“…Noting that coke is a final product in the reaction there are no limitations in the mass transference fluid−solid that involve coke. There is an excess of hydrogen during the reaction and since the equilibrium between gas and liquid phases is reached rapidly, it is valid to consider, as some other authors have, that hydrogen concentration in the liquid phase remain constant and there are not gas−liquid diffusion problems. − Then, for our calculations we assume the hydrovisbreaking process to be kinetically better than diffusionally controlled. 1 Evolution of the different fractions obtained by hydrothermal processing.…”
A residue from deasphalting a syncrude obtained by direct coal liquefaction of a subbituminous Spanish coal was processed by thermal hydrotreatment. Kinetic study of the cracking reaction and coke formation reaction has been performed. The viscosity, coke content, boiling point distribution, elemental analysis, and aromaticity of the reaction products have been determined. The experimental data fits with the first-order kinetic model proposed. The main effects observed with the thermal hydrotreatment have been a large decrease of the viscosity that varies from 4608 cSt in the feedstock to 147 cSt in the products. The conversion of the heavy fraction (bp > 350 °C and soluble in toluene) and asphaltenes increased with the temperature and residence time, and the formation of coke was inhibited even at the hardest reaction conditions used. At 425 °C a kinetic control conducts the reaction, the cracking reaction with lower activation energy was more favorable and the coke formation (condensation) remained almost completely inhibited.
“…Noting that coke is a final product in the reaction there are no limitations in the mass transference fluid−solid that involve coke. There is an excess of hydrogen during the reaction and since the equilibrium between gas and liquid phases is reached rapidly, it is valid to consider, as some other authors have, that hydrogen concentration in the liquid phase remain constant and there are not gas−liquid diffusion problems. − Then, for our calculations we assume the hydrovisbreaking process to be kinetically better than diffusionally controlled. 1 Evolution of the different fractions obtained by hydrothermal processing.…”
A residue from deasphalting a syncrude obtained by direct coal liquefaction of a subbituminous Spanish coal was processed by thermal hydrotreatment. Kinetic study of the cracking reaction and coke formation reaction has been performed. The viscosity, coke content, boiling point distribution, elemental analysis, and aromaticity of the reaction products have been determined. The experimental data fits with the first-order kinetic model proposed. The main effects observed with the thermal hydrotreatment have been a large decrease of the viscosity that varies from 4608 cSt in the feedstock to 147 cSt in the products. The conversion of the heavy fraction (bp > 350 °C and soluble in toluene) and asphaltenes increased with the temperature and residence time, and the formation of coke was inhibited even at the hardest reaction conditions used. At 425 °C a kinetic control conducts the reaction, the cracking reaction with lower activation energy was more favorable and the coke formation (condensation) remained almost completely inhibited.
“…The first one is the direct cracking of the central ring to monocyclic aromatics, and the second one is the isomerization and hydrogenation of the terminal ring with next cracking to bicyclic or monocyclic aromatic hydrocarbons. Wiser et al − showed that 9,10-DHA prefers the hydrogenation and cleavage of the terminal ring rather than the cleavage of the central ring under catalytic and thermal hydrocracking conditions. Cowley et al investigated anthracene hydrocracking to benzene and its alkyl derivatives to determine the thermodynamic possibility of converting multicyclic aromatics into monocyclic aromatics via the selective hydrocracking of the central ring.…”
To investigate the hydrocracking mechanisms of polycyclic aromatic hydrocarbons, we used HZSM-5 with one Al substitution (T1, T3, T5, T7, T11, and T12) as a solid acid catalyst and 9,10-dihydroanthracene as a model substrate on the basis of periodic density functional theory computations. It is found that the intersection of the straight and sinusoidal channels is energetically more favored than the individual sinusoidal and straight channels due to their different local environments. On the basis of the computed Gibbs free energy at 500 °C, the rate-determining step for the formation of 1-benzyl-2-methylbenzene as the first intermediate is the heterolytic activation of H 2 , which is encapsulated in a conjugated frustrated Lewis pair (FLP), generated from the acidic O−H proton transfer to the hydrocarbon substrate. For the subsequent formation of toluene or benzene and o-xylene from 1-benzyl-2-methylbenzene hydrocracking, the rate-determining step, which is the heterolytic activation of H 2 encapsulated in a conjugated FLP, determines the selectivity. On the basis of the apparent Gibbs free energy barriers at 500 °C, the activity has the decreasing order of T5 > T11 > T1 ≈ T12 ≈ T3 ≈ T7. It is noted that there is no correlation between the Gibbs free energy barriers and the acidic strength based on O−H deprotonation Gibbs free energy and the adsorption enthalpy of pyridine as a probe molecule.
“…The reaction pathway characterizing hydrogenation and hydrocracking of six-carbon-membered-ring-containing aromatic compounds such as naphthalene, anthracene, phenanthrene, and pyrene have been reported (Qader and 320, 350, 380 310, 350, 380 380 220, 160, 100 350, 60, 35 8, 15, 20 Hill, 1972; Qader et al, 1973;Qader, 1973;Wu and Haynes, 1975; Huang et al, 1977;Veluswamy, 1977;Shabtai et al, 1978;Wuu, 1983;Stephens and Chapman, 1983;Stephens and Kottenstette, 1985). Typical hydrocracking pathways proceed through terminal-ring hydrogenation followed by possible isomerization to compounds containing a methylcyclopentyl moiety, ring opening, and dealkylation.…”
Catalytic reaction pathways for fluoranthene hydrogenation and hydrocracking were determined at 310 to 380 °C and 153 atm of total pressure. Fluoranthene hydrogenation was catalyzed by a presulfided NiW / A1203 catalyst, whereas its hydrogenation and subsequent hydrocracking were catalyzed by a presulfided NiMo/zeolite-Y catalyst. The activities for conversion of fluoranthene were comparable, as the fluoranthene disappearance rate constant k (cm3 of solution/(g of catalyst s)) = 0.28, 0.70, and 1.2 at 320, 350, and 380 °C, respectively, for the reaction catalyzed by NiW/A1203, suggesting Arrhenius parameters of [log A (cm3 of solution/(g of catalyst s)), E&ct (kcal/mol)] = [6.4, 18.7], whereas k = 0.27, 0.63, and 1.00 at 310, 350, and 380 °C, respectively, with [log A, Eact] = [4.8, 14.2] for the reaction catalyzed by NiMo/zeolite. Hydrocracking of the five-carbon-memberedring-containing fluoranthene had kinetically significant cleavage pathways distinct from those observed for the six-carbon-membered-ring-containing fused-ring polynuclear aromatic compounds. The former should, therefore, be regarded as a separate class in modeling the conversion of heavy oil feedstocks; the data presented here provided a basis for such modeling.Limitations in supplies of petroleum have focused attention on increasingly heavy oils for the production of gasoline, lubricants, and chemicals. Hydrocracking was developed as a process to provide flexibility in refining to make gasoline and light oils from less valuable petroleum stocks such as residua, cycle oils, gas oils, and cracked and
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