气凝胶纳米催化剂流化床内CH4-CO2重整反应的研究
文献类型：学位论文
| 作者 | 郝志刚 |
| 学位类别 | 博士 |
| 答辩日期 | 2008-05-29 |
| 授予单位 | 中国科学院过程工程研究所 |
| 授予地点 | 过程工程研究所 |
| 导师 | 朱庆山 |
| 关键词 | CH4-CO2重整反应 磁场流化床 气凝胶Ni/Al2O3催化剂 气凝胶Co/Al2O3催化剂 MgO助剂 |
| 其他题名 | CO2 Reforming of CH4 over Aerogel Nanoparticle Catalysts in Fluidized Bed Reactors |
| 学位专业 | 化学工程 |
| 中文摘要 | CH4-CO2重整反应制取合成气在合理利用资源和保护环境方面具有双重意义，因而引起许多研究者的广泛关注。从目前的研究现状来看，催化剂易积碳失活是尚未解决的关键问题，而且催化剂的活性也需进一步提高。在众多催化剂中，气凝胶纳米颗粒催化剂由于比表面积高、活性组分粒径小和分散度高等优点，在抑制积碳和提高催化活性等方面表现优异。但是，纳米颗粒催化剂在常规的固定床重整反应时存在活性组分利用率不足、床内压降过高等缺点，流化床操作由于具有优异的气固接触效率和较低的床层压降等特点可以克服固定床操作中的不足，然而目前还没有纳米颗粒催化剂在流化床内进行CH4-CO2重整反应的研究报道。因此，本文采用气凝胶纳米颗粒催化剂在流化床内进行了CH4-CO2重整反应的研究。取得的创新性结果如下： （1）对气凝胶Ni/Al2O3催化剂在流化床内进行了CH4-CO2重整反应的研究，并与其在固定床内的重整反应进行对比。重整反应24h内的对比结果表明，气凝胶催化剂在流化床内具有较高的床层膨胀比和较大的颗粒循环量，较长的气体停留时间使反应物转化率得到14～30％的提高，催化剂颗粒的循环运动加快了碳物种消除的反应速率，因而仅有少量碳沉积；同时，在重整反应的24h内流化床的操作压降仅为16Pa，远低于固定床的1656～2460Pa。但是，当气凝胶Ni/Al2O3催化剂在流化床重整反应延长至48h时，不同Ni含量气凝胶Ni/Al2O3催化剂由于催化剂表面积碳较多而导致反应物转化率有5～10％的降低。在所测试的催化剂中，Ni含量为10wt.%的气凝胶Ni/Al2O3催化剂由于具有较小的Ni颗粒直径和较强的Ni与载体间作用力，因而表现出较低的碳沉积量和较高的催化稳定性。 （2）为增强气凝胶Ni/Al2O3催化剂的抗积碳性能，添加助剂MgO制备出气凝胶Ni/MgAl2O4-Al2O3催化剂并用于CH4-CO2重整反应。催化剂表征结果表明添加MgO助剂可以提高Ni分散度、降低Ni颗粒直径和增强CO2吸附活化能力。研究结果表明Ni含量为10wt.%的气凝胶Ni/MgAl2O4-Al2O3催化剂在流化床内可以连续运行1200h保持热力学平衡转化率而没有失活，比当前文献中Ni/Mg/Al催化剂最长的催化稳定性时间55h提高了约22倍。催化剂稳定性分析认为，流化床操作是气凝胶催化剂稳定运行的基础，气凝胶Ni/MgAl2O4-Al2O3催化剂具有较小的Ni颗粒直径延缓了活性组分的烧结，而较强的CO2吸附活化能力可以保证在重整反应中催化剂表面碳物种的消除快于碳物种的形成，抑制了催化剂表面积碳而保持了很好的催化稳定性。 （3）为提高气凝胶催化剂在流化床内的气固接触效率和减少颗粒夹带现象，在磁性纳米颗粒Co/Al2O3催化剂床层内部引入轴向均匀磁场研究其流化特性并考察反应器操作型式对催化性能的影响。研究结果表明在磁场强度137Oe～320Oe范围内，床层内部的大聚团和大气泡得到有效破碎，由普通流化床的聚团鼓泡流化转变为聚团散式流化，流化质量得到明显改善。对气凝胶Co/Al2O3催化剂在三种不同床型操作条件下的重整反应研究表明，磁场流化床内的催化活性、催化稳定性和抗积碳性能最佳，其次是流化床，而固定床最差。对比结果表明气凝胶Co/Al2O3催化剂在磁场流化床重整反应中优异的流化质量降低了碳沉积速率而延长了催化稳定性，而且磁场力的束缚也抑制了催化剂颗粒的夹带。 （4）为增强气凝胶Co/Al2O3催化剂的抗积碳性能，添加助剂MgO制备出气凝胶Co/MgAl2O4-Al2O3催化剂并用于磁场流化床CH4-CO2重整反应。催化剂表征结果表明该催化剂具有较小的Co颗粒直径、较高的Co分散度和较强的CO2吸附活化能力。研究结果表明Co含量为20wt.%的气凝胶Co/MgAl2O4-Al2O3催化剂可在磁场流化床重整反应的1200h内保持热力学平衡转化率而不失活，比当前文献中Co基催化剂的最长催化稳定性时间120h提高了10倍。催化稳定性分析认为，优异的流化质量和抗积碳性能的催化剂共同作用促使高Co含量气凝胶催化剂在磁场流化床重整反应中抑制了催化剂表面积碳而保持了很好的催化稳定性。 |
| 英文摘要 | Recently, CH4-CO2 reforming to syngas has attracted a growing interest from both environmental and industrial perspectives. According to the present development status of the CH4-CO2 reforming, the main subjects focus on the inhibition of carbon deposition and the improvement of catalytic activity. Among numerous catalysts, much attention has been paid to aerogel nanoparticle catalysts due to the fact that they showed much better catalytic activities and catalytic stability. However, the application of nanoparticle catalysts in industrial-scale fixed bed reactors is unrealistic because the pressure drop of bed would be too high if the particle size decreases to nanometer scale. Fluidized bed reactors are considered to be ideal for processing nanoparticles since the pressure drop is independent of particle diameters in such reactors. The main problem for fluidized bed reactors to handle nanoparticle catalysts lies in the fact that most nano-sized powders are difficult to be fluidized due to the strong cohesive forces among nanoparticles. Although many cold-model investigations have been performed on the fluidization of nanoparticles, CH4-CO2 reforming over nanoparticle catalysts in fluidized bed reactors has not yet been reported up to the present, to the best of our knowledge. In this thesis, the combination of the aerogel nanoparticle catalysts and the fluidized bed reactors was studied in the CH4-CO2 reforming reaction. The following main conclusions have been obtained: (1) CH4-CO2 reforming over aerogel Ni/Al2O3 catalysts was studied in a fluidized bed and compared with that in a fixed bed. The aerogel particles show greater bed expansion ratio and higher particles circulation in the fluidized bed, resulting in 14~30 % increase in CH4 conversions, as compared with those in the fixed bed. Moreover, the pressure drop of the fluidized bed is only 16 Pa, which is much lower than the values of 1656~2460 Pa in the fixed bed during the 24 h reforming. However, 5~10 % conversion degradations have been observed when the reaction time was extended to 48 h. Among all tested aerogel Ni/Al2O3 catalysts, the catalyst with 10 wt.