阅读说明：本技术 一种制备氢氧化铝的方法 (Method for preparing aluminum hydroxide ) 是由 赵利民 王永林 袁胜华 朱慧红 王晶晶 于 2018-06-26 设计创作，主要内容包括：本发明公开了一种制备氢氧化铝的方法。该方法采用的装置包括反应器、膜过滤器和老化装置,将上述装置应用于pH值摆动法制备氢氧化铝,不但能够实现pH值摆动法制备氢氧化铝的连续操作,而且还解决了由于将不同发育阶段的晶体一并从反应器中取出并同时老化,而带来的氢氧化铝粒度分散的问题。本发明能够实现氢氧化铝的连续化、规模化生产,降低生产成本,设备结构简单,易操作,而且保证产品质量稳定。(The invention discloses a method for preparing aluminum hydroxide. The device adopted by the method comprises a reactor, a membrane filter and an aging device, and the device is applied to the pH value swing method for preparing the aluminum hydroxide, so that the continuous operation of preparing the aluminum hydroxide by the pH value swing method can be realized, and the problem of aluminum hydroxide granularity dispersion caused by taking out crystals at different development stages from the reactor and aging at the same time is solved. The invention can realize continuous and large-scale production of the aluminum hydroxide, reduce the production cost, has simple equipment structure and easy operation, and ensures the stable product quality.)

1. A method for preparing aluminum hydroxide, characterized in that the method uses an apparatus comprising: the device comprises a reactor, a membrane filter and an aging device, wherein the reactor is provided with a feed inlet, a circulating material inlet and a discharge outlet, the feed inlet and the circulating material inlet are higher than the discharge outlet, the discharge outlet is connected with the inlet of the membrane filter, the membrane filter is provided with a permeate outlet and a retentate outlet, the permeate outlet of the membrane filter is connected with the circulating slurry inlet of the reactor through a circulating slurry material pipeline, and the retentate outlet of the membrane filter is connected with the aging device; the preparation process of the aluminum hydroxide comprises the following steps:

(a) preparing aluminum hydroxide precipitate in a reactor by adopting a pH value swing method;

(b) when the liquid level of the slurry in the reactor reaches a specified liquid level, discharging the slurry into the membrane filter through the discharge port; separating by a membrane filter to obtain first slurry and second slurry, discharging the first slurry from a permeate outlet of the membrane filter, feeding the first slurry into a reactor through a circulating material inlet of the reactor, discharging the second slurry from a retentate outlet of the membrane filter, and feeding the second slurry into an aging device for aging;

(c) and (4) filtering, washing and drying the slurry after passing through an ageing device to obtain the aluminum hydroxide.

2. The process of claim 1, wherein the reactor is one or more reactors operated in parallel; preferably a plurality of reactors operating in parallel are used; the aging device is provided with two or more aging tanks.

3. The method of claim 1, wherein the reactor is provided with a level controller.

4. The process according to claim 1, characterized in that a circulating slurry heater and/or a static mixer, preferably a circulating slurry heater and a static mixer, are arranged in the circulating slurry feed line between the permeate outlet of the membrane filter and the circulating slurry inlet of the reactor, and the static mixer is located upstream of the circulating slurry heater, which is a plate or tube heater, preferably a plate heater.

5. The method according to claim 1, characterized in that an aging heat exchanger is arranged between the membrane filter and the aging device, and the aging heat exchanger is a plate type or tube type heat exchanger; plate heat exchangers are preferred.

6. The method according to claim 1, wherein membrane modules are intensively loaded in the membrane filter, the membrane modules are preferably vertically discharged, the membrane modules are inorganic membranes or organic membranes, preferably inorganic membranes, the inorganic membrane materials are selected from any one of metal, oxide, inorganic high molecular material and ceramic, preferably ceramic, the membrane pore size is 0.5 ~ 10 μm, preferably 1.5 ~ 7 μm, and the membrane flux of the membrane modules of the membrane filter is 150 ~ 700L/(m m.sup.2L/m.sup.7 μm²H), preferably 300 ~ 650L/(m)²H); the membrane filter adopts a cross-flow filtration modeAnd (5) operating.

