Seeking advice on issues in the slurry process for ethylene polymerization
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Gentle experts, I have just started working in the field of olefin polymerization and have many questions. In the slurry process for ethylene polymerization, such as the CX process and the Hostalen process, how is the multiphase Z-N catalyst, polymer particles, and dispersant (n-hexane) separated after the reaction? Both catalyst particles and polymer particles are solids; how can they be separated from each other?
The processes in Basel involve separation using centrifuges; the catalysts and aluminum alkyls are deactivated in a powder treatment chamber, and after deactivation, the deactivated catalysts and aluminum alkyls are mixed with the powder and then extruded into granules.
n-Hexane is separated by a centrifuge to yield 65-75% hexane, and the remaining hexane is removed through heating in a fluidized drying bed. The powder exiting the fluidized bed is required to have a hexane content of less than 1%. This powder then enters a degassing chamber where it is exposed to a mixture of steam and nitrogen at a temperature of 95-100 degrees Celsius; the steam helps to deactivate the catalysts present in the powder, and the degassing chamber further removes any remaining trace amounts of hexane through temperature control
In current polyolefin production processes, the catalyst remains in the product and no separation is required; generally, deactivation is carried out in the later stages of the process. In principle, the catalyst particles are enclosed within the polyolefin particles, so it’s not possible to separate them. What was said above regarding the removal of hexane explains this clearly
For the slurry process of ethylene polymerization, such as the CX process and the Hostalen process, three methods are generally used to separate catalyst particles from polymer particles: mechanical separation, centrifugal separation, and gravitational separation. Mechanical separation methods can be carried out using filters or filter cloths, while centrifugal separation methods can employ precipitation or centrifuges. The gravitational separation method achieves separation by taking advantage of the difference in forces between molecules composed of different substances in various solvents