Thermodynamic analysis of ethanol steam reforming using Gibbs energy minimization method: A detailed study of the conditions of carbon deposition

• Published in: International journal of hydrogen energy Vol. 34; no. 10; pp. 4321 - 4330
• Main Authors: Lima da Silva, Aline, Malfatti, Célia de Fraga, Müller, Iduvirges Lourdes
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-05-2009; Elsevier
• Subjects: Alternative fuels. Production and utilization; Applied sciences; Carbon; Carbon deposition; Chemical equilibrium; Contact; Energy; Ethanol; Ethanol steam reforming; Ethyl alcohol; Ethylene; Exact sciences and technology; Fuels; Gibbs energy minimization method; Hydrogen; Mathematical analysis; Mathematical models; Thermodynamic analysis; Thermodynamics; Chemical equilibrium; Carbon deposition; Thermodynamic analysis; Ethanol steam reforming; Gibbs energy minimization method; Gibbs free energy; Ethanol; Theoretical study; Deposit formation; Steam reforming; Hydrogen production
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2009.03.029

In this paper, a thermodynamic analysis of ethanol/water system, using the Gibbs energy minimization method, has been carried out. A mathematical relationship between Lagrange's multipliers and carbon activity in the gas phase was deduced. From this, it was possible to calculate carbon activities in both stable and metastable systems. For the system that corresponds to ethanol steam reforming at very low contact times, composed mainly of ethylene and acetaldehyde, carbon activities were always much greater than unity over the whole temperature range, changing from 1.2×107 at 400K to 1.1×104 at 1200K. Furthermore, there was practically no effect of the inlet steam/ethanol ratio on carbon activity values. These results indicate that such a system is highly favorable to carbon formation. On the other hand, by considering a more stable system, in order to represent high contact times, it was observed that carbon activities are much lower and depend greatly on the inlet steam/ethanol ratio employed. Besides, the complete conversion of ethylene and acetaldehyde into other species, such as CO, CO2, CH4 and H2, lowers the total Gibbs energy of the system. By computing carbon activities in experimental systems, it was also possible to explain deviations between thermodynamic analysis and experimental results regarding carbon deposition.