In the alkaline water electrolysis process, the hydrogen gas produced at the outlet of the electrolyzer typically has a purity of over 99.8%, but it carries impurities such as water vapor, trace oxygen, and alkali mist. If not removed, these impurities cannot meet the stringent requirements of modern industrial applications.
For example, in precision industrial fields:
Hard alloy coating processes require hydrogen purity of 99.999% and a dew point below -65°C.
Silicon production for semiconductor materials demands oxygen content in hydrogen to be less than 5 ppm and a dew point below -50°C. This is because dissolved oxygen can alter the resistivity of monocrystalline silicon or even change its conductive type.
Additionally, in high-temperature metal heat treatment, powder metallurgy, microelectronic circuits, optoelectronic components, and chemical synthesis, even trace oxygen or moisture in hydrogen can cause oxidation of raw materials at high temperatures, severely compromising product quality.
Therefore, hydrogen from the electrolyzer outlet often requires multi-stage treatment to meet industrial standards.
1. Gas-Liquid Separation
Purpose: Separate hydrogen and alkali solution from the gas-liquid mixture at the electrolyzer outlet to prevent alkali solution from adversely affecting downstream purification and drying equipment.
Process Flow:
The gas-liquid mixture enters a gas-liquid separator via piping. Due to the significant density difference between hydrogen and the alkali solution, the alkali solution settles downward under gravity, while hydrogen rises, forming a gas-liquid interface. The alkali solution accumulates at the bottom of the separator, while hydrogen passes through a water-filled scrubber in the upper section, where impurities are absorbed or dissolved. A demister inside the separator further captures liquid droplets, which coalesce on mesh pads and fall back into the alkali solution under gravity. The thoroughly separated hydrogen then proceeds to the next treatment stage.
2. Catalytic Deoxygenation
Purpose: Convert residual oxygen in hydrogen into water for oxygen removal.
Process Flow:
The separated hydrogen enters a deoxygenation tank, where a catalytic reaction occurs at high temperatures (150–200°C). Hydrogen and oxygen react over a palladium catalyst to form water. The catalyst adsorbs gas molecules, lowering the activation energy and ensuring complete reaction, reducing oxygen content to below 5 ppm. The reacted gas then passes through a cooler, where some water vapor condenses, yielding purer hydrogen.
3. Adsorption Drying
Purpose: Remove water vapor to meet industrial dew point requirements.
Process Flow:
A three-tank adsorption system is typically employed, with each tank filled with high-capacity, high-performance desiccants.
Hydrogen from the deoxygenation stage enters tank A at the bottom (in adsorption mode). The desiccant adsorbs moisture, and dried gas exits from the top.
Simultaneously, tank B (in regeneration mode) is heated to release adsorbed moisture as steam, which is carried away by hydrogen and condensed in a cooler.
Hydrogen then enters tank C (in standby mode) at the bottom, where residual moisture is adsorbed, and the final product hydrogen exits from the top.
This process achieves a dew point below -70°C (water content <10 ppm).
To ensure continuous operation, the tanks rotate cyclically. When tank A becomes saturated, tank C switches to adsorption mode, tank A enters regeneration, and tank B transitions to standby, maintaining uninterrupted purification.
Future Outlook
With the diversification of hydrogen applications, downstream industries are demanding even stricter purity (e.g., ≥99.999% high-purity hydrogen) and dew point (e.g., ≤-70°C ultra-low dew point) specifications. This trend is driving advancements in gas treatment technologies toward higher efficiency and intelligence, while also guiding performance optimization in hydrogen production systems. As breakthroughs emerge in materials science and process control, next-generation gas treatment technologies—combining rapid response and precise purification—will become a critical enabler for high-quality development across the hydrogen energy industry.
