(95d) Membrane Reactors for PEM Based Micro-Cogeneration Systems

Nowadays a great part of the scientific community agrees that anthropogenic CO₂ emissions need to be reduced significantly in the near future to prevent excessive global warming. A possible solution to this problem is the use of advanced devices able to increase the energy efficiency. In this respect PEM fuel cell based cogeneration systems are potential solutions for further improvement of the energy efficiency. These devices will most likely be fed with hydrogen produced by reforming of light hydrocarbons such as natural gas. Previous studies have shown the advantages of palladium-based membrane reactors (MR) for ultra-pure hydrogen production over conventional natural gas processors for feeding the fuel cell.

In this work, both experimental and simulation studies were carried out to quantify the performance of different technological MR approaches such as fluidized bed membrane reactors and packed bed membrane reactors. In contrast with the packed bed membrane reactors, membrane-assisted fluidized bed reactors offer the possibility to operate under virtually uniform temperature conditions, which is beneficial for the stability of membranes, but also require lower membrane areas for the same performance because concentration polarization is avoided. The experiments have shown that the hydrogen flux through the membranes and the perm-selectivity of the membranes are stable during two weeks continuous operation under bubbling fluidization conditions.

Simulations have shown pronounced axial temperature profiles in packed bed membrane reactors, which are responsible for an increase of up to 25% in the membrane area required in comparison to fluidized bed membrane reactors. In all the cases, a similar total efficiency can be achieved that is 9% higher than the total efficiency of a conventional reformer/fuel cell system (however with different required membrane areas for the packed bed and fluidized bed membrane reactors). A parametric study has been carried out and the possibilities to integrate CO₂ capture inside the PEM micro-cogeneration system have been evaluated.