Biomass composition impacts the storage property of biocrude oil from hydrothermal liquefaction

Abstract

Hydrothermal liquefaction of abundant, renewable resources such as lignocellulosic biomass and organic waste presents a sustainable route to produce biocrude oil, a potential substitute for petroleum-derived fuels and chemicals. However, the practical application of biocrude oil is hindered by its tendency to degrade during storage, which is intrinsically linked to the variable biochemical composition (carbohydrates, proteins, and lipids) of the feedstock. To elucidate this critical relationship, soybean oil, soy protein, and microcrystalline cellulose were employed as model compounds. The results indicate that biocrude (BC) from soybean oil exhibits the lowest viscosity and residue fraction, the highest heating value, and a narrower molecular distribution, rendering it ideally suited for diesel production. Conversely, biocrude from cellulose solidifies within just two days of storage. The viscosity of biocrude from binary mixtures of protein and cellulose (PC) was observed to be the highest, increasing approximately 57 times the original after 7 days. This rapid increase of viscosity surpasses that of biocrude solely derived from individual protein, attributed to the formation of amide compounds produced from Maillard reaction between cellulose and protein. Further analysis using Fourier transform-ion cyclotron resonance mass spectrometry indicates that the nitrogenous and oxygenated compounds present in protein–cellulose derived biocrude (PC-BC) are highly unsaturated. The double bond equivalent values of PC-BC increase with the number of nitrogen and oxygen atoms. The N_1–4O_0–3 species compounds of PC-BC tend to convert into N₄O_x species. The viscosity of biocrude was positively related to the residue fraction, due to polymerizations, condensations, and alkylations causing conversion of the light molecules into heavier ones, potentially resulting in the formation of asphaltene compounds.