Autothermal reforming of isobutanol

Abstract

Catalytic partial oxidation (CPO) of isobutanol to produce synthesis gas with varying H₂/CO ratios has been performed autothermally in a staged millisecond-contact-time reactor. A 1 wt% Rh-1 wt% Ce/α-alumina catalyst was used to carry out CPO of isobutanol over a range of fuel to oxygen ratios (C/O) in ∼20 ms residence times. Steam was added (S/C = 0 to S/C = 3) to promote the water gas shift (WGS) reaction and increase hydrogen production. Without steam addition, the maximum CO and H₂ selectivities obtained were greater than 70%. Steam addition increased the maximum hydrogen selectivity to 103%, at C/O = 1 and S/C = 2. Conversion of isobutanol and oxygen was always > 99% at all C/O and S/C ratios after CPO where the autothermal temperatures were typically between 600 and 1000 °C . A 1 wt% Pt–1 wt% Ce catalyst was added downstream of the CPO stage to further reduce the CO and increase the H₂ concentrations by the WGS reaction. Addition of the WGS stage resulted in a product stream containing 1.7 to 3 mol% CO at S/C of 2 and 3 which is comparable to the exit stream CO concentration of an industrial high temperature shift catalyst. With steam addition, selectivities to hydrogen greater than 100% were obtained at all C/O ratios, with a maximum of 122% at C/O = 0.9 and S/C = 3. At S/C = 3, the H₂/CO ratio increased from ∼3 after the CPO stage to ∼12 after the WGS stage. Also, the WGS catalyst reduced the selectivities of non-equilibrium products like isobutylene and isobutyraldehyde by almost half compared to that after the CPO stage, which can reduce syngas cleanup costs after a reformer. Since the total residence time in the reactor is ∼100 ms and the product distribution can be tuned by addition of steam, this represents a compact and simple system for producing renewable syngas or hydrogen.