To date, the packaging industry remains the largest application area for the plastics industry in China. Experts predict that plastics for packaging will grow by more than 15% year-on-year in 2005 to reach 6.25 million tons. Compared with the growing volume of applications, the recycling of plastics for packaging in China is extremely unpromising. The narrow application field of waste plastic recycling can be regarded as a major obstacle to the development of recycling. This issue of the special introduction of domestic and foreign on the recycling of waste plastics recycling of several major technologies.
Fuel
Initially, plastics recycling was done in large quantities by landfill or incineration, resulting in a large amount of wasted resources. Therefore, foreign countries will be used for waste plastic blast furnace blowing instead of coal, oil and coke, used in cement rotary kiln instead of coal to burn cement, as well as made of refuse solid fuel (RDF) for power generation, the effect is ideal.
RDF technology was originally developed by the United States. In recent years, Japan, in view of the lack of landfill, incinerator treatment of chlorine-containing waste plastics HCI corrosion of the boiler is serious, and the combustion process will produce dioxins to pollute the environment, the use of waste plastics with high calorific value of the characteristics of mixing and matching of a variety of combustible garbage made of calorific value of 20,933kJ/kg and uniform particle size of the RDF, not only the chlorine has been diluted, but also to facilitate the storage, transportation, and other boilers for the industrial boiler, burning instead of coal. It is also easy to store, transport and burn for other boilers and industrial kilns instead of coal.
Blast furnace blowing waste plastics technology is also the use of waste plastics of high calorific value, waste plastics as raw materials made of suitable particle size sprayed into the blast furnace to replace the coke or pulverized coal, a new method of waste plastics. The application of blast furnace blowing waste plastics abroad shows that the utilization rate of waste plastics reaches 80%, and the emission rate is 0.1%~1.0% of the incineration amount, which produces less harmful gases and lower treatment cost. Blast furnace blowing waste plastic technology for the comprehensive utilization of waste plastics and governance "white pollution" opened up a new way, but also for metallurgical enterprises to provide a new means of energy efficiency. Germany, Japan from 1995 has been successfully applied.
Power generation
The earliest application of solid fuel waste power generation in the United States, and there have been 37 RDF power station, accounting for 21.6% of the waste power station. Japan has realized the huge potential of waste plastic power generation. Japan in conjunction with the overhaul has been some small waste incineration stations into RDF production stations in order to centralize the continuous and efficient scale power generation, so that the steam parameters of the waste power station from 30,012 to 45,012 or so, the power generation efficiency from the original 15% to 20% to 25%.
Japan's Ministry of the Environment is strongly supporting the industrial waste power generation business based on waste plastics, and in the 2003 budget to propose a 1 billion yen amount to begin to assist in the preparation of five waste plastics power generation facilities. The plan is to build 150 waste-plastic power generation facilities throughout Japan*** by 2010, making industrial waste power generation an important wing of new energy.
Currently, the total amount of waste plastics formed in Japan each year is nearly 5 million tons, and in 2000 it was 4.89 million tons. Of which 25% as plastic raw materials recovery and recycling; 42% buried; 6% burned for nothing; only 3% for power generation. Of course, if you can 100% recovery and recycling is best, but some of the waste plastics can not be recycled at present.
Generating electricity from waste plastics can reduce coal and oil consumption, as well as carbon dioxide emissions. Japan plans to increase its current waste-to-energy capacity by five times by 2010, bringing annual waste-to-energy capacity to more than 4 million kilowatts.
Oil
Since plastic is a product of petrochemicals, from the chemical structure, plastic is a high molecular hydrocarbons, while gasoline, diesel is a low molecular hydrocarbons, so the waste plastic into fuel is completely possible, but also the focus of the current research areas. Domestic and foreign in this regard have made some encouraging achievements, such as Japan's Fuji Recycling Technology Corporation, the use of plastic olefinization technology, from 1 kilogram of waste plastics in the recovery of 0.6 liters of gasoline, 0.21 liters of diesel fuel and 0.21 liters of kerosene. They also invested 1.8 billion yen to build a recycled waste plastic olefinization plant, the daily processing of 10 tons of waste plastic, regeneration of 10,000 liters of fuel oil. The University of Kentucky in the United States invented a waste plastic into fuel oil high technology, the oil rate of up to 86%. China's Beijing, Hainan, Sichuan and other places have on the conversion of plastics into fuel research results reported, but have not yet seen the industrialization of practical applications.
Construction applications
A variety of waste plastics are varying degrees of dirt, generally have to be cleaned, otherwise it will affect product quality. The use of waste plastics and fly ash manufacturing construction tile on the waste plastic cleaning requirements are not very strict, conducive to industrial applications in the practical operation. Adding appropriate fillers to plastics can reduce costs, reduce molding shrinkage, improve strength and hardness, improve heat resistance and dimensional stability. From the economic and environmental point of view, the choice of fly ash, graphite and calcium carbonate as filler is a better choice. The surface area of pulverized coal is very large, and the plastic has a good bonding force with it, which can ensure that the tiles have high strength and long service life.
