Method for preparing spherical aluminum oxide by utilizing multiple emulsion gelling agents

Abstract

The invention discloses a method for preparing spherical aluminum oxide by using a multi-emulsion gelling agent, which comprises the following steps of: firstly preparing the gelling agent into the gelling agent in a multi-emulsion form, then adding pseudo-boehmite aluminum sol, mixing, and then preparing the mixture into the spherical aluminum oxide by adopting a hot oil column forming method. According to the method, the gelatinizing agent is treated in a two-time emulsification mode, that is, effective components of the gelatinizing agent are wrapped with the oil phase to inhibit release of the gelatinizing agent, and then the problem that the gelatinizing agent cannot be dissolved in the aluminum sol is solved through wrapping with the water phase, so that the operation time of the mixed pseudo-boehmite aluminum sol can be effectively prolonged, and the method is high in stability, low in cost and suitable for large-scale production.

Description

Technical Field

[0001] The present invention belongs to the technical field of inorganic material preparation, and relates to a method for preparing spherical alumina by using a multiple emulsion gelling agent. Specifically, it is a method for prolonging the operation time of preparing spherical alumina by the hot oil column forming method by pre-treating the gelling agent through secondary emulsification to reduce its release rate. Background Art

[0002] Due to the characteristics of good thermal stability, strong adsorption capacity, high surface activity, adjustable specific surface area, and controllable pore structure of alumina, it is widely used in different industrial fields such as catalyst carriers and adsorbents. Industrial applications have certain requirements for the morphology of alumina, and the commonly used shapes include spherical, cylindrical, strip-shaped, clover-shaped, etc. Among them, spherical alumina has a smooth surface, is easy to load and unload, facilitates the reaction and the flow of adsorbed gas, has a small pressure drop in the packed bed after loading, good wear resistance, is not easy to powder, and has strong adaptability, and can almost replace any other shaped catalyst or adsorbent. It is the most widely used shaped alumina in current industrial applications.

[0003] The forming methods of spherical alumina include spray drying method, rotary pelletizing method and oil column forming method. Among them, the oil column forming method is the most widely used forming method at present because of its high sphericity and strong controllability of the product. The general process of the hot oil column forming method is to react the precursor aluminum source with acid to form aluminum sol, then add a gelling agent for mixing and stirring to obtain a mixed solution with appropriate viscosity and solid content, and then drop it into a hot oil column to form balls and further age in an oil bath to improve its curing degree. Finally, spherical alumina carriers are obtained through washing, drying and calcination. At present, when the commonly used gelling agent is made into an aqueous solution and added to pseudo-boehmite aluminum sol, there are problems of too fast gelation of aluminum sol and too short process operable time, which cannot meet the requirements of continuous industrial preparation. Therefore, the industrial efficiency is not high and the economic benefit is poor. Therefore, it has become a feasible method to wrap the effective substances in the gelling agent to make them release slowly. Summary of the Invention

[0004] Aiming at the problems existing in the current hot oil column forming process of spherical alumina using pseudo-boehmite as raw material, the present invention provides a method for preparing spherical alumina by using a multiple emulsion gelling agent. This method prolongs the operable time of the hot oil column forming process using pseudo-boehmite as raw material through secondary emulsification modification of the gelling agent. Moreover, the method is easy to operate, has high stability, low cost, and is suitable for large-scale continuous production.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A method for preparing spherical alumina using a multiple emulsion gelling agent, which first adds a gelling agent solution to an oil phase for preliminary emulsification to form a W / O type emulsion gelling agent, then adds it to an aqueous phase for secondary emulsification to form a W / O / W type multiple emulsion gelling agent, and then mixes the obtained multiple emulsion gelling agent with pseudo-boehmite alumina sol and forms spherical alumina through a hot oil column forming method. It specifically includes the following steps: (1) Add a gelling agent to water, stir and dissolve it to prepare an aqueous gelling agent solution, then put it into a forming oil containing a lipophilic emulsifier for preliminary emulsification, and then add the obtained emulsion to an aqueous solution containing a hydrophilic emulsifier for secondary emulsification to obtain a multiple emulsion gelling agent; (2) Add water and acid to pseudo-boehmite, mix to form a suspension, and obtain alumina sol through mechanical grinding; (3) Add the multiple emulsion gelling agent prepared in step (1) to the alumina sol obtained in step (2), stir and mix evenly, then drop the mixed solution into a hot oil column through an injection pump to form gel beads, and then obtain spherical alumina through aging, washing, drying, and calcination.

[0006] Further, the gelling agent in step (1) is one or more of hexamethylenetetramine, ethylenediamine, urea, ammonium carbonate, ammonium bicarbonate, and tetramethylammonium hydroxide.

[0007] Further, the lipophilic emulsifier in step (1) is one or more of Span 80, Span 85, and polyisobutylene succinimide.

[0008] Further, the forming oil in step (1) is one or more of vacuum pump oil, lubricating oil, edible oil, and turbine oil. Further, the hydrophilic emulsifier in step (1) is one or more of Tween80, Tween20, and PEG-100 stearate.

[0009] Further, the concentration of the aqueous gelling agent solution in step (1) is 20 wt.% - 35 wt.%.