7. The method of claim 1, wherein the membrane filter is provided with a feed chamber at an upper portion, a first slurry chamber at a middle portion, and a second slurry chamber at a lower portion; and stirrers are arranged in the reactor, the second slurry cavity of the membrane filter and the aging device.

8. The method according to claim 1, wherein the pH swing method is used in the step (a) and the reaction system is first swung to the acid side and then swung to the base side or first swung to the base side and then swung to the acid side.

9. The method of claim 1, wherein when one reactor is used, step (a) is as follows:

(a01) preparing working solutions of acidic materials and alkaline materials;

(a02) adding bottom water into a reactor, then respectively adding an acidic material and a basic material in parallel flow, and controlling the pH value to be 5 ~ 8;

(a03) adding alkaline material into the reactor, and controlling the pH value of slurry in the system to be 8.6 ~ 12.0.0, preferably 9.0 ~ 11.0.0;

(a04) after (a 03), adding an acidic material to the reactor, and controlling the pH value of the slurry in the system to be 2.0 ~ 4.0.0, preferably 3.0 ~ 3.5.5;

(a05) repeatedly carrying out pH value swinging operation according to the steps (a 03) and (a 04);

when the level of the slurry in the reactor reaches a prescribed level, the slurry produced by the reactor enters the membrane filter through the discharge port.

10. The method according to claim 1, wherein when a plurality of reactors are used, taking a first reactor and a second reactor as an example, the step (a) is as follows:

(a11) preparing working solutions of acidic materials and alkaline materials;

(a21) adding bottom water into the first reactor and the second reactor respectively, then adding an acidic material and a basic material into the first reactor and the second reactor respectively in a cocurrent manner, and controlling the pH value to be 5 ~ 8;

(a31) adding alkaline material into the first reactor, and controlling the pH value of slurry in the system to be 8.6 ~ 12.0.0, preferably 9.0 ~ 11.0.0;

(a41) adding an acidic material into the second reactor, and controlling the pH value of slurry in the system to be 2.0 ~ 4.0.0, preferably 3.0 ~ 3.5.5;

(a51) after (a 31), adding an acidic material to the first reactor, and controlling the pH value of the slurry in the system to be 2.0 ~ 4.0.0, preferably 3.0 ~ 3.5.5;

(a61) after (a 41), adding an alkaline material to the second reactor to control the pH of the slurry in the system to 8.6 ~ 12.0.0, preferably 9.0 ~ 11.0.0;

(a71) repeatedly carrying out pH value swinging operation according to the steps (a 31) and (a 51) in the first reactor;

(a81) repeatedly carrying out pH value swinging operation according to the steps (a 41) and (a 61) in the second reactor;

the other reactors are operated as the first reactor or the second reactor;

when the liquid level of the slurry in the reactor reaches a predetermined level, the slurry produced in each reactor enters the membrane filter through the discharge port.

11. The process of claim 1, 3, 9 or 10, wherein the pH of step (a) is oscillated at least 2 times, preferably 2 ~ 7 times, when the slurry level in the reactor reaches a specified level.

12. The process according to claim 1, wherein, after the continuous discharge of the reactor, in step (a), the feed rate to the reactor and the discharge rate of the slurry produced by the reactor through the discharge opening are controlled in such a way that the theoretical residence time of the acidic or basic material into the reactor is 30 ~ 120 min, preferably 60 ~ 120 min.

13. The process of claim 1, wherein the pH swing of step (a) is carried out at a reaction temperature of 45 ℃ ~ 100 ℃, preferably 50 ℃ ~ 95 ℃.

14. The method of claim 1, wherein in step (a), the stirring speed of the reactor is controlled to be 30 ~ 2000 r/min, preferably 100 ~ 1000 r/min.

15. The method according to claim 1, wherein in the step (b), when a plurality of reactors are used, the slurry discharged from each discharge port is mixed to obtain a mixed slurry, and the mixed slurry is introduced into a membrane filter, and the pH of the mixed slurry is controlled to 6.0 ~ 8.0.0, preferably 6.0 ~ 7.5.5.

