A continuous pressure wash bleaching reactor and method of bleaching

Abstract

The application discloses a continuous pressure leaching bleaching reactor and a bleaching method thereof. The bleaching reactor comprises a shell and a central rotating shaft rotatably connected with the shell. The central rotating shaft is fixedly sleeved with a screw sleeve, and the outer surface of the screw sleeve is fixedly provided with spiral blades. The shell is respectively provided with a feeding port and a discharging port at two ends. The inside of the shell comprises, in sequence from the feeding port to the discharging port, a feeding sealing unit, a mixing reaction unit, at least one extrusion spraying unit, a first extrusion unit and a discharging sealing unit. The reactor is used for mixing liquid medicine and slurry through the mixing reaction unit, so that the liquid medicine reaction efficiency is improved, and the liquid medicine consumption is reduced. The solvent exchange rate is strengthened through the design of the extrusion unit. The uniform mixing of the organic solvent and the material is ensured through the design of the spraying device. The continuous production under pressure can be realized through the continuous arrangement of the units, the disassembly and assembly time of the equipment is reduced, the output per unit time is improved, and the bleaching efficiency is greatly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of pulp bleaching, and particularly relates to a continuous pressure washing bleaching reactor and a bleaching method thereof. BACKGROUND

[0002] At present, the mainstream pulp bleaching reaction uses an aqueous medium, pulp and bleaching chemicals (the mainstream is hydrogen peroxide and sodium hydroxide) are fully mixed, and then the bleaching reaction is completed in a normal pressure reactor.

[0003] The authorized patent "A method for preparing bleached mechanical pulp with high brightness of bamboo by using alcohol solvent" (authorization number ZL201610348522.X, hereinafter referred to as alcohol bleaching patent) discloses a method for preparing bleached mechanical pulp with high brightness of bamboo by using alcohol solvent. The alcohol bleaching patent has the following characteristics: 1. On the basis of the conventional bleaching process, alcohol solvent (preferably ethanol) is added; 2. The bleaching system is sealed; 3. The temperature is kept higher than the boiling point of the alcohol solvent during the bleaching process. The main advantages of the alcohol bleaching patent are: 1. The solvent molecules are used to destroy the deposits in the micro-pore channels of the fiber raw material, open the penetration channel of the bleaching solution, and help the bleaching solution to penetrate deeply into the pulp; 2. Hydrogen peroxide is active and easily decomposed into oxygen and water. In a normal pressure system, due to the temperature difference, the oxygen generated by decomposition will escape into the air with water vapor, and will not participate in the bleaching reaction. In a sealed system, as the reaction continues, the oxygen in the high-pressure environment will penetrate deeply into the pulp, and will destroy the conjugated chromophore groups of the pulp through its own oxidation. Therefore, the sealed system helps to improve the utilization rate of hydrogen peroxide; 3. Most of the chromophore groups in the pulp exist in the lignin structure, mainly the conjugated structure formed by the benzene ring and its adjacent carbon-carbon double bond, carbonyl group and other groups in the lignin structure. The polarity of this part of the structure is weak, and the solubility in water is small, but the solubility in organic solvents is large. Therefore, adding an organic solvent to the bleaching system is beneficial to the dissolution of the chromophore groups.

[0004] Based on the alcohol bleaching patent, the authorized patent ZL202310067914.9 discloses a sealed condensation circulation bleaching reactor and a high-efficiency bleaching method. The bleaching reactor can realize the alcohol-water binary medium alkaline hydrogen peroxide reaction process involved in the alcohol bleaching patent. However, it can only realize intermittent operation and belongs to a batch reactor. Due to the limited sample loading amount each time and the complicated equipment disassembly and assembly steps, it is not conducive to industrialized continuous production. At the same time, in the batch reactor, the pulp is always in a saturated absorption state of the bleaching solution, the solvent demand is large, and the circulation speed is low. SUMMARY

[0005] In view of the design defects of the batch reactor, the present application aims to provide a continuous pressure leaching bleaching reactor and a bleaching method thereof, through which the pulp can be repeatedly flushed by using organic solvents in a closed pressure reaction system, so that the chromophoric groups are better dissolved out, the bleaching efficiency is improved, and continuous production is realized.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] A continuous pressure leaching bleaching reactor comprises a shell and a central rotating shaft located inside the shell and rotationally connected with the shell, one end of the central rotating shaft is connected with a driving device for driving the rotation thereof, and the driving device is located outside the shell; a screw sleeve is fixedly sleeved on the central rotating shaft, and the central rotating shaft and the screw sleeve can be connected through spline connection; a spiral blade is fixedly arranged on the outer surface of the screw sleeve.

