| Figures 11 and 12 show the kinetic plot of desorption for temperatures 25 and 40ºC, respectively at various pressures. Generally, the rate of desorption increases with pressure at both temperatures, but it is observable that the effect of pressure is more prominent for pressures and temperatures around the critical region.
Figure 11: The effect of pressure on the Figure 12: The effect of pressure on the supercritical desorption rate in caprolactam / desorption rate in caprolactam / GAC-F400, at 25
GAC-F400, at 40 ºC. ºC.
Clearly, at 25ºC (subcritical T) the desorption rate is ‘less sensitive’ to pressure changes than at 40ºC (supercritical). Above T c (31ºC), the CO 2 density (and hence solvating power) is highly sensitive to changes in pressure the factor that is responsible for the ‘tunability’ of SCF properties in that operation region. This is shown in the ‘wide spread’ of desorption rates in Figure 3. Typically, the desorption curves are not linear with time, indicating the effect of intraparticle diffusion within the GAC particles, which is a function of time and position or location of caprolactam molecules within the GAC particles. |