Abstract The single-section and two-stage H2O2 bleaching of CTB were performed to determine the suitable process conditions for H2O2 bleaching. Key words Fine leaf CTMP whiteness H2O2 PC value H2O2 High-Brightness-Bleaching of Eucalyptus (E. tereticorns) Liu Yan Shen Kuizhong (Research Insititute of Chemical Processing and Utilization of Forest Products, CAF Nanjing, 210042) ABSTRACT The one stage and Two stages H2O2 bleaching of CTMP from Eucalyptus (E. tereticorns) were studied in this paper.Suitable conditions of H2O2 bleaching were determined.
As one of the world's three fastest-growing species, Eucalyptus has occupied 1/3 of the world's plantations. Eucalyptus grows fast and has good wood quality. It will have bright prospects for the pulp and paper industry. Foreign eucalyptus has been used for mechanical pulp for many years. How to use eucalyptus pulp to produce fine paper is an issue that needs to be considered with emphasis on its buoyancy. In this paper, the high whiteness bleaching process of CTMP H2O2 was studied and studied. 1 Materials and methods 1.1 Raw material test Acerola wood chip was taken from Yangjiang, Guangdong. 1.2 Preparation of Slurry CTMP is produced by the Andritz sprout-Bauer refinery pilot system in this laboratory. 1.3 Pretreatment conditions The whiteness of the original pulp was 44.3% ISO. The DTPA was used to pretreat the CTMP. DTPA dosage 0.25% ~ 0.30%, temperature 50 ~ 60 °C, pulp concentration 2%, processing time 20min. 1.4 Bleaching conditions Bleaching is carried out in a polyethylene plastic bag. The bleaching temperature is 70° C. and the time is 2 h. The pulp concentration is 15% to 30%. 1.5 Determination of Whiteness About 1.5 g of dry pulp was taken, dispersed, diluted with water to a consistency of 1% pulp, sized on a Buchner funnel, flattened, air-dried, and measured. 1.6 Determination method Residual H2O2, determination of yellowing rate Refer to the relevant determination method in "Pulling and Papermaking Experiment". The relevant slurry performance indicators are all performed according to the national standard. 2 Results and Discussion 2.1 Effect of Single-stage H2O2 Bleaching 2.1.1 H2O2 Dosage on Bleaching Whiteness As can be seen from Figure 1, under certain bleaching conditions, with the increase of H2O2 consumption, whiteness increases and H2O2 consumption also increases, 3%. H2O2 can increase the whiteness of CTMP pulp by 22.3 to 32.4 units, and the whiteness of pulp after bleaching by 4% H2O2 amount to 71.5% to 75% (ISO), hydrogen peroxide from 3% to 4%, and the whiteness does not increase greatly. Therefore, in actual production, it is recommended to use two stages of bleaching to further increase whiteness. Figure 1. Effect of H2O2 Dosage on Bleaching Whiteness 2.1.2 Effects of NaOH Dosage on Bleaching Whiteness Many papers [1] have stated the importance of alkalinity on whiteness in peroxide bleaching. The effect of NaOH dosage on bleaching brightness in this experiment is shown in Figure 2. Figure 2 NaOH/H2O2
As can be seen from FIG. 2 , at the same amount of H 2 O 2 , when the other bleaching conditions are constant, the whiteness of the pulp obtained by the bleaching decreases as the ratio of alkali to H 2 O 2 increases. After regression analysis, there is a suitable amount of NaOH corresponding to different amounts of H2O2 to be used to obtain relatively high whiteness. 2.1.3 Effect of Bleaching Pulp Concentration on Bleaching Whiteness [2] The increase in high-concentration bleaching whiteness is due to the fact that most H2O2 concentrates in the fiber cell walls at high concentrations and are easily bleached, resulting in consumption outside the cell wall. The non-bleaching reaction consumes a small amount of H2O2. High slurry density, H2O2 concentration is also high, the bleaching reaction rate is faster than the alkali-induced color formation reaction.
