PRODUCTION OF POLYESTER

PURPOSE:To produce a polyester excellent in brightness, transparency and processability during molding, by adding glycol-soluble Ca and/or Li salts and a P compound to a reaction system lying under specifed conditions and reacting the mixture. CONSTITUTION:A slurry containing terephthalic acid and ethylene glycol as the principal starting materials at a predetermind molar ratio is fed continuously to the 1st reaction tank 1, esterified, withdrawn by a transfer pump 2 so that the quantity of the solution held in the tank 1 can be kept constant, led to the 2nd reaction tank 3, esterified and then transferred to a catalyst addition tank 4. While agitating the reaction solution so that the Reynolds number in the tank 4 is below 3,500 under conditions in which the concentration of the terminal carboxyl groups of the reaction solution and its average residence time in the tank 4 satisfy the formula, 0.015-0.20wt% glycol-soluble Ca and/or Li salts, 0.003-0.05wt% P compound and a polymerization catalyst are added to the solution. The polycondensation of the reaction mixture is allowed to advance under a weak vacuum in a prepolymerizer 6 and polycondensed to completion in a polymerizer 7.