Alkaline sulfite–anthraquinone (AS/AQ) pulping of wheat straw and totally chlorine free (TCF) bleaching of pulps |
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| Authors: | Sahab Hedjazi Othar Kordsachia Rudolf Patt Ahmad Jahan Latibari Ulrike Tschirner |
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| Institution: | 1. Department of Wood and Paper Science and Technology, Faculty of Natural Resources, Daneshkadeh Street, University of Tehran, Karadj, Iran;2. Federal Research Center for Forest and Forest Product, Institute for Wood Chemistry and Chemical Technology of Wood, Hamburg, Germany;3. Department of Wood Technology, Section Chemical Technology, University of Hamburg, Germany;4. Islamic Azad University, Faculty of Agriculture and Natural Resources, Karadj, Iran;5. Department of Bioproducts and Biosystems Engineering, Faculty of food, Agriculture and Natural Resources, University of Minnesota, 204 KaufertLaboratory, USA;1. Key Lab of Paper Science and Technology of Ministry of Education, Qilu University of Technology, Jinan, Shandong Province 250353, China;2. Limerick Pulp and Paper Centre, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada;1. Jiangsu Provincial Key Lab of Pulp and Paper Science and Technology, Nanjing Forestry University, Nanjing 210037, China;2. Jiangsu Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, Nanjing Forestry University, Nanjing 210037, China;3. China Institute of Chemical Industry of Forestry Products, Chinese Academy of Forestry, Nanjing 210042, China;1. Chemical Wood Technology, Department of Wood Science, University of Hamburg, Leuschnerstr. 91B, 21031 Hamburg, Germany;2. Thünen-Institute of Wood Research, Leuschnerstr. 91B, 21031 Hamburg, Germany;3. Institute of Environmental Technology and Energy Economics, Hamburg University of Technology, Harburger Schloßstraße 36, 21079 Hamburg, Germany;4. Department for Biochemical Conversion, German Biomass Research Centre (DBFZ), Torgauer Straße 116, 04347 Leipzig, Germany;5. Institute of Wastewater Management and Water Protection, Hamburg University of Technology, Eißendorfer Straße 42, 21073 Hamburg, Germany;1. Institute of Crop Science and Resource Conservation (INRES), Renewable Resources, University of Bonn, Klein-Altendorf 2, 53359, Rheinbach, Germany;2. Enzyme Process Technology (AVT.EPT), RWTH Aachen University, Forckenbeckstr. 51, 52074, Aachen, Germany;3. Metsä Tissue GmbH, Hedwigsthal, 56316, Raubach, Germany;4. Field Lab Campus Klein-Altendorf, Faculty of Agriculture, University of Bonn, Klein-Altendorf 1, 53359, Rheinbach, Germany;5. Institute of Biochemical Engineering (ibvt), TU Braunschweig, Rebenring 56, 38106, Braunschweig, Germany;6. Institute of Developmental and Molecular Biology of Plants, Heinrich-Heine-University Düsseldorf, Universitätsstraße 1, 40225, Düsseldorf, Germany;1. Laboratory of Separation and Reaction Engineering – LSRE, Associate Laboratory LSRE/LCM, Department of Chemical Engineering, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal;2. RAIZ – Paper and Forest Research Institute, Quinta de S. Francisco, Apartado 15, 3801-501 Eixo, Aveiro, Portugal |
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| Abstract: | Alkaline sulfite–anthraquinone (AS/AQ) pulping of wheat straw and totally chlorine free (TCF) bleaching of resulting pulps was investigated. Wheat straw was supplied by the Ferdosii University Experimental Station in Northeastern Iran, cleaned and chopped into about 3–5 cm long pieces. In the AS/AQ pulping experiments, the active alkali charge on oven dry wheat straw, heating time to maximum cooking temperature, AQ dose and liquor to straw ratio were kept constant at 16%, 60 min, 0.1% and 4/1, respectively. The alkali ratio, Na2SO3/NaOH, calculated as NaOH, was varied from 20/80 to 80/20. Cooking time at maximum temperature was varied from 30 to 90 min and maximum cooking temperature was adjusted between 152 and 160 °C. Reference soda and soda/AQ pulps were produced.AS/AQ and soda/AQ pulps with kappa numbers below 15 were produced easily. Cooking of corresponding soda pulps under comparable conditions stopped at a kappa number of 25. The characteristics of unbleached AS/AQ, soda/AQ and soda pulps were compared. AS/AQ and soda/AQ pulps had similar tensile strength but tear was in favor to AS/AQ. The latter had much higher yield and brightness.TCF bleaching of AS/AQ pulp was performed in O Q (OP) or O Q (OP) P sequences. Oxygen delignification (O) resulted in a delignification degree of approximately one third. Followed by a chelating treatment (Q) and a subsequent (OP) stage under drastic conditions a brightness of 82.7% ISO was achieved in an O Q (OP) sequence. The sequence O Q (OP) P, with 2% H2O2 in the final P stage, improved brightness from 77.2% ISO after the OP stage to 83.6% ISO. Bleaching led to only small losses in tensile and burst strength but enhanced tear strength. Short beating in a Jokro mill was sufficient to attain good pulp strength. The results of this study indicate that AS/AQ pulping and TCF bleaching is a convincing alternative to produce high-quality pulp from wheat straw for writing and printing paper. |
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