Study of supercritical carbon dioxide pretreatment processes on green coconut fiber to enhance enzymatic hydrolysis of cellulose

Abstract

Green coconut fiber was treated by supercritical CO₂ with the aim to enhance hydrolysis of its enzymatic cellulose. To this end, different static conditions of CO₂ contact times (3 and 5 h) and polarity modifiers (NaOH, NaHSO₄, ethanol) were evaluated at 20 MPa, 70 °C and 1 h of dynamic extraction followed by fast depressurization. After supercritical CO₂ exposition, SEM images showed fiber damage and FTIR spectra showed decreases of phenolic and wax contents, including a reduction in the degree of the hydrogen bond established between lignin and cellulose. Despite the apparent delignification, supercritical CO₂ did not enhance cellulose enzymatic hydrolyses. Fiber exposed to supercritical CO₂ (5 h) demonstrated that the highest sugar content (540.9 μmol glucose likely limited supercritical CO₂ delignification; however, green coconut in natura can be an innovative substrate for fermentation in alcohol production.

Keywords: Cocos nucifera L.; Delignification; Enzymatic hydrolysis; Lignocellulosic material.