阅读说明：本技术 一种草浆的无元素氯漂白方法 (Elemental chlorine-free bleaching method for straw pulp ) 是由 栾飞 何雨彤 袁宝龙 于 2021-07-29 设计创作，主要内容包括：本发明公开了一种草浆的无元素氯漂白方法,首先将草浆与NaOH或氧化白液进行混合,草浆浓度为10％,增大反应氧压与温度,反应一定时间,得到一种被NaOH或氧化白液漂白的麦草浆,然后将麦草浆进行第一次二氧化氯漂白后通入氧气和过氧化氢,同时加入一定量的氢氧化钠进行过氧化氢强化的碱抽提,得到经过碱抽提后的麦草浆,加入螯合剂进行螯合处理,得到螯合处理后的麦草浆,进行第二次和第三次二氧化氯强化漂白,得到漂白后的麦草浆,本发明将漂白技术中因含氯漂白方法所产生的二噁英和AOX减少或消除,从而使纸浆漂白,并且满足日益严格的环境保护要求。(The invention discloses an element-free chlorine bleaching method of straw pulp, which comprises the steps of mixing the straw pulp with NaOH or oxidized white liquor, wherein the concentration of the straw pulp is 10%, increasing the reaction oxygen pressure and temperature, reacting for a certain time to obtain the straw pulp bleached by the NaOH or oxidized white liquor, then introducing oxygen and hydrogen peroxide after carrying out first chlorine dioxide bleaching on the straw pulp, simultaneously adding a certain amount of sodium hydroxide to carry out hydrogen peroxide enhanced alkali extraction to obtain the straw pulp subjected to the alkali extraction, adding a chelating agent to carry out chelating treatment to obtain the chelated straw pulp, and carrying out second and third chlorine dioxide enhanced bleaching to obtain the bleached straw pulp.)

1. An element-free chlorine bleaching method for straw pulp is characterized by comprising the following steps:

step 1, mixing straw pulp with NaOH or oxidized white liquor, wherein the concentration of the straw pulp is 10%, increasing the reaction oxygen pressure and temperature, and reacting for a certain time to obtain wheat straw pulp bleached by the NaOH or oxidized white liquor, wherein the step is an oxygen delignification bleaching section, namely an O section;

step 2, carrying out primary chlorine dioxide bleaching on the wheat straw pulp reacted in the step 1, and bleaching at a higher temperature to obtain the wheat straw pulp bleached by chlorine dioxide, wherein the step is a chlorine dioxide bleaching stage, namely D₀A segment;

step 3, introducing oxygen and hydrogen peroxide into the wheat straw pulp bleached by chlorine dioxide obtained in the step 2, and simultaneously adding a certain amount of sodium hydroxide to perform hydrogen peroxide enhanced alkali extraction to obtain the wheat straw pulp subjected to alkali extraction, wherein the step is a hydrogen peroxide enhanced alkali extraction section, namely an EPO section;

step 4, washing the wheat straw pulp subjected to alkali extraction in the step 3, and adding a chelating agent for chelating treatment to obtain chelated wheat straw pulp, wherein the step is a chelating treatment section, namely a Q section;

step 5, carrying out secondary chlorine dioxide bleaching treatment on the wheat pulp treated in the step 4, wherein the consumption of the secondary chlorine dioxide is less than that of the primary chlorine dioxide, and obtaining secondary chlorine dioxide bleachingIn the straw pulp, this step being a chlorine dioxide bleaching stage, i.e. D₁A segment;

step 6, carrying out third chlorine dioxide enhanced bleaching on the pulp reacted in the step 5, wherein the consumption of the chlorine dioxide is less than that of the chlorine dioxide in the previous two times in the bleaching process, and NaOH is added to control the pH value to obtain the bleached wheat straw pulp, and the process is a chlorine dioxide bleaching stage, namely D₂And (4) section.

2. The method for bleaching straw pulp by using chlorine as claimed in claim 1, wherein NaOH or oxidized white liquor accounts for 2% -5% of the straw pulp in step 1, the treatment time of the oxygen delignification stage is 30-60min, the reaction oxygen pressure is controlled to be 0.7-0.9 MPa, and the temperature is controlled to be 75-85 ℃.

3. The method for bleaching straw pulp by using elemental chlorine as claimed in claim 1, wherein the pH range of the first chlorine dioxide bleaching in the step 2 is 2-3, the bleaching temperature is 40-70 ℃, the bleaching time is 20-40min, and the final concentration of the wheat straw pulp is 10% -13%.

