Recycling of waste plastics in Japan

Editor's note: Japan is the second largest plastic production and consumption country in the world after the United States, with an annual plastic output of more than 14million tons and a consumption of nearly 10million tons. At present, the discharge of waste plastics is about 9million tons, accounting for 30% - 50% of the volume of domestic waste. Japan is a small country with a dense population. An increasing number of waste plastics can no longer be incinerated or buried. Waste plastics pose a serious threat to the living environment of the Japanese public. On the other hand, Japan is short of resources, so it is urgent to recycle waste plastics as resources and establish a resource recycling society

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plastic container packaging materials account for 40% of plastic products in Japan, and are the main part of household garbage. PET bottles are mainly used for the packaging of cool drinks in Japan (accounting for about 80% of PET bottles). The variety is relatively single, which is easy to collect separately, and its recycled materials are suitable for reuse. The average annual growth rate of PET bottle recycling in Japan is 10%. For this reason, Japan has formulated the PET bottle independent design criteria, which stipulates that PET bottles for beverages, soy sauce and alcohol do not use bottom cups, handles, coloring is prohibited, labels that can be removed by physical methods are used, aluminum caps are not used, and only plastic caps are allowed. In order to facilitate the transportation of a large number of collected PET bottles to the recycling treatment plant, the waste PET bottles should be reduced before shipment. Recycled PET bottle resin in Japan is mainly used to manufacture fiber, sheet and non food packaging bottles, and their consumption is roughly the same; At present, the proportion of fiber is gradually increasing, which has exceeded 70%. The above uses of pet in Japan are becoming saturated. With the further increase of PET bottle recycling in the future, it is necessary to develop new uses for recycled PET, such as civil construction materials, food packaging and containers. At present, Japanese companies have used polymer alloy modification technology to process recycled PET into powder coatings with better performance than those made from new PET materials

the most effective solution is to degrade pet into monomers by chemical recovery and re synthesize new PET materials. Therefore, Japan is developing ethylene glycol pyrolysis recovery method of waste PET and supercritical methanol decomposition recovery method of pet

Teijin company of Japan has recently developed a recycling method for DMT (dimethyl terephthalate) and eg from waste PET bottles. This research work has been supported by the National Natural Science Foundation of China (ethylene glycol). First, the waste PET bottles are crushed and cleaned, and then dissolved in ET. it is used to carry out static loading, stretching, tightening, bending, shearing, tearing Under the boiling temperature of ET and the pressure of 0.1MPa, pet is depolymerized to form bis (hydroxyethyl terephthalate) (BHET). After filtration, remove the filter residue and additives, make BHET react with methanol, and generate DMT and eg through transesterification reaction at the boiling temperature of methanol and the pressure of 0.1MPa. After distillation, DMT and eg are separated, and then DMT is refined through recrystallization process; Eg is purified by distillation, and methanol can be recycled. The purity of the recovered DMT and EG is 99.99%, and the production cost is comparable to that of the general DMT and eg method. DMT can be converted into pure TPA (terephthalic acid) for the manufacture of bottle grade PET resin. The circulating device can generate about 10% of the raw materials used by the company for resin production

2. Other waste plastics

Japan has a huge discharge of waste plastic packaging containers, with a total annual discharge of 8.84 million tons of waste plastics, including 4.43 million tons of industrial waste and 4.414 million tons of general waste. Plastic packaging containers other than PET bottles are 3.238 million tons, accounting for more than 73% of general household waste plastics. This part of waste plastics is not only large in quantity, but also mixed in types and different forms, including PE, PP, PVC, PS, PET film, hollow containers, sheets, etc. it cannot be collected according to a single variety like pet bottles, and it is difficult to sort according to types as materials for recycling and reuse. At present, this part of waste plastics is mainly used as heat energy recovery in Japan. Therefore, Japan is developing and improving the following heat energy recovery technologies: (1) direct combustion, energy recovery, including garbage power generation, used in iron smelting blast furnaces to replace coke as reductant and as fuel for cement kilns; (2) After fueling, it can be used in various power boilers, and some of the oily fuel can be used in automobiles, including solid fueling, powder fueling, solid water slurry fueling, thermal decomposition oiling, supercritical water oiling, and coal gasification. The oiling of waste plastics can obtain high-value liquid fuels or chemical raw materials, while other heat recovery and fueling methods can only mention the substitutes of coal or gas, so oiling is the recycling method of mixed waste plastics stipulated by the Japanese government. Although the small oiling units of waste PP, PE and PS in the industrial system have been put into practice, the large oiling units of general waste plastics containing PVC have not been put into practice. At present, the oiling device developed in Japan cannot be used for the oiling of thermosetting resins, nor for the oiling of pet, ABS and PVC. It can only treat 20% of PVC mixed waste plastics. Toshiba successfully researched the technology of continuous dechlorination in the oiling of waste plastics, and trial produced a waste plastic sleeved device containing 50% PVC

