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

Abstract

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 cm2/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 cm2/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.

pH-Driven Self-Assembly of Acidic Microbial Glycolipids

“…Here, the position of the minimum is 0.12 Å -1 , so one can estimate half the section to about 26 Å, a value which, as commented before, must be taken as indicative due to the core-shell nature of the bilayer. However, given the fact that the size of G-C18:0 could reasonably be estimated to be less than 30 Å, using the Tanford formula to estimate the stearic acid moiety (≤ 22 Å, see legend of Table 2 for more details) and estimating the size of β-D-glucose to be less than 8 Å, 38 one can still make the reasonable hypothesis that the membrane is constituted by a double layer of G-C18:0, even if it is not excluded that interdigitation between the top and bottom layers actually occurs. Differently from the CLH case, the SAXS profile above 0.12 Å -1 does not contain diffraction peaks, but it is characterized by the oscillation due to the form factor of the lamellae alone.…”

Dehydration of Xylose into Furfural in the Presence of Crystalline Microporous Silicoaluminophosphates

“…Considering that the ''catalytic pore sizes'' of zeolites are often found to exceed the crystallographic ones (by as much as 2 Å in the case of H-MOR, for example) [28], the xylose molecules may be able to diffuse into the channels of all three framework types, under the reaction conditions used for catalysis. Indeed, according to the literature, the 8.6 Å glucose molecule is able to diffuse into the waterfilled 7.4 Å Y-zeolite pore [29]. In the liquid phase the solute diffuses as a solute-solvent assemblage and catalystsolvent interactions may reduce the effective diffusivity of xylose within the liquid-filled pores of the SAPO materials.…”

Glucose isomerisation into fructose over magnesium-impregnated NaY zeolite catalysts

“…NaY zeolite was selected as support, since it is a large pore zeolite allowing an easier diffusion of the bulky glucose molecules to the interior of its pore system [40], and it presents framework basicity given by the Na-exchange [28]. The attraction of magnesium as dopant lies in the expected formation of MgO in the zeolite pore structure, since MgO has high intrinsic basicity [41].…”