catalogue
white pollution
The history of white pollution
Present situation of white pollution
The source of white pollution
Harm of white pollution
Related contents of preventing and controlling "white pollution" abroad
The Methods of Preventing and Curing "White Pollution" in China
White pollution countermeasures
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white pollution
Interpretation refers to the pollution caused by plastic waste.
Plastic is not easy to degrade, which affects the beauty of the environment and contains potentially harmful components. Because plastic as packaging material is mostly white, it is called white pollution. [ 1]
Polyethylene:
Polyethylene is a thermoplastic resin, which is formed by addition polymerization of ethylene. According to different polymerization conditions, polyethylene with relative molecular weight ranging from tens of millions can be obtained. Polyethylene is a slightly white particle or powder, translucent, non-toxic, tasteless, good chemical stability, acid and alkali corrosion resistance. Commercially, polyethylene is divided into low density, medium density and high density. Generally, low density packaging (0.92g/cm3-0.93g/cm3) without plasticizer is adopted.
Polypropylene:
Who caused the white pollution? The relative molecular weight is between 90000 and 200000. The main chain of polypropylene has a methyl side chain. If all methyl groups are distributed on one side, it is called isotactic polypropylene; If methyl groups are regularly distributed on both sides of the main chain, it is called syndiotactic polypropylene; If methyl groups are randomly distributed in the main chain, it is called random polypropylene. Polypropylene is usually a translucent solid, odorless and nontoxic, with a density of (0.90g/cm3-0.9 1g/cm3), which has higher mechanical strength and better heat resistance than polyethylene. Among the three kinds of polypropylene, isotactic polypropylene has the largest output. Isotactic polypropylene was obtained by polymerization of propylene in hydrogenated gasoline with titanium trichloride-diethyl aluminum chloride as catalyst.
Polyvinyl chloride:
The molecular weight of polyvinyl chloride (PVC) is 50,000-65,438+200,000, which is a thermoplastic resin and is produced by free radical addition polymerization. Amorphous white powder with no fixed melting point, density of (1.35g/cm3-1.45g/cm3) and good chemical stability. Soluble in cyclic ethyl ketone, chlorobenzene, dimethylformamide, toluene-acetone mixed solvent, etc.
Polystyrene:
The average relative molecular weight of tinea corporis is about 200,000. Colorless and odorless transparent resin with good light transmittance. The surface is glossy and flammable, and the density is (1.05g/cm3-1.07g/cm3), which has excellent waterproof, corrosion resistance and electrical insulation.
Production methods: bulk polymerization, suspension polymerization and emulsion polymerization. Ontology aggregation is introduced here. Initiator and a small amount of additives are added to styrene monomer, and then low-temperature polymerization is carried out in a prepolymerization kettle to prepare prepolymer, and then the prepolymer is transferred to a polymerization tower for high-temperature heating, and a certain temperature is maintained in stages. After the reaction, the molten polystyrene is extruded into strips, cooled and hardened in water, then diced and packaged.
These are the main components of "white pollution". In addition, plasticization is added to these pollutants.
Agent, foaming agent and thermal stability Tarim River suffers from white pollution? Medicine, antioxidant, etc. ?
