How to Choose Chemical Filters: Key Procurement Considerations for Acid Gases, Ammonia, and VOCs

When unpleasant odors occur in a factory, or a process requires the control of gaseous molecular contaminants (AMC), procurement specifications often simply state “activated carbon filters.” However, odors can originate from different gases, and the properties of acid gases, ammonia, and various volatile organic compounds (VOCs) differ significantly. Selecting a filter based solely on the presence of activated carbon may result in a filter with suitable dimensions but insufficient evidence of performance against the target contaminants.

How should you select a chemical filter? Start by identifying the target gases, then verify the on-site concentrations, airflow, temperature, humidity, and control objectives. Next, ask the supplier to specify the corresponding filter media type and provide relevant test data. Pressure drop, price, and carbon content can all be included in the comparison, but none of these factors alone can demonstrate a filter’s removal performance for a specific gas.

Table of Contents

• Translate odor concerns into specific contaminant requirements
• Verify the filter media type, not just the V-shaped design
• How to evaluate chemical filter test data
• Consider dimensions, sealing, and replacement criteria
• What information should you prepare before requesting a quotation?
• Frequently Asked Questions (FAQ)
  • Can a standard activated carbon filter handle acids, alkalis, and all VOCs?
  • Does the V-shaped design of a chemical filter mean a higher removal efficiency?
  • If the pressure drop is normal, does that mean the chemical filter does not need replacement?
  • Can a filter be selected based only on the presence of unpleasant odors?

Translate Odor Concerns into Specific Contaminant Requirements

Descriptions such as “acidic odor” or “chemical smell” provide useful clues about site conditions, but they are not sufficient to determine the appropriate filter media. Procurement and engineering personnel should document process materials, emission sources, existing test results, and the times and locations where odors occur. Whenever possible, identify the target gases. Acid gases, ammonia or amines, and different types of VOCs should each be matched with filter media confirmed by the supplier to be suitable for the specific contaminants.

If multiple contaminants are present at the same site, provide their combinations and known concentrations to the supplier. This helps prevent the test results for a single gas from being incorrectly applied to the entire facility. Filtration equipment should not replace source control. Inspect leaks, local exhaust systems, and ventilation pathways first, then determine which portion of the airflow needs chemical filtration. This approach helps establish clear procurement requirements.

Verify the Filter Media Type, Not Just the V-Shaped Design

Hanklin’s V-shaped chemical filter product page lists filter media options for acid gas removal, alkaline gas removal, and VOC removal, with applications including semiconductor manufacturing, microelectronics, and pharmaceuticals. When requesting a quotation, specify the target contaminants and the corresponding filter media model. Not all V-shaped filters should be assumed to contain the same media formulation.

The product page also lists galvanized steel or plastic frames, along with operating conditions of no more than 40°C and a relative humidity of no more than 70% RH. Actual operating limits must still be verified against the technical documentation for the specific model being ordered and the measured conditions at the installation site.

If the air intake is near a heat source or the system may experience condensation, provide temperature and humidity data before selecting a filter. Do not rely solely on assumptions about typical indoor conditions.

How to Evaluate Chemical Filter Test Data

The performance of gaseous contaminant control cannot be demonstrated by particulate filter ratings such as MERV or HEPA classifications. At a minimum, evaluation documents should specify the test gas, inlet concentration, airflow or face velocity, temperature and humidity, and the method used to determine removal efficiency or contaminant breakthrough. Results obtained under different test conditions should not be compared directly without accounting for these differences.

ISO 10121-2 specifies test methods for gas-phase air-cleaning devices used in general ventilation, while ASHRAE 145.2 provides a laboratory evaluation method for gas-phase air-cleaning devices. During procurement, ask suppliers whether they can provide relevant test reports based on these standards, and verify the differences between the test conditions and actual operating requirements.

A statement that a filter has been “tested according to a particular standard” does not mean it will achieve the same removal efficiency for every gas.

Consider Dimensions, Sealing, and Replacement Criteria

When providing equipment opening dimensions, also confirm the actual filter dimensions, frame type, airflow direction, mounting and sealing methods, design airflow, and allowable system pressure drop. If air leaks around the filter, some of the airflow may bypass the filter media. Even when the media is suitable, such leakage can prevent the system from achieving its intended contaminant control performance.

The service life of chemical filter media depends on factors such as inlet concentration, gas type, mixed contaminants, airflow, and humidity. Therefore, a single fixed replacement interval should not be applied to every facility.

Consider establishing a monitoring and recordkeeping program for target gases upstream and downstream of the filter, based on process risks, and discuss replacement criteria with the supplier. Pressure drop helps track airflow resistance, but it cannot independently confirm whether the filter’s gas adsorption capacity has been exhausted.

What Information Should You Prepare Before Requesting a Quotation?

We recommend preparing the following five categories of information:

1. Target gases: Names, sources, and known concentrations of the contaminants.
2. Operating conditions: Equipment airflow, daily operating hours, and intended installation location.
3. Environmental conditions: Inlet air temperature, relative humidity, and the possibility of condensation.
4. Filter specifications: Filter opening dimensions, available installation depth, and mounting requirements.
5. Control objectives: Desired outlet concentrations or process control targets.

If some information is not yet available, explain the known conditions and identify the measurements that still need to be taken. Ask the supplier to help determine what additional data is required.

If your factory, laboratory, or HVAC system needs to control acid gases, ammonia, or VOCs, you can provide the information above to Hanklin and inquire about suitable V-shaped chemical filter media types, frame configurations, and test documentation.

Final filter selection should always be based on the actual contaminants and operating conditions at the installation site.

Frequently Asked Questions (FAQ)

Can a standard activated carbon filter handle acids, alkalis, and all VOCs?

This should not be assumed. Different gases may interact with filter media in different ways, and their removal capacities and test conditions may vary. Provide the names of the target gases and verify the corresponding filter media type and test data with the supplier.

Does the V-shaped design of a chemical filter mean a higher removal efficiency?

The V-shaped design describes the filter’s structural configuration. Its appearance alone does not determine the removal efficiency for a specific gas. Performance data must still be evaluated based on the target gas, airflow, and test conditions.

If the pressure drop is normal, does that mean the chemical filter does not need replacement?

Not necessarily. Pressure drop reflects airflow resistance but cannot independently indicate whether gaseous contaminants have broken through the filter. Replacement decisions should incorporate target gas monitoring, operating records, and supplier recommendations.

Can a filter be selected based only on the presence of unpleasant odors?

Preliminary solutions can be discussed, but the contaminant sources and target gases should be identified before final selection. Airflow, temperature, humidity, and dimensional information should also be provided to reduce the risk of choosing unsuitable filter media.