PROCESS FOR PREPARING A MIXTURE OF RECYCLED TEREPHTHALIC ACID AND ISOPHTHALIC ACID

Abstract

The invention relates to a method for producing a mixture of recycled terephthalic acid (r-TA) and recycled iso-terephthalic acid (r-IA) from condensation polymer waste (CP waste) to obtain a mixture of r-TA and r-IA having set r-IA isomer content between 0.001% by weight and 25% by weight of the mixture, for which waste having different IA contents is mixed and processed.

Claims

1. A method for the production of a mixture of recycled terephthalic acid (r-TA) and recycled iso-terephthalic acid (r-IA) from condensation polymer waste (CP waste), comprising steps of: analyzing CP waste with regard to its IA content, dividing the CP waste into two or more fractions having different IA content, mixing the fractions to achieve a desired IA content in the mixture, and processing the mixture to obtain a mixture of r-TA and r-IA having adjusted r-IA isomer content between 0.001% by weight and 25% by weight of the mixture.

2. The method according to claim 1, in which the CP waste is selected from the polyethylene naphthalates, polyethylene terephthalates, glycol-modified polyethylene terephthalates, polypropylene terephthalates, poly(ethylene terephthalate-co-isophthalate) copolymers, polybutylene terephthalate, polyethylene terephthalate copolymers, individually or in mixtures with 1,4-cyclohexanedicarboxylate structural units.

3. The methods according to claim 1, in which the division of the CP waste into a first fraction having an IA proportion of <0.1% by weight, a second fraction having an IA proportion of >0.1% by weight, preferably >1% by weight, optimally >1.5% by weight, and preferably a third fraction having an IA content of >3% by weight takes place.

4. The method according to claim 1, in which a step of compacting and/or comminuting one or more fractions takes place before the step of mixing.

5. The method according to claim 1, in which the mixing step takes place via gravimetric metering, particularly by means of gravimetric metering units in an extruder, wherein the mixture is preferably adjusted so that the isomer ratio (mol TA to mol IA) is between 100:0 and 75:25, preferably between 99:1 and 90:10 and optimally between 99:1 and 97:3.

6. The method according to claim 1, in which the processing step of processing comprises a base-catalyzed depolymerization in which a diol is obtained and a separation and purification of r-TA and r-IA.

7. The method according to claim 1, in which r-TA and r-IA products are obtained as salts rather than free acids.

8. The method according to claim 1, in which the products obtained are polymerized in a polymerization step to form r-PET products or to form r-PBT products or to form r-polypropylene terephthalate products.

9. A mixture of r-TA and r-IA having an r-IA content between by weight and 25% by weight of the mixture, obtainable by the method according to claim 1.

10. The mixture according to claim 9, wherein the mixture has an r-IA content between 0.01% by weight and 10% by weight of the mixture, particularly an r-IA content between 1.5% by weight and 3% by weight.

11. A use of the mixture according to claim 9 in a polymerization reaction to form r-PET, r-PBT, r-polypropylene terephthalate, further condensation polymers, for the production of alkyd resins or saturated and unsaturated polyester resins.

Description

[0042] The figures described below show:

[0043] FIG. 1: a diagram of the method according to the invention and

[0044] FIG. 2: a diagram of the processing steps of the method according to the invention.

[0045] FIG. 1 shows a block diagram of the method according to the invention. The suitable wastes a-n are washed and comminuted in a first step 1, optionally predried, before they are analyzed for their IA content in a second step 2. Based on the results of this analysis, the waste is divided into fractions or classified as such and a mixing specification is created. Optionally, there is a step 3 of compacting, shown here only for waste fraction c, before an obligatory step 4 of mixing the fractions takes place in order to produce a PET waste having a desired IA content. This is illustrated with the curved arrow, which symbolizes the transfer of the desired fractions in their respective proportions according to the mixing specification into the mixing device, particularly a screw extruder. The mixed fractions are then processed in a step 5 such that at the end, a mixture of r-TA and r-IA having an adjusted r-IA isomer content of between by weight and 25% by weight of the mixture is obtained.

[0046] FIG. 2 shows the processing step 5 in more detail. This begins with a base-catalyzed depolymerization 6 with the addition of NaOH and optionally water. At the end of this step, a stream of MEG, DEG and water is obtained, which stream is subjected to MEG purification 7, at the end of which MEG and DEG are obtained. The pasty material flow from the depolymerization 6 is subjected to a dissolving step 8 with the addition of water and sulfuric acid and residues RES are separated off in a filtering step 9. The desired product and, among other things, NaSO.sub.4 are obtained in a crystallization step 10 with the addition of water and sulfuric acid, including subsequent filtration.

[0047] With great advantage, this method facilitates the obtaining of a mixture of r-TA and r-IA having a predetermined proportion of r-IA for further use as a high-quality starting material for the renewed manufacture of PET products. If this high-quality raw material is used, a step of adding IA in the production of the r-PET products is made superfluous, whereby r-PET products having equally good properties become less expensive. This is made possible by the analysis according to the invention of the starting materials and their mixing before processing. It is these additional steps of analysis and mixing that enable the production of a high quality product.