Technical Research on Supercritical CO2 Fluid in Chemical Reactions

2021-07-21


It has been over a hundred years since Thomas Andrews discovered the existence of critical points in 1869, but the development of supercritical fluid technology has been relatively slow until the late 1970s, when basic and applied research on supercritical fluids developed rapidly due to their potential application prospects.
At present, supercritical fluids have been widely used in various related fields such as food, medicine, energy, environment, and chemical reaction engineering, and will gradually penetrate and develop into broader fields.
In all application fields, chemical reaction under supercritical conditions will be a hotspot and frontier in the research and application of supercritical fluid technology in the future, mainly because of the increasingly serious resource and environmental problems. Replacing traditional organic solvents with supercritical fluids is equivalent to eliminating substances harmful to the environment from the source, which is an important part of "green chemistry"; Supercritical fluids have adjustable properties, that is, they can adjust reaction rate and selectivity by simply changing temperature or pressure, which is difficult for conventional organic solvents to achieve; When using supercritical fluid as the reaction medium, the reaction and separation can be combined to simplify the operation process and achieve economic efficiency of the process.
Based on the above reasons, this paper chooses polymer polymerization reaction in supercritical fluid as the research content, with a focus on studying the effect of co solvents on the reaction. Around this center, before studying polymerization reactions, the properties and density non-uniformity of supercritical fluids (including their long-range density non-uniformity and local density non-uniformity) were first studied, revealing the phenomenon that solvent molecules can aggregate around solutes at high densities in the high compression region. This is precisely the key to the difference between supercritical fluid properties and general solvent properties. The paper studied the binary mixture system of supercritical carbon dioxide tetrahydrofuran using the apparent density of solvents and the partial molar volume of solutes. The negative partial molar volume of solutes under infinite dilution conditions indicates the formation of solvation structures in the solution, where solvents aggregate around the solute, indicating the non-uniformity of solvent long-range density.
The paper also used FT-IR to study the hydrogen bond association between tetrahydrofuran and acetic acid in the ternary mixture system of supercritical carbon dioxide tetrahydrofuran acetic acid. It was observed for the first time that different driving forces for the formation of hydrogen bonds were observed within different compression ranges, namely, high compression zone enthalpy and positive entropy were entropy driven, and low compression zone enthalpy and negative entropy were enthalpy driven. This indicates that in supercritical fluids, not only solute cosolvent interactions exist, And there are also co solvents.

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