Hot compressed water extraction of lignin by using a flow-through reactor

Japanese rice straw, an agricultural by-product, was utilized for the extraction of lignin by hot compressed water at temperatures of 443–503 K and a pressure of 4.0 MPa using a flow-through system, a simple and environmentally friendly extraction method requiring no chemicals other than water. Under these conditions, thermal softening of the Japanese rice straw occurred, allowing the removal of lignin via depolymerization reactions. Lignin as an extraction product was analyzed using utraviolet-visible (UV–vis) spectrophotometry. Lignin recovery approached 85% when the extraction was performed at 443 and 473 K with a flow rate of 4.67 ml min^–1. At a constant residence time, recovery amounts increased with increasing flow rate at each temperature. The results suggested that this process may result in an advanced plant biomass components extraction technology.