Recycling Status of Waste Plastics

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Plastics are everywhere, classified in many ways and in many varieties. According to the classification of use, plastics can be divided into general plastics, engineering plastics and special plastics; According to the interpolymer force classification, plastics can be divided into thermoplastics and thermosetting plastics; According to the classification of plastic polymer components, there may be thousands of theoretically. In addition, scientists and chemical enterprises are still maintaining a certain rate of research and development every year, increasing the types of plastic. At present, the main types of plastics include: PP, PE (LDPE, HDPE), PVC, PET, PS.

 

Global plastic use is huge and increasing year by year, but the overall recycling rate is low. According to Statista, the annual global production of thermoplastics was close to a staggering 400 million tons in 2020, and is expected to grow at a rapid rate of more than 10% every five years. By 2050, the global production of thermoplastics is expected to reach 589 million tons.

Since plastics play an extremely important role in human life, it is difficult to replace them. Therefore, in the face of increasingly severe environmental protection situation, recycling waste plastics has become a topic of widespread concern to the government and the society. In the above context, the professional analysts in the field of environmental protection around waste plastic recycling, from the point of view of science and technology review the current market mainstream recycling technology, popular science in this field of key technology points.

 

Recycling status of waste plastics:

 

Forecast of global thermoplastic production from 2020 to 2050

As shown in the figure above, among the major thermoplastics at present, PP has the largest output, followed by LDPE and HDPE. These three plastics alone account for nearly 50% of all thermoplastics output.

The recycling rate of waste plastics is low, and the difference between regions and different categories is great. Compared with the world's rising plastic production, recycling rates have stagnated. According to the Organization for Economic Co-operation and Development (OCED), only about 14-18% of plastic waste is recycled globally, and about 24% is incinerated, About 58 to 62 percent of plastic waste ends up in landfills or is discarded in the natural environment. The recycling rate of waste plastics varies greatly from region to region. The overall recycling rate of plastic waste in the EU is relatively high worldwide and has stabilized at over 30% since 2014. The recycling rate of plastic waste in China is similar to that of the European Union, reaching 26.7 percent in 2020. Recycling rates in the United States lag far behind other regions, with an overall recycling rate of just 8.7 percent in 2018.

The recovery rate of subdivided plastics varies greatly. The chart below shows the recycling rates of different types of plastic waste in the US sorted by OCED. It can be seen that the overall recovery rate of PET and PE is high, both exceeding 10%, which is higher than the overall recycling level of waste plastics in the United States. However, the recovery rate of PP with the largest annual output is less than 1%, far lower than the overall level of waste plastic recycling.

Biodegradable plastics are emerging, but they are expensive and less technologically mature. The following chart is a summary of current plastic production, technology maturity and price on the market. As can be seen from the figure, compared with mature plastic products such as PE, PP and PET, PBS and other new renewable plastics have no advantages in terms of technological maturity and price.

Therefore, recycling is a more reliable solution than relying on biodegradable plastics to alleviate the plastic waste problem. In addition, compared with the original plastic, the current market share of recycled plastics is low, there is still a lot of room for growth. In this context, understanding the key technical points in the plastic recycling process is of great importance to investors in related fields.

 

Analysis of recycling technology of waste plastics

According to whether the polymer carbon chain in plastics is broken, the waste plastic recycling technology can be divided into physical recycling and chemical recycling.

 

1

Physical recycling(recycling machine)

Physical recycling refers to the method that does not destroy the polymer structure of plastic, but only cleans and breaks the waste plastic and then directly carries on the plastic pelletizing process. Part of the process may also include plasticizing. The common process flow is as follows:

 

Plastic Sorting :

Separation is generally carried out through the physical properties of the feed, such as the use of magnetic force to remove part of the metal in the feed, some difficult to separate substances may also need to be manually sorted. Common separation methods include: manual separation, density separation, magnetic separation, X-ray fluorescence separation, electrostatic separation, etc.

 

Plastic Wash and Dry:

Different impurities have corresponding treatment methods. For example, clean up the plastic surface of the soil, dust, water cleaning can be simply removed; For oil pollution, lye may be needed, but this method also has obvious disadvantages - easy to bring pollution. The drying after cleaning is relatively simple, generally using an industrial dryer to dry the water on the plastic body.

