Dados fundamentais para projeto de processos de dessulfuração e upgrading de gases combustíveis por adsorção

Abstract

In this study, the adsorption of CH4, CO2 and H2S has been studied on commercial activated carbon samples in order to assess its potential for upgrading and desulphurization of Biogas or contaminated natural gas. Different characterization techniques such as Fourier Transform Infrared Absorption Spectroscopy (FTIR), X-ray fluorescence (XRF), pH measurements and textural analysis (by N2 (196 oC) adsorption/desorption isotherms and CO2 (0 oC) adsorption isotherms) were used to study the porous structure of the material and detect the presence of K, Na and Fe and other elements in the samples. Gravimetric experiments were used to measure adsorption capacity of CO2 and selectivity with respect to CH4. Breakthrough curves under dry conditions were performed to evaluate H2S adsorption under dynamic conditions. The materials under study showed high adsorption capacities for both gases in the range of 0.013-0.28 mmol g-1 for H2S and 1.61-2.16 mmol g-1 CO2 under dry conditions, 25 ºC and 1 bar. In addition, selectivity of the samples with respect to CH4 was found to be in the range of 1.2-2.4 mmol g-1, with Desorex K43-BG being the material with the highest retention of H2S and Sorbonorit B4, the material with the greatest adsorption capacity of CO2 and CH4. The data obtained from adsorption experiments were correlated with the textural characteristics and the surface chemistry of the materials. The best compromise between adsorption capacity of H2S and selectivity of CO2 in the presence of CH4 were found for the sample containing Na (Desorex K43-Na), which benefited from both a basic surface chemistry and pore size distribution restricted to the micropore range. Breakthrough curves of H2S in the presence of CO2 have shown that the adsorption capacity of H2S in materials impregnated with alkali metals is considerably reduced: 37% for Desorex K43-BG and 65% for Desorex K43-Na sample. This loss of capacity may be due to the competition for the active sites (linked to the presence of metals) by the gases being co-adsorbed. For the non-impregnated Sorbonorit B4 material, the presence of CO2 in these tests did not cause appreciable loss in H2S adsorption capacity.