Research of the two-step pyrolysis of lignocellulosic biomass based on the cross-coupling of components by Py-GC/MS

Two-step pyrolysis (TSP) of cellulose, hemicellulose, and lignin; the three-component cross-coupling samples; and the acid-washed walnut shell (AWS) were carried out by a pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS) to investigate the effects of components and their proportions on the TSP of biomass. The results showed that different components dominated the formation of different products. Cellulose generated more furans and carbohydrates in both the first (S1) and second steps (S2). Hemicellulose achieved higher selectivity of ketones, acids, and alcohols in S1, and higher selectivity of hydrocarbons in S2. Lignin mainly produced phenols in S1, and hydrocarbons and phenols in S2. The increase of holocellulose (hemicellulose and cellulose) improved the contents of aldehydes, ketones, furans, acids, and alcohols but reduced the content of phenols in S1. In S2, more holocellulose increased the contents of aldehydes, ketones, and acids, but decreased the contents of phenols, hydrocarbons, and alcohols. The generation of carbohydrates was strongly inhibited in S1 by hemicellulose and lignin. More cellulose improved the contents of aldehydes, acids, and furans in S1, and increased the content of ketones but reduced the content of acids in S2. Hemicellulose facilitated the generation of hydrocarbons, but inhabited the produce of carbohydrates in S2. The small amount of the low-content components (protein, alkali and alkaline earth metals, etc.) and the connection structure of the components resulted in the significant difference in the pyrolysis reactions and product distribution of AWS and the mixed sample with corresponding component proportion. Therefore, more influence factors, such as the low-content components, the connection structure of the components, and different pyrolysis conditions, should be considered in the near future to investigate the interactions on the two or more components in TSP.