Biogas reforming for syngas production: The effect of methyl chloride

• CH3Cl reacts with alumina support to produce surface chloride, increasing acidity.
• Surface chloride reversibly poisons reverse water–gas shift reaction.
• Degree of chloride poisoning directly proportional to CH3Cl concentration.
• Degree of chloride poisoning inversely proportional to temperature.
• CH3Cl and HCl likely deposit chloride via a similar mechanism.

Biogas is a mixture of primarily methane and carbon dioxide produced from the anaerobic microbial digestion of biomass. A 4% Rh/Al2O3 catalyst was investigated for its ability to reform biogas in the presence of a chloride impurity, specifically CH3Cl that is often found in biogas systems. The conditions tested included temperatures between 350 °C and 700 °C with CH3Cl concentrations between 0 and 200 ppm at atmospheric pressure and 1050 h−1 WHSV. It was determined that in the dry reforming reaction CH3Cl reacts with the alumina support to produce surface chloride which increases the surface acidity and reversibly poisons the reverse water–gas shift reaction. For example, with the addition of 50 ppm CH3Cl the H2/CO ratio increased by 40% at 350 °C and by 2% at 700 °C. All changes were reversible upon removal of CH3Cl from the feed. Furthermore, less surface chloride was observed using XPS at 700 °C compared to 400 °C, and the effect on selectivity decreased with CH3Cl concentrations less than 50 ppm. Therefore the degree of chloride poisoning is directly proportional to CH3Cl concentration and inversely proportional to temperature.

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