Preparation method for reducing steam consumption of small-hole pseudo-boehmite

Abstract

The invention relates to a preparation method for reducing steam consumption of small-pore pseudo-boehmite, which comprises the following steps: filtering and separating pseudo-boehmite precursor slurry prepared by a carbonization method to obtain a precursor filter cake, effectively reducing the content of Na2O in the pseudo-boehmite filter cake, and repeatedly utilizing high-temperature aging filtrate and high-temperature washing filtrate of pseudo-boehmite for aging to obtain the small-pore pseudo-boehmite. The preparation method comprises the following steps: adding the raw materials into a precursor filter cake, mixing, pulping, aging, adjusting the aging pH value by using a seed precipitation mother solution, enabling the aging solution to be under the conditions of low alkali concentration and high pH value, reducing the aging temperature and time, improving the washing efficiency, and finally drying after urea modification, so that the comprehensive water consumption is reduced by 40%, the steam water consumption is reduced by about 35%, the crystallinity of a finished product is greater than 70%, and the Na < + > impurity content is 0.16-0.22 wt%. The pore volume of gamma-Al2O3 obtained after roasting is 0.35-0.5 mL / g, and the specific surface area is greater than 250 m < 2 > / g. The method is simple in process, stable in quality control, high in product purity, low in production cost, energy-saving and easy for industrial application.

Description

Technical Field

[0001] The invention belongs to the technical field of pseudo-boehmite preparation, and particularly relates to a preparation method for reducing steam consumption of small-pore pseudo-boehmite. Background Art

[0002] Small-pore pseudo-boehmite is a key precursor for fluid catalytic cracking (FCC) catalysts. The mesoporous γ-Al2O3 obtained by calcination can serve as the active matrix and structural stabilizer of FCC catalysts. The crystallinity and peptization properties of small-pore pseudo-boehmite are related to the catalyst strength and directly affect the catalyst lifecycle. Currently, the carbonization process is widely used in industry to produce small-pore pseudo-boehmite. This process involves introducing carbon dioxide gas into a sodium aluminate solution to produce the pseudo-boehmite precursor. The precursor slurry gelling temperature is generally less than 45°C. The pseudo-boehmite is then aged at high temperatures, typically at 95-100°C for 3-5 hours, to improve its crystallinity and peptization properties. This process has significant defects: the heating and insulation during the aging stage consume a large amount of steam, accounting for more than 40% of the total production energy consumption. In addition, in order to remove the residual alkali (Na2O) in the filter cake, it needs to be repeatedly washed with hot water above 85°C. The comprehensive water consumption is as high as 30 to 35 tons per ton of product, and the steam consumption per ton of product is as high as about 5 tons per ton of product.

[0003] To reduce water consumption in the pseudo-boehmite production process, various improvements have been proposed. For example, patent CN101665262B introduces Bayer process seed liquor (Na2O ≥ 100 g / L) during the aging stage, leveraging its high alkalinity to reduce wash water usage. While this solution reduces water consumption, it fails to address the aging process's reliance on high-temperature steam. Patent CN108910925B employs a staged countercurrent washing process and adds dried pseudo-boehmite to improve filter cake permeability, reducing wash water consumption by 50% and drying energy consumption by 40%. However, the aging temperature still needs to be maintained above 95°C, and the addition of the dried product increases process complexity. Patent CN112694111B utilizes a carbonization process combined with lithium sulfate to prepare a precursor slurry, which is then aged at 50-90°C with a pH controlled between 7.5 and 9.5. While this reduces wash water consumption, it introduces sulfate impurities into the product and produces macroporous pseudo-boehmite. In "Research on Reducing Water Consumption in Pseudo-Boehmite Washing", Liu Yandong et al. proposed that in the carbonization method for producing pseudo-boehmite, the aged liquid should be modified by adding liquid A and liquid B. This can reduce water consumption and stabilize the product dissolution rate. However, the formula of the modified liquid and the specific process were not disclosed.

