The effect of aqueous phase recirculation during hydrothermal liquefaction of spent coffee grounds

Abstract

Batch hydrothermal liquefaction of spent coffee grounds was done in this study. The effect of subsequent diluted aqueous phase recirculation was studied at a constant temperature of 275 °C and residence time of 10 minutes. Four recirculation reactions were completed following a control reaction and the results were compared. It was found that the recirculation of the aqueous phase had increased the bio-oil mass yield by 51 %. An increase in the organics and nitrogen concentration was observed in the aqueous phase, while the total organic carbon decreased due to migration of carbon species to the bio-oil product phase. The bio-oil retained its high energy content following the recirculation reactions with a higher heating value of 32.61 MJ/kg. The main component of the bio-oil was identified as C16- C18 aliphatic acids with long carbon chain hydrocarbons