I. Overview of PVC PVC
The recycling of PVC can not only solve environmental problems, but also alleviate the pressure of this resource shortage. Especially in the days when the price of PVC raw materials continues to rise, its recycling and reuse is of great significance. The demand for polyvinyl chloride (PVC) in China is increasing at a rate of 10% per year. The use of PVC in the construction industry is very large. If the waste products can be recycled, the environmental pollution of PVC can be greatly reduced. Recycled plastics create the "Magic Cube" exterior wall of the World Expo
Second, in fact, PVC waste is often mixed with other plastic materials. It is generally necessary to perform plastic sorting first, and then use physical or chemical means for comprehensive utilization.
1. Sorting of PVC:
Bifurcation is a difficult part of the process of plastic waste disposal and one of the key factors determining the outcome of the treatment.
Common plastics are polyvinyl chloride, polystyrene, polypropylene, low (high) density polyethylene, polyamine, polyurethane and the like. There are many disadvantages caused by manual sorting: low efficiency; the workers are in a harmful environment; the errors in material classification are large.
Automated sorting systems have been mostly used in industrial production, and developed countries in the world have studied more in this area. A chemical science and technology association in Germany once invented the technology of using infrared rays to screen PVC from waste plastics, but the objects are limited to transparent bottles, and there are problems of low screening precision and high cost.
Recently, Japan has successfully developed a technology for high-precision screening of polyvinyl chloride resin (PVC) from waste plastics. The technology uses the difference between the heating characteristics of PVC and other plastics (within 50 ° C) and the charging characteristics. The detected PVC is marked with red light and is easily screened by the operator. This method is more accurate than the near-infrared technology, and the cost is only 1/2.
The American Rubber Recycling Center (CPRR) invented a method of separating PVC bottles from other waste containers. The key to this process is the use of an X-ray fluorescence detector developed by Asoma Instruments. The CPRR research staff has developed a computer system. It uses an X-ray from a radioactive isotope to excite all of the electrons in the compound. The chlorine-containing molecules are emitted and emit an X-ray reflection image that is easily displayed by an X-ray fluorescence analyzer. The separation work is done by a set of mechanical devices. It can remove all the bottles containing chlorine atoms through the conveyor belt, or remove the bottles without chlorine atoms.
2, PVC recycling technology
At present, there are three main technologies for recycling PVC: one is physical recycling; the other is comprehensive utilization of chemical recovery; the third is to recover and utilize energy by burning PVC materials. Among them, the comprehensive utilization of physical and chemical methods is a method worthy of admiration. They can recycle waste products again and give full play to the performance of materials.
Physical recycling
Physical recycling means that the recycling process of PVC waste is only treated by mechanical means, mainly through chopping, screening, grinding and other procedures, and finally obtains film, powder, granules or other forms of recycled materials. These recycled materials can be used to produce heavy bags, agricultural water pipes and soles.
3. PVC plastic products are divided into soft products and hard products. Soft products mainly include film, cable sheathing, plastic shoes and leather products; hard products mainly include bottles, pipes, profiles, and sheet materials.
In soft products, agricultural film is a type that is used in a large amount. The agricultural film is made of various materials such as PVC, PE, and EVa. When recycling and recycling, the PVC film should be distinguished from other material films. Agricultural film often contains soil, sand, grass roots and nails, etc., and these impurities should be removed and cleaned, then dried or chopped to make chips or pellets, and then made into agricultural product packaging film, agricultural regeneration. Water pipes and soles, etc. Since the waste agricultural PVC film which is repeatedly recycled is repeatedly subjected to heating processing and mechanical action, partial degradation is inevitably caused, and the strength is lowered. In order to ensure the quality of the product, it is necessary to add some new PVC resin and corresponding additives. If the reclaimed material is made into a secondary plastic film by means of a dense, two-roller or four-roller winding, and different coloring materials are added during the mixing process, the calendered film produced will also exhibit different colors. In addition, about 30% of the plasticizer (mainly DOP) remaining in the waste agricultural PVC film can be recycled and reused after refining.
PVC bottles in hard products are also used in a very large amount, and the waste can be processed into shaped materials, pipes and folded boards. In the plastics processing plant, the PVC chips are first cleaned, dried after removing the caps and labels, and then pulverized into small pieces of less than 0.5 mm. BFGoodrich, one of the major PVC manufacturers in the United States, conducted a test using co-extrusion of new PVC and recycled PVC. The results show that recycled PVC preserves the excellent properties of new materials and can be applied in applications where performance requirements are low.
For the physical recovery method, the quality of the PVC recyclate has a greater relationship with the degree of contamination and the composition of the selected material. The quality of the reclaimed material determines the extent to which the original material can be replaced by the recyclate: “high quality†recyclate can be reused in the same type of PVC application, however “low quality†recyclate from the mixed waste portion can only be “Low-level recycling†into products that are usually made from other materials.
