Effect of hydrogen on the ethylene polymerization process over Ziegler-Natta catalysts supported on MgCl2(THF)2. II. Kinetic studies

Ethylene Polymerization over Supported Vanadium-Magnesium Catalysts with Different Vanadium Content: The Effect of Hydrogen on Molecular Weight Characteristics of the Produced Bimodal Polyethylene

“…As supposed earlier [14], deactivation of the vanadium-magnesium catalyst upon hydrogen introduction is related to the transition of a part of active sites containing vanadium-polymer bonds to a temporarily inactive state due to adsorption of the alkyl aluminum hydride that forms in the presence of hydrogen. In reference [14] it was shown that these sites became active again when hydrogen was removed from the reaction medium, thus enhancing the VMC activity. A more abrupt decrease in the Figure 1.…”

“…As supposed earlier [14], deactivation of the vanadium-magnesium catalyst upon hydrogen introduction is related to the transition of a part of active sites containing vanadium-polymer bonds to a temporarily inactive state due to adsorption of the alkyl aluminum hydride that forms in the presence of hydrogen. In reference [14] it was shown that these sites became active again when hydrogen was removed from the reaction medium, thus enhancing the VMC activity. A more abrupt decrease in the activity of the "low-loading" VC1 catalyst upon introduction of hydrogen in the polymerization medium may be associated with greater accessibility of active sites in the VC1 catalyst to the interaction with alkyl aluminum hydride compared to the active sites present in the VC2 catalyst.…”

“…The composition of the active component may exert a considerable effect on the molecular weight characteristics of HDPE. In particular, supported vanadium-magnesium catalysts (VMCs), which contain vanadium chloride as the active component deposited on MgCl 2 , differ considerably from TMCs regarding the regulation of molecular structure of PE and copolymers of ethylene with α-olefin [2,3,[6][7][8][9][10][11][12][13][14][15][16][17][18]. Unlike TMCs, VMCs make it possible to produce PE with a broad or bimodal MWD in one polymerization reactor with polydispersity (M w /M n values) within the range of 15-33 [7][8][9][10][11][12][13][14][15][16][17][18].…”

“…In particular, supported vanadium-magnesium catalysts (VMCs), which contain vanadium chloride as the active component deposited on MgCl 2 , differ considerably from TMCs regarding the regulation of molecular structure of PE and copolymers of ethylene with α-olefin [2,3,[6][7][8][9][10][11][12][13][14][15][16][17][18]. Unlike TMCs, VMCs make it possible to produce PE with a broad or bimodal MWD in one polymerization reactor with polydispersity (M w /M n values) within the range of 15-33 [7][8][9][10][11][12][13][14][15][16][17][18]. However, the Catalysts 2022, 12, 985 2 of 10 main problem in the application of vanadium-magnesium catalysts for the production of polyethylenes with broad MWD is their deactivation in the presence of hydrogen, which is used to control the molecular weight of PE.…”

Geometry and local environment of surface sites in Vanadium-based Ziegler-Natta catalysts from 51V solid-state NMR Spectroscopy

“…[29][30][31] In this work, we decided to focus on VOCl3@MgCl2(thf)1.5 because of the large set of experimental data for the corresponding Ti systems, TiCl4@MgCl2(thf)1.5. 2,14,32 By confronting experimental 51 V NMR spectra with calculated NMR data obtained from computational models, we elucidate the coordination environment, local geometry and the interacting surface sites of MgCl2.…”