How to configure ULPA in corrosive gas and solvent environments?

This problem is encountered in semiconductor, chemical and pharmaceutical projects. People who ask usually have an implicit expectation: ULPA has a high rating and should be able to 'block' these gases.

But ULPA works on particles. It relies on fiber or membrane media to intercept particles, and gas molecules are several orders of magnitude smaller than particles, so the filtration mechanism is completely different. Corrosive gases and solvent vapors cannot be stopped by ULPA. This is not a product defect, but a functional positioning issue. For the specific division of labor, please refer to the relevant instructions on ULPA and AMC control.

Therefore, when configuring ULPA, the real problem to be solved is not 'how to let ULPA handle gas', but: in this kind of environment, whether ULPA itself can be used, how to use it, and what protection is needed.

First clarify the exposure location and gas source

Where the corrosive gas or solvent comes from and where it contacts the filter determines the direction of the protection plan.

Process exhaust direction. If the filter is located in the process exhaust path and corrosive components are directly in the airflow, both the filter material and the colloid will come into contact. In this case, the gas treatment plan needs to be evaluated first, and the gas cannot be sent directly to the ULPA.

Ambient air entrainment. If the filter is used for clean air supply, the inlet air itself is clean air, but there are traces of corrosive gases or solvent vapors in the workshop environment. These components may enter the system through fresh air or return air. Concentrations are usually lower, but long-term exposure may still affect the material.

Leakage or abnormal working conditions. When equipment leaks, pipelines are damaged, or process abnormalities occur, high-concentration gas may contact the filter in a short period of time. The impact of this emergency situation on materials is different from that of continuous low-concentration exposure, and it needs to be considered as an abnormal working condition in the plan.

Cleaning and maintenance procedures. Volatile components may accumulate near the filter during disinfectant, solvent wipes, or equipment cleaning. Where chlorine-containing disinfectants, peracetic acid or alcohol-based cleaners are used in pharmaceutical projects, this needs to be evaluated separately. For specific cleaning agent compatibility, please refer to the relevant instructions for sealant selection according to working conditions.

Only by clarifying the location and source of exposure can we determine what level of protection the filter requires. Filters located far away from the gas source have completely different protection requirements than those in direct contact with the gas flow. involving For the selection of ULPA ultra-high efficiency filters , gas exposure conditions should be used as input for material screening.

Material compatibility needs to be checked item by item

The composition of ULPA includes filter material, edge sealing glue, sealing gasket, outer frame and surface treatment. Different components have different tolerances to corrosive gases and solvents.

filter media. There are differences in the chemical resistance of fiberglass and PTFE. PTFE is generally chemically inert and stable in most acids, alkalis and organic solvents. The chemical resistance of fiberglass depends on fiber composition and surface treatment, and may be affected by certain strong alkali or hydrofluoric acid environments. For specific comparison, please refer to the relevant instructions on the selection of glass fiber and PTFE.

Edge sealing glue. Colloids are an easily overlooked aspect. The chemical resistance of different systems such as epoxy, polyurethane, and silicone varies greatly. Some solvents may cause the colloid to swell or soften, and some acidic gases may accelerate the aging of the colloid. When selecting, confirm the suitability of the colloid in the target medium and concentration.

Gasket. The chemical resistance of rubber-based sealing materials varies significantly. Fluorine rubber has good resistance to most solvents and acids and alkalis. Silica gel may swell in some solvents, and EPDM may be affected in chlorine-containing environments. Specific material selection is confirmed according to medium type and concentration.

Frame and finish. The anodized layer of aluminum alloys may be damaged in strong alkali or fluorine-containing environments. Stainless steel is resistant to most media, but chlorine-containing environments may cause pitting corrosion. The outer frame of the coating should be checked to see if the coating falls off or releases organic matter after contact with the medium. For specific frame material selection, please refer to the relevant instructions on the comparison between aluminum alloy and stainless steel.

Material designation alone does not prove suitability. 'Stainless steel' does not mean that it is resistant to all corrosion, and 'PTFE' does not mean that all parts are inert. Each material must be supported by corresponding data, and cannot be judged based on the name alone.

Gas treatment needs to be configured separately

If the gas stream does contain corrosive gases or solvent vapors that need to be controlled, this part of the treatment cannot be left to ULPA.

