SC-CO2 Treatment Research Articles

Mechanical property enhancement of flax fibers via supercritical fluid treatment

The desire for lightweight, carbon-negative materials has been increasing in recent years, particularly as the transportation sector reduces its global carbon footprint. Natural fibers, such as flax fiber and their composites, offer a compelling combination of properties including low density, high specific strength, and carbon negativity. However, because of the low modulus and high variability in performance, natural fibers can’t compete with glass fibers as structural reinforcements in polymer composites. In this study, flax technical fibers were treated in supercritical CO2 (scCO2), and the effects of this treatment on the morphology and properties of flax fibers are reported. Treatment in scCO2 successfully resulted in higher fiber modulus and strength by 33% and 40%, respectively. Fiber porosity was reduced by 50% and morphological changes to the fibers were observed. Specifically, fiber lumen collapsed during treatment and micro/mesoporosity was reduced by 27%. Treated flax fibers were used to create 30 vol% unidirectional flax-epoxy composites. ScCO2 treatment raised composite modulus and strength by 33% and 25%, respectively. Because of the dependence between technical fiber size and mechanical properties, the relationship between fiber modulus and fiber size were created and applied to the rule-of-mixtures. This relationship were found to be viable representations of the fiber performance within each composite. Overall, the treatment developed in this study has the potential to significantly improve natural fiber properties, enabling their consideration for use in lightweight, semi-structural composites.

Comparative analysis of the effectiveness of bone matrix purification protocols

Background: This article describes the protocol for the purification of xenogenic bone matrix tested by a team of authors in the article «Determining the effectiveness of a xenogeneic bone matrix decellularization protocol in in vitro and in vivo studies» (the test results were described in the journal N.N. Priorov Journal of Traumatology and Orthopedics. 2023;30(4):431–443, doi: https://doi.org/10.17816/vto622849). AIM: To conduct a comparative analysis of methods of physical and chemical purification of xenogeneic spongy bone tissue by tomographic and morphological studies. MATERIALS AND METHODS: Xenogenic bovine femoral spongiosa tissue was fragmented to the size of 10×10×10 mm and treated with water, hypertonic, hypotonic, hypotonic solutions, and 3% or 6% hydrogen peroxide solution in various combinations. Deep secondary purification with organic solvents or supercritical fluid extraction was then applied, followed by 1H NMR to determine traces of reagents. The efficiency of the optimal protocol was determined by histologic and tomographic studies with calculation of the purification factor by densitometric indices. RESULTS: In accordance with the purification coefficient calculated by densitometric indicators, the intertrabecular space of bone tissue after exposure to flowing water and hypo- and hypertonic solutions followed by cleaning with a 3% H2O2 solution is not sufficiently purified; histological analysis showed the presence of 0 to 60% osteocytes for different cleaning protocols. When replaced with a 6% H2O2 solution, the purification coefficient was higher, but bone destruction was observed. Additional deep purification allows a high purification rate while preserving the structure, but when organic solvents are used, their traces are detected in the matrix; therefore, the use of supercritical fluid extraction is more effective. CONCLUSION: The sequential use of flowing water, 0.5% NaCl solution, 3% H2O2 solution followed by sc-CO2 treatment is an effective protocol for the purification of xenogeneic spongy bone tissue.

Fabrication and Characterization of PLA/PBAT Blends, Blend-Based Nanocomposites, and Their Supercritical Carbon Dioxide-Induced Foams.

