Study On The Process For Production Of Hydrogen From Methane Decomposition On An Aluminum Supported Metal Catalyst In A Fluidized Bed Reactor

It has been understood that production of hydrogen from fossil and carbonaceous fuels with reduced CO2 emission to the atmosphere is key to the production of hydrogen-rich fuels for mitigating the CO2 greenhouse gas climate change problem. The intense interest in fuel cell technology stems from the fact that fuel cells are environmentally benign and extremely efficient. The stringent COx-free hydrogen requirement for the current low temperature fuel cells has motivated the development of COx-free hydrogen production alternatives to the conventional hydrogen production technologies. It is therefore, desirable to explore other avenues for hydrogen production with specific applications for fossil fuel decarbonization and current fuel cells. Methane catalytic decomposition significantly simplifies the conventional hydrogen production process and makes it particularly attractive for fuel cell application.In the present paper, we report the results of catalytic behaviour of 25Ni/Cu-Al2O3 and 75Ni/Cu-Al2O3 catalysts and characterization of formed carbon by XRD and TEM over them during the catalytic decomposition of methane and catalyst regeneration. CO-free H2 was produced intermittently by methane decomposition and the formed carbon combustion in a fluidized bed reactor in cyclic manner. The process involved two reactions: first, catalytic decomposition of methane to H2 and carbon (deposited on the catalyst), and second, gasification of the carbon deposited on the catalyst by air to CO2. The two reactions were carried out separately in cyclic manner by switching a methane-containing feed and a air-containing feed at a predecided interval of time. 25Ni/Cu-Al2O3 catalyst behaves higher stability than 75Ni/Cu-Al2O3 catalyst in the cycle operation. And it reduces with operation temperature increase. The process shows best performance at an optimum value (5min) of the feed switchover time.With the thorough progress of research and application of carbon nanotubes, the Simultaneous process for hydrogen and carbon nanotubes got extensive attention in the world. But some troubles of the operation in a fixed bed reactor such as volume expansion, catalyst loading and carbon product unloading, etc., baffled the progress of the process. So the process for hydrogen and carbon nanotubes from methane decomposition in a fluidized bed reactor was investigated. The effects of some factors such as catalyst composition, reaction temperature, and initial methane concentration on hydrogen yield, hydrogen content in product, carbon nanotube composition and configuration were studied. It was discovered that hydrogen content in product and carbon yield reached ~55%, 9mgC/mgcat respectively at 600oC over 3Ni1Al catalyst. When the catalyst was deposited by metal copper, the reactive temperature range of the catalyst ascended. The corresponding values arrived at 63%and 8mgC/mgcat at 650oC respectively. Carbon formed on catalysts was characterized by TPO, Raman, TEM (HRTEM) and pore measurement. It was found that the quantitative result from TPO was basically consistent to the experimental data. Therefore the quantitative characterization of carbon by TPO may be considered feasible.In fact, reactor type would affect the process for hydrogen production from methane decomposition. So in the next work the processes from methane decomposition in fluidized and fixed bed reactors were compared. Hydrogen production was investigated over 75Ni10Cu15Al, 2Co1Al (atomic ratio) catalysts in two types of reactors respectively. Pure methane was used as reaction gas. It was displayed that the performance in a fluidized bed was obviously higher than that in a fixed bed. The carbon formed at 600oC and 700oC respectively was characterized by TEM. It appeared that the size of metal particle increased with reaction temperature growth. This means that sinter between metal particles had taken place. But at the same reaction temperature it in a fixed bed was bigger than that in a fluidized bed and size distribution was wider. It may be considered that fluidized bed reactor was beneficial to prevent the sinter. The analysis of catalyst deactivation reasons indicated that throwback could prolong the lifetime of catalysts. It may be concluded that the main reason of high performance in a fluidized bed was throwback and relative prevention of sinter between metal particles.The effect of reaction conditions on hydrogen production from methane decomposition and its kinetics were investigated. In the same way, 15Ni3Cu2Al(atomic ratio)was used as the catalyst for methane decomposition. Diluted methane was used as reaction regent, reaction temperature was controlled between 500-680oC and gas volume was selected between 250-360 ml/min. fluidization may be maintained for some trivial. When the initial methane concentration was 48% and reaction temperature was 600oC, hydrogen content in product gas reached 42% and also maintained for over 30 minutes. According to the kinetic experimental data, kinetic models for growing and stability period of carbon growth were posted respectively. The error of theoretical values was less than 2%.Fluidization was affected by the size of catalyst particles and their distribution and the change of methane conversion took place. In order to make the mathematical relationship between them, the quantitative characterization of particle distribution must be made. But it was usually characterized by distribution diagram. In the text two distribution variables were used to characterize the distribution, distribution variable 1 that means width degree of particle distribution and distribution variable 2 that means proportion of particle weight in the secondary distribution region to that in the main distribution region. And then regression analysis was done. Reaction conditions were 15Ni3Cu2Al(atomic ratio)catalyst, reaction temperature 550 oC and gas volume 340 ml/min. Two regression schemes were selected: one in which particle size and distribution factor 1 were choosed as independent variables and another one in which particle size, distribution factor 1 and distribution factor 2 were choosed as independent variables. Regressive results indicated that reliability and veracity were satisfactory. But in the next step for their optimization design, it was found that the last situation was more accorded to the experiment than the first one. This implied that the effect of particle distribution on fluidization was complicated. The above results will be of instructional meaning to the next implication.