Extended Media Surface Rigid Air Filters Carbon Filtration Whitepaper

User Manual: Extended Media Surface Rigid Air Filters

Open the PDF directly: View PDF .
Page Count: 6

Effects of Carbon Filtration Type on Filter Efficiency

and Efficacy: Granular Loose-Fill vs. Bonded Filters

Chambre, Andre: CEO, Air Science, LLC

March 2014

Abstract

Activated carbon is used in a wide variety of purification techniques including

gas and water purification, metal extraction, water purification, pharmaceutical

manufacturing, gas masks, and air filters. Several physical forms of activated

carbon exist, including powdered, bead, and extruded, yet granular activated

carbon is one of the most commonly used for air filtration.

Activated carbon filters are produced in two main styles, granular multi-layer

free fill and bonded filters. Granular multi-layer carbon filters contain loose fill car-

bon media layered to meet specific chemical filtration needs. Bonded filters utilize

various chemical processes to bond the carbon particles into a rigid matrix.

This study tested the hypothesis that granular activated carbon filters, specifically

Air Science filters utilizing the Multiplex™ Filtration System, have a longer useful

life and greater filtering efficiency with no associated performance defects than

bonded filters.

To test this hypothesis, a third-party laboratory (IBR Laboratories) analyzed the

adsorption efficiency of an Air Science granular loose fill filter and a dimensionally

identical bonded carbon filter from RSE Incorporated based on the SEFA 9

(2010) benchmark testing methods.

The Air Science ASTM-001 granular filter retained 1709.7 grams of isopropanol at a

run time of 450 minutes before reaching 1% threshold limit value (TLV). The bonded

filter ASTM200-001 retained 1348.8 grams of isopropanol after 355 minutes before

reaching 1% TLV. This difference of 360.9 grams represents a 26.8% greater efficiency

than a comparable bonded filter. The Air Science filter took 95 minutes longer to

reach the 1% TLV saturation, suggesting a significantly longer useful life than that

of the bonded filter.

The results of this study verify that under similar laboratory settings, Air Science

granular carbon filters have a higher filtering efficiency and will maintain safe

operating conditions for a longer period of time than similarly-sized bonded filters.

Air Science granular carbon filters are also easier for operators to change out,

have greater stability in shipping / packaging, and offer a variety of chemical

impregnation options to meet specific filtration needs.

p:2Andre Chambre, CEO, Air Science, LLC. March, 2014

Air Science 120 6th Street • Fort Myers, FL 33907 • T/239.489.0024 • Toll Free/800.306.0656 • F/800.306.0677 • www.airscience.com

Background

Activated carbon includes a wide range of amorphous car-

bon-based materials prepared to exhibit a high degree of poros-

ity and an extended interparticulate surface area. These qualities

give activated carbon excellent adsorbent characteristics that

make carbon very useful for a wide variety of processes including

filtration, purification, deodorization, decolorization, purification

and separation.

The effectiveness of activated carbon as an adsorbent is

attributed to its unique properties, including “large surface area,

a high degree of surface reactivity, universal adsorption effect,

and pore size” (Figure 1). Due to its increased porosity, a single

gram of activated carbon contains 500-2,000m2 aggregate

surface area.1

Activated carbon is widely used in critical purification techniques

in gas purification, metal extraction, water purification, medicine,

gas masks, and air filters.

Figure 1: Internal Pore of Activated Carbon Granule

GASES AND

CHEMICALS

PORES

ACTIVATED

CARBON

Production

Activated carbon is produced from a wide variety of carbon-rich

raw materials, including wood, coal, peat, coconut shells, nut

shells, bones and fruit stones. New materials are currently under

investigation as sources for activated carbon.

The two primary types of activation are:

• Chemical Activation. This technique is generally used for the

activation of peat and wood based raw materials. The raw

material is impregnated with a strong dehydrating agent;

typically phosphoric acid or zinc chloride mixed into a paste

and then heated to temperatures of 500 - 800°C to activate

the carbon. The resultant activated carbon is washed, dried

and ground to powder.

• Steam Activation. This technique is generally used for the

activation of coal and coconut shell raw material which is

usually processed in a carbonized form. Activation is carried

out at temperatures of 800 - 1100°C in the presence of steam.

1 Value Added Products from Gasification – Activated

Carbon, By Shoba Jhadhav, The Combustion, Gasification

and Propulsion Laboratory (CGPL) at the Indian Institute of

Science(IISc).

