1 Introduction

Silica gel is a dry silica with a two-dimensional spatial network structure.

Gel, a porous solid substance, has a wide range of pores, which is very

The surface is covered with a large number of silanol genes.

Si- OH) has certain activity. Let it become a desiccant and absorb it.

Additives, catalysts and catalyst carriers are widely used in many industries.

In production.

2 process characteristics

Although the production of silica gel mostly goes through gelation, washing and drying.

A * * * sex, but specific to a certain kind of glue, and there are different processes and stages.

Unique personality.

2. 1 gel granulation process

Gel granulation is one of the key steps in silica gel production.

Refers to a certain concentration of dilute sodium silicate solution and dilute sulfuric acid under certain conditions.

Fully react to form a gel-soluble solution, and form a gel after reaching a certain concentration.

Colloidal particles. The shape and size of gel particles fully meet the needs of users.

In order to determine the production capacity of the process, several gluing methods are needed, and more methods have been adopted recently.

When air granulation is used and the particle size is required to be fine, air granulation is considered.

Difficulties, most of them use reaction tank gel granulation, such as micro-powder silica gel.

Production. Acid-base ratio, concentration, temperature and gelation used in gel.

Granulation time is the specific process parameters of gel granulation process.

2. 1. 1 acidic gel formation (acid-base ratio problem), primary gel particles

R (relatively few primary particles are small in size, and it is easy to form fine pore structure when they aggregate.

Silica gel; When alkaline gel is formed, the primary gel particles R are large and easy to aggregate.

Forming coarse porous silica gel. This is the first choice for producing coarse pore glue.

In the production of fine pore glue, the formation of acidic gel is preferred.

2. 1.2 The acid-base concentration should be moderate. High acid-base concentration, primary coagulation

The larger the colloidal particle R is, the larger the pore size is, and the larger the pore size is.

The concentration of primary particle I in the solution is also large, that is, the gel network structure is compact.

When the density increases, it is easy to become fine holes when gathering, and one of them cancels out each other.

This trend. In addition, if the acid-base concentration is too high, the viscosity of the gel solution will increase.

Large, which brings some difficulties to granulation. In addition, the acid-base concentration is also affected by the gel particle size, structure and production design ability.

Restrict.

2. 1.3 The acid-base temperature is too high and the acid-base reaction is too fast. Ifu

The acid-base reaction is exothermic. When the primary particle R is aggregated, it releases heat again.

It is necessary to release heat. Therefore, the primary particle R is very large ". The granulation speed decreases.

Slow down. It is bound to go beyond the scope of process requirements. It is not conducive to granulation growth. Acid-base temperature

It's too low. The primary particle r decreases. It is easy to form pores. However, several gels were formed.

If the solution temperature is too low, the viscosity will increase, which is not conducive to granulation. because

The acid-base temperature should also be moderate.

2. 1.4 Gel granulation time is another time in the process of gel granulation.

Key process parameters. It means from the beginning to the end of the acid-base mixing reaction.

Time elapsed until particle size gel is formed, including gel time.

And granulation time. Gel granulation time is short, and it can be made into gel solution.

Insufficient reaction or insufficient uniformity makes the primary particle concentration r

Uneven distribution. Forming local gel or local close packing. This will produce.

Bubble glue, broken glue or rubber balls with insufficient strength appear during granulation.

Phenomenon. At the same time, the internal structure of colloidal particles is disordered.

One of the main reasons for the large distribution range. Therefore, in production practice,

Medium to medium air granulation. Within the scope of process permission. Large particles.

Glue. As long as possible. For glue with smaller particles, the time can be shorter.

Some. Granulation of ultrafine spherical silica gel by Ifn in reaction kettle.

Glue. It will take longer. Mesh _ needs stirring.

2.2 Glue washing process

Glue washing is an essential process in the production of silica gel.

In order to wash the granular gel formed by nazso, 7{ negative

Cations are controlled by R (mainly H-X, N- expansion, one is also, Si0 passes through iY}r, etc. ).

Make it within the scope of process requirements. At the same time, it is also a regulating particle.

The process of internal structure (i.e. aging).

2.2. 1 exchange adsorption (that is, the exchange of Na X and H X) phenomenon is

One of the wood characteristics of glue washing process. The process of acid bubble is exchange adsorption.

The main processes of. 1}' A' and H 10 are mostly exchanged at the end of this process.

All right. The exchange of water washing process is far from stopping, but the exchange capacity is getting stronger and stronger.

It's getting smaller Acid bubble concentration, washing medium and washing temperature are washed with glue.

The main process parameters of this process affect the exchange speed and quantity.

2.2.2 A good part of the pore characteristics of the finished silica gel is mountain washing glue.

The aging of the process is certain, and the aging degree of this process depends on

Wash the glue medium and temperature several times. Cleaning medium and temperature control at one time.

Particle growth rate ",that is, by adjusting a particle.

The increase of the child "to achieve the purpose of adjusting the hole structure.

The washing of fine pore glue needs to inhibit aging, so it needs to prevent aging when making glue.

After the particles are formed, they are subjected to necessary short-term aging and then acid treatment.

The washing medium of bubbles and glue must be acidic from beginning to end, because acidic medium.

(i.e. H X) can effectively inhibit the' growth' of primary particles.

The amount of acid determines the degree of aging inhibition. At the same time,

The washing temperature is lower, because aging is a process of absorbing energy.

