Common solvent process for producing high molecular weight brominated rubber
View Patent ↗The invention relates to an energy efficient, environmentally favorable process for the preparation of brominated rubbers, in particular bromobutyl rubber, that uses a common medium for both solution polymerization and subsequent bromination of the rubber and which further exhibits an enhanced bromine usage due to the use of a oxidizing agent. More particularly, the invention relates to a process that employs a common aliphatic medium for both solution polymerization and bromination of rubber in the presence of a brominating agent and an oxidizing agent with intermediate removal of un-reacted monomers.
1. A process for the preparation of brominated rubbers, the process comprising:
a) providing a reaction medium comprising
a common aliphatic medium comprising at least 50 wt.-% of one or more aliphatic hydrocarbons having a boiling point of 45° C. to 80° C. at a pressure of 1013 hPa, and
a monomer mixture comprising at least one isoolefin monomer, at least one multiolefin monomer and either no or at least one other co-polymerizable monomer
in a mass ratio of monomer mixture to common aliphatic medium of 40:60 to 99:1,
b) polymerizing the monomer mixture within the reaction medium to form a rubber solution comprising a rubber polymer which is at least substantially dissolved in the medium comprising the common aliphatic medium and residual monomers of the monomer mixture;
c) separating residual monomers of the monomer mixture from the rubber solution to form a separated rubber solution comprising the rubber and the common aliphatic medium, and
d) brominating the rubber in the separated rubber solution using a brominating agent which is at least partially regenerated by an oxidizing agent.
2. The process according to claim 1 , wherein the rubber is a butyl rubber.
3. The process according to claim 2 , wherein the weight average molecular weight of butyl rubber as measured prior to bromination is 200 to 1000 kg/mol.
4. The process according to claim 1 , wherein the monomer mixture comprises 80.0% to 99.9% by weight of the at least one isoolefin monomer and 0.1% to 20.0% by weight of the at least one multiolefin monomer.
5. The process according to claim 1 , wherein the isoolefin monomer is isobutene and the multiolefin monomer is isoprene.
6. The process according to claim 1 , wherein the common aliphatic medium comprises at least 80 wt.-% of one or more aliphatic hydrocarbons having a boiling point of 45° C. to 80° C. at a pressure of 1013 hPa.
7. The process according to claim 1 , wherein the common aliphatic medium has a content of cyclic aliphatic hydrocarbons of less than 25 wt-%.
8. The process according to claim 1 , wherein the common aliphatic medium has a content of cyclohexane of less than 2.5 wt.-%.
9. The process according to claim 1 , wherein the process temperature of step b) is −100° C. to −40° C.
10. The process according to claim 1 , wherein the reaction is performed in a polymerization reactor, and wherein the viscosity of the solution at the discharge of the polymerization reactor is less than 2000 cP.
11. The process according to claim 1 , wherein the solids content of the rubber solution obtained following in step b) is 3 to 25%.
12. The process according to claim 1 , wherein molecular bromine is used as brominating agent.
13. The process according to claim 1 , wherein the amount of brominating agent used is 0.1 to 20% by weight of the rubber.
14. The process according to claim 1 , wherein the oxidizing agent is selected from the group consisting of peroxides and peroxide forming substances.
15. The process according to claim 1 , wherein the oxidizing agent is used in combination with surfactants.
16. The process according to claim 1 , wherein the oxidizing agent is hydrogen peroxide.
17. The process according to claim 16 , wherein the weight ratio of hydrogen peroxide to water within the reaction mixture is below 1:100.
18. The process according to claim 1 , wherein the amount of oxidizing agent used is 0.2 to 5 mol of oxidizing agent per mol of brominating agent.
19. The process according to claim 1 , wherein the oxidizing agent is added concurrently or before the brominating agent is added.
20. The process according to claim 1 , wherein the process further comprises the curing of the brominated rubber obtained in step d).