Simultaneous hydrogen sulphide and carbon dioxide removal from biogas by water–swollen reverse osmosis membrane

• Agro-biogas upgrading.
• Water–swollen membrane.
• Carbon dioxide and hydrogen sulphide removal.
• Membrane choice based on its basic characteristics.

Biogas is a suitable alternative fuel if unwanted impurities are removed to avoid corrosion of the inner parts of an engine. A recent breakthrough in biogas purification showed that a thin hydrophilic composite membrane can create the selective water swollen barrier able to remove unwanted sour gases such as carbon dioxide and hydrogen sulphide owing to significantly higher water solubility of the latter in comparison to methane. This work presents the use of water–swollen membranes for the simultaneous removal of carbon dioxide, hydrogen sulphide and water vapour from agro-biogas. Up to 82 vol.% of carbon dioxide and 77 vol.% of hydrogen sulphide were successfully removed from the feed stream at a pressure of 220 kPa. The selection of the most suitable thin hydrophilic composite membrane based on the knowledge of its basic characteristics is discussed. SEM analysis showed that the surface of the best performing composites changed significantly upon swelling by water. It was found that a compact structure of the upper selective thin layer after the swelling by water is fundamental for obtaining a selective water–swollen membrane. The next key factor is a high porosity of the membrane support. A detailed comparison of various systems and their performance is presented.

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