Disposal of the hottest plastic solid waste I

Treatment of plastic solid waste (I)

it has been a difficult process to produce plastics from oil and coal to replace natural polymer materials. A whole generation of outstanding chemists have worked hard to realize the excellent physical and chemical properties and durability of plastics. The total market value of intelligent composites in structural health monitoring and other sensing applications will reach 560million US dollars. Plastic has replaced a large number of traditional packaging materials with its characteristics of light weight, durability, beauty and low price, which has contributed to a revolution in the packaging industry. But what people expect is that it is precisely these excellent properties of plastics that produce a large number of durable and non corrosive plastic waste. The large amount of discarded plastic packaging after use has become a major hazard to the environment. The main reason is that these plastic garbage are difficult to treat and cannot be decomposed into dust. In the existing municipal solid waste, the proportion of plastic has reached 15% - 20%, and most of them are disposable plastic packaging products. The disposal of plastic waste is not only a problem of the plastic industry, but also has become a public nuisance of the international community

in order to meet the needs of protecting the earth's environment, the world's plastic processing industry has developed many new environmental protection technologies. In terms of saving resources, it mainly includes improving the aging resistance of products, prolonging the service life, multi-function and appropriate product design; In terms of resource reuse, it mainly studies the efficient separation and separation technology of plastic waste, efficient melting recycling technology, chemical recycling technology, fully biodegradable materials, water-soluble materials, edible films; In terms of reduction technology, it is mainly to study the waste plastic compression reduction technology and film bag container technology, and try to make the products thinner on the premise of ensuring the application performance; In the development of CFC substitutes, the outer door of the main 211 building should study carbon dioxide foaming technology; In the research of substitutes, PVC and PVDC substitutes are mainly developed

in the treatment of urban plastic solid waste, there are three main methods: landfill, incineration and recycling. Due to different national conditions, countries differ. The United States is mainly landfill, while Europe and Japan are mainly incineration. Using landfill treatment, because the plastic is generally light in quality and not perishable, it will lead to the landfill land becoming a soft foundation, which will be difficult to use in the future. Using incineration treatment, because plastic has a high calorific value, it is easy to damage the furnace. In addition, the gas generated after incineration will promote the warming of the earth. Some plastics will release harmful gases during incineration and pollute the atmosphere. Using the recycling method, due to the labor consumption, high recycling cost, and the lack of corresponding recycling channels, the world's recycling only accounts for about 15% of the total 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 earth resources. Therefore, at present, countries all over the world have invested a lot of human and material resources to develop key technologies for the recycling of waste plastics, and are committed to reducing the cost of plastic recycling and developing appropriate application fields

I. heat recovery method

most plastics are made of petroleum, and the main components are hydrocarbons, which can be burned. For example, polystyrene burns more heat than dye oil. Some experts believe that sending plastic waste to the incinerator for combustion can provide heat for heating or power generation, because 86% of the petroleum dyes are directly burned, of which only 4% are made into plastic products. It is normal to send plastic after it is used up as heat energy, and the use of heat energy is one of the last methods of plastic recycling, which cannot be underestimated. However, many environmental protection groups oppose the burning of plastics. They believe that the incineration method will concentrate all the messy chemicals and produce toxic gases. For example, half of the PVC component is chlorine, and the chlorine released during combustion has strong corrosive destructive power, and is the culprit of dioxin

at present, there are 200000 tons of PVC waste in Germany every year, 30% of which are burned in incinerators, which makes people panic. The law has to formulate countermeasures for this. The German Federal Environment Agency has stipulated that all incinerators must meet the limit of less than 0.1ng (nanograms) per cubic meter of exhaust gas. Although the air pollution standard of incinerators in Germany has been recognized as a high standard in the world, it still does not dare to say that the combustion method will not release harmful substances due to mechanical failure. Therefore, it can be predicted that environmental protection groups in various countries will still vigorously oppose the incineration method to recover heat energy

