(248d) Evaluation of Assisting Methods on the Fluidization of Agglomerates of Nanoparticles by Studying the Adsorption/Desorption Rate of Moisture

Agglomerates of nanoparticles were fluidized under the influence of assisting methods such as vibration or moving magnetic particles; for comparison purposes they also were conventionally fluidized, i.e., without any assistance. The adsorption/desorption rate of moisture of the fluidized powders was monitored in order to measure the adsorption isotherms at room temperature and to evaluate the impact of the assisting methods.

The powders that were studied consisted of nanoagglomerates of Degussa Aerosil® 200 and Aerosil® 90, having a primary particle size 12 nm and 20 nm, respectively and a specific surface area of 200 m2/g and 90 m2/g, respectively. These powders can adsorb moisture because they are hydrophilic. While Aerosil® 200 can be fluidized even without assistance, Aerosil® 90 does not fluidize at all and shows bubbling, channeling and gas bypassing. However, Aerosil® 90 has been successfully fluidized after using the assisting methods.

The moisture level in the nitrogen used to fluidize the powders was monitored on-line by using relative humidity sensors upstream and downstream of the fluidized bed. The moisture added to the nitrogen was adjusted by bubbling it through water. The amounts of adsorbed/desorbed moisture allowed for the calculation of the adsorption isotherms of the powders at ambient temperature. The adsorption isotherms were also verified by a gravimetric method.

It was found that when the bed of powder is assisted during fluidization, by vibration or moving magnetic particles, the amount of moisture adsorbed/desorbed by the powder is greater than when the powder is conventionally fluidized; also the rate at which the moisture is adsorbed/desorbed is increased. These results indicate that the assisting methods improved significantly the fluidization of the powders.