KOH Removal from Hydrogen Gas — Choosing the Right Coalescing Media
Trace KOH aerosol in a hydrogen stream is removed effectively with borosilicate glass-microfibre coalescing elements for normal, moderate-temperature duty — that is our standard recommendation. Only under high caustic concentration, hot or saturated conditions do we switch the element media to PTFE or PP. In every case the housing is 316L with PTFE seals and a drainable sump.
Recognise the Symptoms
- Trace potassium hydroxide (KOH) aerosol carried over from an alkaline electrolyser or caustic scrubber into the hydrogen stream
- White or crystalline caustic deposits appearing downstream of an existing filter — a sign the media is not holding the aerosol
- Discolouration or shortened life of a glass-microfibre element specifically under hot, saturated or high-concentration caustic — the signal to move up to PTFE/PP media
- Corrosion of housing internals, seals, or drains not rated for alkaline media
- Requirement for a fully caustic-compatible filter: 316L body, PTFE seals, PTFE or PP element media, drainable sump
- Saturated, near-ambient-pressure hydrogen up to ~80 °C that must be cleaned without introducing new corrosion points
Root Causes
Media choice depends on severity
borosilicate glass-microfibre coalescers handle normal KOH aerosol at moderate temperature well and are the standard, cost-effective choice we supply for this duty. Only under high caustic concentration, hot (approaching ~80 °C) or fully saturated conditions does hot wet caustic begin to attack glass; there we specify PTFE or PP element media instead
Elastomer seals degrade in caustic service
NBR and standard FKM (Viton) seals swell and fail in KOH. PTFE seals are required for a durable caustic-resistant assembly
Carbon or plated steel housings corrode
an alkaline aerosol demands a 316L stainless steel body and drain hardware; lesser materials pit and fail
No drainable sump
coalesced caustic liquid must be collected and drained safely rather than re-entrained; a housing without a low-point drain lets liquid contact the element and downstream pipework
Sub-micron aerosol passes simple knock-outs
the fine KOH droplets (0.1–10 µm) generated by vigorous gas evolution require a genuine coalescing or membrane stage, not just a gravity separator
Diagnostic Checklist
- 1Match the element media to severity — borosilicate glass microfibre for normal/moderate KOH duty; sintered PTFE or PP for high concentration, hot or saturated caustic
- 2Specify a 316L stainless steel housing rather than carbon or plated steel
- 3Specify PTFE seals in place of NBR or FKM (Viton)
- 4Ensure the housing has a drainable sump / low-point drain for safe caustic collection
- 5What is the KOH concentration and aerosol loading? Higher concentration and loading push toward a coalescing + membrane combination
- 6Confirm the actual flow (e.g. ~200 SLPM), operating pressure (near ambient) and maximum temperature (e.g. 80 °C) so the housing and element are sized correctly
- 7Decide disposable vs. cleanable — sintered PTFE elements can be ultrasonically cleaned and reused, avoiding repeat consumable handling of caustic media
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