Abstract：A model of two-steps Nylon-6 polymerization process was set up by Aspen Polymer Plus. As the simulational results fit all of the industrial operational data of 20 kt/a manufacture process well, including the composition of caprolactam and cyclic dimer, polymer molecular weight, temperature distribution, and the
water yield from the top of two VK tubes, which indicated that the model was reliable. A sensitivity was analyzed by the model to evaluate the adjust ability of operational parameters, including the water and acetic acid contents in feed, temperature distribution and pressure of each VK tube in polymerization process. The
results showed that low water content in feed, low reaction temperature, low pressure of the first tube and high vacuum of the secend tube contributed to less cyclic dimer fraction in polymer product. The temperature of the low-half section of two tubes strongly affect the cyclic dimer fraction. And the vacuum of
the secend tube had a significant impact on the polymer molecular weight. Aiming to control the cyclic dimer fraction in the polymerization process, optimized operational conditions were obtained by Aspen Plus and the cyclic dimer fraction could decrease by about 16% correspondingly.
