Alkaline silica process In the prior art, precipitation silica is a widely used inorganic functional powder material, which is mainly used in fields such as ordinary rubber, silicone rubber, coatings, inks, pesticides, and papermaking. The main method used for the production of high elastic silicone rubber silica is the precipitation method. The existing precipitation silica production methods generally use liquid water glass and concentrated sulfuric acid as raw materials, and are prepared by precipitation reaction, pressure filtration, pulping, and spray drying. The ph value of ordinary silica is generally controlled at 5-7. Silica with acid on the surface will release hydrogen ions, neutralize the alkaline accelerator, and affect the vulcanization speed. In addition, the specific surface area of ordinary silica is large, and it is slow to eat powder when mixing rubber, and it is easy to heat up and has a high viscosity. , and other shortcomings, which are not conducive to processing.

The purpose of the present invention is to provide an alkaline white carbon black, the pH value is adjustable between 7.5-11, can promote vulcanization, and the specific surface area of the product is small, between 50-110m2/g, easy to process alkaline white carbon The production method of black is used as basic silica for special rubber, such as for the production of polyfluoro rubber and polyacrylate rubber.
The technical scheme of the present invention is as follows: the operation steps of the production method of alkaline silica include dissolving and refining of water glass, synthesis reaction of water glass and dilute sulfuric acid, pressure filtration, washing, pulping, drying processes, water glass and dilute sulfuric acid The synthesis reaction is carried out in three steps. First, the seed crystals are generated, and then the synthesis reaction is carried out. Finally, sodium hydroxide is added to adjust the overall pH value. The surface area is controlled between 50-110m2/g, which is easy to process. The specific steps are as follows:
(1) Refined water glass solution: Add the solid water glass and water into the static dissolving tank in the ratio of 1:1.5-2.5, and then pass in steam after sealing. When the pressure rises to 0.4-0.5mpa, stop the steam and keep the pressure. After 3 hours, put it into the batching tank, add water, configure the water glass to 1.075-1.095g/cm3, and filter the plate and frame for later use.

(2) Synthesis reaction of precipitated silica:

The first step is to inject a certain amount of prepared water glass solution into the reactor (according to 20%-30% of the total amount of reaction in each still), and add a certain amount of 15% sodium sulfate solution (according to the total amount of reaction in each still). 10%-15%), pass in steam, turn on stirring when the temperature rises to 45-50°C, continue to heat up to 89-90°C, and add the prepared sulfuric acid with a mass fraction of 15% into the reaction kettle at a certain flow rate, when suspended When the pH value of the liquid reaches 9.5-10.5, the addition of acid is stopped, and the reaction generates microcrystalline seeds, and the reaction time is 40 minutes; this step obtains primary silica particles with small specific surface area and uniform particle size.

In the second step, water glass and dilute sulfuric acid are added to the reaction kettle at the same time according to a certain flow rate. The amount of water glass added is 70-80% of the total amount of each kettle. The amount of sulfuric acid added requires that the pH value of the suspension should be maintained at 9.5-10.5 during the reaction process. No change, carry out the synthesis reaction, the reaction time is 50 minutes, the reaction temperature is 89-90 ℃, and the reaction pH value is controlled between 10-11. Silica particles different from the primary particles produced in one stage are produced by changing the reaction conditions, and the growth degree of the silica particles is controlled.

The third step, continue to add dilute sulfuric acid, adjust the pH value of the end point to 4-5, add sodium hydroxide, adjust the pH to 7.5, continue stirring for 30 minutes and stop stirring; this step makes the first and second steps unreacted The water glass is completely reacted, and sodium hydroxide solution is added to adjust the pH value.

(3) Pressure filtration and washing of the reaction slurry: The reacted slurry is separated from solid and liquid by a plate and frame filter press, and washed until the conductivity is less than 300us/cm.

(4) Pulping: The filter cake is sent to the beating tank through the belt conveyor, and the slurry is made by two stirring modes of high speed and low speed to provide a uniform slurry for spray drying.

(5) Drying process: After the slurry is dried by a spray drying tower, it is then pulverized by a mechanical pulverizer to a particle size of less than 15 μm, collected with a bag-type pulse dust collector, and then packaged for storage.

In step (2), a small amount of crystal seeds are first generated in the synthesis reaction of precipitation silica, and then a certain amount of sodium sulfate solution is added in the further synthesis reaction to greatly reduce the specific surface area of the product and improve the dispersibility of the product. Add sodium hydroxide solution to adjust pH.

