Conversion of a wet waste feedstock to biocrude by hydrothermal processing in a continuous-flow reactor: grape pomace
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Wet waste feedstocks present an attractive opportunity for biomass conversion to fuels by hydrothermal processing. In this study, grape pomace slurries from two varieties, Montepulciano and cabernet sauvignon, have been converted into a biocrude by hydrothermal liquefaction (HTL) in a bench-scale, continuous-flow reactor system. Carbon conversion to gravity-separable biocrude product up to 56% was accomplished at relatively low temperature (350 °C) in a pressurized (sub-critical liquid water) environment (20 MPa) when using grape pomace feedstock slurry with a 16.8 wt% concentration of dry solids processed at a liquid hourly space velocity of 2.1 h−1. Direct biocrude recovery was achieved without the use of a solvent and biomass trace mineral components were removed by precipitation and filtration so that they did not cause processing difficulties. In addition, catalytic hydrothermal gasification (CHG) was effectively applied for HTL byproduct water cleanup using a Ru on C catalyst in a fixed bed producing a gas composed of methane and carbon dioxide from water-soluble organics. Conversion of 99.8% of the chemical oxygen demand (COD) left in the aqueous phase was demonstrated. As a result, high conversion of grape pomace to liquid and gas fuel products was found with residual organic contamination in byproduct water reduced to <150 mg/kg COD.
KeywordsHydrothermal liquefaction Catalyst Gasification Aqueous phase Grape pomace
The authors acknowledge the support for this research provided by the US Department of Energy through its Bioenergy Technologies Office (BETO). Pacific Northwest National Laboratory is operated for the US Department of Energy by Battelle under Contract DE-AC06-76RL01830. Thanks are extended to Larry Oats of Sleeping Dog Winery in Benton City, Washington and Juan Munoz-Oca, Senior Director of Winemaking, Paterson Group of Wineries, Ste. Michelle Wine Estates, for making the grape pomace feedstocks available for these experiments.
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