Patent GB-560492-A (GB)
Title: Recovery of cellulose and lignin
IPC: D21C3/00
Filed: 1942-06-30
Abstract: Lignin-containing cellulosic material such as wood is digested in a reagent comprising an aqueous solution of a readily soluble salt of an aromatic acid containing one benzene ring only in its molecule. The treatment removes non-cellulosic constituents from the cellulose material, and the lignin may be obtained from the used digestion liquor by precipitation.  Poplar, maple, white pine, spruce, loblolly pine, wallaba, and other wood, and flax straw, wheat straw, jute, bagasse, and like materials may be treated.  The digestion liquor may be reused several times before being treated to recover the lignin therefrom.  The lignin may be precipitated by diluting the liquor with a large quantity of water or by treating it with sodium chloride or other electrolyte.  The precipitated lignin is filtered off and washed.  The salt used for the treatment may be an alkali-metal salt of benzoic, salicylic, xylene sulphonic, cymene sulphonic, benzene sulphonic, phenol sulphonic, or toluene sulphonic acid.  The corresponding ammonium or alkaline-earth salts may also be used.  The salt may be used in concentrations of 5-50 per cent.  The digestion may be carried out in alkaline, neutral, or acid conditions, e.g. at a pH value of 3-10.  The temperature of the digestion may be 150 DEG C. and the pressure may be 55-200 pounds per square inch.  The treatment may be carried out with continuous or intermittent relief of gas pressure.  The treated cellulose is washed with a solution of the same salt as is used for the digestion, and is then washed with water.  It may be bleached by treatment with a solution of chlorine water and a solution of calcium or sodium hypochlorite. The purified cellulose is suitable for use in making artificial silk.  The crude lignin obtained comprises a mixture of two forms p  of lignin which may be isolated by progressively diluting the solution of the crude lignin in a solution of the salt of the aromatic acid and producing fractional precipitation or by treating the precipitated material with a liquid which is a solvent for only one of the constituents. One variety of the lignin is non-fusible, light brown in colour, soluble in acetone and alkalies, but insoluble in chloroform or ethylene dichloride. The other form is thermoplastic, resinous, soluble in chloroform, ethylene dichloride, and alkalies.  The lignin obtained by the process may be used as a filler and anti-oxidant in the rubber industry.  It may be used in the lacquer and varnish industry.  It gives a condensation product with furfural which has properties similar to phenol-furfural condensation products.  The lignin may be benzylated by treatment with benzyl chloride and sodium hydroxide.  It may be used as a source of methanol by heating, preferably with alkali, or by reduction with hydrogen.  It may be used as fuel in the pulp mill.  During the digestion, carbon dioxide is evolved in a substantially pure state.  This may be collected, compressed, and sold as dry ice.ALSO:Lignin-containing cellulosic material such as wood is digested in a reagent comprising an aqueous solution of a readily soluble salt of an aromatic acid containing one benzene ring only in its molecule.  The treatment removes non-cellulosic constituents from the cellulose material, and the lignin may be obtained from the used digestion liquor by precipitation.  Poplar, maple, white pine, spruce, loblolly pine, wallaba, and other wood, and flax straw, wheat straw, jute, bagasse, and like materials may be treated.  The digestion liquor may be re-used several times before being treated to recover the lignin therefrom.  The lignin may be precipitated by diluting the liquor with a large quantity of water or by treating it with sodium chloride or other electrolyte.  The precipitated lignin is filtered off and washed.  The salt used for the treatment may be an alkali-metal salt of benzoic, salicylic, xylene sulphonic, cymene sulphonic, benzene sulphonic, phenol sulphonic, or toluene sulphonic acid.  The corresponding ammonium or alkaline-earth salts may also be used.  The salt may be used in concentrations of 5-50 per cent.  The digestion may be carried out in alkaline, neutral, or acid conditions, e.g. at a pH value of 3-10.  The temperature of the digestion may be 150 DEG C. and the pressure may be 55-200 pounds per square inch.  The treatment may be carried out with continuous or intermittent relief of gas pressure.  The treated cellulose is washed with a solution of the same salt as is used for the digestion, and is then washed with water.  It may be bleached by treatment with a solution of chlorine water and a solution of calcium or sodium hypochlorite. The purified cellulose is suitable for use in making artificial silk.  The crude lignin obtained comprises a mixture of two forms of lignin which may be isolated by progressively diluting the solution of the crude lignin in a solution of the salt of the aromatic acid and producing fractional precipitation or by treating the precipitated material with a liquid which is a solvent for only one of the constituents. One variety of the p  lignin is non-fusible, light brown in colour, soluble in acetone and alkalies, but insoluble in chloroform or ethylene dichloride. The other form is thermoplastic, resinous, soluble in chloroform, ethylene dichloride and alkalies.  The lignin obtained by the process may be used as a filler and anti-oxidant in the rubber industry.