Mild potassium hydroxide-based alkaline integrated biorefinery process of Kash (Saccharum spontaneum)

•A mild two-step KOH based integrated biorefinery process has been proposed.•Dissolved lignin was lower molecular weight and higher phenolic hydroxyl group.•KOH lignin can replace up to 40 % phenol in phenol formaldehyde resin preparation.•Cellulose pulp after two stages treatment was 49.7 % on Kash with kappa number 30.3.•Produced pulp showed good papermaking properties. This research focused on the application of integrated biorefinery concept to Kash (Saccharum spontaneum). This was carried out by 1) pre-extraction using potassium hydroxide (KOH) in order to remove silica, some of the lignin and hemicelluloses, 2) further delignification by KOH at varying KOH charges; both stages were operated under 100 °C. The pre-extraction removed 75.6 % lignin, 40.8 % pentosans and 75 % silica from the Kash. With the second KOH delignification under optimum conditions (12 % alkali, 120 min, 90 °C), a pulp yield of 49.7 % (on Kash) with kappa numbers 30.3 was obtained. KOH Kash pulp was bleached to 86.3 % brightness in D0(EP)D1 bleaching sequence with good papermaking properties. The KOH spent liquor, which contains silica and dissolved organics, was further investigated for value-added utilization. The dissolved biomass in KOH spent liquor improved soil properties, thus increasing Kolmi sag production in pot experiment. The dissolved lignin in KOH spent liquor was isolated and characterized with lower methoxyl content, higher phenolic hydroxyl content and lower molecular weight, consequently it can replace up to 40 % phenol in phenol formaldehyde resin preparation.