Avaliação do potencial de redução do sulfeto de hidrogênio do biogás por absorção com ozônio

Abstract

Biogas is a mixture of gases primarily containing methane (CH4), carbon dioxide (CO2), and hydrogen sulfide (H2S). Due to its toxic and corrosive characteristics, H2S must be removed from biogas. Among promising technologies for desulfurization, the use of ozone (O3) as an oxidizing agent for H2S can be mentioned. Therefore, the present work aimed to evaluate the efficiency of reducing H2S in synthetic biogas using ozone absorption technology. To assess the process efficiency, four bench-scale systems were developed, operating with different flow configurations for H2S and O3 and temperatures (5, 10, 15, 20, and 25 ºC). In the first system (continuous open flow for H2S and O3), the results showed the highest H2S reduction at 20 and 25 ºC, reaching 49% and 47%, respectively. This could be related to the positive enthalpy (∆H>0) of the reaction between H2S and O3, favoring the reaction at higher temperatures. In the second system (continuous closed flow for biogas and stationery for O3), removals of 36 ± 1% were achieved for all temperatures. The third system (stationary flow for biogas and O3) exhibited low reductions in CH4 and CO2 gases (<15%) concerning the agitation parameter. However, regarding H2S, the agitation time showed a positive effect, achieving a 100% reduction in 30 minutes. Concerning the temperature parameter, the system achieved the highest H2S removals at 10 and 15 ºC. Nevertheless, a problem encountered in the system was the high dilution of CO2 and H2S gases (<70%). The fourth system (continuous flow for biogas and O3) showed H2S reduction of 16% at pH 4, 39% at pH 7, and 68% at pH 10 at 20ºC. An in-depth analysis of the four studied systems reveals that the stationary system demonstrates notable H2S reduction capacity at lower temperatures due to the enhanced solubility of O3. In contrast, the continuous system benefits from a continuous supply of O3 molecules, making it more effective at higher temperatures due to the endothermic nature of the reaction between H2S and O3. One of the main conclusions, based on the comparative analysis of desulfurization systems, highlights the influence of operational conditions and chemical properties involved. Each purification route, whether continuous or stationary flow, presents distinct advantages depending on the operating temperatures and chemical reactions involved.