Acetic acid is an important chemical material.In industrial production,acetic acid is usually mixed with water.Pervaporation membrane technology has been industrialized in the dehydration of neutral organic solvent,but the acid resistant membrane for acetic acid/water separation is still under investigation.Mordenite membrane is suitable because of its moderate Si/Al ratio and excellent acid resistance.However,the mordenite membranes reported showed low repeatability and separation performance.In this study,mordenite membrane was prepared by optimizing the seed layer to improve its repeatability,and then the membranes was modified by ion exchange to improve the separation performance of pervaporation acetic acid from water.The second growth method is commonly used to prepare zeolite membrane,and precoating seed is the key step.Mordenite is difficult to form uniform seed layer on the surface of supports because of its high Si/Al ratio,low hydroxyl content and weak capillary force in macroporous supports.Mordenite membranes were prepared by second hydrothermal growth without template by introducing SiO2-ZrO2 sol with poly-hydroxy group into the seed solution to improve the quality of the seed layer.The effects of seed concentration,crystallization time and ultrasonic pretreatment on the morphology and properties of mordenite membranes were investigated under SiO2-ZrO2 sols.The optimal conditions were at 3 wt%large crystal seeds in water with sols,0.2 wt%small crystal seeds in water with sols,the synthetic solution pretreated without ultrasonic,and crystallization at 150°C for 24 h.The membrane prepared under this conditions showed high separation performance.By pervaporation of 90 wt%acetic acid/water solution at 75°C,total flux and separation factor were 0.60 kg·m-2·h-1 and 6914,respectively.SiO2-ZrO2 sol increased the number of crystal seeds on the surface of support,but too large number of crystal seeds resulted in a thicker zeolite membrane.The influence of SiO2-ZrO2 sol concentration in seed solution on seed layer were investigated.With the increase of the concentration of SiO2-ZrO2 sol in the large crystal seed solution,the defects in the crystal seed layer were modified,and the pervaporation performance of the synthesized mordenite membrane were improved.As the concentration of SiO2-ZrO2 sol in the seed solution continued to increase,the performance was slightly decreased.At last,the conditions of zeolite membranes prepared by large crystal seeds containing 0.5 wt%SiO2-ZrO2 sol and small crystal seeds without sol are the optimal.By pervaporation of 90 wt%acetic acid/water solution at 75°C,total flux and separation factor were 0.94 kg·m-2·h-1 and 5285,respectively.In addition,the zeolite membrane has good repeatability and long-term acid resistance.The pore size or surface properties of zeolite membranes have great influence on the membrane properties.Mordenite membranes were modified by ion exchange with monovalent and bivalent cation.The effects of the concentration of ion solution,temperature and treatment time on the pervaporation properties of the membranes were investigated.In the ion exchange,the influence of ionic radius on the flux of zeolite membrane is great.The ionic radius is smaller,the flux of the zeolite membrane is higher.Thus,H+with the smallest radius obtained the highest pervaporation flux.The effect of hydrogen ion on zeolite membrane was mainly investigated by hydrochloric acid treatment.The results showed that the pervapoartion flux were increases largely with a slight decrease of separation factor as the increase of HCl concentration,temperature or time.Howerer,as the concentration of hydrochloric acid or temperature is too high,the selectivity of zeolite membrane separation decreased obviously.Therefore,the mordenite membrane treated at 0.5mol/L hydrochloric acid solution under 60°C for 24 h showed the optimal performance.By pervaporation of 90 wt%acetic acid/water solution at 75°C,total flux and separation factor were 1.52 kg·m-2·h-1and 1443,respectively. |