Preparation And Performance Of Composite Ionic Liquids Catalyst For Propylene Dimerization

Dimers of propylene are valuable chemicals. Especially, the hydrogenation product of 2, 3-dimethy-2-butene is the green additive of aviation and motor gasoline,4-methyl-l-pentene is used as plastic monomer,1-hexene can be used in the manufacture of perfumes and resins. Catalyst of propylene dimerization is mainly based on nickel complexes. Dual-salicylaldehyde nickel complexes and Salen-type nickel complexes have been used to catalyze propylene dimerization and gave high catalytic activity and satisfactory stability in homogeneous catalyses. In this paper, composite catalysts were prepared by nickel complexes combined with MCM-41 molecular sieve grafted by functionalized ionic liquid. Therefore, the catalytic performances of those composite catalysts could be tested by gas-solid phase contimuous fixed-bed reactor. The main contributions are as follows.Firstly, the basic structure and purity of synthesized bis [salicylaldehyde (p-nitrophenyl) imide] nickel, bis [salicylaldehyde (o-methylphenyl) imino] nickel, Salen I nickel complexes and Salen II nickel complexes were identified by FT-IR and melting point test. TSIL 1-(3-propyl-triethoxysilane)-3-methylimidazolium hexafluorophosphate was prepared by two-step method. The presence of the TSIL was confirmed through FT-IR and NMR. The IL grafted molecular seive was obtained by introducing the synthesized TSIL into MCM-41 sieve by grafting method. It was found that the TSIL was combined with molecular sieve MCM-41 by FT-IR and TG detection. The target composite ionic liquid catalysts were prepared by leading nickel complexes into the IL grafted molecular seive through high-pressure immersion method..Then, effect of reaction condition on slectivity of propylene dimerization and slectivity of isomer within dimers were investigated using the catalyst system of dual-saliculaldehyde nickel complexes. It showed that the selectivity of propylene dimerization could reach more than 80.0% by using composite catalyst system of bis [salicylaldehyde (p-nitrophenyl) imino] nickel. By contrast, the selectivity of propylene dimerization was elevated to 90.9% when the composite catalyst system of bis [salicylaldehyde (o-phenyl) imino] nickel was adopted. At the same time, the selectivity of 1-Hex in dimmers was 89.4%.Further, effect of reaction condition on slectivity of propylene dimerization and slectivity of isomer within dimers were investigated using the system of Salen-type nickel composite catalyst. Selectivity of propylene dimerization was slightly lower in composite catalyst system of Salen-type nickel, which has rigid structure, than in composite catalyst system of dual-saliculaldehyde nickel. Selectivity of propylene dimerization attained to 85.7% in Salen Ⅱ-type composited catalyst system. And it was demonstrated that imine part of Salen-type nickel almost gave no difference on the catalytic performance for propylene dimerization. However, selectivity of 4-MP within dimers was increased significantly in Salen Ⅱ-type composited catalyst system, up to 81.2%Finally, the external reaction conditions, such as reaction temperature and pressure, were easier to control in fixed bed operation. By contrast to homogeneous catalysis in batch reactor, the reuse problem of catalyst was overcome. Through gas-solid phase fixed-bed reactor contimuous operation mode, the selectivity of propylene dimerization was maintained more than 80.0%. But the slectivities of isomer within dimers were different under different catalyst.