KR100267722B1 - Process for the preparation of gamma-alumina - Google Patents

Abstract

PURPOSE: A method for preparing a gamma-alumina is provided which controls the particle characteristics of gamma-alumina by controlling the aging time and temperature of intermediate product of boehmite. CONSTITUTION: A method for preparing a gamma-alumina comprises the following steps of: (i) hydrolyzing aluminum isopropoxide; (ii) polycondensing the product of the step (i); and (iii) aging, peptizing, drying and heat-treating the reaction product of the step (ii). Wherein, the polycondensed reaction product of boehmite(gamma-AlO(OH)) is aged at a temperature of more than 82.4 deg.C for more than 16 hours.

Description

Method for preparing gamma-alumina

Ceramic membranes are widely used as carriers and adsorbents for catalysts compared to organic membranes. They have fine pores and excellent properties such as heat resistance at high temperatures, chemical resistance, mechanical strength and fast permeation rate. It is expanding. Despite these advantages, ceramic membranes have not been widely used compared to organic polymer membranes due to high manufacturing cost and difficulty in controlling the microstructure of the membrane.

Conventional alumina synthesis has a powder synthesis method and anodization method, but the powder synthesis method has difficulty in controlling the characteristics of the microstructure, and the anodization method has not been actively used industrially due to incompatibility of mass production. However, with the recent availability of low temperature and liquid sol-gel methods, it has become easy to manufacture ceramic films with fine and uniform pore sizes. and Brownstein, A.K. : "Ceramic Membranes-Growth Prospects and Opportunities", Ceramic Bulletin, 70, 4, 703 (1991).

Ceramic membranes prepared by the sol-gel process have a high pore size in the range of 2.5 to several tens of nanometers, and thus have high industrial value such as gas separation, excellent thermal stability, separation selectivity, and fast permeation rate. And researches for separating and treating environmental pollutants such as NOx, SOx, and COx have been actively conducted [Larcot, A., Fabre, JP, Guizard, C. and Cot, L.: "Inorganic Membranes obtained by Sol Gel Thchniques, J. Memb. Sci., 39, 203 (1988). Uhlhorn, R.J.R., Keizer, K. and burggraaf, A.J. : "Gas Transport and Separation with Ceramic Membranes, Part II. Synthesis and Separation Properties of Microporous Membranes", J. Memb. Sci., 66, 271 (1992). In particular, in the case of gamma-alumina membranes studied in this study, many studies have been made so far, but rather than the basic studies from the sol preparation stage to improve the separation characteristics of membranes, the effect of catalyst additives or the change of microstructure characteristics due to the sintering characteristics, etc. Has been focused on the research of Linn, YS and Burggraaf, A.J. : "Experimental Studies on Pore Size Change of Porous Ceramic Membranes after Modification", J. Memb. Sci., 79, 65 (1993)]. In addition, the concepts of hydrolysis, polycondensation and aging have not been subdivided in the prior art, and thus the gamma-alumina particle characteristics cannot be controlled through this step. Because aluminum alkoxide, the starting material, has a very fast reactivity with water, the sol manufacturing process has not been broken down.

The inventors of the present invention invented a technique for controlling the characteristics of boehmite (gamma-AlO (OH) and gamma-alumina particles, which are intermediate products, by newly defining hydrolysis and polycondensation reactions and aging as process steps after many years of research.

Accordingly, an object of the present invention is to hydrolyze and polycondensate aluminum isopropoxide, and to mature the reactants, peptize drying and heat treatment to produce gamma-alumina. It is to provide a method for controlling the particle characteristics of gamma-alumina by controlling the time and temperature.

It is also an object of the present invention to provide a method for producing gamma-alumina which is capable of controlling particle characteristics by aging conditions for at least 16 hours at the boiling point of isopropyl alcohol.

1 is a process step-by-step diagram for obtaining gamma-AlO (OH) sol solution and gamma-alumina particles from starting materials.

2 is a schematic diagram of a gamma-AlO (OH) sol preparation reactor.

FIG. 3 shows the results of X-ray diffraction analysis of gamma-AlO (OH) particles with aging time at 96 ° C.

