Precipitation of terephthalic acid from post-consumer polyethylene terephthalate waste fractions

Achieving circularity for post-consumer polymers requires to address and overcome significant challenges and limitations such as the efficient removal of additives, colourants, contamination from usage and undesired chain scission. A very effective approach is offered by back-to-monomer recycling processes that break up the polymer matrix, release contaminants and yield virgin-like monomers as starting material for polymer production. This study used post-consumer and post-production polyethylene terephthalate (PET) which were depolymerized by revolPET® technology. As a reaction intermediate disodium terephthalate is obtained, from which the monomer terephthalic acid (TA) can be recovered through acidic precipitation. In this present study, precipitation with acetic acid and sulfuric acid is assessed regarding the impact on recycled terephthalic acid properties and the purification potential at temperatures up to 90°C. Precipitation at elevated temperatures reduces the yellow discolouration of TA, with acetic acid being more effective. With regard to isophthalic acid (IA), a common co-monomer in PET manufacturing, an increase in temperature could reduce the IA content in TA to 90% of the original content using sulfuric acid. Precipitation with acetic acid reduced IA content to less than 20%. The results of this study deliver a novel approach to integrate the purification into the TA formation step.