Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur Removal of sulfur compounds and siloxanes by physical and chemical sorption Chul-u Bak a , Chan-Jong Lim a , Jong-Gyu Lee b , Young-Deuk Kim c, ⁎ , Woo-Seung Kim c, ⁎ a Department of Mechanical Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 04763, Republic of Korea b Climate & Energy Research Group, Research Institute of Industrial Science & Technology, 67 Cheongam-ro, Nam-gu, Pohang, Gyeongsangbuk-do 37673, Republic of Korea c Department of Mechanical Engineering, Hanyang University, 55 Hanyangdaehak-ro, Sangnok-gu, Ansan, Gyeonggi-do 15588, Republic of Korea ARTICLE INFO Keywords: Biogas purification Physisorption Chemisorption Sulfur compounds Siloxanes ABSTRACT The removal of sulfur compounds and siloxanes, which are major impurities in the biogas produced from the anaerobic digestion of sewage sludge, was studied using a bench-scale adsorptive gas purification experimental setup. The main impurities are hydrogen sulfide (H 2 S), carbonyl sulfide (COS), carbon disulfide (CS2), octa- methylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5). The commercially available adsorbents iron oxide (IO), iron oxide hydroxides (IH, IHS), activated carbon (AC), impregnated activated carbon (IAC), silica gels (A2 and NS10) and molecular sieves (5A and 13X) were first extensively characterized using scanning electron microscopy (SEM), X-ray fluorescence (XRF), and BET surface area measurements. IHS, comprising mainly 42% iron oxide hydroxide, 11% silica gel, and 10% activated carbon, exhibited the best adsorption capacities for H2S (539 mg/g) and COS (32 mg/g) among the adsorbents studied, as well as relatively good adsorption capacities for siloxanes D4 and D5. AC and IAC showed the greatest CS2 removal efficiency. A2 demonstrated extremely high adsorption capacities for siloxanes D4 and D5, namely 1055 and 1968 mg/g, re- spectively. 1. Introduction Biogas is a renewable energy source that can be produced by means of anaerobic digestion by anaerobic organisms of sewage, municipal waste, agriculture waste, manure, food waste, etc. Biogas comprises mainly methane (60–70%) and carbon dioxide (30–40%), and contains smaller amounts of nitrogen (< 1%), oxygen, and hydrogen; volatile organic compounds including sulfur compounds, halogenated com- pounds, and organic silicon compounds may also exist [1–4]. Methane, the primary component, can be utilized as fuel in many industrial ap- plications such as heating, combined heat and power, and fuel cells. However, any sulfur compounds present in biogas can induce fatal damage to industrial facilities, especially corrosion damage [5,6]. Si- licon compounds also have a poisoning effect on the anode side of the solid oxide fuel cell, and can form scale on the surface of devices such as turbines, thereby reducing their working efficiency [7]. Thus, to use the methane in biogas industrially, purification is required to avoid corro- sion and scaling problems [8]. Adsorption, absorption, and membrane-based gas separation pro- cesses have been widely used to remove impurities from biogas. Among these purification methods, the adsorption process tends to be the most efficient owing to its simplicity of design, ease of operation, and in- sensitivity to toxic substances [9]. Moreover, it may be suitable for small-scale applications such as fuel cells [6]. To supply biogas as a fuel to these devices, a hybrid purification process has been proposed to combine a physicochemical adsorption process for removing sulfur compounds and siloxanes and a membrane separation process for concentrating methane by means of carbon dioxide separation [5,7,8]. Most recent works on membrane-based gas purification have fo- cused on the removal of hydrogen sulfide or siloxanes (D4, D5) by using activated carbon and impregnated activated carbon [10–14], but very few studies have suggested metal oxides or other inorganic materials as potential adsorbents for hydrogen sulfide removal [15–22]. Thus, most studies have considered adsorption characteristics on a specific ad- sorbent of a specific impurity among the impurities generated from actual biogas. According to Xiao et al. [15], who studied some carbon- based absorbents, the adsorption capacity of impregnated activated carbon for hydrogen sulfide is about 420 mg/g, higher than that of activated carbon. Activated carbon, which has good performance in removing hydrogen sulfide, was evaluated by Bandosz [16]. Activated https://doi.org/10.1016/j.seppur.2018.07.080 Received 16 March 2018; Received in revised form 4 July 2018; Accepted 27 July 2018 ⁎ Corresponding authors. E-mail addresses: youngdeuk@hanyang.ac.kr (Y.-D. Kim), wskim@hanyang.ac.kr (W.-S. Kim). Separation and Purification Technology 209 (2019) 542–549 Available online 29 July 2018 1383-5866/ © 2018 Published by Elsevier B.V. T