Process for obtaining cellulose from ligno-cellulosic raw materials

Claim 1

In a process for obtaining cellulose from ligno-cellulosic raw materials comprising the steps of cooking the raw material in contact with a solution of a reactant for converting lignin present in said raw material into a derivative which is soluble in water or in a water-miscible organic solvent, extracting the thus formed derivative in an aqueous medium, and separating cellulose from the aqueous medium, the improvement which comprises impregnating the raw material, before the cooking step, in the form of fragments, with a solution of said reactant in a solvent which has a boiling point higher than the cooking temperature and which is selected from the group consisting of ethyleneglycol, dipropylengeglycol, glycerol, aniline, diethanolamine and triethanolamine and mixtures of at least one of these substances with water, said reactant being employed in an amount sufficient to solubilize the lignin, whereby the raw material absorbs a portion of the solution, after which the impregnated material is immersed in a liquid which is substantially non-miscible with the solvent of said solution, said liquid having a boiling point higher than the cooking temperature, and which is selected from the group consisting of paraffinic mineral oils, siloxanes, n-butyl acetylricinoleate, n-butyl benzoate, diethyleneglycol monolaurate, propiophenone, dibutylether and mixtures thereof and then maintaining said liquid having the impregnated material immersed therein at the cooking temperature until the lignin has been substantially converted to said derivative.