阅读说明：本技术 一种沉淀水合二氧化硅的制备方法 (Preparation method of precipitated hydrated silicon dioxide ) 是由 白英杰 石清源 于 2019-12-12 设计创作，主要内容包括：本发明涉及一种沉淀水合二氧化硅的制备方法,其原料为硅酸钠、硫酸和自来水,用此方法得到的沉淀水合二氧化硅主要用于各种橡胶做添加补强剂,与普通的沉淀水合二氧化硅相比,具有适中的比表面积和低的吸油值、较小的平均粒径和较低的灼烧减量,在各种橡胶应用中,尤其在高温硫化硅橡胶应用中,在相同的配方和条件下,本发明的沉淀水合二氧化硅相比,混炼胶具有混炼时间短,加工性能优良等特点,橡胶制品具有硬度低、拉伸强度高、透明度高、拉伸不泛白等优点,其特征在于：BET比表面积150-190m<Sup>2</Sup>/g,DBP吸收值200-240ml/100g,灼烧减量3.5-4.0%,平均粒径8.5-9.5μm。(The invention relates to a method for preparing precipitated hydrated silicon dioxide, its raw materials are sodium silicate, sulfuric acid and running water, the precipitated hydrated silicon dioxide obtained by this method is mainly used for various rubbers to make and add the reinforcing agent, compared with ordinary precipitated hydrated silicon dioxide, have moderate specific surface area and low oil absorption value, smaller mean particle size and lower ignition decrement, in various rubber applications, especially in the application of high-temperature vulcanized silicone rubber, under the same formulation and condition, the precipitated hydrated silicon dioxide of the invention compares, the rubber compound has mixing time short, the processing property is good, the rubbery products have hardness low, tensile strength high, transparency high, draw advantage such as not whitening, characterized by: BET specific surface area of 150- 2 (g), DBP absorption value of 200-The diameter is 8.5-9.5 mu m.)

1. A method for preparing precipitated hydrated silica, characterized by the steps of:

(1) raw materials: a: solid sodium silicate with modulus of 3.45-3.5 and ferric oxide content less than 100mg/kg, dissolving, and adding tap water to obtain a solution with density of 1.160-1.162g/cm³And at the temperature of 20 ℃, filtering by using a plate-and-frame filter press to remove impurities to obtain a clear and transparent sodium silicate aqueous solution, b: preparing a 30-35% dilute sulfuric acid aqueous solution by using concentrated sulfuric acid and tap water;

(2) and (3) synthesis reaction:

mixing 0.8-1.2m³Aqueous solution and 15-20m³Adding tap water to 60m³Starting a stirring device in the reaction kettle, simultaneously directly heating by saturated steam, taking the solution in the reaction kettle to measure Na when the temperature reaches 80-88 DEG C₂The content of O% is between 0.22 and 0.26 percent, then the prepared sodium silicate solution and the dilute sulfuric acid are added in parallel, and the flow rate of the sodium silicate solution is 10 to 13m³L, the flow rate of the dilute sulfuric acid is according to the liquid Na in the reaction kettle₂Keeping the O percentage between 0.22 and 0.26 percent, adjusting the parallel flow time for 90 to 120 minutes, keeping the reaction temperature between 80 and 88 ℃ during the parallel flow, stopping adding the sodium silicate solution after the parallel flow is finished, continuously adding the dilute sulfuric acid, requiring 15 to 18 minutes to ensure that the pH value of the reaction solution reaches between 8.5 and 9.5, stopping adding the acid after the pH value requirement is met, ageing the reaction solution for 30 to 40 minutes, then continuously adding the dilute sulfuric acid according to the flow rate of the dilute sulfuric acid, stopping adding the dilute sulfuric acid when the pH value reaches 4 to 5, ageing the reaction kettle for 15 to 20 minutes, finishing the reaction, and keeping the reaction temperature between 80 and 88 ℃ in the process;

(3) filtering and washing:

pumping the reaction suspension into a membrane filter press by a pump, adding a washing filter cake into the filter press, stopping water washing when the conductivity of the washing liquid is less than 150us/cm, introducing compressed air into the membrane filter press, squeezing for 5-7 minutes, and opening the filter press to remove the filter cake;

(4) slurrying, drying and crushing a filter cake to obtain a finished product:

adding the silicon dioxide filter cake into a powerful pulping machine for pulping, conveying the pulped slurry to a slurry storage tank by a pump, conveying the slurry to a centrifugal spray dryer by the pump for drying, controlling the heating decrement of the silicon dioxide to be 5-7%, and crushing to obtain a product with the average particle size of 8.5-9.5 mu m.