In this study, a twin-screw extruder was used to fabricate poly(lactic acid) (PLA)/poly(butylene adipate-co-terephthalate) (PBAT) blends and blend-based nanocomposites with carbon nanotube (CNT) or nanocarbon black (CB) as nanofillers. The fabricated samples were subsequently treated with supercritical carbon dioxide (scCO2) to fabricate the corresponding foams. Bi-phasic morphology and selective distribution of CNTs or CBs in the PBAT phase were observed in the blends/composites through scanning electron microscopy. After the scCO2 treatment, the selective foaming of the PBAT phase in the prepared blends/composites was confirmed. The cellular structure of PBAT phase in scCO2-treated blends is similar to the size/shape of PBAT domains in untreated blends or treated neat PBAT foam. The addition of CNTs or CBs in the blends led to a slight reduction in cell size of the foamed PBAT phase, demonstrating CNT/CB-induced cell nucleation. Differential scanning calorimetry (DSC) results showed that CNTs and CBs played as nucleating agents and increased the initial crystallization temperature up to 14 °C compared with neat PBAT for PBAT in different composites during cooling. The scCO2 treatment induced the bimodal stability of PBAT crystals in different samples, which melted mainly in two temperature regions in DSC studies. Thermogravimetric analyses revealed that compared with parent blends, the addition of CNTs or CBs increased the temperature at 80 wt.% loss (degradation of PBAT portion) up to 6 °C. The electrical resistivity decreased by more than six orders of magnitude for certain CNT- or CB-added composites compared with the parent blends. The hardness of the blends slightly increased after forming the corresponding composites and then declined after the scCO2 treatment.

Diffusive Leakage of scCO2 in Shaly Caprocks: Effect of Geochemical Reactivity and Anisotropy

Summary Supercritical carbon dioxide (scCO2) trapping mechanisms within carbon geostorage (CGS) primarily hinge on the upper caprock system, with shales being favored for their fine-grained nature and geological abundance. Experimental assessments of CO2 reactivity in brine-saturated shales reveal microstructural changes, raising concerns about long-term CO2 leakage risks. Existing models of scCO2 transport through caprocks lack consideration for shale anisotropy. This study addresses these gaps by investigating the diffusive properties and propagation of geochemical reactivity in shaly caprocks, accounting for anisotropy. Horizontal and vertical core samples from three shale formations with varying petrophysical characteristics underwent mineralogical, total organic carbon (TOC), porosity, and velocity measurements. scCO2 treatment for up to 3 weeks at 150°F and 3,000 psi was conducted. The propagation of geochemical reactivity was monitored by multiple surface X-ray fluorescence (XRF) measurements and fine polishing. A nuclear magnetic resonance (NMR)-based H2O-D2O fluid exchange protocol was used to quantify effective diffusivities and tortuosities parallel and perpendicular to bedding. Results indicate preferential surface reactivity toward carbonate minerals; however, the apparent reaction diffusivity of the shaly caprock is notably slow (~10−15 m2/s). This aligns with previous experimental and reactive transport modeling studies, emphasizing long timescales for carbonate dissolution reactions to influence shale caprock properties. Shale-effective diffusivities display anisotropy increasing with clay content, where diffusivities parallel to bedding exceed those perpendicular by at least three times. Faster horizontal diffusion in shaly confining zones should be considered when estimating diffusive leakage along faults penetrating these zones, a significant risk in CGS. Post-scCO2 treatment, diffusivity changes vary among samples, increasing within the same order of magnitude in the clay-rich sample. Nonsteady-state modeling of scCO2 diffusion suggests limited caprock penetration over 100 years, with a minimal increase from 5 m to 7 m post-scCO2 treatment for the clay-rich sample. This study extends existing literature observations on the slow molecular diffusion of scCO2 within shaly caprocks, integrating the roles of geochemical reactions and shale anisotropy under the examined conditions.