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The history of white pollution
As early as forty years ago, it was found that vinyl chloride monomer remained in PVC plastics. When people come into contact with vinyl chloride, there will be symptoms such as wrist and finger edema, skin sclerosis, spleen enlargement, liver injury and so on. In China, almost all the ultra-thin plastic bags we use come from the reuse of waste plastics, which are produced by small enterprises or family workshops. The raw materials used in these factories are discarded plastic barrels, cans and disposable syringes. The degradation time of plastic products currently used in China usually takes at least 200 years. If it is buried and directly occupied, 1000 is difficult to degrade. Waste agricultural films and plastic bags in farmland will remain in the field for a long time, which will affect the absorption of water and nutrients by crops, inhibit the growth and development of crops and cause crop yield reduction. If livestock eat plastic film, it will cause digestive tract diseases and even death. Landfill is still the main method to treat municipal solid waste in China. Due to the low density and large volume of plastic film, it can quickly fill the site and reduce the ability of landfill to treat garbage; Moreover, due to the soft foundation of the landfill, harmful substances such as bacteria and viruses in the garbage can easily penetrate into the ground, pollute the groundwater and endanger the surrounding environment. If PVC is directly burned, it will cause serious secondary pollution to the environment. When plastics are burned, it will not only produce a lot of black smoke, but also produce dioxin, which is by far the most toxic substance. It takes at least 15 months for dioxins to decompose gradually after entering the soil, which is harmful to plants and crops. Dioxin has serious damage to the liver and brain of animals. The environmental pollution caused by dioxins produced by garbage incineration has become a sensitive issue of concern all over the world.
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Present situation of white pollution
As a new type of material, plastic products have the advantages of light weight, waterproof, durability, mature production technology and low cost, and are widely used all over the world, with an increasing trend year by year. The growth rate of plastic packaging materials in the world market is higher than other packaging materials. The average annual growth rate of plastic packaging materials from 1990 to 1995 was 8.9%.
China is one of the top ten countries producing and consuming plastic products in the world. 1995, China's plastic output was 5190,000 tons, and imported plastic was nearly 6 million tons. In that year, China's total plastic consumption was about1100000 tons, of which packaging plastics reached 21100000 tons. Most packaging plastics are discarded in the environment in the form of waste films, plastic bags and foamed plastic tableware. These waste plastic packages are scattered in urban areas, scenic tourist areas, water bodies and roads, which not only affect the landscape and cause "visual pollution", but also cause potential harm to the ecological environment because it is difficult to degrade.
According to the survey, 3% of Beijing's domestic garbage is packed in waste plastics, with an annual total of about 6,543,800 tons. 7% of Shanghai's domestic waste is packaged in waste plastics, with an annual total of about 6,543,800 tons. In Tianjin, the annual waste plastic packaging also exceeds 6,543,800 tons. Every year in Beijing, about 2.3 billion plastic bags, 220 million disposable plastic tableware and 6.75 million square meters of discarded agricultural films are discarded in the environment. People jokingly call it "suburban white."
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The source of white pollution
The main sources of white pollution are food packaging, foamed plastic filling packaging, snack boxes and agricultural plastic films.
White pollution is a unique environmental pollution in China. A large number of discarded plastic products can be seen everywhere in various public places. They come from nature and are made by human beings, but when they finally belong to nature, they are not easily absorbed by nature, thus affecting the ecological environment of nature. From the perspective of saving resources, plastic products should be recycled as much as possible, because the main source is exhausted oil resources, but the production cost of recycling at this stage is much higher than the direct production cost, which is difficult to do under the current market economy conditions. Facing the increasingly serious problem of white pollution, people hope to find a plastic substitute, which can replace the existing plastic properties without causing white pollution. Degradable plastics came into being. The characteristic of this new functional plastic is that after reaching a certain service life, its chemical structure will degrade obviously under certain environmental conditions, which is harmless or less harmful to the natural environment. For example, starch-filled plastics, first of all, the starch contained in it is rapidly decomposed by amylase secreted by microorganisms in the soil in a short time, which leads to the decline of the mechanical properties of the film. At the same time, the self-oxidant added in the formula reacts with the metal salt in the soil to generate peroxide, which breaks the chain of polyethylene and degrades it into small pieces that are easily swallowed by microorganisms, which are absorbed by the natural environment and play a role in improving the soil.
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Harm of white pollution
Pupils appealed to reject white pollution in the form of sitcoms. With the accelerated pace of people's life, social life is developing in a convenient and hygienic direction. In order to meet this demand, disposable foamed plastic lunch boxes, plastic bags, chopsticks, cups and so on began to enter people's daily lives frequently. The appearance of these convenient and low-cost packaging materials has brought a lot of convenience to people's lives. On the other hand, these packaging materials are often discarded after use, resulting in "white pollution"; Form environmental hazards and become a major environmental problem.
