In recent years, due to the further improvement of polymer synthesis technology, the world's plastics industry has developed rapidly. More and more plastic products have entered millions of households and become one of the essential material information in people's daily life. At present, the annual output of plastic products in the world has exceeded 200 million tons and is still increasing at a rate of 30%. However, with the rapid development of the world plastics industry, a large amount of waste plastics have also been produced. Moreover, these waste plastics are still increasing along with the increase in plastic products, but the recycling rate of plastics is low, because of their inherent polymer properties, poor biodegradability, slow decomposition rate, long-term dispersion in the natural environment will cause the environment Pollution and its negative impact on human health.
Regarding how to handle these waste plastics, all countries in the world are actively seeking reasonable and economical methods. Since China is the most populous developing country in the world, the use of plastic products is more common and there are correspondingly more waste plastics. Although China has also invested human and material resources in the research on the disposal of waste plastics, due to various reasons such as human resources, technical conditions, and the importance of the society, our research is still inferior to the United States, Germany, France, Japan, Italy and other powerful countries.
Therefore, my team members would like to take this survey to understand modern plastics processing methods, try to find out the advantages and disadvantages of various methods, put forward their own opinions, try to put forward more effective treatment methods or suggestions. And called on the broad masses of the people to understand the current situation of plastics processing, together to find and study ways to deal with waste plastics, reduce China's "white" pollution, and protect China's ecological environment. The plastic products in daily life can be divided according to their difficulty and pollution degree: (1) The pollution is serious and difficult to recover is plastic bags, foam plastic lunch boxes and food packaging bags and the like; (2) serious pollution and easy Recycling is blow molding bottles and plastic footer materials; (3) Smaller and longer-lasting types of plastic products are relatively light and difficult to recycle. For different kinds of plastics, people have studied how to deal with them. The methods can now be roughly divided into four types: burying, incineration, recovery of heat energy, material regeneration, and chemical recovery.
Among them, burial is the simplest method to deal with waste plastics, but it needs to occupy a large amount of land, but it will not be decomposed in the soil for a long time, which will cause the soil to be in an unstable state for a long time. Cause waste of land resources. At the same time, it will also cause secondary pollution to the environment through its waste impurities, additives, stabilizers, and colorants. Although incineration and recovery of heat energy can handle a large amount of waste plastics and have high efficiency, it will produce a large amount of toxic gases such as dioxane, causing serious air pollution, and further processing of toxic gases will result in long follow-up processes and comprehensive economic costs. Higher. Material regeneration is the re-plasticization of waste plastics after heating and melting to make recycled plastic products. At present, the focus of research on recycling technologies in various countries is chemical recycling. This method can usually be divided into wet and dry methods. Wet process is generally the process of hydrolysis or alcoholysis of waste plastics. Most of them are based on a single type of polycondensate as a raw material. They are made into monomers or low molecular polymers through degradation reactions. They are used as raw materials for polymer synthesis and have a single Sex. The dry method is a thermal cracking process. It is mainly used for the cracking of polyolefin waste plastics to produce hydrocarbon fuels or chemical raw materials. This is the focus of the chemical recycling method. The thermal cracking is mainly based on the production of fuel.
Now let's talk about cracking waste plastics to produce fuel. The use of waste plastics for pyrolysis and preparation of fuel oil is suitable for the treatment of mixed waste plastics. It is an ideal recycling method and has been listed as a research and development method by various countries. At this stage, technologies such as the Veba method in Germany, the BP method in the United Kingdom, and the Fuji recovery method in Japan are more advanced and larger in scale and have entered the commercialization stage. Our country is limited to small-scale industrial tests.
The Fuji recovery process removes impurities that are not suitable for oiling in waste plastics. For example, PVC in waste plastics is removed in advance. Because PVC contains a large amount of Cl, a large amount of harmful HCl will be generated when the temperature is higher than 230°C. Contamination of the atmosphere, crushing of the gaseous hydrocarbons produced by thermal cracking, and then catalytic reforming in catalytic converters. The reformer is filled with catalysts. ¡ Synthetic zeolite ZSM-5. After the product is cooled and fractionally distilled, fractions and gases such as gasoline, kerosene, and diesel can be obtained, and the yield is 80% to 90%.
