Synergistic Effects of Inexpensive Mixed Metal Oxides for Catalytic Hydrothermal Liquefaction of Food Wastes

Abstract

Industrial wastes and natural mixed oxide materials were evaluated as inexpensive heterogeneous catalysts for catalytic hydrothermal liquefaction (CHTL) of food wastes. Red mud and red clay achieved biocrude carbon yields of 47.0 and 39.5% with higher heating values (HHVs) of 40.2 and 37.7 MJ kg–1, respectively, which were much greater than those without the catalyst (biocrude carbon yield of 19.7% and HHV of 36.1 MJ kg–1). Biocrude characterization revealed that similar families of molecules were formed in the presence and absence of catalysts, implying that the main role of the catalyst is to promote rates of thermal reactions, leading to biocrude production without opening new pathways. The crystalline structures of inexpensive mixed oxides were stable under hydrothermal conditions, with modest calcium leaching (7.5%) and trace leaching of other metals. Using red clay or red mud resulted in >40% recovery of the energy in food waste as biocrude, greater than that obtained under noncatalytic conditions (18%) or from any individual constituent oxide (19–27%). The improved CHTL performance of the mixed metal oxides compared with single-metal oxides was attributed to the synergistic effects of base and acid sites present on catalyst surfaces; mixed oxides presented balanced densities of acids and bases, whereas the constituent oxides were either primarily acidic or primarily basic. The percent of energy recovered as biocrude oil was strongly correlated with the base-to-acid site density ratio, providing an important performance predictor for CHTL conversion of food waste to bioenergy.

Lignocellulosic and algal biomass for bio-crude production using hydrothermal liquefaction: Conversion techniques, mechanism and process conditions: A review

“…It is clear that alkalis (homogeneous catalyst) appear to be effective than organic acids that lead to an improvement in its heating value and yield, though, usage of the heterogeneous catalyst by various researchers shows a positive result in the biocrude yield [126][127][128]. More freshly, solid based catalyst (CaO/ZrO 2 ) in 10 wt% is used with the different solvent to improvise the compound selectivity and HHV value [129,130].…”

Waste-to-wealth application of wastewater treatment algae-derived hydrochar for Pb(II) adsorption

“…Currently, most biomass derived carbons are synthesized through hydrothermal carbonization (HTC) or slow pyrolysis (SP) method, in which the char is the main product. Unlike HTC or SP, hydrothermal liquefaction (HTL) is a promising route to generate bio-oil as primary product [16] . In the meanwhile, hydrochar can be obtained from HTL as byproduct with yield ranging from 20 to 40% [17] , which unfortunately has negative effect on the economic benefit.…”

Hydrothermal Liquefaction of Food Waste: Effect of Process Parameters on Product Yields and Chemistry

“…The addition of an acid catalyst to HTL of carbohydrate-rich food waste increased biocrude oil yield from 25 to 43 wt.% (Posmanik et al, 2017). In another study, addition of inexpensive red mud and red clay catalysts to HTL of food waste at 300 • C for 1 h increased the biocrude oil yield and promoted the thermal reaction rate; similar families of molecules in bio-crude oil with and without catalysts were observed (Cheng et al, 2020c). Model compounds have been studied to understand their effects on bio-crude oil yield and physicochemical and thermal properties (Aierzhati et al, 2019;Chen et al, 2019b).…”