Experimental and Theoretical Investigation of Catalyst Poisoning and Regeneration During Biogas Steam Reforming on Nickel

Appari, S and Janardhanan, V (2014) Experimental and Theoretical Investigation of Catalyst Poisoning and Regeneration During Biogas Steam Reforming on Nickel. PhD thesis, IIT Hyderabad.

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Abstract

Biogas is an important source of renewable energy produced by the anaerobic digestion of biomass. The composition of biogas depends on the biomass source and duration of the digestion process. Biogas is an ideal fuel for distributed power generation using Solid-Oxide Fuel Cells (SOFCs), especially in areas that are not grid connected. Biogas may be combusted to produce electricity or can be converted to synthesis gas by reforming over Rh or Ni catalyst. However, the presence of H2S or other sulfur containing compounds is a major problem for reforming of biogas because sulfur poisons most transition metals. The goal of this research is two fold; i) experimental investigation of catalyst deactivation and regeneration, and ii) development of a comprehensive predictive microkinetic model for biogas steam reforming on Ni based catalysts. The kinetic model is developed based on experimental data and further validated by simulating the experiments reported in the literature. The kinetic model is able to capture the performance of a fixed bed reactor used to reform model biogas with and without H2S in the feed gas. The objective of the experimental study is the deactivation and regeneration of Ni catalysts supported on γ-Al2O3 during steam reforming of biogas containing ppm levels of H2S. In order to ensure that the catalyst does not lose activity over time in a non-poisoning atmosphere (without H2S), reforming experiments are performed at 700 and 800 ◦C for 22 hrs and no loss in activity of the catalyst is observed during this period. Catalyst deactivation experiments are then performed for two different temperatures (700 and 800 ◦C) and three different H2S concentrations (20, 50, and 100 ppm). A low S/C ratio is employed to ensure the participation of CO2 in reforming reactions. Low temperature operation (700 ◦C) lead to full deactivation of the catalyst where as at higher temperature (800 ◦C) the catalyst maintained some residual activity. In certain cases, catalyst regeneration is also performed by removing H2S from the feed gas and by increasing the reforming temperature. The fully poisoned catalysts are then regenerated by steam treatment followed by reduction in H2. The regenerated catalyst is tested for its activity by performing steam reforming reaction without H2S in the feed stream. The regenerated catalyst showed stable operation for more than 13 hrs.

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