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焦炉煤气中CO和CO2协同低温甲烷化催化剂的制备及研究
Alternative TitleNovel Catalysts for Low-temperature Co-methanation of CO and CO2 in Coke Oven Gas
RAUF RAZZAQ
Thesis Advisor张锁江
2014-05
Degree Grantor中国科学院大学
Degree Name博士
Degree Discipline化学工艺
KeywordCo和 Co2甲烷化,焦炉气,镍催化剂,氮化钴催化剂
Abstract

焦炉气是在炼焦过程中产生的副产品,主要成分是氢气和甲烷,还有一氧化碳、二氧化碳、烯烃等。每年中国焦炉气的产量约1200亿Nm3,其利用率约为55%,焦炉气通过甲烷化反应,将焦炉气中CO、CO2转化为甲烷,再通过变压吸附生产天然气具有较好经济价值和社会意义。甲烷化是强放热反应,反应器局部温升可以造成碳烃裂解而结碳,还可能容易使甲烷化催化剂烧结而失活。针对焦炉气甲烷化的工艺特点,本研究主要开发适于焦炉气中低温甲烷化催化剂。 本研究对于富氢焦炉气的甲烷化过程进行系统的分析和研究,开发了适于中低温催化甲烷化的三类催化剂,考察了催化剂活性组分、载体、焙烧氛围等因素的影响,发现新型的氮化钴催化剂在低温下具有较高的转化率和选择性。 研究开发了一种双金属的Ni-Co/CexZr1-xO2催化剂,考察了不同制备方法、焙烧温度、活性组分含量对于甲烷化过程的影响,通过固定床反应器的催化活性评价(反应温度:150-450 °C,压力2.0 MPa,空速5,000-15,000 h-1)。通过不同的表征手段如:BET、ICP-EDX、XRD、SEM、TEM、XPS、拉曼等对反应前后的催化剂进行了表征分析,发现催化剂由于铈的氧空位,导致形成了更多的活性中心,从而增强了碳氧化物的吸附能力,促进了甲烷化反应,从而提高了甲烷化的催化性能。同时研究发现,还原后的金属活性组分相比于氧化物组分有利于甲烷化的反应。 进而研究发现不同的还原氛围将极大的影响催化剂的活性,一种新型的NH3还原方法相比于H2还原方法获得了更高活性的Ni/Ce0.12Zr0.88O2甲烷化催化剂。SEM、TEM的表征发现NH3还原氛围更易获得高分散性、颗粒更小的镍活性组分催化剂。 为了进一步降低甲烷化温度,进而减缓催化剂的积碳现象,合成了新型氮化钴催化剂,通过三氧化铝的负载增加比表面积。活性评价发现,温度降低100度的情况下该催化剂能达到与Ni-Co/CexZr1-xO2催化剂活性相当的效果,其甲烷化催化活性和贵金属催化剂相当,分析发现N元素的添加增加了催化剂的表面酸性,提高了催化剂的抗积碳性能,也促进了一氧化碳的解离反应。寿命评价发现其稳定性具有进一步放大的前景。 ;Methanation of carbon oxides (CO and/or CO2, COx) is of great industrial interest, as a novel process for producing synthetic natural gas (SNG) with high calorific value and extensive industrial and commercial use. The coke oven gas (COG) is a by-product from coal coking process at high temperature. The amplification of the CH4 present in COG through the catalytic hydrogenation of CO and CO2 is regarded as a simple and highly efficient way of producing SNG. Herein, we present low-temperature highly active and stable COG methanation catalysts with excellent CH4 selectivity. This thesis summarizes the methods and findings of developing novel catalytic systems, characterization, COG methanation activity, and correlation of catalytic activities to their synthesis parameters and physiochemical properties. The work explores the use of mixed-oxide support materials as active carriers for dispersing transition metals. Further, the type of reducing gas was studied with an emphasis on obtaining high active metal reducibility and dispersion. Moreover, we also proposed supported metal nitrides as novel and highly efficient COG methanation catalysts. Different catalyst characterization techniques were adopted including: N2 sorption studies, elemental analysis, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, temperature programmed studies, X-ray photoelectron spectroscopy, chemisorption and Raman spectroscopic analysis. The COG methanation activity tests were performed in a fixed-bed reactor at temperature (150-450 °C), pressure (2.0 MPa) and gas hourly space velocity (5,000-15,000 h-1). Bi-metallic Ni-Co/CexZr1-xO2 catalysts were developed with highly improved catalytic performance with the formation of oxygen vacancies and their role in COx methanation reaction. It was found that oxygen vacancies generated due to reduction in cerium oxidation state leads to the formation of more active centers resulting in high COx adsorption capacity. It was also found that a reduced metal surface was highly favorable for superior methanation activity. Further, we introduced a new NH3 reduction method for the preparation of highly active Ni-Ce0.12Zr0.88O2 catalysts. The NH3-reduced method lead to the formation of highly reduced and finely dispersed Ni species as compared to H2-reduced method. Currently, most industrial methanation catalysts are alumina supported nickel-based catalysts which are very vulnerable to metal sintering and carbon-deposition. Highly active and stable alumina supported cobalt nitride (Co4N) catalysts are thus introduced as novel catalytic materials with methanation activity comparable to that of noble metal catalysts. The effect of support material towards metal particle size and dispersion was also studied. Co4N exhibits significantly enhanced COx methanation activity with respect to the reduced Co. The addition of N to Co increases the surface basicity of the catalyst resulting in excellent carbon resistance, while promoting the CO dissociation reaction. Moreover, the metal sintering was also less significant owing to its strong metal-support interaction. 

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/26950
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
RAUF RAZZAQ. 焦炉煤气中CO和CO2协同低温甲烷化催化剂的制备及研究[D]. 中国科学院大学,2014.
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