Chemical looping and dry reforming of methane for hydrogen and syngas production

Abstract

A commercial steam reforming of methane is an energy-intensive process with the emission of a large amount of carbon dioxide $(CO_2)$, because it requires the endothermic heat and complex downstream processes to produce the high-purity hydrogen $(H_2)$. To overcome the aforementioned obstacles, this work investigated catalytic methane decomposition, dry reforming, and chemical looping processes as energy-saving and environmental-friendly substitutes for the commercial steam reforming process. In chapter 2, the high-purity $H_2$ was produced on the $CO_2$-derived nickel-carbon core-shell catalyst through the catalytic methane decomposition and the spent catalyst was regenerated by $CO_2$ with the production of the high-purity carbon monoxide (CO). The catalytic activity of the core-shell catalyst was maintained for 15 cycles, providing a potential of enabling the cyclic process. In chapter 3, the long-term stability of the dry reforming reaction was achieved with a minimized carbon deposit on the nickel confined mesoporous silica catalyst synthesized via a PEI-aided route. In chapter 4 and 5, the advanced chemical looping process was proposed by combining the partial oxidation and the dry reforming reactions. Compared with the general chemical looping process, the carbon deposition of the proposed process was dramatically reduced by using $CO_2$ as a co-feed with $CH_4$. Due to the exothermic heat from the oxidation reaction, the net heat duty of the chemical looping process was lower than that of the dry reforming process. To substantiate the rational of the advanced chemical looping process, Ni and $CeO_2$-entrapped $Fe_2O_3/Al_2O_3$ oxygen carriers were synthesized by the sol-gel method. By utilizing these economic oxygen carriers, the high-purity syngas with the $H_2/CO$ ratio of 2 was produced. Based on the synthesized novel catalysts and oxygen carriers, this work suggested the prospective $H_2$ and syngas production processes, which can be deployable solutions to substitute the commercial steam reforming.