Propylene Dimerization On The Alkali Metal Supported Solid Superbase

4-methyl-1-pentene?4MP1?prepared by dimerization of propylene could not only be used as a commoner of high quality linear low density polyethylene?LLDPE?,but also be self-polymerized to a new synthetic material-poly-4-methyl-1-pentene?TPX?which possessses excellent development prospects.Therefore,the 4MP1 has been paid more and more attention in the field of propylene derivative products development.It is significant to study the 4MP1 systhesis process and catalyst preparation for the foundation of industrialization development.The solid superbase K/K₂CO₃ is prepared by the fused loading method and the optimized process is obtained.In addition,the prepared catalyst is applied to the dimerization of propylene to 4MP1.Moreover,the formation mechanism of surface super basic site on 3%K/K₂CO₃ and its catalytic behavior are analyzed briefly.The major conclusions are obtained as follow:1.The preparation processes including loading temperature,loading time,loading capacity and carrier particle have been investigated.And the suitable preparing process is presented as:the loading temperature is150?,the loading time is 1.5h,the loading capacity is 3wt%of the carrier with the average particle size of 120?m.The result in the catalyst preparing process shows that increasing the dispersion degree on carrier is favorable to enhance the propylene conversion and shorten the inducing time;the particle size loaded on carrier is critical to both the dimer selectivity and the 4MP1 selectivity.2.The dimerization process of propylene to 4MP1 in the presence of3%K/K₂CO₃ has been investigated.In the optimum reaction conditions,the conversion of propylene is 43%,the selectivity of dimers is close to100%,and the selectivity of 4MP1 is 86.3%?selectivity of 4MP2 is 5.3%and selectivity of 2MP1 is 5.7%?,the inducing time is 3.3h,the reaction rate of propylene is 0.062g_propylene·g_CAT^-1·h^-1.Without the competition of propylene,average isomerization rate of 4MP1 is 0.016g_propylene·g_CAT^-1·h^-1,which consists 26%of the reaction rate of propylene dimerization.3.The solid superbase catalyst of 3%K/K₂CO₃ has the highest basicity of H_?37,and the concentration of basic sites of H_?35 is about 0.3mmol·g_CA^-11 _T,which corresponds to the opinion that the basicity of the catalyst is high enough to abstract the?-H in propylene to form the active intermediate.The catalyst surface of 3%K/K₂CO₃ is highly dispersed with metal K microcrystalline,which exhibits the bigger specific surface area,and can explain the reason of the high catalytic activity.4.The surface super basic sites on 3%K/K₂CO₃ should be composed of oxygen atom which located in the lattice defect of the metal K microcrystalline.The electron transferred from metal K microcrystalline to the conjoint oxygen atom,which enhances the electron density,reduces the binding energy and improves the capability of donating electron pairs and accepting hydrogen ions,upon that the super basic sites are formed.