Method for preparing dissolving pulp by TCF bleaching of poplar KP

Abstract

The present application relates to a method for preparing dissolving pulp by TCF bleaching of poplar KP, including: preparing poplar KP by pre-hydrolysis kraft process with poplar as a raw material, and OZQP bleaching of the poplar KP to obtain dissolving pulp, wherein O denotes oxygen delignification, Z denotes ozone bleaching, Q denotes chelating treatment, and P denotes hydrogen peroxide bleaching. The dissolving pulp prepared by the same exhibits that all indexes can meet the requirements of excellent products in dissolving pulp industry standard (QB/T4898-2015), and most of the indexes are far superior to those of excellent products, and thus it can completely replace imported dissolving pulp.

Claims

1. A method for preparing dissolving pulp by TCF bleaching of poplar kraft pulp (KP), said method comprising: preparing poplar KP from raw poplar using a pre-hydrolysis kraft process; and performing OZQP bleaching on the poplar KP to obtain dissolving pulp, wherein O denotes oxygen delignification, Z denotes ozone bleaching, Q denotes chelating treatment, and P denotes hydrogen peroxide bleaching, wherein ozone bleaching step Z comprises: placing pulp bleached and concentrated from the O-stage in a reactor, adjusting pH of the pulp to 1.5-3.0 with acetic acid, adding 1.5-3.0% of ozone and 0.3-0.6% of tetrasodium iminodisuccinate (IDS) to obtain a mixture, and subjecting the mixture to a reaction at a temperature of 25-35° C. for 10-30 min while stirring at a speed of 60 revolutions/min; removing excess ozone generated during the reaction through a gas outlet into an absorption device filled with KI solution; and washing the pulp with water to neutral, and adjusting the pulp to a concentration of 8-15%.

2. The method for preparing dissolving pulp by TCF bleaching of poplar KP according to claim 1, wherein the poplar is cut into chips with a length of 3-6 cm and a thickness of 2-5 mm.

3. The method for preparing dissolving pulp by TCF bleaching of poplar KP according to claim 2, wherein the pre-hydrolysis kraft process comprises water pretreatment and kraft cooking.

4. The method for preparing dissolving pulp by TCF bleaching of poplar KP according to claim 3, wherein the water pretreatment comprises steps of: (i) mixing poplar chips with water to form a first poplar chip mixture and heating said first poplar chip mixture at a temperature range of 150° C. to 170° C. for 60-90 min; or (ii) mixing poplar chips with water in the presence of an alkali in an amount (calculated as Na.sub.2O) of 18-25% to form a second poplar chip mixture, and heating said second poplar chip mixture at a temperature range of from 150° C. to 180° C. for 60-120 min.

5. The method for preparing dissolving pulp by TCF bleaching of poplar KP according to claim 1, wherein O-stage comprises steps of: placing the poplar KP in an oxygen bleaching tank, introducing oxygen, adding 1.5-3.5% of NaOH and 0.3-0.8% of MgCO.sub.3, adjusting the concentration of the pulp to 8-15%, and bleaching at 85-100° C. for 25-50 min; washing the pulp to neutrality with water, and concentrating the pulp to a concentration of 25-30%.

6. The method for preparing dissolving pulp by TCF bleaching of poplar KP according to claim 1, wherein Q-stage comprises steps of: placing the pulp bleached in the Z-stage in a closed reactor, adding 0.3-0.7% of tetrasodium iminodisuccinate (IDS) to form a chelating pulp mixture, stirring the chelating pulp mixture of IDS and the pulp uniformly, and performing a chelation treatment at 60-90° C. for 20-40 min.

7. The method for preparing dissolving pulp by TCF bleaching of poplar KP according to claim 1, wherein P-stage comprises steps of: after the reaction in the Q-stage is completed, adding 1.5-3.0% of hydrogen peroxide (H.sub.2O.sub.2) directly to the pulp for bleaching, and also adding 0.6-1.0% of NaOH, 0.3-0.5% of DTPA and 0.1-0.3% of MgCO.sub.3, and performing the bleaching reaction at the temperature of 80-95° C. for 80-100 min forming a peroxided bleached pulp mixture; removing the pulp from the peroxided bleached pulp mixture, washing the pulp to neutrality, and drying the pulp.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) It should be noted that the following detailed descriptions are all exemplary and are intended to provide further explanation of the present application. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the application belongs.

