Efficient conversion of pomelo peel into upgraded bio-crude oil and solid fuel through metal–organic framework catalyzed hydrothermal liquefaction

This study reports on the hydrothermal liquefaction of pomelo peel (PP), with subsequent catalytic upgrading of the bio-crude by metal-organic frame (MOF) catalyst Cu@C. The conversion rate of PP, energy yields of bio-crude oil, and mechanical properties of the hydrochar byproduct after pelletizing were systematically investigated. The Cu@C exerted a good upgrading ability of the bio-crude and was thermal-stable, as was shown upon catalyst recycling tests. The maximum conversion rate of PP was 73.51 ± 0.72 %; and the maximum energy yields of bio-crude oil and hydrochar were 58.53 % and 75.21 %, respectively. The upgraded bio-crude oil produced at 240 °C (CBO240) had the highest C (47.36 wt%) and H (6.96 wt%) contents and the lowest O (40.04 wt%) and N (5.37 wt%) contents, resulting in the highest higher heating value (20.55 MJ/kg). The bio-crude had a high abundance of 3-hydroxypyridine, a product of furfural and ammonia, the former stemming from holocellulose, the latter from proteins. Other cellulose-derived furans and protein-derived diketopiperazines were also observed. The hydrochar pellets had great combustion performance and mechanical strength, making it suitable for solid fuels production.