T. V. Alekseeva

Conversion of isobutylene on decationized superhigh-silica zeolite modified with added vanadium

Conclusions1.The introduction of 0.3% vanadium into decationized SHSZ increases the overall yield of aromatic products in isobutylene conversion at 320°C by a factor of 1.5. This effect is considerably less pronounced at 500°C.2.Increases of the vanadium concentration in the zeolite lead to higher contents of p-xylene in the C8-alkylbenzene fraction.

Catalytic properties of high-silica borosilicate

Conclusions1.High-silica (HS)-borosilicates exhibit a high catalytic activity in the aromatization of unsaturated hydrocarbons, including ethylene.2.A high selectivity in the action of HS-borosilicate with respect to C2-C6 alkenes and C5-C6 cyclenes when compared with the corresponding alkanes and cyclanes has been revealed. HS-borosilicate is an active catalyst for the isomerization of cyclohexene into methylcyclopentene.3.The hypothesis is proposed that the aromatization of aliphatic and cyclic hydrocarbons in the presence of borosilicate takes place via a preliminary stage involving the formation of lower olefins.

Conversion of xylenes in the presence of zeolites with a high SiO2/Al2O3 ratio

Conclusions1.A study has been made of the conversion of m− and o-xylenes in the presence of an ultra-high silica zeolite in the initial and decationized forms and in the presence of decationized and dealuminated mordenite at 150–550°C, atmospheric pressure, and a space velocity of 180 h−1.2.The Na- and H-forms of the ultrahigh-silica zeolite lead mainly to the isomerization of xylenes, while the isomerization and disproportionation of xylenes take place on the mordenites.3.In the presence of the Na- and H-forms of the ultrahigh-silica zeolite, which possesses a high stability in comparison with the decationized mordenite, the isomerization of m- and o-xylenes is characterized by an enhanced selectivity with respect to the formation of pxylene.

Transformations of isobutylene in the presence of various types of zeolites

ConclusionsIn contrast to zeolites with ultrahigh silica content, type A, X, Y, and M zeolites in the Na form and also those modified by decationization, cation exchange, and addition ofγ-Al2O3, Al2O3-SiO2, Pt, and Rh show a low activity in the aromatization reaction of C3-C4 olefins at 450–550°C at times of contact of 2–14.4 sec. The zeolites studied become rapidly deactivated as the result of intense coke formation.

Aromatization of 1-octene in the presence of catalysis based on ultrahigh-silica zeolite and aluminum oxide

Conclusions1.The original form of ultrahigh-silica zeolite shows activity in the aromatization of 1-octene at 400–500°C and atmospheric pressure. Modification of the zeolite by adding Pt, Rh, and V2O5 increases the aromatic hydrocarbon yield.2.In the presence of V2O5-modified ultrahigh-silica zeolite, 1-octene is predominantly converted to p-xylene. The p-xylene content in the catalysate increases with decreasing temperature.3.The hypothesis is proposed that selective formation of p-xylene is caused by blockage of the zeolite channels by the V2O5 additive, leading to difficulty in the desorption of the meta and ortho isomers of the dialkylbenzenes.

Conversions of lower olefins in the presence of a superhigh-silica zeolite catalyst with added V2O5

Conclusions1.Modification of the Na form of superhigh-silica zeolite by the addition of 5% V2O5 considerably increases the selectivity of this catalyst with respect to the formation of p-xylene from C2-C4 olefins, but reduces the overall yields of aromatic hydrocarbons.2.The addition of V2O5 apparently changes the pore structure of the zeolite, hindering the desorption in the gas phase of some of the conversion products of the olefins, in particular m- and o-xylenes, resulting in an increase in the yields of p-xylene.

Effect of composition and calcination temperature on the catalytic properties of ultrahigh-silica zeolite in isobutylene conversions

Conclusions1.As the Na2O content of ultrahigh-silica zeolites increases, the yield of liquid catalysate and aromatic hydrocarbons from isobutylene at 500°C decreases.2.As the temperature of preliminary calcination increases from 500 to 1000°C, the water-sorption capacity of ultrahigh-silica zeolites gradually decreases. Calcination at 800–1000°C hardly affects the total zeolite activity but decreases its activity in the dehydrocyclization and hydrogen redistribution reactions. After zeolite calcination at 1000°C, an increase in selectivity for p-xylene formation is observed.3.The change in the catalytic properties of ultrahigh-silica zeolites after calcination at 800–1000°C is related to the removal of a small number of OH groups which enter into the composition of the active centers. The selectivity increase for p-xylene formation can be attributed to some changes in the pore structure at high temperature which make the diffusion of m- and o-xylene difficult.

Transformations of propylene and isobutylene in the presence of decationized form of ultrahigh-silica zeolite

Conclusions1.Depending on the temperature, in the transformations of propylene and isobutylene on decationized UHS zeolite the oligomerization, isomerization, aromatization, dealkylation, hydrogenation, cracking, and disproportionation of the hydrocarbons can proceed both as consecutive and parallel reactions.2.Isobutylene is selectively oligomerized on the decationized UHS zeolite at 90–210° to give a mixture of 85% isobutylene dimers and 15% trimers in ∿45% yield.3.The decationized zeolite has a high activity and selectivity in oligomerization and aromatization reactions, which permits obtaining higher yields of mixtures of both aliphatic (>90%) and aromatic (∿50%) hydrocarbons at lower temperatures than in the case of the starting form of this zeolite.4.In the reaction with isobutylene the decationized zeolite at 500° and τ=7.2 sec does not lose its catalytic properties for 6 h, and gives a liquid catalyzate, containing 99% of aromatic hydrocarbons, in 47–48% yield.

Catalytic properties of ultrahigh-silica zeolite in transformations of propylene and isobutylene

Conclusions1.In the reactions of propylene and isobutylene in the range 450–580‡ the ultrahighsilica zeolite catalyst (UHSZ-23) has a high aromatizing capacity and makes it possible to obtain liquid catalyzates, which contain 90–93% of aromatic hydrocarbons, in over 40% yield. At temperatures below 320‡ this catalyst actively catalyzes the oligomerization of the starting olefins and also the isomerization, hydrogenation, disproportionation, and cracking of the formed oligomers.2.In 6 h of operation the yields of the liquid catalyzate remain constant (42–43%). However, in the first 2 h of operation the yield of the aromatic hydrocarbons decreases (from 30 to 25%), while the yield of the aliphatic hydrocarbons increases (from 13 to 18%).3.It was established that significant differences are absent in the composition of the liquid and gaseous transformation products of propylene and isobutylene.