Japan's waste plastic recycling technology development trend

Japan is the second largest plastic producer and consumer in the world after the United States. The annual output of plastics exceeds 14 million tons, and the consumption is nearly 10 million tons. At present, the output of waste plastics is approximately 9 million t/a. Waste plastics account for household waste. 30% to 50% of the volume. Japan has a small land area and a dense population. An increasing number of waste plastics can no longer be disposed of by burning or burial. The pollution of waste plastics poses a serious threat to the living environment of the Japanese public. On the other hand, the lack of Japanese resources, the recycling of waste plastics as a resource, and the establishment of a resource-recycling society have become an urgent task.

Japan plans to recycle 65% of waste plastics in 2001 (including heat energy recovery of 50% and material recovery of 15%), and the recycling rate at the beginning of the 21st century will reach 90% (including 70% of heat energy recovery and 20% of material recycling).

1. PET bottles

Plastic container packaging materials account for 40% of Japanese plastic products and are the main part of domestic household waste. PET bottles are mainly used in the packaging of cool drinks in Japan (about 80% of PET bottles). The varieties are relatively simple and can be easily collected separately. The recycled materials are suitable for reuse. In 1996, the world PET bottle recycling rate was 17.5%, China was 5.1%, and Japan was only 2.9%. By 1997, the recovery rate of PET bottles in Japan soared to 9%, from 1998 to 18%, and in 2001 to 27.7%, with an average annual growth rate of 10%. Japan has formulated the “Principles for the Design of PET Bottles for Independent Design”, which stipulates that PET bottles for beverages, soy sauces, and wines do not use cups, handles, prohibit coloring, use physical labels that can be removed, and do not use aluminum caps. Cover with plastic, etc. In order to facilitate the transport of a large number of collected PET bottles to a recycling plant, the waste PET bottles must be reduced to volume before they are shipped. Japan PET bottle recycled resin is mainly used for the manufacture of fibers, sheets and non-food packaging bottles, the consumption of the three is about the same; currently the proportion of fiber is gradually increasing, has exceeded 70%. The above uses of PET in Japan are becoming saturated. With the further increase in the recovery of PET bottles in the future, new uses must be developed for recycled PET, such as 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 PET.

Using chemical recycling method to degrade PET to monomer to re-synthesize PET is the most effective solution. For this reason, Japan is developing a method for recovering and recovering waste PET by ethylene glycol pyrolysis and supercritical methanol decomposition of PET.

Teijin Japan recently developed a recycling method for DMT (dimethyl terephthalate) and EG (ethylene glycol) from waste PET bottles. The waste PET bottles were first crushed and cleaned, and then dissolved in EG. PET was depolymerized at a boiling temperature of EG and a pressure of 0.1 MPa to produce hydroxyethyl bis-terephthalate (BHET). After filtration, the filter residue and additives were removed to react BHET with methanol. After transesterification, DMT and EG were formed at a boiling temperature of methanol and a pressure of 0.1 MPa. After distillation, DMT and EG are separated, and then 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 reaches 99.99%, and the production cost is comparable to that of the general DMT and EG methods. DMT can be converted to pure TPA (terephthalic acid) for the manufacture of bottle grade PET resins. The circulating device can generate about 10% of the company's raw materials for resin production.

2. Other waste plastics

The discharge volume of waste plastic packaging containers in Japan is extremely large. The total amount of waste plastics discharged each year is 8.84 million tons, of which 4.43 million tons are industrial wastes and 4.414 million tons are general wastes. The plastic packaging containers other than PET bottles were 3.238 million tons, accounting for more than 73% of the general life waste plastics. This part of the waste plastics is not only in large quantities, but also in a variety of types and forms, including PE, PP, PVC, PS, PET film, hollow containers, sheets, etc. It cannot be collected as a single species like P bottles, and it is difficult to sort by type. Sorting is reused as material. At present, this part of waste plastics is mainly recycled as heat energy in Japan. To this end, Japan is developing and improving the following various heat energy recovery technologies: (1) Direct combustion, recovery of energy, including waste-to-energy, used in iron-making blast furnaces to replace coke for reduction. Agent, used as a fuel for cement kiln; (2) used in various power generation boilers after fueling; a part of oil fuel can be used in automobiles, including solid fuel, powder fuel, solid water slurry fuel, thermal decomposition oil Supercritical water, oil, coal gasification.
The use of waste plastics to obtain higher value liquid fuels or chemical raw materials, while other heat recovery and fueling methods can only refer to coal or gas substitutes, so the oilification is the Japanese government's method of recycling mixed plastic waste. Although the small-scale oiling devices for waste PP, PE, and Ps in the processed industrial system have been put into practical use, large-scale oiling devices for general plastics containing PVC have not yet been put to practical use. Currently, the oiling device developed in Japan cannot be used for the oiling of thermosetting resins. It is also not suitable for the oilification of PET, ABS, and PVC, and can only treat miscellaneous waste plastics with PVC <20%. Toshiba researched the technology of continuous dechlorination in the waste oil plasticization, and tried to make a waste plastic sleeve unit with 50% PVC.