16. The method according to claim 9 or 10, characterized in that the control of the acid-base swing is performed simultaneously with the switching of the reactor operated in the first reactor mode and the reactor operated in the second reactor mode, i.e. the reactor operated in the first reactor mode is switched into the acidic material at the same time as the reactor is switched into the acidic material, and the reactor operated in the first reactor mode is switched into the basic material at the same time as the reactor is switched into the acidic material.

17. The process of claim 1, wherein in step (b) the acidic material is added to the first slurry before it is recycled to the reactor to control the pH to 2 ~ 6, preferably 2 ~ 4.

18. The process of claim 1, wherein in step (b), the slurry produced by the reactor is discharged from the discharge outlet, and the properties of the reaction slurry are controlled to have a solids content of 80.0 ~ 200.0.0 gA1₂O₃L, 30% or more of grains having a grain size of not less than 4.0. mu.m.

19. The method according to claim 1, wherein in the step (b), the slurry produced in the reactors is supplied to the membrane filter through the discharge port at a flow rate of 2 ~ 50 times, preferably 5 ~ 30 times, the sum of the flow rates of the acidic material and the basic material flowing from the feed port into each reactor, and the membrane filter has a membrane surface flow rate of 1 ~ 10m/s, preferably 2 ~ 6 m/s.

20. The method of claim 1, wherein in step (b), the second slurry contains more than 95% of aluminum hydroxide with a particle size larger than the pore size of the membrane and has a concentration of 150 ~ 500 g A1₂O₃/L。

21. The method of claim 1, wherein the pressure drop across the membrane filter in step (b) is no more than 0.1MPa and the operating temperature of the membrane filter in step (b) is 45 ℃ ~ 100 ℃, preferably 50 ℃ ~ 95 ℃.

22. The method of claim 1, wherein in step (b), the stirring is performed in the second slurry chamber of the membrane filter at a speed of 100 ~ 1000 r/min.

23. The method according to claim 1, wherein the aging in step (c) is carried out under conditions of pH 8.0 to 9.5, aging temperature 55 to 150 ℃, aging time 0.5 ~ 2.0.0 h, and stirring at a stirring speed of 30 ~ 2000 r/min, preferably at least 0.5 higher than the pH of the slurry mixture in the membrane filter, 10 ℃ ~ 100 ℃ higher than the reaction temperature in step (b), aging time 0.5 ~ l.0h, and stirring speed of 100 ~ 1000 r/min.

24. The method of claim 1, wherein in step (c), the second slurry entering the aging process is heat exchanged with the aged slurry to recover a portion of the heat.

Technical Field

The invention relates to a method for preparing aluminum hydroxide, in particular to a method for continuously preparing aluminum hydroxide by a pH value swing method.

Background

Alumina is used as a catalyst and a catalyst carrier, and has a special structure and excellent performance, so that the alumina is widely applied to a plurality of catalytic fields, particularly catalytic conversion processes of petroleum. Therefore, the preparation, structure and performance of alumina are being studied more and more.

Activated alumina is commonly referred to as gamma-Al₂O₃It has relatively high specific surface area, strong adsorption, surface chemical property, certain porosity and pore size distribution, and is often used as catalyst carrier in petrochemical industry. In the aspect of catalytic conversion of petroleum, in recent years, due to the development of heavy residual oil processing technology, a plurality of new requirements are put on catalyst carrier alumina in the processing process. For example, hydrodesulfurization and demetallization of residual oils require moderate surface areas and a proportion of large and small pore distributions; the hydrodenitrogenation catalyst requires a high specific surface area capable of uniformly loading high metal content, a large pore volume and a medium-small pore structure in a proper proportion, and provides a viewpoint of concentrated pores. Usually, gamma-Al₂O₃Is prepared from aluminium hydroxide through calcining at high temp. The pore structure of alumina is determined by the morphology, particle size and aggregation state of its precursor aluminum hydroxide. Therefore, to obtain an alumina support with relatively concentrated pore sizes, the size of the precipitated aluminum hydroxide particles must be uniform. It is well known to produce gamma-Al₂O₃There are various methods for the precursor aluminum hydroxide, and the methods are generally classified into a neutralization method such as NaAlO and an aluminum alkoxide hydrolysis method₂-HNO₃FatsNaAlO₂-Al₂(SO₄)₃Method and AlCl₃-NaOH(NH₃·H₂O) method, etc., which are both concurrent neutralization reactions of acidic and basic liquids. In the traditional aluminum hydroxide preparation process by an aluminum sulfate method, aluminum hydroxide with large pore volume and high specific surface area can be obtained by changing preparation conditions or adding auxiliary components, but particles generated by the initial precipitation reaction rapidly grow and aggregate in the subsequent precipitation process, so that grains with different sizes and amorphous structures are inevitably generated, and uniform grains are difficult to obtain. To change this state, Ono et al invented a new process called pH swing, where the pH of the slurry during precipitation is changed alternately between acid and base, the base side precipitates and the acid side dissolves aluminum hydroxideThe aluminum hydroxide is shaped and precipitated on the generated aluminum hydroxide particles when alkali is added, and the aluminum hydroxide particles with relatively uniform particles and relatively concentrated pore diameters can be generated by circulating the process.

