P. N. Kuznetsov

Study of n-octane hydrocracking and hydroisomerization over Pt/HY zeolites using the reactors of different configurations

The conversion of n-octane over a series of monofunctional HY zeolites, which differed with the contents of Na and over the bifunctional Pt/HY zeolites differed with the contents of Pt, was studied as function of the balance among the specific activity of the components, the distribution of the metallic sites over zeolite surfaces and reaction conditions. The activities of individual metal and zeolite components were quantified in the reactions of 1-hexene hydrogenation and n-octane cracking, respectively. Gradientless reactors of different configurations were applied to rationalize the contribution of hydrogenation, dehydrogenation, cracking, isomerization, oligomerization, and catalyst deactivation reactions to the reaction pathways over the bifunctional Pt/HY zeolites. The conceptual bifunctional mechanism involving the dehydrogenation of n-octane into olefinic counterparts was demonstrated experimentally by using the flow circulation unit equipped with two reactors connected in series and loaded with separated HY and Pt components. The limiting steps were determined depending on the activity of the Pt component in Pt/HY. It was shown that an optimum concentration of Pt sites exists in HY zeolites which corresponds to a maximum cracking activity followed by a significant decrease as the concentration of metallic sites further increases. The effect of diffusion transfer of branched octene intermediates inside the zeolite cavities from the acidic sites to Pt sites on the rates and reaction pathways over Pt/HY zeolites is argued.

Textural properties and crystalline structure of tungstated zirconia, a catalyst for isomerization of lower alkanes

The formation of the crystalline structure and textural properties of zirconia during the thermal activation of a hydroxide precursor with additives of tungstate anions at temperatures of 600–870°C has been studied. It has been found that, in the application of the different methods of mixing (coprecipitation or impregnation) of tungstate anions and zirconium hydroxide in the amount of more than 12.9 mol %, a dispersed phase of tetragonal zirconia having a mesoporous structure with a pore size of 7–8 nm is formed during thermal treatment. The catalytic activity of Pt/WO42−/ZrO2 in the isomerization of n-hexane and n-heptane depends in a nonmonotonic mode on the concentration of tungstate anions. In both reactions at a low temperature, high yields of isomers with a selectivity of at least 87% are achieved on the catalyst that has been prepared by impregnation and contains 17.6 mol % WO42−.

The nature of the synergistic effect of binary tetralin-alcohol solvents in Kansk-Achinsk brown coal liquefaction

Abstract Kansk-Achinsk brown coal hydrogenation and swelling in tetralin, in low molecular alcohols, in other solvents and in binary mixtures were studied. Tetralin was found to be the most effective liquefaction solvent, but methanol and ethanol were the active ones in coal swelling. Synergistic effects were observed when the mixtures of tetralin and methanol or ethanol were used for liquefaction and swelling. The effect of binary solvents was shown to be due to the ability of alcohol components to cause brown coal to swell improving the availability of the fragments of coal matter for the reactive hydrogen donor tetralin molecules.

Coal characterization for liquefaction in tetralin and alcohols

Abstract Kansk-Achinsk lignite hydrogenation in tetralin, isopropanol, ethanol and methanol was studied. Tetralin was the most active solvent. Synergetical effects were observed when the mixture of tetralin and alcohols was used for liquefaction. The variations in liquid product composition were analysed by a mechanistic numerical model incorporating two competing reactions: alkylation and hydrogen donation. The effect of preliminary O -methylation with (CH 3 ) 2 SO 4 , reduction with LiAlH 4 and with K/isopropanol and reductive methylation with K CH 3 J on the oxygen functional group composition and liquefaction behaviour were examined for three coals with different rank. Coal pretreatments were shown to cause dramatic effects on the oxygen-containing group distribution. The liquefaction reactivity with methanol in the presence of ZnCl 2 and NaOH catalysts decreased slightly. The liquefaction behaviour is strongly influenced by coal rank.

Quantitative relation between the macromolecular characteristics of brown coal and its reactivity in conversion with tetralin

Abstract The reactivity of Kansk-Achinsk brown coal in thermochemical conversion with tetralin is a linear function of the network flexibility, which is primarily controlled by ionic cross-linking with carboxylate bridges via polyvalent cations such as Ca2+.

Study of Kansk-Achinsk lignite liquefaction using deuterated alcohol

Abstract Lignite liquefaction in methanol, ethanol, isopropanol and in their deuterium analogues with different deuterium substitution has been studied. Isotope effect has been estimated at deuterium substitution for α-hydrogen in ethanol and isopropanol. Deuterium distribution in maltenes, asphaltenes and solid residues has been shown to increase in the order: solid residues > asphaltenes > maltenes. CH3CD2OH had the lowest deuterating activity. In all cases deuterium has been detected mainly in aliphatic structural groups and only a little in the aromatic ring.

Chemical alteration of coals and their reactivity with tetralin and methanol under liquefaction conditions

Abstract The effect was studied of pretreatment techniques, including O-methylation with (CH 3 ) 2 SO 4 , reduction with both K-isopropanol in THF and LiAlH 4 , reductive methylation with KCH 3 I in THF and combination thereof, on the extractability in THF of coals of different rank and on their reactivity in non-catalytic hydroliquefaction in methanol and tetralin at 380 °C. Dramatic changes in composition of the treated coals and products were found. Chemical pretreatment had a beneficial effect on coal solubility in THF and on hydroliquefaction in tetralin. O-methylation was the most effective for lignite, but reductive methylation had the most beneficial effect for high-rank coal. With methanol as solvent, reduction and O-methylation had a small effect on coal reactivity for liquefaction. The role of cross-links is discussed in order to explain the liquefaction behaviour of coals in solvents.

Methods for the preparation of coal-tar pitch

The production of tar pitches and binding agents for the manufacture of high-quality carbon materials is considered. The progressive scarcity of coal-tar pitch is noted. The necessity of a search for new sources of raw materials and alternative methods for the production of coal-tar pitch substitutes is substantiated. The capabilities of different methods for the thermal and thermochemical processing of coals with the production of pitch-like products are considered. The prospects of a low-temperature process of the thermal dissolution of coals under mild conditions for the preparation of pitch products in a yield much higher that the yield of pitch upon coking are demonstrated.

Activity of the Pt/WO 4 2− /ZrO2 catalyst in hydroisomerization reaction of n-heptane-benzene mixture

The results on investigation of the catalytic properties of platinum-containing, tungstate-modified zirconium dioxide in the hydroisomerization reaction of n-heptane or a n-heptane-benzene mixture have been presented. It has been shown that n-heptane isomerization on the catalysts synthesized was effective in the presence of benzene at 200–225°C. It has been found that the catalytic activity of the Pt/WO42−/ZrO2 catalyst decreases with increasing reaction temperature (250–280°C). The catalysts have been examined by the DSC method. It has been shown that the amount of coke deposed on the catalyst surface increases and its resistance to burning in regeneration is enhanced with an increase in the hydroisomerization reaction temperature.

Structural properties and state of the surface layer of zirconium dioxide modified by tungstate anions

A tetragonal metastable phase of zirconium dioxide formed after the addition of tungstate anions (>13 mol %) to the hydroxide precursor by different methods with heating (600–700°C), as revealed by X-ray diffraction analysis and X-ray photoelectron and IR spectroscopy. The W6+ and W5+ cations formed a solid solution with ZrO2. On the surface of the solid solution, the tungsten cations formed tungstate clusters (−WOx−)n. The formation of the WO3 phase was observed at concentrations of tungstate anions higher than 17.6 mol % or at temperatures of 850–870°C.