Use of graphene and activated carbons for the removal of organic contaminants from MDEA solvent

  • Nafisa Yousif ElSamani Mohamed Ali

Student thesis: Master's Thesis

Abstract

This study aimed at investigating the removal of the major degradation products present in typical MDEA solutions utilized in gas sweetening plants. The study was achieved by assessing various types of adsorbents; which comprised of different types of activated carbon as well as thermally and chemically reduced graphene. The adsorbents were screened to identify the most efficient adsorbents which have the highest affinity towards degradants adsorption. The screening process concluded three types of activated carbon activated carbon (SA-1500, SGL and G 1220 Extra), and chemically reduced graphene, which of which was further assessed. Four types of equilibrium isotherm models were applied for each set of experimental data to assess the adsorption nature and adsorbate distribution and energy. In addition, three different kinetics theories were applied using pseudo first order kinetic model, pseudo second order kinetic model and intra-particle diffusion. Adsorbent performance followed the following order in terms of adsorption capacity; chemically reduced graphene > SA-1500 > G 1220 Extra > SGL. Equilibrium assessment with chemically reduced graphene revealed highest adsorption capacity at 54 °C, where qe values ranged from 140.32 to 242.16 g/g. For equilibrium studies at 38 °C, qe varied from 115.57 to 175.89 g/g, while at 23 °C, qe varied from 92.72 to 129.97 g/g; depending on the graphene loading. Assessment with activated carbon (SA-1500) reflected highest qe values at 54 °C, where qe ranged from 0.44 to 0.58 g/g. For studies at 38 °C and 23 °C, qe ranged from 0.39 to 0.5 g/g and 0.36 to 0.45 g/g; respectively. For G 1220 Extra, the highest qe values also pertained to 54 °C, where they ranged from 0.38 to 41 g/g. For 38 °C, and 23 °C, qe ranged from 0.35 to 0.37 g/g and 0.31 to 0.32 g/g; respectively. On the contrary, SGL demonstrated highest removal at the lowest temperature, as its adsorption was an exothermic process. qe at 23 °C was found to vary from 0.15 to 0.19 g/g, while for 38 °C and 53 °C, qe values varied from 0.13 to 0.16 g/g and 0.12 to 0.14 g/g; respectively. Further to adsorption of DEA on chemically reduced graphene, it was found to fit better with Langmuir isotherm with an R2 value of 0.9859. For the Activated carbons: SA-1500, SGL and G 1220 Extra the Dubinin-Radushkevish model best fits with experimental data with an average R2 value of 0.9925, 0.9974 and 0.9975 respectively. The fitted experimental data reveals that the system obeys Gaussian energy distribution on the adsorbent surface via pore filling mechanism. Moreover, the thermodynamic assessment of the systems reflected an endothermic adsorption with regards to chemically reduced graphene, SA-1500 and G-1220 Extra, where the ΔH was found to be 33,223 J/mol, 2,773 J/mol and 2,475 J/mol respectively. The systems also revealed increased randomness with ΔS of 130 J/mol, 17 J/mol, and 20 J/mol respecting th aforementioned order. The system was found to be spontaneous with Δ G of -3,119 J/mol, -221 J/mol, -3,538 J/mol. For the SGL however, the system was found to be endothermic, with decreased randomness and spontaneous sorption process, associated with the following thermodynamic parameters: Δ H -3,848 J/mol, ΔS -12 J/mol, Δ G -259 J/mol. The R2 regress for chemically reduced graphene and SGL were found to be acceptable, 0.992 and 0.989 respectively. For SA-1500 and G-1220 Extra, thermodynamic parameters were drawn by a correlation reflecting 0.934 and 0.831 respectively. For the four adsorbents system, fitted data was found to obey a second order kinetics, with an average R2 value of 0.9964, 0.9972, 0.9996 and 0.9984 for CRG, SA-1500, SGL and G 1220 Extra respectively. For the four, several mechanisms were found to govern the sorption mechanism, thus, intra-particle diffusion was not the sole mechanism. Moreover, it was found the further to the chemically reduced graphene, SA-1500 and SGL, adsorption was found to be chemical in nature, suggesting bond formation between the adsorbate and adsorbent. Further to G-1220 Extra however, Dubinin-Radushkvich analysis revealed physical adsorption despite that the system kinetics obeyed a second order reaction.
Date of Award2016
Original languageAmerican English
SupervisorFawzi Banat (Supervisor)

Keywords

  • Applied sciences
  • Carbons
  • Contaminants
  • Graphene
  • Mdea
  • Organic
  • Removal
  • Solvent
  • Chemical engineering
  • 0542:Chemical engineering

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