Fig. 8.5 Purification of hardwood sulfite pulps

(HW-S) and eucalyptus prehydrolysis-kraft

Pulp (E-PHK) with cold aqueous NaOH solution

of varying strength [28]. HW-S:

unbleached, kappa number 6; (E/O) pretreated:

kappa 1.6. E-PHK: OZ pretreated,

kappa 0.6. CCE-treatment: 10%consistency,

C, 30 min.

0 20 40 60 80 100

90.0

O-Z treated E-PHK

R18 content [%]

NaOH concentration [g/l]

Fig. 8.6 Purification of eucalyptus prehydrolysis-kraft pulp (EPHK)

With cold aqueous NaOH solution of varying strength

[28]. E-PHK: OZ pretreated, kappa number 0.6. CCE-treatment:

10%consistency, 30 °C, 30 min.

Pulp Purification

Through alkaline treatment, depending on NaOH concentration, is further illustrated

In Fig. 8.7. The different levels of R18 content after cooking and subsequent

Oxygen delignification (O) of the eucalyptus PHK pulps have been adjusted by prehydrolysis

Intensity (P-factor). Even though xylan removal efficiency increases

With increasing initial hemicellulose content, the initial purity must exceed a certain

Level in order to achieve a sufficiently high purity without approaching a

Change in the supramolecular structure.

0 20 40 60 80 100

0.0

Initial R18 content:

96.6% 97.2% 97.6%

Xylan content [%]

NaOH concentration [g/l]

Fig. 8.7 Purification of eucalyptus prehydrolysis-

Kraft pulps (E-PHK) of three different initial

Purity levels with cold aqueous NaOH solution

of varying strength [28]. O-pretreated E-PHK

pulps: (a) R18 = 96.6%, kappa number 3.4; (b)

R18 = 97.4%, kappa number 2.5; (c)

R18 = 97.6%, kappa number = 2.2. CCE-treatment:

10%consistency, 30 °C, 30 min.

8.3.2

Time and Temperature

The influence of temperature on the performance of caustic extraction has been

Discussed in detail in Section 8.2. It is well established that lower temperatures

Cause a high degree of swelling, and this enhances the solubility of hemicelluloses.

The effect of temperature and retention time in the range 30–50 °C and 10–

60 min, respectively, while keeping the NaOH concentration constant at 70 g L–1,

Is illustrated in Fig. 8.8.

It can be seen that extraction time has no influence on the purification efficiency

In the range investigated. The retention time during alkalization is not a

critical parameter because swelling takes place almost instantaneously [4]. However,

the increase in temperature from 30 °C to 50 °C induces a decreased removal

of xylan content of 0.4% (from 1.5% to 1.9% in the residue). This temperature

Cold Caustic Extraction

0 20 40 60

0.0

C 40.C 50.C

Xylan content [%]

Time at Temperature [min]

Fig. 8.8 Influence of time and temperature during CCE treatment

Of eucalyptus prehydrolysis-kraft pulp (E-PHK) at a constant

NaOH concentration of 70 g L–1 [28]. E-PHK: OZ pretreated,

kappa 0.6. CCE-treatment: 10%consistency, 30 min,

70 g NaOH L–1.

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