| 摘要 |
Cellulose is obtained from lignin-containing cellulosic materials by extraction with a caustic alkali solution of concentration above 6 per cent, or with another solution of equivalent alkalinity, at a temperature not exceeding 150 DEG C. and under a pressure greater than that produced by the solution at the temperature employed. The excess pressure may be obtained by means of compressed inert gases or by small quantities of ether or other volatile liquid; the excess pressure may amount to 50--500 lbs. per sq. in. Concentrations of caustic alkali of between 6 and 20 per cent are advantageous, for example, sodium hydroxide solutions of 10--12 per cent may be used. The temperature may be between 100 DEG C. and 130 DEG C., but temperatures of 80 DEG C. and lower may be employed, in particular temperatures up to 65 DEG C. when treating chemical pulps from which the bulk of the lignin has been removed. Prior to the treatment, the cellulosic materials may be treated with dilute alkali for the removal of the resins etc.; and subsequent to the treatment, the cellulose may be subjected to a hypochlorite or other bleaching treatment, or to final extraction with cold alkali, sulphur dioxide, &c. To facilitate the alkali treatment, the wood &c. may be in finely divided form; it may be subjected to a vacuum before contact with the treating liquid; and the materials may be agitated together during the treatment. The product of the treatment is especially suitable for the manufacture of cellulose esters or ethers. Specifications 263,938, [Class 2 (ii)], 371,037, [Group VIII], and 427,626 are referred to. |
