Synergistic microwave–metal interactions in polyurethane/biomass co-pyrolysis: unraveling reaction mechanisms and product selectivity control

Abstract

This work proposed a co-microwave pyrolysis approach for polyurethane and biomass based on microwave–metal interactions. Four metal-modified biochar catalysts (Co/BC, Ce/BC, Cu/BC, and Fe/BC) were synthesized. The influence mechanisms of the pyrolysis temperature, microwave power, and catalyst type on the distribution of co-catalytic pyrolysis products (oil, gas, and char) were systematically investigated. Compared with conventional pyrolysis, microwave pyrolysis significantly reduced the reaction temperature required to achieve the maximum product yield by as much as 150 °C. This reduction in temperature effectively decreased the energy consumption. The synergistic effects of Joule heating and volumetric heating induced by microwave–metal interactions considerably accelerated the heating rate. Microwave-induced plasma effects, in conjunction with metal-modified catalysts, promoted the formation of aromatic hydrocarbons. The Fe/BC catalyst exhibited superior aromatization performance, achieving a maximum aromatic hydrocarbon yield of 58.2 wt%, representing a 122% increase compared with that of conventional pyrolysis. In contrast, the Cu/BC catalyst was the most favorable for the production of nitrogen-containing compounds, reaching a yield of 25.0 wt%. Rapid heating enhanced the reverse Boudouard reaction, thereby increasing CO production while simultaneously facilitating dehydrogenation reactions. Finally, based on experimental findings and correlation analysis, potential formation mechanisms of aromatic hydrocarbons and nitrogen-containing compounds during the microwave co-catalytic pyrolysis of polyurethane and biomass were proposed.