Tag Archives: ion-exchange forms
Among the factors influencing the adsorption activity of zeolites should give the number of cations in the zeolite, their availability for the adsorbate molecules and cationic charge density and radius of the cation. Synthesized samples of powdered zeolite LSX high phase purity and 100% crystallinity in NaK , Li, Na, K , Ca and Mg – forms. By X-ray analysis and the low-temperature nitrogen adsorption was studied the effect of the chemical nature of the cation exchange on the phase composition and characteristics of the porous structure of the zeolite LSX. The equilibrium adsorption capacity of the sample zeolite type LSX in NaK, Li, Na, K, Ca and Mg- forms of the water vapor. It has been shown that zeolite type LSX high degree of crystallinity and phase purity in Li- Na- forms can be synthesized starting from NaK- form, and K, Ca and Mg- forms – only from its Na- form. According to the low-temperature nitrogen adsorption determined that by replacing the cations NaK cations Li and Na, an increase, and when replacing the cations K, Ca and Mg – decreased availability of the crystal structure of the microporous zeolite LSX. Found that replacing cations can affect the limiting adsorptive capacity for water vapor ion-exchanged forms of zeolite LSX in the range of 0.27-0.34 cm3/g. Maximum values of the equilibrium water adsorption capacity are characteristic of zeolite LSX in Li- form.
This paper is dedicated to synthesis of MOR-type zeolite specimens in Na- and H-form of high phase purity and having crystallinity degree of nearly 100% with molar ratio of SiO2/Al2O3 = 15-24 in deep-decationated form, and investigation of their properties. To obtain chemically homogeneous silica-alumina hydrogel, mixing of crystal-forming components was implemented with reaction mass being continuously stirred. The stirring was still continuing during the process of crystallization. Crystallization was conducted at a temperature of 150-160 ºС. The compositions of oligomers were quantified by high-performance liquid chromatography. The conversion of the initial olefin, its composition and amount of its isomers, the amount of low molecular weight oligomers (with a molecular weight less than the dimers) as well as the number of dimer were measured by gas-liquid chromatography. The dimer fraction was extracted by reaction mixture distillation under reduced pressure and analyzed by nuclear magnetic resonance (NMR) ¹H, ¹³C, IR- and mass spectrometry methods. By method of temperature-programmed ammonia desorption it was found that with zeolite module increasing there was an increase in strength of zeolite acid sites. For evaluation of catalytic properties of the derived H-form of MOR-type zeolite specimens with various modules, model reaction of a-methylstyrene dimerization was used. It was found that with zeolite module increasing there was an increase in cyclic dimers formation selectivity from 20 to 52%. The α-methylstyrene conversions on MOR-type zeolite specimens were investigated at a temperature of 80 ºС with a 10% catalyst in nitrogen atmosphere. The catalyst was calcinated prior to the reaction at a temperature of 300 ºС during 2-3 hours with rare gas current in the reaction flask. Implementation of the method developed makes it possible to expand the raw materials base, simplify the synthesis and reduce the cost of powdery mordenite type zeolite.