The characteristics of the invention are: compared with the traditional process, the three-step synthesis process is adopted, and sodium sulfate auxiliary agent is added to reduce the specific surface area of the product, improve the dispersibility, and has the advantages of small specific surface area, low oil absorption value, large bulk density, and the end of the end-point reaction. Then add sodium hydroxide solution to adjust the pH value to ensure that the pH value of the product is within the required range. The production process of the patent of the present invention improves the production process of the traditional precipitation method silica, and achieves the pH value of the product between 7.5-11 and the specific surface area between 50-110m2/g by optimizing the process parameters and optimizing the auxiliary agent. (Reduce the specific surface area by adding sodium sulfate additives and the reaction process control of step 1 and step 2) to ensure the application of the product in special rubber (such as for the production of polyfluororubber and polyacrylate rubber).

Detailed ways

Below in conjunction with specific embodiment, the production process of a kind of white carbon black of the present invention is described in further detail.

(1), the embodiment and its specific operation steps

Example 1

The specific operation steps of the production method of basic white carbon black are as follows:

1. Refined water glass

Take 40m³ of water glass dissolved by steam, configure it into water glass with a specific gravity of 1.080-1.085g/cm³, filter it through the plate and frame, and take the clear liquid for use.

2. Synthesis of silica

Add 11m³ of bottom material to the 55m³ reaction kettle, and at the same time add sodium sulfate of the same quality, pass steam to heat up, start stirring when the temperature rises to 50 degrees, continue to heat up, and start adding sulfuric acid dropwise when the temperature reaches 87 degrees, sulfuric acid per hour Add 0.15m³ dropwise, react until the pH value is between 10-11, start the second-stage reaction, add water glass and sulfuric acid dropwise at the same time, dropwise add 19m³ of water glass every hour, and add 0.42m³ of sulfuric acid every hour, and react until the pH value is at 10 Stop dripping between -11, start the three-stage reaction, add sulfuric acid dropwise, adjust the pH value of the reaction end point, the flow rate is 0.38m³ per hour, adjust the pH value between 4.5-5.5, and adjust the pH value after adding sodium hydroxide At around 7.5, the synthesis reaction was completed, and it was aged for 30 minutes.

3. Hydraulic filtration and washing of reaction slurry

The reacted slurry is separated from solid and liquid by a plate and frame filter press, and washed with water with a conductivity of 100us/cm until the conductivity is less than 300us/cm, and the sodium sulfate content is less than 0.15%.

4. Pulping

The filter cake is sent to the beating tank through a belt conveyor, and is pulped by two stirring modes of high speed and low speed to provide a uniform slurry for spray drying.

5. Drying process

After the slurry is dried by the spray drying tower, it is pulverized by a jet mill, collected by a bag-type pulse dust collector, and then packaged and put into storage.

Example 2

The specific operation steps of the production method of basic white carbon black are as follows:

1. Refined water glass

Take 50m³ of water glass dissolved by steam, configure it into water glass with a specific gravity of 1.085-1.090g/cm³, filter it through the plate and frame, and take the clear liquid for use.

2. Synthesis of silica

Add 13m³ of bottom material to the 55m³ reaction kettle, and at the same time add sodium sulfate of the same quality, pass steam to heat up, start stirring when the temperature rises to 45°C, continue to heat up, and start adding sulfuric acid dropwise when the temperature reaches 88°C, sulfuric acid per hour Add 0.16m³ dropwise, react until the pH value is between 10-11, start the second-stage reaction, and add water glass and sulfuric acid dropwise at the same time. Stop the dropwise addition between -11, start the three-stage reaction, add sulfuric acid dropwise, adjust the pH value of the reaction end point, the flow rate is 0.35m³ per hour, adjust the pH value between 4.5-5.5, and adjust the pH value after adding sodium hydroxide. 8 or so, the synthesis reaction was completed, and it was aged for 30 minutes.

3. Hydraulic filtration and washing of reaction slurry

The reacted slurry is separated from solid and liquid by a plate and frame filter press, and washed with water with a conductivity of 100us/cm until the conductivity is less than 300us/cm, and the sodium sulfate content is less than 0.15%.

4. Pulping

The filter cake is sent to the beating tank through a belt conveyor, and is pulped by two stirring modes of high speed and low speed to provide a uniform slurry for spray drying.

5. Drying process

After the slurry is dried by the spray drying tower, it is pulverized by a jet mill, collected by a bag-type pulse dust collector, and then packaged and put into storage.

2. Analysis of the results of specific examples

The performance index comparison of the white carbon black prepared by the above two embodiments and ordinary white carbon black is shown in Table 1 and Table 2:

Table 1 Comparison of comprehensive indicators of various products

After the product is prepared, take the basic formula of polyfluororubber as an example to do a comparative test with diatomite:

Table 2 Comparison of physical properties of each product。