Abstract:Direct methanation of CO 2 over ceria-and alumina-supported nickel catalysts in the feed stream containing methane and traces of H 2 S is reported. Stability tests for 20 h at 350 and 600°C with a packed-bed reactor showed high resistance of the catalysts to sintering processes. Higher conversion at 350°C was observed for ceria supported nickel catalyst. Thermodynamic analysis indicated that CO 2 contained in biogas can be converted to methane without carbon formation under specific reaction conditions. An int… Show more
“…Both catalysts showed higher CO 2 conversion and higher CH 4 selectivity at 350 • C than at 600 • C. Compared to the reference experiment, the catalysts achieved a lower CO 2 conversion, which decreased to about the same value (81-82%) with CH 4 in the inlet gas [99]. The CO 2 conversion decreased by about 6% for Ni20/Al 2 O 3 and by about 10% for Ni40/Al 2 O 3 at 350 • C (Table 4).…”
Section: Influence Of Ch 4 On Ni/al 2 Omentioning
confidence: 62%
“…At 350 • C and no CH 4 present, both catalysts achieved 100% CH 4 selectivity. Over 20 h, conversion rate and selectivity remained constant in both cases [99].…”
Section: Influence Of Ch 4 On Ni/al 2 Omentioning
confidence: 88%
“…In a second series of experiments with the same catalysts, the effect of CH 4 was tested for about 70 h in microchannel reactors (Table 8) [99]. The resulting CO 2 conversions in the microchannel reactor (12.5 bar) were higher than in the experiments with the fixed-bed reactor, which were performed at 2 bar (Table 4).…”
Section: Influence Of Ch 4 On Ni/al 2 Omentioning
confidence: 99%
“…A third study investigated the influence of CH 4 in the inlet gas on two unpromoted Ni catalysts prepared by impregnation [99]. The reaction conditions for the first series of experiments in a fixed-bed reactor are given in Table 7.…”
Section: Influence Of Ch 4 On Ni/al 2 Omentioning
confidence: 99%
“…The reaction conditions for the first series of experiments in a fixed-bed reactor are given in Table 7. The experiments with CH 4 in the inlet gas were performed at 300 • C and 600 • C for 20 h respectively, while the reference experiment with no CH 4 in the inlet gas was performed at 350 • C for 20 h and then set to 600 • C for another 20 h [99]. The addition of CH 4 was compensated by the reduction of Ar concentration in the inlet gas (Table 4) to leave the inlet content of H 2 and CO 2 unaffected.…”
Biogas, with its high carbon dioxide content (30–50 vol%), is an attractive feed for catalytic methanation with green hydrogen, and is suitable for establishing a closed carbon cycle with methane as energy carrier. The most important questions for direct biogas methanation are how the high methane content influences the methanation reaction and overall efficiency on one hand, and to what extent the methanation catalysts can be made more resistant to various sulfur-containing compounds in biogas on the other hand. Ni-based catalysts are the most favored for economic reasons. The interplay of active compounds, supports, and promoters is discussed regarding the potential for improving sulfur resistance. Several strategies are addressed and experimental studies are evaluated, to identify catalysts which might be suitable for these challenges. As several catalyst functionalities must be combined, materials with two active metals and binary oxide support seem to be the best approach to technically applicable solutions. The high methane content in biogas appears to have a measurable impact on equilibrium and therefore CO2 conversion. Depending on the initial CH4/CO2 ratio, this might lead to a product with higher methane content, and, after work-up, to a drop in-option for existing natural gas grids.
“…Both catalysts showed higher CO 2 conversion and higher CH 4 selectivity at 350 • C than at 600 • C. Compared to the reference experiment, the catalysts achieved a lower CO 2 conversion, which decreased to about the same value (81-82%) with CH 4 in the inlet gas [99]. The CO 2 conversion decreased by about 6% for Ni20/Al 2 O 3 and by about 10% for Ni40/Al 2 O 3 at 350 • C (Table 4).…”
Section: Influence Of Ch 4 On Ni/al 2 Omentioning
confidence: 62%
“…At 350 • C and no CH 4 present, both catalysts achieved 100% CH 4 selectivity. Over 20 h, conversion rate and selectivity remained constant in both cases [99].…”
Section: Influence Of Ch 4 On Ni/al 2 Omentioning
confidence: 88%
“…In a second series of experiments with the same catalysts, the effect of CH 4 was tested for about 70 h in microchannel reactors (Table 8) [99]. The resulting CO 2 conversions in the microchannel reactor (12.5 bar) were higher than in the experiments with the fixed-bed reactor, which were performed at 2 bar (Table 4).…”
Section: Influence Of Ch 4 On Ni/al 2 Omentioning
confidence: 99%
“…A third study investigated the influence of CH 4 in the inlet gas on two unpromoted Ni catalysts prepared by impregnation [99]. The reaction conditions for the first series of experiments in a fixed-bed reactor are given in Table 7.…”
Section: Influence Of Ch 4 On Ni/al 2 Omentioning
confidence: 99%
“…The reaction conditions for the first series of experiments in a fixed-bed reactor are given in Table 7. The experiments with CH 4 in the inlet gas were performed at 300 • C and 600 • C for 20 h respectively, while the reference experiment with no CH 4 in the inlet gas was performed at 350 • C for 20 h and then set to 600 • C for another 20 h [99]. The addition of CH 4 was compensated by the reduction of Ar concentration in the inlet gas (Table 4) to leave the inlet content of H 2 and CO 2 unaffected.…”
Biogas, with its high carbon dioxide content (30–50 vol%), is an attractive feed for catalytic methanation with green hydrogen, and is suitable for establishing a closed carbon cycle with methane as energy carrier. The most important questions for direct biogas methanation are how the high methane content influences the methanation reaction and overall efficiency on one hand, and to what extent the methanation catalysts can be made more resistant to various sulfur-containing compounds in biogas on the other hand. Ni-based catalysts are the most favored for economic reasons. The interplay of active compounds, supports, and promoters is discussed regarding the potential for improving sulfur resistance. Several strategies are addressed and experimental studies are evaluated, to identify catalysts which might be suitable for these challenges. As several catalyst functionalities must be combined, materials with two active metals and binary oxide support seem to be the best approach to technically applicable solutions. The high methane content in biogas appears to have a measurable impact on equilibrium and therefore CO2 conversion. Depending on the initial CH4/CO2 ratio, this might lead to a product with higher methane content, and, after work-up, to a drop in-option for existing natural gas grids.
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