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The production of fine particles by green technology like supercritical carbon dioxide requires the assessment of substantial solubility data at high pressures. This study represents the first determination of the solubility of methyldopa in carbon dioxide at pressures and temperatures ranging from 12 to 30 MPa and from 313.2 to 343.2 K, respectively. The mole fractions were obtained under the aforementioned conditions and ranged from 0.805 × 10⁻5 to 11.345 × 10⁻5. Four empirical models (Chrastil, Bartle et al., Mendez-Santiago, & Teja, and Kumar-Johnston) and two equations of state (Peng-Robinson and Soave-Redlich-Kwong) were used to correlate drug solubility. The K-J model demonstrated the highest accuracy, with an AARD of 8.38% and a R2 value of 0.988. Furthermore, the enthalpy values for the drug in SC-CO₂ were estimated using the Chrastil and Bartle models, resulting in values of 34.35 and 56.87 kJ·mol⁻¹, respectively. The results demonstrate that the SRK more pronounced results than the PR model, with an AARD% of 23.03 and a R2 value of 0.903 compared to 26.42 and 0.837. The article's conclusions provide a valuable reference for the application of green method in the production of fine particles of methyldopa. [ABSTRACT FROM AUTHOR]

The results of experimental modeling of glassy carbon production from high-pressure supercritical fluid (SCF) in the C–O–H system at a temperature of 800°C and pressures of 500 – 1000 atm are presented. Acomprehensive characterization of the carbon material is presented, using the data from CHNS-O analysis, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), x-ray and electron diffraction, infrared and multiwavelength Raman spectroscopy (Raman). In light of the characteristics and outcomes of the comparison with industrial glassy carbon, the synthesized carbon material was classified as a glassy substance. The findings of the experimental studies provide evidence for potentially different mechanisms of formation and, consequently, polygenicity of the glassy state of carbon. The material obtained through a radically distinct production method (polycondensation) may possess distinctive surface and bulk properties. [ABSTRACT FROM AUTHOR]

We show that supercritical fluids or melts are verifiable by critical high-temperature and high-pressure minerals like diamond, lonsdaleite, and others in crustal rocks as foreign minerals. In combination with the pseudo-binary solvus curves (temperature versus water content of silicate melts) with the Lorentzian distribution of some ore-forming elements, which are untypical for hydrothermal forming processes, we have solid proof for the interaction of mantle fluids and crustal rocks (granites). In this contribution, we restrict ourselves to a small number of critical observations, in particular on cassiterite polytypes. [ABSTRACT FROM AUTHOR]

A high-temperature supercritical CO 2 (ScCO 2)-assisted post-treatment strategy is developed to simultaneously modify the bulk and surface structures of graphitic carbon nitride (g-C 3 N 4) using ScCO 2 as penetrant and a small amount of methanol/acetonitrile mixture as modifiers. Specifically, the product of modified g-C 3 N 4 is obtained through the post-treatment of pristine g-C 3 N 4 in a homogeneous ScCO 2 /methanol/acetonitrile system, continuously heating to reach a target temperature (330 °C, 15.2 MPa) without a residence time. With the assistance of ScCO 2 , organic molecules penetrate the interlayers of g-C 3 N 4 and subsequently modify the in-plane structure of g-C 3 N 4. Methanol induces the partial transformation of g-C 3 N 4 into a carbon nitride with a poly(heptazine imide)-like structure and with abundant methyl and hydroxyl groups. Simultaneously, acetonitrile polymerizes into 2,4,6-trimethyl-1,3,5-triazine, which is then covalently grafted onto the surface of modified g-C 3 N 4. Remarkably, the entire post-treatment process is completed within 5 min, achieving a final product yield of 92.3 %. The modified g-C 3 N 4 photocatalyst achieves an H 2 -evolution rate of 2126.1 μmol·h−1·g−1 and a CO 2 -to-CO conversion rate of 874.1 µmol·h−1·g−1. This work provides a green, efficient, high-yield, and scalable strategy for preparing layered and porous non-metallic photocatalysts using supercritical fluids technology. [Display omitted] • High-temperature supercritical CO 2 -assisted strategy is developed to modify g-C 3 N 4. • Supercritical CO 2 functions as penetrant and organic solvents serve as modifiers. • CH 3 OH modifier causes formation of isotype heterojunction in the bulk structure. • CH 3 CN modifier causes graft of triazine functional group on the surface. • Bulk and surface modifications synergistically enhance the photocatalytic activity. [ABSTRACT FROM AUTHOR]

The solution of a supercritical fluid flowing into a constricted narrow channel is presented in this study. The compressible Navier-Stokes equations in the lubrication limit coupled with the energy equation and the isothermal and non-isothermal van der Waals fluid and perfect gas have been solved. In order to find the semi-analytical solution of these non-linear coupled equations, homogenization technique in the transverse direction has been applied. Because of the high compressibility and high thermal expansion of supercritical fluids, waviness is observed in the flow and thermal fields near the exit of the channel. This effect is attributed to the channel constriction where the slope is maximum, where a strong coupling between the pressure and density gradients exists. Moreover, the density difference between the exit and inlet of the channel drastically increases when one approaches the critical point, corroborating the data from existing literature. [ABSTRACT FROM AUTHOR]

Heat transfer at supercritical pressure (SCP) transiting from liquid-like (LL) to gas-like (GL) state is a compressible flow featured by a nonuniform density field. Pulsating flow has been confirmed as an effective approach to enhance heat transfer. However, pulsating flow introduces pressure waves, the interaction of which with the nonuniform density field remains an open question. This paper numerically studies a fundamental interaction problem to bridge the research gap. The physical model is a round GL fluid surrounded by LL fluid, forming a circular pseudo-interface for CO 2 at an SCP of 7.6 MPa. A compression wave is introduced into the domain by the sudden moving of an imaginary piston at 1 m/s. The compression wave induces a complex wave system after interacting with the pseudo-interface. The nonuniform acceleration by the compression wave results in a higher velocity in the GL region than in the LL one. Due to the Kelvin–Helmholtz instability, decomposition and mixing of the GL region then take place. Overall, the uniformity of density and temperature is improved on the microsecond timescale, manifesting that heat transfer is enhanced. This paper reveals nonuniform acceleration and Kelvin–Helmholtz instability as fundamental mechanisms for enhancing heat transfer at supercritical pressures via pulsating flow. • Wave interacting with a nonuniform temperature/density field under a supercritical pressure is explored. • Nonuniform acceleration of the compression wave makes low-density region move faster. • Ensuing Kelvin–Helmholtz instability leads to homogenization. • They are underlying mechanisms for the enhanced heat transfer in pulsating flows. [ABSTRACT FROM AUTHOR]