Journal of Supercritical Fluids最新文献

The concentration of oxygenated monoterpenes (oxyterpenes) in orange peel oil by supercritical fluid adsorption (SFA) was investigated varying pressure (10–24 MPa) and temperature (40–60 ºC) and using silica aerogels as adsorbent. Dynamic solubility experiments were conducted to obtain the solubility of the monoterpenes in supercritical CO₂, revealing that it increases with pressure regardless of temperature. For SFA, 10 MPa and 60 ºC was the most appropriate condition to concentrate oxyterpenes, leading to the lowest solubility of oxyterpenes and highlighting the advantage of lower densities for SFA’s selectivity. Furthermore, this condition yielded the highest concentration factors for oxyterpenes (4.3 for linalool and 6.5 for α-terpineol) within the 80–90 min interval. These findings contribute with valuable insights to SFA processes to concentrate oxyterpenes from orange peel oil, which has the potential to enhance the market value and functionality of this important product from citrus industries.

The catalytic oxidation of benzene with nitrous oxide (N₂O) over ZSM-5 zeolite has been carried out in a continuous-flow reactor under supercritical conditions and compared with the results of the gas-phase reaction. Aromatic substrates and nitrous oxide under the conditions of supercritical experiments (300–435 °C, 6.0–18.0 MPa) are both reagents and the supercritical medium. It has been established that the productivity of the supercritical oxidation of benzene into phenol significantly exceeds the productivity of the gas-phase process owing to the limited reversible deactivation of the catalyst under supercritical conditions and the in situ removal of the coke precursors by the dense reaction medium. In addition, it has been demonstrated that a successful in situ regeneration of the deactivated oxidation catalyst can be carried out during the transition from gas-phase reaction conditions to supercritical conditions in one experiment.

An approach to predict the gas permeability of membrane polymers after supercritical CO₂ treatment is proposed. The approach is based on the connection of the temperatures of secondary relaxation transitions with the effective sizes of mobile free volume elements in the polymers. The correlation between permeability of nitrogen and effective sizes of mobile holes for a set of polymers is established. The effect of supercritical CO₂ on the nitrogen permeability of polycarbonate, polysulfone, polyvinylbutyral is analyzed by FTIR spectroscopy of low-molecular weight conformationally-inhomogeneous compounds introduced in the polymers. Membranes were exposed at 40 MPa and 333 K for 4 h through static treatment and dynamic treatment separately. For polyvinylbutyral, the nitrogen permeability did not change after supercritical CO₂ modification while for polysulphone, the effective volume of mobile holes increased, but the nitrogen permeability decreased. For polycarbonate after supercritical CO₂, the effective volume of mobile holes and the nitrogen permeability increased.

In this paper, a new semi-empirical density-based model was developed to correlate drug compounds solubility in supercritical carbon dioxide (SC-CO₂) as a function of temperature and density of supercritical carbon dioxide. The proposed approach has successfully predicted the solubility of 282 pharmaceutical compounds accounting for 7469 experimental data points collected from literature published between 1994 and 2024. Several statistical metrics, including average absolute relative deviation (AARD=7.24 %), coefficient of correlation (R=0.9987), and coefficient of determination (R²=0.994) were used to validate the reliability of the proposed model and compared with twenty existing density-based models. The overall results demonstrate the accuracy of the proposed model and its suitability for the correlation of solubility.

Sequential extraction (SE) using supercritical CO₂ plus ethanol was applied to separate resin from bacuri fruit shell, where process parameters such as particle size, pressure and cosolvent use were studied. The extracts obtained were also analyzed for phenolic compounds and antioxidant capacity. The extraction results showed that SE was able to separate the resin, which is the first report described in the literature, resulting in a patent. Furthermore, the smaller particle size (0.25 mm) showed the higher extraction rates, providing good yields of lipid extracts (up to 10.09 wt%) and ethanolic extracts (up to 13.78 wt%). The extracts presented good levels of phenolic compounds, which was associated with its high antioxidant capacity. Thus, the application of SE added value to bacuri fruit shell, enabling new strands for potential applications in the food, pharmaceutical and cosmetic industries, placing this by-product in the Amazon bioeconomy scenario.

This action described the experimental equilibrium solubility of aprepitant (APT), an antiemetic drug for chemotherapy, in subcritical water (SW) with/without ethanol as co-solvent, acquired through a static method between 298.15 and 393.15 K and 0–15 % (w/w) of ethanol and the constant pressure of 10 bar. The mole fraction of APT was obtained in the range of 0.39×10⁻⁴ to 9.10×10⁻⁴ while its mole fraction by cosolvent varied from 0.75×10⁻⁴ to 22.98×10⁻⁴. The obtained results represented the significant effect of solvent temperature on the solubility of APT. For both studied systems, the solubility data was successfully correlated with two well-known semi-empirical temperature-based models, namely the linear and modified Apelblat models. Results from applying statistical criteria exhibited that the modified Apelblat model had the highest accordance with experimental data. Finally, using the obtained correlation results, the apparent thermodynamic analysis including enthalpy, entropy, and Gibbs free energy of dissolution for APT dissolved in SW was obtained.

