Preparation method of high-temperature discharging in-situ gas phase hydrophobic modified indirect zinc oxide

Abstract

The application discloses a preparation method of high-temperature discharging in-situ gas-phase hydrophobic modified indirect zinc oxide. Under the hot-state condition of zinc oxide cloth bag discharging, a gas-solid contact coating is carried out between a gasification modifier and a powder to form a monomolecular hydrophobic layer, so that the modification is realized in a wet-free, continuous and on-line mode. The process utilizes waste heat, does not produce waste water and does not stick to the wall. The product has excellent moisture-proof, anti-sticking and anti-caking performances and is suitable for high dispersion required fields such as rubber and paint.

Description

Technical Field

[0001] This invention belongs to the field of inorganic powder surface modification technology, specifically relating to a continuous preparation method that utilizes the residual heat from the discharge of zinc oxide bag filter in an indirect method to achieve gas-phase monolayer hydrophobic coating under hot powder conditions, thereby inhibiting powder moisture absorption and agglomeration. Background Technology

[0002] Indirect zinc oxide is widely used in rubber vulcanizing activators, thermally conductive fillers, coatings, and other fields. In traditional production processes, the temperature of zinc oxide discharged from the oxidation chamber or baghouse dust collector is typically 100–200℃. Direct cooling presents the following problems: 1. High-temperature powders have high surface energy, and during the cooling process, particles are prone to cold welding and adhesion, forming hard agglomerates; 2. Zinc oxide has many hydroxyl groups on its surface, making it prone to moisture absorption. It clumps severely during storage, which is not conducive to automatic batching and makes downstream dispersion difficult. 3. Conventional dry modification is mostly carried out at room temperature or low temperature, resulting in uneven coating and easy detachment; wet modification introduces moisture, which aggravates agglomeration and increases drying energy consumption and process steps. 4. During rubber compounding, agglomerated zinc oxide is difficult to break up, resulting in uneven vulcanization and fluctuations in mechanical properties.

[0003] Existing technologies lack an industrialized modification process for in-situ, continuous, dry, and thin-coating of materials at high temperatures immediately after discharge, thus failing to suppress agglomeration at the source. Summary of the Invention

[0004] To address the problems of existing zinc oxide materials such as stickiness upon cooling, easy agglomeration during storage, poor dispersibility, and inconvenience for automated batching, a method for in-situ vapor-phase hydrophobic coating modification at high temperature discharge is provided. This method achieves moisture-free, continuous, and uniform modification, thereby inhibiting the agglomeration of zinc oxide produced by indirect methods from the source.

[0005] The present invention is implemented as follows: a method for preparing zinc oxide by in-situ vapor-phase hydrophobic modification at high temperature discharge via an indirect method, comprising the following steps: (1) After the indirect zinc oxide undergoes an oxidation reaction, it is collected by a bag filter and the discharge temperature is controlled at 100–180℃. It is then introduced into a gas phase modification section before entering the cooler / silo. (2) The low-boiling-point hydrophobic modifier is vaporized and then fully mixed and contacted with the high-temperature zinc oxide powder in the mixer under the action of the carrier gas; (3) Complete the in-situ hydrophobic coating on the powder surface under hot conditions to form a monomolecular hydrophobic layer; (4) After cooling, a hydrophobic, moisture-proof, and anti-agglomeration zinc oxide product is obtained.

[0006] Furthermore, In step (1), the discharge temperature of the high-temperature zinc oxide is preferably 120–160℃.

[0007] In step (2), the modifier is selected from one or more of alkylsilanes, alkylsiloxanes, and fatty acid esters, and is used in an amount of 0.2–1.5 wt% of the zinc oxide mass. The carrier gas is dry nitrogen with a dew point ≤ -20℃; The mixer is a swirling gas-solid mixer, and the residence time of the material in the mixing chamber is 3–15 seconds.

[0008] Furthermore, in step (2), the modifier is preferably one or more of propylsilane, methylsiloxane, and vinyltrichlorosilane.

[0009] Compared with existing technologies, the beneficial effects are: 1. Hot in-situ modification: Utilizes residual heat for reaction, requiring no additional heating and resulting in low energy consumption.

