110th Anniversary: Influence of Solvents on Biocrude from Hydrothermal Liquefaction of Soybean Oil, Soy Protein, Cellulose, Xylose, and Lignin, and Their Quinary Mixture

We perform hydrothermal liquefaction (HTL) on five materials that model the major biochemical components in a wide array of biomass feedstocks: soybean oil, soy protein, cellulose, xylose, and lignin. The influence of different solvents (dichloromethane, acetone, methyl tert-butyl ether (MTBE)) on the yield, and the elemental content of the biocrude recovered from isothermal and fast HTL of these model compounds is determined. MTBE gives an ∼30% lower biocrude yield and about twice the solids yield, compared with dichloromethane (DCM) and acetone for both fast and isothermal HTL of a mixture of the five materials; however, the MTBE-recovered biocrude has the largest higher heating values (HHVs). The three solvents give similar biocrude yields for HTL of soybean oil and soy protein individually. Acetone recovers the highest biocrude yields from both isothermal and fast HTL of cellulose, xylose, or lignin individually, but the carbon content, hydrogen content, and HHV of the acetone-recovered biocrude are the lowest. The biocrude yields from the different feedstocks do not consistently vary monotonically with the normalized solvent polarity (ETN), which indicates that this property alone is not the controlling factor. Moreover, high yield and large HHV of the biocrude may not be available simultaneously with the pure solvents explored herein, which suggests there may be opportunities for solvent engineering in HTL product recovery. The biocrude yields from fast HTL of a quinary mixture of the model compounds are slightly higher than those from isothermal HTL conditions, which provides another example of the efficacy of fast HTL in valorizing biomass.