SUPERCRITICAL FLUIDS have emerged as a unique and promising class of materials for various applications owing to their tunable physical and chemical properties. These FLUIDS are characterized by their state above the critical temperature and pressure, where they exhibit properties of both liquid and gas phases. Their properties, including density, viscosity, and diffusivity, can be finely tuned by precisely controlling their pressure and temperature. Furthermore, they possess excellent solvating properties that can dissolve a wide range of organic and inorganic compounds. SUPERCRITICAL FLUIDS are utilized in diverse fields, including materials science, pharmaceuticals, energy, and environmental remediation. Some of the popular applications include SUPERCRITICAL fluid extraction, SUPERCRITICAL drying, SUPERCRITICAL fluid chromatography, and SUPERCRITICAL fluid in materials sciences. This review provides an overview of the basic principles of SUPERCRITICAL FLUIDS, their unique properties, and their recent advances and applications in different scientific fields

The aim of this paper is to provide a comprehensive mathematical model to describe the SUPERCRITICAL fluid extraction of vegetable oils. The complexity of the plant solid matrix structure, the effect of size, controlling effect of phase equilibrium, interaction between solute and solid matrix have been taken into account as well as axial dispersion in fluid phase. As two new attempts, profile of concentration for the inner region of particle along with concept of free solute on the surface of the particle was considered and equilibrium concentration dependence on concentration of free solute was presented. Obtained differential equations are partial and solved numerically. The ability of the model to predict the extraction yield was checked out under changing operating parameters of solvent flow rate, pressure, temperature and particle size, for the extraction of neem seed oil that percentage of sum of squared differences (SSD%) between the model prediction and the experimental data obtained 1%, 0.4%, 0.3% and 0.3%, respectively. Also for the extraction of sunflower seed oil, the effect of solvent flow rate was investigated that the SSD% was obtained 0.5%.

The main puropose of this work is to study the influence of the equations of state on the prediction of the performance of SUPERCRITICAL fluid extraction of herbal essential oils. The applied equations are van der Waals, Redlich-Kwong and the Peng-Robinson equations of state with their related mixing rules. To study of the performance of these equations on the solubility prediction, Mint (Spearmint) essential oil was choosen as the solute and SUPERCRITICAL carbon dioxide as the solvent. An experimental apparatus was used for extraction of Mint essence and the best operating conditions were reached after many experiments. Thermodynamic properties of Carvone, as the specific compound of Mint essential oil, including critical pressure; critical temperature and eccentric factor have been estimated. According to the experimental results, Peng-Robinson equation of state with its mixing rules was the best selected equation of state to assess the solubility of essential oils in SUPERCRITICAL carbon dioxide and showed the best results.

In many applications, convection heat transfer is coupled with conduction and radiation heat transfer, which generate temperature gradients along the walls and may greatly affect natural convection heat transfer. The main objective of this study is to calculate the heat-transfer characteristics for natural convection from a non-isothermal vertical at plate into a SUPERCRITICAL uid. The inuence of the non-uniformity of wall temperature on the heat transfer by natural convection along a vertical plate, having a linearly distributed temperature (characterized by the slope S) is also investigated. The thermal expansion coefficient is considered as a function of the temperature, the pressure, the van der Waals constants and the compressibility factor. The trends of the curves obtained with this equation and with values from tables of thermodynamic properties were similar and diverged at a critical point. These features confirmed the validity of this equation. Then, the governing systems of partial differential equations are solved numerically using the finite difference method. The local Nusselt number was then calculated and plotted as a function of the local Rayleigh number. It was observed that a positive slope of temperature distribution increases the heat transfer rate and a negative slope decreases it.

SUPERCRITICAL carbon dioxide (scCO2) has the remarkable ability to penetrate graphite layers with significant force and low viscosity, effectively overcoming Van der Waals (VdW) forces and converting graphite into mono/bilayer graphene. By utilizing data from Design Expert software (version 7.0) and conducting laboratory experiments, it has been demonstrated that various parameters such as temperature (T), pressure (P), initial amount of graphite, surfactant and co-solvent addition, duration of sample placement in the cell, CO2 gas release duration, ultrasonic and centrifuge operation time, and power can significantly enhance the exfoliation process. The graphene produced was meticulously analyzed using advanced techniques such as RAMAN spectroscopy, High Resolution Transmission Electron Microscopy (HRTEM), Fourier Transform InfraRed (FT-IR) spectroscopy, Zeta potential analysis, and Atomic Force Microscopy (AFM). The results conclusively showed that under optimal conditions, mono/bilayer graphene was successfully achieved. This was confirmed by the presence of the G-Band at 1581 cm-1 in the RAMAN spectroscopy. The HRTEM images clearly displayed the formation of graphene layers under the applied conditions, while FT-IR results indicated that graphene sheets were successfully synthesized after applying appropriate conditions, with a thickness of 1.49 nm as observed in the AFM. The zeta potential value for this nanofluid was measured at -39.7 mV, indicating excellent stability. This innovative method offers a straightforward and cost-effective approach that eliminates the need for toxic or expensive chemicals, positioning it as a highly lucrative alternative to more complex graphene production methods, such as heating silicon carbide.