4 is an X-ray diffraction analysis result of the gamma-alumina particles obtained by heat treatment at 600 ℃ according to the ripening time at the ripening temperature of 96 ℃.

5 is a result of infrared absorption analysis according to the ripening time at the ripening temperature of 96 ℃.

6 is an infrared absorption analysis result of gamma-alumina particles obtained by heat treatment at 600 ℃ according to the aging time at 96 ℃ aging temperature.

7 is a photograph of gamma-AlO (OH) sol according to the aging time at a aging temperature of 96 ℃.

8 is a size distribution diagram of particles in a gamma-AlO (OH) sol solution prepared by varying the aging time at a aging temperature of 96 ° C.

9 is a diagram showing the change in specific surface area of gamma-AlO (OH) particles with aging time at 90 ° C and 96 ° C aging temperature.

10 is a change in the average pore diameter of gamma-AlO (OH) particles according to the aging time at 90 ℃ and 96 ℃ aging temperature.

FIG. 11 is a change in specific surface area of gamma-alumina particles obtained by heat-treating gamma-AlO (OH) particles prepared at varying aging times at 90 ° C and 96 ° C at 600 ° C.

FIG. 12 is a change in average porosity of gamma-alumina particles obtained by heat-treating gamma-AlO (OH) particles prepared at varying aging times at 90 ° C. and 96 ° C. at 600 ° C. FIG.

13 is a comparison of the TGA curve of gamma-AlO (OH) according to the ripening time at the ripening temperature of 96 ℃.

Gamma-alumina (γ-Al2O3) particles have very fine pores, high porosity, and have a large specific surface area and are widely used as separators, catalysts or carriers of catalysts, and adsorbents. In order to prepare such gamma-alumina particles, it is preferable to prepare gamma-AlO (OH) sol. Because gamma-AlO (OH) sol is monohydrate (Al ₂ O ₃ · H ₂ O), compared to trihydrate (Al ₂ O ₃ · 3H ₂ O), the mass loss generated during firing can be reduced by about 20%. Therefore, it is possible to alleviate the shrinkage phenomenon accompanying the removal of the structural water, thereby greatly reducing the cracks accompanying the film production [Yoldas. BE: "Hydrolysis of Aluminum Alkoxides and Bayerite Conversion", J. appl. Chem. Biotechnol., 23,803 (1973). It is also because of its high adhesion to the support without additional organic additives, and easy transition to gamma-alumina over a wide firing temperature range of 450-900 ° C, making it easy to manufacture [Leenaars, AFM, Keizer, K. and Burggraaf, AJ: "The preparation and Characterization of Alumina Membranes with Ultra-fine Pores. Part 1. Microstructural Inversigations on Non-supported Membranes", J. Mat. Sci., 19, 1077 (1984)].

The microstructural properties of gamma-alumina particles are sensitively affected by the transition from the starting material Al (OC ₃ H ₇ ) ₃ to gamma-AlO (OH) sol, gel and gamma-alumina particles. Therefore, the present invention observed the microstructure characteristics by aging in the process step of manufacturing gamma-AlO (OH) sol in order to control the microstructure characteristics of the gamma-alumina particles.

The present invention will be described in more detail with the following experimental examples and examples.

Method for preparing gamma-AlO (OH) particles:

