低浓度甲烷在铜基催化剂上的燃烧反应及动力学特性

发布时间：2018-01-03 18:45

本文关键词：低浓度甲烷在铜基催化剂上的燃烧反应及动力学特性　出处：《重庆大学》2015年硕士论文　论文类型：学位论文

【摘要】：低浓度甲烷广泛存在于煤层气及工业废气中,当其在过渡金属催化剂上燃烧时,其燃烧反应特性及动力学分区等有待进一步深入研究;另外,低浓度甲烷在抽采时往往具有一定的含湿量,有必要弄清水蒸气对其催化燃烧特性的影响规律。因此,对低浓度甲烷在铜为代表的过渡金属催化剂上的燃烧反应及动力学特性展开研究具有重要的学术意义及工程应用价值。采用Cu/?-Al2O3颗粒作为催化剂,实验研究了低浓度甲烷在固定床微分反应器中的催化燃烧及动力学特性,分析了催化剂在反应前后的表面微观结构、催化活性及表面反应物的变化,重点研究了表面氧对甲烷催化的影响,探讨了氧的覆盖率变化对甲烷催化活性的影响以及氧覆盖率不同而引起的催化燃烧分区的迁移,通过水蒸气对氧的可逆吸附与结合,分析了水蒸气对甲烷催化活性以及相关反应动力学参数的影响规律。研究表明,甲烷在Cu金属表面的催化反应、氧化脱氢按反应物分压的差别可分为三个反应区:富氧燃烧区(Region 1,O2/CH42)、稀氧燃烧区(Region 2,0.1O2/CH42)、缺氧燃烧区(Region 3,O2/CH40.1)。富氧燃烧区(?+?)甲烷氧化脱氢反应由甲烷分压控制,与氧分压无关;稀氧燃烧区(?+?)反应速率由甲烷和氧气分压共同控制;缺氧燃烧区(?+?)反应速率由氧分压控制,与甲烷分压无关。反应级数在三个分区也明显不同:Region 1,=0.9,=0;Region2,=0.43,=0.68;Region 3,=0,=1.77;其活化能依次为:146.3 k J/mol,99.8 k J/mol,and 60.8 k J/mol。由富氧区到缺氧区,反应控速步骤由甲烷在吸附性氧上的脱氢转变为氧在活性金属团簇上的活化。另一方面,当反应气流中含有水蒸气时,甲烷催化反应将明显受到抑制。水蒸气在反应中可与催化剂表面活性氧发生吸附作用,并生成羟基。含水蒸气气氛下,甲烷转化率快速下降,氮气吹扫可使催化活性完全恢复。在富氧条件下,氧分压的变动对含水蒸气甲烷的反应速率无影响,而甲烷分压波动对反应速率影响较大。当水蒸气分压上升后,甲烷速率曲线下移,且斜率降低,甲烷反应级数降低。动力学实验表明,含水蒸气条件下,甲烷催化燃烧表观活化能迅速上升,水蒸气与甲烷竞争吸附在表面氧上,导致甲烷活化能升高,水蒸气反应级数也随之升高。低温下水蒸气的覆盖率在80%以上,而干燥气氛下的覆盖率仅为30%;随着温度的升高,含水蒸气或不含水蒸气的表面覆盖率将趋于一致。本文的研究结果对低浓度甲烷的高效转化及利用提供了理论依据。
[Abstract]:Methane with low concentration widely exists in coalbed methane and industrial waste gas. When it is burned on transition metal catalyst, its combustion reaction characteristics and kinetic zoning need to be further studied. In addition, low concentration methane often has a certain moisture content in extraction, it is necessary to understand the effect of water vapor on its catalytic combustion characteristics. It is of great academic significance and engineering value to study the combustion reaction and kinetic characteristics of low concentration methane on transition metal catalysts represented by copper. The catalytic combustion and kinetic characteristics of low concentration methane in a fixed-bed differential reactor were studied by using -Al _ 2O _ 3 particle as catalyst. The surface microstructure of the catalyst before and after the reaction was analyzed. The effect of surface oxygen on methane catalytic activity and surface reactants was studied. The effect of oxygen coverage on the catalytic activity of methane and the migration of catalytic combustion zone caused by different oxygen coverage were discussed. The reversible adsorption and binding of oxygen to water vapor were carried out. The effects of water vapor on the catalytic activity of methane and the kinetic parameters of the reaction were analyzed. The results showed that the catalytic reaction of methane on the surface of Cu metal. The oxidative dehydrogenation can be divided into three reaction regions according to the difference of reactant partial pressure: region 1 / O 2 / Ch 42 and region 2. 0.1 O _ 2 / Ch _ 42N, O _ 2 / H _ 2O _ 2 / Ch _ 40.1 O _ 2 / O _ 2 / H _ 2O _ 2 / H _ 2O _ 2 combustion zone? ? ) the oxidative dehydrogenation of methane is controlled by the partial pressure of methane, independent of the partial pressure of oxygen. ? ) the reaction rate is controlled by the partial pressure of methane and oxygen. ? ) the reaction rate is controlled by partial pressure of oxygen and independent of partial pressure of methane. Region _ 2 (0.43) ~ 0.68; Region _ 3 was 1.77; The activation energies are:: 146.3 k / mol / mol 99.8 k / mol and 60.8 k / mol / mol, from oxygen-enriched region to anoxic region. The reaction rate control step changes from the dehydrogenation of methane on adsorbed oxygen to the activation of oxygen on active metal clusters. On the other hand, when water vapor is present in the reaction flow. The catalytic reaction of methane will be inhibited obviously. Water vapor can adsorb with active oxygen species on the catalyst surface and form hydroxyl group. The conversion of methane decreases rapidly in the atmosphere of water vapor. Nitrogen blowing can completely restore the catalytic activity. Under the condition of oxygen enrichment, the change of oxygen partial pressure has no effect on the reaction rate of methane containing water vapor. The partial pressure fluctuation of methane has a great influence on the reaction rate. When the partial pressure of water vapor increases, the curve of methane rate moves down, and the slope decreases, and the order of methane reaction decreases. The apparent activation energy of methane catalytic combustion increases rapidly, and the water vapor and methane compete to adsorb on the surface oxygen, which leads to the increase of methane activation energy. The water vapor reaction order also increased. The water vapor coverage was more than 80% at low temperature, but only 30 in dry atmosphere. With the increase of temperature, the surface coverage of water vapor or non-water vapor will be consistent. The results of this paper provide a theoretical basis for the efficient conversion and utilization of low concentration methane.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TK16

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