[0004] Therefore, there is an urgent need to develop a small-pore pseudo-boehmite production process that can not only deeply reduce the steam consumption used for aging and washing, but also ensure the stability of crystallinity and peptization performance. Summary of the Invention

[0005] In view of the above problems existing in the prior art, the present invention provides a preparation method for reducing steam consumption of small-pore pseudo-boehmite, comprising the following steps:

[0006] Step (1), low-temperature gelation and filtration: intermittently introduce carbon dioxide gas into a sodium aluminate solution with an aluminum oxide concentration of 40-45 g / L for carbonization decomposition, control the decomposition end temperature to 35-42° C., react for 10-15 minutes, and obtain a pseudo-boehmite precursor slurry, which is filtered through a belt filter to obtain a precursor filter cake;

[0007] Step (2), mixing, beating and filtrate circulation: mixing and beating the precursor filter cake obtained in step (1) with at least one of the aged filtrate, the washing filtrate and the hot water to obtain a mixed slurry with a solid content of 50 to 70 g / L;

[0008] Step (3), seed liquor regulation and aging: pump the mixed slurry of step (2) into the aging tank at 1.5-2.5m 3 Add the seed solution at a flow rate of / h, adjust the pH value of the system to 11.5-12.5, and age at 85-89℃ for 2-3h;

[0009] Step (4), separation and post-treatment: The aged product is separated and washed by filter pressing, and urea is added during the last washing to modify it, and then solid-liquid separation and wet filter cake drying are performed to obtain a pseudo-boehmite product with a crystallinity of >70%; the pseudo-boehmite product is calcined at 600°C to obtain a γ-Al2O3 pore volume of 0.35-0.5 mL / g and a specific surface area of ​​>250 m 2 / g.

[0010] Furthermore, the aged filtrate is the filtrate produced by filter pressing after pseudo-boehmite aging, wherein the concentration of Na2O is less than 12g / L, and the concentration of Na2O is less than 12g / L. k The concentration is 1 to 3 g / L; the washing filtrate is the filtrate produced by filter pressing after washing the pseudo-boehmite, wherein the Na2O concentration is less than 3 g / L, Na2O k Concentration <0.5g / L; the Na2O concentration is the Na2O converted from sodium carbonate c Concentration and Na2O converted from sodium hydroxide k Sum of concentrations.

[0011] Furthermore, in step (2), the mixed flow ratio of the aging filtrate and the washing filtrate is 0:1 to 5:1.

[0012] Furthermore, in step (2), when the system is initially started, the hot water is evaporated condensed water after heating in the main process of pseudo-boehmite preparation, and the temperature is ≥85°C.

[0013] Furthermore, the seed liquor in step (3) is the mother liquor produced by the seed decomposition of the sodium aluminate solution by the sintering process, the caustic coefficient αk>3.5, Na2O k Concentration>90g / L.

[0014] Furthermore, the ratio of the amount of urea added in step (4) to the volume of the aged product slurry is 0.5 to 1 kg / m 3 .

[0015] Furthermore, the Na + The impurity content is 0.16-0.22wt%.

[0016] The present invention has the following advantages:

[0017] (1) The present invention reuses the pseudo-boehmite high-temperature aging filtrate and the washing filtrate for aging, adjusts the pH value by using the seed liquor, reduces the aging temperature and time, and utilizes the waste heat of the waste liquid to reduce steam injection, so that the steam consumption in the aging process can be reduced by about 55%.

[0018] (2) In the pseudo-boehmite precursor slurry of the present invention, Na2O mainly exists in the form of sodium carbonate, and in the seed denominator liquid, Na2O mainly exists in the form of strong alkali sodium hydroxide. During the aging process, only a small amount of seed denominator liquid is needed to maintain a relatively high pH value. The Na2O concentration in the aging liquid is reduced from 50-60 g / L to below 12 g / L. By adopting low alkali concentration and high pH value aging, the Na2O content in the pseudo-boehmite filter cake can be effectively reduced after separation, and the washing efficiency is improved, so that the washing water energy consumption is reduced by about 25%, thereby further reducing steam consumption.

