Process for the regeneration and further processing of inactive, linear polyalkylene terephthalates

A process for the regeneration and further condensation of a linear polyalkylene terephthalate which is inactive after recondensation and which has a viscosity number of at least 60 cc/g as measured in a solution of 0.23 g of polyalkylene terephthalate in 100 ml of phenol/1,1,2,2-tetrachloroethane (weight ratio 60:40) at 25.degree. C., the process being conducted in the solid phase, in two stages and at an elevated temperature, in the presence of an alkanediol, and comprising, in a first stage, treating the inactive polyalkylene terephthalate at a reaction temperature of 30.degree.-80.degree. C. below its melting point, with 0.3-3.5% by weight, based on the weight of the polyalkylene terephthalate, of an alkanediol whose boiling point under normal pressure is 20.degree.-70.degree. C. above the reaction temperature, in an inert gas stream, wherein the amount of inert gas passed through per hour, measured under standard conditions, corresponds to 0.3-2 times the gross reactor volume and wherein the first stage is conducted until the polyalkylene terephthalate has achieved essentially its minimum carboxy end group concentration;

• and in a second stage, condensing the polyalkylene terephthalate at a temperature of 5.degree.-25.degree. C. below its melting point in an inert gas stream, wherein the amount of inert gas passed through per hour, measured under standard conditions, corresponds to 2.5-10 times the gross reactor volume.