The Development of Recycling Process of Waste PET to TPA and Oxalic Acid by Alkaline Hydrolysis-oxidation

近年来，由于在世界范围内难以建立作为焚烧炉或用于回收的土地的中间处理厂，因此废弃物的处理作为每个人都熟悉的环境问题之一已经成为当前的焦点。聚对苯二甲酸乙二醇酯（PET）树脂不仅用于许多行业，而且还用于日常生活，因为它价格便宜，重量轻，透明，坚韧且易于加工。特别是用于瓶子，其需求量逐年增加。在这项工作中，使用PET薄片在NaOH溶液中通过氧气氧化。在这种情况下，PET通过水解转化为对苯二甲酸（TPA）和乙二醇（EG），并且仅EG同时氧化为草酸。这是国内首次研究回收废旧PET中的TPA和草酸。研究了以废PET切片为原料高收率制备草酸的最佳工艺条件，并对废PET在NaOH溶液中氧化制备TPA和草酸的工艺条件进行了研究。PET在加热过程中首先完全水解为TPA和EG，并通过通氧生成草酸和CO_2。由于微溶于浓NaOH溶液中的对苯二甲酸钠对氧化是稳定的，TPA的产率达到约。在所有条件下100unit%。另一方面，EG通过碱催化氧氧化被氧化成草酸，草酸的最大产率为60.7unit %。此外，市售透明薄片和来自PET瓶的透明和绿色薄片的混合物的草酸产率分别达到65.9单位%和71.4单位%。

Recently, a disposal of waste materials has been in current focus as one of the environmental problems familiar to every people, since it is difficult to set up intermediate treatment plants as an incinerator or the land for reclamation in the world. Polyethylene terephthalate (PET) resin is used not only in many industries but also in daily life, since it is inexpensive, light, transparent, tough and easy in processing. In particular, it is used for bottles, the demand for which is increasing year by year.In this work, used PET flakes were oxidized by oxygen in NaOH solutions. In this case, PET was converted to terephthalic acid (TPA) and ethylene glycol (EG) by the hydrolysis, and only EG was oxidized simultaneously to oxalic acid. This is the first study recycling of used PET to TPA and oxalic acid particular. The optimum conditions were investigated to obtain oxalic acid in high yield from used PET flakes.Oxidation of post consumer PET to TPA and oxalic acid in NaOH solutions was studied to disclose the optimum conditions. PET was completely hydolyzed first to TPA and EG during heating, and oxalic acid and CO_2 were formed by oxygen introduction. Since sparingly soluble sodium terephthalate in concentrated NaOH solutions is stable to the oxidation, the yield of TPA was reached ca.100unit% under all conditions. On the other hand, EG was oxidized to oxalic acid by base-catalyzed oxygen-oxidation and the maximum yield of oxalic acid was 60.7 unit%. Also, the yields of oxalic acid for commercial transparent flakes and mixture of transparent and green-colored flakes from PET bottles reached 65.9 unit% and 71.4 unit%, respectively.