Effect of supercritical carbon dioxide on protein structure modification and antimicrobial peptides production of Mongolian cheese and its in vitro digestion

The aim of this research was to investigate the effects of supercritical carbon dioxide (SC-CO2) treatment on protein structure in Mongolian cheese. The peptides during the digestive process of the SC-CO2 treated cheese were also studied. SC-CO2 technology was utilized to treat Mongolian cheese at three temperatures (45, 55 and 65 °C) and three pressures (7.5, 12.5 and 17.5 MPa). The results of fluorescence, ultraviolet–visible, Fourier transform infrared spectroscopy and free sulfhydryl groups showed that SC-CO2, particularly at 65 °C and 17.5 MPa, modified the protein structure in Mongolian cheese effectively. The data of LC-MS/MS-based peptidomics showed that the content of antimicrobial peptides found in the SC-CO2 treated Mongolian cheese was 1.55 times that of the untreated Mongolian cheese; the content of unique antimicrobial peptides in the digested SC-CO2 treated Mongolian cheese was 1.46 times that of the digested untreated Mongolian cheese, which proved that SC-CO2 could help produce antimicrobial peptides in cheese not only during the process of SC-CO2 treatment but during subsequent simulated gastrointestinal digestion as well. In conclusion, SC-CO2 could be considered a promising method to develop cheese products with potential health benefits.

Effect of supercritical carbon dioxide on pore structure and methane adsorption of shale with different particle sizes

Supercritical carbon dioxide (SCCO2) fracturing significantly enhances shale gas recovery, which is influenced by particle size. We soaked shale in SCCO2 and investigated the impact of SCCO2 on different particle sizes. Large-particle shales showed the largest percentage changes in specific surface area and total pore volume (54.11 %, 87.87 %; 58.59 %, 76.32 %) followed by small-particle size shales. This trend was also observed in other pore structure parameters. The particle-size effect is: Large-particle shale, with abundant microfractures, enhances SCCO2 flow and pore alteration. Small-particle shale's high specific surface area facilitates SCCO2 penetration. Medium-particle shale is less affected due to balanced interactions of these factors. Methane is primarily found in large and medium pores and microfractures. Methane adsorption in shale mainly involves multi-layer adsorption. Following SCCO2 treatment, pore fractures narrowed, increasing the proportion of methane molecules adsorbed as a single-layer. This study is crucial for evaluating the fracturing effects on shale gas wells.

Micromechanical property evolution and damage mechanism of coal subjected to ScCO2 treatment

Carbon dioxide (CO2) injection into deep coal seams holds considerable significance in both carbon mitigation and enhanced recovery of clean coalbed methane (CBM). The CO2-coal interaction leads to changes in the physicochemical properties, potentially impacting the stability of the target sequestration coal reservoir. This study applied the nanoindentation, scanning probe microscopy (SPM), X-ray diffraction (XRD), and electron probe X-ray Micro-Analyzer (EPMA) techniques to probe the micromechanical property change and damage mechanism of coal subjected to ScCO2 injection. The result shows that the load-displacement behavior of the tested coal changes with continuous ScCO2 treatment, and the mechanical strength significantly weakens after 4 days of ScCO2 treatment. The nanoindentation test indicates that the peak and creep displacements of tested coal increased by 168.79 % and 1046.32 % respectively with 4-day ScCO2 treatment, inferring that the coal deformation increases and changes from elastic to plastic after ScCO2 injection. As the ScCO2 treatment time increases, Young's modulus and hardness of coal exhibit an exponential decay trend and rapidly decrease by 77.77 %∼89.76 % and 68.37 %∼81.63 % respectively after the initial 3-day treatment, followed by a slow decrease with the ScCO2 duration prolonging. The XRD and EPMA results show that the carbonate minerals reacted preferentially with ScCO2, and silicate minerals experienced gradual dissolution, while the amorphous carbon fluctuated almost unchanged in the tested coal. Carbonate minerals in tested coal have decreased by 70.68 % within the first 1-day ScCO2 treatment, making the most significant contribution to the initial rapid weakening of coal mechanics. The mineral distribution is closely related to the mechanical anisotropy of coal, which is confirmed by the phenomenon that the coal anisotropy gradually weakens with the mineral reaction process. It is inferred that the mineral component and distribution of coal seams are important indicators for evaluating the intensity of physical and chemical reactions in ScCO2-injected reservoirs, which directly determines the mechanical damage behavior of sequestration reservoirs. This research provides basic support for site selection and safety assessment of carbon sequestration in deep coal seams.

