The kinetics of methanol decomposition: a part of autothermal partial oxidation to produce hydrogen for fuel cells

Methanol is considered as a renewable energy source for fuel processor-fuel cell systems. The determination of the kinetics of methanol autothermal partial oxidation can be simplified if the problem is divided into subproblems. As a first step, the kinetics of methanol decomposition (Me) are studied. To describe this subproblem, a reaction system consisting of four reactions is assumed. The reactions are: Me, dimethyl ether (DME) formation, steam reforming, and water gas shift (WGS) which are studied on a commercial copper containing catalyst (5 wt.% copper on alumina). The dehydration of methanol to DME is a second order reaction and essentially provides an excess of water over the whole reactor allowing first order kinetic assumptions for steam reforming and WGS. The WGS reaction proves to be slow, compared to the other reactions, and equilibrium limited. The activation energies (kJ/mol) are estimated: Me 76 (+/-4%), DME formation 117 (+/-2%), steam reforming 81 (+/-7%), WGS 50 (+/- 25%). Turnover frequencies for Me are estimated based on copper surface areas determined by the nitrous oxide pulse reduction method. At 220 degreesC, values of 0.05 s(-1) are estimated compared to a literature value of 0.019 s(-1) at 200 degreesC. (C) 2001 Elsevier Science B.V. All rights reserved.