Thin film reactors - technology that may enable industrial production of nano-barium sulfate

Nano barium sulfate has the characteristics of high refractive index, high whiteness, stable chemical properties, non-toxic and harmless, and low price. It is widely used in coatings, papermaking, plastics, radiation protection materials and other fields. In addition, barium sulfate is also often used in the base material of composite materials to make composite materials such as titanium oxide-barium sulfate, vanadium oxide-barium sulfate, graphene-barium sulfate, etc., to improve the performance of the material and reduce the cost.

In order to make these composite materials have better properties, barium sulfate powder needs to have higher fineness, better dispersibility, larger specific surface area, narrower particle size distribution and other characteristics. However, as far as the particle size of barium sulfate is concerned, many products are not ultrafine enough at present, and the particle size distribution is wide, and the application of high-end products is very limited.

1

Present Status of Nano-Barium Sulfate Preparation Technology

At present, the traditional preparation method of barium sulfate is Glauber's salt black ash method, which is simple to operate and has a wide source of raw materials. Due to the fast precipitation speed of barium sulfate and the low mixing intensity of the traditional preparation method, the prepared barium sulfate particles have large particle size and wide particle size distribution, so that nano-scale barium sulfate particles cannot be obtained. In order to improve mixing strength and slow down sedimentation, special equipment or the addition of large amounts of surfactant is usually required.

Nano barium sulfate can be prepared by precipitation method, microreactor method, microemulsion method, anion exchange method, surfactant method, mixed solvent method, etc., but it is convenient for industrial application, and there are still not many technologies that can produce high-quality products in large quantities. . Fang et al. used the hypergravity method to prepare barium sulfate particles with a particle size of 10-17 nm in a rotating packed bed, but there are problems such as high energy consumption, complicated operation, and the need for large-scale equipment; Niemann et al. Barium sulfate particles with controllable particle size, controllable morphology and minimum particle size of 6 nm are prepared from alkane-alkyl polyethylene glycol, but this method requires the addition of a large amount of surfactants and organic solvents, which is costly, complicated to operate, and Great pollution to the environment. Therefore, it is very necessary to improve the preparation method of nano barium sulfate.

Schematic diagram of the experimental setup for the preparation of nano-barium sulfate in a membrane dispersion microreactor

2

Preparation of Nano-Barium Sulfate by Thin Film Reactor

The thin film reactor uses a microporous membrane or a microfiltration membrane as the dispersing medium, and under the promotion of the pressure difference, one phase enters the other phase uniformly, and finally achieves the effect of complete separation of the two phases. The biggest advantage of using membrane dispersion technology to prepare ultrafine particles is that it can effectively control the supersaturation of the entire system in the traditional simple precipitation process, improve the uniformity of the system, and provide favorable conditions for instant nucleation. Therefore, it is also suitable for the preparation of high-performance Ultrafine particles.

2.1 Case 1

Deng Nan et al. used a membrane dispersion microreactor as the reaction device, using barium hydroxide and sulfuric acid as raw materials, and studied the preparation method of high-suspension nano-barium sulfate under normal and low temperature aging conditions respectively.

TEM image of barium sulfate particles prepared by membrane dispersion microreactor 1

According to the experimental TEM image 1, the particle size of the barium sulfate samples is relatively small when aged at room temperature, and the size distribution is more uniform than that prepared by the stirring method. This is because the micropores on the sintered membrane in the membrane dispersion microreactor can quickly disperse the disperse phase sulfuric acid solution into uniform and fine droplets, which are then quickly and uniformly mixed with the continuous phase barium sulfate to form a uniform and high Supersaturation eliminates the phenomenon of low local supersaturation caused by uneven local stirring in the traditional stirring method. Therefore, the barium sulfate particles prepared by the membrane dispersion microreactor are small in size and uniform in distribution, which fully shows that the membrane dispersion microreactor The advantages of the device in the rapid precipitation reaction can not only obtain barium sulfate particles with better quality, but also save the time spent dropwise adding the raw material solution and the energy consumed by stirring.

TEM image of barium sulfate particles prepared by membrane dispersion microreactor 2

According to the experimental TEM image 2, during low temperature aging, the particle size of barium sulfate particles under XRD is only 32 nm, which is basically consistent with the preparation conditions, but compared with the particle size of the sample H3 prepared by the normal temperature aging method, which is 50 nm, the low temperature aging method The particle size of the prepared barium sulfate particles is significantly reduced. This is because the Ostwald ripening process occurs during the normal temperature aging process, the small particles are continuously decomposed, and the raw materials are provided for the growth of large particles, resulting in the continuous increase of the particle size, and the low temperature conditions will greatly reduce the molecular heat. The movement rate slows down the Ostwald effect during aging, slows down the decomposition of small particles, avoids the rapid growth of nuclei, and makes the particle size distribution of barium sulfate particles narrower.

2.2 Case 2

Chen Guiguang et al. prepared barium sulfate particles with different particle sizes and morphologies by membrane dispersion precipitation method and direct stirring precipitation method. The experimental results show that flake BaSO4 particles with a particle size of 0.3~1μm can be obtained by the direct stirring precipitation method, while spherical particles with an average particle size of 10~100nm can be obtained by the membrane dispersion precipitation method. The method has low energy consumption and can be operated continuously, and is an excellent method for preparing ultrafine barium sulfate.