Hydrogen production FBMRs

Different types of membrane reactors for hydrogen production have been proposed in the literature. Most of the previous work has been performed in packed bed membrane reactors (PBMRs) however, there is an increasing interest in novel configurations such as fluidized bed membrane reactors (FBMRs) and membrane micro-reactors (MMRs), especially because better heat management and decreased mass transfer limitations can be obtained in these novel reactor configurations. 

Even though Rahimpour and co-workers often used FBMRs for distributive hydrogen feeding in methanol reactors [35-37], most of the literature has focussed on pure hydrogen production through Pd-based membranes (see among others [38-41]) and on autothermal reforming reactions (see a.o. Ref. [29,42-44]). 

The studies have proven that both MRs can realize better performance in terms of methane conversion and hydrogen production than the CRs, working also at milder operating conditions. By making a comparison between the two reactor configurations, it has been shown that a PBMR has a very simple configuration whereas an FBMR is typically characterized by enhanced mass and heat transfer rates, which favor more uniform temperature profiles. Nevertheless, possible bubble-to-emulsion mass transfer... 

A typical one-dimensional two-phase model for a membrane-assisted FB reactor can be used for the simulation of the FBMR for hydrogen production via methane reforming. A schematic representation of the gas flows between the compartments of the bubble and emulsion phases is depicted in Figure 3.12. The model main assumptions are ... 

Figure 7.2 Schematic representation of FBMRs for hydrogen production (a) bubbling fluidization regime (b) turbulent fluidization regime (c) fast fluidization regime. U = superficial gas velocity [7 = minimum bubbling velocity U =velocity of transition from bubbling to turbulent fluidization regime U =velocity of transition from turbulent to fast fluidization regime/significant entrainment ROG = reactor off-gas V=reactor volume. Reproduced from [6]. With permission from Elsevier.

Figure 7.4 shows the structure of an FBMR with plate-type Pd-Ag dense metal membranes for hydrogen production [8, 9]. Two-sided planar membrane panels are suspended vertically in the reactor. Each side of the panels consists of 25 pm thick Pd-Ag foil mounted on a porous stainless steel base with a barrier layer to prevent interdiffusion... 

Recently, a new reactor has been proposed by combining the MR features with the chemical looping features for heat production with inherent CO2 capture. The novel reactor concept called Membrane Assisted Chemical Looping Reforming (MA-CLR) was introduced by Medrano et al. [55]. In this system (Figure 3.16), a FBMR is located in the fuel reactor of a CLR system, where the incorporation of membranes substitutes the WGS and PSA steps of the traditional CLR process. The selective extraction of hydrogen provides a pure H2 stream and also displaces the thermodynamic equilibria. Flence, reaction and... 

Two FBMR concepts for the production of ultrapure hydrogen with integrated CO2 capture have been proposed by our group (see Path et al. (2005), Van Sint Annaland et al. (2006)) and patented in collaboration with Shell Global Solutions BV. The two concepts are depicted in Fig. 4.1. 

In FBMRs, the membranes are inserted inside the fluidized catalyst bed, serving as a product extractor or a reactant distributor. Figure 7.1 shows a typical FBMR structure for selective removal of a product (hydrogen) [4,5]. Pd-membrane tubes are placed vertically in the FBMR.The reactant gas is fed through the gas distribution plate at the bottom of the reactor to fluidize the fine particulate catalysts. Entrained solids are separated from the reaction product gas stream by internal cyclone separator and then returned to the reactor catalyst bed. 

Figure 7.4 Schematic structure of FBMR with Pd-membrane panels for autother-mal production of hydrogen. Reproduced from [8]. With permission from Elsevier.

FBMRs have shown the promise of industrial commercialization of MR technology, especially in the production of pure hydrogen for fuel cell applications. However, there are still many issues to be addressed before successful commercialization - such as the complexity of construction, the costs of membranes, and their long-term durability in harsh fluidization conditions. The challenges faced by the commercial viability of FBMRs include ... 

---