Study On Hydrogen Production From Chemical Looping Steam Methane Reforming In Micro Reactor

Hydrogen energy is the most promising energy source and energy carrier,and the development of fuel cells provides a new direction for the efficient use of hydrogen energy,but the source of hydrogen in hydrogen fuel cells limits the development and application of fuel cells.Micro reactors have the characteristics of large specific surface area,high energy density,good heat and mass transfer,etc.The use of micro reactors for hydrogen production provides new ideas to solve the above problems.Chemical looping steam methane reforming（CL-SMR）allows the simultaneous production of high quality syngas and pure hydrogen without the need for additional energy-intensive separation units,with the advantage of low energy consumption and no pollution.Highly active oxygen carriers and reaction process intensification are the two main keys for CL-SMR implementation.In this thesis,a highly selective calcium and iron oxygen carrier combined with a tiny reactor with high specific surface area and high energy density was used to investigate the CL-SMR hydrogen production process as follows.Firstly,the reaction characteristics of Ca₂Fe₂O₅ oxygen carrier in the Chemical looping steam reforming of methane were studied in this paper.The optimal experimental conditions were determined by comparing different temperatures and flow rates.Under the conditions of reaction temperature of 850℃and total gas flow rate of50 ml/min,the average methane conversion of Ca₂Fe₂O₅ oxygen carrier was 36.33%,CO selectivity was 78.79%,syngas yield was 7.81 mmol/g,hydrogen yield during hydrolysis was 3.72 mmol/g.Ten redox cycling experiments showed the cycling performance of this oxygen carrier,demonstrating the potential of Ca₂Fe₂O₅ oxygen carrier in chemical looping steam methane reforming for hydrogen production.Secondly,a series of Ca₂Fe_2-xAl_xO₅（x=0,0.2,0.4,0.6,0.8）oxygen carriers were prepared by aluminum doping in order to improve the reactivity and stability of Ca₂Fe₂O₅.It was found that the doping of Al helps Ca₂Fe₂O₅ oxygen carriers to form more oxygen vacancies and have good redox properties.Among them,Ca₂Fe_1.6Al_0.4O₅oxygen carrier has the best performance,At 850°C,the average CH₄ conversion was43.38%,the CO selectivity was 89.01%,the syngas yield was 8.89 mmol/g,and the hydrogen yield was 4.64 mmol/g,compared with the oxygen carrier without Al doping,the improvements are 19.41%,8.18%,13.83%and 24.73%,respectively.In addition,the generation of Ca₃Al₂O₆ ensured the structural stability of the oxygen carriers during the oxygen gain and loss process,and the reaction performance was stable after 10 redox cycles without obvious sintering and agglomeration.Therefore,the aluminum-doped Ca₂Fe_2-xAl_xO₅ oxygen carrier is a very promising oxygen carrier.Finally,chemical looping steam methane reforming experiments based on different sizes of micro reactors for Ca₂Fe_1.6Al_0.4O₅ oxygen carriers were conducted.The reduction of the tube diameter and the same mass of oxygen carriers had a higher packing height,which increased the specific surface area,enhanced the contact effect between reactants,the methane conversion reached 53.87%in 12 minutes,which was significantly improved,and the enhancement of chemical looping steam methane reforming process by micro reactor was investigated.In addition,the effects of different flow field structures on fluid flow were investigated,and a micro reactor integration device suitable for chemical looping steam methane reforming hydrogen production process was designed to provide basic theoretical information for subsequent research on chemical looping steam methane reforming for hydrogen production in tiny reactors.