Nitric Acid-Potassium Hydroxide Fractionation of Rice Straw: an Integrated Biorefinery Initiative

Abstract Rice straw was fractionated with nitric acid in order to avoid the cooking liquor recovery in pulp production from agricultural residue (rice straw). The rice straw treated with 11.03% nitric acid at 90 ℃ for 3hr yields 53.09% pulp. The nitric acid treated rice straw pulp had high amount of lignin and minerals. However, further treatment of nitric acid pulp with low potassium hydroxide reduced the lignin and ash sufficiently as well as the pulp yield. Pulp yield reduced from 53.09 to 34.27%. The papermaking properties of the nitric acid followed by KOH treated pulp showed better quality than the nitric acid pulp. Nitric acid liquor was used several times. Pulp yield decreased in every step of reusing of the nitric acid spent liquor although residual lignin content increased. The final effluent liquor was rich with potassium, nitrogen and biomass that can be used as soil nutrient for cultivation.