BHET Crystallization\nin Water-Free PET Glycolysis\nSystems

Research in the last\nyears has predominantly focused on optimizing\nthe depolymerization step of polyethylene terephthalate (PET) glycolysis,\noften overlooking the at least equally critical downstream steps in\nrecovering the monomer bis(2-hydroxyethyl) terephthalate (BHET). This\nstudy focused on BHET crystallization, a pivotal unit operation in\nthe downstream of PET glycolysis. We successfully implemented a water-free\nPET glycolysis process, eliminating complications associated with\ninternal solvent and homogeneous catalyst recycling found in the most\ncommonly applied PET glycolysis processes. Based on BHET solubility\nmeasurements in real reaction mixtures, crystallization experiments\nwere performed in a 180 mL batch lab-scale setup. The simplest method\n(natural cooling, no stirring) yielded the most efficient result,\nwhereas the first experiments employing established crystallization\ntechniques (seeding, controlled cooling, stirring) did not succeed.\nThe simple approach resulted in a crystallization time of 180 min,\nand a filtration time of about 4.5 min, giving an overall process\nyield of 71%. Further, our BHET monomer/dimer product was successfully\nrepolymerized, demonstrating the potential of our more environmentally\nfriendly PET glycolysis process compared to conventional literature\nmethods. This study lays the groundwork for future experiments aimed\nat recycling solvent and homogeneous catalysts within the process\nto minimize resources and energy demand.