The effect of bleaching consistency on bleaching brightness is shown in Figure 3. With the increase of the concentration from 15% to 30%, the whiteness also increases. After the pulp concentration is higher than 20%, the whiteness increases slowly, and the suitable pulp density for bleaching should be 20% to 30%. Fig. 3 Effect of bleaching pulp consistency on bleaching brightness (MgSO4 0.05, Na2SiO3 1.5%, temperature 70°C, time 2h) 2.1.4 Effect of different puree whiteness and different compression ratio on the whiteness of bleaching Wood chips are compressed differently The results of the single-stage H2O2 bleaching of the CTMP pure pulp with different brightness were compared as shown in Table 1. Table 1 H202 Bleaching Results of CTMP Single-Stage HBT with Different Compression Ratios and Different Whiteness. Item Whiteness % After ISO Bleaching % Whiteness Increment % ISO Bleaching Process Compression Ratio 3% H2O2/2.25% NaOH
Low compression ratio 4:1 46.6 76.7/76.4 30.1/29.8 43.6 76.0 32.4 47.7 77.3 29.5 High compression ratio >4:1 44.3 71.4 27.1 44.2 70.7 26.5 43.7 70.5 26.8
Note: MgSO4 0.05%, Na2SiO3 1.5%, DTPA 0.25% ~ 0.3% (for dry pulp), temperature 70 °C, time 2h, concentration 20%.
From Table 1, it can be seen that the CTMP obtained from wood chips with different compression ratios has different bleaching whiteness under the same bleaching conditions, and the CTMP with low compression ratio under the same whiteness. The pulp has a 4 to 6 percent higher whiteness after bleaching than the CTMP with high compression ratio. This may be due to the fact that the low compression ratio CTMP is higher than the high compression ratio CTMP in the pulping process. Absorb chemical liquids (such as NaOH, Na2SO3) to the minimum.
It can also be seen from Table 1 that the whiteness of CTMP after bleaching is different between the same compression ratio and whiteness of the original pulp. The lower the whiteness of the original pulp, the higher the whiteness increase value obtained with the same amount of H2O2. 2.1.5 Effect of different freeness of CTMP pure pulp on bleaching whiteness Different free pulp, H2O2 bleaching results of the same bleaching process as shown in Table 2. Table 2 H2O2 bleaching results of different freeness puree and same bleaching process single item Whiteness and whiteness increment after compression of original pulp Free of charge CSF %ISO %ISO Low compression ratio 4:1 203 77.3 29.5 240 76.4 29.8 420 76.0 32.4 High compression ratio >4:1 190 70.5 26.8 202 70.7 26.5 379 71.4 27.1
Note: H2O23%, NaOH 2.25%, MgSO4 0.05%, NaSiO3 1.5%, temperature 70 °C, time 2h, pulp concentration 20%, chelate before the appropriate amount of DTPA.
From Table 2, it can be seen that there is no significant difference in the whiteness after the single-stage bleaching in the same compression ratio and different freeness puree. This shows that the freeness of the CTMP original pulp before bleaching has little effect on the whiteness after bleaching. 2.1.6 Effect of Different Chelating Agents on Bleaching Whiteness The effect of different chelating agent amounts on bleaching whiteness is shown in Figure 4.
The effect of DTPA dosage in the range of 0.2% to 0.6% on the whiteness of bleaching was studied. With the increase of DTPA dosage, the whiteness increases. After the DTPA dosage is increased to 0.3%, the whiteness improvement effect is not obvious. When the DTPA dosage is increased to 0.5%, the whiteness decreases. It is more appropriate to consider the total economic cost to be controlled at 0.3%.
In the experiment, before H2O2 single-segment bleaching, after DTPA pre-treatment, comparing the H2O2 single-stage bleaching whiteness after chelating and non-washing, it was found that the whiteness of the post-chelation washing was improved by 1.0 percentage point . Fig.4 Effect of different chelating agent dosages on bleaching brightness (MgSO4 0.05%, Na2SiO3 1.5%, temperature 70°C, time 2h) 2.1.7 The effect of bleaching with or without MgSO4 on the bleaching whiteness The same unbleached pulp sample, In the same bleaching process, with and without MgSO4 added during the bleaching process, it was found that the whiteness of the pulp after adding MgSO4 was 0.5 to 1 percentage point higher than the whiteness of the pulp after the bleaching without MgSO4. 2.1.8 Effect of Different Acids After Bleaching on Bleaching Whiteness H2O2 bleached slurries are treated with acid, especially with reducing weak acids, which can effectively improve whiteness [3].
