Effect of Treatment with Carbon Dioxide of the Zn Form of the TsVK Zeolite on Its Acid and Catalytic Properties in the Conversion of Methanol to Hydrocarbons

It is shown that it is possible to increase the yield of liquid hydrocarbons of the benzene fraction in the Mobil process by use of a catalyst modified by treatment with CO₂ of the Zn form of the TsVK zeolite. It is established that on treatment with CO₂ of the Zn-TzVK zeolite the concentration of strongly acidic -centers is increased. As a result of alkylation of C₂-C₄ olefins by methanol at these sites more of the high molecular C₅-C₈ aliphatic hydrocarbons are formed. Selectivity of conversion of methanol to liquid C₅-C₁₀ hydrocarbons of the benzene fraction is increased, but selectivity with respect to the light C₂-C₄ fractions is decreased.     

Effect of Methods of Modification of Synthetic Mordenite with Respect to Acidity and Catalytic Activity in the Conversion of Methanol

The acid properties of samples of the H-form of decationated and dealuminated synthetic mordenite, prepared respectively from the NH₄ form or by treatment of the Na-form of the zeolite with hydrochloric acid solution, were studied by programmed thermodesorption of ammonia. The sample of dealuminated synthetic mordenite had a smaller content of weakly acidic -centers than the decationated sample, which led to deactivation of the zeolites in methanol conversion. It was established that on this sample, in contrast to a sample of decationated synthetic mordenite, methanol was converted at temperatures above 613 K into C₂-C₄ volatile and C₅-C₁₀ liquid hydrocarbons of the benzene fraction.     

Study of acidity of various zeolites by thermal desorption of ammonia

Using the method of thermal desorption of ammonia, we have studied the acidity of hydrogen forms of a number of zeolites: type Y, ultrahigh silica TsVK, synthetic and natural mordenite (M). The hydrogen forms of the TsVK and M zeolites have similar acidity spectra. But for HTsVK, the overall concentration of acidic centers is sufficiently lower than for HM, including weak centers (2.5–3 times) and strong centers (1.5 times). The concentration and strength distribution of acidic centers are very close in samples of synthetic and natural mordenite.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 2, pp. 244–247, March–April, 1989.     

Methanol conversion on high-silica zeolites with different alumosilicate modules and prepared in different ways

High-silica zeolites in the H-form that differ in the SiO₂/Al₂O₃ ratio and the method of synthesis, have similar acidity spectra but different distributions of the acidic centers with respect to strength. A symbatic change in the concentration of the strongly acidic centers and of the degree of conversion of methanol has been observed, as well as a change in selectivity for C₂–C₄ aliphatic and aromatic hydrocarbons. It has been established that the stages of dehydration of methanol and dimethyl ether, and of aromatization and alkylation occur on strongly acidic centers of high-silica zeolites, and polymerization reactions on weakly acidic centers.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 3, pp. 380–383, May–June, 1987.     

Oscillator strengths for Rydberg states in ArH calculated in QDT approximation

With the help of a simple semi-analytical procedure the oscillator strengths for Rydberg electronic transitions in the ArH molecule are calculated by accounting for the effects of non-spherical symmetry of the molecular core’s field due to its dipole moment. Such effects result in non-zero oscillator strength values for some transitions which are forbidden in the widely used atom-like model of molecular Rydberg states. For the allowed transitions we also report the difference between the atom-like calculations and the calculations which take into account the dipole moment of the molecular core.     

Methanol conversion of various cation-exchanged forms of high-silica zeolites

Studies of the methanol conversion on various cation-exchanged forms of high-silica zeolites have revealed that the activity and selectivity of the intact pore structure zeolites depend on the cation composition. On decationated forms the selectivity of methanol conversion to aromatic hydrocarbons is much higher than on the hydrogen form, and it decreases with respect to paraffins.

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Conversion of methanol on a high-silica zeolite with divalent cations

The influence of divalent cations introduced into a high-silica zeolite by an ion exchange on its acidity and catalytic properties has been studied. The nature of the divalent cations has an influence on the distribution of the acid sites according to their strength, as well as on the activity and selectivity of action of the zeolite in the conversion of methanol. The primary conversion products of methanol, viz., dimethyl ether and ethylene, form on the acid sites of moderate strength. The hydrogen-redistribution reactions take place predominantly on the strong acid sites.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 1, pp. 114–118, January–February, 1986.