Background: The ability of SUPERCRITICAL FLUIDS (SCFs), such as carbon dioxide, to dissolve and expand or extract organic solvents and as result lower their solvation power, makes it possible the use of SCFs for the precipitation of solids from organic solutions. The process could be the injection of a solution of the substrate in an organic solvent into a vessel which is swept by a SUPERCRITICAL fluid. The aim of this study was to ascertain the feasibility of SUPERCRITICAL processing to prepare different particulate forms of fluticasone propionate (FP), and to evaluate the influence of different liquid solvents and precipitation temperatures on the morphology, size and crystal habit of particles. Method: The solution of FP in organic solvents, was precipitated by SUPERCRITICAL carbon dioxide (SCCO2) at two pressure and temperature levels. Effects of process parameters on the physicochemical characteristics of harvested microparticles were evaluated.Results: Particle formation was observed only at the lower selected pressure, whilst at the higher pressure, no precipitation of particles was occurred due to dissolution of FP in SUPERCRITICAL antisolvent. The micrographs of the produced particles showed different morphologies for FP obtained from different conditions. The results of thermal analysis of the resulted particles showed that changes in the processing conditions didn’t influence thermal behavior of the precipitated particles.Evaluation of the effect of temperature on the size distribution of particles showed that increase in the temperature from 400C to 500C, resulted in reduction of the mean particle size from about 30 μm to about 120m.Conclusion: From the results of this study it may be concluded that, processing of FP by SUPERCRITICAL antisolvent could be an approach for production of diverse forms of the drug and drastic changes in the physical characteristics of microparticles could be achieved by changing the type of solvent and temperature of operation.

In this work the volume expansion for the binary systems of ethanol and toluene, as industrial organic solvents, in the presence of nearcritical and SUPERCRITICAL carbon dioxide, CO2, at a temperature range of 293 to 333 K has been meticulously measured. The effect of the temperature and pressure of binary systems on volume expansion for organic solvents have also been investigated. It can be observed that by increasing the pressure of the system at a constant temperature, the volume of the liquid phase increases smoothly, while at higher pressures a sudden volume expansion can occur. The range of pressure that can lead to a sudden increase in the volume expansion of the liquid phase in each specified temperature can be reported as a proper condition in producing micro and nanoparticles. The experimental data for the volume expansion of organic solvents were modeled using the conventional cubic Peng Robinson equation of state. The Average Absolute Relative Deviation percent (AARD%) for the binary systems of ethanol + CO2 and toluene + CO2 were reported as 14.9% and 15.1%. As inferred, it is vital to develop a thermodynamic model with greater accuracy in order to correlate the volume expansion of the systems studied in this work at various conditions.

Introduction: SUPERCRITICAL fluid extraction (SCFE) is a promising technique that has been attracted by some scientist recently due to the moderate operational condition. Moreover, SCFE products are pure and free of residual solvents. Mathematical modeling of SUPERCRITICAL extraction is a useful tool for deducing the SCF extraction systems, prediction of optimum operational conditions and system design variables, and scale-up to the pilot and industrial scales.Materials and Methods: A new mathematical model modified by Sovova, based on the concept of broken and intact cells, has been applied to understand the variables effect on extraction efficiency in a SCF extraction system. System was made in order to extract the essential oil from orange peel. This model simulates the experimental data points adequately for two separate times using combined pattern of phase equilibrium equations, solute/matrix interaction and internal diffusion rules in the solid particles. Model equations for plug flow are ordinary differential equations and are solved by matlab using numirical method. A number of physical parameters have been determined by experimental data fitting.Results: Extraction curves have been presented on the form of extraction yield versus relative amount of passed solvent. The effect of operational parameters including grinding efficiency, bed void fraction, number of mixers and external mass transfer coefficient have been also investigated.Conclusion: The most desirable result is obtained from grinding efficiency and external mass transfer coefficient of 0.7 and 0.011 respectively, within 20 mixers. The model results present a good agreement with the experimental results. Average absolute deviation between experimental data and the modeling results is about 6%.