Ultrasound Enhanced Devolatilization Of Polyethylene

Condensate mediums were introduced into fluid bed reactor to increase the Space-Time-Yield (STY) in gas phase polymerization of ethylene. Polyethylene particle from fluid bed contained much ethylene, comonomer and condensate medium. Because these hydrocarbon micromolecules were dissolved in the polyethylene it requires a much longer time for effective removal. So it is necessary to improve the devolatilization for the continous production of polyolefine.Ultrasound-enhanced devolatilization is one of the most promising methods. Ultrasound can overcome the affinity of the adsorbates with the adsorbent surface and accelerate the molecular transport towards and from the adsorbent surface.In the thesis ultrasound was adopted to enhance the devolatilization of polyethylene, it consists of four parts:The n-hexane devolatilization processes of DGM1820, ML2202 polyethylene were investigated with and without ultrasound at different conditions. The rate of devolatilization was faster and the devolatilization time was shorten with increasing temperature and purge gas flux in the experiment range. On all the operation condition, the total desorption time required less about 35% and the diffusion coefficient increased about 40-80% with ultrasound. The major mechanism of ultrasonic enhancement on devolatilization is ultrasonic cavitation resulting in non- thermal effects.The devolatilization processs of DGM1820 polyethylene was divided into two steps. The devolatilization rate can be computed by using thequasi-homogeneous spherical model: .Accroding tothe model, the diffusion and transfer coefficient can be larger with ultrasound than that of without ultrasound.The devolatilization process of ML2202 polyethylene can be considered to be one step, and the devolatilization rate can be calculated by using the model: which meet the experimental data very well.The crystallinity of polyethylene didn't change after ultrasound radiation,which showed that ultrasound would not destroy the internal structure of polyethylene.Study results showed that it would be efficient for the devolatilization process of polyethylene if ultrasound was used properly in industry. Using ultrasound, degassing process will be enhanced largely. Ultrasound-enhanced devolatilization could be a better way to improve the productivety of polyolefine resins.