Hopcalite Catalyst: An Indispensable CO Removal Solution for Air Separation Systems and High-Purity Gas Production

In air separation and high-purity gas manufacturing, carbon monoxide – though typically present only at trace levels (ppm range) – poses far greater consequences than its concentration suggests. If not effectively removed, CO can condense and accumulate under cryogenic conditions, interfering with the stable operation of heat exchangers and low‑temperature equipment. In products such as electronic‑grade nitrogen, high‑purity oxygen, and specialty shielding gases, even trace CO can compromise purity specifications, directly affecting yield in downstream precision processes like semiconductor and photovoltaic manufacturing. To address this technical challenge, Hopcalite catalyst, leveraging its unique room‑temperature catalytic oxidation capability, efficiently converts CO into CO₂ without any external energy input, and when combined with downstream molecular sieves or adsorbers, achieves deep removal. Single‑pass conversion through a Hopcalite bed typically exceeds 99%; in an optimally designed pre‑purification system, CO levels can be reduced from approximately 1000 ppb to about 1.0 ppb, corresponding to a removal efficiency of 99.9%. Owing to its high reaction efficiency, mature technology, stable operation, and significant cost advantage over noble‑metal catalysts, the combined process of Hopcalite catalytic oxidation followed by CO₂ adsorption has become one of the most reliable and cost‑effective CO removal solutions in the air separation and high‑purity gas sectors.

Why Must Air Separation Systems Pay Close Attention to CO Control?

Ambient air typically contains low levels of CO, but in industrial environments, concentrations can rise due to various factors – high‑temperature cracking of compressor lubricating oils, ingress of combustion exhaust, surrounding traffic emissions, or nearby chemical operations – all of which may elevate the CO level at the air separation unit inlet above normal.

If CO is not adequately removed in an air separation unit, three categories of problems typically arise.

Increased risks to cryogenic system operation. The core process of an air separation unit is cryogenic distillation, operating at extremely low temperatures – the top of the nitrogen distillation column is about ‑196°C, and the bottom of the oxygen column about ‑183°C. At such low temperatures, while CO does not freeze and plug the system as water and CO₂ do, its solubility in liquid oxygen is limited, and it can gradually concentrate in the liquid oxygen. When the CO concentration in liquid oxygen accumulates to a certain level, potential safety hazards emerge. Additionally, CO adsorption and accumulation on cryogenic heat exchanger surfaces may impair heat transfer efficiency.

Difficulty in meeting high‑purity gas specifications. Electronic‑grade nitrogen, high‑purity oxygen, and specialty shielding gases typically have extremely stringent limits on CO. In the semiconductor industry, for instance, even ppb‑level CO in shielding gases can cause oxidation process instability and thin‑film deposition degradation, leading to massive scrap. In high‑purity nitrogen production, the CO content in the product gas is generally required to be below 1 ppm, and some ultra‑high‑purity applications even demand less than 0.1 ppm.

Contamination of downstream process equipment. Some adsorbents, membrane separation materials, or precision analytical instruments used in high‑purity applications are highly sensitive to CO. If front‑end purification is insufficient, CO can break through subsequent polishing units, shortening equipment life and increasing maintenance costs.

Therefore, although CO is a trace impurity, it must be specifically addressed in high‑purity gas systems, and the required removal depth is extremely demanding.

Technical Principles and Engineering Layout of CO Removal Using Hopcalite Catalyst

Hopcalite catalyst is essentially a copper‑manganese mixed oxide system, composed of active manganese dioxide (MnO₂) and copper oxide (CuO) in a specific ratio, with a typical composition of MnO₂:CuO = 1:0.8. Its core function is to oxidize CO to CO₂ via catalytic oxidation: 2CO + O₂ → 2CO₂. This reaction does not require high temperatures – Hopcalite works efficiently at ambient temperatures (0‑40°C) with no external heating. Its activity stems from the reversible redox cycling between Cu²⁺/Cu⁺ and Mn⁴⁺/Mn³⁺. CO reacts with lattice oxygen on the catalyst surface to form CO₂, and the reduced active sites are then re‑oxidized by gas‑phase O₂, restoring catalytic activity.

In terms of performance indicators, the specific surface area of Hopcalite catalyst typically falls between 120‑220 m²/g, and the active component content can exceed 80%. Under dry and clean inlet conditions, single‑pass CO conversion through a Hopcalite bed generally exceeds 99%. In an air separation pre‑purification unit with an optimized catalytic layer configuration, CO can be reduced from approximately 1000 ppb to about 1.0 ppb.

