PVC recycling technology introduction
2019-08-31 12:06:54
The demand for polyvinyl chloride ( PVC ) in China is increasing at a rate of 10% annually. The recycling of PVC can not only solve environmental problems, but also alleviate the pressure of shortage of resources. Especially in the continuous rise in the price of PVC raw materials, its recycling and reuse is of great significance.
The use of PVC in the construction industry is very large. If waste products can be reused, the environmental pollution of PVC can be greatly reduced .
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In fact, PVC waste is often mixed with other plastic materials. It is generally necessary to sort plastics first, and then use physical or chemical means for comprehensive utilization.
Sorting of PVC
Delivery is a difficult part of the plastic waste disposal process, and it is also one of the key factors in determining the results of the treatment.
Common plastics are polyvinyl chloride, polystyrene, polypropylene, low (high) density polyethylene, polyamines, polyurethane and so on. There are many disadvantages to manual sorting: inefficiency; the operator is in a hazardous environment; the material classification has large errors and so on.
Most automated industrial sorting systems have been used in industrial production. The developed countries in the world have more research in this area. A German chemical science and technology association once invented the technology of using infrared light to screen PVC from waste plastics . However, objects are limited to transparent bottles, which has the problem of low screening accuracy and high cost.
Recently, Japan has successfully developed a technique for accurately screening polyvinyl chloride resin ( PVC ) from waste plastic . This 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 easily screened by the operator. This method is more accurate than near-infrared technology and costs only 1/2 of it .
The US Rubber Recycling Center ( CPRR ) has 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 . CPRR researchers have developed a computer system. It uses a X-rays from a radioactive isotope, X-ray excitation the reflected electron images of all the chlorine-containing molecules emit X-ray fluorescence analyzer readily displayed after irradiated compound. Separation work is done by a set of mechanical devices. It can remove all vials containing chlorine atoms from conveyor belts and remove bottles that do not contain chlorine atoms.
PVC recycling technology
At present, there are three main technologies for recycling PVC : First, recycling by physical methods; second, comprehensive utilization of chemical recycling methods; and third, recycling and utilizing energy by burning PVC materials. Among them, the comprehensive utilization of physical and chemical methods is a method worthy of respect. They can recycle used products again and give full play to the performance of materials.
Physical recovery method
Physical recovery means that the recycling process of PVC waste is only handled by machinery, mainly through the procedures of shredding, screening, grinding, etc., to finally obtain thin films, powders, particles or other forms of recycled materials. These recycled materials can be used to produce heavy bags, agricultural water pipes and shoe soles.
PVC plastic products are divided into soft and hard products. Soft products mainly include films, cable jackets, plastic shoes and leather products; hard products include bottles, tubes, profiles, plates and sheets.
In soft products, agricultural films are used in a larger category. Agricultural film manufacturing materials include PVC , PE , EVA and many other materials. When recycling and recycling, the PVC film should be distinguished from other materials. Agricultural films often contain dirt, sand, grass roots, and nails. These impurities must be removed and cleaned, and then dried or chopped into fragments or pellets to make agricultural product packaging films and agricultural recycled water pipes. And soles and so on. Due to repeated heat treatment and mechanical action of recycled agricultural waste PVC film, partial degradation will inevitably occur and the strength will decrease. In order to ensure the quality of the product, some new PVC resins and corresponding additives need to be added . If the recycled material is to be made into a secondary plastic film after splicing, two-roll, four-roller rewinding, etc., and different color materials are added in the smelting process, the produced rolled film will also show different colors. In addition, about 30% of the plasticizer (mainly DOP ) remaining in the waste agricultural PVC film can be recovered and reused after refining.
The PVC bottle in the hard product is also a product with a very large amount of use, and its waste can be processed into molding materials, pipe materials, folding plates, and the like. In the plastic processing plant, the PVC chips are first cleaned, the caps and labels are removed, dried, and then comminuted into pieces smaller than 0.5 mm . One of the major US PVC manufacturers, BF Goodrich , conducted a test using new PVC and recycled PVC co-extruded. The results show that recycled PVC retains the excellent properties of new materials and can be used in applications where performance requirements are low. .
For the physical recycling method, the quality of the PVC recyclate is related to the degree of contamination and the composition of the selected material. The quality of the recyclate determines the degree to which the original material can be replaced by the recyclate: "high-quality" recyclate can be reused in the same type of application as PVC , whereas "low-quality" recyclate from the mixed waste portion can only be "Low-level recycling" to products usually made of other materials.
