Hydrothermal Extraction of Coconut Fiber Components in the Presence of Ethanol and Supercritical Carbon Dioxide

A new approach to fractionating coconut fiber by the hydrothermal method using ethanol and supercritical (SC) CO2 as cosolvents has been proposed. The efficiency of the method for extracting valuable components due to the synergistic effect of hydrothermal treatment and enhanced solubility of biomass in the ethanol–water–SC-CO2 system has been shown. A 15-min treatment at a temperature of 110°C, a pressure of 12 MPa, and a fiber-to-ethanol weight ratio of 1 : 20 has led to a maximum lignin yield of 65%, which is more than 2 times higher than the yield in the case of hydrothermal extraction with the addition of ethanol (26%). Using IR and NMR spectroscopy, it has been shown that carbonyl groups and the native ratio between G (guaiacyl) and S (syringyl) structural units are preserved in the extracted lignin in accordance with the published data.