Membrane gas separations

Since the 1980s, gas permeation has seen strong industrial development in gas separation and purification, a field long reserved for traditional processes such as distillation, absorption or adsorption. Today, it is widely used to produce nitrogen from air, purify hydrogen, treat natural gas and biogas, dry gases and recover volatile organic compounds (VOCs).

The achievement of this objective was preceded by a long period of research and development, during which a series of achievements were made in the field of materials (development of selective structures with very thin active layers), membrane modules (production and assembly techniques, sizing, potting, flow control) and overall industrial system design (module protection chain against dust and contaminants, ageing limitation, shutdown/restart management). In the end, gas permeation was able to position itself in a wide range of applications, identified on the basis of techno-economic analyses, mainly for functions involving the concentration or depletion of gas mixtures in a component with a fast (hydrogen, oxygen, VOCs) or slow (nitrogen, methane) permeation rate in dense polymers. For applications requiring high purity, its use is generally unsuitable, and hybrid processes or alternative technologies are preferable.

More generally, the gas permeation process offers a number of key advantages, particularly in the context of sustainable production: continuous operation (no regeneration stage), no waste production (physical separation), compact and lightweight system, energy efficiency, implementation requiring only a compression stage (or taking advantage of a pressurized resource). Multiple variants introducing recycling, multiple compression or sweeping can be proposed to meet the specifications, but the search for a solution using the simplest arrangement (typically one or two permeation stages) remains a priority.

For engineers wishing to learn more about the fundamentals, we offer information on materials and the theoretical basis of membrane separation.

For readers faced with a specific problem and wishing to assess the possibilities and limits of gas permeation, we have provided a number of elements to guide their thinking: methodological tools for process design, enabling analysis of the influence of material characteristics (selection criteria), operating conditions (pressure ratio, sampling rate) and process architecture (single or multi-stage systems).

Finally, we wanted to present the state of the art, giving examples of the main current industrial applications and discussing potential developments.

At the end of the article, readers will find a glossary and table of acronyms, notations and symbols....