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Supercritical extraction with modified ethane was used for the separation of triglycerides from waste frying oil in a semicontinuous system. Cosolvents used to modify pure solvent behavior were ethanol, methanol, acetone, and hexane. They were selected because of their different capacity to form hydrogen bonds. The effect of cosolvent type on extraction yield and oil solubility followed the order: ethanol > methanol > acetone > hexane. However, their efficiency to separate triglycerides from polar species showed the opposite trend: ethanol < methanol < acetone < hexane. Regarding the effect of cosolvent concentration, yields and solute solubilities increased with increasing values of the variable. However, the separation efficiency was almost independent of cosolvent concentration. Finally, the extraction process was further analyzed in a continuous packed column. At the best conditions 95% of triglycerides were recovered, being the polar content of the extract only slightly higher than of the fresh oil. [ABSTRACT FROM AUTHOR]

Abstract: The extraction of triglycerides from used frying oil with liquid and supercritical ethane has been studied in a semibatch system at different temperatures (25–80°C) and pressures (150–250kg/cm2). It has been found that isobaric decreases of temperature and isothermal increases of pressure lead to both increasing extraction yields and decreasing separation efficiencies. Lipid fractions recovered in the high density region had acceptable concentrations of polar compounds. Results with ethane have been compared to those reported for CO2 in earlier works. At similar reduced densities of the solvents, oil solubility in ethane was higher than in CO2, being the separation efficiency of polar fractions slightly better when using ethane. The extraction process was further analyzed in a packed countercurrent column. At optimum conditions (250kg/cm2, 25°C, and solvent-to-oil ratio 45g:g) about 85% of the triglycerides were recovered, being 11.2% the polar content of the triglyceride fraction recovered. [ABSTRACT FROM AUTHOR]

Abstract: Liquid and supercritical ethane has been used as a solvent for the recycling of used lubricant oils. The aim of the work has been to identify the best processing conditions to separate base oil suitable for the formulation of new lubricants, avoiding the coextraction of oxidation products and metallic compounds. The effect of pressure (40–145kg/cm2) and temperature (25–95°C) on the separation efficiency and yields has been investigated. In the pressure range analyzed no effect on metallic compounds removal was found. However, it did affect the extraction yields (they increased with pressure) and the separation of oxidation products (removed more efficiently at low pressures). As regards to temperature, at a given pressure the extraction yields were found to be independent of the variable as long as ethane remained as a liquid, but they decreased with increasing temperature with supercritical ethane. As expected, gas ethane could not dissolve base oil at all. On the other hand, at constant pressure metallic and oxidation compounds removal increased as temperature was increased. [Copyright &y& Elsevier]

Graphical abstract Highlights • TNFs synthesized with supercritical fluids exhibit unique physicochemical properties. • These properties are intimately related to the photocatalytic activity of TNFs. • TNFs with enhanced visible light absorption lead to higher CO and CH 4 production rates. • These production rates are higher than those of TiO 2 particles synthesized with SCFs. Abstract The photocatalytic reduction of CO 2 with water vapour using titania nanofibers (TNFs) synthesized in supercritical medium has been assessed. TNFs have been produced from titanium isopropoxide (TTIP) precursor at different pressures (200–240 bar) and temperatures (40–80 °C). Synthesized materials were later characterized by scanning and transmission electron microscopy, BET surface area analysis, X-ray diffraction, and UV–vis diffuse reflectance spectroscopy. Better defined morphologies were obtained at the highest pressure and temperatures tested, so the catalyst synthesized at 240 bar and 60 °C was doped with copper (0.4–2 wt. %) in order to study the influence of metal doping on CO 2 reduction. All undoped and Cu-doped TNFs have been found to exhibit higher CO 2 reduction rates than commercial catalyst (P-25) and other TNF-based catalysts produced with traditional methods, although methane and CO remain the only two reaction products. Moreover, it has been found that copper doping improves CO 2 conversion in comparison with the equivalent undoped catalyst. [ABSTRACT FROM AUTHOR]

Converting carbon dioxide (CO 2 ) to hydrocarbons that can be used as fuel is beneficial from both environmental and economic points of view. However, more efficient catalysts should be developed to bring the process from laboratory to commercial scale. Thus, in this study, in order to improve the CO 2 conversion process, Pd doped photocatalysts based on titanium dioxide (Pd/TiO 2 ) are synthesized. The new catalysts are produced from alcohols and precursors of titania and Pd in the presence of supercritical carbon dioxide so the dispersion of metal species (palladium) into the TiO 2 lattice is possible. Following this approach, photocatalysts with better or similar features (higher values of crystallinity, surface area, and improved absorbance in visible range) than those of commercial TiO 2 have been produced. Moreover, methane and CO production rates up to 22 and 2 times higher than those corresponding to the commercial catalyst, respectively, have been attained with Pd/TiO 2 photocatalysts synthesized in this work. [ABSTRACT FROM AUTHOR]

