GB647129A - Process for treating cellulosic raw materials - Google Patents

Abstract

The process of the parent Specification in which cellulosic raw material is treated with water under pressure in an autoclave at a temperature ranging from 160-210 DEG C. to obtain a cellulosic pulp and a solution containing organic matter including sugars, is modified in that the duration of the treatment is between 1 1/2 and 4 1/2 hours at 160 DEG C., and the temperature of treatment and duration are so related that for each 10 DEG C. rise above 160 DEG C. the time is reduced by at least one half. Within these conditions, the intensity of the treatment may be varied according to the nature of the raw material and the nature of the products to be obtained. The amount of water present must be sufficient continuously to immerse, sprinkle, or wash the cellulosic material, so that in addition to the pulp there is obtained a solution containing sugars and other organic matter. For obtaining pulp suitable for making cardboard, straw may be treated with water at 160 DEG C. for 3 hours, at 170 DEG C. for 1 1/2 hours, or at 180 DEG C. for 1/2 hour. Green phragmites may be treated at 170 DEG C. for 50-60 minutes; ripe yellow phragmites would require 1 1/4 -1\ba1/2 hours at the same temperature to produce similar pulp and old phragmites cut after the winter would require 1 3/4 -2\ba1/4 hours. If desired, the spent liquor may be used for treating a further quantity of raw material. Wash-water recovered from the washing of the treated material may also be utilized. In both these cases, the time of treatment may be reduced. The time may also be reduced by adding a very small proportion of acid to the treating water, the pH being adjusted to a value which must be higher than 2.5 before the treatment. Sulphuric, hydrochloric, nitric, phosphoric, acetic, oxalic, formic, or citric acid may be added. In the case of strong acids the normality should be less than 1/100 and in the case of weak acids it should not be more than 2/10. Straw may be treated for 30 minutes at 175 DEG C. with acidified water equivalent to 1/250 normal sulphuric acid. The pulp obtained gives a paper of good strength. Sodium or calcium phosphates may be added to the water instead of acids. The acidity of the treating water may be controlled or reduced by the addition of neutralizing salts such as calcium carbonate. The materials may be pretreated with hot water. Following the main treatment, the cellulosic products may be malaxated with milk of lime, and may be bleached with calcium hypochlorite solution. Specification 19621/07, [Class 5], is referred to.