The Desorption of Toluene from a Montmorillonite Clay Adsorbent in a Rotary Kiln Environment

The vaporization  of toluene from  pre-drled, 3 mm  montmorillonite   clay  particles was studied  In a  130 kW pilot-scale  rotary   kiln  with Inside dimensions of 0.61 by 0.61 meters. Vaporization rates were obtained with a  toluene  weight fraction of 0.25 percent as a function of  kiln  fill fractions from 3 to 8 percent, rotation rates from 0.1 to 0.9 rpm, and  kiln wall temperatures from 189 to 793°C.

Toluene   desorption  rates were obtained from gas-phase measurements and interpreted using a  desorption  model that incorporates the slumping frequency of the solids, the fill fraction of the  kiln, the diffusion of toluene  in the bed, and the rate of particle  desorption using an Arrhenius-type expression that Is a function of bed temperature and average bed concentration. The model included three adjustable  desorption  parameters which were obtained by fitting the experimental data at one set of conditions with a least squares technique.

Solid and  kiln -wall temperatures were continuously recorded and used in the model for the  toluene   desorption  predictions. The model was successful at predicting the effects of fill fraction and rotation rate over a range of temperatures. Both the data and the model indicated that an increase in  kiln  temperature or rotation rate increased  toluenedesorption  rates. A decrease in  kiln  fill fraction also caused an increase in  desorption  rate.  Desorption  predictions were performed using both predicted and measured temperature profiles^ good agreement was achieved in both instances. In addition, the model was used to perform sensitivity tests examining the relative importance of bed diffusion and particle  desorption  resistances.

A methodology for predicting full-scale performance was developed. Full-scale  toluenedesorption  predictions were completed for different operating temperatures.