Odorous molecules typically belong to the category of VOCs, as they are mainly organic molecules with a strong tendency to be present in the vapor phase. However, not all VOCs have a characteristic and/or unpleasant smell at all.
The process that leads to recognize the presence of an odorous molecule in the air is very fascinating. First of all, in this process can be identified two steps:
- Physiological processes: the receptors inside the nose are stimulated by odorous molecules present in the air. This stimulus results in an electrical signal, which through the nerve pathways is sent to a specific area of our brain. The brain, therefore, decodes the signal and associates it with the signals of the various substances already recorded.
- Psychological processes: at this point our personal reaction to the smell that has been perceived at the neuronal level comes into play. It is important to note that this component is highly subjective: while one person may have associated pleasant sensations with the smell in question, another person may have associated unpleasant sensations with the same smell.
Categories of compounds that typically have a characteristic odour
Sulfur compounds
Sulfur molecules tend to have a characteristic pungent odor. They tend to be emitted in anaerobic processes: H2S (hydrogen sulfide), for example, smells like rotten eggs. Other
Oxygenated compounds
Many types of molecules can be included in this category, such as: alcohols, which have the characteristic smell of alcohol; aldehydes, which typically have a strong (and sometimes pungent) smell of fruit; ketones, in a similar way, have a strong and sweetish smell, which tends to be unpleasant. Ethers and esters also belong to this category.
Volatile fatty acids
They are typically generated by incomplete oxidation of lipids and have a pungent and rancid odor.
Terpenes
Molecules belonging to this category, which includes, for example, limonene and α-pinene, derives mainly from plants. In particular, it derives from bio-degradation processes of ligno-cellulosic materials. They give the sensation of that characteristic smell of “nature”.
Nitrogenous compounds
Also in this category are included different types of molecules (ammonia, amines..etc), which have pungent and annoying odors.
Which industrial sectors are affected?
At the industrial level, in which processes are these categories of molecules emitted? The most relevant ones from the point of view of odour emissions are:
- Waste treatment and disposal
- Livestock farms and agricultural facilities
- Industrial production (chemical, petrochemical, pharmaceutical, food, tanning …)
EXUS solutions for VOC emissions
Since odorous molecules are typically a particular class of VOCs(Volatile Organic Compounds), it is possible to treat them with equipment suitable for VOCs, such as:
The most common types are
-
Activated carbon filterWet scrubberRTO (Rigenerative Thermal Oxidizier)