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M. Gryta

Concentration of aqueous solutions of caprolaclam by membrane distillation

Polimery 2006, No 9, 665



DOI: dx.doi.org/10.14314/polimery.2006.665


Summary

The process of concentration of waste aqueous solutions of ε-caprolactam (generated during nylon-6 production) by multistage membrane distillation (MD) was described. The own MD experimental set (Fig. 1) has been used. During the MD process the time dependence (up to approximately 50h) of change of the permeate flux obtained, dependently on the feed concentration expressed as total organic carbon (OWO) content, was determined. The values of electrical conductivity and pH of distillate (Fig. 6 and 7) as well as OWO content in the feed and distillate (Fig. 5) were determined the same time. The high degree of organic compounds' separation was achieved (more than 99.9%). The distillate obtained was nearly pure water containing barely 220mg/dm3 of organic carbon and 60mg/dm3 of nitrogen. That distillate was successfully used for polyamide extraction, after its polymerization. The observed in MD process the phenomenon of decrease in membranes' permeability was attributed to membrane pores' wetting as well as to settling of the deposits on the surface (investigations by SEM method, Fig. 2 and 4). It was found that hot water effectively leaches the deposit, consisted of oligomers formed as by-products during ε-caprolactam polymerization.


Key words: nylon-6, ε-caprolactam, wastewaters, membrane distillation, pure water recovered


e-mail: marek.gryta@ps.pl


M. Gryta

Concentration of aqueous solutions of caprolaclam by membrane distillation