Influencing mechanism of zinc mineral contamination on pyrolysis kinetic and product characteristics of corn biomass.

The metal mineral has a complex influence on the thermal decomposition of biomass due to the sophisticated structure of biomass and parallel reactions. Therefore, the influencing mechanisms of metal minerals on biomass decomposition kinetic expressions needed to be thoroughly investigated. In this study, the decomposition of the three major components of biomass was considered separately. The iso-conversional method and integral master-plots method based on thermogravimetry were firstly introduced to explore the kinetic model changes after the introduction of zinc mineral. The thermogravimetric results showed that the presence of zinc mineral had discrepant influences on different biomass components, demoting the fragmentation of hemicellulose while promoting cellulose degradation. In the kinetic analysis, the presence of zinc mineral, the activation energy of three pseudo-components (91.90, 184.64 and 210.91 kJ mol-1) increased to 178.84, 299.05, and 359.45 kJ mol-1, respectively. The kinetic models were altered from 2.0-order reaction (F2.0) for hemicellulose, random nucleation (A1.8) for cellulose, and 2.3-order reaction (F2.3) for lignin to F2.8, F3.0, and F3.2, respectively. This indicated that the zinc mineral was beneficial to the occurrence of multimolecular repolymerization of the primary degradation products. In products analysis, the increment of biochar yields and the C4-C5 products of cellulose (especially furfural) in metal-polluted biomass pyrolysis were detected, which confirmed the simulated reaction mechanisms. The obtained results are expected to provide a mechanism reference to practical applications of metal-contaminated biomass.