A microchannel reactor is being developed for the reforming of methane gas (CH₄) to CO₂and H₂gas using steam (H₂O vapor) at high temperature. Prior to entering the reforming reactor, CH₄(species A) and H₂O vapor (species B) at a nonreactive temperature of 400°C are mixed within a microchannel gas preheater zone with an inner diameter of only 50 microns (0.0050 cm). The Peclet number, defined as

must be at least 2.0 before this gas stream is fed into the reforming reactor. It is also desired to keep the gas velocity (v_ˆž) constant at 4.0 cm/s. For purposes of calculation, it may be assumed that CH₄ is diluted in H₂O gas.

a. What is the Knudsen diffusion coefficient for CH₄ inside the microchannel? Is Knudsen diffusion important?

b. At what total system pressure (P) should the process be operated at to meet the aforementioned design constraints of Pe = 2.0 and v_ˆž = 4.0 cm/s? At this total system pressure, what is the gas-phase molecular diffusion coefficient of CH₄ in H₂O?

Transcribed Image Text:

Vood Pe = Ae