(684e) Hydrothermal Liquefaction of Wet Organic Wastes Using Sub-Stoichiometric Homogenous Oxidant

The United States produces more than 24 billion gallons of wastewater per day. Treating this volume of wastewater requires more than 30 TW-hr of energy and are burdened by the production of 6 million dry tons of biosolids – an organic byproduct containing 5 times the needed energy to operate treatment facilities. A high-water content limits energy recovery to 15% of biosolids via incineration. Hydrothermal liquefaction (HTL) offers a promising alternative to incineration for recovering the energy content of wastewater solids, thereby making wastewater treatment energy-neutral or even net energy-producing.

HTL heats organic waste streams to 250-400 °C while maintaining a liquid water phase. After reaction times ranging from minutes to an hour, an energy-dense biocrude product is formed due to depolymerization and recombination reactions. HTL has yet to be commercialized because current technology is limited to approximately 40% carbon recovery as biocrude, with the rest of the carbon forming gases, a carbon-rich solid char, and aqueous soluble products. HTL proceeds via a complex network of covalent and radical reactions. In this study, we added hydrogen peroxide as an oxidant, exothermic reaction partner, and radical source to promote HTL. We find that the sub-stoichiometric addition of hydrogen peroxide boosts biocrude yields from 40% to 60% at optimal conditions of 300 °C and 10 min of reaction time, with a corresponding decrease in char yields from 10 to 5%. Interestingly, gas and aqueous phase yields are not affected by hydrogen peroxide addition. Similarly, the biocrude obtained from the hydrogen peroxide promoted HTL reaction has carbon and hydrogen content similar to that found under standard HTL conditions, indicating its suitability for upgrading to transportation fuel. Combining HTL with the hydrogen peroxide reaction promoter is a powerful new way to increase biocrude yields, decrease char yields, and pave the way for commercial deployment.