Vol 59, No 7 (2019)

The study of cotransformation of petroleum fractions with vegetable oils on dual-zeolite cracking catalysts has revealed that vegetable oils differing in fatty acid composition admixed to vacuum gas oil, characterized by a high aromatics content, facilitate the conversion and increase the yields of the gasoline fraction and light olefins. In the case of vacuum gas oil cocracking with a vegetable oil having a high unsaturation index (sunflower oil), the oil content in the mixture should not exceed 5 wt %, since its higher content in the mixture leads to enhanced coking of the dual-zeolite catalyst and simultaneous reduction in the yield of the desired cracking products. The effect of preliminary impregnation of HREEY and HZSM-5 zeolites with ammonium hydrogen phosphate before their incorporation into the composition of dual-zeolite catalysts has been investigated as well. It has been found that the modification results in a decrease in the total acidity of zeolites. In the cracking of a mixture of vacuum gas oil and sunflower oil, it has been determined that the modification of zeolites leads to an increase in the total yield of the propane–propylene and butane–butylene fractions with high olefin content. Keywords: vacuum gas oil, vegetable oils, dual-zeolite catalyst, gasoline fraction

The features of the catalytic conversion of acetone and glycerol in a mixture with a hydrotreated vacuum distillate in the presence of zeolite catalysts containing Y and ZSM-5 have been studied. It has been shown that in the presence of zeolite Y, the highest yield of total C₂–C₄ olefins (24.1%) is achieved in the case of the conversion of the petroleum feedstock with an acetone-rich additive. The introduction of a catalytic additive based on ZSM-5 can significantly increase the yield of light olefins in the cracking of glycerol-rich feedstock. A synergistic effect in the transformation of a mixture of acetone and glycerol under these conditions has been observed, which is manifested in a decrease in the yield of C₂–C₄ olefins and an increase in the yield of gasoline fraction components. A significant influence of oxygenated feedstock additives on the intensity of hydrogen transfer reactions catalyzed by a combination of zeolites Y and ZSM-5 has been revealed.

A series of samples of zeolite MFI with the same morphology, but different concentrations of Brønsted acid sites, have been obtained by means of ion exchange. Methods of temperature-programmed desorption of ammonia (TPD NH3) and IR spectroscopy of absorbed 2,6-di-tert-butylpyridine have demonstrated that the samples differ in the ratio of acid sites in the bulk of zeolite and on the external surface. Stability of the samples against deactivation has been determined in the oligomerization reaction of butylenes using the accelerated deactivation test under severe conditions. It has been shown that the main contribution to deactivation is made by acid sites located on the external surface of zeolite crystals.

The base catalyst HY-BS, which is binder-free zeolite Y in the acid H⁺ form, has been synthesized and modified with hydrochloric and citric acid solutions. It has been shown that all the obtained catalysts exhibit high activity and selectivity in the reaction of liquid-phase alkylation of benzene with ethylene. It has been first found that the ethylbenzene concentration in the alkylate and the selectivity for ethylbenzene in the liquid-phase benzene alkylation reaction on the catalyst modified with 0.3 N hydrochloric acid are higher when either the hydrogenated or the nonhydrogenated ethane–ethylene fraction of pyrolysis is used as an alkylating agent instead of polymerization-grade ethylene.

Single-stage gas-phase synthesis of isoprene from formaldehyde and isobutylene in the presence of zeolite catalysts of the MFI, BEA, and FAU(Y) framework types and Al–BEA, Zr–BEA, Sn–BEA, and Nb–BEA catalysts synthesized by isomorphous substitution methods has been studied. Catalytic tests have shown that the isoprene yield increases in the following order: Zr–BEA < Sn–BEA < Nb–BEA < Al–BEA, which is in agreement with the content of Brønsted acid sites in the samples, whereas the formation of the major byproduct—carbon monoxide resulting from the decomposition of formaldehyde—increases with an increase in the number of Lewis acid sites. Comparison of the catalytic properties of zeolites of the different framework types has shown that the highest isoprene selectivity is exhibited by medium-pore MFI zeolites with a pore diameter of 5.5 Å.

It has been shown by the example of zeolites with the MTT (Al-ZSM-23 and Fe-ZSM-23) and MFI (Al-ZSM-5 and Fe-ZSM-5) structures that mesoporous zeolites are efficient catalysts for the gas-phase isomerization of ethylene oxide to acetaldehyde. At 300–400°C and complete conversion of ethylene oxide, the selectivity of its conversion to acetaldehyde (S_AA) reaches at least 90%. The key factors determining the selectivity and stability of the catalyst are the topology of the zeolite and its acid properties. Unidimensional zeolites with the MTT structure demonstrate higher S_AA in comparison with the samples with the three-dimensional MFI structure. Decreasing the strength of Brønsted acid sites by replacing Al by Fe in the zeolites of both structural types also leads to a growth in S_AA. The samples are arranged in following order of decreasing S_AA: Fe-ZSM-23 > Fe-ZSM-5 = ZSM-23 > ZSM-5. The main byproduct of the reaction is crotonic aldehyde, the formation of which is promoted by strong Brønsted acid sites. The crotonic aldehyde selectivity over aluminosilicate samples is above 6%.

Comparative analysis of deactivation of the catalyst SAPO-34 for methanol conversion to lower olefins was carried out in fixed-bed flow reactors, in fluidized-bed reactors, and slurry reactors with the catalyst dispersed in a polydimethylsiloxane (PDMS) medium. It has been found that the deactivation rate of the catalyst essentially depends on the reactor type. The uniform contact of methanol with the fluidized catalyst makes it possible to increase by one and a half the on-stream stability compared with the fixed bed catalyst. However, the reaction run in the PDMS medium in the slurry reactor leads to significant acceleration of deactivation, which is due to high solubility of olefins and methanol in PDMS and results in an increase in the contact time of the catalyst with the reactants and products. A method has been proposed for measuring the solubility of gases in liquid polymers at high temperatures using mass-spectroscopic detection of effluent gases.

This research is devoted to the preparation of cerium-containing layered double hydroxides (LDHs) and exploring the possibility of stabilizing cerium in the unstable valence state (III) in their structure. It has been shown that the best result is achieved in the case of using hydrothermal treatment in the synthesis process. A sample of an LDH obtained via this method possesses characteristics typical for this class of compounds, as has been demonstrated using a set of instrumental methods (XRD, IR, TG–DSC). It has been proved by cerium L₃-edge X-ray absorption spectroscopy that cerium is only partially oxidized to Ce(IV) during the synthesis process.