Uhde Inventa-Fischer’s VK-tube process polymerizes ?-caprolactam (LC) monomer to produce polycaproamide (nylon-6) chips.
Liquid LC is continuously polymerized in a polymerization unit (one- or two-stage) (1) in the presence of water, stabilizer and modifying additives at elevated temperatures. The polymerization process has proven to be very reliable, easy to operate and economical. Prepolymerization is available to reduce reactor volume for large capacity
units. The polycaproamide chips are formed from the melt using strand pelletizing systems and are conveyed to the extraction column (2).
The chips — containing about 9% of monomer and cyclic oligomers — are treated with hot water in the extraction column. The extractables are removed, to a very large extent, to achieve a good polymer quality and high performance when processed further.
Wet chips are sent to the centrifuge (3) and dried by hot, dry nitrogen in a two-zone dryer (4, 5). The nitrogen gas is regenerated in separate cycles. In the bottom zone of the dryer, the chips are cooled via a heat exchanger.
The drying unit can be extended to a solid-state postcondensation, i.e., drying and solid-state postcondensation occurs in one process stage. Thus, high viscosity chips for industrial yarns, films and extrusion molded parts can be produced.
Low utility and energy consumptions are achieved by using closed circuits of water and nitrogen as well as by recovering heat. The recovery process for the recycling of the extractables reduces raw material cost. Extract water is concentrated and directly re-fed (6) to the polymerization unit.
Batch and continuous process units are available to meet all potential requirements regarding polymer grades as well as regarding flexibility in output rates and capacities. Special attention is devoted during plant design to attain minimal operating expenses for raw material, utilities and personnel.
Licensor: Uhde Inventa-Fischer
