PET bottle recycling

PET bottles are not only widely used for packaging carbonated beverages, drinking water, juices, and tea beverages. They are the most widely used beverage packaging and are widely used in many fields such as food, chemical, and pharmaceutical packaging. Every year, there are tens of billions of PET bottles produced in China. It is estimated that by 2005, more than 500,000 tons of PET will be used for the manufacture of PET bottles. The recycling of PET bottles not only can solve environmental problems, but also can be used as a new raw material resource to ease the shortage of PET raw materials in China.

The packaging waste is mixed in the rubbish of the city and sorting out the reusable materials is a very important task. Sorting can be said to be a prerequisite for the recycling of all materials.

Germany has already begun to set up a special beverage empty bottle recycling machine at the entrance of Chaoshan. The machine uses photography to identify the shape and material of the bottle. Consumers put the empty beverage bottle into the recycling machine in return for corresponding compensation. However, this is only the beginning. Compared with the large number of beverage empty bottles, the bottle recycled through this machine is a glass of water.

There are many specific ways to sort PET bottles out of many wastes. There are two main types: one is that the shape of the bottle is not damaged, and the sorting is done mainly by hand; the other is that all the waste is broken into pieces and then sorted by various physical means.

The main problems with manual sorting are: inefficiency; the operator is in a harmful environment; and there is a large error in material classification. Therefore, automated sorting systems are mostly used in industrial production. Generally, most of the impurities are removed first by means of winnowing or water selection, and then the selected materials such as PET are sorted from a relatively small range of materials by various sorting methods such as infrared photography and X-ray detection. .

Physical recycling method

The physical recycling method of PET bottles is relatively simple, mainly to dry and granulate the washed PET bottles. The physical treatment of PET bottles is closely related to the sorting process.

There are two kinds of physical recycling methods. First, the waste PET bottles are shredded into pieces. HDPE, aluminum, paper and adhesive are separated from PET. The PET chips are washed, dried and pelletized; Non-PET bottle caps, bottoms, labels and other impurities on PET bottles are mechanically separated, washed, broken, and granulated.

Recycled PET must not contain PVC impurities, otherwise it will affect the color of PET. When the amount of PVC mixed is small, it can be manually separated on the conveyor belt. That is, when the torsional force is applied, the PVC and the PET bottle produce different physical phenomena in the force part, the PVC bottle shows opaque marks, and the PET bottle does not. Some companies also use different melting points of PVC and PET. Fragments of broken PET and PVC are passed through a belt equipped with a heater and a temperature controlled conveyor. The PVC is melted and adhered to the conveyor belt so that it can be separated from the PET.

The label on the beverage bottle can be removed after the bottle is crushed with a blower and cyclone separator. It can also be separated by the suction tower separation device. The broken PET pieces are added vertically from the top of the separation tower. The debris and the updraft flow are countercurrent. The difference in specific gravity between PET and the label is used. The label is pumped and the PET comes out from the bottom of the separator. To ensure label separation efficiency, more than two sets of separation devices can be used in production.

The washing of PET chips is very important. Wash the detergent with 80-100°C hot water to soften or dissolve EVA adhesives or other adhesives that adhere to the label and the base. Add additives to the water to prevent the peeled adhesives from adhering to the PET chips. Germanium, emulsifiers or other special chemicals. The cleaning solution is generally determined by the factory based on the source and adhesive properties of the waste bottle. The composition and content of the cleaning solution can be filtered and the impurities can be filtered and re-heated. The cleaning can be performed in a special cleaning tank equipped with a stirrer. The effect of cleaning, washing can use two-stage washing process.

The PET chips usually use a centrifugal dehydrator to reduce the moisture content of the chips to 2%, and then dried by a belt or tube dryer to reduce the moisture content to 0.5%.

Krones Germany successfully developed a high-quality PET bottle recycling system, which can process 15,000 tons of PET beverage bottles in a year. The processed PET raw materials can be directly made into other PET containers, and the production cost is greatly reduced. The PET bottle recycling system utilizes a chemical coating removal technology to burn erbium as a chemical coating remover to remove contaminants adhering to the surface of the PET bottle and to recycle any type of PET bottle. The recycled products processed by this technology can not only be mixed directly to produce preforms. At the same time, recycled products can meet the purity and quality requirements due to the low content of acetaldehyde and yellow pigments, and are particularly suitable for products in the food and beverage industry. Packaging costs 20% to 30% lower than general new materials.

