Preparation, Characterization And Application Of Transition Metal Cr, Ni And Pd Catalysts For Olefin Polymerization

With the highest production capacity and the widest application areas within all the polymer materials, polyolefin resins have exceeded100million metric tons of consumption per year in the world. Nowadays, polyolefins are widely used in many fields such as industry, agriculture, military, medical hygiene and everyday life because of their light mass, impact resistance, erosion resistance, insulation, transparency, non-toxicity and low price etc. Polyethylene (PE) has the highest production of the polyolefins. The catalysts are the key technology of the polyethylene production process, which mainly consist of Ziegler-Natta type titanium-based catalyst, chromium-based catalyst, metallocene catalyst and late transition metal catalyst etc. Therein, chromium-based catalyst resin has the unique role for its special long chain branched structure, broad molecular distribution, easy-processing behavior. However, chromium-based catalysts are more sensitive to trace of moisture and oxygen compared with titanium-based catalysts, which leads to the difficulty of research and development. The polymerization mechanism upon chromium-based catalysts is still unknown and the research of the polymerization kinetics, especially gas phase polymerization kinetics, is not reported yet. Therefore, it is indispensable to prepare new chromium-based catalysts and to develop high property and value-added PE resins via the research of gas phase polymerization mechanism and kinetics of chromium-based catalysts. Moreover, as a new type of polyethylene catalysts, late transition metal catalyst mainly including nickel and palladium homogeneous catalysts is attracting more and more attention in polyolefin field. The design, synthesis and application of new nickel and palladium catalysts possess the significant academic value and potential application.The dissertation is mainly comprised of four parts.Part one:Research of [(C6H5)3SiO]2CrO2/AlR3/SiO2catalystA series of supported [(C6H5)3SiO2CrO2AlR3/SiO2catalysts were prepared using bis(triphenylsilyl)chromate(BC) as the active component. The catalyst morphology and structural properties were characterized and the possible mechanism of initiation reaction at the early stage of ethylene polymerization upon the catalyst was discussed. By special inner structure polymerization reactor and experimental procedure, gas phase ethylene polymerization upon the chromium catalyst in the lab was conducted for the first time, and chromium content and Al/Cr molar ratio effects on the catalyst and polymer properties were also investigated. Moreover, gas phase ethylene polymerization of the three typical [(C6H5)3SiO]2CrO2AlR3/SiO2catalysts of Al/Cr molar ratio3.0,4.2,6.0were systematically investigated.1) The particle size distribution, pore structure and morphology of the catalyst and the initial silica support are similar, which are not affected by the preparation procedure of the catalyst. The produced initial polymer particle duplicates the catalyst particle morphology.2) ESR characterization results show that chromium valence of the catalyst changes dramatically before and after exposure to ethylene. The polymerization active sites are low valence states of the chromium. Before exposure to ethylene, high valence states such as CrⅥ and CrⅤ are the major states of the catalyst while low valence states such as CrⅡ and CrⅢ are the dominating states after exposure to ethylene and initiation of polymerization.3) The activity of the catalyst with the Al/Cr molar ratio as follows:catalyst activity rises firstly, reaches the maximum value and then decreases with the Al/Cr molar ratio increases. The highest activity occurs at the Al/Cr mole ratio being4.2-4.6.4) During the gas phase ethylene polymerization process, the catalyst activity rises and molecular weight of the produced polymer lowers when the polymerization temperature increases or the polymerization pressure decreases.5) As for [(C6H5)3SiO]2CrO2/AlR3/SiO2catalysts of Al/Cr molar ratio4.2, hydrogen as a chain transfer agent attacks the Cr-polymer bond to produce Cr-H species, which leads to lower molecular weight and higher melt fluid index of the produced polymer. At the same time, hydrogen results in ethylene partial pressure reduction and decrease of catalyst activity.1-Butene as the comonomer can introduce the short chain branches in the main chain and reduce density and crystallinity of the produced polymer, while1-Butene as the