The Preparation And Application On The Dehydration Of Chloromethane Of NaA Zeolite Membrane

Chloromethane is a methane chloride, and gas at room temperature.Most of chloromethanes are used to product organic silicon.With demands enlarging of organic silicon,chloromethane demands are expanding.But water concentration of choromethane is far from national standard. Pervaporation(vapor permeation)is a new-type separation technology.It allows separation of some mixtures that are difficult to separate by distillation.Pervaporation process has obvious technical and economical advantages in the removal fractional water from organics.It is high-efficient,energy-saving,environmental and economic.NaA zeolite membranes,with small pore size(～0.41nm),three-dimensional open-framework and high hydrophilicity, have been found some potential applications on dehydration of organic solution by pervaporation(vapor permeation),and have high selectivity to water,which make them have wide application prospective. However, it restricts its application in the industry that high quality NaA zeolite membrane can not be prepared on the macropore supports.Based on current research status of NaA membranes all over the world, afrer investigating various influencing factors and optimizing synthesis conditions,NaA zeolite membranes with high flux and separation factor are synthesized on porousα-Al₂O₃ support by second hydrothermal syntheses. Then XRD,SEM and single gas permeation are used to characterize the as-synthesized NaA zeolite membranes.At last, the successful as-synthesized NaA zeolite membranes are used to separate water/chloromethane mixture by vapor permeation.First of all, NaA zeolite seeds on membranes are prepared and NaA zeolite membranes are synthesized by second hydrothermal method.Then the effects of seeds concentration ,seeds size,seeding times, seeding method and synthesis solution on the forming and performance of NaA zeolite membranes are discussed.Through XRD,SEM and single gas permeation, NaA zeolite membranes synthesized under the optimal conditions are proven that it is dense,continuous,integral,high permeation and has certain molecular sieving property. The permeation of the hydrogen of the membrane is 21×10^-7 mol·m^-2·s^-1·Pa^-1, and the ideal selectivity of H₂/N₂,H₂/n-C₄H₁₀ were 5.99 and 25.4, respectively, which are both much higher than that of Knusen diffusion, 3.74 and 5.39.The as-synthesized NaA zeolite membranes under optimal conditions are applied to dehydration of water/chloromethane mixture by vapor permeation.Two different methods in order to obtain low pressure on the permeation side are studied.And vacuum method is decided.Forthemore, the influence of operation temperature,operation time, operation pressure difference on performances of the removal of water from water/chloromethane mixture are discussed systemicly.The membranes showed high selectivity for water/chloromethane mixture,and separation factor as high as 74831 is obtained for the water feed concentration of 0.2582 wt.% at optimal operation conditions.To the best of our knowledge,the application of NaA zeolite membrane to dehydration of water/chloromethane mixture in this thesis is first up to now.