【作者】 张佳瑾；

【导师】 李建伟；

【作者基本信息】 北京化工大学 ， 化学工程与技术， 2012， 博士

【摘要】 本文针对煤层气中低浓度甲烷（Vol.%≤1%）流向变换催化燃烧脱除及其化学能回收，系统开展了以堇青石为载体的、甲烷催化燃烧整体式催化剂制备、性能表征及动力学特性等方面的研究；以所研制的、性能较优的催化剂为基础，深入开展了带有中间换热装置的低浓度甲烷流向变换催化燃烧反应器性能模拟研究；在山西潞安集团五阳煤矿完成了煤矿通风乏气处理量为1000Nm³/h的流向变换催化燃烧中试实验。所取得的结论为实现低浓度甲烷煤层气能源的高效、洁净利用奠定了应用和技术基础。酸蚀预处理和涂敷层改性对γ-AL₂O₃/COR（堇青石）整体式复合载体本体结构及其涂敷能力影响的实验结果表明：在满足机械强度的要求下，经过适宜的酸处理（10%的HNO₃浸渍堇青石2h）可以提高堇青石载体与涂层载体的结合力；选择溶胶固含量30wt%，n（H⁺）/n（AlOOH）=0.08的制备条件配制过渡涂层AlOOH溶胶，经涂覆层改性后的堇青石载体比表面积由0.81m2/g增至50m2/g，且孔径分布在0nm²0nm之间，有利于活性组分在载体表面的分散。以上述改性γ-AL₂O₃/COR为载体，制备了一系列贵金属Pd、双金属Pd-Co和铜锰复合氧化物为活性组分的低浓度甲烷催化燃烧整体式催化剂，并以实验评价和SEM、ICP-AES、XPS、N₂-吸脱附、TPR/O等表征相结合的方式对所制备催化剂进行了性能特性考察。在所考察的四种不同Pd负载量的贵金属整体式催化剂中，以Pd负载量为0.1%时，活性组分Pd⁰/PdO在载体表面分散最为均匀，且Pd⁰和PdO的配比最优，有利于晶格氧在PdO→Pd→PdO氧化还原过程中的流动，进而提高催化剂的活性。在430oC和20000h^-1的空速条件下，甲烷转化率可达90%以上。虽然0.1%Pd负载型整体式催化剂具有很好的活性，但对于甲烷催化燃烧这一结构敏感反应，存在活性组分在载体表面分散度越好，越容易烧结，并最终导致催化剂热稳定性变差的问题，因此，为了充分提高催化剂活性相和载体之间的协同效应，本文采用掺杂过渡金属Co的方法对负载型贵金属催化剂进行改性。结果表明：适量Co元素的添加可以与载体形成比较稳定的晶体簇CoAl2O4，从而改善活性相和载体间的结合力，保护Pd0/PdO活性位不被烧结；同时，Co-O键的断裂为活性相Pd0/PdO提供了更多的晶格氧(O^2-)，从而使催化剂氧化能力进一步提高。其中，以0.1%Pd-0.25%Co/γ-AL₂O₃/COR整体式催化剂性能最佳，在410oC和20000h^-1的空速条件下，甲烷转化率即可达90%以上，且热稳定性也相对提高。贵金属催化剂对低浓度甲烷催化燃烧具有较高活性，但成本偏高，以非贵金属作为替代具有重要意义。本研究中采用铜锰复合氧化物来替代贵金属作为甲烷催化燃烧活性组分，制备了一系列Cu-Mn-O/γ-AL₂O₃/COR整体式催化剂，系统考察了制备工艺、活性组分负载量及辅助助剂等因素对催化剂性能的影响。表征和评价结果表明：采用等体积浸渍法制备的负载量为12%的催化剂催化效果相对较好。在650°C和GHSV=20000h^-1反应条件下，甲烷转化率可达80%以上。进而，为了提高铜锰复合氧化物整体式催化剂对甲烷的低温催化燃烧性能，以稀有金属氧化物CeO₂、ZrO₂、La₂O₃和CeO₂-ZrO₂为助剂，考察了加助剂对催化剂性能的影响。结果表明：稀有金属氧化物的添加调节了催化剂表面孔径分布，不仅提高了催化剂比表面积，而且使反应物气体在催化剂表面的扩散吸附与甲烷催化燃烧反应更好的耦合；此外，助剂的添加使活性组分和载体间的电子重新分布，从而提高了活性位上晶格氧的流动性，进而有利于提高催化剂的氧化能力。其中以添加ZrO₂的效果更佳，在570°C，空速20000h-1的条件下，甲烷转化率达90%以上。对上述分别以Pd、Pd-Co和铜锰复合氧化物为活性组分制备的三种优选催化剂性能对比可见，在甲烷初始浓度1.0vol.%、空速20000h^-1和甲烷转化率90％工况下，三者所需温度依次为：0.1%Pd-0.25%Co/γ-AL₂O₃/COR （410°C）＜0.1%Pd/γ-AL₂O₃/COR（430°C）＜12%Cu-Mn-Zr-O/γ-AL₂O₃/COR （570°C）。因此，0.1%Pd-0.25%Co/γ-AL₂O₃/COR具有比其他两种催化剂更高的低温活性，基于低能耗和自热平衡上的考虑，本文随后的反应器性能模拟和动力学实验将基于该催化剂进行。基于所制备的0.1%Pd-0.25%Co/γ-AL₂O₃/COR整体式催化剂，通过在线质谱动态响应实验，结合催化剂表征分析结果，对该催化剂上甲烷催化燃烧反应机理和动态行为特性进行了研究。结果表明，CH₄在催化剂表面快速形成吸附态CH₃⁺，在O2过量的反应条件下，CH₃⁺同时与晶格氧(O^2-)和气相氧（O₂）发生氧化反应，并且气相氧（O2）补充表面晶格氧(O^2-)的消耗。在贫燃富氧的反应条件下，甲烷被完全氧化，反应产物只有CO₂和H₂O，符合Mars and van-Krevelen氧化还原机理。根据该氧化还原机理，建立了在Pd-Co/γ-Al₂O₃/COR催化剂上的由吸附态甲烷和气相氧表面反应控制的甲烷催化燃烧反应速率模型。采用等温积分反应器（Φ10×2mm），在常压、温度范围350°C⁴50°C、空速40000h^-150000h^-1和甲烷体积浓度0.1%¹%的条件下，对Pd-Co/γ-Al₂O₃/COR催化剂上低浓度甲烷催化燃烧本征动力学进行了系统的实验研究。并基于所建立的、吸附态甲烷和气相氧表面反应为控制步骤的甲烷催化燃烧反应速率模型，以单纯形法对动力学模型参数进行优化估值，最终建立了与实验数据良好相容的、低浓度甲烷催化燃烧双曲型本征动力学模型。针对煤层气中低浓度甲烷的催化燃烧处理和化学能回收，设计了一种带有中间换热装置的甲烷流向变换反应器，并建立了其行为描述的一维非均相动态数学模型。以该模型为基础，对1000Nm3/h煤层气乏风处理能力的中试规模装置进行了模拟研究，系统考察了换向周期、伴热层温度和进料浓度等工况条件对反应器性能的影响。结果表明，换向周期是影响反应器性能的重要操作参数，过长的换向周期将会导致反应器“熄火”，而过短的换向周期不利于反应器自热平衡操作；选择适宜的伴热温度既可以保证反应器的良好自热平衡操作，又能够将能源有效利用；在所考察的范围内，较低的甲烷浓度（Vol.%≤0.5%）会导致反应器“熄火”。因此，工况条件的优化控制既可以保障催化反应器处于良好的操作状况，同时对于节能降耗和降低操作费用也是大有裨益的。以上述模拟研究结果为基础，设计并在山西潞安集团五阳煤矿搭建了处理量为1000Nm³/h的、带有中间取热的流向变换催化燃烧中试装置。中试实验结果表明，在煤矿通风中甲烷浓度只有0.34%⁰.54%的条件下，经过适当的反应气预热，并选择合适的周期变换时间，流向变换反应器在较低的能耗条件下可维持自热。矿井通风气经流向变换催化燃烧后，排放到大气中的甲烷含量低于0.06%。以上结果为流向变换强制对流操作技术在煤矿乏风中的推广应用提供了应用基础和技术参考。更多还原

