Summarizing the practical experience of preventing and controlling "white pollution" at home and abroad, now China's prevention and control of "white pollution" should follow the principle of "publicity and education as the guide, strengthening management as the core, recycling as the main means, and alternative products as supplementary measures". Alternative products as a complementary measure" principle.
Prevention of "white pollution", first of all, to solve the "visual pollution" problem, so that the cityscape, landscape has improved significantly. This is mainly rely on publicity and education, guide the public to form good habits; at the same time to strengthen the management of the law, to promote enterprises and individuals into their own waste plastic packaging materials properly collected and disposed of. Prevention and control of "white pollution", it is more important to solve the waste plastic packaging on the ecological environment of long-term, deep-rooted harm. This is mainly through the development and implementation of recycling-friendly regulations and economic policies, the implementation of comprehensive recycling of waste plastic packaging; prevention and treatment of "white pollution", should also strengthen the research and development of alternative (green) packaging supplies in line with the actual. Now on the acceleration of China's prevention and control of "white pollution" process to put forward the following countermeasures:
Strengthening publicity and education
Prevention and control of "white pollution" is a systematic project that requires the **** with the efforts of various sectors and industries, and requires the active participation of the whole society and all citizens. Society and the active participation of all citizens. To vigorously carry out publicity and education to improve people's understanding of the harm of "white pollution", improve the environmental awareness of society as a whole, and educate people to develop good hygiene habits. In their own strict compliance with environmental regulations at the same time, actively stop the bad behavior around.
Unify ideological understanding, strengthen management
In accordance with the "publicity and education as the guide, to strengthen management as the core, recycling as the main means to alternative products as a complementary measure" of the prevention and control principles, one is to enhance the "white pollution The first is to strengthen the "white pollution" hazardous publicity, guide and educate the public to consciously prevent and control "white pollution"; the second is to produce a large number of waste plastic packaging industry (such as railroads, water transport, civil aviation, tourism, hotels, restaurants, catering, retailing, etc.), to strengthen the management of the change of no one is responsible for the unorganized piling, random abandonment phenomenon; the third is to take mandatory measures, and the third is to adopt the principle of the prevention and control of the "white pollution". Phenomenon; three is to take mandatory measures, starting from the recovery of waste plastic packaging produced centrally (such as disposable foam lunch boxes), and gradually improve the recycling rate of waste plastic packaging; four is to strengthen the development of alternative packaging products, research, and efforts to reduce the amount of waste plastic packaging produced, etc..
Laws and regulations
As soon as possible to formulate and promulgate the national prevention and control of "white pollution" of the relevant laws and regulations, clear producers, sellers and consumers to recycle waste plastic packaging obligations and legal responsibilities. Should be the production of plastic packaging, business, consumption and other links, respectively, the development of specific control measures and guidance policies to control the amount of waste plastic packaging is not easy to recycle, encourage to improve the recycling rate of waste plastic packaging.
Economic policy
Develop appropriate economic policies to establish a benign mechanism for the elimination of "white pollution" under the conditions of market economy. The use of economic means to encourage and promote the waste plastic packaging "reduction, resource utilization, harmless", saving and comprehensive utilization of resources, prevention and treatment of "white pollution", to protect the ecological environment.
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 occupy a large space; the natural degradation of plastics requires more than a hundred years; precipitation additives to pollute the soil and groundwater and so on. Therefore, the development trend of waste plastics treatment technology is recycling, but the recycling and regeneration of waste plastics has a low utilization rate. The reason for this is that there are problems in management, policy and recycling link, but more importantly, the recycling technology is not perfect enough.
Waste plastics recycling technology is diverse, there can be recycled a variety of plastics technology, there are also specialized in recycling a single resin technology. Plastic recycling technology has made a lot of welcome progress, this article mainly for the more general technology to do a summary.
