Preparation And Pervaporation Study Of Zeolite T Membrane

Pervaporation is a fast developing and highly efficient membrane separation technology.It is one of the most promising high-tech technologies in the chemical industry in the 21^st cen-tury.The outstanding advantage of pervaporation is that the energy required for separation is low,and it is especially suitable for the separation of close boilling point mixtures and constant boiling point mixtures.As an important pervaporation membrane material,zeolite membrane not only has good mechanical strength,thermal and chemical stabilities,but also has good sep-aration performances in term of flux and separation factor.Zeolite T membrane having silica to aluminum ratio between 3 and 4,shows good hydrothermal stability and acid resistance and has important research values in the field of industrial pervaporation dehydration.The purpose of this research is to promote the industrial application of zeolite T membrane for pervaporation based dehydration,and to explore the separation performance of zeolite T membrane prepared on different lengths ofα-Al₂O₃ tube support.The main results of this re-search are as follows:（1）In organic-template system（1SiO₂:0.055Al₂O₃:0.231Na₂O:0.082K₂O:0～0.150TMAOH:11.687H₂O）,zeolite T were hydrothermally prepared at 100℃for 48 h.The addition of TMAOH can reduce the size of the zeolite T from 2μm to 600 nm.Using aluminum powder as the aluminum source and decreasing the synthesis solution preparation temperature to 4℃can inhibit the aggregation of[Al O₄]and[SiO₄]and make chemical reaction system uniformly nucleated,and then zeolite T with a size of 200 nm were prepared.Moreover,zeolite T with a size of 1～1.5μm were prepared in a template-free system by adding a small amount（1.0 wt.%）of seed crystals.（2）Zeolite T membranes were prepared on different length of（50,100,200 mm）α-Al₂O₃tubes at 150℃for 4 h by hydrothermal crystallization method using a molar ratio of 1SiO₂:0.05Al₂O₃:0.26Na₂O:0.09K₂O:0.05MF（3Na F:KF）:35H₂O.As the length of theα-Al₂O₃ tube increased,the growth of zeolite T membranes were not uniform due to the influence of gravity during the crystal growth process,and the pervaporation performance of zeolite T membranes also decreased.The repeatability and the stability of the zeolite T membranes prepared by hy-drothermal crystallization method with length of 200 mm were excellent.The permeation flux for90 wt.%ethanol/water at 75℃was stable at 0.71 kg·m^-2·h^-1and water content in permeate side was higher than 99.5%.The permeation flux for 35 g/L sodium chloride/water at 75℃was stable at 5.40 kg·m^-2·h^-1,and the ion rejection was greater than 99.9%.（3）In gel system with a molar ratio of 1SiO₂:0.05Al₂O₃:0.26Na₂O:0.09K₂O:0.05MF（3Na F:KF）:14H₂O,zeolite T membranes were prepared on different length of（50,100,200 mm）α-Al₂O₃ tubes by wet gel crystallization method.As the length of theα-Al₂O₃ tube in-creased,the water content in the gel solution had a greater impact on the pervaporation perfor-mance of zeolite T membranes.The repeatability and the stability of the zeolite T membranes prepared by wet gel crystallization method with length of 200 mm were excellent.The perme-ation flux for 90 wt.%ethanol/water at 75℃was stable at 1.33 kg·m^-2·h^-1and water content in permeate side was higher than 99.5%.The permeation flux for 35 g/L sodium chloride/water at75℃was stable between 8.45～8.60 kg·m^-2·h^-1 and the ion rejection was greater than 99.9%.