In the experiment, bleached pulps of the same bleaching conditions were acidified with oxalic acid and SO2 after single-stage bleaching with H2O2. The results are shown in Table 3.
From the results in Table 3, it can be seen that, under the same bleaching conditions, the acidity of oxalic acid and SO2 after the single-stage bleaching of H2O2, there is no significant difference in whiteness, but the acidity of the oxalic acid after the PC is lower than the acidification of SO2, indicating acidification with oxalic acid Slurry, its high stability of whiteness. Table 3 The same bleaching and acidification conditions, acidification of acidification of different acidification on bleaching pulp whiteness acidification conditions pulp concentration pH temperature time H2O2 after single bleaching PC value of acidification acid% °C min I oxalic acid 3 4.61 25 ~ 27 20 ~ 30 76.7 0.636 SO2 3 4.86 25 ~ 27 20 ~ 30 76.9 0.991 II Oxalic Acid 3 4.64 25 20 ~ 30 75.1 0.526 SO2 3 4.51 25 ~ 27 20 ~ 30 75.4 1.710
*I, II Bleaching process conditions are the same, pulp consistency is different, H2O2 dosage is 3% 2.1.9 Impact of acetone washing after bleaching on bleaching whiteness According to relevant studies [4], acetone is used for suction filtration of masson pine SGW bleached pulp. , Can greatly improve the brightness of H2O2 bleached pulp.
In the experiment, 15 to 20 ml of acetone was used to wash and filter after bleaching. It was found that the whiteness of the acetone-washed pulp was 0.5 to 1 unit higher than that of the pulp-washed pulp, but the PC value decreased slightly. Especially in the sun quickly return to yellow. 2.2 Two-stage H2O2 Bleaching 2.2.1 The total H2O2 consumption is constant. The effect of H2O2 distribution change in P1 and P2 segments on the two-stage bleaching brightness is shown in Table 4. The two stages of H2O2 bleaching are the same when the total amount is 5% H2O2. The distribution ratio of H2O2 between the two stages (P1:P2) has a greater impact on the whiteness of bleached pulp. From the perspective of H2O2 consumption and consumption, the ratio of H2O2 (P1:P2) between the first and second segments is 3:2, and the whiteness is the highest. The whiteness of 5% H2O2 two-stage bleached pulp was higher than that of 5% H2O2 single-stage bleaching. The total whiteness of the two stages of bleaching was increased from 28% to 31%, and the ratio of alkali to H2O2 was controlled at 0.75:1 for the first stage and 0.5:1 for the second stage. 2.2.2 The effect of low compression ratio and different whiteness of CTMP on the final whiteness of bleaching It can be seen from Table 5 that under the same bleaching process, the lower the whiteness of the pure pulp, the lower the whiteness of the original pulp, the final whiteness The larger the increment. 2.2.3 Effect of Different Acidizing Acids on Final Whiteness of Bleaching Both bleaching stages are acidified by SO2 or oxalic acid under the same process conditions. It is found that the former is 1 to 1.5 percentage points higher than the latter, but the PC value is the latter. Lower than the former, indicating that the latter acidification, its high stability of whiteness. 2.3 Aging 2.3.1 Effect of H2O2 and NaOH dosage on the yellowing of bleaching pulp When the H2O2 consumption is fixed, the whiteness stability of the bleached pulp of the fine leafhopper CTMP decreases with increasing the amount of NaOH during heat aging. This is because in the H2O2 bleaching of CTMP pulp, the amount of phenol produced increases with the increase of the HCO-concentration, and NaOH addition in the bleached pulp helps phenol formation, which in turn causes whiteness loss during heat-induced aging[5] . Therefore, the appropriate amount of NaOH should be selected. 2.3.2 Effect of post-treatment on yellowing Appropriate post-bleaching treatment can improve the whiteness and whiteness stability of the pulp. The single-stage H2O2 post-wash wash had a slightly lower PC value than the unwashed pulp (approximately a 0.6 to 0.7 percentage point reduction in PC value). The experiment also found that after SO2 or oxalic acid post-treatment can further improve the whiteness of bleached pulp and whiteness stability of heat aging, and the stability of the later treated whiteness is higher. Table 5 Effect of low compression ratio and different whiteness of CTMP on the final whiteness of the project Item Whiteness Whiteness Whiteness Whiteness Incremental compression ratio % %ISO ISO Low compression ratio 4:1 43.6 80.2 36.6 46.6 79.6 33.0 47.7 79.4 31.7
Note: The amount of DTPA chelate before bleaching; one segment: H2O2 3%, NaOH 2.25%; two segments: H2O2 2%, NaOH 2%; temperature 70°C; time 2h; pulp consistency 20%-25%; appropriate amount of MgSO4; Na2SiO3. 2.3.3 Effect of bleaching method The experimental data show that using H2O2 as a single bleaching agent, increasing the number of bleaching stages can improve the whiteness of the bleached pulp and the stability of the heat aging whiteness (the heat aging PC value decreases from 1.0 to 1.40 to 0.62 to 0.78). . 3 Conclusions (1) Optimum process conditions for bleaching of CTMP H2O2.
