Fractionation of Used Frying Oil by Supercritical CO₂ and Cosolvents

Abstract

Supercritical extraction with pure and modified CO2 has been used for the fractionation of waste frying oil at different temperature and pressure conditions (25−80 °C and 300−400 kg/cm2). The cosolvents used to modify the CO2 behavior were ethanol, methanol, acetone, and hexane. They were selected because of their capacity to form hydrogen bonds. Both extraction rate and oil yield were larger under high density conditions (high pressure and low temperature). Further, when cosolvents were used, higher values of both variables were attained at softer operating pressures. Regarding the effect of cosolvents on these variables, it was found to follow this order: ethanol > methanol > acetone > hexane. The relative separation efficiency (RSE) of triglycerides (TG) from polar compounds with molecular weight higher than triglycerides (HMWC) was not greatly dependent on the operating conditions (pressure, temperature, cosolvent type, and cosolvent concentration). However, better values of the separation efficiency of TG from polar compounds with molecular weight lower than triglycerides (LMWC) were attained under low density conditions and using hexane as cosolvent. On the basis of the results relative to extraction rate, oil yield, and separation efficiency, the best extraction conditions were selected to separate a purified TG fraction from used frying oil. They were P = 300 kg/cm2, T = 40 °C, cosolvent type = hexane, and cosolvent concentration = 0.1 g of hexane/g of solvent. However, when processing the oil at these conditions, the polar content of the lipid fraction recovered still was about twice the fresh frying oil polar content. For this reason, a two-stage supercritical fluid extraction was performed. The composition of the fraction recovered in the two-stage process was very close to that of the fresh oil, a fact that clearly shows that the supercritical extraction with CO2 + hexane is an efficient method for the purification of the TG fraction of waste frying oil.

Preparation of TiO2-based catalysts with supercritical fluid technology: characterization and photocatalytic activity in CO2reduction

“…Briefly, the supercritical synthesis of TiO 2 is based on the thermal hydrolysis of a titania precursor by an alcohol in the presence of supercritical CO 2 . The unique feature of supercritical fluids is that they combine density and solvent power of liquids with viscosity and diffusivity of gases, these properties being tunable with simple modifications of pressure and temperature . Moreover, CO 2 is non‐toxic, non‐flammable, with low critical temperature, high compressibility degree and low cost …”

“…The unique feature of supercritical fluids is that they combine density and solvent power of liquids with viscosity and diffusivity of gases, these properties being tunable with simple modifications of pressure and temperature. 26,27 Moreover, CO 2 is non-toxic, non-flammable, with low critical temperature, high compressibility degree and low cost. 28,29 The purpose of this work is to assess the use of supercritical fluids in the synthesis of TiO 2 in order to improve catalyst characteristics such as surface, structure, and other physico-chemical properties, together with its photocatalytic activity in the CO 2 photoreduction process.…”

Improving the photo‐reduction of CO2 to fuels with catalysts synthesized under high pressure: Cu/TiO2

“…2,11 In our earlier studies, in order to increase the yield of the CO 2 photocatalytic reduction, TiO 2 -based nanoparticles were synthesized in supercritical medium. [3][4][5][6] In principle, supercritical fluid properties [12][13][14] allow facile control of the catalyst characteristics that will be important for its final application. 15 Among these desirable properties of a photocatalyst should be mentioned the following: large surface area and well-developed suitable porosity (reactants adsorption), crystal phase and high crystallinity (efficient charge separation), suitable band gap and threshold limit (visible light harvesting), and appropriate metal dispersion (reproducibility, selectivity).…”

Equilibrium Solubilities of Diisooctyl Sebacate in Supercritical Carbon Dioxide

“…In addition, under these conditions the change of solvent density is more effective The solubility behavior of this work showed the same trends with previous researches; for example, according to Kitchens et al, 10 supercritical CO 2 was used to extract the remaining fat from rendered poultrymeal, and fat solubility increased with pressure but decreased with temperature. According to Rincoń et al 20 and Zhao et al, 21 the solubility of a solute in supercritical CO 2 increased with increasing pressure under isothermal conditions while the effect of temperature showed different trends depending on the pressures. An undegraded triglycerides fraction was recovered from the waste frying oil by supercritical CO 2 extraction; the maximum extraction yields obtained about 70 % under investigated pressure and temperature, indicating supercritical carbon dioxide extraction technology is feasible for the recycle of waste frying oil.…”