(757a) Catalyst Screening for the Hydrothermal Liquefaction of Food Waste

Hydrothermal Liquefaction (HTL) is a promising route for conversion of food waste into biocrude oil.^1–3 However, the obtained crude oil has a high heteroatom content, similar to that of the initial food waste. This negatively influences the quality and heating value of the biocrude oil. Hence, removing the N, S and O from the biocrude oil is required to produce a finished fuel. Deoxygenation, denitrogenation and desulfurization can be promoted by using proper catalysts in the HTL process.^4,5 Therefore, in this study, we focused on catalytic HTL (350 °C, 40 min) of food waste by testing several heterogeneous supported metal catalysts (Ni/C, Pt/C, Ru/C, Pd/C, Ni/SiO₂-Al₂O₃, Pt/Al₂O₃ and Ru/Al₂O₃) in the presence and absence of high-pressure hydrogen, metal oxides (CaO, Al₂O_3, CeO₂, La₂O₃ and SiO₂), and a series of acid and base additives. Supported metal catalysts and additives did not increase biocrude yield, but three of the metal oxides led to higher yields with the following order SiO₂>La₂O₃>CeO₂. The elemental compositions and heating values of the biocrudes were sensitive to the catalysts used, especially with the presence of high pressure hydrogen. The supported Ni catalysts regardless of the support types, with or without H₂ gas, resulted in sulfur content below the detection limit (500 ppm). Supported metal catalysts all caused high H content in the crude oil with the highest amount of 8.57 wt%, achieved by Ni/C under high pressure hydrogen. The biocrude oil from HTL with Ni/C under high pressure hydrogen also had the heating value of 33.6 MJ/kg, which was higher than 29.7 MJ/kg for the bio-oil obtained from the HTL with no catalyst. The chemical compositions of the biocrudes were examined by conducting Gas Chromatography- Mass Spectrometry (GC-MS) analysis. The results showed that the amount of fatty acids, the most abundant compounds in biocrude oil from HTL of this particular simulated food waste, is sensitive to the type of catalysts used. Finally, since the biocrude oil yields were affected the most by metal oxide catalysts, these biocrudes were analyzed by thermogravimetric analysis to see how the catalysts affected the relative amounts of heavy and light compounds. Ultimately, the results of this study promotes our understanding of the role of different type of catalysts in HTL of food waste and can guide the selection of catalysts or additives to improve the quality of the biocrude oil.

References:

1. Maag, Alex R., Alex D. Paulsen, Ted J. Amundsen, Paul E. Yelvington, Geoffrey A. Tompsett, and Michael T. Timko. "Catalytic hydrothermal liquefaction of food waste using CeZrOx." Energies11, no. 3 (2018): 564.
2. Aierzhati, Aersi, Michael J. Stablein, Niki E. Wu, Chih-Ting Kuo, Buchun Si, Xu Kang, and Yuanhui Zhang. "Experimental and model enhancement of food waste hydrothermal liquefaction with combined effects of biochemical composition and reaction conditions." Bioresource technology284 (2019): 139-147.
3. Zastrow, Dustin Jay, and Paul A. Jennings. "Hydrothermal liquefaction of food waste and model food waste compounds." PhD diss., Florida Institute of Technology, 2013.
4. Duan, Peigao, and Phillip E. Savage. "Hydrothermal liquefaction of a microalga with heterogeneous catalysts." Industrial & Engineering Chemistry Research50, no. 1 (2011): 52-61.
5. Sánchez-Bayo, Alejandra, Rosalía Rodríguez, Victoria Morales, Nima Nasirian, Luis Fernando Bautista, and Gemma Vicente. "Hydrothermal Liquefaction of Microalga Using Metal Oxide Catalyst." Processes8, no. 1 (2020): 15.