[0010] Further, the content of the lipophilic emulsifier in the forming oil containing the lipophilic emulsifier in step (1) is 3 wt.% - 10 wt.%.

[0011] Further, the preliminary emulsification in step (1) is carried out by stirring and emulsifying at a speed of 800 rpm - 1200 rpm for 40 min - 60 min.

[0012] Further, the oil-water ratio of the emulsion obtained after preliminary emulsification in step (1) is 2 / 5 - 10 / 5.

[0013] Furthermore, the content of the hydrophilic emulsifier in the aqueous solution containing the hydrophilic emulsifier in step (1) is 2 wt.% to 9 wt.%.

[0014] Furthermore, in step (1), the secondary emulsification is carried out by stirring and emulsifying at a rotation speed of 400 rpm to 800 rpm for 20 min to 30 min.

[0015] Furthermore, the water-to-oil ratio of the multiple emulsion gelling agent obtained in step (1) is 1 / 3 to 2 / 1.

[0016] Furthermore, the acid in step (2) is one or more of nitric acid, hydrochloric acid, sulfuric acid, acetic acid, and citric acid.

[0017] Furthermore, the mass ratio of the acid to water added in step (2) is 1:50 to 1:150.

[0018] Furthermore, the solid content of the suspension obtained in step (2) is 10 wt.% to 30 wt.%, where the molar ratio of H + / Al2O3 is 0.03 to 0.10.

[0019] Furthermore, the dosage of the multiple emulsion gelling agent in step (3) is converted according to the molar ratio of the gelling agent contained therein to Al2O3 in the aluminum sol being 0.01 to 0.1.

[0020] Furthermore, the temperature of the hot oil column in step (3) is 60 °C to 140 °C, and the height of the oil column is 1 m to 2.5 m.

[0021] Furthermore, the temperature of the aging in step (3) is 100 °C to 200 °C, and the time is 2 h to 24 h.

[0022] Furthermore, the temperature of the drying in step (3) is 40 °C to 120 °C, and the time is 6 h to 24 h.

[0023] Furthermore, the temperature of the calcination in step (3) is 500 °C to 1200 °C, and the time is 2 h to 8 h.

[0024] By carrying out secondary emulsification modification and encapsulation on the gelling agent, the present invention can reduce the ammonia release rate. After mixing it with the pseudo-boehmite aluminum sol, the solidification rate of the mixed solution is reduced, thereby extending the operation time.

[0025] The remarkable advantages of the present invention are as follows: (1) The present invention uses a forming oil as the oil phase to modify the gelling agent by emulsion, encapsulating the active ingredients in the gelling agent, and then using deionized water as the water phase to perform secondary emulsification modification on the emulsion, enabling the gelling agent in the form of multiple emulsions to be well dispersed in the aluminum sol, while reducing the release rate of ammonia and solving the problems of too fast solidification of the mixed liquid and too short operable time in the preparation of spherical alumina carriers by the hot oil column forming process using pseudo-boehmite as the raw material.

[0026] (2) The method of the present invention is easy to operate, has high stability and low cost, and is suitable for large-scale production. Description of the Drawings

[0027] Figure 1 Curves of the viscosity of the gels prepared in Comparative Examples 1 and 2 and Examples 1 - 3 varying with time. Specific Embodiments

[0028] A method for preparing spherical alumina using a multiple emulsion as the gelling agent, which includes the following steps: (1) Add a lipophilic emulsifier to the forming oil and mechanically stir and mix for 5 min to 10 min to prepare an oil phase with an emulsifier content of 3 wt.% to 10 wt.%. (2) Stir the oil phase at a speed of 400 rpm to 500 rpm, and simultaneously add an aqueous solution of the gelling agent with a concentration of 20 wt.% to 35 wt.% to prepare a suspension with an oil-water ratio of 2 / 5 to 10 / 5, and then stir at a speed of 800 rpm to 1200 rpm for 40 min to 60 min to prepare an emulsion. (3) Add a hydrophilic emulsifier to deionized water and mechanically stir and mix for 5 min to 10 min to prepare a water phase with an emulsifier content of 2 wt.% to 9 wt.%. (4) Stir the water phase at a speed of 400 rpm to 500 rpm, and simultaneously add the emulsion obtained in step (2) to prepare a suspension with a water-in-oil emulsion water-oil ratio of 1 / 3 to 2 / 1, and then stir at a speed of 400 rpm to 800 rpm for 20 min to 30 min to prepare a multiple emulsion gelling agent. (5) Add an acid and water with a mass ratio of 1:50 to 1:150 to pseudo-boehmite, mix to prepare a suspension with a solid content of 10 wt.% to 30 wt.% and an H + / Al2O3 molar ratio of 0.03 to 0.10, and then obtain an aluminum sol through mechanical grinding. (6) With the molar ratio of gelling agent / Al2O3 being 0.01 - 0.1, add the multiple emulsion gelling agent prepared in step (4) to the aluminum sol obtained in step (5). After stirring and mixing evenly, drop the mixture into a hot oil column at 60 °C - 140 °C (the height of the oil column is 1 m - 2.5 m) through an injection pump to form gel beads. Then age at 100 °C - 200 °C for 2 h - 24 h, wash, dry at 40 °C - 120 °C for 6 h - 24 h, and calcine at 500 °C - 1200 °C in an air atmosphere for 2 h - 8 h to obtain high pore volume spherical alumina.

