Control Strategy Of Cyclic Dimer In Nylon6Manufacture Process

Due to its high melting point, Cyclic dimer of caprolactam accumulates easily in the Nylon6manufacture process with extraction concentrate recycled, and that causes problems such as low polymer quality or pipe block. This paper studies the control strategy of cyclic dimer in Nylon6manufacture process, which includes reducing cyclic dimer formation in polymerization and removing it by pyrolysis process. The model of a two-step Nylon6polymerization process was built with Aspen Polymer software. The reliability of this model was testified with the industrial data. Sensitivity study results indicated that water in feed and temperature of CSTR-1, CSTR-3, PFR-2have a significant impact on the cyclic dimer concentration in polymerization product. A set of experimental method about cyclic dimer pyrolysis was developed, which includes experimental apparatus, sample treatment and HPLC quantitative analysis method of cyclic dimer. The pyrolysis kinetics of cyclic dimer was proposed, and model parameters have been regressed on the basis of experimental data, the calculation results can match the experimental data well. The simulation of the process with extraction concentrate cracked and recycled (ECCR) was carried out while the industrial cracking reactor is supposed as a CSTR, the simulation results showed that long residence time, high temperature, high pressure and more water in concentrate in cracking reactor can contribute to a high conversation of cyclic dimer, which is also good for decreasing the accumulation of cyclic dimer. The simulation of the process with extraction concentrate recycled directly (ECRD) was also conducted. The effect of and the ratio of extraction concentrate to fresh caprolactam and water content in concentrate on polymer quality and accumulation of cyclic dimer are studied. ECCR shows great advantage than ECRD in the control the accumulation of cyclic dimer.