[0019] (3) The present invention adds urea for modification before drying, which can eliminate the influence of low temperature and high pH aging on the specific surface at a higher crystallinity, and can retain a higher specific surface area after drying. The pseudo-boehmite product prepared by the method of the present invention has high crystallinity and good peptization performance. The alumina obtained by calcination has a small pore volume and a large specific surface area, which meets the performance requirements of FCC catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flow chart of the preparation process for reducing steam consumption of small-pore pseudo-boehmite according to the present invention. DETAILED DESCRIPTION

[0021] Example 1

[0022] Precursor preparation: Sodium aluminate solution with an aluminum oxide concentration of 42 g / L is used as raw material, and carbon dioxide gas (concentration 35-38%, pressure 0.1-0.3 Pa) is intermittently introduced into the decomposition tank. The decomposition end temperature is controlled at 40°C, and the pseudo-boehmite precursor is obtained after decomposition for 12 minutes.

[0023] Filtration: Pour the pseudo-boehmite precursor into a buffer tank through a pump and filter it through a belt filter with a filtration area of ​​12m 2 , the operating frequency is controlled at 40 Hz and monitored by a flow meter to obtain the precursor filter cake.

[0024] Beating: Pseudo-boehmite aging filtrate and washing filtrate are continuously mixed with the precursor filter cake for beating. The beating tank is filled with water and discharged at the same time. The frequency of the beating tank discharge pump is controlled to keep the beating tank liquid level stable. Among them, the flow rate of pseudo-boehmite aging filtrate is controlled at 20m 3 / h, the flow rate of washing filtrate is controlled at 4m 3 / h, the slurry solid content is 60g / L.

[0025] Aging: When the volume of slurry in the aging tank reaches 20m 3 When the filtered seed liquor (Na2Ok concentration 95g / L) is pumped at 2m 3 / h into the aging tank, and use the PH online detector to interlock with the metering pump to slowly adjust the PH value to 12.0, and control the aging temperature at 88℃ by controlling the steam electric regulating valve, and age for 2.5h.

[0026] Separation and post-processing: The aged product is separated and washed by filtration, and then 3 15kg of urea was added to the slurry, and after separation, drying and other subsequent processes, a pseudo-boehmite product with a crystallinity of >70% was obtained. The pore volume of the finished product obtained after roasting was 0.35-0.5ml / g, and the specific surface area was >250m 2 / g, meeting the FCC catalyst strength requirements.

[0027] Example 2

[0028] Precursor preparation: Sodium aluminate solution with an aluminum oxide concentration of 40 g / L is used as raw material, carbon dioxide gas (concentration 35-38%, pressure 0.1-0.3 Pa) is introduced into the decomposition tank, the decomposition end temperature is controlled at 38°C, and pseudo-boehmite precursor is obtained after decomposition for 15 minutes.

[0029] Filtration: Pour the pseudo-boehmite precursor into a buffer tank through a pump and filter it through a belt filter with a filtration area of ​​12m 2 , the operating frequency is controlled at 35 Hz and monitored by a flow meter to obtain the precursor filter cake.

[0030] Beating: Pseudo-boehmite aging filtrate and washing filtrate are continuously mixed with the precursor filter cake for beating. The beating tank is filled with water and discharged at the same time. The frequency of the beating tank discharge pump is controlled to keep the beating tank liquid level stable. Among them, the flow rate of pseudo-boehmite aging filtrate is controlled at 15m 3 / h, the flow rate of washing filtrate is controlled at 5m 3 / h, and the slurry solid content is 55g / L.

[0031] Aging: When the volume of slurry in the aging tank reaches 20m 3 When the filtered seed liquor is pumped at 1.5m 3 / h into the aging tank, and use the PH online detector to interlock with the metering pump to slowly adjust the PH value to 11.5, and control the aging temperature at 85℃ by controlling the steam electric regulating valve, and age for 3h.

[0032] Separation and post-processing: The aged product is separated and washed by filtration, and then 3 30kg urea is added to the slurry, and after separation, drying and other subsequent processes, a pseudo-boehmite product with a crystallinity of more than 70% is obtained. The pore volume of the finished product is 0.35-0.5ml / g and the specific surface area is more than 250m 2 / g.

[0033] Example 3 (pulping with washing filtrate only)

[0034] Beating: The precursor filter cake is mixed with the washing filtrate, and the washing filtrate flow rate is controlled at 24m 3 / h, and the solid content of the slurry after beating is 70g / L.

