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Advisor(s)
Abstract(s)
Biogas is a gas mixture obtained by the anaerobic decomposition of organic matter, being mainly
composed by methane, carbon dioxide and other compounds in minor amounts, such as nitrogen,
hydrogen sulfide, water vapor and others. Due to the high quantity of methane (higher than 50%), the
biogas can be used as a fuel, but, it’s necessary to go through a process of purification, to remove CO2
and transform it in biomethane (around 95%), a fuel similar to natural gas [1,2].
In this way, gas adsorption equilibrium of CO2, CH4 and N2 were investigated in three different types of
zeolite BETA materials namely H-BETA-25, Na-BETA-25 and H-BETA-150 at temperatures 313, 373 and
423 K under partial pressures between 0.33 and 4.16 bar. For this experimental analysis a gas
chromatographic system was utilized. The isotherm data has been satisfactorily demonstrated with the
Langmuir model and the amount adsorbed follows the decreasing order as CO2 > CH4 > N2 for all
materials used. Considering experimental temperature, all materials show better absorption at the lowest
temperature (313 K) for obvious reason.
First, when we compare two zeolites containing the same SiO2/Al2O3 molar ratio but different
compensation cations (H-BEA-25 and Na-BEA-25), interesting results are obtained. It is found that only
due to presence of Na+ cationic center, zeolite Na-BETA-25 adsorbed quite higher amount of gases than
H-BETA-25 (2.84, 1.59 and 0.97 mol/kg, and 2.28, 1.31 and 0.83 mol/kg respectively of CO2, CH4 and N2
gases at 313 K).
In second comparison between two different SiO2/Al2O3 molar ratio (H-BETA-25 and H-BETA-150), zeolite
H-BETA-25 adsorbed a little bit higher amount of gases than H-BETA-150 (2.23, 0.98 and 0.58 mol/kg).
But when we consider selectivity of gases the zeolite H-BETA-150 (adsorbs lowest amount of gases)
showed to be the best over other two materials with decreasing value in pair order CO2/N2 > CO2/CH4 >
CH4/N2 (6.65, 3.24 and 2.05 at 313 K). The selectivity order is the same for all three zeolites at mentioned
temperatures.
The mass transfer studies were made using the Zero Length Column (ZLC) technique, at 313 K. But it is
very difficult to determine the mechanism that controls the diffusion onto three zeolites, as experiments
are so fast that ZLC studies were made in equilibrium conditions. Accordingly, it was not possible to
obtain kinetic information for the adsorbents. However, it can be said that there are no resistances to the
mass transfer in the studied conditions.
Description
Keywords
Adsorption
Citation
Henrique, Adriano; Silva, José A.C.; Rodrigues, Alírio E. (2017). Adsorption equilibrium and kinetics of CO2, CH4 and N2 on zeolite BETA with different cations and SiO2/Al2O3 ratio. In 10º Encontro Nacional de Cromatografia. Instituto Politécnico de Bragança. ISBN 978-972-745-234-7
Publisher
Instituto Politécnico de Bragança