Application of supercritical carbon dioxide to enhance the aroma of whole sorghum flour for use in 3D printing of sorghum cookies

Sorghum is a promising ingredient for new food products due to its high fiber content, slow digestibility, drought resistance, and gluten-free nature. One of the main challenges in sorghum-based products is the unpleasant aroma compounds found in grain sorghum. Therefore, in this study, sorghum flour was treated via supercritical carbon dioxide (SC-CO2) to remove undesired aroma compounds. The resulting SC-CO2-treated flours were used to generate dough for 3D food printing. At the optimized conditions, sorghum cookies were 3D-printed using 60 % water and a nozzle diameter of 1.5 mm. All dough samples produced with untreated and SC-CO2-treated sorghum flours exhibited shear-thinning behavior. Changing the treatment pressure (8–15 MPa) or temperature (40–60 °C) did not significantly affect the viscosity of the dough samples. Moreover, the sorghum cookie doughs had higher G′ and G″ values after the SC-CO2 treatments (G′ >G″). Doughs generated from flours treated at 15 MPa − 40 °C and 8 MPa − 60 °C showed lower adhesiveness compared to the ones produced from untreated flour, whereas 15 MPa − 60 °C treatment did not affect the adhesiveness. After baking, the 3D-printed cookies from SC-CO2-treated flour exhibited significantly lower redness (a*), but the hardness of the cookies was not affected by SC-CO2 treatment. Overall, the SC-CO2 treatment of sorghum flour did not negatively affect the quality parameters of the 3D-printed cookies while enhancing the aroma of the flour.

Supercritical Impregnation of PETG with Olea europaea Leaf Extract: Influence of Operational Parameters on Expansion Degree, Antioxidant and Mechanical Properties.

PETG (poly(ethylene glycol-co-cyclohexane-1,4-dimethanol terephthalate)) is an amorphous copolymer, biocompatible, recyclable, and versatile. Nowadays, it is being actively researched for biomedical applications. However, proposals of PETG as a platform for the loading of bioactive compounds from natural extract are scarce, as well as the effect of the supercritical impregnation on this polymer. In this work, the supercritical impregnation of PETG filaments with Olea europaea leaf extract was investigated, evaluating the effect of pressure (100-400 bar), temperature (35-55 °C), and depressurization rate (5-50 bar min-1) on the expansion degree, antioxidant activity, and mechanical properties of the resulting filaments. PETG expansion degree ranged from ~3 to 120%, with antioxidant loading ranging from 2.28 to 17.96 g per 100 g of polymer, corresponding to oxidation inhibition values of 7.65 and 66.55%, respectively. The temperature and the binary interaction between pressure and depressurization rate most affected these properties. The mechanical properties of PETG filaments depended greatly on process variables. Tensile strength values were similar or lower than the untreated filaments. Young's modulus and elongation at break values decreased below ~1000 MPa and ~10%, respectively, after the scCO2 treatment and impregnation. The extent of this decrease depended on the supercritical operational parameters. Therefore, filaments with higher antioxidant activity and different expansion degrees and mechanical properties were obtained by adjusting the supercritical processing conditions.

