Contents lists available at ScienceDirect Catalysis Today journal homepage: www.elsevier.com/locate/cattod CO 2 adsorption over modified AC samples: A new methodology for determining selectivity Burcu Acar a , Melek Selcen Başar a , B. Merve Eropak a , Burcu Selen Caglayan b , A. Erhan Aksoylu a, ⁎ a Department of Chemical Engineering, Boğaziçi University, 34342 Bebek, Istanbul, Turkey b Advanced Technologies R & D Center, Boğaziçi University, 34342 Bebek, Istanbul, Turkey ARTICLE INFO Keywords: CO 2 adsorption Activated carbon Selective adsorption K 2 CO 3 Alkali modification ABSTRACT Activated carbon (AC) based adsorbents having high and stable CO 2 adsorption capacity with enhanced CO 2 selectivity in presence of CH 4 were developed. Alkali modified AC samples were prepared, their CO 2 adsorption capacities were measured, a new methodology for selective adsorption capacity determination under multi- component gas mixture flow was developed, and the results were analyzed to determine the preparation pro- cedure yielding optimum adsorbent design. Two groups of adsorbents were prepared by K 2 CO 3 impregnation on air and HNO 3 oxidized forms of a commercial AC followed by calcination at various temperatures. The resulting adsorbents were named according to calcination temperatures as ACxK-calT. The highest CO 2 adsorption ca- pacity was measured on AC3K-300 sample as 110 mg/g adsorbent at 1000 mbar CO 2 and 25 °C. CO 2 adsorption was confirmed reversible, whereas CH 4 adsorption was found partially irreversible. The highest mass based CO 2 :CH 4 selectivity, ca. 3.7, was achieved over AC2K-200 at 25 °C for the 50%CO 2 -50%CH 4 mixture. AC2K-200 was further tested at higher total pressures, for 0–5000 mbar pressure range, at 25 °C. CO 2 adsorption capacity was measured as 197 mg/g adsorbent at 5000 mbar CO 2 . Among Langmuir, Freundlich and Dubinin- Radushkevich (D-R) isotherm models, D-R was found to be the most successful one explaining CO 2 adsorption behavior of AC samples. 1. Introduction Presently 85% of the total energy requirement of the world is sup- plied by fossil fuel based power production plants (coal, oil, gas), which are responsible for 40% of CO 2 emission into the atmosphere. Since anthropogenic production and atmospheric accumulation of CO 2 is the main reason for global warming and climate change, its capture, se- questration and utilization (CCS & U) is one of the most challenging issues of environmental sustainability. As CCS is an expensive process, cost effective CCS options need to be developed and proliferated [1]. CO 2 emission mitigation in power plants can be accomplished through post-combustion, pre-combustion and oxyfuel-combustion [2]. Among the available capturing methods involved in all those technol- ogies, adsorption has been considered as the most promising owing to its low energy requirement led by the exothermicity of the process, cost advantage and ease of applicability over a relatively wide range of temperatures and CO 2 partial pressures. An efficient adsorbent must have high adsorption capacity, selectivity towards CO 2 , fast adsorption and desorption kinetics, good physical and chemical stability, and re- generability by modest pressure and temperature to minimize operational energy costs [3]. Current potential adsorbent materials for CO 2 capture are carbon materials such as carbon molecular sieves, carbon nanotubes, and ac- tivated carbons (ACs), zeolites and metal organic frameworks [4]. AC is the most preferred adsorbent in industries due to its low cost, high surface area, high porosity, adequate mechanical strength after re- peated adsorption and desorption cycles and high CO 2 adsorption ca- pacity at ambient pressure and temperature. ACs originate from different carbonaceous materials like bituminous coal, petroleum/coal tar pitch, nutshell, coconut husk, wood and lig- nite, and are activated with different procedures, such as CO 2 activa- tion, steam (physical) activation or chemical activation via oxygena- tion, nitrogenation, hydrogenation, etc. agents. Depending on the origin and preparation method, adsorption capacity is highly affected by the surface chemistry and pore structure [5]. Various basic groups are incorporated on AC aiming to increase the CO 2 adsorption capacity via enhancing CO 2 affinity [6]. Introduction of Lewis bases onto AC surfaces may increase the capture performance due to mildly acidic nature of CO 2 . There are several ways of increasing the basicity of AC including removal/neutralization of the acidic http://dx.doi.org/10.1016/j.cattod.2017.10.011 Received 5 December 2016; Received in revised form 26 September 2017; Accepted 11 October 2017 ⁎ Corresponding author. E-mail addresses: burcu.acar@boun.edu.tr (B. Acar), selcen.basar@boun.edu.tr (M.S. Başar), merve.eropak@boun.edu.tr (B.M. Eropak), selenbur@boun.edu.tr (B.S. Caglayan), aksoylu@boun.edu.tr (A.E. Aksoylu). Catalysis Today xxx (xxxx) xxx–xxx 0920-5861/ © 2017 Elsevier B.V. All rights reserved. Please cite this article as: Acar, B., Catalysis Today (2017), http://dx.doi.org/10.1016/j.cattod.2017.10.011