Membrane separation — compact, flexible, and growing fast

Not every biomethane project needs to be a large, centralised plant. Across Europe, small to medium-sized biogas facilities increasingly produce high-quality biomethane closer to where the feedstock comes from — on farms, at waste treatment facilities, or near industrial sites. Membrane separation is one of the upgrading technologies driving that decentralisation, and it’s growing faster than any other option in the sub-1000 Nm³/h segment.

How membrane separation works

Membrane systems exploit selective permeability: different gases pass through a polymer membrane at different rates depending on molecule size and chemistry. CO₂ molecules are smaller and pass through faster than methane. Run the gas through a membrane stack and the methane concentrates on one side while CO₂ enriches the other.

The process in brief:

• Compression — raw biogas is pressurised to a working pressure that drives the membrane separation.
• First pass — gas flows across a semi-permeable membrane. Smaller molecules (CO₂, water vapour) pass through faster than larger methane molecules, so the methane concentration on the inlet side increases as the stream advances.
• Multi-stage configuration — typical plants run two or three membrane stages in series, each driving methane purity higher. The inter-stage retentate streams are recycled to recover any methane that crossed the membrane.
• Pre-treatment — operators must remove H₂S, moisture, and particulate matter ahead of the membranes, both for safety and to prevent fouling.

The result is biomethane at 97%+ CH₄ — pipeline-quality, ready for compression, storage, or grid injection.

Advantages

• Compact footprint — membrane systems are physically smaller than equivalent PSA or water-scrubbing plants. They fit on sites where larger upgrading technologies don’t.
• Energy efficient at small to medium scale — the per-Nm³ energy demand is competitive, particularly under the throughput threshold where alternative technologies become economically competitive.
• Modular and scalable — adding a stage or a parallel train as production grows is straightforward; the modular nature is part of the appeal for projects expecting capacity increases over time.
• No water or chemicals required — operations are simpler than water-based upgrading; consumables are limited to membrane replacement on a multi-year cycle.

Considerations

• Pre-treatment is mandatory — H₂S, water, and particulates have to come out ahead of the membranes, which adds equipment.
• Multi-stage investment — achieving the highest purity often involves multiple membrane passes; the curve is steeper than for PSA at the high-purity end.
• Fouling sensitivity — oils, dust, and residual contaminants can degrade membrane performance over time. The mitigation is robust pre-treatment.

When membrane separation is the right choice

Membrane upgrading shines in three configurations:

• Decentralised plants without pipeline access — the small footprint and modular scaling fit perfectly.
• Projects planning gradual capacity growth — adding stages is easier than scaling other technologies.
• Operators seeking low-maintenance, modular, water-and-chemical-free systems.

For projects targeting the very highest methane purity at large scale, PSA often remains the right answer. For mid-sized operations that need a clean, compact, scalable upgrading path, membranes have become the default.

From upgrading to delivery

Once your membrane system produces clean biomethane, the next step is moving it to the customer. Gaznet’s Type-IV composite MEGC containers bridge the gap between production and market: fillable on-site at the upgrading plant, transportable anywhere by road or rail, ADR-approved for compliant European delivery, and lightweight enough to keep transport economics favourable. Membrane upgrading plus MEGC transport means biomethane can be produced anywhere and delivered everywhere.

A scoping conversation takes about an hour and ends with a numbers-backed configuration for your specific project.