At present, the process for producing aluminum hydroxide by a pH value swing method is an intermittent reaction, the production efficiency is low, the labor intensity of operators is high, and the properties of the prepared aluminum hydroxide are different due to the difference of reaction conditions of different batches.

CN201310605035.3 discloses a reactor and a preparation method of pseudo-boehmite thereof. The reactor barrel is internally provided with a partition board which divides the inner cavity of the reactor into two areas along the axial direction, the partition board is arranged on a central shaft, and the partition board rotates along with the rotation of the central shaft; in each zone, a feed inlet is arranged at the lower part of the corresponding reactor cylinder, at least one material circulating pipeline is arranged at the outer side of the corresponding reactor cylinder, a circulating material outlet is arranged at the upper part, a circulating material inlet is arranged at the bottom, and an overflow port is arranged at the upper part of the corresponding reactor cylinder and is higher than the circulating material outlet. The reactor can realize continuous gel forming by a pH value swing method. But the reactor has complex structure, difficult operation, rotating parts and difficult sealing of the rotating partition plate, and is not beneficial to the long-period operation and large-scale of equipment; and the crystal of different development stages is taken out from the reactor and aged to disperse the particle size of the obtained pseudoboehmite.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a method for preparing aluminum hydroxide. The invention not only can realize the continuous operation of preparing the aluminum hydroxide by the pH value swing method, but also solves the problem of aluminum hydroxide granularity dispersion caused by taking out the crystals at different development stages from the reactor and aging at the same time. The invention can realize continuous and large-scale production of the aluminum hydroxide, reduce the production cost, has simple equipment structure and easy operation, and ensures the stable product quality.

The invention relates to a method for preparing aluminum hydroxide, which adopts a device comprising: the device comprises a reactor, a membrane filter and an aging device, wherein the reactor is provided with a feed inlet, a circulating material inlet and a discharge outlet, the feed inlet and the circulating material inlet are higher than the discharge outlet, the discharge outlet is connected with the inlet of the membrane filter, the membrane filter is provided with a permeate outlet and a retentate outlet, the permeate outlet of the membrane filter is connected with a circulating slurry inlet of the reactor through a circulating slurry material pipeline, and the retentate outlet of the membrane filter is connected with the aging device; the preparation process of the aluminum hydroxide comprises the following steps:

(a) preparing aluminum hydroxide precipitate in a reactor by adopting a pH value swing method;

(b) when the liquid level of the slurry in the reactor reaches a specified liquid level, discharging the slurry into the membrane filter through the discharge port; separating by a membrane filter to obtain first slurry and second slurry, discharging the first slurry from a permeate outlet of the membrane filter, feeding the first slurry into a reactor through a circulating material inlet of the reactor, discharging the second slurry from a retentate outlet of the membrane filter, and feeding the second slurry into an aging device for aging;

(c) and (4) filtering, washing and drying the slurry after passing through an ageing device to obtain the aluminum hydroxide.

Further wherein the reactor is one or more reactors operated in parallel; preferably, a plurality of reactors operated in parallel are used.

Further, the reactor is provided with a liquid level controller.

