Steam methane reforming membrane configurations

A selective membrane device can be integrated into a reaction environment in two different ways directly inside the reaction environment, or assembled in a series of reaction units according to an open architecture. In the following sections, these two configurations are described and evaluated with a steam methane reforming reaction used as an example to elucidate benefits and drawbacks. 

Marigliano et al. compared the performance of two different types of tubular methane steam reforming membrane reactors by numerical simulations [413]. In the first, the catalyst was packed into the palladium/silver membrane tube, and in the second it was positioned in the annular region surrounding the membrane tube. Both configurations were heated from the outside. Owing to the indirect heat transfer to the catalyst bed inside the membrane tube, methane conversion was lower in this instance, and under certain conditions it was even inferior to a conventional fixed bed... 

Northwest Power Systems obtained U.S. Patent 5,997,594 in 1999 for a Steam Reformer with Internal Hydrogen Purification. This process is based on a steam reformer that has a membrane separation system and a methanation system in close proximity to the area in which the reforming reaction occurs. Several potential equipment configurations are described in the patent. 

A fixed-bed reactor often suffers from a substantially small effectiveness factor (e.g., 10 to 10 for a fixed-bed steam reformer according to Soliman et al. [1988]) due to severe diffusional limitations unless very small particles are used. The associated high pressure drop with the use of small particles can be prohibitive. A feasible alternative is to employ a fluidized bed of catalyst powders. The effectiveness factor in the fluidized bed configuration approaches unity. The fluidization system also provides a thermally stable operation without localized hot spots. The large solid (catalyst) surface area for gas contact promotes effective catalytic reactions. For certain reactions such as ethylbenzene dehydrogenation, however, a fluidized bed operation may not be superior to a fixed bed operation. To further improve the efficiency and compactness of a fluidized-bed reactor, a permselective membrane has been introduced by Adris et al. [1991] for steam reforming of methane and Abdalla and Elnashaie [1995] for catalytic dehydrogenation of ethylbenzene to styrene. 

Figure 10.14a Configuration I of a nuidizcd-bed membrane reactor for steam reforming of methane (Adris el al., 1991]...

Caravella A, Di Maio FP, Di Renzo A (2010) Computational study of staged membrane reactor configurations for methane steam reforming. I. Optimization of stage lengths. AIChE J 56(l) 248-258... 

Mori N et al (2007) Reactor configuration and concentration polarization in methane steam reforming by a membrane reactor with a highly hydrogen-permeable membrane. Ind Eng Chem Res 46 1952-1958... 

The methane combustion configuration is sketched in Figure 3.14 and consists of two sections [44]. Hydrogen permselective membranes are integrated in a fiuidized reform-ing/shift top section where ultra-pure H2 is extracted and the energy required for the SR is supplied via in situ methane oxidation in a separate fluidized bottom section, where oxygen is selectively fed to the methane/steam feed via oxygen permselective membranes. 

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