Thermodynamic analysis of methane reforming with CO 2 , CO 2 + H 2 O, CO 2 + O 2 and CO 2 + air for hydrogen and synthesis gas production Antonio C.D. Freitas, Reginaldo Guirardello * School of Chemical Engineering, University of Campinas (UNICAMP), Av. Albert Einstein 500, 13083-852 Campinas, SP, Brazil 1. Introduction In recent years, hydrogen has been attracting great interest as a clean fuel for combustion engines and fuel cells [1]. Among all the potential sources of hydrogen, natural gas, which has methane as main component, has been considered a good option because it is clean, abundant and it can be easily converted to hydrogen [2]. Currently, the main routes to produce hydrogen from methane are the catalytic reforming technologies, such as steam reforming (SR), dry reforming (DR), oxidative reforming (or partial oxidation) (OR) and autothermal reforming (ATR). Among these, the main industrial route to produce hydrogen and syngas from methane is SR, this reaction produces a syngas with a high H 2 /CO molar ratio (close to three) [3]. The dry reforming process becomes industrially advantageous when compared to steam reforming or partial oxidation for syngas production, as the H 2 /CO molar ratio in the product is close to 1.0/ 1.0 [4]. This low H 2 /CO ratio is suitable for further use in Fischer– Tropsch synthesis of long-chain hydrocarbons, dimethyl ether and methanol; all of which require lower H 2 /CO ratios than that obtained by conventional SR process [5–7]. The major drawback of DR is that high temperatures are required to reach high conversion levels due to the highly endothermic nature of the process. These severe operating conditions combined with the tendency of the process to produce large quantities of coke (C (s) ) result in deactivation of the catalysts by coke deposition [8,9]. The problem of C (s) deposition can be resolved either (i) by developing catalysts that minimize the rate of coke formation, or (ii) by adding steam [4,10–12], or oxygen [4,13–17] to the feed gas stream. The main possible reactions in CO 2 , CO 2 + H 2 O and CO 2 + O 2 reforming’s process are summarized in Table 1. Research on thermodynamic behaviors of reaction systems by calculating equilibrium compositions have been utilized in understanding the feasibility of a variety of reactions [18–24]. The evaluation of the thermodynamic behavior of the reactions provides the first step to analyze the limits of temperature, pressure and feed ratios on equilibrium compositions. In the present work, a complete thermodynamic analysis of CO 2 , CO 2 + H 2 O and CO 2 + O 2 reforming of methane were performed. The effect of molar feed compositions, pressure and temperatures were evaluated over the reaction performances. For this, we used the Gibbs energy minimization and entropy maximization methods to Journal of CO 2 Utilization 7 (2014) 30–38 A R T I C L E I N F O Article history: Received 27 March 2014 Received in revised form 29 May 2014 Accepted 25 June 2014 Available online 18 July 2014 Keywords: Gibbs energy minimization Entropy maximization Methane reforming reactions Hydrogen production Synthesis gas production A B S T R A C T The main objective of this work is performing a thermodynamic evaluation of methane reforming with CO 2 , CO 2 + H 2 O, CO 2 + O 2 and CO 2 + air. These evaluations were carried out by Gibbs energy minimization, in conditions of constant pressure and temperature, and entropy maximization, at constant pressure and enthalpy, methods, to determine the equilibrium compositions and equilibrium temperatures, respectively. Both cases were treated as optimization problems (using non-linear programming formulation), satisfying the restrictions imposed by atom balance and non-negativity of number of moles. The GAMS 1 23.1 software and the CONOPT solver were used in the resolution of the proposed problems. All calculations performed presented a low computational time (less than 1 s). The calculated results were compared with previously published experimental and simulated data with a good agreement between them for all systems. The H 2 and syngas production were favored at high temperature and low pressure conditions. The addition of H 2 O or O 2 proved to be an effective way to reduce the coke formation in the systems. The CO 2 reforming presented endothermic behavior, but the addition of O 2 or air reduced this trend and in some conditions autothermal behavior was observed. ß 2014 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +55 19 3521 3955; fax: +55 19 3521 3910. E-mail addresses: acdfreitas@feq.unicamp.br, tonyfrt12@gmail.com (Antonio C.D. Freitas), guira@feq.unicamp.br (R. Guirardello). Contents lists available at ScienceDirect Journal of CO 2 Utilization jo ur n al ho m ep ag e: www .els evier .c om /lo cat e/jc o u http://dx.doi.org/10.1016/j.jcou.2014.06.004 2212-9820/ß 2014 Elsevier Ltd. All rights reserved.