Oct-2011

Detection of VOCs demands continuous innovation in calibration gases

With an ever-increasing number of processing plants coming on stream worldwide to keep up with the burgeoning petrochemical industry, the focus on the release of volatile organic compounds (VOCs) into the atmosphere is coming under intense scrutiny by environmental authorities.

Stephen Harrison, Linde Gas

Article Summary

For example, the US Environmental Protection Agency (EPA) regulates the emissions of VOCs to prevent ground-level ozone formation — a constituent of photochemical smog. The release of VOCs from industrial processes not only poses a potential hazard to human health, but can also represent a risk of financial losses to the operator.

VOCs are effectively petrochemicals of different kinds. They are numerous, varied and ubiquitous, emanating mostly from hydrocarbon processing plants, although the natural world also emits a measure of naturally occurring chemical compounds. The risks associated with industrial VOCs are aggravated by the fact that hazardous concentrations are usually very low and the health issues they can cause can be accumulative and slow to develop.

Detection and analysis of industrial VOCs demands continuous innovation to assist companies in complying with tightening legislation and mitigating the financial implications of VOC emissions. Certainly, the financial factor is a significant incentive to keep VOCs inside the process. If emitted, they not only pose possible health issues and generally become an atmospheric irritation for people working and living close to the emission source owing to their offensive smell, but companies are rapidly becoming aware that every gram that is lost means money lost. By measuring ambient air, processing plants are able to determine if any of their raw materials, process intermediates or end products are in the air and, if so, also determine the emission source and address it. In the petrochemical industry, this applies to a broad spectrum of components.

A major source of man-made VOCs is solvents. As with other VOCs, when solvents increase in temperature, as in a production process exhaust stream, they evaporate and enter the atmosphere, where they create a foul smell, potentially cause a variety of health problems and also require the company concerned to purchase the solvents lost in the process. There are several different technologies to reduce or remove solvents from exhaust streams, such as destruction or recovery and reuse, depending on the recovery value and concentration of the solvents.

One of the most effective ways to recover solvent vapours is to condense and capture them using liquid nitrogen as a cooling media in a process called low-temperature or cryogenic condensation. When liquid nitrogen is used to cool the condenser, VOC emissions are reduced to low levels very rapidly, by trapping the VOCs at extremely low temperatures. They can then be reintroduced to the industrial process.

Increasing regulatory requirements have created more rigorous demands in measurement and, with new compounds to evaluate, laboratories performing environmental analysis of air quality are constantly confronted with new challenges. They find themselves under continuous pressure to expand their scope and expertise. Innovative, next-generation calibration gas mixtures are essential to enable new air quality analysis technologies and meet the needs of laboratories engaged in process control, emissions monitoring and research.

Chemical processing plants generally have their own unique signature of emissions based on their specific processes, the raw materials used and the final product being produced. With the ever-increasing awareness of the potential for negative health effects from the air we breathe, the requirements for low-level traceable calibration standards are becoming of greater importance. Emerging knowledge and technologies are the driving forces behind the measurement of many more compounds and at ever-lower concentrations.

Calibration is vital for accurate measurement in order to produce reliable information about the quality of the environment around us. Technologically complex and sophisticated gas standards for calibration are becoming essential to deliver greater efficiency and confidence to laboratories.

Adverse influences on health
While not quite a daily event, it is becoming a common occurrence when local newspapers, television and radio report that asthma and other respiratory diseases are on the rise, affecting both young and old. While there are many causes of these ailments, it is generally recognised that some VOCs can have severe, adverse influences on human health in several areas. These include sensory stimulation, tissue inflammation, anaphylaxis and nerve toxic reactions. A few VOCs can also easily constrain the normal function of the central nervous system, causing headaches, fatigue, drowsiness and discomfort. Research indicates that alcohols, aromatic hydrocarbons and aldehydes have the potential to stimulate mucous membranes and upper respiratory tracts. Furthermore, a number of VOCs are proven carcinogens or potential carcinogens, such as benzene, trichloroethylene and formaldehyde.

It is a disquieting fact of life that we are routinely exposed to VOCs throughout our daily activities, from driving our cars to working in our offices. In fact, because of the airtight design of many buildings, the concentrations of VOCs inside can be greater than the VOCs in the ambient air outside the building because the VOCs are emitted from paint on the walls, carpets and furniture. Many researchers around the world have presented papers on indoor air quality (IAQ). The Japanese even have a more descriptive name for this: sick building syndrome.

The growing demand for accurate identification and quantification of VOCs across both ambient and indoor environments has initiated requests from chemical analysts around the world for low-level multicomponent VOC calibration gas mixture standards.

Designing a new gaseous calibration standard
Technicians begin the process of designing a new gaseous calibration standard by determining the safety issues associated with working with the pure compound, as well as the new calibration standard, in order to establish appropriate safety procedures for personnel working in the development laboratory.