Principles of Adsorption

The main principle on which the filtration of gas molecules

is based is the concept of adsorption. Two main processes

by which adsorption take place are physical adsorption

and chemisorption.2

Physical Adsorption

Physical adsorption is non-specific and adsorption of the gas

molecule is by diffusion (Brownian movement) or adsorption/

condensation using Van Der Waals’ forces.The gas molecules

move into an empty area and diffuse into the pore where they

impact the walls and are trapped. The number of pores present

in the carbon is vast and therefore the total surface area is

extremely large. Depending on the carbon used and the type of

filter, aggregate surface area can be in the range of 2,000m2/g

(roughly equivalent to about 4 football fields).3

Chemisorption

The physical process of adsorption is followed by chemical

adsorption (chemisorption). This is a chemical reaction in which

the two substances react together and the resultant chemical

is trapped on the filter material.The impregnation of filter media

can greatly extend the range of gases that can be removed from

the air stream.

A number of physical forms of activated carbon exist, including

powdered, bead, and extruded, yet granular activated car-

bon is the most commonly used for air filtration. Compared to

powdered activated carbon, granular activated carbon has a

much larger particle size with a small external surface, which

increases its diffusion rate and makes it the carbon of choice for

vapor adsorption. Activated carbon filters can be manufactured

in a number of forms, including bonded, multi-layer free fill, and

hybrid which can be impregnated with chemicals to assist in the

adsorption process and increase filter efficacy.

2 Value Added Products from Gasification – Activated

Carbon, By Shoba Jhadhav, The Combustion, Gasification

and Propulsion Laboratory (CGPL) at the Indian Institute of

Science(IISc).

3 www.airscience.com/22

p:3Effects of Carbon Filtration Type on Filter Efficiency and Efficacy: Granular Loose-Fill vs. Bonded Filters

Regulations / Compliance

Carbon filter manufacturers can perform testing and compliance

reviews for a number of state, local, and internal company

standards; however the methods most widely used as general

industry guidelines are the Scientific Equipment & Furniture

Association (SEFA) 9-2010 Recommended Practices for Ductless

Enclosures. Manufacturers will typically request a questionnaire

be completed during the purchase of a filter to ensure that the

list of chemicals to be used in the fume hood are sufficiently

compatible with the filter type based on SEFA 9-2010 standards.4

The SEFA 9-2010 guidelines provide recommended benchmark

testing for ductless fume hood filtration according to three

classifications:

• DH I: Nuisance odors and non-toxic vapors only.

No testing required.

• DH II and DH III: General laboratory fume hoods

containing noxious or potentially harmful fumes.

Testing, hood maintenance, and calibration must

be closely monitored and recorded.4

Filter monitoring should aim to detect the period of initial break-

through (Figure 2) and in all cases should warn the operator well

before the permissible exposure level (PEL) is reached.5 For the

purposes of this study, reaching 1% threshold limit value (TLV)

was a sufficient benchmark in both concentration and temporal

monitoring to determine the efficiency of carbon filtration under

normal operating conditions. Threshold limit value is the level

at which the American Conference of Governmental Industrial

Hygienists (ACGIH) believes a worker can be exposed to a chemi-

cal daily for a working lifetime without adverse health effects.5

A concentration of 1% TLV captured for most chemicals is deter-

mined an accurate measure of filter efficiency, as determined

by SEFA 9-2010, 4.3.1 (for more information on benchmark testing

procedures see SEFA 9-2010, 4.3.1 and ASHRAE 110-1995 for

instrumentation setup).

Figure 2: Chemical Adsorption and Breakthrough

of Carbon Filter

ACTIVE FILTER

ZONE NEW FILTER MIDLIFE END OF USE

Adsorption takes place in a filter bed in what is known as the active

filter zone (represented above as dark saturated area). As the filter

is used this active zone progressively moves up the filter bed until it

approaches the top surface of the filter. At this point there is an initial

breakthrough by the contaminant vapor(s), and thereafter the percent-

age of contaminant gas that escapes filtration increases.

4 Recommended Practices for Ductless Enclosures. Scientific

Equipment & Furniture Association (SEFA) 9-2010. Fourth

Edition, Version 1.0.

