Study On Preparation Optimization Of Silicalite-1 Molecular Sieve And Its Pervaporation Performance

Silicalite-1 molecular sieve membrane is widely used in the field of organic matter/water separation because of its unique pore structure,excellent hydrophobic property and stable physical,chemical and thermodynamic properties.In order to improve the separation performance of Silicalite-1 molecular sieve membrane and widen its application field,this paper uses a secondary synthesis method to prepare Silicalite-1 molecular sieve membrane for research on the separation performance of ethanol/water.The pervaporation separation of low concentration ethanol/water solutions by Silicalite-1 molecular sieve membranes was studied.The effects of seed concentration,crystallization temperature and crystallization time on the pervaporation separation performance of Silicalite-1 molecular sieve membrane were investigated by single factor experiment.Response surface analysis(RSM)was used to study the effects of three operating factors on the separation coefficient and permeate flux,namely,the temperature of feed liquid,ethanol concentration and vacuum pressure.The main conclusions are as follows:In the preparation process of Silicalite-1 molecular sieve,its orientation is enhanced with the extension of crystallization time.Under the condition of 80 ℃,the seed layer is evenly distributed and tightly bonded to the carrier tube.The thickness of seed layer is about 1 μm.The Silicalite-1 molecular sieve membrane is uniform and dense,with no voids or holes found.The membrane layer is tightly embedded on the surface of carrier tube.The thickness of the membrane layer is about 8 μm and the contact Angle of water on the surface is 63±2°.The results of single factor experiments showed that the Silicalite-1 molecular sieve membrane prepared under the condition of seed concentration 0.3 wt.%,crystallization temperature 175 ℃ and crystallization time 7 h exhibited the preferable pervaporation separation effect of ethanol aqueous solutions.According to the RSM results,the separation coefficient and permeate flux were significantly affected by feed-liquid temperature,feed-liquid ratio,and vacuum pressure.The polynomial model was established according to RSM and the optimal conditions of the model prediction were verified by experiments,in which the experimental results were in good agreement with the model prediction.At the feed temperature of 70℃,ethanol concentration of3.49 wt.%,and vacuum pressure of 7.82 k Pa,the deviations of the actual separation coefficient and permeate flux from the predicted values were less than 5.46 % and7.39 %,respectively.The results showed that the surface hydrophobicity of Silicalite-1 zeolite membrane was greatly improved after DTMS modification,and 1.2 wt.% was greatly improved.The water contact angle of the modified film was increased from 63° to 133°.The pervaporation separation coefficient of Silicalite-1 zeolite membrane modified by different contents of DTMS for ethanol/water system was increased,and the permeation flux was reduced.In comparison,the DTMS content was 0.8 wt.% was the best modification condition,and its pervaporation performance showed a stable trend in the 120 h continuous operation experiment,indicating that the DTMS modification enhanced the stability of Silicalite-1 molecular sieve membrane.