GB703418A - Manufacture of vanillin - Google Patents

Abstract

A method for producing vanillin from a lignin-containing waste liquor from a wood pulping process which liquor has been rendered alkaline, comprises subjecting the alkaline liquor to the action of air or oxygen at a temperature above about 200 DEG C. and a pressure above about 1,000 lb. per sq. in. for a time not exceeding about 10 minutes, cooling the treated liquor and separating vanillin therefrom. The starting material may be an alkaline waste sulphite liquor or black liquor from the Kraft process or soda pulping process. The process may be carried out continuously using a reaction vessel through which the liquor flows as a thin film and has a large surface exposed to the air passing through the reactor. Generally, the liquor or the air or oxygen or both are heated prior to introduction into the reaction vessel. Adiabatic compression of the air may be employed if desired. Gaseous products and oxidized liquor are withdrawn continuously from the reaction at a rate such that the liquor remains in the reaction zone for not more than 10 minutes and the latter is cooled as rapidly as possible, e.g. by sudden reduction of pressure and evaporation of part of the water. The vanillin may be recovered from the processed liquor, e.g. by extraction with a water immiscible alcohol, i.e., n-butanol, and purified by vacuum distillation and recrystallization. Nitrogen may be recovered from the gaseous effluent. The waste liquor may comprise sulphite liquor from the pulping of various species of wood, such as spruce, hemlock and balsam. Sulphite liquors from deciduous woods, e.g. aspen or birch give syringic aldehyde in addition to vanillin. Sulphite waste liquors in which the sugars have been fermented to alcohol or for propagating yeast may be used as starting material. In the example a continuous process using air and alkaline sulphite waste liquor as starting materials is described. Specification 490,646 is referred to.