碳化硅负载镍基催化剂高温甲烷化性能研究

发布时间：2018-04-24 20:25

本文选题：镍催化剂 + 碳化硅　；参考：《太原理工大学》2017年硕士论文

【摘要】：能源与环境是人类社会可持续发展所面临的两大挑战,长期以煤为主的能源消费结构导致我国的环境问题日益突出。发展煤制天然气可以实现煤炭的清洁高效利用,缓解国内市场天然气供需矛盾。煤制天然气的核心是甲烷化反应器的设计及高效催化剂的研发。CO加氢甲烷化反应属于强放热过程,会导致催化剂的活性组份烧结和产生积碳,严重影响工业装置的安全稳定运行。SiC具有良好的热稳定性和化学惰性,而且导热性能很强,有助于反应放热的及时传导,抑制催化剂床层“热点”的形成。本论文采用微波辅助碳热还原法制备SiC载体,负载金属镍后用于CO甲烷化反应,与γ-Al_2O_3载体进行了比较研究;此外,考察了添加Ce助剂对于改善Ni/SiC催化剂的抗积碳和抗烧结性能影响,主要研究结果总结如下:(1)采用纳米二氧化硅和石墨作为原料,通过微波辅助碳热还原法制备碳化硅粉体,优化的制备条件为:Si/C原子比1:1.2,微波输出功率2.5 kW,加热温度为1100~1400°C,恒温时间30 min;制得的碳化硅粉体的晶相为3C-SiC,比表面积为8.8 m~2g~(-1);(2)采用SiC和γ-Al_2O_3负载金属镍后进行CO甲烷化反应性能评价,结果显示,10Ni/Al_2O_3的低温反应活性较高,CO转化率在320°C时达到95.6%,到400°C时与10Ni/Si C接近;10Ni/SiC在500~600°C高温段表现出明显优势,CO转化率和CH_4选择性分别为94.9%和82.3%,而10Ni/Al_2O_3上的CO转化率和CH_4选择性为91.9%和80.2%;(3)在10Ni/Si C中添加7 wt.%的CeO_2助剂催化性能达到最佳。选取10Ni/Al_2O_3、10Ni/SiC和7Ce-10Ni/SiC在600°C进行CO甲烷化反应活性评价,当空速由15 000 mL g-1 h-1增加至60 000 mL g-1 h-1,10Ni/Al_2O_3在前20 h活性保持不变,随后CO转化率和CH_4选择性逐渐降低,反应进行至62 h时由于严重积碳导致反应器堵塞被迫终止;当10Ni/SiC反应进行到100h后,反应器前压略微升高,达到1.2 MPa,反应活性及选择性略微下降;7Ce-10Ni/SiC在100 h的反应过程中表现出极高的稳定性,CO转化率和CH_4选择性均保持同一水平;(4)对10Ni/SiC和10Ni/Al_2O_3的表征结果显示,10Ni/SiC上Ni的晶粒尺寸更小、分散度更高,因此可以提供更多的反应活性位点;对反应后催化剂的表征结果显示,10Ni/Al_2O_3、10Ni/SiC和7Ce-10Ni/SiC上Ni晶粒出现了不同的增长,积碳速率分别为0.01935 g/h、0.00528 g/h、0.00465 g/h,10Ni/Al_2O_3上的积碳量最大,积碳以石墨碳或类石墨化碳居多,并且形成较多碳纤维,从而导致Ni被剥离的现象;分析认为,SiC的表面惰性和良好的导热性能可以将反应放热及时移出,因而表现出良好的抗烧结和抗积碳性能;(5)对7Ce-10Ni/SiC的表征结果显示,CeO_2均匀分散在Ni颗粒周围,有效阻止了Ni晶粒的团聚,增加了Ni分散度,而且增强了金属与载体之间的作用力;此外,Ce3+/Ce4+氧化还原电子对增加了Ni的电子云密度,促进了CO的解离,因此加快了甲烷化反应速率。
[Abstract]:Energy and environment are two major challenges faced by the sustainable development of human society. The energy consumption structure, which is dominated by coal for a long time, has caused the environmental problems of our country to become increasingly prominent. The clean and efficient utilization of coal can be realized by developing coal-made natural gas, and the contradiction between supply and demand of natural gas in domestic market can be alleviated. The core of coal to produce natural gas is the design of methanation reactor and the development of high efficient catalyst. The methanation of CO hydrogenation is a strong exothermic process, which will lead to the sintering of the active component of the catalyst and the formation of carbon. Sic has good thermal stability and chemical inertia, and has strong thermal conductivity, which is helpful to the timely conduction of reaction exothermic and restrain the formation of "hot spot" in catalyst bed. In this thesis, SiC carrier was prepared by microwave-assisted carbothermal reduction method, and then loaded with nickel metal for CO methanation reaction. The results were compared with 纬 -Al _ 2O _ 3 carrier. The effect of ce additive on carbon deposition and sintering resistance of Ni/SiC catalyst was investigated. The main results were summarized as follows: (1) Silicon carbide powder was prepared by microwave-assisted carbothermal reduction