Synthesis And Evaluation Of Adsorbent For Normal Paraffins

5A molecular sieve has the LTA structure, containing a straight channel system with aelliptical8-membered ring.5A molecular sieve can be used in the separation process ofn-paraffins and iso-paraffins for its hole size between normal paraffins and iso-paraffins.5Ais usually prepared by hydrothermal synthesis (HTS). Silicon source and aluminum sourceaccording to certain proportion to form gel synthesis, join the binder for molding. However,samples synthesized by this way contain binder, which increases economic costs, resulting inlow separation properties. Thus, much work should be done to decrease its crystal size andseparation properties, either by changing the synthetic materials, synthesis conditions, andmolding methods.In this paper,5A molecular sieves were synthesized by gel conversion and Kaolinconversion methods. The results show that, the crystallization time and crystallizationtemperature are the key factors in gel conversion synthesis. Synthesis conditions such asaging time and calcium ion-exchange capacity have little influence on the synthesis. In Kaolinconversion methods, the calcination temperature of kaolin is the key factor during thesynthesis, the effect of synthesis is best when the calcination temperature between650°C~850°C. At the same time, the crystallization time and crystallization temperature also havegreat effect on the synthesis. However, aging time is too long can lead to the formation ofamorphous species instead of5A molecular sieve.XRD patterns of samples show that synthesized samples by gel conversion method havethe bigger degree of crystallinity, less impurity peaks, and more pure than the synthesizedsample by kaolin conversion method. SEM images of samples show that the synthesizedsamples by gel conversion method have smaller crystal size and fairly dispersive crystals,which can greatly reduce the particle size. However, like kaolin conversion method, thesecrystals aggregate together to form large spherical particles. The values of pore volume andsurface area of synthesized samples by gel conversion method are larger than those of samplemade by kaolin conversion method. In terms of mechanical strength, synthesized sample bygel conversion method without binder has more strong mechanical strength than those made by kaolin conversion method containing binder and gel conversion method containing binder,whose mechanical strength is stronger than that of sample by kaolin conversion method.The adsorption-separation effect of5A molecular sieves in fixed bed was investigated.The results was obtained by gas chromatograph analysis of various components, Thesynthesized sample by gel conversion method without binder has better separation efficiencythan those of kaolin conversion method without binder and gel conversion method containingbinder.