NAFA Guide To Air Filtration

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

2. Agenda • Contaminant Control • Removal Options • Adsorption • Chemisorption • Catalysis • Media Types • Definitions • Filter Options

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

4. Molecular Filtration • TYPES • Physical - Adsorption • Activatedcarbons • Chemical - Chemisorption • Potassium permanganate impregnated media • Chemically treated activated carbons • Catalysis

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

6. Types • 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

7. Types • 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.

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

9. Definitions • RESIDENCETIME • 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.

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

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

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

13. Thank you. Other Questions?