1 the introduction

Silica gel is a two-dimensional space mesh structure of a dry silica gel, belongs to the porous solid material, aperture distribution range is wide, and greatly than tables, table and cover a large number of silane alcohol gene Bi Si - OH), has a certain activity. Make it a desiccant, adsorbent, catalyst and catalyst carrier, etc., widely used in several industrial production.

2 process characteristics

Although the production of silica gel is mostly through gels, washing and drying, it is specific to a certain type of glue, and there are different characteristics of different processes and differences.

2. 1 gel granulation process.

Gel granulation is one of the key steps of silica production, refers to a certain concentration of diluted bubble spent lye and dilute sulphuric acid in certain conditions fully reaction to form soluble gel solution, up to a certain concentration to form gel particles. Gel particle shape, size and so on complete mountain user requirements and process production capacity decision, pass "several gel method, has many USES air granulation, for fine granularity, considering the difficulty of granulation, the air is mostly adopts the reaction tank gel granulation, micro powder silica gel production. The acid base ratio, concentration, temperature and time of gel granulation are the specific process parameters of the gel granulation process.

2.1.1

In the case of acid base ratio problem, a gel particle r(relatively few primary grain to small, easy to form the pore structure of silica gel; When the alkali is gelatinized, the gel particle r is large, and it is easy to form the coarse - porosity silica gel. This is the production of crude pore glue and the production of the basic glue, fine pore glue production is preferred to the acid glue.

2.1.2 the acid base concentration should be moderate.

Acid-base concentration is too high, a gel particle r is larger, gather into a coarse pore size of silica gel, Ifn one grain of gel solution concentration is also big, I the increase of gel network structure tightness, gather and easily become pores, things tend to cancel each other out. Moreover, acid and alkali concentration is too high, increase the viscosity of the gel solution, bring certain difficulty to granulation, in addition, the size of the concentration of acid and alkali are gel particle size, structure, design and production capacity, etc.

2. 1. 3 acid base temperature is too high.

Acid-base reaction too fast. Ifu acid-base reaction wood is exothermic reaction. A grain of r gather and exothermic. So. Makes a grain of r had big ". Granulation has slowed. Beyond the technological requirements. Bad for granulation; The acid base temperature is too low. One grain r decreases. It is easy to form fine pores.

The solution temperature is too low and the viscosity increases. So the acid base temperature should be moderate.

2. 1. 4

Gel granulation time is another important process parameter in the process of gel granulation. It refers to the amount of time that is experienced from the beginning of the acid and alkali mixing reaction to the formation of the particle size gel. Gel granulation time is short. May make the gel solution of inadequate or evenness enough. Makes a grain of r. The concentration distribution of the unevenness of the formation of local gel or close packing. This leads to the bubble gum in the process of granulation. The phenomenon such as rubber or rubber ball strength is not enough. At the same time, this is also the cause of the internal structure disorder of colloidal particles. So. In production practice. For "a few air granules. In the process allowable range. Granule large glue. The time should be as long as possible. Small particles of glue. The time can be relatively short. Ifn pairs "a few microspheres of silica gel granulated in the reaction kettle. The time is longer. The eyes should be stirred.

2. 2 washing process

Wash is necessary in the production of silicone glue process. In order to wash granular gel formed by NazSO}, {7 to the Yin and Yang from r (mainly for 10 H, N enlarge, SO a, iY} r Si0 wear, etc.) within the scope of control to the process requirement. At the same time, it is also a process of adjusting the internal structure of particles (i.e. aging).

2. 2. 1 exchange adsorption.

The phenomenon of the exchange between Na 10 and H 10 is one of the wooden characteristics of the process of cleaning rubber. The acid bubble process is the main process of exchange adsorption. The exchange of 1}' a' and H 10 is more than that in this process. The exchange of the washing process is far from stopping but the exchange is getting smaller and smaller. Acid bubble concentration, water washing medium and washing temperature are the main process parameters of the washing process, affecting the exchange rate, quantity and so on.

2 2. 2.

A large part of the pore characteristics of the finished silica gel is determined by the aging process of the mountain cleaning process, and the aging degree of this process depends on the cleaning medium and temperature. The main factor of controlling the growth rate of a particle is the cleaning medium and temperature, which is to adjust the growth of the particle to achieve the purpose of adjusting the pore structure.

