Removal during polymer recycling

During solution polymerization the monomer, catalyst, and diluent are introduced to a reactor maintained at a temperature between 175 and 250 °C. The resulting polymer forms a viscous solution in the solvent, which is pumped out of the reactor. If necessary, the solution can be filtered to remove the catalyst residue. Solvent is removed from the solution and recycled, leaving behind a mixture of isotactic and a small amount of atactic polypropylene. 

In the solution process, the reaction is carried out in the presence of an inert hydrocarbon which dissolves the polymer as it is formed. The solvent may contain a portion of cycloparaffin. Both monomer and polymer remain in solution during the reaction while the catalyst is maintained in suspension by agitation. Reaction temperatures range from about 125°-175°C. and reaction pressures from 20-30 atm. The reactor product is withdrawn, and monomer is flashed off and recycled. Suspended catalyst is then removed by filtration, and solvent is flashed from the filtrate with steam. 

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