A. E. Koklin

Alkylation of isobutane with C 4 olefins under conventional and supercritical conditions

The solid acid alkylation of isobutane with butylenes on the ultrastable zeolite Y is studied in the temperature range from 120 to 150°C and in a pressure range of 20–120 atm. The catalyst service life becomes longer on passing from the conventional (liquid- and gas-phase) conditions of alkylation to supercritical conditions. The maximum period of complete butylene conversion at 150°C and 120 atm is 3.5 h. The composition of the reaction products is determined by the phase state of the reaction mixture, the reaction time, and the conversion of the C4 olefins. When the alkylation is carried out under supercritical conditions, the C8 hydrocarbon selectivity varies between 30 and 40%. Thermoanalytical data suggest that the surface of the spent catalyst contains carbon deposits indicating the formation of oligomeric and cyclic structures.

Gas-phase and supercritical n-pentane isomerization on H-mordenite

The skeletal isomerization of supercritical n-pentane on the H form of mordenite under flow conditions was studied for the first time. It was found that the conversion of supercritical n-pentane was 30–35% at 90% selectivity for isopentane at 260°C, 130 atm, and a liquid hourly space velocity of 30 h−1. The catalyst was deactivated as the temperature was increased above 280°C. According to differential thermal analysis data, the deactivation was related to the deposition of condensation products on the surface. The resistance of the H form of the zeolite to poisoning in n-pentane isomerization in a gas phase at 1–8 atm was lower than that under supercritical conditions. It was found that H-mordenite deactivated under gas-phase reaction conditions at 260°C and 8 atm can be regenerated by passing to supercritical isomerization conditions (260°C and 130 atm).

Transformation of aqueous solutions of glucose over the Pt/C catalyst

The transformations of glucose over the Pt/C catalyst in a flow reactor in the temperature range 140–200°C at a pressure of 5.0 MPa have been studied. The main routes of glucose conversion in an aqueous phase in the presence of hydrogen, helium, or air have been considered. A product formation scheme depending on the reaction parameters has been proposed. At 140°C, glucose hydrogenation into sorbitol occurs with a selectivity of 77%. In an oxidizing atmosphere, glucose transforms into gluconic acid (with 73% selectivity at 140°C); here, the formation of sorbitol and mannitol (with a selectivity of 5–7% at 180–200°C) is also possible. Glucose transformation by-products, such as C3–C5 polyatomic alcohols, ketones, acids, and furfural derivatives, have been identified. The degree of glucose reforming in the aqueous solution with the formation of the gaseous products H2 and CO2 is no higher than 10% at 200°C.

Conversion of isobutane-butenes mixtures on H-USY and SO42−/ZrO2 catalysts under supercritical conditions: Isobutane alkylation and butenes oligomerization

The conversion of isobutane-butenes mixtures on the H-form of ultrastable zeolite Y and sulfated zirconia under supercritical conditions at 150–160°C and 80 atm was studied. The isobutane/C4-olefins molar ratios (I/O) were 1.5, 14, and 28. In isobutane alkylation (I/O = 14 and 28), sulfated zirconia was more stable: at 150°C and 80 atm, the olefin conversion above 90% was retained for 5 h. Under the same conditions, the deactivation of the zeolite catalyst started after 1–2.5 h (depending on the initial I/O ratio). Selectivity for the formation of C8 hydrocarbons was 30–40%. An increase in the butene content of the initial mixture led to the domination of the dimerization of butenes over the alkylation of isobutane.

Catalytic activity of H-forms of zeolites in the isomerization of supercritical n-pentane and their physicochemical properties

The acidic properties of the H-forms of zeolites ZSM-5, Beta, Y, and mordenite are studied by diffuse reflectance IR spectroscopy using n-pentane as a probe molecule. The decreasing order of Brønsted acid site strengths is constructed. The isopentane selectivity in n-pentane isomerization under supercritical conditions (260°C, 130 atm) increases in the order H-ZSM-5 < H-Beta < H-mordenite(11) ≈ H-Y with decreasing strength of Brønsted sites. Catalytic data are analyzed jointly with the results of physicochemical studies of H-mordenite (temperature-programmed ammonia desorption, benzene adsorption, and IR spectroscopy). Under the supercritical conditions, the conversion of n-pentane on mordenite is determined by the total acidity of the zeolite and also by the accessibility of the acid sites inside the zeolite channels to the reactant.

