(99c) Catalytic Hydrothermal Liquefaction of Food Waste Using Inexpensive Catalysts

A recent DOE study showed that more than 13.6 million dry tonnes of food waste is produced every year in the United States[1], most of which is disposed of in landfills. Globally, there is an estimated 1.3 billion tonnes of food disposed of in landfills annually[2]. Therefore, food waste represents a significant organic resource which is inexpensive, has a high energy density and has the potential to be converted into drop-in transportation or heating fuels[3]. In addition, repurposing food residues helps divert a significant percentage of material from landfills and hence reduces the greenhouse gas emissions produced by the subsequent biodegradation of the organic waste.

Hydrothermal liquefaction (HTL) is a promising method of the conversion of organic waste and biomass streams with high water content, into a carbon rich bio-oil, along with bio-char and residual aqueous phases[4]. However, organic compounds partitioning into the HTL aqueous phase reduce the oil recovery and require costly water purification steps. Therefore, in order to reduce the water-soluble HTL organics, carbon-carbon and other coupling reactions are desirable to increase the product molecular weight, hence the oil phase solubility. Catalysts can promote such coupling reactions. In the literature, both homogenous and heterogeneous catalysts are utilized with HTL to increase the bio-oil yields and energy recovery[5-8]. Recently, we reported the use of CeZrO_x catalyst for HTL of food waste[8]. CeZrO_x catalyzed HTL showed significant improvement to the bio-oil yield and energy recovery compared to non-catalyzed and Na₂CO₃-catalyzed HTL, while reducing the organic content of the aqueous phase. Using model compounds, it was shown that CeZrO_x promotes carbon-carbon coupling aldol reactions. In addition, CeZrO_x exhibits hydrothermal stability at 300°C. However, this is a relatively expensive catalyst material containing the rare earth metal cerium.

In this study, we evaluated the catalytic viability of inexpensive acid and base solid oxide catalysts, including red mud (Bayer process waste), red art clay and fly ash (from coal combustion power plants) using batch HTL reactions on a representative consumer food waste at 300 °C and 20.7 MPa. HTL bio-oil products were evaluated for their energy content using higher heating values and total organic content of the aqueous phase product was determined using total organic carbon (TOC) analyzer. The results show that red mud and red clay improved the total oil recovery relative to non-catalyzed HTL reactions by reacting water-soluble organics.

Acknowledgements

This work was funded by a Department of Energy SBIR (Grant Number DE-SC0015784). Carla Roma, Caroline Murphy, Lawrence Valeros and Joseph Esposito supported the experimental work on this project.

References

[1] U.S. Department of Energy. Biofuels and Bioproducts from Wet and Gaseous Waste Streams: Challenges and Opportunities; U.S. Department of Energy: Washington, DC, USA, 2017.

[2] Food and Agriculture Organization of the United Nations, http://www.fao.org/save-food/resources/keyfindings/en/

[3] Sanjib Kumar Karmee, Renewable and Sustainable Energy Reviews, 53 (2016) 945–953.

[4] S.S. Toor, L. Rosendahl and A. Rudolf, Energy 36 (2011) 2328-2342.

[5] L. Nazari, Z. Yuan, S. Souzanchi, M. B. Ray and C. Xu, Fuel 162 (2015) 74–83.

[6] Zhu, Y.; Biddy, M.J.; Jones, S.B.; Elliott, D.C.; Schmidt, A.J. Appl. Energy 2014, 129, 384–394.

[7] Ross, A.B.; Biller, P.; Kubacki, M.L.; Li, H.; Lea-Langton, A.; Jones, J.M. Fuel 2010, 89, 2234–2243.

[8] Alex R. Maag, Alex D. Paulsen, Ted J. Amundsen, Paul E. Yelvington, Geoffrey A. Tompsett and Michael T. Timko, Energies 2018, 11, 564, 1-14.