جستجوی مقالات مرتبط با کلیدواژه « ethylene polymerization » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

The porosity of silica-based chromium catalysts is one of the important issues in the petrochemical industry due to the high catalytic activity attracted by university and industrial researchers. One of the most important parameters that strengthens the structure of the hydrogel is the aging process that is considered in this study. By performing the aging operation on the primary silica hydrogel, the size of the initial particles increases and the surface area decreases. By doing the drying process, the pore volume of silica is reduced due to the capillary force. With changing the solvent from water to alcohols and ethyl acetate, the pore volume of the silica supported also increases. This is due to the reduction in surface tension between the silica wall and the water in the cavities.

The formation of supported silica using sol-gel method and the parameters affecting it have been investigated. Also, in the drying step by azeotropic distillation method, five solvents such as water, 1-propanol, 2-propanol, 1-butanol and ethyl acetate were used. FTIR, SEM and BET analyses were used to identify silica supported.

The effect of organic solvents on pore volume was investigated; so that all hydrogels were synthesized under the same conditions, while different solvents were used in the drying step by azeotropic distillation method. The use of different organic solvents did not show significant changes in the specific surface area of the supported silica but caused significant changes in the its pore volume. The results showed that the morphology of the silica support was improved by solvent replacement using organic solvents and the best morphology and crack-free structure of the ethyl acetate solvent were reported. The highest catalytic activity of 80 kgPE/gCr.h was obtained for slurry polymerization with silica support dried by ethyl acetate solvent.

The late transition metal catalysts based on end group of transition metals in the periodic table like Ni, Fe, Co, Pd, Pt were developed rapidly in polyolefin industrial productions. These metals with suitable ligands exhibited specific properties and appropriate activities in the production of polyolefins. These catalysts based on bulky bisimine ligands usually depend on the structures of the ligands and the ortho group position on the aryl ligands show very interesting behaviors in olefin polymerization. When these groups, located in the ortho positions of aryl ligands, become larger, it would have lesser chance in leading to β hydrogen elimination reactions. The ligand 1,4-bis (2,6-diisopropyl phenyl) acenaphthene was synthesized by reaction of 2,6- diisopropyl aniline and acenaphthene quinone. The synthesized ligand was then added on nickel (II) dibromide salt that produced the 1,4-bis(2,6-diisopropyl phenyl) acenaphthene nickel (II) dibromide catalyst. The structure of the catalyst was fully characterized by IR, NMR techniques. Ethylene polymerization was performed using the prepared catalyst and the effects of parameters such as, polymerization temperature, cocatalyst, to catalyst molar ratio and monomer pressure, were investigated. One of experimental design methods (Box Behnken) was used to minimize the number of tests. The highest activity of catalyst [1420 kgPE/molNih] was obtained at monomer pressure 5 atm, [Al]:[Ni] = 1000 and polymerization temperature of 25°C. Some of the produced polymers were characterized by DSC and 13CNMR. The branched structures with higher methyl branch contents were observed in some polyethylene products.

In this study, the slurry polymerization of ethylene over TiCl4/MgCl2/AlEt3 was obtained. Firstly, to obtain the optimum value of [Al]/[Ti], the effect of [Al]/[Ti] on polymerization rate and catalyst yield was studied. Also, the effect of catalyst content on yielding, crystallization, melting point and density of product were obtained. To determine the order of reaction, the monomer pressure was varied, and hyedrogen was used as transfer agent. Also, we used 1-butene as comomomer. According to the results, hydrogen decreases the catalyst efficiency, melting temperature and molecular weight and increases the melt flow index. The crystallinity is increased first and then it is reduced with increasing H2 content and the density of the product has changed slightly by variation of hydrogen pressure. Also, with increase in 1-butene content, as a comonomer to control polymer density, the density, crystallinity, melting temperature and thickness of crystal lamella decrease and the melt flow index increases. Likewise, the rate of polymerization is initially increased and then it is decreased with comonomer content.