Chemisorption and physisorption - How activated carbon can bind pollutants in biogas plants

The use of biogas plants plays an important role in sustainable energy production and the circular economy. To prevent corrosion in the plant, hydrogen sulfide and organic pollutants must be removed. Activated carbon has proven to be particularly suitable for this purpose, as it can bind pollutants through both chemisorption and physisorption. However, the suitable method depends on the individual specifications of the biogas plant.

The challenge: removal of hydrogen sulfide and organic pollutants

Biogas contains not only methane and carbon dioxide but also hydrogen sulfide (H₂S), siloxanes, and other organic impurities (VOCs). These substances can cause corrosion to technical components and lead to operational disruptions. Therefore, targeted gas cleaning is required to ensure high gas quality and improve the economic efficiency of the plant.

The selection of suitable gas treatment processes is crucial for the efficient operation of biogas plants. In addition to biological processes and washing methods, the use of activated carbon has proven to be particularly effective.

The solution: activated carbon as an effective adsorbent

Activated carbon is successfully used to remove hydrogen sulfide, organic pollutants, and siloxanes from biogas. Various types of activated carbon are available, specifically developed for the requirements in biogas plants.

How activated carbon binds pollutants:

• Chemisorption (H₂S Removal): Occurs through a chemical reaction with impregnated activated carbon. Optimal conditions: 50–70% humidity, 30–60°C temperature, and sufficient oxygen.
• Physisorption (VOCs): Binding through Van der Waals forces. Optimal conditions: dry and cool gas.

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Conflict between H₂S and VOC removal

The optimal conditions for one group of pollutants can impair the adsorption of the other. While H₂S removal requires moisture and oxygen, VOCs need a dry and cool environment. Therefore, the priority should be set according to the main problem of the plant.

In addition to pollutant removal, the upgrading of biogas to biomethane is increasingly coming into focus, especially when injection into the natural gas grid is targeted.

Biomethane upgrading and injection into the natural gas grid

Biogas plants can be expanded with an appropriate upgrading unit to produce high-quality biomethane. For injection into the natural gas grid, the CO₂ content must be significantly reduced, as it lowers the energy content of the gas.

Carbon molecular sieves (CMS), originally developed in Essen, enable the efficient separation of CO₂ using pressure swing adsorption (PSA). This ensures that the quality requirements for injection into the natural gas grid are reliably met.

We are happy to assist you in selecting the appropriate activated carbon for your biogas plant. In addition to providing high-quality activated carbons, we also offer consulting services for process optimization.

Our partner, CarboTech AC GmbH, is one of the world's leading suppliers of powdered and granular activated carbons. The processing or reactivation is also carried out at CarboTech in Essen, Germany. The fluidized bed process makes the reactivation of activated carbon more efficient than in the usual rotary kiln – with correspondingly positive effects on its performance.