The properties and phase equilibria of fluid mixtures can have great influence on chemical product formation and process development. In this work, examples are presented that illustrate the reaction and separation characteristics of high temperature water, supercritical carbon dioxide, and ionic liquids based on real-time images made with diamond anvil cells or visual cells. In the formation of ferrosilite from quartz (SiO2) and fayalite (Fe2SiO4), the diffusion of SiO2 to the solid fayalite substrate requires less than seconds to occur in water at high temperatures due to the enhanced solubility of SiO2, which has great technological significance for developing processes for industrially important luminescent materials. It is proposed that luminescent materials based on the zinc silicate (Zn2SiO4) family can be made with low environmental burden. The enhanced solubility of natural products in water at high temperatures allows for the fractionation of biomass to produce fermentable feedstocks and chemical products as well as for the efficient separation of natural products. The volumetric properties of n-alkylphenolics with CO2 can allow for efficient separation from their solid matrix due to viscosity reduction and foaming induced by changes in pressure. The lack of solubility of ionic liquids in supercritical CO2 allows for biphasic systems that can be used to efficiently separate phenolic compounds. Equations of state can provide suitable correlation. The viscosity reduction provided by solvents such as water, supercritical carbon dioxide, or organic liquids on ionic liquids allows ionic liquids to be put into a metastable state so that chemical conversions can occur in ionic liquids below their melting point at room temperature. The physical properties and phase behavior of water and carbon dioxide and mixtures with target compounds are very important for developing new green chemical processes.
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