Ceramic Membrane Reactors

 

Membranes formed from mixed ionic electronic conducting (MIEC) mixed metal oxides have the ability to selectively transport oxygen from air at elevated temperature.  The main class of MIEC membranes utilised in our research group is based on the cubic perovskite structure of general formula ABO3.  The A-site and B-site can be doped with a host of metal cations, within size constraints, allowing us to tune the properties of the oxide.  The oxide can be formed into simple planar geometries or more sohpisticated microtubular membranes to provide a high surface area.  The pure transported oxygen can be used in reactions such as; the partial oxidation of methane (POM) to produce hydrogen and carbon monoxide (synthesis gas), complete combustion of methane for carbon dioxide capture or steam reforming of methane in which water replaces air as the source of oxygen through water splitting.  This produces a stream of hydrogen from the water splitting and a stream of synthesis gas from the methane feed from the transported oxygen.  The oxygen transport membrane (OTM) technology parallels chemical looping (CL) technology; OTM separated reactants and products in space and CL separates them in time.

High temperature O2 permeable membrane reactors

Oxygen permeable ceramic membranes can be utilised in a variety of clean energy applications such as a natural gas combustion process to produce virtually pure CO2 offering a realistic solution for the mitigation of CO2 emissions. These materials can also be used for ultra-pure hydrogen production using membrane-based water-gas-shift steam reforming of methane reactions. Our current work looks into these two routes for H2 production. In addition we are working with dual-layer membranes with tailor-made catalytic properties for stability and performance improvement and at the role of impurities (such as sulphur) on the long term performance of the membrane. Our work is mostly focused on perovskite materials of the La1-xSrxCo1-yFeyO3-δ and Ba1-xSrxCo1-yFeyO3-δ families, but we are also interested in novel materials and membrane structures. We have a long-standing collaboration with the group of Prof. Kang Li at Imperial College London in the area of mixed ionic-electronic conducting micro-tubular (hollow fibre) membranes. In addition the group is part of Supergen 14, the EPSRC funded consortium on the delivery of sustainable hydrogen.

Dual phase membrane reactors for CO2 separation

    Membrane separation technology is a possible breakthrough in post-combustion carbon dioxide (CO2) capture process since membranes can offer selective CO2 separation from flue gases.  In this project, we aim to fabricate a dual-phase membrane reactor (MR) to separate CO2 from N2 at medium to high temperatures (600°C-900°C) at ambient pressure.  The dual-phase host membrane substrate is made from porous perovskite-type La0.6Sr0.4Co0.2Fe0,8O3-δ (LSCF6428) commercial powder.  This new concept of the carbonate-ceramic dual-phase membrane is based on the idea of the molten carbonate fuel cells (MCFCs) which consist of a porous mixed-conducting ionic and electronic (MIEC) ceramic substrate and a molten carbonate phase (usually a Li/Na/K carbonate eutectic mixture).

By using the dual-phase membrane, CO2 from the feed gas combines with oxygen ion (O2-) at the surface of the MIEC membrane substrate to form ionic carbonate (CO32-) in the molten carbonate electrolyte, the CO32- ion is transported across the membrane through the molten phase carbonate at high temperatures under a chemical potential gradient and released as gaseous CO2 on the permeate side.  This simultaneous transport of O2- and CO2 should allow us to permeate CO2 against its own chemical potential difference.  Uphill transport of CO2 may be important for, e.g., post-combustion carbon dioxide capture processes.  Flue gases are close to atmospheric pressure which means that if a high mole-fraction carbon dioxide stream is to be produced compression is required.  Uphill transport means that the chemical potential of oxygen in the flue gas stream can be harnessed to reduce compression costs.