A continuous process for preparing a
polyamide by reacting at least one aminonitrile with water comprises:(1) reacting at least one aminonitrile with water at a temperature from 90 to 400° C. and a pressure from 0.1 to 35x106 Pa in a flow tube containing a Brönsted acid catalyst selected from a beta-
zeolite catalyst, a sheet-
silicate catalyst or a
titanium dioxide catalyst comprising from 70 to 100% by weight of
anatase and from 0 to 30% by weight of
rutile and in which up to 40% by weight of the
titanium dioxide may be replaced by
tungsten oxide to obtain a reaction mixture,(2) further reacting the reaction mixture at a temperature from 150 to 400° C. and a pressure which is lower than the pressure in step 1, in the presence of a Brönsted acid catalyst as in (1), the
temperature and pressure being selected so as to obtain a first
gas phase and a first liquid or a first
solid phase or a mixture of first
solid and first
liquid phase, and the first
gas phase is separated from the first liquid or the first
solid phase or from the mixture of first liquid and first solid phase, and(3) admixing the first liquid or the first solid phase or the mixture of first liquid and first solid phase with a gaseous or
liquid phase comprising water at a temperature from 150 to 370° C. and a pressure from 0.1 to 30x106 Pa to obtain a product mixture.