SOLVENT REMOVAL FROM ETHYLENE-PROPYLENE ELASTOMERS

Ethylene-propylene elastomers have been produced commercially for approximately 20 years. However, the devolatilization step has been practiced without a fundamental understanding of the mechanism of mass transfer. This work was performed to elucidate this mechanism in the hope that the devolatilization step could be made more efficient. This would result in a reduction in fugitive solvent emissions in synthetic rubber plants. The devolatilization of two different ethylene-propylene copolymers has been studied in a one gallon steam stripper. Effective diffusion coefficients for n-hexane diffusion in wet rubber have been measured by stripping solid sheet at 105(DEGREES)C. Both materials have the same effective diffusion coefficient for hexane diffusion at this temperature. It has been found that the presence of water in the rubber decreases the diffusion coefficient at zero penetrant concentration substantially.; Porous rubber crumb, taken from a commercial plant stripper, has been stripped and the rate of stripping has been found to be practically independent of crumb diameter in the range 1/4 to 1/2 inch and independent of temperature in the range 105 to 115(DEGREES)C. Effective radii have been fit to stripping rate data for crumb particles and these radii are on the order of 1 mm for 1/4 and 1/2 inch diameter particles. Evidently, some pores penetrate the particles and divide them into subregions which strip into the surface connected pores.; Particle structure has been related to stripping rate by measurements made on regions of wet rubber remaining in thin sections of partially dried crumb. These wet regions represent zones in the particle which are not penetrated by surface connected pores. It is concluded that crumb stripping rate can be increased by introducing more surface connected pores into the particles.