A static equilibrium apparatus was built for determining solid solubility in supercritical fluid. Solubilities of polystyrene in supercritical propane were determined by the static equilibrium method at temperature from 383.15 K to 408.15 K and pressure from 10.0 MPa to 35.0 MPa. The effects of temperature and pressure on the solubility of polystyrene were investigated. The results showed that the solubility of polystyrene in supercritical propane increased with the increase of temperature and pressure. It was also shown that retrograde area could not exist within the temperature and pressure range. Furthermore,the solubility data of polystyrene in supercritical propane were correlated with the fairly good accuracy by a solution model presented in literature. The average absolute relative deviation (AARD) was 4.93%.
A nickel-diimine catalyst [N, N'-bis(2,6-diisopropylphenyl)-1,4-diaza-2,3-dimethyl-1, 3-butadiene nickel dibromide, DMN] was supported on palygorskite clay for ethylene slurry polymerization. The effect of supporting methods on the catalyst impregnation was studied and compared. Pretreatment of the support with methylalumi-noxane (MAO) followed by DMN impregnation gave higher catalyst loading and catalytic activity than the direct impregnation of DMN. Catalyst activity as high as 5.42×105g PE·molNi-1·h-1 was achieved at ethylene pressure of 6.87×105 Pa and polymerization temperature of 20℃. In particular, the morphological change of the support during MAO treatment was characterized and analyzed. It was found that nano-fiber clusters formed during the support pretreatment, which increased the surface area of the support and favored the impregnation of the catalyst. The investigation of polymerization behavior of supported catalyst revealed that the polymerization rate could be kept at a relatively high level for a long time, different from the homogeneous catalyst. By analyzing the SEM photographs of the polymer produced by the supported catalyst, the morphological evolution of polymer particles was preliminarily studied.
A series of heterogeneous catalysts with Cp2TiCl2 supported on palygorskite were prepared and evaluated by ethylene slurry polymerizations. The so-called direct supported catalyst, for which the pretreatment of palygorskite with MAO or Al（i-Bu）3 was not necessary, gave the highest activity among these supported catalysts and could be more robust than homogeneous Cp2TiCl2. With the direct supported catalyst, no significant activity loss was observed under low Al/Ti molar ratios （Al/Ti=300） and the decay of polymerization rate was slower when compared to the other supported catalysts. It was found that the surface Lewis acidity of palygorskite after thermal treatment played an important role in activation of metallocene compound and resulted in high catalyst activity.
Xiao Wei YAN Jing Dai WANG Yi Bing SHAN Yong Rong YANG
