FORMATION OF TITANOCENE DICHLORIDE MICROPARTICLES BY RAPID EXPANSION OF SUPERCRITICAL SOLUTION AND CATALYZED ETHYLENE POLYMERIZATION
One of the existing problems of metallocene catalyst is the difficulty in controlling its polymer morphology despite of its numerous advantages. According to the morphology replication nature of ethylene polymerization,polymer morphology could be improved by catalyst particle morphology improvement. The catalyst microparticles with narrow particle size distribution were obtained by rapid expansion from supercritical solution (RESS). Propane was chosen as a supercritical solvent and Cp 2TiCl 2 was selected as metallocene sample to catalyze ethylene in hexane medium. As a necessary fundamental research on rapid expansion of supercritical solution (RESS),the solubilties of titanocene dichloride in supercritical propane were measured by the static equilibrium method at temperatures from 383.15 to 408.15 K and pressure from 10.0 to 35.0 MPa. The solubility data were correlated with the Peng-Robinson (PR) equation of state and the AARD was 3.27%. RESS experiments were performed at different operation conditions,including solute concentration,pre-expansion temperature,nozzle length and diameter,and sample collection distance. The size of quasi-spherical and spherical particles formed in the RESS process with several microns decreased with the increase of solution concentration,the decrease of pre-expansion temperature,the increase of nozzle diameter and the decrease of nozzle diameter. And the particle size increased with increasing collection distance until 87 mm. The catalyst particles were characterized through ethylene slurry polymerization to obtain the polymer. It was found that polymerization rate of ethylene was accelerated greatly and induced time was shortened for the RESS-reformed catalyst by comparing with the original catalyst particles. And the size distribution of reformed catalyst particles and the morphology of polymer were greatly improved.