【Abstract】 In this work, reverse flow catalytic combustion of lean methane inmine ventilation air （≤1.0%CH₄） was researched for exhaust removal andrecycling of chemical energy. The preparation, characterization anddynamic characteristics of catalysts with cordierite carrier for methanecombustion were studied systematically. Based on the optimal catalyst,depth research about simulation of lean methane reverse flow catalyticcoumbusiton reacor with heat exchanger in the middle of the reactor wascarried out. A pilot plant （processing capacity of1000Nm3/h） of leanmethane reverse flow catalytic combusiton was designed and constrctedat Lu’an Group Wuyang Coal Mine. The obtained conclusion can providetechnical basis for the efficient and clean use of the energy of lowconcentrations of methane.The modified experimental results of acid treatment and washcoatloading for γ-AL₂O₃/Cordierite indicated that acid treatment （impregnatedcordierite in10%HNO₃for2h） can improve the adhesion capacity ofcordierite carrier and washcoat carrier under the premise of mechanicalstrength; AlOOH gel prepared on the condition of n（H⁺）/n（AlOOH）0.08, solid content30%, after coating modified, the surface ofγ-Al₂O₃/cordierite was improved from0.81m2/g to50m2/g, and the poresize distribution of the support was between0nm to20nm, which wasfavorable to improve the dispersion of the active component on thesurface of the support.With the γ-Al₂O₃/cordierite above as carrier, a series of γ-Al₂O₃/CORsupported catalysts applied to lean methane combustion were preparedwhich the active component include monometallic palladium （Pd）,bimetallic cobalt （Co） and palladium （Pd）, and Cu-Mn complex oxides.The catalysts were characterized by SEM，ICP-AES，XPS，TPR/O andN₂-adsorption-desorption.Compared four different Pd loading of monolithic catalyst, on thecatalyst surface of0.1%Pd loading, the active phase of Pd0/PdO scatteredevenly, and the ratio of Pd⁰and PdO achieved better, which wasconducive to the mobility of lattice oxygen on the Pd^O→Pd→PdO redoxprocess, thereby increased the activity of the catalyst. On the condition of430oC and GHSV20000h^-1, the methane conversion was over90%.The methane catalytic combustion on the supported catalyst isgenerally considered to belong to the structure-sensitive reaction: betterdispersion of active component on the surface of the carrier, easier toagglomerate, leading to poor thermal stability. Although the0.1%Pdloading monolithic catalyst performed excellent in activity, in order to improve the synergies between active phase and carrier, the transitionmetals Co was used to modify the supported Pd catalysts. The resultsshowed that, appropriate amount of Co addition can form stable crystalcluster CoAl₂O₄on the catalysts surface which can improve the