Solar Upgrade of Methane Using Dry Reforming In Direct Contact Bubble Reactor

cms.solarpaces2012.org International audience The reforming behavior of a direct contact bubbling CH4-CO2 mixture, was quantitatively investigated, in an alkali carbonate based molten salt system containing suspended Ni-Al2O3 catalyst. A thermodynamical process of a solar reformer of dry methane reforming was proposed to operate in a temperature range of 600-800oC. The selectivity of the thermal fluid have been validated according to specific requirements including lower melting point, thermal and chemical stability, acting simultaneously as heat transport and sensible heat storage. A ternary mixture of alkali carbonates system Na2CO3, K2CO3 and Li2CO3 of ratio 1:2:2 fulfills our requirements for the direct contact bubble reactor of the solar reformer, in which a CO2-rich mixture of methane was reformed to produce synthesis gas. The reforming behavior was experimentally investigated to quantify the product compositions, pursuing to maximize the methane conversion and H2 yield, while minimizing coke depositions and carbonization effects. Three types of Ni-loading (10%, 15% & 20 wt. %) - Al2O3 catalysts were prepared by impregnation using nickel nitrate solution. The results exhibited that 15%Ni-Al2O3 catalyst showed the highest activity and selectivity with respect to H2 % yield (or H2:CO production ratio) and carbon deposition rates. The thermodynamic analysis showed the positive effect of excess CO2 on the process of dry CH4 reforming in alkali carbonate salts; the higher CO2/CH4 ratio, the lower reaction temperature can be achieved; subsequently, minimizing the thermal decomposition of alkali carbonates. However, the experimental results expressed the increase of CO2/CH4 ratio in terms of higher methane conversion, whereas the H2:CO production ratio was significantly decreasing, attributed to increase in water formation as a result of Reverse Water Gas Shift (RWGS) reaction. While, the carbon deposition is decreasing as per the theoretical results.