Process and apparatus for treating viscous products
In a process for treating viscous products, especially for performing polymerization processes, especially for homo- or copolymerizing thermoplastics and elastomers, wherein monomer(s) and/or catalysts and/or initiators are added to a backmixed mixing kneader, especially with a length/diameter ratio of 0.5-3.5, heat is supplied to the product which is backmixed with already reacted product and the reacted product is removed from the mixing kneader, the product in the mixing kneader shall be heated up to its boiling temperature, portions of the product shall be evaporated and exothermicity of the product shall be absorbed by evaporative cooling.
1. A polymerization process, comprising:
(a) providing a mixing kneader having a backmixing stirrer shaft, wherein the mixing kneader has a length/diameter ratio of between 0.5-3.5;
(b) continuously feeding to the mixing kneader monomers, catalysts and initiators to form a mixed product; and
(c) heating the mixed product in the mixing kneader to its boiling temperature, wherein portions of the product are vaporized and an exotherm of the product is absorbed by evaporative cooling, including vaporizing the product by providing energy input consisting of mechanical kneading energy and heat transfer via contact with kneader heat-exchange surfaces, up to just above the point of collapse of the vaporization rate, and the thus pre-evaporated viscous bed of product is continuously admixed with new low-viscous product solution such that the vaporization rate remains above the point of collapse.
2. A process according to claim 1 wherein the vaporized portions of the product are at least partly condensed and returned as condensate back into the mixing kneader to cool the remaining product.
3. A process according to claim 2 wherein the condensate is returned to the mixing kneader at a location where product is evaporated.
4. A process according to claim 2 wherein the boiling temperature in the mixing kneader is adjusted by changing the pressure in the mixing kneader.
5. A process according to claim 1 including building up a vacuum in the mixing kneader so as to withdraw vapors.
6. A process according to claim 1 including backmixing the mixed product to attain a predetermined viscosity for the product and maintaining the viscosity by the continuous addition of further monomers, catalysts and initiators.
7. A process according to claim 1 including influencing the kneading energy by varying the rotary speed of the stirrer shaft of the mixing kneader.
8. A process according to claim 1 including continuously backmixing the product in the mixing kneader.
9. A process according to claim 1 including continuously discharging the product from the mixing kneader and introducing the discharge product into a second mixing kneader or extruder.
10. A process according to claim 9 including heating the discharged product from the mixing kneader prior to introduction into the second mixing kneader or extruder.
11. A process according to claim 10 wherein the discharged product from the mixing kneader is fed to an extruder and subjecting the extruder to plug flow.
12. A process according to claim 11 , including subjecting the product in the extruder to surface renewal.