Dairy product manufacturers contend with large volumes of waste ice cream (WIC) that cannot be sold due to allergen contamination and/or failed product specifications. Simultaneously, there is a significant need and opportunity to thermochemically upgrade biomass into higher-value products, such as sustainable aviation fuel and biochar. As a two-pronged solution to both issues, we studied the hydrothermal liquefaction (HTL) of WIC, where our goals were to (1) optimize process conditions for producing value-added products and (2) determine the distribution of proteinaceous nitrogen into specific products. Two types of melted WIC (standard and high-fat content) underwent HTL for 1 h at varying temperatures (210−330 °C), catalysts and additives (Ru/C, Pt/C, Pd/C, and Na2CO3), and gaseous environments (N2, H2). HTL at 210 °C without any additives produced the highest yields of hydrochar compared to other conditions. Mass yield of hydrochar directly correlated with yield of nitrogen in the hydrochar. Addition of sodium carbonate doubled the yield of biocrude and increased the efficiency of nitrogen partitioning into the hydrochar. Under reducing conditions with Ru/C, HTL produced the highest yields of paraffinic biocrude. However, HTL under catalytic hydrotreating conditions tended to increase unwanted partitioning of the proteinaceous nitrogen into the biocrude. Catalytic hydrotreatment of the biocrude produced products from both decarboxylation and hydrodeoxygenation pathways. To maximize yield and minimize nitrogen in biocrude, a two-step hydrotreatment process is recommended by first treating at 210 °C using 2 wt % Na2CO3, whereby a subsequent catalytic hydrotreatment on only the oil (330 °C and above) will convert free fatty acids into paraffin hydrocarbons.
Elkasabi et al. (Wed,) studied this question.