Effect of Solvent on Nanoparticle Production of β‐Carotene by a Supercritical Antisolvent Process

Production of micro‐ to nano‐sized particles of β‐carotene was investigated by means of solution‐enhanced dispersion by supercritical fluids (SEDS). β‐Carotene was dissolved in dichloromethane (DCM), N,N‐dimethylformamide (DMF), n‐hexane, or ethyl acetate, and supercritical CO₂ served as an antisolvent. The effects of the organic solvents, operating pressure, and temperature were examined. The morphologies of the particles produced by the SEDS were observed by field emission‐scanning electron microscopy and particle sizes were determined by image analysis. Irregularly shaped microparticles were produced in the system with DCM and DMF solution. Plate‐like microparticles were generated by using n‐hexane solution and irregular nanoparticles by ethyl acetate solution. The optimum operating conditions were found to be ethyl acetate as solvent in a defined pressure and temperature range.     

Design of a Cost‐Reduced Flexible Plant for Supercritical Fluid‐Assisted Applications

A novel batch plant for supercritical CO₂ applications is proposed which is not equipped with expensive components, such as high‐pressure pumps, making it particularly suitable for bench‐scale use. For the first time, the use of a hanging scale is suggested to weigh the amount of CO₂ required for the experiment and the use of the thermodynamics to reach the working conditions. The rig is able to cover different applications, e.g., aerogel drying, impregnation, and extraction, showing high flexibility. An approximate cost analysis has been performed considering as a reference a 150‐mL vessel. It has been calculated that both the setup and running costs are considerably lower than the common batch and semicontinuous rigs.     

Effect of Stearic Acid as a Co‐solvent on the Solubility Enhancement of Aspirin in Supercritical CO2

The solubility of aspirin in supercritical CO₂ (SC‐CO₂) with stearic acid as a co‐solvent was measured at various pressures and temperatures. The experimental data were obtained by a static method. Stearic acid had a significant effect on the enhancement of solubility, as the aspirin solubility increased by up to 16 times. Further, the effect of stearic acid on the solubility enhancement of aspirin was compared with that of other co‐solvents. Different semi‐empirical models from the literature were applied for correlating the experimental data, proving good agreement with the experimental data. The model of Sung and Shim exhibited the lowest deviation from the obtained data. The results of the solubility test can be employed to produce aspirin‐based pharmaceuticals using supercritical fluid technology (SFT).     

Fabrication of Silicone Rubber Foam with Tailored Porous Structures by Supercritical CO2

In spite of great concern on the wide application of silicone rubber foams, few works have been reported about easy‐operating foaming method. In this study, the effects of silica content and foaming process on the porous structure of high‐temperature‐vulcanized silicon rubber foams are evaluated, which are prepared by supercritical CO₂ at different conditions, with fumed silica used for reinforcement. Silicone rubber foams with cell size in 8–120 μm, cell density in 10⁵–10⁸ cm⁻³, and density between 0.45 and 0.9 g cm⁻³ are prepared under different saturation conditions. The results show that increasing silica content can decrease cell size. It is also found that cell density improves exponentially with increasing saturation pressure and decreasing saturation temperature. Besides, it demands less than 1 h for specimens to reach equilibrium on thickness around 3 mm. All the results indicate that the porous structures of silicone foams can be tailored by foaming process parameters facilely and are predictable with fitted equation.

     

From Electron Density Flow Towards Activation: Benzene Interacting with Cu(I) and Ag(I) Sites in ZSM-5. DFT Modeling

The effects of support pretreatment with nC₁–C₅ alcohols on the performance of Rh–Mn–Li/SiO₂ catalyst in the synthesis of C₂-oxygenates from syngas have been investigated by CO hydrogenation reaction, transmission electron microscopy (TEM), pulse adsorption of CO and H₂, and Fourier Transform infrared (FT-IR) spectroscopy. The catalysts prepared from the pretreated silica supports exhibited higher space time yields of C₂-oxygenates (STY_C2-oxy) and selectivities towards C₂-oxygenates (S_C2-oxy) than that prepared from the untreated silica support. The enhancement in the hydrophobicity of the pretreated silica supports would be favorable for increasing Rh dispersion and ratio of Rh⁺/Rh⁰ sites, therefore increasing the number of active sites, especially the active sites for CO insertion. Such variations are responsible for the improvements in the catalytic performance of the Rh–Mn–Li/SiO₂ catalyst.