Further, a circulating slurry heater and/or a static mixer is arranged on a circulating slurry material pipeline between the permeate outlet of the membrane filter and the circulating slurry inlet of the reactor, and the circulating slurry heater can be a plate-type or tube-type heater, preferably a plate-type heater. Preferably, a circulating slurry heater and a static mixer are provided, with the static mixer being located upstream of the circulating slurry heater.

Further, the membrane filter is intensively filled with membrane components, the membrane components are inorganic membranes or organic membranes, preferably inorganic membranes, the inorganic membrane materials are preferably any one of metal, oxide, inorganic polymer material and ceramic, the membrane pore diameter is 0.5 ~ 10 [ mu ] m, preferably 1.5 ~ 7 [ mu ] m, and the membrane flux of the membrane filter membrane components is 150 ~ 700L/(m < 2 >)²H), preferably 300 ~ 650L/(m)²H). The membrane filter is operated in a cross-flow filtration mode.

Further, preferably, the membrane filter is centrally filled with vertically-discharged membrane modules, and the membrane modules are inorganic membranes, and the inorganic membranes are ceramic.

Further, a feeding cavity is arranged at the upper part of the membrane filter, a first slurry cavity is arranged at the middle part of the membrane filter, and a second slurry cavity is arranged at the lower part of the membrane filter; and mechanical stirring systems are arranged in the reactor, the second slurry cavity of the membrane filter and the aging device.

Furthermore, the stirrer of the stirring system of the membrane filter is arranged at the lower part of the second slurry cavity of the membrane filter, is in a lower stirring mode and is provided with a shaft seal device resistant to solid particles, the stirrer is a turbine type stirrer, preferably an open-type blade turbine type stirrer, a wall baffle is arranged in the second slurry cavity, and a gap of 5 ~ 60mm, preferably 15 ~ 30mm, is reserved between the baffle and the wall of the second slurry cavity to prevent the solid particles from being retained.

Further, an aging heat exchanger is arranged between the membrane filter and the aging device, and the aging heat exchanger can be a plate type or tube type heat exchanger, preferably a plate type heat exchanger.

Further, the aging device may be provided with two or more aging tanks.

Further, the pH value swing method employed in step (a) is to swing the pH value to the acid side by adding an acidic material to the reaction system, to swing the pH value to the alkali side by adding an alkaline material to complete a pH value swing, and then to repeat the above-mentioned acid-base swing operation, or to swing the pH value to the alkali side by adding an alkaline material to the reaction system, to swing the pH value to the acid side by adding an acidic material to complete a pH value swing, and then to repeat the above-mentioned acid-base swing operation.

Further, in the step (a), the step of preparing the aluminum hydroxide precipitate in the reactor by using a pH value swing method can adopt one reactor or a plurality of reactors.

When one reactor is used, the step (a) is specifically prepared as follows:

(a01) preparing working solutions of acidic materials and alkaline materials;

(a02) adding bottom water into a reactor, then respectively adding an acidic material and a basic material in parallel flow, and controlling the pH value to be 5 ~ 8;

(a03) adding alkaline material into the reactor, and controlling the pH value of slurry in the system to be 8.6 ~ 12.0.0, preferably 9.0 ~ 11.0.0;

(a04) after (a 03), adding an acidic material to the reactor, and controlling the pH value of the slurry in the system to be 2.0 ~ 4.0.0, preferably 3.0 ~ 3.5.5;

(a05) and (c) repeatedly carrying out the pH value swinging operation according to the steps (a 03) and (a 04).

In step (a 02), the cocurrent reaction time was controlled to 10 ~ 30 minutes.

When a plurality of reactors are adopted, taking a double reactor as an example, wherein the double reactor is respectively a first reactor and a second reactor, the step (a) is specifically prepared as follows:

(a11) preparing working solutions of acidic materials and alkaline materials;

(a21) adding bottom water into the first reactor and the second reactor respectively, then adding an acidic material and a basic material into the first reactor and the second reactor respectively in a cocurrent manner, and controlling the pH value to be 5 ~ 8;

(a31) adding alkaline material into the first reactor, and controlling the pH value of slurry in the system to be 8.6 ~ 12.0.0, preferably 9.0 ~ 11.0.0;

(a41) adding an acidic material into the second reactor, and controlling the pH value of slurry in the system to be 2.0 ~ 4.0.0, preferably 3.0 ~ 3.5.5;