[0008] Both ends of the shell are respectively provided with a feeding port and a discharging port, and the inside of the shell sequentially comprises a feeding sealing unit, a mixing reaction unit, at least one extrusion spraying unit, a first extrusion unit and a discharging sealing unit from the feeding port to the discharging port; the extrusion spraying unit comprises a spraying unit and a second extrusion unit; wherein: the spiral blades in the areas of the feeding sealing unit, the first extrusion unit, the second extrusion unit and the discharging sealing unit gradually reduce in spacing; the spiral blades in the areas of the mixing reaction unit and the spraying unit are equidistant blades; the feeding port is located at the upper end of the front end of the feeding sealing unit, and the discharging port is located at the lower end of the rear end of the discharging sealing unit; as for the shell, the shell at the positions of the units can be an integral structure formed by integral machining, or can be a segmented structure, and then an integral structure is formed by flange connection.

[0009] A plurality of dosing ports and steam inlets are arranged at the front end of the shell in the area of the mixing reaction unit; the first extrusion unit and the second extrusion unit are the same in structure, and a plurality of liquid discharge ports are arranged at the lower end of the shell in the areas thereof; the liquid discharge ports are externally connected with steam drain valves; the spraying unit further comprises a spraying device for conveying organic solvents into the shell. Further, the spraying device comprises a spraying pipeline, a plurality of spraying heads are connected below the spraying pipeline, and the liquid outlets of the spraying heads are located inside the spraying unit, so that the organic solvents can be uniformly sprayed onto the pulp through the spraying heads, and the bleaching reaction is promoted.

[0010] As a preferred technical scheme, the dosing ports in the mixing reaction unit comprise a first dosing port for adding hydrogen peroxide and a second dosing port for adding a bleaching mixed liquor, the composition of the bleaching mixed liquor comprises sodium hydroxide, sodium silicate, a chelating agent and an organic solvent, hydrogen peroxide and the bleaching mixed liquor are respectively added through the first dosing port and the second dosing port in the mixing reaction unit, high-temperature steam is introduced through the steam inlet to maintain the temperature required by the bleaching reaction, the bleaching material is mixed with the bleaching chemicals in the unit, and most of the bleaching reaction is completed.

[0011] As a preferred technical solution, the driving device is a geared motor, and the output end of the geared motor is fixedly connected to the central rotating shaft. Specifically, a connecting device can be used for connection. The geared motor drives the central rotating shaft to rotate, thereby causing the screw sleeve and the spiral blades to rotate synchronously. The rotation of the spiral blades enables the slurry in the reactor to be sequentially transported to each unit for bleaching reaction.

[0012] As a preferred technical solution, the number of extrusion spray units is two. The number of extrusion spray units is mainly set according to the requirements of the specific bleaching process, and structural units can be flexibly replaced or added.

[0013] The present invention also provides a bleaching method using the above-described continuous pressurized rinsing bleaching reactor, comprising the following steps:

