Plastic recycling method

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; 5 Degradable plastics.

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: the recycling of clean waste plastics recovered from the scraps of resin plants and processing plants; and 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 of burning burning oil and fuel gas by pyrolyzing selected waste plastics.

(3) Energy recovery Energy recovery is a method of using heat generated when waste plastic is burned.

(4) Recycling chemical raw materials, some kinds 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) Others, in addition to the recycling methods for waste plastics mentioned above, there are various methods for using waste plastics, such as mixing the waste 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 add adhesives pressed into mat material.

Plastic solid waste disposal

The use of 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 devoted great efforts to achieving the excellent physical and chemical properties and durability of plastics currently available. 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 and non-corrupted 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 urban 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, high-efficiency melting regeneration technology, Chemical recycling technology, completely biodegradable materials, water-soluble materials, and edible films; in terms of reduction technology, the research is mainly focused 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.

For the treatment of solid waste in urban plastics, three methods are currently used for landfill, incineration and recycling. Because of different national conditions, different countries, the United States to landfill, Europe, Japan, mainly incineration. 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 treatment, due to the large heat of plastic, easy to damage the stove, plus the gas generated after incineration will promote the global warming, and some plastics will 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 developing suitable applications for reducing the cost of plastic recycling.

one. Recovered heat energy method

Most plastics use petroleum as raw material, and the main component is hydrocarbons, which can be burned. For example, polystyrene burns more calories 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, and only 4% of them are made into plastic products. When the plastic is used up, it is 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. For example, half of the PVC components are chlorine. The chlorine released from combustion has a strong erosive effect, and it is the culprit that causes 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 organizations 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 in a solution state at room temperature, and they were sent to a sealed container for heating and then sent to a lower pressure “flash chamber” where the solution quickly evaporated ( Recycling and 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.

four. Hydrolysis method

Many experts believe that hydrogenation can be used to process mixed plastic products. The mixed plastic chips are placed in a hydrogen reactor and subjected to a specific temperature and pressure to produce raw materials such as synthetic crude oil and gas. This treatment can be used to treat PVC waste, which has the advantage of not producing toxic dioxins and chlorine. Using this method to process mixed plastic articles, according to different plastic components, 60%-80% of them can be refined into synthetic crude oil. Three chemical companies in Germany and other countries, BASF, pointed out in their common research report that hydrogenation is the best method for thermal cracking, and the synthetic crude oil obtained from the analysis has good quality and can be used for oil refining.

The University of Kentucky in Lexington, United States, invented a process for converting waste plastic into high-quality plastic fuel oil. The fuel produced in this way is very much like crude oil, even lighter than crude oil and more easily extracted into high-octane fuel oil. This kind of fuel oil produced from waste plastics does not contain sulfur and has very few impurities. A similar method is used to liquefy the plastic with coal. Can also produce high quality fuel oil.

Researchers mixed various plastics and zeolite catalysts, tetralin, etc. in a shower and put them in a reactor called a “pipe bomb”. They pressurize and heat with hydrogen to promote macromolecular plastics. Decomposes into smaller molecular weight compounds. This process is similar to that in crude oil processing. After this waste plastic processing, the oil production rate is very high, and the polyethylene plastic bottle's oil output rate can reach 88%. When waste plastic and coal are mixed and liquefied in a roughly 1:1 ratio, better quality fuel oil can be obtained. After the economic benefits of this process are evaluated, it is expected that the use of waste plastics to produce fuel oil will be transformed into a blast furnace benefit within 5-10 years. At present, Germany has begun to establish a reactor with the hope of producing 200 tons of plastic fuel in Botepo.

Fives. Subtractive design method

Research and development departments taking into account the need for recycling and dismantling when designing products, and materials that are suitable for recycling in the United States, do not focus on which type of plastic should be used to produce individual parts, but consider the materials that can be widely used. This is a revolutionary change in conception.

In order to facilitate recycling, designers began to avoid using multiple plastics when designing products. The US company BMW plans to reduce its plastics category by 40% in its new vehicle design, with the aim of facilitating the recycling of waste plastics. The reason why the automotive industry has reduced the use of plastics and considered the additional nature in the design is mainly to expect to win an excellent image that respects environmental protection and is appreciated by consumers. At present, this design concept is gradually infecting the entire plastics processing industry.

However, every effort has not been made to eliminate any of the 20 types of plastics in the market. After all, the diversity of the products has led to the ever-changing categories of plastics, such as the production of plastics for computers and the production of plastics for automobiles.

To this end, experts recommend the establishment of relevant recycling standards, which stipulate that special industries can only use specified materials, otherwise they cannot control effective recycling. The electronics and automotive industries have already started to establish such standards.

The world's electrical and electronic market has paid attention to the recycling of waste plastics. International Business Machines Corporation (IBM) has started to code plastic parts for computers and business machines, and is developing reusable plastic electronic components and simplifying disassembly equipment. Product structure, while also considering the elimination of the components of the table