Simulação de uma unidade de adsorção com modulação de pressão para separação da mistura CH4-CO2-H2O empregando simultaneamente como adsorventes a zeólita 13X e carvão ativado

Abstract

The aim of this work was to evaluate the effect of moisture on the separation of the CH4-CO2-H2O mixture by the pressure swing adsorption process using an adsorbent bed composed of babassu coconut shell activated carbon (CACC) and zeolite 13X. For this purpose, an adsorption equilibrium study was conducted for pure components, using experimental data from literature. The Langmuir and Multisite Langmuir adsorption isotherm models were evaluated, and the selectivity in relation to carbon dioxide were calculated. A study of the adsorption kinetics of CH4 and CO2 components was also made by obtaining experimental data from breakthrough curves in diluted systems (CH4:He and CO2:He) and by evaluating two mathematical models (LDF and Bi-LDF). For the validation of the equilibrium and kinetic studies in single-component systems, experimental breakthrough curve data for the binary CH4-CO2 system were obtained and compared with the predictions of mathematical models (LDF and Bi-LDF). Subsequently, simulations of a pressure swing adsorption (PSA) unit were carried out, operating in a Skarstrom type cycle, with two columns packed with CACC and zeolite 13X under different adsorption pressure conditions (1 to 5 bar) to evaluate the impact of moisture on the separation of the CH4-CO2-H2O mixture. The equilibrium study indicated that up to a pressure of 6 bar, both isotherms similarly describe the adsorption equilibrium of the pure components, and from this pressure, the Multisite Langmuir isotherm describes better the experimental data. At this stage, it was also found that zeolite 13X has practically no selectivity for CO2 in the presence of H2O, while CACC maintains the ability to remove CO2 from the mixture in the presence of H2O. The kinetic study (single-component and binary) indicated that both mathematical models evaluated (LDF and Bi-LDF) describe the experimental data well and similarly. Finally, the PSA unit simulations indicated that increasing the adsorption pressure leads to higher CH4 purity values and lower values of CH4 recovery ([1 bar, 71.9%, 87.2%]; [3 bar, 92.3%, 53,9%]; [5 bar, 95.5%, 21.8%]), therefore, the use of a bed composed of babassu coconut shell activated carbon and zeolite 13X is shown to be a potential alternative for the production of biomethane from the enrichment of the CH4-CO2 mixture in the presence of up to 1%mol moisture.