Co-pyrolysis of cellulose with urea and chitosan to produce nitrogen-containing compounds and nitrogen-doped biochar: Product distribution characteristics and reaction path analysis

Abstract

Using lignocellulose to produce nitrogen-rich bio-oil and nitrogen-doped biochar in the presence of nitrogen-carrying bodies has become a research hotspot in recent years for high-value conversion and utilization of biomass. Different nitrogen carriers significantly influence biomass pyrolysis and conversion process and products. This study aimed to produce nitrogen-containing chemicals through co-pyrolysis of cellulose and nitrogen carrier (urea and chitosan). The optimal conditions for producing these high-value-added chemicals by nitrogen-rich cellulose pyrolysis were analyzed and summarized. The results showed that the main nitrogen compounds in the co-pyrolysis with urea were pyridine, pyrrole, imidazole, and nitrile. In contrast, those in the co-pyrolysis with chitosan were pyridine, pyrazine, and nitrile. The optimum reaction temperature and mixing ratio of nitrogen-rich pyrolysis were 550 °C and 50%, respectively. The addition of chitosan significantly promoted the biochar yield, reaching 36.56%. The nitrogen content of urea biochar gradually decreased with the increase in temperature. The nitrogen content of chitosan biochar increased to a certain extent with the increase in temperature but reached the lowest at 750 °C, mainly because the amino group retained the solid products in the pyrolysis process. The presence of amino groups also promoted the formation of nitrogenous compounds. In addition, this study discussed the reasons for the differences and the possible reaction paths during pyrolysis based on the differences in the main components of the two nitrogenous compounds to provide some help for the subsequent scale production.