Membranes for green processes

The interest for renewable resources and eco-sustainable processes that allow production of renewable energy with low environmental impact is currently one of the driving forces in the field of green chemistry. Emission of CO2, related to the use of fossil fuels, is considered one of the main causes of global warming and climate change. The reduction of CO2 emission into the atmosphere as a result of human activity is one of the most important environmental challenges to face in the next decennia. A possible solution is the increased use of renewable sources of energy, with the promotion of plans for CO2 capture and reutilization (CCU). In this scenario, the production of biomethane from organic waste, is one of the most promising strategies to reduce fossil fuel consumption and greenhouse gas emission. Unfortunately, traditional biogas upgrading still produces CO2 as a waste product. This work presents a study on an advanced biogas upgrading process, aimed at the simultaneous purification of methane and CO2 via different steps, including CO2/CH4 separation by polymeric membranes. The innovative aspect is the further purification of CO2, from a useless by-product to a food-grade quality gas for commercial application in the food industry. The final result is a biorefinery, that produces bioenergy from biomass and closes the CO2 loop in biogas production, completely eliminating its release into the atmosphere. The study was performed on a pilot plant constructed by Tecno Project Industriale Srl, Italy. The anaerobic digestion plant (Montello Spa), has a digestive capacity of 400.000 ton of biomass/year and can treat over 6.250 m3/hour of biogas from FORSU. The chemical purity of the gas streams was analysed and compared with the guidelines of the European Industrial Gases Association and the International Society of Beverage Technologists (EIGA /ISBT) for CO2 used in the food industry. The microbiological purity was compared with the limit values defined in the European Collaborative Action. With a purity of 96.3 vol%, the produced methane respects the purity requirement for the household network. With a purity of 98.1% before, and 99.9% after the final distillation process, CO2, proves to be chemically and microbiologically suitable for food-grade applications. The process produces renewable energy and it is environmentally impact-free CO2, respecting the principles of green chemistry and of the circular economy.