Abstract: Wood chips are digested at a temperature above 100.degree. C in contact with a solution of a hydroxide or salt of an alkali metal or alkaline earth metal or ammonium in a solvent which boils above 100.degree. C at atmospheric pressure, such as ethylene glycol. The cellulose pulp is then separated from the dissolved lignin. The dissolved lignin may be precipitated and removed from the solvent and the solvent may then be recycled, so that there is no waste spent liquor. Examples of salts which may be used are sodium phenoxide and a combination of sodium bisulfite and an aldehyde or a ketone.

Abstract: Prior to cooking, fragments of raw ligno-cellulosic material are impregnated with a solution of a lignin-solubilizing reactant in an organic solvent which has a boiling point higher than the cooking temperature in order for the material to absorb an amount of solution containing at least the amount of reactant required for solubilizing the lignin, then 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 said liquid is maintained at the cooking temperature until the lignin has been substantially converted to a derivative which is soluble in water or a water-miscible organic solvent.