RNG (renewable natural gas) is a renewable gas obtained by putting raw biogas through a purification process called upgrading. Raw biogas can be obtained from anaerobic digestion of various raw materials: agricultural biomass (by-products, agricultural waste and animal waste), agro-industrial waste (waste from the processing of the food chain) or the organic fraction of municipal solid waste (OFMSW).
Once the biogas-to-RNG upgrading has been carried out, it must be refined, in order to eliminate the components that are not suitable for feeding the gas into the network (CO₂).
As it is produced from agricultural biomasses, agro-industrial waste and organic waste, RNG can be considered to all intents and purposes a renewable and sustainable source: in addition to reducing emissions into the atmosphere, it is carbon neutral, that is, it totally offsets the emissions produced, as it returns organic matter to the soil.
RNG adapts flexibly to multiple uses, from energy production to distributed generation and fuel for the transport sector. It is completely similar to natural gas and can therefore make use of existing transport and storage infrastructures.
In the agricultural sector, RNG can contribute to significantly reduce production costs and at the same time to increase competitiveness. The digestate (what remains after the anaerobic digestion process of agricultural matrices) can in fact be used as a natural fertilizer, capable of increasing the capacity of the soil to absorb and store carbon.
Biogas-to-RNG upgrading is a complex treatment whose end result is the removal of CO₂ from raw biogas. The process consists of several phases: a first pre-treatment step, followed by a purification phase, i.e. of removal of pollutants (H₂S, VOCₛ) from biogas coming from the anaerobic digester and a final phase of methane separation (CH₄) from carbon dioxide.
The end result is a renewable energy source, biomethane, which reduces emissions, exploiting existing networks and increasing national production, with positive repercussions in terms of circularity in the use of resources in the agri-food sector.
Different biogas-to-RNG upgrading technologies are available on the market, which are based on different chemical-physical principles related to gas separation.
Among the most widespread and effective there is the biogas-to-RNG upgrading using selective membranes, also chosen by AB for BIOCH4NGE®: the use of particular polymeric materials that have a selective permeability to separate CH4 and CO₂ and that guarantee perfect purification from carbon dioxide, thus reducing biogas loss during upgrading to almost zero.