The study on mechanism of water–rock reaction in shale oil formation rich in alkaline minerals in Mahu Sag by using supercritical CO2

The Mahu Sag of Junggar Basin, China is rich in alkaline minerals. Generally, the water–rock reactions between hydraulic fluid and alkaline minerals during the hydraulic fracturing process will lead to the precipitation of minerals and block the pore or wellbore, thereby affecting the recovery efficiency. Supercritical carbon dioxide (ScCO2) regarded as a fracturing fluid can significantly improve the recovery of shale oil resources, but there is limited research on the reaction of ScCO2 to water and rock in shale samples rich in alkaline minerals. Therefore, ScCO2 treatment experiments were conducted on shale samples rich in alkaline minerals under 80°C and 10 MPa. Before the experiments, X-ray powder diffraction (XRD) was applied to characterise the mineral properties of the three shale samples. In addition, the duration time of ScCO2 treatment was set at 7 and 20 days to observe the treatment time impacts on the pore structure. Scanning electron microscopy (SEM) analysis and the Mann–Whitney U test were conducted before and after ScCO2 treatment. SEM images show the changes in pore structure. Opening pores are observed due to the interaction between the alkaline mineral and ScCO2. The Mann–Whitney U test shows the changes in fracture toughness. The changes in pore structure also play an important role in fracture toughness. This study investigated the ScCO2 impacts on shale samples rich in alkaline minerals and the analysis of changes in pore structure and fracture toughness can provide theoretical and data evidence to enable on-site optimisation of the ScCO2 fracturing scheme.

Supercritical cartilage decellularization: Cosolvent effect on mechanical properties

Decellularized animal tissue may serve as scaffolds in tissue engineering. Despite the well-disseminated use of sodium dodecyl sulfate (SDS) for decellularization, SDS-based methods are time-consuming and may cause extracellular matrix (ECM) denaturation. This study explores supercritical CO2 (scCO2) extraction as an alternative to decellularize chicken sternum cartilage. Various scCO2 decellularization methods were tested, including pure scCO2, scCO2 with water, ethanol, or their mixture. SDS outperformed in decellularization but caused the highest extracellular matrix damage. Pure scCO2 treatment for 2 h reduced mechanical resistance due to dehydration. scCO2 with 99 % ethanol led to extensive tissue dehydration, while the addition of 70 % ethanol increased cell removal without significant tissue damage. Further research is recommended to optimize scCO2 decellularization of this tissue with other cosolvents while maintaining adequate hydration.

Supercritical CO2 Treatment to Modify Techno-Functional Properties of Proteins Extracted from Tomato Seeds.

Tomato seeds are a rich source of protein that can be utilized for various industrial food purposes. This study delves into the effects of using supercritical CO2 (scCO2) on the structure and techno-functional properties of proteins extracted from defatted tomato seeds. The defatted meal was obtained using hexane (TSMH) and scCO2 (TSMC), and proteins were extracted using water (PEWH and PEWC) and saline solution (PESH and PESC). The results showed that scCO2 treatment significantly improved the techno-functional properties of protein extracts, such as oil-holding capacity and foaming capacity (especially for PEWC). Moreover, emulsifying capacity and stability were enhanced for PEWC and PESC, ranging between 4.8 and 46.7% and 11.3 and 96.3%, respectively. This was made possible by the changes in helix structure content induced by scCO2 treatment, which increased for PEWC (5.2%) and decreased for PESC (8.0%). Additionally, 2D electrophoresis revealed that scCO2 hydrolyzed alkaline proteins in the extracts. These findings demonstrate the potential of scCO2 treatment in producing modified proteins for food applications.

Mechanism of SC-CO2 extraction-induced changes to adsorption heat of tectonic coal

To investigate the change and control mechanism of coal adsorption behavior under supercritical CO2 (SC–CO2), the changes in coal composition, structure and adsorption of coals before and after SC-CO2 action were addressed by means of Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), low temperature liquid nitrogen adsorption instrument and calorimeter. The influence of changes in coal composition and structure on its adsorption was quantitatively analyzed by grey correlation analysis. The results show that the effect of SC-CO2 fluid treatment is proportional to the degree of coal damage. After SC-CO2 treatment, the integral adsorption heat of CO2 changes from −11.10 J/g to 13.744J/g, and the microcrystalline structure parameters and inorganic components in coal have the greatest influence on it. At the same time, it is also affected by temperature and pressure. With the increase of microcrystalline structure parameters d002, La and Lc, the integral adsorption heat of the samples showed a 'V' trend, and the increasing trend was the same as the decreasing trend of ash yield. On the whole, SC-CO2 fluid treatment enhances the adsorption of gas by coal samples to a certain extent.

