致密透氧膜用于甲烷部分氧化制合成气的实验研究

引　言钙钛矿型致密透氧膜在高温下具有氧离子、电子混合导电性 .当膜两侧存在氧分压梯度时 ,高压侧的氧在膜表面经化学吸附解离成氧离子、电子 ,于膜主体内扩散至另一侧 ,并重新结合、脱附至低氧压体系 .将致密透氧膜反应器用于甲烷部分氧化制合成气反应为天然气利用开辟了一条崭新的路径 ,近年来受到普遍关注 .该过程集空分与反应于一体 ,降低了大量的操作成本 ,通过膜壁控制氧气的进料有效控制了反应进程 .提高膜的透氧量 ,解决还原性气氛下膜的稳定性等问题 ,是该过程实现工业化的关键 .Ｂａｌａｃｈａｎｄｒａｎｄ[1] 、Ｔｓａｉ[2 ] …     

基于Ba-Ce-Co-Fe-O膜反应器的甲烷部分氧化反应研究

为开发稳定性和透氧量俱佳并适用于甲烷部分氧化反应(POM)的透氧膜材料,采用溶胶凝胶工艺合成了具有纯相钙钛矿结构的BaCe0.1Co0.4Fe0.5O3-δ混合导体陶瓷材料。POM操作结果表明:BaCe0.1Co0.4Fe0.5O3-δ膜反应器透氧量高于同类材料,875℃时透氧量达到了8.9 mL/(cm2.m in)。在1 000 h寿命实验中,膜反应器各项反应指标没有出现任何衰减,反应性能稳定,甲烷转化率和CO的选择性都在97%以上。SEM表征表明,反应后膜片表面微观结构的变化虽然不可避免,但是其仍然保持比较完整的结构。因此,该材料良好的透氧量和稳定性说明其具有较好的应用前景。     

管式致密透氧膜用于甲烷部分氧化制合成气的研究

采用钙钛矿型管式致密透氧膜反应器,在Ｎｉ／Ａｌ２Ｏ３催化剂上进行了甲烷部分氧化制合成气的实验研究,考察了进料气中甲烷的摩尔分数和反应温度对反应结果的影响,并对膜在反应条件下的稳定性作了分析     

氧泵型催化膜反应器中甲烷氧化偶联反应(Ⅰ)——氧泵型催化膜的制备及其反应性能

本文采用1％Sr/La_2O_3-Ag-YSZ氧泵型催化膜反应器进行了甲烷氧化偶联反应研究。比较了不同制备方法的催化膜的反应性能,结果发现浸涂法(Ag-YSZ管随旋转轴转动涂制)制备的膜性能最佳。研究了操作条件对甲烷氧化偶联反应的影响。研究证明,传递氧与气相氧同时进料是一种较好的反应方式。结果表明,利用该反应器不仅可以简化分离过程,而且还可得到更高的C_2烃选择性。     

氧泵型催化膜反应器中甲烷氧化偶联反应(Ⅰ)——氧泵型催化膜的制备及其反应性能

本文采用1％Sr/La_2O_3-Ag-YSZ氧泵型催化膜反应器进行了甲烷氧化偶联反应研究。比较了不同制备方法的催化膜的反应性能,结果发现浸涂法(Ag-YSZ管随旋转轴转动涂制)制备的膜性能最佳。研究了操作条件对甲烷氧化偶联反应的影响。研究证明,传递氧与气相氧同时进料是一种较好的反应方式。结果表明,利用该反应器不仅可以简化分离过程,而且还可得到更高的C_2烃选择性。     

钙钛矿型致密膜透氧过程的应用研究

对钙钛矿型致密膜的透氧过程进行了实验研究,验证了所建数学模型的正确性,并对数学模型中的材料参数、应用范围、模型对厚度的敏感性及模型在极限条件下的适用性等进行了分析研究,力图实现以模型为手段,优化实验操作条件,用模型来预测不同工艺条件对膜透氧速率的影响,减少探索性实验的工作量,进而为实现其工业化应用提供指导。     

钙钛矿型混合导体透氧膜的研究

详细地介绍了近年来国内外有关钙钛矿型混合导体透氧膜的透氧机理、研究进展以及其应用范围,对其制备方法及表征进行了阐述,并对此类材料的应用前景作了展望。     

氧泵型催化膜反应器中甲烷氧化偶联反应(Ⅱ)——动力学研究

在1％Sr/La_2O_3-Bi_2O_3-Ag-YSZ氧泵型催化膜反应器中,进行了甲烷氧化偶联反应动力学研究,提出了反应途径及机理,并建立了速率方程。结果表明,在该氧泵型催化膜反应器中,甲烷氧化偶联反应满足Rideal-Rdox机理。采用固体电解质电位测定技术进行了内扩散影响的考察。     