The so-called "white pollution" refers to the environmental pollution caused by discarded agricultural films, plastic films for packaging, plastic bags and disposable plastic tableware (collectively referred to as plastic packaging). Because waste plastic packaging materials are mostly white, they are called "white pollution". China is one of the top ten countries producing and consuming plastic products in the world, so "white pollution" is becoming more and more serious. From 65438 to 0995, the total consumption of plastics in China was about 1 1 10,000 tons, including 2 1 1 10,000 tons of packaging plastics. Most of the plastics used for packaging are discarded at will in the form of waste films, plastic bags and foamed plastic tableware. According to the survey, 3% of Beijing's domestic garbage is packed in waste plastic, with an annual output of about 6.5438+0.4 million tons. 7% of domestic waste in Shanghai is packaged in waste plastics, with an annual output of about 6.5438+0.9 million tons. Waste packaging plastics not only affect the city appearance and natural landscape in the environment, causing "visual pollution", but also are difficult to degrade, which will also cause potential harm to the ecological environment, such as: mixing into soil, affecting the absorption of nutrients and water by crops, leading to crop yield reduction; The seepage of plasticizers and additives will lead to groundwater pollution; Burning with municipal waste will produce harmful gases, pollute the air and endanger human health; Landfill treatment will occupy land for a long time, and so on. The annual expenditure on white pollution control in China is about18.5 million yuan.
The main hazards of "white pollution" are "visual pollution" and "potential harm";
"visual pollution"
Waste plastic packaging scattered in cities, tourist areas, water bodies and roads brings bad stimulation to people's vision, affects the overall aesthetic feeling of cities and scenic spots, and destroys the cityscape, thus causing "visual pollution".
"potential harm"
Waste plastic packaging is difficult to degrade after entering the environment, resulting in long-term and deep-seated ecological and environmental problems. First of all, the mixing of waste plastic packaging materials into soil will affect the absorption of nutrients and water by crops, leading to crop yield reduction; Second, waste plastic packaging on land or in water is swallowed by animals as food, which leads to animal death (such cases are common in zoos, pastoral areas and oceans); Thirdly, it is difficult to package and treat the waste plastics mixed with domestic garbage: landfill will occupy a lot of land for a long time, domestic garbage mixed with plastic is not suitable for composting, and it is difficult to recycle the classified waste plastics because it cannot guarantee the quality.
At present, people have a strong reaction to the problem of "visual pollution", but most people still lack understanding of the long-term and deep-seated "potential harm" of waste plastic packaging.
Specifically, it can be said from the following points:
First, excessive land occupation. Plastic waste also stays in nature for a long time, generally up to 200-400 years, and some up to 500 years.
Second, pollute the air. Plastics, scraps of paper and dust fly with the wind.
Third, pollute the water source. Plastic bottles and lunch boxes floating on the rivers and seas, plastic bags and bread paper hanging from branches above the water surface not only cause environmental pollution, but also endanger the health of animals by eating white garbage by mistake, and even starve to death due to indigestion in the digestive tract.
Fourth, fire hazards. Almost all white garbage is combustible, and combustible gases such as methane will be produced during natural stacking. Fire accidents easily caused by open flame or spontaneous combustion often occur, often causing heavy losses.
Fifth, white garbage may become a nest of pests, which can provide food, shelter and breeding places for mice, birds and mosquitoes and flies, and the residues in it are often the source of infectious diseases.
Sixth, waste plastic packaging is difficult to degrade after entering the environment, causing long-term and deep-seated ecological and environmental problems. First of all, the mixing of waste plastic packaging materials into soil will affect the absorption of nutrients and water by crops, leading to crop yield reduction; Secondly, if livestock eat plastic film, it will cause digestive tract diseases and even death.
