Straw pulp bleaching technique

Abstract

The invention discloses a bleaching process with low pollution used for straw pulp by virtue of elemental chlorine-free bleaching agents such as oxygen, chlorine dioxide, hydrogen peroxide and the like. The invention is characterized in that the process comprises the steps as follows: (1) on oxygen delignification section, sealing, sifting and washing are carried out; (2) on chlorine dioxide delignification section, washing is carried out; (3) on alkaline extraction section, washing is carried out; (4) on chlorine dioxide whitening section, washing and papermaking are carried out. The process of the invention is simple and feasible, applicable for reed pulps and the mixed pulp thereof and anaphalis yedoensis, the final brightness of the pulp of the reed pulps (ISO) reaches 78-85%, the brightness stability and the strength are good, and tear index is more than or equal to 8.0mN.m<2> / g; as no elemental chlorine joins the bleaching process, the generation amount of organic chloride during the bleaching process is greatly lowered and the pollution to ecological environment is reduced, thus having obvious social and economic benefits.

Description

Technical field:

[0001] The invention relates to a bleaching process for removing lignin from straw pulp, in particular to a straw pulp bleaching process using element-free chlorine bleaching agent. Background technique:

[0002] my country is a big producer of straw pulp, and the output of straw pulp accounts for more than half of the world's output. In our country, the bleaching of straw pulp has always been using hypochlorite (H) single-stage bleaching or hypochlorite (HH) two-stage bleaching or chlorine-alkali treatment-hypochlorite (CEH) and other chlorine-containing bleaching. craft. When this process is used for bleaching, the bleaching loss of the slurry is large, the whiteness stability is poor, and it is easy to return to yellow, especially in the bleaching process. Phenols, some are extremely toxic, and even contain very toxic dioxins. These toxic substances are extremely harmful to humans and the ecological environment. Therefore, many countries have imposed str...

Examples

Embodiment 1

[0020] A kind of straw pulp bleaching process, it comprises the following steps:

[0021] (1) oxygen delignification treatment section, closed screening, washing; (2) chlorine dioxide delignification section, washing; (3) alkali extraction treatment section, washing; (4) chlorine dioxide whitening section, washing , send copy paper.

[0022]When the present invention carries out oxygen delignification treatment to the straw pulp after washing (the straw pulp used in this embodiment is reed pulp obtained by continuous kraft cooking), in order to ensure the hardness of the pulp, the potassium permanganate value is from 10-12 (10.5 in this embodiment) is reduced to 6-8 to minimize the content of residual lignin in the slurry without significantly damaging the strength of the fiber. It is necessary to add enough oxygen and alkali to the slurry and provide suitable process conditions. In step (1), the slurry reaction concentration of the oxygen delignification treatment (0) secti...

Embodiment 2

[0033] The slurry used in this example is reed pulp obtained by continuous kraft cooking, with a potassium permanganate value of 9.5.

[0034] In the oxygen delignification section: the reaction concentration of the slurry is 9.5%, the reaction temperature is 95°C, the addition amount of sodium hydroxide is 12kg / t, the oxygen consumption is 25kg / t, and the reaction pressure is 350Kpa for 55 minutes.

[0035] In the chlorine dioxide delignification section: the addition of chlorine dioxide is 12kg / t, the reaction concentration is 9.5%, the end point pH value is 3.0, the reaction temperature is 52°C, and the reaction time is 65min.

[0036] In the alkali extraction section: the slurry reaction concentration is 10%, the reaction temperature is 70°C, the amount of hydrogen peroxide added is 4.0kg / t, the reaction time is 100min, and sodium hydroxide is added to make the reaction end point pH 10.5, and the slurry is washed Finally, enter the bleaching section.

[0037] In the chlor...

Technical field:

[0001] The invention relates to a bleaching process for removing lignin from straw pulp, in particular to a straw pulp bleaching process using element-free chlorine bleaching agent. Background technique:

[0002] my country is a big producer of straw pulp, and the output of straw pulp accounts for more than half of the world's output. In our country, the bleaching of straw pulp has always been using hypochlorite (H) single-stage bleaching or hypochlorite (HH) two-stage bleaching or chlorine-alkali treatment-hypochlorite (CEH) and other chlorine-containing bleaching. craft. When this process is used for bleaching, the bleaching loss of the slurry is large, the whiteness stability is poor, and it is easy to return to yellow, especially in the bleaching process. Phenols, some are extremely toxic, and even contain very toxic dioxins. These toxic substances are extremely harmful to humans and the ecological environment. Therefore, many countries have imposed str...

Examples

Embodiment 1

[0020] A kind of straw pulp bleaching process, it comprises the following steps:

[0021] (1) oxygen delignification treatment section, closed screening, washing; (2) chlorine dioxide delignification section, washing; (3) alkali extraction treatment section, washing; (4) chlorine dioxide whitening section, washing , send copy paper.

[0022]When the present invention carries out oxygen delignification treatment to the straw pulp after washing (the straw pulp used in this embodiment is reed pulp obtained by continuous kraft cooking), in order to ensure the hardness of the pulp, the potassium permanganate value is from 10-12 (10.5 in this embodiment) is reduced to 6-8 to minimize the content of residual lignin in the slurry without significantly damaging the strength of the fiber. It is necessary to add enough oxygen and alkali to the slurry and provide suitable process conditions. In step (1), the slurry reaction concentration of the oxygen delignification treatment (0) secti...

Embodiment 2

[0033] The slurry used in this example is reed pulp obtained by continuous kraft cooking, with a potassium permanganate value of 9.5.

[0034] In the oxygen delignification section: the reaction concentration of the slurry is 9.5%, the reaction temperature is 95°C, the addition amount of sodium hydroxide is 12kg / t, the oxygen consumption is 25kg / t, and the reaction pressure is 350Kpa for 55 minutes.

[0035] In the chlorine dioxide delignification section: the addition of chlorine dioxide is 12kg / t, the reaction concentration is 9.5%, the end point pH value is 3.0, the reaction temperature is 52°C, and the reaction time is 65min.

[0036] In the alkali extraction section: the slurry reaction concentration is 10%, the reaction temperature is 70°C, the amount of hydrogen peroxide added is 4.0kg / t, the reaction time is 100min, and sodium hydroxide is added to make the reaction end point pH 10.5, and the slurry is washed Finally, enter the bleaching section.

[0037] In the chlor...