Plastic pollution is becoming more and more serious worldwide, and plastic recycling is of great significance. This article will introduce the current status of plastic recycling and mainstream recycling methods for waste plastics. We believe that in several plastic recycling methods, plastic pyrolysis combines many advantages into one, which will be the future of waste plastic recycling.
1、Global Plastic Recycling Status and Waste Plastic Quantity
1.1 The amount of global plastic waste
Since the 1950s, photographer Alexander Parks has invented plastics. Plastics are used in a wide range of applications worldwide. They have the advantages of light weight, chemical stability, corrosion resistance, wear resistance, good insulation, and low cost, so they can be seen in all walks of life around the world.
In 2015, more than 300 million tons of plastic products were produced worldwide. Humans have produced more than 9.1 billion tons of plastics since the 1950s, 9.1 billion tons equivalent to 1 billion elephants, or 25,000 New York Empire State Buildings.
Plastic Garbage that Can Be Seen Everywhere in Life
However, while enjoying the convenience that plastic brings to our lives, plastic waste is pouring into our lives just as tides. Due to the non-degradability of plastics, plastic waste has seriously deteriorated our living environment. A report from the Journal of the American Association for the Advancement of Science on “Analysis of Globally Produced Plastics” warns that, in the case of existing plastics, “by 2050, more than 13 billion tons of waste plastics will be disposed of in landfills and in the environment."
A large number of animals died from plastic pollution
Among these plastic wastes, plastics that flow into the ocean have become a huge threat. In 2010, up to 4.8 million tons to 12.7 million tons of plastic waste flowed into the ocean, equivalent to a truckload of plastic waste being poured into the ocean every minute. Because of the difficulty of degradation, there are five trillion plastic fragments in our ocean today, enough to surround the Earth for more than 400 weeks. These plastic wastes cause hundreds of thousands of marine animals to die every year. They also appear in the food chain in the form of micro-plastics, plastic fragments, etc., entering drinking water and on the table, affecting human health.
1.2 Waste Plastic Source
(1) Industrial source waste plastic
Mainly from the plastic product molding processing plant, when the thermoplastic resin is directly processed into a product, it is inevitable that there will be waste products and scraps, etc., and the waste plastics can be directly recycled and reused, and most of them are such items.
(2) Urban life waste plastics
Mainly from the use and consumption process of various types of plastic products in people's daily life, mainly in the three fields of agricultural plastics, packaging plastics, plastic daily necessities, such waste plastic recycling is difficult because of its large amount of use and high frequency of use. Moreover, it is highly random, and most of it is mixed with soil domestic garbage, and the composition is complicated. White pollution is mainly caused by such waste plastics.
1.3 Waste plastic recycling status
At present, the recycling rate of plastic waste is extremely low all over the world. The recovery of 7 billion tons of plastic waste is only 10%. Jia Baker, an associate professor of engineering at the University of Georgia, said: "Most plastics can't do meaningful biological decomposition, so plastics garbage caused by humans can be with us for hundreds or even thousands of years. If you don't think of a solution as soon as possible, the earth will eventually be surrounded by rubbish and become the garbage planet seen in the movie.
In the late 1980s, the recycling rate of waste plastics in the United States was nearly 10%. By the end of the 20th century, the recycling rate of waste plastics reached more than 35%. The treatment method also changed. The recycling energy of incineration waste plastics increased to 18%, and the landfill dropped to 37%.
In 2014, about 26% of the waste plastics produced in 28 EU countries and in Norway and Switzerland were recycled effectively, of which the packaging sector accounted for up to 62%. Italy is currently the best country in Europe to recycle used plastics. Italy's waste plastics account for about 4% of municipal solid waste, with a recovery rate of 28%.
Japanese Workers Working in A Waste Plastic Recycling Factory
In recent years, Asian countries have begun to pay more attention to the recycling of waste plastics. Various countries have successively promulgated laws and regulations related to the recycling of waste plastics. Among them, Japan is the second-largest plastics producer and consumer in the world after the United States. Currently, the annual discharge of waste plastics is about 9 million tons. Japan's land area is small and its population is dense. Waste plastics pose a serious threat to the living environment of the Japanese people. On the other hand, Japan lacks resources, recycling waste plastics as resources, and establishing a resource-recycling society has become a top priority. In the early 1990s, the recycling rate of waste plastics in Japan was 7%, and the heat utilization rate of combustion was 35%.
Countries around the world have reached a relatively unified consensus. Traditional waste plastic processing methods such as a landfill or direct incineration will be gradually abandoned, and more environmentally friendly and efficient waste plastic recycling methods will be adopted.