4. The method for bleaching straw pulp without element chlorine as claimed in claim 1, wherein the treatment temperature in step 3 is 40-60 ℃, the treatment time is 60-90min, and the final concentration of straw pulp is 10-15%.

5. The elemental chlorine-free bleaching method of straw pulp as claimed in claim 1, wherein the chelating agent in step 4 is EDTA, and the pH of EDTA treatment is 3-5.

6. The method as claimed in claim 1, wherein the second chlorine dioxide enhanced bleaching in step 5 has a pH in the range of 3 to 4; the bleaching temperature is 55-75 deg.C, and the bleaching time is 60-120 min.

7. The method as claimed in claim 1, wherein the third chlorine dioxide enhanced bleaching in step 6 has a pH in the range of 3.5-4.5; the bleaching temperature is 60-85 deg.C, and the bleaching time is 60-120 min.

Technical Field

The invention belongs to the technical field of pulping and bleaching, and particularly relates to an elemental chlorine-free bleaching method for straw pulp.

Background

Since the 20 th century and the 80 th century, the CEH three-stage bleaching technology is mostly adopted for the bleaching treatment of the straw pulp in industry, but the straw pulp wastewater bleached by the method contains a large amount of toxic substances such as dioxin, AOX and the like. The CEH bleaching method contains chlorine element, and the unreacted chlorine gas and other generated chlorides after bleaching not only pollute the environment, but also are harmful to the health of human beings. Moreover, the adoption of chlorine-containing bleaching methods is already forbidden in China. Therefore, a method for bleaching straw pulp without chlorine element should be invented as soon as possible so as to meet the requirement of environmental protection.

Disclosure of Invention

The invention aims to provide an element-free chlorine bleaching method for straw pulp, which reduces or eliminates dioxin and AOX generated by a chlorine-containing bleaching method in a bleaching technology so as to bleach the paper pulp and meet increasingly strict environmental protection requirements.

The technical scheme adopted by the invention is that the elemental chlorine-free bleaching method of the straw pulp is implemented according to the following steps:

step 1, mixing straw pulp with NaOH or oxidized white liquor, wherein the concentration of the straw pulp is 10%, increasing the reaction oxygen pressure and temperature, and reacting for a certain time to obtain wheat straw pulp bleached by the NaOH or oxidized white liquor, wherein the step is an oxygen delignification bleaching section, namely an O section;

step 2, carrying out primary chlorine dioxide bleaching on the wheat straw pulp reacted in the step 1, and bleaching at a higher temperature to obtain the wheat straw pulp bleached by chlorine dioxide, wherein the step is a chlorine dioxide bleaching stage, namely D₀A segment;

step 3, introducing oxygen and hydrogen peroxide into the wheat straw pulp bleached by chlorine dioxide obtained in the step 2, and simultaneously adding a certain amount of sodium hydroxide to perform hydrogen peroxide enhanced alkali extraction to obtain the wheat straw pulp subjected to alkali extraction, wherein the step is a hydrogen peroxide enhanced alkali extraction section, namely an EPO section;

step 4, washing the wheat straw pulp subjected to alkali extraction in the step 3, and adding a chelating agent for chelating treatment to obtain chelated wheat straw pulp, wherein the step is a chelating treatment section, namely a Q section;

step 5, carrying out second chlorine dioxide bleaching treatment on the wheat pulp treated in the step 4, wherein the using amount of the second chlorine dioxide is less than that of the first chlorine dioxide, and obtaining the wheat pulp subjected to the second chlorine dioxide bleaching, wherein the step is a chlorine dioxide bleaching section, namely D₁A segment;

step 6, carrying out third chlorine dioxide enhanced bleaching on the pulp reacted in the step 5, wherein the consumption of the chlorine dioxide is less than that of the chlorine dioxide in the previous two times in the bleaching process, and NaOH is added to control the pH value to obtain the bleached wheat straw pulp, and the process is a chlorine dioxide bleaching stage, namely D₂And (4) section.

The present invention is also characterized in that,

in the step 1, NaOH or oxidized white liquor accounts for 2-5% of the amount of the straw pulp, the treatment time of the oxygen delignification section is 30-60min, the reaction oxygen pressure is controlled to be 0.7-0.9 MPa, and the temperature is controlled to be 75-85 ℃.

