LU500936B1

LU500936B1 - Bleaching method for improving whiteness of mixed hardwood pulp

Info

Publication number: LU500936B1
Application number: LU500936A
Authority: LU
Inventors: Lupeng Shao
Original assignee: Univ Qilu Technology
Priority date: 2021-12-01
Filing date: 2021-12-01
Publication date: 2022-06-01

Abstract

The present disclosure discloses a bleaching method for improving whiteness of mixed hardwood pulp. According to the bleaching method, the resin content is greatly reduced to facilitate the liquid medicine impregnation, the bleaching efficiency is improved, and the quality of the formed pulp is improved. The whiteness of the formed pulp reaches 88-92% ISO, the tearing index is 8-10 mN.m2/g, and the tensile index is 70-80 N.m/g.

Description

BLEACHING METHOD FOR IMPROVING WHITENESS OF MIXED HARDWOOD PULP TECHNICAL FIELD

[01] The present disclosure relates to a technical field of papermaking, and more particularly to a bleaching method for improving whiteness of mixed hardwood pulp.

BACKGROUND ART

[02] Natural resins refer to amorphous organic substances derived from plant secretions in nature, such as rosin and amber. If these substances are present in the fiber slurry, the quality of pulp and paper will affected, paper breaks will be causes and the operation of the paper machine will be reduced. These resins will contaminate paper machine fabrics such as dryers and blankets, increase the cleaning times, and reduce the service life of equipment and felt net. During the storage of wood chips, as the air-drying of wood chips, the resin content decreases; however, due to the influence of the supply and demand of raw materials, the storage period of wood chips is significantly shortened, which leads to pitch trouble in the chemical pulping process, and affects the subsequent papermaking process, thereby affecting the pulping quality.

SUMMARY

[03] In order to solve the problems in the prior art and further optimize the existing process, the present disclosure provides a bleaching method for improving whiteness of mixed hardwood pulp, so as to achieve the purposes of reducing resin content, improving pulp whiteness and reducing organic chloride content in wastewater.

[04] In order to solve the above technical problems, the present disclosure adopts the following technical solution:

[05] A bleaching method for improving whiteness of mixed hardwood pulp is characterized by comprising the steps of cooking, oxygen delignification bleaching, ozone bleaching, DO-stage chlorine dioxide bleaching, biological treatment and EOP and D1-stage chlorine dioxide bleaching.

[06] In the cooking step, the alkali consumption is 18-22%, the degree of vulcanization is 22%, and the liquid-wood ratio is 3-3.5.

[07] In the cooking step, aluminum sulfate is also added, and the aluminum sulfate consumption is 0.2-0.3% of the mass of oven dry pulp.

[08] In the oxygen delignification bleaching step, the first-stage oxygen delignification treatment temperature is 70-90 °C, the oxygen top pressure is 4-6 bar, and the time is 15-20 min; and the second-stage oxygen delignification treatment temperature is 95-105C, the oxygen top pressure is 1-2 bar, and the time is 60-90 min.

[09] In the ozone bleaching step, the pH value is 2.5-3.5, the temperature is 75-80°C, the pressure is 4.5-5.5 bar, and the time is 0.5 min.

[10] In the DO-stage chlorine dioxide bleaching step, the pressure is 2.0-2.5 bar, the time is 15-18 min, and the chlorine dioxide consumption is 0.5-1% of the mass of oven 1 dry pulp. LU500936

[11] In the DO-stage chlorine dioxide bleaching step, talcum powder is added, and the talcum powder consumption is 0.1-0.3% of the mass of oven dry pulp.

[12] In the DO-stage chlorine dioxide bleaching step, a chemical cleaning agent is also added, and the chemical cleaning agent comprises N-methyl pyrrolidone and diethylene glycol monobutyl ether based on the mass ratio of (1-1.8): 1; and the chemical cleaning agent consumption is 0.26-0.3% of the mass of oven dry pulp.

[13] In the biological treatment step, lipase and a surfactant are added, and the lipase consumption is 12-15 IU/g; and the surfactant consumption is 0.1-0.2% of the mass of oven dry pulp.

[14] The surfactant is one or two of fatty acid diethanol amide and fatty alcohol polyoxyethylene ether.

[15] The pH value of EOP is 10.5-11.5, the temperature is 85-95 °C, and the alkali extraction time under normal pressure is 90 min; and the sodium hydroxide consumption is 0.8-1.2% of the mass of oven dry pulp, the hydrogen peroxide consumption is 0.5-1% of the mass of oven dry pulp, and the oxygen consumption is

0.2-0.3% of the mass of oven dry pulp.

