Supercritical water gasification (SCWG) enables the direct conversion of high-moisture biomass waste into combustible gases, providing high efficiency and economic benefits owing to the absence of a drying process. Sake residue, a biomass waste with high moisture and low ash content, shows potential as a novel source of bioenergy. Therefore, understanding the characteristics of SCWG is crucial. In this study, a continuous-flow reactor was used to conduct experiments on different phases of sake residue (mixed phase, solid phase, and liquid phase) under a pressure of 25MPa and a temperature of 600 °C, with varying residence times. A kinetic model for the SCWG of sake residues was established to confirm the detailed reaction mechanism and elucidate the reaction characteristics. The data were empirically fitted using a pseudo-first-order model under the present conditions, and the model fit the experimental data well. The results indicated no interaction between the different phases of the sake residue, with the solid phase decomposing faster than the liquid phase. Additionally, the impact of adding activated carbon, known to promote the water-gas shift reaction in the SCWG of sake residue, was investigated.
Reduced graphene oxide (rGO) is a promising electrode material for supercapacitors, yet its electrochemical performance is often limited by poor conductivity and a severe restacking tendency. Heteroatom doping with nitrogen (N), sulfur (S), and fluorine (F) can significantly improve the surface and electronic properties of rGO. Herein, we synthesized and compared co-doped rGO structures using NH4F and NaF as doping precursors, while optimizing the precursor concentration for the NaF doped samples. Interestingly, a controlled amount of Na+ ions from NaF could affect on the electrochemical active sites. SEM observation reveals that the porous rGO structure remains intact after doping. Deconvolution of the Raman spectra shows higher ID/IG and AD/AG ratios for the NaFSN-rGO samples, indicating successful defect generation by the dopant atoms. Furthermore, EDX analysis confirms the successful incorporation of dopants into the rGO matrix, showing excellent agreement with other characterization methods. The XRD spectra exhibit a broadening of the (002) peak from rGO to the doped rGO structures, reflecting a transition toward a more amorphous phase with increased interlayer spacing. Cyclic voltammetry curves confirm the pseudocapacitive charge storage mechanisms of the various co-doped samples NFS-rGO, NS-rGO and NaFSN-rGO. Pronounced redox peaks were observed for the NaFSN-rGO 0.2 sample, which achieved the highest specific capacitance of 176.67 F/g.These results highlight the critical role of precursor selection in producing active sites and accessible pathways on the rGO matrix for efficient charge transfer. Ultimately, both NaF and NH4F provide unique charge-transfer characteristics that enhance performance in electrochemical energy storage devices.
The Supercritical AntiSolvent (SAS) process exploits the chemical and thermodynamic properties of supercritical fluids, particularly upercritical CO2, to promote the controlled micronization and crystallization of target compounds. This technique has been successfully employed in the pharmaceutical industry for the production of solid Active Pharmaceutical Ingredients (APIs). The numerical modeling of SAS processes is commonly based on population balance equations formulated within a fully Eulerian framework. However, nucleation and crystal growth are intrinsically discrete phenomena, characterized by localized events occurring at the particle scale. In the present study, a novel modeling strategy is proposed in which the solid phase is treated using a Lagrangian approach, enabling explicit particle tracking resolved in both space and time. The investigated configuration consists of the injection of a minocycline-ethanol solution into a supercritical CO2 environment within a two-dimensional splitter-plate geometry, simulated using the compressible CFD solver SiTCom-B. The results demonstrate the capability of the proposed framework to generate particles consistently with the local thermodynamic and flow conditions.