This work has focused on the synthesis of Cu nanostructured electrocatalysts for CO 2 electroreduction by supercritical fluid deposition (SFD) technique. Different synthesis strategies such as the suppression of cosolvent (methanol) and/or reducing agent (hydrogen) have been studied. Good copper deposition yields (around 85%) have been attained in the absence of hydrogen. This material (C-200Me) has been tested as catalyst in the electrochemical reduction of CO 2 in gas phase and the results obtained have been compared with those achieved with a catalyst synthesised using H 2 as reducing agent (C-200H 2 Me). CO and formic acid have been the main reduction products with both catalysts. CO 2 conversion rate has been almost six times higher with C-200H 2 Me, what may be probably attributed to a higher proportion of Cu0/Cu+ species in this catalyst. These results indicate the higher catalytic activity of Cu0 (than that of Cu 2 O) in the electrocatalytic reduction of CO 2 in gas phase. [Display omitted] • Supercritical fluid deposition of copper-based nanoparticles. • Deposition yields around 70% without hydrogen or methanol. • Cu0 nanoparticles more active than Cu 2 O in the electroreduction of CO 2 in gas phase. • CO and formic acid are the main CO 2 electroreduction products. • SFD allows controlling the copper species formed in the synthesised nanomaterial. [ABSTRACT FROM AUTHOR]

• Cu-based nanoparticles deposited on carbon nanotubes (Cu/CNT) have been synthesized. • Synthesis methods: precipitation, microemulsion and supercritical fluid deposition. • Supercritical fluid deposition technique led mainly to the formation of metallic Cu. • The main CO 2 reduction product has been CO followed by formic acid and methane. • Supercritical fluid deposition catalyst attained high CO 2 conversion rate. One of the most promising technologies for the mitigation of CO 2 emissions involves its electrocatalytic reduction to valuable products. However, the development of effective catalysts is still a challenge. In this work, three different techniques have been compared for the synthesis of catalysts involving Cu-based nanoparticles deposited on carbon nanotubes (Cu/CNT): precipitation, microemulsion and supercritical fluid deposition (SFD). According to XRD, SFD allows obtaining mainly copper nanoparticles, while copper oxides are obtained by precipitation. Crystallite size of predominant Cu species of catalysts are between 7 (microemulsion) and 16 nm (SFD). The use of these catalysts in the electrochemical reduction of CO 2 in gas phase produce carbon monoxide as main CO 2 reduction product, followed by formic acid and methane. The catalyst obtained by microemulsion exhibited poor reproducibility. The catalyst synthesized by SFD achieved the largest CO 2 conversion rate, a 30 % higher than that obtained with the one synthesized by precipitation. [ABSTRACT FROM AUTHOR]

• CNT/TiO 2 synthesized with supercritical fluids exhibit unique physicochemical properties. • These properties are intimately related to the photocatalytic activity of CNT/TiO 2. • CNT/TiO 2 with enhanced visible light absorption lead to higher CO and CH 4 production rates. • These production rates are higher than those of TiO 2 particles and nanofibers synthesized with SCFs. Previous works with titanium dioxide based photocatalysts synthesized with supercritical fluids led to improved catalyst properties in comparison to those prepared by traditional methods, but still insufficient CO 2 reduction rates. In this work, in order to upgrade this type of catalysts, two supercritical methods have been used to prepare CNT/TiO 2 and CNT/TiO 2 /Cu nanocomposites. The effect on photocatalytic performance of CNT/TiO 2 ratio and Cu load has been investigated. Decreasing photocatalytic activities were observed when the CNT/TiO 2 relationship separated from unit. Regarding the effect of copper doping, it was overshadowed by the effect of CNT support. Finally, because of the excellent properties of CNTs, synthesized composites showed greater catalytic activities than bare TiO 2. Specifically, the catalyst with largest activity led to CO and CH 4 production rates of 8.1 and 1.1 μmol g−1 h−1, which were much higher than those on P25 (4 times for CO and 15 times for CH 4). [ABSTRACT FROM AUTHOR]