Study on the Industrial Production of Organic Fine Powders Using Supercritical Carbon Dioxide

2004 Fiscal Year Final Research Report Summary

• Project/Area Number: 15560654
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Properties in chemical engineering process/Transfer operation/Unit operation
• Research Institution: HIROSHIMA UNIVERSITY
• Principal Investigator: TAKISHIMA Shigeki Hiroshima University, Graduate School of Engineering, Professor, 大学院・工学研究科, 教授 (10188120)
• Co-Investigator(Kenkyū-buntansha): SATO Yoshiyuki Tohoku University, Graduate School of Engineering, Associate Professor, 大学院・工学研究科, 助教授 (50243598)
• Project Period (FY): 2003 – 2004
• Keywords: Supercritical Fluid / Polymer / Fine Powder / PGSS Method

Research Abstract

Conventional processes for micronization of polymers have several disadvantages. Recently, PGSS (Particles from Gas Saturated Solutions) process that uses supercritical fluids (SCF) attracts much attention as a solution of the disadvantages. SCF is dissolved in a molten polymer and the high-pressure mixture is rapidly depressurized through a nozzle. By cooling effect in course of expansion the polymer is solidified leading to particle formation by precipitation. Since PGSS process do not require the dissolution of polymers in SCF phase, this process can be applied to wide range of polymers and the application is investigated to pharmaceuticals, catalysts, paints, biopolymers, and foods. However, researches of this process are scare for polymers and mechanism of micronization and effect of process parameters are not known enough.
The objective of the present work is to investigate the effect of initial temperature, pressure, SCF concentration and nozzle structure on the average particle size, particle size distribution and shape of resulting particles. Experiments were carried out for poly (ethylene glycol) (PEG) and polyester with supercritical carbon dioxide. As the results, fine particles of PEG with average molecular weight of 4000 could be obtained quickly at temperatures higher than 313 K, pressures higher than 10 MPa and CO_2 concentrations higher than 70 wt%. The average diameter decreased with decreasing temperature, increasing pressure, and increasing CO_2 concentration. By simulating the path of temperature and pressure during the decompression based on the energy balance, it was found that the period when the polymer is in liquid state decreased with decreasing temperature, decreasing pressure and increasing CO_2 concentration, and therefore the average diameter decreased and the shape changed to non-sphere. However, the effect of pressure in this simulation was opposite to the experimental results and the reason for this was considered to the change in the velocity of the mixture in the nozzle.