A reactor as shown in FIG. 2 was installed, and a fixed amount of water (fixed molar ratio of H ₂ O / Al in sol concentration range suitable for the production of gamma-alumina membrane to 100 was fixed in the reactor [Yoldas, BE: "Alumina Sol Preparation from Alkoxides ", Amer. Ceram. Soc. Bull., 54, 3, 289 (1975)].), Using a thermostat to maintain the temperature of the water in the reactor at 90 ℃ temperature, the aluminum iso reactant Propoxide (Al (OC ₃ II ₇ ) ₃ , Fluka Chemie, AG) was added and stirred at 1000 rpm. This experiment suppresses the production of trihydrates (Al (OH) ₃ , Al ₂ O ₃ · 3H ₂ O) produced below 80 ° C and removes isopropyl alcohol from chemical reactions. The reaction was carried out at a reaction temperature of (82.4 ° C.) or more, and an aspirator was attached to the reactor to remove simultaneously with the production of isopropyl alcohol, thereby preventing a reverse reaction. Since the rate of hydrolysis and condensation polymerization of aluminum isopropoxide with water is very fast, it is very difficult to control the properties of gamma-AlO (OH) particles and gamma-alumina particles by controlling the reaction rate of this step. Therefore, the effects of this step were fixed by fixing the reaction conditions for hydrolysis and polycondensation at 90 ° C. for 30 minutes under all experimental conditions. In this step, the reaction time of 30 minutes was the time when the temperature of the solution in the reactor, which rose due to the exothermic reaction when the aluminum isopropoxide was added to the heated water, reached the equilibrium temperature. Therefore, the aging period after the hydrolysis and polycondensation reaction was based on the reaction time after 30 minutes. The effects of aging conditions were investigated while varying the aging time (1, 24, 48, 72 hours) at aging temperatures of 90 ° C and 96 ° C. In addition, after aging, the obtained gamma-AlO (OH) sample is in the aggregated precipitated state, and the peptizing process must be performed for effective dispersion of the particles in the sol solution. For peptizing, acid electrolytes that do not form complexes with Al ions should be selected.In this experiment, hydrochloric acid (Merck, 32%), which is a strong electrolyte and does not form complexes with aluminum ions in order to have the required charge effect at low concentrations, is selected. ) Was selected as an ante electrolyte to proceed with the discourse process. At this time, the peptizing process was carried out at Yoldas [Yoldas, BE: "Alumina Gels that Form Porous Transparent Al ₂ O ₃ ", J. Mat. Sci., 10, 1856 (1975)] was fixed at a molar ratio of 0.07 HCl / Al, the range of the appropriate acid concentration.

Experimental Method and Equipment:

The gamma-AlO (OH) particle state used in the experiment was used for analysis after drying the gamma-AlO (OH) sol solution prepared through aging under constant drying conditions (40 ° C., 48 hours). The crystallinity of gamma-AlO (OH) particles according to aging conditions was determined using X-ray diffraction analyzer, Rigaku, DuKα Filter (Scanning speed 2 ° / min, 30kV, 20mA, 10 °) Analysis under ≤ 2θ ≤ 70 ° scanning range. In addition, Fourier Transform-Infrared Spedtrometer (MIDAS) was performed to analyze the change of the bond group in the gamma-AlO (OH) particles according to aging. After uniformly mixing at a ratio of 200: 1, it analyzed in 400-4000 cm <^-1> wavenumber range. The size and particle size distribution of the sol particles in the sol solution obtained by performing a peptizing reaction (0.07 HCl / Al molar ratio, reaction time 24 hours, reaction temperature 96 ℃) to the gamma-AlO (OH) sample prepared by changing the aging time Size of particles dispersed in sol solution under the following analysis conditions (10mW He-Ne laser, Wavelength 633nm, 2 ~ 3000nm size range) using particle size analyzer (Particle Size Analyzer, Zetasizer 3000, Malvern instrument ltd., UK) And distribution. In addition, nitrogen adsorption / desorption analysis (N ₂ adsorption / desorption analyzer (BET), Micromeritics, ASAP2000) was performed to analyze the microstructural changes of gamma-AlO (OH) particles with the change of aging time. The gamma-AlO (OH) analysis sample used at this time was gamma-AlO (OH) sol solution prepared by aging and peptizing process at 40 ° C for 48 hours in a gamma-AlO (OH) particle state at 150 ° C. After degasing for 11 hours in a vacuum oven, 0.2g of the sample was collected and BET analysis was performed. In addition, the content of residual isopropyl alcohol contained in the sol solution prepared through a certain peptizing reaction to the gamma-AlO (OH) sample prepared by changing the aging time was analyzed by gas chromatography (Gas Chromatography, Shimadju). The thermal mass spectrometer (Thermogravimetric Analyzer, Dupont, 9900) was used to analyze phase transition temperature and mass loss from gamma-AlO (OH) particles to gamma-alumina particles according to the heat treatment temperature. In this case, the gamma-AlO (OH) particles prepared by aging and peptizing were dried at 40 ° C. for 48 hours at 10 ° C./min up to a temperature range of 30 to 750 ° C. under nitrogen atmosphere. The analysis was performed while raising the temperature.

