Hydrothermal Liquefaction of Organic Waste Model Compounds: The Effect of the Heating Rate on Biocrude Yield and Quality from Mixtures of Cellulose–Albumin–Sunflower Oil

Hydrothermal liquefaction (HTL) is a promising technology for the conversion of high-moisture biomass into a liquid biofuel precursor without predrying treatment. This study investigated the effects of the heating rate (20–110 °C/min) and feedstock composition on phase repartition of the HTL products. HTL tests were carried out using as feedstocks cellulose, egg albumin, and sunflower oil as model compounds for carbohydrates, proteins, and lipids, alone and in binary mixtures. The biocrude, solid residue, and aqueous phase were characterized in terms of composition and elemental percentage. The effects of binary interactions were studied in terms of product yields and compositions. It was observed that higher heating rates resulted in lower solid yields from all the cellulose-containing feedstocks and, in most cases, in higher biocrude yields and higher energy recovery. The results showed that the heating rate influences also the oil composition. Biocrude and solid yields were compared with their prediction based on the combination of the yields of single model compounds, showing a general increase in biocrude yields and a decrease in solid yields. The most significant deviation is observed with the mixture cellulose–albumin both for the biocrude and solid yields. In fact, the main interactions were recognized for carbohydrate–protein mixtures followed by carbohydrate–lipid and protein–lipid mixtures.