chain transfer agent can also changes the molecular weight and MFR of the produced polymer drastically.6) The three catalysts have similar kinetic curves as follows:firstly rise, reach the maximum value and decline slowly. In comparison,[(C6H5)3SiO]2CrO2AlR3/SiO2catalysts of Al/Cr molar ratio4.2has the higher activity and longer time to the maximum polymerization rate (40mins), while [(C6H5)3SiO]2CrO2/AIR3/SiO2 catalysts of Al/Cr mole ratio3.0and [(C6H5)SiO]2CrO2/AlR3/SiO2catalysts of Al/Cr mole ratio6.0have lower activity and shorter time to the maximum activity value (20-25mins).Part two:Preparation, characterization and catalytic ethylene polymerization of CrOx/AlR3/SiO2catalystSupported CrOx/AlR3/SiO2catalyst was prepared via impregnation, dryness, activation and reduction steps using cheap and low toxic alkaline chromium acetate as the starting material. By a series characterization techniques of FT-IR, TG-DTA, XPS, DSC, SEM and ESR, we systematically investigated the mechanism of the catalyst supporting and activation, and studied on the effects of catalyst preparation procedure and formula on the catalyst and produced polymer properties and gas phase polymerization kinetics. The new chromium catalyst CrOx/AlR3/SiO2possesses the following advantages such as low cost, low toxicity, high activity, hydrogen sensitivity and good copolymerization behavior.1) The decomposition temperature of alkaline chromium acetate supported on the silica decreases from314℃to299℃because higher Cr species dispersion on silica results in easier decomposition of chromium compound. FT-IR results show that oxidation decomposition of Cr3(CH3COO)7(OH)2strengthens at300℃and almost end at400℃. The process produces CrO3, H2O and CO2, and CrO3goes on esterification with surface silanol group to produce chromate species. Meanwhile, FT-IR and TG-DTA results show that inductive decomposition of CrO3to Cr2O3occurs at430-460℃. CrO3supported or not has dramatic effect on its decomposition because of its low melting point and tendency of inductive reduction to stable aggregation of Cr2O3at high temperature. As for CrO3/SiO2sample, the esterification is liable to occur at242-304℃.2) Alkaline chromium acetate and CrO3exhibit stable Y signal assigned to Cr5+when the activation temperature is at300℃and this signal still exists stably when the temperature is at600℃. The result indicates that during the catalyst activation process most of Cr species react with surface silanol to produce chromate species of VI valence state while a small portion of Cr exists stably as the supported form of V valence state.3) During the catalyst preparation process, chromium content, activation temperature and reduction agent have some effects on catalyst and produced polymer properties. Using DEAE as reduction agent, prepared catalyst exhibits medium activity and produced polymer has medium molecular weight. With chromium content of the catalyst increase, catalyst activity rises and molecular weight of the produced polymer reduces. Activation temperature at600℃, the catalyst exhibits maximum activity and produced polymer has medium molecular weight. Al/Cr molar ratio of the catalyst between1.5and8.0, with Al/Cr molar ratio increase, the catalyst activity rises and produced polymer has the medium molecular weight when Al/Cr mole ratio between4.5and6.0. Therefore, catalyst and produced polymer properties can be adjusted through preparation formula and process conditions.4) Polymerization temperature, pressure, hydrogen and comonomer have some effects on the catalytic polymerization behavior and properties of produced polymer. With the polymerization temperature increase, catalyst activity rises and produced polymer molecular weight lowers. With the polymerization pressure increase, catalyst activity rises and produced polymer molecular weight increases. With the addition of hydrogen to polymerization system, catalyst activity reduces somewhat and polymer molecular weight lowers. Comonomer of1-butene within a certain range can enhance the catalyst activity and lower polymer density.5) Gas phase polymerization kinetics of the catalyst belongs to a type of increase first and then slow decline curve, which is stable reaction. Catalyst formula and polymerization process conditions such as temperature, pressure, hydrogen and comonomer have some effects on the polymerization kinetics.Part three:Research of [(C6H5)3SiO]2CrO2/CrOx/AlR3/SiO2catalystBased on CrO3/SiO2catalyst,[(C6H5)SiO]2CrO2CrOx/AlR3/SiO2catalyst was prepared. New catalyst preparation and polymerization