Diffusion of Glucose and Glucitol in Microporous and Mesoporous Silicate/Aluminosilicate Catalysts

The effective diffusivities of glucose and its linear analog glucitol were measured by a liquid chromatographic technique at 30 °C within water-filled silica and aluminosilicate catalysts of mean pore size ranging from 7.4 to 116 Å. For glucose, the effective diffusivity decreased from 1.08 × 10 -6 to 1.77 × 10 -9 cm 2 /s as the mean pore size decreased from 116 to 7.4 Å. All values were significantly lower than the molecular diffusivity of 7.02 × 10 -6 cm 2 /s. The effective diffusivities for glucitol were three times lower than those for glucose over the same pore size range due to differences in solute size, structure, and solute−adsorbent interactions. The 8.6 Å glucose molecule was able to diffuse into the 7.4 Å Y-zeolite pore, possibly as its acyclic form. However, the 9.7 Å glucitol molecule could not diffuse into the Y-zeolite pore. The reduced diffusivity was correlated to the reduced pore diameter using the Ternan model.