Up to now, the packaging industry is still the largest application field of China plastics industry. Experts predict that packaging plastics will increase by more than 15% in 2005, reaching 6.25 million tons. Compared with the increasing application, the recycling situation of packaging plastics in China is far from optimistic. The narrow application field of waste plastics recycling is a big obstacle to the development of recycling. This paper introduces several main plastic recycling technologies at home and abroad.
fuel
At first, a lot of plastics were buried or burned for recycling, which caused a lot of waste of resources. Therefore, foreign countries use waste plastics to replace coal, oil and coke for blast furnace injection, cement rotary kiln to replace coal to burn cement, and waste solid fuel (RDF) to generate electricity, and the effect is ideal.
RDF technology was originally developed by the United States. In recent years, in Japan, due to the shortage of landfills, the serious corrosion of boilers caused by HCl when incinerators treat chlorine-containing waste plastics, and the environmental pollution caused by dioxins during combustion, various combustible wastes are mixed with waste plastics to make RDF with a calorific value of 20933 kj/kg and uniform particle size, which not only dilutes chlorine, but also facilitates storage, transportation and combustion, and is used in other boilers and industrial kilns to replace coal.
The technology of injecting waste plastics into blast furnace is also a new method to treat waste plastics by using the high calorific value of waste plastics to make them into suitable particle size instead of coke or pulverized coal. The application of injecting waste plastics into blast furnaces abroad shows that the utilization rate of waste plastics reaches 80%, and the discharge amount is 0. 1%~ 1.0% of the incineration amount, with less harmful gases and low treatment cost. The technology of injecting waste plastics into blast furnace opens up a new way for the comprehensive utilization of waste plastics and the treatment of "white pollution", and also provides a new means for metallurgical enterprises to save energy and increase efficiency. Germany and Japan applied successfully from 1995.
generate electricity
Garbage solid fuel power generation was first applied in the United States, with 37 RDF power stations, accounting for 2 1.6% of garbage power stations. Japan has realized the great potential of waste plastics to generate electricity. In Japan, some small-scale waste incineration stations have been combined and modified into RDF production stations, so that continuous and efficient large-scale power generation can be carried out after concentration. The steam parameters of waste power stations have been improved from 300 12 to about 450 12, and the power generation efficiency has been improved from 15% to 20%~25%.
Japan's Ministry of the Environment is vigorously supporting industrial waste power generation, and in the 2003 annual budget, it proposed a quota of 6,543.8 billion yen to help build five waste plastic power generation facilities. It is planned to build 150 waste plastic power generation facilities in Japan by 20 10, making industrial waste power generation an important wing of new energy.
At present, the total amount of waste plastics formed in Japan is nearly 5 million tons every year, compared with 4.89 million tons in 2000. 25% of them are recycled as plastic raw materials; 42% was buried; 6% burned in vain; Only 3% is used for power generation. Of course, it is best to recycle 100%, but at present, some waste plastics cannot be recycled.
Using waste plastics to generate electricity can reduce the consumption of coal and oil and the emission of carbon dioxide. Japan plans to increase the current garbage power generation by five times by 20 10, so that the annual garbage power generation will reach more than 4 million kilowatts.
Oilization
Because plastics are products of petrochemical industry, from the chemical structure, plastics are high molecular hydrocarbons, while gasoline and diesel are low molecular hydrocarbons. Therefore, it is completely possible to convert waste plastics into fuel oil, which is also the focus of current research. Some gratifying achievements have been made in this regard at home and abroad. For example, Fuji Recycling Technology Company of Japan recovered 0.6 liter gasoline, 0.2 1 liter diesel oil and 0.2 1 liter kerosene from1kg waste plastics by using plastic oiling technology. They also invested 65.438+08 billion yen to build an oil refinery for recycling waste plastics, which can handle 654.38+00 tons of waste plastics and 654.38+00,000 liters of recycled fuel oil every day. The University of Kentucky invented a high-tech technology to convert waste plastics into fuel, and the oil yield was as high as 86%. Beijing, Hainan, Sichuan and other places in China have reported the research results of plastic conversion into fuel oil, but there is no practical application of industrialization.
Architectural application
All kinds of waste plastics are stained with dirt to varying degrees, and generally need to be cleaned, otherwise the product quality will be affected. Using waste plastics and fly ash to make building tiles does not require strict cleaning of waste plastics, which is beneficial to practical operation in industrial application. Adding proper fillers to plastics can reduce the cost, molding shrinkage, strength and hardness, heat resistance and dimensional stability. Considering economy and environment comprehensively, it is better to choose fly ash, graphite and calcium carbonate as fillers. The surface area of pulverized coal is large, and the plastic has good binding force with it, which can ensure the high strength and long service life of ceramic tiles.
