Potassium hydroxide pulping of rice straw in biorefinery initiatives M. Sarwar Jahan a,⇑ , Fahmida Haris a,b , M. Mostafizur Rahman a , Purabi Rani Samaddar b , Shrikanta Sutradhar a a Pulp and Paper Research Division, BCSIR Laboratories, Dhaka, Dr. Qudrat-i-Khuda Road, Dhaka 1205, Bangladesh b Department of Chemistry, Eden Girls College, Dhaka, Bangladesh highlights  KOH pulping of rice straw and wheat straw were carried out.  Pulp was bleached and papermaking properties were evaluated.  Pulp yield and bleachability were better than the corresponding soda pulp.  Silica and lignin were separated from the black liquor of KOH black liquor.  Silica, lignin and hemicelluloses separated waste water can be used in irrigation. article info Article history: Received 11 June 2016 Received in revised form 2 August 2016 Accepted 3 August 2016 Available online 5 August 2016 Keywords: Potassium hydroxide Pulp yield Kappa number Papermaking properties Bleaching Silica Lignin abstract Rice straw is supposed to be one of the most important lignocellulosic raw materials for pulp mill in Asian countries. The major problem in rice straw pulping is silica. The present research is focused on the sep- aration of silica from the black liquor of rice straw pulping by potassium hydroxide (KOH) and pulp eval- uation. Optimum KOH pulping conditions of rice straw were alkali charge 12% as NaOH, cooking temperature 150 °C for 2 h and material to liquor ratio, 1:6. At this condition pulp yield was 42.4% with kappa number 10.3. KOH pulp bleached to 85% brightness by D 0 EpD 1 bleaching sequences with ClO 2 consumption of 25 kg/ton of pulp. Silica and lignin were separated from the black liquor of KOH pulping. The amount of recovered silica, lignin and hemicelluloses were 10.4%, 8.4% and 13.0%. The papermaking properties of KOH pulp from rice straw were slightly better than those of corresponding NaOH pulp. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Bangladesh is very small country with high population density. But GDP growth rate in Bangladesh is above 6 since last 10 years except 2009–10, consequently living standard of people is increas- ing. Global production of paper and paperboard in 2014 was 400.2 million tones (FAO, 2016). The per capita paper and board con- sumption in Bangladesh is about 3.5–4 kg, which is much lower than the advanced countries (300 kg/capita), the world average (ffi50 kg/capita) and the Asian average ((ffi50 kg/capita) (Quader, 2011). To reach the paper and board consumption to Asia level, our consumption will increase to 10 times of current consumption. So Bangladesh needs alternative fibrous raw materials as forest resources is very limited. Rice straw and wheat straw are the most abundant agriculture residues those are produced in large quantity in Asian countries. Non-wood materials, particularly wheat straw, rice straw, bagasse, bamboo are exploited as the main raw material for papermaking in China and India. The main problem that hin- ders the intensive use of non-wood raw materials in papermaking industry is the environmental pollution caused by black liquor. The major agricultural waste in Bangladesh is rice straw, which produced around 34.4 million tons of rice in FY 2013-14 (FAO, 2016). Every kilogram of grain harvested is accompanied by pro- duction of 1–1.5 kg of the straw (Maiorella, 1985). As a result 34–52 4 million tons of rice straw is produced in Bangladesh. Like many other lignocellulosic biomass, rice straw is mainly composed of cellulose (32–47% by dry weight), hemicellulose (19–27%), and lignin (15–24%) (Binod et al., 2010). The abundance of carbohy- drates in straw renders it as a potential source for biofuel and bio- chemicals in addition to pulp production. Silica is a problem http://dx.doi.org/10.1016/j.biortech.2016.08.008 0960-8524/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: sarwar2065@yahoo.co.uk (M.S. Jahan). Bioresource Technology 219 (2016) 445–450 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech