Process for brominating butadiene/vinyl aromatic copolymers
View Patent ↗A polybutadiene brominating method uses a quaternary ammonium tribromide as the brominating agent. The brominating is performed in solution, and dual extractions recover the spent brominating agent and recombine it with fresh bromine to regenerate an active tribromide. Solvent and aqueous extraction streams can be purified and recycled as needed.
1. A process comprising
a. contacting a starting butadiene polymer containing aliphatic carbon-carbon double bonds with a quaternary ammonium tribromide under conditions such that the starting butadiene polymer and the quaternary ammonium tribromide react to produce a brominated butadiene polymer and a quaternary ammonium monobromide byproduct, wherein the reaction of the starting butadiene polymer is conducted in the presence of a solvent in which the starting butadiene polymer and the quaternary ammonium tribromide are both soluble under the conditions of the reaction and in which the brominated butadiene polymer is at least partially soluble, and such that a solution or slurry of the brominated butadiene polymer in the solvent is formed in the reaction,
b. extracting the solution or slurry of the brominated butadiene polymer with an aqueous phase containing a reducing agent to form an aqueous quaternary ammonium monobromide salt stream and a washed solution or slurry of the brominated butadiene polymer,
c. contacting the aqueous quaternary ammonium monobromide salt stream obtained in step b with elemental bromine and a solvent stream to form an aqueous raffinate stream and a solution of the quaternary ammonium tribromide in the solvent, and
d. recycling the quaternary ammonium tribromide solution obtained in step c into step a.
2. The process of claim 1 , further comprising:
e. recovering the brominated butadiene polymer from the washed solution or slurry obtained in step b to produce a solid brominated butadiene polymer and a solvent stream, and
f. recycling at least a portion of the solvent stream obtained in step e into step c.
3. The process of claim 2 , wherein step e is conducted by e1) forming the washed solution or slurry into fine droplets, e2) thermally stripping the solvent from the droplets to form particles of the brominated butadiene polymer and, before or after the thermal stripping step, e3) washing the droplets or particles in water.
4. The process of claim 3 , further comprising:
g. after step e3), separating the droplets or particles of brominated butadiene polymer from the wash water and recycling at least a portion of the wash water into at least one of step a, step b or step e.
5. The process of claim 4 wherein step g is conducted by centrifuging and drying the solid brominated butadiene polymer.
6. The process of claim 5 wherein at least one additive is added to the solid brominated butadiene polymer obtained in step e or in step g.
7. The process of claim 5 further comprising
h. after step g, compacting the dried brominated butadiene polymer.
8. The process of claim 3 , wherein in step e2), the droplets are steam stripped.
9. The process of claim 1 , wherein at least one additive is added to the droplets or particles of the brominated butadiene polymer after step b.
10. The process of claim 4 wherein at least one additive is added to the washed solution or slurry of the brominated butadiene polymer obtained in step b.
11. The process of claim 10 wherein step g is conducted by centrifuging and drying the particles of brominated butadiene polymer and which further comprises
h. after step g, compacting the dried brominated butadiene polymer.
12. The process of claim 1 , wherein the solvent is one or more of carbon tetrachloride, chloroform, dichloromethane, bromochloromethane (CH 2 BrCl), dibromomethane, 1,2-dichloroethane, cyclohexane, toluene, bromobenzene, chlorobenzene and dichlorobenzene.
13. The process of claim 1 , wherein the quaternary ammonium tribromide is at least one of phenyltrimethylammonium tribromide, benzyltrimethylammonium tribromide, tetramethylammonium tribromide, tetraethylammonium tribromide, tetrapropylammonium tribromide and tetra-n-butylammonium tribromide.
14. The process of claim 1 , wherein the starting butadiene polymer is a butadiene homopolymer or a random, block or graft copolymer of butadiene and at least one vinyl aromatic monomer.
15. The process of claim 1 , wherein the starting butadiene polymer is a block copolymer of butadiene and styrene.