Mechanism of pore expansion and fracturing effect of high-temperature ScCO2 on shale

To elucidate the mechanisms underlying the alteration of shale pore fractures by high-temperature supercritical carbon dioxide (ScCO2), this study employed medium–low maturity shale samples from a specific region as research subjects. The samples were subjected to high-temperature ScCO2 reactions in a corrosion-resistant high-pressure reaction vessel at various temperatures. A suite of analytical techniques, including X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), ImageJ image processing software, N2 and CO2 adsorption experiments, thermal gravimetric-differential thermal analysis (TG-DTG) of CO2 pyrolyzed shale oil, and gas chromatography (GC) analysis, were utilized to investigate and analyze the microstructural changes in the shale samples before and after ScCO2 treatment.The results reveal a subtle increase in the content of clay minerals and quartz, accompanied by a decrease in the content of carbonates, potassium feldspar, and calcite. These mineral transformations, encompassing dissolution, precipitation, and swelling processes, exert a substantial impact on the shale surface microstructure and modify the internal pore structure. Consequently, a shift in the mechanical properties of the rock is observed, which bears significance for its fracturing behavior.The experimental results reveal a steady growth in fracture area following high-temperature ScCO2 treatment. Importantly, the extent of initial fracture development plays a crucial role in determining the efficacy of hydraulic fracturing, indicating a positive correlation. Moreover, the connection between fracture area and temperature exhibits a clear trend marked by an initial rise, a subsequent decline, and finally, a resurgence. In particular, the thermal fracturing threshold temperature for the shale samples was found to be around 400 °C.From the analysis, it can be inferred that ScCO2, when subjected to an elevated temperature range of 100-200℃, exhibits mutual interactions with the shale. This results in effective extraction of organic matter and dissolution of mineral constituents within the shale matrix. Consequently, this treatment process leads to a significant reduction in the number of micropores (pore sizes less than 2 nm), while the quantities of mesopores (pore sizes between 2 and 50 nm) and macropores (pore sizes greater than 50 nm) display a noticeable increase.Upon exposure to a temperature range of 200-300℃, a remarkable affinity of the shale for CO2 adsorption becomes evident. The adsorption process contributes to the expansion of the matrix material and deposition of minerals, effectively filling the pore spaces. As a result, the contraction of mesopores and macropores is mitigated, with the predominant change being an increase in the number of micropores.When temperatures reach 300-500℃, the intensified heat initiates thermal decomposition of the kerogen, culminating in the release of pore spaces. This phenomenon prompts an increase in the number of micropores and mesopores, thereby augmenting the pore volume and specific surface area of the shale.

Influence of Supercritical Carbon Dioxide on the Activity and Conformational Changes of α-Amylase, Lipase, and Peroxidase in the Solid State Using White Wheat Flour as an Example.