Chemical filtration section. For acidic, alkaline gases or specific organic matter, corresponding chemical filter materials can be selected. The media type, filling volume and replacement cycle are determined according to the gas type, concentration and treatment objectives.

Pre-washing or absorbing device. In high-concentration or high-load situations, scrubbers, absorption devices, or other pretreatment means may be needed to reduce the gas concentration to a level that can be processed by subsequent filtration sections.

Resistance accounting for combined systems. Adding gas treatment sections will increase the total system resistance. The resistance of ULPA itself is already high. After adding chemical filtration or other treatment stages, whether the fan still has enough residual pressure needs to be calculated together in the planning stage. Supporting FFU fan filter unit or The system of the fan filter unit at the EFU equipment end and the working point of the entire machine must also be re-confirmed.

ULPA location. In combined systems, ULPA is usually placed at the end and is responsible for final particle control. If the gas treatment section is upstream of the ULPA and the treated gas flow contacts the ULPA, the material selection is confirmed based on the residual composition after treatment. For specific combined system verification methods, please refer to the relevant instructions for pre-filter configuration.

What should you pay attention to during maintenance and operation?

In corrosive gas or solvent environments, the maintenance rhythm and inspection focus need to be adjusted.

Check the status of materials regularly. When replacing the filter element, check whether the colloid changes color, becomes soft or cracks, whether the sealing gasket is swollen or hardened, and whether there are signs of corrosion on the surface of the outer frame. These checks provide a better indication of material condition than just looking at pressure differentials. For specific glue seam inspection methods, please refer to the relevant instructions on glue seam cracking.

Record exposure events. If a leak, unusual discharge, or high-concentration exposure has occurred, record the time, location, and estimated concentration. Such events may accelerate material aging and should be paid attention to during subsequent inspections. involving The operating records of HEPA/ULPA air filters should contain these abnormal information.

The replacement cycle may need to be shortened. In corrosive environments, the long-term stability of materials may be lower than under normal operating conditions. The replacement cycle cannot simply use the experience value of the ordinary environment, but must be adjusted according to the actual inspection results.

Spare parts should be stored segregated. Uninstalled filters should be kept away from chemical storage areas to avoid contamination of packaging or materials during storage.

Project judgment example

A chemical workshop needs to configure a filter for the air supply at the equipment end. The air flow contains trace amounts of acidic gases.

The preliminary plan considers using ULPA directly, believing that high-grade filters can solve both particle and gas problems. After investigation, it was confirmed that acidic gases need to be treated separately - ULPA can only control particles and has no ability to remove acidic gases.

Adjusted configuration: Before the airflow enters the ULPA, a chemical filtration section is set up to handle acidic components. ULPA is placed at the end and is responsible for particle control. At the same time, based on the residual components after chemical filtration, confirm whether the ULPA filter material, colloid and sealing gasket are suitable. The total system resistance is recalculated, and the fan working point is confirmed according to the combined resistance curve.

The key to this case is: ULPA handles particles and gas handles separately. In corrosive environments, whether ULPA itself can be used and what materials it is made of is another question that needs to be answered separately. involving ULPA ultra high efficiency filter or HEPA high-efficiency filters are the same. The selection and configuration logic of

Selection and Acceptance Checklist

About Aili Industrial’s corrosion-resistant configuration packages

The core of ULPA configuration in corrosive gas or solvent environments is two things: gas treatment belongs to gas treatment, and ULPA itself is selected according to the suitability of the material. Only by doing the two things separately can the plan be established.

Aili Industry has independent manufacturing capabilities in filters, fans, control systems and sheet metal processing, and can provide ULPA ultra high efficiency filter、HEPA high-efficiency filter and supporting air supply equipment. For projects that come into contact with corrosive media, the gas composition, concentration, exposure time and installation conditions can be combined to assist in checking the filter material type, colloid scheme, seal material and outer frame treatment method. When the filter is matched with equipment such as FFU and EFU, the resistance calculation and fan operating point of the combined system can also be evaluated together during the planning stage.

Providing gas composition, concentration, contact conditions and treatment targets when requesting a quote will help confirm appropriate material options and system configurations. The specific selection is subject to the technical documents and test results confirmed by the project.