The Shape and Performance of Solid Adsorbent of Activated Alumina
1. Shape and performance of activated alumina
Solid adsorbents are used in reactors with different particle shapes. Early adsorbents did not pay attention to the shape, and often only crushed the bulk material, and then screened out the particles with uneven particle size and irregular shape for use. Due to the indeterminate shape, the airflow distribution during use is very uneven, and the adsorption reaction is affected. The sieved small particles and powder materials cannot be used and discarded, thus causing a lot of waste. With the continuous improvement of the performance requirements of the adsorbent and the rapid development of the molding technology, the shape requirements of the activated alumina adsorbent are gradually consistent with the practical performance.
The solid sorbent is at least uniformly granular or microsphere-like so as to be uniformly packed into the industrial reactor. Therefore, molding has become an important process in the manufacture of adsorbents. The shape and molding process of the adsorbent greatly affect the performance of the adsorbent. For small or particulate adsorbents used in ebullated beds, generally only the particle size and particle size distribution of the adsorbent are concerned, and less attention is paid to adsorption. In fact, the shape of the adsorbent does not need to be adjusted, but the necessary molding means are lacking. With the development of molding technology, the shapes of fixed-bed adsorbents with particle sizes larger than 4-5 um have become rich and diverse. From the early amorphous and spherical mainly to the cylindrical, bar, ring, sheet, honeycomb, internal and external gear shape, clover shape and chrysanthemum shape, the shape of the adsorbent is more and more closely related to its performance.
The shape, size and surface roughness of the activated alumina adsorbent will affect the activity, selectivity and strength, airflow resistance and other properties of the adsorbent. The most important is to affect the activity, bed pressure drop and heat transfer. The activity of the adsorbent has a great relationship with its surface area. Therefore, as long as the mechanical strength and pressure drop of the adsorbent allow, the surface utilization rate of the adsorbent should be improved as much as possible. The larger the external surface area of the adsorbent contained in the unit volume reactor, the higher the adsorption capacity and the higher the production efficiency.
2. The reactor’s requirements for the shape and size of activated alumina
Due to the different working principles of the reactor, the shape of the adsorbent required for operation is also very different. Spherical particles are easy to roll, fill evenly, have high wear resistance, small loss of surface components by air scouring, and a large amount of reactor filling per unit volume, which is conducive to improving the production capacity of the reactor, and is a commonly used adsorbent shape for fluidized bed reactors. Cylindrical regular, smooth surface, easy to roll, evenly filled; hollow cylindrical density, although it is conducive to the diffusion of substances, but the apparent density of the adsorbent will be reduced, so the mass of each adsorbent will be reduced, so that the surface area of each adsorbent will be correspondingly reduced, which is not conducive to the purification and adsorption. On the contrary, if the pore size distribution of the macropores is too small, the internal diffusion resistance will increase, and although the surface area of each activated alumina adsorbent can be increased, it is not conducive to the diffusion of substances.
Therefore, it is necessary to experiment to find the most suitable adsorbent particle density. The double-pore distribution type purification adsorbent retains the advantages of macropores and small pores, and overcomes their respective shortcomings. Theoretical analysis shows that the smaller the pore size is, the more favorable the double pore distribution of the purifying adsorbent is. Compared with the purification adsorbent with a single pore distribution, the efficiency of the double-pore distribution purification adsorbent can be increased by 3 to 6 times, but the minimum pore size should be close to 1/10 of the molecular mean free path. reduce. The large pore size is preferably about 10 times the molecular mean free path, because the diffusion coefficient is little affected by the pore size.