Seventh, "white pollution" still exists after the "plastic restriction order". Due to the low density and large volume of plastic film, it can quickly fill the site and reduce the ability of landfill to treat garbage; Moreover, due to the soft foundation of the landfill, harmful substances such as bacteria and viruses in the garbage can easily penetrate into the ground, pollute the groundwater and endanger the surrounding environment.
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Related contents of preventing and controlling "white pollution" abroad
1985 The per capita consumption of plastic packaging in the United States reached 23.4 kg, and that in Japan was 20. 1 kg. In the 1990s, the per capita consumption of plastic packaging in developed countries was more (from the consumption point of view, it seems that the "white pollution" in developed countries should be very serious, but it is not. The reasons are as follows: first, the developed countries have long been strict in city appearance management, which basically put an end to "visual pollution"; Second, the harmless treatment rate of domestic garbage in developed countries is high)
Now people have established a strict classification and recycling system, most of the waste plastic packaging materials are recycled, and a few are converted into energy or treated harmlessly in other ways, basically eliminating the potential harm of waste plastic packaging materials.
The United States has enacted the Law on Resource Protection and Recovery, which clearly stipulates the technical research, system construction, operation and development planning of solid waste management, resource recovery and resource protection. Japan has made special provisions in the Renewable Resources Law, the Law on Supporting Energy-saving Renewable Resources and the Law on Recycling Packaging Containers, in order to promote manufacturers to simplify packaging and clarify the recycling obligations of manufacturers, sellers and consumers. Germany clearly stipulates in the circular economy law that whoever manufactures, sells and consumes packaged goods has the obligation to avoid producing, recycling and treating waste.
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The Methods of Preventing and Curing "White Pollution" in China
At present, China has begun to take administrative and technical measures to prevent and control "white pollution".
Administrative aspect
1. Strengthen management
It is forbidden to use disposable plastic packaging materials that are difficult to degrade. Hangzhou is the first city in China to ban the use of disposable foamed tableware. By taking the above measures, the harm of "white pollution" has been alleviated to some extent. However, from the results of practice, it is difficult to completely solve the problem of "white pollution" simply by banning it. All cities that have issued the ban require paper products or degradable plastic products to replace the original fire-resistant foam plastic products. However, substitutes cannot compete with ordinary plastic products in price and quality. Therefore, under the condition of market economy, it is very difficult to operate only by administrative orders without considering the adjustment of economic leverage.
2. Compulsory recycling.
Clean waste plastic packaging can be reused, or used for granulation, oil refining, paint making, building materials and so on. Recycling conforms to the general principle of "reduction, recycling and harmlessness" in solid waste treatment. Recycling can not only avoid "visual pollution", but also solve "potential harm", relieve the pressure on resources, reduce the load of urban solid waste treatment, save land and achieve certain economic benefits.
Recycling of waste plastics
Waste plastics are usually disposed of by landfill or incineration. Incineration will produce a large number of toxic gases, causing secondary pollution. Landfill will take up a lot of space; It takes more than one hundred years for plastics to degrade naturally; The precipitated additives pollute the soil and groundwater. Therefore, the development trend of waste plastics treatment technology is recycling, but the recycling rate of waste plastics is low at present. There are problems in management, policy and recycling, but more importantly, the recycling technology is not perfect enough.
There are various technologies for recycling waste plastics, including technologies for recycling various plastics and technologies for recycling single resin. In recent years, plastic recycling technology has made many gratifying progress. This paper mainly summarizes the common technologies.
1 separation and separation technology
One of the key links in plastic recycling is the collection and pretreatment of waste plastics. Especially in China, the important reason for the low recovery rate is the low degree of garbage classification and collection. Because the melting point and softening point of different resins are quite different, in order to recycle waste plastics better, it is best to classify a single variety of resins, so separation and screening is an important link in the utilization of plastic recycling. For small batches of waste plastics, manual sorting can be used, but the efficiency of manual sorting is low, which will increase the recycling cost. A variety of separation and separation methods have been developed abroad.