[0029] Among them, the forming oil used in step (1) is one or more of vacuum pump oil, lubricating oil, edible oil, and turbine oil; the lipophilic emulsifier used is one or more of Span 80, Span 85, and polyisobutylene succinimide.

[0030] The gelling agent used in step (2) is one or more of hexamethylenetetramine, ethylenediamine, urea, ammonium carbonate, ammonium bicarbonate, and tetramethylammonium hydroxide.

[0031] The hydrophilic emulsifier used in step (3) is one or more of Tween80, Tween20, and PEG - 100 stearate.

[0032] The acid used in step (5) is one or more of nitric acid, hydrochloric acid, sulfuric acid, acetic acid, and citric acid.

[0033] To make the content of the present invention easier to understand, the technical solutions of the present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0034] The properties of the commercial pseudo - boehmite used are as follows: Specific surface area: 210 ± 20 m 2 / g; Pore volume: 0.8 ± 0.05 cm 3 / g; Average pore diameter: 21 ± 1 nm; Alumina content: 73% Peptization index: 84 ± 1%.

[0035] Measurement method Viscosity of the mixture: Use an HR20 type rotational rheometer. Weigh 10 g of the pseudo - boehmite sample to be tested and transfer it to a 50 ml beaker. Add a certain amount of water and acid, and configure it into a pseudo - boehmite sol through mechanical stirring (it is necessary to ensure that the samples have the same solid content after adding the gelling agent). Add the gelling agent to the pseudo - boehmite sol and stir for 30 s to obtain a mixture. Transfer 2 ml of the mixture to the test bench of the rotational rheometer for viscosity testing.

[0036] Sphericity and particle size: Using a CAMSIZER X2 dynamic image method particle size and shape analyzer, 100 g of the sample was poured into the test bench for testing.

[0037] Specific surface area: Tested using an ASAP 2460 automatic sorptometer (produced by Micromeritics, USA). Weighed about 0.25 g of the sample, after pretreatment, the N2 adsorption - desorption curve was measured and obtained. The BET method was used to calculate the specific surface area of the tested sample, the single - point method was used to calculate the pore volume of the sample, and the BJH method was used to calculate the pore diameter of the sample.

[0038] Comparative Example 1: Preparation of alumina sol: 50 g of commercial pseudo - boehmite powder was placed in a beaker, added 126.91 g of deionized water and stirred for 30 min for pulping, then added 7 g of nitric acid solution with a mass concentration of 20 wt.%, and mixed to obtain a suspension with a solid content of 20 wt.% and an H + / Al2O3 molar ratio of 0.062. Stirred for 2 h to prepare alumina sol, and the viscosity - time change curve was plotted in Figure 1 .

[0039] Comparative Example 2: (1) Preparation of alumina sol: 50 g of commercial pseudo - boehmite powder was placed in a beaker, added 120.55 g of deionized water and stirred for 30 min for pulping, then added 7 g of nitric acid solution with a mass concentration of 20 wt.%, stirred for 2 h to prepare alumina sol, and then dropped 9.78 g of hexamethylenetetramine aqueous solution with a mass concentration of 35 wt.%, and mixed to obtain a mixture with a solid content of 20 wt.% and an H + / Al2O3 molar ratio of 0.062. Continued to stir to further gel it, and the viscosity - time change curve was plotted in Figure 1 .

[0040] (2) Shaping: Using a sleeve to heat the hot oil column, the height of the oil column was 180 cm, the temperature of the oil column was 100 °C, and a hot oil circulation pump was used for hot oil filling. After the hot oil filling was completed, an injection pump equipped with a 0.5 - mm inner diameter needle was used to drop the sol prepared in step (1) into the shaping column; the dropping speed of the balls was 2.5 g / min (calculated based on the mass of the raw material powder).

[0041] (3) Post-treatment: Drain the hot oil in the oil column, place the formed gel particles in the original container for aging at an aging temperature of 120 °C and an aging time of 12 h. After aging, transfer them to a crucible, rinse with petroleum ether 2 - 3 times, then place in an oven for drying at a drying temperature of 60 °C and a drying time of 14 h. After drying, transfer the sample to a muffle furnace for calcination at a calcination temperature of 500 °C, a calcination time of 4 h, and a calcination atmosphere of air. After calcination, cool to room temperature to obtain spherical alumina products.

[0042] Example 1: (1) Gelatinizer emulsification treatment: Take 10 g of gelatinizer solution (35 wt.% hexamethylenetetramine aqueous solution), add it to 6 g of vacuum pump oil (containing 0.25 g of lipophilic emulsifier) and emulsify for 45 min, then add it to 5.33 g of water (containing 0.16 g of hydrophilic emulsifier) for secondary emulsification for 25 min to obtain a hexamethylenetetramine multiple emulsion.

