Preparation Of Oxygen Permeable La_0.6Ca_0.4Co_0.2Fe_0.8O_3-δ Hollow Fiber Membrane For Methane Catalysis

Dry reforming of methane（DRM）,with CO₂ and CH₄ as feedstocks,not only mitigate the greenhouse effect but also obtain syngas（H₂+CO）for chemical production.The disadvantage of the DRM reaction is that it requires high energy and is often accompanied by coke accumulation and sintering of the catalysts during the reaction,which in turn affects the catalytic performance and leads to complete deactivation of the catalyst in severe cases.Previous studies have found that dense mixed ion-electron conductor membrane can introduce oxygen from the air into the reaction system,allowing the combination of the endothermic DRM with the exothermic partial oxidation of methane（POM）,which not only reduces energy requirements but also effectively mitigates coke accumulation of catalysts.In this thesis,three kinds of La_0.6Ca_0.4Co_0.2Fe_0.8O_3-δ（LCCF）hollow fiber membranes were fabricated by changing the internal coagulant and the oxygen permeation of the resulted membranes under different conditions were tested.The LCCF hollow fiber membrane was assembled with 10 wt.%Ni/LCCF catalyst to form an oxy-CO₂ reforming of methane（OCRM）membrane reactor,and the OCRM performance was tested under various conditions.Firstly,LCCF powders were prepared by sol-gel method and oxygen permeable LCCF hollow fiber membranes（LCCF-H₂O,LCCF-Et OH and LCCF-0.7NMP）with three different internal coagulants（100 wt.%H₂O,100 wt.%Et OH and 70 wt.%NMP+30 wt.%Et OH mixed solution）were fabricated by phase inversion-sintering technique.The oxygen permeation flux increased with the temperature,the air and sweep gas flow rate,or the oxygen permeation partial pressure difference.The LCCF-0.7NMP hollow fiber membrane achieved an oxygen permeation flux of 4.92 m L·min^-1·cm^-2 at 1000°C with He sweep flow rate of 120 m L·min^-1 and air flow rate of 100 m L·min^-1.At the same temperature and air flow rate,an oxygen permeation flux of 8.83 m L·min^-1·cm^-2 was obtained when sweeping with 40 m L·min^-1 CH₄,demonstrating that the driving force from the CH₄ reaction was greater than that of the He sweep gas.When LCCF-0.7NMP was swept with 100 m L·min^-1CO₂ at 950°C,the oxygen permeation flux fell to 2.65 m L·min^-1·cm^-2.After changing the sweep gas back to He,the oxygen permeation flux gradually increased and eventually returned to the initial level,indicating that the LCCF-0.7NMP hollow fiber membrane had excellent CO₂ resistance.Using LCCF powder as the carrier and NiO as the nickel source,Ni/LCCF catalysts with Ni content of 10 wt.%（10 wt.%Ni/LCCF）were finally obtained by mechanical mixing and hydrogen reduction.The methane catalytic performance of the catalysts and the hollow fiber membrane were investigated at different temperatures.The catalysts and LCCF hollow fiber membrane were assembled into an OCRM membrane reactor and the effects of reaction temperature,air flow rate,CH₄/CO₂ feed ratio and total feed flow rate on the membrane reactor performance were investigated.However,the increase of air flow rate,CH₄/CO₂ feed ratio,and total feed volume would decrease the CO selectivity and carbon balance.At 825℃and tested for 50 h,the CO selectivity and carbon balance were maintained at about 99%,and the oxygen permeation was maintained at about 2.08 m L·min^-1.Scanning electron microscopy（SEM）,X-ray diffraction（XRD）,Energy dispersion X-ray spectrometer（EDS）and thermal gravity（TG）were performed on the spent catalyst after the OCRM reaction,and the results showed that the indroduction of oxygen could significantly inhibit the coke accumulation of catalyst.