© 2017 The Authors. Published by Center for Pulp and Paper, Ministry of Industry, Indonesia
Application of PO (Peroxide - Oxygen) stage in the ECF
80
Chemicals reagent analysis (PA) are made of Vietnam and China, along with specialized laboratory equipment standards of the EU, Germany, the US and India is used.
Method Bleaching
Pulps sample is bleached in plastic bags and heated in the thermostat. Stage (PO) is conducted in pressure equipment, volume of 5 litres. There is a washing stage with clean water between different stages, and distilled water is used in the final phase. In stage (DhQ), EDTA is added before 15 minutes at the end Dh bleaching stage. The bleaching conditions are given in the table below.
Table 1. Technological conditions of (DhQ)(PO)D process
Technological conditions (DhQ) (PO) D
Pulp concentration, % 10 10 10
Temperature, 0C 90 75
Time, minutes 120 120 120
Last pH 2-3 - 3-4
Active chlorine, (% Cl-) 2,2 - 0,5
Oxygen Pressure, bar - 6 -
NaOH, % - -
MgSO4,% - 0,2 -
H2O2, % - -
Na2SiO3, % 0,25
ETDA, % 0,5
Notes: Conditions of dosage of H2O2 and NaOH, temperature of (PO) bleaching stage are needed parameters
Standard test methods
Brightness: TCVN 1865:2000; tensile strength: TCVN 1862–1:2000; tear strength: TCVN 3229:2000; burst index: TCVN 3228:2000; Viscosity: TCVN 7072 : 2002
RESULTS AND DISCUSSION
Experimental planning method named Box - Wilson was used (Tuyen and Thiem, 2005). The three largest factors affecting the quality of the (PO) are H2O2 (x1, %), NaOH (x2, %) and temperature (x3, C). x1 was varied between 0.4% to 1.0%; x2 was changed of about 1.0% to 1.6%; x3 was changed in about 70C to 110C.
y objective function was used to assess the effectiveness of the bleaching process via a brightness (%ISO), viscosity (mL/g) and physical properties. Here, we will use brightness as objective function, viscosity and physical properties will be determined as conditions. Form of full objective is:
y = b0 + b1x1 + b2x2 + b3x3 + b12x1x2 + b13x1x3 + b23x2x3 + b123.x1x2x3 (1) Experimental planning with full matrix, experimental = N = 23 = 8
Conditions of experiment were given in Table 2.
81 Table 2. Exprimental Conditions of Variables in Bleaching
Experiment x1, % H2O2 x2, % NaOH x3, C
M1 0.4 1.0 70
M2 1.0 1.0 70
M3 0.4 1.6 70
M4 1.0 1.6 70
M5 0.4 1.0 110
M6 1.0 1.0 110
M7 0.4 1.6 110
M8 1.0 1.6 110
Experimental results on the model are given in Table 3 and Table 4.
Table 3. Results of Experimental Samples Experiment Brigtness
%ISO
Viscosity, mL/g
Breaking length, m
Tear index mN.m2/g
Burst index kPa.m2/g
M1 83.75 655.2 7020 8.67 4.25
M2 85.66 632.5 7170 8.81 4.21
M3 84.92 657.2 7080 8.57 4.10
M4 86.05 621.9 7150 8.81 4.58
M5 84.91 648.4 7070 9.42 4.21
M6 85.53 661.2 7280 8.90 4.46
M7 85.03 654.2 7380 8.76 4.41
M8 85.75 612.8 7450 9.09 4.27
M9* 85.04 651.9 7510 9.50 4.61
(*)M9, 9th experiment at center
Table 4. The Experimental Data on the Model
Experiment Variables Objective function, %ISO
x1 x2 x3 y1 y2 y3 yTB
M1 - - - 83.66 83.81 83.78 83.75
M2 + - - 85.45 85.58 85.95 85.66
M3 - + - 84.88 84.92 84.96 84.92
M4 + + - 85.83 85.91 86.41 86.05
M5 - - + 84.91 84.89 84.93 84.91
M6 + - + 85.49 85.63 85.47 85.53
M7 - + + 84.59 85.17 85.33 85.03
M8 + + + 85.79 85.81 85.65 85.75
M9 0 0 0 84.83 85.14 85.15 85.04
After calculating the coefficients, form of obtained regression equation is
y =+85.2000+0.5475x1+0.2375x2+0.1050x3-0.0850x1x2-0.2125x1x3-0.1525x2x3+0.1100 x1x2x3 (2).