(a51) after (a 31), adding an acidic material to the first reactor, and controlling the pH value of the slurry in the system to be 2.0 ~ 4.0.0, preferably 3.0 ~ 3.5.5;

(a61) after (a 41), adding an alkaline material to the second reactor to control the pH of the slurry in the system to 8.6 ~ 12.0.0, preferably 9.0 ~ 11.0.0;

(a71) repeatedly carrying out pH value swinging operation according to the steps (a 31) and (a 51) in the first reactor;

(a81) repeatedly carrying out pH value swinging operation according to the steps (a 41) and (a 61) in the second reactor;

the other reactors are operated as the first reactor or the second reactor;

when slurry produced in each reactor enters the membrane filter through the discharge port.

In step (a 21), the cocurrent reaction time was controlled to 10 ~ 30 minutes.

In the step (a), the operation of the first reactor and the second reactor can be synchronously performed, or can be asynchronously performed, preferably synchronously performed, and the pH value swing method in the step (a) adopts the reaction temperature of 45 ℃ ~ 100 ℃, preferably 50 ℃ ~ 95 ℃.

Further, the pH value swing method in the step (a) adopts a conventional neutralization method to prepare an acidic material and a basic material used in the precipitation of the aluminum hydroxide. The concentrations and methods of formulation of the working solutions of acidic and basic materials are well known to those skilled in the art. For example, the acidic material is an acidic aluminum-containing compound, the basic material is a basic aluminum-containing compound or a basic precipitant, and for example, the acidic material is an acidic precipitant and the basic material is a basic aluminum-containing compound. The acidic aluminum-containing compound is typically AlCl₃ 、Al₂(SO₄)₃Or A1(NO)₃Preferably Al₂(SO₄)₃The concentration of the acidic aqueous solution of the aluminum-containing compound is A1₂O₃30 ~ 160g/L, the basic aluminum-containing compound is selected from NaA1O₂Or KA1O₂The concentration of the basic aqueous solution of the aluminum-containing compound is A1₂O₃Calculated as 70 ~ 350g/L, the alkaline precipitant is generally NaOH, (NH)₄)₂CO₃Or NH₄OH。

Further, in step (a), it is necessary to control the stirring speed of the reactor, which is generally 30 ~ 2000 r/min, preferably 100 ~ 1000 r/min.

Further, after the reactor is continuously discharged, in step (a), the feeding rate of the reactor and the discharging rate of the slurry generated by the reactor through the discharging port are controlled in such a manner that the theoretical residence time of the acidic material or the basic material into the reactor is 30 ~ 120 min, preferably 60 ~ 120 min.

Further, in the step (b), when a plurality of reactors are used, the slurry discharged from each discharge port is preferably mixed to obtain a mixed slurry, and the pH of the mixed slurry is controlled to 6.0 ~ 8.0.0, preferably 6.0 ~ 7.5.5, and when the acidic material and the basic material are alternately fed, it is preferable that the reactor in the first reactor operation mode is controlled to be synchronized with the reactor switching material in the second reactor operation mode, that is, the reactor in the second reactor operation mode is switched to the basic material while the acidic material is switched to the reactor in the first reactor operation mode, the acidic material is switched to the reactor in the second reactor operation mode while the basic material is switched to the reactor in the first reactor operation mode, and that the pH of the mixed slurry fed to the membrane filter is controlled to 6.0 ~ 8.0.0, preferably 6. 6.0 ~ 7.5.5.

In step (b), when 2 reactors are used, the residence time of the acidic material fed to the feed port of the first reactor is preferably the same as the residence time of the basic material fed to the feed port of the second reactor, and the residence time of the basic material fed to the feed port of the first reactor is preferably the same as the residence time of the acidic material fed to the feed port of the second reactor, and the pH of the mixed slurry fed to the membrane filter is controlled to 6.0 ~ 8.0.0, preferably 6.0 ~ 7.5.5.

Further, in the step (b), when the slurry produced by the reaction is discharged from the discharge port, the properties of the reaction slurry are controlled so that the solid content is 80.0 ~ 200.0.0 gA1₂O₃L, 30% or more of grains having a grain size of not less than 4.0. mu.m.

