Syngas production via catalytic oxidative steam reforming of glycerol using a Co/Al coprecipitated catalyst and different bed fillers

Abstract

Syngas production has been investigated via oxidative steam reforming of concentrated glycerol aqueous solutions (Steam-to-Carbon molar ratio = 4 and 6 vol% O2 in N2). Results obtained using different (bulk) bed materials (SiO2, SiC and γ-Al2O3) were compared with results achieved while using a cobalt aluminate catalyst prepared by coprecipitation dispersed in each of those same bed fillers. The effects on conversion and gas production of the filler bed material, activation temperature (1023 K, 1073 K and 1123 K) and reaction temperature (823 K, 923 K and 1023 K) were studied, as well as the catalyst reuse (at 1023 K) to assess its performance after regeneration. High glycerol conversion levels (above 80%) were attained at 1023 K without the catalyst. The main gaseous products were H2, CO, CO2 and CH4. Using a bed of commercial γ-Al2O3, around 90% of the C fed into the reactor could be converted into gaseous products, yielding syngas with H2/CO molar ratio close to 1. In what concerns the use of the Co aluminate catalyst in the oxidative steam reforming of glycerol, very high overall conversion levels (above 90% in all cases) were achieved, as well as significantly higher H2/CO molar ratios (within the 2.0–2.5 range). The Co catalyst helped in effectively converting approximately 90% of the glycerol in the feed into product gases at temperatures as low as 823 K, and up to 94% of overall C conversion to gas could be achieved at 1023 K. Higher activation or reforming reaction temperatures did not improve the catalyst performance, the glycerol conversion or gas production. The catalyst could be effectively used during 20 h on stream in four consecutive reaction/regeneration cycles. Catalyst deactivation by encapsulating carbon caused drastic changes in the catalyst structure, which evolved into a core-shell configuration when deactivated. Upon regeneration by air oxidation and subsequent activation, the catalyst recovered its original structure and initial activity.These new insights allowed to propose the use of a pre-reforming step over relatively inexpensive bulk bed materials, where thermal decomposition of glycerol processes dominate followed by the catalytic oxidative steam reforming, to obtain high syngas production at moderate conditions (823 K).