1 Separation and sorting technology
One of the key links in the recycling of waste plastics is the collection and pretreatment of waste plastics. Especially in China, the important reason for the low recycling rate is the low degree of waste classification and collection. As the melting point and softening point of different resins differ greatly, in order to make better recycling of waste plastics, it is best to classify and treat single varieties of resins, so separation and screening is an important part of waste plastics recycling. For small quantities of waste plastics, artificial sorting method can be used, but the artificial sorting efficiency is low, will make the recovery cost increase. Foreign countries have developed a variety of separation and sorting methods.
1.1 Instrument identification and separation technology
Italy's Govoni company first used X-ray detectors and automatic classification system to separate PVC from mixed plastics [1]. The U.S. Plastics Recycling Technology Research Center developed an X-ray fluorescence spectrometer, which can be highly automated to separate PVC containers from rigid containers. Refrakt in Germany, on the other hand, utilizes heat source identification technology to separate molten PVC from mixed plastics at lower temperatures by heating [1].
Near-infrared light has the function of recognizing organic materials, and the speed of recognizing plastics by the light filter using near-infrared technology [1] can reach more than 2,000 times/second, and the common plastics (PE, PP, PS, PVC, PET) can be clearly differentiated, and when the mixed plastics pass through the near-infrared spectral analyzer, the device can automatically sort out the five common plastics, and the speed can be as fast as 20～30 pieces/min.
1.2 Hydraulic Cyclone Separation Technology
The Japan Society for the Promotion of Plastic Processing developed a hydraulic cyclone separator by utilizing the principle of cyclone separation and the density difference of plastic. Mixed plastics are pre-treated by crushing, washing and other pre-treatment and loaded into a storage tank, and then quantitatively transported to the agitator, the slurry formed by centrifugal pumps into the cyclone separator, where plastics with different densities are discharged separately. Similar technology has been developed by Dow Chemical Company in the United States, which replaces water with liquid hydrocarbons for separation and has achieved better results[2].
1.3 Selective dissolution method
The Kellogg Company in the United States and Rensselaer Polytechnic Institute*** jointly developed a technology that utilizes solvent selective dissolution to separate recycled waste plastics. Mixed plastics are added to the xylene solvent, which can selectively dissolve and separate different plastics at different temperatures, where the xylene can be recycled with little loss [1, 3].
Belgium Solvay SA developed Vinyloop technology, the use of methyl ethyl ketone as a solvent, separation and recycling of PVC, recycled to the density of PVC and new raw materials, but the color is slightly gray. Germany also has a solvent recovery Delphi technology, the use of esters and ketones solvents than Vinyloop technology is much less.
1.4 Flotation Separation Method
A materials research institute in Japan has successfully separated plastic mixtures of PVC, PC (polycarbonate), POM (polyoxymethylene), and PPE (polyphenylene ether) by using common impregnating agents, such as sodium lignosulfonate, tannic acid, Aerosol OT, and saponin [4].
1.5 Electrical separation technology [5]
The separation of mixed plastics (e.g., PAN,, PE, PVC, and PA) by friction-generated electricity. The principle is that two different non-conductive materials friction, they gained through the electron gain or loss of the opposite charge, in which the material with a high dielectric constant with a positive charge, the material with a low dielectric constant with a negative charge. Plastic recycling mixed materials in the rotating pot frequent contact and generate charges, and then be sent as another surface charged pot and be separated.
2 incineration recovery energy
Polyethylene and polystyrene combustion heat up to 46000kJ/kg, more than the average fuel oil value of 44000 kJ/kg, PVC calorific value is also as high as 18800 kJ/kg. Waste plastics combustion speed, low ash, foreign countries to use it instead of coal or oil used in the blast furnace blowing or rotary kiln cement. Because PVC combustion will produce hydrogen chloride, corrosion of boilers and pipelines, and the exhaust gas contains furans, dioxins and so on. The U.S. has developed RDF technology (Refuse Solid Fuel), which mixes waste plastics with waste paper, wood chips, fruit shells, etc., which not only dilutes the chlorine-containing components, but also facilitates storage and transportation. For those technically impossible to recover (such as a variety of composite materials or alloy mixing products) and difficult to regenerate waste plastics can be incinerated to recover heat energy. The advantages are large treatment quantities, low cost and high efficiency. The disadvantage is the production of harmful gases, the need for specialized incinerators, equipment investment, loss, maintenance and high operating costs.