[0043] (2) Preparation of alumina sol: Place 50 g of commercial pseudo-boehmite powder in a beaker, add 115.5 g of deionized water and stir for 30 min for pulping, then add 7 g of nitric acid solution with a mass concentration of 20 wt.%, stir for 2 h to prepare alumina sol, and then drop in 20.86 g of the prepared hexamethylenetetramine multiple emulsion, mix to obtain a mixture with a solid content of 20 wt.% and an H + / A2O3 molar ratio of 0.062, continue to stir to further gel it, and the viscosity-time change curve is plotted in Figure 1 .

[0044] (3) Molding: Heat the hot oil column using a sleeve, with the height of the oil column being 180 cm and the oil column temperature being 100 °C. Use a hot oil circulation pump for hot oil filling. After the hot oil filling is completed, use a syringe pump equipped with a 0.5 mm inner diameter needle to drop the sol prepared in step (2) into the molding column; the dropping speed of the balls is 2.5 g / min (calculated based on the mass of the raw material powder).

[0045] (4) Post-treatment: Drain the hot oil in the oil column, place the formed gel particles in the original container for aging at an aging temperature of 120 °C and an aging time of 12 h. After aging, transfer them to a crucible, rinse with petroleum ether 2 - 3 times, then place in an oven for drying at a drying temperature of 60 °C and a drying time of 14 h. After drying, transfer the sample to a muffle furnace for calcination at a calcination temperature of 500 °C, a calcination time of 4 h, and a calcination atmosphere of air. After calcination, cool to room temperature to obtain spherical alumina products.

[0046] Example 2: (1) Emulsification treatment of gelling agent: Take 10 g of gelling agent solution (35 wt.% hexamethylenetetramine aqueous solution), add it to 9.40 g of vacuum pump oil (containing 0.6 g of lipophilic emulsifier) and emulsify for 45 min, then add it to 6.33 g of water (containing 0.33 g of hydrophilic emulsifier) for secondary emulsification for 25 min to obtain a hexamethylenetetramine multiple emulsion.

[0047] (2) Preparation of alumina sol: Place 50 g of commercial pseudo-boehmite powder in a beaker, add 114.36 g of deionized water and stir for 30 min to slurry, then add 7 g of nitric acid solution with a mass concentration of 20 wt.%, stir for 2 h to prepare alumina sol, and then drop in 26.08 g of the prepared hexamethylenetetramine multiple emulsion, mix to obtain a mixed solution with a solid content of 20 wt.% and an H + / Al2O3 molar ratio of 0.062, continue to stir to further gel it, and the viscosity-time change curve is plotted in Figure 1 .

[0048] (4) Shaping: Use a sleeve to heat the hot oil column, the height of the oil column is 180 cm, the temperature of the oil column is 100 °C, use a hot oil circulation pump to fill the hot oil, and after the hot oil filling is completed, use a syringe pump equipped with a 0.5 mm inner diameter needle to drop the sol prepared in step (3) into the shaping column; the dropping speed of the balls is 2.5 g / min (calculated based on the mass of the raw material powder).

[0049] (5) Post-treatment: Drain the hot oil in the oil column, place the shaped gel particles in the original container for aging, the aging temperature is 120 °C, and the aging time is 12 h. After aging, transfer to a crucible, rinse with petroleum ether 2 - 3 times, then place in an oven for drying, the drying temperature is 60 °C, and the drying time is 14 h. After drying, transfer the sample to a muffle furnace for calcination, the calcination temperature is 500 °C, the calcination time is 4 h, the calcination atmosphere is air, and after calcination, cool to room temperature to obtain spherical alumina products.

[0050] Example 3: (1) Emulsification treatment of gelling agent: Take 10 g of gelling agent solution (35 wt.% hexamethylenetetramine aqueous solution), add it to 16.56 g of vacuum pump oil (containing 1.44 g of lipophilic emulsifier) and emulsify for 45 min, then add it to 8.87 g of water (containing 0.47 g of hydrophilic emulsifier) for secondary emulsification for 25 min to obtain a hexamethylenetetramine multiple emulsion.

[0051] (2) Preparation of alumina sol: Place 50 g of commercial pseudo-boehmite powder into a beaker, add 111.87 g of deionized water, stir for 30 min for pulping, then add 7 g of nitric acid solution with a mass concentration of 20 wt.%, stir for 2 h to obtain alumina sol, and then drop in 36.5 g of the prepared hexamethylenetetramine multiple emulsion. Mix to obtain a mixture with a solid content of 20 wt.% and an H + / Al2O3 molar ratio of 0.062. Continue stirring to further gel it. The viscosity-time curve is plotted in Figure 1 .

[0052] (4) Shaping: Use a sleeve to heat the hot oil column. The height of the oil column is 180 cm and the temperature of the oil column is 100 °C. Use a hot oil circulation pump to fill the hot oil. After the hot oil filling is completed, use a syringe pump equipped with a needle with an inner diameter of 0.5 mm to drop the sol prepared in step (3) into the shaping column; the dropping speed of the balls is 2.5 g / min (calculated based on the mass of the raw material powder).

[0053] (5) Post-treatment: Drain the hot oil in the oil column. Place the shaped gel particles in the original container for aging. The aging temperature is 120 °C and the aging time is 12 h. After aging, transfer them to a crucible, rinse with petroleum ether 2 - 3 times, and then place them in an oven for drying. The drying temperature is 60 °C and the drying time is 14 h. After drying, transfer the sample to a muffle furnace for calcination. The calcination temperature is 500 °C, the calcination time is 4 h, the calcination atmosphere is air. After calcination, cool to room temperature to obtain spherical alumina products.

