| 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, including the straight chain terminal olefins of C4 and above it, and high molecular weight polyethylene with its derivatives. Polyethylene can be roughly divided into four parts:low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE) and any other special function of polyethylene material. Linear alpha olefins have different purposes. Such as the light fraction (1-C4,1-C6 and 1-C8) can be used for the production of polyolefin comonomer, 1-C10, 1-C12 and 1-C14 can be used to produce synthetic oil, detergent, shampoo and other senior supplies for daily use, while≥1-C20 are the integral component of lubricating oil additives, oil field chemicals and other products. Many scientists at home and abroad did a lot of research work around the development of catalysts on ethylene oligomerization and polymerization, including the development of transition metal single site catalysts for olefin polymerization as a hotspot.In this paper, with the design, synthesis and characterization of two novel pyrazole ligands, the catalytic systems of ligand, transition metal based and methylaluminoxane (MAO) were structured for ethylene oligomerization and polymerization. The effects of reaction temperature, Al/Cr molar ratio and so on were investigated. The main research work is as follows:(1)The catalytic systems of pyrazolyl ligand, chromium compound and MAO were structured for ethylene oligomerization toward linear α-olefin. The effects of reaction temperature, reaction pressure, Al/Cr molar ratio and solvent on the performance of the catalytic systems for ethylene oligomerization were investigated. With a series of reaction conditions such as 50℃,2 MPa and so on, the results revealed that the catalytic system of 3,5-dimethylpyrazole/CrCl3(THF)3/MAO showed good selectivity of linear a-olefin towards ethylene oligomerization with activities up to 97.89% and 1-C6-～1-C12= to 66.28% with activity to 4.19×106 g/mol Cr.h.(2)Bis(pyrazolyl)silane (L1) was synthesized, characterized the structure of the ligand with 1H-NMR and 13C-NMR, and complexed with the transition metal of Fe, Ti, V, Zr, Cr, Ni. The performance of transition metal complexes on ethylene polymerization and oligomerization was studied under the condition of MAO as cocatalyst. The effects of reaction temperature and Al/M molar ratio on the performance of the catalytic systems were investigated. The molecular weight of polymerization products and the melting temperature were determined. The results revealed that the influence on reaction temperature and Al/M mole ratio to different complex showed different results. The catalysts using Fe, Ti, V, Zr,Cr as the active center showed the effect of ethylene polymerization. The order of catalytic activity showed that V and Cr was the highest activity of catalysts, then Ti, Zr, Fe. The product with the catalyst of V obtained the higher molecular weight, and the weight average molecular weight of complex 4 (V catalyst) was 800 to 2100 kg/mol, while others was below 1000 kg/mol. The molecular weight distribution is mostly 2 to 4, the melting temperature was 129.0 to 137.6℃. The catalysts using Ni as the active center showed the effect of ethylene oligomerization, the better activity of it was at 70℃ and Al/Ni mole ratio 800, while at 30℃ and Al/Ni mole ratio 800, the catalyst showed good electivity of linear α-olefin towards ethylene oligomerization (C4= and C6=) with 97.89% of the product, and C4= with 96.8%, activity of it was 189 kg/mol Ni.h.(3) 3,5-dimethyl-n-diphenylphosphine pyrazole (L2) was synthesized, characterized the structure of the ligand with 1H-NMR and 31P-NMR, and complexed with the transition metal of Fe, Co, Ti, V, Zr, Cr, Ni. The performance of transition metal complexes on ethylene polymerization and oligomerization was studied under the condition of MAO as cocatalyst. The effects of reaction temperature and Al/M molar ratio on the performance of the catalytic systems were investigated. The molecular weight of polymerization products and the melting temperature were determined. The results revealed that the influence on reaction temperature and Al/M mole ratio to different complex showed different results. The catalysts using Fe, Co, Ti, V, Zr as the active center showed the effect of ethylene polymerization, And among them, the catalyst using VCl4 as the active center showed the highest activity of 315.4 kg/mol V.h, the product has the highest molecular weight (>1000 kg/mol)and a narrow molecular weight distribution (2 to 3), while the product of the melting temperature and crystallinity were lower to others because of branching. CoCl2, TiCl3, VCl3, ZrCl4 and other metal complexes also had good activity of polymerization. The catalysts using Cr, Ni as the active center showed the effect of ethylene oligomerization. The oligomer of CrCl3 complex showed wide molecular weight distribution. Ethylene oligomerization activity of NiBr2 complex was higher than L1,and with 50℃, Al/Ni mole ratio 800 it has better electivity of linear α-olefin. |
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