The structural characteristics and pyrolysis products properties based on cotton stalks and husks

Cotton is a widely cultivated crop in China, and it could generate the numerous agricultural wastes, which is prohibited to combust in recent decades. Pyrolysis represents a convenient method for waste treatment, whereby cotton waste can be converted into bio-oil, biochar and pyrolysis gas, thus increasing its economic value. In this study, the microstructural differences between cotton stalks (CS) and cotton husks (CH) were primarily investigated through ultimate, proximate, and NMR analysis. Subsequently, the two feedstocks were subjected to pyrolysis in a carbonization furnace at 550 °C. The characteristics of the three-phase products (bio-oil, bio-char and pyrolysis gas) were systematically detected and analyzed. The proportion of holocellulose in CS was determined to be 72.06 %, while that of cotton husks was 74.79 %. 2D NMR analysis revealed that the CS exhibited a greater proportion of G monomers compared to CH. It was demonstrated that the pyrolysis products of CS and CH exhibited comparable distributions. However, the bio-oil composition of CS and CH differed significantly. CS exhibited the higher phenol and acid contents, while CH displayed the higher ketone and ester contents. The pyrolysis gas of CS has a high calorific value, and the biochar exhibits the low oxygen and sulfur content, which may be favorable for clean combustion and agricultural application. Besides, the economic assessment showed that CH has more profit than CS. Therefore, this study provides a theoretical rationale for high value utilization of cotton waste, and delivers valuable references for the sequent research on the pyrolysis products application. • Cotton stalks possessed more G units than in cotton husks through 2D-HSQC. • The pyrolysis products yields are similar in CS and CH but the properties are not. • CSV was rich in ketones and phenols but CHV contained more acids. • The biochar from CS had less N and O elements as compared to those in CH. • The profit of CH was higher than CS during pyrolysis by economic assessment.