Appendix C: PULPING CHEMICAL PREPARATION AND ANALYSIS
151
APPENDIX C
PULPING CHEMICAL PREPARATION AND ANALYSIS
C.1
White liquor preparation
1. To prepare 50 L of white liquor, add 50 L of deionized water into a stainless steel tank.
2. Add required amount of NaOH (solid) into the tank.
3. Turn on the mixer.
4. Add required amount of Na2S (solid) into the tank.
5. Let the mixer on for about 5 to 10 minutes to mix the solution homogenize.
6. Leave it for overnight to allow the solution cool down because of the exothermic reaction.
Sample Calculation:
Let white liquor be y L
Target sulfidity = A, in fraction
EA concentration = (target 75 g/L) = z g/L × y L = x g
The calculation as follows:
sulfidity = A =
Na2 S
Na2 S + NaOH
A × NaOH + A × Na2 S = Na2 S
NaOH =
Na2 S (1 − A)
A
Conc. EA = x = NaOH +
1
Na S
2 2
(C.1)
(C.2)
(C.3)
(C.4)
Appendix C: PULPING CHEMICAL PREPARATION AND ANALYSIS
NaOH = x −
Na2 S =
NaOH =
1
Na S
2 2
2 Ax
as Na2O
2− A
2 x − Na2 S
as Na2O
2
152
(C.5)
(C.6)
(C.7)
Since Na2S has purity of 45% as Na2O
Na2 S (asNa2 S ) =
Na2 S (asNa2 S )
% purity
(C.8)
Since NaOH has purity of 97.8% as NaOH, therefore,
NaOH (asNaOH ) =
NaOH (asNa2 S )
62
× % purity
80
(C.9)
where, molecular weigh of Na2O = 62 mole/g
molecular weigh of 2NaOH = 80 mole/g
Sample Calculation:
To prepare 50 L of white liquor and sulfidity is 30%:
Na 2 S =
NaOH =
2 × 0.3 × 75 g / L × 50 L
2 − 0.3
(C.10)
Na 2 S = 1324 g
(C.11)
2 × 75 g / L × 50 L − 1324 g
2
(C.12)
Appendix C: PULPING CHEMICAL PREPARATION AND ANALYSIS
NaOH = 3088 g
153
(C.13)
Purity of Na2S is 45% and NaOH is 97.8%
Therefore,
1324g
0.45
(C.14)
Na 2 S = 2942 g
(C.15)
Na s S =
and
NaOH =
3088 g
62
× 0.978
80
NaOH = 4074 g
C.2
(C.16)
(C.17)
White Liqour Analysis
The relative proportions of NaOH and Na2S are determined by titration with HCl in so-called
“ABC titration”.
1. Pipet 25 ml of white liqour into 500 ml volume flask.
2. Add carefully about 100 ml of deionized water to rinse off the neck.
3. Add 25 ml of 10% BaCl2 as an excess. BaCl2 is added to precipitate carbonate anion
according to the reaction: Ba2++CO32- <=> BaCO3
4. Add the remaining with deionized water to make the volume of 500 ml.
5. Shake well to mix the solution and let stand overnight to settle the precipitate.
6. Next day, pipet out 50 ml clear sample into 250 ml Erlenmeyer flask and use deionized
water to rinse along the wall of the flask.
Appendix C: PULPING CHEMICAL PREPARATION AND ANALYSIS
154
7. Titrate with 0.5N HCl to the phenolphthalein endpoint of colourless from pink colour. The
amount of acid corresponds to the effective Alkali (EA).
8. Do not refill the buret, add few drops of methly orange indicator, the sample should turn into
brown coluor, continuous to titrate until the colour turn pink. The amount of acid
corresponds to the Active Alkali (AA).
500 ml
0.5 N HCl
Figure C.1: Titration of white liquor method.
Sample calculation:
Let
Phenolphthalein endpoint = EP1 ml
Methyl orange endpoint = EP2 ml
Normality of HCl ≈ 0.5 mole/l
Molecular weight of Na2O = 62 g/mole
Note: All concentration express as g/l as Na2O
First, the molar relationship between two species is expressed as
Appendix C: PULPING CHEMICAL PREPARATION AND ANALYSIS
2 NaOH ⇔ Na2 O + H2 O
155
(C.18)
From this relationship the gravimetric factor is determined as follows:
1moleNa2 O
62 gNa2 O
31gNa2 O
×
=
2moleNaOH 1moleNa2 O 1moleNaOH
(C.19)
The following are the equations for EA, AA, percent of Sulfidity, concentration of Na2S and
concentration of NaOH:
31
g
mole
 mole 
EA( g / l ) = EP1(ml ) × N HCl 
×
 l   25ml