Experimental Example 1

Effect of Crystallinity on Aging:

In the present invention, the characteristics of gamma-AlO (OH) particles by aging were examined. As a result, the crystallinity of the gamma-AlO (OH) particles in the sol solution increased with the aging time. The gamma-AlO (OH) solution prepared by varying the aging time at 96 ℃ aging temperature was dried for 48 hours at 40 ℃ drying temperature, and the aging time was increased by X-ray diffraction analysis of gamma-AlO (OH) particles. As a result, the transition from the pseudo-boehmite structure with low crystallinity to the crystalline-boehmite structure with improved crystallinity gradually increased. The results are shown in FIG. X-ray diffraction of γ-Al ₂ O ₃ particles obtained by heat treatment of γ-AlO (OH) particles at 600 ° C for 1 hour to investigate the effect of gamma-AlO (OH) particle characteristics on the particle properties of gamma-alumina Analyzed with an analyzer. As a result of analysis, the crystallinity of the gamma-alumina particles obtained by heat treatment at 600 ° C. was determined according to the crystallinity of the gamma-AlO (OH) particles of FIG. 3. The results are shown in FIG. This indicates that the properties of the gamma-AlO (OH) particles with the aging time also affect the final properties of the gamma-alumina particles.

In order to analyze the change of the bonding group according to the aging time at 96 ℃ aging temperature, after mixing γ-AlO (OH) particles dried at 40 ℃ for 48 hours in KBr with 0.5wt% mixed with KBr, 400 ~ 4000cm ^-1 The analysis was carried out in the frequency range. The results are shown in FIG. Ed. Wilson, MJ; According to "Clay Mineralogy: Spectroscopic and chemical Determinative Methods", CHAPMAN & HALL (1994), the three absorption bands of 495, 630 and 750 cm ^-1 are absorption bands by Al-O- in γ-AlO (OH) and 1075 cm- ^. The absorption band of ¹ is known as the absorption band of Al-OH. The experimental results, as the aging time increases, the fifth assist the strength of Al-O- absorption band of Al-OH absorption band with 400~1000cm ^-1 range of 1075cm ^-1 was increased. Gamma-AlO (OH) sol particles prepared by varying aging time at 96 ° C. aging temperature were analyzed by infrared absorber of gamma-alumina particles sintered at 600 ° C. for 1 hour. The results are shown in FIG. As a result, as the aging time increases, the absorption bands of 548 and 880 cm ⁻¹ exhibited by the bond groups of the gamma-alumina particles gradually increase. This is because, as in the X-ray diffraction analysis, the properties of the gamma-AlO (OH) particles determined by aging have an effect even after the sintering treatment.

In order to investigate the change of particle size according to the aging time, a constant peptizing reaction (0.07 HCl / Al molar ratio, reaction time 24hour, reaction to gamma-AlO (OH) solution prepared by changing the aging time at 96 ℃ aging temperature) Temperature 96 ° C.), the state of the sol formed was observed. As shown in FIG. 7, it was found that the transmittance of the sol particles in the gamma-AlO (OH) sol solution gradually decreased with increasing aging time. This is because the scattering degree of light is increased by increasing gamma-AlO (OH) particles with increasing aging time, resulting in a decrease in light transmittance.

The size and distribution of particles in γ-AlO (OH) sol solution prepared by varying the aging time at 96 ℃ aging temperature are shown in Fig. 8 and shown in Fig. 8 The average particle size of is shown in Table 1.

TABLE 1

Average particle size

In the analysis results, the average particle size increased from 26.3 to 294.0 nm with increasing aging time in the range of 1 to 72 hours at 96 ℃ aging temperature conditions, and as shown in FIG. The particle size distribution of the AlO (OH) sol solution was uniform.

