(137a) Hydrogen Production by Ethanol Reforming Driven by Solar Energy

Production of hydrogen from ethanol is a very attractive process since bio-ethanol is a renewable material mainly produced from biomass fermentation [1,2]. As recently proposed for methane reforming, the energy needed for the endothermic ethanol reforming reaction can be supplied via coupling of membrane reformer and molten salts plant [3,4]. The molten salts act as energy carrier between the membrane reformer and a solar plant. The same approach can be used by coupling a conventional multi-tubular reactor with molten salt plant. In this paper hydrogen production via reforming of ethanol has been studied in a novel hybrid plant consisting in an ethanol reformer and a concentrating solar power (CSP) plant by means of a molten salt stream. The heat required by the reforming of ethanol has been supplied to the system by molten salts produced by solar energy. The temperature drop in the molten salt is few K (less than 20K) making the molten salt stream still suitable for steam and electricity production in the co-generative plant. A 2D mathematical model has been formulated and used in order to simulate the performance of the reformer coupled with heat integration through molten salt. The results show that the hybrid plant proposed here is a good solution for sustainable hydrogen production. An optimised set of operating conditions have been found. 99% ethanol conversion is achieved with 4.5 m long reactor, while the simulations indicate that both reactor diameter and molten salt flow rate need to be further optimized in order to find the best heat management. A small temperature drop (17 K) in the molten salt stream has however been observed which makes the integration of hydrogen production inside a solar power system really attractive. On the other hand there is a compromise between temperature and CO content in the exhaust stream. High temperature is required for achieving high ethanol conversion and to convert the methane produced in the first part of the reactor. The high temperature makes the CO shift reaction not complete so that a downstream low temperature shift reactor is needed. A solution to be studied in the future can be the use of membrane solar ethanol reforming.

REACTOR MODEL The ethanol steam reformer heated up by the molten salt stream is modeled in detail by a two-dimensional mathematical model based on mass, energy and momentum balances with the intrinsic kinetic equations reported by Mas et al. [5]. The ethanol reaction system consists on the following 4 reactions: C2H6O = CH4 + CO + H2 (1) C2H6O + H2O = CH4 + CO2 + 2H2 (2) CH4 + H2O = CO + 3H2 (3) CH4 + 2H2O = CO2 + 4H2 (4) The comparison between experimental literature values and model results shows that the model predicts fairly well the experimental results at high temperatures where the error is almost always lower than 5%.

References [1] Badmaev SD, Snytnikov PV, Hydrogen production from dimethyl ether and bioethanol for fuel cell applications, Int J Hydrogen Energy, 2008;33:3026?30. [2] Ni M, Leung DYC, Leung MKH, A review on reforming bioethanol for hydrogen production, Int J Hydrogen Energy , 2007;32:3238?47 [3] De Falco, M., Giaconia, A., Marrelli, L., Tarquini, P., Grena, R., Caputo, G., Enriched methane production using solar energy: an assessment of plant performance, Int. J. Hydrogen En., 34(1), (2009) 98-109 [4] M. De Falco, A. Basile, F. Gallucci, Solar membrane natural gas steam reforming process: evaluation of reactor performance, Asia Pacific J Chem. Eng., DOI 10.1002/apj.368 [5] V. Mas, M.L. Bergamini, G. Baronetti, N. Amadeo, M. Laborde, A kinetic study of ethanol steam reforming using a nickel based catalyst, Topics in Catal., 2008;51(1-4):39-48