[16] In the D1-stage chlorine dioxide bleaching step, the reaction is performed under normal pressure for 110-120 min, and the chlorine dioxide consumption is

0.5-0.6% of the mass of oven dry pulp.

[17] In the D1-stage chlorine dioxide bleaching step, a bleaching assistant is added, and the bleaching assistant consumption is 0.05-0.1% of the mass of oven dry pulp.

[18] The bleaching assistant comprises the following components in parts by weight: 0.05-0.1 part of a scale inhibitor, 2-5 parts of a chelating agent, 0.1-0.5 part of an accelerant and 1-3 parts of a surfactant.

[19] The scale inhibitor comprises 2-acrylamido-2-methylpropane sulfonic acid and 2, 2, 3, 4, 4, 4-hexafluorobutyl methacrylate based on the mass ratio of (3-5): 1.

[20] The chelating agent is one or more of diethylenetriamine disuccinic acid tetrasodium, 8-hydroxyquinoline and o-phenanthroline.

[21] The accelerant comprises sodium lignin sulfonate and potassium N-methyldithiocarbamate based on the mass ratio of 1: (0.2-0.3).

[22] In the D1-stage chlorine dioxide bleaching step, the residual chlorine after washing is 0.2-0.3 g/l.

[23] By adopting the above technical solution, the present disclosure has the following beneficial effects:

[24] 1. The bleaching method for improving the whiteness of the mixed hardwood pulp is beneficial to liquid medicine impregnation, so that the delignification in the bleaching process is easily carried out, the bleaching efficiency is improved, the whiteness of the formed pulp is high, and the whiteness of the formed pulp reaches 88-92% ISO.

[25] 2. By adopting the bleaching method for improving the whiteness of the mixed hardwood pulp, the resin content is greatly reduced, the quality of the formed pulp is improved, specifically, the freeness is 500-600 ml, the dust degree is 0-10 mm?/m?, the folding strength is 800-1000 times, the bursting index is 4-6 kpa.m?/g, the 2 tearing index is 8-10 mN.m?%/g, and the tensile index is 70-80 N.m/g. LU500936

[26] 3. By adopting the bleaching method for improving the whiteness of the mixed hardwood pulp, the content of organic chlorides in sewage is greatly reduced, the AOX of the organic chlorides reaches 0-0.05 kg/ADMT, the fiber content of the sewage is 10-30 mg/l, the organic chlorides in the bleaching wastewater are effectively reduced, and the environmental protection burden is reduced. And

[27] 4. By adopting the bleaching method for improving the whiteness of the mixed hardwood pulp, the content of adhesives in tail water is reduced, the consumption of fresh water is reduced, the CODcr in the sewage is 6-15 kg/ADMT, and the sewage amount is 3-6 m*/ADMT.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[28] The present disclosure will be further explained below in conjunction with specific examples.

[29] Example 1 Elemental chlorine free bleaching in a bleaching method for improving whiteness of mixed hardwood pulp specifically comprised the following steps:

[30] 1. Wood preparation:

[31] Wood chips were matched proportionally, wherein the wood chips were 25 mm long and 4 mm thick.

[32] The wood chips included the following components in percentage by weight: 50% of Acacia, 40% of eucalyptus and 10% of miscellaneous wood.

[33] 2. Cooking:

[34] A sulfate-process continuous cooking process was carried out for cooking pulping.

[35] The alkali consumption was 18%, the degree of vulcanization was 22%, and the liquid-wood ratio was 3 during continuous cooking.

[36] Aluminum sulfate needed to be added during continuous cooking, and the aluminum sulfate consumption was 0.2% of the mass of oven dry pulp.

[37] 3. Oxygen delignification bleaching:

[38] NaOH and magnesium sulfate were added into an oxygen reactor, oxygen was introduced, and first-stage oxygen delignification treatment was performed on the wood chips, wherein the first-stage oxygen delignification treatment temperature was 72 °C, the oxygen top pressure was 4 bar, and the time was 15 min; and the NaOH consumption is 1% of the mass of oven dry pulp, and the magnesium sulfate consumption is 0.1% of the mass of oven dry pulp.

