Insight into the synergistic reaction mechanism of biomass pseudocomponents and polyamide by TG-MS and Py-GC/MS: Pyrolysis properties, reaction kinetics and N-containing species evolution

To unveil the nitrogen migration and conversion characteristics, catalytic copyrolysis of biomass pseudo components and polyamide (PA) with different blend ratios (1:0, 5:1, 3:1, 1:1, 1:3, 1:5, 0:1) under an ammonia atmosphere was proposed to boost the yield of N-containing compounds (NCCs) and N-rich biochar. The evolution and distribution of NCCs in liquid, gas and biochar were systematically investigated with a combination of TG-MS, Py-GC/MS and EPR. Synergistic effects and possible reaction pathways were also evaluated. Experimental results showed that PA could obviously boost biomass conversion due to increasing the chance of secondary cleavage, and the comprehensive synergistic effect of biomass-derived H* radicals, acid sites of the catalyst and cracking reactions (-C-N and C-C bonds) that reduced the reaction energy barrier and enhanced the NH3 and HCN yields. NH3 comes from the amino acids that are released from the amino acid pyrolysis and hydrolysis of HCN on the surface of char, while HCN is from the secondary cracking of primary pyrolysis products. Adding biomass increased CO2, CO, CH4, C-O and C=O emissions from co-pyrolysis. Additionally, significant synergetic effects were observed when Biomass/PA= 3:1, which improved the NCCs and pyridine yields by 78.58% and 48.23%, respectively, under the HZSM-5 catalyst. A lower proportion of PA addition facilitated the Maillard reaction and amide bond cleavage to enhance the NCCs content and suppressed pi-conjugated ring structure compound evolution and coke-derived O-containing compound polymerization, while a higher content of PA was favorable for amine and diaza heterocycle compound formation. Moreover, the addition of PA reduced the HHV and N content in biochar, resulting in lower pyrrole-N content and graphitization degree due to secondary cross-polymerization reaction of reaction volatiles, but it enhanced the polarity due to higher oxygen content (14.98%).