Number of model coefficient B = 8
* Check the meaning of the coefficients in equation (2): based on the standard of Student t (refer to the table St = (f, N)), under the following conditions:
Inside :
.t S
bi b (3)
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Sb: The variance of the determined coefficient
t: Standard Student numbers are determined by looking up the table St = (f,N), f = N (k-1) with k is the number of repetitions of the experiment
+ Calculate the variance:
The fraction variance for each experiment, calculated according to the formula:
with
→ S2y = 0.04265
The distribution variance for each measurement, calculated as the formula:
→ S2y
TB = 0.014217
The distribution variance for each regression coefficient, calculated by the formula:
→ S2b = 0.001777 or Sb = 0.042155 + Check table St (f, N) (Tuyen and Thiem, 2005).
f = (k-1) = (3-1) = 2; k: the number of repetitions of the experiment (k=3, N=8) St (2, 8) with p = 0.05 (uncertainty of the determination) → t = 4.3 and Sb.t = 0.18127
Compared with the coefficients of the regression equation (2) we see in all the coefficients only factors b3; b12b23và b123< Sb.t; (0.1050; 0.0850; 0.1525 và 0.1100 < 0.18127), So the model coefficients B' = 4 and the form of regression equation is:
y = 85.2000 + 0.5475x1 + 0.2375x2 – 0.2125x1x3 (4)
Table 5. Figures Calculated on a Model
Experiment x1 x2 x3 yi
TB
(%ISO)
Si
2 yTT
(%ISO)
S2iTT
M1 - - - 83.75 0.0063 83.84 0.0081
M2 + - - 85.66 0.0673 85.58 0.0064
M3 - + - 84.92 0.0016 84.84 0.0064
M4 + + - 86.05 0.0988 86.14 0.0081
M5 - - + 84.91 0.0004 85.00 0.0081
M6 + - + 85.53 0.0076 85.45 0.0064
M7 - + + 85.03 0.1516 84.95 0.0064
M8 + + + 85.75 0.0076 85.84 0.0081
Total 0.3412 0.0580
Check the compatibility of the model: Based on the Fisher standards, conditions for adaptive model is FTT
+ Ftable = g(f1, f2), f1 =(k-1), f2= N - B’. So that Ftable = g (2, 4) = 6.94 (Tuyen and Thiem, 2005).
+ FTT is calculated as follows:
B S S
2 yTB 2
b
N 1 i
2 i 2
y S
N
S 1
k 1 l
TB 2 k l, 2
i (y y )
1 k S 1
k S S
2 2 y
yTB
) ) ,
, 2
tu 2 y
2 y 2 tu TT min(S
S max(S F
S
(5)
83 S2tu corresponding variance S2tu of each experiment was calculated by the formula
In that yTT is the value of the corresponding objective function of each experiment according to the regression equation, B' is the meaninful coefficient of equation (4). These figures are calculated on the model presented in Table 4. From the above figures we calculated
S2tu = 0.0580; S2y = 0.04265
So that FTT = (0.058/0.04265) = 1.36; FTT < Fbảng = 6.94 (Tuyen and Thiem, 2005), Therefore, this model is compatible
* Perform the step up: The found model presents the posture of the space contour of brightness and physical properties of the pulp. From this, method should be shown which variables need to be mobile and whiteness and physical properties of the pulp reach the extreme (optimal). Part optimal start in the experiment was conducted with factor at zero (0), and the coordinates of the variables will be calculated using the formula:
xki = xk-1i i. (8)
To select a based variable, we calculate the value of an area | bii |, where bi is the coefficient corresponding to the variable xi, i is about change of variables:
Pameters selection :
y = 85.20 + 0.5475x1 + 0.2375x2 – 0.2125x1x3 (9)
+ 1 = (1.0% – 0.4%)/2 = 0.3 (%) |b11| = |0.5475 . 0.3| = 0.16425 + 2 = (1.6% – 1.0%)/2 = 0.3 (%) |b22| = |0.2375 . 0.3| = 0.07125
The chosen temperature of penetration was so close to reality, therefore b3 factor does not exist, or over a period of 70 – 1100C, this factor does not affect the quality of pulp.
