Low Cost Synthesis Of NaA Zeolite Membranes

Pervaporation has attracted much attentions as an advanced energy-efficient technique for the separation of azeotropic or close-boiling liquid mixtures.Due to the low ratio of silica to alumina and uniform pore size,NaA zeolite membrane with good chemical and thermal stability shows high hydrophilicity,which is applicable for separating water from organic solvent.The industrial demonstration plant of NaA zeolite membrane for the dehydration of alcohol/water mixtures was established first by Mitsui Engineering&Shipbuilding Co.,Japan in 1999.However,complex synthesis process of zeolite membrane and high cost of the support result in the high manufacturing costs,which limits the wide industrailiztion of zeolite membrane.In order to reduce the production cost,following researches were investigated.Firstly,a novel succeeding seeding method was developed for the preparation of NaA membrane at low-cost.The present generation of NaA membrane could be obtained by the secondary growth procedure of the prior generation of dried mother liquor overα-Al₂O₃tube,which is named succeeding seeding method（SSM）.Various original mother liquor were obtained by altering the crystallization time of the gel,and the effect of original mother liquor on the separation performance of NaA membrane was explored.The results revealed that the NaA membrane with the crystallization time of 12.5 min showed the best pervaporation performance with the separation factor larger than 10000 and the flux of 1.25kg/m²·h for the dehydration of 90wt.%ethanol solution at 70°C.Then,five generations of NaA membranes were synthesized in sequence by SSM under the optimal conditions above.Five generations of NaA membranes showed analogous crystallinity,surface morphology and thickness,so similar pervaporation performances with the separation factor larger than 10000 and the flux of ca.1.25 kg/m²·h were achieved.Therefore,highly reproducible NaA membrane with good separation performance could be obtained by SSM.Compare with the traditional tube support,ceramic flat support has the advantages of high filling density,low investment and low operation cost.Based on the study above,a modified succeeding seeding method（MSSM）was developed for the fabrication of the high-performance NaA zeolite membrane on the ceramic plate support.Since the performance of the NaA membrane would be affected drastically by the property of seeding layer over the support,the preparation process of seeding layer on the flat support was modified by thermal treatment.The effect of treated temperature and time of the seeding layer on the synthesis of NaA membrane was explored.The NaA membrane,which was prepared with the seeding layer calcined at 500℃for 3 h,exhibited the best pervaporation performance for alcohol dehydration,the flux of H₂O was 2.21kg/m²h and the separation factor was greater than 10,000 at 60℃.Ten generations of NaA zeolite membrane were continuously synthesized by modified succeeding seeding method,and they all showed analogous pervaporation performance for alcohol dehydration.At the same time,a single-component gas test was carried out on the membrane synthesized by MSSM,the results showed that the ideal separation factor of H₂/C₃H₈was 6.40,which exceeded the Nussen diffusion coefficient of 4.69,indicating that few defect existed on NaA membrane.Therefore,the NaA membrane on cheap ceramic plate support with good reproducibility,few defect and prominent pervaporation property could be obtained by MSSM.In this study,the cost of NaA zeolite membrane was effectively reduced by developing novel synthesis method and the application of cheap ceramic plate support,which provided good technical support for the wide application of NaA zeolite membrane...