a. Single-stage bleaching of H2O2 3%, NaOH 2.25%, MgSO4 0.05%, Na2SiO3 1.5%, pulp concentration 20%, float temperature 70°C, time 2h, chelation with 0.25% to 0.3% DTPA before bleaching, pulp brightness It can be increased from 46.0% of the original pulp to 75% to 76% (low compression ratio), and the whiteness increase is 29.5% to 32.4%.
b. Two-stage bleaching P1: H2O2 3%, NaOH 2.25%, MgSO4 0.05%, Na2SiO3 1.5%, pulp concentration 20%, float temperature 70° C., time 2 h, 0.25% to 0.3% DTPA chelate, oxalic acid post-treatment before bleaching , adjust the pH 4.5 to 5.
P2: H2O2 2%, NaOH 2%, MgSO4 0.05%, Na2SiO3 1.5%, pulp concentration 20-25%, float temperature 70°C, time 2h, oxalic acid post treatment, pH adjustment 4.5-5.
Whiteness can be increased from 44.3% to 46.0% of the original pulp to 74.6% (high compression ratio) to 81.0% (low compression ratio). The second increase in whiteness was 2.8% to 4.0%.
(2) When the amount of H2O2 is the same, the bleaching stage number is increased, and the whiteness and whiteness stability of the slurry are improved. Drift DT
As one of the world's three fastest-growing species, Eucalyptus has occupied 1/3 of the world's plantations. Eucalyptus grows fast and has good wood quality. It will have bright prospects for the pulp and paper industry. Foreign eucalyptus has been used for mechanical pulp for many years. How to use eucalyptus pulp to produce fine paper is an issue that needs to be considered with emphasis on its buoyancy. In this paper, the high whiteness bleaching process of CTMP H2O2 was studied and studied. 1 Materials and methods 1.1 Raw material test Acerola wood chip was taken from Yangjiang, Guangdong. 1.2 Preparation of Slurry CTMP is produced by the Andritz sprout-Bauer refinery pilot system in this laboratory. 1.3 Pretreatment conditions The whiteness of the original pulp was 44.3% ISO. The DTPA was used to pretreat the CTMP. DTPA dosage 0.25% ~ 0.30%, temperature 50 ~ 60 °C, pulp concentration 2%, processing time 20min. 1.4 Bleaching conditions Bleaching is carried out in a polyethylene plastic bag. The bleaching temperature is 70° C. and the time is 2 h. The pulp concentration is 15% to 30%. 1.5 Determination of Whiteness About 1.5 g of dry pulp was taken, dispersed, diluted with water to a consistency of 1% pulp, sized on a Buchner funnel, flattened, air-dried, and measured. 1.6 Determination method Residual H2O2, determination of yellowing rate Refer to the relevant determination method in "Pulling and Papermaking Experiment". The relevant slurry performance indicators are all performed according to the national standard. 2 Results and Discussion 2.1 Effect of Single-stage H2O2 Bleaching 2.1.1 H2O2 Dosage on Bleaching Whiteness As can be seen from Figure 1, under certain bleaching conditions, with the increase of H2O2 consumption, whiteness increases and H2O2 consumption also increases, 3%. H2O2 can increase the whiteness of CTMP pulp by 22.3 to 32.4 units, and the whiteness of pulp after bleaching by 4% H2O2 amount to 71.5% to 75% (ISO), hydrogen peroxide from 3% to 4%, and the whiteness does not increase greatly. Therefore, in actual production, it is recommended to use two stages of bleaching to further increase whiteness. Figure 1. Effect of H2O2 Dosage on Bleaching Whiteness 2.1.2 Effects of NaOH Dosage on Bleaching Whiteness Many papers [1] have stated the importance of alkalinity on whiteness in peroxide bleaching. The effect of NaOH dosage on bleaching brightness in this experiment is shown in Figure 2. Figure 2 NaOH/H2O2