Experimental Example 2

Effect of Microstructure on Aging:

Nitrogen adsorption and desorption analyzer (BET) was used to investigate the change of specific surface area and average pore size of gamma-AlO (OH) particles with aging time at 90 and 96 ℃. The results are shown in FIGS. 9 and 10 degrees. 9 is a change in specific surface area of gamma-AlO (OH) particles with aging time, and FIG. 10 is a change in average pore diameter of gamma-AlO (OH) particles. As shown in the analysis results of FIGS. 9 and 10 degrees, in the 90 ° C ripening temperature, the microstructural characteristic change is distinguished from 24 hours, whereas in the 96 ° C ripening, the microstructural change is distinguished at 16 hours. As such, the microstructure changes have different slopes according to the aging time.

This, in the early stage of aging, leads to a drastic change in the microstructure, while the late stage of aging shows a gentle change in the microstructure. This shows that the change of sol particle characteristics goes through different mechanisms in the early and late stages of fermentation. In the early stages of fermentation, it was found in pseudo-boehmite with low crystallinity formed by early 30 minutes hydrolysis and polycondensation. This is because the remaining OR group undergoes hydrolysis and polycondensation reaction at the early stage of aging, and at the same time, the microstructure changes rapidly due to the transition of crystalline-boehmite with improved crystallinity. Yoldas, Yoldas, B.E .: "Molecular and Microstructural Effects of Condensation Reactions in Alkoxide-Based Alumina Systems", des. Mackenzie, J.D. and Ulrich, D.R., John Wiley & Sons, 333 (1988) reported that after hydrolysis with heated water at 80 ° C. or higher, it contained about 5-6% of OR groups in the formed pseudo-boehmite phase.

After aging, the residual OR group contained in the sol solution prepared through a constant peptizing reaction (0.07 HCl / Al molar ratio, reaction time 24 hours, reaction temperature 96 ℃) was analyzed by gas chromatography. The results are shown in Table 2. As a result, the content of isopropyl alcohol of 0-7% was detected depending on the aging time. This analysis shows that the amount of isopropyl alcohol remaining in the sol solution decreases with increasing aging time and is not detected at all after 48 hours of aging.

TABLE 2

Isopropyl Alcohol Concentration with Aging Time

In the late maturing step, as shown in Table 2, since most of the residual OR group was removed in the sol solution, it is difficult to explain that the change of particle characteristics occurs due to further hydrolysis and condensation polymerization of the residual OR group. However, the X-ray diffraction analysis results of FIG. 3 and the infrared absorption analysis results of FIG. 5 show that the production of Al-OH and Al-O groups continues to increase during this ripening period. This is because the growth mechanism of the particles is mainly small particles aggregate and grow by condensation polymerization between particles and transfer to polycrystalline-boehmite particles.

The specific surface area of the gamma-alumina particles obtained by sintering the gamma-AlO (OH) sol particles prepared by varying the aging time at 90, 96 ° C. aging temperature is shown in FIG. 11, and the gamma-alumina particles. Figure 12 shows the change in the average pore diameter. In FIGS. 11 and 12, the microstructure characteristics of the gamma-AlO (OH) particles are similar to the aging time. That is, it can be seen that the final microstructure characteristics of the gamma-alumina particles were determined by the microstructure characteristics of the gamma-AlO (OH) sol particles as well as the effect of crystallinity. This indicates that the microstructure of gamma-alumina particles is controllable by aging.

After gamma-AlO (OH) particles prepared by varying the aging time at 96 ° C. aging temperature were dried at 40 ° C. for 48 hours, the thermal behavior obtained by using a thermal mass spectrometer (TGA) under nitrogen atmosphere was observed. The phase transition was performed by removing water adsorbed on the surface of gamma-AlO (OH) particles at about 100 ° C and removing structural water at around 467 ° C. The results are shown in FIG. In FIG. 13, the thermal behavior of the gamma-AlO (OH) particles prepared by varying the aging time showed different behavior when the adsorbed water near 100 ° C. was removed. That is, the amount of adsorbed water removed as the aging time increases. As shown in the results of the nitrogen adsorption and desorption analysis of FIGS. 9 and 11 degrees, the growth of the particles resulted in a decrease in specific surface area as the aging time increased, resulting in a decrease in the amount of absorbed water adsorbed on the surface. On the other hand, the mass loss due to the removal of structured water during the transition to gamma-alumina is consistent with the theoretical values. That is, since the molecular weight of gamma-AlO (OH) is 59.99 g / mol and the molecular weight of gamma-alumina is 101.96 g / mol, the mass loss when transitioned as in Scheme (1) is 18.02 g.mol, theoretically 15.02. Regardless of the aging conditions, the mass loss was about 15 to 16% until the temperature reached near 467 ° C, which is the temperature at which gamma-alumina is formed.