3 Molten regeneration technology
Molten regeneration is to heat and melt the waste plastics and then re-plasticize. According to the nature of the raw material, can be divided into simple regeneration and composite regeneration two kinds. Simple regeneration mainly recycles the marginal waste of resin and plastic product factories and those disposable consumer products that are easy to pick and clean, such as polyester beverage bottles and food packaging bags. After recycling, its performance is similar to that of new materials.
The raw materials for composite recycling, on the other hand, are collected from different channels of waste plastics, which are characterized by many impurities, complex varieties, diverse forms, and dirt, etc. Therefore, the recycling processing procedures are more complicated, and the separation technology and screening workload is large. Generally speaking, the nature of composite recycled plastics is unstable, easy to become brittle, often used to prepare lower grade products. Such as construction filler, garbage bags, microporous sandals, raincoats and packaging materials for instruments.
4 Cracking for Recovery of Fuels and Chemicals
4.1 Thermal Cracking and Catalytic Cracking Technology
Due to the increasing theoretical research on cracking reactions [6-11], many advances have been made in the development of cracking technology both at home and abroad. Cracking technology is divided into two types depending on the end products: one is to recover chemical raw materials (such as ethylene, propylene, styrene, etc.) [12], and the other is to get fuels (gasoline, diesel, tar, etc.). Although both convert waste plastics into low molecular substances, the process routes are different. The production of chemical materials is to heat the waste plastics in a reaction tower and reach the decomposition temperature (600-900°C) in a boiling bed, which generally does not produce secondary pollution, but the technical requirements are high and the cost is also high. Cracking olefinization technology, on the other hand, usually have two kinds of thermal cracking and catalytic cracking.
Japan's Fuji Cycle's waste plastics into gasoline, kerosene and diesel technology, the use of ZSM-5 catalysts, through two reactors for the conversion reaction will be cracked plastic into fuel. Each kilogram of plastic can generate 0.5L gasoline, 0.5L kerosene and diesel. Amoco (USA) has developed a new process to convert waste plastics into basic chemicals in a refinery. Pretreated waste plastics are dissolved in hot refinery oil and decomposed into light products under the action of high temperature catalytic cracking catalyst. LPG and aliphatic fuels are recovered from PE; aliphatic fuels are recovered from PP, and aromatic fuels can be obtained from PS.Yoshio Uemichi et al [13] developed a composite catalytic system for the degradation of polyethylene, with the catalysts being silica/alumina and HZSM-5 zeolite. Experiments showed that this catalyst is more effective for selective production of high-quality gasoline, the resulting gasoline yield of 58.8%, octane number 94.
Domestic Li Mei et al [14] reported that waste plastics at a reaction temperature of 350-420 ℃, reaction time of 2-4s, can be obtained MON73 gasoline and SP-10 diesel fuel, can be produced in continuous production of the process. Li Jianhong et al [3] carried out a study of catalysts for the degradation process of waste plastics. The ideal catalyst for the catalytic cracking process with PE, PS and PP as raw materials is a molecular sieve type catalyst with acidic surface, an operating temperature of 360°C, a liquid yield of more than 90%, and a gasoline octane rating of more than 80. Liu Gongzhao [15] researched and developed a pilot plant for the catalytic cracking of waste plastics into gasoline and diesel fuel in a single step, which can produce 2t of gasoline and diesel fuel per day, and can realize the gasoline and diesel fuel The cracking reactor is characterized by good heat transfer and large production capacity. With the catalyst addition of 1-3% and the reaction temperature of 350-380℃, the total yield of gasoline and diesel can reach 70%, the octane number of gasoline produced from waste polyethylene, polypropylene and polystyrene is 72, 77 and 86 respectively, and the freezing point of diesel is 3, -11, -22℃, the process is safe to operate and there is no emission of three wastes. Yuan Xingzhong [16] studied the technology of catalytic cracking of waste plastics in fluidized moving bed reactor for the problems of slag removal from the bottom of the kettle and pipe gumming. It lays the foundation for realizing safe, stable, long cycle continuous production, reducing energy consumption and cost, and improving yield and product quality.
