Recycling of chemicals: What you need to know about it

Through chemical recycling, the products are changed so that they can give life to new items, equal or different from the initial products. With different characteristics to mechanical recycling, chemical
recycling opens new possibilities for the plastics industry. With the development of technology, chemical recycling allows recovering part of the initial characteristics of polymers.

Understand what chemical recycling is

"We know that recycling is a process in which the physical, chemical or biological state of a material that would no longer be used in a reusable raw material is transformed. However, the processes and techniques applied vary according to the type of Material that will be reused,” explains Guilherme Arruda, CEO of VG Resíduos.

According to the expert, chemical recycling is the transformation of plastic waste into chemical inputs, fuels or raw materials for the manufacture of new plastic products.
"Basically, it consists in returning the polymer to its primary composition (mixtures of monomers or hydrocarbons) through chemical change."

Arruda explains that the product originated from chemical recycling is the closest to virgin plastic, precisely due to the depolymerization of plastic waste, that is, the reversion of a polymer to its monomer. "To complete and make recycling purer, the monometers are purified and again subjected to polymerization," he adds. The process allows the recycling of different plastic mixtures. In addition to accepting a certain degree of contaminants such as paints, papers,
among other materials. Chemical recycling allows waste treatment, reducing pretreatment costs, collection and selection costs. In addition to allowing to produce new products with the same original quality ".

How the process works

According to Arruda, there are different processes of transformation of plastic waste through chemical recycling. They are:

1. Hydrogenation

In the method, the polymer chains of plastic waste are broken down, he explains. "This decomposition is initially carried out thermally and using oxygen.
The results are highly reactive free radicals that are subsequently saturated with hydrogen, producing light hydrocarbons (such as methane, ethane, propane) and a mixture of hydrocarbons in the Gasoline and Diesel range."

Arruda says the method is widely used to recycle phenolic resins, melanin resins and unsaturated polyester. In addition, hydrogenation allows recycling to be used as raw material in refineries.

2. Gasification

"In this chemical recycling, oxygen is inserted to produce the combustion of the carbon contained in the matter. That is, the process occurs in the limited presence of oxygen (in the form of air, steam or pure oxygen)," he explains.

The residue is burned at high temperatures (from 800 ° C to 1000 ° C) and during the gasification CO and H2 are recovered, as well as small amounts of CH4, CO2, H2O and some inert gases.

"The gas produced meets many practical applications, including combustion in engines or turbines for power generation. Or the use in irrigation pumps, direct heat generation and production of raw material for chemical synthesis."

 3. Pyrolysis

Arruda explains that, in this method, the molecules are broken down by the action of heat in the absence of oxygen, which can happen in two ways:

·        At low temperature: The residue degrades at high temperature in the absence of air or oxygen deficiency. In this method, depolymerization occurs and the formation of small amounts of aromatic compounds and light gases such as methane.

·        At high temperature: The residue decomposes through heat in the absence of air or oxygen deficiency. In this process oils and gases are formed which will then be purified by standard petrochemical methods.

"Pyrolysis produces a wide variety ofdecomposition products that are difficult to separate and also have a lower commercial value than hydrolysis products".

4. Chemolysis

Finally, in chemical recycling by chemolysis, substances such as methane, water and glycol are used for the partial or total decomposition of plastics in monomers.

How to perform chemical recycling in the industry?

"The circular economy sees the recycling of plastic waste as a sustainable source of raw material for several segments. Chemical recycling provides a solution to the problems of plastic waste, since it has a better environmental performance compared to other scenarios," says Arruda

According to the professional, the method avoids the environmental impacts caused by waste, such as terrestrial ecotoxicity, photochemical oxidation, acidification and eutrophication.
Therefore, when followed correctly, the process doesn’t cause loss of material and environmental pollution.

"The basic structure for applying the chemical recycling process of plastic comprises a waste washing tank, a material reducing crusher to ensure efficient chemical recycling, a washing water dryer and an extruder, preferably with a vacuum system, intended for the removal of contaminants and compounds that can be produced during recycling," he explains.