| 摘要 |
Digestion of cellulose pulp with solvents is done by using ethanol, methanol, formic acid or the like by conducting the organic solvent in counterflow into the cellulose-containing fibre material being treated. The process can be a batchwise or a continuous digestion. During the process, the pH of the material being treated is rather neutral and constant, and it can be regulated to maintain the process generally neutral by removing the acids forming at the start of the boiling, i.e., together with the solvent used, and it can be further stabilised by adding alkali to the material being treated just before it is brought into counterflow contact with the organic solvent. A catalyst, e.g., alkaline earth metal salts or organic alkali, can also be added to the fibre material in order to promote the dissolving of the lignin. The treated pulp is washed, and the solvent can be separated by distillation from the washing liquid resulting from the washing stage. The material being treated can be attenuated prior to the boiling. The liquid, the organic solvent used, containing lignin can also be distilled, whereupon the organic solvent is returned to the boiling, the water is separated and recycled, and the lignin is burned.
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