In the step 2, the pH range of the first chlorine dioxide bleaching is 2-3, the bleaching temperature is 40-70 ℃, the bleaching time is 20-40min, and the final wheat straw pulp concentration is 10% -13%.

In the step 3, the treatment temperature is 40-60 ℃, the treatment time is 60-90min, and the final wheat straw pulp concentration is 10-15%.

In the step 4, the chelating agent is EDTA, and the pH value of EDTA treatment is 3-5.

In the step 5, the pH range is 3-4 when the chlorine dioxide is intensively bleached for the second time; the bleaching temperature is 55-75 deg.C, and the bleaching time is 60-120 min.

In the step 6, the pH range of the third chlorine dioxide enhanced bleaching is 3.5-4.5; the bleaching temperature is 60-85 deg.C, and the bleaching time is 60-120 min.

The invention has the beneficial effects that: an element-free chlorine bleaching method for straw pulp, which carries out chlorine dioxide sectional bleaching on the pulp after oxygen delignification, wherein D₀The sections being mainly delignifying sections, D₁The stage is a bleaching stage D₂The section is a whitening section, so that the whiteness of the final pulp is obviously improved. Because the straw pulp contains a large amount of mixed cells, the lignin content in the straw pulp is high, paper pulp produced by the straw pulp is easy to turn yellow, the turning yellow of the bleached straw pulp can be obviously reduced through chelating treatment and alkali extraction, metal ions in the pulp are effectively eliminated, and the ClO is reduced₂Thereby reducing the AOX content during bleaching. Because the chlorine dioxide section is an acid bleaching section, and the oxygen delignification and the hydrogen peroxide alkali extraction are alkali bleachingAnd in the white section, two sections of water countercurrent washing can be carried out during washing, so that the economic benefit is improved, and the pollution load is reduced.

Drawings

FIG. 1 is a flow diagram of a method for elemental chlorine-free bleaching of grass pulp in accordance with the present invention.

Detailed Description

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

The invention discloses an elemental chlorine-free bleaching method of straw pulp, which is implemented by the following steps as shown in a flow chart shown in figure 1:

step 1, mixing straw pulp with NaOH or oxidized white liquor (white liquor is commonly known as a cooking liquor in the paper industry and comprises sodium hydroxide and sodium sulfide, and the oxidized white liquor is prepared by oxidizing the sodium sulfide in the white liquor into sodium sulfate), wherein the concentration of the straw pulp is 10 percent, the reaction oxygen pressure and temperature are increased, and the reaction is carried out for a certain time to obtain wheat straw pulp bleached by the NaOH or the oxidized white liquor, and the step is an oxygen delignification bleaching section, namely an O section;

in the step 1, NaOH or oxidized white liquor accounts for 2-5% of the amount of the straw pulp, the treatment time of the oxygen delignification section is 30-60min, the reaction oxygen pressure is controlled to be 0.7-0.9 MPa, and the temperature is controlled to be 75-85 ℃.

Step 2, carrying out primary chlorine dioxide bleaching on the wheat straw pulp reacted in the step 1, wherein in order to improve the bleaching efficiency of chlorine dioxide and shorten the bleaching time, higher temperature can be adopted for bleaching to obtain the wheat straw pulp bleached by chlorine dioxide, and the step is a chlorine dioxide bleaching section, namely D₀A segment;

in the step 2, the pH range of the first chlorine dioxide bleaching is 2-3, the bleaching temperature is 40-70 ℃, the bleaching time is 20-40min, and the final wheat straw pulp concentration is 10% -13%.

Step 3, introducing oxygen and hydrogen peroxide into the wheat straw pulp bleached by chlorine dioxide obtained in the step 2, and simultaneously adding a certain amount of sodium hydroxide to perform hydrogen peroxide enhanced alkali extraction, wherein the oxygen and the hydrogen peroxide can perform a synergistic action to obtain the wheat straw pulp subjected to the alkali extraction, and the step is a hydrogen peroxide enhanced alkali extraction section, namely an EPO section;

in the step 3, the treatment temperature is 40-60 ℃, the treatment time is 60-90min, and the final wheat straw pulp concentration is 10-15%.

Step 4, washing the wheat straw pulp subjected to alkali extraction in the step 3, and adding a chelating agent for chelating treatment to obtain chelated wheat straw pulp, wherein the step is a chelating treatment section, namely a Q section;

in the step 4, the chelating agent is EDTA, and the pH value of EDTA treatment is 3-5.

