Patent EA-005296-B1 (EA)
Title: Method for continuos production of polyesters or copolyesters
Inventor: REISEN MICHAEL
IPC: C08G63/78
Filed: 2001-11-27
Abstract: 1. A process of producing polyesters and copolyesters by continuous esterification of dicarboxylic esters and diols or by continuous transesterification of dicarboxylic esters with diols in n reaction pressure stages (2, 4, 32, 34, 36) connected in series, wherein the pressure existing in the first reaction pressure stage (2, 32), which is higher as compared to the remaining reaction pressure stages (4, 34, 36), successively decreases from reaction pressure stage to reaction pressure stage, the combined vapor flows of the individual reaction pressure stages ate introduced into a rectifying column (12, 47) and rectified, and the diol component obtained at the bottom of the rectifying column is recirculated at least to the first reaction pressure stage, characterized in that at least the last reaction pressure stage has a vacuum, the pressure in the rectifying column (12, 47) is larger than in 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. 2. The process as claimed in claim 1, characterized by 2 to 4 reaction pressure stages (2, 4, 32, 34, 36) connected in series. 3. The process as claimed in any of claims 1 and 2, characterized in that for producing PET esterification product, the feed mixture is supplied to a first reaction pressure stage (32) operated with a pressure of 1.1 to 5.0 bar, which is followed by a second reaction pressure stage (34) operated with a pressure of 0.5 to 1.5 bar and then by a third reaction pressure stage (36) operated with a vacuum of 0.1 to 0.9 bar. 4. The process as claimed in any of claims 1 and 2, characterized in that for producing PTT esterification product, the feed mixture is supplied to a first reaction pressure stage (2) operated with a pressure of 1.0 to 5.0 bar, which is followed by a second reaction pressure stage (4) operated with a pressure of 0.5 to 1.3 bar. 5. The process as claimed in any of claims 1 and 2, characterized in that for producing PBT transesterification product, the starting substances are supplied to a reaction pressure stage (2) operated with a pressure of 0.8 to 1.2 bar, which is followed by a second reaction pressure stage (4) operated with a pressure of 0.2 to 0.8 bar. 6. The process as claimed in any of claims 1 to 5, characterized in that the vapors discharged from the last reaction pressure stage (4, 36) are condensed by means of a compressor or ventilator. 7. The process as claimed in any of claims 1 to 5, characterized in that the vapors discharged from the last reaction pressure stage (4, 36) are condensed by means of a gas jet pump (8, 40). 8. The process as claimed in claim 7, characterized in that as operating fluid for the gas jet pump (8, 40) vapors of the first reaction pressure stage (2, 32) are used. 9. The process as claimed in any of claims 1 to 8, characterized in that the pressure existing in the rectifying column (12, 47) is controlled by a residual gas exhaustion (27, 54) provided behind the condenser (16, 49) disposed at the head of the rectifying column. 10. The process as claimed in claim 9, characterized in that the residual gas exhaustion (27, 54) is performed by means of a liquid jet pump, a liquid ring pump or a blower. 11. The process as claimed in any of claims 1 to 10, characterized in that the esterification products or transesterification products are subjected to a prepolycondensation and polycondensation. 12. The process as claimed in any of claims 1 to 11, characterized in that an aliquot of the diol recirculated to the first reaction pressure stage via line (22, 59) is branched off via line (22a, 59a) and used for preparing the paste.