Preparation Of Ti-HMS-1Micro/Mesoporous Composite Molecular Sieve Membrane By In Situ Hydrothermal Synthesis Method

Mesoporous molecular sieve membranes have pore sizes ranging from 2nm to 50nm, regular pore structure, narrow pore size distribution, tunable pore size and high surface area. As a new type of inorganic membrane, mesoporous molecular sieve membranes have catalytic activity and molecular sieving function and good chemical stability. Compared with microporous molecular sieve membranes, they overcome the defects of the microporous that cannot accommodate larger molecules. They have great application potential in the separation of larger molecular catalysis.HMS mesoporous molecular sieve has worm-like and interconnected channels. This unique channel advantage is conducive to the objective molecules diffusion in the pore, which gives HMS mesoporous molecular sieves extensive application. However, the hole wall of mesoporous molecular sieves are composed of amorphous material, so the hole wall is thin and instable, which leads to the poor (hydrothermal) thermal stability and limits their application in industry to a certain extent. Many methods have been put forward to improve the (hydrothermal) thermal stability of mesoporous materials, among which introducing the micropore structures into the hole walls of mesoporous material and preparing micro/mesoporous composite structure become a research hotspot in recent years.In this paper, the Ti-HMS-1 micro-mesoporous composite molecular sieve membrane was successfully synthesized on a α-Al2O3 for the first time by in situ hydrothermal synthesis method. The TS-1 microporous structures was introduced into the hole walls of pure silicon HMS mesoporous molecular sieve by two-step crystallization. The preparation process of composite molecular sieve membranes can be summed up as following:preparation of a sol that containing TS-1 microporous structure unit with the first step crystallization; preparation of Ti-HMS-1 synthesis mixture and preparation of molecular sieve membranes with second step crystallization. We investigated the influence of the parameters, including the aging time of Ti-HMS-1 synthesis mixture, second step crystallization temperature and time, synthesis mixture volume, the first step crystallization time of TS-1 sol, on the structure of Ti-HMS-1 molecular sieve membranes, the influence of Ti/Si ratio in TS-1 sol on the form of titanium element also was discussed. The structure of the membranes was obtained by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM), the morphology and thickness of membranes were characterized on scanning electron microscopy (SEM), single gas permeability was used to check the denseness of the membranes, ultraviolet visible diffused reflection (UV-vis) was applied to analyze the existing form of titanium element. The results of the Ti-HMS-1 molecular sieve membranes are as follows:1. The Ti-HMS-1 membranes were prepared with the synthesis mixture ageing for 14h:At lower crystallization temperature (100℃) with 50mL synthesis mixture, up to 96h the Ti-HMS-1 molecular sieve membrane was obtained, and there were some cracks in the membrane layer. At higher crystallization temperature (140℃) with 50mL synthesis mixture, after 48h crystallization the Ti-HMS-1 molecular sieve membrane was obtained, there were no cracks, but some holes in the membrane.2. The Ti-HMS-1 membranes were prepared with the synthesis mixture ageing for 10 min:The continuous membrane was prepared with the TS-1 sol crystallization for 2h at 140℃ and the micro-mesoporous membrane crystallization for 48h at 140℃, the membrane was about 8-9μm thick; The continuous membrane can also been obtained with the TS-1 sol crystallization for 3h at 140℃ and the micro-mesoporous membrane crystallization for 48h at 120℃, the membrane was about 26μm thick; The single gas permeability show that both the molecular sieve membranes were continuous and dense, the diffusion of gas in membrane layer mainly follow Knudsen diffusion mechanism, and the separation factor of hydrogen and nitrogen gas is about 3.26 and 3.36 respectively, close to the ideal separation factor of 3.74.