Of course, the quality of the final product is inseparable from the recycling equipment itself. At present, Germany has achieved a very high level of equipment and processes for recycling PVC waste. The contaminant content of less than 1% , obtained PVC secondary crushed material can be processed into a variety of products using various methods. The Polyvinyl Chloride Association of the American Plastics Industry Association also strongly encourages the recycling of PVC . It intends to start the recovery of PVC bottles and to drive the recycling of other PVC products.
Chemical recovery
Chemical recovery refers to the use of the chemical nature of polymers to convert polymers to small molecules or simple compounds. The method of chemical decomposition has high utilization of resources, but the process is complex and the cost is high, thus affecting the recycling of plastic products.
For PVC , in addition to the breaking of the polymer chain, the chlorine atoms attached to the chain are also released in the form of HCI . HCI is either reused after purification, or it must be neutralized to form different products, some can be reused, and some must be disposed of, depending on the technology used in the process. All countries in the world have strengthened their research in this area.
The waste plastic recycling and recycling technology developed in China can be used to recover waste PVC film and greenhouse film, and then to produce oil products, paraffin and building materials. With the continuous production of the technology equipment, the ability to dispose of used agricultural film on a daily basis is strong, the oil output rate can reach 40% to 80% , and the conversion rate of gasoline and diesel oil is high, which meets the standards for vehicle fuel oil and environmental discharge standards. In addition, since the PVC film contains 30% to 37% of dioctyl phthalate, DOP technology can be used at room temperature solvent extraction to recover the solvent at a temperature lower than 800 ° C . DOP is a widely used plasticizer, the current market price of 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.
Europe also has two more advanced solvent recovery PVC processes. Solvay Belgium invested 10.6 million euros to build the world's first soft PVC resin recycling plant in Italy . The device uses VinyLoop batch process, which can regenerate 8,500 tons of PVC annually from 10,000 tons of waste plastic (mostly composed of PVC ) . Its technology uses methyl ethyl ketone mixture as a solvent, in the 100 ° C ~ 140 ° C and under pressure conditions, selectively dissolve PVC and additives, the solution can be precipitated by the soft PVC containing additives . The cost of recycling PVC in this process is comparable to the production of new PVC , and the resulting PVC contains additives, so the resin price is higher. Using VinyLcop technology can reduce the impact of PVC , especially soft PVC on the environment. The second VinyLoop device will be put into operation in France in 2004 and is designed to recover PVC- coated linings and fabrics.
Another European recovered solvent is a new process for recovering PVC from PVC entire automotive wiring board. The process was jointly developed by automotive manufacturers in Wuppertal and Delphi , Germany, and Wuppertal University. Three years ago, it was industrialized by Wiefek GmbH , an automotive parts recycler in Nohfelden-Fisen , Germany . Using this process to recycle PVC costs less than 20% of the new PVC price . The process uses esters and ketones as solvents, but the amount of solvent is much less than the Vinyloop process. PVC waste solvent is not completely dissolved, but rather it will soften, making it easy to separate the copper, and the resultant was used in copper recovery costs payment process PVC. Wiefek has invented a process for separating plastics and solvents using centrifugation and has obtained patent rights. The company's recycled PVC production line established according to this process can recycle 225 tons of reusable PVC each year .
Recovered heat energy method
At present, obtaining energy through incineration of PVC products is also one of the methods for reusing PVC . However, this method has been eliminated.
During the incineration, the PVC waste generates hydrochloric acid (hydrogen chloride) and is released with the flue gas. These gases need to be neutralized. The method is to add neutralizing substances to the incinerator. The most common application is limestone, which can neutralize the acidic components of the incineration gas. Because chlorine emitted from the combustion of PVC has a strong erosive power and is the culprit of dioxins, environmental groups in various countries strongly oppose the use of incineration to recover heat energy.
PVC plastic recycling generally refers to the use of PVC , after crushing, cleaning, drying, heating and plasticizing, drawing, cooling, granulation, processing, after the formation of PVC particles , for re-made PVC related products, Especially as a raw material dosage. Since PVC is used in large quantities in pipes and fittings, and because of its hygiene and other reasons, it can only be used once. Therefore , equipment for recycling PVC has always been a concern. Separating PE general PVC, pp, focus can also be recovered granulation (with a waste plastic recycling granulator DY do PP, PE, ABS, etc.). Recycling of various waste plastics has attracted widespread attention. Generally speaking, plastic crushers are common. Other equipment is the same as PVC recycling equipment. The recycling and treatment equipment configuration is different, and the quality of recycled plastics is also different. The key is cleaning and manufacturing. The degree of good or bad grain.
  The general plastic recycling process is:
Pvc plastic → pvc plastic → automatic cleaning → plastic forming → wire cutting pellets → quality inspection packaging
 Recycling        classification        crush        cool down        Granulation        Particles
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