Preparation Of Clean Fuel By Mechanochemical Method Using Metal Hydride And Metal Carbonate

The development of modern economy(chemical industry,power plant,transportation,etc.)is essentially dependent on non-renewable fossil fuels,which account for more than 85%of the world's energy consumption.Searching and developing new sources of energy that replaces fossil fuels has become the hope of sustainable development in today's world.Compared with hydrogen,metal hydrides can store large amount of hydrogen in solid form under mild conditions,with high hydrogen storage density.Therefore,light metal hydrides is considered to be an excellent solid hydrogen storage medium.Global warming caused by increased concentrations of greenhouse gases such as carbon dioxide in the atmosphere is considered to be one of the greatest environmental threats of our society.How to make efficient use of abundant carbon dioxide has attracted the close attention of researchers.The development of an effective CO2 capture process and its subsequent chemical conversion can greatly reduce the cost of energy production,and meeting global energy needs.At present,the technology of using metal oxides to absorb carbon dioxide to form carbonates has been gradually mature.Inorganic carbonates have the potential to become renewable resources for the production of fuels and chemicals,and they can be quickly replenished through the carbonation process.Therefore,we has designed traditional carbon dioxide used as carbon source was replaced by metal carbonate,and hydrogen which was difficult to transport and store used as hydrogen source was replaced by metal hydride.Further,the mixed fuel of hydrogen and methane was successfully acquired by the metal carbonate-metal hydride system under the condition of mechanochemical reaction,and the effect of metal carbonate-metal hydride system on the gas products after the reaction was explored under different research conditions,thus,the comprehensive utilization of carbon dioxide was achieved indirectly1.In the study of the mechanical reaction of metal carbonate with metal hydride,It had been found that the cheap metal carbonate can effectively induce the hydrogen desorption of MgH2 under the condition of mechanical ball milling.Meantime,the dehydrogenation efficiency of M2H2 was changed with the type of metal carbonate,rate and duration of ball milling,and the proportion of reaction mixture.It was showed that the MgCO3-MgH2(MgCO3/MgH2=1/1 mol/mol)composite had the best dehydrogenation performance after milling at a ball milling rate of 350 rpm for 12 h,and the yield of pure hydrogen without COx was 94%.This work established a new way to achieve the efficient dehydrogenation of MgH2 at room temperature.2.On the basis of the experimental results in the previous chapter,we further studied a convenient,effective and highly selective method for CO2 methanation by using alkaline earth metal carbonate and alkaline earth metal hydride,which hydrogen/methane mixed fuel without COx was synthesized by the reaction of alkaline carbonate with metal hydride induced by mechanical ball milling.In the reaction process,MgCO3/CaCO3 and MgH2/CaH2 are used as carbon source and hydrogen source which are cheap and plentiful,respectively.Mechanochemical investigations of the above room-temperature reactions indicate that some alkaline carbonates can be reduced by metal hydrides under catalyst-free conditions to selectively afford CH4 as the sole hydrocarbon product in yields of up to 73%.In addition,we also found that the content and yield of methane in the gaseous products mainly was depended on the properties of metal carbonate/hydride,the rate and duration of ball milling,and the composition of the reaction mixture.Therefore,this study established a new method for the utilization of solid carbonate and the synthesis of a mixture of hydrogen and methane free of COx.3.Finally,we systematically explored the relationship between the products formed by metal carbonate and metal hydride system and the type of metal carbonate/hydride,the proportion of reaction mixture,rate and duration of ball milling under the condition of mechanochemical reaction.The results showed that the metal carbonate and metal hydride formed by the second main group elements have the best methanation performance in the mechanical ball milling process according to the studied system,and CH4 is the only hydrocarbon product,meantime.The methane yield of CaCO3-CaH2 system increased by 16%compared to the previous study in Chapter 3.Therefore,The results was found that the metal carbonates and metal hydrides formed by the second main group elements have the best methanation performance in the mechanical ball milling process,in which the methane yield of CaCO3-CaH2(CaH2/CaCO3=4 mol/mol)system was up to 89%after milling at 550 rpm for 48 h.