(784a) Ammonia-Based Cox Free Hydrogen Production by Membrane Reactors

Ammonia decomposition in a bimodal catalytic membrane reactor (BCMR) consisting of a Ru/γ‑Al₂O₃/α‑Al₂O₃ bimodal catalytic support and a hydrogen‑selective silica membrane in a single unit was proposed for CO_x‑free hydrogen production in the present study. The bimodal catalytic membrane showed a H₂ permeance of 6.2×10^‑7 mol/(m² s Pa) at 500 °C, with H₂/NH₃ and H₂/N₂ permeance ratios of 200 and 720, respectively. Ammonia conversion was surprisingly enhanced form 45 to 95% at 450 °C in the BCMR after selective H₂ extraction. The BCMR showed excellent stability with respect to both gas permeation properties and catalytic activities. Moreover, based on quantitative discussion on the effect of bimodal structure on the gas permeation, pore structure and catalytic activity of the bimodal catalytic membrane reactors, the optimal preparation conditions for the membrane reactor was then obtained. An interesting phenomenon that NH₃ conversion increased as the feed pressure was increased in the membrane reactor was observed, although high pressure was thermodynamically not beneficial to the NH₃ decomposition.

A mathematical model was formulated for the simulated study of NH₃ decomposition in a co-current configuration membrane reactor, and the effect of Damköhler number (Da), permeation number (θ), and membrane selectivity on membrane reactor performance was discussed theoretically. The required membrane performance for autothermal decomposition of NH₃ in a bimodal catalytic membrane reactor was calculated based on theoretic simulation. Moreover, the effect of various operating conditions on the membrane reactor performance was studied experimentally, and the results showed good agreement with those calculated by the proposed simulation model.

 (1)    Gang Li, Masakoto Kanezashi, Toshinori Tsuru. Highly enhanced ammonia decomposition in a bimodal catalytic membrane reactor for CO_x-free hydrogen production. Catalysis Communications, 15 (2011) 60–63.

(2)    Gang Li, Masakoto Kanezashi, Tomohisa Yoshioka, Toshinori Tsuru. Ammonia decomposition in catalytic membrane reactors: Simulation and experimental studies. AIChE Journal, doi: 10.1002/aic.13794, in press.

(3)    Gang Li, Masakoto Kanezashi, Hye Ryeon Lee, Tomohisa Yoshioka, Toshinori Tsuru. Preparation of a novel bimodal catalytic membrane reactor and its application to ammonia decomposition for CO_x-free hydrogen production. International Journal of Hydrogen Energy, under review.