Síntese das membranas zeolíticas (NaA e SAPO-34 suportadas em alfa-Alumina) e membranas MOF (ZIF-8/alfa-Alumina) visando aplicação preditiva na síntese do metanol via hidrogenação do CO2.

Abstract

Zeolite membranes and metal-organic framework (MOF) membranes have been widely proposed as a promising solution for gas separation and pervaporation applications, technologies that can more effectively replace processes such as distillation. Methanol synthesis has received continuous improvement for nearly a century, as it represents the raw material for the production of a range of other chemicals and solvents, including formaldehyde, methyl butyl ether, and, in the context of Brazil, biofuel production. This study aims to produce different materials: alpha-alumina ceramic support, NaA zeolite, NaA zeolite membrane, SAPO-34 zeolite, SAPO-34 zeolite membrane, ZIF-8 metallurgical structure, and ZIF-8 membrane. The work was carried out in four stages. In the first stage, the alpha-alumina ceramic supports were prepared using dry uniaxial compaction, sintering at 1300°C for two hours, then polished and subjected to characterization techniques: X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Energy Dispersive X-ray Fluorescence Spectroscopy (ED-XRF), Mercury Intrusion Porosimetry, Mechanical Resistance, Contact Angle Testing, and the Bubble Point Method. These supports were used in the preparation of the zeolitic membranes and ZIFs. In the second stage, NaA zeolites and zeolitic membranes were prepared using hydrothermal synthesis at 100°C for four hours. The temperature and synthesis time parameters were set to evaluate how sources of silica, such as sodium pentahydrate metasilicate, Aerosil 380, colloidal silica, and TEOS influenced the products obtained. In the third stage, SAPO-34 zeolites and zeolitic membranes were prepared using hydrothermal synthesis, beginning at 38°C for 24 hours, followed by 200°C for 24 hours. The temperature and synthesis time parameters were set to evaluate how the sources of silica, such as Aerosil 380, colloidal silica, and TEOS influenced the products obtained. The synthesis products of these materials (NaA and SAPO-34) were subjected to the following characterization techniques: XRD, SEM and ED-XRF. In the fourth stage, the ZIF-8 metallorganic structures and membranes were prepared using solvothermal syntheses from two different synthesis methods and the influence of the synthesis method on the products was investigated. ZIF-8 and ZIF-8 membrane were synthesized at a temperature of 25ºC, using precursors of zinc nitrate hexahydrate and 2-methylimidazole. The main difference between the two methods were the solvents used. In method 1, the solvent used was a mixture of methanol and water with a reaction time of two hours. In method 2, the solvent used was pure methanol and the reaction time was one hour. The products obtained (ZIF 8.1 and ZIF-8.2) were characterized by XRD, SEM, physical adsorption of N2, thermogravimetric analysis, infrared (IR) spectroscopy, and CHN elemental analysis. Based on the characterization techniques used to study the properties of the alpha-alumina ceramic support, its production was determined to be satisfactory. It was concluded that sodium metasilicate pentahydrate exhibited higher crystallinity and perfect crystal formation compared to other silica sources for the synthesis of zeolite and zeolite NaA membrane. The NaA/alpha-alumina zeolitic membranes presented a homogeneous and uniform distribution of defect-free and crack-free zeolitic crystals corresponding to the NaA phase, confirming the formation of the zeolitic membrane structure. It was proved that the best source of silica for the synthesis of zeolite and zeolite membrane SAPO-34 was Aerosil 380 silica. The SAPO-34/alpha-alumina zeolitic membranes presented a homogeneous and uniform distribution of zeolite crystals corresponding to a defect-free and crack-free SAPO-34 phase, confirming the formation of the zeolitic membrane structure. X-ray analysis of the ZIF-8 metallurgical structure demonstrated the material to be of high crystallinity. The formation of the structure was also confirmed by IV and TG. From the results of the Physical Adsorption of N2 test, high specific surface area values (1003 and 1145 m²/g) were observed. SEM analysis confirmed the morphology of the nanocrystals, corroborating the other characterization analyses. From the SEM images, it was possible to measure the particle sizes of the ZIF-8 metallurgical structure: 140 nm for method 1 and 47 nm for method 2. The ZIF-8/alpha-alumina MOFs membranes showed a homogeneous and uniform distribution of zeolitic crystals corresponding to a defect-free and crack-free ZIF-8 phase, confirming the formation of the MOF membrane structure. As a general conclusion, it was possible to prepare the NaA and SAPO-34 zeolitic membranes using hydrothermal synthesis method and the ZIF-8 MOFs membranes using the solvothermic method. All membranes were of high quality, however the MOF ZIF-8 membrane is most promising for use in methanol synthesis via CO2 hydrogenation, due to the characteristics it presented.