NAFA Guide To Air Filtration Chapter 11 Airborne Molecular Contaminants presented by the National Air Filtration Association Fourth Edition

Agenda Contaminant Control Contaminant Control Removal Options Removal Options –Adsorption –Chemisorption –Catalysis Media Types Media Types Definitions Definitions Filter Options Filter Options

Control Options Source Control Source Control –Remove the contaminant source Ventilation Ventilation –Increase outdoor air Removal Control Removal Control –Remove contaminants via physical or chemical means

Molecular Filtration TYPES TYPES –Physical - Adsorption Activated carbons Activated carbons –Chemical - Chemisorption Potassium permanganate impregnated media Potassium permanganate impregnated media Chemically treated activated carbons Chemically treated activated carbons –Catalysis

TypesTypes Adsorption - The process by which one substance is attracted and held onto the surface of another. Adsorption - The process by which one substance is attracted and held onto the surface of another. –Surface phenomena. –Capacity is independent of particle size size –Adsorption rate is inversely proportional to particle size. proportional to particle size. –High temperatures, may cause desorption. –Humidity has adverse effect –The contaminant being removed is called the adsorbate

TypesTypes Chemisorption - The result of chemical reactions on and in the surface of the adsorbent. Chemisorption - The result of chemical reactions on and in the surface of the adsorbent. –Fairly specific and depends upon chemical nature of media and the contaminant –Irreversible & essentially instantaneous –Oxidation - changes harmful gases to harmless solids –Higher temperatures will increase the reaction rate in chemisorption –Humidity is favorable toward the reaction

Types Catalysis Catalysis –Changing the rate of a chemical reaction, (usually increasing) where the catalyst is not consumed in the process Carbon impregnated with various metals can aid in the reaction of a product difficult to adsorb. Carbon impregnated with various metals can aid in the reaction of a product difficult to adsorb.

Media Overview Activated Carbon Activated Carbon –adsorption –may be reactivated Chemically Treated Carbon Chemically Treated Carbon –chemisorption Specific to a compound or family of compounds Specific to a compound or family of compounds –not reversible Potassium Permanganate Potassium Permanganate –chemisorption broad based oxidizer broad based oxidizer –not reversible

DefinitionsDefinitions RESIDENCE TIME RESIDENCE TIME –The time it takes air to cross a distance equal to the thickness of the filter without accounting for the resistance of the media through which it travels.

Definitions REMOVAL EFFICIENCY REMOVAL EFFICIENCY –The fraction of the contaminant that, once in contact with the media, is removed by either physical or chemical means. CAPACITY CAPACITY –The amount of contaminant the media is capable of removing. This determines the life of the filter.

Filter Options Partial bypass Partial bypass –easy to retrofit –lower cost –low efficiency –low media weights –shorter life –Disposable Total Retention Total Retention –packed bed systems –higher cost –high efficiency –high media weight –longer life –may be recycled depending upon media

Sample Questions Two main methods for molecular contaminant removal are? Two main methods for molecular contaminant removal are? Adsorption and Chemisorption Humidity can hinder? Humidity can hinder?Adsorption Particle bypass cells allow for retrofit without? Particle bypass cells allow for retrofit without? Large pressure increases in the system

Thank you. Other Questions?