US Patent 7153927 Process of continuously producing polyesters or copolyesters

Process for producing polyesters and copolyesters, wherein a continuous esterification of dicarboxylic esters and diols or a continuous transesterification of dicarboxylic esters with diols is effected in “n” reaction pressure stages connected in series, the pressure in the first reaction pressure stage is higher than that of the remaining reaction pressure stages, and successively decreases from reaction pressure stage to succeeding reaction pressure stage, the combined vapor flows of the individual reaction pressure stages are rectified in a rectifying column, and the diol component obtained at the bottom of the rectifying column is recirculated at least to the first reaction pressure stage, and wherein at least the last reaction pressure stage operates at a vacuum, the pressure in the rectifying column is greater than that of the last reaction pressure stage, and the vapors discharged from the last reaction pressure stage are condensed to the pressure existing in the rectifying column.