## 2 The Technologies
### Membranes and Membrane Contactors to Remove Hazardous H\({}_{2}\)S from Gas Streams
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Membrane** & **Feed Gas** & **Working Conditions** & **H\({}_{2}\)S Capture** & **Reference** \\ \hline Crosslinked poly(ethylene & 5\% H\({}_{2}\)S & T = 25 \({}^{\circ}\)C & 0.08–25 barrier & [54] \\ glycol membrane & 5–20\% H\({}_{2}\)S & P = 800 psi & 0.08–25 barrier & [54] \\ Vinyl-poly(norborene) & 5–20\% H\({}_{2}\)S & T = 25 \({}^{\circ}\)C & Depending on feed gas & [55] \\ membrane & 5–20\% H\({}_{2}\)S & P = 800 psi & composition & [55] \\ Cellulose triacetate HFM & 20 mol\% H\({}_{2}\)S & T = 35–50 \({}^{\circ}\)C & 140 GPU & [52] \\ Dense polymer membrane & 0.5–20\% H\({}_{2}\)S & T = 35 \({}^{\circ}\)C & Depending on membrane type & [53] \\  & & P = 7–46 bar & & \\ Copolymide membranes & 20\% H\({}_{2}\)S & T = 22 \({}^{\circ}\)C & & \\  & & P = 24–46 bar & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: H\({}_{2}\)S removal by membrane technologies. The use of an ionomer material (PFSA) as a membrane material in the removal of H\({}_{2}\)S from a gas stream is described in [61]. Experimental work has considered a series of variables in the investigation, including humidity, temperature, and pressure. It has been demonstrated that the ionomer material has a great dependence on temperature and water activity and is an excellent material to separate gases from mixtures of them, i.e., H\({}_{2}\)S is conveniently separate from CO\({}_{2}\) and CH\({}_{4}\) from a ternary gas mixture. Hollow fiber membrane bioreactors (HFMBs) are used to investigate the removal of H\({}_{2}\)S at various bed residence times [62] and other operational variables: pH, biomass types, etc. H\({}_{2}\)S removal is higher when biotic bioreactors are used, sulfate being the principal species encountered in the reactor after the end of the operation. Data about other operational results are included in the reference. A biogas containing ammonia and H\({}_{2}\)S is cleaned in a hollow fiber membrane bioreactor [63]. Under different operational conditions, both gases are eliminated (up to 99%) from the biogas, H\({}_{2}\)S having a greater critical loading rate than ammonia. After operation, different sulfur-bearing species (SO and sulfate) together with nitrogen are found in the  
Figure 1: Hollow fiber membrane module for gas removal in counter-current operational mode. Figure 2: Mass transfer in the hollow fiber module. Multiple curve black lines represented membrane micropores. bioreactor. This device is filled by several biomasses, including _Sulfuricurum_ sp., _Smithella_ sp., _Sulfurilates_ sp., _Rhodanobacter_ sp., and _Thiobacillus_ sp. The removal of toxic H\({}_{2}\)S gas has also been investigated using a lignin carbon-based membrane [64]. From this material, and after carbonization, an alkali lignocarbon is derived, and from this several hybrid materials are also derived using casting methodology (Table 4). Results indicated that the inclusion of copper species into the raw material clearly improves the deodorization properties of these Cu-bearing composites if compared with those of the pristine raw material. It was also demonstrated that in the copper-doped hybrid materials, nano-CuO is the key active site in the H\({}_{2}\)S removal from the gas stream.