부산대학교 도서관

Acetic acid (AcOH) is one of the top 50 chemicals used as raw materials for the production of many acetates such as vinyl acetate monomer, terephthalic acid C1-C4 acetates and acetic anhydride. During the production of AcOH, water is produced as a byproduct. The purity of AcOH is highly dependent on the content of water molecules in AcOH. Due to high solubility in water, the separation of both molecules is the energy-intensive process through distillation separation. In this regard, membrane-based technologies specifically pervaporation (PV) is proposed as cost-effective and eco-friendly separation technology along with achieving high degree of purity. Among membranes materials, zeolites based materials show promising results for the separation of organic solvents and they are highly stable in the harsh acidic environment. For this purpose, we prepared, ZSM-5 membranes on α-alumina capillary support and used for the dehydration of acetic acid at 70 ℃. The effect of various parameters such as seed depositions and Si/Al ratio in the synthesis solution on the pervaporation performance of the membrane was investigated. The optimum seed layers on capillary supports were used to synthesize ultra-thin ZSM-5 membranes by secondary growth hydrothermal treatment. Under the wide range of seed suspension 0.1 ~ 0.5 wt. %, the membranes prepared with 0.5 wt. % nanosized seed suspension provided a compact and thin membrane growth on the capillary supports. The membrane with Si/Al ratio of 20 was around 1.61 µm thicker with prism-like morphology. The as-synthesized ZSM-5 membrane exhibited a total flux of 4.07 kg m-2 h-1 and separation factor of ∞ for dehydration of 90 wt. % AcOH/water at 70 ℃. The high water permeation flux of ZSM-5 membranes is due to high porosity of capillary support, high hydrophilicity and ultra-thin zeolite layers responsible for high separation performance. Furthermore, to improve the separation performance and permeation flux of ZSM-5 membranes, two-dimensional (2D) zeolite nanosheets are important for the synthesis of high flux zeolite membranes due to their lateral size in a preferred orientation. A way to obtain 2D zeolite nanosheets is to exfoliate interlocked structures generated during the hydrothermal synthesis. The mechanical and polymer-assisted exfoliation process leads to mechanical damage in nanosheets and short lateral size. In the present study, polyvinylpyrrolidone (PVP) was introduced as an exfoliation agent and dispersant, so that multilamellar interlocked silicalite-1 zeolite nanosheets successfully exfoliated into a large lateral size (individual nanosheets 500~1200 nm). The good exfoliation behavior was due to the strong penetration of PVP into multilamellar nanosheets. Sonication assisted by mild milling helps PVP molecules to penetrate through the lamellar structure, contributing to the expansion of the distance between adjacent layers and thus decreasing the interactions between each layer. In addition, the stability of exfoliated nanosheets was evaluated with a series of organic solvents. The exfoliated nanosheets were well dispersed in n-butanol and stable for 30 days. Therefore, the PVP-assisted solution-based exfoliation process provides a high aspect ratio MFI zeolite nanosheets in organic solvents for a long period.