(560c) Hydrothermal Liquefaction: Effect of Various Waste Streams As Reaction Medium

Abstract

Hydrothermal liquefaction of biomass is the thermochemical conversion of biomass into liquid fuels by processing in a hot, pressurized water environment for sufficient time to break down the solid biopolymeric structure to mainly liquid components. Typical hydrothermal processing conditions are 250–374 °C of temperature and operating pressures from 40 to 220 bar. The process is meant to provide a sustainable treatment of wet materials without the need for drying and to exploit ionic reaction conditions by maintaining a liquid water processing medium. The temperature range is sufficient to initiate pyrolytic mechanisms in biopolymers while the pressure is sufficient to maintain a liquid water processing phase.

The current hurdles for HTL commercialization are the cost associated with the very high operating pressure as well as low and often unpredictable conversion efficiencies. A significant amount of research and development on catalytic HTL has been undertaken in order to provide higher yields. The most commonly considered “catalyst” has been different alkalis, which modify the ionic medium to favor base-catalyzed condensation reactions and lead to formation of aromatic oils. Dairy manure, sewage sludge from water treatment plant, and digestate from anaerobic digester are slightly basic mainly because of the presence of urine, alkaline solution, and ammonium hydroxide, respectively. Moreover, these wastes contain significant amount of inorganics, ranging between 10% and 40% based on their dry organic matter. While these wastes maybe considered as liability in the dairy and waste treatment industries, an alternative, value-added approach for processing the waste is presented in this work.

In this study, feasibility of waste streams e.g. dairy manure, sewage sludge etc. as reaction medium for HTL of pine wood (pinus taeda) was evaluated. HTL conditions for this study were limited to 250-300 °C and 5-30 min. The quality of the biocrude was determined by means of heating value, elemental analysis, viscosity, density, and GC-MS analysis. In the absence of catalysts, the biocrude yield was shown to increase with HTL time and temperature. The results also revealed an increase in the yield by addition of sewage sludge and dairy manure to the lignocellulosic biomass feedstock. GC-MS spectra pointed out that despite the similar energy value of the biocrude; the chemical constituents depend upon the reaction media. The presence of different inorganics in the reaction medium most probably had a catalytic effect, in turn altering the biocrude composition. These studies suggest that waste streams applied as reaction medium for HTL of woody biomass improve yield and reduce the reaction temperature (and pressure).  The presentation will give a snapshot of the status of the ongoing experimental program, and the direction for future research.