Effects of aging time and aging temperature on particle size of aluminum hydroxide
As a common catalyst carrier, alumina has a very complex system with various morphologies. It is the same crystal phase, and its pore structure, physicochemical properties and catalytic performance are also different. The characteristics of alumina depend on the purity, dispersion, crystallinity, etc. of the precursor.
The particle size of aluminum hydroxide particles does not change much with aging time, and the particle size is mainly controlled by the neutralization temperature.
When neutralizing aluminum hydroxide from sodium metaaluminate and dilute nitric acid, the effect of neutralization temperature on the particle size of aluminum hydroxide is greater than that of aging time. Therefore, in order to obtain larger particle size aluminum hydroxide, it is necessary to increase the neutralization temperature. When neutralizing and preparing aluminum hydroxide at lower temperatures, a shorter aging time should be selected, generally controlled at 0.5h. When neutralizing and preparing aluminum hydroxide at higher temperatures, according to actual requirements, the general aging time can be controlled at 0.5~ 1h.
Therefore, to prepare aluminum hydroxide with larger particles, it is best to use a higher neutralization temperature. For cost reasons, reducing the aging temperature by 25 ° C does not have a great impact on the particles, and the aging time does not need to be too long. Generally, it is appropriate to control it at 0.5h; to obtain aluminum hydroxide with a smaller particle size (< 20μm), it is necessary to control a lower neutralization temperature and aging temperature. The neutralization temperature can be selected at 50 ° C, and the aging time can be selected at 0.5h.
The aluminum hydroxide slurry prepared by neutralizing sodium metaaluminate and dilute nitric acid is aged for different times at different neutralizing temperatures, and its particle size changes little.
Under the condition of high temperature neutralization at 70 ° C, the median particle size of aluminum hydroxide is 28-30 μm, and the median particle size of aluminum hydroxide obtained by neutralization at 50 ° C is 17-20 μm. The effect of aging time on the particle size of aluminum hydroxide is higher than that of neutralization. The effect of temperature on it is much smaller.
After neutralization at 40 ° C, the particle size of aluminum hydroxide will become smaller at different temperatures, so low temperature aging can be adopted; and after neutralization at 75 ° C, the effect of different temperature aging on the particle size of aluminum hydroxide is not very significant, The particle size change is very small, so low temperature aging can also be used.
If you want to get larger particles of aluminum hydroxide, neutralize at a lower temperature, the aging time should be shortened as much as possible, generally 0.5h can be used, and neutralize at a higher temperature, the aging time does not have a great effect on its particle size. According to the required aging time, 0.5~ 1h.3) can be used to directly filter and dry the slurry for XRD test, and it is found that the aging time has little effect on the crystal phase of aluminum hydroxide, indicating that after neutralization, the crystal transformation of aluminum hydroxide is basically completed. With the extension of subsequent aging time, its crystal form remains unchanged. (jwl)