Suppressing the formation of N-heteroaromatics during hydrothermal liquefaction of proteinaceous model feedstock

Abstract

AbstractHydrothermal liquefaction was applied to model mixtures containing lard oil (lipid), cellulose (carbohydrate), and bovine serum albumin (protein), representing biogenic organic waste feedstocks. The content of protein was kept constant for every experiment, while the lipid and cellulose content was changed, which is expressed by the lipid to protein (LtoP) or cellulose to protein (CtoP) ratio. The reactions were conducted at 350 °C with a residence time of 20 min in 25 ml micro autoclaves. Afterwards, the lumped recovery of carbon and nitrogen into the different product phases was investigated and representative compounds were identified to get an overview of the composition on a molecular level. A high LtoP ratio results in an increased biocrude yield and eventually higher carbon recovery, while the nitrogen recovery is slightly lowered. The formation of nitrogen containing heteroaromatic species could be suppressed by the addition of lipids from 6.10 to 0.03% for pyrazines and 2.69 to 0.43% for indoles. Consequently, the formation and nitrogen recovery by heteroaliphatic amide species increased from 0.00 to 8.77%. Different reaction pathways for the formation of the different species are proposed. It turned out that reactive amine from protein degradation can be “trapped” in stable amides, preventing the formation of nitrogen heteroaromatics with oxygenated from carbohydrates. Graphical abstract