Pyrolysis and in-line catalytic decomposition of excavated landfill waste to produce carbon nanotubes and hydrogen over Fe- and Ni-based catalysts – Investigation of the catalyst type and process temperature

Abstract

Undeniably, non-sanitary landfills existing worldwide pose considerable environmental risks related to air, water and soil pollution. Despite that, the landfill mining concept does not spread swiftly around the world. To prevent its fading into oblivion, it is necessary to transform the perception of landfills as waste to seeing them as stocks of valuable materials. Guided by this idea, this novel study investigates the possibility of producing carbon nanotubes (CNTs) and hydrogen-rich gas, materials crucial for our transition towards a more sustainable future, from excavated waste as these. To the best of our knowledge, this is the first study on catalytic pyrolysis of excavated waste. For this purpose, excavated waste was subjected to pyrolysis followed by in-line catalytic decomposition of the produced pyrovapours. The impact of the catalyst type and catalyst bed temperature on the process performance was analysed. Six types of monometallic and bimetallic Ni- and Fe- based catalysts, synthesised using two methods (the sol–gel and the impregnation method), were considered. Three catalyst bed temperatures were taken into account, namely 700 °C, 800 °C, and 900 °C. The results showed that the bimetallic catalyst prepared by using the sol–gel method (FeNi/Al_Sg) outperformed the other analysed catalysts, yielding 9 mmol/gsample_daf of H2 and 76 mg/gsample_daf of CNTs at 800 °C. The product yields and quality were comparable to those reported in the open literature for homogeneous plastic waste pyrolysis. Eventually, the future research directions were discussed.