Applications of porous inorganic-organic hybrid solid in membrane reactors and catalysis for hydrogen production.
Thesis DisciplineChemical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Hydrogen based energy system is considered to be a promising solution to address the energy shortage and environment pollution issues. Due to the increasing demand of hydrogen, different processes have been developed to produce this useful molecule in an efficient and economical way, such as the water gas shift reaction (WGSR) which is one of the important approaches in industry at present. In the meantime, the by-product CO2 generated in WGSR must be separated to produce the high purity product H2 and to reduce the greenhouse gas emission. Membrane gas separation technology provides an environmental friendly and low cost solution to separate the mixture products in WGSR. Derived from the membrane technology, membrane reactor (MR) is an integrated unit by combining the heterogeneous catalysis and membrane separation process, which owns the instinct advantages of simplified facilities and improved productivity in many applications. In this work, the objective is to develop a porous hybrid solid membrane reactor system for hydrogen production and separation in WGSR. Herein, zeolitic imidazolate framework-8 (ZIF-8) was firstly screened out from various proposed porous materials as the candidate membrane material of the MR for WGSR, since this new emerging material was a novel catalysts host and in the meantime the ZIF-8 membrane showed promising H2/CO2 and H2/CO separation performance. Later on, the applicability of ZIF-8 material was firstly examined from the practical perspectives of catalyst and membrane under different environments. The results showed the stability of ZIF-8 strongly depends on the gas phase environment, whereas the ZIF-8 structure remained unchanged under inert atmosphere at 300ºC for 24 h. Subsequently, the ZIF-8 membrane was successfully fabricated with a simple polishing procedure which was developed to repair the defect membrane. The gas separation performance of the well-prepared ZIF-8 membrane was evaluated with respect to a simulated syngas stream in the presence and absence of steam. In addition, a synthesis method was developed for a core-shell metal/ZIF-8 composite catalyst which consists of a ZIF-8 core incorporated with the metal nanoparticles and a ZIF-8 protect membranous layer formed from secondary crystallization. The catalyst exhibited high selectivity and anti-poisoning property in the alkenes hydrogenation reactions. Finally, WGSR were carried out in the conventional packed bed reactor and the ZIF-8 membrane based MR. MR advantages were demonstrated and the required improvement in MR development was discussed. This study concluded that the ZIF-8 membrane based MR could provide benefit on higher CO conversion and purified hydrogen in WGSR compared to the traditional packed bed reactor. However, the porous material ZIF-8 may have bright application future in the applications of catalysis and separation membrane under the mild conditions, although progress modification of the ZIF-8 structure is inevitable in the applications under harsh conditions, like MR for WGSR.