Sulfuric acid bleaching of kraft pulp 1: Bleaching of hardwood and softwood kraft pulps |
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Authors: | Tsutomu Ikeda Shuji Hosoya Yoichi Tomimura Kengo Magara Isao Takano |
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Institution: | (1) Wood Chemistry Division, Forestry and Forest Products Research Institute, Wood Chemistry Laboratory, Tsukuba Norin Kenkyu Danchi-nai, PO Box 16, 305-8687 Ibaraki, Japan;(2) Institute of Agricultural and Forest Engineering, The University of Tsukuba, 305-0006 Tsukuba, Japan |
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Abstract: | To develop a new nonchlorine bleaching technology, hardwood and softwood kraft pulps, before and after oxygen-alkali predelignification, were treated with dilute sulfuric acid solutions (pH 1.0-1.8) at 100°C for 1 h and then extracted with aqueous sodium hydroxide at 70°C for l h. Hardwood kraft pulp was successfully bleached. The delignification selectivity was similar to that seen with oxygen-alkali bleaching; and it was greatly enhanced by the addition of sodium nitrate and sodium nitrite. The sulfuric acid bleaching can replace the presently adopted oxygen and chlorine stages if the additives are allowed. This bleaching process was also effective for oxygen-bleached hardwood kraft pulp, but it was less effective for softwood kraft pulp and oxygen-bleached softwood kraft pulp. The effectiveness of the addition of sodium nitrate and sodium nitrite was more apparent for softwood kraft pulp than for hardwood kraft pulp.Part of this report was presented at the 7th International Symposium on Wood and Pulping Chemistry, Beijing, July 1993 |
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Keywords: | Sulfuric acid Nonchlorine bleaching Kraft pulp Residual lignin |
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