Fine Kong Jiao washing for inhibiting aging, therefore, is necessary after gel granulation formation and short after aging for acid soak, wash the gel medium must show acidity throughout, because acid medium (i.e., H 10) can effectively restrain a particle "grow up", the size of the mesh _ acid content that determine the size of the inhibition of aging degree. At the same time, the gel temperature should be lower, because aging is a process of absorbing energy, low temperature, low energy supply, and natural aging degree. That is to say, the washing of fine pores is to adjust the pore structure by inhibiting the "growing" of a particle. In particular, the structure of several holes is required to be strict (i.e., small hole distribution scope). The density of the pile is also required to be produced in a certain range of fine pores, for example, for the production of the special fine pore glue for the variable pressure adsorption COz. The amount of acid and temperature of washing water should be strict. The washing temperature is low and the exchange rate is slow, so the washing time is longer, but it cannot be too big. The time is too long.

The production of coarse pore glue requires the promotion of aging. Follow the principle of alkaline medium, high temperature hot water to promote aging, to take in high temperature hot water before acid soak, _ trying to make it show alkaline, raising the temperature in the process of washing, 7 {at the end of the end l from, adding certain concentration of ammonia, in order to add 0 H - the concentration of the ions and other measures, prompting a particle 'grow up ", expanding the aperture, achieve the goal of aging. It is not difficult to see that during the whole washing process, the aging degree is increasing. Mountain "several water temperature high, not only the particles inside a particles grew up, eye _ especially between powder particles between particles also have a tendency to" grow up ", this is washed at high temperature, easy to agglomerate, powder gathering place of adhesive and powder ball table and another main reason.

For coarse pore size, such as the production of T3 type glue between thick and thin pores, moderate aging can be used, and sometimes it is used to buffer the liquid form in the drying process, and the water washing is finished and processed. The temperature of the mountain is too high, the time is too long, the existence of the treatment solution will change the glue ball, so the application of the treatment solution will be limited by the drying process conditions.

2. 3 drying process

The drying is in the liquid form and the tension function, which causes the moisture evaporation volume of the colloidal particles to shrink, and 7{to make one particle reunite JI 'to grow' to achieve the purpose of deep aging. In order to inhibit the aging, fine pores are often controlled by the amount of acid in the rubber ball. In the production practice, the thickness of the fine pores in the general high temperature conditions. The higher the drying temperature is, the greater the speed of a single particle r is, and the larger the pore diameter is. This is the reason for roasting and expanding holes. For the system

It is often used to reduce the liquid form and the tension is achieved by the method of reducing the liquid form.

2. 4 quality parameters of the finished product and the characteristics of silica gel process.

Department of

The process characteristic of silica gel determines the quality parameter index of the finished product. In turn, the quality parameter index of the finished glue is required to control the process characteristics. In this paper, we analyze the relationship of the glue heap density. The pile density is one of the important quality parameters in the analysis of silica gel finished product, and it can directly reflect the physical parameters of the internal pore structure of the silica gel particles. Silica gel is a kind of porous solid particle, and its apparent volume V u} is composed of two parts. The first part is the actual hole in the silica gel particle, and the volume is expressed as V a}. The first part is the pore between particles in the accumulation, in V},}. The second part is the volume of the silicone kidney frame, which is Vi. Said. So V u}} - = V, a}} + V + V t, =, n, for the quality of the silica gel, a quick - = m/V} relation, '}}} + V + V I, Porgy = = (different from "a few silicone density mlVa} + Vi ', =).

2. 4. 1

Same conditions, A certain pore size of silica gel, corresponding to A certain bulk density, A, T3, C aperture of two types of adhesive, entrance, in turn, increases, the V u} in turn decreases, and this is the bulk density into the difference between A, T3, C two types on the basis of glue, even the same type glue, bulk density will be roughly the size of the silica gel particles within the pore structure.

2 2. 4.

Generally, acid gel, a small grain of r, gathered into a small aperture of gel particles, the same conditions, the formation of the finished product silica gel pore size is small, a certain volume of silicone Va: small, bulk density, natural alkaline gel, the bulk density is small. When the air is granulated, if the bubble gum is formed, the structure is loose, or the concentration of the gel is reduced due to other reasons, etc., all of which will increase the V a} of the finished product, reducing the Par from the Ifn.

2. 4. 3

Wash glue condition affecting the bulk density of the rubber product, type A rubber case production, mountain "A few washing adhesive have been for the acidic medium, _ temperature is low, the size of A grain of r" grow up "small, namely the aging degree of small, finished product rubber V} A small, Pir natural big, acid content is different, inhibit the aging degree is also different, Pir is different also. This is one of the main basis for the analysis of the aging degree of various stages during the process of washing rubber. For "a few rough Kong Jiao production mountain" taken acid with alkaline hot water bubble before aging for a period of time, JI _ high temperature hot water washing, sometimes treated with ammonia eventually l from rubber, due to the aging condition of Ifn makes big, finished product gel pore size, Pir is small.