Direct Conversion of Lignocellulosic Biomass to Water-Soluble Compounds Using Metal Hydroxides in Subcritical Water

One-path conversion of lignocellulosic biomass to small organic molecules has attracted much attention as a substitute for materials derived from petroleum chemistry. To develop a new process that can replace the present alkaline digestion technique, various solutions of metal hydroxides and oxides were examined for solubilization of sugi (Japanese cedar, Cryptomeria japonica) powder in subcritical water and 5 Mpa of N-2, because the sulphur contained in the alkaline digestion technique may poison subsequent catalytic processes. The solubilization of sugi powder was accomplished in the presence of LiOH, NaOH, KOH, RbOH, CsOH, Sr(OH)(2), or Ba(OH)(2). The effect of the quantity of hydroxides, reaction temperature, and reaction time were systematically investigated. Full solubilization was achieved at 493 K and a pH of 13 or higher. Sugi powder was dissolved in the following order; hemicellulose, amorphous cellulose, lignin, and crystalline cellulose. The dissolution rate of lignin was 15 times faster than that of crystalline cellulose. Unfortunately, most of the products could not be determined quantitatively. The observed major product was lactic acid with an approximate 14% yield.