High-concentration liquid medicine mixing method for chemimechanical pulp alkaline hydrogen peroxide process

Abstract

The invention discloses a high-concentration liquid medicine mixing method aiming at a chemimechanical pulp alkaline hydrogen peroxide process, which is completed by utilizing an extrusion type mixing bleaching reactor and comprises the following steps: adding alkaline hydrogen peroxide bleaching liquid into chemimechanical pulp to obtain a premix; the working state of a plurality of groups of extrusion units in the extrusion type mixed bleaching reactor is set to be that the extrusion units with adjacent heights operate alternately; the premix is added into the conveying pipeline from the top inlet of the conveying pipeline, the premix can move downwards under the action of gravity, the alkaline hydrogen peroxide bleaching liquid and the chemimechanical pulp are fully and uniformly mixed under the extrusion of the extrusion unit, and a mixture is obtained at the bottom outlet of the conveying pipeline. Under the condition of the same bleaching liquid dosage, the mixed material obtained by adopting the mixing method disclosed by the invention is higher in pulp whiteness after being bleached. The chemical mechanical pulp and the alkaline hydrogen peroxide liquid medicine can be uniformly mixed at a high concentration, the input cost is low, and continuous production can be realized.

Description

Technical Field

[0001] The invention relates to the technical field of pulping and bleaching, and in particular to a high-concentration liquid mixing method for an alkaline hydrogen peroxide process of chemical mechanical pulping. Background Art

[0002] As the main function of paper products gradually changes from information carriers to packaging materials, chemical mechanical pulp that can provide paper bulk has developed rapidly. In order to save costs and increase the utilization rate of chemical solutions, the bleaching process in the chemical mechanical pulping process is mostly carried out at a concentration of 20-30% (i.e., the ratio of the total mass of solids in the material to the total mass of the material). The alkaline hydrogen peroxide bleaching process is currently the mainstream bleaching process for chemical mechanical pulp. It mainly uses the strong oxidizing property of hydrogen peroxide at a pH of about 11.5 to destroy the conjugated chromophores in the pulp to achieve the effect of bleaching pulp. Its process requirements are mainly as follows: (1) Because hydrogen peroxide will be catalytically decomposed into water and oxygen when it encounters transition metal ions, although oxygen has oxidizing properties, it is easy to separate from the material system and enter the atmospheric environment. Therefore, it is necessary to heat the material to above 85°C as soon as possible after adding the chemical to quickly complete most of the bleaching reaction; (2) The chemical solution, especially sodium hydroxide, must be evenly mixed with the material, because hydrogen peroxide has the strongest oxidizing ability at a pH of about 11.5. If the pH value is too low or too high, hydrogen peroxide cannot perform at its best performance. The main characteristics of fiber raw materials are that the chemical structure of the material surface is rich in alcohol hydroxyl groups and has good hydrophilicity. This characteristic results in the absence of free water in the system at a high concentration of 20-30%, and the added liquid cannot be quickly mixed in the fiber raw material through the concentration difference. Uneven mixing of the liquid will directly affect the uniformity of chemical bleaching treatment, reduce the reaction efficiency of chemicals, and affect the whiteness of pulp.

[0003] The existing mixers used for mixing liquid in the bleaching process mainly include paddle mixing type, spray type and variable diameter spiral type. For slurry with a concentration of 20-30%, because there is no free water, the viscosity is high and it does not have fluidity. To achieve continuous production, a conveying screw must be used in the pipeline, so there is no space for a paddle mixer. Because the surface of the material is rich in hydrophilic groups, when a spray mixer is used, after the liquid contacts the material, the adsorption force of the material on the liquid is much greater than the diffusion force caused by the concentration difference. At this time, the liquid stays at the initial contact position and cannot achieve spontaneous diffusion, resulting in a poor effect of the spray mixer. Although the variable diameter spiral mixer can achieve a certain extrusion effect on the material that absorbs the liquid medicine while realizing continuous production, the extruded liquid medicine is mostly accumulated at the bottom of the pipe due to gravity, and the redistribution effect of the liquid medicine is not good. At the same time, in order to realize continuous generation of materials, this type of equipment needs to cooperate with the motor, main shaft and blades to realize the extrusion and transportation of materials. The structure is complex, and the extrusion equipment is in direct contact with the slurry and chemicals. It has high requirements on the corrosion resistance and strength of the material, the construction cost and operating costs are high, and the equipment maintenance is time-consuming, which seriously affects the stable production of chemical-mechanical pulp enterprises. Summary of the invention