[0054] Example 4: (1) Emulsification treatment of the gelling agent: Take 10 g of the gelling agent solution (35 wt.% hexamethylenetetramine aqueous solution), add it to 16.56 g of vacuum pump oil (containing 1.44 g of lipophilic emulsifier) and emulsify for 45 min, then add it to 8.87 g of water (containing 0.47 g of hydrophilic emulsifier) for secondary emulsification for 25 min to obtain a hexamethylenetetramine multiple emulsion.

[0055] (2) Preparation of alumina sol: Place 50 g of commercial pseudo-boehmite powder into a beaker, add 111.87 g of deionized water, stir for 30 min for pulping, then add 7 g of nitric acid solution with a mass concentration of 20 wt.%, stir for 2 h to obtain alumina sol, and then drop in 36.5 g of the prepared hexamethylenetetramine multiple emulsion. Mix to obtain a mixture with a solid content of 20 wt.% and an H + / Al2O3 molar ratio of 0.062. Continue stirring to further gel it.

[0056] (4)Forming: Use a sleeve to heat a hot oil column. The height of the oil column is 180 cm, and the temperature of the oil column is 100 °C. Use a hot oil circulation pump to fill the hot oil. After the hot oil filling is completed, use a syringe pump equipped with a 0.5 mm inner diameter needle to drop the sol prepared in step (3) into the forming column; the dropping speed of the droplets is 2.5 g / min (calculated based on the mass of the raw material powder).

[0057] (5)Post-treatment: Keep the height of the hot oil in the oil column and maintain the hot oil temperature through the jacket. The formed gel particles are placed in the original container for pressure aging. The aging temperature is 120 °C, and the aging time is 12 h. After aging, transfer them to a crucible, rinse with petroleum ether 2 - 3 times, and then place them in an oven for drying. The drying temperature is 60 °C, and the drying time is 14 h. After drying, transfer the sample to a muffle furnace for calcination. The calcination temperature is 500 °C, the calcination time is 4 h, the calcination atmosphere is air. After calcination, cool to room temperature to obtain spherical alumina products.

[0058] Example 5: (1)Emulsification treatment of gelling agent: Take 10 g of gelling agent solution (35 wt.% hexamethylenetetramine aqueous solution), add it to 16.56 g of vacuum pump oil (containing 1.44 g of lipophilic emulsifier) and emulsify for 45 min, then add it to 8.87 g of water (containing 0.47 g of hydrophilic emulsifier) for secondary emulsification for 25 min to obtain a hexamethylenetetramine multiple emulsion.

[0059] (2)Preparation of alumina sol: Place 50 g of commercial pseudo-boehmite powder in a beaker, add 111.87 g of deionized water and stir for 30 min to make a slurry, then add 7 g of nitric acid solution with a mass concentration of 20 wt.%, stir for 2 h to prepare an alumina sol, and then drop 36.5 g of the prepared hexamethylenetetramine multiple emulsion, mix to obtain a mixture with a solid content of 20 wt.% and an H + / Al2O3 molar ratio of 0.062, and continue to stir to make it further gel.

[0060] (4)Forming: Use a sleeve to heat a hot oil column. The height of the oil column is 180 cm, and the temperature of the oil column is 100 °C. Use a hot oil circulation pump to fill the hot oil. After the hot oil filling is completed, use a syringe pump equipped with a 0.5 mm inner diameter needle to drop the sol prepared in step (3) into the forming column; the dropping speed of the droplets is 2.5 g / min (calculated based on the mass of the raw material powder).

[0061] (5) Post-treatment: The formed gel particles are placed in a hydrothermal autoclave and hot oil is added to a height of 2 / 3 of the hydrothermal autoclave. The gel particles are aged in the hydrothermal autoclave at an aging temperature of 120 °C for 12 h. After aging, they are transferred to a crucible, rinsed 2 - 3 times with petroleum ether, and then placed in an oven for drying at a drying temperature of 60 °C for 14 h. After drying, the sample is transferred to a muffle furnace for calcination at a calcination temperature of 500 °C for 4 h in an air atmosphere. After calcination, it is cooled to room temperature to obtain spherical alumina products.

[0062] Example 6: (1) Gelatinizer emulsification treatment: Take 10 g of gelatinizer solution (35 wt.% hexamethylenetetramine aqueous solution), add it to 16.56 g of vacuum pump oil (containing 1.44 g of lipophilic emulsifier) and emulsify for 45 min. Then add it to 8.87 g of water (containing 0.47 g of hydrophilic emulsifier) for secondary emulsification for 25 min to obtain a hexamethylenetetramine multiple emulsion.

[0063] (2) Preparation of alumina sol: Place 50 g of commercial pseudo-boehmite powder in a beaker, add 111.87 g of deionized water and stir for 30 min for pulping. Then add 7 g of nitric acid solution with a mass concentration of 20 wt.%. After stirring for 2 h to prepare the alumina sol, 36.5 g of the prepared hexamethylenetetramine multiple emulsion is dropped in, and a mixture with a solid content of 20 wt.% and an H + / Al₂O₃ molar ratio of 0.062 is obtained, and stirring is continued to further gel it.

