In the existing municipal solid waste, the proportion of plastics has reached 15%-20%, and most of them are disposable plastic packaging products. The treatment of plastic waste is not only a problem in the plastic industry, but also a common concern of the international community.
In order to meet the needs of protecting the earth's environment, the world plastic processing industry has developed many new technologies for environmental protection. In terms of saving resources, it is mainly to improve the aging resistance of products, prolong their life, be multifunctional and design products properly; In the aspect of resource reuse, it mainly studies the efficient sorting and separation technology of plastic waste, efficient melting and recycling technology, chemical recycling technology, completely biodegradable materials, water-soluble materials and edible films; In the aspect of reduction technology, we mainly study the compression and volume reduction technology of waste plastics and the technology of thin film bag container, and make the products as thin as possible on the premise of ensuring the application performance; In the development of CFC substitutes, carbon dioxide foaming technology is mainly studied; In the research of substitutes, it is mainly to develop substitutes for PVC and PVDC.
At present, the treatment of municipal plastic solid waste mainly adopts landfill, incineration and resource utilization. Due to different national conditions, there are differences among countries. Landfill is the main method in the United States, while incineration is the main method in Europe and Japan.
1. Landfill treatment: As the plastic system is generally light in weight and not easy to rot, it will become a soft foundation after landfill, and it will be difficult to use in the future.
2. Incineration: Due to the high calorific value of plastics, it is easy to damage the furnace, and the gas generated after incineration will promote global warming. Some plastics will also release harmful gases during incineration, polluting the atmosphere. By recycling, due to labor consumption, high recycling cost and lack of corresponding recycling channels, recycling only accounts for about 15% of the global plastic consumption. However, due to the limited oil resources in the world, the recycling of plastics is of great significance from the perspective of saving the earth's resources. To this end, countries all over the world have invested a lot of manpower and material resources to develop various key technologies for recycling waste plastics, and are committed to reducing the cost of plastic recycling and developing its applicable application fields.
3. Heat recovery method: Most plastics are made of petroleum, and the main component is hydrocarbons, which can be burned. For example, polystyrene burns more heat than dye oil. Some experts believe that sending plastic waste to an incinerator can provide heat for heating or power generation, because 86% of petroleum dyes are directly burned and only 4% are made into plastic products. It is normal for plastics to be sent to burn as heat energy after being used up. The utilization of heat energy is one of the last methods of plastic recycling, which should not be underestimated. However, many environmental organizations are opposed to burning plastics. They think that burning all the messy chemicals will produce toxic gases. For example, half of PVC is chlorine, and the chlorine gas released during combustion has strong corrosive destructive power, which is the chief culprit of evil English.
At present, there are 200,000 tons of PVC garbage in Germany every year, and 30% of them are burned in incinerators, which makes people panic and the law has to draw up countermeasures. According to the German Federal Environment Agency, all incinerators must meet the exhaust gas value limit below 0. 1 nanogram per cubic meter. Although the air pollution standard of incinerators in Germany has been recognized as a high standard in the world, it is still not dare to say that the combustion mode will not release harmful substances due to mechanical failure. Therefore, it can be predicted that environmental groups in various countries will still strongly oppose incineration to recover heat energy.
4. Classified recycling method: As plastic recycling, the most important thing is classification. Common plastics are polystyrene, polypropylene, low density polyethylene, high density polyethylene, polycarbonate, polyvinyl chloride, polyamide, polyurethane and so on. It is difficult for ordinary people to tell the difference between these plastics. At present, most of the plastic classification work is done manually. Recently, new research progress has been made in machine classification. A chemical science and technology association in Germany invented the infrared identification category, which is fast and accurate, but the sorting cost is high.
5. Chemical reduction method: Researchers began to try to extract chemical components from plastics for reuse. The technological method adopted is to cut off the long chain of polymer and restore its original properties. The cracked raw materials can be used to make new plastics. Some methods promote the chemical cracking of bonded carbon atoms by adding chemical elements, or promote their thermal cracking by adding energy.