As can be seen from FIG. 2 , at the same amount of H 2 O 2 , when the other bleaching conditions are constant, the whiteness of the pulp obtained by the bleaching decreases as the ratio of alkali to H 2 O 2 increases. After regression analysis, there is a suitable amount of NaOH corresponding to different amounts of H2O2 to be used to obtain relatively high whiteness. 2.1.3 Effect of Bleaching Pulp Concentration on Bleaching Whiteness [2] The increase in high-concentration bleaching whiteness is due to the fact that most H2O2 concentrates in the fiber cell walls at high concentrations and are easily bleached, resulting in consumption outside the cell wall. The non-bleaching reaction consumes a small amount of H2O2. High slurry density, H2O2 concentration is also high, the bleaching reaction rate is faster than the alkali-induced color formation reaction.
The effect of bleaching consistency on bleaching brightness is shown in Figure 3. With the increase of the concentration from 15% to 30%, the whiteness also increases. After the pulp concentration is higher than 20%, the whiteness increases slowly, and the suitable pulp density for bleaching should be 20% to 30%. Fig. 3 Effect of bleaching pulp consistency on bleaching brightness (MgSO4 0.05, Na2SiO3 1.5%, temperature 70°C, time 2h) 2.1.4 Effect of different puree whiteness and different compression ratio on the whiteness of bleaching Wood chips are compressed differently The results of the single-stage H2O2 bleaching of the CTMP pure pulp with different brightness were compared as shown in Table 1. Table 1 H202 Bleaching Results of CTMP Single-Stage HBT with Different Compression Ratios and Different Whiteness. Item Whiteness % After ISO Bleaching % Whiteness Increment % ISO Bleaching Process Compression Ratio 3% H2O2/2.25% NaOH
Low compression ratio 4:1 46.6 76.7/76.4 30.1/29.8 43.6 76.0 32.4 47.7 77.3 29.5 High compression ratio >4:1 44.3 71.4 27.1 44.2 70.7 26.5 43.7 70.5 26.8
Note: MgSO4 0.05%, Na2SiO3 1.5%, DTPA 0.25% ~ 0.3% (for dry pulp), temperature 70 °C, time 2h, concentration 20%.
From Table 1, it can be seen that the CTMP obtained from wood chips with different compression ratios has different bleaching whiteness under the same bleaching conditions, and the CTMP with low compression ratio under the same whiteness. The pulp has a 4 to 6 percent higher whiteness after bleaching than the CTMP with high compression ratio. This may be due to the fact that the low compression ratio CTMP is higher than the high compression ratio CTMP in the pulping process. Absorb chemical liquids (such as NaOH, Na2SO3) to the minimum.
It can also be seen from Table 1 that the whiteness of CTMP after bleaching is different between the same compression ratio and whiteness of the original pulp. The lower the whiteness of the original pulp, the higher the whiteness increase value obtained with the same amount of H2O2. 2.1.5 Effect of different freeness of CTMP pure pulp on bleaching whiteness Different free pulp, H2O2 bleaching results of the same bleaching process as shown in Table 2. Table 2 H2O2 bleaching results of different freeness puree and same bleaching process single item Whiteness and whiteness increment after compression of original pulp Free of charge CSF %ISO %ISO Low compression ratio 4:1 203 77.3 29.5 240 76.4 29.8 420 76.0 32.4 High compression ratio >4:1 190 70.5 26.8 202 70.7 26.5 379 71.4 27.1
Note: H2O23%, NaOH 2.25%, MgSO4 0.05%, NaSiO3 1.5%, temperature 70 °C, time 2h, pulp concentration 20%, chelate before the appropriate amount of DTPA.
