Journal of Supercritical Fluids最新文献

Investigation of the transcritical coaxial swirl injectors, considering their geometrical features along with the thermodynamics nonidealities, is of central importance in science and technology. Toward this aim, the mixing dynamics of transcritical bi-swirling jets has been investigated numerically. The scale-adaptive simulation method which allows formation of a turbulent spectrum is employed to close the governing equations. The Soave-Redlich-Kwong equation-of-state along with a required portion of standard database of the national institute of standards and technology are applied to the numerical framework to estimate the real-gas thermodynamic and transport properties, respectively. Results reveal that the present numerical framework accommodating a rather low-cost turbulence approach is capable of predicting the main characteristics of transcritical coaxial injectors, including central vortex core, central recirculation zone, Kelvin-Helmholtz instabilities, and vortex interaction. Analyzing oscillatory flowfield dynamics via the power-spectral-density and proper-orthogonal-decomposition techniques highlights the prominent influences of shedding, pairing, and merging of the vortices as well as the hydrodynamic Kelvin-Helmholtz instabilities on nearfield mixing dynamics. Effects of transcritical injector back-pressure on the characteristics flow features have been studied for the first time within a wide pressure range. Numerical simulations indicate that mixing quality, in terms of characteristics time- and length-scales, increases with the ambient pressure.

The sequential extraction of spent coffee grounds (SCG) oil by compressed propane and butane (CPE and CBE) followed by the extraction of phenolic compounds by supercritical CO₂ (scCO₂) plus solvent was studied. Extraction with CPE and CBE at different conditions of pressure (2 – 10 MPa), temperature (40 – 80 ˚C), particle size (0.356 and 0.867 mm), static extraction time (0, 10, 30 and 60 min), dynamic extraction time (25 and 60 min) and solvent flow rate (1, 2 and 3 g/min) reached the maximum extraction yield around 11.5 wt%, and with similar overall extraction curves. The second step of extraction with scCO₂+EtOH (2:1) increased the recovery of phenolics (expressed as GAE, gallic acid equivalent) from 0.9 mg GAE/g_SCG (single-step extraction scCO₂+EtOH (2:1) to 3.88 mg GAE/g_SCG (second step of sequential extraction). The results showed the technical feasibility of the extraction of oil and phenolic extracts by the studied approach.

The study aimed to investigate the partial upgrading of bitumen in the absence of water (non-water) and the presence of supercritical water (SCW). Partial upgrading experiments were conducted at the target temperature of 420 °C, with the reaction time varying from zero to 60 min in a batch reactor. The liquid products were analyzed for density, viscosity, composition, total acid number (TAN), olefin content, and elemental analysis. The gas composition and morphology of solid products were also studied. The experimental results revealed that while partial upgrading of bitumen with SCW could accelerate improvement in oil quality, particularly in terms of API and viscosity, it concurrently led to elevated gas and coke formation levels. Moreover, the difference in the distribution of oil fractions between the two environments (absence and presence of SCW) tends to diminish with an extended residence time. Additionally, as the residence time increases, the efficiency of TAN reduction under SCW conditions is less pronounced compared to the non-water conditions. Liquid products obtained in an SCW environment exhibited higher olefin content (between 3 and 4 wt %) compared to non-water conditions (between 1.8 and 2.7 wt %). In both environments, the olefin content was initially increased up to a residence time of 20 min and then decreased. Regarding heteroatoms, the sulphur (S) and nitrogen (N) contents decreased up to 36 % and 72 %, respectively, while a greater reduction was observed in the presence of SCW. More non-hydrocarbon gases (H₂S, CO₂ and CO) were produced in the presence of SCW. SEM images showed that an extended residence time led to a shift in coke morphology towards a more uniform and compact structure, regardless of the upgrading environment. However, the porous structures of coke samples obtained under SCW are distinguished from those formed without water, which is attributed to the phase inversion of precursors. The findings of this study confirm that SCW plays a beneficial role as a solvent in the partial upgrading of bitumen, expediting the process. However, the increased level of coke formation and olefin contents suggest that it may not function effectively as a hydrogen donor in the process.

This study focused on the effects of the CO₂ phase on the formation mechanisms of residual water. Based on nine groups of core-flooding experiments, the order of residual water saturation was gaseous CO₂ > supercritical CO₂ > liquid CO₂, and a quantitative power function relationship between residual water saturation and displacement time for different CO₂ phases was proposed. The experimental results show that when CO₂ transitions from the gaseous phase to the supercritical phase and then to the liquid phase, the decrease in the interfacial tension and cosine value of the contact angle in two-phase flow can lead to a decrease in residual water saturation. Meanwhile, an increase in the viscosity ratio of two-phase flow weakens the viscous fingering phenomenon and can also lead to a decrease in residual water saturation. However, the logCa-logM stability phase diagram reveals that the viscous force is the primary factor influencing all core-flooding experiments.