2、Current mainstream waste plastic processing methods
2.1 Direct landfill
Direct landfill plastics will not only occupy a large amount of land, but the occupied land will not be restored for a long time, affecting the sustainable use of the land. Most of the plastic components used in daily life are polystyrene + polyethylene, which are formed under high temperature and high pressure, chemically stable, and extremely resistant to acid and alkali corrosion. If it is landfilled, it will not degrade for at least 200 years, which will result in:
(1) Agricultural development is hindered. The accumulation of waste plastics in the soil will affect the absorption of nutrients and water by crops, resulting in reduced crop yields.
(2) The survival of animals is threatened. After the waste plastic landfilled in the land is swallowed by the animal, the plastic will remain in the stomach for a long time and cannot be digested, causing the animal to starve to death.
(3) The pressure on land resources has increased dramatically. Due to the large volume-to-weight ratio of waste plastics, landfill waste plastics will occupy a large amount of land. These lands have not been restored for a long time and affect the sustainable use of land.
2.2 Incineration power generation
The use of incineration power generation facilities to treat waste plastics has high waste recycling rates and will save a lot of land resources. According to a survey, the amount of waste plastics processed by about 450 waste incineration power plants is equivalent to the amount that can be processed by 5,000 landfills. Moreover, the disposal of waste plastics by incineration power generation will save landfills. Taking Guangzhou, China as an example, waste plastics incineration power generation saves 11.13 yuan per ton compared to waste plastic landfill treatment.
Waste Plastics Incineration Power Plant
However, because the plastic generates a large amount of heat, the life of the incinerator is greatly reduced. And the gas produced after incineration will cause the earth to warm, and some plastics will release harmful gases and pollute the atmosphere when incinerated. For example, the burning of halogen-containing plastics will produce dioxins, a toxic gas that can cause cancer. In addition, the cost of waste plastics incineration power generation facilities is very high, and the cost of inputs may not be recovered in the short term.
Therefore, although waste plastics incineration power generation has many obvious advantages, it is still not the best solution.
2.3 Pyrolysis
Pyrolysis technology can convert waste plastic into high value-added energy products that are easy to store, easy to transport, high in energy density and easy to use under high temperatures and oxygen-free conditions, such as plastic pyrolysis oil. This oil has a high calorific value and can be used for power generation in power plants or further purification into standard diesel oil, etc., and has a very high economic value.
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MoreGreen Waste Plastics Plant
Since the pyrolysis is carried out in a closed environment, it is equipped with a complete exhaust gas treatment unit. Therefore, no toxic gases will enter the atmosphere. The price of this pyrolysis equipment is much lower than that of incineration power generation equipment, and the subsequent maintenance costs are low, requiring only 2-3 operators to meet the daily operation of the equipment.
After the addition of the catalyst, the waste plastic is subjected to pyrolysis to obtain high-quality pyrolysis oil and carbon black. And the reaction rate is fast, the energy consumption is low, the operation is flexible, and the running cost is low.
It should be noted that the pyrolysis rate of waste plastics of different materials is also different. The following are the oil yields of some common plastics (high purity):
- Polyvinyl chloride (PVC), polyethylene (PE) plastics, such as films, plastic bottles, wires, plastic bags, etc.: oil yield is about 95%
- Polypropylene (PP) plastics, such as film, plastic pots, caps, plastic furniture, etc.: oil yield is about 90%
- Polystyrene (PS) plastics, such as electrical enclosures, plastic cups, electrical accessories, toys, etc.: oil yield is about 90%
- ABS engineering plastics: oil yield is about 40%
In comparison, pyrolysis equipment requires less capital investment, a small footprint, high economic efficiency, and is environmentally friendly. In recent years, due to the importance of environmental protection issues in various countries, the development of waste plastic pyrolysis technology has also been greatly promoted. In the near future, pyrolysis may be the main method of waste plastics processing.
3、Summary and outlook
At this stage, the amount of waste plastic waste in the world is still huge, which has seriously affected the global environment and the normal life of human beings. The underdeveloped regions and countries are even more affected. The good news is that governments in various countries around the world have realized the seriousness of the problem and have successively enacted relevant environmental laws and regulations to control the flood of plastic waste.
To solve the "garbage siege", we mainly need to start from two aspects. On the one hand, human beings must form good environmental habits. On the other hand, relying on advanced waste plastic pyrolysis technology to achieve green recycling of waste plastics.
