Continuous preparation of nylon with diamine recycling

A process for the preparation of a nylon, which comprises

• (a) passing an aqueous solution of a salt of a dicarboxylic acid of 6 to 18 carbon atoms and a diamine of 6 to 17 carbon atoms through an evaporator zone, a residence time of from 10 to 40 seconds being maintained,
• (b) heating the aqueous solution in the evaporator zone to 250.degree.-300.degree. C. under superatmospheric pressure of from 1 to 10 bar, with the formation of a mixture of a vapor phase of, and not less than 93% conversion of the salt and a prepolymer containing not more than 7% by weight of water,
• (c) separating off the prepolymer from the vapor phase,
• (d) transferring the prepolymer to a condensation zone,
• (e) condensing the prepolymer in the condensation zone under superatmospheric pressure of from 1 to 10 bar and at from 250.degree. to 300.degree. C.,
• (f) rectifying the vapor obtained in stage (c) in a column, with separation into steam and diamine, and recycling of the diamine to stage (a), and
• (g) discharging the nylon obtained in stage (e) through a discharge zone with removal of water, cooling and comminuting the nylon, and condensing the nylon in the solid phase, with the steam separated off in stage (f), until the desired viscosity is obtained.