Activity loss of zeolite based materials for natural gas drying: A study of fresh and spent samples from ASAB-0 unit 24-D-603A

Abstract

This project is part of a larger GRC sponsored project called Activity Loss of Zeolite Materials for Natural Gas Drying coded GRC15002. It is the first experimental effort. A set of 5 samples were received from GASCOs ASAB plant: a fresh sample of adsorbent (zeolite 4A) and 4 spent samples taken from different positions in the reactor1. The reactor had been operating for 3 years before shut down. The goal of the current project is first to investigate the reasons for the loss of performance by analyzing these samples and secondly to identify suitable experimental techniques for doing this. For deep dehydration, needed to meet the specifications of sales gas and natural gas liquids (NGL) from the GASCO gas processing facilities, molecular sieve based materials are widely used. The zeolite component of these materials has a strong interaction with water molecules, consequently the equilibrium water partial pressure is very low (ppmv range) as required. However, the activity of the desiccant under consideration has declined with time to an unacceptable level and consequently it was decided to change it out. The samples in this particular study originate from a liquid (NGL) dehydration unit (ASAB-0, Unit 603A, changeout April 2015). The performance loss may have resulted from caking, coking and/or structural collapse. An investigation on the fresh and spent molecular sieves was carried out by series of adsorption experiments as well as various characterization techniques such as, Fourier transform infrared spectroscopy, X-ray diffraction, thermo-gravimetric analysis, scanning electron microscopy and nitrogen sorption analysis. Also an investigation on the nature of adsorption sites of the molecular sieve was conducted to study the affinity of the adsorbate for strong and weak hydrophilic sites. The results indicate that the capacity downfall of the spent samples is mainly due to coke formation and to a lesser extent to caking. The structure integrity is retained in the spent samples as the X-ray diffraction patterns are unaltered. Following a suggestion from literature, tetraethyl_orthosilicate (TEOS) modification of the surface was tried to further enhance the adsorption capacity by provision of weak hydrophilic silanol groups on the extra-framework surface. 1The adsorbent was used for drying of natural gas liquid rather than the methane richer gas phase. Samples from a gas dryer were obtained in a much later phase and were not studied yet. In the current context this is not relevant.

Date of Award	2016
Original language	American English