Removal Of Hydrogen Sulfide From Biomass Derived Producer Gas Using Activated Carbon Based Adsorption

Author : Wenying Quan
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (12 download)

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Download or read book Selective Hydrogen Sulfide Removal from Biogas on Nitrogen-Modified Adsorbents written by Wenying Quan and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Biogas is a renewable energy source derived from the fermentation of organic materials which contains high concentrations of methane (CH4, 40-60 vol%) and carbon dioxide (CO2, 10-40 vol%). However, the presence of hydrogen sulfide (H2S) in biogas limits its environmentally-friendly applications, thereby making the H2S removal a priority task for enhancing biogas utilization. The existence of a large amount of CO2 in biogas can strongly impede the H2S removal using conventional methods. The selective H2S removal in the presence CO2 is still challenging in the field of biogas processing. Therefore, the objective of the present work is to achieve selective H2S removal from biogas on nitrogen-modified adsorbents, by specifically (i) studying the effect of surface modifications with different N-containing groups on H2S removal from CO2-containing gas mixtures, and (ii) clarifying the effect of key factors that affect the sorption performance, including CO2 concentrations, type of amine groups, pore structure, and surface functional groups.First, by loading tertiary amines on SBA-15, tetramethyl hexanediamine (TMHDA), the sorption selectivity of H2S was enhanced dramatically in the presence of CO2. On carbon-based solid sorbents including TMHDA-loaded activated carbons (TMHDA/ACs) and nitrogen-doped carbons (NCs), it is interesting that the H2S sorption performance was significantly enhanced in the presence of CO2. Characterization was conducted to shed light on the surface chemical properties-textural property-sorption performance relationship. On the silica-based sorbents, the H2S sorption capacity was closely related to the silanol groups on the surface of SBA-15, where the silanol groups were responsible for anchoring the TMHDA molecules which determined the number of active sites for H2S sorption. On the carbon-based sorbents, not only the surface chemistry but also the textural properties affect the H2S sorption performance. The surface pH value, double-bonded oxygen functional groups, and surface density of nitrogen all contributed to the observed enhancement of sorption capacity, likely through acid-basic interaction, while micropores in carbon materials offered higher adsorption potential towards H2S. It is noteworthy that this work, to our best knowledge, first discovered that the presence of CO2 can dramatically promote the H2S sorption on certain carbon-based sorbents, which is accompanied by the formation of solid sulfur deposit along with the release of CH4, both of which are valuable chemical products. The CO2-promoting effect likely originated from its interaction with H2S on the sorption sites on the carbon surface and the delocalized electrons on the carbon planes. Additionally, other factors, such as inlet CO2/H2S concentrations and sorption temperatures, were also investigated. The H2S sorption capacity remained stable on TMHDA-loaded SBA-15 and NC_800 with increasing the inlet CO2 concentration up to 40 vol%, however, the sorption capacity exhibited a volcano-shape trend within the same range of CO2 concentrations on AC-based adsorbents. The sorption capacity decreased monotonically with the increasing temperature from 25 to 75 on TMHDA-loaded adsorbents. The estimated H2S sorption heat on TMHDA/SBA-15 was 15.4 kJ/mol by fitting with Langmuir isotherm, while the heat on NC_800 was less than 20 kJ/mol by fitting with both Langmuir and Dubinin-Radushkevich (DR) isotherms. Such relatively low sorption heat indicates that the H2S interaction with surface sites is relatively weak and thus higher density of adsorption sites would be desirable.