5 www.acgih.org

Types of Carbon Filters

Activated carbon filters are constructed in two main styles,

granular multi-layer free fill and bonded filters. Granular multi-

layer carbon filters contain loose fill carbon media layered to

meet specific filtration needs. Granular carbon media is filled into

a solid filter frame which allows minimal media settling for optimal

airflow through the loose carbon fill. Granular activated carbon

filters can contain carbon impregnated for a single target analyte

or can be layered with carbon impregnated for a number of

analytes, increasing the range of containment. Granular filtration

maintains the original physical and chemical properties of

the carbon and offers the greatest amount of surface area for

chemical bonding sites.

Bonded filters utilize the same granulated carbon as loose-fill

carbon filters, but use various chemical processes to bond the

carbon together into a solid matrix. This creates a rigid carbon

filtration system that is often chosen for its convenience of

handling. Bonded filter manufacturers claim that due to the solid

nature of the filter, there is less chance of user exposure to the

chemicals contained within a used filter. Bonded filters are also

typically claimed to be “dust-free” because the carbon particles

are bonded together in a solid form. It is possible, however, that

as a result of the brittleness of the bonded filter, that partial filter

erosion may take place in shipping and allow fine particles to

be exhausted during initial fume hood start-up following a filter

change out.

Figure 3: Granular Loose-Fill vs Bonded Carbon

Filter Construction

LOOSE-FILL

CARBON

BONDED

CARBON

p:4Andre Chambre, CEO, Air Science, LLC. March, 2014

Air Science 120 6th Street • Fort Myers, FL 33907 • T/239.489.0024 • Toll Free/800.306.0656 • F/800.306.0677 • www.airscience.com

Issues with Bonded Carbon Filters

Bonded carbon filters are widely marketed as having equal,

if not better efficacy than loose fill granulated carbon filters.

Manufacturers claim that a solid filter matrix minimizes dead

zones in the filters and maximizes capacity. Others in the industry,

however, have questioned the effect that a solid matrix has on

filter performance.

Regardless of the proprietary process, to create a solid matrix

from loose granulated carbon, the physical and chemical

properties of the carbon particles must be altered. These

alterations likely have detrimental effects on the ability of the

carbon particles to bond with target compounds and could

also decrease flow rate compared to a loose fill filter.

The Bonding Process

The bonding process typically requires the activated carbon

be soaked in water for approximately 24-hours prior to being

bonded. This soaking can leach out the impregnated chemicals

required to effectively manage certain types of vapors, decreas-

ing the efficacy of the final filter.

Additionally, the bonding agents used to create bonded

carbon filters are normally a type of resin, such as polystyrene.

The amount of resin used has a critical impact on the adsorption

capacity of the filter and it is not inconceivable that over half

of the space on the carbon granules can be covered with the

bonding agent. This renders the filtering capacity of the carbon

granules at least temporarily useless and may have long term

effects on filter efficiency.

This study was derived to test the efficacy and performance of

granular loose fill filters (specifically Air Science Brand, ASTM001

filters) against that of a general purpose bonded filter (RSE

Incorporated) based on all of the aforementioned performance

issues with bonded filters.

Hypothesis

Granular Activated Carbon filters, specifically Air Science filters

utilizing the Multiplex Filtration System, have a longer useful life

than bonded filters with none of the associated performance

defects. Granular loose fill filters will have a greater filtering

efficiency (higher retention capacity) than bonded filters do

and will have a longer life before reaching 1% of TLV.

Granular loose fill filters may also have additional perform-

ance benefits in the form of ease of handling, more stability

in shipping / packaging, and fewer chemical impregnation

issues compared to bonded filters.

Methods

To test this hypothesis, a third-party laboratory (IBR Laboratories)

analyzed the adsorption efficiency of an Air Science granular

loose fill filter compared to a dimensionally identical bonded

carbon filter from RSE Incorporated based on the SEFA 9-2010

benchmark testing methods.

The carbon filters were loaded into a Purair 10 Advanced Ductless

Fume Hood and 99.9% isopropanol was evaporated from a hot

plate placed inside the hood. Total mass of isopropanol evap-

orated and the concentration of isopropanol in downstream

sample air (parts per million or ppm) was measured over time

by a MIRAN® SapphIRe Ambient Air Analyzer placed 18 inches

above the center of the exhaust grid. Air concentration readings

were recorded every 15 minutes until the reading measured 1%

of TLV as determined by SEFA 9-2010 recommendations.6,7

Similar cabinet conditions were maintained throughout testing

for both the granular loose fill filter and the bonded filter. Table

1 depicts environmental and equipment conditions maintained

during testing of both filter types.