From Table 2, it can be seen that there is no significant difference in the whiteness after the single-stage bleaching in the same compression ratio and different freeness puree. This shows that the freeness of the CTMP original pulp before bleaching has little effect on the whiteness after bleaching. 2.1.6 Effect of Different Chelating Agents on Bleaching Whiteness The effect of different chelating agent amounts on bleaching whiteness is shown in Figure 4.
The effect of DTPA dosage in the range of 0.2% to 0.6% on the whiteness of bleaching was studied. With the increase of DTPA dosage, the whiteness increases. After the DTPA dosage is increased to 0.3%, the whiteness improvement effect is not obvious. When the DTPA dosage is increased to 0.5%, the whiteness decreases. It is more appropriate to consider the total economic cost to be controlled at 0.3%.
In the experiment, before H2O2 single-segment bleaching, after DTPA pre-treatment, comparing the H2O2 single-stage bleaching whiteness after chelating and non-washing, it was found that the whiteness of the post-chelation washing was improved by 1.0 percentage point . Fig.4 Effect of different chelating agent dosages on bleaching brightness (MgSO4 0.05%, Na2SiO3 1.5%, temperature 70°C, time 2h) 2.1.7 The effect of bleaching with or without MgSO4 on the bleaching whiteness The same unbleached pulp sample, In the same bleaching process, with and without MgSO4 added during the bleaching process, it was found that the whiteness of the pulp after adding MgSO4 was 0.5 to 1 percentage point higher than the whiteness of the pulp after the bleaching without MgSO4. 2.1.8 Effect of Different Acids After Bleaching on Bleaching Whiteness H2O2 bleached slurries are treated with acid, especially with reducing weak acids, which can effectively improve whiteness [3].
In the experiment, bleached pulps of the same bleaching conditions were acidified with oxalic acid and SO2 after single-stage bleaching with H2O2. The results are shown in Table 3.
From the results in Table 3, it can be seen that, under the same bleaching conditions, the acidity of oxalic acid and SO2 after the single-stage bleaching of H2O2, there is no significant difference in whiteness, but the acidity of the oxalic acid after the PC is lower than the acidification of SO2, indicating acidification with oxalic acid Slurry, its high stability of whiteness. Table 3 The same bleaching and acidification conditions, acidification of acidification of different acidification on bleaching pulp whiteness acidification conditions pulp concentration pH temperature time H2O2 after single bleaching PC value of acidification acid% °C min I oxalic acid 3 4.61 25 ~ 27 20 ~ 30 76.7 0.636 SO2 3 4.86 25 ~ 27 20 ~ 30 76.9 0.991 II Oxalic Acid 3 4.64 25 20 ~ 30 75.1 0.526 SO2 3 4.51 25 ~ 27 20 ~ 30 75.4 1.710
*I, II Bleaching process conditions are the same, pulp consistency is different, H2O2 dosage is 3% 2.1.9 Impact of acetone washing after bleaching on bleaching whiteness According to relevant studies [4], acetone is used for suction filtration of masson pine SGW bleached pulp. , Can greatly improve the brightness of H2O2 bleached pulp.
