Biogas purification on Na-X Zeolite: Experimental and numerical results Piero Bareschino ⇑ , Erasmo Mancusi, Annunziata Forgione, Francesco Pepe Dipartimento di Ingegneria - Università degli Studi del Sannio, P.zza Roma 21, 82100 Benevento, Italy highlights  H2S adsorption in a packed bed Na-X zeolite was experimentally studied and modelled.  Bed complete saturation could never be achieved as a consequence of H2S oxidation.  Bed H2S adsorption capacity decreases with aging as a result of sulfur poisoning.  A 1-D mathematical model able to describe the observed behaviour was developed.  Physical parameters governing H2S reactive adsorption were consequently established. article info Article history: Received 19 September 2019 Received in revised form 1 April 2020 Accepted 22 April 2020 Available online 28 April 2020 Keywords: H 2 S adsorption Biogas purification Reactive adsorption Na-X zeolite Mathematical model abstract In the present paper, H 2 S adsorption from a synthetic biogas mixture in a laboratory–scale fixed bed adsorption column was studied and modelled. Na–X zeolite was used as bed material. Breakthrough and equilibrium data were obtained in a number of experiments carried out under typical operating conditions of industrial applications. Experimental results show that complete saturation of the bed could never be achieved, since outlet H 2 S concentration approaches an asymptotic value always lower than inlet one as a consequence of catalytic oxidation reactions of hydrogen sulphide. A one- dimensional coupled heat and mass transfer model, based on the ‘‘linear driving force” assumption and accounting for both H 2 S oxidation reaction and zeolite deactivation due to sulfur poisoning, was pur- posely developed and tailored to match experimental results. Consequently, the assessment of the effects of variation in H 2 S concentration, adsorption temperature and adsorbent age on the performances of the removal process was carried out. Ó 2020 Elsevier Ltd. All rights reserved. 1. Introduction Biogas is a gaseous mixture produced by methanogenic bacteria through anaerobic digestion of organic matter. Its production and utilization are constantly increasing, as it represents a renewable energy vector easily and cheaply obtainable. Only in the European Union, its production increased from 5849 ktoe in 2007 up to 16,600 ktoe in 2016 (Eurostat, 2017). Biogas is mainly composed of methane (50–70%), carbon dioxide (20–45%), water vapor (5 –10%), and, depending on the biomass matrix (Alonso-Vicario et al., 2010), trace amounts of other species such as hydrogen sulphide, ammonia, siloxanes, carbonyls, terpenes, and aromatic or halogenated compounds. In order to improve its energetic con- tent, biogas is processed (upgraded). A complete biogas upgrading process involves a number of steps, starting with water condensa- tion, desulphurization, and CO 2 removal, according to several well- established and widely used technologies. These include chemical and/or physical absorption, cryogenic or membrane separation, and fixation by biological or chemical methods (Abatzoglou and Boivin, 2009). With respect to sulfur compounds removal, several methods can be used, namely chemical, biological, and physical ones. One of the oldest and most widely used technique is the iron sponge process, a chemical method based on the reaction between H 2 S and ferric oxide or hydroxide to produce iron sulfide and water, although only a hydrogen sulphide removal percentage as high as about 90% can be reached (Speight, 2007). Several others chem- ical species, such as metal oxides, iron salts, NaOH, etc., can be used to oxidize hydrogen sulfide so to generate elemental sulfur. Never- theless, all of these processes are expensive as a consequence of continuous chemicals addition and/or regeneration and can pose serious danger since unhealthy secondary wastes are generated (Ozekmekci et al., 2015). In biological processes, H 2 S is converted into sulfate or sulfur through acidophilic or neutrophilic microbes: https://doi.org/10.1016/j.ces.2020.115744 0009-2509/Ó 2020 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: piero.bareschino@unisannio.it (P. Bareschino). Chemical Engineering Science 223 (2020) 115744 Contents lists available at ScienceDirect Chemical Engineering Science journal homepage: www.elsevier.com/locate/ces