[0035] Aging: Add 2.5ml of seed solution 3 / h, pH was adjusted to 12.2, and aging was carried out at 90℃ for 2 hours.

[0036] The process parameters of the remaining steps are the same as those in Example 1.

[0037] Example 4 (beating with hot water only)

[0038] Beating: The precursor filter cake is mixed with 85℃ evaporated condensed water, and the evaporation condensed water flow rate is controlled at 20m 3 / h, the solid content of the slurry after beating is 50g / L.

[0039] Aging: Add 2.5ml of seed solution 3 / h, pH was adjusted to 12.2, and aging was carried out at 90℃ for 2 hours.

[0040] The process parameters of the remaining steps are the same as those in Example 2.

[0041] Comparative Example (Traditional Process)

[0042] The precursor slurry was directly heated to 98°C and aged for 4 hours. The aged product was then subjected to filter press separation, washing, drying, and other subsequent processes to obtain the pseudo-boehmite product. The total water consumption was 32 tons per ton of product. Steam consumption was 1.7 times that of Example 1, and the finished product had a crystallinity of 68%.

[0043] Table 1 Water consumption, steam consumption and physicochemical properties of pseudo-boehmite prepared in various embodiments and comparative examples

[0044]

[0045] The above are preferred embodiments of the present invention. Any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A preparation method for reducing steam consumption of small-pore pseudo-boehmite, characterized in that: The following steps are involved: (1) Low-temperature gelation and filtration: Carbon dioxide gas is intermittently introduced into a sodium aluminate solution with an Al2O3 concentration of 40-45 g / L for carbonization decomposition. The decomposition endpoint temperature is controlled at 35-42°C and the reaction is carried out for 10-15 minutes to obtain a pseudo-boehmite precursor slurry, which is then filtered through a belt filter to obtain a precursor filter cake; (2) Mixing and beating with filtrate circulation: mixing and beating the precursor filter cake obtained in step (1) with at least one of the aging filtrate, the washing filtrate and hot water to obtain a mixed slurry with a solid content of 50 to 70 g / L; (3) Control and aging of the denominator: The mixed slurry obtained in step (2) is pumped into the aging tank at a temperature of 1.5 to 2.5 m 3 / h flow rate to add the seed solution, adjust the system pH to 11.5-12.5, and age at 85-89 ° C for 2-3h; (4) Separation and post-treatment: The aged product is separated and washed by filter pressing, and urea is added during the last washing to modify it. The product is then subjected to solid-liquid separation and drying to obtain the pseudo-boehmite product; The crystallinity of the pseudo-boehmite product is greater than 70%, and the pore volume of the γ-Al2O3 obtained after calcination at 600°C is 0.35-0.5 mL / g, and the specific surface area is greater than 250 m 2 / g.

2. The method according to claim 1, characterized in that The aged filtrate is the filtrate produced by filtration after pseudo-boehmite aging, wherein the concentration of Na2O is less than 12g / L, and the concentration of Na2O is less than 12g / L. k The concentration is 1 to 3 g / L; the washing filtrate is the filtrate produced by filter pressing after washing the pseudo-boehmite, wherein the Na2O concentration is less than 3 g / L, Na2O k Concentration <0.5g / L; the Na2O concentration is the Na2O converted from sodium carbonate c Concentration and Na2O converted from sodium hydroxide k Sum of concentrations.

3. The method according to claim 1 or 2, characterized in that The mixed flow ratio of the aging filtrate and the washing filtrate in step (2) is 0:1 to 5:

1.

4. The method according to claim 1, wherein In step (2), when the system is initially started, the hot water is the evaporated condensed water after heating in the main process of pseudo-boehmite preparation, and the temperature is ≥85°C.

5. The method according to claim 1, characterized in that The seed liquor in step (3) is the mother liquor produced by the seed decomposition of the sodium aluminate solution by the sintering process, with a caustic coefficient αk>3.5, Na2O k Concentration>90g / L.

6. The method according to claim 1, characterized in that The ratio of the amount of urea added in step (4) to the volume of the aged product slurry is 0.5 to 1 kg / m 3 .

7. The method according to any one of claims 1 to 6, characterized in that Na in the prepared pseudo-boehmite product + The impurity content is 0.16-0.22wt%.

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