The physical and chemical properties and preparation methods of zeolite (1)

[Physicochemical properties] zeolite known as zeolite, molecular sieve, zeolite steel, crystalline aluminosilicate, which is the main chemical components of SiO ₂ , followed of Al ₂ O _.
3 , of CaO, of MgO and of Na ₂ O and the like
.

Zeolite is the general name of zeolite group minerals.

[Preparation method] The synthetic method of zeolite is made by using sodium silicate , sodium hydroxide , aluminum hydroxide , potassium chloride , sodium chloride , sulfuric acid, etc.
as raw materials, mixed with specific impurity elements, and prepared by hydrothermal synthesis under normal pressure There are different types of zeolites
.

① The raw materials used in this method of hydrothermal synthesis are alkali, alumina, silica and water
.

The alkali raw material may be sodium oxide, potassium oxide, lithium oxide, calcium oxide, etc.

The silica raw material can be water glass, silicic acid, silica sol, halogenated silane and various active amorphous silicas
.

Now take the synthesis of type A molecular sieve as an example to illustrate the general process of producing molecular sieve

Since zeolite crystallizes under the condition of excessive alkali, a large amount of hydroxide must be attached to the crystal grains, so it must be washed, otherwise the performance of the zeolite will be affected
.

For this reason, it is necessary to repeatedly wash with water at 60-80°C until the pH value reaches about 9

② Alkali treatment method Alkali treatment method is also called hydrothermal conversion method, its essence is to hydrothermally convert some solid aluminosilicate into zeolite in the presence of excess alkali
.

The raw materials used in this method are divided into two categories: one is natural minerals, such as kaolin, bentonite, diatomaceous earth, diasmolite, volcanic glass rock, etc.

In the latter method, the ingredients and roasting process are the same as the previous method, except that the added sodium hydroxide is configured into a sodium metaaluminate solution, which is added at the beginning of the crystallization reaction
.

Experiments show that due to the addition of aluminum, the ratio of silica to alumina in the mixture is more suitable for the formation of faujasite, and the crystallization time can be greatly shortened, the amount of alkali can be reduced by 1/2, and the output can be increased by 1 Times

The general process of synthesizing zeolite using industrial silica-alumina raw materials is to first mix silica sol or aluminum sol and hexamethyltetramine into the molding oil to make it into microsphere gel particles, and then process the gel microspheres appropriately The hydrothermal treatment can generate the corresponding zeolite
.

Although the purity of the zeolite synthesized by the alkali treatment method is not as high as that of the hydrothermal synthesis method, it has the advantages of low production cost and high product strength
.

③ Synthesis of Zeolite Membrane Synthesis of Zeolite Membrane Polycrystalline zeolite membrane prepared on a porous carrier provides a new solution for gas-gas and liquid-liquid separation.
Therefore, more and more people pay attention to it.
Zeolite membrane has high temperature stability and The characteristics of being suitable for harsh chemical conditions provide broad prospects for its potential applications in industry
.

In the past ten years, the synthesis of zeolite membranes has become a hot spot in the field of inorganic membranes.

The huge application potential of zeolite membrane in separation has made it the forefront of inorganic membrane research
.

Although there are many research reports on zeolite membranes, most of them are at the stage of laboratory theoretical research, and there is still a long way to go before successful industrialization

The activation and modification of natural zeolite can significantly increase its porosity and surface activity, improve adsorption performance, ion exchange performance and exchange capacity, etc.
, thereby increasing its use value
.
There are three main types of zeolite modification: activation treatment, surface modification and structure modification
.