(2) It should be noted that the terminology used herein is only for describing specific embodiments and is not intended to limit the exemplary embodiments according to the present application. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. Also, it should be understood that when the terms “comprising” and/or “including” are used in the specification, they indicate there are features, steps, operations, devices, components, and/or combinations thereof.

(3) As described in the background, the current dissolving pulp is not good in quality and may cause serious environmental pollution. In view of this, the present invention provides an environmentally-friendly method for preparing dissolving pulp by bleaching poplar KP. The dissolving pulp prepared by the same has a high yield, and exhibits that all indexes can meet the requirements of excellent products in dissolving pulp industry standard (QB/T4898-2015), and most of the indexes are far superior to those of excellent products, and thus it can completely replace imported dissolving pulp.

(4) An environmentally-friendly method for preparing dissolving pulp by bleaching poplar KP, in which fast-growing broad-leaved poplar is used as raw materials, comprising the following steps:

(5) Cutting the naturally air-dried and purified poplar into poplar pieces with a length of 3-6 cm and a thickness of 2-5 mm;

(6) performing hot water pretreatment on the poplar pieces: mixing the poplar pieces with water according to the liquid ratio of 1:4-1:7, heating up to 150-170° C., and holding for 60-90 min;

(7) cooking the pre-treated poplar pieces by the kraft process for 60-120 min at the liquid ratio of 1:4-1:6, the holding temperature of 150-180° C., the amount of alkali (calculated as Na.sub.2O) of 18-25%, and the degree of vulcanization of 18-25%; after the cooking is completed, the resulting substance is washed and concentrated to obtain poplar KP;

(8) performing OZQP bleaching on the poplar KP (0-oxygen delignification, Z-ozone bleaching, Q-chelation treatment, P-hydrogen peroxide bleaching) to obtain dissolving pulp.

(9) O-stage comprises steps of: placing the poplar KP in an oxygen bleaching tank, introducing oxygen to an oxygen pressure of 0.4-0.8 Mpa, adding 1.5-3.5% of NaOH and 0.3-0.8% of MgCO.sub.3, adjusting the concentration of the pulp to 8-15%, and then performing the bleaching reaction at 85-100° C. for 25-50 min; after the bleaching is completed, the pulp is washed to neutrality with water and concentrated to the concentration of 25-30%.

(10) Z-stage comprises steps of: placing the pulp bleached and concentrated in O-stage in a reactor, adjusting the pH of pulp to 1.5-3.0 with acetic acid, adding 1.5-3.0% of ozone and 0.3-0.6% of tetrasodium iminodisuccinate (IDS), and then performing the reaction at 25-35° C. for 10-30 min while stirring at a speed of 60 r/min; excess ozone generated during the reaction enters the absorption device filled with KI solution through the gas outlet for absorption; after the reaction is completed, the pulp is washed with water to neutral and is adjusted to the concentration of 8-15%.

(11) Q-stage comprises steps of: placing the pulp bleached in Z-stage in a closed reactor, adding 0.3-0.7% of IDS (tetrasodium iminodisuccinate), stirring to mix IDS and the pulp uniformly, and then performing a chelation treatment at 60-90° C. for 20-40 min.

(12) P-stage comprises steps of: after the reaction in Q-stage is completed, adding 1.5-3.0% of hydrogen peroxide (H.sub.2O.sub.2) directly to the pulp for bleaching, and also adding 0.6-1.0% of NaOH, 0.3-0.5% of DTPA and 0.1-0.3% of MgCO.sub.3, and then performing the bleaching reaction at the temperature of 80-95° C. for 80-100 min; after the reaction is completed, the pulp is taken out, and then is washed to neutrality and dried to obtain dissolving pulp.

(13) All chemical reagents used in the present invention are chemically pure.

