Synthesis And Immobilization Of Iron Acetylacetonate/Bis(imino)pyridyl Ligand Catalysts For Ethylene Oligomerization

Linearα-olefins are important petrochemical materials and they are used primarily for production of linear low-density polyethylene,detergents,plasticizers and synthetic lubricants additives. Currently, the main method to produce linearα-olefins is ethylene oligomerization. The bis(imino)pyridyl iron complexes developed by Brookhart and Gibson group, because of its high activity and selectivity in ethylene oligomerization, have became an very important research field. Generally, these catalysts can be obtained by the reaction of bis(imino)pyridyl ligands with FeCl2,FeCl3 or FeBr2. The preparation process of these catalysts is relatively complex. Acetylacetone iron is a cheap organic metal compounds, usually used together with AlR3,electron donor as catalysts for the polymerization of conjugated diene and the copolymerizaton of maleic anhydride with isoprene, in addition, this catalytic systems also used as catalysts for production of polyethylene with different molecular distribution, but its use for the production of linearα-olefins have not been reported.Based on the idea that the catalytic activity and products distribution in ethylene oligomerization can be control by tailoring the center late transition metal's coordination environment and regulation of reaction conditions, we investigated the ethylene oligomerization behavior of the catalyst systems containing bis(imino)pyridyl ligands with different structure,acetylacetone iron and MAO, as well as the iron catalysts immobilized on MCM-41,ZSM-5 molecular sieves. Firstly, five bis(imino)pyridyl ligands with different structure were synthesized and used together with acetylacetone iron,MAO as efficient catalysts for ethylene oligomerization, then discussed the steric and electronic effect of the ligands on the catalytic activity and the distribution of the oligomerization products. Secondly we investigated the co-oligomerization behavior of ethylene with 1-pentene or 1-hexene, as well as the dimerization behavior of 1-hexene, giving an explanation for production of non-linearα-olefin in the reaction process. In addition, we immobilized the homogeneous iron catalysts on MCM-41 and ZSM-5 molecular sieves, then invesgated the effect of the structure of molecular sieve and temperature on the ethylene oligomerization behavior. Our work in more detail:1.Five bis(imino)pyridyl ligands (2-R1N=C(Me)-6-R2N=C(Me)C5H3N) (L1:R1=R2=C6H5; L2:R1=R2=2-MeC6H4; L3:R1=R2=2-Me-4-(OMe)C6H3; L4: 2-Me-4-(Cl)C6H3; L5:2-Cl-4-(Me)C6H3) were synthesized and used together with acetylacetone iro,MAO as efficient catalysts for ethylene oligomerization, with activity between 106-107 g/mol Fe-h-bar and linear a-olefins selectivity more than 95%. The preparation process of these catalysts is very simple, whick increase the efficiency of the preparation process and reduced the cost. Bis(imino)pyridyl ligands play a vital role in the catalytic system. Without the bis(imino)pyridyl ligands, activated by MAO, the iron acetylacetonate can not catalyze the ethylene oligomerization reaction.2.The effect of structure of the bis(imino)pyridyl ligands,cocatalysts,temperatures Al/Fe molar ratio and pressure on the oligomerization behavior of the iron catalysts is studied. MAO is more efficient than TEA and TIBA for ethylene oligomerization, with better catalytic activity and selectivity for linearα-olefins. Catalytic activities and distributions of oligomers for bis (imino) pyridyl iron acetylacetonate complexes are influenced greatly by the structures of the ligands, the proper size and electronic effect of the substituents are the main effects on the catalytic behavior. The temperature has a significant effect on catalytic activities and oligomers distribution.With the increase of reaction temperature, the activities decrease rapidly and more low-molecular-weight products are produced. With the Al/Fe molar ratio increasing from 500 to 3000, catalytic activities increase rapidly at first, and reach the highest activities at Al/Fe=2000, then decrease slowly. The distribution of obtained oligomers is almost invariant with the Al/Fe molar ratio; as the ethylene pressure increased, the catalytic acticity increased almost linearly, while more low-molecular-weight oligomers are produced.3. A mechanism is proposed for production of non-linear a-olefin in the reaction process is illustrated. In addition to the oligomerization of ethylene, the low molar-mass a-olefins (such as 1-hexene) produced by ethylene oligomerization process may co-oligomerize with ethylene or dimerize with itself. This is the reason why non-linear olefins produced during the reaction process.4. Iron catalysts immobilized on MCM-41 and ZSM-5 molecular sieves were prepared and the effect of the reaction condition on the catalytic behavior were investigated. Compared with the homogeneous iron catalysts, the immobilized catalysts have lower activity at 30℃and 50℃but better thermal stability, when the temperature reaching 70℃, the immobilized catalysts have higher activity. In addition to its high temperature performance, the molecular sieve-immobilized catalyst possessed relatively high selectivities for low molar-mass a-olefin compared to the homogeneous catalyst. ZSM-5 immobilized catalyst possessed relatively high selectivities for low molar-massα-olefin than MCM-41-immobilized catalyst. The distribution of obtained oligomers catalyzed by molecular sieve-immobilized catalyst is almost invariant with the Al/Fe molar ratio.