With biogas upgrading being limited by the amount of energy required by separation technologies such as cryogenic distillation or liquefaction, new methods involving Metal-Organic Framework (MOF)-based membrane technology are being considered.
Membranes provide filtration of a gas stream, in the case of biogas methane (CH4) is retained while carbon dioxide (CO2) is allowed through, separating the gases and potentially allowing for the CO2 to be captured or stored.
In addition to the thickness of the membrane material, the type of material provides various levels of efficacy when it comes to gas separation. The two main types are polymeric (organic) and inorganic materials.
Each type has inherent advantages and disadvantages. Inorganic membranes provide better permeability, selectivity, and chemical and thermal stability, but have a shorter lifespan due to low mechanical resistance.
Polymeric membranes, though not as permeable, are considered more flexible and easier to process, making them suitable for real-world applications. Mixed Matrix Membranes (MMMs), a way to increase permeance and selectivity of the native polymer material, were created from attempts to improve polymeric membranes.
These MMMs – considered ‘hybrid’ membranes - contain MOFs to increase CO2 adsorption on the membrane, allowing for increase permeance of the gas and better stability at high temperatures.
Applications where MOFs have seen success include sensors, catalysts, drug carriers, energy storage, and gas separation.
Tests were conducted on the MOF-based membrane with separation of CO2/CH4 equimolar (having the same molar concentration). The results showed that MOFs increase the selectivity of the membrane by a factor of at least 3.
For uses in biogas, membrane technology could provide significant upgrading advantages by allowing for low energy consumption, an ease of scalability, and a reduction in the use of hazardous chemicals.
Innovative MOF developer novoMOF has conducted significant research and development in the MOF sector, in addition to studying the benefits of membrane technology.