VOCs and purification technologies: industrial solutions for the abatement of Volatile Organic Compounds

Adsorption is an extremely important process which allows substances to accumulate on a solid surface thanks to the bonds formed with molecules which are present in the gaseous phase.

This phenomenon thus leads to a separation of the relevant molecules, which pass from the gaseous phase to the solid phase until the material becomes saturated. To restore adsorption, it is then necessary to replace the saturated material.
To optimise this process, it is advisable to use highly porous materials with a high specific surface, as a larger contact area improves the adsorption of chemical species.

Activated carbon, made from carbon-rich raw materials, is an excellent material for adsorption. Placed inside the Chemsorb® activated carbon filter, which is manufactured by Tecnosida®, it allows the Volatile Organic Compounds (VOCs) to be removed from the airflow which passes through it.
This technology has been successfully used in various industrial applications, such as:

• VOCs and dust purification on a photovoltaic panel production line;
• ATEX activated carbon filter installed in a production plant for chemical intermediates;
• Filtration of VOCs, aliphatic vapours and styrene in the packaging and printing sector.

After analysing the phenomenon of adsorption, it is now time to explore the physical principle of absorption involving a gaseous phase and a liquid phase. Let’s examine it in more detail paying particular attention to the technology that uses its principle: the wet scrubber!

Absorption consists of the passage of chemical species from a gaseous phase to a liquid phase. When analysing this phenomenon, it is important to consider two different aspects:

• Thermodynamics: it analyses the amount of chemical species that can be absorbed by the liquid. This figure varies depending on the physicochemical characteristics of pollutants, temperature and other factors. Specific chemicals can be added to the liquid to increase absorption efficiency;
• Kinetics: it analyses how long it takes for absorption. This aspect is influenced by fluid dynamics conditions, concentration gradients, and by the gas/liquid contact surface.

The technology used to obtain an effective contact between the gaseous phase and the liquid phase is called wet scrubber. Thanks to its considerable expertise, Tecnosida® has developed WETCLEAN: a washing tower which can be adapted to the specific needs of different production processes.
On our dedicated page four real implementations can be found, where the wet scrubber was used for the abatement of inorganic vapours and VOCs in the chemical, metallurgical and detergent production sectors.

Now we only have one option left to analyse: thermal degradation of VOCs through a post-combustion system!

Thermal oxidation allows the VOCs in an airflow to be burned, thus transforming them into harmless substances (mainly carbon dioxide and water).

This process is carried out by means of thermal oxidizers, which can be:

• direct;
• recuperative;
• regenerative;
• catalytic.

These technologies are generally composed of:

• a burner that keeps the mixture of polluting gases at a temperature which is suitable for their combustion or destruction;
• only for catalytic combustors, a catalyser which allows the oxidation process to be accelerated, thus reducing the reaction temperature;
• a heat exchanger which allows the heat generated in this process to be reused profitably for both incoming fumes and a third fluid, if sufficient thermal power is available

It is important to point out that thermal post-combustion is an appropriate solution if:

• VOCs concentration is sufficiently high: in this case, the heat generated by combustion allows the process to be self-sustained as regards energy, resulting in lower operating costs;
• VOCs molecules are mainly hydrocarbon-based: if volatile molecules contain significant percentages of atoms other than carbon, hydrogen and oxygen, related acidic species are produced in the combustion process. For example, in a current containing a significant amount of hydrogen sulfide (H2S), the combustion process would lead to the formation of sulphur oxides (SOx) and the production of sulphuric acid.

To learn more about the application areas and the operation of thermal oxidizers, you can read our dedicated articles:

• “Thermal oxidizer“: an oxidizer designed by Tecnosida® for VOC oxidation;
• “Regenerative thermal oxidizers for VOC and fume abatement“: three real cases in which we applied this technology in the automotive, chemical, and packaging sectors;
• “The 3Ts of combustion“: an in-depth blog on the fundamental elements that enable the correct oxidation of VOCs.

After analysing the three different technologies suitable for the purification of Volatile Organic Compounds (VOCs), another question arises: are other technologies available for the purification of Volatile Organic Substances?
To give an answer, it must be considered that there is a particular class of VOCs: odorous molecules. This pollutant is removed by appropriate traditional technologies or innovative systems, as described in our dedicated article: “Industrial odour elimination: available technologies”.
There are therefore numerous technologies that are used to reduce Volatile Organic Compounds and the choice must be made taking into account the type of compounds to be treated and their physicochemical characteristics. For this important choice do not rely on chance, rely on Tecnosida®: since 1979 we have been designing and manufacturing tailor-made systems for an effective treatment of air pollutants!