Several preparation methods of pseudo-boehmite with high specific surface and large pore volume

In modern petrochemical and chemical industries, the most commonly used catalyst carrier is activated alumina.

Honeycomb catalyst carrier

Why don't you come to find out about such an easy-to-use pseudo-boehmite?

Pseudo-boehmite (AlOOH·nH2O, n=0.

Pseudo-boehmite powder

Pseudoboehmite stone industrialized production method comprises hydrolysis of aluminum alkoxides, alkaline (acid-precipitation method) and an acid method (alkali precipitation method), the carbonization method, acid method or the like

Among them, the aluminum alkoxide method is widely used in the preparation of high-purity pseudo-boehmite.

With the increasing requirements for deep processing of raw materials worldwide, the main energy structure is gradually developing towards macromolecules and high carbon.

Therefore, the research on the preparation method of pseudo-boehmite with high specific surface and large pore volume has gradually become an important direction

From the perspective of the preparation process of pseudo-boehmite, the usual preparation process includes gel formation, aging, washing, drying, molding and roasting.

The following is a study on the preparation method of pseudo-boehmite with high specific surface and large pore volume in recent years:

1.
Control method during the precipitation of pseudo-boehmite

(1) pH swing method

The pH swing method refers to a method in which the pH is repeatedly oscillated between the alkali side and the acid side for many times during feeding, thereby increasing the pore size and pore volume of the precipitated pseudo-boehmite
.

China's Luoyang Petrochemical Company used Al2(SO4)3 and NaAlO2 as raw materials to carry out industrial scale-up experiments of the pH swing method at the Changling Refining and Chemical Company Catalyst Plant.
Under the recommended conditions, the grain size of 80nm, 80nm, can be obtained when the pH swings 4 times.
Pseudo-boehmite dry rubber powder with pore volume 0.
56cm3·g-1
.

The advantage of this method is that it can obtain pseudo-boehmite with relatively uniform crystal grains, relatively concentrated pore size and large pore volume; the disadvantage is that the industrial implementation of pH swing is difficult, and the increase in product pore volume will also lead to its specific surface area.
Down
.

(2) Organic solvent synthesis method

This method uses an organic solvent as the reaction medium under certain conditions.
Some researchers were inspired by the partial insertion of the diol into the boehmite when the diol thermal method is used to treat the gibbsite.
Alcohol thermal synthesis of honeycomb pseudo-boehmite with large pore volume, and found that the grain size of pseudo-boehmite is related to the type of glycol, according to ethylene glycol, 1, 3-propanediol, hexanediol and The order of 1,4-butanediol increases
.

(3) Surfactant assembly method

The surfactant assembly method is based on the electrostatic, hydrogen bond, van der Waals force and covalent bond between organic and inorganic substances, and can be used to synthesize metal oxides with narrow pore size distribution and controllable pore structure including alumina.

。Material .

For example, the assembly of polyethylene oxide can better control the morphology and particle size of pseudo-boehmite, and obtain thermally stable, large-pore, high-surface pseudo-boehmite
.
Another method is to hydrolyze aluminum sec-butoxide in the presence of an amine surfactant to prepare scaffold-shaped nano-boehmite-amine composite particles.
This structure is formed by the aggregation of nano-boehmite fibers and intercrystalline growth.
In the process of transforming pseudo-boehmite with mesoporous structure into γ-Al2O3, amine can play a role in nano-assembly and obtain higher pore volume and specific surface area
.

(4) Microwave heating method

In recent years, microwave heating technology has received attention in the synthesis of porous inorganic materials such as adsorbents, catalysts and membranes.
Microwaves can activate water molecules to form active water molecules that are not associated with hydrogen bonds; microwave rapid body heating and high-frequency oscillation It can also form a uniform energy and concentration distribution environment in the reaction system, thereby greatly accelerating the synthesis and crystallization speed of the product, and significantly improving its quality
.

Compared with the ordinary hydrothermal method, the microwave heating method can prepare the pseudo-boehmite with a uniform distribution of high specific surface and large pore volume.
The disadvantage is that the corresponding microwave reactor needs to be developed
.

Second, the post-treatment method after the precipitation of pseudo-boehmite

(1) Hydrothermal treatment method

Hydrothermal treatment is also called water vapor treatment, which is to heat pseudo-boehmite or alumina in the presence of water vapor.
During the hydrothermal treatment process, the crystal grains of pseudo-boehmite grow up, the crystallization becomes more complete, and the crystallinity increases.
So as to realize the effect of reaming
.

(2) Organic solvent replacement method

This method is to wash the pseudo-boehmite with an organic solvent after the precipitation, the organic solvent enters the crystallite gap to replace the water molecules, which can prevent agglomeration
.
Azeotropic distillation is also an important organic solvent replacement method.
By adding an organic solvent with a higher boiling point and lower surface tension than water and water in the gel to form a binary azeotropic system, the gel is taken away as much as possible in azeotropic manner.
The water in the gel does not replace it and exists in the gel, which fundamentally eliminates the hard agglomeration that occurs during drying
.

This method can realize the regulation and control of the pore volume of pseudo-boehmite.
The disadvantage is that the consumption of organic solvent is large and the recovery cost is high.

(3) Unconventional drying method

When the pseudo-boehmite filter cake is washed by water washing, it is very easy to damage the original pore structure due to pore shrinkage and pore collapse in the subsequent conventional drying and roasting process, and produce hard agglomeration
.
The supercritical drying method and freeze drying method are all drying methods tried to maintain the distance between particles in the gel, weaken or eliminate the interaction force of the particles; weaken or even eliminate the capillary contraction caused by the surface tension of water
.

(4) Hole expanding method with expanding agent or sintering aid

It is also an effective method to prepare pseudo-boehmite with large pores and high specific surface area by introducing auxiliary agents or pore expanders that are easy to decompose at high temperature during post-treatment processes such as the precipitation or forming of pseudo-boehmite gel
.
These auxiliary substances decompose and escape during roasting, which can achieve the purpose of increasing the pore volume and controlling the pore size distribution
.

Concluding remarks

The application prospect of pseudo-boehmite is extremely wide, especially under the current development trend of industrial transformation and increasing environmental protection, pseudo-boehmite with high specific surface and large pore volume is very useful
.
At present, the domestically developed pseudo-boehmite production is mainly the types with small and medium pore volume and small surface area.
In contrast, although the production of large pore volume with high specific surface is more difficult, the application range is wider.
The added value of the product is high, the application advantages and economic benefits are more prominent, it is worthy of relevant enterprises to invest energy to research breakthroughs
.

Reference source:

Preparation of pseudo-boehmite and γ-Al2O3 with high specific surface, large and medium pores, Cai Weiquan, Yu Xiaofeng (1.
School of Chemical Engineering, Wuhan University of Technology, Wuhan, 430070; 2.
Hanjiang Group Yunxian Fengyuan Electrochemical Manufacturing Co.
, Ltd.
, Yunxian , 442500)