Ultra-clean hydrogen production by ammonia decomposition

Abstract

A rigorous heterogeneous mathematical model is used to simulate a cascade of multistage fixed bed membrane reactors (MSFBMR) with inter-stage heating and fresh sweep gas for the decomposition of ammonia to produce high purity hydrogen suitable for the PEM fuel cells. Different reactor configurations are compared. The comparison between a single fixed bed reactor (FBR) and a single fixed bed membrane reactor (FBMR) shows that the FBMR is superior to the FBR and gives 60.48% ammonia conversion higher than the FBR. However, 20.91% exit ammonia conversion obtained by the FBMR is considered to be poor. The FBMR is limited by the kinetics at low temperatures. The numerical results show that the MSFBMR of four beds achieve 100.0% ammonia conversion. It was found that the membrane plays the prime role in the displacement of the thermodynamic equilibrium. The results also show that, a linear relationship exists between the number of beds and the feed temperature and a correlation has been developed. A critical point for an effective hydrogen permeation zone has been identified. It is observed that the diffusion limitation is confined to a slim region at the entrance of the reactor. It is also observed that the heat load assumes a maximum inflection point and explanations offered. The results show that the multistage configuration has a promising potential to be applied successfully on-site for ultra-clean hydrogen production.

Recent progress in ammonia fuel cells and their potential applications

“…237 However, as detailed in previous chapters, SOFCs greatly rely on high operating temperatures to fully appreciate fuel utilisation. 238 Along with this, it is well established that the rate of ammonia conversion is somewhat slow and requires use of a suitable catalyst. This is particularly important in SOFC-Os, where another factor that must be considered is NOx formation due to the presence of water at the anode.…”

Ammonia deep chemical looping combustion on perfect and reduced Fe 2 O 3 : A theoretical account

“…To understand the effect of the gradual reduction of Fe 2 O 3 on the NH 3 CLC, Figure 12 depicts the relationship between E a (for DeH of CH 4 and generation of H 2 , N 2 , NO, and H 2 O, respectively) and the reduced state of iron oxide. The E a for NO formation is significantly higher than that of N 2 on the surface of iron oxide at different reduction state, indicating that NH 3 CLC is difficult to generate NO pollutant corresponding to the related CLC experimental results, 47 showing that the concentration of N 2 and NO in the generated nitrogen‐containing gas in the FR is 92.91% and 2.47% 48 . Besides, it has been verified that the reaction temperature shows only slightly influence on the oxidation of NH 3 to NO x and N 2 , while the NO formation could be promoted by high concentrations of NH 3 and decreased by the high concentrations of syngas 22 .…”

Designing Nanoparticles and Nanoalloys for Gas-Phase Catalysis with Controlled Surface Reactivity Using Colloidal Synthesis and Atomic Layer Deposition

“…In recent years, the reverse reaction of NH 3 synthesis, i.e., NH 3 decomposition into N 2 and H 2 , has become a topic of interest for CO x -free H 2 fuel cells for clean energy [ 82 , 83 , 84 ]. Li and co-workers [ 85 ] confirmed the size-dependency of NH 3 decomposition on Ni/MCF-17 through the use of uniform NPs with size distributions from 1.5 to 8 nm, tailored by adjustment of the colloid synthesis temperature.…”