VOCs – Volatile Organic Compounds: what are they, why they are hazardous and how to eliminate them
An in-depth look at the nature and effects of VOCs
In this article, we will discuss VOCs: what they are, why they are considered hazardous pollutants, their main chemical classes and how to effectively intervene in industrial processes to reduce them.
Definition of Volatile Organic Compounds
A simple analysis of the term reveals that it contains the words “organic” and “volatile.” What do these terms mean?
- Organic: VOCs are based on carbon chemistry, i.e., organic chemistry. The chemical species that we will analyse are characterised by sets of atoms that determine their physicochemical behaviour and reactivity.
- Volatile: VOCs have a marked tendency to transition into the vapour phase. In other words, they pass from the liquid state to the gaseous state even at room temperature.
Volatile Organic Compounds (VOCs) are organic molecules that pass to the gaseous state at room temperature, meaning they are highly volatile.
This makes them easily dispersible in the air, contributing to air pollution.
Let’s explore the main categories of molecules that fall under this definition.
Classes of Volatile Organic Compounds?
Before identifying the different types of VOC molecules, note that they may have different origins:
- biogenic: molecules which come from natural sources, such as plants. Examples include methane (CH4), unsaturated hydrocarbons called terpenes, and other organic compounds such as esters, aldehydes, ketones, and peroxides;
- anthropogenic: compounds that result primarily from industrial transformation and production processes.
We’re most interested in anthropogenic compounds, so let’s take a look at them together!
Volatile Organic Compounds from industrial processes
Aliphatic hydrocarbons: VOCs in fuels
These chemical species contain carbon and hydrogen atoms, bound together by single bonds. They represent a significant portion of oil and are widely used in fuels.
Alkenes and VOCs from the petrochemical industry
These hydrocarbon species contain double bonds. They result from production processes in the petrochemical industry and are important intermediates in synthesising many compounds.
Aromatic volatile organic compounds: benzene, toluene, xylene
These very stable molecules are used in many products, such as paints, varnishes, glues and lacquers.
Aldehydes and ketones in industrial VOCs
These partially oxidised molecules are characterised by a carbonyl bond. They are widely used in the chemical, agricultural, cosmetic, and pharmaceutical industries. These compounds are also naturally present in perfumes and fruits during the ripening stage.
Acids
These molecules are characterised by a carboxyl group. They are mainly used in the food industry as intermediates in the synthesis of more complex molecules.
Alcohols, esters and ethers: Volatile Organic Compounds (VOCs) in solvents
Let’s take a look at them together:
- alcohols: molecules characterised by a hydroxyl bond. They are widely used as solvents in most industries or as intermediates in important chemical processes;
- ethers: molecules characterized by the R-O-R’ bond. These substances are found in specific contexts. For example, THF (tetrahydrofuran) is an industrial solvent, and MTBE (methyl-tertiary-butyl-ether) is widely used as antiknock agent in green gasoline;
- esters: molecules characterized by a carboxyl bond. They are widespread in the food industry, especially in the flavour industry, and they are the basis for the scent of ripening fruit.
Alcohols are extensively used as solvents or intermediates in important chemical processes. Recently, they have been gaining importance in the field of automotive fuels.
Halogenated organic compounds
Generally volatile, hydrophobic and toxic compounds. They are used as pesticides, cooling fluids and solvents.
Organic sulphur compounds
Also called mercaptans, these compounds are characterised by a very low olfactory perception threshold. In fact, they are added to methane gas to give it its characteristic odour. These compounds are also emitted during wastewater treatment, in animal waste, and in petroleum refining processes. While they are not a serious environmental concern on a large scale, they can be harmful locally.
Organic nitrogen compounds
This category includes many chemical species, such as amines, amides and nitriles, which are used in various fields. Among them we can find dye production, pharmaceutical/chemical industry, photography and rubber and polymer production.
| COMPOUNDS | FORMULA | MOLECULAR MASS (g/mol) | BOILING POINT (°C) | Kcal/Kg | H2O SOLUBILITY | CATEGORY |
|---|---|---|---|---|---|---|
| ACETIC ACID | C2H4O2 | 60,052 | 118,1 | 3.128 | 1000 g/l (25 °C) | Aliphatic acids |
| ACETONE | C3H6O | 58,079 | 56 | 6822 | soluble | Ketone |
| BENZENE | C6H6 | 78,112 | 80,1 | 9.588 | 1,770 g/l a 293 K | Aromatic hydrocarbon |
| BUTANE | C4H10 | 58,122 | -1 | 10.919 | insoluble | Aliphatic hydrocarbon |
| ETHANOL | C2H5OH | 46,068 | 78,37 | 6.403 | soluble | Alcohols |
| METHYL ETHYL KETONE | C4H8O | 72,106 | 79,64 | 7.512 | 292 g/l (20 °C) | Ketone |
| ISOPROPYL ALCOHOL | C3H8O | 60,095 | 82,5 | 7.289 | soluble (20 °C) | Alcohols |
| STYRENE | C8H8 | 104,149 | 145 | 9.675 | 0,24 g/l a 293 K | Aromatic hydrocarbon |
| TOLUENE | C7H8 | 92,138 | 110,6 | 9.679 | 0,52 g/l a 293 K | Aromatic hydrocarbon |
| XILENE | C8H10 | 106,165 | 139 | 9.745 | insoluble | Aromatic hydrocarbon |
What impact do VOCS have on the environment?
To adopt effective solutions against Volatile Organic Compounds (VOCs), it is essential to understand their environmental impact.
In general, each air pollutant has a characteristic residence time in the atmosphere related to its chemical and physical properties.
The longer this time is, the more the pollutant can disperse into the atmosphere through winds and currents, altering the atmosphere chemical balance. Some VOCs affect the balance of methane (CH₄) in the atmosphere, indirectly contributing to the greenhouse effect and climate change.
It is also important to note that many VOCs are hazardous to humans and animals. For example:
- benzene is a highly volatile carcinogenic compound;
- formaldehyde is a toxic compound produced in large quantities and used in many production processes;
- halogenated compounds are highly volatile and toxic. Since they tend to be hydrophobic, they can accumulate in the body.
How can emissions of Volatile Organic Compounds (VOCs) be reduced?
After analysing the effects of VOCs, you may wonder how industrial processes can minimise VOC emissions into the atmosphere.
Many technologies are available for VOC treatment, and the choice depends on the specific characteristics of the compounds and the production process. We have written a blog article that explores these issues in a more detailed way: VOCs – Volatile Organic Compounds – Filtration and abatement.
The main technologies for treating VOCs include:
- Chemsorb®: an activated carbon filter for VOC adsorption;
- WETCLEAN: a wet scrubber for odour and VOC abatement;
- Thermal oxidizer: thermal destruction of VOCs at high temperatures;
- BIOCLEAN: a biofilter for the biological treatment of VOCs.
Real examples of the abatement of Volatile Organic Compounds (VOCs)
You can also find case histories related to VOC abatement below:
- VOC, odour and inorganic vapor treatment: scrubber application in chemical, metallurgical, and detergent production industries;
- VOCs from photovoltaic production: using an activated carbon adsorption plant to reduce VOC emissions from solar panel production plants;
- Dust and VOC filtration and purification in the chemical sector: using multistage ATEX plants in the production of chemical agents and household products;
- VOCs and dust in the paint field: installing ATEX plants for the treatment of VOCs emitted from spray painting operations and methacrylate production.
Subscribe to stay up to date with Tecnosida® news!