Hydrogen Production by Water Gas Shift Reaction Following Dry Reforming of Biogas Methane in Membrane and Packed Bed Tubular Reactors
The goal of this study was to develop a high performance catalyst for the water gas shift reaction of reformate gas obtained from the dry reforming of biogas methane, in order to produce bio-renewable hydrogen suitable for feed to a fuel cell. Accordingly, three phases of the study were executed involving the identification and optimization of the catalyst, application in a membrane reactor and kinetic studies of the water gas shift reaction. A portfolio of ternary oxide catalysts with a nominal composition of 3Ni5Cu/CeZrM (where M = La, Mg, Y, Gd, Ca) were developed and prepared by surfactant assisted route. A binary oxide catalyst was also prepared to serve as a benchmark for comparing the effect of incorporating a promoter element. The catalysts were screened for the water gas shift reaction at 500oC at atmospheric pressure in a packed bed tubular reactor using 30% CO/balance N2 gas and the catalyst with Ca promoter element showed the best performance. This catalyst was further tested using reformate gas comprising of 46.2%CO, 8.5% CH4, 7.2% CO2 and 38.1 % H2 to simulate a realistic product stream from a biogas dry reformer. Again, the Ca catalyst fared well even under such conditions without any deactivation, making it a potential candidate for possible commercialization. To optimize the catalyst preparation method, the method of impregnation was varied using atmospheric pressure or vacuum conditions; the amount of surfactant used and calcination temperature were also varied. Subsequently, the operating conditions were also varied including reaction temperature, steam/CO ratio and reactor pressure. An extended TOS stability test was performed for 12 hours to evaluate the continuous performance of the catalyst over extended time duration. Several characterization techniques were also employed to investigate the correlation between the catalyst structure and the performance exhibited. The techniques employed include TPR, TPO, XRD, ICP-MS, N2 Physisorption, and H2 Chemisorption. Several statistical methods including Analysis of Variance (ANOVA) and two level factorial design of experiment (DOE) analysis were used to determine the main effects and interacting effects contributing to the observed activity based on the catalyst structure and operating conditions. The catalyst developed was further tested in a membrane reactor in order to investigate the possibility of reducing the number of units usually required in a conventional water gas shift process. The results from the membrane tests showed a better performance compared to the conventional packed bed reactor whilst allowing for the production of 100% pure hydrogen. As part of the membrane studies, permeation tests were performed to correlate the amount of hydrogen recovered through the membrane with pressure and temperature. Furthermore, kinetic studies were performed on the packed bed tubular reactor operating at atmospheric pressure and high pressure (200 psi) in addition to the membrane reactor. The parameters varied were temperature ranging between 400 – 500oC and W/FA0 ranging from 1.1 to 1.6 g-cat.hr/mol. An empirical power law model was used to correlate the resulting experimental data giving orders with respect to CO of 1.27, 1.78, 0.24 and activation energies of 137.2 kJ/mol, 190.3 kJ/mol and 99.8 kJ/mol for the packed bed (atmospheric), packed bed (high pressure) and membrane reactors, respectively. These kinetic results re-emphasized the benefit of incorporating a membrane reactor into the water gas shift reaction process.
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Faculty of Graduate Studies and Research, University of Regina