Application of Carbon Monoxide Removal Catalyst in Air Purification of Air Separation Prepurifier (PPU)

1. Introduction

The air separation unit (ASU) is the core equipment for the production of industrial gases (such as oxygen, nitrogen, and argon). The pre-purification unit (PPU) at the front end is crucial for the purification of raw air. If trace amounts of carbon monoxide (CO) in the air are not effectively removed, they will accumulate during the cryogenic distillation process, causing safety hazards (such as explosion risks) or affecting product purity. As a key material for PPU , the carbon monoxide removal catalyst converts CO into harmless CO₂ through catalytic oxidation , ensuring the safe and efficient operation of the air separation system.

2. Challenges of CO removal in PPU

 Low concentration, high toxicity: The CO concentration in the air is usually 1-10ppm, but it needs to be reduced to ppb level to meet process requirements.

 Competing Response Interference:  PPU needs to simultaneously remove combustibles such as H₂ and CH₄ , and the catalyst needs to have high selectivity.

 Complex working conditions: Normal temperature to low temperature (-40°C to 50°C) and variable humidity (humidity fluctuations during the adsorption cycle) environment pose challenges to the activity and stability of the catalyst.

3. Principles and characteristics of CO removal catalysts

3.1 Catalytic mechanism

CO removal is mainly achieved through low-temperature catalytic oxidation reaction: 2CO+ O₂ = 2CO₂

Commonly used catalysts use transition metal oxides ( Cu - Mn ) as active components.

3.2 Key Performance Indicators

 Low temperature activity: Maintain high conversion rate under normal temperature/low temperature conditions of PPU (such as CO conversion rate >99%  at ≤10°C).

 Anti-poisoning ability: Tolerant to interference from H₂O , CO₂ and trace sulfides (such as H₂S ).

 Long life: Need to match the regeneration cycle of PPU adsorbent (such as molecular sieve, activated aluminum) (usually 5-10 years).

4. Integrated application of catalysts in PPU process

4.1 Typical process flow

PPU usually adopts "adsorption + catalysis" two-stage purification:

1. Pre-adsorption tower: removes H₂O , CO₂ and some hydrocarbons.

2. Catalytic reaction layer: CO removal catalyst bed, reacts with residual O₂ to generate CO₂ .

3. Post-adsorption tower: captures the generated CO₂ to ensure the safety of downstream cryogenic equipment.

4.2 Industrial Cases

A large air separation plant uses Minstrong carbon monoxide removal catalyst to reduce CO from 5 ppm to < 5 ppb at 10°C and an air velocity of 5000 h⁻¹ , and runs synchronously with the molecular sieve regeneration cycle, with a service life of 8 years.

5. Conclusion

Carbon monoxide removal catalyst is the core link of air separation PPU efficient purification. Its low temperature activity and long-term stability are directly related to the safety and economy of air separation unit. In the future, with the progress of material science and process optimization, catalyst will play a greater role in energy efficiency improvement and cost control.