[0064] (4) Shaping: A hot oil column is heated by a sleeve, the height of the oil column is 180 cm, and the temperature of the oil column is 100 °C. A hot oil circulation pump is used for hot oil filling. After the hot oil filling is completed, the sol prepared in step (3) is dropped into the shaping column using a syringe pump equipped with a needle with an inner diameter of 0.5 mm; the dropping speed of the balls is 2.5 g / min (calculated based on the mass of the raw material powder).

[0065] (5) Post-treatment: The formed gel particles are aged in 10 wt.% ammonia water for 12 h. After aging, they are transferred to a crucible, rinsed 2 - 3 times with petroleum ether, and then placed in an oven for drying at a drying temperature of 60 °C for 14 h. After drying, the sample is transferred to a muffle furnace for calcination at a calcination temperature of 500 °C for 4 h in an air atmosphere. After calcination, it is cooled to room temperature to obtain spherical alumina products.

[0066] Example 7: (1)Emulsification treatment of gelling agent: Take 10 g of gelling agent solution (35 wt.% hexamethylenetetramine aqueous solution), add it to 16.56 g of vacuum pump oil (containing 1.44 g of lipophilic emulsifier) and emulsify for 45 min. Then add it to 8.87 g of water (containing 0.47 g of hydrophilic emulsifier) for secondary emulsification for 25 min to obtain a hexamethylenetetramine multiple emulsion.

[0067] (2)Preparation of alumina sol: Place 50 g of commercial pseudo-boehmite powder into a beaker, add 111.87 g of deionized water and stir for 30 min for pulping. Then add 7 g of nitric acid solution with a mass concentration of 20 wt.%, stir for 2 h to prepare alumina sol, and then drop 36.5 g of the prepared hexamethylenetetramine multiple emulsion into it, and mix to obtain a mixture with a solid content of 20 wt.% and an H + / Al2O3 molar ratio of 0.062, and continue to stir to further gel it.

[0068] (4)Forming: Use a sleeve to heat the hot oil column, the height of the oil column is 180 cm, the temperature of the oil column is 100 °C, use a hot oil circulation pump to fill the hot oil. After the hot oil filling is completed, use a syringe pump equipped with a needle with an inner diameter of 0.5 mm to drop the sol prepared in step (3) into the forming column; the dropping speed of the balls is 2.5 g / min (calculated based on the mass of the raw material powder).

[0069] (5)Post-treatment: Drain the hot oil in the oil column, place the formed gel particles in the original container for aging, the aging temperature is 120 °C, and the aging time is 3 h. After aging, transfer it to a crucible, rinse it with petroleum ether 2 - 3 times, and then place it in an oven for drying, the drying temperature is 60 °C, and the drying time is 14 h. After drying, transfer the sample to a muffle furnace for calcination, the calcination temperature is 500 °C, the calcination time is 4 h, the calcination atmosphere is air, and after calcination, cool it to room temperature to obtain spherical alumina products.

[0070] Example 8: (1)Emulsification treatment of gelling agent: Take 10 g of gelling agent solution (35 wt.% hexamethylenetetramine aqueous solution), add it to 16.56 g of vacuum pump oil (containing 1.44 g of lipophilic emulsifier) and emulsify for 45 min. Then add it to 8.87 g of water (containing 0.47 g of hydrophilic emulsifier) for secondary emulsification for 25 min to obtain a hexamethylenetetramine multiple emulsion.

[0071] (2) Preparation of alumina sol: Place 50 g of commercial pseudo-boehmite powder into a beaker, add 111.87 g of deionized water, stir for 30 min to slurry, then add 7 g of nitric acid solution with a mass concentration of 20 wt.%, stir for 2 h to obtain alumina sol, and then drop in 36.5 g of the prepared hexamethylenetetramine multiple emulsion. Mix to obtain a mixed solution with a solid content of 20 wt.% and an H + / Al2O3 molar ratio of 0.062, and continue stirring to further gel it.

[0072] (4) Shaping: Use a sleeve to heat the hot oil column. The height of the oil column is 180 cm, and the temperature of the oil column is 100 °C. Use a hot oil circulation pump to fill the hot oil. After the hot oil filling is completed, use a syringe pump equipped with a 0.5 mm inner diameter needle to drop the sol prepared in step (3) into the shaping column; the dropping speed of the balls is 2.5 g / min (calculated based on the mass of the raw material powder).

[0073] (5) Post-treatment: Drain the hot oil in the oil column, place the shaped gel particles in the original container for aging. The aging temperature is 120 °C, and the aging time is 7 h. After aging, transfer to a crucible, rinse with petroleum ether 2 - 3 times, and then place in an oven for drying. The drying temperature is 60 °C, and the drying time is 14 h. After drying, transfer the sample to a muffle furnace for calcination. The calcination temperature is 500 °C, the calcination time is 4 h, the calcination atmosphere is air, and after calcination, cool to room temperature to obtain spherical alumina products.

