新型不对称双相混合导体透氧膜的制备及透氧机理研究

Dual-phase mixed conducting membranes, due to the oxygen permeability, high selectivity, excellent long-term stability and mechanical strength at elevated temperature and large oxygen partial pressure gradient, show wide application prospects in oxygen production, partial oxidation of methane to syngas and oxygen-fuel combustion. However, their low permeability becomes the most important problem to be resovled.In this study,the solid electrolyte Ce0.8Sm0.2O2-δ is used as ionic conducting phase of the dual-phase membrane, while the mixed conductor Ca3Co2O6-δ is used as the electronic conducting phase due to its low thermal expansion coefficient, high catalytic activity and ionic/electronic conductivity.The ionic conductivity and surface exchange of the membrane are increased, resulting the improvement of the oxygen permeation flux. Moreover, asymmetric membrane structure is proposed, in which the Ce0.8Sm0.2O2-δ porous support provides the membrane mechanical strength and the Ce0.8Sm0.2O2-δ-Ca3Co2O6-δ thin dense layer reduces the ion transmission loss. Thus, the permeability of the dual phase membrane is enhanced. The effects of the pore morphology, the dual phase ratios and the membrane thickness on the oxygen perpeaion flux, stability and mechanical strength are investigated. The roles of the oxygen surface exchange and ionic transmission in the oxygen permeation process are also studies for the dual-phase asymmetric membrane. This study will enrich the theory system of asymmetric research, and expand the value of dual-phase membrane in practical applications.

双相混合导体膜由于在高温下和高氧浓度梯度下具有氧渗透特性、选择性、良好的工作稳定性和机械性能，在纯氧制备、膜反应器及燃料的纯氧燃烧等方面显示出广阔的应用前景。双相混合导体膜的透氧率较低，成为目前亟待解决的重要问题。本研究拟采用固体电解质Ce0.8Sm0.2O2-δ为离子相，具有低热膨胀、高催化活性和离子/电子传输能力的混合导体Ca3Co2O6-δ为电子相组成双相膜，以提高离子电导率和氧表面交换进而提高透氧率；膜结构拟采用新型双相不对称膜，多孔Ce0.8Sm0.2O2-δ基体保证膜的机械性能，极薄的Ce0.8Sm0.2O2-δ-Ca3Co2O6-δ致密层降低了氧离子传输损耗，进一步提高透氧率。揭示了多孔层微结构、两相比例和膜厚对透氧率、稳定性和机械性能的影响规律，阐明了氧表面交换和氧离子体扩散对双相不对称膜透氧过程的作用机理。本研究可望丰富不对称膜的理论体系，拓展双相混合导体膜的应用价值。

双相混合导体膜由于高温时能够同时传导氧离子和电子，因而在纯氧制备、甲烷部分氧化制合成气、富氧燃烧等方面显示出广阔的应用前景。目前双相膜的透氧率普遍较低，提高双相膜的透氧率成为目前亟待解决的关键问题。针对上述问题，本项目提出了制备新型Ce0.8Sm0.2O2-δ-Ca3Co2O6-δ不对称双相膜，通过降低膜厚提高透氧率，同时多孔Ce0.8Sm0.2O2-δ基体保证了膜片的机械强度。此外，Ce0.8Sm0.2O2-δ-Ca3Co2O6-δ双相材料具有极低的热膨胀系数（14.23×10-6 K-1），接近固体电解质Ce0.8Sm0.2O2-δ，有效降低了制备过程中由于基体和致密层热匹配不一致而导致的开裂风险。新型不对称双相膜可以显著提高双相膜的透氧率尤其是低温时的透氧率，当测试温度为800℃时，氧离子体传输为透氧过程的主要限速步骤，其透氧率达到2.07×10-7 mol cm-2s-1，远高于厚膜材料的1.30×10-7 mol cm-2s-1。通过本项目的研究，发展了一种制备新型双相透氧膜的可行途径，推进制备技术及理论的发展和应用进程。