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Summary

This study focuses on the simulation of packed bed adsorber for separation of BTX (benzene, toluene, m xylene) in presence of other molecules such as CO2, H2O and H2S using Aspen Adsim® package. The breakthrough curves were generated for the silica based adsorbent (mKIT-6) which is surface modified KIT-6 using 0.006% 3-aminopropyl triethoxysilane. The surface modifications were performed with the intent of maximizing the aromatic adsorption and minimizing the other component adsorption. The experimental adsorption isotherm data of pure BTX and the other components for mKIT-6 adsorbents were generated using a gas phase gravimetric analyzer. A comparative adsorption on mKIT-6 indicates adsorption in the following order Xylene > Toluene >Benzene > H2O > H2S > CO2. The presence of contaminants on the BTX breakthrough was found to be insignificant due to their low adsorption on mKIT-6. The competitive adsorption of BTX and other molecules were accounted through the Ideal Adsorption Solution Theory model (IAST). With the column cut-off being 20% of the inlet concentration of the toluene molecule, a reasonable cut-off duration of near 38 hours could be achieved for a 10m by 3m column size.

Introduction

Crude oil and natural gas contain acid gases (H2S and CO2) and trace amounts of benzene, toluene and xylene (BTX) and other volatile organic compounds (VOCs) [Crevier, 2007]. The gas processing plant essentially includes number of separation processes that purify the gas from contaminants such as H2S, CO2, N2, Hg, H20 etc. In the amine sweetening process, minor amounts of BTX, COS are being released along with H2S and CO2 that would find its way to Claus process for recovery of elemental sulfur.

The presence of BTX in the Claus feed gas tend to poison the Claus catalyst at a faster rate tending to pose several technical and operational problems. Various methods have been proposed for BTX removal such as; thermal destruction in the furnace, refrigeration of feed gas, most of these methods result in high energy costs. Adsorption is one method which is most promising since adsorbents can be regenerated and reused. Saudi Aramco installed carbon beds before their SRUs for removal of BTX which guaranteed extended life of Claus catalyst, due to rapid reduction in the catalyst poisoning rate [Crevier, 2007].

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