II. Classified recycling method

as plastic recycling, the most important thing is to classify. Common plastics include polystyrene, polypropylene, low-density polyethylene, high-density polyethylene, polycarbonate, polyvinyl chloride, polyamide, polyurethane, etc. the differences between these plastics are difficult for ordinary people to distinguish. Now the plastic classification work is mostly done manually. Recently, there has been new research progress in machine classification. A German Chemical Technology Association invented infrared to identify categories, which is fast and accurate, but the sorting cost is high

III. chemical reduction method

researchers began to try to extract the chemical components in plastic for reuse. The technological method adopted is to cut off the long chain of the polymer and restore its original properties. The raw materials cracked can be used to make new plastics. Some methods are to add chemical elements to promote the chemical cracking of combined carbon atoms, or add energy to promote their thermal cracking

Bayer company of Germany developed 5.6. The cleanliness of hydraulic oil complies with the American hydraulic industry NAS ⑴ 638 grade 7 standard. A hydrolytic chemical reduction method is used to crack PUC sponge pads. Experiments have proved that the chemical reduction method is technically feasible, but it can only be used to treat clean plastics, such as corner powder and other plastic wastes produced in the production process. However, it is difficult to use chemical decomposition method to deal with the plastic contaminated with other pollutants used in the family. The application of this reduction method will not use hydrolysis to treat waste materials in large quantities until the 21st century. Some new chemical decomposition methods are still in the process of research. Ford Motor Company of the United States is currently applying ester hydrolysis to the treatment of automotive waste plastic parts

rensser Institute of technology has developed a solution that can decompose plastic waste. This patented solution is heated with six different types of plastics mixed together. Six polymers can be extracted at different temperatures. In the experiment, polystyrene plastic fragments and relevant solutions are mixed into a dissolved state at room temperature, and then sent to a sealed container for heating, and then sent to a low pressure "flash chamber". The solution evaporates rapidly (recyclable and reused), and the rest is pure polystyrene that can be reused

it is said that the purification device used in the research can purify 1kg of polymer per hour. The New York state government and the Niagara Mohawk power company are planning to jointly build a small-scale pilot plant. Investors claim that after the completion of the plant, 4T of polymer raw materials can be recycled per hour. Its cost is only 30% of the production raw materials, which has very obvious commercial value

IV. hydrogenolysis

many experts believe that hydrogenation can be used to treat mixed plastic products. Put the mixed plastic fragments into the hydrogen reaction furnace and apply specific temperature and pressure to produce raw materials such as synthetic crude oil and gas. This treatment method can be used to treat PVC waste, and its advantage is that it will not produce toxic dioxin and chlorine. Using this method to treat mixed plastic products, 60% - 80% of the components can be refined into synthetic crude oil according to different plastic components. In a joint research report, three chemical companies from Germany, such as BASF, pointed out that hydrogenation is the best way of thermal cracking, and the synthetic raw oil produced by analysis is of good quality and can be used for oil refining

the University of Kentucky in Lexington, USA, invented a process method to turn waste plastics into high-quality plastic fuel oil. The fuel produced by this method is much like crude oil, even lighter than crude oil, and it is easier to refine into fuel oil with high octane number. The fuel oil produced from waste plastics does not contain sulfur and has few impurities. Plastics are liquefied with coal in a similar way. It can also produce high-quality fuel oil

researchers mixed various plastics with zeolite catalyst and tetralin in the shower, and then put them into a reaction furnace called "pipe bomb", which was pressurized and heated with hydrogen to promote the decomposition of macromolecular plastics into compounds with small molecular weight. This process is similar to the combination in crude oil treatment. 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 in a ratio of approximately 1:1, higher quality fuel oil can be obtained. After evaluating the economic benefits of this process, it is expected that the production of fuel oil from waste plastics will become degenerated in 5-10 years, with blast furnace benefits. At present, Germany has begun to build a reaction furnace with a daily output of 200t plastic oil in botop