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What Is Driving the Global Shift Toward Green Hydrogen?
The world’s energy demand is still largely supplied by fossil fuels, resulting in over 32.3 billion metric tons of CO2 emissions from combustion alone. These emissions, along with other pollutants, are major contributors to climate change, and their effects are increasingly visible through severe weather events.
Governments around the world are accelerating the transition to a low carbon future. The European Green Deal targets carbon neutrality by 2050, and even major oil exporting nations lole Saudi Arabia are investing in sustainable developments like NEOM. Investment in renewable energy is also rising quickly across the United States and Asia, including solar, wind and renewable diesel.
Hydrogen is becoming a key enabler of this shift. It produces only water vapor when used as fuel, and when generated from renewable sources, green hydrogen supports deep decarbonization across mobility, energy storage, industrial processes and power generation.
How Is Hydrogen Produced and What Makes “Green” Hydrogen Different?
Hydrogen can be produced through multiple pathways, each categorized by color:
- Grey hydrogen: produced by steam methane reforming of natural gas; lowest cost at ~$1.25–$3.50/kg.
- Blue hydrogen: steam reforming with added carbon capture to eliminate CO2 emissions.
- Green hydrogen: produced by electrolysis powered by renewable energy (wind, solar, hydropower).
Global hydrogen demand exceeds 70 million tons per year, primarily for refining and ammonia production. By 2050, demand is expected to reach 500 million tons, requiring massive expansion of green hydrogen production capacity. Although technically feasible, high capital costs and stringent purity specifications remain major barriers.
Hydrogen production process
What Are the Main Electrolysis Technologies for Green Hydrogen Production?
Electrolysis splits water into hydrogen (cathode) and oxygen (anode). The three major electrolyzer types are:
- AEL (Alkaline Electrolyzer) uses liquid KOH electrolyte; most widely used.
- PEM (Polymer Electrolyte Membrane) uses solid polymer electrolyte; rapidly gaining adoption.
- SOEC (Solid Oxide Electrolyzer Cell) uses solid ceramic electrolyte; least developed and not yet commercial at scale.
Regardless of technology, the output hydrogen stream requires extensive purification to meet fuel cell grade specifications (e.g., max 5 ppm oxygen and 5 ppm water). Typical post electrolysis impurity levels exceed these limits significantly.
Comparison of AEL, PEM, and SOEC electrolyzers used for green hydrogen production.
Contaminants in Hydrogen & How They Are Removed
Hydrogen produced by electrolysis contains liquid, solid and gaseous contaminants that must be removed to achieve required purity levels. For fuel cell applications, hydrogen must meet 5 ppm oxygen and 5 ppm water, yet alkaline systems can produce 2000–6000 ppm oxygen and >2000 ppm water, making purification essential.
Contaminants Present
- Liquids: Water and electrolyte (AEL), plus additional water and compressor oil droplets formed after compression.
- Solids: Particles from incoming water, electrolyte (AEL), corrosion and wear from pumps/compressors, and dryer adsorbent fines.
- Gaseous: Oxygen carried over from the electrolysis reaction, requiring removal by catalytic recombination.
Purification Sequence
- Liquid/gas separation to remove bulk water and electrolyte using gravity separators, vane separators, mist eliminators, or high efficiency coalescers.
- Post compression coalescing to remove newly condensed water and compressor oil droplets before deoxygenation.
- Deoxygenation via catalytic recombination, which also produces additional water.
- Drying using TSA or PSA units to remove remaining moisture.
- Final particulate filtration with absolute rated filters to capture solids and drier fines.
How Are Liquid Contaminants Removed After Electrolysis?
Immediately after the electrolyzer, the hydrogen/water mixture enters the liquid/gas separation stage, where bulk liquid is removed before compression.
Separation options include:
- Gravity separators (knock out drums): remove large droplets (>300 µm).
- Mist eliminator pads: remove droplets down to ~10 µm; require large vessels and low gas velocities.
- Vane separators: also remove ~10 µm droplets while operating at higher gas velocities.
- High efficiency liquid/gas coalescers: capture droplets as small as 0.1 µm with no re entrainment and minimal pressure drop.
Coalescers provide the highest performance and enable compact system design compatible with the downstream steps shown in the diagram.
Pall high efficiency coalescer solutions:
- SepraSol™
- SepraSol™ Plus
- Medallion™
- Coreless liquid/gas coalescers
Typical process flow for hydrogen production using an AEL electrolyzer, highlighting key liquid, gas and solid removal steps.
| # | Application | Technology |
|---|---|---|
| 1 | Water intake conditioning, particulates removal | Micro-/Ultra-Filtration |
| 2 | Alkalyne Electrolyser purification. KOH | Particulate Filter |
| 3 | Water separation, compressor protection | Liquid/Gas Coalescer |
| 4 | Water separation, catalyst protection | Liquid/Gas Coalescer |
| 5 | Water separation, solids removal, drier protection | Gas Filter, Liquid/Gas Coalescer |
| 6 | Solids removal, product quality | Gas Filter |
Why Is Filtration After Compression Essential?
During compression, additional water and compressor oil droplets condense into the hydrogen stream. These contaminants can damage deoxygenation catalysts and reduce system efficiency.
High efficiency coalescers downstream of compressors provide reliable removal of both water and oil aerosols. Pall’s SepraSol™ and SepraSol™ Plus technologies are widely used in hydrogen and gas processing industries.
Pall liquid/gas high efficiency coalescer system
Depending on where solids appear in the process, filtration solutions may include:
- UltiKleen™ and IonKleen™ filters for ultrapure water treatment in PEM systems
- Ultipleat® High Flow filters for electrolyte filtration in AEL systems, and gas particle filters downstream of drying units to capture remaining fines.
Case Studies: How Are Pall Solutions Used in Green and Blue Hydrogen?
Liquid/Gas Separation in AEL Systems
Liquid/Gas Separation After Compression
Char Removal in Blue Hydrogen
What Happens After Hydrogen Production? (Storage & Purification)
After production, hydrogen is stored as compressed gas, in salt caverns, or converted to ammonia through the Haber Bosch process. During storage and transfer, the gas may pick up fine solids or compressor oil, so Pall gas filters and coalescers help maintain the required quality for end uses such as fuel cells. Pall also supports ammonia production with more than 200 filtration and coalescer installations worldwide.
Pall’s Role in the Future of Green Hydrogen
Green hydrogen is essential for decarbonization but remains costly due to high electrolyzer prices and strict purity specifications. Pall supports the industry with a full portfolio of separation and purification technologies, including liquid and gas coalescers, absolute rated particle filters, and ultrapure water systems. Continued innovation will help improve efficiency and support wider adoption of green hydrogen.
Download the full white paper for a deeper look at contamination challenges and purification solutions in green hydrogen production.