Abstract
Carbon-based nanomaterials, particularly in the form of N-doped networks, are receiving the attention of the catalysis community as effective metal-free systems for a relatively wide range of industrially relevant transformations. Among them, they have drawn attention as highly valuable and durable catalysts for the selective hydrogen sulfide oxidation to elemental sulfur in the treatment of natural gas. In this contribution, we report the outstanding performance of N-C/SiC based composites obtained by the surface coating of a non-oxide ceramic with a mesoporous N-doped carbon phase, starting from commercially available and cheap food-grade components. Our study points out on the importance of controlling the chemical and morphological properties of the N-C phase to get more effective and robust catalysts suitable to operate H2S removal from sour (acid) gases under severe desulfurization conditions (high GHSVs and concentrations of aromatics as sour gas stream contaminants). We firstly discuss the optimization of the SiC impregnation/thermal treatment sequences for the N-C phase growth as well as on the role of aromatic contaminants in concentrations as high as 4 vol.% on the catalyst performance and its stability on run. A long-term desulfurization process (up to 720 h), in the presence of intermittent toluene rates (as aromatic contaminant) and variable operative temperatures, has been used to validate the excellent performance of our optimized N-C2/SiC catalyst as well as to rationalize its unique stability and coke-resistance on run.
Highlights
Natural gas (NG) is certainly the cleanest fossil fuel employed for energy purposes
Current catalytic technologies allow a selective and almost complete hydrogen sulfide conversion into elemental sulfur [6], they still suffer from technical limitations linked to a progressive catalyst deactivation when desulfurization process is operated under harsh reaction conditions (gas hourly space velocity (GHSV) close to those employed in industrial plants), or in the presence of contaminants such as heavy hydrocarbons and aromatics (i.e., benzene, toluene and xylene (BTX)) [2] that are commonly present in untreated natural gas streams
The SiC coating with the N-C phase was accomplished following two alternative sequences of the solid support soaking in a standardized impregnation solution and successive thermal treatments
Summary
Natural gas (NG) is certainly the cleanest fossil fuel employed for energy purposes. At odds with other natural sources (i.e., petroleum and charcoal) [1], NG holds important environmental merits because it can produce more heat and light energy by mass while keeping its environmental impact significantly lower in terms of carbon footprint and other pollutants that contribute to smog and unhealthy air. Current catalytic technologies allow a selective and almost complete (up to 99.9%) hydrogen sulfide conversion into elemental sulfur [6], they still suffer from technical limitations linked to a progressive catalyst deactivation when desulfurization process is operated under harsh reaction conditions (gas hourly space velocity (GHSV) close to those employed in industrial plants), or in the presence of contaminants such as heavy hydrocarbons and aromatics (i.e., benzene, toluene and xylene (BTX)) [2] that are commonly present in untreated natural gas streams Such impurities deeply impact the performance, stability, and lifetime of catalysts and detrimentally burden on the overall process economy balance. Complementary and valuable technological options such as the use of either amine or solvent enrichment units (Acid Gas Enrichment units—AGE) [8] or the use of activated carbon beds [9] housed upstream of the catalytic desulfurization (SRU) unit, have successfully been implemented for BTX fractions removal
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