Journal of Supercritical Fluids最新文献

For the crystallization of an API in supercritical CO₂, a two – step nucleation mechanism involves the apparition of metastable liquid droplets in the vapour phase composed of the API dissolved in the CO₂, before crystallization. To find out the pressure and temperature conditions such a two – step mechanism could be observed, we studied the stability / metastability / instability for {(S)-Naproxen + CO₂} and {(RS)-Ibuprofen + CO₂} vapour binary mixtures. Thermodynamic computations proposed in the paper, have shown that a mixture of API and CO₂ at elevated pressures can be unstable and/or metastable with respect to a liquid-vapour equilibrium and at the same time with respect to a solid-vapour equilibrium. Depending on the degree of supersaturation, such a mixture can potentially first decompose via spinodal decomposition into coexisting liquid and vapour phases, which turn due to nucleation and growth theory to a solid-fluid equilibrium.

Melting and crystallization temperatures of poly(ε-caprolactone)(PCL) exposed to CO₂ and N₂ have been evaluated at pressures up to 125 bar using High Pressure Torsional Braid Analysis. It is shown that in contrast to CO₂, exposure to high pressure N₂ does not lead to a significant depression of T_m or T_c. Instead, these transition temperatures tend to increase in nitrogen, reflecting more of a hydrostatic pressure rather than a solvent effect. Another factor that may play a role is the fluid-induced crystallization which tends to increase the melting temperature. By conducting foaming at properly selected temperatures along the rigidity reduction paths which are scaled with respect to the melting temperatures in CO₂ or N₂, foams with low bulk foam densities of about 0.2 g/cm³ could be generated in CO₂ at 100 bar and in N₂ at 200 bar.

Porous surfaces show great potential for superhydrophobic applications. Supercritical CO₂ foaming is a green technology for preparing porous materials, but it is rarely used to prepare porous surfaces due to the non-porous skin caused by the escape of gas. In this study, a porous thermoplastic polyurethane (TPU) surface with dense cell and small cell spacing is prepared by employing bilayer TPU sheet to restrict the escape of gas from surfaces. The influence of the foaming pressure and temperature on the cells of the TPU surface is researched. Furthermore, bimodal cells are obtained by regulating the foaming process and the effect of cell structure on wettability is investigated. Subsequently, a flexible superhydrophobic material with low water-adhesion, mechanical stability, and self-cleaning properties is successfully prepared by modifying fluorinated silica particles on porous TPU surfaces.

Olive pomace has high economic potential and the supercritical technology for extraction produces oil with potential use in the food and biofuels industries. The remaining solid can be used to obtain fermentable sugars from the hydrolysis. The present work aims to evaluate the effect of supercritical fluid extraction (SFE) of pomace olive oil at 60 and 40 °C and 18 and 22 MPa on oil yield and composition. Furthermore, use the remaining solid of SFE to obtain fermentable sugars from enzymatic hydrolysis. Kinetic curves were obtained for SFE, with the best oil yields 19.36 ± 2.43 wt% obtained at 40 °C / 22 MPa. The antioxidant activity was better for (60 °C / 22 MPa) presenting 137.87 ± 1.04 µmol TEAC / g am. dry. The highest yield of fermentable sugar (Y_FS) was 41.02 ± 4.79 g defatted olive pomace (DOP) for 26 Filter Paper Unit (FPU) / 1% solid loading (CS).

This study explores the efficacy of electrospun polyvinyl alcohol (PVA) nanofibers loaded with C.I. Disperse Red 60 (DR60) as dyeing agents for polyethylene terephthalate (PET) fabrics in a supercritical carbon dioxide environment. The fabrication of DR60-loaded PVA nanofibers (DR60/NF-1) involved a spinning solution containing water and dimethyl sulfoxide. Analysis revealed that PET fabrics treated with DR60/NF-1 exhibited significantly higher K/S values (8.51) compared to those treated with DR60 powder (3.19), resulting in visibly distinct coloration among dyed fabrics (ΔEab: 17.77). Additionally, DR60/NF-1 demonstrated superior dye uptake by PET fabrics (15.07 mg/g) at a dosage of 3% (o.w.f.) compared to DR60 powder (13.19 mg/g) at a dosage of 4% (o.w.f.). These findings underscore the potential of DR60-loaded PVA nanofibers to enhance coloration and dye uptake in PET fabric dyeing processes conducted under supercritical carbon dioxide conditions, offering promising avenues for advancing efficiency and sustainability in textile manufacturing.

Supercritical hydrothermal combustion is a novel, clean, and efficient combustion method. In this work, a mechanism-based kinetic model of ethanol appropriate for high-pressure hydrothermal environment was developed. Combined with theoretical analysis and continuous ignition experiments, the transient ignition process, ignition temperature, and extinction temperature were discussed. A turbulent combustion model coupling detailed kinetics was constructed to analyze the co-flow diffusion hydrothermal flame. It was found that the ethanol kinetic model can well predict the reaction process, critical ignition temperatures, extinction temperatures, and diffusion combustion process of hydrothermal combustion. The ignition temperatures of 2.40–5.72 wt% ethanol ranged between 500–390 °C, and OH was a significant ignition indicator. As an auxiliary fuel, ethanol is superior to methanol. During co-flow hydrothermal combustion, the interfacial reaction between fuel and oxidant in jet core area had an important influence, and the local high-temperature flame was mainly distributed near the downstream of fuel jet.