[39] After degassing and washing, the wood chips were added into an oxygen delignification reaction kettle again, NaOH, magnesium sulfate and hydrogen peroxide were added, and second-stage oxygen delignification treatment was carried out, wherein the second-stage oxygen delignification treatment temperature was 95 °C , the oxygen top pressure was 1 bar, and the time was 70 min; and the NaOH consumption was 1% of the mass of oven dry pulp, the magnesium sulfate consumption was 0.1% of the mass of oven dry pulp, and the hydrogen peroxide consumption was 1% of the mass of oven dry pulp.

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[40] 4. Ozone bleaching: LU500936

[41] After washing wood pulp, the concentration was adjusted to 10%, sulfuric acid was added to adjust the pH value to 2.8, and ozone was introduced for ozone bleaching at the temperature of 75°C under the pressure of 4.5 bar for 0.5 min.

[42] 5. Chlorine dioxide bleaching (DO stage):

[43] The concentration of the paper pulp was adjusted to 10.5%, sulfuric acid was added to adjust the pH value to 3.0, a chemical cleaning agent and talcum powder were added, then chlorine dioxide was added for bleaching at the temperature of 75°C under the pressure of 2.0 bar for 15 min, the chlorine dioxide consumption was 0.5% of the mass of oven dry pulp, and then washing was carried out.

[44] The chemical cleaning agent included N-methyl pyrrolidone and diethylene glycol monobutyl ether based on the mass ratio of 1.2: 1.

[45] The chemical cleaning agent consumption was 0.26% of the mass of oven dry pulp.

[46] The talcum powder consumption was 0.15% of the mass of oven dry pulp.

[47] The whiteness was measured to be 62% ISO after this bleaching.

[48] 6. Biological treatment:

[49] The concentration of liquid pulp was adjusted to 11%, lipase and a surfactant were respectively added, the pH value was adjusted to 4.0, and the treatment temperature was 50°C, and the biological treatment time was 60 min.

[50] The lipase consumption was 13 IU/g.

[51] The surfactant consumption was 0.1% of the mass of oven dry pulp.

[52] The surfactant was fatty acid diethanol amide.

[53] 7. EOP (oxygen and hydrogen peroxide reinforced alkali extraction bleaching):

[54] The paper pulp was washed, the concentration was adjusted to 10%, sodium hydroxide and hydrogen peroxide were added, oxygen was introduced, and alkali extraction was performed for 90 min at the pH value of 10.5, the temperature of 85°C and the normal pressure; and the sodium hydroxide consumption was 1.2% of the mass of oven dry pulp, the hydrogen peroxide consumption was 0.5% of the mass of oven dry pulp, and the oxygen consumption was 0.3% of the mass of oven dry pulp.

[55] The whiteness was measured to be 78% ISO after this bleaching.

[56] 8. Chlorine dioxide bleaching (D1 stage):

[57] The reaction concentration was adjusted to 10.5%, sulfuric acid was added to adjust the pH value to 3.0, a bleaching assistant was added, and chlorine dioxide bleaching was performed at the normal pressure, wherein the temperature was 75°C, the time was 120 min; and the chlorine dioxide consumption was 0.5% of the mass of oven dry pulp, and the bleaching assistant consumption was 0.05% of the mass of oven dry pulp.

[58] The bleaching assistant included the following components in parts by weight:

0.05 part of a scale inhibitor, 2 parts of a chelating agent, 0.1 part of an accelerant and 1 part of a surfactant.

[59] The scale inhibitor included 2-acrylamido-2-methylpropane sulfonic acid and 2, 2, 3, 4, 4, 4-hexafluorobutyl methacrylate based on the mass ratio of 3: 1.

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[60] The chelating agent was tetrasodium diethylenetriamine disuccinate. LU500936

[61] The accelerant included sodium lignin sulfonate to potassium N-methyldithiocarbamate based on the mass ratio of 1: 0.2.

[62] The surfactant was fatty acid diethanol amide.

[63] 0.15% of sodium thiosulfate was added after the reaction, and the reaction was terminated; and washing was performed by a pulp washer, the residual chlorine at the D1 stage was 0.28 g/l, and then pulp was obtained.

[64] According to the bleaching method in the example 1, the prepared pulp had the following quality indexes: the whiteness of the formed pulp reached 88.5% ISO, the freeness was 545 ml, the dust degree was 3.6 mm?/m?, the folding strength was 980 times, the bursting index was 5.8 kpa.m?/g, the tearing index was 9.6 mN.m?/g, and the tensile index was 76.8 N.m/g.

