GB481631A - Process for the decomposition of wood for the production of cellulose - Google Patents

Abstract

In the manufacture of cellulose, wood is pretreated before applying thereto any lignin-removing or oxidizing treatment, with a controlled mixture of steam and oxygen or air, and then without intermediate oxidizing treatment with a known reagent to remove the greater part of the lignin. Temperatures and pressures in the lignin-removing step may be lower than usual due to the pretreatment. The steam and air mixture may be produced by causing hot air to act upon damp wood, part of the moisture content of the wood being given off as steam. The ratio between the partial pressures of steam and oxygen is preferably between 2 : 1 and 5 : 1 and the preferred temperature range is 100-200 DEG C. The wood may be subjected to a preliminary treatment with weakly acid or alkaline liquids, small quantities of substances to catalyze the oxidizing action, e.g. ferric nitrate being employed if desired. These preliminary treating solutions are not strong enough to effect decomposition themselves. A preliminary steaming treatment may also be employed. The ratio of oxygen to steam in the treating mixture may be reduced during the process if desired. Suitable encrustant solvents for the final treatment are alkalies, alkali hypochlorites, or organic solvents such as alcohols, ketones, phenols, or dioxane, hydrous or anhydrous. This treatment may be combined with a disintegration treatment. Organic solvents are readily recoverable. In examples: (1) spruce chips are steamed, treated with a mixture of equal volumes of steam and air, the ratio of oxygen to steam being reduced towards the end of the treatment, and then digested with alkali and disintegrated; (2) moist beech wood chips are heated in an autoclave with compressed air. Hot air or steam may be fed in and steam-air mixture may be let out and the partial pressure of the steam is kept just below saturation point. The current of air fed in may be increased and diminished several times in succession and is finally cut off altogether. The material is subsequently treated for a time with saturated steam, and then extracted with dilute alcohol and disintegrated. Other examples treat pine wood chips, the final treatment being with alkali; and aspen wood chips, the final treatment being with alkali and chlorine, in lower concentrations than those normally employed.