Membrane technology is a set of closely packed, semi-permeable hollow fibres which separates nitrogen from air by allowing the nitrogen from compressed air to pass through whilst oxygen and carbon dioxide are released into the atmosphere. This occurs due to the different molecule sizes of these gases. Nitrogen gas molecules are larger than oxygen and carbon dioxide molecules, so whilst the oxygen and carbon dioxide are purged from the membrane the nitrogen continues through.
The lower the flow rate passing through the membrane the higher the purity of nitrogen is achieved. The purity can be further enhanced by increasing the temperature.
The other option, Pressure Swing Adsorption, cycles gas at high and low pressure, flushing compressed air through a bed of carbon beads, also known as a Carbon Molecular Sieve. Nitrogen molecules are allowed to pass through the carbon bed but the oxygen and carbon dioxide molecules are too large to pass through and are vented off. PSA generators can be scaled up to provide very large quantities of nitrogen gas for entire labs or for manufacturing and process industries.
So which generator should you choose? The decision comes down to the purity required. For labs needing 99.5% purity and above, PSA is the optimum choice but for labs with lower purity requirements membrane generators are far more cost effective. When it comes to choosing your gas generator the cost is directly correlated to the purity, the more purity required, the more the generator will cost.
The final consideration a lab must make is whether they require a compressor based system or not. If a lab has an in-house supply of high quality compressed air a compressor less generator will be suitable, if not a compressor based system will be needed.
Compressor based systems feature moving parts and are therefore subject to general wear and tear over time and will require servicing at regular intervals. A service contract comes highly recommended for labs with this equipment in order to avoid unplanned costs should a breakdown occur. Generators without compressors do not contain moving parts and therefore their service requirements are dramatically reduced in cost and frequency.