bindingforce between the active phase and carrier to protect Pd0/PdO active sitenot to be sintered; on the other hand, the Co-O bond cleavage can providemore lattice oxygen (O^2-) to the active phase of Pd0and Pd^O, improvedthe oxidative capacity of the catalyst. Among of which, the0.1%Pd-0.25%Co/γ-Al₂O₃/COR catalyst performed best, on the conditionof410oC and GHSV=20000h^-1, methane conversion was over90%, andthermal stability of the catalyst was relative increased.Taking into account the cost of catalysts, the Cu-Mn complex oxideswas used to instead of Pd as the active component for methanecombustion. And the factors which influenced the catalytic performancesuch as active component loading method, active component loading andadditives were investigated. Characterization and evaluation resultsshowed that the the catalyst prepared by impregnation method with theloading12%performed better for methane combustion. On the conditionof650oC and GHSV=20000h^-1, methane conversion was over80%.Furthermore, in order to improve the low-temperature catalyticcombustion performance of Cu-Mn composite oxide monolithic catalysts,the influence of promoters such as CeO₂、ZrO₂、La₂O₃&CeO₂-ZrO₂ additives was investigated. The results indicated that with theintroduction of CeO₂、ZrO₂、La₂O₃&CeO₂-ZrO₂as the promoter toCu-Mn composite oxide monolithic catalysts, the specific surface area ofthe catalysts increased obviously, resulting in an enhancement of activecomponent dispersion and oxygen species concentration on the catalystsurface. Therefore, the surface oxidation reactivity of the catalysts isimproved. Besides, the pore structure of the catalysts was also adjustedwell, which was beneficial for matching the diffusion-reaction couplingbehavior on the catalyst. In addition, the promoter can change theinteraction between the active phase and the carrier, re-distribute theelectronic around Cu, Mn, Al and O, improve the mobility of latticeoxygen, and enhance the oxidation of the catalyst. Among the testedpromoters, ZrO₂shows the best promoting effect. The methaneconversion over Cu-Mn-Zr-O/γ-Al₂O₃/COR monolithic catalyst is up to90%under the conditions of570oC and GHSV=20000h^–1.Compared the three different active components of the monolithiccatalysts for lean methane combustionon the condition of space velocity20000h-1and methane concentration1.0vol.%, these catalysts formethane completely oxided with desired temperature:0.1%Pd-0.25%Co/γ-Al₂O₃/COR＜0.1%Pd/γ-Al₂O₃/COR＜12%Cu-Mn--Zr-O/γ-Al₂O₃/COR。