The temperature is low, the energy supply is less, and the aging degree is naturally small. I.e. fine pore.

Washing is to adjust the pores by inhibiting the "growth" of primary particles.

The purpose of the structure. In particular, the structure of several holes should be strict (that is, the distribution of holes)

Small scale) mesh _ bulk density requires a certain range of fine pore glue.

Production, for example, for the production of special microporous adhesives for pressure swing adsorption of carbon dioxide.

Production. When washing glue, the acid content and temperature of washing water should be strictly controlled.

Beg. The washing temperature of porous rubber in Shanji is low and the exchange speed is slow, so

It takes a long time to wash, but it can't be too big and too long, especially

Near the end of l, accelerate aging.

The production of coarse pore glue needs to promote aging. Follow the basic media

The principle that high-quality and high-temperature hot water promotes aging is taken before acid soaking.

High temperature hot water, in order to make it alkaline, improve the washing process.

Temperature, 7{ At the end of the last L, add a certain concentration of ammonia water to.

Measures such as increasing hydrogen ion concentration make primary particles longer.

Big ",expand the aperture, to achieve the purpose of aging. It is not difficult to see that throughout

In the washing process, the aging degree showed an upward trend. Shan Shan has washed it several times.

At high temperature, not only the primary particles inside the particles grow up, but also the reticular particles are very special.

Especially between rubber powder particles, there is a tendency to grow up, which is washing.

When the temperature is high, the rubber powder is easy to agglomerate at the gathering place and the rubber ball is sticky.

Another major reason.

For glue with large pore size, that is, between thick and thin holes, such as T3 glue.

Production, moderate aging, sometimes in the process of buffer drying.

The surface tension of the liquid plays a role, and the surface treatment is carried out after cleaning. Several mountains

If the temperature is too high and the time is too long, the existence of the treatment solution will change the rubber ball.

Therefore, the application of the treatment liquid is limited by the drying process conditions.

2.3 drying process

Drying is carried out on the surface of the liquid, and tension acts on it, thus making colloidal particles.

The evaporation of water is reduced, which makes the primary particles reunite for a long time.

Big ",to achieve the purpose of deep aging. In order to inhibit aging, fine pore glue

This degree is usually achieved by controlling the acid content in rubber balls during drying. In production practice, coarse and fine pore adhesives are generally higher.

Dry in warm conditions. The higher the drying temperature is, the more primary particles R aggregate 7{

The greater the degree, the larger the aperture. This is the truth of baking hinges. For the system

Silica gel with little or no pore-forming hydrocarbon shrinkage is usually used to reduce pore size.

The method of low liquid surface tension can achieve the goal of Japan.

2.4 Relationship between quality parameters of finished rubber and technological characteristics of silica gel

tie

The technological characteristics of silica gel determine the quality parameters of finished rubber.

Conversely, the standard requires that the quality parameters of the finished rubber are determined.

Process characteristic control. Now take the density of finished rubber pile as an example to analyze one of them.

The relationship. Bulk density is an important quality parameter in the analysis of silica gel products.

One of the numbers can intuitively and simply react the pore knot inside silica gel particles with Ifn.

Physical parameters of the structure. Silica gel is a porous solid particle.

The apparent volume V u} consists of two parts. The first part is

The actual pore space inside the silica gel particles and the volume of the flake are expressed by V a}.

The first part is the pores between particles during stacking, which are represented by V},} and}.

The second part is the volume of silica gel kidney frame, which is measured by Vi. Express delivery.

In this way, V u}-= V}, }+ V a}+ V t, =, let n be the mass of silica gel, i.e.

Get Pug-= m/V},' }+ V}}+ V i', = (different) several kinds of silica gel density Porgy=

mlVa}+ Vi '，=).

2.4. 1 Under the same conditions, there is one silica gel with a certain pore volume.

Fixed bulk density, pore size and pore volume of A, T3 and C adhesives.

The second increase, V u} decreases in turn, that is, the pile density becomes a zone.

The basis for distinguishing glue A, T3 and C, even if they are of the same type.

Glue, the size of the packing density will roughly determine the silica gel particles inside.

Pore structure.

2.4.2 Generally speaking, when an acidic gel is formed, the primary particles R are small and numerous.

The pore size of integrated gel particles is small, and the finished product is formed under the same conditions.

The pore size of silica gel is also small, and a certain volume of silica gel Va: small and piled up.

Natural high density, alkaline gel formation and low bulk density. In the process of air granulation,

If bubble gum is formed, the structure is loose, or gel is caused by other reasons.

The decrease of primary R concentration will increase the VA of finished rubber,

Reduce the Par of Ifn.

2.4.3 rubber washing conditions affect the bulk density of finished rubber, for example, production a.

In the molding process, the cleaning medium of the mountain machinery is always acidic and the temperature is low.

The growth range of secondary particle r' is small, that is, the aging degree is small, and the finished rubber is obtained.

Small V a}, large natural Pir, different acid content, and different degree of inhibition on aging.

It's also different, and so is Pir. This is the passing point in the process of washing glue.

The pile density was detected by stage sampling, and the aging degree of each stage was analyzed.

Main basis. "Coarse porous rubber production mountain" adopts acid foam.

Aging with alkaline hot water for a period of time, washing with high-temperature hot water,

Sometimes, ammonia water is used to treat the last L in the glue, which will lead to the aging of Ifn.

The greater the degree, the larger the pore volume of the finished rubber, and the smaller the Pir.