Application of Microporous Zeolite Molecular Sieve

2022-03-25

Because of its hydrothermal stability, microporous zeolite molecular sieves have been investigated by scientists for desulfurization reactions. Microporous materials are widely distributed in nature and are commonly used microporous materials. They are silicon-aluminum-based materials with a high degree of crystallinity with a microporous structure. At present, it can be obtained by artificial synthesis for a long time. They have the following characteristics: uniform molecular-level pore size (0.3-1 nm), hydrothermal stability, good selectivity and reactivity.

Zeolite molecular sieves are widely used in catalytic cracking reactions or adsorption reactions. In addition, due to the good modifiability characteristics of microporous molecular sieves, functional groups can be grafted by impregnation or by introducing heteroatoms during synthesis and by ion exchange, so that they can be used in catalytic cracking, Adsorption and desorption, membrane separation and other fields have played different uses.

1 Application of natural zeolite in desulfurization

The desulfurization performance of natural clinoptilolite in the temperature range of 100-600 ^oC. Experiments show that the sulfur capacity of the desulfurizer decreases significantly as the temperature increases from 100 to 600 ^oC, from 8.7g elemental sulfur/100g desulfurizer to 3g elemental sulfur/100g desulfurizer. By optimizing the properties of clinoptilolite with different components, the retained sulfur capacity at 300^oC vulcanization temperature is 6.3g elemental sulfur/100g desulfurizer. Although the sulfur capacity of clinoptilolite is relatively low, it has a stable structure and high specific surface area, which enables the regenerable operability of the desulfurizing agent. Scientists have done a lot of research on the application of porous materials.

2 Application of synthetic ZSM-5 in desulfurization

Used a desulfurization agent prepared by manganese-based oxide supported on ZSM-5 zeolite, and tested the desulfurization performance at 871^oC. The addition of the metal oxide particles supported on the zeolite molecular sieve solves the problems of easy pulverization and poor mechanical properties of the desulfurizer prepared from pure metal oxides, and greatly increases the durability and stability of the desulfurization performance of the renewable desulfurizer. Due to the structural characteristics of the microporous material, the uneven distribution of the supported metal oxide active particles leads to a low utilization rate of the active components of the desulfurizer, and the small pore size of the micropores restricts the passage of H₂S molecules, making desulfurization Accuracy is low. The desulfurization accuracy of the desulfurizer can only remove the amount of hydrogen sulfide in the simulated gas from the untreated 2000ppmv to 200ppmv of the treated gas. In addition to the investigation of the desulfurization accuracy, they found that the preparation method of the desulfurizer coated with metal oxides can reduce the wear of the desulfurizer in application. In the vulcanization-regeneration cycle activity experiment of the desulfurizer for many times, the activity performance of the desulfurizer remained stable and the mechanical strength did not decrease significantly after being regenerated for many times.

3 Application of activated carbon in desulfurization

Activated carbon has a high specific surface area (up to 2000m²/g) and developed pore structure, and its adsorption capacity is very strong. It can be used in decolorization and filtration, adsorption of various gases and vapors, chromatography column packing, etc. Can be used as a catalyst carrier. [3] prepared copper oxide, manganese oxide and zinc oxide-supported desulfurizers on activated carbon by supercritical impregnation method. They found that the ratio of active components, the roasting temperature of the desulfurizer and the immersion time for preparing the desulfurizer were the three major factors affecting the desulfurization activity. The above factors will affect the micropore volume, specific surface area and distribution of active components of the desulfurizer. This kind of desulfurizer has unsatisfactory performance in the desulfurization performance test.

4 Application of red mud in desulfurization

At high desulfurization temperatures, due to the accompanying reduction and volatility of zinc oxide, researchers have prepared zinc titanate by doping TiO₂ as a desulfurizing agent, and its desulfurization accuracy is almost the same as that of pure zinc oxide. However, studies have shown that TiO₂ undergoes crystal transformation in a high temperature environment, which destroys the activity of the component, resulting in a rapid decline in its utilization rate. One of our scientist prepared a series of iron-based desulfurizers by adding MgO and TiO₂. In the temperature range of 623-873K, the desulfurization performance of iron-based desulfurizers doped with MgO and MgO/TiO₂ were tested. The results show that adding MgO can not only achieve desulfurization accuracy, but also sulfur capacity. They also found that the water vapor contained in the coal gas was detrimental to the desulfurization activity of the MgO desulfurizer, and strangely, the water vapor inhibited the formation of iron carbide. By comparing the experimental performance test, it is found that the presence of TiO₂ cannot carry out desulfurization in a very high temperature range, but the sulfur capacity of the desulfurizer is partially limited. In the temperature range of 673-723K, the desulfurization of iron-based desulfurizers of MgO and TiO₂ can realize the deep removal of H₂S and COS in coal gas.

5. Application of fly ash in desulfurization

Fly ash is the solid residue after coal combustion in power plants, and its components are silicon oxide and aluminum oxide. Since it is a solid waste, it is in the perspective of environmental protection and can be reused. The properties of fly ash formed at very high temperatures are relatively stable. Due to the high specific surface area and abundant pore structure of fly ash, a series of desulfurization performance experiments were carried out on the desulfurizer prepared by fly ash as a carrier. They used fly ash as the carrier of iron-based desulfurizers and prepared desulfurizers of iron oxide, molybdenum oxide, fly ash and kaolin by physical mixing. The addition of molybdenum oxide can improve the desulfurization activity and desulfurization accuracy of iron-based desulfurizers. The better mechanical strength of fly ash can make the regeneration performance of desulfurizer not significantly decrease. However, the small microporous structure of fly ash is not conducive to the diffusion and transport of reactive gas molecules.