The Catalytic Characteristic Of Solid Superbase K/K₂CO₃ In Synthesis Of 4-methyl-1-pentene

The synthesis of 4-methyl-l-pentene（4MP1）can be widely used for the copolymer synthesis of linear low density polyethylene（LLDPE）,and thermoplastic-poly-4-methyl-1-pentene（TPX）of the self-polymer of 4MP1,which is a kind of important novel thermoplastic plastics.Therefore,it is very significant to study and develop the synthetic technology of 4MP1 for the Industrialization development of superior olefin.In this study,the preparation of 4MP1 was studied with alkali metal supported catalyst K/K₂CO₃,and the catalytic surface characteristic was presented by FT-IR,TG-DSC and XRD.In addition,the suitable preparing condition of solid superbase K/K₂CO₃ and catalytic synthesis of 4MP1 reaction conditions are obtained.The major results are given as follows:（1）According to the characterization of surface basic site on catalyst pre-treated under different preparation parameter,acid extraneous component could be easily desorbed when carrier is treated under high temperature for a long time,which is also help to the formation of basic site on carrier surface.And high alkali metal loading amount,high carrier particle size and short loading time could obviously increase the microcrystal size on catalyst surface,improving the carrier basicity.But alkali metal on catalyst surface will lost in a high speed as catalyst pre-treated under high temperature for a long time.（2）The preparation processes including carrier pre-treated temperature,pre-treated time;alkali metal loading temperature,loading time,loading amount and carrier particle size have been investigated.And the suitable preparing process is presented as:carrier with average particle size 300 μ 3 is pre-treated under 320℃ for 2h,and then loaded on 4.3wt%potassium under 150℃ for 1.5h.The result in the catalyst preparing process shows that increasing the alkali metal dispersion degree on carrier and catalyst basicity could result in a high catalytic activity of catalyst in propylene dimerization,reaching 20%conversion per pass of propylene and 88%selectivity of 4MP1.（3）The reaction conditions including reaction temperature,reaction pressure,catalyst dilution rate,LHSV of propylene has been investigated.And under the optimum reaction condition of 150℃,8MPa,catalyst dilution rate 1:1,1.Oh-1,the conversion of propylene is 20%and the selectivity of 4MP1 is more than 88%.Solid super-base K/K₂CO₃ is implemented in fix bed reactor for more than 200h,reaching 19%conversion per pass of propylene and 87%selectivity to 4MP1.（4）Isomerization of 4MP1 increase with the reaction temperature rising up.When reaction temperature higher than 180℃,isomerization of 4MP1 almost consists 35.6%of the reaction rate of propylene dimerization.Decreasing reaction temperature and increasing LHSV of propylene could obviously reduce the amount of isomer.Propylene is more likely adsorbed on surface basic site of K/K2C03 than 4MP1,which could weaken the isomerization of 4MP1 under high reaction pressure.Without feeding with propylene,high reaction pressure apparently accelerate the isomerization of 4MP1.