Removed

[kg odt–1]

0 100.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

16.8 88.8 2.7 3.0 16.6 50.4 0.2 3.3 4.2 1.6 1.8 2.6 3.0

30.2 79.9 3.0 3.7 66.0 102.4 0.7 4.2 5.2 2.4 2.8 3.6 4.5

47.8 74.7 3.2 4.0 92.6 132.3 2.3 4.4 5.3 3.2 3.8 5.2 6.4

60.0 72.4 3.6 4.4 107.2 148.3 3.9 4.4 5.3 3.5 4.1 6.4 8.0

74.8 70.3 4.0 4.8 110.2 152.6 6.3 3.7 5.3 4.1 5.0 6.8 8.6

90.9 69.1 5.1 6.3 113.8 156.2 10.3 3.7 5.3 5.0 5.5 7.1 9.0

118.6 68.2 5.7 6.7 109.5 161.2 19.1 3.3 5.5 5.4 5.9 7.5 9.4

189.0 68.4 5.2 9.1 92.8 166.5 34.9 2.4 5.7 5.6 7.9 5.9 9.4

0 50 100 150 200

0.00

0.25

0.50

0.75

1.00

Xyl Ara Man Glu Gala

Monomer fraction

Time at 170.C, min

Fig. 4.102 Proportion of monomeric sugars as a function of

reaction time during water prehydrolysis of beech wood at

170 °C (according to [39]). Liquor-to-solid ratio = 10:1.

During the early stage of water prehydrolysis, the predominant fraction of the

released carbohydrates originate as oligomers. As mentioned earlier, the oligomers

are easily hydrolyzed to the monomers with progressive prehydrolysis

(Fig. 4.102).

Applying a prehydrolysis intensity typical for dissolving kraft pulp production

(1 h at 170 °C), xylose and mannose predominantly exist as oligomers. The highest

molecular weight was found to be approximately 3000 for dissolved polysaccharides

isolated from the prehydrolyzates of both pine [41]and beech [42]. The degradation

of polysaccharides to a size of this magnitude enables diffusion of the

degraded polysaccharides from the cell wall layers into the liquor [41,43].

Recently, the macromolecular properties of the water prehydrolyzate from beech

wood after a treatment of 1 h at 170 °C at a liquor-to-solid ratio of 10:1 was characterized

by both size-exclusion chromatography and liquid chromatography,

coupled with mass spectrometry [44]. Based on the carbohydrate analysis, more

than 80% of the dissolved xylose is present as oligomer. With the exception of arabinose,

which is quantitatively hydrolyzed to the monomer under these prehydrolysis

conditions, all other neutral sugars are predominantly released as oligosaccharides

(Tab. 4.46).

The molar mass distribution of the neutral sugar fraction of the prehydrolyzate

revealed a trimodal distribution following the RI detection. The weight-average

(Mw) and number-average (Mn) molecular weights were calculated from the RI-signal

by universal calibration with a mix of cello-oligomer and pullulan standards

(Fig. 4.103).

4.2 Kraft Pulping Processes 339

Tab. 4.46 Mono- and oligosaccharides present in the water

prehydrolyzate from beech wood after a treatment of 1 h

at 170 °C at a liquor-to-solid ratio of 10:1 (according to [44]).