Abstract
In a typical polymerization process, the raw polymer product contains significant amounts of unreacted monomer and other materials. To remove these contaminants, the raw polymer resin is passed to large bins, where nitrogen is used to purge them out. The off gas from this step contains nitrogen, unreacted olefin monomers and other process-specific materials. Unreacted monomers are quite expensive and they have to be recovered for reuse. A common current treatment for off gas is to flare it. Therefore, it causes significant economical loss and air pollution problems. Amount of CO2 generated from flaring are aggravating the atmosphere of plant workers and green house effect. In this work we developed the hybrid system of membrane and cold-condensation, which can overcome the problems encountered with appreciable performances. The off-gas stream was pressurized and cooled, and some unreacted monomer in the off gas was condensed. The remaining off gas containing some of uncondensed monomer was introduced into membrane module and the monomer content in the retentate stream was reduced to the level for vent. Novel organophilic polymer composite membranes were prepared by silica filled PDMS coating process, which allow in process recycling and concentrating of the permeate stream. The simulated feed gas with 30 mol % propylene monomer and nitrogen was prepared for the test. The efficiency of propylene monomer removal and recovery reached up to 95 % by this hybrid system. Various operating parameters were optimized by real tests and simulation based on thermodynamic data.