SC-CO₂ fracturing technology is a feasible method for green extraction of unconventional oil and gas reservoirs. However, due to a series of problems such as sand transportation during SC-CO₂ fracturing, CO₂ thickening has become the focus of current research. Polymer thickeners have been widely used in oilfields. Due to the macroscopic nature and limitations of laboratory experiments, we have not been able to elucidate the microscopic mechanism of polymer thickening CO₂ and the viscosity change of the CO₂ fracturing fluid system downhole after polymer addition. In this study, we used all-atom modeling and molecular simulation of the COMPASSII force field. We selected nine polymers to study their microscopic properties and the factors affecting their effects. Finally, we simulated the viscosity change of the CO₂ system after the addition of polymer tackifiers in the wellbore under the CO₂ fracturing construction conditions by combining the data from one well in the oilfield.

In this study, strontium titanate (SrTiO₃) nanoparticles were obtained utilizing a one-step supercritical continuous solvothermal synthesis process involving acetylacetonate precursors for both strontium and titanium cations instead of the historical alkoxide ones. These precursors are expensive, difficult to access (especially for strontium isopropoxyde) and inadequately stable, forcing the use of a glove box and controlled atmospheres, which is not the case for acetylacetonates. Pure SrTiO₃ nanoparticles with a crystallite size of roughly 20 nm were successfully synthesized. In addition to the cubic structure of SrTiO₃, FTIR revealed surface functions that are typical of "wet" processes, while Raman spectroscopy showed the activation of non-centrosymmetric modes brought on by non-linear contributions. The nanoparticles show a faceted shape and are stable at elevated temperatures (up to 800 °C), according to in-situ high temperature XRD measurements. However, due to a chemical deficiency in strontium, titanium dioxide (TiO₂) phases are formed at higher temperatures. In-situ high temperature HRTEM investigations showed the existence of two populations of particles, with a better stability for the bigger-sized particles after thermal treatment as well as the sintering and restructuring of the smallest ones. Also, the microscopy results suggest the possibility of a chemical inhomogeneity within the crystallites. Overall, this study offers important new knowledge on the physicochemical characteristics of the synthesized SrTiO₃ nanoparticles and their thermal stability using a novel supercritical continuous solvothermal approach based on the use of acetylacetonate precursors.

Hydrothermal extraction of green coffee beans was examined by using a semi-batch type apparatus and an optical cell for extracting beneficial compounds. Extraction curves were evaluated across varying temperatures (373–523 K) and pressures (0.6–2.1 MPa). At 473 K, increasing pressure enhanced the extraction of caffeoylquinic acids (CQAs), total phenolic content (TPC), antioxidant capacity (AOC), and caffeine. At 2.1 MPa, TPC remained constant with temperature, while AOC, CQAs, and caffeine initially increased then decreased at higher temperatures. Direct observations confirmed high temperature promoted extraction. An extraction model was proposed to account for decomposition of components at high temperatures, effectively reproducing experimental curves. This model estimated equilibrium values and rate constants representing initial extraction rate. The obtained results indicate that adjusting temperature, extraction time, and pressure can control extract composition during hydrothermal extraction of green coffee beans.

In this work, we simulated the heat transfer in a two-vessel (1-m³, length-to-diameter ratio of 4) industrial plant to assess the effect of the temperature gradients formed during the reconditioning stage on the extraction curves. We simulated the extraction of 1-mm particles using 5 mm/s of CO₂ at 48 MPa and 40 °C (case with an imposed temperature gradient) or 60 °C (case with temperature gradients from the reconditioning stage), with the service fluid at 60 °C. The results of these non-isothermal extractions were compared with those obtained in representative isothermal cases. The temperature gradients slightly affected the cumulative extraction curves in non-isothermal cases. We considered the presence of a basket containing the solid substrate. We also changed the superficial CO₂ velocity to 3 or 10 mm/s and the particle size to 0.50 or 1.25 mm to compare the extraction curves. The effects of the basket and the changes in superficial CO₂ velocity and particle size were minor. We simulated a limit case with higher temperature and pressure (80 °C and 70 MPa), where the extraction time was extremely short (10 min) and more significant temperature gradients were formed during the reconditioning stage. We observed more significant differences at this extreme extraction condition than when using an isothermal process at the required extraction temperature.