Molecular dynamics simulations were used to obtain a detailed understanding of the self-diffusion of methanol in NaY zeolite. A force-field term was derived with which to describe the interactions between methanol molecules and extra framework cations. Via the simulations, it was shown that diffusive behavior in the high-temperature range consisted of a combination of both short- and long-range motions at low and intermediate loadings. This type of motion was characterized by an activation energy that decreased as the loading increased. At low loadings, short-range diffusive behavior based upon a surface-mediated mechanism was also observed. The short-range behavior corresponded to motion only on the length-scale of an FAU super-cage, whereas the long-range behavior involved intercage diffusion. At saturation loading, corresponding to 96 methanol molecules per unit cell, only short-range motion within the same super-cage predominated.
Diffusion of Methanol in Zeolite NaY: a Molecular Dynamics Study. D.F.Plant, G.Maurin, R.G.Bell: Journal of Physical Chemistry B, 2007, 111[11], 2836-44
Table 55
Calculated Diffusion Coefficients for Methanol in NaY Zeolite
Loading(mol/unit-cell) | Temperature (K) | D(m2/s) |
8 | 400 | 4.713 x 10-11 |
8 | 450 | 6.102 x 10-11 |
8 | 500 | 5.785 x 10-10 |
8 | 550 | 9.037 x 10-10 |
8 | 600 | 1.139 x 10-9 |
8 | 650 | 2.069 x 10-9 |
8 | 700 | 2.989 x 10-9 |
16 | 450 | 3.134 x 10-10 |
16 | 500 | 4.828 x 10-10 |
continued
Table 55 (continued)
Calculated Diffusion Coefficients for Methanol in NaY Zeolite
Loading(mol/unit-cell) | Temperature (K) | D(m2/s) |
8 | 400 | 4.713 x 10-11 |
8 | 450 | 6.102 x 10-11 |
8 | 500 | 5.785 x 10-10 |
8 | 550 | 9.037 x 10-10 |
8 | 600 | 1.139 x 10-9 |
8 | 650 | 2.069 x 10-9 |
8 | 700 | 2.989 x 10-9 |
16 | 450 | 3.134 x 10-10 |
16 | 500 | 4.828 x 10-10 |
16 | 550 | 1.414 x 10-9 |
16 | 600 | 1.931 x 10-9 |
16 | 650 | 2.304 x 10-9 |
16 | 700 | 3.030 x 10-9 |
32 | 400 | 3.603 x 10-10 |
32 | 450 | 4.205 x 10-10 |
32 | 500 | 7.230 x 10-10 |
32 | 550 | 1.519 x 10-9 |
32 | 600 | 2.075 x 10-9 |
32 | 650 | 2.580 x 10-9 |
32 | 700 | 3.165 x 10-9 |
48 | 500 | 2.885 x 10-10 |
48 | 550 | 5.487 x 10-10 |
48 | 600 | 6.229 x 10-10 |
48 | 650 | 9.719 x 10-10 |
48 | 700 | 1.094 x 10-9 |