What should be paid attention to when choosing activated alumina?

1. Drying of liquid organic compounds, usually by adding activated alumina to the liquid organic compounds, the activated alumina used must not have chemical or catalytic effects with the organic compounds.

2. Activated alumina should be insoluble in the liquid organic compound.

3. When selecting activated alumina that combines with water to form hydrate, the water absorption capacity and drying efficiency of activated alumina must be considered. Water absorption capacity refers to the amount of water absorbed per unit weight of activated alumina, and drying efficiency refers to the degree to which the liquid is dried when it reaches equilibrium. For example, anhydrous sodium sulfate can form Na2SO4 10H2O, that is, 1g Na2SO4 can absorb 1.27g water, its water absorption capacity is 1.27, but the water vapor pressure of its hydrate is also large (255.98Pa at 25°C), so the drying efficiency Difference. Calcium chloride can form CaCl2·6H2O, its water absorption capacity is 0.97, the water vapor pressure of this hydrate at 25 ℃ is 39.99Pa, so the water absorption capacity of anhydrous calcium chloride is small, but the drying efficiency is strong. Therefore, suitable activated alumina should be selected according to the specific requirements of removing moisture during drying operation. Sometimes for systems with more water, activated alumina with high water absorption is often used first, and then activated alumina with strong drying efficiency is used. Usually, a certain equilibrium time is required for this type of activated alumina to form hydrate, so it must be placed for a period of time after adding activated alumina to achieve the dehydration effect.

The activated alumina that has absorbed water will be dehydrated after being heated, and its vapor pressure will increase with the increase of temperature. Therefore, the activated alumina must be filtered out before distillation of the dried liquid.