What are volatile organic compounds?
(Volatile Organic Compounds – (VOC) are a family of organic compounds with high vapor pressure at room temperature. The family includes both anthropogenic chemicals (human-made) and those found naturally in the environment. Various VOC compounds are emitted as gases from solid and liquid sources, mainly found indoors. Accordingly, indoor VOC concentrations tend to be consistently higher than those measured outdoors. At the industrial level, VOC emissions pose a risk factor that is mostly not properly managed. These emissions are particularly common in printing houses, laboratories, and in the medical, chemical, and petrochemical industries.
There are many and diverse VOC compounds; not all of them are toxic to humans, and of those that are, not all are acutely toxic. However, many VOC compounds are known to be carcinogens in animals, and some are suspected or known to cause cancer in humans as well. One example is benzene, a substance recognized as a human carcinogen, which is found as a byproduct of tobacco smoke, stored fuels, and vehicle exhaust gas. Benzene is also widely used in the production of plastics, resins, and synthetic fibers. Symptoms of short-term (acute) exposure to toxic VOC compounds include irritation of the eyes, nose, and throat, headaches, nausea and vomiting, dizziness, and worsening of asthma symptoms. Long-term (chronic) exposure may cause damage to the liver and kidneys, cancer, and nervous system impairment. Most VOC gases are invisible to the naked eye, even at toxic concentrations.
There are several methods for treating VOC compounds at the industrial level:
- Regenerative Thermal Oxidizers (RTO) are widely used as a means of preventing air pollution. These devices are versatile and highly efficient. The systems oxidize VOC compounds at high temperatures. RTOs are particularly effective for continuous processes where air flow rates are large and inlet concentrations are relatively low. The significant disadvantage of these systems is the high energy required due to the need to reach very high temperatures (1000 degrees Celsius) in order to oxidize the compounds to the required level. Many factories around the world spend large amounts of money every year on the energy needed to reach the high temperatures in RTO facilities.
- Catalytic oxidizers utilize metal catalysts such as palladium, which react with VOC compounds to lower the activation energy required for the oxidation of organic compounds. The direct implication of using catalytic oxidizers is a significant reduction in the energy costs needed for the oxidation of organic vapors, since the oxidation temperature required is considerably lower compared to the solution using the RTO method. The oxidation temperature required for catalytic oxidizers depends on the type of pollutant to be oxidized, but it can be assumed that most substances are oxidized in the temperature range of 300-500 degrees Celsius.
Click here to read more about catalytic oxidizers. - Scrubbers can be used to treat VOCs under suitable conditions and for certain compounds; this is only true when the VOC compounds in the process are water-soluble and the Henry's law constant of the process has an appropriate value.
Click to read more about scrapers.
- VOC adsorption in activated carbon systems is a long-established and well-known technology. This technology can be used efficiently and economically in processes where emission concentrations are not high, or in non-continuous (batch) processes. This is because for high emission concentrations, the technology is not economical due to the high costs associated with carbon replacement.
Attention must be given during system design to the risk of forming heat pockets that cannot be detected, due to the high insulating properties of the carbon particles. In every design of an industrial activated carbon system, consultation with professionals who are aware of the hazards associated with the use of this technology is required.
Click to read more about liquid activated carbon filters.
- Biological reactors (bioreactors) can be suitable for treating certain types of volatile organic compounds (VOCs), but the process must be stable and continuous. This is because biological reactors rely on a medium of microorganisms whose growth can take many months. Any change in the process - such as emission composition, temperature, humidity level, or type of pollutant - may constitute a critical change for the bacteria and lead to failure of the microorganisms.
We do not recommend the use of such reactors in industrial applications, since current regulatory requirements do not allow waiting many months for a damaged microbial medium to regenerate. An additional drawback is the large footprint required for installations of this type.
Scrubber for treating VOC emissions, acids or bases Activated carbon systems for treating solvents or odors
Catalytic oxidizer for VOC combustion