Patent GB-433783-A (GB)
Title: Improvements in the production of cellulose from lignocellulosic materials
IPC: D21C3/20
Filed: 1934-02-16
Abstract: 433,783. Production of cellulose from ligno - cellulosic materials. BRITISH CELANESE, Ltd., 22, Hanover Square, London, GROOMBRIDGE, W. H., and MELLERS, E. V., c/o British Celanese, Ltd., Spondon, near Derby. Feb. 16, 1934, No. 5166. [Class 96] A process for the production of cellulose suitable for the manufacture of cellulose derivatives or paper, from ligno-cellulosic materials such as wood, straw and grass comprises extracting the lignin from the materials by solution in a solvent mixture comprising at least 20 per cent of water and an organic solvent from at least two of the following classes; monohydric alcohols of the fatty series; simple aliphatic ketones ; cyclic diethers; aromatic hydrocarbons. Suitable mixtures are alcohol 45 parts, water 45 parts, benzene 10 parts, or for a homogeneous mixture alcohol 65 parts, water 25 parts, benzene 10 parts, or 30-60 per cent water, and a mixture of 20-80 per cent acetone and 80-20 per cent alcohol. Mixtures of water with more than two organic solvents may be employed, e.g. water, acetone or methylethyl ketone, cyclic ethers such as dioxane, and aromatic hydrocarbons. The ligno-cellulosic material is preferably finely divided, e.g., wood as chips or mechanical pulp, and treatment is preferably carried out at temperatures above 100‹ C., e.g. 150-240‹ C., and may be in closed digesters, the pressure being if desired in excess of that generated by the solvent mixture as described in Specification 416,549. The vessel may be partially evacuated before addition of the solvent mixture. Impregnation of the materials may be aided by a sudden release of pressure within the materials, e.g. as described in Specification 374,047. The treatment may be single, two or multi-stage or may be continuous, the materials and solvent mixture passing in counter-current. The used solvent may be separated from the dissolved lignin and employed again. Resins may be extracted from the materials with benzene or benzenealcohol before the process. If the extracted cellulose is to be used for cellulose derivatives it may be treated with a lower fatty acid, or a two-stage treatment may be employed as described in Specification 249,173, [Class 96]. In an example wood chips are sprayed with their own weight of a mixture of 30 parts of concentrated hydrochloric acid and 70 parts of glacial acetic acid and are left at atmospheric temperature for 6 hours, and then washed, and mixed with 8-10 times their weight of a mixture comprising 15 parts by volume of acetone, 35 parts of water and 50 parts of alcohol in an autoclave, and heated to 180-200‹ C., for 2-3 hours. The solvent is withdrawn, preferably without reduction of pressure and further solvent introduced. In the second or later stages of the extraction temperatures of 210-220‹ C., may be employed. Extraction is complete after 6-9 hours. In a second example 65 parts by volume of ethyl alcohol mixed with 25 parts of water and 10 parts of benzene forms the solvent mixture, and in a third example a mixture of 50 parts of dioxane, 30 parts of water and 20 parts of acetone is employed. Specification 416,558 also is referred to. According to the Provisional Specification the solvent mixture comprises broadly water and two or more solvents of different polarities, and examples of solvents not mentioned in the Complete Specification are given.