Preparation And Dehydration Of Acetic Acid Of Zsm-5Zeolite Membranes

Acetic acid is one of the most important organic intermediates. In recent years, the world demand for acetic acid is rising gradually. Relative volatility of acetic acid and water is close to unity, much energy is required for distillation to separate acetic acid from aqueous mixtures. As a new membrane separation technology, pervaporation has many advantages such as efficient, energy-saving, non-pollution and so on.High chemical stability makes zeolite membranes have potential application for dehydration of concentrated acetic acid. Hydrophilic zeolite membranes has used in dehydration of organic. As the chemical stability of zeolite membrane with increasing Si/Al ratios in the framework while the hydrophilicity decreases. The Si/Al of ZSM-5zeolite membrane is5～∞and it can be changed using appropriate methods to balance the relation of hydrophilic and acid-stability.The porous α-Al2O3tube was modified by composite seeding method. ZSM-5zeolite membrane with the Si/Al of10was prepared on the outer surface of seeding tube by the secondary crystallization in the fluorine system. The effects of some parameters including the content of F-, the ratio of Si/Na2O Si/Al、H2O/Si, the different aluminum source in synthesis solution, and synthesis temperature and time on the formation of ZSM-5zeolite membrane were discussed in detail. The as-synthesized ZSM-5zeolite membranes were characterized with SEM, XRD, and pervaporation. The results showed that the best ZSM-5zeolite membrane, which was well inter-grown and continuous, was achieved under the gel composition of0.2Na2O:0.05Al2O3:1SiO2:5OH2O:1NaF, aluminum source of Al2(SO4)3·18H2O, crystallization time of48h, temperature of crystallization of175℃. When dehydration of the90wt.%acetic acid at80℃and100Pa, the total flux of the membrane reached1.01kg/(m2·h), and the water content in permeates is100wt.%, so the separation factor was nearly∞. Over the20d acid stability test, the membrane almost kept the highest pervaporation performance.The ZSM-5zeolite membrane was used in the sepration of acetic acid/water、isopropyl alcohol/water and ethanol/water. The influnce of temperature and conditions of feed solution to the pervaporation performance was diccussed. The result showed that when dehydration of the90wt.%at80℃and100Pa, the total flux of the membrane reached1.74kg/(m2·h), and the water content in penetration is100wt.%towards the isopropyl alcohol/water. The pervaporation performance of ethanol/water is not well, the total flux of the membrane reached1.03kg/(m2-h), but the water content in penetration is only98.6wt.%.