Mathematical modeling and simulation of gel drying with supercritical carbon dioxide

Abstract

Mathematical models of alumina/silica gel supercritical drying with carbon dioxide were studied using supercritical drying experimental data. An alumina/silica gel with zinc chloride was synthesized and dried with superciritical carbon dioxide, and its weight change was monitored as a function of drying time. The pore size distribution of the obtained aerogel was determined using the BET method and nitrogen adsorption/ desorption. The mathematical model of the supercritical drying of the wet gel was represented as unsteady and one-dimensional diffusion of solvent through the aerogel pores filled with supercitical carbon dioxide. Parallel pore model and pores in series model were developed on the basis of the measured porous structure of the aerogel. It was found that these models which use different effective diffusivity value for each pore size were in much better agreement with the experimental data than models which use an overall effective diffusivity. The local effective diffusivity coefficients were calculated using different tortuosity values for each pore size, and they were distributed according to the pore size distribution data. Model simulations of the superciritical drying with carbon dioxide confirmed that the drying temperature and gel particle diameter have a significant influence on the drying time.

Experimental and theoretical investigation of supercritical drying of silica alcogels

“…Eqs. (10) and (12) show that the convective mass flux of ethanol at the alcogel surface is equal to diffusive mass flux of ethanol at the interface between the alcogel and the flowing stream.…”

“…Orlović et al [12] investigated supercritical drying of alumina/silica alcogel with carbon dioxide in a 70 cm 3 tubular extractor (Autoclave Engineers Supercritical Extraction Screening System) at 313 K and 80 bar. The pores of the gel were entirely filled with of 1-butanol (solvent).…”

Experimental and theoretical investigation of drug loading to silica alcogels

“…As shown in Figure In some studies, the tortuosity value was reported to be in the range of (1-6) including the calculated tortuosity value for this study [23][24][25][26] .…”

Kinetics of Supercritical Drying of Gels

“…As an example of 1D mass transfer models, the study of Orlovic et al, on the drying of alumina/silica alcogel the pores of which were filled with 1-butanol can be given [86]. The developed model was represented as an unsteady one-dimensional diffusion of solvent through pores of the gel.…”

“…However, the findings of the study of Orlovic et al indicated that increasing the temperature affected the drying time considerably. As elevated temperatures led to an increased solubility of the solvent used (1-butanol), drying times were significantly reduced [86]. It was shown that changing operating conditions such as temperature and pressure affected the diffusion coefficient which thereby affected the drying time.…”