## 3 Simultaneous and Selective H\({}_{2}\)S-CO\({}_{2}\) Removal: A Case Study
In fact, with the latter, the experimental selective factor was found to be 3.88, whereas in the case of the former, the value increased to 15.81. Other relevant simultaneous H\({}_{2}\)S/CO\({}_{2}\) removal investigations are resumed below. It is a normal practice in several waste locations that electrical power is produced by burning the biogas produced in the same sites. Next, reference [74] investigated the desulfurization of the biogas by coupling H\({}_{2}\)S/CO\({}_{2}\) absorption units coupled to a photobioreactor. Total H\({}_{2}\)S removal from the biogas was accomplished by the use of a bubble column or airlift and under various operational conditions. Some aspects in relation to the removal of CO\({}_{2}\) make the use of bacteria-microalgae biocultures on these systems of interest. Amine-based reactions and an industrial acid gas removal process were used to design and simulate a gas cleaning process in [75]. The results indicated that the best results are given by a mixture of piperazine and methyldiethanolamine, saving operational cost and carbon emissions with respect to the use of the mixture of methyldiethanolamine and diethanolamine. The generation of biogas has different sources, vinasse being one of them. Different alternatives are investigated for the elimination of water, CO\({}_{2}\), and H\({}_{2}\)S from the biogas [76]. In practice, it has been demonstrated that the use of an anaerobic lagoon is preferred over a series of upflow anaerobic sludge blanket reactors, and from the various investigated alternatives to clean the biogas, water is best removed by silica gel adsorption, and after, both H\({}_{2}\)S and CO\({}_{2}\) are absorbed on an Fe/EDTA solution. Amine groups bearing ionic liquids supported on membranes have been used in the removal of CO\({}_{2}\) and H\({}_{2}\)S and separating both from methane [77]. Facilitated transport is the mechanism responsible for CO\({}_{2}\) transport using the ionic liquid [DMP-DAH][Tf2N] (containing a primary amine), the gas transport being greatly dependent on trans-membrane pressure. In the simultaneous removal of both gases, apparently, absorption is the most used technology with the greatest technology readiness level, alkaline salts and amine being the most used absorbents; moreover, physical solvents are used in this absorption role. Adsorption processing continues investigations in this field in order to improve adsorbents' performance and/or creating new ones, allowing higher efficiencies in the removal of H\({}_{2}\)S and a complete regeneration to be used in further cycles. Both absorption and adsorption technologies have a complete rationalization in their use, i.e., absorption in the treatment of the most contaminated streams and adsorption to be used in the case of gases containing \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Technology** & **Characteristics** & **Industrial Use** & **Reference** \\ \hline Ionic liquid absorption & \begin{tabular}{c} Azole-based protic ionic \\ liquids \\ \end{tabular} & No & [66] \\ Inorganic membranes & \begin{tabular}{c} Ceramic-based \\ Carbon molecular sieve \\ \end{tabular} & No & [73] \\ Hybrid membrane & \begin{tabular}{c} Metal organic \\ framework-polymidine mixed \\ \end{tabular} & No & [67] \\ Adsorption on pristine materials & \
\begin{tabular}{c} Molecular-sieve bases \\ materials \\ \end{tabular} & Yes & [26; 68] \\ Adsorption on composite materials &
\begin{tabular}{c} Metal oxide/silica \\ Metal oxide/activated carbon \\ \end{tabular} & No & [26; 68] \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Technologies for the simultaneous H\({}_{2}\)S-CO\({}_{2}\) removal. low concentrations of the contaminants. The above technologies need the regeneration of the adsorbent and the solvent; thus, they have intensive energy requirements [78]. The use of membranes needed a step ahead of pilot scale to show its potential in this industrial issue [79].