Argon (Ar) is a rare gas widely used in metallurgy, welding, chemical industries, and other fields. The production of argon mainly relies on separating the different gas components in the air, as the concentration of argon in the atmosphere is about 0.93%. The two primary methods for industrial argon production are Cryogenic Distillation and Pressure Swing Adsorption (PSA).

Cryogenic Distillation

Cryogenic distillation is the most commonly used method for argon separation in industry. This method utilizes the differences in boiling points of various gas components in the air, liquefies the air at low temperatures, and separates the gases through a distillation column.

Process Flow:

Air Pre-treatment: First, the air is compressed and initially cooled to remove moisture and carbon dioxide. This step is typically achieved by using a dryer (CD) or molecular sieve adsorber to remove moisture and impurities.

Air Compression and Cooling: After drying, the air is compressed to several megapascals of pressure, and then cooled through a cooling device (e.g., an air cooler) to bring the air temperature close to its liquefaction point. This process lowers the air temperature to -170°C to -180°C.

Air Liquefaction: The cooled air passes through an expansion valve and enters a cryogenic distillation column. The components in the air are gradually separated inside the column based on their boiling points. Nitrogen (N₂) and oxygen (O₂) are separated at lower temperatures, while argon (Ar), having a boiling point between nitrogen and oxygen (-195.8°C for nitrogen, -183°C for oxygen, and -185.7°C for argon), is collected in specific sections of the column.

Fractional Distillation: In the distillation column, liquid air evaporates and condenses at different temperatures, and argon is effectively separated. The separated argon is then collected and further purified.

Argon Purification:

Cryogenic distillation generally yields argon with purity above 99%. For certain applications (e.g., in the electronics industry or high-end material processing), further purification may be required using adsorbents (such as activated carbon or molecular sieves) to remove trace impurities like nitrogen and oxygen.

Pressure Swing Adsorption (PSA)

Pressure Swing Adsorption (PSA) is another method for generating argon, suitable for smaller-scale production. This method separates argon from the air by utilizing the different adsorption characteristics of various gases on materials such as molecular sieves.

Process Flow:

Adsorption Tower: The air passes through an adsorption tower filled with molecular sieves, where nitrogen and oxygen are strongly adsorbed by the molecular sieves, while inert gases like argon are not adsorbed, allowing them to separate from nitrogen and oxygen.

Adsorption and Desorption: During one cycle, the adsorption tower first adsorbs nitrogen and oxygen from the air under high pressure, while argon flows out through the tower's outlet. Then, by reducing the pressure, nitrogen and oxygen desorb from the molecular sieves, and the adsorption tower's adsorption capacity is restored through pressure swing regeneration.

Multi-Tower Cycle: Typically, multiple adsorption towers are used alternately—one for adsorption while the other is in desorption—allowing continuous production.

The advantage of the PSA method is that it has a simpler setup and lower operating costs, but the purity of the produced argon is generally lower than that of cryogenic distillation. It is suitable for situations with lower argon demand.

Argon Purification

Whether using cryogenic distillation or PSA, the generated argon usually contains small amounts of oxygen, nitrogen, or water vapor. To improve the purity of argon, further purification steps are typically required:

Condensation of Impurities: Further cooling of the argon to condense and separate out some impurities.

Molecular Sieve Adsorption: Using high-efficiency molecular sieve adsorbers to remove trace amounts of nitrogen, oxygen, or water vapor. Molecular sieves have specific pore sizes that can selectively adsorb certain gas molecules.

Membrane Separation Technology: In some cases, gas separation membrane technology can be used to separate gases based on selective permeation, further enhancing the purity of argon.

Precautions for On-Site Argon Production

Safety Measures:

Cryogenic Hazard: Liquid argon is extremely cold, and direct contact with it should be avoided to prevent frostbite. Operators should wear specialized cryogenic protective clothing, gloves, and goggles.

Asphyxiation Hazard: Argon is an inert gas and can displace oxygen. In enclosed spaces, argon leakage can lead to a decrease in oxygen levels, resulting in asphyxiation. Therefore, areas where argon is produced and stored need to be well-ventilated, and oxygen monitoring systems should be installed.

Equipment Maintenance:

Pressure and Temperature Control: Argon production equipment requires strict control of pressure and temperature, especially in the cryogenic distillation column and adsorption towers. Equipment should be regularly inspected to ensure all parameters are within normal ranges.

Leak Prevention: Since the argon system operates under high pressure and low temperatures, seal integrity is crucial. Gas pipelines, joints, and valves should be periodically checked to prevent gas leaks.

Gas Purity Control:

Precision Monitoring: The purity of argon required varies depending on the application. Gas analyzers should be used regularly to check the purity of the argon and ensure the product meets industrial standards.

Impurity Management: In particular, in cryogenic distillation, the separation of argon may be affected by the distillation column design, operating conditions, and cooling effectiveness. Further purification may be necessary depending on the final use of argon (e.g., ultra-high purity argon for the electronics industry).

Energy Efficiency Management:

Energy Consumption: Cryogenic distillation is energy-intensive, so efforts should be made to optimize cooling and compression processes to minimize energy loss.

Waste Heat Recovery: Modern argon production facilities often utilize waste heat recovery systems to recover the cold energy produced during the cryogenic distillation process, improving overall energy efficiency.

In industrial production, argon primarily depends on cryogenic distillation and pressure swing adsorption methods. Cryogenic distillation is widely used for large-scale argon production due to its ability to provide higher purity argon. Special attention is required during production to ensure safety, equipment maintenance, gas purity control, and energy efficiency management.