In the experiment, 15 to 20 ml of acetone was used to wash and filter after bleaching. It was found that the whiteness of the acetone-washed pulp was 0.5 to 1 unit higher than that of the pulp-washed pulp, but the PC value decreased slightly. Especially in the sun quickly return to yellow. 2.2 Two-stage H2O2 Bleaching 2.2.1 The total H2O2 consumption is constant. The effect of H2O2 distribution change in P1 and P2 segments on the two-stage bleaching brightness is shown in Table 4. The two stages of H2O2 bleaching are the same when the total amount is 5% H2O2. The distribution ratio of H2O2 between the two stages (P1:P2) has a greater impact on the whiteness of bleached pulp. From the perspective of H2O2 consumption and consumption, the ratio of H2O2 (P1:P2) between the first and second segments is 3:2, and the whiteness is the highest. The whiteness of 5% H2O2 two-stage bleached pulp was higher than that of 5% H2O2 single-stage bleaching. The total whiteness of the two stages of bleaching was increased from 28% to 31%, and the ratio of alkali to H2O2 was controlled at 0.75:1 for the first stage and 0.5:1 for the second stage. 2.2.2 The effect of low compression ratio and different whiteness of CTMP on the final whiteness of bleaching It can be seen from Table 5 that under the same bleaching process, the lower the whiteness of the pure pulp, the lower the whiteness of the original pulp, the final whiteness The larger the increment. 2.2.3 Effect of Different Acidizing Acids on Final Whiteness of Bleaching Both bleaching stages are acidified by SO2 or oxalic acid under the same process conditions. It is found that the former is 1 to 1.5 percentage points higher than the latter, but the PC value is the latter. Lower than the former, indicating that the latter acidification, its high stability of whiteness. 2.3 Aging 2.3.1 Effect of H2O2 and NaOH dosage on the yellowing of bleaching pulp When the H2O2 consumption is fixed, the whiteness stability of the bleached pulp of the fine leafhopper CTMP decreases with increasing the amount of NaOH during heat aging. This is because in the H2O2 bleaching of CTMP pulp, the amount of phenol produced increases with the increase of the HCO-concentration, and NaOH addition in the bleached pulp helps phenol formation, which in turn causes whiteness loss during heat-induced aging[5] . Therefore, the appropriate amount of NaOH should be selected. 2.3.2 Effect of post-treatment on yellowing Appropriate post-bleaching treatment can improve the whiteness and whiteness stability of the pulp. The single-stage H2O2 post-wash wash had a slightly lower PC value than the unwashed pulp (approximately a 0.6 to 0.7 percentage point reduction in PC value). The experiment also found that after SO2 or oxalic acid post-treatment can further improve the whiteness of bleached pulp and whiteness stability of heat aging, and the stability of the later treated whiteness is higher. Table 5 Effect of low compression ratio and different whiteness of CTMP on the final whiteness of the project Item Whiteness Whiteness Whiteness Whiteness Incremental compression ratio % %ISO ISO Low compression ratio 4:1 43.6 80.2 36.6 46.6 79.6 33.0 47.7 79.4 31.7
Note: The amount of DTPA chelate before bleaching; one segment: H2O2 3%, NaOH 2.25%; two segments: H2O2 2%, NaOH 2%; temperature 70°C; time 2h; pulp consistency 20%-25%; appropriate amount of MgSO4; Na2SiO3. 2.3.3 Effect of bleaching method The experimental data show that using H2O2 as a single bleaching agent, increasing the number of bleaching stages can improve the whiteness of the bleached pulp and the stability of the heat aging whiteness (the heat aging PC value decreases from 1.0 to 1.40 to 0.62 to 0.78). . 3 Conclusions (1) Optimum process conditions for bleaching of CTMP H2O2.
a. Single-stage bleaching of H2O2 3%, NaOH 2.25%, MgSO4 0.05%, Na2SiO3 1.5%, pulp concentration 20%, float temperature 70°C, time 2h, chelation with 0.25% to 0.3% DTPA before bleaching, pulp brightness It can be increased from 46.0% of the original pulp to 75% to 76% (low compression ratio), and the whiteness increase is 29.5% to 32.4%.
b. Two-stage bleaching P1: H2O2 3%, NaOH 2.25%, MgSO4 0.05%, Na2SiO3 1.5%, pulp concentration 20%, float temperature 70° C., time 2 h, 0.25% to 0.3% DTPA chelate, oxalic acid post-treatment before bleaching , adjust the pH 4.5 to 5.
P2: H2O2 2%, NaOH 2%, MgSO4 0.05%, Na2SiO3 1.5%, pulp concentration 20-25%, float temperature 70°C, time 2h, oxalic acid post treatment, pH adjustment 4.5-5.
Whiteness can be increased from 44.3% to 46.0% of the original pulp to 74.6% (high compression ratio) to 81.0% (low compression ratio). The second increase in whiteness was 2.8% to 4.0%.
(2) When the amount of H2O2 is the same, the bleaching stage number is increased, and the whiteness and whiteness stability of the slurry are improved. Drift DT
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