Verfahren und Vorrichtung zur kontinuierlichen Herstellung von Bis-2-hydroxyäthylterephthalat und -isophtalat oder deren Gemischen bzw. deren niederen Polymeren

Bis - 2 - hydroxyethyl terephthalate, bis-2-hydroxyethyl-isophthalate or mixtures of these or their polymers containing up to 10 monomer units are obtained by reacting dimethyl terephthalate, dimethyl isophthalate or mixtures of these with ethylene glycol in the presence of a transesterification catalyst in a heated apparatus subdivided into a plurality of parts, the ethylene glycol and methyl ester being introduced continuously into the reactor and an inert gas being conducted through the reactor in contact with and coutercurrent to the flow of the reaction mixture at such a rate that the flow of vapours in the same direction as the liquid reaction is substantially prevented. The inert gas is preferably nitrogen. The pressure is preferably in the range 1-4 atm. abs. and the temperature in the range 150-240 DEG C. and may increase in the direction in which the reaction proceeds. The process may be carried out in a vacuum-tight horizontal cylindrical casing which can be heated on all sides and is subdivided into a series of baffle chambers separated from one another by discshaped baffle elements which have apertures to determine the level of liquid in each chamber, the aperture being connected to a siphon or immersion tube having its free end in the following chamber at a level lower than the aperture in the following chamber, and have slit openings above the liquid level to provide a passage for vapours and inert gas. The apparatus may be fitted with a stirrer comprising an axial horizontal shaft having radial perforated blades, the dimensions of the shaft being such that it may be introduced through the slit openings.