Sour Gas Adsorption on Silica Gels

One of the essential factors for water adsorption on silica gels is the concentration of silanol groups on the silica surface. However, no systematic investigation on the adsorption of sour gas components, methane (CH₄), carbon dioxide (CO₂), and hydrogen sulfide (H₂S) on silica gels with different textural properties and surface silanol concentrations, has been conducted. Three silica gels of 22, 30, and 60 Å pore sizes, with silanol concentrations of α_total = 2.516, 2.340, and 2.152 OH nm^-2, respectively, were studied in this work. The adsorption data for CH₄, CO₂, H₂S, and H₂O at T = 0, 25, and 50 °C on the 22 and 30 Å pore size silica gels were presented, and a comparison of the data for the 60 Å pore size silica gel on the same adsorbates was conducted. All three silica gels showed an adsorption affinity in the order of H₂O > H₂S > CO₂ > CH₄. The isosteric heats of adsorption of H₂O and H₂S had a greater dependence on the silanol concentration than CO₂ and CH₄. At p < 10 bar, there was no difference in the adsorption per m² of CH₄ between the silica gels (n ^ads = 1.7 mmol m^-2, for all silicas at p = 10 bar), while higher pressures resulted in greater adsorption capacity in the larger pore volume silica gels (at p = 20 bar: n ^ads = 3.0, 3.3, and 3.4 mmol m^-2 for the 22, 30, and 60 Å pore size silicas, respectively). H₂S adsorption at low pressures (p < 4 bar) was larger on the samples with larger silanol concentrations (at p = 3 bar: n ^ads = 6.1, 4.7, and 4.5 mmol m^-2 for the 22, 30, and 60 Å pore size silicas, respectively), but above p = 4 bar, the 60 Å pore size silica had a greater adsorption capacity than the 30 Å pore size (at p = 5 bar: n ^ads = 8.0, 6.0, and 6.2 mmol m^-2 for the 22, 30, and 60 Å pore size silicas, respectively).