How plastic decomposes
Average decomposition time of plastic products created using different technologies,
The main concerns are related to the fact that plastics,Once in the ground, they break down into small particles and can release into the environment chemicals added to them during production. It can be chlorine, various chemicals, for example, toxic or carcinogenic anti-flames. These chemicals can seep into groundwater or other nearby sources, which can cause serious harm to those who drink the water.
In addition, the so-called biodegradable plastic, as it decomposes, can release methane, which is a very powerful greenhouse gas, which makes a significant contribution to global warming.
When it gets to landfills, plastic does not representpotentially no threat, since the landfill is a special engineering structure that is created to protect the environment and human health and prevents pollution, including soil and groundwater.
Most of the harm is caused by the plastic that the person himself throws out in unintended places or that ends up in spontaneous landfills.
Companies are also developing new ways to speed up the process of plastic decomposition and coming up withNew types of biodegradable plastics that break down in three to six months.
Such materials are not made from petroleum products,as usual, but from starch, fats, corn or other biomass. But to increase the production of these materials, it will be necessary to expand the cultivated land by reducing forests and other natural zones.
Types of plastic processing
- Physical
Mechanical recycling
Among the physical methods, the most common is mechanical recycling.in the shredding, crushing and grinding of plastic materials to obtain recycrate, a polymeric material that is subsequently used to make other plastic products.
At the first stage, the waste is sorted according to the type of plastic, the condition of the material and the degree of contamination.Then the material goes through the stage of pre-crushing. Subsequently, the plastic is re-sorted and washedand dried, and then processed in thermal installations to obtain a melt of a homogeneous consistency – recyclate.
Subsequently, the already melted materialare sent to an extruder to form intermediate granules or directly secondary products. For the implementation of the process, crushers and granulation plants are used.
- Chemical recycling
As a result of this method, plasticsnew materials are formed. Chemical recycling is used to process polymer molecules, resulting in the formation of new structures, which are subsequently used as raw materials for the production of new products.
Many large international companies such asAdidas, Unilever, P&G, Danone and Interface are actively investing in the development of this area. It is based on the process of depolymerization or chemical destruction of the polymer binder.
As a result of the process, a ready-maderecyclables such as new plastics (polymers), monomers for making new plastics, naphtha for making new plastics and chemicals, basic chemicals such as methanol, transportation fuels for aviation and automobiles, waxes for candles and crayons, and synthetic crude oil ...
The advantage of the chemical method isthe ability to recycle plastic when separating it for mechanical recycling is either economically ineffective or technically impossible. Most often, the method is used to recycle contaminated material.
Hydrolysis and glycolysis
During hydrolysis, plastic interacts with water in an acidic, alkaline, or neutral environment. As a result, the material is depolymerized and decomposed into monomers.
Solvolysis
Solvolysis is the most commonly usedby chemical recycling and is realized using a wide range of solvents, temperatures, pressures and catalysts such as supercritical water and alcohols.
Alkaline salts act as a catalyst.metals. Compared to pyrolysis, the solvolysis process requires lower temperatures. The process generates recovered fiber and a chemical that can then be used commercially.
Methanolysis
The method is based on the splitting of plastic whenusing methanol in tanks with high temperatures. The process uses catalysts such as magnesium acetate, cobalt acetate and lead dioxide.
Thermocatalysis
A recycling process has been developed in Russiaplastic into liquid fuel components using a one-time catalyst based on sludge from some metallurgical industries. Initially, plastic waste is crushed and then, with the addition of a catalyst, enters a reactor where the mixture is heated to over 400 °C.
The resulting mixturehydrocarbons are fed for combustion as a finished fuel oil, which can also work as a plasticizer for some components of the road surface. Subsequently, the product can be processed to produce gasoline, diesel and fuel oil.
The advantage of the method is lowenergy consumption, and among the disadvantages stands out the complexity of control of the process and technological equipment due to the need to conduct the process at high pressure.
- Thermal
The mechanisms of thermal destruction of polymers are classified by oxygen content into several types: pyrolysis, methanolysis, gasification, combustion.
Pyrolysis
Pyrolysis is one of the most effective, butat the same time expensive methods of processing plastic. When using the pyrolysis method, waste is processed under high temperatures in specially equipped chambers without access to oxygen. As a result of the chemical process, gas, thermal energy and fuel oil are formed.
When splitting plastic waste by pyrolysis, a gasoline fraction is obtained, which can reach up to 80% of the mass of the feedstock.
The process involves thermal decompositionplastic waste at various temperatures (300–900° C) in the absence of oxygen, resulting in thermal decomposition and the release of hydrogen particles contained in the plastic. A number of hydrocarbons are formed that can be used as fuel bases.