[0014] The drive unit is activated, and the material to be bleached is added to the feed sealing unit through the feed inlet. The chemical agents and organic solvents required for bleaching are added through the dosing port of the mixing reaction unit. The chemical agents include sodium hydroxide, sodium silicate, chelating agents, and ethanol, and the organic solvents are at least one of methanol, ethanol, ethylene glycol, 1-propanol, 2-propanol, propylene glycol, and glycerol. Simultaneously, high-temperature steam is introduced through the steam inlet to maintain the required bleaching temperature. After the material enters the extrusion spray unit, it is first extruded through the second extrusion unit to discharge the bleaching residue. Then, organic solvent is added to the reactor through the spray unit to achieve the purpose of rinsing the material. The residual solvent in the material is then squeezed out through the first extrusion unit. To avoid a drop in system pressure due to the discharge of residual liquid from the first and second extrusion units, a steam drain valve is connected to the outlet to allow steam to be introduced, ensuring the system pressure while promptly discharging the residual liquid. Finally, the material is squeezed into a tight plug in the discharge sealing unit and discharged from the outlet. Preferably, the temperature of the high-temperature steam mentioned above is 95-105°C, and the organic solvent is ethanol.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The continuous pressurized bleaching reactor provided by the present invention includes a feed sealing unit, a mixing reaction unit, at least one extrusion spraying unit, a first extrusion unit, and a discharge sealing unit. By designing the blade spacing of the spiral blades in the feed sealing unit and the discharge sealing unit to gradually decrease, the material located between the two units is in a pressurized environment during the bleaching process, thereby promoting the bleaching process. The principle is as follows: When the material enters the feed sealing unit, the blade spacing of the spiral blades gradually decreases, and the material is pushed to the end by the spiral blades to form a dense plug, which can maintain the system pressure of the subsequent process. When the material enters the discharge sealing unit, based on the similar principle in the feed sealing unit, the material enters this unit and forms a tight plug at the end, which can maintain the system pressure of the front-end process. Through this dense plug formed at the beginning and end, the material in the mixing reaction unit between these two units is bleached under a certain pressure environment. In addition, in the bleaching reactor provided by this invention, the blade spacing of the spiral blades in the first extrusion unit and the second extrusion unit area also gradually decreases. The purpose of this design is to make the material be subjected to appropriate extrusion in the unit so that the bleaching residue absorbed by the material is squeezed out. In order to avoid the pressure inside the reactor decreasing due to the extrusion of bleaching residue, a steam drain valve is connected to the drain port of this unit to ensure the pressure inside the system while timely discharge of bleaching residue. The bleaching reactor provided by the present invention has a steam inlet in the mixing reaction unit. By introducing high-temperature steam into the reactor, the temperature required for the bleaching reaction is maintained, thereby promoting the bleaching process and improving the bleaching effect.

[0017] The continuous pressurized bleaching reactor provided by this invention improves the reaction efficiency of the chemical solution and reduces chemical consumption by designing a dedicated mixing reaction unit for mixing the chemical solution and slurry. The designed extrusion unit enhances the solvent exchange rate, and the spraying device ensures uniform mixing of the organic solvent and materials. Through the continuous arrangement of its various units, the continuous pressurized bleaching reactor provided by this invention enables continuous pressurized production, reducing equipment disassembly and assembly time, increasing output per unit time, and significantly improving bleaching efficiency. Attached Figure Description

[0018] Figure 1 A schematic diagram of the structure of a continuous pressurized rinsing and bleaching reactor with a squeezing spray unit in Embodiment 1 of the present invention;

[0019] Figure 2 A schematic diagram of the structure of the continuous pressurized rinsing and bleaching reactor with two extrusion spraying units in Embodiment 2 of the present invention;

[0020] Reference numerals: 1-Outer shell, 2-Drive device, 3-Screw sleeve, 4-Helical blade, 5-Inlet, 6-Outlet, 7-Inlet sealing unit, 8-Mixing reaction unit, 9-Extrusion spraying unit, 91-Spraying unit, 92-Second extrusion unit, 93-Spraying device, 10-First extrusion unit, 11-Outlet sealing unit, 12-First dosing port, 13-Second dosing port, 14-Steam inlet, 15-Drainage port, 16-Spraying device. Detailed Implementation

[0021] The present invention will be further described below with reference to the embodiments and accompanying drawings, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0022] In this invention, unless otherwise explicitly specified and limited, the terms "fixed," "connected," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components. "Rotary connection" refers to two parts connected together and capable of relative rotation. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0023] In the description of this invention, it should be understood that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations of this invention. The terms "first" and "second" used in this invention do not represent a specific quantity or order, but are merely used for distinguishing names.