× 50ml

 500ml
g
31
 mole 
mole
AA( g / l ) = EP2(ml ) × N HCl 
×
 l   25ml


× 50ml

 500ml
Sulfidity (%) =
2 × [ AA( g / l ) − EA( g / l )]
AA( g / l )
(C.20)
(C.21)
(C.22)
Conc.Na 2 S ( g / l ) = 2 × [ AA( g / l ) − EA( g / l )]
(C.23)
Conc.NaOH ( g / l ) = [AA( g / l ) − Conc.Na 2 S ( g / l )]
(C.24)
Definition of terms
The following definitions are from TAPPI Technical Information Sheet 0601-05:
Active alkali (AA): The sum of the active ingredients in the pulping process.
AA = NaOH + Na2S (expressed as Na2O)
(C.25)
Appendix C: PULPING CHEMICAL PREPARATION AND ANALYSIS
156
Effective alkali (EA): EA is the sum of sodium chemicals that will produce OH- during kraft
pulping. NaOH is completely ionized and for every two sodium atoms of Na2S, there will be one
OH- produced.
EA = NaOH + ½ Na2S (expressed as Na2O)
(C.26)
Sulfidity: In the white liquor, sulfidity is the ratio of Na2S to the active alkali, expressed as a
percent. Typically, a mill runs in the vicinity of 25-30% sulfidity, depending largely on the
wood species pulped. Sulfidity increases the rate of delignification, which occurs by
nucleophilic action of the hydrosulfude anion (HS-) and appears to protect cellulose against
degradation.
Sulfidity =
Na2 S
× 100% (as Na2O)
NaOH + Na2 S
(C.27)
Appendix C: PULPING CHEMICAL PREPARATION AND ANALYSIS
C.3
157
Black Liqour Analysis
1. Pipet 25 ml of black liqour and put into 500 ml volume flask.
2. Add carefully about 100 ml of deionized water to rinse off the neck.
3. Add 50 ml of 10% BaCl2 and swirl gently to avoid bubbling.
4. Add the remaining with deionized water to make the volume of 500 ml.
5. Shake to mix the solution and let stand overnight to settle the precipitate.
6. Next day, pipet out 50 ml clear sample into 100 ml beaker.
7. Titrate with 0.1N HCl by using titroprocessor.
8. After the endpoint (pH=8.36), the endpoint is recorded in the printout.
Sample calculation:
Let
Endpoint = EP ml
Normality of HCl = 0.1mole/l
Liquid to Wood ratio = 4.5ml/1g
Molecular weight of Na2O = 62 g/mole
REA(%) = EP(ml ) × 0.1
g
mole
ml
1
1l
× 31
× 4.5 ×
×
× 100% (C.28)
l
mole
g 2.5ml 1000ml
REA( g / l ) =
REA(%)


ml
1/
 4.5 ×
× 100% 
g 1000ml


(C.29)
Appendix C: PULPING CHEMICAL PREPARATION AND ANALYSIS
C.4
158
Kappa Number Determination
1. Measure required bone dry pulp in gram from the oven
2. Measure 425 mL of deionized water
3. Pulp the pulp into a small blender with some deionized water to disintegrate the pulp for
about 1 minute.
4. Measure 25 mL of 8 N sulfuric acid into the beaker with pulp
5. Measure 50 mL of 0.1 N KMnO4
6. Put KMnO4 into beaker and right away start the timer ( for 10 mins)
7. After 5 minutes, take the temperature by thermometer
8. Prepare 15 mL of Potassium iodide solution (KI)
9. At 10 minutes, put KI into the beaker.
10. Add Starch indicator (the color turn dark brown)
11. Start the titration by using 0.2 N Sodium thiosulfate solution (Na2S2O3)
12. When the mixture turns colorless, stop the titration and record the reading.
13. Carry out a blank determination suing exactly the same method as above but without the
pulp.
Calculations:
Calculate kappa number as follows:
 p
log κ = log   + 0.00093( p − 50 )
 w
(C.30)
or
κ = 10
 p
log   + 0.00093 ( p − 50 )
w
(C.31)
Appendix C: PULPING CHEMICAL PREPARATION AND ANALYSIS
159
If the temperature is not higher than 30 0C not lower than 20 0C, correct the kappa number as
follows:
κ = 10
 p
log   + 0 .00093 ( p − 50 )
w
× [1 + 0 .013 (25 − T )]
(C.32)
and
p=
(b − a )N
0.1
(C.33)
where:
κ = kappa number
f = factor for correction to a 50% permanganate consumption, dependent on the value of p
w = weight of moisture-free pulp in the specimen, g
p = amount of 0.1 N permanganate actually consumed by the test specimen, mL
b = amount of the thiosulfate consumed in the blank determination, mL
a = amount of the thiosulfate consumed by the test specimen, mL
N = normality of the thiosulfate
T = actual reaction temperature in degrees Celsius