[0004] Aiming at the problem that it is difficult to evenly mix chemical mechanical pulp and alkaline hydrogen peroxide bleaching solution at a higher system concentration (>20%) in the prior art, resulting in poor bleaching uniformity and difficulty in further improving the pulp whiteness, the purpose of the present invention is to provide a high-concentration solution mixing method for the chemical mechanical pulp alkaline hydrogen peroxide process. The method provided by the present invention has low investment cost, high pulp whiteness, and can achieve continuous production.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A high-concentration liquid mixing method for an alkaline hydrogen peroxide process of chemical mechanical pulp is completed by using an extrusion type mixing bleaching reactor, the extrusion type mixing bleaching reactor comprises a vertically arranged feed pipe, a plurality of groups of extrusion units for extruding the feed pipe are arranged from top to bottom on the outside of the feed pipe, the feed pipe can be elastically deformed under the extrusion of the extrusion units, the elastic deformation of the feed pipe is used to promote the flow of the material inside the feed pipe, and the material can flow again during the deformation recovery process, and the purpose of promoting the uniform mixing of the materials can be achieved through several cycles of extrusion;

[0007] The high-concentration liquid mixing method comprises the following steps: adding alkaline hydrogen peroxide bleaching liquid into chemical mechanical pulp to obtain a premix, wherein the mass fraction of chemical mechanical pulp in the premix is ​​20-30%; setting the working state of several groups of extrusion units in an extrusion-type mixing bleaching reactor so that the extrusion units at adjacent heights run alternately; adding the premix into the feed pipe from the top inlet of the feed pipe, the premix moves downward under the action of gravity, and the alkaline hydrogen peroxide bleaching liquid and the chemical mechanical pulp are fully and evenly mixed under the extrusion of the extrusion unit, and obtaining a mixture at the bottom outlet of the feed pipe.

[0008] As a preferred technical solution, the shape of the feed pipe is narrow at the top and wide at the bottom, so as to prevent the occurrence of pile-up and bridging during the material extrusion and transportation process, and ensure that the material can move downward smoothly under the action of gravity. Further preferably, the bottom angle of the feed pipe ranges from 70° to 85°, and the specific expansion angle depends on the material conditions. The material of the feed pipe is silicone, and other similar wear-resistant and easy-to-extrusion materials can also be used.

[0009] As a preferred technical solution, the number of extrusion units is at least three groups; each group of extrusion units includes a pair of extrusion plates arranged oppositely on both sides of the material delivery pipeline, the extrusion plates are connected to a power unit for driving them to reciprocate, and the width of the extrusion plates is preferably designed to be the maximum diameter of the material delivery pipeline; the movement directions of the extrusion plates at adjacent heights are different, preferably, the movement directions of the extrusion plates at adjacent heights are perpendicular to each other. Further preferably, the power unit is a cylinder.

[0010] As a preferred technical solution, the extrusion stroke of the extrusion plate on the feed pipe driven by the power unit is 1 / 2 to 3 / 5 of the radius of the feed pipe to ensure that the pulp concentration is higher than 40% after each extrusion. Further preferably, the extrusion stroke of several groups of extrusion units gradually decreases from top to bottom, but cannot be lower than 1 / 2 of the radius of the feed pipe at the corresponding height. Because the mixing uniformity of the alkaline hydrogen peroxide bleaching liquid and the chemical mechanical pulp in the material gradually increases from top to bottom, the lower the material extrusion degree requirement is, and a smaller extrusion degree is sufficient.