2. The process for preparing a precipitated hydrated silica as claimed in claim 1, wherein the BET specific surface area is 150-190m²240ml/100g of DBP absorption value 200-.

3. A process for the preparation of a precipitated hydrated silica as claimed in claim 1 wherein the sodium silicate has a modulus of from 3.45 to 3.50, an iron oxide content of less than 100mg/kg and a formulated density of from 1.160 to 1.162g/cm³At a temperature of 20 ℃.

4. A process for the preparation of a precipitated hydrated silica as claimed in claim 1 wherein the step of synthesis is carried out at a rate of from 0.8 to 1.2m³Aqueous sodium silicate solution and 15-20m³Adding tap water to 60m³Starting a stirring device in the reaction kettle, simultaneously directly heating by saturated steam, taking the solution in the reaction kettle to measure Na when the temperature reaches 80-88 DEG C₂The percentage content of O is between 0.22 and 0.26 percent, then the prepared sodium silicate solution and the dilute sulphuric acid are added in parallel, and the flow rate of the sodium silicate solution is 10 to 13m³L, the flow rate of the dilute sulfuric acid is according to the liquid Na in the reaction kettle₂Keeping the O percentage between 0.22 and 0.26 percent, adjusting the parallel flow time for 90 to 120 minutes, keeping the reaction temperature between 80 and 88 ℃ during the parallel flow, stopping adding the sodium silicate solution after the parallel flow is finished, continuously adding the dilute sulfuric acid, requiring 15 to 18 minutes to ensure that the pH value of the reaction solution reaches between 8.5 and 9.5, stopping adding the acid after the pH value requirement is met, ageing the reaction solution for 30 to 40 minutes, then continuously adding the dilute sulfuric acid according to the flow rate of the dilute sulfuric acid, stopping adding the dilute sulfuric acid when the pH value reaches 4 to 5, ageing the reaction kettle for 15 to 20 minutes, finishing the reaction, and keeping the reaction temperature at 80 to 88 ℃ in the process.

Technical Field

The invention relates to the field of white carbon black chemical industry, in particular to a preparation method of precipitated hydrated silicon dioxide.

Background

In the prior art, precipitated hydrated silica, namely precipitated silica white, is mainly used as an added reinforcing agent for various rubbers, and in recent years, precipitated hydrated silica is low in price and is widely applied to high-temperature vulcanized silicone rubber as the added reinforcing agent, in the application of high-temperature vulcanized silicone rubber, a user generally selects proper precipitated hydrated silica as the added reinforcing agent according to the requirements of rubber products, and generally selects BET specific surface area of 150-180m for silicone rubber products with low tensile strength requirements²Precipitation in gThe precipitated hydrated silica has a low oil absorption value which is generally 240ml/100g at 200-; for rubber products with high tensile strength requirements, the BET specific surface area is generally selected to be 190-²The precipitated hydrated silicon dioxide has a high oil absorption value which is generally between 230-280ml/100g, high ignition loss (4.0-5.5%), large average particle size (10-13 mu m), high tensile strength and good transparency of a prepared rubber product, but long mixing time, poor processability, high product hardness and slight whitening phenomenon in stretching, so that the application of the precipitated hydrated silicon dioxide in high-temperature vulcanized silicone rubber is limited due to the defects of the conventional precipitated hydrated silicon dioxide in high specific surface area.

Disclosure of Invention

The invention aims to overcome the defects of the technology and provides a preparation method of precipitated hydrated silicon dioxide, the precipitated hydrated silicon dioxide obtained by the method has moderate BET specific surface area, low oil absorption value, smaller average particle size and lower ignition loss, and compared with the common precipitated hydrated silicon dioxide, the precipitated hydrated silicon dioxide has the characteristics of short mixing time, excellent processing performance and the like in the mixing process under the same formula and conditions in various rubber applications, particularly in high-temperature vulcanized silicone rubber applications, and rubber products have the advantages of low hardness, high tensile strength, high transparency, no whitening in stretching and the like, the BET specific surface area is 150-²240ml/100g of DBP absorption value 200-.