(14) In the present application, dissolving pulp is prepared by steps of preparing poplar KP by pre-hydrolysis of poplar as a raw material, and then performing totally chlorine-free OZQP bleaching on the poplar KP, and specifically by the following steps:

(15) (1) Material preparation: cutting the naturally air-dried and purified poplar into poplar pieces with a length of 3-6 cm and a thickness of 2-5 mm.

(16) (2) Hot water pretreatment of poplar pieces: mixing the poplar pieces with water according to the liquid ratio of 1:4-1:7, heating up to 150-170° C., and holding for 60-90 min.

(17) (3) Kraft cooking of poplar: cooking the poplar pieces pretreated with hot water for 60-120 min at the liquid ratio of 1:4-1:6, the holding temperature of 150-180° C., the amount of alkali (calculated as Na.sub.2O) of 18-25%, and the degree of vulcanization of 18-25%; after the cooking is completed, the resulting substance is washed and concentrated to obtain poplar KP.

(18) (4) Oxygen delignification (O-stage) treatment: placing the poplar KP in an oxygen bleaching tank, introducing oxygen to an oxygen pressure of 0.4-0.8 Mpa, adding 1.5-3.5% of NaOH and 0.3-0.8% of MgCO.sub.3, adjusting the concentration of the pulp to 8-15%, and then performing the bleaching reaction at 85-100° C. for 25-50 min; after the bleaching is completed, the pulp is washed to neutrality with water and concentrated to the concentration of 25-30%.

(19) (5) Ozone bleaching (Z-stage): placing the pulp bleached and concentrated in O-stage in a reactor, adjusting the pH of pulp to 1.5-3.0 with acetic acid, adding 1.5-3.0% of ozone and 0.3-0.6% of tetrasodium iminodisuccinate (IDS), and then performing the reaction at 25-35° C. for 10-30 min while stirring at a speed of 60 r/min; excess ozone generated during the reaction enters the absorption device filled with KI solution through the gas outlet for absorption; after the reaction is completed, the pulp is washed with water to neutral and is adjusted to the concentration of 8-15%.

(20) (6) Chelation treatment (Q-stage): placing the pulp bleached in Z-stage in a closed reactor, adding 0.3-0.7% of IDS, stirring to mix IDS and the pulp uniformly, and then performing a chelation treatment at 60-90° C. for 20-40 min.

(21) (7) Hydrogen peroxide bleaching (P-stage): after the reaction in Q-stage is completed, adding 1.5-3.0% of hydrogen peroxide (H.sub.2O.sub.2) directly to the pulp for bleaching, and also adding 0.6-1.0% of NaOH, 0.3-0.5% of DTPA and 0.1-0.3% of MgCO.sub.3, and then performing the bleaching reaction at the temperature of 80-95° C. for 80-100 min; after the reaction is completed, the pulp is taken out, and then is washed to neutrality and dried to obtain dissolving pulp. Various indexes of the dissolving pulp are measured.

(22) The specific steps comprise:

(23) (1) Cutting the naturally air-dried and purified poplar into poplar pieces with a length of 3-6 cm and a thickness of 2-5 mm.

(24) (2) Mixing the poplar pieces with water according to the liquid ratio of 1:4-1:7, heating up to 150-170° C., and holding for 60-90 min.

(25) (3) Cooking the poplar pieces pretreated in step (2) for 60-120 min at the liquid ratio of 1:4-1:6, the holding temperature of 150-180° C., the amount of alkali (calculated as Na.sub.2O) of 18-25% and the degree of vulcanization of 18-25%; after the cooking is completed, the resulting substance is washed and concentrated to obtain poplar KP.

(26) (4) Performing oxygen delignified (O-stage) on the poplar KP obtained in step (3): placing the poplar KP in an oxygen bleaching tank, introducing oxygen to an oxygen pressure of 0.4-0.8 Mpa, adding 1.5-3.5% of NaOH and 0.3-0.8% of MgCO.sub.3, adjusting the concentration of the pulp to 8-15%, and then performing the bleaching reaction at 85-100° C. for 25-50 min; after the bleaching is completed, the pulp is washed to neutrality with water and concentrated to the concentration of 25-30%.

