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The release of volatile organic compounds (VOCs) has a wide range of adverse effects on the environment and human health. A novel air sensor is being developed between scientists from the University of Navarra in Pamplona, Spain, and the ACTPHAST 4R innovation hub of the European Union to prevent compound release from industrial fuel tanks.
What are Volatile Organic Compounds (VOCs)?
Volatile organic compounds (VOCs) are a group of hydrocarbon organic chemicals associated with high vapor pressures.
As a result of these high pressures, VOCs can escape from both solids and liquids in the gaseous state. VOCs can exist naturally within nature, typically due to either terrestrial or ocean biogenic reactions. However, VOCs produced from industrial processes are more widely studied.
This latter type of VOC is emitted into the atmosphere following the evaporation of organic solvents and fossil fuels' combustion.
The release of VOCs through both natural and human-made methods can have harmful effects on both human health and the environment.
When ingested through contaminated water supplies, VOCs cause a wide range of adverse human health effects. VOCs include:
- Trichloroethylene (TCE)
- Vinyl chloride
- Methylene chloride
- Cis- and trans-1,2-dichloroethylene (DCE)
In terms of its environmental impact, certain VOCs have been identified as precursors to the ozone, contributing to the tropospheric ozone's pollution. Therefore, public exposure to VOCs is a public health concern that must be carefully monitored, particularly at industrial sites where this byproduct is routinely released into the environment.
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VOC Sources in Chemical Plants
A primary industrial source of VOCs is the production processes and storage tanks used within petroleum refinery plants.
Recent studies have found that alkanes are responsible for up to 80% of the total VOCs released from petroleum refinery plants. Of these alkanes, propane is considered to be the richest compound with a volume mixing ratio of 15.3%. This is followed by n-butane, ethane, isobutane, n=pentane, isopentane, and n-hexane with mixing ratios of 11.0%, 9.6%, 8.4%, 6.6%, 5.8%, and 4.7%, respectively.
Regardless of their source, VOCs can get released from the storage tanks when liquid is filled or emptied into the tank. As the liquid rises, the vapor pressure within the tank becomes higher than the relief pressure.
Comparatively, when liquid is emptied from the tank, VOC vapors can expand and subsequently get saturated, causing the vapors to expand beyond the tank's capacities and release.
How are VOCs in fuel tanks currently monitored?
Despite the wide range of severe issues that can occur when VOCs are released from industrial fuel tanks, there are no current technological methods to monitor VOCs present in fuel tanks in real-time.
As a result, industrial plant workers must often climb into these tanks to monitor chemical vapor and liquid chemical levels. VOCs often evaporate quickly and can even cause explosions upon their interaction with friction or static electricity within the environment.
The known health effects associated with VOCs' inhalation, combined with the fact that many industrial workers are directly exposed to these chemicals while monitoring their levels, pose serious occupational hazards that can be deadly to the workers and costly to the companies.
Although certain electronic sensors have been developed for measuring VOC levels in fuel tanks, these sensors are often limited in their ability to function when exposed to temperatures beyond 150°C.
Many of these electronic sensors comprise metallic oxides that pose other limitations during the shipment of chemical solvents. For example, the interaction between VOCs and certain semiconductor metallic oxides can cause the oxides to experience a change in electric resistivity, preventing these sensors' ability to provide accurate results.
A Novel VOC Sensor
The current methods of monitoring VOCs in fuel tanks are insufficient to meet the industry's current need to ensure the protection of their employees while simultaneously limiting their impact on the environment and public health.
Scientists from the University of Navarra in Pamplona, Spain, have partnered with the European Union (EU) photonics innovation hub ACTPHAST 4R to develop a novel air sensing technology that can detect the presence of VOCs in industrial fuel tanks.
Through the use of optical fibers, the team led by Cesar Elosua Aguado has designed an air sensing system that will measure the interaction that occurs between the cladding modes and the sensitive coating of the sensor.
When the air sensor identifies VOCs, the interaction between the cladding modes and the coating will produce an independent and readable signal. Whereas zinc oxide will be used to coat the sensor's surface, the cladding modes will be comprised of components that travel around the cladding through a distributed Braff reflector.
Rather than utilizing the metallic oxide material to detect electrical conductivity changes, this air sensor instead relies on the refractive index of the zinc oxide sensing material to determine when VOCs are present.
The sensor’s reactivity to the gas will be determined by the specific properties of each VOC present molecule within the test sample.
Ultimately, Aguado’s team believes that its novel sensor response system will be able to train a future artificial intelligence (AI) system to identify specific VOCs within the samples and provide information on their distinguishing qualities.
References and Further Reading
Rajabi, H., Mosleh, M. H., Mandal, P., et al. (2020). Emissions of volatile organic compounds from crude oil processing – Global emission inventory and environmental release. Science of the Total Environment 727. doi:10.1016/j.scitotenv.2020.138654.
National Research Council (US) Committee on Contaminated Drinking Water at Camp Lejeune. Contaminated Water Supplies at Camp Lejeune: Assessing Potential Health Effects. Washington (DC): National Academies Press (US). (2009). 3, Systemic Exposures to Volatile Organic Compounds and Factors Influencing Susceptibility to Their Effects. Available from: https://www.ncbi.nlm.nih.gov/books/NBK215288/.
Saikomol, S., Thepanondh, S., & Laowagul, W. (2019). Emission losses and dispersion of volatile organic compounds from tank farm of petroleum refinery complex. Journal of Health Science & Engineering 17(2); 561-570. doi:10.1007/s40201-019-00370-1.
Air-Sensing Technology Combats Dangerous Chemical Exposure [Online]. Available from: https://www.photonics.com/Articles/Air-Sensing_Technology_Combats_Dangerous_Chemical/a66398.
New air sensor to make chemical plants safer [Online]. Available from: http://www.dpaonthenet.net/article/182018/New-air-sensor-to-make-chemical-plants-safer.aspx.