| dc.description.abstract | Recycling Poly(ethylene terephthalate) (PET) bottles has been discussed widely since its omnipresence and not biodegradable characteristic. It has been reported that PET can be recycled by alkaline hydrolysis. The recycled terephthalate disodium salt can be further converted to terephthalic acid (TPA) by treating with sulfuric acid (H2SO4). Since TPA is almost insoluble in aqueous media, its fast precipitation after the recovery via acidification causes very small TPA particles. They get lumped together to form a hard cake, and as a result, make filtration and drying difficult. Therefore, the aim of my research is to enhance the particle size to improve the downstream processing such as filtration and drying. First, a certain amount of PET flakes and aqueous solution of NaOH were added into an autoclave containing a Teflon cup of 200 mL size. The autoclave was then placed in a preheated oven at 200oC, then the autoclave was cooled to room temperature overnight along with the oven by turning it off. The solids and/or other impurities remaining in the autoclave were then filtered, dried at 40oC, weighed and characterized by FTIR. All experiments were carried out in a 0.5 L sized jacketed glass stirred tank, equipped with a four-bladed impeller, and a water jacket at different temperatures. The agitator was set to 300 rpm. The reaction mixture from PET recycling was acidified by aqueous H2SO4 solution to obtain TPA. To improve the properties of recovered TPA, many experiments were performed to engineer TPA precipitates. Experiments with the variables, such as different concentrations of aqueous NaOH solutions, reaction temperatures, DMSO volumes, and H2SO4 concentrations/volumes were carried out in this thesis. Cubic addition method was employed here to reduce the nucleation rate of TPA precipitation. Furthermore, to avoid the occurrence of fast precipitation of TPA by acidification or feeding, a ‘‘cooling’’ operation and a temperature cycle were applied to produce larger crystals of TPA. By means of sampling during the course of TPA recovery, the evolution of particle size and morphology could be observed and evaluated. After precipitation of TPA, the slurry was filtered and dried so that the specific cake resistance and drying time could be calculated. The addition of the reaction solution into the pre-charged DMSO could be used to slow down the nucleation rate so as to produce a larger size of TPA particles. Operating temperature was the dominant parameter for enhancement crystal size of TPA. The higher operating temperature was, the higher solubility of TPA in DMSO was. The higher solubility provided a wider operating window to achieve larger particle size of TPA and the smaller specific cake resistance. The results of the specific cake resistance approximately agreed with the trend in the particle size distribution of TPA. The solid-state characterizations for all sample solids by optical microscopy (OM), Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (PXRD), and nuclear magnetic resonance (NMR) were carried out for ensuring the chemical and structural identity of the recovered TPA. | en_US |