Synthesis of X-Type Zeolite in Low Water Content System and Quantitative Relationship Between SiO2/Al2O3 Ratio and Alkalinity
The X-type zeolites were hydrothermally synthesized in the potassium-sodium systems of different water contents(n(H2O)/n(SiO2))and alkalinity(n(M2O)/n(H2O),M represents K and Na).The X-type zeolites were characterized using X-ray fluorescence spectrum,X-ray diffraction,scanning electron microscope,29Si MAS NMR and 27Al MAS NMR.Moreover,an evaluation was performed on the static adsorption of mixed C8 aromatics over Ba2+exchanged X-type zeolites.The results show that when n(SiO2)/n(Al2O3)is 2.8,the n(M2 O)/n(SiO2)range of the obtained pure phase X-type zeolites increases from 1.3 to 3.1 with the increase of n(H2O)/n(SiO2)from 21 to 60.When the n(SiO2)/n(Al2O3)of the synthetic system remains unchanged,the n(SiO2)/n(Al2O3)of X-type zeolite is linearly correlated with the single influencing factor n(M2O)/n(H2O),and the correlation coefficient R2 of 0.90.When n(SiO2)/n(Al2O3)and n(M2O)/n(H2O)are the same,there is no significant difference in particle size,non-skeleton aluminum species and pore volume of X-type zeolites prepared by n(H2O)/n(SiO2)of 40 and 60,respectively.In contrast,the crystal structure of X-type zeolite obtained from the low water system has a higher proportion of Si(4Al)species,and the adsorption selectivity of p-xylene to ethylbenzene is higher(3.19),and the adsorption selectivity of p-xylene to o-xylene and m-xylene is lowered to 3.25 and 6.84,respectively.
FAU topologyX-type zeoliteadsorptive separationp-xylenelow water content
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