Development of a Catalyst/Sorbent for Methane Reforming (2008)

This project led to the further development of a combined catalyst and sorbent for improving the process technology required for converting CH{sub 4} and/or CO into H{sub 2} while simultaneously separating the CO{sub 2} byproduct all in a single step. The new material is in the form of core-in-shell pellets such that each pellet consists of a CaO core surrounded by an alumina-based shell capable of supporting a Ni catalyst. The Ni is capable of catalyzing the reactions of steam with CH{sub 4} or CO to produce H{sub 2} and CO{sub 2}, whereas the CaO is capable of absorbing the CO{sub 2} as it is produced. The absorption of CO{sub 2} eliminates the reaction inhibiting effects of CO{sub 2} and provides a means for recovering the CO{sub 2} in a useful form. The present work showed that the lifecycle performance of the sorbent can be improved either by incorporating a specific amount of MgO in the material or by calcining CaO derived from limestone at 1100 C for an extended period. It also showed how to prepare a strong shell material with a large surface area required for supporting an active Ni catalyst. The method combines graded particles of {alpha}-alumina with noncrystalline alumina having a large specific surface area together with a strength promoting additive followed by controlled calcination. Two different additives produced good results: 3 {micro}m limestone and lanthanum nitrate which were converted to their respective oxides upon calcination. The oxides partially reacted with the alumina to form aluminates which probably accounted for the strength enhancing properties of the additives. The use of lanthanum made it possible to calcine the shell material at a lower temperature, which was less detrimental to the surface area, but still capable of producing a strong shell. Core-in-shell pellets made with the improved shell materials and impregnated with a Ni catalyst were used for steam reforming CH{sub 4} at different temperatures and pressures. Under all conditions tested, the CH{sub 4} conversion was large (>80%) and nearly equal to the predicted thermodynamic equilibrium level as long as CO{sub 2} was being rapidly absorbed. Similar results were obtained with both shell material additives. Limited lifecycle tests of the pellets also produced similar results that were not affected by the choice of additive. However, during each lifecycle test the period during which CO{sub 2} was rapidly absorbed declined from cycle to cycle which directly affected the corresponding period when CH{sub 4} was reformed rapidly. Therefore, the results showed a continuing need for improving the lifecycle performance of the sorbent. Core-in-shell pellets with the improved shell materials were also utilized for conducting the water gas shift reaction in a single step. Three different catalyst formulations were tested. The best results were achieved with a Ni catalyst, which proved capable of catalyzing the reaction whether CO{sub 2} was being absorbed or not. The calcined alumina shell material by itself also proved to be a very good catalyst for the reaction as long as CO{sub 2} was being fully absorbed by the core material. However, neither the alumina nor a third formulation containing Fe{sub 2}O{sub 3} were good catalysts for the reaction when CO{sub 2} was not absorbed by the core material. Furthermore, the Fe{sub 2}O{sub 3}-containing catalyst was not as good as the other two catalysts when CO{sub 2} was being absorbed.