Pyrolysis of coal and biomass in a fixed bed with internals to produce volatiles with respectively enriched light and heavy fractions

• Internals-regulated pyrolysis enables respective enrichment of light and heavy fractions. • Light oil fraction through catalyst-free enrichment surpasses most catalytic studies. • The enrichment approach demonstrates broad applicability across various conditions. • Selective cracking of heavy-species-rich oil can maximize the yield of light oil. Achieving respective enrichment of light and heavy fractions in fuel pyrolysis poses a significant challenge. In this study, we devised the regulation of pyrolysis reactions in a fixed bed with internals (internals-regulated pyrolysis) to allow progressive pyrolysis using Shenmu coal, Naomaohu coal, walnut shell biomass, and corn stalk biomass as feedstocks, thus achieving the respective collection of volatiles at different stages of pyrolysis. During the initial stage of pyrolysis, it produced pyrolysis oil rich in light species, although without using any catalyst. The fraction with boiling points below 350 °C was over 82 wt%, being actually higher than the usual values obtained in catalytic upgrading. In the late stage of pyrolysis, the produced oil contained more heavy species . It was found that the furans and phenols with relatively low and high boiling points were enriched in the initial and late stages of biomass pyrolysis, respectively. The efficient enrichment is achieved under the conditions of different feedstock types, heating temperatures and bed thicknesses, demonstrating the universality of enrichment approach. The light oil yield based on the Gray-King method is 59 wt% for catalytic cracking of oil rich in heavy fraction and 54 wt% for catalytic cracking of all oil components, highlighting the essential requirement for selective cracking of heavy species using the newly developed approach.