The main technical application of plastic recycling

So far, the packaging industry is still the largest application area of ​​China's plastics industry. Experts predict that in 2005 packaging plastics will increase by more than 15% year-on-year to 6.25 million tons. Compared with the continuous increase in the number of applications, China's plastic packaging recycling is extremely optimistic. The narrow application of waste plastic recycling can be described as a major obstacle to the development of recycling. In this issue, we will introduce several major technologies for the recycling and reuse of waste plastics at home and abroad.


fuel

Initially, plastic recycling was heavily landfilled or incinerated, resulting in substantial waste of resources. Therefore, foreign countries use waste plastics instead of coal, oil, and coke for blast furnace blast furnaces, cement cement rotary kiln instead of coal, and waste solid fuel (RDF) for power generation.

The RDF technology was originally developed by the United States. In recent years, due to the shortage of landfills and the use of incinerators for the treatment of chlorine-containing waste plastics, HCI has severely corroded the boilers and produces dioxin-contaminated environment during the combustion process. The use of waste-plastics has a high calorific value to mix various types of waste. Combustible waste is made of 20,933 kJ/kg heat and uniform RDF, even though chlorine is diluted, it is also easy to store, transport, and substitute coal for other boilers and industrial kilns.

The technology of blast-injection of waste plastics in blast furnaces also uses the high calorific value of waste plastics. It uses waste plastics as a raw material to make a new method for treating waste plastics in place of coke or pulverized coal, which is sprayed into blast furnaces at a suitable particle size. The application of waste plastics injected by blast furnaces in foreign countries shows that the utilization rate of waste plastics reaches 80%, and the emissions are 0.1% to 1.0% of the incineration amount, resulting in fewer harmful gases and lower processing costs. The technology of blast furnace waste plastic injection has opened up a new way for the comprehensive utilization of waste plastics and treatment of “white pollution”, and it also provides a new means for energy conservation and efficiency enhancement of metallurgical enterprises. Germany and Japan have had successful applications since 1995.

Power generation

Waste solid fuel power generation was first applied in the United States, and there were 37 RDF power stations, accounting for 21.6% of the waste power stations. Japan has realized the great potential of waste plastics for power generation. Japan's combined overhaul has changed some small garbage incineration stations to RDF production stations so that continuous high-efficiency power generation can be carried out after concentration, so that the steam parameters of the garbage power station will increase from 30,012 to about 45,012, and the power generation efficiency will increase from 15% to 20%. ~25%.

The Ministry of the Environment of Japan is strongly supporting the industrial waste-based power generation industry, which is mainly based on waste plastics. It has also set a quota of 1 billion yen in the 2003 budget to start supporting the preparation of five waste plastic power generation facilities. It is planned to build a total of 150 waste plastic power generation facilities throughout Japan by 2010, making industrial waste power generation an important new energy source.

At present, the total amount of waste plastics that Japan forms each year is nearly 5 million tons, and in 2000 it was 4.89 million tons. Of these, 25% were recycled as recycled plastic raw materials; 42% were buried; 6% white burned; only 3% was used to generate electricity. Of course, if 100% recycling is the best, some waste plastics cannot be recycled.

Power generation from waste plastics can reduce the consumption of coal, oil, and carbon dioxide emissions. Japan plans to increase the current generation of waste power by 5 times by 2010, so that the annual waste power generation will reach 4 million kilowatts or more.

Oilification

Since plastics are the products of petrochemicals, plastics are high-molecular hydrocarbons, while gasoline and diesel are low-molecular hydrocarbons. Therefore, it is entirely possible to convert waste plastics into fuels. This is also the current research. Focus areas. Both domestic and foreign countries have achieved some gratifying results in this regard. For example, Fuji recovery technology company in Japan uses plastic oil technology to recover 0.6 liters of gasoline, 0.21 liters of diesel and 0.21 liters of kerosene from 1 kilogram of waste plastic. They also invested 1.8 billion yen in the construction of a recycling and waste plastics oil plant, processing 10 tons of waste plastics daily and regenerating 10,000 liters of fuel oil. The U.S. University of Kentucky invented a high-tech technology that converts waste plastic into fuel, with an oil yield of 86%. China, Beijing, Hainan, Sichuan and other places have reported reports on the transformation of plastics into fuel, but they have not yet seen the practical application of industrialization.

Building application

All kinds of waste plastics are stuck to the dirt to varying degrees, and generally need to be cleaned, otherwise it will affect the product quality. The use of waste plastics and fly ash for the manufacture of architectural tiles eliminates the need for strict cleaning of waste plastics and is conducive to practical operation in industrial applications. Adding suitable fillers to plastics can reduce costs, reduce mold shrinkage, increase strength and hardness, and increase heat resistance and dimensional stability. From the economic and environmental perspectives, choosing fly ash, graphite and calcium carbonate as fillers is a better choice. Powder coal has a large surface area and plastics have a good combination of strength, which can ensure that tiles have a higher strength and a longer service life.

