Pulping of lignocellulose with aqueous methanol/ catalyst...

Details Pulping of lignocellulose with aqueous methanol/ catalyst... Pulping of lignocellulose with aqueous methanol/ catalyst...

D - Textiles, Paper

21

C

9/31

D21C 3/00 (2006.01) D21C 3/20 (2006.01)

Patent

CA 1131415

ABSTRACT OF THE DISCLOSURE Lignocellulosic plant material is chemically converted to separated fiber of superior pulp properties having almost native cellulose strength with low residual lignin, by cooking fragments of lignocellulose in an aqueous methanol solvent mixture containing a recoverable metal salt catalyst, or a combination of a metal salt and a minor quantity of strong acid such as HC1, in a pressure vessel at temperatures between 185°C and 205°C, and preferably between 190 C and 200°C, for durations from 15 minutes to over one hour. A wood/liquor proportion between 1:4 and 1:20 or higher is maintained,with a preferred ratio 1:5 to 1:10, and the water/ methanol ratio is between 1:1 to 1:4, the preferred ratio being 3:7. The metal salt catalyst is a chloride or nitrate of one of the metals calcium, magnesium or barium, and is useful in concentr- ations between 0.005 molar to 1.0 molar. For cooking hardwood the preferred range is 0.05 to 0.1 molar, while for softwood the range preferred is 0.2 molar to 0.05 molar. Addition of HCl when cooking hard-to-delignify wood such as Spruce, in amount 0.0005 normal to 0.008 normal enhances rate and extent of delignification without significant damage to cellulose. High pulp yields of the order of 54% to 56% of wood weight for Spruce with TAPPI (0.5) viscosity of 20 cps at Kappa number 35 are obtained, within 45 minutes, while Aspen can be cooked to a pulp yield of 62% with TAPPI (0.5) viscosity 22 cps at Kappa number 25 in less than 30 minutes. Lignin is recovered by precipitation through liquor cooling and volatilizing methanol therefrom, as an undegraded low molecular weight powder soluble in usual lignin solvents; the part of the hemicelluloses converted to dissolved monomers and oligosaccharides is recoverable from the residue, and the catalyst may be obtained for re-use.

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