Solid-state post-condensation:Vacuum treatment of polyamides and polyesters
Solid-state post-condensation of polyamides and polyesters is an effective way of obtaining high-quality starting materials. The process involves gently increasing the molar mass (intrinsic viscosity (IV)) of the pellets to the desired value in the tumble reactor under a vacuum and with input of heat while simultaneously efficiently stripping out volatile impurities.
ProTec's tumble reactor
ProTec's tumble reactor is a rotary solid-state reactor which has an energy-saving bin design and can be heated and evacuated. The reactor's oblique position to the horizontal axis of rotation brings about a tumbling motion which ensures constant, gentle and homogeneous mixing of the flowable bin contents. Heat-transfer oil is used to heat the single-walled bin to the reaction temperature necessary for the product (up to at most 250°C) and to cool it back down as required by the process. High heating and cooling rates minimize dead time and ensure economic process times. The bin can be evacuated down to 0.1 mbar (absolute). Automatic sampling is possible at any time without interruption and material changes are quick and easy. The high positioning accuracy of the gearwheel direct drive enables fully automatic filling and emptying of the reactor. The reactor is available in various sizes from 16 m³ to 44 m³. Thanks to the optimized weight of the reactor bin and the direct drive, energy consumption has been cut by around 25 % in comparison with its double-walled predecessor and, at the same, batch treatment time has been reduced.
Ensuring uniform product quality by batch operation
Batch reactor operation has a positive impact on product properties: each pellet has exactly the same residence time and, thanks to homogeneous intermixing, is subjected to the same conditions during the process. Precise control of temperature, vacuum and process duration parameters means that the properties of polyesters such as PBT or PET and of polyamides (PA6, PA66 etc.) for producing demanding products, such as fibers, industrial yarns, tire cord and monofilaments, can be purposefully raised to a defined level.
The tumble reactor can likewise be used for drying sensitive polymer pellets with a high water content and granular products in the chemicals and pharmaceuticals industry in line with FDA and GMP guidelines. Not only powders, but also highly sensitive substances such as black powder, antibiotics and active pharmaceutical ingredients can be reliably processed. For the drying process, the pressure in the bin water circuit is raised to 6 bar and the water heated. The higher system pressure means the temperature of the process can be increased, so accelerating drying. This approach is possible thanks to the bin's designed higher pressure tolerance in comparison with double-walled bins.
ProTec relies on its extensive process know-how to design and supply complete lines with optimized peripherals, including the vacuum pump set, the heating/cooling station and the fully automatic reactor filling and emptying system. Systems are monitored and controlled using a high-performance Industry 4.0 capable controller with extensive process data acquisition. On-site control by tablet via WLAN and remote maintenance via the internet are likewise possible.
- Integration into fully automatic hopper and conveying system controller
- Integration of customers' peripherals into line and controller
- Integration of heating/cooling station into existing heat-transfer systems