Total total mon olig mon olig mon olig mon olig mon olig

[% odw] [% odw] [% odw] [% odw] [% odw] [% odw] [% odw] [% odw]

Mg 433 18 7.3 6.3 0.2 3.9 0.4 0.0 0.3 0.5 0.0 0.0 0.1 0.4 0.1 2.0 0.4 0.2

Mg 434 37 12.2 13.4 0.9 7.1 0.3 0.0 0.2 0.6 0.0 0.2 0.1 0.5 0.1 3.5 0.8 0.4

Mg 435 60 15.0 17.9 2.7 7.2 0.2 0.0 0.3 0.5 0.0 0.4 0.2 0.4 0.2 4.6 0.8 0.5

Mg 436 90 17.1 21.8 6.0 4.6 0.2 0.0 0.4 0.3 0.1 0.2 0.4 0.3 0.3 5.6 1.6 0.6

Mg 437 130 18.6 23.8 9.0 1.0 0.2 0.0 0.7 0.2 0.4 0.1 0.6 0.0 0.5 6.1 3.1 0.7

Mg 438 160 21.2 24.1 10.8 0.2 0.2 0.0 1.0 0.2 0.5 0.3 0.6 0.0 0.8 6.5 4.0 0.7

Mg 439 180 21.5 24.1 10.7 0.0 0.2 0.0 1.1 0.1 0.6 0.2 0.6 0.0 1.0 6.9 3.7 0.9

Mg 420 210 21.6 24.2 10.4 0.0 0.2 0.0 1.4 0.0 0.8 0.0 0.6 0.0 1.1 7.0 3.6 0.9

M 408 249 21.8 24.2 9.7 0.0 0.1 0.0 1.9 0.0 0.9 0.0 0.7 0.0 1.4 6.8 3.7 0.9

0 50 100 150 200 250

Dissolved carbohydrate derived

compounds [% odw]

H-Factor

Xylose Arabinose Glucose Mannose

Galactose Furfural Acetic Acid

Xylonic Acid Methanol

Fig. 4.170 Course of dissolved carbohydrate

derived components present in the spent

liquor from beech dissolving pulp production

using the magnesium sulfite process [13].

Cooking conditions comprise a total SO2

concentration of 0.76 mol L–1, a free SO2 concentration

of 0.32 mol L–2 free SO2, a liquor-towood

ratio of 2.4:1, and a cooking temperature

of 148 °C.

when the hydrogen sulfite ion concentration is very low, only little or no aldonic

acids are formed. Consequently, the amount of combined SO2 regulates the yield

of the aldonic acid formation. As expected from the carbohydrate composition of

the applied wood species, the spent liquor from hardwood cooks contains predominantly

xylonic acid, whereas mannonic and xylonic acid are almost equally present

in the spent liquor from a softwood sulfite cook. The compositions of both the

pulp and spent liquor of dissolving pulp production from spruce and beech wood

are listed in Tab. 4.60. This comparison is based on a viscosity of 700 mL g–1 for

both pulps. As the free SO2 concentration is approximately 20% lower for the

spruce as compared to the beech sulfite cook, the ratio of aldoses-to-aldonic acids

is slightly shifted to a higher aldonic acid concentration in case of the former.

4.3 Sulfite Chemical Pulping 447

Tab. 4.60 Pulp and spent liquor compositions of both beech and

spruce sulfite cooks for the production of a dissolving pulp with

an intrinsic viscosity of 700 mL g–1 (according to [14]).