Catalyzed pyrolysis of coffee and tea wastes

The pyrolysis of food waste has a double environmental advantage as it contributes to the management and treatment of waste and allows the production of renewable fuels. Spent coffee and tea grounds, were characterized by thermogravimetry to determine their composition and evaluating the pyrolysis kinetics of each lignocellulosic pseudocomponent and pyrolyzed in a fixed bed reactor. Tea grounds had about twice the cellulose and higher pyrolysis activation energy than the coffee grounds sample. At 673 K the pyrolysis of the coffee grounds led to a 42% bio-oil yield while the tea grounds produced only 18% of liquid product, which is compatible with its higher cellulose content and the higher activation energy for pyrolysis. The alkaline carbonates used as pyrolysis catalysts led to an increase in the production of a gaseous product, bio-gas, with a reduction in the production of bio-oil but accompanied by a significant increase in the volatile fraction of the produced bio-oils. Pyrolysis data shows that both coffee and tea residues can be used as raw materials to produce pyrolysis bio-oil and that low-value materials such as alkaline carbonates can be used as pyrolysis catalysts improving the characteristics of bio-oils produced such as acidity and volatility. [Display omitted] •Spent coffee and tea grounds, food wastes, were pyrolyzed in a fixed bed reactor.•Tea grounds composition has twice the cellulose of coffee grounds.•The calculated activation energy was higher for tea than for coffee grounds wastes.•Na and Ca carbonates catalysts improved gasification during pyrolysis.•Catalysts increased the volatile fraction (T