SE7403451L - - Google Patents

Abstract

1500011 Delignifying lignocellulosic material MO OCH DOMSJO AB 6 March 1975 [14 March 1974] 9446/75 Headings DIP and D2W In a method for the delignification of lignocellulosic material of low manganese content which comprises treating the material with a gas containing molecular oxygen at an oxygen pressure or partial pressure of at least one bar and with an alkali at a pH, which during the major part of the delignification is 6.5-11, at least a part of the delignification is carried out in the presence of an added manganese compound. The lignocellulosic material may be subjected to pre-treatment, for example, with hot water, an aqueous acidic solution or an aqueous solution of a complexing agent to remove deleterious metal compounds prior to the oxygen-alkali delignification process. Specified acids include sulphurous acid, hydrochloric acid, sulphonic acid, nitric acid, phosphoric acid, and organic acids. Specified complexing agents include phosphates, aminopolycarboxylic acids, or salts thereof, and amines. In the pretreatment of wood chips, a basic compound such as sodium hydroxide, or sodium carbonate or bicarbonate, may be included in the pretreatment liquid. The pre-treated material is preferably washed prior to delignification. The temperature during the major part of the delignification process is preferably maintained at 100-170‹C. The manganese compound added may be an oxide or hydroxide, salt, or complex thereof. Subsequent to delignification, the pulp may be treated with sulphuric acid to remove residual manganese compounds. The manganese compound is preferably added prior to or during an early stage of the delignification process. Delignification may be effected in the presence of an added magnesium compound. The lignocellulosic material treated may be wood chips, wood pulp, saw dust, straw, bagasse, or jute. The delignified material may be bleached in accordance with known methods.