Engineering terephthalic acid product from recycling of PET bottles waste for downstream operations

Since global oil prices have declined, the price of virgin PET has dropped dramatically, and caused the recycling of PET more challenging. To make the situation worse, the rapid precipitation of terephthalic acid (TPA) from alkaline hydrolysis of PET resulted in very small particles of TPA with unfavorable filtration and drying behaviors. The aim of this work was to engineer product properties of TPA for downstream operations with the existing processing steps. The size effects of TPA crystals/precipitates on filtration, and on drying behaviors, were conducted in terms of specific cake resistance and drying-rate curve, respectively. The whole operating windows was determined for a process optimization by varying operating temperature, feeding strategy, the proportion of water to dimethyl sulfoxide, and the introduction of a cooling operation. Our whole process could be achieved within 8 h at the optimal conditions. As compared to the literature method for chemical recycling of PET, the optimal case exhibited much improved specific cake resistance of ~4.8 × 10⁶ m/g by two orders, and shortened the drying time to 3 h by three times. The TPA crystalline products were also characterized by FTIR for identification, NMR for purity, PXRD for crystallinity, and SEM for particle morphology.