using nano-silica and graphite as raw materials. The optimized preparation conditions are as follows: 1: 1.2, microwave output power 2.5 kW, heating temperature 1100,1400 掳C, constant temperature time 30 min, the crystalline phase of the prepared silicon carbide powder is 3C-SiC, the specific surface area is 8.8 m ~ (2) g / C ~ (-1), the methanation reaction performance is evaluated by SiC and 纬 -Al _ 2O _ 3 loaded nickel metal. The results showed that 10Ni / Al _ 2O _ 3 had higher activity at low temperature and CO conversion reached 95.6C at 320 掳C, and close to 10Ni- / sic at 400 掳C showed obvious superior CO conversion and CH_4 selectivity of 94.9% and 82.3% for 10Ni/Al_2O_3 at 500-600 掳C, respectively, while the CO conversion on 10Ni/Al_2O_3 and CH_4 were 82.3%. The selectivity is 91.9% and 80.2% respectively. The best catalytic performance is achieved by adding 7wt.% CeO_2 promoter to 10Ni/Si C. 10Ni- / Al2O3Ni- / sic and 7Ce-10Ni/SiC were selected to evaluate the methanation activity of CO at 600 掳C. The activity of CO methanation was increased from 15 000 mL g -1 h-1 to 60 000 mL g-1 h-110Ni- Al2O3 at 600 掳C. the activity of CO conversion and CH_4 selectivity decreased gradually in the first 20 h. The reactor blockage was forced to terminate at 62 h due to serious carbon deposition, and the pre-reactor pressure increased slightly after the 10Ni/SiC reaction reached 100h. Up to 1.2 MPa, the activity and selectivity of 7Ce-10Ni- / sic decreased slightly during the 100h reaction. During the 100h reaction, the CO conversion and CH_4 selectivity remained at the same level. The characterization of 10Ni/SiC and 10Ni/Al_2O_3 showed that the grain size of Ni on 10Ni / sic was smaller. The results of the characterization of the catalyst after the reaction show that the 10Ni- / Al2O3Ni- / sic and the Ni grains on 7Ce-10Ni/SiC have different growth, and the carbon deposition rate is 0.00528g / h 0.00465g / h 0.00465g / h 0.00465g / h 0.00465g / h ~ 0.00465g / h ~ 0.00465g / h ~ 0.00465g / h ~ 0.00465g / h ~ 0.00465g / h ~ 0.00465g / h ~ 0.00465g / h ~ 0.00465g / h ~ 0.00465g / h ~ 0.00465g The carbon deposition is mainly graphite carbon or graphitized carbon, and more carbon fibers are formed, which results in the exfoliation of Ni. It is considered that the surface inertia and good thermal conductivity of sic can remove the reaction exothermic heat in time. The results of 7Ce-10Ni/SiC characterization show that CeO-2 is uniformly dispersed around Ni particles, which effectively prevents the agglomeration of Ni grains, increases the dispersion of Ni, and enhances the interaction force between metal and support. In addition, ce _ 3 / ce _ 4 redox electron pair increased the electron cloud density of Ni, promoted the dissociation of CO, and accelerated the rate of methanation reaction.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36

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