Water Vapor Adsorption Capacity Loss of Molecular Sieves 4A, 5A, and 13X Resulting from Methanol and Heptane Exposure

Prabhu Azhagapillai; Maryam Khaleel; Fouad Zoghieb; Gisha Luckachan; Liyamol Jacob; Donald Reinalda

doi:10.1021/acsomega.1c03370

Water Vapor Adsorption Capacity Loss of Molecular Sieves 4A, 5A, and 13X Resulting from Methanol and Heptane Exposure

ACS Omega. 2022 Feb 17;7(8):6463-6471. doi: 10.1021/acsomega.1c03370. eCollection 2022 Mar 1.

Authors

Prabhu Azhagapillai^{1

2}, Maryam Khaleel^{1

2}, Fouad Zoghieb^{1

2}, Gisha Luckachan², Liyamol Jacob², Donald Reinalda^{1

2}

Affiliations

¹ Gas Research Center, Khalifa University, P.O. Box, 127788 Abu Dhabi, United Arab Emirates.
² Department of Chemical Engineering, Khalifa University, P.O. Box, 127788 Abu Dhabi, United Arab Emirates.

Abstract

Zeolite-based molecular sieves are applied in industrial dehydration units for their high water uptake capacities and extremely low equilibrium pressure of water vapor. During their operational life, they tend to lose their water vapor adsorption capacity slowly. To optimize the usage of molecular sieves in dryer units, it is vital to understand the mechanism(s) leading to deactivation. In this work, the capacity loss was studied by exposing LTA- and FAU-type zeolites to methanol and heptane vapors under relatively harsh conditions using repetitive adsorption/regeneration cycles. A simple microflow unit was designed and used for the deactivation experiments. The water vapor adsorption capacity of the resulting samples was measured using a gravimetric analyzer. In addition, they were characterized by classic XRD, ¹³C NMR, and TGA techniques. The crystallinity of fresh and spent zeolite XRD patterns was not drastically affected even after exposure to the contaminants. It was found that methanol easily gave rise to a severe loss of water vapor adsorption capacity, much more so than heptane. Water vapor uptake in the methanol exposed samples is ∼50% lower than that for the fresh zeolites. This is attributed to nonvolatile, residual hydrocarbons.