The defoamed waste polystyrene foam is added with a certain amount of low-boiling liquid modifiers, foaming agents, catalysts, stabilizers, etc., and the polystyrene beads can be pre-foamed by heating and then heated in the mold A rigid polystyrene foam plate with fine closed cells can be used as a sealing material for buildings and has good heat insulation properties.

Composite regeneration

The waste plastics used for compound regeneration are collected from different sources, have more impurities, and are characterized by diversity, miscellaneousness, and fouling. Since the physical and chemical properties of various plastics vary widely and are incompatible with each other, their mixtures are not suitable for direct processing. Different types of separations must be carried out before regeneration, so the recycling and recycling processes are relatively complicated. Internationally advanced separation equipment can systematically sort out different materials, but the investment in equipment is high at one time. In general, composite recycled plastics are unstable and brittle, so they are often used to make lower grade products such as building fillers, garbage bags, micro sandals, and rain boots. At present, domestic Fuyang, Qingdao, Zhuzhou, Handan, Baoding, Zhangjiakou, Guilin, and Beijing, Shanghai, and other places have introduced more than 20 sets of (Taiwan) melting-recycling devices for the recycling of waste plastics from Japan and Germany, mainly for the production of building materials. , recycled plastic products, civil materials, paints, plastic fillers, etc.

Synthetic new material

Hungarian scientists have developed new technologies that convert plastic waste into industrial raw materials and reuse them, thus changing the practice of discarding or burning them indiscriminately.

According to reports, scientists use this new technology to process plastic waste into a new type of synthetic material. Experiments show that this kind of synthetic material can be used to pave the road after being mixed with asphalt in order to increase the hardness of the road surface and reduce the appearance of crush marks. It can also be made into heat insulation materials and widely used in buildings. Experts believe that because this technology is the transformation of plastic waste into new industrial raw materials, it is not only significant in terms of environmental protection, but also can reduce the use of primary energy such as oil and natural gas to achieve the effect of energy conservation.

The SPS high-efficiency water-reducing agent series developed by the scientists of the Guangzhou Institute of Chemistry of the Chinese Academy of Sciences for many years can give the concrete good plastic-retaining performance, waterproof performance and anti-freezing performance. SPS superplasticizer is mainly composed of waste polystyrene plastics. According to the nature of polystyrene, it is easier to introduce ionic groups. Through chemical reaction, the ionic groups are introduced into the waste polystyrene benzene ring, so that the modified Waste polystyrene, with the role of surfactants, can make cement lose the ability to wrap mixing water and achieve water reduction. In addition, since polystyrene is a high-molecular-weight high molecular material, during the solidification process of cement concrete, the modified polystyrene molecules can form a film on the surface of the cement particles to increase the adhesion between the cement particles, thereby enhancing the cement concrete. The strength, and thus become excellent cement waterproof, water reducer and enhancer.

Preparation of basic chemical raw materials, monomers

Mixed waste plastics can be obtained by thermal decomposition of liquid hydrocarbons, ultra-high temperature gasification can be obtained water gas, can be used as chemical raw materials. Germany's Hoechst, Rule, BASF, Kansai Electric, and Mitsubishi Heavy Industries have all developed technologies that use waste plastics to produce synthesis gas from ultra-high temperature gasification and then produce methanol and other chemical raw materials. They have also been industrialized.

In recent years, waste plastic monomer recovery technology has also received increasing attention, and has gradually become the mainstream direction, and its industrial applications are under research. At present, the research level has reached a monomer recovery rate of 90% for polyolefins, 97% for polyacrylates, 92% for fluoroplastics, 75% for polystyrene, and 80% for nylon and synthetic rubber. The industrial application of these results is also under study, and it will have huge benefits for the environment and resource utilization.

Battelle Memorial Research Institute of the United States has successfully developed technology for 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 US$3.3/kg.

Artificial sand

Since 2004, Japan's V-ARC Corporation has begun crushing waste plastics from home appliances and automobiles into artificial sand. Artificial sand made of waste plastics will be used for ground improvement materials and secondary concrete products. Examples of reuse of waste plastics as artificial sand are very rare. V-ARC plans to develop it into a large-scale business with a production value of 500 million yen in May 2005.

According to the data, about 5 million tons of waste plastics are not reused in Japan each year, and most of them have to be disposed of and burned. V-ARC intends to effectively use these waste plastics as artificial sand. The particle size of the artificial sand is between 1.5 mm and 7.0 mm and can be freely set according to the application.

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, ground improvement materials, tiles, tiles, and exterior wall materials.