Reaction kinetics and characterisation of species in renewable crude from hydrothermal liquefaction of monomers to represent organic fractions of biomass feedstocks

Abstract

Hydrothermal liquefaction (HTL) can be used to convert a range of biomass feedstocks to a renewable crude with solid, aqueous and gas co-products. In order to characterise the HTL process so that the products can be predicted for a range of reaction conditions from varying feedstock, bulk kinetic models that predict the yield of each phase from the organic composition of the feed biomass, including carbohydrate, lipid, protein and lignin components are required. Due to the complexity of the reactions and variation in the organically rich wet feedstocks being considered for HTL, investigations using model compounds have been performed by numerous researchers. In the current work monomer model compounds including glucose, oleic acid, alanine and guaiacol have been used in multivariate HTL experiments in a batch reactor at reaction temperatures of 250, 300 and 350 °C for reaction times of 5 to 60 min. The resulting yields of renewable crude, solid, aqueous and gas products allowed a model to be developed for HTL of these monomer model compounds that could be compared to a second model previously developed for products from HTL of polymer compounds from the same families. Gas chromatography-mass spectrometry analysis of renewable crude products identified that lipid produced fatty acids. Carbohydrates produced crude consisting of phenol, furans, aldehydes, aromatics and ketones. HTL of the protein monomer resulted in a renewable crude composed of amides, aromatics, amines, carboxylic acids and short hydrocarbon chains and phenolic compounds made up the majority of the renewable crude from the lignin model compound.