JPS59162131A - Pore-size control in porous alumina - Google Patents

Abstract

PURPOSE:Porous alumina is impregnated with a melting salt, dried, sintered, then cooled and the salt is leached out with water or a diluted acid solution to effect easy control of the pore size distribution and surface acidity. CONSTITUTION:An aqueous solution of aluminum sulfate and urea is heated to form alumina gel and the alumina gel is sintered into porous alumina. The resultant alumina is impregnated with a melting salt such as boric acid, sodium hydroxide or calcium chloride, dried, sintered, cooled down, then the salt is leached out with water or a dilute aqueous acid to give the objective porous alumina. In this process, the amount and the kind of the melting salts are selected to enable the control of pore size and surface acidity of the porous alumina.

Description

[Detailed description of the invention] The pores are impregnated with molten salt such as boric acid, alkali hydroxide, calcium chloride, etc., and after being fired at a predetermined temperature,
This relates to a method for controlling the pore size and surface acidity of alumina by extracting and removing the impregnated salt by treating it with hot water or dilute acid. In general, porous solids are used as catalysts or as carriers for catalysts. However, it is essentially impossible to prepare a porous solid having a desired pore size distribution through the engineering of silica-alumina, alumina, silica, and other metal oxides, among others.

Preparation methods for porous solids include precipitation, pyrolysis, and other methods.
There are special methods such as neutralization with carbon dioxide gas,
Although preparations have been carried out by changing the p I-T during precipitate formation in the precipitation method, or by changing the decomposition temperature in the thermal decomposition method, these methods specifically control the pore size distribution. That is difficult.

Pores in porous solids are voids between crystals or particulates. If the particle size of crystals or fine particles can be uniformly controlled, the pores, which are the voids thereof, should also be controlled along the particle size distribution. However, when this porous solid is used as a catalyst support, it is pre-calcined at a temperature higher than the reaction temperature, or activated by high-temperature firing to regenerate the catalyst activity, so the crystal size grows and the pore size increases. The distribution changes, which contributes to the deactivation of the catalyst activity.

Therefore, it becomes industrially disadvantageous. In addition, the pore diameter has a large effect on the selectivity of the reaction. For example, when the reaction product is a compound larger than the pore diameter, this compound is virtually not produced, increasing the selectivity of the reaction.

A typical multilayer solid with this effect is zeolite 1-. Since the probes 14 of zeolites 1 to 14 are voids determined by interatomic bonds in the crystal, their size varies depending on the crystal structure. teshi)ru.shika)shi, Zeolai 1
Since it is a crystal synthesized from silica and alumina,
The same results cannot be expected even if similar methods are used to form crystals on silica alone, alumina alone, or other oxides.

The present inventor succeeded in developing the present invention as a result of research into a method for controlling the pores of ordinary alumina as well as its surface acidity. That is, the present invention involves impregnating porous alumina with an aqueous solution of molten salts, drying the impregnated alumina, heating and calcining the impregnated alumina, and then cooling the impregnated alumina with water or a dilute acid aqueous solution to elute and separate the impregnated salts. The present invention provides a method for controlling pore size.

The porous alumina used in the method of the present invention is one obtained by a conventional method such as a precipitation method or a thermal decomposition method, or a mixed acid salt of aluminum sulfate and urea, a nitrate salt,
It can be produced using aluminum alkoxide such as chloride or isopropoxide as a raw material, and using ammonia or urea as an alkalizing agent in the precipitation method. In addition, a method of decomposing aluminate salt with carbon dioxide gas is also a common method for alumina. The meltable salts are compounds with a relatively low melting point that melt around the firing temperature of alumina, and salts that are easily soluble in water are preferably used. Examples of such compounds include boric acid, alkali hydroxide, calcium chloride, phosphoric acid, etc. These molten salts are usually used alone, but two or more types can also be used in combination. O In these cases,
It is preferable to use alumina obtained by calcining an alumina gel obtained by heating an aqueous solution of a mixture of aluminum sulfate and urea to 95 to 100 °C, and use alumina obtained by heating an aqueous solution of a mixture of aluminum sulfate and urea to 95 to 100 °C. When the porous alumina is impregnated with molten salts and sintered, the porous alumina begins to sinter, but the method utilizes the phenomenon that the impregnated molten salts prevent the sintering of the alumina. The alumina impregnated with molten salts obtained by firing in this way is cooled, and the impregnated salts are extracted and removed with water, preferably hot water or dilute acid, and the residue appears as new pores. At the same time, the surface has a new surface acidity. Therefore, this controlled preparation method is highly universal and can be applied not only to alumina but also to a wide range of other solid pore control methods, and can be used for the production of controlled porous solids for many solids. You can expect to do so.

Hereinafter, the present invention will be explained in detail with reference to Examples.