[0011] As a preferred technical solution, a discharger is installed at the bottom of the feed pipeline, and the discharge amount can be more conveniently adjusted according to the feed amount and mixing time through the discharger.

[0012] The present invention has the following beneficial effects:

[0013] (1) The high-concentration liquid mixing method for the alkaline hydrogen peroxide process of chemical mechanical pulp provided by the present invention utilizes an extrusion-type mixing bleaching reactor to uniformly mix the chemical mechanical pulp and the alkaline hydrogen peroxide bleaching liquid at a high concentration. The mixing process is analyzed as follows: the chemical mechanical pulp material is subjected to multiple multi-directional extrusions in the feed pipeline. On the one hand, the bleaching liquid absorbed by the material is forced to be extruded and adsorbed multiple times. On the other hand, the materials are forced to mix multiple times, which can achieve uniform distribution of the bleaching liquid in the material. In addition, because the material moves from top to bottom, the pressurized liquid will diffuse in both the upper and lower directions at the same time, and can directly contact the materials in the upper and lower non-pressurized areas, thereby avoiding the accumulation of the pressurized liquid somewhere in the equipment. Moreover, after multiple extrusions and diffusions from top to bottom, the mixing uniformity can be further promoted.

[0014] (2) The extrusion-type mixed bleaching reactor provided by the present invention has a simple structure, does not require a material transmission shaft, and uses gravity to achieve continuous production; the feed pipeline uses non-metallic materials, which are inexpensive and easy to replace; the extrusion unit does not directly contact the pulp and chemicals, so cheap materials can be used, and no anti-corrosion treatment is required, so the cost is low.

[0015] (3) The extrusion type mixed bleaching reactor used in the present invention can improve the reaction efficiency of the bleaching solution and the overall utilization efficiency of the system heat while making the chemical mechanical pulp and the alkaline hydrogen peroxide bleaching solution uniformly mixed. The principle analysis is as follows: The biggest feature of the alkaline hydrogen peroxide bleaching process is that after hydrogen peroxide and alkali are in contact, the oxidizing property of hydrogen peroxide is the strongest when the pH of the system is about 11.5, and the system will release a large amount of heat at this time. Since transition metal ions such as iron, manganese and copper are inevitably present in the chemical mechanical pulp material, these transition metal ions will catalyze the decomposition of hydrogen peroxide into water and oxygen at high temperatures. In the specific use process of the present invention, at the top of the feed pipeline, since the bleaching solution and the material have just started to contact, an exothermic reaction has not yet occurred. After 1-2 times of mixed extrusion, hydrogen peroxide and the alkali solution are fully in contact and begin to release heat. The more heat is released at the bottom of the feed pipeline, the more the bleaching solution and the material are in contact, and the more oxygen is decomposed. Since the direction of material movement in the present invention is from top to bottom, and the temperature of the material is lower at the top, the reaction degree is lower. After normal operation, the oxygen decomposed at the bottom will pass through the upper material. Since the permeability of gas molecules is stronger than that of liquid molecules, the decomposed oxygen will not be wasted. While transferring the reaction heat of the lower material to the upper material to increase the material temperature, it will also fully contact with the upper material to destroy the conjugated structure in the material through oxidation reaction. That is, full utilization of thermal energy is achieved to preheat the slurry, and the oxidizing property of oxygen that is wasted under normal conditions is utilized as much as possible. Therefore, the design of the present invention can improve the reaction efficiency of chemicals and improve the overall utilization efficiency of the system heat; compared with the prior art, under the same amount of bleaching solution, the whiteness of the mixed material obtained by the mixing method of the present invention is further improved after bleaching. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a structural schematic diagram of an extrusion-type mixed bleaching reactor (relaxed state);