Further, in the step (b), the slurry produced by the reaction is transferred by the feed pump through the discharge port to the membrane filter at a flow rate of 2 ~ 50 times, preferably 5 ~ 30 times, the flow rate of the acidic material and the basic material flowing from the feed port into each reactor, and the membrane filter has a membrane surface flow rate of 1 ~ 10m/s, preferably 2 ~ 6 m/s.

Further, in the step (b), stirring is carried out in the second slurry cavity of the membrane filter, and the stirring rotating speed of the membrane filter needs to be controlled, wherein the rotating speed is 100 ~ 1000 r/min.

Further, in the step (b), controlThe pore diameter of the membrane component of the membrane filter is such that the aluminum hydroxide with the particle diameter larger than the pore diameter of the membrane in the second slurry accounts for more than 95 percent and the concentration is 150 ~ 500 g A1₂O₃/L。

Further, the operating temperature of the membrane filter of step (b) is 45 ℃ ~ 100 ℃, preferably 50 ℃ ~ 95 ℃.

Further, in the step (b), the pressure drop of the membrane filter does not exceed 0.1 MPa.

Further, in step (b), an appropriate amount of an acidic material is added to the first slurry before it is recycled to the reactor to control the pH to 2 ~ 6, preferably 2 ~ 4.

Further, aging conditions need to be controlled in the step (c), wherein the pH value is 8.0-9.5, the aging temperature is 55-150 ℃, the aging time is 0.5 ~ 2.0.0 h, preferably 0.5 ~ h, preferably the aging temperature is 10 ℃ to ~ 100 ℃ higher than the reaction temperature in the step (b), preferably 20 ℃ to ~ 70 ℃ higher than the aging tank, and the aging process can be continuously completed by alternately switching the aging tanks, and further preferably, the pH value during aging is controlled to be higher than the pH value of slurry in the membrane filter by at least 0.5.

Further, in the step (c), the stirring speed of the aging apparatus is controlled, and the stirring speed is generally 30 ~ 2000 r/min, preferably 100 ~ 1000 r/min.

Further, in the step (c), the second slurry entering the aging process exchanges heat with the aged slurry, so that the temperature of the second slurry entering the aging process is increased, and the temperature of the aged slurry is reduced to recover part of heat.

The aluminum hydroxide obtained by the method has concentrated particle size distribution, mainly concentrates on 4 ~ 20 μm, especially 10 ~ 20 μm, the particle size distribution rate of 4 ~ 20 μm is more than 97%, and the particle size distribution rate of 10 ~ 20 μm is more than 50%.

The method of the invention has the following advantages:

1. the method realizes the continuous and large-scale production of preparing the aluminum hydroxide by the pH swing method, reduces the production cost and ensures the stable product quality.

2. The method provided by the invention can be used for selectively taking out the aluminum hydroxide crystals at different growth stages in the reaction process, so that the particle size distribution of the aluminum hydroxide product is more concentrated, and the problems of different swing times and particle size dispersion of the aluminum hydroxide caused by aging when the crystals at different growth stages are taken out from the reactor in the production process of the current pH swing method and are aged are solved.

3. In the method for preparing the aluminum hydroxide, the pH value of the mixed slurry entering the membrane filter is preferably controlled to be 6.0 ~ 8.0.0, the complete crystal form and the complete grain size of the grains can be maintained, the separated grains are complete and uniform in grain size, and the yield of the aluminum oxide is high.

4. According to the invention, the acidic material is preferably added into the first slurry, the pH value is controlled to be 2 ~ 6, small crystal grains and amorphous structures included in the crystalline aluminum hydroxide are dissolved before the first slurry enters the reactor, the purpose of strengthening and shaping the continuously growing crystal grains is achieved, the aluminum oxide is completely crystallized, and the uniform growth of the crystal grains is facilitated.

