Producing biomethane by valorising CO2 waste

In 2022 the European Commission gave a strong response to the energy crisis caused by the conflict in Ukraine, in order to limit dependence on Russian gas: with the REPowerEU plan, included in the PNRR funds, the aim is to finance investments and key reforms to diversify energy supply sources in Europe. Among others, biomethane plays a primary role: the goal set for 2030 is in fact to achieve an annual production in the EU of 35 billion cubic meters, against the current 3 billion cubic meters per year (2021 figure, EBA). The second objective is 95 billion cubic meters by 2050. The challenge facing European countries is therefore considerable.

Among the actions promoted by the REPowerEU plan, there is investment in research and innovation for the development and consolidation of new biomethane production technologies. It is in this context that our process of direct production of biomethane from biogas by catalytic method, developed in recent years, finds its application.

It has two main advantages: 100% efficiency and total absence of CO2 emissions into the atmosphere.

Biomethane: contextualization and current critical issues

#Biogas is produced starting from the anaerobic fermentation of biomasses which can have different origins, from the organic fraction of urban solid waste, to agricultural processing waste, to livestock manure. The biogas, after purification from contaminants such as siloxanes, ammonia, sulfur gases, is composed of methane (45-85%) and carbon dioxide (15-55%), in variable percentages based on the raw material that feeds the digester. Exploited for several years to produce heat and electricity through co-generation, today biogas is the primary source for the production of biomethane.

Biomethane is a green fuel that is produced through biogas upgrading, a process that involves the separation of methane from carbon dioxide. The most common techniques are: separation using selective membranes, water scrubbing, chemical scrubbing, pressure swing adsorption (EBA, 2020). However, these solutions do not address the problem of the release of CO2 into the atmosphere, which causes:

• a high environmental impact: even if the CO2 produced by a biogas plant is considered "neutral" since it derives from non-fossil sources, it is nevertheless a climate-altering gas. Carbon Capture, Utilization and Storage (CCUS) technologies are currently hardly implemented at upgrading plants. Furthermore, they only move the problem, precisely to the storage sites. The situation is destined to worsen, given the objective of 35 billion m3 of biomethane per year to be reached by 2030 (x12 compared to current production);
• a loss of bio-fuel productivity, if compared to the quantity of raw material that feeds the fermenter, as the carbon balance ends in negative.

Catalytic production of biomethane from biogas

The solution we have developed to solve the above problems is a process for the catalytic production of biomethane starting from biogas.

The process patented by our start-up consists in directly treating the purified biogas, without any separation or upgrading, in a newly designed multistage catalytic reactor. The Sabatier reaction takes place inside it: the CO2 contained in the biogas comes into contact with the hydrogen, converting into methane and water. The necessary H2 is produced by an electrolysis stage, powered by renewable energy: it is therefore green hydrogen.

The choice of the best configuration for the reactor, the operating conditions, the catalyst, is the key to obtaining a highly pure biomethane. The unit also makes optimal use of the high exothermicity of the reaction, to considerably reduce the energy consumption required to carry out the process.

The result is twofold:

• CO2 is no longer a waste, but a resource: with this technology there are no carbon dioxide emissions into the atmosphere;
• efficiency is 100%, as all the carbon contained in CO2 is used to produce new, highly pure CH4, which can be injected into the national gas grid or used as fuel for vehicles.

The technology has been validated in the laboratory and is very promising. We are currently in the process of building a prototype for demonstration in an industrially relevant environment.