The technical solution of the invention is as follows:

a method of preparing precipitated hydrated silica comprising the steps of:

raw materials: a: solid sodium silicate with modulus of 3.45-3.5 and ferric oxide content less than 100mg/kg, and dissolving and adding tap waterThe density of the product is 1.160-1.162g/cm³Filtering the solution at the temperature of 20 ℃ by a plate-and-frame filter press to remove impurities to obtain a clear and transparent sodium silicate aqueous solution, b: preparing a 30-35% dilute sulfuric acid aqueous solution by using concentrated sulfuric acid and tap water;

and (3) synthesis reaction:

mixing 0.8-1.2m³Aqueous solution and 15-20m³Adding tap water to 60m²Starting a stirring device in the reaction kettle, simultaneously directly heating by saturated steam, taking the solution in the reaction kettle to measure Na when the temperature reaches 80-88 DEG C₂The content of O% is between 0.22 and 0.26 percent, then the prepared sodium silicate solution and the dilute sulfuric acid are added in a concurrent flow manner, and the flow rate of the sodium silicate solution is 10 to 13m³/L), the flow rate of the dilute sulfuric acid is determined according to the liquid Na in the reaction kettle₂Keeping the O percent between 0.22 and 0.26 percent, adjusting the parallel flow time for 90 to 120 minutes, keeping the reaction temperature between 80 and 88 ℃ during the parallel flow, stopping adding the sodium silicate solution after the parallel flow is finished, continuously adding the dilute sulfuric acid, requiring 15 to 18 minutes to ensure that the pH value of the reaction solution reaches between 8.5 and 9.5, stopping adding the acid after the pH value requirement is met, ageing the reaction solution for 30 to 40 minutes, then continuously adding the dilute sulfuric acid according to the flow rate of the dilute sulfuric acid, stopping adding the dilute sulfuric acid when the pH value reaches 4 to 5, ageing the reaction kettle for 15 to 20 minutes, finishing the reaction, and keeping the reaction temperature at 80 to 88 ℃ in the process.

Filtering and washing:

pumping the reaction suspension into a membrane filter press by a pump, adding a washing filter cake into the filter press, stopping water washing when the conductivity of the washing liquid is less than 150us/cm, introducing compressed air into the membrane filter press, squeezing for 5-7 minutes, and opening the filter press to remove the filter cake;

slurrying, drying and crushing a filter cake to obtain a finished product:

adding the silicon dioxide filter cake into a powerful pulping machine for pulping, conveying the pulped slurry to a slurry storage tank by a pump, conveying the slurry to a centrifugal spray dryer by the pump for drying, controlling the heating decrement of the silicon dioxide to be 5-7%, and crushing to obtain a product with the average particle size of 8.5-9.5 mu m.

The invention has the advantages that:

1. the modulus of the sodium silicate adopted by the invention is 3.45-3.50,the preparation density is 1.160-1.162g/cm³(20 ℃), the concentration of the dilute sulphuric acid is 30-35%, and the reaction temperature is controlled to be 80-88 ℃ because the concentration of the sodium silicate solution and the dilute sulphuric acid is high, and the reaction solution Na₂O% can form a large amount of fine silica primary particles instantly under the condition of 0.22-0.26%, because the sodium silicate and the dilute sulfuric acid used for reaction have high concentration, and a large amount of instantly formed primary particles have more collision opportunities, so that the formed fine silica secondary particles with compact structures are formed, and the secondary particles are combined with each other to form silica agglomerates to settle down, thereby obtaining the precipitated hydrated silica with low oil absorption value and small particle size.

2. When the pH value of the synthetic reaction liquid reaches 8.5-9.5, the synthetic reaction liquid is aged for 30-40 minutes, and silanol groups on the surfaces of the formed precipitated hydrated silicon dioxide particles can be promoted to be mutually combined to form water, so that the silanol groups on the surfaces of the precipitated hydrated silicon dioxide particles are reduced, the intermiscibility of the precipitated hydrated silicon dioxide and rubber is increased, the processability of rubber compound is improved, and the mixing time is shortened.

3. In the production process, the precipitated hydrated silicon dioxide obtained by the invention is found to have the average particle size which is 1-2 mu m smaller than that of the common precipitated hydrated silicon dioxide and reaches 8.5-9.5 mu m under the same crushing condition, which shows that the silicon dioxide obtained by the invention has better dispersibility, can increase the tensile strength and transparency of rubber products and can improve the phenomenon of tensile whitening.

Detailed Description