Easy handling without prior drying of the biogas

Biogas offers a wide range of applications – for example as fuel, for heat generation, or as a basis for fertilizers and chemical products. Until now, upgrading biogas to bio-methane has been technically complex and hardly economical for small plants. Conventional methods require elaborate pre-drying and gas scrubbing. This is precisely where the Bio4Value project comes in: a newly developed membrane process that does not require pre-drying of the biogas promises significant simplification. New flat membranes, developed at Fraunhofer IAP, form the central component. They separate methane from CO₂ directly from the moist biogas stream. As a result, no additional energy is needed for cooling and reheating the raw biogas before membrane separation. Long-term tests also showed that the newly developed membranes are resistant to hydrogen sulfide contained in raw biogas.

More than energy: material use of CO₂ and methane

The targeted separation of CO₂ and methane directly at the source is an important step in avoiding emissions and efficiently utilizing the separated gases. "The recovered CO₂ can be used as a valuable raw material for industrial processes, such as electrosynthesis, fuel production, or chemical manufacturing. It can also serve as a carbon source in greenhouses or be used for producing sparkling water," explains Dr. Steffen Tröger-Müller from Fraunhofer IAP, who coordinates the project.

Methane, in turn, primarily serves as a bio-based fuel (bio-CNG, compressed natural gas from biogas) for agricultural vehicles or for feeding into the natural gas grid. However, it can also be used materially, for example as a feedstock for chemical syntheses such as ammonia or methanol production.

From polymer to highly selective flat membrane

One of the main challenges in developing suitable membrane materials is industrial applicability. To achieve the required selective separation of methane and CO₂ at comparatively low pressures using untreated raw biogas, new materials had to be developed – commercially available polymers do not meet these requirements. Fraunhofer IAP has therefore specifically synthesized suitable polymers and produced flat membranes from them. The long-standing expertise of the researchers in membrane and process development played a key role. "Our newly developed flat membranes meet all requirements and are particularly characterized by mechanical stability and extremely thin, flow-optimized separation layers," says Tröger-Müller.
 

From membrane to market-ready module

To ensure that the technology can also be operated independently in small biogas plants in rural areas, KS Kunststoffbau GmbH is working on compact, modular solutions. "Our goal is to develop a market-ready module that can be used locally and is easy to handle even for users without special technical expertise. The newly developed flat membranes make this possible," explains Markus Huth from KS Kunststoffbau GmbH.

ATB is responsible for integrating the process into existing biogas plants and evaluating the new technology in terms of its material use. "We are investigating how the membrane module can be integrated into real biogas processes – here we see great potential," says Dr. Christiane Herrmann from ATB. ATB is also analyzing the techno-economic aspects of the process and conducting life cycle assessments. "Thanks to the energy savings enabled by the newly developed membrane, we see a strong opportunity to use the membrane technology decentrally in small biogas plants," adds Herrmann.

Validated technology seeks partners for industrial implementation

Currently, the technology for biogas upgrading is in the validation phase at laboratory scale. "Our goal is to further develop the technology so that it can be demonstrated under real conditions in follow-up projects and scaled up by industrial partners. Companies from the biogas, energy, or chemical sectors are warmly invited to participate in further development," says Tröger-Müller.