Step 5, carrying out second chlorine dioxide bleaching treatment on the wheat pulp treated in the step 4, wherein the using amount of the second chlorine dioxide is less than that of the first chlorine dioxide, and obtaining the wheat pulp subjected to the second chlorine dioxide bleaching, wherein the step is a chlorine dioxide bleaching section, namely D₁A segment;

in the step 5, the pH range is 3-4 when the chlorine dioxide is intensively bleached for the second time; the bleaching temperature is 55-75 deg.C, and the bleaching time is 60-120 min.

Step 6, carrying out third chlorine dioxide enhanced bleaching on the pulp reacted in the step 5, wherein the consumption of the chlorine dioxide is less than that of the chlorine dioxide in the previous two times in the bleaching process, and NaOH is added to control the pH value to obtain the bleached wheat straw pulp, and the process is a chlorine dioxide bleaching stage, namely D₂And (4) section.

In the step 6, the pH range of the third chlorine dioxide enhanced bleaching is 3.5-4.5; the bleaching temperature is 60-85 deg.C, and the bleaching time is 60-120 min.

Example 1

In the oxygen delignification bleaching stage (O stage), the amount of NaOH used in the wheat straw pulp is 2%. The treatment time of the oxygen delignification section is 30 min.

In the chlorine dioxide bleaching stage (stage D), D₀Stage pH 2.0, D₁Stage pH of 3.0, D₂The stage pH was 3.5. The temperatures used were: d₀Segment 40 ℃ C, D₁Segment 55 ℃, D₂Section 60 ℃. The treatment time is respectively as follows: d₀Segment 20min, D₁Segment 60min, D₂And the period is 60 min.

In the alkaline extraction stage (EOP stage) intensified by oxygen and hydrogen peroxide, the treatment temperature of the EOP stage is 40 ℃, the treatment time is 60min, and the concentration of the treated straw pulp is 11%.

In the chelation treatment stage (stage Q), the pH of the EDTA treatment was 3.5.

After the treatment, the whiteness of the bleached straw pulp is 87.5 percent ISO, and the tearing index is 4.1 mN.m²The AOX content in the wastewater was 0.8 (Kg/ton pulp).

Example 2

In the oxygen delignification bleaching stage (O stage), the amount of NaOH used in the wheat straw pulp is 3%. The treatment time of the oxygen delignification section is 45 min.

In the chlorine dioxide bleaching stage (stage D), D₀Stage pH 2.6, D₁Stage pH 3.4, D₂The stage pH was 4.1. The temperatures used were: d₀Segment 50 ℃ C., D₁Segment 60 ℃, D₂Section 65 ℃. The treatment time is respectively as follows: d₀Segment 25min, D₁Segment 90min, D₂And the period is 90 min.

In the alkaline extraction stage (EOP stage) intensified by oxygen and hydrogen peroxide, the treatment temperature of the EOP stage is 45 ℃, the treatment time is 70min, and the concentration of the treated straw pulp is 12%.

In the chelation treatment stage (stage Q), the pH of the EDTA treatment was 4.0.

After the treatment, the whiteness of the bleached straw pulp is 88.5 percent ISO, and the tearing index is 4.3 mN.m²The AOX content in the wastewater was 0.9 (Kg/ton pulp).

Example 3

In the oxygen delignification bleaching stage (O stage), the amount of NaOH used in the wheat straw pulp is 4%. The treatment time of the oxygen delignification section is 55 min.

In the chlorine dioxide bleaching stage (stage D), D₀Stage pH 2.7, D₁Stage pH 3.8, D₂The stage pH was 4.5. The temperatures used were: d₀Segment 55 ℃, D₁Segment 65 ℃ C., D₂Section 70 ℃. The treatment time is respectively as follows: d₀Segment 30min, D₁Segment 100min, D₂And the period is 100 min.

In the alkaline extraction stage (EOP stage) intensified by oxygen and hydrogen peroxide, the treatment temperature of the EOP stage is 50 ℃, the treatment time is 80min, and the concentration of the treated straw pulp is 15%.

In the chelation treatment stage (stage Q), the pH of the EDTA treatment was 4.5.

After the treatment, the whiteness of the bleached straw pulp is 89.5 percent ISO, and the tearing index is 4.2 mN.m²The AOX content in the wastewater was 1.1 (Kg/ton pulp).

TABLE 1D₂Influence of different pH values on bleaching results