[0017] Figure 2 for Figure 1 A top view of

[0018] Figure 3 It is a structural schematic diagram of an extrusion type mixed bleaching reactor (extrusion state);

[0019] Figure 4 for Figure 3 A top view of

[0020] Figure 5 The following are photos of the mixed material (a) obtained in Example 1 and the pulp (b) obtained after bleaching;

[0021] Figure 6 The following are photos of the mixed material (a) obtained in Example 2 and the pulp (b) obtained after bleaching;

[0022] Figure 7 The following are photos of the mixed material (a) obtained in Comparative Example 1 and the pulp (b) obtained after bleaching;

[0023] Figure 8 The following are photos of the mixed material (a) obtained in Comparative Example 2 and the pulp (b) obtained after bleaching;

[0024] Figure numerals: 1-oil cylinder, 2-feeding pipeline, 3-extrusion plate, 4-discharger. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with the embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0026] In addition, unless otherwise specified, the preparation processes in the following embodiments are all conventional means in the prior art in the art, and therefore, they are not described in detail.

[0027] The structural schematic diagram of the extrusion type mixed bleaching reactor used in the present invention is shown in FIG. Figures 1 to 4 ,in: Figure 1 and Figure 2 This is a schematic diagram of the structure of the extrusion unit in the extrusion mixed bleaching reactor in a relaxed state. Figure 3 and Figure 4 It is a schematic diagram of the structure of the extrusion unit in the extrusion mixed bleaching reactor in the extrusion state. The reactor includes a vertically arranged feed pipe 2. In order to prevent the occurrence of piles and bridges during the extrusion and transportation of materials, the shape of the feed pipe is designed to be narrow at the top and wide at the bottom. Furthermore, the bottom angle range of the feed pipe is 70° to 85°, and the specific expansion angle depends on the material conditions. Several groups of extrusion units for extruding the feed pipe are arranged from top to bottom on the outside of the feed pipe 2, and the feed pipe can be elastically deformed under the extrusion of the extrusion unit. The number of extrusion units is at least three groups; each group of extrusion units includes a pair of extrusion plates 3 arranged relatively on both sides of the feed pipe, and the width of the extrusion plate is preferably designed to be the maximum diameter of the feed pipe. The extrusion plate 3 is connected to a power unit for driving it to reciprocate, and the power unit is preferably a cylinder 1. The movement directions of the extrusion plates at adjacent heights are different; preferably, the movement directions of the extrusion plates at adjacent heights are perpendicular to each other. The extrusion stroke of the extrusion plate 3 on the feed pipe driven by the power unit is 1 / 2 to 3 / 5 of the radius of the feed pipe to ensure that the slurry concentration is higher than 40% after each extrusion. Further preferably, the extrusion stroke of several groups of extrusion units gradually decreases from top to bottom, but cannot be lower than 1 / 2 of the radius of the feed pipe at the corresponding height. In order to adjust the discharge amount according to the feed amount and mixing time, a discharger 4 is installed at the bottom of the feed pipe.

[0028] Example 1

[0029] A high-concentration liquid mixing method for an alkaline hydrogen peroxide process of chemical mechanical pulp is completed by using an extrusion mixing bleaching reactor. The extrusion mixing bleaching reactor used in this embodiment contains 4 groups of extrusion units, the movement directions of the extrusion units at adjacent heights are perpendicular to each other, and the bottom angle of the feed pipeline is 85°.

[0030] The high concentration liquid medicine mixing method comprises the following steps:

[0031] Prepare eucalyptus mechanical pulp equivalent to 0.5 kg of absolute dry weight. Adjust the motor frequency to adjust the equipment capacity to 1 kg / h. Add chemicals to the pulp according to the process parameters of Example 1 in Table 1 to obtain a premix. After the premix passes through an extrusion mixing and bleaching reactor, a uniformly mixed mixture is obtained. The effect diagram of the mixture is shown in Figure 5 Figure a in the middle.

