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

Abstract

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 toluene desorption 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 toluene desorption predictions were completed for different operating temperatures.