Absorption of BTX using silica based adsorbents

  • Thamsanqa Ncube

Student thesis: Master's Thesis

Abstract

This work was carried out to assess the BTX (Benzene, Toluene, and Xylene) adsorption on silica based adsorbents. It was proposed that incorporation of nitrogen groups on mesoporous silica pores would enhance the surface polarity hence adsorption of aromatics. Additionally it has also been reported that the process of incorporation of the nitrogen groups on the surface of the porous material would result in damage to the pore structure, reducing the available surface area, depending on the process of incorporation. In order to assess the effect of surface modification through incorporation of nitrogen groups on the silica based adsorbents, a preliminary screening was performed covering a wide variety of silica based mesoporous adsorbents in the literature. Among the popular list of silica based adsorbents, KIT-6 was found to be superior and was selected for subsequent surface modification studies. KIT-6 was modified with APS (3-Aminopropyltriethoxysilane) according to the factorial design of experiments technique with APS concentration, temperature and time as control factors, the response variable was the adsorbent surface area. The results showed that APS concentration was the only significant factor and it affected negatively the surface area. Benzene adsorption was highest on unmodified KIT-6 adsorbent, whilst m-xylene and toluene had their highest values on 0.006% Aptes adsorbent (KIT-6 modified with 0.006% v/v APS). The BTX adsorption decreased with an increase in APS concentration used in the functionalization reaction as follows; 0.006% Aptes>0.33% Aptes>0.66% Aptes>8% Aptes. m-Xylene had the highest adsorption capacity on all modified silica adsorbents followed by toluene except for 8% Aptes adsorbent where toluene had the highest. The desorption (423K) /adsorption (318K) study showed that 0.006% Aptes adsorbent fully regains its activity after each cycle when helium purging is used. When desorption is done without helium purging the activity decreases with number of cycles. BTX adsorption on the virgin as well as the surface modified adsorbents were found to be physical. 0.006% Aptes adsorbent was selected as the best adsorbent for BTX adsorption. Freundlich isotherm and Pseudo first order was found to be the best models to describe m-xylene adsorption with KF of 6515 mg (n–1) / ng-1 L1/n, n of 2.18 and a rate constant of 0.1158 min-1 respectively at 318K. The activation energy for m-xylene adsorption on 0.006% Aptes adsorbent was found to be 19.5 kJ/mol.
Date of Award2016
Original languageAmerican English
SupervisorChandrasekar Srinivasakannan (Supervisor)

Keywords

  • Applied sciences
  • APS Aptes adsorbent
  • BTX adsorption
  • Silica
  • Chemical engineering
  • 0542:Chemical engineering

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