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

2. Agenda Contaminant Control Removal Options Media Types Definitions
Adsorption
Chemisorption
Catalysis
Media Types
Definitions
Filter Options
Here’s what we are going to cover in this chapter

3. Control Options Source Control Ventilation Removal Control
Remove the contaminant source
Ventilation
Increase outdoor air
Removal Control
Remove contaminants via physical or chemical means
There are three main ways to control molecular contaminants and they are the same as particulate contaminants – source control, Ventilation or dilution, and Removal control.

4. Molecular Filtration TYPES Physical - Adsorption
Activated carbons
Chemical - Chemisorption
Potassium permanganate impregnated media
Chemically treated activated carbons
Catalysis
The two main types of removal control include medias that utilize physical adsorption or chemical reaction, or a combination of these two with a catalyst

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
Adsorption is…

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

9. 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.

10. REMOVAL EFFICIENCY CAPACITY Definitions
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. Filter Options Partial bypass Total Retention 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

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?