【作者】 程红伟；

【导师】 丁伟中； 鲁雄刚；

【作者基本信息】 上海大学 ， 钢铁冶金， 2009， 博士

【摘要】 高效、大规模和低成本的制氢技术是实现质子交换膜燃料电池在能源和交通等领域广泛应用的前提。作为炼焦过程的副产品,焦炉煤气富含氢气且量大价廉,被认为是一种优质的制氢原料,已引起人们广泛的关注。利用催化剂对焦炉煤气中的焦油组分进行处理,是实现终端氢组分大幅度增加和科学有效利用焦炉煤气物理显热、化学能的重要过程。本文以甲苯为焦油模型化合物,在MgO-Al₂O₃复合氧化物为载体的Ni基催化剂上开展焦油催化转化研究。在常压、富氢和低水碳比条件下,着重考察了催化剂焙烧温度、化学组成、助剂和评价条件对催化剂加氢和蒸汽重整反应性能的影响,开发了一些具有应用前景的催化剂体系。同时,对焦炉煤气蒸汽重整和部分氧化重整制氢过程进行了初步探索,得到了一些有意义的结果。焙烧温度对NiO/30%Al₂O₃-MgO催化剂的催化活性有较大的影响。BET、XRD、H₂-TPR和TEM表征结果显示,随着焙烧温度的升高,催化剂的比表面积急剧下降,（Ni,Mg）Al₂O₄尖晶石相逐渐增多,金属与载体之间的相互作用逐渐增强。但是,当焙烧温度高于950℃时,催化剂上有游离态或与载体相互作用较弱的NiO出现。在较低和较高温度下焙烧的催化剂还原后金属颗粒容易聚集。催化剂活性评价实验结果表明,850℃焙烧的NiO/30%Al₂O₃-MgO催化剂具有最好的活性和稳定性。在NiO/x%Al₂O₃-MgO催化剂中,当载体中Al₂O₃的含量为30%时,载体的前体可以形成结构完整、晶相单一的典型类水滑石结构。前体具有类水滑石结构的催化剂比表面积较大,催化活性好。H₂-TPR、TG-TPO和TG-TPR表征结果显示,添加CeO₂、La₂O₃和ZrO₂能增强金属与载体之间的相互作用,使Ni/Mg₃（Al）O催化剂的甲苯加氢催化活性和抗积碳性能明显得到改善。在采用共沉淀法制备的双金属催化剂Ni_0.25-Me_0.25/Mg_2.5（Al）O（Me=Co, Fe, Cu, Zn, Mn）中,850℃焙烧的Ni_0.25Co_0.25/Mg_2.5（Al）O催化剂比表面积较大,形成了尖晶石和固溶体相,且活性金属与载体之间的相互作用较强,还原后活性金属颗粒小、且均匀分布,具有优异的活性和稳定性。在常压、800℃、水碳比0.7和体积空速12,000 mL/（g·h）的条件下,甲苯被完全转化为CH₄和CO,且具有较好的稳定性。活性评价实验后,SEM和TEM表征结果显示催化剂上有少量须状碳生成,但绝大部分的积碳可以被H₂消除,反应过程中催化剂上的积碳是一个可逆的过程。少量贵金属Pd引入Ni/Mg₃（Al）O后,在甲苯的加氢和蒸汽重整反应中显现出优良的催化性能,在800 oC、空速为3,000 mL/（g·h）、水碳比为0.42的条件下,0.5%Pd-12%Ni催化剂对甲苯的转化率、CH₄和CO的产率分别为94%、53%和41%。采用尿素分解均匀共沉淀法制备的Ni_x/Mg_2.33-x（Al）O催化剂在焦炉煤气蒸汽重整制氢过程中具有优良的催化活性。H₂-TPR、SEM和TEM表征结果显示,当催化剂中的Ni含量较低时,金属与载体之间的相互作用较强,活性金属颗粒细小且分布均匀,并具有较好的抗积碳能力。反应温度对催化剂的反应性能影响显著,当反应温度高于800 oC时,实验结果与热力学计算值能较好的吻合。较高的水碳比有利于甲苯和CH4的转化,当水碳比为1.7时,甲苯和CH4被完全转化为H₂和CO,反应后出口气中H₂的量是实验前反应气中的4倍以上。同时,NiO/30%Al₂O₃-MgO催化剂具有较好的耐硫性能,在焦炉煤气中H₂S含量为500 ppm的条件下仍具有较好的活性。最后,在BaCo_0.7Fe₉0.2)Nb_0.1O_3-δ（BCFNO）混合导体透氧膜反应器中对焦炉煤气部分氧化重整制氢进行了初步探索。实验结果表明,膜片的透氧量随着空气流量的增加而增大,但当空气流量超过300 mL/min后继续增大时,其对膜片透氧量的影响较小。反应温度对膜反应器性能的影响显著,较高的温度可以获得较大的透氧量。催化剂对膜片的透氧量有很大的影响,以类水滑石结构为前体的Ni/Mg（Al）O催化剂具有优异的活性和抗积碳性能。催化剂经稀土氧化物改性后,活性金属颗粒较小且分布更加弥散,可以显著提高催化剂的活性和抗积碳能力。在875℃和采用La₂O₃改性的Ni/Mg（Al）O催化剂时,BCFNO膜片的透氧量高达15.1 mL/cm²/min,此时,甲苯、CH₄和CO₂的转化率分别为100%、88.5%和92.7%,而H₂和CO的产率则分别为86.8%和87.2%。同时,出口气中H₂的量是实验前反应气体中的2倍以上。实验后,膜片渗透侧表面的钙钛矿结构遭到损坏,但被破坏的厚度较小,不影响膜反应器的安全运行。更多还原

