Molecular Filtration National Air Filtration Association Technical Seminar

Molecular Filtration National Air Filtration Association Technical Seminar May, 2004 Paula Levasseur, CAFS Cameron/Great Lakes

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

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

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

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

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

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.

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

Definitions • 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 – 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.

Filter Options • 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