Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1995-06-01
1997-06-10
Lipman, Bernard
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
5153328, 5153329, 5153331, 5153332, 5153341, C08F 822
Patent
active
056376499
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a continuous process for the halogenation of elastomers and more particularly concerns a continuous process of halogenation of an unsaturated elastomer dissolved in an organic solvent. The invention furthermore concerns an apparatus for performing this process.
The known techniques of halogenation of elastomers require the mixing and distribution of gaseous or liquid halogen in a highly viscous solution of an elastomer. This is conventionally effected by means of a so-called batch process, in which considerable consumption of energy is required for stirring the viscous mass. To avoid high local concentrations of halogen, the addition is very slow, with low productivity and continuous expenditure of mixing energy. In spite of various technical expedients adopted, the quality of the product suffers from the non-homogeneous dispersion of the halogen in the whole of the stirred mass.
A continuous process for the halogenation of highly viscous solutions has been proposed, so as to avoid certain disadvantages of the abovementioned batch process.
U.S. Pat. No. 3,966,692 has described a process for the halogenation of elastomer solutions of high viscosity (from 1500 to 6000 cps) which are made to flow through a pipe in such a way that the Reynolds number is less than 100, the process being carried out under pressure, so as to assist the dissolution of the halogen and avoid the formation of gas bubbles, which would interfere with the laminar character of the flow.
The inventors of the present invention have now found that the use of a stream of an elastomer solution of lower viscosity (for example <1000 cps), kept in turbulent motion and avoiding flow inversion phenomena, makes it possible to improve the dispersion and diffusion of the halogen, avoiding high local concentrations of halogen which result in significant degradation of the elastomer chain.
Accordingly, the main object of the present invention is to provide a process for the halogenation of elastomers which permits the dispersion and diffusion of the halogen to be improved whilst avoiding high local concentrations of the said halogen. The invention furthermore proposes to provide an apparatus for performing the abovementioned process.
In accordance with these objects, the present invention provides a continuous process for the halogenation of elastomers, in which a halogenating agent is introduced into a solution of an elastomer in an organic solvent, essentially characterised in that it consists in mixing the said halogenating agent in a continuous stream of the said elastomer solution, thus dissolving the said halogenating agent and causing it to react with the said elastomer in the same continuous stream, and in keeping the said continuous stream of the elastomer solution in turbulent motion during the course of the reaction between the said halogenating agent and the said elastomer.
In the apparatus for performing the abovementioned process, the turbulence of the solution is assisted by means of mechanical means which promote turbulence, which means may be static or dynamic, such as Raschig rings inserted into a pipe such as a column reactor, in which the organic solution of the elastomer is caused to flow continuously.
Advantageously, an inert gas is added to the said elastomer solution, in order to assist the dispersion of the halogen, increase the turbulence and reduce the local concentrations of halogenating agent and of the halogenidric acid thus formed.
The addition of the halogenating agent to the continuous stream of the said elastomer solution is carried out at atmospheric pressure, given the high speed of the reaction under the operating conditions employed.
Further advantageous features of the present invention will emerge from the claims, which are understood to be fully incorporated herein.
By means of the process according to the invention the local concentration of halogen is reduced and the distribution and diffusion of the same is increased, thus giving a more homogeneous and consistent halogenate
REFERENCES:
patent: 3966692 (1976-06-01), Driscoll et al.
Maffezzoni Carlo
Marchegiano Alfredo
Moretti Enrico
Penati Amabile
Straneo Paolo
Lipman Bernard
Pressindustria A.G.
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