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H2O2 high whiteness bleaching of thin leaves according to CTMP

abstract the single-stage and two-stage H2O2 bleaching of thin leaves according to CTMP was studied, and the suitable process conditions for H2O2 bleaching were determined. Keywords thin leaves according to CTMP whiteness H2O2 PC value H2O2 high brightness blending of Eucalyptus (refractories) Liu Yan Shen Kuizhong (Research Insitute of chemical processing and utilization of forest products, CAF Nanjing, 210042) abstract the one stage and two stages H2O2 bleeding of CTMP from EUC improve the double performance of lithium battery materials Alyptus (retirns) were studied in this itable conditions of H2O2 bleeding were determined

Eucalyptus is one of the three fast-growing tree species in the world, and its artificial afforestation area has accounted for 1/3 of the world's artificial forests. Eucalyptus grows fast and has good wood quality. It will have a bright future for the pulp and paper industry. Eucalyptus has been used in mechanical pulp for many years abroad. How to use eucalyptus pulp to produce high-grade paper, one of the key issues to be considered is its bleachability. In this paper, CTMP H2O2 high whiteness bleaching process of Eucalyptus tenuifolia was explored and studied. 1 materials and methods 1.1 raw materials

Eucalyptus gracilis chips for the test were taken from Yangjiang, Guangdong. 1.2 preparation of slurry

Eucalyptus globulus CTMP is produced by the Andritz sprout Bauer grinding pilot system of our laboratory. 1.3 pretreatment conditions

the whiteness of the original pulp is 44.3% ISO. In the experiment, CTMP of Eucalyptus globulus was pretreated with DTPA. The dosage of DTPA is 0.25% - 0.30%, the temperature is 50 ~ 60 ℃, the slurry concentration is 2%, and the treatment time is 20min. 1.4 bleaching conditions

bleaching is carried out in polyethylene plastic bags. The bleaching temperature is 70 ℃, the time is 2h, and the pulp concentration is 15% - 30%. 1.5 whiteness measurement

take about 1.5g absolutely dry pulp, disperse it, dilute it with water to 1% pulp concentration, copy it into pulp tablets on Buchner funnel, flatten it, air dry it, and measure it. 1.6 determination method

the determination of residual H2O2 and yellowness value refers to the relevant determination methods in the pulping and papermaking experiment, and the relevant pulp performance indicators are implemented in accordance with the national standard. 2 results and discussion 2.1 single 5. Under the condition of ensuring that the oil return valve is closed, segment H2O2 bleaching 2.1.1 the effect of H2O2 dosage on bleaching whiteness

it can be seen from Figure 1 that under certain other bleaching conditions, with the increase of H2O2 dosage, whiteness increases, H2O2 consumption also increases, 3% H2O2 can increase the whiteness of CTMP pulp by 22.3 ~ 32.4 units, the whiteness of bleached pulp after 4% H2O2 dosage reaches 71.5 ~ 75% (ISO), and hydrogen peroxide from 3 ~ 4%, The value-added of whiteness is not large, so in actual production, it is recommended to use two-stage bleaching to further improve whiteness. Figure 1 Effect of H2O2 dosage on bleaching whiteness 2.1.2 effect of NaOH dosage on bleaching whiteness

many literatures [1] have described the importance of the effect of alkalinity on whiteness in peroxide bleaching. The effect of NaOH dosage on bleaching whiteness in this experiment is shown in Figure 2. Figure 2 naoh/h2o2

it can be seen from Figure 2 that under the same amount of H2O2, when other bleaching conditions are certain, the whiteness of the bleached pulp decreases with the increase of the ratio of alkali to H2O2. Through regression analysis, there is a suitable amount of NaOH corresponding to different amount of H2O2, and a relatively high whiteness can be obtained. 2.1.3 the effect of bleach pulp concentration on bleach whiteness has been reported in the literature [2]. The increase of bleach whiteness at high concentration is because most H2O2 is inhaled into the fiber cell wall at high concentration, and it is easy to carry out bleaching reaction. As a result, the non bleaching reaction consumed outside the cell wall consumes a small amount of H2O2. With high pulp concentration and high H2O2 concentration, the bleaching reaction rate is faster than the colored matter formation reaction caused by alkali

