Conversion of Methane to Syngas by a Membrane‐Based Oxidation–Reforming Process

Abstract

Rational use of abundant natural gas is gaining importance as petroleum oil reserves are diminishing. Methane, the main component of natural gas, can be converted to liquid fuels, hydrogen, and other value-added chemicals through a syngas intermediate, a mixture of CO and H 2 . Currently, syngas is produced by reacting methane with steam at high temperatures and pressures. This process is very energy-and capitalintensive, as the reaction is highly endothermic. An alternative process to produce syngas is the partial oxidation of methane (POM) with pure oxygen in the presence of a catalyst. [1,2] The exothermic nature of POM makes the process attractive in terms of energy consumption. The other advantage of POM over the steam-reforming process is that the H 2 /CO ratio of~2 of the as-produced syngas is highly suitable for subsequent conversion to environmentally friendly liquid fuels through a Fischer-Tropsch process. The main difficulty with POM lies in the consumption of large quantities of expensive pure oxygen that is produced by the cryogenic separation of air. A recent development in syngas production technology is the use of oxygen-permeable dense ceramic membranes [3,4] integrating the oxygen separation and POM processes in a single space.[5] The formidable problem for this approach is that the membrane must be chemically and mechanically stable at elevated temperatures in a large oxygen gradient with one side of the membrane exposed to oxidizing atmosphere (air) and the other side to the reducing atmosphere (the mixture of hydrogen and carbon monoxide). Herein we propose a two-stage membrane reactor, as depicted in Figure 1 a, which may reduce the requirement on the stability of the membrane materials. In this reactor, part of the methane is converted into CO 2 and H 2 O by reaction with oxygen permeated through the membrane from the air, and the resultant mixture is transferred to a catalyst bed where the remaining methane is reformed to syngas.A ceramic composite of Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3Àd (97.5 mol %) and Co 3 O 4 (2.5 mol %) was used to construct a membrane reactor. The major phase of the composite was intended for separating oxygen from air [6] and the minor phase at the surface for catalyzing the reaction of methane with permeated oxygen; [7] in terms of mechanics, small cobalt oxide particles embedded in the bulk may also reinforce the major phase. The dense tubular membrane of the required phase composition was prepared by extrusion followed by sintering at 1100 8C for 10 h. A g-Al 2 O 3 -supported catalyst was prepared with a nickel loading of 12.5 wt % and sieved to 40~60 mesh.[8] The reactor consisted of a membrane of length 2.14 cm, inner diameter 0.76 cm (membrane surface area 5.10 cm 2 ), and wall thickness 0.13 cm, and a catalyst bed containing 0.2 g Ni/g-Al 2 O 3 ; the membrane tube and the catalyst bed were separated by a distance of 2.5 cm (see Figure 1 b). In order to improve the flow pattern in the reactor, an alumina cylinder was placed inside the reactor (not shown in Figure...

Natural Gas to Fuels and Chemicals: Improved Methane Aromatization in an Oxygen‐Permeable Membrane Reactor

“…[13] Recently, we developed a series of membranes for versatile applications, for example, CO 2 capture integrated in oxy-fuel power plants, [14] direct decomposition of NO and NO 2 , [15] and the coupling of two reactions such as water splitting with the partial oxidation of methane/oxidative dehydrogenation of ethane. [16] Herein we integrate the oxygen generation and MDA in a membrane reactor system, which is considered to offer a significant advantage for MDA.…”

CO2‐Stable and Cobalt‐Free Dual‐Phase Membrane for Oxygen Separation

“…However, there are two main problems for the proper application of this kind of membrane. First, perovskite membranes with cobalt doping usually show high permeability but poor stability under harsh working conditions; [5] by avoiding cobalt, the stability of MIEC membrane materials can be enhanced. [6] Second, for numerous applications such as the oxyfuel process or hydrocarbon partial oxidations, where some CO 2 is formed as a byproduct of an undesired deeper oxidation, the oxygen transporting membranes must sustain their phase stability and oxygen transport properties.…”

Perovskite Hollow‐Fiber Membranes for the Production of Oxygen‐Enriched Air

“…[20] A further problem is the poor operational safety of such systems. In the event of a membrane leak, air, methane, and synthesis gas would mix at 800 8C, thus causing serious trouble if not handled properly.…”