Two-step pyrolysis of corncob for value-added chemicals and high-quality bio-oil: Effects of alkali and alkaline earth metals

Two-step pyrolysis (TSP) of corncob(CC) coupled with water and acid washing pretreatment was conducted to investigate the effects of alkali and alkaline earth metals (AAEMs) on TSP by Py-GC/MS. TG-FTIR was used to analyze the pyrolysis characteristics of the samples. The results showed that the removal of AAEMs postponed the pyrolysis process and significantly influenced the distribution of the pyrolysis products. As the content of AAEMs decreased, the bio-oil yield increased and the biochar yield decreased. TSP of CC achieved high selectivities for phenols and ketones in the first step and for hydrocarbons in the second step. TSP of acid-washed corncob (ACC) achieved high selectivities for furans in the first step and for sugars in the second step. Additionally, some value-added chemicals such as furfural (11.54%, ACC), 4-vinylphenol (23.57%, CC) and levoglucosan (43.05%, ACC) were also enriched in TSP. Therefore, a promising polygeneration scheme of TSP for the efficient utilization of biomass was proposed. (C) 2019 Elsevier Ltd. All rights reserved.