基于NiFe_2O_4载氧体的化学链蒸汽重整制氢实验研究

Performance of NiFe_2O_4 oxygen carrier in hydrogen production by chemical looping steam reforming

采用并流共沉淀法合成了具有尖晶石结构的NiFe_2O_4载氧体,研究了其在化学链蒸汽重整制氢过程中的氧化-还原反应性能。并利用X射线衍射(XRD)、拉曼光谱分析(Raman)、扫描电镜(SEM)、H_2程序升温还原(H_2-TPR)和热重分析对NiFe_2O_4载氧体进行表征和分析。结果表明,还原态载氧体在水蒸气气氛中可恢复部分晶格氧,热重实验进一步发现合成载氧体的反应活性显著高于商业载氧体,且其在约14 h的连续实验中展现了优异的循环反应性能。固定床实验表明,载氧体能显著促进生物质挥发分中大分子中间热解产物转化为小分子气体,特别是初次焦油的催化裂解,从而明显改善气体品质。由于Fe-Ni协同效应,经CO还原后的载氧体具有较强的制氢能力,每克还原态载氧体可产生232 mL纯氢。由于热力学限制使还原态载氧体在水蒸气气氛中只能恢复部分晶格氧至Ni、Fe3O4和Ni1-xFe2+xO4的三元混合物相。

NiFe2O4 oxygen carrier with spinel structure is synthesized by co-current precipitation method,its oxidation-reduction performance in the process of hydrogen production through chemical looping steam reforming is investigated in detail and its characterizations are performed by means of X-ray diffraction（XRD）,Raman spectroscopy（Raman）,scanning electron microscopy（SEM）,H2-TPR and thermogravimetric experiments.It is found that the oxygen carrier in the reduction state can recover part of lattice oxygen under steam atmosphere.The thermogravimetric experiment further reveals that the reactivity of the synthetized oxygen carrier is significantly higher than that of commercial oxygen carrier.Additionally,the synthetized oxygen carrier exhibits excellent cycling performance in around 14 h of continuous experiments.The fixed-bed experiments illustrate that oxygen carrier can significantly promote the intermediate pyrolysis products of macromolecules in biomass volatiles to change into small molecular gases,especially the catalytic cracking of primary tars,thereby evidently improving gas quality. Due to the present of Fe-Ni synergistic effect,the oxygen carrier reduced by CO owns a strong capacity of hydrogen production. One gram of oxygen carrier in the reduction state can produce 232 mL of pure hydrogen.The oxygen carrier in the reduction state can only recover part of lattice oxygen to Ni,Fe3O4,and Ni1-xFe2＋xO4 ternary mixture phase under steam atmosphere because of the thermodynamic limitations.