Comparative Assessment of Proportions of Urea in Blend for Nitrogen-Rich Pyrolysis: Characteristics and Distribution of Bio-Oil and Biochar

This study aimed to investigate the effect of the urea content on the characteristics and distribution of nitrogen-rich bio-oil and nitrogen-doped biochar. Cellulose, cellobiose, and glucose were used as feedstock. Urea was used as the exogenous nitrogen source in nitrogen-rich pyrolysis at 500 °C. The order of the nitrogen increase in the nitrogen-doped biochar was cellulose < cellobiose < glucose. Nitrogen-doped biochar consisted of abundant nitrogen and nitrogenous functional groups, and the stability of biochar was optimal. The nitrogen-doped biochar obtained from cellulose showed the optimal adsorption performance for diethyl phthalate with 50% urea addition. When the proportion of urea was 20%, the content of anhydro-sugars in bio-oil reached the maximum value (61.86%). Furans and other small-molecule oxygenates were intermediates to produce nitrogenous heterocyclic compounds (NHCs) from cellulose. When the proportion of urea was 40%, the bio-oil had the highest selectivity (91.63%) of NHCs. The NHCs in the obtained bio-oil mainly consisted of pyrroles, pyrimidines, pyridines, imidazoles, and pyrazines. Therefore, the excellent proportion of urea in the blend could promote the generation of high-value NHCs and nitrogen-doped biochar from the nitrogen-rich pyrolysis of cellulose (and its model compounds).