Pyrolysis destroys 99% of harmful complexsubstances that make up plastic, which makes it one of the most environmentally friendly options for recycling waste, but requires a lot of energy.
Gasification
When gasifying from unsorted dirtymaterials form synthetic gas, which can subsequently be used both for the construction of new polymers and for the generation of thermal and electrical energy, methanol, electricity, feed proteins and various biomass.
Waste is treated with a plasma flow attemperature of 1200 ° C, due to which toxic substances are destroyed and tar is not formed. Subsequently, the garbage turns into ash, which is often pressed into briquettes and laid in the foundations of buildings. The gasification method has gained particular popularity in Japan.
The main advantage of the method is the ability to process plastic without sorting. Among the disadvantages, there is a high probability of emission of harmful gases into the atmosphere.
Experimental Methods
- Depolymerization
Thermal depolymerization is one of theexperimental physical and chemical methods. It is built on a pyrolysis process using water. As a result of thermal depolymerization, both a mixture of hydrocarbons suitable for the creation of synthetic fuels and new plastic materials are obtained.
In the process of depolymerization, monoplastics likePET bottles are split back into monomers that can be recycled into new PET materials. Thermal depolymerization allows mixed plastics to be processed, but creates potentially hazardous by-products.
- Radiation
The radiation method is based on the use ofhigh-energy radiation to destroy the polymer matrix, while the physical characteristics of the filler remain unchanged. It is assumed that in the future, this still experimental method will pose the main method of recycling reinforced plastic.
Among the disadvantages of the process, there is an increased radiation load on humans and the environment. Moreover, only thin-layer plastics are recycled.
- Decomposition by microbes from the stomach of cows
Researchers in Austria have found that bacteria from a cow's rumen, one of the four sections of her stomach, can break down plastic.
Scientists suggested that such bacteria could be beneficial because cows have natural plant polyesters in their diets: they are similar in structure to plastic.
The authors of the work considered three types of polymers:PET, PBAT and polyethylene furanoate. The results showed that all three plastics can be broken down by microorganisms from the stomachs of cows, with plastic powders breaking down faster than plastic film.
- Larval decomposition
The problem of plastic contamination can besolved with the help of beetles widespread in Korea. Beetle larvae from the order Coleoptera (Plesiophthophthalmus davidis) can decompose polystyrene. The intestinal flora of the insect can oxidize and change the surface properties of the polystyrene film.
- Reuse
In the form of polyurethane foam
New Zealand scientists have developed a method for converting biodegradable plastic knives, spoons and forks into foam that can be used as wall insulation or in flotation devices.
As an experiment, scientists placed canteensdevices in a special chamber filled with carbon dioxide. By changing the level of pressure, the researchers observed how carbon dioxide expanded inside the plastic, creating foam, and later scientists received foam.
Every time plastic is recycled itloses its strength a little. But for foam, this is not important: in many applications, strength is not required from it. This material is used as wall insulation or in flotation devices.
As vanillin
Scottish scientists have developed a unique way to recycle plastic waste. With the help of genetically modified bacteria, it was turned into vanillin flavoring.
Two researchers from the University of Edinburgh inScotland has genetically engineered bacteria to convert terephthalic acid to vanillin. The fact is that both substances have a similar chemical composition. As a result, bacteria only need to make minor changes in the number of hydrogen and oxygen atoms associated with the same carbon skeleton.
In the form of fuels and lubricants
Scientists in the United States have come up with a way to convert plastics into useful materials. They can be used immediately as jet or diesel fuel and lubricants.
Researchers from the Center for Innovation in the fieldPlastic at the University of Delaware (CPI) in the United States has developed a direct method for converting single-use plastic packaging (bags, yoghurt packaging, plastic bottles, bottle caps, and others) for use as jet or diesel fuel and lubricants.
Researchers used a new catalyst anda unique process for the rapid destruction of hard-to-process plastics - polyolefins. They account for 60–70% of all plastics produced today.
Plastic recycling problems
The biggest challenge in recycling plasticwaste lies in the high cost of collecting and processing materials - plastics are rarely presented in “pure” form and are most often a combination of different types of polymers.
Along with contamination of the incoming materialthis makes the sorting and cleaning process labor-intensive and costly. Moreover, the system of organized waste collection and recycling is implemented only in a limited number of countries.
Thus, most plastic waste is not recycled and is thrown into the environment or, in a more organized approach, incinerated.
Read more
The first plague: how did the "black death" originate and who started the epidemic
Scientists have determined why Mercury has such a large core
The conversations of the deceased Soyuz-11 crew have been declassified: what they talked about before their death