In addition, the surface area shown in the examples was determined by the B P '1'' method, the total pore volume was determined by the helium-mercury method, and the pore radius was determined by the BJH method using the desorption isotherm of nitrogen gas at liquid nitrogen temperature (the above method). is specified in the Catalyst Engineering Course Vol. 4, pages 50-83, edited by Jidaishokan, Catalysis Society.) In addition, Process-1, 2, and 3 described in Examples 1 to 5
, 4 refer to the following contents.

Process-1: After drying the alumina gel, it is fired at 550°C to obtain ordinary porous alumina.

℃ to obtain a mixture of alumina and molten salt.

Process-4: The mixture obtained in step 3 is extracted with hot water or dilute acid, dried, and then calcined at 550°C to obtain alumina with new pores.

Example 1: Aluminum sulfate (1002) and urea (2502) were placed in a 3 liter beaker, 2 liters of deionized water was added to dissolve it, and the mixture was heated to 95°C or higher in the aqueous solution, resulting in approx. The sedimentation will be completed after 1 hour.Filter this.
The resulting cake was washed with water and dried at 120°C for 1 day.
Alumina was obtained by firing at 550°C for 3 hours (Alumina A).
). Next, using boric acid as the molten salt, alumina with varying amounts of boric acid impregnation was prepared according to the above process 3, and the measurement results obtained are shown in Table 1. However, the amounts of boric acid added in experiment numbers 1 and 2.3 were 5 and 10.2, respectively.
It is 0% by weight.

Table 1 Example 2 Example 1. Porous alumina was prepared in exactly the same manner as in Example 1, except that 10% by weight of each of 1-lium hydroxide (Experiment No. 4) or calcium chloride (Experiment No. 5) was impregnated in place of boric acid. Similar measurement results for both samples in each process are shown in Table 2.

Table 2 Example 3 This example shows the case where alumina A is reduced (Process-2)
This is an example. Alumina A was exposed to hydrogen gas for 85 hours under different heating conditions to prepare three types of reduced alumina. The heating conditions were 300°C (experiment number 6) and 400°C, respectively.
℃ (same as 7) and 450℃ (same as 8), each with 1
Porous alumina having controlled pore diameters was obtained from each O sample impregnated and supported with 0 weight percent boric acid according to Processes -4 and -5. The various properties of each sample in each process are
Shown in the table.

Table 3 Example 4 4507 aluminum sulfate was placed in a 3 liter beaker, 2 liters of deionized water was added to dissolve it, 2N aqueous ammonia was added and the mixture was thoroughly stirred. The resulting cake was dried at 120°C and then calcined at 550°C for 3 hours to obtain alumina (referred to as alumina B).

Alumina 13 was impregnated with an aqueous solution of helium hydroxide and dried to support 10 weight percent of helium hydroxide. Alumina with a controlled pore size was prepared according to Processes -3 and -4, but when hot water was used as the eluent (Experiment No. 9) and when dilute hydrochloric acid was used (Experiment No. 10).
) Table 4 Table 4 Example 5 Porous alumina having the surface area, total pore volume, and pore radius shown in Table 5 was prepared using the above process-3 and pore radius. Porous alumina with controlled pore size was prepared according to A-4. Experiment No. 11 used boric acid as the molten salt, and Experiment No. 12 used calcium chloride as the molten salt, and each was supported at 10% by weight. The results are shown in Table 5.

Table 5 Reference Example Boric acid was added to 1° alumina A in an amount of 0 to 20% by weight, and Processes 1, 3, and 4 were performed, and the molecular sieve effect of each of the obtained aluminas was investigated. The experimental conditions were a column length of 5cr11.
The flow rate was carried out using a gravity flow method, and the sample that initially flowed out was analyzed using a gas chroma 1-graph method to investigate its composition. The composition of the stock solution is said to be an equimolar mixture.

Table 6 Note: 0 expressed as the adsorption and adsorption rate of benzene, para-xylene, and normal hexane. The surface acidity of alumina in Experiment No. 11 was investigated. This measurement method was carried out by the indicator method (Jijin Shokan, edited by the Catalyst Society, Catalyst Engineering Course Vol. 4, p. 161). The measurement results are shown in Table 7.

Table 7 Note) (+) indicates the acid strength present on the surface.

As is clear from the above examples and reference examples, porous alumina having a controlled pore size can be easily prepared by the method of the present invention, and the acidity of the alumina surface can be easily adjusted as desired. can be controlled.

Claims (1)

[Claims] A method for controlling the pore diameter of porous alumina, which comprises impregnating and drying porous alumina with molten salts, heating and baking the impregnated alumina, cooling the alumina, and dissolving and removing eluted components with water or a dilute acid aqueous solution.