This study explores the core-shell structure formation mechanisms of primary carbon nanospheres (PCNs) through hydrothermal carbonization (HTC) of glucose at 200 °C, focusing on key phase-change polymerization reactions. Colloidal carbon nanoparticles in the aqueous phase filtrate self-assembled into secondary carbon nanospheres (SCNs) with intrinsic hollow structures during room temperature storage. FTIR results revealed similar functional groups on the surfaces of PCNs and SCNs due to esterification reactions during HTC cooling. XPS and ¹³ C NMR analyses identified HMF aldol condensation and etherification as dominant reactions for PCNs, while esterification and aldol condensation with levulinic acid were dominant for SCNs. The hypothesis suggests that PCNs initially formed hollow microframeworks but collapsed due to consumption of encapsulated organics, resulting in hydrophobic cores. These cores grew through aggregation (linear) and surface reactions (exponential), internalizing hydrophilic surfaces into hydrophobic cores, forming the final core-shell structure of PCNs.

Dichlone, also known as 2,3-dichloronaphthalene-1,4-dione, is a solid organic substance employed in the field of agriculture for its fungicidal properties and as a retardant for vegetable decomposition. The bioactive properties of dichlone can be enhanced by modifying its structure, specifically through the synthesis of new derivatives achieved by replacing the functional groups within its molecular structure. Two new solid dichlone derivatives were synthesized in this work, namely 2-chloro-3-((4-fluorobenzyl)amino)naphthalene-1,4-dione (dCl-2B-F) and 2-chloro-3-((4-fluorophenethyl)amino)naphthalene-1,4-dione (dCl-3 P-F) and measured their solubility in supercritical carbon dioxide at (313, 323, and 333) K and pressures between (9. to 32) MPa. The results indicated that solubility ranged between 30.5 and 47.9 µmol of solute/mol of CO₂ for dCl-2B-F, and from 2.2 to 243.5 µmol of solute/mol of CO₂ for dCl-3 P-F. The solubility data of dichlone and its synthesized derivatives (dCl-2B-F, dCl-3 P-F, 2-chloro-3-((4-chlorobenzyl)amino)naphthalene-1,4-dione (dCl-2B-Cl), 2-chloro-3-((4-chlorophenethyl)amino)naphthalene-1,4-dione (dCl-3 P-Cl), 2-(benzylamino)-3-chloronaphthalene-1,4-dione (dCl-2B) and 2-chloro-3-(phenethylamino)naphthalene-1,4-dione (dCl-3 P)) was compared using the density-based correlation of Chrastil and the Statistical Associating Fluid Theory of Variable Range Mie-potential (SAFT-VR Mie) equation of state (EoS), to better comprehend the effects of the structural differences on the solubility. As a result, for the Chrastil model, a root mean square deviation (rmsd) of 3% was obtained for dCl-2B-F and 16% for dCl-3 P-F, whereas for the SAFT-VR Mie equation, it averaged 24% for dCl-2B-F and 28% for dCl-3 P-F. It was found that the solubility of the homologous compounds, differing only in one methylene group, increased with solute size (-2B derivatives were less soluble in CO₂ than the −3 P ones), contrary to the expected trend, which could be attributed to the increased probability of ring-to-ring interactions as the chain length connecting the rings decreases. This demonstrates that geometric factors, along with the pressure and temperature, affect the behavior of the solubility and these should be accurately represented in the predictive models.

This study investigates the production of furfural via formic acid-catalyzed dehydration of xylose and the effect of simultaneous extraction of furfural using supercritical carbon dioxide (Sc-CO₂). The addition of Sc-CO₂ results in a secondary reaction pathway comprised of two steps: CO₂-catalyzed isomerization of xylose into the reactive intermediate xylulose, followed by furfural production from xylulose, catalyzed by formic acid. Xylose dehydration with CO₂ in both batch and semi-batch systems yielded a higher furfural yield and selectivity compared with systems without CO₂. The Sc-CO₂ extraction in a semi-batch system prevents furfural degradation by maintaining high productivity, even with increased initial xylose concentration. A maximum furfural yield of 68.5% (71.4% selectivity and 99% separation efficiency) was achieved after 5 h at 140 °C and 20 MPa with a constant flow rate of 5 g/min of CO₂ and initial concentrations of 10 g/L of xylose and 10 wt% of formic acid.

To investigate the aerodynamic loss mechanisms in supercritical carbon dioxide turbine (CT) and steam turbine (ST) stages, entropy generation and entropy generation rate are used to analyze various losses in stage passages. The results reveal that under sealing clearance at 2.5 % blade height, the leakage losses of CT and ST constitute over 7 % of total available energy. Rotor and stator losses of CT and ST decrease as the Mach number of stage outlet increases. The endwall losses of CT and ST rotor are both predominant, constituting over 1.78 % of total available energy, with lower endwall losses of CT rotor. Furthermore, the stator profile loss of CT represents the majority of stator loss and is notably higher than that of ST. The impact loss and separation loss are more pronounced in CT. The conclusions will provide direction, guidance, and data support for the design and optimization of CT and ST.