| Ethylene is one of the largest chemical products around the world. Nowadays it mainly uses in the production of low molecular weight linear alpha olefin (straight chain terminal olefins with four carbon atoms or above) and high molecular weight polyethylene and its derivatives. Linear alpha olefin (LAO) is a kind of important raw materials. It has been widely used in the production of polyethylene copolymer monomer, surfactant intermediates, alcohols used for plasticizer synthesis, lubricants, fuel additives and so on. Polyethylene (PE) is the important chemical supplies in people’s daily life and can be divided into four categories:low density polyethylene (LDPE), linear low density-polyethylene (LLDPE), high density polyethylene (HDPE) and ultra-high molecular weight polyethylene (UHMWPE). There are many methods for LAO production, and among them the ethylene oligomerization method is a very important method. The production amount of alpha olefin produced by ethylene oligomerization method is 94.1% of that of total alpha olefin. In our country, the alpha olefin production based on ethylene oligomerization method is almost blank. The comonomers such as 1-hexene,1-octene and 1-decene depend almost totally on imports, and the PE imports are among the top of the five general-purpose plastics. Therefore, the development of the catalysts and techniques for ethylene oligomerization and polymerization with independent intellectual property rights is particularly urgent.In this dissertation, two kinds of new-type phosphinoamine ligands, PNP and NP type, were designed, synthesized and characterized. Under the function of co-catalyst methylaluminoxane (MAO), the above ligands were reacted with CrCl3(THF)3 to produce complexes which could catalytic ethylene oligomerization or polymerization. The effects of reaction temperature, reaction pressure and n(Al)/n(Cr) on the catalyst catalytic performance for ethylene oligomerization or polymerization were investigated. The main research work is as follows:(1) PNP type ligands (L1, L2, L3) have been synthesized and characterized. The effects of reaction temperature, reaction pressure and n(Al)/n(Cr) on the catalytic performance of PNP/Cr(Ⅲ)/MAO for ethylene oligomerization were investigated. The results revealed that all the three catalysts have shown good catalytic activity for ethylene oligomerization and good linear a-olefin selectivity, and the obtained ethylene oligomerization products all possessed a narrow distribution. Under the reaction condition that the cyclohexane was used as solvent, the reaction temperature was 50℃, the reaction pressure was 3.0 MPa and n(A\)/n(Cr) was 300, the catalytic activity could reach 35.7×104 g/(mol Cr·h), the selectivity of 1-Cs= in liquid was 75.6%, and the selectivity of 1-C6= and 1-C8- could reach 88.6% for the L1/Cr(Ⅲ)/MAO catalysts. Under the same condition, for L2/Cr(Ⅲ)/MAO catalysts, the catalytic activity could reach 20.7×104 g/(mol Cr·h) and the selectivity of 1-C6= and 1-C8= in liquid could reach 91.0%. For L3/Cr(Ⅲ)/MAO catalysts, the catalytic activity could reach 25.4×104 g/(molcr·h) and the selectivity of 1-C6= and 1-Cs= in liquid could reach 91.9% under the same condition. Compare these three PNP type catalysts, it was found that the catalyst catalytic property would decrease, the selectivity of 1-C6- would increase and the selectivity of 1-C8- would decrease when the S atom was introduced into the N substituent; while the catalyst catalytic property would improve when the carbon chain in the N substituent was growed.(2) NP type ligands (L4, L5, L6) have been synthesized and characterized. The effects of reaction temperature, reaction pressure and n(AI)/n(Cr) on the catalytic performance of NP/Cr(Ⅲ)/MAO catalysts for ethylene polymerization were investigated, and also the molecular weight and melting temperature of the polymerization products were determined. The results revealed that L5 catalyst showed good catalytic activity for ethylene polymerization, and the weight-average molecular weight (Mw) of the polymerization products was relatively small and the molecular weight possessed a relatively wide distribution (polyethylene molecular weight distribution value. PDI. was at around 5.8-17.5). The Mw of the polymerization products for L4/L6 catalysts was bigger than that for L5 catalysts, and the molecular weight possessed a relatively narrow distribution (PDI was at around 1.9-5.3). The polyethylene produced through ethylene polymerization catalyzing by L4, L5 or L6 catalysts was all linear polyethylene. Under the reaction condition that the cyclohexane was used as solvent, the reaction temperature was 50℃. the reaction pressure was 3.0 MPa and n(Al)/n(Cr) was 300, the catalytic activity could reach 576.5 kg/(mol Cr·h), Mw was 698 kg/mol, PDI was 17.5 and the melting temperature (Tm) was 136.9℃ for the L5/Cr(Ⅲ)/MAO catalysts. Under the same condition, the catalytic activity could reach 42.9 kg/(mol Cr·h), Mw was 1687 kg/mol. PDI was 2.0 and Tm was 133.3℃ for L6/Cr(Ⅲ)/MAO catalysts. Compare these three NP type catalysts, it was found that the catalytic property of the catalysts would increase, Mw and number-average molecular weight (Mn) would decreased and PDI would increase significantly when the S atom was introduced into N substituent; while the catalytic property of the catalysts would decrease, Mw and Mn would increase and PDI would decrease significantly when the carbon chain in N substituent was growed. |
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