[0074] Example 9: (1) Emulsification treatment of gelling agent: Take 10 g of gelling agent solution (35 wt.% hexamethylenetetramine aqueous solution), add it to 16.56 g of vacuum pump oil (containing 1.44 g of lipophilic emulsifier) and emulsify for 45 min, then add it to 8.87 g of water (containing 0.47 g of hydrophilic emulsifier) for secondary emulsification for 25 min to obtain hexamethylenetetramine multiple emulsion.

[0075] (2) Preparation of alumina sol: Place 50 g of commercial pseudo-boehmite powder into a beaker, add 111.87 g of deionized water, stir for 30 min to slurry, then add 7 g of nitric acid solution with a mass concentration of 20 wt.%, stir for 2 h to obtain alumina sol, and then drop in 36.5 g of the prepared hexamethylenetetramine multiple emulsion. Mix to obtain a mixed solution with a solid content of 20 wt.% and an H + / Al2O3 molar ratio of 0.062, and continue stirring to further gel it.

[0076] (4) Shaping: A hot oil column is heated using a sleeve, with the height of the oil column being 180 cm and the temperature of the oil column being 100 °C. A hot oil circulation pump is used for hot oil filling. After the hot oil filling is completed, a syringe pump equipped with a needle with an inner diameter of 0.5 mm is used to drop the sol prepared in step (3) into the shaping column; the dropping speed of the spheres is 2.5 g / min (calculated based on the mass of the raw material powder).

[0077] (5) Post-treatment: The hot oil in the oil column is drained, and the formed gel particles are placed in the original container for aging. The aging temperature is 100 °C, and the aging time is 7 h. After aging is completed, they are transferred to a crucible, rinsed 2 - 3 times with petroleum ether, and then placed in an oven for drying. The drying temperature is 60 °C, and the drying time is 14 h. After drying is completed, the sample is transferred to a muffle furnace for calcination. The calcination temperature is 500 °C, the calcination time is 4 h, the calcination atmosphere is air, and after calcination is completed, it is cooled to room temperature to obtain spherical alumina products.

[0078] Example 10: (1) Emulsification treatment of the gelling agent: Take 10 g of the gelling agent solution (35 wt.% hexamethylenetetramine aqueous solution), add it to 16.56 g of vacuum pump oil (containing 1.44 g of lipophilic emulsifier) for emulsification for 45 min, and then add it to 8.87 g of water (containing 0.47 g of hydrophilic emulsifier) for secondary emulsification for 25 min to obtain a hexamethylenetetramine multiple emulsion.

[0079] (2) Preparation of alumina sol: Place 50 g of commercial pseudo-boehmite powder into a beaker, add 111.87 g of deionized water and stir for 30 min for pulping, then add 7 g of a nitric acid solution with a mass concentration of 20 wt.%, stir for 2 h to prepare the alumina sol, and then drop in 36.5 g of the prepared hexamethylenetetramine multiple emulsion. Mix to obtain a mixture with a solid content of 20 wt.% and an H + / Al2O3 molar ratio of 0.062, and continue to stir to further gel it.

[0080] (4) Shaping: A hot oil column is heated using a sleeve, with the height of the oil column being 180 cm and the temperature of the oil column being 100 °C. A hot oil circulation pump is used for hot oil filling. After the hot oil filling is completed, a syringe pump equipped with a needle with an inner diameter of 0.5 mm is used to drop the sol prepared in step (3) into the shaping column; the dropping speed of the spheres is 2.5 g / min (calculated based on the mass of the raw material powder).

[0081] (5) Post-treatment: Drain the hot oil in the oil column, place the formed gel particles in the original container for aging, the aging temperature is 110 °C, and the aging time is 7 h. After aging, transfer them to a crucible, rinse with petroleum ether 2 - 3 times, and then place them in an oven for drying, the drying temperature is 60 °C, and the drying time is 14 h. After drying, transfer the sample to a muffle furnace for calcination, the calcination temperature is 500 °C, the calcination time is 4 h, the calcination atmosphere is air, and after calcination, cool it to room temperature to obtain spherical alumina products.

[0082] Figure 1 Curves of the viscosity of the gels prepared in Comparative Examples 1 and 2 and Examples 1 - 3 versus time are shown. It can be seen from the comparison in the figure that the alumina sol prepared without adding hexamethylenetetramine can maintain a relatively low viscosity for a long time (Comparative Example 1), while the alumina sol prepared by adding hexamethylenetetramine solution will not be able to drip smoothly from the syringe pump due to excessive viscosity around 250 s. By subjecting the hexamethylenetetramine solution to multiple emulsion treatment, the hexamethylenetetramine solution can be slowly released, and at the same time, the problem that the oil phase cannot be dispersed in the alumina sol is solved, so that the mixture can maintain a relatively low viscosity for a long time, and the operable time for hot oil column forming after mixing the aluminum sol and the gelling agent is increased. At the same time, the slow release effects of multiple emulsions prepared with different ratios on hexamethylenetetramine are different, and the slow release effect of Example 3 is the most significant.

[0083] The physical property parameters of the obtained spherical alumina products in the examples and comparative examples are shown in Table 1.

