Synthesis of Bimodal Polyethylene Using Ziegler-Natta Catalysts by Multiple H_2 Concentration Switching in a Single Slurry Reactor

摘要

A simple, inexpensive and powerful method for synthesizing bimodal PE using Ziegler-Natta catalysis by multiple switching of the H_2 concentration in a single slurry reactor is reported. The effects of polymerization type, hydrogen concentration, reaction time distribution and switching times on the MWD are investigated. The results show that the MWD produced by forcibly removing the gas during the switching process are much broader than those of PEs produced by directed replacement. In addition, the former can prominently enhance the value of M_w/M_n compared to conventional methods, showing an increase from 7 to 27. The MWDs obtained are bimodal for H_2 concentrations ranging from 63 to 75 vol.-% and have different shapes under different conditions.