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

Abstract

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 (E T N), 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.

A Review of Hydrothermal Liquefaction of Biomass for Biofuels Production with a Special Focus on the Effect of Process Parameters, Co-Solvents, and Extraction Solvents

“…Hence, the polarity of a solvent cannot be the sole determinant in evaluating an extraction solvent's performance. There seems to a strong agreement from Valdez et al [154], Xu et al [158], Watson et al [159], and Lu et al [68] that solvent type plays a critical role in the yield and chemical composition of heavy oil extracted from HTL products.…”

“…The aqueous medium consists of a water-soluble organic phase and inorganic phase based on the type and composition of feedstock and the catalyst used. Instead of acetone, many other extractive solvents, such as tetrahydrofuran (THF) [67], toluene [32], dichloromethane (DCM), methyl tert-butyl ether (MTBE) [68], ethyl acetate (EAC), isopropyl alcohol (IPA), and hexane [69] have been tested.…”

“…Polarity of solvent cannot be the sole determinant of evaluating its performance during the extraction process. [68] Yang et al [156] performed sequential selective extraction and separation of bio-oil obtained from liquefaction of Salix psammophila using nine different organic solvents with different polarities. The order of solvents for bio-oil extraction yield from high to low: THF > toluene > EAC > acetone > ether > methylene chloride > methanol > petroleum ether > n-hexane.…”

“…Lu et al [68] experimented with different solvents (DCM, acetone, MTBE) to understand their effect on the yield and elemental composition of heavy oil recovered from HTL processes on different feedstocks (soybean oil, soy protein, cellulose, xylose, lignin, and quinary mixture). Heavy oil yields derived from soybean oil and soy protein did not vary with different solvents, though acetone was found to produce a high yield of heavy oil during the HTL of feedstocks that were high in cellulose, xylose, and lignin.…”

“…Heavy oil yields derived from soybean oil and soy protein did not vary with different solvents, though acetone was found to produce a high yield of heavy oil during the HTL of feedstocks that were high in cellulose, xylose, and lignin. Lu et al [68] observed that the yield of heavy oil from the HTL of feedstocks that are rich in saccharides and lignin is greatly affected by what type of solvent is used for extraction. Acetone exhibited the highest yield of heavy oil extracted, whereas DCM produced the lowest yields of heavy oil, which indicates that even solvents such as acetone and DCM with similar polarities produce varying yields of bio-oil.…”