While ductless fume hoods do provide considerable benefits over ducted systems by eliminating ductwork and utility placement concerns, they are limited by the types of chemicals and the quantities of those chemicals that can be effectively managed.
To maximize your ductless fume hoods, you must select the correct filter for your application. To make the filter selection process easier, Filtco Filters offers a comprehensive, searchable Chemical Guide.
Simply enter the chemical you need to filter and click on the correct chemical name in the results to view the recommended filter.
Or read on to learn more about chemical families and filtration.
Ductless technology has many benefits. Those benefits, however, can only be realized if the design of the hoods or cabinets used in facilities are properly filtering air. Most ductless fume cabinets incorporate activated carbon filters, which filter the incoming air through physical adsorption and chemisorption. Physical adsorption is non-specific adsorption of gas molecules by diffusion and is based on overall surface area of the carbon molecules. Chemisorption is a chemical reaction in which two substances react to each other and cause one substance to be trapped on the filter material.
The effectiveness of activated carbon as an adsorbent is attributed to its large surface area, a high degree of surface reactivity and overall pore size.
Carbon filter life is dependent on the chemicals used in the hood and the chemical quantity being processed into the filter. Carbon filters have known retention capacities for certain chemicals that are dependent on a number of factors. In general, chemicals with a molecular weight over 30 and a boiling point higher than 60°C are candidates for adsorption with carbon filters.
Vapors and Chemicals
Fume hoods and fume storage cabinets remove vapors and gases from a variety of chemical families, dependent on the filter choice and treatments implemented.
Carbon filters can be developed to capture:
- Methyl iodide vapors
- Mercury vapors
- Hydrogen sulfide
- Hydrogen cyanide
- Oxidize formaldehyde
- Glutaraldehyde fumes
- Diethyl ether
Carbon filtration technology is best suited to uses that produce relatively low volumes of harmful vapors. Because activated carbon filters have finite capacities, recirculating or ductless enclosures are not direct replacements for traditional externally ducted equipment.