Table 1: Conditions of Ductless Fume Hoods During Testing

Granular Filter Bonded Filter

Temperature ºF 71 70

Relative Humidity % 46 49

Barometric Pressure mm Hg 739 737

Face Velocity FPM 100 100

6 IBR Test Report: Job Number 14709, January 11, 2014. IBR

Laboratories.

7 IBR Test Report: Job Number 113576A, January 21, 2013. IBR

Laboratories.

p:5Effects of Carbon Filtration Type on Filter Efficiency and Efficacy: Granular Loose-Fill vs. Bonded Filters

Results

The graphs below depict the concentration of isopropanol

absorbed over time by each of the two filters. The Air Science

ASTM-001 granular filter was able to retain 1709.7 grams of isopro-

panol at a run time of 450 minutes before reaching 1% TLV. The

bonded filter ASTM200-001 retained 1348.8 grams of isopropanol

after 355 minutes before reaching 1% TLV. This difference of 360.9

grams represents a 26.8% greater efficiency than comparable

bonded filter. Additionally, the Air Science filter took 95 minutes

longer to reach the 1% TLV saturation, indicating a significantly

longer useful life than that of the bonded filter.

Graph 1: Filtration Efficiency of a Granular Loose-Fill

Carbon Filter Compared to a Bonded Carbon Filter

0.0

1.0

2.0

3.0

4.0

5.0

0.0

0.0 200 400 600 800 1000 1200

114.0 228.0 341.9 455.9 569.9 683.9 797.9 911.9 1025.8 1139.8 1253.8 1367.8

1400

concentration

Evaporated Ivo...

0.0

1.0

2.0

3.0

4.0

5.0

0.0 250 500 750 1000 1250 1500 1750

concentration

Time

.0

.20

.40

.60

.80

1.4

1.2

1.0

1.6

percentage

.0

.20

.40

.60

.80

1.4

1.2

1.0

percentage

0 75 150 225 300 375 450

Downstream Concentration (PPM)

Total Mass of lsopropanol Evaporated (grams)

5

4

3

2

1

0

0250 500 750 1,000 1,25 0 1,500 1,750

Bonded Carbon Filter Granular Carbon Filter

Graph developed from the provided IBR Laboratories data, showing

concentration of isopropanol over time for both filters comparatively.

Graph 2: Time to Reach TLV for a Granular Loose-Fill

Carbon Filter and a Bonded Carbon Filter

0.0

1.0

2.0

3.0

4.0

5.0

0.0

0.0 200 400 600 800 1000 1200

114.0 228.0 341.9 455.9 569.9 683.9 797.9 911.9 1025.8 1139.8 1253.8 1367.8

1400

concentration

Evaporated Ivo...

0.0

1.0

2.0

3.0

4.0

5.0

0.0 250 500 750 1000 1250 1500 1750

concentration

Time

.0

.20

.40

.60

.80

1.4

1.2

1.0

1.6

percentage

.0

.20

.40

.60

.80

1.4

1.2

1.0

percentage

0 75 150 225 300 375 450

Percentage of TLV

0200 400 600 800 1,000 1,200

Time (minutes)

100

75

50

25

0

Bonded Carbon Filter Granular Carbon Filter

50% TLV

AT 960 MIN

10 0% TLV

AT 1,155 MIN

0.0

1.0

2.0

3.0

4.0

5.0

0.0

0.0 200 400 600 800 1000 1200

114.0 228.0 341.9 455.9 569.9 683.9 797.9 911.9 1025.8 1139.8 1253.8 1367.8

1400

concentration

Evaporated Ivo...

0.0

1.0

2.0

3.0

4.0

5.0

0.0 250 500 750 1000 1250 1500 1750

concentration

Time

.0

.20

.40

.60

.80

1.4

1.2

1.0

1.6

percentage

.0

.20

.40

.60

.80

1.4

1.2

1.0

percentage

0 75 150 225 300 375 450

1% TLV

AT 355 MIN

1% TLV

AT 450 MIN

A Granular Filter and

a Bonded Filter at 1% TLV

Graph showing 1% TLV, 50% TLV, and 100% TLV for granular loose-fill

carbon filter as determined by SEFA 9-2010 testing.

