1. Pulping and Bleaching PSE 476/Chem E 471 Lecture #15 Kraft Pulping Review of Reactions/Kinetics Lecture #15 Kraft Pulping Review of Reactions/Kinetics

2. Kraft Pulping Bulk Phase Initial Phase Impregnation zone Residual Phase 70°C 137°C 170° C

3. Kraft Pulping Kinetics: Initial Phase

4. Initial Reactions: Low Temperature Carbohydrates »Alkaline hydrolysis of acetyl groups on xylan (see next slide). »Removal of certain soluble carbohydrates. -Certain galactoglucomannans. -Arabinogalactans. Extractives »Alkaline hydrolysis of fats (saponification), waxes, and other esters. »Neutralization of extractives. -There are a number of acidic extractives which consume NaOH. Carbohydrates »Alkaline hydrolysis of acetyl groups on xylan (see next slide). »Removal of certain soluble carbohydrates. -Certain galactoglucomannans. -Arabinogalactans. Extractives »Alkaline hydrolysis of fats (saponification), waxes, and other esters. »Neutralization of extractives. -There are a number of acidic extractives which consume NaOH.

5. Alkaline Hydrolysis: Example Using Acetyl Groups Esters are cleaved in alkaline solutions through hydrolysis reactions forming carboxylic acids and alcohols. Hydrolysis of acetyl groups occurs readily in alkaline solutions. »Reaction occurs rapidly even at room temperature. Reaction consumes alkali. Esters are cleaved in alkaline solutions through hydrolysis reactions forming carboxylic acids and alcohols. Hydrolysis of acetyl groups occurs readily in alkaline solutions. »Reaction occurs rapidly even at room temperature. Reaction consumes alkali.

6. Saponification of Fats (Review slide from PSE 406) Treatment of fats with alkali converts them to fatty acids and glycerol through saponification. Once again this reaction consumes part of the alkali charge.

7. Removal of Glucomannans: Effect of Effective Alkali Why doesn’t EA affect glucomannan removal? Peeling reaction not sensitive to OH concentration Rapid removal at the beginning of the cook (dissolving) Over 100  C greater rate of peeling 70% removed rate drops again

8. Kraft Pulping Kinetics: Initial Phase

9. Lignin Removal: Effect of Sulfidity Sulfidity effect zero order in initial delignification (this means that changing sulfidity has no effect on initial rate) »Sulfidity is important during bulk delignification »Effects final lignin/carbohydrate ratio -HS - does not react with carbohydrates Sulfidity effect zero order in initial delignification (this means that changing sulfidity has no effect on initial rate) »Sulfidity is important during bulk delignification »Effects final lignin/carbohydrate ratio -HS - does not react with carbohydrates It depends on: Wood species EA Cooking temp. Hardwoods 20% Softwoods 25%

10. Removal of Xylans: Effect of Effective Alkali Why does EA affect xylan removal? Stable at the beginning Hydrolysis and 2 nd peeling

11. Kraft Pulping Kinetics: Bulk Phase

13. Kraft Pulping Kinetics: Residual Phase