Catalytic Steam Hydrolysis of Polyethylene Terephthalate to Terephthalic Acid followed by Repolymerisation

Abstract

A novel industrial cleaning process (DEECOM®, B&M Longworth, Blackburn) hydrolyses polyethylene terephthalate (PET) on contaminated filters using superheated steam at elevated temperature and pressure (300°C and 3 barg). The technology is being adapted to depolymerise waste textiles. This study first involved an assessment of the current large-scale cleaning process’ PET conversion and yield of terephthalic acid (TPA). Then a zinc chloride homogenous catalyst, and, zinc and platinum loaded zeolite beta heterogeneous catalysts, were investigated using a laboratory-scale autoclave reactor to mimic the process. In addition, the industrial waste stream of crude terephthalic acid (TPA) was then purified, repolymerised into PET via the dimethyl terephthalate (DMT) synthesis route, characterised and compared with commercial PET data. Characterisation methods of the repolymerised PET include DSC, TGA, GPC. While still a work in progress, this shows proof-of-concept in terms of closing the loop and moving to a circular economy.