Green technologies using renewable and alternative sources, including supercritical carbon dioxide (sc-CO2), are becoming a priority for researchers in a variety of fields, including the control of enzyme activity which, among other applications, is extremely important in the food industry. Namely, extending shelf life of e.g., flour could be reached by tuning the present enzymes activity. In this study, the effect of different sc-CO2 conditions such as temperature (35-50 °C), pressure (200 bar and 300 bar), and exposure time (1-6 h) on the inactivation and structural changes of α-amylase, lipase, and horseradish peroxidase (POD) from white wheat flour and native enzymes was investigated. The total protein (TPC) content and residual activities of the enzymes were determined by standard spectrophotometric methods, while the changes in the secondary structures of the enzymes were determined by circular dichroism spectrometry (CD). The present work is therefore concerned for the first time with the study of the stability and structural changes of the enzyme molecules dominant in white wheat flour under sc-CO2 conditions at different pressures and temperatures. In addition, the changes in aggregation or dissociation of the enzyme molecules were investigated based on the changes in particle size distribution and ζ-potential. The results of the activity assays showed a decrease in the activity of native POD and lipase under optimal exposure conditions (6 h and 50 °C; and 1 h and 50 °C) by 22% and 16%, respectively. In contrast, no significant changes were observed in α-amylase activity. Consequently, analysis of the CD spectra of POD and lipase confirmed a significant effect on secondary structure damage (changes in α-helix, β-sheet, and β-turn content), whereas the secondary structure of α-amylase retained its original configuration. Moreover, the changes in particle size distribution and ζ-potential showed a significant effect of sc-CO2 treatment on the aggregation and dissociation of the selected enzymes. The results of this study confirm that sc-CO2 technology can be effectively used as an environmentally friendly technology to control the activity of major flour enzymes by altering their structures.

CO2‐Induced Strong Room‐Temperature Ferromagnetism in BiFeO3

AbstractWith humongous demand for data storage and processing, two‐dimensional (2D) ferromagnetic‐based materials, is emerged as the next‐generation nanoelectronic devices due to their low power consumption and optimal memory and processing capabilities. BiFeO3 as a single‐phase multiferromagnetic material is expected to find potential applications in electromagnetic devices. Herein, 2D room‐temperature ferromagnetic BiFeO3 is obtained with the help of supercritical carbon dioxide (SC CO2). The rhombic phase of BiFeO3 is converted to cubic with the creation of Ov and Fe2+ defects over the SC CO2 treatment, leading to significant ferromagnetic enhancement. More importantly, it is found that SC CO2 can destroy the cycloidal spin structure of BiFeO3 leading to an increase in the Fe─O─Fe bond angle, which generates stronger superexchange interactions. Ultimately, the saturation magnetization strength of BiFeO3 is increased by nearly 23 times. A new strategy is provided for ferromagnetic induction in 2D materials, which is favorable for promoting their practical applications on device architectures in the future.

Mechanical properties and failure characteristics of supercritical carbon dioxide soak in water-bearing coal rocks

Water has an important influence on the mechanical properties of coal rock during CO2 sequestration. In this paper, uniaxial and true triaxial mechanical tests were conducted on bituminous coal under different moisture contents before and after SCCO2 treatment. The experimental results demonstrate that SCCO2 and water deteriorate the coal sample strength and elastic modulus under uniaxial conditions, and the reduction rate exhibits a trend of first increasing and then decreasing. When the water saturation is 80 %, the maximum strength reduction rate of coal samples before and after SCCO2 treatment reached 39.30 %. However, under deep in-situ stress, the strength and elastic modulus of bituminous coal do not exhibit a marked weakening effect under the action of SCCO2 and water, the average strength reduction rate is only 4.03 %. The CT results demonstrate that under the action of water and SCCO2, the failure mode of bituminous coal changes from brittle failure to ductile failure. The cohesion and internal friction angle of coal sample have a near-linear relationship with moisture content. When the water saturation was 65%–80 %, the SCCO2–water–coal reaction was violent, and the damage degree peaked.

Enhancing the aroma of white whole sorghum flour using supercritical carbon dioxide

