Sustainable Hydrogen Production by Co-pyrolysis of Coffee Grounds and Tea Bag Waste

Abstract

Energy demand continues to increase both in Türkiye and globally, driven by factors such as population growth and industrialization. The increasing generation of organic waste and the usage of fossil fuels demonstrate the critical need for alternative renewable energy sources. The current research investigated hydrogen-rich syngas generation by pyrolysis of tea bag residues and spent coffee grounds individually and combined as a 1:1 mixture. The batch pyrolysis reactor in the laboratory scale under N₂ flow at 850 °C was used. The products for coffee grounds were 55.6% syngas and 35.59% yield of hydrogen, while tea bag residue produced 36.0% syngas and 32.44% hydrogen. Pyrolysis of the combined wastes provided 45.6% syngas with the highest content of hydrogen being 39.13% and a calorific value of 4568 kcal/kg, confirming there was a synergy effect. In contrast to the single feedstock pyrolysis, the mixture enhanced hydrogen production and gas quality. These findings demonstrate the potential of co-pyrolysis to simultaneously valorise two widely available residues and generate clean hydrogen-rich syngas. This work addresses a gap in the literature by evaluating tea and coffee residues together and highlights their contribution to sustainable waste management and renewable energy pathways.