1. 1 instrument identification and separation technology
The Italian company Govoni used X-ray detector and automatic classification system to separate PVC from mixed plastics for the first time [1]. The American Plastic Recycling Technology Center has developed an X-ray fluorescence spectrometer, which can automatically separate PVC containers from hard containers. Germany's Refrakt Company used heat source identification technology to separate molten PVC from mixed plastics at a lower temperature by heating [1].
Near infrared has the function of identifying organic matter. The optical filter [1] using near infrared technology can identify plastics at a speed of more than 2000 times per second, and ordinary plastics (PE, PP, PS, PVC, PET) can be clearly distinguished. When the mixed plastics pass through the near infrared spectrum analyzer, the device can automatically sort out five common plastics at the speed of 20 ~ 30 pieces per minute.
1.2 hydraulic spinning technology
According to the principle of cyclone separation and the density difference of plastics, Japan Plastics Processing Promotion Association developed a hydraulic cyclone separator. The mixed plastics are put into a storage tank after pretreatment such as crushing and cleaning, and then quantitatively transported to a stirrer, and the formed slurry is sent to a cyclone separator through a centrifugal pump, and plastics with different densities are discharged respectively. Dow Chemical Company of the United States also developed a similar technology, using liquid hydrocarbon instead of water for separation, and achieved good results [2].
1.3 selective dissolution method
Kellogg Company of the United States and Rensselaer Institute of Technology jointly developed the technology of solvent selective dissolution for recycling waste plastics. Adding mixed plastics into xylene solvent can selectively dissolve and separate different plastics at different temperatures, in which xylene can be recycled with little loss [1, 3].
Vinyloop technology was developed by Solvay SA company in Belgium, which used methyl ethyl ketone as solvent to separate and recover PVC. The density of recycled PVC is almost the same as that of new raw materials, but the color is slightly gray. German also has Delphi technology for solvent recovery, and Bivini nylon technology for ester and ketone solvents is much less.
1.4 flotation separation method
A material research institute in Japan successfully separated PVC, PC (polycarbonate), POM (polyoxymethylene) and PPE (polyphenylene ether) by using common wetting agents, such as sodium lignosulfonate, tannic acid, aerosol OT and saponin [4].
1.5 Electroseparation Technology [5]
SePAration of mixed plastics (such as PAN, PE, PVC and pa) by triboelectricity. The principle is that when two different non-conductive materials rub, they get opposite charges through the gain and loss of electrons, in which the material with high dielectric constant is positively charged and the material with low dielectric constant is negatively charged. Plastic recycling mixture often contacts in a rotating tank to generate charge, and then it is sent to another tank with a charged surface for separation.
Incineration to recover energy.
The combustion heat of polyethylene and polystyrene is as high as 46000 kJ/kg, which exceeds the average value of fuel oil of 44000 kJ/kg, and the calorific value of PVC is as high as18,800 kJ/kg. Waste plastics have fast combustion speed and low ash content, and are used to replace coal or oil in blast furnace injection or cement rotary kiln abroad. Because the combustion of PVC will produce hydrogen chloride, which will corrode boilers and pipelines, and the waste gas contains furan, dioxin and so on. The United States has developed RDF technology (garbage solid fuel), which mixes waste plastics with waste paper, sawdust and fruit shells. It not only dilutes the chlorine-containing components, but also facilitates storage and transportation. For those waste plastics that are technically unrecoverable (such as various composite materials or alloy mixed products) and difficult to regenerate, incineration can be used to recover heat energy. Its advantages are large processing capacity, low cost and high efficiency. Disadvantages are that harmful gases are generated, special incinerators are needed, and equipment investment, loss, maintenance and operation costs are high.
