Multiple stage devolatilization process for mass processable polymers

Claim 1

A multiple-stage vacuum flash devolatilization process for removing volatiles selected from the group consisting essentially of unreacted monomers, dimers, and trimers from a thermoplastic polymeric material consisting essentially of a mass processable polymer containing said volatiles to produce a polymeric material containing less than about 0.1% by weight of volatiles, comprising the steps of: (a) heating said thermoplastic polymeric material to a temperature at least above its softening point but below its degradation temperature; (b) feeding said heated thermoplastic polymeric material through a first flash devolatilization zone maintained at a first sub-atmospheric pressure sufficient to vaporize and remove a major portion of said volatiles from said polymeric material but which is above the pressure at which mechanical refrigeration is needed to condense the vaporized volatiles, whereby there is produced in said first flash devolatilization zone a partially devolatilized thermoplastic polymeric material; (c) withdrawing a first stream of vaporized volatiles at said first sub-atmospheric pressure from said first flash devolatilization zone; (d) feeding said partially devolatilized thermoplastic polymeric material to at least one additional flash devolatilization zone, maintained at a second sub-atmospheric pressure which is below said first sub-atmospheric pressure of said first flash devolatilization zone and which is sufficient to vaporize and remove the remaining amount of said volatiles from said polymeric material to produce a finally devolatilized thermoplastic polymeric material containing less than about 0.1% by weight of volatiles; (e) withdrawing a second stream of vaporized volatiles at said second sub-atmospheric pressure from said additional flash devolatilization zone; (f) feeding the second stream of volatiles from said additional flash devolatilization zone into the first stream of volatiles withdrawn from said first flash devolatilization zone, to produce a combined stream of volatiles at first sub-atmospheric pressure; and (g) condensing the combined stream of volatiles by contacting said combined stream with a heat transfer surface which has been cooled by cooling water which itself has been cooled without the use of mechanical refrigeration to a temperature sufficient to condense said volatiles at said first sub-atmospheric pressure.