The extraction of hexamethylenediamine from aqueous solution by pH control and salt addition

This paper details an investigation into the separation of Hexamethylenediamine (HMD) from dilute aqueous solutions by exploiting phase separation. HMD is a monomer used in the production of Nylon-6,6 and as such this separation is potentially useful in extracting purifying HMD produced from biological sources or reclaimed from waste made by the production of nylon. An investigation was undertaken into the effect of using sodium hydroxide (NaOH) to promote the phase separation, and a model was derived to predict this behaviour. Furthermore, the effect of various salts on this phase separation was investigated, and it was found that sodium sulphate and sodium carbonate promote the phase separation, but are unable to cause phase separation without the presence of sodium hydroxide. •Hexamethylenediamine and sodium hydroxide are each individually soluble in water, but when both are present phase separation can occur.•The amount of sodium hydroxide required to cause phase separation decreases with increasing concentration of hexamethylenediamine.•A mathematical model was developed for the concentrations of each species in samples which undergo phase separation.•Various salts were shown to have a shown to have positive or negative effect on the formation of the secondary phase.•No salt was able to cause the formation of a secondary phase in the absence of any sodium hydroxide.