Ruolo della reazione di Water Gas Shift nella produzione di gas di sintesi da bio gas

The reaction of Water Gas Shift (WGS) plays a key role in the production of H2 or syngas, widely employed in the chemical industry. More than 90% of the H2 is currently produced by Steam Reforming (SR) of the natural gas or low molecular weight hydrocarbons, with an increasing role of its production from alternative sources such as the clean biogas (CBG), mixture of CH4 and CO2 obtained by elimination of S- and N-containing compounds from the gas mixture obtained by anaerobic fermentation of biomass. Compared to the mixture obtained in the SR of the natural gas, that obtained from CBG shows more hard conditions related to a higher CO concentration and a lower Steam/Dry Gas (S/DG) ratio. By hypothesizing a 2 steps process, the tests at high temperature (HTS, 350-450 °C) performed feeding the mixture obtained from CBG showed that Cu/Zn/Al catalysts (Cu 4 wt%) doped with small amount of Ga (Al/Ga = 50) can be usefully employed considering the higher activity and stability in comparison to a reference un-doped catalyst. The H2/CO ratio depended on the amount of the CO in the feed mixture and amount of steam fed. The best performances of the catalyst doped by Ga can be attributed to a higher dispersion and stability of the active phase, such as evidenced by a study of model catalysts and by the DRIFTS analysis in the adsorption/desorption of CO. An alternative to the two steps process is a single step process operating at medium temperature (MTS, 250-350 °C) using only one reactor. On the basis of previous studies, Cu/Zn/Al catalysts (Cu 20 wt%) have been investigated doped with small amounts of promoters (Al/Ce or Al/Zr 50), using a S/DG = 0,55 ratio. At 350°C Ce and Zr improve the catalityc activity, with a deactivation in presence of Zr only of 4%. On the contrary the catalyst containing Ce was stable at increasing reaction temperature.