Plastic Recycling and Recycling Technology Analysis (I)

The output of synthetic resin in the world has reached 200 million tons, and the disposal of large quantities of post-consumer plastics has become a hot spot for the protection of the earth today. At present, there are several ways to treat post-consumer plastics: 1. landfill; 2. incineration; 3. composting; 4. recycling and regeneration; 5. degradable plastics.

Section 1 Plastic Recycling Method

Recycling methods for plastic recycling include: melting regeneration, thermal cracking, energy recovery, recycling of chemical raw materials and other methods.

(1) Melt regeneration Melt regeneration is a method of re-thermoplasticizing waste plastics. From the sources of waste plastics, this method can be divided into two categories: First, the recycling of clean waste plastics recovered from the scraps of resin factories and processing plants; and second, the recycling of various plastic products mixed after use. . The former said that simple regeneration, can produce better performance of plastic products; the latter said that the compound regeneration, generally can only prepare relatively poor performance of plastic products, and the recycling process is more complicated.

(2) Thermal cracking The thermal cracking method is a method in which the selected waste plastics are pyrolyzed to produce burning oil and fuel gas.

(3) Energy recovery Energy recovery is a method that uses heat generated when waste plastic is burned.

(4) Recovery of chemical raw materials, some varieties of plastics, plus polyurethane can be obtained through hydrolysis of raw materials for synthesis. This is a method of using chemical decomposition of waste plastics into chemical raw materials for recycling.

(5) In addition to the above methods for recovering waste plastics, there are various methods for using waste plastics, such as mixing waste plastic polystyrene foam into the soil to improve the water retention, air permeability and drainage of the soil. Or as a filler mixed with cement made of lightweight concrete, or by adding an adhesive pressed into a mat material.

Recycling plastics and plastics and processing plastics solid wastes Using petroleum and coal as raw materials to produce plastics instead of natural polymer materials has undergone a difficult process. An entire generation of outstanding chemists have achieved excellent physics and chemistry at present. Characteristics and durability are hard work. Plastics, with its light weight, durability, aesthetics, and low cost, replaced a large number of traditional packaging materials and contributed to a revolution in the packaging industry. However, contrary to the expectations of the people, it is precisely these excellent properties of plastics that produce a lot of durable plastic waste. The large amount of discarded plastic packaging after use has become a major environmental hazard. The main reason is that these plastic wastes are difficult to handle and cannot be decomposed and turned into dust. In the existing municipal solid waste, the proportion of plastics has reached 15%-20%, and most of them are disposable plastic packaging products. The disposal of plastic waste is not only a problem in the plastics industry, but it has now become a widespread concern in the international community of public hazards.

In order to meet the needs of protecting the global environment, the world plastics processing industry has developed many new environmental protection technologies. In respect of saving resources, it is mainly to improve the endurance performance of products, extend the life span, and multi-functionalize the design of the products. In the aspect of resource reuse, it mainly deals with the efficient sorting of plastic waste, separation technology, and high-efficiency melt recycling technology. Chemical recycling technology, completely biodegradable materials, water-soluble materials, and edible films; in terms of reduction technology, the research mainly focuses on the technology of compression and volume reduction of waste plastics and the technology of film-packed containers, and on the premise of ensuring application performance, The thinning technology of products; the development of CFC substitutes is mainly focused on carbon dioxide foaming technology; on the research of substitutes, PVC and PVDC substitutes are mainly developed.

In the field of plastic solid waste disposal in cities, three methods are currently used for landfill, incineration and recycling. Because of different national conditions, different countries, the United States to landfill, Europe, Japan to burn mainly. With landfill treatment, the quality of plastics is generally light, and it is not easy to rot, which will cause the landfill to become a soft foundation and it is difficult to use it in the future. The use of incineration processing, due to the large heat of plastic, easy to damage the stove, plus the gas generated after burning will promote the global warming, and some plastics will also emit harmful gases in the burning and pollute the atmosphere. The use of recycling methods, due to man-hours, high recycling costs, and the lack of appropriate recycling channels, the world's recycling and reuse accounted for only about 15% of the total plastic consumption. However, due to limited world oil resources, from the perspective of saving the earth's resources, the recycling of plastics is of great significance. To this end, all countries in the world have invested a lot of manpower and material resources to develop various key technologies for the recycling of waste plastics, and have devoted themselves to the development of suitable applications for reducing the cost of recycling plastics.

one. Recovered heat energy method

Most plastics use petroleum as the raw material, 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 the heat for heating or power generation. Because 86% of petroleum dyes are directly burned, only 4% of them are made into plastic products, and plastic is used up and sent as heat energy. Burning is normal, and the use of heat energy is one of the last methods for plastic recycling and should not be taken lightly. However, many environmental groups oppose the burning of plastics. They believe that the incineration method will concentrate all the chaos of chemicals and cause toxic gases. If half of the PVC component is chlorine, chlorine emitted from combustion will have a strong erosive effect, and it will be the culprit for causing dioxin.

At present, Germany has 200,000 tons of PVC waste each year, of which 30% is burned in the incinerator, burning people's minds, and the law has to formulate countermeasures. The Federal Environment Agency of Germany has stipulated that all incinerators must meet a limit of less than 0.1 ng (nanograms) per cubic meter of exhaust gas. Although the air pollution standards for incinerators in Germany are already recognized as high standards in the world, they still do not dare to say that the combustion methods will not release harmful substances due to mechanical failure. Therefore, it is foreseeable that environmental protection groups in various countries will strongly oppose the incineration method to recover heat energy.

two. Sorting recovery method

As plastic recycling, the most important is to classify. Common plastics are polystyrene, polypropylene, low-density polyethylene, high-density polyethylene, polycarbonate, polyvinyl chloride, polyamide, polyurethane, etc. The difference between these plastics is generally difficult to distinguish. Most of the current plastics classification work is done manually. Recent advances in machine classification have led to new research. A German chemical science and technology association has invented infra-red to identify categories. It is fast and accurate, but it has high sorting costs.

three. Chemical reduction

Researchers began to try to extract the chemical composition of plastics for reuse. The process used is to cut the long chains of polymers and restore their original properties. The cracked materials can be used to make new plastics. Some methods promote the chemical cracking of bonded carbon atoms by adding chemical elements, or add energy to promote thermal cracking.

German company Bayer developed a hydrolytic chemical reduction method to crack the PUC sponge pad. Tests have shown that the chemical reduction method is technically feasible, but it can only be used to handle clean plastics, such as corner powders and other plastic wastes produced in the manufacturing process. Plastics that have been used in the home and are contaminated with other contaminants are difficult to dispose of using chemical decomposition. The application of this reduction method, until the 21st century will not be a large number of use of hydrolysis to deal with waste. Some new chemical decomposition methods are still in the process of research, the United States Ford Motor Company is currently using esterification method to deal with automotive plastic parts.

The American Institute of Technology in Ransom developed a solution that can break down plastic waste, heating this patented solution together with six different types of plastic that are mixed together. At different temperatures, six polymers can be extracted separately. In the experiment, the polystyrene plastic chips and related solutions were mixed at room temperature into a dissolved state, which was sent to a sealed container for heating, and then sent to a lower pressure “flashing chamber” where the solution quickly evaporated. Recycling, and the rest is pure polystyrene that can be reused.

It was alleged that the purification device used in the research could purify 1 kg of polymer per hour. New York State Government and Niagara. Mohawk Power is planning to join forces to build a small pilot plant. Investors claim that after the plant is completed, 4 tons of polymer material can be recovered per hour. Its cost is only 30% of the raw materials for production and it has very obvious commercial value.