Into cellulose II.

However, in cases where oxidative degradation is desired to reduce pulp viscosity,

The CCE treatment should be placed immediately after ozonation.

The placement of CCE in the bleach sequence is open to debate, but depends

Ultimately on the prevailing circumstances in industrial practice.

O-treated A-Z-CCE-P A-Z-P-CCE CCE-A-Z-P

Xylan

Viscosity [ml/g]

Xylan content [%]

Intrinsic viscosity

Fig. 8.12 Influence of CCE placement within an AZP sequence

On xylan removal efficiency and final viscosity of a hardwood

PHK pulp [28]. O-treated E-PHK: kappa number 2.4; CCEtreatment:

70 g L–1 NaOH, 30 min, 30 °C.

8.3.5

Specific Yield Loss, Influence on Kappa Number

Cold caustic extraction is a rather selective purification process because it mainly

Involves physical changes in the corresponding pulp substrate. The yield losses

reported in the literature are 1.2–1.5% per 1% increase in alpha-cellulose content

[4] or 1.2–1.8% for a 1% gain in R10 [27]. These values are in close agreement

With recent results obtained from hardwood sulfite and PHK dissolving pulps

[28], as illustrated in Fig. 8.13.

On average, the yield loss calculates to 1.6% for a 1% reduction in xylan content.

Closer examination of the results shows that CCE treatment on HW-PHK pulps is

Slightly more selective as compared to that of HW-S pulps, as indicated by a specific

yield loss per 1% decrease in xylan of 1.4% for the former, and 1.8% for the latter.

Pulp Purification

0 1 2 3

CCE of unbleached&(E/O)-treated HW-S CCE of O-treated HW-PHK

Xylan Removed [% od]

Yield Loss [% od]

Fig. 8.13 Yield loss as a function of the

Amount of xylan removed from hardwood sulfite

(HW-S) and hardwood prehydrolysis-kraft

(HW-PHK) dissolving pulps during CCE

treatment [28]. CCE-treatment for HW-S: 50–

100 g L–1 NaOH, 25–30 °C, 30–60 min; CCEtreatment

for HW-PHK: 40–70 g L–1 NaOH,

30–50 °C, 10–60 min.

It has already been pointed out that a certain lignin fraction is removed through

CCE treatment. It may be speculated that the delignifying performance of CCE

Exceeds that of normal alkaline extraction (E) at elevated temperature, known as

Operation to remove leachable residual lignin (see Section 7.3.7.2, tables 7.24 and

7.25, Process technology: oxygen delignification), because part of the xylan being

Removed during CCE may be covalently linked to the residual lignin. The rather

high delignification removal efficiency of CCE (14–25%) despite the very low initial

lignin content (2.1. 0.15 – 6.0. 0.15 = 0.3% – 0.9%) is demonstrated in

Tab. 8.1.

Tab. 8.1 Average kappa number values before and after CCE

Treatment of differently pretreated hardwood sulfite and

hardwood PHK dissolving pulps [28]. For details of CCE

Treatments, see Fig. 8.13.

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