Medical oxygen supplies plays an important role in healthcare, supporting the treatment of respiratory conditions, surgical procedures, and emergency interventions.
Whether delivered through oxygen tanks or concentrators, medical oxygen must meet strict purity standards to ensure safe and effective use. Oxygen therapy is widely used for patients suffering from respiratory diseases, and not all oxygen is suitable for medical use. It requires specific production and purification processes to achieve the purity level of 99.5% or higher, as set by medical standards worldwide.
Thus, the production of medical oxygen involves complex procedures that transform atmospheric air into purified oxygen. This process ensures that impurities, other gases, and contaminants are removed, leaving oxygen that is safe for patients.
The most common methods include cryogenic distillation, pressure swing adsorption (PSA), and membrane separation – each involving a series of steps aimed at isolating oxygen from other components in the air and purifying it to meet healthcare standards. In this article we will discuss how medical oxygen is produced and purifed.
The following five key steps are followed in the production and purification of medical oxygen:
Air Intake and Filtration
Air contains roughly 21% oxygen, 78% nitrogen, and trace amounts of other gases, including argon, carbon dioxide, and water vapour. Before oxygen can be separated from these other gases, the air must first be filtered to remove particulate contaminants, dust, and pollutants. This step is crucial, as contaminants in the air could affect the purity of the oxygen, potentially posing health risks to patients.
During air intake, powerful compressors draw in large volumes of air, which then passes through several filters to remove impurities. Filters are designed to capture particles of various sizes, from large dust particles to microscopic pollutants.
For oxygen production systems located in urban or industrial areas, advanced filtration is essential, as these environments tend to have higher levels of pollution. By ensuring that the air is as clean as possible before entering the separation process, this stage establishes a foundation for producing high-purity medical oxygen.
Once filtered, the clean air moves on to the next step, where the oxygen separation process begins.
Cooling and Compression
The next stage involves cooling and compressing the filtered air. This is particularly vital in the cryogenic distillation method, one of the most common techniques for producing medical-grade oxygen.
Cryogenic distillation requires extremely low temperatures to separate oxygen from other gases, so the air must be cooled to a point where its components can be liquefied.
To achieve these temperatures, the air is compressed under high pressure, and is then passed through a series of heat exchangers that gradually cool it to temperatures as low as -200°C.
By cooling the air to this extreme level, nitrogen, oxygen, and other gases can be transformed into liquid form, allowing for their separation in the next step. The cooling process is precise, as each gas in the air has a specific boiling point.
While cryogenic cooling is not necessary in all oxygen production methods (such as pressure swing adsorption), it is essential for processes involving cryogenic distillation.
Separation of Oxygen from Nitrogen and Other Gases
After cooling, the separation of oxygen from nitrogen and other gases takes place – the heart of the oxygen production process and achieved through different methods, depending on the type of production system. In cryogenic distillation, separation occurs in a distillation column, where the liquefied gases are carefully heated to their specific boiling points.
Inside the distillation column, nitrogen, which has a lower boiling point than oxygen, rises to the top as it evaporates, while oxygen remains at the bottom. The oxygen is then siphoned off as a purified liquid.
Pressure swing adsorption (PSA) is another common method for separating oxygen. PSA does not require cryogenic temperatures but instead uses molecular sieves that selectively adsorb nitrogen under high pressure, allowing only oxygen to pass through. This method is particularly useful in portable or on-site oxygen concentrators, as it does not rely on complex cooling systems and can be more energy-efficient than cryogenic distillation.
Purification of Oxygen
Once the oxygen has been separated, further purification is needed to remove any residual gases or impurities. Even small amounts of nitrogen, carbon dioxide, or other trace gases must be eliminated to meet the stringent purity requirements for medical oxygen.
In the cryogenic process, purification often occurs as part of the distillation, where various gases are gradually removed at different stages. However, additional purification measures are sometimes applied, including passing the oxygen through activated carbon or other purification materials that can trap contaminants at a molecular level.
For PSA-based systems, the molecular sieve material not only separates oxygen from nitrogen but also adsorbs other trace gases and impurities, acting as an additional filtration mechanism.
Storage and Quality Control
Storage of medical oxygen typically involves transferring the gas into specialised high-pressure cylinders or cryogenic tanks, depending on its intended form of delivery. Liquid oxygen is often stored at cryogenic temperatures in insulated tanks, while gaseous oxygen is compressed and stored in metal cylinders.
Quality control is an essential part of this stage, as any impurities or deviations from the required purity levels must be identified and corrected. Testing procedures include analysing the oxygen for contaminants, verifying its concentration, and ensuring that it meets regulatory standards for medical use.