A very convenient method was developed to synthesize five dispersed anthraquinone dyestuffs using the readily available starting material 1,4-diaminoanthroquinone. This dye was prepared for coloration on nylon fabrics with supercritical carbon dioxide (ScCO₂). All the synthesized dyes were characterized by ¹H NMR, ¹³C NMR, and HRMS techniques. The UV-Vis absorbance measurements for all the dyes were carried out, and the results indicated that the absorption peak wavelength of the dyes was approximately 570–641 nm in the blue region. Further, these dispersed dyes were dyed on nylon fabrics with supercritical CO₂. After dyed fabrics were tested, the color strength of K/S value and color fastness were tested using like washing, crocking, and sunlight. Additionally, it determines the sweat fastness of dyed nylon fabrics under acidic and basic conditions. The dyes are readily involved in the nucleophilic addition of amino (-NH₂, nylon) functional groups to nylon fabrics in an alkaline medium. Therefore, our results showed that these dyes are commercially the most satisfactory, environmentally efficient dyes and practically exhibit sufficient color uniformity.

The kinetics of supercritical extraction from L. rivularis stalks using CO₂ were studied in terms of temperature (40−60ºC), pressure (18–30 MPa), specific CO₂ consumption (30−50 kg/kg d.s.), and particle diameter (0.5−1.1 mm). The extraction yield was found to range from 17.30 to 27.23 g/kg d.s. The highest extraction yield was obtained at 40°C, 30 MPa, 30 kg CO₂/kg d.s., and mean particle size of 0.5 mm. The yield increased with pressure and decreased with temperature and particle size (p≤0.05). The diffusion model based on Fick's 2nd law adequately described the cumulative extraction curves, using the effective diffusion coefficient (D_e) as the adjusted parameter, which ranged between 3.50 and 19.26×10⁻¹² m²/s. The Biot number was estimated, indicating a prevalence of internal control to mass transfer resistance. Additionally, the “apparent solubility” was obtained from the initial slope of the cumulative extraction curves. The extraction yield correlated positively with apparent solubility (p≤0.05) and D_e coefficient (p≤0.05).

In order to design a NiCr coating with the strongest corrosion resistance, the corrosion behavior of Ni, Ni10Cr and Ni20Cr coatings was studied using molecular dynamics, in which Ni20Cr coating exhibited the best corrosion resistance. The corrosion behavior of Fe9Cr heat-resistant steel with or without Ni20Cr coating in a supercritical CO₂ at 650 ℃ and 15 MPa for 1000 h was carried out by corrosion test, which significantly reduced the experimental period and cost. The Ni20Cr coating was intact and uniform after exposure for 1000 h. A dense and continuous Cr-rich oxide film with low growth stress could rapidly formed on the Ni20Cr coating. The Ni20Cr coating could effectively enhance the corrosion and carburization resistance of Fe9Cr heat-resistant steel.

Experimental and modelling investigations of supercritical CO₂ extraction of oil from Juglans regia L. kernels were conducted at 200 and 400 bar, 313 and 333 K at a CO₂ flow rate of 0.1 kg/h. Regardless of the pressure and the temperature, the highest achievable yield was estimated at about 0.7 kg_oil / kg_biomass. The extraction kinetics were modeled with Sovová’s broken and intact cells model. Walnut oil apparent solubility in supercritical CO₂ was determined and modelled with the Chrastil equation. A retrograde solubility behaviour was observed at 200 bar, the faster extraction kinetics were found at 400 bar and 333 K. The fatty acid composition of the supercritical CO₂ extracted oil was compared to the quality of the oil extracted by press and n-hexane Soxhlet extraction.

A practical, stable and non-conventional supercritical carbon dioxide deposition precursor was used to prepare Pd/MWCNT nanoparticles. The bis(2,2’bipyridyl)palladium(II) chloride precursor has a similar solubility value to commercially used precursors while advantageously it can be reduced at moderate temperatures. Palladium nanoparticles, whose particle size distribution were estimated around 10.5 nm, was deposited on multi-walled carbon nanotube support at 80 ºC and under 20.6 MPa. The catalyst showed higher performance for the selected model Suzuki-Miyaura cross-coupling reaction when compared with a similar catalyst which was prepared under similar supercritical conditions but from a different precursor. In general temperature and pressure is the main parameters to tune material properties for this method. Hence, this study reveals how different precursors in supercritical deposition method may affect the material properties for the target applications.

The transformation of thermoplastic polyurethanes into polymeric foams is attracting great interest nowadays. However, this technology has some challenges that it is necessary to resolve, being one of the most important the shrinkage suffered by the polymeric foams over time. For that reason, this work explores several alternatives to mitigate this phenomenon. These alternatives are divided into two groups: on the one hand, the refoaming of the shrunken foams using supercritical CO₂ and N₂ was explored; on the other hand, the foaming using mixtures of supercritical CO₂ and N₂ as foaming agents was carried out. After experiments, it was seen that, the refoaming with N₂ of shrunken foams obtained by supercritical CO₂ technology can increase and keep constant the initial expansion ratio of the shrunken foams. Moreover, it was also observed that ratios of CO₂/N₂ between 80/20 and 60/40 can avoid the shrinking issues suffered by the polymeric foams after foaming using supercritical technology.