The placement of the Hopcalite catalytic bed in an air separation system follows a clear engineering logic. The typical process train is: air compression → cooling and water removal → filtration and dust removal → adsorption drying → Hopcalite catalytic oxidation of CO → CO₂ adsorption removal → cryogenic distillation. The core rationale is to position the Hopcalite bed after the drying unit and before the CO₂ adsorber. Hopcalite is extremely sensitive to moisture – when ambient humidity exceeds 45%, the catalyst rapidly deactivates due to water vapor adsorption. Measured data show that at 25°C and 40% relative humidity, a sample with a Cu:Mn molar ratio of 1:1.5 exhibits an initial CO conversion of 98.2%; however, when the relative humidity rises to 80%, the conversion of the same sample drops from 96% to 43% within just 2 hours. Therefore, the inlet air to the catalytic bed is typically required to have a dew point below ‑40°C and a relative humidity below 10%. At the same time, the CO₂ generated by the catalytic reaction must be adsorbed downstream using 13X molecular sieve or activated alumina to below 1 ppm, to prevent CO₂ from entering the cryogenic system and causing freeze‑up.

Comparative Advantages of Hopcalite Catalyst Over Alternative Solutions

In industrial gas purification, there are multiple options for CO treatment, but the Hopcalite catalytic system is widely adopted in air separation due to several advantages. To better visualize its competitiveness, the following table compares Hopcalite with conventional noble‑metal catalysts (e.g., Pt/Pd‑based) across key dimensions:

Based on this comparison, Hopcalite catalyst offers significant advantages in terms of no external heating, lower capital investment, and operational costs, making it particularly suitable for large‑flow, continuous air separation pre‑purification. Noble‑metal catalysts, on the other hand, remain irreplaceable in certain high‑temperature, high‑humidity, or specialty‑purity niches – they are complementary choices for different operating conditions, rather than simple substitutes.

Critical Engineering Considerations in Practical Applications

Although Hopcalite catalyst is a mature technology in air separation systems, several key factors must be addressed in actual engineering to ensure long‑term stable operation.

Moisture control: the most critical constraint. This is the single most important aspect of Hopcalite application. In one documented air separation plant incident, improper regeneration settings on the dryer caused the gas entering the catalytic bed to have a dew point of only ‑20°C (far above the required ‑40°C). After about three months of operation, the CO concentration at the bed outlet exhibited breakthrough exceeding specifications. A shutdown inspection revealed significant caking and reduced strength in the middle section of the catalyst bed, with catalytic efficiency dropping from an initial 98% to 62%, ultimately forcing an early replacement of the entire catalyst charge. This case demonstrates that moisture control not only affects catalytic efficiency but directly determines the service life of the catalyst. Experimental data similarly show that after one year of operation at 50% humidity, the specific surface area of the catalyst can decrease from 200 m²/g to 120 m²/g, and catalytic efficiency drops from 95% to 70%.

Inlet temperature matching. The optimal operating temperature for Hopcalite is ambient (0‑40°C). At lower temperatures, the reaction rate declines; at temperatures exceeding 100°C, the active components may undergo irreversible sintering. In air separation systems, compressed air, after cooling and drying, typically falls within the ambient range, matching Hopcalite’s preferred temperature window.

Space velocity design. Space velocity (the ratio of gas volumetric flow rate to catalyst bed volume per hour) directly affects CO conversion. Too high a space velocity results in insufficient gas‑catalyst contact time, allowing CO to break through before complete reaction; too low a space velocity increases catalyst inventory and capital costs. For air separation applications, Hopcalite space velocities are generally designed in the range of 10,000‑50,000 h⁻¹.

Prevention of sulfur, chlorine, and other poisons. Sulfides (e.g., H₂S, SO₂) and chlorides are catalyst poisons for Hopcalite; even ppm‑level concentrations can permanently occupy active sites. Therefore, upstream desulfurization and dechlorination pretreatments are typically required.

Regular monitoring and maintenance. Air separation systems usually operate continuously, and catalyst performance degrades gradually. It is advisable to periodically monitor the CO concentration at the bed outlet. When the breakthrough concentration approaches product specification limits, the catalyst should be replaced or regenerated. Some partially deactivated Hopcalite can recover some activity through thermal regeneration.

Conclusion

In practical air separation system design, Hopcalite catalyst, with its combination of ambient‑temperature efficiency, process maturity, and cost‑effectiveness, has become the standard choice for CO removal. From the pre‑purification unit in cryogenic air separation to trace impurity polishing in high‑purity gas production lines, Hopcalite catalyst reliably guards the final gateway of gas purity. As domestic demand for ultra‑high‑purity gases continues to grow, driven by the semiconductor, photovoltaic, and advanced equipment manufacturing industries, the control specifications for trace impurities – especially CO – in air separation systems are becoming increasingly stringent. As a mature solution with high domestic availability, stable supply chains, and independently controllable technology, the Hopcalite catalytic system will continue to play an essential and foundational role in this industrial upgrade. Understanding its working principles, mastering its application boundaries, and adhering to engineering best practices are the keys to ensuring long‑term reliable operation of air separation systems.

author：Gloria
date:2026-07-30