Discussion

The results of this study verify that under similar laboratory

settings, granular carbon filters will maintain safe operating

conditions for a longer period of time than bonded carbon filters.

Bonded manufacturing causes some of the pores on the carbon

(sites of reaction) to be crushed or destroyed, which decreases

the adsorption capabilities. This can lead to additional negative

effects, including a noticeable pressure drop in the fume hood

and less efficient air filtering capabilities over the life of the filter.

Additional Downsides to Bonded Carbon Filters

Bonded filters tend to weigh more than granular filters (34 lbs.

for the bonded filter versus 22 lbs. for the granular carbon filter

in this test) which can make filter change out more difficult, while

their brittle nature can lead to quality issues in the shipping and

handling process.

Additionally, bonded filters are typically only offered with a

single type of impregnation due to the difficulty associated with

leaching during the bonding process. This can limit the use of

the fume hood in which bonded filters are installed and increase

the expense of maintaining compliance for certain laboratory

operating procedures.

Benefits of Air Science Granular Carbon Filters

Air Science granular carbon filters have none of the issues associ-

ated with bonded filters, and provide a higher retention capabil-

ity over the useful life of the filters. This decreases the frequency

and associated downtime and expense of filter change outs.

Air Science granular carbon filters utilize the MultiplexFiltration

System, which consists of a pre-filter, main filter and optional

safety filter to create a combination of chemical and physical

architecture customized to each application. The multiplex

option permits one or more filtration types to be combined within

a single filter housing to meet a wider range of multiple-use

applications. Multiplexing allows for the capture of acids, bases,

and when paired with HEPA or ULPA filters, particulates such as

biological aerosols.8

An additional benefit of the Air Science granular carbon filter is

fire suppression. Granular carbon filters used in enclosure fire tests

resisted ignition and helped suppress the fire. It is suspected that

under similar test conditions, bonded filters would display some

ignition due to the various chemical resins used to bond the

carbon particulates together.

The Air Science granular carbon filter outperforms bonded filters in

nearly every way. Air Science granular carbon filters are self-con-

tained assemblies sized to fit the specified product model number,

and configured to optimize air flow across 100% of the filter surface

area for maximum efficiency, prolonged filter life, optimal diffusion

and saturation capacity, and enhanced user safety.

8 www.airscience.com

1% TLV AT

1709.7 GRAMS

1% TLV AT

1348.8 GRAMS

120 6th Street • Fort Myers, FL 33907

T/239.489.0024 • Toll Free/800.306.0656 • F/800.306.0677

www.airscience.com

©2014 Air Science OW 10578 03/14

Effects of Carbon Filtration Type on Filter Efficiency and Efficacy: Granular Loose-Fill vs. Bonded Filters

Air Science, Multiplex and Purair are registered trademarks of Air Science Corporation.

p:6

Andre Chambre

Andy Chambre is the founder and CEO of Air Science, LLC and

has been associated with the ductless fume hood industry for

more than 25 years. He was formerly the US Vice President for

Captair Labx and President of Astec Microflow US. He was named

President of Filtco Corporation in 2003 and currently also serves

as a Director of Air Science Technologies Ltd. in the UK.

Mr. Chambre has written numerous articles on fume hood

safety and assisted in the development of safety standards by

serving on various committees such as the Canadian Standards

Association subcommittee on fume hoods and the SEFA 9

Ductless Enclosures Committee.

Acknowledgements

This study was completed as an independent test by IBR

Laboratories on products provided by Air Science USA LLC.

Sources

• Value Added Products from Gasification – Activated

Carbon, By Shoba Jhadhav, The Combustion, Gasification

and Propulsion Laboratory (CGPL) at the Indian Institute of

Science(IISc).

• Recommended Practices for Ductless Enclosures. Scientific

Equipment & Furniture Association (SEFA) 9-2010. Fourth

Edition, Version 1.0. Accessed: www.sefalabs.com/files/

public/SEFA-9-2010-Ductless.pdf.

• IBR Test Report: Job Number 14709, January 11, 2014.

IBR Laboratories.

• IBR Test Report: Job Number 113576A, January 21, 2013.

IBR Laboratories.

Additional Information Sources

• www.airscience.com/22

• www.acgih.org