[0010] 2. The introduction of the swirling gas-solid mixer allows the mixed gas of the carrier and the gasification modifier, as well as the high-temperature zinc oxide powder, to enter the mixing chamber through the tangential inlet, forming a high-speed swirling flow. Under the action of centrifugal force and shear force, deep mixing at the molecular level is achieved, ensuring the coating modification effect.

[0011] 3. The gas-phase monolayer coating is uniform and does not agglomerate, thus not affecting the activity of zinc oxide.

[0012] 4. Excellent moisture-proof and non-sticking properties: This solution involves installing a swirling gas-solid mixer after the bag filter and before the cooler, ensuring that the material is always in a water-free, closed system. Furthermore, the mixed gas of the modifier must also be water-free. After modification, the powder surface is coated with a hydrophobic layer, preventing the material from coming into contact with water of various phases during subsequent storage and use, thereby avoiding problems such as agglomeration, stickiness, clumping, and poor flowability. Detailed Implementation To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below. Example 1:

[0013] This invention provides a method for preparing zinc oxide via in-situ vapor-phase hydrophobic modification at high temperature discharge, comprising the following steps: (1) After the indirect zinc oxide undergoes an oxidation reaction, it is collected by a bag filter and the discharge temperature is controlled at 160°C. It is then introduced into a gas phase modification section before entering the cooler / silo. (2) After the mixture of methylsiloxane and vinyltrichlorosilane (total amount is 1.5 wt% of the mass of zinc oxide) is vaporized, it is fully mixed and contacted with high-temperature zinc oxide powder in a swirling gas-solid mixer under the action of dry nitrogen, and the residence time in the chamber is not less than 3 seconds. (3) Complete the in-situ hydrophobic coating on the powder surface under hot conditions to form a monomolecular hydrophobic layer; (4) After cooling, a hydrophobic, moisture-proof, and anti-agglomeration zinc oxide product is obtained. Example 2:

[0014] (1) After the indirect zinc oxide undergoes an oxidation reaction, it is collected by a bag filter and the discharge temperature is controlled at 120°C. It is then introduced into a gas phase modification section before entering the cooler / silo. (2) Propylsilane (0.2 wt% of the mass of zinc oxide) is vaporized and then mixed and contacted with high-temperature zinc oxide powder in a swirling gas-solid mixer under the action of dry nitrogen. The residence time in the chamber is not less than 3 seconds. (3) Complete the in-situ hydrophobic coating on the powder surface under hot conditions to form a monomolecular hydrophobic layer; (4) After cooling, a hydrophobic, moisture-proof, and anti-agglomeration zinc oxide product is obtained.

[0015] Comparative Example 1: The difference from Example 1 is that the same zinc oxide is used, but high-temperature in-situ vapor phase coating is not performed; instead, it is directly cooled.

[0016] Comparative Example 2: The difference from Example 1 is that the zinc oxide prepared by the indirect method in Comparative Example 1 by direct cooling was added to a high-speed mixer. The same type and weight of modifier as in Example 1 were used to directly modify the surface of the zinc oxide at room temperature and pressure without vaporization. The high-speed mixing lasted for no less than 5 minutes, and the finished product was obtained by discharging.

[0017] To evaluate the effectiveness of this method, the products of Example 1 and Comparative Examples 1 and 2 were subjected to the following tests: 1. Moisture absorption rate test Accurately weigh 2.00 g of the sample, spread it evenly in a clean, dry weighing bottle, and place it in a constant temperature and humidity test chamber at 25 ℃ and 85% relative humidity for 24 h. Afterward, remove the sample and weigh it quickly. Calculate the moisture absorption rate using the following formula: Moisture absorption rate = (Mass after moisture absorption - Initial mass) ÷ Initial mass × 100% 2. Evaluation of storage stability and clumping tendency Take 500 g of sample and place it in a sealed bag. Store it at room temperature for 30 days and 90 days respectively. Observe and record the powder agglomeration. Judge according to the following grades: • No clumping: The powder flows freely without sticking together; • Slight lumps: can be easily broken up with a light tap; • Obvious clumping: requires crushing to disperse; • Hard aggregates: cannot be mechanically broken up.

