Improving the recovery of phenolic compounds from spent coffee grounds by using hydrothermal delignification coupled with ultrasound assisted extraction.

This study focuses on the maximization of the phenolic compounds of spent coffee grounds, by coupling hydrothermal delignification with ultrasonic assisted extraction. Temperatures of 200°C, 230 °C and 260 °C were applied for hydrothermal treatment for 1h and 3h. Produced hydrochars contain high values of fuel ratio (0.35 - 0.69) compared to raw feedstock (0.20). The increment of the reaction severity decreases the energy yield from 95.23 % to 82.99 %.   After the hydrothermal treatment, the total phenolic content (TPC of the process water), determined relatively to a gallic acid standard (GAE), was found to be in a similar range for all process conditions (9.52 – 8.07 mg GAE / mg of dry sample). Using methanol as a solvent into produced dry hydrochars during ultrasonic assisted extraction reveals the highest values of TPC (20.33 – 11.66 mg GAE/ mg of dry sample).This study focuses on the maximization of the phenolic compounds of spent coffee grounds, by coupling hydrothermal delignification with ultrasonic assisted extraction. Temperatures of 200°C, 230 °C and 260 °C were applied for hydrothermal treatment for 1h and 3h. Produced hydrochars contain high values of fuel ratio (0.35 - 0.69) compared to raw feedstock (0.20). The increment of the reaction severity decreases the energy yield from 95.23 % to 82.99 %.   After the hydrothermal treatment, the total phenolic content (TPC of the process water), determined relatively to a gallic acid standard (GAE), was found to be in a similar range for all process conditions (9.52 – 8.07 mg GAE / mg of dry sample). Using methanol as a solvent into produced dry hydrochars during ultrasonic assisted extraction reveals the highest values of TPC (20.33 – 11.66 mg GAE/ mg of dry sample).