Polyamide production processes and modeling

The primary commercial route for nylon 6 production involves the ring-opening polymerization of caprolactam. The first stage of this process involves hydrolysis of the caprolactam monomer  

Only a small amount of water is required, because step-growth polymerization of the resulting linear molecules regenerates water, which can participate in further caprolactam ring opening  

Chain-growth polymerization reactions, where caprolactam adds directly to the ends of linear chains, are also important in nylon 6 production [38], for example  

Substantial amounts of cyclic dimer form, due to condensation reactions between the end-groups on hnear dimer molecules. Like caprolactam, cyclic dimer molecules are consumed by hydrolytic ring-opening reactions and chain-growth polymerization reactions. 

In the second stage of the process, the salt solution is boiled at atmospheric pressure to remove much of the water from the initial solution and water generated by oligomerization reactions. The evaporation process continues until the combined monomer and oligomer concentration is approximately 65-75 wt%. HMD vapor, which evaporates along with the steam, may be recovered and recycled. The evaporation stage can be carried out using either a batch or a continuous reactor. 

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