After defoaming the waste polystyrene foam add a certain dose of low boiling point liquid modifier, foaming agent, catalyst, stabilizer, etc., by heating the polystyrene beads pre-foaming, and then heated in the mold to produce a rigid polystyrene foam board with micro-fine closed pores, can be used as a sealing material for the building, good heat preservation performance.
Compound regeneration
Compound regeneration of waste plastics used from different channels to collect, more impurities, with diverse, mixed, dirty and so on. Because of the physical and chemical properties of various plastics differ greatly and have more incompatibility, their mixtures are not suitable for direct processing, before regeneration must be carried out in different kinds of separation, so the recycling process is more complicated. Internationally, there are advanced separation equipments that can systematically sort out different materials, but the one-time investment in the equipments is high. Generally speaking, the nature of composite recycled plastics is unstable and easy to become brittle, so it is often used to prepare lower grade products, such as building fillers, garbage bags, micro-perforated sandals, rainboots and so on. At present, the domestic Shenyang, Qingdao, Zhuzhou, Handan, Baoding, Zhangjiakou, Guilin, as well as Beijing, Shanghai and other places, respectively, from Japan, Germany, the introduction of more than 20 sets (Taiwan) melt method of regeneration processing and utilization of waste plastics device, mainly used for the production of building materials, recycled plastic products, civil engineering materials, coatings, plastic fillers and so on.
Synthesis of new materials
Hungarian scientists have researched a new technology to convert plastic waste into industrial raw materials and reuse, thus changing the previous practice of casually discarding or incinerating these wastes.
According to the report, the scientists used the new technology to process plastic waste into a new type of synthetic material. Experiments have shown that this synthetic material mixed with asphalt in proportion can be used to pave the road, increasing the hardness of the road surface, reducing the appearance of traces of crushing, but also can be made into a thermal insulation materials and widely used in buildings. Experts believe that because the technology is plastic waste into new industrial raw materials, not only in environmental protection is significant, but also can reduce the use of oil, natural gas and other primary energy, to achieve the effect of energy saving.
Scientists at the Guangzhou Institute of Chemistry of the Chinese Academy of Sciences have developed a series of SPS high-efficiency water-reducing agent products over the years, which can give concrete good plasticity, waterproofing and anti-freezing properties. SPS high-efficiency water-reducing agent is mainly composed of waste polystyrene plastic, according to the nature of polystyrene is easier to introduce ionic groups, through a chemical reaction, the ionic groups are introduced to the waste polystyrene benzene ring, so that the modified waste polystyrene will be used as a new industrial raw material. Through chemical reaction, the ionic group is introduced into the benzene ring of the waste polystyrene, so that the modified waste polystyrene has the effect of surfactant, which can make the cement lose the ability of wrapping the mixing water and achieve the effect of water reduction. In addition, because polystyrene is a high molecular weight polymer material, in the cement concrete solidification process, this modified polystyrene molecules can form a film on the surface of cement particles, improve the adhesion between cement particles, so as to enhance the strength of cement concrete, and thus become an excellent waterproofing of cement, water-reducing agent and reinforcing agent.
Making basic chemical raw materials, monomers
Mixed waste plastics can be made by thermal decomposition of liquid hydrocarbons, ultra-high-temperature gasification can be made of water gas, can be used as chemical raw materials. Germany Hoechst, Rule, BASF, Japan Kansai Electric Power, Mitsubishi Heavy Industries in recent years have developed the use of waste plastics ultra-high-temperature gasification of syngas, and then the system of methanol and other chemical raw materials technology, and has been industrialized production.
In recent years, waste plastics monomer recycling technology is also growing attention, and gradually become the mainstream direction, its industrial application is being studied. At present, the level of research has reached the monomer recovery rate of polyolefins for 90%, polyacrylates for 97%, fluorine plastics for 92%, polystyrene for 75%, nylon, synthetic rubber for 80% and so on. These results of industrial applications are also under study, it will have a huge benefit on the environment and resource utilization.
The Battelle Memorial Institute in the U.S. has successfully developed a technology to recover ethylene monomer from mixed waste plastics such as LDPE, HDPE, PS, PVC, etc., with a recovery rate of 58% (mass fraction) at a cost of $3.3/kg.
Manmade sand
Starting from 2004, Japan's V-ARC has started to make home appliances and automobiles into artificial sand by crushing waste plastics. The artificial sand made from waste plastics will be used as foundation improvement materials and secondary concrete products. This is a rare example of recycling waste plastics into artificial sand, and V-ARC plans to develop it into a 500 million yen-a-year business by May 2005," the company said.
Data shows that about 5 million tons of waste plastics in Japan cannot be reused every year, and most of them have to be disposed of by landfill or incineration. V-ARC intends to crush these waste plastics and effectively utilize them as artificial sand. The particle size of artificial sand ranges from 1.5 mm to 7.0 mm, and can be set freely according to the purpose.
Compared with natural sand, artificial sand is characterized by low cost, light weight (less than half of natural sand); uniform particle size and no water content. Artificial sand can be used in various building materials, green roof materials, foundation improvement materials, tiles, ceramic tiles, and exterior wall materials.