Correlation of the heats of immersion of 3A, 5A and 10A zeolites with their adsorption characteristics in polar and non-polar liquids

Abstract

The adsorption of water and cyclohexane vapours at 35 °C by 3A, 5A and 10A zeolites (where 3A, 5A and 10A denote pore dimensions of 3 Å, 5Å and 10 Å respectively) and by their thermal dehydration products obtained between 110 and 800 °C was investigated. The samples were precharacterized by nitrogen adsorption. The cyclohexane uptake of the 10A zeolites was much greater than that of the 3A and 5A zeolites. This is due to the large size of the cyclohexane molecule which limits its accessibility to narrow pores. In contrast, the water uptake of the 5A and 10A zeolites was less than the nitrogen uptake. This is because water interacts with the zeolite surface via specific forces only, whereas in the case of nitrogen the enhanced adsorption potential in the micropores and its effect on the polarizability of the nitrogen molecule enhance both its specific quadrupole-dipole interaction and its non-specific interaction with the zeolite surface. The integral heats Δ H i of immersion of the 3A, 5A and 10A zeolite samples and of their thermal dehydration products obtained between 110 and 800 °C were measured at 35 °C in both water and cyclohexane liquids. The integral heats of immersion in both liquids increased with increasing dehydration temperature up to 400 °C and thereafter decreased. The heats of immersion in cyclohexane were much lower than those in water, perhaps because of the inaccessibility of the bulky cyclohexane molecule to a large fraction of the internal pores. The values of Δ H i cyc were in the order 10A zeolite > 5A zeolite > 3A zeolite, whereas the Δ H i values for water were in the order 3A zeolite > 5A zeolite > 10A zeolite. This behaviour demonstrates the correlation between pore narrowing in zeolites and the increased energetic interaction in polar wetting liquids.