The kinetics of ethylene polymerization with $CrO_3/SiO_2/Al(i-Bu)_3$ has been investigated in the range of temperature between 323 and 353 K and in the range of pressure between 116.7 and 268.7 psia. The effects of aluminum alkyl on the formation and the deactivation of active sites were discussed.
The rate of polymerization was considered to occur between adsorbed monomer and an active center and the change of the polymerization rate at the initial period was described by formation of active sites from the interaction of adsorbed aluminum alkyl with preactive sites. Decay of the polymerization rate, which was independent of the monomer concentration, was ascribed to the excess aluminum alkyl that could poison the active sites by the Langmuir-Hinshelwood mechanism. Activation energy obtained from the maximum polymerization rates between 323-353 K was 8.8 kcal/mol. The apparent negative activation energy was obtained above 343 K which is ascribed to the destruction of active sites.
Dimerization of ethylene to 1-butene catalyzed by $Ti(O-nC_4H_9)_4-AlEt_3$ was investigated. The kinetics at the initial period and deactivation was studied with various aluminum alkyl concentration. The mechanisms of formation and deactivation were discussed and deactivation was ascribed to the oligomerization of active sites with aluminum alkyl. The number of active sites was determined by CO-poisoning method. The maximum number of active sites was 35% of total titanium at 303 K and the Al/Ti molar ratio of 5.4. $^K_D$, rate constant of dimerization, was calculated as 75.2 1/mol sec. The active site for dimerization of ethylene is believed to be uniform. The CO-poisoned sites can be reactivated by re-admission of triethylauminum.
Compatibility study of catalysts system for in situ production of LLDPE with ethylene monomer only was carried out. The dimerization catalysts component was $Ti(O-nC_4H_9)_4-AlEt_3$. And several Mg-supported Ziegler-Natta catalysts, $TiCl_3\cdotAA$/THF/$MgCl_2$, $TiCl_4/THF/MgCl_2$, and ($AlEt_2Cl$ treated $TiCl_3\cdotAA$/THF/$MgCl_2$) were tested. All the polyethylene produced with these catalyst components were LLDPE. The $AlCl_3$ in $TiCl_3\cdotAA$/THF/$MgCl_2$ catalyst quickly poisons the dimerization active sites. However, the existence of THF in supported catalysts can diminish the poisoning by the complex formation such as $AlEt_2Cl\cdotTHF$. With $TiCl_4/THF/MgCl_2-Ti(O-nC_4H_9)_4-AlEt_3$ catalysts system, the rate enhancement was observed. One reason for this rate enhancement must be comonomer enhancement. And the kinetic profiles changed from non-decaying to decaying type after rate enhancement. The ($AlEt_2Cl$ treated $TiCl_3\cdot$AA/THF/$MgCl_2$)-$Ti(O-nC_4H_9)_4-AlEt_3$ catalyst system showed much higher rate enhancement than $TiCl_4/THF/MgCl_2-Ti(O-nC_4H_9)_4-AlEt_3$ catalysts system. And kinetic profiles maintained non-decaying type after the rate enhancement. These different kinetics must be due to different active sites which have unique catalytic characteristics such as monomer enhancement and catalyst deactivation.
Chrome and nickel coimpregnated on $SiO_2$ catalyst (Cr-Ni/$SiO_2$) cocatalyzed with $Al(i-Bu)_3$ produced HDPE. The existence of $Al(i-Bu)_3$ must interfere with the oligomerization activity in Cr-Ni/$SiO_2$ catalyst. The catalyst of $TiCl_4/THF/MgCl_2$ impregnated on $NiCl_2/SiO_2$ produced HDPE. The aluminum alkylchlorides which are necessary for the dimerization component of $NiCl_2$ poison the polymerization component of $TiCl_4/THF/MgCl_2$. Also the different mechanisms, dimerization with cationic mechanism and polymerization with coordination mechanism, interfere with the in situ production of LLDPE.
