Preparation And Characterization Of NaA Zeolite Membrane With Methylcellulose

The NaA zeolite membrane is a hydrophilic zeolite membrane,which is especially suitable for the desalination and organic dehydration of alcohols through pervaporation technology.In this paper,macro porous?-A1₂O₃ is used as a substrate.Firstly,Large and medium seed crystal of NaA zeolite are coated on the?-A1₂O₃ substrate.The NaA zeolite membrane was successfully prepared by adding methyl cellulose.Compared with the zeolite membrane prepared without methylcellulose,the pervaporation performance and hydrothermal stability of the two different mixtures were investigated.Following Factors that affect its performance are investigated.?1?Preparation of NaA zeolite molecular sieve by hydrothermal synthesis method,the effects of aging time,crystallization time and addition of methyl cellulose on the crystallinity,morphology and particle size of NaA molecular sieve.The experimental results exhibits that the optimized synthesis conditions are the ageing carried out at 25? for 15 h and crystallization at 100? for 12 h.Moreover,the addition of methyl cellulose not only increases the crystallinity of the product,but also reduces the particle size to 200-300 nm,which is smaller than the particle size of the NaA molecular sieve prepared without adding methyl cellulose.?2?By controlling the molar ratio of the synthetic liquid at a fixed ratio of silica to aluminum?n?Al₂O₃:?n?SiO₂:?n?Na₂O:?n?H₂O=1:2:2.2:240 during synthesis.The morphology and separation performance of the zeolite membrane were investigated by the addition methylcellulose,crystallization temperature,crystallization time,alkalinity and concentration of the small seed solution.The results showed that adding methyl cellulose with 1wt%,during the crystallization time of 5 hours at 100?,the best performance NaA zeolite membrane can be prepared.The morphology and crystallinity of the film were characterized by SEM and XRD.The results show that the zeolite membrane with methyl cellulose addition has a complete and compact surface structure with dense growth and excellent performance.The thickness of the film is around 2-4?m.The separation performance was investigated by pervaporation test at 75? with 90 wt%ethanol water.The flux was up to 2.15 kg/?m ²·h?,the water content on the permeate side was 99.925 wt%,and the separation factor was greater than 10,000.?3?First,the membrane M to which methylcellulose was added and the membrane N to which methylcellulose was not added were tested for PV properties in a brine mixture.The experimental results show that the increase of temperature will increase the permeation flux to a certain extent,but the ion retention rate will be decreased to some extent.The increase of the concentration of the raw material liquid will reduce the permeate flux and have little effect on the separation performance.When the temperature is raised from 30? to 90?,the water flux of membrane M increases from 2.87 kg/?m²·h?to 11.77 kg/?m²·h?,and the concentration increases from 0.2 mol/L to 1 mol/L.The water flux of membrane M decreased from 12.33 kg/?m²·h?to6.33 kg/?m²·h?,and the ion rejection was stable at about 99.95 wt%.Meanwhile,membrane M still maintained high separation performance under long-time PV experiment.The separation performance of membrane M in mixed brine was lower than that in NaCl solution,but maintained flux around 9.51 kg/?m²·h?and ion rejection of 99.88%.These indicate that the addition of methyl cellulose has a significant improvement in the separation performance and hydrothermal stability of the zeolite membrane.PV test was carried out on the membrane M under different conditions of the alcohol-water mixture.As the amount of water in the aqueous ethanol solution was reduced from 25 wt%to 10 wt%,the time required for the membrane M separation performance to decrease was longer;the temperature of the alcohol solution was from 60? is increased to 75?,the time for the separation performance of the membrane M is shortened from 2400 min to 1000 min,which indicates that the larger amount of water,higher temperature and shorter time required for the performance of the zeolite membrane to decrease.?4?In order to make the NaA zeolite composite membrane,that can be further applied to dehydration of organic mixture under acidic conditions,1 wt%of NaA small crystal seeds were dispersed into the BTESM solution.In the next step,the prepared solution was applied on the substrate?preheated 170??modified with big NaA crystals to get composite membranes by hot coating.The prepared composite membrane was further applied to dehydrate 75 wt.%ethanol aqueous solution of pH=3.The composite membrane showed excellent stability and separation performance with flux 2.41 kg/?m²·h?.After 2200 min,the permeation flux of the composite membrane was stabilized at 1.83 kg/?m²·h?,the water permeation was still greater than 98.80wt%.The results showed that the NaA zeolite membrane combined with BTESM is subjected to pervaporation test in a long time acidic organic solution,showing good separation performance and acid resistance stability.