In this study, treatment of multi-layer plastics in a semi-batch reactor using subcritical water was conducted to reveal the decomposition, elution, and recovery behavior. In particular, we performed non-steady operation of temperature ramping during the decomposition experiment and conducted qualitative analysis using UPLC/MS of 46 kinds of expected decomposition products, assuming sequential decomposition of the polymers. Nylon-6 underwent decomposition in two steps, where ε-caprolactam was first produced at around 120 °C, followed by the generation of ε-aminocaproic acid at around 270 °C. PET-derived decomposition products were also generated at a maximum temperature of 270 °C. In addition, PE remained undecomposed and could be recovered as a solid residue. Since individual recovery of decomposition products by simply varying the flow rate or temperature ramping rate proved challenging, we tried a two-stage heating process that included a holding temperature. The individual recovery of ε-caprolactam was partially achieved by holding the temperature at 100 °C to 150 °C.
The application of spoilers to rectangular printed circuit heat exchanger (PCHE) and the comparative assessment of their thermo‑hydraulic performance represents a relatively underexplored topic. In this work, a numerical investigation is performed on a rectangular PCHE and a conventional semicircular PCHE with hydraulic diameter (3.3mm) using supercritical CO₂ as the working fluid. The numerical model is validated against experimental data, with a maximum deviation of 16.0%, which is acceptable for engineering predictions. Simulations are conducted under low‑temperature recuperator conditions: hot side at 8–9MPa and 353–463K, cold side at 19.0–21.0MPa and 323–353K. Within the parameter ranges examined, the results indicate that heat transfer on the hot side is largely governed by specific heat capacity, whereas on the cold side, it is influenced by both specific heat capacity and thermal conductivity. The buoyancy‑induced secondary flow improves field synergy and heat transfer in the rectangular PCHE, but flattens the velocity profile and degrades heat transfer in the semicircular counterpart. Quantitative data indicate that, the rectangular configuration is recommended for the design of hot‑side channels in PCHE, as its comprehensive performance is expected to increase by 11.5% overall. Benchmarking classical supercritical CO₂ heat transfer correlations against simulation datasets reveals universal underprediction for the rectangular PCHE. Revised empirical correlations are separately developed for the hot and cold sides, yielding maximum deviations of 2.4% and 6.8%, respectively, from the simulation data.
Cosolvent-assisted supercritical CO2 (SC-CO2) extraction provides a promising strategy for the clean removal of organosulfur compound from coal. However, different cosolvents lead to different desulfurization performances, and the underlying molecular mechanisms remain insufficiently understood. In this work, molecular dynamics simulations were performed to investigate organosulfur dissolution behavior in SC-CO2-cosolvent mixed solvents and coal-cosolvent interfacial interactions using nine representative cosolvents. The results show that dibenzothiophene (DBT) exhibits the highest dissolution extent in the SC-CO2-hexane solvent, but complete dissolution is not achieved in any of the investigated systems. DBT dissolution in SC-CO2-cosolvent systems is influenced by multiple factors, including solvent-solute polarity matching, molecular structure, and cosolvent molecular size. Analysis of coal-cosolvent interfacial interaction energies shows that van der Waals interactions dominate interfacial stabilization in all systems. Among the investigated cosolvents, methanol exhibits the strongest interaction with coal, with a relatively large electrostatic contribution. These results indicate that enhancing coal-cosolvent interfacial affinity, rather than solely increasing organosulfur dissolution ability, is important for improving SC-CO2-based coal desulfurization. This work provides molecular-level guidance for the rational screening and design of cosolvents for clean coal utilization.