the effect of bleaching pulp concentration on bleaching whiteness is shown in Figure 3. With the increase of concentration from 15% to 30%, the whiteness also increases. When the pulp concentration is higher than 20%, the whiteness increases slowly. The suitable pulp concentration for bleaching should be 20% to 30%. Fig. 3 Effect of bleach pulp concentration on bleach whiteness (MgSO4 0.05, Na2SiO3 1.5%, temperature 70 ℃, time 2H) 2.1.4 effect of different raw pulp whiteness and different compression ratio on bleach whiteness

single stage H2O2 bleaching results of Eucalyptus globulus CTMP raw pulp with different whiteness prepared by wood chips with different compression ratio are shown in Table 1. Table 1 thin leaves with different compression ratios and whiteness according to CTMP single-stage H202 bleaching results

project raw pulp whiteness%iso whiteness after bleaching%iso 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 pressure 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 absolute dry pulp), temperature 70 ℃, Time 2h, concentration 20%

it can be seen from table 1 that the bleached pulp whiteness of Eucalyptus globulus CTMP prepared by treating wood chips with different compression ratios is different under the same bleaching process conditions. Under the same pulp whiteness, the bleached whiteness of Eucalyptus globulus CTMP raw pulp with low compression ratio is 4-6 percentage points higher than that of Eucalyptus globulus CTMP raw pulp with high compression ratio and strong adsorption. This may be because in the pulping process, The CTMP of Eucalyptus tenuifolia with low compression ratio absorbs less chemical solutions (such as NaOH and Na2SO3) than that of Eucalyptus tenuifolia with high compression ratio

Table 1 also shows that eucalyptus globulus with the same compression ratio and different pulp whiteness has different whiteness after CTMP bleaching. The lower the pulp whiteness, the higher the whiteness increase obtained by the same H2O2 dosage. 2.1.5 effect of CTMP pulps with different degrees of freedom on bleaching whiteness

the results of single-stage H2O2 bleaching of pulps with different degrees of freedom are shown in Table 2. Table 2 single stage H2O2 bleaching results of raw pulp with different freeness and the same bleaching process

whiteness and whiteness increment compression ratio of the project raw pulp after freeness bleaching 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 ℃, time 2h, pulp concentration 20%, appropriate amount before bleaching.Dtpa chelation

it can be seen from table 2 that there is little difference in whiteness after single-stage bleaching of raw pulps with the same compression ratio and different freeness. This shows that the CTMP original pulp freeness before bleaching has little effect on the whiteness after bleaching. 2.1.6 effect of different chelator dosage on bleaching whiteness

the effect of different chelator dosage on bleaching whiteness is shown in Figure 4

the effect of DTPA dosage in the range of 0.2% - 0.6% on bleaching whiteness was studied. The whiteness increases with the increase of DTPA dosage. When the DTPA dosage increases to 0.3%, the whiteness improvement effect is not obvious. When the DTPA dosage increases to 0.5%, the whiteness decreases. Considering the comprehensive economic cost, it is appropriate to control the dosage at about 0.3%

in the experiment, before H2O2 single-stage bleaching and after DTPA pretreatment, the whiteness of H2O2 single-stage bleaching after chelating washing was compared with that after non washing. It was found that the whiteness after chelating washing was 1.0 percentage points higher than that of non washing pulp. Fig. 4 Effect of different chelating agent dosage on bleaching whiteness (MgSO4 0.05%, Na2SiO3 1.5%, temperature 70 ℃, time 2H) 2.1.7 effect of adding and not adding MgSO4 on bleaching whiteness

for the same unbleached pulp sample, the same bleaching process, comparing the bleaching process with and without MgSO4, it is found that the whiteness of bleached pulp with MgSO4 is 0.5 ~ 1 percentage point higher than that of bleached pulp without MgSO4. 2.1.8 effect of different acids used in post bleaching acidification on bleaching whiteness

h2o2 bleached pulp is treated with acid, especially with reducing weak acid, which can effectively improve whiteness [3]

in the experiment, the bleached pulp under the same bleaching conditions was acidified with oxalic acid and SO2 after H2O2 single-stage bleaching. The results are listed in Table 3

it can be seen from the results in Table 3 that under the same bleaching conditions, after H2O2 single-stage bleaching, acidification with oxalic acid and SO2 has little difference in whiteness, but the PC value of the pulp acidified with oxalic acid is lower than that acidified with SO2, indicating that the pulp acidified with oxalic acid has high whiteness stability. Table 3 same bleaching and acidification conditions Effects of different acidification acids on the whiteness of bleached pulp

