Min 240 min at temperature

R18 content [%]

Temperature [.C]

Fig. 8.25 R18 content of a hardwood sulfite

Pulp (HW-S) as a function of temperature during

Hot caustic extraction using MgO as a

base, at two different reaction times [39]. HW-S

for 120 min reaction time: kappa number 6.2,

viscosity 640 mL g–1, 91.0%R18; HW-S for

240 min reaction time: kappa number 9.9, viscosity

600 mL g–1, 90.9%R18.

Pulp Purification

Figure 8.25 illustrates the successful use of MgO to obtain degrees of purification

Sufficiently high for the production of viscose staple fiber pulps. The main

Drawback when using MgO is the high temperature needed to achieve the necessary

Purification. Another problem may be to achieve homogeneous distribution

Of Mg(OH)2 within the pulp suspension in order to obtain a uniform pulp quality.

The prolongation of retention time from 120 to 240 min may reduce the temperature

by almost 10 °C, while maintaining the same R18 content. Moreover, the

MgO-based hot caustic extraction appears to be more selective than the conventional

system, with a specific yield loss of only 2.4% per 1% increase in R18

(Fig. 8.26).

91 93 95 97

E

MgO

- 240 min E

NaOH

E

MgO

- 120 min

Purification Yield [%]

R18 content [%]

Fig. 8.26 Purification yield as a function of R18 content for

MgO- and NaOH-based hot extraction processes of a hardwood

sulfite pulp (HW-S) [39]. Pulp substrate and conditions:

EMgO according to Fig. 8.25; ENaOH according to Fig. 8.18.

References 963

References

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Pulp Purification

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