Understanding the Membrane Module: The Heart of a Vapor Recovery Unit
Every membrane-based vapor recovery unit depends on one component for its performance: the membrane module. This is the part that separates hydrocarbon molecules from air, and its design, materials and operating conditions determine how much fuel is recovered and how clean the discharged air is. This article explains what is inside the module, how it works, and how to operate it correctly.
What is a membrane module?
A membrane module is a spiral-wound element: layers of flat membrane sheet are wrapped around a central collection tube, with spacers between the layers to create flow channels. Gas flows along the outside of the element under pressure. Hydrocarbon molecules permeate through the membrane into the permeate side, where a vacuum pump maintains negative pressure, and are collected at the center tube. The remaining air, which does not permeate, flows out through the other end.
The membrane material is a polymer (PDMS-based) that is selective: hydrocarbon molecules dissolve into and diffuse through it far more readily than air molecules. This selectivity is what makes the separation possible without any chemical reaction or consumable.
Key parameters of the VOHON membrane module
The membrane modules used in VOHON vapor recovery units are produced in-house. The standard module (80 × 1050 mm) has the following design characteristics:
- Membrane area: 6 m² per module
- Material: PDMS-based selective layer
- Permeate-side operating pressure: -0.05 to -0.09 MPa (vacuum)
- Recommended inlet pressure: 0.3–0.6 MPa
- Maximum inlet temperature: 45 °C
- Design life: 10+ years under normal operation
Production capacity for membrane material is above 1.2 million m² per year, with more than 30,000 modules manufactured per year. The membranes are used not only in service-station vapor recovery but also in industrial VOCs recovery systems.
Operating rules that protect the membrane
The membrane is durable, but three rules keep it performing:
- Never apply reverse pressure to the module — this can delaminate the membrane layers.
- Keep the inlet gas free of particles and liquid oil — a pre-filter or knockout pot protects the module.
- Keep inlet temperature at 45 °C or below — high temperature accelerates membrane aging.
Why this matters for station owners
Because the membrane does the separation without consumables, there is nothing to replace during its service life — no activated carbon, no desorption cycles. The only routine task is checking the vacuum pump oil and replacing it periodically. For the station, this means low running costs and predictable performance over a decade or more.
For more information: +86 135 2699 0215 / lixiang@vohonoilpipe.com