Chemical recovery method: chemical treatment method is to reduce or decompose PET bottles into raw materials or monomers for making PET resin by chemical methods. Due to the limitation of physical recycling of PET raw materials, most of the recycled PET resins can only be used to make non-food packaging or textiles. Therefore, many enterprises tend to treat waste PET bottles by chemical methods to decompose them into raw materials or intermediates for making PET resin, so as to achieve the purpose of complete reuse.
Chemical treatment also requires physical sorting and cleaning of pet waste in advance. Because of the different process routes, the products prepared by decomposition are also different. Therefore, most chemical treatment methods are a set of technological systems developed by large enterprises.
For example, Teijin Company of Japan has developed a recycling method to recycle DMT (dimethyl terephthalate) and ethylene glycol (ethylene glycol) from waste PET bottles. Firstly, the waste PET bottles were broken and cleaned, then dissolved in EG, and PET was depolymerized at the boiling temperature of EG and the pressure of 0. 1Mpa to produce hydroxyethyl terephthalate (BHET). After filtration, the filter residue and additives were removed, so that BHET reacted with methanol, and transesterification was carried out at the boiling temperature of methanol and the pressure of 0. 1Mpa to generate DMT and EG. After distillation, DMT and ethylene glycol were separated, and then DMT was refined by recrystallization. Ethylene glycol is purified by distillation, and methanol can be recycled. The purity of recovered DMT and EG can reach 99.99%, and the production cost is equivalent to that of ordinary DMT and EG methods. DMT can be converted into pure TPA (terephthalic acid), which can be used to make bottle-grade PET resin. The circulating device can produce about 10% of resin raw materials.
TSK also invented a recycling process, which can recycle high-purity terephthalic acid (TPA) and EG from waste polyester bottles. In this process, PET resin chips and sodium carbonate react for 40-60 minutes under certain conditions. PET depolymerized into EG and TPA, and the latter formed sodium terephthalate (NaTP). Because NaTP is insoluble in EG, EG is separated and recovered by filtration and distillation. After NaTP was dissolved in water, sulfuric acid was added in two steps at a temperature slightly higher than 90℃, and TPA crystals were obtained in sodium sulfate solution. The crystals were filtered and washed to obtain high purity TPA, and sodium sulfate was recovered.
TSK Company conducted a pilot test of100t/year for this process, and its TPA recovery rate was about 98%. Due to the low operating pressure and short reaction time, the production cost is expected to be relatively moderate. The company estimates that the investment of a set of 8000 tons/year industrial production equipment is about 1 1 ten thousand dollars. Considering the saving of PET processing cost, the equipment of this scale is economically feasible.
PETrecycle Company in Australia has developed a patented technology called Penew. This patent is made by Italian M & amp； After the acquisition of G Group, an industrial-scale PET recycling device was built in West Virginia, USA, which can handle 100kt PET bottles every year.
The advantage of this process is that it can be treated? Colored or coated PET waste bottles. The process is to steam the PET bottle with ethylene glycol steam for one hour to make it brittle, then grind it into particles with the size of 1mm, remove impurities and alcoholize it into oligomers, including part of terephthalic acid monomer. Then, pigment additives or paint impurities are removed through a special filtration process. Finally, it was mixed with fresh monomer in the existing production device and esterified to obtain colorless PET.
In particular, the recycled PET bottles are mainly used for beverage packaging. Although several enterprises in the United States have applied for the inspection and certification of FDA, they can recycle PET packaging in cleaning products and cosmetics industries. In Europe, due to prudent consideration, the share of non-edible PET in recycled materials does not exceed 65,438+0%.