Remoção de sulfeto de hidrogênio do biogás por solução de ferro quelado

Abstract

Biogas is mainly composed of methane (CH4) and carbon dioxide (CO2), being defined as a flammable gaseous mixture resulting from the anaerobic digestion of various types of organic materials. The same can be used in the generation of electric energy, thermal or vehicular fuel. After refining or upgrading, there is an increase in the CH4 content of the biogas, which gives it greater calorific value. Biogas can be classified as biomethane (a potential substitute for natural gas) when the methane concentration is equal to or greater than 90% mol. However, the presence of impurities such as H2S is one of the biggest obstacles in the application of this biofuel, because in addition to being toxic, it has corrosive characteristics. In this sense, it is necessary that biogas purification technologies be adopted for the removal of hydrogen sulfide (H2S). Given this premise, the objective of the present work was to evaluate the absorption potential of the iron/chitosan complex (Fe(III)/CS) in the removal of H2S from biogas. From the experimental data obtained with the aid of the Box-Behnken type planning, a survey of deactivation curves of the solution was carried out to evaluate the response variables: deactivation time (tb) and absorption capacity in deactivation (qb), aiming at obtaining process kinetic data. The controlled variables were: concentration of Fe(III), chitosan and acetic acid. These were submitted to the following operating conditions: pressure of 1 atm, temperature of ~24°C, flow rate of 10 mL s-1 and H2S gas stream of 1000 ppmmol with N2 balance. The solutions before and after the absorption test were submitted to Molecular Absorption Spectroscopy (UV-Vis) and Dynamic Light Scattering (DLS) analysis. And the post reaction solid fraction was characterized by X-Ray Diffractometry (XRD); Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Infrared Region Spectroscopy (FTIR). The results obtained are promising in terms of the potential of the Fe(III)/CS(HAc) complex in the removal of H2S from biogas, with better results, presenting solution deactivation time (tb = 893.34 min), greater capacity absorption rate (qb = 3.318 mg g-1 ) and H2S removal efficiency of 99.28% during 14 h of reaction. From the characterization techniques, it was possible to determine the presence of elemental sulfur in the post-reaction precipitate, indicating the occurrence of the redox reaction, thus making it possible to evidence the potential of the Fe(III)/CS/HAc complex in the process of removing H2S from the biogas.