Cracking waste materials to produce chemical raw materials and fuels is an important way to recover resources and avoid secondary pollution. Germany, the United States, Japan and other large-scale factories, our country in Beijing, Xi'an, Guangzhou has also built a small-scale waste plastic olefinization plant, but there are still many problems to be solved. Due to the poor thermal conductivity of waste plastics, the plastic is heated to produce high viscosity melt, not conducive to transportation; waste plastics containing PVC leads to HCl, corrosion of equipment at the same time make the catalyst activity is reduced; carbon residue adhering to the reactor wall, not easy to remove, affecting the continuous operation; catalyst service life and low activity, so that the high cost of production; production of oil residue produced by the production of a better way to deal with, and so on. There are still many domestic reports on pyrolysis oleochemical[43-54], but how to absorb the existing results and overcome the technical difficulties is what we urgently need to do.
4.2 Supercritical oiling method
The critical temperature of water is 374.3 ℃, the critical pressure is 22.05Mpa. critical water has the performance of organic solutions in the normal state, can dissolve organic matter and can not dissolve inorganic substances, and can be completely miscible with air, oxygen, nitrogen, carbon dioxide and other gases. Japanese patents useful supercritical water for waste plastics (PE, PP, PS, etc.) for recycling report, the reaction temperature of 400 ~ 600 ℃, reaction pressure of 25Mpa, reaction time of 10min or less, you can get more than 90% of the oleochemical yield. The advantages of using supercritical water for the degradation of waste plastics are obvious: water as a medium is inexpensive; carbonization during pyrolysis can be avoided; the reaction is carried out in a closed system, which does not bring new pollution to the environment; the reaction is fast, and the production efficiency is high. Qiu Ting et al [17] summarized the progress of supercritical technology in the recycling of waste plastics.
4.3 Gasification Technology
Gasification has the advantage of being able to mix municipal waste without separating the plastics, but the operation requires higher temperatures than pyrolysis (typically around 900°C). Germany Espag's Schwaize Pumpe refinery can process 1,700t of waste plastics into municipal gas per year. rWE plans to gasify 220,000t of lignite, 100,000t of plastic waste and petroleum sludge produced by town oil processing plants each year. Germany Hoechst company uses high-temperature Winkler process to gasify mixed plastics, and then converted into water gas as a raw material for synthetic alcohols.
4.4 Hydrogenation cracking technology
Germany Vebaeol company set up a hydrogenation cracking device, so that the waste plastic particles in the 15 ~ 30Mpa, 470 ℃ hydrogenation, to produce a synthetic oil, of which 60% of the chain alkanes, 30% of the cycloalkanes, aromatics for 1%. The effective utilization rate of energy of this processing method is 88%, the material conversion efficiency is 80%
5 Other utilization technologies
Waste plastics also have a wide range of uses. Texas State University in the United States used yellow sand, stone, liquid PET and curing agent as raw materials to make concrete, and Bitlgosz [18] used waste plastics as raw materials for cement. Xie Liping et al [19] used waste plastics with wood and paper to prepare mesoporous activated carbon, Lei Yanying et al [20 reported the application of waste polystyrene to make paint, and Li Lingling [21] reported that plastics can be turned into wood. Song Wenxiang [22] describes the production of high-strength plastic sleepers from abroad using HDPE as raw material by a special method to make glass fibers of different lengths in the mold in the same direction along the axial direction of material flow. Pu Tingfang [23] and others used waste polyethylene to make high value-added polyethylene wax. Li Chunsheng et al [24] reported that polystyrene, compared with other thermoplastics, is characterized by low melt viscosity and high fluidity, so that after melting, it can be well infiltrated with the surfaces contacted to play a good adhesive role. Zhang Qiangqi et al [25] modified asphalt with waste plastics, one or more plastics in a certain proportion of uniformly dissolved in asphalt, so that the road performance of asphalt has been improved, thereby improving the quality of asphalt pavement, extending the life of the pavement.