In this study, hydrothermal leaching of LiFePO4 (LFPO) cathode materials with citric acid was conducted with the purpose of achieving high leaching efficiencies of Li, Fe, and P at high pulp densities within 10min. As two most critical parameters, the temperature and acid concentration were mainly optimized. The results indicate that conditions of 100 °C with 2mol/L citric acid and 180 °C with 4mol/L citric acid are conducive to maintaining high leaching efficiencies at high pulp densities. With consideration of reducing energy and chemical consumption, the former condition was selected, achieving high leaching efficiencies for Li, Fe, and P at 100%, 98.8%, and 95.3%, respectively, at a pulp density of 30g/L. Furthermore, a process of separating elements from leachates obtained from hydrothermal leaching of LFPO with citric or oxalic acid was proposed. High-purity (>99.6%) Li3PO4 microparticles were obtained with P separation efficiencies exceeding 92.5% using both leaching agents. Meanwhile, high-purity (99.4%) Fe products with 98.5% separation efficiency were recovered from the citric acid leachate in the form of iron hydroxides, FeOOH, and Fe3O4 precipitates. In contrast, in the oxalic acid system, 99.0% of Fe was directly recovered as FeC2O4 during the oxalic acid hydrothermal leaching process, with a purity of 99.2%. This work significantly advanced the hydrothermal leaching of LFPO using citric or oxalic acid, contributing to the sustainable recycling of spent lithium-ion batteries and promoting the potential industrial application of the organic acid-based hydrothermal leaching technology.
Pumpkin seed oil is oil rich in oleic, linoleic, and palmitic acids fatty. In our study, a two-stage extraction method has been used to encourage a higher yield and the quality of the oil. The first step was carried out with supercritical carbon dioxide (scCO₂) in the pressure range from 200bar to 800bar and temperatures of 40 °C and 60 °C. For the second step subcritical propane was used, at a pressure of 50bar and 100bar, and the same temperatures that were used previously for the first step of scCO2 extraction. The extraction kinetics were modelled using Brunner’s semi-empirical approach, which showed good agreement with the experimental data (R² > 0.97), confirming its suitability for both solvents. The combination of both extraction steps increased the overall yield, with the highest value of 45.3% obtained within the investigated pressure range (200-800bar) at conditions of 600bar and 60 °C (scCO₂) and 100bar and 60 °C (propane). An analysis of the fatty acids (FA) by gas chromatography (GC) showed a stable fatty acid profile dominated by oleic acid (up to 48.56%), followed by linoleic acid. The second extraction step with propane enabled recovery of the residual oil remaining in the matrix successfully after the scCO₂ extraction. The presented integrated approach demonstrates that sequential application of environmentally friendly solvents can increase the overall recovery of pumpkin seed oil while providing solvent-free extracts with a high content of unsaturated fatty acids.
Hybrid aerogels combining high-performance and renewable fibers offer a promising pathway for the fabrication of lightweight and thermally efficient insulation materials. In this study, aramid fiber–reinforced jute aerogel composites were fabricated via supercritical carbon dioxide drying. Nanostructural analysis revealed the formation of a three-dimensional interconnected network wherein aramid nanofibers (ANFs) and jute-derived nanofibers synergistically constructed a robust supporting framework. The incorporation of ANFs significantly enhanced the mechanical performance of the aerogels by approximately 22%−69% depending on the ANF content (25%−75%). The resulting aerogels exhibited low density (∼0.036gcm−3), high porosity (∼97%), large specific surface area ∼501m2g−1, high compressive strength (∼3.59MPa), and low thermal conductivity (∼0.027Wm−1K−1) at room temperature (23∘C). The enhanced performance was attributed to the synergy between rigid ANFs and flexible cellulose nanofibers, leading to improved structural integrity and thermal resistance. By integrating one of the strongest natural fiber material with a high-performance synthetic counterpart, this work presents a class of hybrid aerogels with great application potential in lightweight thermal insulation.
