Supercritical ethanol

Powders from organometallics. Fine pigment powders are also possible. Metal alkoxides such as titanium isopropoxide, which is soluble in supercritical ethanol, can undergo rapid expansion spraying to form submicronic titanium dioxide powders. 

The superior solvation qualities of supercritical fluids over conventional liquids have been known for more than a century, since 1879 in fact, when Hannay and Hogarth investigated the solubility of different inorganic salts in supercritical ethanol. But it was not until the late 1960s that the extraction potential of supercritical fluids was recognized. 

Near-critical and supercritical ethanol were studied by Eckert and coworkers141 using the probe pair 8/7 to obtain their fi values. For liquid ethanol, these declined with increasing temperatures from 0.8 at ambient conditions to 0.3 in ethanol at equilibrium with its vapor at 250 °C. For sub-critical (gaseous) ethanol at 250 °C, fi increased somewhat from ca 0.05 at low pressures to ca 0.2 at 17 MPa (170 bar). 

Figure 5, (a) ISLS sound speed data and corresponding calculations for supercritical methanol along a 250° C isotherm (b) Data and corresponding calculations for supercritical ethanol along a 250° C isotherm. The difference between MeOH and EtOH sound speeds is typically less than 3 % in this pressure/temperature regime. Raman spectra taken from MeOH at 6.51 GPa indicate that a liquid to glass transition occurred and accounts for the discontinuous increase in velocity compared to the fluid state. 

Polycarbonate (Huang et al., 2006) PC Supercritical ethanol solvolysis Bisphenol A 90, diethylcarbonate 89%... 

Huang J, Huang K, Zhou Q, Chen L, Wu YQ, Zhu ZB. Study of depolymerization of polycarbonate in supercritical ethanol. Polym Degrad Stab 2006 91 (10) 2307-2314. 

The first reported observation of the occurrence of a supercritical phase was made by Baron Cagniard de la Tour in 1822. He noted visually that the gas/liquid boundary disappeared when heating each of them in a closed glass container increased the temperature of certain materials. From these early experiments, the critical point of a substance was first discovered. The first workers to demonstrate the solvating power of supercritical fluids for solids were Hannay and Hogarth in 1879. " They studied the solubility of cobalt(II) chloride, iron(III) chloride, potassium bromide, and potassium iodide in supercritical ethanol (Tc = 243°C, = 63 atm). 

Vieitez, I., C. da Silva, G. R. Borges, F. C. Corazza, J. V. Oliveira, M. A. Grompone, and I. Jachmanian. 2008. Continuous Production of Soybean Biodiesel in Supercritical Ethanol-Water Mixtures. Energy Fuels 22 (4) 2805-2809. 

The earliest indication of this property of SCF is to be found in the work of J.B. Hannay and J. Hogarth (1879), who reported that an increase in pressure of supercritical ethanol caused increased dissolution of certain inorganic salts such as potassium iodide, while conversely a relaxation in pressure resulted in the precipitation of the salts as "a white snow."... 

Metal alkoxides can by decomposed in supercritical alcohols to produce various oxides, such as Ti02 (73-75). Metal alkoxides also react readily with water to form hydroxide species that are easily dehydrated into oxides upon heating. As a solution of the alkoxides and alcohol is heated, some of the alcohol decomposes into water and aldehyde. The metal alkoxides react with the water formed and then undergo dehydration at the elevated temperatures. Compared with samples made via conventional sol-gel synthesis, powders synthesized in supercritical ethanol exhibit a higher degree of crystallinity and contain less hydroxide. 

Shuna Cheng, Carolynne Wilks, Zhongshun Yuan, et al. Hydrothermal degradation of alkali lignin to bio-phenolic compounds in sub/supercritical ethanol and water-ethanol... 

Supercritical alcohol drying typically induces hydrophobic properties even in nonmodified (hydrophobized) silica gels. At the high process temperatures and pressures, free silanol groups react with ethanol, leaving behind mostly alkoxy-decorated gel. This surfece chemistry, however, is not hydrolytically stable under normal ambient conditions. A TEOS-based HTSCD aerogel dried in supercritical ethanol loses its hydrophobicity within a few hours when stored in ambient air. 

Balat, M., 2008. Biodiesel fuel production from vegetable oils via supercritical ethanol transesterification. Energy Sources, Part A Recovery Utilization, and Environmental Effects 30,429-440. 

Rapeseed-based biodiesel production has been widely studied in terms of optimization and kinetics of alkali catalyzed transesterihcation reaction (Luque et al., 2011). Recaitly, production of solid base catalysts, such as Ca/Zr mixed oxide catalysts (Liu et al., 2015), CaO-based catalysts or4-sulfophenyl activated carbon-based solid acid catalyst, has been reported with a performance similar to commacial heterogeneous catalyst Amberly st-15 (Malins et al., 2015). Present researches are also focusing on the use of supercritical ethanol and methanol as reagents to avoid drawbacks due to the use of homogeneous catalysts (Farobie and Matsumura, 2015a,b). Technoeconomic and performance studies on the use of supercritical methanol concluded that lower direct costs and environmental impacts are achieved at highest biodiesel yields, where oil consumption per unit of biodiesel... 

Supercritical ethanol was used together with ionic hquid [HMim][HS04] catalyst, yielding 97.6% biofuel in only 45 min, and the catalyst was not affected by high pressures, temperatures, or the presence of water, which imphes a sustainable alternative for WFO valorization (Caldas et al., 2016). 

Farobie, O., Sasanami, K., et al., 2015. A novel spiral reactor for biodiesel production in supercritical ethanol. Applied Energy 147, 20—29. 

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