acidification conditions pulp concentration pH temperature time H2O2 single-stage bleaching whiteness PC value acidification acid% ℃ min Ⅰ oxalic acid 3 4.61 25 ~ 27 20 ~ 30 76.7 0.6 the beneficial conditions for the export of plastic extruders in China are increasing 36 SO2 34.86 25 ~ 27 20 ~ 30 76.9 0.991 Ⅱ oxalic acid 3 4.64 25 20 ~ 30 75.1 0.526 SO2 34.51 25 ~ 27 20 ~ 30 75.4 1.710

according to the relevant research shows that [4], the whiteness of Masson Pine SGW bleached pulp can be greatly improved by suction filtration with acetone

in the experiment, 15 ~ 20ml acetone was used to wash and filter after bleaching. It was found that the whiteness of the slurry washed and filtered with acetone was 0.5 ~ 1 unit higher than that of the slurry not washed and filtered with acetone, but the PC value decreased slightly. Especially under sunlight, it turns yellow quickly. 2.2 two stage H2O2 bleaching 2.2.1 with a certain total amount of H2O2, the effect of H2O2 distribution changes in P1 and P2 on the whiteness of two-stage bleaching

it can be seen from table 4 that under the same total amount of 5% H2O2, the H2O2 distribution ratio between the first and second stages (p1:p2) has a great impact on the whiteness of bleached pulp. From the perspective of H2O2 consumption and consumption, the H2O2 distribution ratio (p1:p2) between the first and second sections is 3:2, and the whiteness is the highest at this time. The whiteness of 5%h2o2 two-stage bleaching is higher than that of 5%h2o2 single-stage bleaching. The total whiteness increment of two-stage bleached pulp is 28% - 31%, and the ratio of alkali to H2O2 should be controlled at 0.75:1 in the first stage and 0.5:1 in the second stage. 2.2.2 effect of CTMP with low compression ratio and different whiteness of raw pulp on final bleaching whiteness

it can be seen from table 5 that for Eucalyptus globulus with low compression ratio, under the same bleaching process, the lower the whiteness of raw pulp, the greater the final whiteness increment. 2.2.3 effect of different acidification acids on final bleaching whiteness

under the same process conditions, both stages of bleaching are acidified by SO2 or oxalic acid. It is found that the final whiteness of the former is 1 ~ 1.5 percentage points higher than the latter, but the PC value of the latter is lower than the former, indicating that acidification with the latter has high whiteness stability. 2.3 aging 2.3.1 effect of the amount of H2O2 and NaOH on the yellowing of bleached pulp

when the amount of H2O2 is constant, the whiteness stability of Eucalyptus globulus CTMP bleached pulp during thermal aging decreases with the increase of the amount of NaOH. This is because in the H2O2 bleaching of CTMP pulp, the amount of phenol produced increases with the increase of Hoo concentration, and the increase of NaOH in the bleaching pulp contributes to the formation of phenol, which then causes the loss of whiteness in the heat induced aging [5]. Therefore, the appropriate amount of NaOH should be selected. 2.3.2 effect of post-treatment on yellowing

proper post-treatment of bleaching can improve the whiteness and whiteness stability of pulp. The PC value of washed pulp after single-stage H2O2 bleaching is slightly lower than that of unwashed pulp (PC value decreases by about 0.6 ~ 0.7 percentage points). It was also found that SO2 or oxalic acid post-treatment can further improve the whiteness of bleached pulp and the stability of heat aging whiteness, and the latter treatment has higher whiteness stability. Table 5 Effect of CTMP with low compression ratio and different original pulp whiteness on final bleaching whiteness

original pulp whiteness of the project final 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: appropriate amount of DTPA chelation before bleaching; First stage: H2O2 3%, NaOH 2.25%; Second stage: H2O2 2%, NaOH 2%; Temperature 70 ℃; Time 2H; Slurry concentration 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 and increasing the number of bleaching stages can improve the whiteness and thermal aging whiteness stability of bleached pulp (thermal aging PC value decreases from 1.0 ~ 1.40 to 0.62 ~ 0.78). Conclusion

(1) the suitable process conditions for CTMP H2O2 bleaching of Eucalyptus globulus

a. single stage bleaching

h2o2 3%, NaOH 2.25%, MgSO4 0.05%, Na2SiO3 1.5%, pulp concentration 20%, bleaching temperature 70 ℃, time 2h, chelate with 0.25% - 0.3% DTPA before bleaching, and the brightness of the pulp can be 46.0 of the original pulp