 

Plastics after simple sorting and cleaning, in order to facilitate the subsequent treatment, generally use industrial shredders for plastic crushing treatment. Industrial shredders generally use blades to crush plastics inside, and different industrial shredders will be used according to the hardness or shape of the feed. The smaller the particle size after crushing is, the higher the crushing cost.

 

Feed and plasticize:

In order to ensure the quality of finished products in the production line, part of the process may include plasticizing steps. Generally speaking, for thermoplastics, the purpose of charging is to reduce the cost; For thermosetting plastics feeding is to reduce the cost and modification. Plasticizing is the use of kneading machine in the temperature of about 100-200 to mix the filler and waste plastic, to generate a lump, convenient subsequent extrusion.

 

Plastic Extrusion Granulation:

Generally, extruder is used to make reclaimed plastic particles from pellets, and the reaction temperature is about 150-250.

 

Physical recovery process is relatively simple, generally can accept most of the common plastics on the market. However, the disadvantages are also obvious. The plastics produced after physical recycling are usually low-value plastics, and the performance of plastics will be reduced after repeated physical recycling, so it is difficult to achieve infinite physical recycling. As a result, some manufacturers may limit the type of plastic they feed into their recycling production line to ensure that the product is a high-value plastic, while others may only recycle PET bottles. In summary, the application scenarios of physical reclamation are limited in a number of ways.

 

2

Chemical recycling:

Chemical recycling is the conversion of polymer carbon chains in plastics into small molecules to produce fuel, chemicals, electricity or other products. Common chemical recycling methods include:

Incineration power generation

Also known as the peroxide process, it can deal with all types of waste plastics. The process converts carbon and hydrogen from waste plastic into carbon dioxide and water, generating heat that is eventually converted into electricity that is fed into the transmission system.

Incineration power generation generally has three parts: fermentation, incineration and waste disposal. The waste plastic is mixed with other waste and then simply fermented before being burned in an incinerator. The heat generated during incineration is used to heat water in the boiler and produce steam, which is used to drive a turbine to generate electricity. The slag produced in the process and the fly ash collected in the flue gas are disposed of and sent to landfills or reused, and the flue gas is discharged into the atmosphere after treatment.

 

Chemical recycling is the conversion of polymer carbon chains in plastics into small molecules to produce fuel, chemicals, electricity or other products. Common chemical recycling methods include:

 

Incineration power generation

Also known as the peroxide process, it can deal with all types of waste plastics. The process converts carbon and hydrogen from waste plastic into carbon dioxide and water, generating heat that is eventually converted into electricity that is fed into the transmission system.

The advantages and disadvantages of incineration power generation are also obvious, the advantage is that the feed requirements are not high, can handle all types of plastic; The disadvantage is that the waste gas produced by combustion generally contains pollutants. If there is waste plastic containing chlorine in the feed, there may be toxic and harmful gases such as dioxins.

 

Partial oxidation process

It is suitable for polyolefin waste plastics. Unlike incineration, there is no excess oxygen involved in the reaction. A small amount of oxygen reacts with the feed to generate syngas (carbon monoxide and hydrogen mixture), and the final product can be used in coal chemical industry to produce methanol and ammonia.

Partial oxidation processes generally include separation, cleaning and drying, crushing, melting, and gasification. The process of sorting, cleaning, drying and crushing is the same as that of physical recovery. Other processes are mainly described below:

 

Melting: The temperature is generally 100-500°C. Some processes have only one melting, and some processes may have multiple melting for melting effect. In the melting process, some light component gas is produced, which can be used as the heat source during melting. In addition, if the feed contains halogen-containing plastics, halogen-containing acid gases and halogen-containing compounds may also be produced. The generation of halogen-containing compounds will reduce the yield, and the generation of halogen-containing compounds can be avoided by passing proper amount of steam.

Gasification: The reaction temperature is about 1000-1600°C. In the process, just enough air or oxygen is injected to achieve partial oxidation, converting carbon and hydrogen atoms in the plastic into carbon monoxide and hydrogen, respectively. The final gasification products may include carbon monoxide and hydrogen, as well as a small amount of carbon dioxide, water vapor, halogen gases, etc., and a certain amount of impurity removal depending on the final use of the product. In addition, in addition to gas products, slag is usually produced. After proper treatment, the slag can be sent to landfill or for secondary use.

 

 

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In summary

Waste plastic recycling as an important part of the carbon neutral era proposition, we believe that in the foreseeable future through technology enabling low-value plastic waste into treasure, or become the next environmental protection industry to solve the plastic problems.

 

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