Effects of using K2CO3-promoted alumina as carrier for Ni in sorption enhanced steam methane reforming

Sammanfattning: Sorption enhanced steam methane reforming (SE-SMR) has the advantage of enhancing the production of hydrogen in addition to being a possible carbon capture system. Sorption also allows the steam reforming process to occur at relatively lower temperature as well as facilitates separation of carbon dioxide within the reactor and thus, avoids separation equipment which would otherwise be required. The above mentioned SE-SMR process is a suitable option for hydrogen production in small scale plant and can as well be combined with heat and power production plant and such an application is targeted in this study. The main focus of the project is to combine the catalyst and the adsorbent. Furthermore, the use of K-promoted alumina as both CO 2 adsorbent and carrier of Ni is the aim of the project. To achieve this, fixed bed experiments both in the absence and presence of steam as well as steam reforming experiments are conducted. A steam to carbon ratio of 4 is maintained in the experiments involving steam and the space velocity used is 184 h-1. 16.7 w% K-promoted samples were used, where K2CO3 was used for promotion. The experimental variables considered are temperature (ranging from 300 °C to 500 °C) and Ni loading on catalyst (5, 10 and 15 w%). Performance indicators observed are the adsorption capacity and kinetics of the adsorption and desorption in both dry and wet conditions as well as the CH4 conversion. BET, XRD and FT-IR are used to characterise morphology, bulk and surface of the catalyst. The results show that the use of K-alumina as sorbent is best suited for low temperatures (300 °C) and 10 w% Ni/K-alumina showed best performance as adsorbent at higher temperatures (500 °C) for steam reforming conditions. The desorption process was found to be better at low temperatures and in the absence of steam. Steam reforming experiments were performed after apparent partial reduction of NiO and partial decomposition of K 2CO3 and the results suggest that CH4 conversion is retained at 100% for longer times at higher temperatures (500 °C) on using at least 10 w% Ni in the catalyst-sorbent. The better adsorption of CO2 in the presence of K seems to be due to bicarbonate formation on the surface and the Ni seems to catalytically improve the formation of surface bicarbonates at higher temperature.