[0024] Example 1

[0025] Figure 1 This is a schematic diagram of the continuous pressurized rinsing bleaching reactor provided in Example 1, which has a squeeze spray unit, and the specific structure is as follows:

[0026] It includes a housing 1 and a central rotating shaft (not shown) located inside the housing and rotatably connected to the housing. One end of the central rotating shaft is connected to a drive device 2 for driving its rotation. The drive device is located outside the housing. The drive device is preferably a geared motor. The output end of the geared motor is fixedly connected to the central rotating shaft. A threaded sleeve 3 is fixedly sleeved on the central rotating shaft. The central rotating shaft and the threaded sleeve can be connected by a spline. A helical blade 4 is fixed on the outer surface of the threaded sleeve.

[0027] The outer casing 1 has an inlet 5 and an outlet 6 at its two ends, respectively. The interior of the outer casing, from the inlet 5 to the outlet 6, includes an inlet sealing unit 7, a mixing reaction unit 8, at least one extrusion spray unit 9, a first extrusion unit 10, and an outlet sealing unit 11. The extrusion spray unit 9 includes a spray unit 91 and a second extrusion unit 92. The spacing between the spiral blades in the areas of the inlet sealing unit 7, the first extrusion unit 10, the second extrusion unit 92, and the outlet sealing unit 11 gradually decreases. The spiral blades in the areas of the mixing reaction unit 8 and the spray unit 91 are equally spaced blades. The inlet 5 is located at the upper front end of the inlet sealing unit 7, and the outlet 6 is located at the lower rear end of the outlet sealing unit 11. For the outer casing, the outer casing at each unit position can be an integral structure formed by integral processing, or it can be a segmented structure connected by flanges to form an integral structure.

[0028] The front end of the outer shell of the mixing reaction unit 8 is provided with several dosing ports and a steam inlet 14. Specifically, the dosing ports include a first dosing port 12 for adding hydrogen peroxide and a second dosing port 12 for adding bleaching mixture. The steam inlet 14 is used to introduce high-temperature steam into the reactor. The first extrusion unit 10 and the second extrusion unit 92 have the same structure, and the lower end of the outer shell of each unit is provided with several drain ports 15. Steam drain valves are connected to the drain ports. The spraying unit 91 also includes a spraying device 16 for conveying organic solvent into the outer shell. Further, the spraying device includes a spray pipe, and several spray heads are connected to the lower part of the spray pipe. The outlet of the spray head is located inside the spraying unit. The spray head can evenly spray the organic solvent onto the slurry, promoting the bleaching reaction.

[0029] Example 2

[0030] The main structure of the continuous pressurized rinsing bleaching reactor provided in Example 2 is roughly the same as that in Example 1, the only difference being that the reactor in Example 2 has two extrusion spray units. Figure 2 This is a schematic diagram of the continuous pressurized rinsing bleaching reactor with two extrusion spray units in Example 2. In practical applications, the number of extrusion spray units is mainly set according to the requirements of the specific bleaching process, and structural units can be flexibly replaced or added.

[0031] Compare Application Example 1 with Application Examples 1 and 2 of the present invention.