(27) (5) Performing ozone bleaching (Z-stage) on the pulp obtained in step (4): adjusting the pH of pulp to 1.5-3.0 with acetic acid, adding 1.5-3.0% of ozone and 0.3-0.6% of tetrasodium iminodisuccinate (IDS), and then performing the reaction at 25-35° C. for 10-30 min while stirring at a speed of 60 r/min; excess ozone generated during the reaction enters the absorption device filled with KI solution through the gas outlet for absorption; after the reaction is completed, the pulp is washed with water to neutral and is adjusted to the concentration of 8-15%.

(28) (6) Performing chelation treatment (Q-stage) on the pulp obtained in step (5): placing the pulp bleached in step (5) in a closed reactor, adding 0.3-0.7% of IDS, stirring to mix the pulp and IDS uniformly, and then performing a chelation treatment at 60-90° C. for 20-40 min.

(29) (7) Performing the bleaching (P-stage) on the pulp obtained in step (6): adding 1.5-3.0% of hydrogen peroxide (H.sub.2O.sub.2) directly to the pulp for bleaching, and also adding 0.6-1.0% of NaOH, 0.3-0.5% of DTPA and 0.1-0.3% of MgCO.sub.3, and then performing the bleaching reaction at the temperature of 80-95° C. for 80-100 min; after the reaction is completed, the pulp is taken out, and then is washed to neutrality and dried to obtain dissolving pulp.

(30) (8) Drying the pulp obtained in step (7) to obtain dissolved pulp after, which is mainly used for the production of viscose fiber.

(31) The technical solutions of the present application will be described below by specific embodiments. The following percentages (%) are mass percentages unless otherwise specified.

(32) Example 1: The dissolving pulp is prepared by bleaching hot water pretreated poplar KP, and specifically by the following steps:

(33) (1) Material preparation: cutting the naturally air-dried and purified poplar into poplar pieces with a length of 3-6 cm and a thickness of 2-5 mm.

(34) (2) Hot water pretreatment of poplar pieces: mixing the poplar pieces with water in a reactor according to the liquid ratio of 1:5, heating up to 165° C., and holding for 90 min.

(35) (3) Kraft cooking of poplar: cooking the poplar pieces pretreated with hot water for 90 min at the liquid ratio of 1:5, the temperature of 165° C., the amount of alkali (calculated as Na.sub.2O) of 22%, and the degree of vulcanization of 24%; after the cooking is completed, the resulting substance is washed and concentrated to obtain hot water pretreated poplar KP.

(36) (4) Oxygen delignification (O-stage) treatment: placing a certain mass (absolutely dry) of poplar KP in an oxygen bleaching tank, introducing oxygen to an oxygen pressure of 0.6 Mpa, adding 2.5% of NaOH and 0.5% of MgCO.sub.3, adjusting the concentration of the pulp to 10%, and then performing the bleaching reaction at 90° C. for 30 min; after the bleaching is completed, the pulp is washed to neutrality with water and concentrated to the concentration of 28%.

(37) (5) Ozone bleaching (Z-stage): placing the pulp bleached and concentrated in O-stage in a reactor, adjusting the pH of pulp to 2.5 with acetic acid, adding 2.0% of ozone and 0.5% of IDS, and then performing the reaction at 25° C. for 20 min while stirring at a speed of 60 r/min; excess ozone generated during the reaction enters the absorption device filled with KI solution through the gas outlet for absorption; after the reaction is completed, the pulp is washed with water to neutral and is adjusted to the concentration of 10%.

(38) (6) Chelation treatment (Q-stage): placing the pulp bleached in Z-stage in a closed reactor, adding 0.5% of IDS, stirring at a speed of 60 r/min to mix IDS and the pulp uniformly, and then performing a chelation treatment in a water bath at 70° C. for 30 min.

(39) (7) Hydrogen peroxide bleaching (P-stage): after the reaction in Q-stage is completed, adding 2.0% of hydrogen peroxide (H.sub.2O.sub.2) directly to the pulp for bleaching, and also adding 0.8% of NaOH, 0.3% of DTPA and 0.3% of MgCO.sub.3, and then performing the bleaching reaction at the temperature of 90° C. for 90 min; after the reaction is completed, the pulp is taken out, and then is washed to neutrality and dried to obtain dissolving pulp. Various indexes of the dissolving pulp are measured and compared with those of the products in industry standard.

