CO2-cofed catalytic pyrolysis of tea waste over Ni/SiO2 for the enhanced formation of syngas.

To valorize tea waste (TW), catalytic pyrolysis was done as a practical measure for recovering energy as a form of syngas. Considering CO2 as a reactive gas medium in place of conventional pyrolysis gas, a sustainable pyrolysis platform was established. In addition, mechanistic effectiveness of CO2 on TW pyrolysis was examined. In the presence of CO2, homogeneous reaction with volatile organic compounds (VOCs) derived from TW pyrolysis contributed to CO formation. To enhance the formation of syngas at low pyrolysis temperature, catalytic pyrolysis over a Ni/SiO2 was investigated. The synergistic effects of Ni/SiO2 catalyst and CO2 promoted thermal cracking of VOCs and further homogeneous reaction with CO2, thereby resulting in the substantial enhancement (28 times more) of H2 and CO production than non-catalytic pyrolysis. It was also confirmed that CO2 could be considered a reactive gas medium to produce biochar (34-35 wt.% yield), having competitive porosity and surface area, in comparison to that from pyrolysis in N2. Therefore, CO2 can be employed to build a sustainable waste conversion platform for energy and biochar production through pyrolysis instead of using N2.