Membranes to make benzene from methane: Methane gas is expensive to ship. It is usually converted into carbon monoxide and hydrogen and then liquefied. This is economically feasible only on very large scales. Hence, methane produced in small amounts at remote locations is either burned or not extracted. A promising alternative is conversion to benzene and hydrogen with molybdenumzeolite catalysts. Unfortunately, these catalysts deactivate because of carbon buildup; plus, hydrogen has to be removed to drive the reaction forward. Morejudo et al. address both of these problems with a solid-state BaZrO ₃ membrane reactor that electrochemically removes hydrogen and supplies oxygen to suppress carbon buildup. Science , this issue p. 563

Oxygen transport membranes made of Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) were manufactured by tape casting and co-firing. The disk-shaped membranes consisted of a top gastight layer (70 mu m thick) and a porous substrate (830 mu m thick) with 34% open porosity. The variation of the permeation operation conditions allowed (i) the identification of the different limitations steps in the permeation process, i.e., bulk oxygen ion diffusion, catalytic surface exchange and gas phase diffusion in the membrane compartments and porous substrate, and (ii) the ultimate optimization of the oxygen flux. The variables considered in the systematic permeation study included the inlet gas flow rate of the sweep and air feed, the temperature and the nature of the oxygen feed gas (air or pure oxygen). Moreover, the influence of the deposition of a catalytic activation layer (17 mu m thick) made of BSCF on top of the thin gastight layer was investigated. As a result of this parametric study, unpreceded oxygen flux values were achieved, i.e., a maximum flux of 67.7 ml(STP) min(-1) cm(-2) was obtained at 1000 degrees C using pure oxygen as the feed and argon as the sweep, while a flux of 12.2 ml(STP) min(-1) cm(-2) at 1000 degrees C was obtained when air was used as the feed. (C) 2011 Elsevier BM. All rights reserved