Preparation Of Ceramic-Ceramic Dual Phase Mixed Conducting Membranes And Performance Study On Membrane Reactors

This paper optimized the oxide materials with electronic conductivity aiming at the problem of lower membrane separation performance caused by good proton conductivity but poor electronic conductivity of partially doped perovskite structure oxide.The results showed that both SrFeO₃ and Y_0.8Ca_0.2Cr_0.8Co_0.2O_3-δ（YCCC）are incapable of using as the electronic conductor due to the reduction of SrFeO₃in reducing atmosphere and the phase reaction between Ba Ce_0.9Y_0.1O_3-δ（BCY）and YCCC at high temperature.And good chemical compatibility between Y_0.2Ce_0.8O_2-δ（YDC）and BCY provides a guarantee for selecting YDC as electronic conductor in dual-phase ceramic membranes.The BCY+40 vol.%YDC dual-phase hollow fiber membrane was successfully fabricated by the phase conversion-sintering technology.The hydrogen permeation test showed that the hydrogen flux through the dual-phase hollow fiber membrane increases with the increase of the temperature and hydrogen partial pressure.The hydrogen flux reached 0.18 mL·min^-1·cm^-2when 90%H₂/He as feed gas at 900 ℃.Two kinds of membrane reactors for ammonia decomposition were fabricated,i.e.naked membrane reactors and surface modified membrane reactors coated with a layer of Ni catalyst.And their ammonia decomposition and hydrogen separation efficiency were preliminarily studied.The results showed that the ammonia decomposition efficiency and the hydrogen permeation flux of the surface modified membrane reactors are higher than that of the naked membrane reactors,but the hydrogen separation efficiency of the surface modified membrane reactors is lower than that of the naked membrane reactors.This conclusion revealed that the hydrogen permeation rate is lower than ammonia decomposition rate in surface modified membrane reactors.Membrane composition,membrane structure and rea ctor structure should be further optimized.Therefore,mixed protonic-electronic conducting ceramic membranes with independent and regular distribution structure were constructed.Mixed protonic-electronic conducting ceramic（MPEC）membranes with independent and regular distribution structure of SrCe_0.9Y_0.1O_3-δ（SCY）as proton conductor and Sm_0.2Ce_0.8O_2-δ（SDC）as electronic conductor have been constructed and prepared using a tape c asting combined with the co-pressing technique.And the phase composition,micromorphology and membrane properties of independent distributed membranes have been characterized and investigated by X ray diffractometer,scanning electron microscop,thermal expension instrument and gas chromatograph.The results showed good chemical and thermodynamic compatibility between SCY and SDC,and the good thermodynamic compatibility between two phases provides a guarantee for the preparation of an independent distributed membrane with cracks-free on SCY|SDC interface.The hydrogen permeation test show ed that the hydrogen fluxes of 0.163 mL·min^-1·cm^-2through the SCY/SDC dual-phase ceramic membranes with independent distribution structure is higher than that of 0.077mL·min^-1·cm^-2through the dual-phase composite membranes at 900 ℃.And the H₂ permeation flux through the independent distributed membranes decreases with the increases of the phase layer thickness due to the influence of transverse resistance.Moreover,the independent distributed membranes also exhibit stability in the mixed gases contained CO ₂ due to the protective effect of SDC.