| 摘要 |
<p>In a method of producing celluloses with low lignin contents, lignin substances are extracted from cellulose-con-taining vegetable material at an elevated temperature and an elevated pressure with aqueous organic solvents and, if desired, the celluloses are bleached. In order to obtain a cellulose by using solvents recoverable by distillation, which cellulose is further processable into an easily filterable viscose, the extraction is carried out in at least two steps. The crude cellulose resulting from the first extraction step is post-extracted in a further extraction step at a temperature lower than in the first extraction step with a medium having a swelling effect on the cellulose and dissolving lignin or lignin particles. The medium may be dimethylformamide, dimethylsulfoxide, phenol, dioxan, methanol/benzene, ethanol/benzene, ethanol/ammonia, phenol/water or mixtures thereof.</p> |