Carbon dioxide-rich streams may occur in high-pressure systems containing alcohols and glycols as thermodynamic hydrate inhibitors. Although binary CO2 + alcohol and CO2 + glycol systems have been investigated previously, experimental data on ternary mixtures of CO2, methanol, and ethylene glycol remain scarce, particularly at high CO2 contents. In this work, the phase behavior of CO2 + methanol + ethylene glycol mixtures was experimentally investigated and thermodynamically modeled. Two liquid-mixture compositions were evaluated: methanol-rich and ethylene glycol-rich systems. A total of 47 transition pressures were measured, including liquid–vapor, liquid–liquid, liquid–liquid–vapor, and near-critical transitions over a wide range of CO2 mole fractions. The results showed considerably higher CO2 solubility in methanol-rich mixtures, whereas ethylene glycol-rich systems exhibited limited CO2 miscibility. For the methanol-rich mixture containing 80 mol% CO2, an unusual density inversion between the coexisting liquid phases was observed and attributed to compressibility differences during depressurization. Thermodynamic modeling was performed using PC-SAFT, with new pure-component parameters for ethylene glycol and an optimized MEG + CO2 binary interaction parameter, and the Peng–Robinson equation of state coupled with HV-NRTL mixing rules. PR + HV-NRTL provided the best overall description of the experimental phase boundaries, whereas PC-SAFT showed stronger dependence on the adopted binary interaction parameters. Neither model reproduced the experimentally observed density inversion at the measured temperature. The new experimental data contribute to understanding high-pressure phase equilibria in mixtures containing thermodynamic hydrate inhibitors.
Incorporating inorganic nanoparticles into polymer films enabled the fabrication of functional polymer materials, but conventional approaches had limitations: melt mixing could bury the particles, while immersion-drying led to poor dispersion and weak adhesion. Supercritical carbon dioxide (scCO2) offered a solvent-free alternative, but the size of the nanoparticles, which was much larger than the dye molecules typically dissolved in scCO2, limited their dispersion and long-range transport, thereby restricting loading efficiency. Against this background, two scCO2-assisted supply pathways were developed to introduce decanoic acid-modified cerium oxide (CeO2) nanoparticles into polypropylene (PP) films: one was a supercritical dyeing method (SCDM), in which the nanoparticles were dispersed in situ within the bulk scCO2 phase; the other was a drop-casting-assisted supercritical impregnation method (DC-SIM), where the nanoparticles were pre-positioned on the surface of PP. Loading and distribution were characterised using UV–visible spectrophotometry, SEM/EDX and TEM/EDX. Control experiments confirmed that scCO2 was indispensable, and the swelling-induced free volume was necessary for incorporation. The bulk-transport-governed SCDM increased with time, temperature, and pressure, but the relationship with dosage was non-monotonic, reaching about 2.2 µg/cm2, whereas surface pre-positioning via DC-SIM raised the loading nearly tenfold, reaching approximately 19.8 µg/cm2, with near-linear dosage dependence and no saturation. Cross-sectional TEM/EDX revealed a cerium-rich band beneath the surface, confirming effective near-surface penetration. These two pathways thus operated complementarily and offered viable strategies for scCO2-assisted polymer functionalisation.
This work aimed to investigate the simultaneous pressurized liquid extraction (PLE) of oil from canola seeds (CS) and rice bran (RB). Ethanol was used as a solvent and the influence of temperature (40, 60 and 80 °C) and CS:RB ratio (60:40, 70:30 and 80:20, w/w) on oil removal and composition was determined. Soxhlet extraction was conducted for comparative purposes. The highest recoveries obtained by PLE were achieved at 80 ºC and CS:RB of 60:40 and 80:20, considering oil yield and active compound content. At this temperature, oil recovery from CS was 3.8 times higher than that obtained from RB. The fatty acid profile showed a balanced distribution between saturated and unsaturated fatty acids, with greater solubilization of the unsaturated fraction at 40 °C. The content of lipophilic compounds was influenced by temperature, since heating favored the extraction of γ-tocopherol and phytosterols (β-sitosterol and stigmasterol). γ-oryzanol, strongly associated with RB, showed a higher content in the oil obtained at 40 °C and CS:RB 60:40. Higher concentrations of phenolic acids were detected in oils obtained from extractions using higher concentrations of RB. Nicotinic acid was efficiently removed by PLE at 60 °C and 80 °C. The oils obtained at 80 °C and CS:RB 60:40 showed greater antioxidant potential, especially associated with ferulic acid. The oxidative stability of the oils was shown to be highly correlated with the levels of tocopherols and γ-oryzanol, compounds that act in protecting the oil against oxidation.