[65] By adopting the bleaching process, the produced sewage included 0.02 kg/ADMT of organic chloride ADX, 10 mg/l of sewage fibers, and 6.5 kg/ ADMT of sewage CODcr, and the sewage amount was 3.6 m*/ADMT.

[66] Example 2 Elemental chlorine free bleaching in a bleaching method for improving whiteness of mixed hardwood pulp specifically comprised the following steps:

[67] 1. Wood preparation:

[68] Wood chips were matched proportionally, wherein the wood chips were 30 mm long and 5 mm thick.

[69] The wood chips included the following components in percentage by weight: 50% of Acacia, 40% of eucalyptus and 10% of miscellaneous wood.

[70] 2. Cooking:

[71] A sulfate-process continuous cooking process was carried out for cooking pulping.

[72] The alkali consumption was 21%, the degree of vulcanization was 22%, and the liquid-wood ratio was 3.5 during continuous cooking.

[73] Aluminum sulfate needed to be added during continuous cooking, and the aluminum sulfate consumption was 0.3% of the mass of oven dry pulp.

[74] 3. Oxygen delignification bleaching:

[75] NaOH and magnesium sulfate were added into an oxygen reactor, oxygen was introduced, and first-stage oxygen delignification treatment was performed on the wood chips, wherein the first-stage oxygen delignification treatment temperature was 88 °C, the oxygen top pressure was 6 bar, and the time was 17 min; and the NaOH consumption is 1.2% of the mass of oven dry pulp, and the magnesium sulfate consumption is 0.1% of the mass of oven dry pulp.

[76] After degassing and washing, the wood chips were added into an oxygen delignification reaction kettle again, NaOH, magnesium sulfate and hydrogen peroxide were added, and second-stage oxygen delignification treatment was carried out, wherein the second-stage oxygen delignification treatment temperature was 102 °C, the oxygen top pressure was 2 bar, and the time was 90 min; and the NaOH consumption was 1.5% of the mass of oven dry pulp, the magnesium sulfate consumption was 0.1% of the mass of oven dry pulp, and the hydrogen peroxide consumption was 1% of the mass of oven dry pulp. LU500936

[77] 4. Ozone bleaching:

[78] After washing wood pulp, the concentration was adjusted to 11%, sulfuric acid was added to adjust the pH value to 3.2, and ozone was introduced for ozone bleaching at the temperature of 80°C under the pressure of 5.5 bar for 0.5 min.

[79] 5. Chlorine dioxide bleaching (DO stage):

[80] The concentration of the paper pulp was adjusted to 10%, sulfuric acid was added to adjust the pH value to 3.0, a chemical cleaning agent and talcum powder were added, then chlorine dioxide was added for bleaching at the temperature of 80°C under the pressure of 2.5 bar for 15 min, the chlorine dioxide consumption was 1% of the mass of oven dry pulp, and then washing was carried out.

[81] The chemical cleaning agent included N-methyl pyrrolidone and diethylene glycol monobutyl ether based on the mass ratio of 1.8: 1.

[82] The chemical cleaning agent consumption was 0.3% of the mass of oven dry pulp.

[83] The talcum powder consumption was 0.2% of the mass of oven dry pulp.

[84] The whiteness was measured to be 67% ISO after this bleaching.

[85] 6. Biological treatment:

[86] The concentration of liquid pulp was adjusted to 11%, lipase and a surfactant were respectively added, the pH value was adjusted to 4.5, and the treatment temperature was 60°C, and the biological treatment time was 90 min.

[87] The lipase consumption was 13 IU/g.

[88] The surfactant consumption was 0.1% of the mass of oven dry pulp.

[89] The surfactant was fatty alcohol polyoxyethylene ether.

[90] 7. EOP (oxygen and hydrogen peroxide reinforced alkali extraction bleaching):

[91] The paper pulp was washed, the concentration was adjusted to 10%, sodium hydroxide and hydrogen peroxide were added, oxygen was introduced, and alkali extraction was performed for 90 min at the pH value of 11.5, the temperature of 95°C and the normal pressure; and the sodium hydroxide consumption was 1.2% of the mass of oven dry pulp, the hydrogen peroxide consumption was 1% of the mass of oven dry pulp, and the oxygen consumption was 0.3% of the mass of oven dry pulp.

[92] The whiteness was measured to be 82% ISO after this bleaching.

