Patent ID: 6534619
Filing Date: 2003-03-18
Classification: B01D,C08F,C08G

Abstract:
A multi-step continuous process for evaporating polymer solutions of thermoplastic polymers by indirect heat exchange, the polymer solution being passed through a drying device, the process comprisingA) concentrating a polymer solution containing 5 to 20 wt. % of polymer to produce a solution containing polymer in an amount of 60 to 75 wt. % in a combination of a member selected from the group consisting of a shell-and-tube heat exchanger, a film evaporator and a coiled-tube evaporator with in each case with a downstream separator, at a temperature of 150Â° C. to 250Â° C., the pressure in the separator being from about 0.1 to 0.4 MPa, B) concentrating the solution produced in A) to produce a solution that contains at least 95 wt. %, polymer in a shell-and-tube heat exchanger and a downstream separator, at a temperature of 250Â° C. to 350Â° C., the shell-and-tube heat exchanger containing vertical, heated, straight tubesâ€”with or without incorporated static mixersâ€”said tubes having an internal diameter of 5 to 30 mm, a length of 0.5 to 4 m, and the flow rate through the tubes being 0.5 to 10 kg/h, based on the polymer, and the pressure in the separator being 0.5 kPa to 0.1 MPa, C) concentrating the polymer solution obtained in B) to bring the content of solvent and/or other volatile constituents to 5 to 500 ppm in a shell-and-tube heat exchanger with downstream separator or in an extrusion evaporator with separator at a temperature of 250Â° C. to 350Â° C., the shell-and-tube heat exchanger containing vertical, heated, straight tubes having an internal diameter of 5 to 30 mm, a length of from 0.2 to 2 m, and the flow rate through the tubes being from 0.5to 10 kg/h, based on the polymer, and the pressure in the separator 15 being from 0.05 kPa to 0.1 kPa, and D) isolating the product of C) and optionally granulating the isolated product to obtain a granulated polymer.