Burner permeate

It is often desirable to operate the reactor and the catalyst under isothermal conditions to achieve high reactor performance. Heat requirement of an endothermic reaction in a membrane reactor to maintain an isothermal condition can be challenging as in most of the dehydrogenation reactions such as conversions of ethylbenzene to styrene and prc pane to propylene. Maintaining an isothermal condition implies that some means must be provided to make the adequate heat input (e.g., from a burner) that is longitudinally dependent It is not trivial to make the temperature independent of the longitudinal position because the permeate flow also varies with the location in the axial direction. 

Figure 2.8 Example of carbon dioxide separation from power plant flue gas using a two-step membrane process with two options for managing the permeate from the second membrane step. In Option 1 purple double-dotted lines), air is used directly in the burner while a vacuum pump creates partial pressure driving force in the second membrane step with return of the second step permeate to front of membrane process. In Option 2 blue dashed lines), the combustion air is used as a countercurrent permeate sweep gas in the second membrane step. Adapted from Figs. 11 and 12 in Merkel TC, Lin H, Wei X, Baker R. Power plant post-combustion carbon dioxide capture an opportunity for membranes. J Membr Sci 2010 359(1—2) 126—139.

Kikuchi [111] described a natural gas MR, which had been developed and operated by Tokyo Gas and Mitsubishi Heavy Industries to supply PEM fuel cells with hydrogen. It was composed of a central burner surrounded by a catalyst bed filled with commercial nickel catalyst. Into the catalyst bed 24 supported palladium membrane tubes were inserted. The membranes had been prepared by electroless plating and were 20 pm thick. Steam was used as sweep gas for the permeate. The reactor carried 14.5 kg catalyst. It was operated at 6.2 bar pressure, S/C ratio of 2.4, and 550°C reaction temperature. The conversion of the natural gas was close to 100%, wdiile the equilibrium conversion was only 30% under the operating conditions. The retentate composition was 6 vol.% hydrogen, 1 vol.% carbon monoxide, 91 vol.% carbon dioxide, and 2 vol.% methane. 

Figure 7.43 Permeate burner of the methanol fuel processor developed by Hansen efo/. within the scope ofa European Joule I project [553].

A methanol fuel processor based on steam reforming in a fixed catalyst bed and membrane separation was described by LedjefF-Hey et al. [401]. The system consisted of an evaporator, a steam reformer, which was supplied with heat by a catalytic burner, and a membrane separation module, which carried membranes of a very high thickness of 7.5 mm. At 5-bar system pressure and S/C ratio of 2.0, a hydrogen flow equivalent to 1.1-kW thermal power was generated by the system, which had an overall efficiency of 54%. Between 40 and 62% of the hydrogen produced by the reformer could be separated by the membrane module. Leakages in the sealing of the membrane module led to carbon monoxide spill-over to the permeate, but this was limited to carbon monoxide concentrations well below 100 ppm. 

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