利于提取木素的两段硫酸盐法蒸煮技术的研究

Study on Two-stage Kraft Pulping Suitable for Lignin Extraction from Black Liquor

研究了巨尾桉两段硫酸盐法蒸煮技术,该技术利于从黑液中提取木素。第一段蒸煮利用木片在蒸煮过程中产生的酸性物质降低黑液的p H值,以利于从黑液中提取木素。第二段改良蒸煮条件,以保证细浆得率和卡伯值。通过参数优化得出了在实验室条件下可以稳定运行的两段蒸煮技术参数。第一段蒸煮:黑液用量66%(相对于总液量),升温时间30 min,保温时间30 min,最高温度130℃,液比1∶5;第二段蒸煮:用碱量20%(以Na OH计),硫化度35%,升温时间90 min,保温时间90 min,最高温度160℃,液比1∶5。在此条件下,第一段蒸煮黑液的pH值可以降到10. 5左右,其中的木素易于通过酸析法提取。与传统蒸煮相比,在细浆得率保持相近的情况下,两段蒸煮的总用碱量可降低2个百分点,卡伯值降低1. 4个单位。

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.