% Ni loading exhibits the slowest carbon deposition rate and the best catalytic stability, possibly due to the small Ni particle size and the strong metal-support interaction. (2) In order to improve the resistance to carbon deposition, MgO was employed as the promoter in the aerogel Ni/Al2O3 catalysts. It has been revealed that the addition of MgO in the Ni/Al2O3 catalysts can improve the Ni dispersion, reduce the Ni particle size and enhance the adsorption of CO2. The optimized 10 wt.% Ni/MgAl2O4-Al2O3 catalyst exhibits the highest catalytic stability in the fluidized bed, where after 1200 h time on stream nearly no deactivation of the catalyst has been observed. Characterizations of the catalysts indicates that the improved Ni dispersion in the Ni/MgAl2O4-Al2O3 catalyst can reduce the Ni sintering, while the strong adsorption and activation of CO2 can ensure fast removal of deposited carbon, which are helpful to inhibit carbon deposition and obtain excellent catalytic stability. (3) The fluidization characteristics of aerogel Co/Al2O3 catalyst were investigated in a magnetic fluidized bed in order to improve the gas-solid contact efficiency and reduce the elutriation of catalyst particles. The CH4-CO2 reforming was investigated in fluidized beds with and without the magnetic field. It showed that large agglomerates and bubbles can be effectively disrupted under the magnetic field intensity ranging from 137 to 320 Oe, and the fluidization of the aerogel Co/Al2O3 particles gradually transforms from channeling, slugging, bubbling fluidization to agglomerate particulate fluidization with increasing the magnetic field intensity. The investigations demonstrated that the magnetic fluidized bed reforming exhibited the best catalytic activity and the slowest performance degradation among the reactors investigated, which was attributed to the excellent gas-solid contact efficiency that enhances catalytic performance. Moreover, the application of the magnetic field also markedly reduces the elutriation of catalyst particles. (4) MgO was added as the promoter to the aerogel Co/Al2O3 catalyst in order to improve the resistance to carbon deposition, and the catalytic performance of the aerogel Co/MgAl2O4-Al2O3 catalyst was consequently studied for the CH4-CO2 reforming in the magnetic fluidized bed. It revealed that the aerogel Co/MgAl2O4-Al2O3 catalyst exhibited excellent catalytic stability under the magnetic fluidized bed operation, where after 1200 h time on stream nearly no deactivation of the catalyst has been observed. The excellent catalytic performance could be mainly attributed to the good gas-solid contact efficiency resulted from the application of the magnetic field and the slow carbon deposition due to the addition of MgO that improves Ni dispersion, reduces Ni particle size and enhances adsorption of CO2. The long-term catalytic stability together with the low catalyst elutriation makes the aerogel Co/MgAl2O4-Al2O3 catalyst promising for the CH4-CO2 reforming. |
| 语种 | 中文 |
| 公开日期 | 2013-09-13 |
| 页码 | 157 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1097]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 郝志刚. 气凝胶纳米催化剂流化床内CH4-CO2重整反应的研究[D]. 过程工程研究所. 中国科学院过程工程研究所. 2008. |
入库方式： OAI收割
来源：过程工程研究所
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