Patent GB-416558-A (GB)
Title: Improvements in the manufacture of cellulose from ligno-cellulosic materials
IPC: D21C3/20
Filed: 1933-03-07
Abstract: 416,558. Production of cellulose pulp. DREYFUS, H., 22, Hanover Square, London. March 7, 1933, No. 21749/34. Divided out of 416,416. [Class 96.] In a process for the production of cellulose for the manufacture of paper or of cellulose derivatives from ligno-cellulosic materials e.g. wood, straw or grass, lignin is extracted from the materials which are preferably finely divided e.g. wood chips or mechanical pulp by solution in a solvent mixture comprising an organic liquid with substantially no dipole moment and a liquid with a dipole moment, or comprising two or more organic liquids with molecules containing groups of differing dipole moments. Examples of suitable mixtures are mixtures of alcohols, ketones, aldehydes, esters or acids with non-polar solvents such as benzene, toluene or other hydrocarbons, carbon tetrachloride or hexachlorethane. Strongly polar liquids such as alcohols, ketones, aldehydes, esters or acids may be used with less polar liquid such as ether e.g. diethyl or di-isopropyl ether. Mixtures of three or more organic liquids may be used e.g. mixtures of ketones, ethers, and hydrocarbons or non-polar chlorinated hydrocarbons. Examples are 90 per cent alcohol and 10 per cent benzene, 40 to 60 parts of dioxane with 60 to 40 parts of acetone, or 40 to 70 parts of methylene or ethylene chloride with 60 to 30 per cent of methyl, ethyl, or iso-propyl alcohol, or 40 to 60 parts of acetone or alcohol with 60 to 40 parts of di-ethyl or di-iso-propyl ether. Preferably a raised temperature is used, between 50 and 200‹ C. and the reaction may be performed in a closed digester, which may be evacuated before the treatment, although the pressure during the extraction may be above atmospheric. Methods such as those described in Specification 374,047 may be employed to obtain efficient contact between the material and the extracting mixture. The extraction may be performed in a single or multi-stage process and in a continuous or discontinuous manner. The material may travel counter to the direction of a stream of solvent mixture, and the solvents may be distilled from the lignin for re-use. Other substances having a softening effect on the materials may be present such as mineral or organic acids or alkalies. Preferably these substances are used in a pretreatment of the cellulosic materials. If desired resins may be extracted prior to the extraction of the lignin by treatment with benzene, or benzene-alcohol mixtures. If the cellulose is to be used for the manufacture of cellulose acetate, the extracted material is preferably pretreated before the esterification, e.g. with a lower fatty acid if one has not been used in the extraction process. A two-stage pretreatment as described in Specification 249,173, [Class 96], may be used. In a specific example wood chips are sprayed with their own weight of a mixture of 30 per cent concentrated hydrochloric acid and 70 per cent glacial acetic acid and left for 6 hours. They are then washed, first with water, and then with a mixture of di-isopropyl ether and ethyl alcohol in equal parts by volume. They are then extracted in an autoclave at 180 to 200‹ C. for 2 to 3 hours with 8 to 10 times their weight of a mixture of equal volumes of isopropyl ether and ethyl alcohol. The solvent is then withdrawn, preferably without reduction of pressure, and further solvent introduced. The extraction carried out thus in stages is generally complete after about 9 or 12 hours. In the later stages of the extraction the temperature may be raised to about 220-230‹ C. The remaining cellulosic material may be washed e.g. with water, or with alcohol, or with a mixture of isopropyl ether and alcohol. In other examples, the extracting agent is a mixture of 50 parts by volume of dioxane with 50 parts of acetone, or is a mixture of 50 parts by volume of alcohol, 30 parts of acetone and 20 parts of benzene, or is a mixture of equal parts of methylene chloride and methyl alcohol used at a temperature of 170-180‹ C. Specification 398,801 also is referred to.