3 melting regeneration technology
Melting regeneration is to re-plasticize waste plastics after heating and melting. According to the properties of raw materials, it can be divided into simple regeneration and compound regeneration. Simple recycling mainly recycles leftover waste from resin factories and plastic products factories, as well as disposable consumer goods such as polyester beverage bottles and food packaging bags, which are easy to select and clean. The performance after recycling is similar to that of new materials.
The raw material of compound regeneration is waste plastics collected from different channels, which has the characteristics of many impurities, complex varieties, diverse forms and dirt, so the regeneration treatment procedure is complicated and the separation technology and screening workload are heavy. Generally speaking, composite recycled plastics are unstable and fragile, and are usually used to prepare lower-grade products. Such as building fillers, garbage bags, microporous sandals, raincoats, equipment packaging materials, etc.
4 cracking to recover fuel and chemical raw materials
4. 1 thermal cracking and catalytic cracking technology
Due to the in-depth study of cracking reaction theory [6- 1 1], the development of cracking technology at home and abroad has made many progress. Cracking technology can be divided into two types due to different final products: one is to recover chemical raw materials (such as ethylene, propylene, styrene, etc.). ) [12], and the other is to obtain fuel (gasoline, diesel, tar, etc.). ). Although all waste plastics are converted into low molecular substances, the process routes are different. The preparation of chemical raw materials is to heat waste plastics in a reaction tower and reach the decomposition temperature (600 ~ 900℃) in a fluidized bed, which generally does not produce secondary pollution, but it has high technical requirements and high cost. Cracking oil technology usually includes thermal cracking and catalytic cracking.
Japan's Fuji Cycle Company converts waste plastics into gasoline, kerosene and diesel oil, and uses ZSM-5 catalyst to crack plastics into fuel through conversion reactions in two reactors. Each kilogram of plastic can produce 0.5L gasoline, 0.5L kerosene and diesel oil. Amoco has developed a new technology to convert waste plastics into basic chemicals in refineries. Pretreated waste plastics are dissolved in hot refined oil and decomposed into light products under the action of high temperature catalytic cracking catalyst. Recovering liquefied petroleum gas and aliphatic fuel from polyethylene; Aliphatic fuel can be recovered from polypropylene and aromatic fuel can be obtained from polystyrene. Yoshio Uemichi et al. [13] developed a composite catalytic system for polyethylene degradation. The catalysts are silica/alumina and HZSM-5 zeolite. The experimental results show that the catalyst can effectively and selectively prepare high-quality gasoline with a gasoline yield of 58.8% and an octane number of 94.
Domestic Li Mei et al. [14] reported that gasoline of MON73 and diesel oil of SP- 10 can be obtained from waste plastics after reacting at 350 ~ 420℃ for 2 ~ 4 s, which can be continuously produced. Li et al. [3] studied the catalysts in the degradation of waste plastics. In the process of catalytic cracking with polyethylene, polystyrene and polypropylene as raw materials, the ideal catalyst is a molecular sieve catalyst with acidic surface, operating temperature of 360℃, liquid yield of over 90% and gasoline octane number of over 80. Liu [15] developed a pilot plant for catalytic cracking of waste plastics to produce steam and diesel oil once, with a daily output of 2 tons, which realized the continuous operation of separation and slag discharge of steam and diesel oil. The cracking reactor has the characteristics of good heat transfer effect and large production capacity. When the amount of catalyst is 1 ~ 3% and the reaction temperature is 350 ~ 380℃, the total yield of gasoline and diesel oil can reach 70%. The octane number of gasoline made of waste polyethylene, polypropylene and polystyrene is 72, 77 and 86 respectively, and the freezing point of diesel oil is 3,-1 1, -22℃. This process Yuan [16] studied the catalytic cracking technology of waste plastics in fluidized moving bed reactor, and solved the problems of slag cleaning at the bottom of the reactor and pipeline cementation. It lays a foundation for realizing safe, stable and long-term continuous production, reducing energy consumption and cost, and improving output and product quality.
