Intermediate temperature water–gas shift kinetics for hydrogen production

Abstract

The water–gas shift (WGS) reaction is an attractive process for producing hydrogen gas from lignocellulosic biomass conversion applications. The goal of this study was to investigate hydrogen production via the WGS reaction using carbon monoxide (CO), one of the significant non-condensable gases formed during biomass fast pyrolysis, as reactant over the range of the intermediate-temperature shift (ITS). WGS reaction is typically carried out as a low-temperature shift (LTS;150–300 °C) or a high-temperature shift (HTS; 300–500 °C) with each shift using a different catalyst. In this study, the WGS was conducted at an intermediate temperature range (200–400 °C) relevant to lignocellulosic biomass fast pyrolysis hydrodeoxygenation over a copper (Cu) based catalyst in a CO-lean environment (70 vol% steam, 20 vol% He, and 10 vol% CO). The experimental temperatures were tested over three different weight hourly space velocities (WHSV = 1220, 2040, and 6110 cm3 g−1 min−1). CO conversion increased with increasing temperature and catalyst weight, with a maximum CO conversion of 94% achieved for temperatures greater than 300 °C. We evaluated four models including two mechanistic Langmuir–Hinshelwood (LH) models, one redox mechanistic model, and one reduced order model (ROM). The first (LH1) and second (LH2) Langmuir–Hinshelwood models differ by the intermediate formed on the catalyst surface. LH1 forms product complexes while LH2 produces a formate complex intermediate. LH2 best described our experimental kinetic data, based on statistical and regression analysis, and provided apparent activation energies between 60 and 80 kJ mol−1 at different space velocities. Furthermore, the ROM fit the experimental data well and, due to its simplicity, has potential for incorporation into computationally expensive simulations for similar experimental conditions.