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Abstract

High yield pulping is achieved by cooking a lignocellulosic material in a confined chamber in the absence of added oxygen at elevated temperatures up to 240.degree. C. with an initially neutral or acidic mixture of alcohol and water in volume ratio between 50:50 and virtually anhydrous alcohol cooking liquor, using a lower aliphatic alcohol namely methanol, ethanol or n-propanol, carrying in solution at least about 0.002 moles per liter of a magnesium, calcium or barium salt as a primary catalyst soluble in at least catalytic amounts in the mixture to form barium, calcium and magnesium ions. The cooking time may range from at least two (2) minutes to under three (3) hours. The process yields bright, free-fiber pulp even at residual lignin of 80 Kappa number as high as 80% of softwood and up to 75% of hardwood weight, of viscosity (TAPPI 0.5% Cu En) above 18 up to 60 centipoise. Addition of trace amounts of an acidic compound as a secondary catalyst increases the rate of delignification. Elevated pressures on the cooking solvent mixture also increases the rate of delignification.

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