Removal of undesired odor-active compounds from sorghum flour is vital for the widespread production of sorghum-based foods. This study investigated the use of supercritical carbon dioxide (SCCO2) for the extraction of volatile compounds (VCs) from white sorghum flour. The extraction temperature (33.18–66.81 °C), pressure (8.18–41.82 MPa), and time (1.32–4.68 h) were optimized for the removal of 11 VCs (decane, undecane, tetradecane, dodecane, hexanal, nonanal, hexanol, dodecanol, limonene, styrene, and butylated hydroxytoluene) from whole white sorghum flour using a central composite response surface design. The maximum VC removal (∼89%) was obtained at 60 °C and 15 MPa with 2 h extraction time. SCCO2 extraction at higher pressures (> 15 MPa) or lower temperatures (<60 °C) did not improve the VC removal. After SCCO2 treatment, water absorption index, oil absorption capacity, and swelling power increased, whereas moisture/lipid contents, water solubility index, and particle size reduced significantly (p<0.05). The lightness of the sorghum flour treated with SCCO2 increased significantly compared to untreated sorghum flour, while the yellowness decreased after SCCO2 extraction (p<0.05). Overall, this study developed a novel green approach to enhancing the aroma of sorghum flour, which has a high potential for scale-up, and generating sorghum flours with more neutral flavors for numerous food applications.

Non-Thermal Supercritical Carbon Dioxide Processing Retains the Quality Parameters and Improves the Kinetic Stability of an Araticum Beverage Enriched with Inulin-Type Dietary Fibers.

Fruit-based beverages have been considered excellent food vehicles for delivering prebiotics. However, the conventional thermal processes currently used to microbiologically and enzymatically stabilize these products may cause significant losses in their sensory, physicochemical, nutritional, and bioactive characteristics. Thus, in this study, we evaluate the effect of different levels of pressure (8, 15, and 21 MPa) and temperature (35 and 55 °C) on the characteristics of an inulin-enriched araticum beverage processed with non-thermal supercritical carbon dioxide (SC-CO2) technology. The temperature showed a significant effect on total soluble solids, pH, particle size distribution, and kinetic stability. In contrast, pressure affected only the particle size distribution. The interaction between pressure and temperature influenced the total soluble solids, pH, and particle size distribution. Color parameters, ζ-potential, and glucose and fructose contents were not modified after all SC-CO2 treatments. Moreover, the SC-CO2 treatments preserved the inulin molecular structure, thus maintaining its prebiotic functionality. Overall, the SC-CO2 treatment did not alter the sensory, nutritional, and functional quality of the beverage, while improving its physical stability during storage. Therefore, non-thermal SC-CO2 treatment can be an alternative to current conventional processes for stabilizing inulin-enriched fruit-based beverages.

Relationship between pore structure and mechanical properties of bituminous coal under sub-critical and super-critical CO2 treatment

Geological sequestration of CO2 in unminable coal seams is one of the effective ways to reduce greenhouse gas emissions and increase coalbed methane production. However, changes in the pore structure after CO2 injection may affect the mechanical properties of the coal reservoir, posing a challenge to the long-term safety of CO2 sequestration. Therefore, a proper understanding of the relationship between pore structure and mechanical properties of coal under CO2 treatment is essential. In this paper, Low-field nuclear magnetic resonance tests were carried out on bituminous coal after sub/super-critical CO2 (Sub-CO2/Sc-CO2) treatment, and uniaxial compression tests were used to analyze the mechanical properties and energy evolution of coal samples. The results demonstrate that the CO2 treatment increased the porosity and proportion of macropores, and the effect of Sc-CO2 treatment on the pore structure was more significant. Compared to the Sub-CO2 treated sample, the uniaxial compressive strength and elastic modulus decreased more in the Sc-CO2 treated sample, which may be related to the extraction capacity of Sc-CO2. Analysis of the energy evolution shows that more energy was converted into dissipated energy in the loading process of Sc-CO2 treated coal samples, which was used to form, expand and connect fractures. Moreover, the correlation between the rate of change in porosity and the rate of change in uniaxial compressive strength was 0.9579, indicating that changes in pore structure were the main cause of the change in the mechanical properties of coal. A conceptual model was proposed to explain the mechanism of the effect of the pore structure on the mechanical properties, and pressure selection during CO2 sequestration was discussed. Therefore, the results of this study are expected to provide references for the long-term safety assessment and injection pressure selection of CO2 sequestration.