MgAl-layered double hydroxides catalyzed hydrothermal liquefaction of tigernut for bio-oil production

Tigernut is an oil-rich perennial tuber well developed in non-arable land of Xinjiang, China. It is recognized as a potential feedstock for biofuel production owing to its high lipid content, less water demand, and no arable land demand. However, most of previous works focus on transesterification of tigernut for biodiesel production without totally transfer of carbons into bio-oil, limiting the bio-oil yield. Comparatively, hydrothermal liquefaction (HTL) of whole biomass including conversion of carbohydrates and proteins in pressurized hot water provides a sustainable way for bio-oil production. Accordingly, MgAl-layered double hydroxides with tunable Mg/Al ratios (MgAl-LDHx) were firstly evoked to catalyze HTL of tigernut for bio-oil production. The results indicate that increasing reaction temperature from 200 to 320 ? is favorable to MgAl-LDHx-catalyzed HTL of tigernut, while increasing of reaction time after 0.5 h is negative to bio-oil yield possibly owning to tandem gasification of light and re-polymerization of bio-oil. A maximum bio-oil yield of 38.7% is observed at reaction temperature of 320 ?, time of 2 h, and MgAl-LDH2 loading of 5 wt%, possibly owning to the decomposition of carbohydrates and proteins. Meanwhile, increase of Mg/Al ratio benefits to both bio-oil yield and deoxygenation because more acidic and basic sites supplied with increase of Mg/Al ratio enhance both hydroxylation of cellular compounds and tandem decarboxylation of fatty acids, respectively. This study reveals that MgAl-LDHx are promising catalysts for both decomposition of tigernut and hydrodeoxygenation of bio-oil, providing a potential strategy for bio-oil production.