G. V. Isagulyants

Splitting of aromatic hydrocarbons under the effect of methanol on high-silicon zeolites

Conclusions1.The phenomenon of catalytic splitting of the aromatic nucleus with the formation of lower olefins in the presence of methanol and other compounds containing an alkoxy group was found by the radioisotopic method in conditions of catalysis on HSZ. The possible mechanisms of the reaction were discussed.2.Passage of the isotopic label from the aromatic nucleus to the alkyl substituent of the hydrocarbon does not take place on HSZ.

Characteristics of the mechanism of aromatization of low-molecular-weight aliphatic compounds on ultrahigh-silicate zeolites

Conclusions1.With the help of14C-labeled compounds, we studied the transformations of methanol, lower olefins, and 1,3-pentadiene on ultrahigh silica zeolites (UHSZ) and obtained knowledge of the mechanism of growth of hydrocarbon skeletons in formation of olefins from methanol and aromatic hydrocarbons from 1,3-pentadiene.2.We demonstrated experimentally the possibility of building up hydrocarbon chains by conversion of methanol on UHSZ by means of its reaction with olefins. At high and medium concentrations of lower olefins, the rate of this reaction is significantly higher than the rate of transformation of methanol into ethylene and the polymerization of ethylene, which, under these conditions, does not play a significant role in the formation of higher olefins.3.We have shown that on formation of aromatic hydrocarbons from 1,3-pentadiene the formation of the hydrocarbon skeleton of arenes proceeds by way of fragmentation of pentadiene and subsequent buildups with the assistance of the fragments being formed from the dienes; cyclopolymerization of the initial 1,3-pentadiene does not play a significant role in the formation of aromatic hydrocarbons.4.The basis of the suggestion that on reaction of methanol with 1,3-pentadiene on the surface of the UHSZ forms active particles (fragments), their reactions with the molecule of olefin or diene is characteristic of the UHSZ method of buildup of the hydrocarbon skeleton to the dimensions making possible the formation of an aromatic ring.

Mechanism for the aromatization of N-hexane on an alumina-chromium-iron catalyst

Conclusions1.The formation of an aromatic hydrocarbon from a paraffin on an alumina-chromium-iron catalyst not containing alkali proceeds through the sequential dehydrogenation of the aliphatic molecule, i.e., through a mechanism which is well known for oxide aromatization catalysts.2.The contribution of aromatization pathways through the formation of cyclic products in the first reaction steps is either very small or absent completely.

Transformations o f 1,5-hexadiene and 1,3,5-hexatriene on aluminum, gallium, and indium oxides

Conclusions1.On the example of the transformations of 1,5-hexadiene at 450 and 520°, and of 1,3,5-hexatriene at 300 and 450°, on aluminum, gallium, and indium oxides it was shown that Al2O3 has a very weak, while Ga2O3 and In2O3 have a strong aromatizing (dehydrogenating) ability, but one that is less than that of Cr2O3. All three oxides catalyze migration of the double bond in dienic hydrocarbons. The main transformation products of 1,5-hexadiene are benzene and hexadienes, which are isomeric with the starting material, and benzene and cyclohexadienes in the case of 1,3,5-hexatriene. Hydrogenation products are also formed, as well as small amounts of hydrocarbons with a five-membered ring.2.The obtained results can be explained by the fact that the formation of benzene from aliphatic C6 hydrocarbons on Ga2O3 and In2O3 proceeds by the same scheme as on other oxide catalysts.3.The change in the aromatizing (dehydrogenation) ability when going from Al2O3 to Ga2O3 and In2O3 correlates with their ability to be reduced and is opposite to the change in the heats of formation of these oxides.

Transformations of n-hexane and 1-hexene on aluminum, gallium, and indium oxides

Conclusions1.A study of the transformations of n-hexane and 1-hexene under pulse conditions disclosed that the oxide Al2O3 has a very weak, while Ga2O3, and especially In2O3, have a strong aromatizing (dehydrogenation) and hydrogenation activity, but these are still inferior to the oxide Cr2O3.2.The studied oxides of the Group III elements catalyze the migration of the double bond in olefins.3.The aromatization of hexane on Ga2O3 and In2O3 proceeds by the same mechanism as holds for other oxide catalysts for the aromatization of hydrocarbons.

Conversion of piperylene to isoamylenes

Conclusions1.The conversion of piperylene to isoamylenes in the presence of NiSO4-Al2O3 occurs in two stages: a) hydrogenation of the diene to n-olefins, and b) skeletal isomerization of the n-olefins.2.The content of 2-pentenes in the fraction of n-pentenes at low influence by skeletal isomerization is appreciably greater than that at thermodynamic equilibrium, whereas for 1-pentene it is lower than the equilibrium value. The ratio of trans-2-pentene to the cis isomer is significantly greater than the equilibrium value.3.In conditions of skeletal isomerization, the ratio of 2-methyl-2-butene yield to 2-methyl-1-butene exceeds the thermodynamic equilibrium value, consequently, 2-methyl-2-butene is the primary product of isomerization of n-pentenes.

Isomerization of paraffins under conditions of aromatization on an alumina-chromium-potassium oxide catalyst☆

Abstract 1. 1. It was shown by a kinetic isotope method that during aromatization of n-hexane and n-hexenes on an alumina-chromium-potassium oxide catalyst at 530° isohexadienes are formed by skeletal isomerization of these hydrocarbons. Isomerization of n-hexane may also take place before dehydrogenation to olefin. 2. 2. It was found that rates of skeletal isomerization of n-hexane and n-hexenes under conditions of aromatization are much lower (by one order of magnitude and more) than corresponding rates of dehydrogenation. 3. 3. An assumption was put forward that skeletal isomerization of paraffins and olefins on an alumina-chromium-potassium oxide catalyst takes place by a sole mechanism via alkyl or alkylene intermediate surface forms with a positive charge.