[0018] 3. Angle of repose test The fixed funnel method was used to determine the angle of repose of the powder. The sample was allowed to fall freely from a fixed height to form a cone. The height H and the diameter D of the base of the cone were measured, and the angle of repose θ was calculated using the following formula: Tanθ = 2H ÷ D A smaller angle of repose indicates better powder flowability.

[0019] 4. Hydrophobicity evaluation The sample was pressed into a flat specimen, and deionized water was dropped onto the surface. The shape of the water droplets and the wetting situation were observed.

[0020] 5. Evaluation of the dispersibility of rubber compounds Zinc oxide was added to natural rubber according to a standard rubber formulation. After passing through a two-roll mill 10 times, the rubber was sheeted and left to stand at room temperature for 24 hours. The white spots and agglomerated particles on the surface of the sheet were observed, and the dispersion grade was evaluated. • Advantages: Smooth surface, no white spots or particles; • Good: Occasionally, extremely minute details are observed; • Poor: Obvious white spots and aggregated particles are present.

[0021] The test results are shown in the table below: Table 1: Comparison of the effects of zinc oxide modification

[0022] Analyzing the evaluation results of the above aspects, it can be seen that: the zinc oxide prepared by the indirect method in the traditional way is unmodified and has serious hygroscopicity. Storage will lead to obvious stickiness and clumping problems, and will also bring a series of troubles to its subsequent application effect and automatic conveying. The product prepared by the present invention has significant advantages, improves the utilization efficiency of powder, and provides customers with the convenience of batching and conveying.

Claims

1. A method for preparing zinc oxide via in-situ vapor-phase hydrophobic modification at high temperature discharge, characterized in that, Including the following steps: (1) The high-temperature zinc oxide powder collected by the cloth bag is controlled at a temperature of 100–180℃; (2) The low-boiling-point hydrophobic modifier is vaporized and then fully mixed and contacted with the high-temperature zinc oxide powder in the mixer under the action of the carrier gas; (3) Complete the in-situ hydrophobic coating on the powder surface under hot conditions to form a monomolecular hydrophobic layer; (4) After cooling, a hydrophobic, moisture-proof, and anti-agglomeration zinc oxide product is obtained.

2. The method for preparing zinc oxide by in-situ vapor-phase hydrophobic modification at high temperature according to claim 1, characterized in that, The preferred discharge temperature for the high-temperature zinc oxide is 120–160℃.

3. The method for preparing zinc oxide by in-situ vapor-phase hydrophobic modification at high temperature according to claim 1, characterized in that, The modifier is selected from one or more of alkylsilanes, alkylsiloxanes, and alkylchlorosilanes.

4. The method for preparing zinc oxide by in-situ vapor-phase hydrophobic modification at high temperature according to claim 1, characterized in that, The modifier is preferably one or more of propylsilane, methylsiloxane, and vinyltrichlorosilane.

5. The method for preparing zinc oxide by in-situ vapor-phase hydrophobic modification at high temperature according to claim 1, characterized in that, The amount of the modifier is 0.2–1.5 wt% of the zinc oxide mass.

6. The method for preparing zinc oxide by in-situ vapor-phase hydrophobic modification at high temperature according to claim 1, characterized in that, The carrier gas is dry nitrogen with a dew point ≤ -20℃.

7. The method for preparing zinc oxide by in-situ vapor-phase hydrophobic modification at high temperature according to claim 1, characterized in that, The mixer is a swirling gas-solid mixer.

8. The method for preparing zinc oxide by in-situ vapor-phase hydrophobic modification at high temperature according to claim 1, characterized in that, The residence time of the material in the mixing chamber is 3–15 seconds.

9. The method for preparing zinc oxide by in-situ vapor-phase hydrophobic modification at high temperature according to claim 1, characterized in that, The coating is a monolayer hydrophobic coating that does not introduce moisture and does not cause adhesion to the wall.

10. The zinc oxide product prepared according to any one of claims 1-9, characterized in that, The product has hydrophobic, moisture-proof, non-stick, and anti-caking properties, making it suitable for applications requiring high dispersion, such as rubber and coatings.

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