GB474188A - Improvements in or relating to the production of cellulose from cellulose containing materials for the manufacture of viscose rayon, and paper - Google Patents

Abstract

In a process for the production of cellulose for viscose rayon manufacture, from vegetable material having a high silicic acid content, e.g. Indian corn stalks, the raw material is subjected to an alkaline treatment divided into two stages, the first effected at relatively high temperature and pressure with a weak solution of caustic soda containing hemicellulose equivalent to at least 50 per cent of the caustic soda to remove incrusting substances and silicic acid, and the second at atmospheric pressure and a relatively low temperature with a more concentrated caustic soda solution to remove hemicellulose from the treated material and increase its a -cellulose content. The solution expressed from the treated raw material after the first stage treatment or a freshly prepared solution containing 0,8--1,2 per cent caustic soda and half that amount of hemicellulose is used for a single stage alkaline treatment at high temperature and pressure, e.g. 140--160 DEG C. and 3--5 kgs./sq. cm. to produce cellulose for paper from vegetable raw material with a high silicic acid content. The first of the two stages of the alkaline treatment is effected at 140--160 DEG C. and 3--5 kgs./sq. cm. for 4--6 hours with 1,5--2,0 per cent NaOH solution containing hemicellulose. The solution recovered by pressing the raw cellulose batch after this treatment contains 8--12 gms./litre of caustic soda. The second stage of the alkaline treatment is at 80--90 DEG C. for 1--2 hours with 2,0--4,0 per cent caustic soda. The viscosity of the product is adjusted to desired degree by treatment with hydrochloric acid solution at a pH of 0,6--1,0 and temperature of 60--80 DEG C. The cellulose may be bleached after either alkaline treatment or after the acid treatment. In a specific example, Indian-corn stalks are washed to remove earthy residues and are heated in an autoclave at atmospheric pressure to a temperature of 100--105 DEG C. Cold caustic soda containing hemicellulose is added, the autoclave covered and the temperature brought to 100 DEG C. for 1 hour and then raised to 140--150 DEG C. during 2 hours, and is held there for a further 2 hours. The material, removed from the autoclave is pressed to recover the caustic soda solution for use in a paper-making process. The pressed material is washed and caustic soda added to bring the content of the batch to 3 per cent. This paste is maintained at 80--90 DEG C. for 1--2 hours at atmospheric pressure. The alkaline solution is then recovered by pressing and after adjustment of its alkali and hemicellulose concentrations is used for the first stage of a subsequent treatment. The pulp is washed and bleached, e.g. with calcium hypochlorite. It is then further washed, treated at 60--80 DEG C. with dilute hydrochloric acid for about 3 hours, and finally washed again. The hemicellulose is obtained from the caustic soda solution used for mercerizing cellulose in the viscose process, and a suitable alkaline solution containing hemicellulose may be obtained by controlling the usual dialysis of the caustic soda from said mercerizing process.