Scheme 1

2γ-AlooH → γ-Al ₂ O ₃ + H ₂ O ↑

As the aging time increased, the heating temperature point required to remove the adsorbed water decreased. This is a phenomenon that the specific surface area of the particles decreases due to aging, and thus the amount of adsorbed water adsorbed on the surface of the particles decreases, so that the amount of adsorbed water decreases by the decrease of the specific surface area as the aging time increases. Because it can be removed. The results are shown in FIG.

As can be seen in the above experimental example, the present invention considers the effect of the sol manufacturing process parameters involved in the film preparation for the purpose of controlling the microstructural properties of the gamma-alumina film stable at high temperature, the aging gamma-AlO ( It was found that the OH) sol particles and the gamma-alumina film had a significant effect on the microstructural properties. As aging, gamma-AlO (OH) particles showed significant changes in microstructural properties, such as crystallinity change, mean pore size increase, and specific surface area decrease. In particular, the microstructural properties of gamma-AlO (OH) particles showed different slopes with aging time. In the early stage of fermentation, the -OR group remaining in the low crystallinity pseudo-boehmite phase undergoes further hydrolysis and condensation polymerization reaction during the fermentation, and the condensation polymerization reaction between particles leads to the formation of -OH group and -O- group. In the late stage of aging, all the OR groups remaining in the sol solution are removed, and the resulting particles aggregate and grow by condensation polymerization between particles. As a result, the microstructure changes more slowly than the early stages of maturation because it is transferred to more dense and larger polycrystalline-boehmite particles.

In view of the fact that the microstructural characteristics change of the sol particles according to the aging are directly related to the microstructural characteristics of the gamma-alumina particles obtained by sintering, the sol preparation was performed to improve the separation characteristics of the sol particles when applied to the gamma-alumina membrane. It is important to consider the effects of the maturation of the stage.

According to the above experimental considerations, a method of preparing gamma-alumina is shown in the following examples.

Example 1

100 mol of deionized distilled water was maintained at 90 DEG C using a thermostat in a reactor to which an inhaler was attached, and 1 mol of aluminum isopropoxide was added thereto, followed by stirring at 1000 rpm. Aged for 24 hours and stirred with hydrochloric acid in the resulting sol solution. The gamma-AlO (OH) thus obtained was dried at 40 degrees for 48 hours and sintered at 600 degrees for 1 hour.

Example 2

100 mol of deionized distilled water was maintained at 90 DEG C using a thermostat in a reactor to which an inhaler was attached, and 1 mol of aluminum isopropoxide was added thereto, followed by stirring at 1000 rpm. Aged for 16 hours and stirred with hydrochloric acid in the resulting sol solution. The gamma-AlO (OH) thus obtained was dried at 40 ° C. for 48 hours and sintered at 600 ° C. for 1 hour.

An effect of the present invention is that gamma-alumina having desired particle characteristics can be produced.

Claims (2)

In a method for producing gamma-alumina by subjecting aluminum isopropoxide to hydrolysis and polycondensation, and aging, peptizing, drying and heat treating the reactant, the polycondensed reactant is subjected to a temperature above the boiling point of isopropyl alcohol. Method for controlling the particle characteristics of alumina sol (boehmite, γ-AlO (OH)) characterized in that aged for 16 hours or more. In the preparation of gamma-alumina by hydrolysis and polycondensation reaction using isopropoxide and aging, peptization, drying and heat treatment, the aging temperature is 82.4 ° C to A method of controlling the particle characteristics of gamma-alumina (γ-Al ₂ O ₃ ) by adjusting the aging time to 16 to 72 hours at 100.0 ° C.