钙钛矿型致密膜透氧过程的模拟研究

由于钙钛矿型致密膜的透氧机理十分复杂,影响因素较多,因此对过程进行数学模拟是实现其工业化应用的一个重要步骤,本文将影响其高温透氧过程的主体扩散和表面交换反应有机结合起来,同时考虑膜表面气固相交界层内的传递阻力,建立了钙钛矿型致密膜透氧过程的数学模型,并对模型的适用范围进行了理论分析,以便为钙钛矿型致密膜透氧过程的实验研究提供前瞻性预测。     

氧泵型反应器及在甲烷氧化偶联反应中的应用

本文介绍了氧泵型反应器构造、原理和固体氧离子电解质的性能表征。通过对催化剂、氧泵的作用、催化膜制备方法及反应历程几方面近期来研究的途述和总结,分析了氧泵型甲烷氧化偶联的研究现状,介绍了ＮＥＭＣＡ效应及其研究手段和主要结论。对氧泵型反应器甲烷氧化偶联存在的问题和今后的研究方向提出了看法。     

Failure mechanisms of ceramic membrane reactors in partial oxidation of methane to synthesis gas

In the course of generating synthesis gas (H₂, CO) from methane, we have observed two types of fractures occurring on the Sr(Co, Fe)O_x-type oxygen membrane reactors. The first type occurred shortly after the reaction started and the second type often occurred days after the reaction. To determine the causes of these fractures, we have examined the starting material and fractured membranes using a combination of X-ray diffraction and thermogravimetric analyses. We found that the first type of fracture was the consequence of an oxygen gradient in the membrane, pointing from the reaction side to the air side. This causes a lattice mismatch inside the membrane, leading to fracture. The second type of fracture, however, was the result of a chemical decomposition. We found that the Sr(Co, Fe)O_x-type membrane had been reduced to SrCO₃, and elemental Co and Fe by the synthesis gas generated in the reaction. The decomposition causes enormous expansion leading to a large crack along the axis of tube.     

Design of mixed conducting ceramic membranes/reactors for the partial oxidation of methane to syngas

The performance of mixed conducting ceramic membrane reactors for the partial oxidation of methane (POM) to syngas has been analyzed through a two‐dimensional mathematical model, in which the material balance, the heat balance and the momentum balance for both the shell and the tube phase are taken into account. The modeling results indicate that the membrane reactors have many advantages over the conventional fixed bed reactors such as the higher CO selectivity and yield, the lower heating point and the lower pressure drop as well. When the methane feed is converted completely into product in the membrane reactors, temperature flying can take place, which may be restrained by increasing the feed flow rate or by lowering the operation temperature. The reaction capacity of the membrane reactor is mainly determined by the oxygen permeation rate rather than by the POM reaction rate on the catalyst. In order to improve the membrane reactor performance, reduction of mass transfer resistance in the catalyst bed is necessary. Using the smaller membrane tubes is an effective way to achieve a higher reaction capacity, but the pressure drop is a severe problem to be faced. The methane feed velocity for the operation of mixed conducting membrane reactors should be carefully regulated so as to obtain the maximum syngas yield, which can be estimated from their oxygen permeability. The mathematical model and the kinetic parameters have been validated by comparing modeling results with the experimental data for the La_0.6Sr_0.4Co_0.2Fe_0.8O_3‐α (LSCF) membrane reactor. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Partial oxidation of methane to syngas in BaCe0.15Fe0.85O3−δ membrane reactors

Dense planar Ba_0.15Ce_0.85FeO_3−δ (BCF1585) membrane reactors were investigated to produce syngas from methane. Firstly, the membrane itself catalytic activity to methane was investigated using a blank BCF1585 without any catalysts. Then a LiLaNi/γ-Al₂O₃ catalyst was packed on the BCF1585 membrane surface to test the synergetic effects of the membrane and catalyst. It was found that the membrane itself has a poor catalytic activity to methane. The main products are CO₂ and C₂, and methane conversion is low due to the low oxygen permeation flux. However, after the catalyst was packed on the membrane surface, both methane conversion and oxygen permeation flux were greatly improved by the synergetic effect between the membrane and catalyst. Carbon monoxide selectivity reached at 96% with methane conversion of up to 96%. The oxygen permeation flux reached at 3.0 mL/cm² min at 850 °C for a 1.5 mm disk membrane and can effectively be increased by reducing the thickness of the membranes. After operation for 140 h at 850 °C, the used membrane was examined with SEM and EDXS. The results revealed that the decomposition of the membrane materials could not be avoided under such conditions. Oxygen partial pressure gradient across the membranes is suggested as a critical factor to accelerate the kinetic decomposition of the materials.     

