(421h) The Effect of Chlorine On a Rh/γAl2O3 Catalyst for Reforming Landfill Gas to Syngas

Landfills are the second-largest source of anthropogenic methane emissions in the U.S., accounting for 22% of CH₄ emissions¹. Landfill gas (LFG) is primarily composed of CH₄ and CO₂, and currently less than 10% of this is used for energy².  Because landfills will continue to be used for the foreseeable future, more complete utilization of LFG is becoming more important as the demand for energy increases.  Catalytically reforming LFG produces syngas (H₂ and CO) that can be converted to liquid fuels or mixed into the LFG stream to produce a more reactive, cleaner burning fuel.  It has been demonstrated that injecting up to 5% syngas into a simulated LFG mixture prior to entering a combustion engine decreases CO, UHC, and NOx emissions by 73%, 89%, and 38%, respectively³.  One barrier to using LFG in a catalytic system is the contaminant content of the LFG, including chlorine and sulfur compounds, higher order hydrocarbons, aromatics, and siloxanes that have the potential to poison a catalyst.  Chlorinated compounds are currently not removed from LFG and are present at 10-100ppm levels⁴, which may be enough to deactivate a catalyst. 

This research explores the effect of chlorine on the activity of a Rh/γ-Al₂O₃ catalyst while reforming LFG mixtures to syngas.  Flow-through reactor studies will be performed with a catalyzed Rh/γ-Al₂O₃ monolith at 1atm total pressure at temperatures between 20°C to 900°C.  The reactor is coupled to an Agilent μGC (3000) to measure product composition.  Methyl chloride, CH₃Cl will be used as the Cl surrogate at concentrations from 10-1000 ppm to reflect the amount of chlorocarbon species found in LFG. The effect of CH₃Cl while dry reforming and auto-thermally reforming LFG will be explored, as shown below:

CH₄ + CO₂ + CH₃Cl (ppm) --> 2H₂ + 2CO + HCl (ppm)

CH₄ + CO₂ + O₂ + CH₃Cl (ppm) --> H₂ + CO + H₂O + CO₂ + HCl (ppm)

Previous research disagrees as to whether Cl acts as an inhibitor or poison when present in steam reforming or hydrogenation reactions^5-9.  To our knowledge there is no previous work on the effect of Cl on a catalyst during dry reforming or auto-thermal reforming of CH₄, CO₂ mixtures.  It is thought that during dry reforming the CH₃Cl will deposit Cl on the catalyst surface, requiring H₂ to remove the Cl as HCl.  Therefore the amount of H₂ present on the surface or in the gas phase, which is dependent on reactor temperature, will be a critical factor for reducing the catalyst deactivation due to chlorine.

While reforming LFG with O₂ the same mechanism of H₂ or H₂O “cleaning” of the surface may exist, but Cl may also affect the selectivity of the reaction toward partial oxidation products H₂ and CO or complete oxidation products H₂O and CO₂.  This has been suggested because Cl may compete with O₂ for surface sites, affecting the Ocoverage on the surface¹⁰, but this has not been tested for the oxidation of CH₄, CO₂ mixtures on a Rh/γAl₂O₃ catalyst.  This work will provide insights into catalyst stability while reforming LFG mixtures with chlorocarbon contamination, and the likely deactivation mechanism.

 [1]Environmental Protection Agency. Landfill Methane Outreach Program.

[2]Themelis, N., & Ulloa, P. Renewable Energy 32(2007) 1243-1257.

[3]Kohn, M., Lee, J., Basinger, M., Castaldi, M. Ind. Eng. Chem. Res. 50 (6) (2011), 3570–3579

[4]Tchobanoglous, G., Theisen, H., Vigil, S. “Integrated Solid Waste Management.” McGraw-Hill. 1993.

[5]Duprez, D., Pereira, P., Miloudi, A., Barbier, J., Maurel, R. React. Kinet. Catal. Lett. 14 (1980) 495-499

[6]Aboul-Fotouh, S., Aboul-Gheit, A. App. Cat A: General. 208 (2001) 55-61

[7]Coq, B, Ferrat, G., Figueras, F. J. Catalysis 101 (1986) 434-445.

[8]McMinn, T., Moates, F., Richardson, J. App. Cat B: Environmental 31 (2001) 93-105

[9]Musso, J.C., Parera, J.M. Applied Catalysis 30 (1987) 81-90.

[10]Rostrup-Nielsen, J.R. Catalyst Deactivation (1991) 85-101