GB409081A - An improved process for the production of wood pulp - Google Patents

Abstract

409,081. Preparation of paper pulp. FORESTAL LAND, TIMBER, & RAILWAYS CO., Ltd., Regis House, King William Street, London, FONTANA, A., 19, Gran via Layetana, Barcelona, Spain, PHILLIPS, R. 0., 82, Chittern Court, Baker Street, London, and ROTTSIEPER, E. H. W., 16, Harpenden Rise, Harpenden, Hertfordshire. Dec. 31, 1932, No. 37018. [Class 96.] A process for producing pulp from wood, and preferably hard wood such as wattle, maple, or chestnut comprises impregnating the wood in the form of chips or relatively small pieces with an aqueous solution of alkali at normal or room temperatures, or temperatures only slightly above normal, heating the impregnated material with an approximately neutral mixture of sulphites and bisulphites, having preferably a pH value between 7.5 and 5.5, and then submitting the treated material to mechanical disintegration and hydration. The aqueous alkali used preferably contains up to 10 per cent of sodium hydroxide and the impregnation is carried out at 10‹-30‹ C., the vessel being subjected to alternations of pressure below atmospheric pressure, and a higher pressure to aid the impregnation. The second treatment is carried out at 20‹-150‹ C. for a period of 2-8 hours, the temperature being slowly brought up to a maximum value. To prepare the mixture of sulphites and bisulphites, either the aqueous alkali is separated from the chips, and sulphurous acid is added thereto, allowance being made for the amount absorbed by the chips, and the liquid is then filtered and poured back on to the chips or the excess impregnating solution is removed from the chips and only sufficient sulphurous acid is added to the chips to convert the alkali absorbed by the chips into the mixture of sulphites and bisulphites. After heating the treated material is washed and mechanicallv disintegrated and hydrated in a beater, pulpbreaker, rod mill or similar apparatus. The pulp may be bleached either during or after the mechanical treatment bv the addition of any usual bleaching agent such as calcium or sodium hypochlorite or chlorine in one or more stages between each of which the pulp may be treated with small quantities of alkalies. Instead of or in addition to the treatment with the oxidizing bleaching agents mentioned above, the pulp may be treated with sodium or zinc hydrosulphite or a substance or substances capable of reacting to produce hydrosulphites. This treatment may come before or after the use of oxidizing bleaching agents.