(90e) Hydrothermal Liquefaction of Food Waste and Remediation of Aqueous Byproducts

Thermochemical processing via hydrothermal liquefaction (HTL) is capable of processing a broad range of feedstocks, has a favorable fossil energy ratio, and produces an energy-dense liquid bio-oil product and hydrochar co-product with emerging markets. However, there is a well-known obstacle facing current HTL processes that has hampered the adoption of this technology, namely the HTL process produces a considerable amount of aqueous organic byproducts. As such, the carbon yield to bio-oil is reduced and the organic content of the aqueous waste stream exceeds the environmental standards for discharging the water.

The project team is developing HTL technologies to produce bio-oil from commercial and institutional food waste. Using a two-pronged approach, we have demonstrated an improved HTL oil yield while also reducing aqueous contaminants. First, we have successfully identified a stable and active heterogeneous HTL catalyst capable of improving bio-oil yields (dry mass basis) from 19% to 28% compared to traditional homogeneous base catalysts. IR spectra, GC/MS chromatograms, and model compound experiments revealed that the heterogeneous catalyst increased oil molecular weight, increased ketone and ether content, and decreased alcohol content, thereby driving products out of the aqueous phase and into the organic oil phase. Second, we have tested two active hydrothermal gasification (HTG) catalysts capable of converting 93%–98% of aqueous organics to permanent gases composed primarily of hydrogen, methane, and carbon dioxide. In addition to reducing aqueous contaminants and simplifying waste water disposal, the hydrogen-rich gas produced from HTG can be recycled to the HTL reactor to improve oil yield and reduce the required residence time.