[0032] Take 50g of the mixture and bleach it in a water bath. The bleaching reaction temperature is 95°C and the total reaction time is 1 hour. After bleaching, pour the resulting slurry into 1L of distilled water, stir it thoroughly, and then use a suction filtration device to wash the slurry with distilled water in a Buchner funnel lined with filter cloth until the pH value of the filtrate is 7.0±0.5. Figure 5 Figure b in the middle. The pulp whiteness is measured according to GB / T 7974-2002: (Determination of brightness (whiteness) of paper, paperboard and pulp (diffuse / vertical method)).

[0033] Example 2

[0034] A high-concentration liquid mixing method for an alkaline hydrogen peroxide process of chemical mechanical pulp is completed by using an extrusion mixing bleaching reactor. The extrusion mixing bleaching reactor used in this embodiment contains 8 groups of extrusion units, the movement directions of the extrusion units at adjacent heights are perpendicular to each other, and the bottom angle of the feed pipeline is 70°.

[0035] The high concentration liquid medicine mixing method comprises the following steps:

[0036] Prepare eucalyptus mechanical pulp equivalent to 0.5 kg of absolute dry weight. Adjust the motor frequency to adjust the equipment capacity to 1 kg / h. Add chemicals to the pulp according to the process parameters of Example 2 in Table 1 to obtain a premix. After the premix passes through an extrusion mixing and bleaching reactor, a uniformly mixed mixture is obtained. The effect diagram of the mixture is shown in Figure 6 Figure a in the middle.

[0037] Take 50g of the mixture and bleach it in a water bath. The bleaching reaction temperature is 95℃ and the total reaction time is 1 hour. After bleaching, pour the resulting slurry into 1L of distilled water and stir it thoroughly. The effect of the slurry is shown in the figure. Figure 6 Figure b. Wash the slurry with distilled water in a Buchner funnel lined with filter cloth using a suction filtration device until the pH value of the filtrate is 7.0±0.5. Measure the slurry whiteness in accordance with GB / T7974-2002: (Determination of brightness (whiteness) of paper, paperboard and pulp (diffuse / vertical method)).

[0038] Comparative Example 1

[0039] Comparative Example 1 uses a spraying method to mix the liquid. The specific operation is: prepare eucalyptus mechanical pulp slurry equivalent to 0.5kg of absolute dry weight. Adjust the conveying screw speed to 1kg / h, and spray the bleaching chemicals into the slurry according to the process parameters of Comparative Example 1 in Table 1. The effect is shown in Figure 7 Figure a in .

[0040] Take 50g of the mixed slurry and bleach it in a water bath. The bleaching reaction temperature is 95℃ and the total reaction time is 1 hour. After bleaching, pour the obtained slurry into 1L of distilled water, stir it thoroughly, and then use a suction filtration device to wash the slurry with distilled water in a Buchner funnel with a filter cloth until the pH value of the filtrate is 7.0±0.5. Figure 7 Figure b in the middle. The pulp whiteness is measured according to GB / T 7974-2002: (Determination of brightness (whiteness) of paper, paperboard and pulp (diffuse / vertical method)).

[0041] Comparative Example 2

[0042] Comparative Application Example 2 uses a horizontal variable diameter spiral mixer to mix the liquid medicine. The specific operation is: prepare eucalyptus mechanical pulp slurry equivalent to 0.5kg of absolute dry weight. Adjust the conveying spiral speed to 1kg / h, add bleaching chemicals to the slurry according to the process parameters of Comparative Example 2 in Table 1, and the effect of the mixture obtained after the horizontal variable diameter spiral mixer is shown in Figure 8 Figure a in the middle.

