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You are here : Home > Training > EFPG Days > 5- Reasons for yield loss in kraft cooking (slides 11-20)
        Last update : August 05, 2003
 
                  Second Session : The yield issue                  
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  Logo EFPG     V - Reasons for yield losses during kraft cooking.
Possible strategies for yield increase


D. Lachenal (EFPG)
 

A - Origin of yield loss (continued, slides 11-20)

 
11 - End of peeling mechanism
Due to the peeling mechanism in alkaline conditions, 30 to 100 sugar units are removed. Another mechanism interfers with the peeling mechanism. As a consequence, the peeling process is eventually stopped.   
50 to 150 units        
   
12 - Effect of peeling on cellulose and hemicellulose
This mechanism affects both hemicellulose and cellulose. However, the hemicelluloses will in general be more affected, since their number of sugar units (50 to 150) is low.
50 to 150 units
Hemicellulose
10.000 units
Cellulose
 
 
13 - Effect of peeling on glucomannanes and xylans
Among the hemicelluloses, the glucomannanes
 are almost totally degraded already at 100C.
   
On the contrary, the xylans are quite resistant,
because of their peculiar structure.
 
 
14 - Peeling mechanism in alkaline conditions
 
 
15 - Alkaline hydrolysis (1)
This peeling reaction (primary peeling) alone does not explain the
huge loss in carbohydrates.
At high temperature (> 130 C), in alkaline conditions, the
mechanism of alkaline hydrolysis operates as shown:
 
 
16 - Alkaline hydrolysis (2)
 
 
17 - Alkaline hydrolysis (3)
 
 
18 - Alkaline hydrolysis (4)
 
 
19 - Alkaline hydrolysis (5)
Peeling can start again (secondary peeling)
This mechanism is favored by high alkalinity
 
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