Production of sulphate cellulose

In a modification of the sulphate process for separating cellulose from wood-pulp and the like, sodium hydroxide free from sulphide is obtained from a "melt-soda" comprising sodium carbonate and sulphide. The "melt-soda" is treated with a quantity of water sufficient to dissolve all the sodium sulphide, but leave more than half the sodium carbonate undissolved. This dissolving process can be carried out continuously by the countercurrent method. The undissolved sodium carbonate can then be dissolved in and recrystallized from a further quantity of water, and then redissolved and causticized.ALSO:In the treatment of cellulosic fibrous material by the sulphate process, the formation of malodourous substances such as methyl mercaptan, methyl sulphide and methyl disulphide is prevented by a pretreatment of the material with an alkaline liquor before the digestion with the sulphate liquor. The alkali used may be sodium hydroxide or a black liquor from a previous sulphate digestion. The pretreatment liquor may be wholly or partially separated from the fibrous material before the sulphate liquor is added. The pretreatment may be carried out in the digestion vessel or in a separate vessel.