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    Hydrogen sulphide removal from biogas by zeolite adsorption: part I. GCMC molecular simulations

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    In this work Grand Canonical Monte Carlo (GCMC) simulations have been used to study hydrogen sulfide (H2S) removal from biogas streams by different zeolites such as FAU (Faujasite, NaX and NaY), LTA (zeolite A (Lynde division, Union Carbide)) and MFI (Zeolite Socony Mobil – five). Additionally, quantum mechanics (QM) molecular simulations have been performed to obtain structures and partial charges of some sorbates. The computational procedure adopted has been validated by comparison with experimental data available for H2S removal in atmospheric environment by zeolite NaY. In order to obtain a priority list in terms of both H2S isotherms and adsorption selectivity, adsorption simulations for pure H2S at low pressures and for a prototype biogas mixture (i.e., CO2, CH4, and H2S) have been performed and compared. The adsorption mechanisms and competition for accessible adsorption sites in terms of thermodynamic behavior have been also examined. Overall, the results obtained in this work could be routinely applied to different case studies, thus yielding deeper qualitative and quantitative insights into adsorption pollutant removal processes in environmental fields

    Hydrogen sulphide removal from biogas by zeolite adsorption: part II. A MD simulation

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    Coupled Grand Canonical-Canonical Monte Carlo and molecular dynamics (MD) simulation techniques have been used to investigate in details the adsorption of low-pressure hydrogen sulfide (H2S) in zeolites, and the selective adsorption behavior towards carbon dioxide and methane, the main biogas constituents. Results from Monte Carlo (MC) simulations indicated, among many others, zeolite NaY as the best option for H2S removal. Afterwards, deterministic simulations have been performed to investigate hydrogen sulfide pathway inside NaY, with respect to other adsorbed molecules (methane and carbon dioxide), as a function of zeolite loading and H2S partial pressure (i.e., biogas composition). Thermodynamic evaluations for 2D molecular dynamic simulations in terms of binding energy evolution vs. time confirm and reinforce the results obtained from Monte Carlo simulations, testifying the greater affinity for H2S to NaY zeolite framework. Results give also new quantitative insights in terms of pathways, binding energies, and equilibration time inside zeolite pores for stabilization

    Going Beyond Counting First Authors in Author Co-citation Analysis

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    The present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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