It is an important way to recycle resources and avoid secondary pollution to make chemical raw materials and fuels by cracking wastes. Germany, the United States, Japan and other countries have large factories, and China has also built small waste plastic oiling plants in Beijing, Xi, Guangzhou and other places, but there are still many problems to be solved. Due to the poor thermal conductivity of waste plastics, plastics produce high viscosity melt when heated, which is not conducive to transportation; PVC in waste plastics will produce HCl, which will corrode equipment and reduce catalyst activity. Carbon residue adheres to the reactor wall, which is difficult to remove and affects continuous operation; The catalyst has low service life and activity and high production cost; At present, there is no better treatment method for oil residue produced in production, and so on. There are still many reports on pyrolysis to produce oil in China [43-54], but how to absorb the existing achievements and overcome the technical difficulties is an urgent task before us.
4.2 Supercritical refueling method
The critical temperature of water is 374.3℃, and the critical pressure is 22.05Mpa. Critical water has the properties of normal organic solution, which can dissolve organic matter but not inorganic matter, and is completely miscible with air, oxygen, nitrogen and carbon dioxide. Japanese patent reports waste plastics (PE, PP, PS, etc. ) can be recycled with supercritical water. The reaction temperature is 400 ~ 600℃, the reaction pressure is 25Mpa, the reaction time is below 65438±00min, and the oil yield can reach above 90%. The advantages of using supercritical water to degrade waste plastics are obvious: the cost of using water as medium is low; Carbonization can be avoided during pyrolysis; The reaction is carried out in a closed system, which will not bring new pollution to the environment; Fast reaction speed, high production efficiency, etc. Qiu Ting et al [17] summarized the progress of supercritical technology in plastic recycling.
4.3 gasification technology
The advantage of gasification method is that it can treat municipal solid waste in a mixed way without separating plastics, but the operation needs to be higher than that of thermal decomposition method (generally around 900℃). Schwaize Pumpe Refinery in Espag, Germany can process 1700 tons of waste plastics into city gas every year. RWE plans to gasify 220,000 tons of lignite, more than 654.38 million tons of plastic waste and petroleum sludge produced by town petroleum processing plants every year. Hoechst Company of Germany gasifies the mixed plastics by high-temperature Winkler process, and then converts it into water gas as the raw material for alcohol synthesis.
4.4 Hydrocracking Technology
Vebaeol Company of Germany has set up a hydrocracking unit to hydrogenolysis waste plastic particles at 15 ~ 30 MPa and 470℃ to produce a synthetic oil, which contains 60% paraffin, 30% cycloalkane and 1% aromatic hydrocarbon. The effective utilization rate of energy and the effective conversion rate of substances are 88% and 80% respectively.
5 Other utilization technologies
Waste plastics also have a wide range of uses. Texas State University uses yellow sand, stones, liquid PET and curing agent as raw materials to make concrete, while Bitlgosz [18] uses waste plastics as cement raw materials. Xie Liping [19] prepared mesoporous activated carbon from waste plastics, wood and paper, Lei et al. [20] reported that waste polystyrene was used as coating, [2 1] reported that plastics could be turned into wood. Song Wenxiang [22] introduced that foreign countries used HDPE as raw material, and through special methods, glass fibers with different lengths were made to flow in the same direction along the axial direction of the material in the mold, thus producing high-strength plastic sleepers. Pu et al. [23] used waste polyethylene to make high value-added polyethylene wax. Li Chunsheng et al. [24] reported that compared with other thermoplastics, polystyrene has the characteristics of low melt viscosity and high fluidity, which can well infiltrate the contact surface after melting and play a good bonding role. Zhang Zhengqi et al. [25] modified asphalt with waste plastics, and dissolved one or several plastics evenly in asphalt according to a certain proportion, which improved the road performance of asphalt, thus improving the quality of asphalt pavement and prolonging the service life of pavement.
Technical status quo