【Abstract】 High efficiency, large scale, and low-cost technologies for producing hydrogen are urgently demanded to meet the needs of the development of proton exchange membrane fuel cells as the power source for power, transportation and other applications. As a by-product generated in the process of producing coke from coal, coke oven gas （COG） is gaining increasing attention as one of the most attractive sources of hydrogen production. The treatment of tar in COG over catalyst is the key issue for the hydrogen amplification and rational utilization of energy. This thesis investigated the catalytic conversion of toluene as a model tar compound over nickel-based catalysts with the mixed MgO-Al₂O₃ as the support. Under the conditions of atmospheric pressure, hydrogen-rich atmosphere and low steam/carbon molar ratio, the influences of calcination temperature, compositions, promoters and the evaluation condition on the catalyst performance of hydrogenation and steam reforming were systematically studied. Also, the hydrogen production by steam reforming and partial oxidation reforming of COG were explored preliminarily. Based on these experimental results, several conclusions were drawn from the investigations.The catalytic performance of the NiO/30%Al₂O₃-MgO catalyst was sensitive to calcination temperature. The characterization results of BET, XRD, H₂-TPR and TEM techniques indicated that the BET surface area dramatically decreased, the （Ni,Mg）Al₂O₄ spinel phase and the interaction between the metals and carrier both increased with increasing the calcination temperature. However, free NiO and those of weak interaction with the carrier appeared when the calcination temperature was higher than 950 oC; and the metals particles agglomerated obviously when the catalyst was calcined at a lower or higher temperature. NiO/30%Al₂O₃-MgO calcined at 850 oC had the best activity and stability. When the content of Al₂O₃ was 30% in the NiO/x%Al₂O₃-MgO catalysts, the precursor of the carrier had the typical hydrotalcite structure and the catalyst showed higher specific surface area and good activity. The addition of CeO₂, La₂O₃ and ZrO₂ enhanced the interaction between the metals and carrier and improved the performance of toluene hydrogenation and resistance to carbon formation.The Ni_0.25-Me_0.25/Mg_2.5（Al）O（Me=Co, Fe, Cu, Zn, Mn） bimetallic catalysts were synthesized with the coprecipitation method. The Ni_0.25Co_0.25/Mg_2.5（Al）O catalyst calcined at 850 oC showed higher specific surface area, stronger interaction between metals and carrier due to the formation of spinel and solid solution phases as well as smaller particulates and highly homogeneous dispersion of active metals. A toluene conversion of 100% had been achieved for 35 h over the catalyst at 800 oC under atmospheric pressure and GHSV of 12,000 mL/（g·h） with a steam/carbon molar ratio of 0.7. After the activity test, a small amount of whisker carbon was observed on the used catalyst, and most of them could be removed in the hydrogen-rich atmosphere, indicting that the carbon deposition on catalysts was a reversible process. Furthermore, with the addition of a small amount of noble metals Pd, the Ni/Mg₃（Al）O catalyst presented excellent catalytic performance for the hydrogenation and steam reforming of toluene. A toluene conversion of 94%, a CH₄ yield of 53% and a CO yield of 41% had been achieved over the 0.5%Pd-12%Ni catalyst at 800 oC and GHSV of 3,000 mL/（g·h） with a steam/carbon molar ratio of 0.42.The Ni_x/Mg_2.33-x（Al）O catalysts were prepared by a homogeneous precipitation method using urea hydrolysis and had good activity in the process of steam reforming of COG. H₂-TPR, SEM and TEM results showed that the catalyst with low Ni content had higher specific surface area, stronger interaction between metals and carrier, and highly homogeneous dispersion of active metals. Reaction temperature had obvious influence on the performance of the catalysts. And when the temperature was higher than 800 oC, the experimental results agreed well with the calculated results. The increase of the steam/carbon molar ratio promoted the conversion of toluene and CH4 to H₂ and CO. The toluene and CH4 could completely be converted to H₂ and CO in the catalytic reforming of COG, and H₂ in the reaction effluent gas was about 4 times more than that in original COG when steam/carbon molar ratio was 1.7. Moreover, the NiO/30%Al₂O₃-MgO catalyst showed excellent sulfur resistant character so that it still had good activity when the H₂S content in the COG was 500 ppm.Hydrogen production by partial oxidation reforming of COG in BaCo_0.7Fe_0.2Nb_0.1O_3-δ（BCFNO） membrane reactor was also investigated in this thesis. The experimental results showed that the increase of air flow rate was beneficial to improve the oxygen permeation flux. However, it had little influence on the oxygen permeation flux when the air flow rate was more than 300 mL/min. The oxygen permeation flux increased with the increase of the reaction temperature. And the oxygen permeation flux was sensitive to the catalysts. The Ni/Mg（Al）O catalyst with the precursor of hydrotalcite structure had good activity and resistance to coking. The rare earth added to the Ni/Mg（Al）O catalysts could improve the activity, resistance to coking, and dispersion of active metals. At optimized reaction conditions, the dense oxygen permeable membrane had an oxygen permeation flux around 15.1 mL/cm²/min and a H₂ yield of 86.8% and a CO yield of 87.2% had been achieved over the La₂O₃ modified Ni/Mg（Al）O catalyst at 875°C. And the conversions of toluene, CH₄ and CO₂ were 100%, 88.5% and 92.7%, respectively. The amount of H₂ in the reaction effluent gas was about 2 times more than that of original H₂ in the reactant gas. The permeation sides of the used membrane were destroyed after the experiments, but the structure changes were only up to several micrometers, which had no effect on the safety work of the membrane reactor.更多还原