More environmentally friendly bags, less plastic bags
As a result of a large number of waste packaging plastic film, plastic bags and one-time use of non-biodegradable plastic tableware surge, and arbitrary abandonment of the large and medium-sized cities are generally formed a serious white pollution. It has been listed with the car exhaust, phosphorus detergents together as this year's three major focuses of China's environmental governance.
Plastic is a kind of difficult to deal with the life of the garbage, it is mixed into the soil can affect the crop absorption of water and nutrients, resulting in crop yield; landfill, occupy the land and hundreds of years to be degraded. Large quantities of plastic can also be accidentally ingested by animals, as in the case of the elk in Beijing's Nanyuan Park, who died after eating a plastic bag that flew in from a nearby garbage dump. Plastic is easy to form bundles, it can even block the water flow, resulting in water conservancy facilities, urban facilities failures, resulting in disasters.
China's foam tableware production and use of a huge amount of food packaging, shopping for groceries, the number of plastic bags used is also alarming. According to rough estimates, this century, China's white trash is about more than 8 million tons. Plastic products are one of the most difficult to deal with all the domestic waste, has been a worldwide problem, generally speaking, the use of sanitary landfills, high-temperature composting and incineration of these three methods, basically can make the waste treatment to achieve the reduction of quantitative, resource and harmless. However, the situation in China is not optimistic, since the former garbage collection and treatment is far from forming an orderly system. Taking Beijing as an example, the garbage collection has not yet completed the bagging of garbage, not to mention the classification of collection.
The incineration of plastic bags can be destroyed, but the construction of a waste incineration plant is the same size landfill 20 times the investment. As for the practice of artificial degradation to produce organic oils, it requires a higher purity of plastic products, large-scale processing is unrealistic. Therefore, sanitary landfills have become the main way to be able to collect plastics. Beijing has built three sanitary landfills, Asuwei, North Shenshu and Anding, with a thick impermeable layer at the bottom of the landfill, and as the garbage piles up, the top is constantly covered with soil, and then recreated with vegetation, in order to ensure that the garbage is in a confined space around the scope of the space, and will not contaminate the groundwater, the soil, and the surrounding air. But a 300-acre piece of land at the Anding landfill, for example, is only enough for a Xuanwu district in Beijing for 14 years.
The boycott of non-biodegradable plastics was echoed by some shopping malls not long ago, which tried to sell biodegradable garbage bags, but few bought them because they cost more than 1 yuan and could not hold much weight. Wankelong promotes the use of cloth bags, the results are also unsatisfactory.
The best way to solve the problem is to treat both the symptoms and the root causes, experts believe that, on the one hand, we should deal with the existing garbage in a timely and effective manner, on the one hand, we can use degradation, easy to degrade the products instead of plastics.
November 1998, a kind of straw made of disposable tableware for the first time on the fast food table of the Beijing Parkson Shopping Center. This kind of tableware is not only safe and hygienic, but also a one-time use into the soil that is fertilizer, into the water can become fish feed, discarded by the side of the road, a few days after the wind went away. In December 13, 1998 "green disposable tableware exchanges", more than 100 companies showed their rice husk, pulp, starch and other raw materials for the production of tableware. A biodegradable disposable fast-food box has passed the test after nearly three years of research by more than 30 researchers from the Beijing Light Research Institute. The test confirms that the lunch box is exposed to nature after use, and all of it will be changed into water and carbon dioxide within 40 days. This lunch box to starch (corn, tapioca starch) as raw materials, adding annual plant fiber powder and biological waterproof glue sprayed into the mold heated foam molding. A variety of nascent alternative products are in their infancy, but have not yet reached the level of mass production and promotion.
