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| Study on Two-stage Kraft Pulping Suitable for Lignin Extraction from Black Liquor |
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| DOI：10.11980/j.issn.0254-508X.2019.04.002 |
| Key Words:two-stage kraft pulping black liquor lignin extraction |
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| Abstract:A novel two-stage kraft pulping process for eucalyptus grandis urophylla was developed which benefited lignin extraction from black liquor. In the first stage，acidic substance produced from wood chips during pulping made the pH of black liquor reduce that was beneficial to the extraction of lignin. In the second stage， the cooking conditions were modified to ensure the reasonable pulp yield and kappa number. And the two-stage cooking process could be operated stably by optimizing the parameters. The optimum cooking conditions were determined as follows: the first stage added 66% of black liquor( based on total liquor），the heating up time was 30 min， the time at maximum temperature was 30 min， the maximum temperature was 130℃， liquor to wood ratio was 5∶1; In the second stage ， the alkaline charge was 20%（as NaOH）， sulfidity was 35%， and the heating up time was 90 min， the time at maximum temperature was 90 min. the maximum temperature was 160℃，liquor to wood ratio was 5∶1， The result showed that the pH value of black liquor from the first stage could be reduced to about 10.5 which was in favor of lignin extraction by acid. Compared with conventional kraft pulping， the alkali charge of the two-stage process decreased by two percentage points（on wood）and the kappa number decreased by 1.4，while the pulp yield was similar. |
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