Pressure, Diffusion, and S/M Ratio Effects in Methanol Steam Reforming Kinetics

The kinetics and diffusion effects of methanol steam reforming reaction over commercial Cu/ZnO/Al2O3 catalyst was studied for steam to methanol (S/M) ratios of 0 to 1 and pressures below 6 bar. Our objective is the development of a novel high-pressure propulsion technology based on the concepts of thermochemical recuperation (TCR) and onboard hydrogen production. A simple kinetic model assuming methanol decomposition followed by water–gas-shift was used to estimate the rate constants (kMD, kWGS). The apparent activation energy of kMD was estimated as 45–55 kJ/mol for large pellets and S/M = 1.0, 0.5, and 0.0; kMD for S/M = 0 (and the conversions obtained) were smaller than those of S/M = 1, probably due to CO inhibition. At temperatures above ∼500 K, the WGS is at equilibrium. Strong pore-diffusion limitations are evident at 1 bar for the 3 mm catalyst, evident experimentally as well as by analysis; the apparent kMD is almost diffusion free for particles of 0.7 mm in diameter. This resistance increases, o...