Modeling investigation of geometric size effect on pervaporation dehydration through scaled-up hollow fiber NaA zeolite membranes

A mass transfer model in consideration of multi-layer resistances through NaA zeolite membrane and lumen pressure drop in the permeate side was developed to describe pervaporation dehydration through scaled-up hollow fiber supported NaA zeolite membrane. It was found that the transfer resistance in the lumen of the permeate side is strongly related with geometric size of hollow fiber zeolite membrane, which could not he neglected. The effect of geometric size on pervaporation dehydration could be more significant under higher vacuum pressure in the permeate side. The transfer resistance in the lumen increases with the hollow fiber length but decreases with lumen diameter. The geometric structure could be optimized in terms of the ratio of lumen diameter to membrane length. A critical value of d1/L （Rc） to achieve high permeation flux was empirically correlated with extraction pressure in the permeate side. Typically, for a hollow fiber supported NaA zeolite membrane with length of 0.40 m, the lumen diameter should be larger than 2.0 mm under the extraction pressure of 1500 Pa.

Preparation of hollow fiber membranes from mullite particles with aid of sintering additives

Porous mullite hollow fiber membranes were prepared with a combined phase-inversion and sintering method,using three sintering additives including yttrium stabilized zirconia(YSZ),small mullite particles(SMP),and titanium oxide(TiO2)to promote the particle sintering.The results indicated that all the three additives could improve the sintering performance of mullite hollow fiber membranes due to the decrease in activation energy of mullite grains.Both YSZ and T i02 could react with mullite grains to generate composite oxides(e.g.,ZrSi04 and Al2Ti05)during sintering,following a reaction-sintering mechanism.Interestingly,the newly generated ZrSiO4 was instable and further decomposed into monoclinic ZrO2 and SiO2 in the sintering process.The decomposition could avoid excessive embedment of composite oxides among mullite grains which have negative impact on mechanical strength of mullite hollow fibers.Overall,the doping of YSZ provided a better promotion effect on the sintering of mullite hollow fiber membranes,where the microstructural and mechanical properties are insensitive to the doping content and sintering temperatures,so it could be used as the candidate for the large-scale preparation of mullite hollow fibers.