Comparative analysis of hydrogen production from ammonia decomposition in membrane and packed bed reactors using diluted NH3 streams.

Ammonia decomposition is a key technology for its use as a hydrogen carrier and in the recovery of H 2 from waste streams containing ammonia. The coupling of the catalytic decomposition of ammonia with an H 2 permeoselective membrane improves the process by mitigating thermodynamic constraints and producing a flux of high-purity hydrogen, not requiring further separation/purification. In this study, we compare the behaviour of an eggshell catalyst 1.3 wt % Ru/Al 2 O 3 catalyst in a packed bed reactor (PBR) and a packed bed membrane reactor (PBMR) using an ultrathin Pd membrane (3.4 μm). Tests were made at 11 bar(a) with a weight hourly space velocity of NH 3 in the 0.560–1.68 Lꞏg−1ꞏh−1 range and temperatures of 350–400 °C, e.g. milder conditions than the conventional ammonia cracking catalysts. Under optimised conditions (0.56 Lꞏg−1ꞏh−1, 400 °C, sweep gas flow 0.55 L min−1), the PBMR shows excellent performance, achieving NH 3 conversion, H 2 productivity and recovery factor of 99%, 47 mmol H2 ·g Ru −1·min−1, and 94.9%, respectively. PBMR increases by ∼50% the conversion rate compared to PBR. Without a sweep gas, PBMR performances are lower, even still higher than in PBR. For the first time, superior or comparable performance was demonstrated compared to similar systems using pure ammonia in terms of conversion, hydrogen recovery, H 2 productivity, and Ru utilisation. These results can be further enhanced with vacuum systems to convert diluted ammonia streams into high-purity hydrogen for small-scale distributed systems and can be extended to other reactions. • An egg-shell Ru/Al 2 O 3 with an ultra-thin Pd membrane achieved 99% NH 3 conversion at 400 °C in PBMR, outperforming PBR. • Ultra-thin Pd membranes and sweep gas allow 94.88% H 2 recovery factor by decomposition of diluted ammonia. • Dilute NH 3 can improve safety and decrease noble metal usage, offering economic and environmental benefits. [ABSTRACT FROM AUTHOR]