Hydrogenation of biphenyl and isomeric terphenyls over a Pt-containing catalyst

Catalytic hydrogenation of benzene, biphenyl, and ortho-, metha-, and para-isomers of terphenyl over a 3 wt.% Pt/C at 180 °C and 70 atm was studied. The directions of hydrogenation of each substrate were revealed. Relationships between structures of the substrate and hydrogen consumption rates were found. It was shown that hydrogenation rate decreases on going from benzene to terphenyl and with increasing degree of the substrate hydrogenation. Hydrogenation rate of terphenyl isomers decreases in the following order: p-terphenyl > > m-terphenyl > o-terphenyl.

Production of fatty acid methyl esters that are the basis for biodiesel fuel from mycelial fungi lipids extracted by supercritical CO2

Lipids are produced with a 60 wt % yield in terms of dry biomass in the course of fermentation of oleaginous fungi at 27–28°C for 4–5 days. Triglycerides are extracted by supercritical carbon dioxide in a flow regime at 80–100°C and 50 MPa. The fatty acid methyl esters (FAME) are synthesized via a two-step transesterification of triglycerides with a 98% yield. It is demonstrated using a combined method of chromatography-mass spectrometry that the fatty acid composition of the fungal lipids from Cunninghamella echinulata is close to that of rapeseed oil.

Partial oxidation of toluene with nitrous oxide under supercritical conditions

The partial oxidation of toluene with nitrous oxide over the H-ZSM-5 catalyst under supercritical conditions at temperatures of 370–420°C and pressures of 70–160 atm has been investigated for the first time. The maximum cresol selectivity under these conditions is 32%. The amounts of the resulting cresol isomers form the following decreasing sequence: m-cresol > o-cresol > p-cresol. The partial oxidation of toluene is accompanied by disproportionation and biphenyl formation.

Hydrogenation of Anthracene and Dehydrogenation of Perhydroanthracene on Pt/C Catalysts

The hydrogenation of anthracene on a heterogeneous catalyst containing 3 wt % Pt/C (Aldrich) at 215, 245, and 280°C and the pressures of 40 and 90 atm is studied. The hydrogenation of anthracene to a completely hydrogenated product is considered in detail. The final product (perhydroanthracene) consists of five conformational isomers with total selectivity of more than 99%. The ratio of perhydroanthracene isomers in the end product is shown to be determined by the conditions (P, T) of hydrogenation. The rate of hydrogenation is found to slow upon an increase in the degree of benzene ring saturation. A mixture of perhydroanthracene isomers is dehydrogenated in an autoclave at 260−325°C on 3 wt % Pt/C catalyst (Aldrich) and in a flow reactor at 300–360°C on 3 wt% Pt/Sibunit catalyst. The reactivity of perhydroanthracene isomers in dehydrogenation is shown to differ.

Interaction of Phenol and Cyclohexanol with Supercritical Water

Transformation of phenol and cyclohexanol was studied in supercritical water (SCW) in a flow reactor at 300 bar, 500–750°С, and LHSV = 1.2–2.0 h–1. At 500–600°С the only products of phenol conversion are aromatic hydrocarbons—benzene, toluene, naphthalene and polycyclic aromatic hydrocarbons. Almost complete conversion of phenol is achieved at 750°С with selectivity to gaseous products (H2, CO2, CH4, C2H4, C2H6) not higher than 30%. A preliminary catalytic hydrogenation of phenol to cyclohexanol facilitates both overall reaction with SCW and the formation of gaseous products. At temperatures as low as 600°С gaseous products are formed from cyclohexanol, and its complete conversion is achieved at 700°С. In the latter case, the yield of the gaseous products reaches 70%, including 40% of C1–C2 hydr°Carbons. The differences in the rate of conversion in SCW and in selectivity to gaseous products between phenol and cyclohexanol at 500–750°С are associated with the stability of the aromatic ring.