Nylon 6, 6 Production from Adipic Acid & HMDA (Continuous Process)

The process under analysis comprises three major sections: (1) salt generation; (2) polymerization; and (3) finishing.

Salt generation. An adipic acid solution is formed by mixing adipic acid powder with water and molten HMDA. The solution is fed to a recirculation reactor, from which a 60 wt% nylon salt solution is withdrawn. The solution must be further treated for impurities removal before being fed to an intermediate tank.

Polymerization. The nylon salt solution from the intermediate tank is concentrated in an evaporator to about 80 wt% and fed to the first of three polymerization stages. The elevated reaction temperatures cause water and minor amounts of HMDA to evaporate and be collected by a column at the top of the reactor. HMDA is recovered and recycled to the reactor, while water is purged from the process. The liquid reaction mixture is than transferred to the second polymerization stage. At this point, it comprises 10 wt% water. In the second stage, further conversion is achieved by temperature increase. The polymer melt obtained is further reacted in a third stage at reduced pressures for residual moisture removal and finally transferred to the finishing section.

Finishing. The polymer melt is cut into pellets in an underwater pelletizing strand system and subsequently fed to a fluid bed dryer for moisture removal. The dry pellets are finally homogenized in mixing silos and fed to the packing system.