[0084] Table 1 Properties of the finished spherical alumina

[0085] In Table 1, by comparing Examples 1 - 3, it can be seen that the sphericity of the alumina particles prepared by hot oil column forming with the emulsion ratios of Examples 1 and 2 is poor; while the emulsion ratio of Example 3 can keep the obtained alumina particles with good sphericity while wrapping the gelling agent.

[0086] It can be seen from the comparison between Example 3 and Examples 4 - 6 that different gel particle aging methods have a certain impact on the sphericity of the product. The sphericity of the spherical alumina obtained by pressure aging and direct aging is not much different, while hydrothermal autoclave aging and ammonia aging will have a greater impact on the sphericity because the incompletely determined gel particles need to be transferred.

[0087] It can be seen from the comparison between Example 3 and Examples 7 and 8 that reducing the aging time can significantly improve the sphericity of alumina, and the sphericity of alumina obtained when the aging time is 7 h is the best; and it can be known from the comparison between Example 8 and Examples 9 and 10 that reducing the aging temperature can improve the sphericity of spherical alumina, so aging at 110 °C for 7 h is the best.

[0088] The above are only the preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims

1. A method for preparing spherical alumina using a multiple emulsion gelling agent, characterized in that: The gelling agent solution is first added to the oil phase for preliminary emulsification to prepare a W / O type emulsion gelling agent, and then added to the water phase for secondary emulsification to prepare a W / O / W type multiple emulsion gelling agent, which is then mixed with pseudo-boehmite aluminum sol and prepared into spherical alumina through a hot oil column molding method.

2. The method for preparing spherical alumina using a multiple emulsion gelling agent according to claim 1, characterized in that: The following steps are involved: (1) adding a gelling agent into water and stirring to dissolve the gelling agent aqueous solution, then placing the gelling agent into a forming oil containing a lipophilic emulsifier for primary emulsification, and then adding the obtained emulsion into an aqueous solution containing a hydrophilic emulsifier for secondary emulsification to obtain a multiple emulsion gelling agent; (2) adding water and acid to pseudo-boehmite, mixing to form a suspension, and then mechanically grinding to obtain aluminum sol; (3) Add the multiple emulsion gelling agent prepared in step (1) to the aluminum sol obtained in step (2), stir and mix, and then drip the mixture into the hot oil column through an injection pump to form gel beads, which are then aged, washed, dried and calcined to obtain spherical alumina.

3. The method for preparing spherical alumina using a multiple emulsion gelling agent according to claim 2, characterized in that: The gelling agent in step (1) is one or more of hexamethylenetetramine, ethylenediamine, urea, ammonium carbonate, ammonium bicarbonate, and tetramethylammonium hydroxide; the lipophilic emulsifier is one or more of Span 80, Span 85, and polyisobutylene succinimide; the molding oil is one or more of vacuum pump oil, lubricating oil, edible oil, and turbine oil; and the hydrophilic emulsifier is one or more of Tween80, Tween20, and PEG-100 stearate.

4. The method for preparing spherical alumina using a multiple emulsion gelling agent according to claim 2, characterized in that: The concentration of the aqueous solution of the gelling agent in step (1) is 20 wt.%~35 wt.%; the content of the lipophilic emulsifier in the molding oil containing the lipophilic emulsifier is 3 wt.%~10 wt.%; the preliminary emulsification is carried out by stirring and emulsifying at a speed of 800 rpm~1200 rpm for 40 min~60 min; the oil-water ratio of the emulsion obtained after the preliminary emulsification is 2 / 5~10 / 5; the content of the hydrophilic emulsifier in the aqueous solution containing the hydrophilic emulsifier is 2 wt.%~9 wt.%; the secondary emulsification is carried out by stirring and emulsifying at a speed of 400 rpm~800 rpm for 20 min~30 min; the water-to-emulsion ratio of the obtained multiple emulsion gelling agent is 1 / 3~2 / 1.

5. The method for preparing spherical alumina using a multiple emulsion gelling agent according to claim 2, characterized in that: The mass ratio of the acid and water added in step (2) is 1:50 to 1:150; wherein the acid is one or more of nitric acid, hydrochloric acid, sulfuric acid, acetic acid, and citric acid.

6. The method for preparing spherical alumina using a multiple emulsion gelling agent according to claim 2, characterized in that: The solid content of the suspension obtained in step (2) is 10 wt.% to 30 wt.%, wherein H + The molar ratio of / Al2O3 is 0.03~0.

10.

7. The method for preparing spherical alumina using a multiple emulsion gelling agent according to claim 2, characterized in that: The amount of the multiple emulsion gelling agent used in step (3) is calculated based on a molar ratio of the gelling agent contained therein to Al2O3 in the aluminum sol of 0.01-0.

1.

8. The method for preparing spherical alumina using a multiple emulsion gelling agent according to claim 2, characterized in that: The temperature of the hot oil column in step (3) is 60°C to 140°C.

9. The method for preparing spherical alumina using a multiple emulsion gelling agent according to claim 2, characterized in that: The aging temperature in step (3) is 100°C to 200°C, and the aging time is 2 h to 24 h.

10. The method for preparing spherical alumina using a multiple emulsion gelling agent according to claim 2, characterized in that: The calcination temperature in step (3) is 500°C to 1200°C, and the calcination time is 2 h to 8 h.

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