(40) TABLE-US-00001 TABLE 1 Comparison of indexes of dissolving pulp prepared by OZQP bleaching of poplar KP and those of products in industry standard Indexes of excellent/qualified Measured Items Unit products in industry standards indexes Alkali resistance≥ % 93.0/90.0 98.2 Polypentose≤ % 4.0/4.5 3.6 Ash content≤ % 0.12/0.15 0.10 Iron content≤ mg/kg 15.0/20.0 9.2 D.sub.65 brightness≥ % 82.0 90.8 Dichloromethane extract≤ % 0.30/0.40 0.15 Intrinsic viscosity mL/g 380~500/320~500 442 Dustiness 0.05 mm.sup.2~3.0 mm.sup.2≤ 60/80 60   30.6 >3.0 mm.sup.2 none none

(41) Example 2: The dissolving pulp is prepared by bleaching hot water pretreated poplar KP, and specifically by the following steps:

(42) (1) Material preparation: cutting the naturally air-dried and purified poplar into poplar pieces with a length of 3-6 cm and a thickness of 2-5 mm.

(43) (2) Hot water pretreatment of poplar pieces: mixing the poplar pieces with water in a reactor according to the liquid ratio of 1:4, heating up to 150° C., and holding for 90 min.

(44) (3) Kraft cooking of poplar: cooking the poplar pieces pretreated with hot water for 100 min at the liquid ratio of 1:4, the temperature of 170° C., the amount of alkali (calculated as Na.sub.2O) of 20%, and the degree of vulcanization of 22%; after the cooking is completed, the resulting substance is washed and concentrated to obtain poplar KP.

(45) (4) Oxygen delignification treatment (O-stage): placing a certain mass (absolutely dry) of poplar KP in an oxygen bleaching tank, introducing oxygen to an oxygen pressure of 0.4 Mpa, adding 1.5% of NaOH and 0.3% of MgCO.sub.3, adjusting the concentration of the pulp to 12%, and then performing the bleaching reaction at 100° C. for 50 min; after the bleaching is completed, the pulp is washed to neutrality with water and concentrated to the concentration of 25%.

(46) (5) Ozone bleaching (Z-stage): placing the pulp bleached and concentrated in O-stage in a reactor, adjusting the pH of pulp to 2.0 with acetic acid, adding 1.5% of ozone and 0.6% of IDS, and then performing the reaction at 30° C. for 30 min while stirring at a speed of 60 r/min; excess ozone generated during the reaction enters the absorption device filled with KI solution through the gas outlet for absorption; after the reaction is completed, the pulp is washed with water to neutral and is adjusted to the concentration of 12%.

(47) (6) Chelation treatment (Q-stage): placing the pulp bleached in Z-stage in a closed reactor, adding 0.4% of IDS, stirring at a speed of 60 r/min to mix IDS and the pulp uniformly, and then performing a chelation treatment in a water bath at 60° C. for 40 min.

(48) (7) Hydrogen peroxide bleaching (P-stage): after the reaction in Q-stage is completed, adding 1.5% of hydrogen peroxide (H.sub.2O.sub.2) directly to the pulp for bleaching, and also adding 0.6% of NaOH, 0.4% of DTPA and 0.3% of MgCO.sub.3, and then performing the bleaching reaction at the temperature of 90° C. for 80 min; after the reaction is completed, the pulp is taken out, and then is washed to neutrality and dried to obtain dissolving pulp. Various indexes of the dissolving pulp are measured and compared with those of the products in industry standard.

(49) TABLE-US-00002 TABLE 2 Comparison of indexes of dissolving pulp prepared by OZQP bleaching of poplar KP and those of products in industry standard Indexes of excellent/qualified Measured Items Unit products in industry standards indexes Alkali resistance≥ % 93.0/90.0 94.1 Polypentose≤ % 4.0/4.5 4.1 Ash content≤ % 0.12/0.15 0.12 Iron content≤ mg/kg 15.0/20.0 13.4 D.sub.65 brightness≥ % 82.0 87.3 Dichloromethane extract≤ % 0.30/0.40 0.25 Intrinsic viscosity mL/g 380~500/320~500 455 Dustiness 0.05 mm.sup.2~3.0 mm.sup.2≤ 60 60   39.5 >3.0 mm.sup.2 none none

(50) Example 3: The dissolving pulp is prepared by bleaching poplar KP, and specifically by the following steps:

(51) (1) Material preparation: cutting the naturally air-dried and purified poplar into poplar pieces with a length of 3-6 cm and a thickness of 2-5 mm.

