injection displacement, intersecting double Y-shaped complex fractures are formed along the vertical axis. On the other hand, increasing the injection rate generates secondary fractures along the direction of non-principal stress. The insights gained from this study are valuable for guiding the design of pre-SC-CO2 hybrid fracturing in shale oil reservoirs.

Important carotenoids derived from marine biomass: Extraction, stabilization, and potentiality in food, cosmetics, and pharmaceutical application

Marine organisms are an important source of bioactive compounds, among which marine carotenoids have garnered attention for their health benefits. Hundreds of carotenoids are extracted from different natural biomass; among them marine carotenoids always have special appeal due to their unique properties. This review discusses recent literature on marine carotenoids, extraction and stabilization methods, and their applications in various industries. Green extraction techniques that use supercritical carbon dioxide (SC–CO2) and natural deep eutectic solvents were highlighted in addition to conventional extraction solvents. As most natural carotenoids are highly unstable, this review describes recent advances to stabilize these bioactive compounds. This work offers new insights into marine carotenoids and their potential application in the food, pharmaceutical, and cosmetic industries.

Effects of turbulent Prandtl number on supercritical carbon dioxide turbulent flow with high heat flux in vertical round tube

Supercritical carbon dioxide (sCO2) is a promising working medium for coal-fired power plants, high-temperature solar power systems, nuclear reactor systems, and fuel cells owing to its high efficiency and inertness. In these cases, the sCO2 is in a round tube under high temperature and pressure, far from the pseudo-critical point. Here, the thermophysical properties of sCO2 changes, resulting in large prediction errors. In this study, a conjugate heat transfer model with the k-ε turbulent model was created to analyze the tube performance of the sCO2, and the effects of turbulent Prandtl number (Prt) on the sCO2 turbulent flow with high heat flux were examined through experimental and numerical investigations. Prt had a considerable effect on the performance of the sCO2 turbulent flow far from the pseudo-critical point. The mean relative errors of the inner wall temperature and convective heat transfer coefficient were reduced by approximately 13% and 27%, respectively, when Prt was decreased from 1 to 0.55. For the sCO2 turbulent flow with a high heat flux, constant Prt values of 0.55–0.6 were applicable. The findings afford key insights for the development of sCO2 turbulent flow with high heat flux.