Fast pyrolysis of soybean straw mixed with different nitrogen sources for the production of nitrogen-containing compounds

Abstract

The abundance of oxygen-containing functional groups in bio-oil can be used to produce nitrogen-containing compounds (NCCs), resulting in an increase in the value of biomass utilisation. This paper investigates the effect of nano-alumina (NA) and different nitrogen sources (urea (UR), ammonium carbonate (AC), melamine (ME)) on the fast pyrolysis of soybean straw (SS) for the preparation of bio-oil rich in nitrogen-containing compounds (NCCs). At the Catalyst/Samples ration of 1, after the mixing ratio of urea in the samples had increased from 0% to 50%, the relative content of NCCs and pyrroles increased from 4% and 0.97–46.82% and 22.7%, respectively. Compared with pure soybean straw catalytic pyrolysis, the addition of urea was more beneficial in increasing the relative content of NCCs and pyrroles. The addition of melamine and ammonium carbonate had no significant effect on the promotion of pyrroles in bio-oils.The addition of nano-alumina significantly increased the selectivity of pyrroles compounds in NCCs. When the addition ratio of UR in the samples was 50%, after increasing the ratio of Catalyst/Samples from 0 to 2, the selectivity of pyrroles compounds in NCCs was enhanced from 15.44% to 52.42%. Compared with pure SS pyrolysis, when the urea in the samples was added at a ratio of 50% and the Catalyst/Samples ratio reached 2, the relative content of NCCs increased from 13.7% to 71.27%, the relative content of pyrroles compounds increased from 0% to 37.36% and the selectivity of pyrroles compounds in NCCs increased from 0% to 52.42%. The nano-alumina was able to promote the decarbonylation, cyclisation and the Maillard reaction and had significant catalytic properties for the production of pyrroles compounds from SS with UR. These studies can provide theoretical guidance for the valuable utilization of SS.