The Nature Of The Supercritical Fluids In Chemical Reactions

It has been more than one hundred years passed since Thomas Andrews found out critical point in 1869. During the past 100 years, the development of supercritical fluid (SCF) technology is very slow. But from the late of 70s this century, the theoretical and application research on SCF became more and more widespread because of the present problems of source and environment. Present now, SCF is widely used in food, medicine, energy, environment, and chemical reaction engineering. Among all the fields, chemical reaction in SCF is especially important. This is due to the following reasons. First, because of the increasing environmental and ecological problem in the world, supercritical fluid can be used to replace traditional organic solvents to eliminate environmental pollution. Second, when chemical reactions are conducted in SCF, the reaction environment (solvent properties) can be tuned by the temperature or pressure, so the reaction rate can be increased and the selectivity of reaction can be improved. Third, when chemical reactions are conducted in SCF, the transport limitation on reaction rate can be eliminated and the reaction and product separation can be integrated. On the basis of these reasons, polymerization reaction acrylic acid (AA) in SCF was selected to be studied. And the effect of cosolvent on the polymerization reaction in SCF was stressed.Before the study of polymerization reaction, the specialties of SCF, such as the inhomogeneousity of density and molecular interaction are studied first. From the study, it explores that there exist apparent clusters of solvent molecules about solute molecules in the region of higher isothermal compressibility. There are two parts in the study of properties of SCF. One is the study of SC CO₂-tetrahydrofuran (THF) binary mixture system by means of apparent densities of the solvent and partial mole volume of solute. The result suggests that long-range density inhomogeneousity of thesolvent. The other part is the study of the hydrogen bonding of THF and acetic acid in SC CO2-THF-acetic acid ternary mixture system by using FT-IR. And the form of hydrogen bonding is the probe to investigate the short-range density inhomogeneousity of the SCF. In addition, it is the first to observe the different driven force for the form of hydrogen bonding in different compressibility region, i.e., it is the entropy-driven in high isothermal compressibility region and the enthalpy-driven in the low isothermal compressibility region.On the premise of studying the specialties of SCF, the effects of acetic acid, ethanol, and THF as the cosolvents on the polymerization