Compared with pyrolysis oilification, supercritical water oilification can accelerate the decomposition of plastics. The required equipment is small. The main recovery is light oil with almost no by-products. Nippon Electric Power Co., Ltd. established a test device with a processing capacity of 0.5 t/a. It was put into operation in January 1998 and was used to dispose of waste plastics in the public power industry, such as waste wire wrappers. The waste plastic is crushed and mixed with water, heated and pressurized to 3740C and 22.1MPa to decompose into oil in a supercritical state.

Replacing coke with plastic waste not only has high energy efficiency, but also produces less CO2 than coke. However, PVC must be added to the waste plastic. The methods currently used in Japan mainly include the following: Gravity separation method to remove PVC; Pelletizing of mixed waste plastics after granulation for blast furnace ironmaking; PVC separated from general waste plastics after furnace decomposed and dechlorinated to be used as blast furnace reducing agent. At present, the processing capacity has reached 3 to 60,000 t/a.

Japan's Tokuyama Soda Co., Ltd., which produces PVC and produces cement, pulverizes waste plastics with PVC to a size below 25 mm. It is used for cement kiln instead of pulverized coal, and has been processed successfully. The processing capacity has reached ten thousand. More than tons. At present, the company is also using a PVC system to decompose and dechlorinate waste plastics and then use it as a cement burning fuel system. HCI produced by dechlorination is reused in the manufacture of PVC.

Residues of waste plastics burning in the kiln remain in the cement as fillers. Thermosetting resin fines may also act as a cement kiln fuel. The above four heat energy recovery methods are suitable for large-scale processing of a large number of mixed waste plastics, and are currently the focus of research and development. Other recovery methods such as solid fuel method, powder fuel method, etc. are only suitable for certain specific small-scale processing occasions.

Japan is a big producer and consumer of household appliances, and it produces a large amount of household electrical appliances every year. The plastic shell is taken off at normal temperature and crushing process, then the metal and glass are separated, the remaining plastic is sent to the metal and the resin mixture is fueled, and the dry distillation process turns the waste plastic into fuel.

In Japan, about 5 million cars are scrapped each year, and the plastic on each car accounts for about 7.5% of the car's weight. Mainly for the bumper, dashboard, seat skin, wire wrapping and other recycled resin materials.

3. Recovery of thermosetting plastics

Thermosetting plastics do not melt when heated, and it is impossible to reactivate the materials. It is also difficult to use the thermal decomposition method for oilification. The thermosetting plastics such as phenolic resins and polyurethanes used in household appliances, calculators, and automobiles that are scrapped each year must be recycled. Some Japanese research institutes in the same country are studying methods for recovering thermosetting plastics. Wells have made great progress. The Japan Institute of Resources and Environment Research has successfully used the liquid-phase decomposition method of hydrogen tetrasolvent to decompose waste phenolic resin into monomers. This method can also be used for oil recovery of epoxy resin, polyurethane, FRP, and the like. The Osaka Institute of Industry uses pulverized phenolic resin to substitute wood flour for the reinforcement of phenolic resin products. Compared with conventional products, the water resistance is increased by 6 times, the electrical insulation is improved by 10 times, and the heat resistance is also good. After the waste polyester is crushed, it is mixed with phenol, heated under acidic conditions, and then reacted with formaldehyde to produce phenolic resin. Adding hexamethylenetetramine as a curing agent can produce phenolic resin with good strength, toughness and heat resistance. Resin products. The chemical recovery method generally has a large investment and high cost. Japan is still a relatively small number of researches and there are only a few practical examples.