| Supercritical antisolvent (SAS) is a new technique for micronization in some fields: explosives, polymer microspheres, superconductors, catalyst precursors and dyes, showing a wide potential application prospect. Manganese oxide is an efficient catalyst which can enhance the degradation of waste water containing phenol in supercritical water oxidation reaction. In this paper, SAS is used to produce manganese acetate nanoparticles that is manganese dioxide precursor. Methanol was sieved as solvent in SAS process by comparison of physical properties and calculation of volume expansion curve. The critical curve of CO2/Methanol mixture and solubility of methanol in CO2 were also measured. Results indicated that influence of temperature on particle size(PS) was non-monotonic because of its influence on fluid density and diffusion coefficient. Minimum of PS appeared at 48℃. Temperature also had an influence on particles morphology. Gelatinous structure was formed under the condition near CO2 critical temperature, while regular sphere particles appeared at higher temperature. Increasing pressure resulted in smaller PS and narrower particle size distribution (PSD). Minimum of PS appeared at 16 MPa. However, when pressure exceeded 20 MPa, PS increased slightly because CO2 diffusion coefficient became smaller. The influences of solution concentration, nozzle size and mixture of solvents on this process were investigated at the same time, and manganese acetate nanoparticles were produced at suitable process parameters which were 16MPa, 48℃, 1.5wt%. On the basis of above works, theoretical analysis on SAS was performed in atomization of solution, diffusion in two directions between CO2 and solution, and nucleation of solute. Influence of some process parameters on product particles, such as pressure, temperature and concentration were discussed. Nucleation mechanism of this process is concluded that more than one particle were formed in one primary droplet...
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