Sustainable Fuel Desulfurization and Natural Gas Upgrading

Dear Colleagues,

The current demand for clean energy sources has motivated the need for efficient desulfurization processes for transportation liquid fuels and natural gas (NG, >90% CH₄) upgrading. The upgrading of NG and renewable biogas (or municipal/landfill gas) to biomethane requires the removal of mainly H₂S, moisture (H₂O) and CO₂, and other impurities. CO₂ capture for natural gas purification using the established chemical absorption process, utilizing amine-based solvents (e.g., monoethanolamine, MEA), suffers two major drawbacks: Large absorption body and high regeneration energy; and, therefore, could require the use of low heat of absorption solvent and process intensification to improve mass transfer and reaction rates. The removal of sulfur-containing compounds from liquid fuel and NG has traditionally been achieved by the catalytic hydrodesulfurization (HDS) process using sulfide Ni-MO/Al₂O₃ and Co-MO/Al₂O₃ catalysts and operating at high reactor temperature and pressures. HDS relies on the energy-intensive reaction of oil-based sulfur compounds with H₂ to form gaseous H₂S and a corresponding hydrocarbon (HC) fragment. Additionally, HDS has a significant carbon footprint due to the high energy consumption and the extensive use of H₂ since the production of H₂ is energy-intensive and results in the formation of CO₂. In addition, fuel cells to produce clean electrical energy require a clean, essentially sulfur-free HC feed (<1 ppmw) to prevent poisoning of the anode catalyst. Therefore, more sustainable, non-H₂ consuming and compact fuel processor to produce ultra-low sulfur fuels are desirable.

Some emerging desulfurization techniques include biodesulfurization (BDS), adsorptive desulfurization (ADS) and oxidative desulfurization (ODS). BDS explores a biochemical pathways to remove sulfur, which results in an unacceptable loss of fuel content, because sulfur removal occurs along with the overall degradation of HC compounds. A successful sorbent must exhibit very high selectivity, especially to recalcitrant sulfur compounds. Several adsorbents including zeolites, activated carbon, alumina, zirconia, silica gel, and other materials, have been studied and used from ambient temperature to 250 °C and/or under elevated pressures. In ODS, sulfur-containing compounds are initially oxidized to respective highly polar sulfone and/or sulfoxide, which can be separated by extraction with water-soluble polar solvents. Recently, ODS has been coupled with ultrasound irradiation, the so-called, ultrasound-assisted oxidative desulfurization (UAODS) and other advanced oxidation processes (AOPs) involving in situ generated strong oxidative radicals and H₂O₂. UAODS process is environmentally friendly, operates at ambient temperatures and atmospheric pressures, and is highly efficient. Examples include H₂O₂/organic acids, H₂O₂/heteropolyacid, H₂O₂/Ti-containing zeolites, H₂O₂/WOx/ZrO₂, H₂O₂/metal-loaded Al₂O₃ catalysts, Ti-SiO₂-based catalysts and other non-H₂O₂ systems (e.g., t-butyl hydroperoxide, O₂, etc.).

This Special Issue seeks sustainable biological, green chemical (including the use of ionic liquids or reaction rate and/or mass transfer intensification methods), catalytic and/or adsorptive systems (including metal-organic framework or MOP materials), catalytic membrane-based, AOP-based and innovative compact or modular processes for sulfur removal and CO₂ capture.

Prof. Dr. Yusuf G. Adewuyi
Guest Editor

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• Clean liquid fuel
• Natural gas and biogas upgrading
• Catalytic Oxidative and adsorptive desulfurization
• Ultrasound and cavitation-assisted desulfurization
• Advanced oxidation process-based desulfurization
• Combinative or hybrid sulfur and CO2 removal
• Green chemical-based removal processes
• Ionic liquids-based removal processes
• Catalytic membrane-based processes
• Process intensification
• Compact and modular desulfurization systems
• Fuel cell applications