Separation and recovery of products obtained in catalytic processes of preparing acrylonitrile polymers or copolymers

Claim 1

A method of separating and recovering both sulphur dioxide and unreacted monomer from the polymer or copolymer slurry obtained from polymerizing acrylonitrile monomer or from copolymerizing a mixture of acrylonitrile monomer and a further ethylenically unsaturated monomer copolymerizable therewith, the polymerizing or copolymerizing occurring in an aqueous medium and in the presence of a catalytic redox system which includes sulphur dioxide or a sulfite in combination with a compound selected from the group consisting of peroxides, persulfates and chlorates; said method comprising the steps of 1. admixing with said slurry a polymerization inhibitor and a mineral acid for adjusting the pH of said slurry to 1.8 to 2.5; 2. removing sulphur dioxide from said slurry by volatilization in a first vaporization stage conducted at a pressure of from 60 to 150 mm mercury and at a slurry temperature of from 40° to 60°C; 3. scrubbing the sulphur dioxide vapors obtained from (2) with water having a temperature of from 1° to 15°C, and recycling the aqueous solution obtained to the polymerization or copolymerization medium; 4. thereafter, removing unreacted monomer from said slurry by volatization in a second vaporization stage conducted at a pressure of from 1 to 60 mm mercury and at a slurry temperature of from 30° to 55°C; and 5. scrubbing vapors obtained from (4) with water having a temperature of from 1° to 30°C, and recycling the aqueous solution obtained to the polymerization or copolymerization medium.

Claim 2

A method of separating and recovering both sulphur dioxide and unreacted monomer from the polymer or copolymer slurry obtained from polymerizing acrylonitrile monomer or from copolymerizing a mixture of acrylonitrile monomer and a further ethylenically unsaturated monomer copolymerizable therewith, the polymerizing or copolymerizing occurring in an aqueous medium and in the presence of a catalytic redox system which includes sulphur dioxide or a sulfite in combination with a compound selected from the group consisting of peroxides, persulfates and chlorates; said method comprising the steps of 1. admixing with said slurry a polymerization inhibitor and a mineral acid for adjusting the pH of said slurry to 1.8 to 2.5; 2. removing sulphur dioxide from said slurry by volatilization in a first vaporization stage conducted at a pressure of from 60 to 150 mm mercury and at a slurry temperature of from 40° to 60°C; 3. scrubbing the sulphur dioxide vapors obtained from (2) with water having a temperature of from 1° to 15°C, and recycling the aqueous solution obtained to the polymerization or copolymerization medium; 4. thereafter, removing unreacted monomer from said slurry by volatization in a second vaporization stage conducted at a pressure of from 1 to 60 mm mercury and at a slurry temperature of from 30° to 55°C; and 5. scrubbing vapors obtained from (4) with water having a temperature of from 1° to 30°C, and recycling the aqueous solution obtained to the polymerization or copolymerization medium.