In order to reduce the energy consumption of leanmethane catalytic combustion in a reverse flow reactor,0.1%Pd-0.25%Co composition of monolithic catalyst was choosed to use for simulation andexperimental of pilot scale.Based on transient responses to step-change in feed composition, themechanism and the dynamic characteristics of the methane combustionon0.1%Pd-0.25%Co/γ-Al₂O₃/COR catalyst were reasearched. It showedthat the adsorbed CH³⁺was oxidized both by the lattice oxygen (O^2-) andgas oxygen （O₂）. And the consumed lattice oxygen (O^2-) was renewed bygas oxygen （O₂）. On the condition of lean methane and superfluousoxygen, methane was completely oxidized; the reaction products wereCO₂and H₂O only. Methane catalytic combustion on the catalystcomplied with the Mars and van-Krevelen redox mechanism. Accordingto the redox mechanism, the intrinsic kinetic models of catalyticcombustion of methane over Pd-Co/γ-Al₂O₃/COR catalysts weredeveloped with surface-reaction of CH₃⁺and gas oxygen controlassumption.The intrinsic kinetic experiments of catalytic combustion of methaneover Pd-Co/γ-Al₂O₃/COR catalysts were undertaken in an integralmicro-recator（Φ10×2mm） on the condition of atmospheric pressure,temperature350°C⁴50°C, space velocity40000h-1to50000h^-1, methanevolume concentration0.1%¹%. Before the experiments, the influence ofinternal diffusion、external diffusion and the impact of heat transfer wereeliminated. Model parameters of surface-reaction of CH₃⁺and gas oxygen control assumption were estimated with Simolex methods. Statistical testshowed that the model was highly accepted.At the background of mine ventilation air purification, andmonolithic catalysts used in the flow reactor, a one-dimensionalheterogeneous dynamic mathematical model for RFR was established, inorder to simulatie the pilot-scale device with handling capacity of1000Nm3/h CBM. The influence of switch time, working conditions ofthe adiabatic layer and feed concentration on the reactor performancewere investigated. The results showed that the switch time was animportant operating parameter for the impact of reactor performance, toolong for the switch time would cause the reactor to "turn off"; too shortswitch time would not be conducive to the reactor heat balance operation.The appropriate choice of adiabatic layer temperature can not only ensuregood reactor thermal equilibrium operation, but also to the efficient use ofenergy. In the range of inspection, reactor would be"extinct" at the lowerconcentration of methane （Vol.%≤0.5%）. Therefore, the optimization ofoperating conditions control could protect the catalytic reactor is in goodworking condition, while saving energy and reducing operating costs wasof great benefit.According to the simulation results, a pilot plant （processingcapacity of1000Nm³/h） with heat exchanger was designed and constrctedat Lu’an Group Wuyang Coal Mine. The pilot experimental results showed that, on the condition of methane concentration0.34%⁰.54%inmine ventilation air, the reactor can operate normally with appropriatepreheat and proper switch time. The methane content of emissions waslower than0.06%after reverse flow catalytic combustion.The experimental and simulation result can provide technicalsupport for the application of RFR in mine ventilation air.更多还原