[0032] Bleaching pulp: Green bamboo mechanical pulp

[0033] Comparative Application Example 1

[0034] Comparative Application Example 1 uses a bleaching method employing the closed-loop condensing bleaching reactor disclosed in authorized patent ZL 202310067914.9. The steps are as disclosed in Application Example 1 of the patent's specific embodiments. Specifically, 50g of dry weight of green bamboo mechanical pulp is weighed, and bleaching chemicals are added according to the process parameters in Table 1 (Application Example 1). One-third of the ethanol is mixed with the pulp for the initial bleaching reaction, and two-thirds of the ethanol is placed at the bottom of the reactor for reflux rinsing. After thorough mixing, the pulp is loaded into the reactor of this invention and bleached in a water bath at 95°C for a total reaction time of 2 hours. Initially, all valves are closed. When the reactor temperature exceeds the solvent boiling point and the pressure gauge shows a rise in the closed system pressure, the exhaust port of the reactor lid and the sealing valve of the condenser are opened to expel air from the reactor using solvent vapor. After the pressure gauge shows zero pressure, the exhaust port and sealing valve are closed, and the system temperature is further increased to the process design temperature. After the reactor temperature reaches the set temperature, keep all valves closed. After the reaction has proceeded for 0.5 hours, inject cooling water into the condenser. Continue the reaction for another 1.5 hours, then stop heating. Open vent 14 to introduce the steam from the reactor into the tail gas collection system. When the pressure gauge shows that the pressure inside the reactor is at atmospheric pressure, close the vent, open the quick-opening flange, and remove the pulp. Pour the obtained pulp into 1L of distilled water, stir thoroughly, and then use a vacuum filtration device to wash the pulp with distilled water in a Buchner funnel lined with filter cloth until the pH of the filtrate is 7.0±0.5. Measure the pulp whiteness according to GB / T7974-2002:(Determination of brightness (whiteness) of paper, paperboard and pulp (diffuse / vertical method)).

[0035] Application Example 1 describes a bleaching method using the continuous pressurized rinsing bleaching reactor provided in Example 1 of this invention. The specific operation is as follows: Prepare mechanical pulp equivalent to 2.5 kg of oven-dry weight of green bamboo. Adjust the motor frequency to set the equipment capacity to 1 kg / h. Prepare bleaching chemicals according to the process parameters in Application Example 1 in Table 1, wherein hydrogen peroxide, sodium hydroxide, sodium silicate, and DTPA are added in section B. Ethanol is divided into two parts: half is added in the mixing reaction unit, and half is added in the spraying unit. Control the flow rate of the chemicals to ensure that all chemicals are added to the reactor at a uniform rate over 2.5 hours. Control the system temperature to 95°C using steam. Control the ethanol in the spraying unit to be added to the equipment at a uniform rate over 2.5 hours. Receive the pulp at the outlet. Take 50 g of pulp and pour it into 1 L of distilled water. After stirring thoroughly, use a vacuum filter to wash the pulp with distilled water in a Buchner funnel lined with filter cloth until the pH of the filtrate is 7.0 ± 0.5. Pulp whiteness was measured according to GB / T 7974-2002: (Determination of brightness (whiteness) of paper, paperboard and pulp (diffuse / vertical method)).

[0036] Application Example 2 describes a bleaching method using the continuous pressurized rinsing bleaching reactor provided in Example 2 of this invention. The specific operation is as follows: Prepare mechanical pulp equivalent to 2.5 kg of oven-dry weight of green bamboo. Adjust the motor frequency to set the equipment capacity to 1 kg / h. Prepare bleaching chemicals according to the process parameters in Application Example 2 in Table 1, wherein hydrogen peroxide, sodium hydroxide, sodium silicate, and DTPA are added in the mixing reaction unit. Ethanol is divided into three parts: 1 / 3 of the ethanol is added in the mixing reaction unit, 1 / 3 in the first extrusion spray unit, and 1 / 3 in the second spray unit. Control the flow rate of the chemicals to ensure that all chemicals are added to the equipment at a uniform rate over 2.5 hours. Control the system temperature to 95°C using steam. Control the ethanol at both spray units to be added to the equipment at a uniform rate over 2.5 hours. Receive the pulp at the outlet. Pour 50g of pulp into 1L of distilled water, stir thoroughly, and then wash the pulp with distilled water using a vacuum filtration apparatus in a Buchner funnel lined with filter cloth until the pH of the filtrate is 7.0±0.5. Measure the pulp brightness according to GB / T 7974-2002:(Determination of brightness (whiteness) of paper, paperboard and pulp (diffuse / vertical method)).

[0037] The reaction conditions and experimental results for each application example are shown in Table 1 below:

[0038] Table 1. Reaction conditions and experimental results for each application example.

[0039]

[0040] *: The ratio of total solids to total mass in the system.

