Iron powder in-situ catalytic pyrolysis on coated wooden board: Kinetic, products, and recovery

Catalytic pyrolysis is a promising method for the resource utilization of wooden waste, and in-situ catalysis enhances the process and reduces treatment costs. The selection of catalysts is crucial, as their catalytic effect and service life directly impact treatment effectiveness and economic benefits. In this study, iron powder was utilized to examine its potential in in-situ catalytic pyrolysis of coated wooden boards. The results showed that some of the iron powder could compete for oxygen from lignin/ hemicellulose during the early pyrolysis stage, resulting in the formation of FeO and a decrease in CO2. The formed FeO then promoted cellulose decomposition, reducing the pyrolysis activation energy by 26% ∼ 48%. Despite the addition of iron powder, no obvious impact was observed on the distribution of product yields. However, there are differences in the specific composition: the gas products showed a decrease of CO2 by 26% and CH4 by 13%, while the bio-oil showed an increase of phenol by 8%. This revealed that the iron powder primarily changed the energy barrier of the pyrolysis reaction. There was magnetic separation followed by particle size screening for the recovery of solid products. After separation, the recovery rate of iron powder was determined to be only 65.39%. Two kinds of char particles appeared in the separated products: magnetic (M3) and non-magnetic (NM). Approximately 44.45% of total Fe (from Fe powder and coating materials) contents and 73.62% of total Ti (main metal in the primary coating) were found in M3, while only 1.32% and 10.90% in NM, respectively. Interestingly, the distribution of elements Zn, Ba, and Mg was found to be opposite to that of Fe, which mainly distributed in NM and M2. It might be attributed to the primary coating on the M3 surface, which likely to help facilitated the adsorption of iron particles according to the combination of SEM/EDS and ICP-MS results. The adsorption competition effect of Fe and other metals resulted in significant differences in the distribution of metals on several char particles.