| 摘要 |
In this process, lignin substances are extracted from cellulosic vegetable material at elevated temperature, in particular at 170 DEG C to 210 DEG C, and under an elevated pressure by means of aqueous organic solvents, and the pulp is bleached, if desired. In order to obtain, with exclusive use of solvents which are recoverable by distillation, a pulp which, after a conventional bleach, can be processed further to give a readily filterable viscose, the extraction is carried out in at least two stages, the raw pulp arising after the first extraction stage being re-extracted in a further extraction stage with a medium, which has a swelling action on pulp and dissolves lignin or lignin constituents, from the group comprising dimethylformamide, dimethyl sulphoxide, phenol, dioxane, methanol/benzene, ethanol/benzene, ethanol/ammonia, phenol/water or mixtures thereof, at a lower temperature than in the first extraction stage.
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