Drawings

FIG. 1 is a schematic view of the process of the present invention;

wherein, 1, a first reactor; 2. a second reactor; 31. a first reactor feed inlet I; 41. a first reactor feed inlet II; 32. a feed inlet I of the second reactor; 42. a feed inlet II of the second reactor; 51. a first reactor agitator; 52. a second reactor agitator; 61. a first reactor discharge port; 62. a second reactor discharge port; 71. a first reactor liquid level controller; 72. a second reactor liquid level controller; 8. a membrane filter; 101. a first reactor slurry circulation material inlet; 102. a second reactor slurry circulation material inlet; 11. a membrane filter retentate outlet; 12. a membrane filter permeate outlet; 131. a membrane filter first slurry; 141. a membrane filter second slurry; 15. a first slurry circulation heater; 16. aging the heat exchanger; 17. a first aging tank; 18. a second aging tank; 19. a first slurry circulating static mixer; 20. a static mixer for mixing the slurry.

Detailed Description

The following describes in further detail a specific embodiment of the present invention with reference to fig. 1. The following examples are intended to illustrate the technical solutions of the present invention, but are not intended to limit the scope of the present invention. In the present invention, wt% is a mass fraction.

The method for preparing aluminum hydroxide according to the present invention uses an apparatus, as shown in fig. 1, which is composed of two reactors, including a first reactor 1 and a second reactor 2, a membrane filter 8, a first slurry circulation heater 15, an aging heat exchanger 16, a first aging tank 17, a second aging tank 18, a first slurry circulation static mixer 19, a mixed slurry static mixer 20, and the like, by taking two reactors as an example. The first reactor upper portion sets up first reactor feed inlet I31, first reactor feed inlet II 41 and first reactor thick liquid circulation material entry 101, 1 lower part of first reactor sets up first reactor discharge port 61, set up agitator 51 in the first reactor, first reactor sets up liquid level controller 71, second reactor upper portion sets up second reactor feed inlet I32, second reactor feed inlet II 42 and second reactor thick liquid circulation material entry 102, 2 lower parts of second reactor set up first reactor discharge port 62, set up agitator 52 in the second reactor, first reactor sets up liquid level controller 72.

The first reactor 1, the second reactor 2, the mixed slurry static mixer 20, the membrane filter 8, the first slurry circulating static mixer 19 and the first slurry circulating heater 15 are connected through pipelines to form slurry circulation, and the reaction and reactant separation process is completed. And the second slurry 141 of the membrane filter discharged from the retentate outlet 11 of the membrane filter enters an aging heat exchanger 16, is switched to enter a first aging tank 17 and a second aging tank 18 after heat exchange, alternately undergoes an aging process, and then undergoes filtering, washing and drying processes. Wherein the first reactor and the second reactor adopt a pH value swing gel-forming method to continuously prepare the aluminum hydroxide slurry.

Wherein, the slurry generated by the first reactor 1 is discharged through a first reactor discharge port 61, and the slurry generated by the second reactor 2 is discharged through a second reactor discharge port 62 and then mixed to enter the mixed slurry static mixer 20.

In this case, a first slurry circulation static mixer 19 is provided upstream of the first slurry circulation heater 15.

The first slurry circulation heater 15 may be a plate heater or a tube heater, preferably a plate heater, and heats the returned overflow liquid to maintain the temperature in the reactor.

The membrane filter 8 is provided with a feeding cavity at the upper part, a first slurry cavity at the middle part and a second slurry cavity at the lower part, the second slurry cavity of the membrane filter is provided with a mechanical stirring system to suspend particles in the second slurry cavity and prevent deposition and blockage, a stirrer of the stirring system is arranged at the lower part of the second slurry cavity of the membrane filter 8 and is in a lower stirring mode and is provided with a shaft seal device resistant to solid particles, the stirrer is in a turbine mode, preferably an open type blade turbine type stirrer, a wall baffle is arranged in the second slurry cavity, a gap of 5 ~ 60mm, preferably 15 ~ 30mm is reserved between the baffle and the wall of the.

The aging heat exchanger arranged between the membrane filter 8 and the aging tanks 17 and 18 may be a plate heat exchanger or a tube heat exchanger, preferably a plate heat exchanger. The second slurry of the membrane filter and the aged slurry exchange heat, the aging feeding temperature is improved, the aging is facilitated, and the energy-saving purpose is achieved.

Wherein, the ageing tank can be provided with two or more, accomplishes continuous ageing process through the switching in turn of ageing tank.