|b11| is maximum value, therefore 1 = 0.10(%) was chosen as based jump. As fomula
2 = 0.043378(%), choose 1 = 0.05 (%).
Table 6. Experimental Matrix as Forward Method Experiment x1
(%H2O2)
x2
(%NaOH)
x3 (0C)
Brigtness
%ISO
Viscosity, mL/g
1 0.7 1.30 90 85.04 651.9
2 0.8 1.35 90 86.76 640.6
3 0.9 1.40 90 88.13 621.2
4 1.0 1.45 90 88.73 590.9
It can be seen fromthe experimental results, the quality of pulp is quite good. However when using H2O2 and NaOH : increased H2O2 level in the impregnating period from 0.7% to 0.8% and increased NaOH level used in the bleaching stage from 1.3% to 1.35%, the brightness of the pulp after bleaching increases up 1.7% ISO but viscosity decreases 11.3 mL/g. When used level H2O2 increased
N 1 i
2 iTT 2
tu S
B' - N
S 1 (6)
2 TB i TT i 2
iTT (y y )
S (7)
cs cs cs
i i
i .
. b
.
b Δ
λ
Δ λ (10)
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to 0.9% and NaOH level increased to 1.45%, the viscosity also has a downward trend. From the above results, the most suitable level of H2O2, NaOH and temperaturein (PO) stage are 0.80%, 1.35% and 900C, respectively.
CONCLUSION
It can be indicated from the experimental results that, for 6-year-old eucalyptus raw materials (E.Urophylla) grown in Tam Son - Phu Tho, Vietnam, in order to achieve the brightness of >
86%ISO, viscosity > 640mL/g, the optimal conditions for bleaching stage (PO) of the process (DhQ)(PO)D is at 90oC temperature, 1.35% NaOH and 0.8% H2O2. Quality of bleaching pulp is equivalent to thepulp from the process (D0E0D1ED2) with total active chlorine used is 4.5% (based on oven-dry weight pulp).
REFERENCES
Barbosa, L. C. A., Maltha, C. R. A., Vilas Boas, L. A., Pinheiro, P. P. F. and Colodette, J. L. (2008)
‘Profiles of extractives across the ZDht(PO)D and Dht(PO)D bleaching sequences for a eucalyptus kraft pulp’, Appita Journal, 61(1), p. 64.
Benca AMEC Ltd, (2004), Study report for: Independent advice on the development of environmental guidelines for any new bleached eucalypt kraft pulp mill in Tasmania. p.23-28 p.40-63, p.79-88, Ragnar, M. (2005) ‘2-stage bleaching of oxygen delignified HW kraft pulp to full brightness:
Practically possible by changing D0 to D*’, Pulp and Paper Canada, 106(4), pp. 56–58.
Tuyen, N. M., Thiem, P. V., (2005). ‘Systems Engineering Chemical Engineering’, pages 194-235, Vol. 1, Publisher of scientific and technical, Vietnam.
© 2017 The Authors. Published by Center for Pulp and Paper, Ministry of Industry, Indonesia