process conditions were investigated, and the produced polymer properties and optimum reaction conditions were also studied. The new catalyst was prepared by chromium acetate of III valence state as the starting material instead of the traditional toxic bis(triphenylsilyl)chromate, which decreases harm during catalyst preparation and new catalyst has simple preparation method with low cost.1) On the basis of [(C6H5)3SiO]2CrO2/CrOx AlR3/SiO2catalyst characterization, polymerization, produced polymer and starting material cost, the optimum value of TPS addition should be Si/Cr=1.5.2) The experimental results of catalyst activity and cocatalyst amount show that TEA is the suitable cocatalyst for the new catalyst system. AlR3/SiO2catalyst by MAO as cocatalyst exhibits one times higher activity of ethylene polymerization than [(C6H5)3SiO]2CrO2/AlR3/SiO2catalyst.3)[(C6H5)3SiO]2CrO2/CrOx/AlR3/SiO2catalyst content has drastic effect on the catalyst activity. Low slurry concentration of catalyst content favors to its activity.4) The hydrogen and comonomer experimental results of [(C6H5)3SiO]2CrO2/CrOx/AlR3/SiO2catalyst show that with the comonomer of1-hexene addition, melt peak of produced polymer become broader and bimodal. And with addition amount of1-hexene increase, the low melt peak become bigger, which indicates the number of short chain branch rises.[(C6H5)3SiO]2CrO2/CrOx/AlR3/SiO2catalyst exhibits equivalent hydrogen response with [(C6H5)SiO]2CrO2/AlR3/SiO2catalyst.Part four:Preparation, characterization and catalytic ethylene polymerization of new P^N ligands and their Ni, Pd complexesOn the basis of design and synthesis of new transition metal complexes for catalytic ethylene reaction, two new P^N ligands bearing bulky strong electron-withdrawing group-bis(2,4,6-tris(trifluromethyl)phenyl)phospino pyridine were successfully prepared. The transition metal complexes of nickel and palladium were prepared by the reaction of corresponding ligands and metal halide. These complexes are active for ethylene oligomerization and/or polymerization. The relationship between the ligand environment of electronic and steric effects and the catalytic activity were elucidated.1) Two new bearing bulky strong electron-withdrawing group-bis (2,4,6-tris (trifluromethyl)phenyl)phospino pyridine were initially prepared. In order to prepare bis(2,4,6-tris(trifluromethyl)phenyl)phospino chloride, the side product2,4,6-tris (trifluromethyl)phenyl phospino dichloride was conducted to keep on reacting with tris(trifluromethyl)phenyl lithium salt and the target compound yield was successfully increased from35%to90%, which supplied enough material for the further synthesis of the ligands. Pyridine alcohol compound was activated through n-butyl lithium to accomplish the preparation of bis(2,4,6-tris(trifluromethyl) phenyl)phospine P^N ligands, which solved the difficulty of triethylamine reacting with bis(2,4,6-tris (trifluromethyl)phenyl)phospino chloride.2) A neutral nickel complex containing the above ligand was prepared, and the relevant1H NMR,31P NMR and catalytic ethylene reaction were briefly studied.1H NMR and31P NMR spectra show broad peak. The results indicate that the neutral nickel complex is paramagnetic and the space configuration is tetrahedron centered metal nickel. The nickel complex is active for ethylene reaction activated by MAO. The results show that the nickel complex is active for ethylene polymerization. The catalytic life is for about3.5hr at latm of ethylene pressure and room temperature. The catalytic activity of the complex was improved from130to151molC2H4/molNi.h by elevation of Al/Cr molar ratio from140to350.3) Two neutral and cationic palladium complexes bearing the above ligands were synthesized and characterized. X-ray crystal determination of the complexes verified that the complexes are ligated by P^N and their geometries around the metal centers are square planar. The cationic complexes are active for ethylene oligomerization. The catalytic activity of the complex exhibits30-50molCaH4/molPd.h at latm of ethylene pressure and20℃while showes200-350molC2H4/molPd.h at20atm of ethylene pressure and20℃. The inner olefins like CH3CH=CHCH3are the major products. Ortho-H of pyridine substituted by methyl, steric effect of the corresponding complex and coverage to central palladium strengthen and the cationic complex catalytic reactivity for ethylene oligomerization lowers. On the other hand, the steric effect also hinders β-H elimination which leads to increased C6olefins content of oligomeric product.