What Is a Membrane Nitrogen Generator?

A membrane nitrogen generator uses hollow-fiber polymer membranes to separate nitrogen from compressed air based on the principle of permeation. Compressed air enters a prefiltration train that removes oil, water, and contaminants. The clean, dry air is then forced through a bundle of hollow-fiber membranes at 100 to 150 PSI. Oxygen, water vapor, and CO2 permeate through the thin fiber walls faster than nitrogen, allowing them to vent off as waste gas. Nitrogen passes through the fiber bores into the product outlet and buffer tank.

A hollow fiber membrane is a micro-thin polymer tube, typically less than 1 millimeter in diameter. Thousands of these fibers are bundled together inside a pressure vessel. The fiber walls are permeable, meaning different gases pass through them at different rates. Nitrogen passes through the bore (the hollow center) while oxygen and water vapor permeate through the walls. This selective permeability is the basis for membrane-based gas separation.

The hollow-fiber membrane bundle typically lasts 5 to 7 years under normal operating conditions. When the bundle reaches the end of its life, it can be replaced without replacing the entire system, making maintenance relatively simple and cost-effective. The lifespan can be extended with proper prefiltration and regular maintenance of the compressor inlet and air handling components.

Membrane systems produce nitrogen in the range of 95% to 99.5% purity under practical operating conditions. The exact purity achievable depends on inlet pressure, temperature, the specific membrane material, and the desired flow rate. For applications requiring purity higher than 99.5%, a PSA (pressure swing adsorption) system is a better choice.

Choose membrane when your application requires low to moderate purity (95 to 99.5%), has space or weight constraints, or prioritizes simplicity and lower upfront cost. Membrane systems are ideal for marine inerting, fire suppression, off-shore platforms, tire inflation, and portable nitrogen carts. Choose PSA if you need higher purity (above 99.5%), have a high-volume continuous-duty application, or expect long equipment life (20+ years) to justify the higher initial investment.

Membrane systems require a clean, dry compressed air supply at 100 to 150 PSI inlet pressure. The specific air volume depends on the desired nitrogen output. As a rule of thumb, a membrane system typically consumes roughly 3 to 4 standard cubic feet (SCF) of compressed air per 1 SCF of nitrogen produced, depending on the target purity. Your compressed air source must include adequate prefiltration (oil coalescer, dryer, dust filter) to protect the membrane.

Hollow-fiber membranes have an optimal operating temperature range of 40 to 150 degrees F (4 to 65 degrees C). Performance is temperature-sensitive: cooler inlet air slightly reduces throughput, while warmer air increases both throughput and purity output. Membranes can be damaged by temperatures above 150 degrees F, so proper air dryer and cooling are important for long equipment life and consistent purity.

Membrane system pricing depends on the desired nitrogen flow rate, purity specification, and any ancillary components (dryer, buffer tank, controls). A small portable membrane system might cost a few thousand dollars, while a larger industrial system can cost tens of thousands. Generally, membrane systems have a lower upfront cost than PSA systems of equivalent size, but higher long-term cost-per-unit for high-purity, high-volume applications. Contact us with your flow and purity requirements for a specific quote.