compared with thermal decomposition and oiling, supercritical water oiling can accelerate the decomposition of plastics, requiring less equipment, mainly light oil, and almost no by-products. Tohoku electric power company of Japan has established a test device with a treatment capacity of 0.5 tons to treat waste plastics from the power industry, such as waste wire wrappers. After crushing, the waste plastic is mixed with water, heated and pressurized to 374c ° and 22.1mpa supercritical state to decompose into oil

replacing coke with waste plastics not only has a high energy utilization rate, but also produces less carbon dioxide than coke. However, PVC should be attached to waste plastics. At present, the main methods used in Japan are: gravity separation method to remove PVC; The mixed waste plastics are used for blast furnace ironmaking after dechlorination and granulation; PVC separated from general waste plastics is used as reducing agent for blast furnace after decomposition and dechlorination in rotary kiln. At present, the processing capacity has reached 30000 ~ 60000 tons

refractory material testing machine Japan Deshan caoda company, which produces both PVC and cement, crushed the waste plastic from PVC to a particle size of less than 25mm without granulation, and directly used it in cement kilns to replace the fuel used for pulverized coal. The processing capacity has reached more than 10000 tons. At present, the company is also experimenting with the system of decomposing and dechlorinating waste plastics containing PVC and using them as fuel for cement burning. The HCI produced by dechlorination is reused in the manufacture of PVC

the residue of waste plastics after burning in the kiln remains in the cement as a filler. The fine crushing of thermosetting resin may also act as cement kiln fuel. The above four heat recovery methods are suitable for large-scale treatment of a large number of mixed waste plastics, and are the focus of current research and development. Other recovery methods such as solid fuel method and powder fuel method are only suitable for some specific small-scale treatment occasions

Japan is a large country in the production and consumption of household appliances, which produces a large amount of household appliance waste every year. The plastic shell is not sent to the normal temperature crushing process, and then the metal and glass are separated. The remaining plastic is sent to the fuel chemical process of metal and resin mixture. After carbonization, the waste plastic is turned into fuel and returned to this kind of algae. It is a renewable resource

there are about 5million scrapped cars in Japan every year, and the plastic on each car accounts for about 7.5% of the vehicle weight. It is mainly recycled resin materials such as bumpers, instrument panels, seat skins, wire covers, etc

3. Recycling of thermosetting plastics

thermosetting plastics do not melt when heated, and it is impossible to reacts with materials, and it is difficult to oilize by thermal decomposition. A large number of thermosetting plastics such as phenolic resin and polyurethane in household appliances, calculators and automobiles that are scrapped every year must be treated and recycled. Some research institutions in Japan are studying the recycling methods of thermosetting plastics, and great progress has been made. The Japanese Institute of resources and environment has successfully developed a liquid-phase decomposition method to decompose waste phenolic resin into monomers using tetralin as a hydrogen donor solvent. This method can also be used for the oily recovery of epoxy resin, polyurethane, FRP, etc. Osaka Industrial Research Institute crushed the waste phenolic resin to replace wood powder as the reinforcing material of phenolic resin products. Compared with traditional products, the water resistance was increased by 6 times, the electrical insulation was increased by 10 times, and the heat resistance was also good. The Institute crushed the waste polyester and mixed it with phenol, heated it under acidic conditions, and then reacted with formaldehyde to produce phenolic resin. Hexamethylene tetramine was added as curing agent to make phenolic resin products with good strength, toughness and heat resistance. Chemical recovery method generally has large investment and high cost. At present, there is little research in Japan, and there are only a few practical examples

source: China's packaging industry