【作者】 王志刚；

【导师】 谭小耀； 孟波；

【作者基本信息】 山东理工大学 ， 应用化学， 2010， 硕士

【摘要】 采用新型的相转化与高温烧结技术,用NMP(N-甲基吡咯烷酮)和去离子水的混合溶液作为中空纤维膜内部的凝固液,用自来水作为膜外部的凝固液,制备出高度非对称的致密La0.6Sr0.4Co0.2Fe0.8O3-δ(LSCF)中空纤维陶瓷透氧膜。该膜结构包含一个厚度仅为88μm的致密外层和一个多孔内层。分别以空气和氦气作为膜外和膜内的吹扫气体,在不同温度下测试了LSCF中空纤维膜的透氧性能。结果显示,该高度非对称中空纤维膜在650-1000℃范围内的透氧量为0.11-2.19 mL·cm-2·min-1,是普通三层结构中空纤维膜在相同温度下透氧量的2.6-10.5倍。同时,还发现在较低温度下中空纤维膜制造透氧量的大小主要取决于膜表面交换反应,但在高温情况下,温度大于900℃时,膜体的离子扩散速率将成为决定膜透氧量的重要因素。用传统的相转化与高温烧结技术制备的LSCF中空纤维陶瓷膜,由于存在三层致密层,从而导致了该纤维膜比较低的透氧性能。采用不同的酸溶液对传统的LSCF中空纤维膜表面进行酸蚀改性,考察了不同的酸种、酸浓度、酸蚀时间对膜表面的微观形貌以及膜的透氧性能的影响。运用扫描电子显微镜(SEM)对酸腐蚀前后中空纤维膜的微观结构进行了观察,用XRD观察其晶相结构,然后运用气相色谱检测了酸腐蚀后膜的透氧性能变化。实验结果表明,经过HCl和H2SO4腐蚀后的LSCF中空纤维膜表面呈现了一个多孔状的新结构,膜的透氧量比原始膜分别提高了5.9和18.6倍。与HCl腐蚀的效果相比,经H2SO4腐蚀后的膜具有更大的表面面积。例如,用浓度为98%的浓硫酸腐蚀40 min后,在800℃下,膜内氦气吹扫气流速为44.6 mL·min-1时,LSCF中空纤维膜的透氧量最大可达0.509 mL·cm-2·min-1。采用相转化法制备LSCF中空纤维膜前驱体湿膜,在室温下用去离子水和自来水分别作为膜内部和外部的凝固液纺制。用于准备纺制中空纤维膜的浆料的配比是68.75 wt%LSCF粉体,6.25 wt%聚醚砜(PESf)和25.0 wt%N-甲基-2-吡咯烷酮(NMP)。将纺制出的中空纤维膜的前驱体在高温管式炉中吊烧,采用不同的烧结温度1200-1500℃,不同的烧结时间2-8 h,考察其对LSCF中空纤维膜微观结构、晶相状态、机械强度、透氧性能的影响。LSCF中空纤维膜的机械强度随着烧结温度的增加而增加,当烧结温度达到1500℃时,强度达到最大的115 MPa。欲得到致密的LSCF中空纤维膜,烧结温度必须在1250℃以上,烧结时间要在2 h以上。但当烧结温度高于1350℃时,纤维膜很容易形成硫酸盐类的不纯净相,导致LSCF中空纤维膜的透氧性能明显降低。制备致密高透量LSCF中空纤维膜的最适合的烧结温度应为1300℃左右,烧结时间控制在2-4 h。更多还原

【Abstract】 Highly asymmetric Lao.6Sro.4Coo.2Feo.803-δ(LSCF) hollow fiber ceramic membrane was prepared by a new phase-inversion and the sintering technique with a mixture of N-methyl-2-pyrrolidone (NMP) and water as internal coagulant, tap water as external coagulant. The gastight LSCF hollow-fiber membranes with a highly asymmetric structure comprising a dense layer of thickness ca.88μm integrated with a porous substrate. Oxygen permeation fluxes through the obtained hollow fiber membranes were measured under air/He gradients at different conditions. The results indicate that the highly asymmetric hollow-fiber membranes possess an oxygen permeation flux of 0.11-2.19 mL·cm-2min-1 in the temperature range of 650-1000℃, which is 2.6-10.5 times higher than that of the sandwich-structured hollow-fiber membranes. Oxygen permeation in the hollow fiber membranes is limited primarily by the surface exchange reactions at lower temperatures, but ionic bulk diffusion will have a rate-limiting effect at temperatures higher than 900℃.LSCF hollow fiber ceramic membrane, which was prepared by original phase-inversion and the sintering technique, exhibited low oxygen fluxes due to the existence of three fully densified layers unfavourable for oxygen permeation. The membrane was further improved by surface modification via an acid-etching technique. The effect of acid concentration and etching time on the microstructure of membrane surface and oxygen permeability was researched. The fibres were characterised by SEM and XRD and tested for air separation. Experimental results revealed that HC1 or H2SO4 etching can create a new membrane structure and improve the oxygen fluxes by a factor of up to 5.9 or 18.6, respectively. Comparatively, H2SO4 was a better acid for controlling the reaction to yield a porous surface with higher surface area. For example, at helium sweep rate of 44.6 mL/min, the oxygen fluxes through the membrane etched by 98wt%sulfuric acid for 40min had the highest oxygen flux of 0.509 mL·cm-2 min-1 as the temperature was 800℃.LSCF hollow fiber membrane precursors were prepared by spinning a starting suspension containing 68.75 wt% LSCF powders,6.25 wt% polyethersulfone (PESf), and 25.0 wt%N-methy1-2-pyrrolidinone (NMP) at room temperature using deionized water and tape water as the internal and external coagulants, respectively. High temperature sintering was carried out in a range of 1200-1500℃and 2-8 h to study the influences of the sintering process on the properties of the LSCF hollow fiber membranes including the microstructure, crystalline phase, mechanical strength, as well as the oxygen permeability. Mechanical strength of the LSCF hollow fibers increased with increasing sintering temperature and reached a maximum of 115 MPa at 1500℃sintering temperature. To obtain gastight LSCF hollow fiber membranes, the sintering temperature must be higher than 1250℃, and the sintering time must be longer than 2 h. However, higher than 1350℃sintering temperature would facilitate the formation of sulfate impurity phases, resulting in noticeable reduction of oxygen permeation flux. The optimum sintering temperature should be around 1300℃, and the sintering time should be within the range of 2-4 h to obtain the gastight and high flux LSCF hollow fiber membranes.更多还原