PYROLYSIS: REACTION OF WOOD, OIL AND ALKANES - CHEMISTRY - 2024

The pyrolysis is a thermal decomposition process where -of type organic origin substances in their great majority are subjected to high temperatures in inert medium (without oxygen). When organic matter is treated by means of pyrolysis, products that are used in the industrial field are obtained.

One of the elements that can be obtained is coke, which is used as a type of fuel with industrial characteristics. You can also get biochar (known as biochar), which is used to modify or improve soils.

Pyrolysis converts organic matter into its constituent substances in a gaseous state, a solid residual species made up of carbon and ash, and a liquid substance known as bio-oil.

This reaction gives rise to other compounds, such as non-condensable gases or liquids that can be condensed, at the same time that it irreversibly transforms matter.

Although this technique is very important and has many applications, it can generate elements that are harmful to the environment and present a risk of toxicity for living beings.

Chemical reaction of pyrolysis

The pyrolysis reaction, as mentioned previously, involves the application of very high temperatures in an atmosphere without oxygen, to induce changes in the physical and chemical properties of substances through their thermal decomposition.

In this sense, this process converts the matter of organic origin into the substances that compose it in the gaseous phase, a residual species in the solid phase formed by carbon and ash, and a liquid substance with oily characteristics known as bio-oil.

This reaction is used to remove polluting substances from organic matter, and it accomplishes that purpose through two means:

- The fragmentation of contaminating molecules by breaking the bonds to form species with a smaller molecular weight (known as destruction).

- The separation of these harmful compounds from matter without destroying them.

Therefore, the pyrolysis technique is widely used in the treatment of organic substances that suffer fracture or decomposition when exposed to heat, such as polycyclic aromatic hydrocarbons.

On the contrary, this reaction is unsuccessful if it is to be used to eliminate inorganic species such as metallic compounds; however, it is possible to use it in processes that render these metals inert.

Reaction of wood

In the case of the pyrolysis reaction in wood, this process involves the application of very high temperatures (approximately 1000 ° C) in an air-free environment. Depending on the products to be obtained, there are several processes that are regularly used.

One of the techniques is carbonization, in which conical shaped wooden columns are erected and covered with earth to heat it in metal furnaces; This originates different products, such as activated carbon, drugs, fireworks, among others.

On the other hand, destructive distillation causes acetic acid, tar and other substances through the heating of the wood gradually, gradually increasing the temperature in the closed rooms used for this purpose.

Liquefaction is also used, which is a procedure commonly used in the production of a liquid phase fuel known as pyrolytic oil, which is produced in tanks designed for this purpose.

Oil reaction

When it comes to petroleum pyrolysis, it refers to the process of decomposition or fractionation of the high molecular weight hydrocarbons contained in the mixtures that make up this substance.

Thus, when some products derived from crude oil are subjected to certain conditions of pressure and temperature, the molecules of greater weight contained in them undergo a process of cracking or "cracking" that fragments them into lighter hydrocarbons (with a lower point of boiling and lower weight).

This procedure, which uses mostly the heavier fractions of oil, transforms large amounts of aliphatic hydrocarbons into aromatic molecules and helps in the production and improvement of fuels such as gasoline, diesel, aviation fuel, among others.

In this sense, molecules such as alkanes, alkenes and other low molecular weight species produced by this reaction can be separated and purified in order to obtain raw material of great relevance for other procedures, such as the synthesis of certain organic compounds.

Biomass reaction

The pyrolysis reaction of biomass (organic matter deposited from living beings) involves the breaking of chemical bonds in high molecular weight compounds, such as hemicellulose or cellulose, which are considered macromolecules.

These substances are fragmented into smaller gaseous species through complex reactions of cleavage, ring opening and depolymerization, for the transformation of biomass into potentially usable matter in terms of energy.

According to the state of aggregation in which they are found under normal environmental conditions, biomass pyrolysis can give rise to three types of substances: coal, tar and gas; These can lead to valuable products such as biofuel.

Reaction of alkanes

As previously mentioned, pyrolysis consists of the decomposition of organic substances by the application of heat and, in the case of alkanes, a closed chamber is used at high temperatures in a similar way to the types of pyrolysis that have been explained.

However, as these are large alkenes, the carbon-carbon bonds are broken - randomly - along the molecule and different radical species originate.

So, when the alkyl chain of these compounds is fragmented, smaller alkanes are produced, some alkenes (mainly ethylene) and other smaller species such as alkyl radicals, in addition to hydrogen in less important quantities.

References

1. Wikipedia. (sf). Pyrolysis. Retrieved from en.wikipedia.org
2. Britannica, E. (nd). Pyrolysis. Recovered from britannica.com
3. Wang, S., and Luo, Z. (2017). Pyrolysis of Biomass. Obtained from books.google.co.ve
4. Berlin, AA (2005). Chemical Physics of Pyrolysis, Combustion, and Oxidation. Recovered from books.google.co.ve
5. Moldoveanu, SC (2009). Pyrolysis of Organic Molecules: Applications to Health and Environmental Issues. Obtained from google.co.ve