ABSTRACT A kinetic study for steam reforming of methanol on a Cu/Zn/Al2O3 catalyst has been performed in the temperature range 513-573 K and at atmospheric pressure. The mechanistic kinetic model using Langmuir–Hinshelwood (L-H) approach has been developed. Effects of reaction temperature and contact time on methanol conversion and product distributions have been investigated and fitted to the kinetic model for parameter estimation.

Keywords: Steam reforming of methanol; Hydrogen; Kinetics; Cu/Zn/Al2O3. _____________________________________________________________________________________________________________________

INTRODUCTION

The realistic alternative to the conventional combustion engine of automobile carriers can be a fuel cell, which does not emits the toxic pollutants. The hydrogen required for the functioning of polyelectrolyte membrane (PEM) fuel cell can either be stored in pressurized tank or generated on-board using liquid hydrogen carrier such as methanol that offers several advantages [1]. In the present study kinetic modeling of steam reforming of methanol over Cu/Zn/Al2O3 catalyst has been done to predict the methanol conversion as well as hydrogen production and CO formation, which is useful for the accurate design of reformer and for the determination of the amount of hydrogen produced and fed to the PEM fuel cell.

RESULTS AND DISCUSSION

The catalysts were prepared by the wet impregnation method, described elsewhere [1]. Surface area, pore volume and pore size of catalysts were measured using N2 adsorption-desorption surface area analyzer, and different crystalline phases presents in fresh and spent catalysts were identified by X-ray powder diffraction. Catalysts performance evaluated in a fixed–bed stainless steel reactor (19 mm i.d.) with 1-3 gm catalyst loading after pre-reduction of crushed catalysts of 20-25 mesh size in chemical reaction controlling regime. Operating temperature varied from 493-593 K, contact time 3-15 kg cat./(mol/s of methanol) at atmospheric pressure in an electrically heated furnace. The reaction schemes considered in the development of kinetic model are the surface reactions of steam reforming of methanol (SRM) reaction and the reverse water gas-shift (rWGS) reaction.

CH3OH + H2O ↔ CO2 + 3H2 (steam reforming of methanol :SRM) (1)

CO2 + H2 ↔ CO + H2O (Reverse Water Gas shift reaction : rWGS) (2)

The following are the final kinetic rate expressions (Eq.3 and 4) developed using L-H approach. Some surface reactions have been chosen based on literature [2-3].

The parameters of kinetic model were estimated using non-linear regression, which matched well with the parameters available in the literature [2]. Model predicted methanol conversion and product yields are shown in the Fig.1 (a) and (b), which closely matched eachother.

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