(52) (2) Hot water pretreatment of poplar pieces: mixing the poplar pieces with water in a reactor according to the liquid ratio of 1:6, heating up to 170° C., and holding for 60 min.

(53) (3) Kraft cooking of poplar: cooking the poplar pieces pretreated with hot water for 70 min at the liquid ratio of 1:5, the temperature of 175° C., the amount of alkali (calculated as Na.sub.2O) of 22%, and the degree of vulcanization of 24%; after the cooking is completed, the resulting substance is washed and concentrated to obtain poplar KP.

(54) (4) Oxygen delignification treatment (O-stage): placing a certain mass (absolutely dry) of poplar KP in an oxygen bleaching tank, introducing oxygen to an oxygen pressure of 0.8 Mpa, adding 3.5% of NaOH and 0.7% of MgCO.sub.3, adjusting the concentration of the pulp to 10%, and then performing the bleaching reaction at 100° C. for 30 min; after the bleaching is completed, the pulp is washed to neutrality with water and concentrated to the concentration of 30%.

(55) (5) Ozone bleaching (Z-stage): placing the pulp bleached and concentrated in O-stage in a reactor, adjusting the pH of pulp to 1.5 with acetic acid, adding 3.0% of ozone and 0.6% of IDS, and then performing the reaction at 25° C. for 20 min while stirring at a speed of 60 r/min; excess ozone generated during the reaction enters the absorption device filled with KI solution through the gas outlet for absorption; after the reaction is completed, the pulp is washed with water to neutral and is adjusted to the concentration of 10%.

(56) (6) Chelation treatment (Q-stage): placing the pulp bleached in Z-stage in a closed reactor, adding 0.6% of IDS, stirring at a speed of 60 r/min to mix IDS and the pulp uniformly, and then performing a chelation treatment in a water bath at 80° C. for 30 min.

(57) (7) Hydrogen peroxide bleaching (P-stage): after the reaction in Q-stage is completed, adding 3.0% of hydrogen peroxide (H.sub.2O.sub.2) directly to the pulp for bleaching, and also adding 1.0% of NaOH, 0.5% of DTPA and 0.3% of MgCO.sub.3, and then performing the bleaching reaction at the temperature of 80° C. for 100 min; after the reaction is completed, the pulp is taken out, and then is washed to neutrality and dried to obtain dissolving pulp. Various indexes of the dissolving pulp are measured and compared with those of the products in industry standard.

(58) TABLE-US-00003 TABLE 3 Comparison of indexes of dissolving pulp prepared by OZQP bleaching of poplar KP and those of products in industry standard Indexes of excellent/qualified Measured Items Unit products in industry standards indexes Alkali resistance≥ % 93.0/90.0 98.3 Polypentose≤ % 4.0/4.5 2.8 Ash content≤ % 0.12/0.15 0.1 Iron content≤ mg/kg 15.0/20.0 9.4 D.sub.65 brightness≥ % 82.0 92.2 Dichloromethane extract≤ % 0.30/0.40 0.15 Intrinsic viscosity mL/g 380~500/320~500 409 Dustiness 0.05 mm.sup.2~3.0 mm.sup.2≤ 60 60   32.7 >3.0 mm.sup.2 none none

(59) Finally, it should be noted that the above examples are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the foregoing embodiments, it can still modify the technical solutions described in the foregoing embodiments, or equivalently replace some of them for those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall be included in the protection scope of the present invention. Although the specific embodiments of the present invention are described above, they do not limit the scope of protection of the present invention. Those skilled in the art should understand that based on the technical solution of the present invention, various modifications or deformations that can be made by those skilled in the art without creative effort are still within the protection scope of the present invention.