[93] 8. Chlorine dioxide bleaching (D1 stage):

[94] The reaction concentration was adjusted to 12%, sulfuric acid was added to adjust the pH value to 4.0, a bleaching assistant was added, and chlorine dioxide bleaching was performed at the normal pressure, wherein the temperature was 80°C, the time was 120 min; and the chlorine dioxide consumption was 0.6% of the mass of oven dry pulp, and the bleaching assistant consumption was 0.1% of the mass of oven dry pulp.

[95] The bleaching assistant included the following components in parts by weight:

0.1 part of a scale inhibitor, 5 parts of a chelating agent, 0.5 part of an accelerant and 3 parts of a surfactant.

[96] The scale inhibitor included 2-acrylamido-2-methylpropane sulfonic acid and 6

2, 2, 3, 4, 4, 4-hexafluorobutyl methacrylate based on the mass ratio of 5: 1. LU500936

[97] The chelating agent was tetrasodium diethylenetriamine disuccinate.

[98] The accelerant included sodium lignin sulfonate to potassium N-methyldithiocarbamate based on the mass ratio of 1: 0.3.

[99] The surfactant was fatty acid diethanol amide.

[100] 0.15% of sodium thiosulfate was added after the reaction, and the reaction was terminated; and washing was performed by a pulp washer, the residual chlorine at the D1 stage was 0.21 g/l, and then pulp was obtained.

[101] According to the bleaching method in the example 2, the prepared pulp had the following quality indexes: the whiteness of the formed pulp reached 91.0% ISO, the freeness was 550 ml, the dust degree was 2.7 mm?/m?, the folding strength was 917 times, the bursting index was 4.8 kpa.m?/g, the tearing index was 8.7 mN.m?/g, and the tensile index was 78.5 N.m/g.

[102] By adopting the bleaching process, the produced sewage included 0.05 kg/ADMT of organic chloride ADX, 12 mg/l of sewage fibers, and 10 kg/ ADMT of sewage CODcr, and the sewage amount was 5.5 m*/ADMT.

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Claims

WHAT IS CLAIMED IS: LUS00936

1. A bleaching method for improving whiteness of mixed hardwood pulp, comprising the steps of cooking, oxygen delignification bleaching, ozone bleaching, DO-stage chlorine dioxide bleaching, biological treatment and EOP and D1-stage chlorine dioxide bleaching.

2. The bleaching method according to claim 1, wherein in the cooking step, aluminum sulfate is added, and the aluminum sulfate consumption is 0.2-0.3% of the mass of oven dry pulp.

3. The bleaching method according to claim 1, wherein in the biological treatment step, lipase and a surfactant are added, and the lipase consumption is 12-15 IU/g; and the surfactant consumption is 0.1-0.2% of the mass of oven dry pulp.

4. The bleaching method according to claim 3, wherein the surfactant is one or two of fatty acid diethanol amide and fatty alcohol polyoxyethylene ether.

5. The bleaching method according to claim 1, wherein in the DO-stage chlorine dioxide bleaching step, the pressure is 2.0-2.5 bar, the time is 15-18 min, and the chlorine dioxide consumption is 0.5-1% of the mass of oven dry pulp; in the DO-stage chlorine dioxide bleaching step, talcum powder is added, and the talcum powder consumption is 0.1-0.3% of the mass of oven dry pulp; in the DO-stage chlorine dioxide bleaching step, a chemical cleaning agent is also added, and the chemical cleaning agent comprises N-methyl pyrrolidone and diethylene glycol monobutyl ether based on the mass ratio of (1-1.8): 1; and the chemical cleaning agent consumption is 0.26-0.3% of the mass of oven dry pulp.

6. The bleaching method according to claim 1, wherein in the D1-stage chlorine dioxide bleaching step, the reaction is performed under normal pressure for 110-120 min, and the chlorine dioxide consumption is 0.5-0.6% of the mass of oven dry pulp; in the D1-stage chlorine dioxide bleaching step, a bleaching assistant is added, and the bleaching assistant consumption is 0.05-0.1% of the mass of oven dry pulp; the bleaching assistant comprises the following components in parts by weight: 0.05-0.1 part of a scale inhibitor, 2-5 parts of a chelating agent, 0.1-0.5 part of an accelerant and 1-3 parts of a surfactant; the scale inhibitor comprises 2-acrylamido-2-methylpropane sulfonic acid and 2, 2, 3, 4, 4, 4-hexafluorobutyl methacrylate based on the mass ratio of (3-5): 1; the accelerant comprises sodium lignin sulfonate and potassium N-methyldithiocarbamate based on the mass ratio of 1: (0.2-0.3).

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