Application of Raman spectroscopy in chemical investigation of impregnated activated carbon spent in hydrogen sulfide removal process

We present an application of Raman spectroscopy for understanding the chemisorption catalytic processes occurred in impregnated activated carbon used in hydrogen sulfide (H2S) adsorption from biogas. Downstream of an H2S adsorption capacity study, conducted employing commercial carbon at different operating conditions as sorbent in a fixed bed flow reactor, spent carbon samples who returned suitable H2S removal performances were studied by means of Raman spectroscopy. Raman analysis showed that among all the H2S metal impregnates, copper was the chemical responsible for H2S adsorption, since observed Raman spectra exhibited a perfect overlapping with copper sulfide (CuS) signature. A further confirmation was given by a thermal decomposition test conducted through the Raman optical apparatus over an H2S-exposed carbon sample, by estimating anti-Stokes and Stokes Raman processes relative efficiency. Raman results turned out to be consistent with thermogravimetry tests results executed over the same spent carbon samples. The experiment witnesses the capability of Raman spectroscopy to determinate the chemical nature of compounds resulting from H2S adsorption, overcoming the lack in chemical information encountered by elemental techniques such as energy-dispersive X-ray. We thus propose Raman spectroscopy as a way to integrate traditional chemical investigation procedures.