[0043] Take 50g of the mixed slurry and bleach it in a water bath. The bleaching reaction temperature is 95℃ and the total reaction time is 1 hour. After bleaching, pour the obtained slurry into 1L of distilled water, stir it thoroughly, and then use a suction filtration device to wash the slurry with distilled water in a Buchner funnel with a filter cloth until the pH value of the filtrate is 7.0±0.5. Figure 8 Figure b in the middle. The pulp whiteness is measured according to GB / T 7974-2002: (Determination of brightness (whiteness) of paper, paperboard and pulp (diffuse / vertical method)).

[0044] Table 1 Reaction conditions and experimental results of various embodiments and comparative examples

[0045]

[0046]

[0047] *: Ratio of total solid matter to total mass in the system

[0048] from Figure 5-8 It can be seen that the material mixing effect of the conventional spray dosing in Comparative Example 1 and the horizontal extrusion spiral mixing effect in Comparative Example 2 are poor, and the apparent color of the materials before and after mixing shows significant regional differences. In Examples 1 and 2, the materials using the extrusion liquid medicine mixer of the present invention show good uniformity in color before and after mixing, and the more extrusion sections, the better the liquid medicine mixing effect. From the results in Table 1, it can be seen that under the same processing conditions, the slurry whiteness of the mixture obtained by the mixing method in Examples 1 and 2 is significantly higher than that of Comparative Examples 1 and 2, and the slurry whiteness of Example 2 with more extrusion mixing times is the highest. The main reason is the difference in liquid medicine mixing effect and use efficiency under different processing processes.

[0049] Obviously, the described embodiments are only some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. A high concentration liquid mixing method for chemical mechanical pulping alkaline hydrogen peroxide process, characterized in that: The method is completed by using an extrusion type mixed bleaching reactor, which includes a vertically arranged feed pipe, and a plurality of groups of extrusion units for extruding the feed pipe are arranged from top to bottom on the outside of the feed pipe, and the feed pipe can be elastically deformed under the extrusion of the extrusion units; The high-concentration liquid medicine mixing method comprises the following steps: adding alkaline hydrogen peroxide bleaching liquid into chemical mechanical pulp to obtain a premix, controlling the working state of a plurality of groups of extrusion units so that the extrusion units at adjacent heights operate alternately; adding the premix into the feed pipeline from the top inlet of the feed pipeline, the premix moves downward under the action of gravity, and the alkaline hydrogen peroxide bleaching liquid and the chemical mechanical pulp are fully and evenly mixed under the extrusion of the extrusion unit, and obtaining a mixture at the bottom outlet of the feed pipeline.

2. The high concentration liquid medicine mixing method according to claim 1, characterized in that: The shape of the material conveying pipeline is narrow at the top and wide at the bottom.

3. The high concentration liquid medicine mixing method according to claim 2, characterized in that: The bottom angle of the conveying pipeline ranges from 70° to 85°.

4. The high concentration liquid medicine mixing method according to any one of claims 1 to 3, characterized in that: The number of the extrusion units is at least three groups; each group of extrusion units includes a pair of extrusion plates arranged relatively on both sides of the material conveying pipeline, and the extrusion plates are connected to a power unit for driving them to reciprocate; the movement directions of the extrusion plates at adjacent heights are different.

5. The high concentration liquid medicine mixing method according to claim 4, characterized in that: The power unit is an oil cylinder.

6. The high concentration liquid medicine mixing method according to claim 4, characterized in that: The extrusion stroke of the extrusion plate on the material conveying pipeline driven by the power unit is 1 / 2 to 3 / 5 of the radius of the material conveying pipeline.

7. The high concentration liquid medicine mixing method according to claim 6, characterized in that: The extrusion strokes of the plurality of groups of extrusion units gradually decrease from top to bottom, but cannot be less than 1 / 2 of the radius of the material conveying pipeline at the corresponding height.

8. The high concentration liquid medicine mixing method according to claim 1, characterized in that: A discharger is installed at the bottom of the material conveying pipeline.

9. The high concentration liquid medicine mixing method according to claim 1, characterized in that: The mass fraction of the chemical mechanical pulp in the premix is ​​20-30%.

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