Preparation Of Carbon Dioxide Resistant Dense Ceramic Oxygen Permeable Membrane And Performance Of Membrane Reactor

The emission of methane（CH₄）and carbon dioxide（CO₂）leads to the intensification of the greenhouse effect.Dry reforming of methane（DMR）can convert these two gases into syngas gas（H₂+CO）,which is beneficial to mitigate global warming and achieve carbon neutrality.High energy demand and catalyst deactivation are the two major challenges of DMR.The addition of oxygen into the reaction system using dense ceramic oxygen permeable membranes can alleviate these two problems,and the coupling of air separation and reaction makes the membrane reactor more efficient and safer.In this paper,the oxygen permeation performance,carbon dioxide resistance and long-term stability of40 wt.%La_0.8Ca_0.2Al_0.3Fe_0.7O_3-δ–60 wt.%Sm_0.2Ce_0.8O_2-δ（LCAF-SDC）dual-phase hollow fiber membranes were investigated.The LCAF-SDC hollow fiber membrane was assembled with 10 wt.%Ni/LCAF-SDC catalyst powder to form membrane reactors,and the performance of the membrane reactor for oxy-CO₂reforming of methane（OCRM）reaction was investigated.In this paper,LCAF and SDC powders were prepared by sol-gel method,and LCAF-SDC dual phase powders were obtained by ball milling and mixing.The LCAF-SDC hollow fiber membranes were prepared by phase transformation-sintering technique.The LCAF-SDC dual phase powders and hollow fiber membranes were characterized by XRD,SEM,TEC,etc.Single perovskite phase LCAF and fluorite phase SDC were obtained at a lower calcination temperature of 900℃.No impurity phases and dense dual phase hollow fiber membrane was obtained by sintering at 1450°C for 5 h.Finger-like pore channels were distributed in the cross-section of hollow fiber membrane.The inner and outer surfaces of the membrane were dense.And the two kinds of grains were uniformly and continuously distributed,which indicated that a good oxygen ion and electron transport channel was formed in the membrane.The oxygen permeation rates of hollow fiber membranes increased with the increase of temperature,purge gas flow rate and air flow rate.The oxygen permeation rate reached 1.84 m L·min^-1·cm^-2at 950°C.At950℃,after the purge gas was switched from He to CO₂,although the oxygen permeability decreased slightly from 2.05 m L·min^-1·cm^-2to 1.67 ml·min^-1·cm^-2,the oxygen permeability remained stable for a long time in 200 h,indicating that LCAF-SDC hollow fiber membrane has good CO₂resistance at high temperature.Using LCAF-SDC as the catalyst support and Ni O as the nickel source,a catalyst with a composition of 10 wt.%Ni/LCAF-SDC was prepared by ball milling,mixing,calcination and reduction.The catalytic performance of the catalyst powder for the DRM reaction was investigated under different conditions.Increasing the temperature or the concentration of methane in the feed gas can improve the reaction effect.Membrane reactors were composed of catalyst and hollow fiber membrane.The effects of air flow rate,reaction temperature and CH₄/CO₂feed ratio on the performance of the membrane reactor were investigated.The increase in air flow rate increased the side reactions and was not favorable for the OCRM reaction.Since the CO₂reforming of methane reaction was a strong heat absorption reaction,the temperature increase enhanced the reactor performance.The increase of CH₄/CO₂feed ratio leaded to a significant increase of CO₂conversion and product selectivity.At 900℃,the CH₄conversion,CO₂conversion,H₂selectivity and CO selectivity were 99.8%,79.9%,79.2%,and 91.3%,respectively,within the 50 h.