After defoaming, a certain amount of low boiling point liquid modifier, foaming agent, catalyst and stabilizer are added. Adding it into waste polystyrene foam plastics, heating to pre-foam polystyrene beads, and then heating in a mold to make a rigid polystyrene foam plastic board with fine closed holes, which can be used as building sealing materials and has good thermal insulation performance.
Compound regeneration
The waste plastics used for composite recycling are collected from different channels, with many impurities, many kinds, miscellaneous and dirty. Because the physical and chemical properties of various plastics are quite different, and most of them are incompatible with each other, their mixture is not suitable for direct processing, and different kinds of separation must be carried out before regeneration, so the recovery process is complicated. There are advanced separation equipment in the world, which can separate different materials systematically, but the one-time investment of the equipment is high. Generally speaking, composite recycled plastics are unstable and fragile, so they are often used to prepare low-grade products, such as building fillers, garbage bags, microporous sandals, rain boots and so on. At present, China's Shenyang, Qingdao, Zhuzhou, Handan, Baoding, Zhangjiakou, Guilin, Beijing, Shanghai and other places have introduced more than 20 sets of devices for recycling waste plastics from Japan and Germany, which are mainly used to produce building materials, recycled plastic products, civil materials, coatings, plastic fillers and so on.
Synthetic new materials
Hungarian scientists have developed a new technology that can transform plastic waste into industrial raw materials and reuse them, thus changing the previous practice of throwing them away or burning them casually.
It is reported that scientists can use this new technology to process plastic waste into a new type of synthetic material. Experiments show that this kind of synthetic material mixed with asphalt in proportion can increase the hardness of pavement and reduce the appearance of rolling marks. It can also be made into heat insulation materials, which are widely used in buildings. Experts believe that this technology is not only of great significance in environmental protection, but also can reduce the use of primary energy such as oil and natural gas and achieve energy-saving effect.
SPS superplasticizer series products developed by scientists from Guangzhou Institute of Chemistry, China Academy of Sciences for many years can endow concrete with good plastic retention, waterproof and frost resistance. SPS superplasticizer is mainly composed of waste polystyrene plastics. According to the property that polystyrene is easy to introduce ionic groups, ionic groups are introduced into the benzene ring of waste polystyrene through chemical reaction, so that the modified waste polystyrene has the function of surfactant, which makes cement lose the ability to wrap mixed water and achieves the effect of water reduction. In addition, because polystyrene is a high molecular weight polymer, this modified polystyrene molecule can form a film on the surface of cement particles during the solidification of cement concrete, which improves the adhesion between cement particles, thus enhancing the strength of cement concrete and becoming an excellent waterproof, water reducing agent and reinforcing agent for cement.
Prepare basic chemical raw materials and monomers
Liquid hydrocarbons can be obtained by thermal decomposition of mixed waste plastics, and water gas can be obtained by ultra-high temperature gasification, which can be used as chemical raw materials. In recent years, Germany's Hust Company, Rules Company, BASF Company, Kansai Electric Power Company, Mitsubishi Heavy Industries, etc. have developed the technology of producing synthesis gas by ultra-high temperature gasification of waste plastics, and then producing methanol and other chemical raw materials, and have been industrialized.
In recent years, the recycling technology of waste plastic monomer has been paid more and more attention and gradually become the mainstream direction, and its industrial application is under study. At present, the research level has reached the monomer recovery rate of 90% for polyolefin, 97% for polyacrylate, 92% for fluoroplastics, 75% for polystyrene and 80% for nylon and synthetic rubber. The industrial application of these achievements is also under study, which will bring great benefits to the environment and resource utilization.
The Bater Memorial Institute has successfully developed the technology of recovering ethylene monomer from mixed waste plastics such as LDPE, HDPE, PS and PVC, with a recovery rate of 58% (mass fraction) and a cost of 3.3 USD/kg.
Artificial sand
Since 2004, V-ARC Company of Japan began to crush the waste plastics produced by household appliances and automobiles into artificial sand. Artificial sand made of waste plastics will be used for foundation improvement materials and secondary concrete products. It is very rare to reuse waste plastics as artificial sand. V-ARC plans to develop it into a large enterprise with an annual output of 500 million yen in May 2005.
According to the data, about 5 million tons of waste plastics in Japan cannot be reused every year, and most of them have to be buried and burned. V-ARC intends to crush these waste plastics and effectively use them as artificial sand. The particle size of artificial sand is between 1.5mm-7.0mm, which can be set freely according to the use.
Compared with natural sand, artificial sand is characterized by low cost and light weight (less than half of natural sand); Uniform particle size, no water, etc. Artificial sand can be applied to various building materials, roof greening materials, foundation improvement materials, tiles, tiles and exterior wall materials.