Evolution mechanisms of bio-oil from conventional and nitrogen-rich biomass during photo-thermal pyrolysis.

Photo-thermal (PT) pyrolysis has emerged as a promising technique for efficiently converting biomass into high-quality bio-oil. The pyrolysis characteristics of rice straw (RS) and rapeseed cake (RC) were analyzed using a photo-thermal reactor with heating rates of 20, 200 and 500 °C/min and compared with 20 °C/min fixed-bed (FB) pyrolysis at 750 °C. Due to the uneven temperature distribution caused by its limited heating area, fast PT heating significantly increased the presence of high molecular weight components (>650) in the bio-oil. PT pyrolysis of RS exhibited higher phenolic contents compared to FB pyrolysis, whereas RC oil showed enhanced decomposition of fatty acids through ketonization. In terms of N-compounds, PT slow pyrolysis oil contained more nitriles but fewer linear amines/amides than FB, while more cyclic amides were formed under fast PT pyrolysis. Furthermore, the analysis of heavy components revealed that more aromatic compounds with low H/C ratios were produced in fast PT pyrolysis oil. Overall, PT heating exerted dual effects by reducing secondary reactions and synergistically enhancing inner-particle reactions with fast heating. This study provides valuable insights into the mechanism of bio-oil evolution under PT pyrolysis. [Display omitted] • PT pyrolysis produces bio-oil with more MW > 650 components. • Phenols in RS oil reach 33.2% in fast PT pyrolysis, but only 19.4% in fixed-bed. • PT pyrolysis benefits the fatty acids decomposition to ketones in RC oil. • Nitriles and lactams are promoted in RC slow and fast PT pyrolysis respectively. • Fast PT pyrolysis enhances the aromaticity of the heavy components. [ABSTRACT FROM AUTHOR]