Applicability of a double-membrane reactor for thermal decomposition of water: a computer analysis R.P. Omorjan * , R.N. Paunovic, M.N. Tekic Faculty of Technology, University of Novi Sad, Bul.Cara Lazara 1, YU-21000 Novi Sad, Yugoslavia Received 22 June 1998; received in revised form 11 September 1998; accepted 15 September 1998 Abstract A theoretical study of applicability of double-membrane reactor for direct thermal decomposition of water is presented. The analysis is based on an isothermal, steady state, plug ¯ow reactor model. One of the two membranes was supposed to be hydrogen permeable, and the other one, oxygen permeable. The simulations were performed for T2000 K, it being the upper limit of temperatures of practical interest. With a high vacuum in separation zones, the double-membrane con®guration theoretically enables complete conversion providing high values of Damkohler number and total rate ratio. When a sweep gas is introduced into separation zones, signi®cant water conversions can also be provided by a countercurrent single membrane reactor, but considerably lower than those obtained in a double-membrane reactor. The double-membrane reactor seems to be a promising solution for the water splitting reaction, deserving experimental investigations. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Membrane reactor; Double-membrane con®guration; Water splitting; Modeling; Plug ¯ow 1. Introduction The decomposition of water to hydrogen and oxy- gen could be the most attractive chemical process for achieving energy storage. Theoretically, the simplest method of water splitting seems to be the direct thermal decomposition (thermolysis). Unfortunately, the water molecule is very stable, e.g. the total free energy of hydrogen and oxygen, at normal tempera- ture, is much higher than the free energy of water. Consequently, the main problems in this approach are: (a) low conversion of water even at very high tem- peratures (2500±3000 K) [1]; (b) removing of pro- ducts to increase the conversion by means of equilibrium shift. Namely, as pointed out by Ihara [2], the process should not be operated at very high temperatures if an ef®cient separation method was implemented. Considering the disastrous environmen- tal damage caused by using fossil fuel sources or nuclear energy, the only practical energy source for the temperature range of interest is concentrated solar thermal energy. The utilization of solar radiation for the production of hydrogen by direct thermal splitting of water was extensively investigated theoretically and practically [1±8]. Adequate solution to the problem of the separation of products has not been worked out so Journal of Membrane Science 154 (1999) 273±280 *Corresponding author. Tel.: +381-21-450-413; fax: +381-21- 450-278; e-mail: omorr@uns.ns.ac.yu 0376-7388/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S0376-7388(98)00291-9