Characterizing Semivolatile Organic Compounds of Biocrude from Hydrothermal Liquefaction of Biomass

Abstract

Hydrothermal liquefaction of biomass produces a complex bio-crude, which can be further upgraded to biofuel or chemicals, but there is a need for improved molecular understanding of product composition and reaction pathways. This study extensively characterizes semi-volatile compounds in bio-crudes from hydrothermal liquefaction (HTL) of microalgae (N. gaditana, C. vulgaris), macroalgae (L. hyperborea), residue (Dried Distillers Grains with Solubles), and lignocellulosic (M. x giganteus). The bio-crudes were analyzed using 2D gas chromatography coupled to time-of-flight mass spectrometry with in-situ silylation. A total of 73 fatty acids were detected of which C18 and C20 compounds were most diverse while palmitic acid was the single most abundant fatty acid. Multiple fatty acid amides were detected in bio-crude from N. gaditana while being almost absent in samples from other lipid and protein containing feedstocks. Several alkylated indoles and quinolines were observed in bio-crudes from protein containing feedstocks. Monoglycerides, indanones, and alkylated benzenediols and chromen-2-ones, which are typically not reported, were also detected. These results provide new knowledge of a bio-crude fraction, which is difficult to characterize.

Continuous Hydrothermal Liquefaction of Biomass in a Novel Pilot Plant with Heat Recovery and Hydraulic Oscillation

“…Other studies have also identified the presence of fatty amides in Spirulina bio-crudes [12]. It has previously been shown that fatty amides co-elute with fatty acids when silylation is employed [49]. However, we have observed a range of fatty amides by using a different instrumental set-up.…”

“…Lignocellulosic biomass is well known to produce a wide range of phenolics mainly from lignin but also from carbohydrates, which also produce alkylated cyclopent-2-enones [47,48]. The most abundant compounds from Miscanthus bio-crude were phenol and catechol derivatives along with series of alkylated hydroquinones and chrom-2-enones previously identified from lignocellulosics [49]. A number of alkylated cyclopent-2-enones were also present although in lower abundance compared to other studies.…”

Qualitative characterization of solid residue from hydrothermal liquefaction of biomass using thermochemolysis and stepwise pyrolysis-gas chromatography-mass spectrometry

“…Potassium carbonate, dichloromethane (HPLC grade), and tetramethylammonium hydroxide (25 wt.% in water) were purchased from SigmaAldrich. Poplar was supplied by Department of Agroecology, Aarhus University (Denmark).…”

“…17 Additionally some indanones and chrom-2-ones were identified along with 1-monopalmitate, which have also been observed in the bio-crude. 25 The presence of trapped or adsorbed bio-crude in the SR means that potentially increased yields are possible for batch HTL with improved product separation. The majority of continuous HTL systems take advantage of in-line filtering 26 and bio-crude is less likely to end up in the SR, which apart from the solvent extraction could explain some of the difference in yields between batch and continuous HTL.…”

Rapid Determination of Water, Total Acid Number, and Phenolic Content in Bio-Crude from Hydrothermal Liquefaction of Biomass using FT-IR

“…7 Lignin is the most important source of phenolics in bio-crudes but may also arise from degradation of carbohydrates and proteins. 8,9 They are present in the volatile and semi-volatile fraction as derivatives of phenols, catechols, hydroquinones, and hydroxypyridines. 9,10 While phenolics exhibit medium to high reactivity towards deoxygenation, hydrogenation of the benzene ring requires increased amounts of hydrogen increasing the expense of the upgrading process.…”