Of course, the quality of the ultimate product is inseparable from the recycling equipment itself. At present, the equipment and process for recycling PVC waste in Germany has reached a high level. The content of the pollutants is less than 1%, and the obtained PVC secondary pulverized material can be processed into many products by various methods. The Polyvinyl Chloride Association of the American Plastics Industry Association also strongly encourages the recycling of PVC. It is planned to start the recycling of PVC bottles and drive the recycling of other PVC products.
Chemical recovery: Chemical recovery refers to the conversion of a polymer into a small molecule compound or a simple compound using the chemical properties of the polymer. The method of chemical decomposition has higher utilization rate of resources, but the process is complicated and the cost is high, thus affecting the recycling of plastic products.
For PVC, in addition to the polymer chain is broken, the chlorine atoms attached to the chain are also released in the form of HCI. HCI is either reused after purification, or must be neutralized to form different products, some can be reused, and some must be disposed of, which is determined by the technology used in the process. Countries in the world have strengthened research in this field.
The recycling and recycling technology of waste plastics developed in China can recycle PVC waste film and film, and then produce oil, paraffin, building materials and so on. With this technology and equipment in the case of continuous production, the daily processing capacity of abandoned agricultural film is strong, the oil yield can reach 40%~80%, the conversion rate of gasoline and diesel is high, and it meets the standards of vehicle fuel and environmental emission standards. In addition, since the PVC film contains 30% to 37% of dioctyl phthalate, the solvent can be extracted by normal temperature solvent extraction, and the solvent can be recovered at a temperature lower than 800 °C. DOP is a widely used plasticizer. The current market price is 7,000 yuan to 8,000 yuan / ton. Recycling 1 ton of waste PVC film can make more than 2,000 yuan and eliminate environmental pollution.
There are also two more advanced solvent recovery PVC processes in Europe. Belgian Solvay invested 10.6 million euros to build the world's first soft PVC resin recycling unit in Italy. The device uses the VinyLoop batch process to regenerate 8,500 tons of PVC per year from 10,000 tons of waste plastics (mostly composed of PVC). The technology uses a mixture of methyl ethyl ketone as a solvent, selectively dissolves PVC and an additive at a temperature of 100 ° C to 140 ° C under pressure, and the solution is precipitated to obtain a soft PVC containing an additive. The process for recycling PVC is equivalent to the production of new PVC, and the resulting PVC contains additives, so the resin is sold at a higher price. The VinyLcop process reduces the environmental impact of PVC, especially soft PVC. The second VinyLoop unit will be commissioned in France in 2004 and will be designed to recycle PVC-coated varnishes and fabrics.
Another new process for the recycling of PVC in Europe by solvent is used to recover PVC from the entire automotive wiring board. The process was jointly developed by the automotive manufacturers in Wuppertal and Delphi, Germany, and the University of Wuppertal. It was industrialized three years ago by Wiefek GmbH, an auto parts recycler in Nohfelden-Fisen, Germany. The recycling of PVC by this process is less than 20% of the price of new PVC. The process uses esters and ketones as solvents, but the solvent usage is much less than the Vinyloop process. The solvent does not completely dissolve the waste PVC, but simply softens it to make it easier to separate from the copper wire, and the resulting copper wire can be used to pay for the recycling process. Wiefek has invented a process for separating plastics and solvents by centrifugation and has obtained a patent. The company's recycling PVC production line established by this process can recycle 225 tons of reusable PVC per year. Recovery heat method
At present, obtaining energy by incinerating PVC products is also one of the methods of PVC recycling. But this method has a tendency to be eliminated.
During the incineration process, the PVC waste produces hydrochloric acid (hydrogen chloride) and is released with the flue gas, which needs to be neutralized. The method is to add neutralizing substances to the incinerator, the most common of which is limestone, which neutralizes the acidic components of the incineration gas. Because the chlorine released during the burning of PVC has a strong corrosive destructive power and is the first evil causing dioxins, environmental groups in various countries strongly oppose the use of incineration to recover heat.
The recycling of PVC plastic generally refers to the use of PVC, after crushing, cleaning, drying, plasticizing, drawing, cooling, granulating, processing, and natural PVC, for re-formed PVC related products, In particular, it is used more as a raw material. Since PVC is widely used in pipes and tools, and can only be used once for reasons such as hygiene, equipment for recycling PVC has been a concern. Generally, PE and pp are separated on PVC, and the same can be used for centralized recycling and granulation (using DY waste plastic recycling granulator for PP, PE, aBS, etc.). The recycling of various waste plastics has been widely concerned. Generally speaking, plastic crushers are common. Other equipments are the same as PVC recycling equipment. The equipments for recycling and processing are different, and the quality of recycled plastics is different. The key is cleaning and manufacturing. The degree of good or bad. The general plastic recycling processing process is: Pvc plastic → pvc plastic → automatic cleaning → plastic molding → drawing and dicing → quality inspection packaging
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