Chemical recycling method

The chemical treatment method is a chemical method of reducing or decomposing a PET bottle into a raw material or a monomer for producing a PET resin.

Because physical recycling of PET raw materials has certain limitations in use, most of the recycled PET resins can only be used to make non-food packaging or textiles. Therefore, many companies tend to use chemical methods to dispose of waste PET bottles. Decomposes into raw materials or intermediates for the manufacture of PET resin for complete reuse.

However, chemical treatment also requires physical sorting and cleaning of PET waste in advance. Due to different process routes, the products produced by the decomposition are not the same. Therefore, chemical treatment methods are mostly a set of process systems developed by large companies.

For example, Teijin Corporation in Japan developed a recycling method for recovering DMT (dimethylphthalate terephthalate) and EG (ethylene glycol) from used PET bottles. It first crushes and cleans the waste PET bottle and then dissolves it in EG to depolymerize the PET at the boiling temperature of EG and 0.1 Mpa to form bis-hydroxyethyl terephthalate (BHET). After filtration, the filter residue and additives were removed to react BHET with methanol, and DMT and EG were produced by transesterification reaction at the boiling temperature of methanol and 0.1 Mpa pressure. After distillation, DMT and EG are separated, and DMT is refined through a recrystallization process; EG is purified by distillation and methanol can be recycled. The purity of the recovered DMT and EG can reach 99.99%, and the production cost is comparable to the cost of the common DMT and EG methods. DMT can be converted to pure TPA (terephthalic acid) for the manufacture of bottle grade PET resins. The circulation device can produce about 10% of raw materials for the resin.

Japan's Tsukishima Machinery Co., Ltd. (TSK) has also invented a recycling process to recover high-purity terephthalic acid (TPA) and EG from waste polyester bottles. In this process, the PET resin sheet is reacted with sodium carbonate under certain conditions for 40-60 minutes. PET is depolymerized into EG and TPA, the latter forming sodium terephthalate (NaTP). Since NaTP is insoluble in EG, EG is separated and recovered by filtration and distillation. After the NaTP was dissolved in water, sulfuric acid was added in two steps at a temperature just above 90° C., and TPA crystals were obtained in a sodium sulfate solution. The crystals were filtered, washed to obtain high-purity TPA, and sodium sulfate was recovered.

TSK has conducted a pilot test of 100 tons/year on this process, and its TPA recovery is about 98%. Due to the low process operating pressure and short reaction time, it is expected that the production cost will be relatively modest. The company estimates that an investment of 8000 tons/year of industrialized production equipment will be approximately US$11 million. Considering the cost savings of PET processing, this scale of equipment is economically viable.

Australian Petrecycle developed a patented technology called Penew. After the patent was purchased by the Italian M & G Group, an industrial scale PET recycling plant was built in West Virginia, USA, which can process 100kt PET bottles per year.

The advantage of this process is that it can handle colored or coated PET bottle waste. The process involves the steaming of PET bottles for one hour with ethylene glycol to embrittle them and then grinding them to 1 mm sized particles to remove impurities and alcoholysis to oligomers, including some terephthalic acid monomers. The special filtration process removes the pigment additives or coating impurities. The final product can be made into colorless PET by mixing with fresh monomers and esterifying in the existing production device.

It is particularly worth mentioning that the PET bottles currently recycled are mainly PET bottles for beverage packaging. Although several U.S. companies have applied for inspections and certifications by the US FDA, PET bottles for cleaning products and cosmetics can be recycled, but in Europe, due to careful consideration, the current share of non-food PET in recycled materials Not more than 1%.

Comparing the advantages and disadvantages of physical and chemical methods, chemical treatment has advantages in ensuring the cleanliness of recycled raw materials, especially for food packaging, which is also the main reason for the rapid development of chemical recycling methods. Of course, the physical recycling method also has its advantages, that is, the processing cost is low.