[0041] As can be seen from the experimental results in Table 1, compared with Comparative Application Example 1, under the same amount of bleaching chemicals, the slurry obtained by using the continuous condensation circulation bleaching reactor provided by the present invention has higher whiteness. Moreover, the present invention can realize continuous production, increase the output per unit time, and greatly improve production efficiency.

[0042] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A continuous pressurized rinsing bleaching reactor, characterized in that: It includes an outer shell and a central rotating shaft located inside the outer shell and rotatably connected to the outer shell. One end of the central rotating shaft is connected to a drive device for driving its rotation. The drive device is located outside the outer shell. A threaded sleeve is fixedly fitted onto the central rotating shaft, and a helical blade is fixed on the outer surface of the threaded sleeve. The outer casing has an inlet and an outlet at its two ends, respectively. The interior of the outer casing, from the inlet to the outlet, sequentially includes an inlet sealing unit, a mixing reaction unit, at least one extrusion spray unit, a first extrusion unit, and an outlet sealing unit. The extrusion spray unit includes a spray unit and a second extrusion unit. The spacing between the spiral blades in the inlet sealing unit, the first extrusion unit, the second extrusion unit, and the outlet sealing unit gradually decreases. The spiral blades in the mixing reaction unit and the spray unit are equally spaced blades. The inlet is located at the upper front end of the inlet sealing unit, and the outlet is located at the lower rear end of the outlet sealing unit. The front end of the outer shell within the mixing reaction unit area is provided with several dosing ports and steam inlets; the first extrusion unit and the second extrusion unit have the same structure, and the lower end of the outer shell within their respective areas is provided with several drain ports; the drain ports are connected to steam discharge valves; the spraying unit also includes a spraying device for conveying organic solvents into the outer shell.

2. The continuous pressurized rinsing bleaching reactor according to claim 1, characterized in that: The spraying device includes a spray pipe, and several spray heads are connected to the bottom of the spray pipe. The liquid outlet of the spray head is located inside the spraying unit.

3. The continuous pressurized rinsing bleaching reactor according to claim 1, characterized in that: The dosing ports in the mixing reaction unit include a first dosing port for adding hydrogen peroxide and a second dosing port for adding bleaching mixture.

4. The continuous pressurized rinsing bleaching reactor according to claim 1, characterized in that: The driving device is a geared motor, and the output end of the geared motor is fixedly connected to the central rotating shaft.

5. The continuous pressurized rinsing bleaching reactor according to any one of claims 1 to 4, characterized in that: The central shaft and the threaded sleeve are connected by a spline.

6. The continuous pressurized rinsing bleaching reactor according to any one of claims 1 to 4, characterized in that: The number of the extrusion spray units is two.

7. A bleaching method using a continuous pressurized rinsing bleaching reactor as described in any one of claims 1 to 6, characterized in that: Includes the following steps: Turn on the drive unit and add the material to be bleached into the feed sealing unit through the feed inlet; add the chemical agents and organic solvents required for bleaching through the dosing port of the mixing reaction unit, and simultaneously introduce high-temperature steam through the steam inlet to maintain the temperature required for bleaching; when the material enters the extrusion spray unit, it is first extruded through the second extrusion unit to expel the bleaching residue, and then organic solvent is added into the reactor through the spray unit to achieve the purpose of washing the material; then the residual solvent in the material is squeezed out through the first extrusion unit; in order to avoid the pressure drop of the system due to the discharge of residual liquid in the first and second extrusion units, a steam drain valve is connected to the outside of its drain port, and steam is introduced to achieve timely discharge of residual liquid while maintaining the pressure in the system; finally, the material is squeezed into a tight plug in the discharge sealing unit and discharged from the discharge port.

8. The bleaching method according to claim 7, characterized in that: The chemical agents include sodium hydroxide, sodium silicate, chelating agents, and ethanol; the organic solvent is at least one of methanol, ethanol, ethylene glycol, 1-propanol, 2-propanol, propylene glycol, and glycerol.

9. The bleaching method according to claim 7, characterized in that: The temperature of the high-temperature steam is 95-105℃.

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