Bayer company in Germany developed a hydrolysis chemical reduction method to crack PUC sponge pad. Experiments show that the chemical reduction method is technically feasible, but it can only be used to treat plastic wastes generated in the manufacturing process of clean plastics, such as corner powder. However, plastics contaminated by other pollutants used in households are difficult to be treated by chemical decomposition. With the application of this reduction method, a large number of wastes will not be hydrolyzed until 2 1 century. Some new chemical decomposition methods are still in the process of research. Ford Motor Company of the United States is currently applying ester decomposition method to the treatment of automobile waste plastic parts.
Rensselaer Institute of Technology has developed a solution that can decompose plastic waste. This patented solution is to mix six different types of plastics and heat them together. Six polymers can be extracted at different temperatures. In the experiment, polystyrene plastic fragments and related solutions were mixed into a dissolved state at room temperature, then heated in a sealed container, and then sent to a low-pressure "flash chamber", and the solution quickly evaporated (recyclable), leaving reusable pure polystyrene.
It is said that the purification device used in the study can purify 1kg of polymer per hour. The New York State Government and Niagara Mohawk Power Company are planning to jointly establish a small-scale pilot plant. Investors claim that after the completion of the factory, 4t polymer raw materials can be recovered every hour. Its cost is only 30% of the production raw materials, and it has very obvious commercial value.
6. Hydrogenation: Many experts believe that hydrogenation can be used to treat mixed plastic products. Raw materials such as synthetic crude oil and gas can be produced by putting the mixed plastic fragments into a hydrogen reactor and adding specific temperature and pressure. This treatment method can be used to treat PVC waste, and its advantage is that it will not produce toxic dioxins and chlorine. The mixed plastic products are treated by this method, and 60%-80% of the components are refined into synthetic crude oil according to the different plastic components. Three chemical companies, such as BASF in Germany, pointed out in the same research report that hydrogenation is the best thermal cracking method, and the synthetic crude oil products obtained by decomposition are of good quality and can be used for refining.
The University of Kentucky in Lexington, USA, invented a technical method to turn waste plastics into high-quality plastic fuel oil. The fuel produced by this method is very similar to crude oil, even lighter than crude oil, and it is easier to be refined into high octane fuel oil. This kind of fuel oil produced from waste plastics contains no sulfur and few impurities. Plastics and coal liquefy in a similar way. But also can produce high-quality fuel oil.
The researchers mixed all kinds of plastics with zeolite catalyst and tetralin in a bath, then put them into a reactor called "pipeline bomb" and heated them under pressure with hydrogen to promote the decomposition of macromolecular plastics into compounds with smaller molecular weight. This process is similar to combination in crude oil processing. After this treatment, the oil yield of waste plastics is very high, and the oil yield of polyethylene plastic bottles can reach 88%. When waste plastics and coal are mixed and liquefied at the ratio of about 1: 1, better fuel oil can be obtained. After evaluating the economic benefits of this process, it is predicted that the fuel oil produced from waste plastics will be transformed into blast furnace benefits within 5- 10 years. At present, Germany has started to build a reactor in Botup that is expected to produce 200 tons of plastic fuel per day.
7. Simplify the design method: R&D department considers the needs of recycling and disassembly when designing products. The focus of consideration is not which plastic should be the most suitable for making a single part, but the material that can be widely used. This is a revolutionary change in concept.
In order to facilitate recycling, designers began to avoid using a variety of plastics when designing products. American BMW is going to reduce the types of plastics by 40% in its new car design to facilitate the recycling of waste plastics. The reason why the automobile industry reduces the use of plastics and considers additionality in design is mainly to win a good image of attaching importance to environmental protection and get the appreciation of consumers. At present, this design concept is gradually infecting the whole plastic processing industry.
However, all efforts still can't make any of the 20 kinds of plastics on the market disappear. After all, the diversity of products leads to the diversity of plastics, for example, the plastics used in the production of electronic computers are different from those used in the production of automobiles. To this end, experts suggest that relevant recycling standards should be formulated, stipulating that only designated materials can be used in special industries, otherwise effective recycling of electronics and automobiles cannot be controlled.