Oxygen selective ceramic hollow fiber membranes for partial oxidation of methane

A BaCo_xFe_yZr_zO_3?δ (BCFZ) perovskite hollow fiber membrane was used to construct reactors for the partial oxidation of methane (POM) to syngas. The performance of the BCFZ fibers in the POM was studied (i) without any catalyst, (ii) with catalyst‐coated fibers, and (iii) with catalyst packed around the fibers. In addition to the performance in the POM, the stability of the BCFZ hollow fiber membranes was investigated for the different catalyst arrangements. Best stability of the BCFZ hollow fiber membrane reactor in the POM could be obtained if the reforming catalyst is placed behind the oxygen permeation zone. It was found that a direct contact of the catalyst and the fiber must be avoided which could be achieved by coating the fiber with a gold film. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Catalytic partial oxidation of methane to synthesis gas in a ceramic membrane reactor

Methane has been selectively converted to synthesis gas using a two-zone fixed bed of a Ni/Al₂O₃ catalyst inside a modified ceramic membrane. The first zone of the reactor was surrounded by an impervious wall, and therefore behaved as a conventional fixed bed reactor. In the second zone, some of the reaction products could preferentially diffuse out of the reactor, which yielded higher than equilibrium methane conversions. The influence of the different operating conditions has been studied, and the performance of the membrane reactor has been compared to that of a fixed bed reactor. The membrane reactor has also been used at pressures above atmospheric (2 bar), with good conversions and selectivities.     

Improving selectivity during methane partial oxidation by use of a membrane reactor

A reactant-swept catalytic membrane reactor for partial oxidation of methane to formaldehyde has been modeled. Kinetic parameters were taken from the literature for a V₂O₅/Sio₂ methane partial oxidation catalyst, and membrane parameters characteristic of commercially available materials were used. The models show that the selectivity for formaldehyde can be significantly improved by using a membrane reactor.     

SrFe0.6Cu0.3Ti0.1O3-δ透氧膜反应器中甲烷部分氧化反应工艺及膜稳定性考察

采用SrFe_0.6Cu_0.3Ti_0.1O_3-δ混合导体透氧膜组装成膜催化反应器,进行甲烷部分氧化制合成气反应,考察了反应温度、空速、催化剂粒径等条件的影响,并分析了反应气氛引起的透氧膜结构变化情况。结果表明,在膜反应器内,催化反应与透氧过程存在相互制约和相互促进的关系。在膜反应器内进行甲烷部分氧化反应后,透氧膜的两侧表面均发生蚀刻现象,结晶度显著降低,反应侧蚀刻现象较为严重,膜表面形成了疏松的多孔层,反应气氛使膜表面晶体结构发生了较大改变,Sr容易从钙钛矿结构中析出并与CO₂结合形成SrCO₃,Sr的析出导致组成不平衡,促进了钙钛矿结构分解及其他物相的产生。     

天然气甲烷部分氧化制合成气的研究进展

甲烷部分氧化制合成气是高转化率、高选择性、高空速、低H2/CO、温和的放热反应,综述了近几年来甲烷部分氧化制合成气的催化剂、反应机理及活性中心的研究进展及反应中的存在问题。     

掺杂Ni制备Ca2FeCo1-xNixO6催化剂及其催化甲烷燃烧性能

采用共沉淀法制备双钙钛矿Ca_2FeCo_(1-x)Ni_xO_6系列催化剂。采用XRD、BET和H_2-TPR等对样品进行表征,通过催化甲烷燃烧对其进行催化性能测试。结果表明,不同Ni~(2+)掺杂量均可以形成完整的钙钛矿晶型,随着Ni~(2+)掺杂比例升高,催化剂的比表面积逐渐增大;不同Ni~(2+)掺杂量制备的催化剂结构和活性不一样,样品Ca_2FeNiO_6催化甲烷燃烧活性最好,起燃温度T_(10%)为430℃,T_(90%)为640℃。