In addition; the public's awareness of environmental protection is still relatively backward, which is actually an important factor hindering the management of white pollution. The first step in the treatment of white waste is the separation of garbage, which is only expected to be carried out after the conscious environmental protection awareness of the majority of the people has been established. Therefore, the most important point in the fight against white pollution is to raise everyone's environmental awareness. Because white trash takes more than a hundred years to degrade naturally in nature, solving its pollution problem can really be called a hundred-year problem.
I. Civilian packaging products
(1) Life often use the ultra-thin plastic carry bags, but also we often see in the supermarket plastic bags.
(2) plastic products used in the outer packaging of tobacco and alcohol.
(3) garment tanning industry and the plastic products used for packaging.
(4) Children's toys used in plastic products and packaging products.
(5) Packaging products used for food.
(6) cultural and office supplies and stationery used in plastic products and packaging plastic products.
(7) rain gear, fishing gear, protective gear and other plastic products used.
(8) plastic products for the catering industry.
(9) Plastic products used in culture and film.
(10) Other types of life and the plastic products used for packaging.
Two, industrial packaging products
(1) plastic film packaging materials used in light industry.
(2) Composite plastic products used in advertising.
(3) The outer packaging of industrial products and plastic products.
(4) Plastic products for industrial production.
(5) Plastic packaging materials for home appliances.
(6) Plastic materials used in the electronics industry.
(7) Plastic products used in the manufacture of furniture.
(8) Plastic products used in the automobile transportation industry.
(9) Plastic products used in the chemical industry.
(10) Plastic products used in the construction industry.
(11) Various other plastic products used in industry and plastic products for packaging.
Three, the military category
(1) weapons and communications using plastic protective equipment.
(2) Clothing and plastic products for war preparation.
(3) Military supply of plastic products and packaging composite plastic products.
(3) Plastic packaging products used in the military medical system.
(4) Plastic products used in aerospace and aviation.
(5) scientific research system using equipment and packaging plastic products.
Four, agricultural plastic products
(1) agricultural film insulation plastic products.
(2) agricultural equipment and tools used in plastic products.
(3) food processing and seed packaging and other plastic products.
(4) fertilizer packaging and transportation and other categories of plastic products.
Fifth, the medical system and pharmaceutical plastic packaging products
(1) plastic products for medical equipment.
(2) Pharmaceutical packaging plastic products.
(3) other categories of medical plastic products.
Plastic products have penetrated into every aspect of our human life, the serious pollution of the environment by plastic waste has sounded the alarm to our humanity. The recycling of plastic waste is a good project for the country and the people, and a good thing for future generations. The restriction direction of the "Plastic Restriction Order" should be changed to the landfill and incineration of plastic products, only the production of ultra-thin shaped packaging products, and accelerate the development of alternatives to ultra-thin shaped plastic products in packaging. The decisive factor for the implementation of the "Plastic Restriction Order" is the local government, and the management inaction of the government departments is the main factor leading to the obstruction of the implementation of the national administrative order. How to change this unfavorable institutional management factor? The central government should introduce more stringent legal measures. The key lies in how to monitor and implement them. The motivation of local government officials is the main problem. Local governments must be allowed to put plastic waste management on the first agenda, determine the responsibility and accountability of the first hand of local governments, and form a tiered gatekeeping mechanism of governmental sub-level management. Establish a centralized study group on plastic waste disposal, with unified leadership and implementation by the State Council. Establish local regional plastic waste recycling organizations and comprehensive waste sorting and processing plants, accelerate the introduction of advanced equipment from abroad, and form and implement them by regional governments, and prohibit landfill disposal and incineration of domestic waste. Strictly administer the judicial management system, elevate the treatment of plastic waste to the legal level, and formulate a perfect legal constraints system. Implement an accountability system for removing officials from office for inaction. Develop a system of communicating centralized letters and visits, and implement a thorough reform of the letter and report system, so that reports are handled at whichever level they come to. Only by improving policy constraints and legal constraints will administrative orders flow smoothly and the regional environment be well improved. Only in this case, "plastic limit order" is not a piece of paper.