A comparable study on the hot-water treatment of wheat straw and okra stalk prior to delignification

Wheat straw and okra stalk were studied to evaluate their potential use for integrated lignocellulosic biorefining. Besides chemical pulp, a wide spectrum of value-added by-products were prepared by hot-water extraction of the feedstocks under varying conditions (140 °C for 60 and 240 min and 150 °C for 25 and 100 min) prior to sulfur-free soda-anthraquinone (AQ) pulping (NaOH charge 15 and 20% by weight on o.d. feedstock for wheat straw and okra stalk, respectively, with an AQ charge of 0.05% by weight on o.d. for both feedstocks). During the hot-water pre-treatment, the most significant mass removal, respectively, 12% (w/w) and 23% (w/w) of the initial wheat straw and okra stalk was obtained at 150 °C with a treatment time of 100 min. The hydrolysates were characterized in terms of pH and the content of carbohydrates (6–20% (w/w) of the initial amount), volatile acids (acetic and formic acids), and furans. The pre-treatment stage also facilitated the delignification stage, and, for example, the pulp yields (w/w), 57% (145 °C, 15 min, and kappa number 18) and 41% (165 °C, 180 min, and kappa number 32) were obtained for the pre-treated (150 °C, P200) wheat straw and okra stalk, respectively. Results clearly indicated that both non-wood materials were suitable for this kind of biorefining approach.