Predicting the Chemical Composition of Aqueous Phase from Hydrothermal Liquefaction of Model Compounds and Biomasses

Abstract

Hydrothermal liquefaction (HTL) is a promising technique for conversion of wet biomasses containing varying amounts of carbohydrate, protein, lipid, and lignin. In this work, mixtures of these model compounds were subjected to HTL at 335 °C. As many as 67 compounds were quantitated in the aqueous phase, including small organic acids, cyclic oxygenates, fatty acids, nitrogenates, and oxygenated aromatics. The concentrations correlated with the ratio of the model compounds. Principal component analysis separated samples on the basis of their quantitative results which could be linked to their biochemical composition. Concentrations of the analytes were modeled with partial least squares regression, and high-quality predictions were made from quality control (QC) samples and to varying degrees from Dried Distillers Grains with Solubles (DDGS), Miscanthus x giganteus, and Chlorella vulgaris. Values for total organic carbon (TOC), total nitrogen (TN), and pH were also predicted from QC samples, DDGS, M. x giganteus, and C. vulgaris. Carbohydrate and lipid contents mainly influenced TOC values and could be used for minimizing loss of organics, for techno-economic analysis, and for assessing potential for anaerobic digestion and thermal gasification. Pyrazines were modeled using linear, exponential, and second-degree polynomial fits, depending on whether carbohydrate or protein was the limiting biochemical component, which could be a way of controlling nitrogen and carbon displacement to the aqueous phase. This work shows that TOC, TN, pH, and concentrations of single compounds in the aqueous phase from HTL can, in many cases, be predicted from HTL of mixtures of biomass constituents.

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

“…Figure S2 in supplementary data shows the GC-MS chromatograms of the bio-crudes from HTL of Miscanthus, Spirulina and sewage sludge. 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].…”

“…The literature data shows that higher carbon recoveries to the bio-crude are possible in continuous flow HTL reactors and this is an area we aim to improve the operation by, for example, recycling process water, optimising the use of oscillation for increased mixing, increasing the DM content of slurries to the pumpable maximum, improved product separation and potentially longer residence times. In any case, HTL water contains a significant portion of the carbon present in the feedstock, mainly small organic acids [48], which needs to be further utilised either by recycling of HTL water back to the reactor or by further processing (e.g., anaerobic digestion, or hydrothermal gasification).…”

Techno-economic Assessment of Integrated Hydrothermal Liquefaction and Combined Heat and Power Production from Lignocellulose Residues

“…Several treatment methods to enhance carbon recovery have received attention in literature for the aqueous yield such as recirculation, anaerobic digestion, condensed phase ketonization and subsequent gasification, all of which have shown various opportunities and drawbacks [43]. A more direct recovery/upgrading approach is the separation of the organic content through mechanical or thermal separation technologies.…”

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

“…31 A few other small organic acids were observed, which included succinic acid and methylsuccinic acid that are both abundant in the AqP from HTL of carbohydrates and protein. 37…”