The feature of this process is to utilize the centrifuge in the pipeline to circulate and heat the molten material in the thermal cracking reactor to make the heat transfer uniform and to separate the solid residue in the circulating material, thus avoiding the thermal cracking of the solid material. Accumulation and slagging in the kettle.
The Kurata method developed by the Japan Institute of Physical and Chemical Research uses five metals such as Ni, Cu, and Al as catalysts. The process has the following characteristics: (1) The Kurata method has a HCl neutralization device behind the process, and thus PVC in waste plastics. There is no clear limit to the content of (2) the produced oil produced by this method is mainly kerosene. The German company Veba uses a mixture of vacuum residue, lignite and waste plastics as raw materials and brown coal as a catalyst. Na2CO3 and CaO are used to neutralize the HCl produced by PVC; the products are C1-C4 gaseous hydrocarbons, C5 or more alkanes, naphthenes, aromatics, this method needs to be carried out under the pressure of hydrogen, and the investment and operation costs are expensive.
The BP company in the United Kingdom uses a sand furnace to fluidize the cracking reactor. The disadvantage is that it allows the waste plastic to contain 2% PVC. The advantage is that the impurity metal deposits on the sand and is eventually removed as solid waste.
At present, China has developed a one-step process for direct catalytic degradation of liquid polyolefins into gaseous hydrocarbon oils. The method uses multiple modified Y-type zeolite and high activity aluminum hydroxide composite catalyst to directly catalytically degrade liquid waste polyolefin plastics; the obtained gaseous hydrocarbon oil obtains gasoline and diesel through fractionation, and the total yield is 85%-87. %. Zhengzhou City Plastics Co., Ltd. took the lead in the domestic research of successful oil technology, including 3 ~ 30t/a
5 series of industrial production technologies, products #70 gasoline ~ # 10 light diesel.
Beijing Likun Chemical Factory uses waste PE, PP, and PS as raw materials and uses two-stage process and atmospheric pressure reaction. Gasoline and diesel are produced with a yield of 75%. The technology is simple, capable of continuous production, low investment, and low production costs.
The pyrolysis recovery technology for waste plastics in China is still in the experimental stage, and the number of plants developed is still relatively small. However, for PVC, there is still no good treatment method in China. The pyrolysis recovery technology of used plastics in some developed countries has entered a practical stage, and a commercial waste plastics processing device has been set up. In contrast, there is a large gap in China's technology, and the technology and equipment used are also relatively backward, and there is a lack of comprehensive consideration of the cracking characteristics of used plastics.
The recycling of used plastics is an urgent matter. For technical, policy, and awareness issues, members of our group want to put forward our personal views and suggestions.
Technically, the removal of HCl, the development and application of catalysts, poor heat transfer, and easy coking have been resolved. Can the removal of HCl be considered in terms of collecting it or neutralizing it with alkali to produce valuable salts? Problems such as poor heat transfer, easy coking, etc., can cause the furnace to cause long flat areas with large contact areas, and useless sand or other deposits. In addition, for difficult-to-recycle plastic bags and the like, it is hoped that it can be transformed through technological transformation so that it can rot in the soil in a short period of time, or reduce harmful components, and can be solved by burning.
In policy,
(1) We hope that the disposal of plastics will receive the attention of the government, and the proportion of human, material, and financial resources will increase, which will benefit scientific research and practice.
(2) Establish a commercial system for the recycling of waste plastics and recycle all kinds of plastics to the factory as a profession.
(3) Use legislative and administrative measures to impose penalties on improperly handled plastic factories.
(4) Carry out publicity and education campaigns on plastic pollution and solutions to raise people's awareness.
In terms of consciousness, we appeal to the broad masses of people to start from scratch, reduce the use of unnecessary plastic products, and classify and dispose of plastic waste; educate the next generation, raise their environmental awareness, encourage them to recognize plastics, and actively devote themselves to the recycling of plastics. The research work will present its own strength to the motherland, the world, and the environmental protection cause for all mankind!
Source: China Plastics Industry Network