A 35S radioisotope pulse tracer method using 35S-labeled H2S was used to investigate the sulfidation state of Mo-based catalysts supported on TiO2. Despite the coverage of Mo species on the TiO2 support, sulfidation of the TiO2 support still occurred at 300°C. The sulfided catalysts could be reduced under H2 atmosphere. A 35S radioisotope tracer method using 35S-labeled dibenzothiophene ([35S]DBT) was used to determine the sulfur mobility on the working sulfided Mo/TiO2 catalysts. The amount of labile sulfur (So), which represents the amount of active sites, and the release rate constant of H2S, which represents the mobility of the active site (kRE), were estimated. Compared with Mo/Al2O3 catalyst, Mo/TiO2 catalyst had slightly higher So and about 2 times higher kRE, which indicate that new mobile active sites were formed on sulfided Mo/TiO2 catalyst. Comparison of the kRE and So of titania-based and alumina-based catalysts suggested that the active phase consisted of a ‘TiMoS’ phase exhibiting a promoting effect similar to the well-known ‘CoMoS’ phase (promotion of the MoS2 active phase by Ti atoms). Hydrodesulfurization (HDS) of DBT was evaluated over Mo catalysts supported on titania synthesized by the pH swing method, which provides a TiO2 carrier with a high specific surface area (134 m2·g-1) and excellent mechanical properties. The activity increased linearly with Mo content up to ca. 16 wt% MoO3 and then decreased for higher Mo loadings. The optimal Mo dispersion on this catalyst was 5.2 atom/nm2, which is higher than the optimal Mo dispersion on 70 m2·g-1 TiO2 (4.2 atom/nm2). [35S]DBT HDS catalyzed by CoMo/TiO2 showed that So increased in parallel with the catalytic activity up to a Co/Mo molar ratio of 0.4. Only a slight increase in kRE was observed with Co addition, unlike CoMo/Al2O3 catalysts.
The steam reforming of ethanol for producing hydrogen was evaluated over 5 wt% Co catalysts supported on perovskite-type oxides, La1-xSrxBO3 (B = Al, Cr, Mn, Fe, x = 0-0.2) at 823 K with a molar H2O/C2H5OH ratio of 6. Co/LaAlO3 showed higher catalytic activity and stability than Co catalysts supported on LaCrO3, LaFeO3 and LaMnO3. The molar La/Al ratio markedly affected the stability of Co/LaAlO3 catalyst and a molar La/Al ratio of 1 was the most suitable, suggesting that the properties of the perovskite structure are important in the catalytic activity and stability. Partial substitution of Sr2+ for La3+ in LaAlO3 resulted in further remarkable improvement of catalytic activity and hydrogen yield. We consider that enhanced mobility of lattice oxygen in La1-xSrxAlO3-δ allows more frequent participation in the oxidation of intermediates over metallic cobalt, leading to both high catalytic activity and stability of Co/La1-xSrxAlO3-δ in comparison with Co/LaAlO3.
The synergism of hydrogen bond-type ultraviolet absorbers (UVA), such as phenyl salicylate and benzotriazole type UVA, and hindered amine light stabilizers (HALS) was investigated and compared with that of benzophenone type UVA. Phenyl salicylate and benzotriazole type UVA showed a similar synergistic and antagonistic interactions with HALS to those for benzophenone type UVA, but the synergism exceeded the antagonism. The order of their synergism of preventing photooxidation was benzotriazole > phenyl salicylate > benzophenone for UVA. The order and the degree of the synergism agreed completely with those of the regeneration of new UVA by the reaction of UVA quinones, accidentally formed by scavenging peroxy radicals, with HALS. Therefore, such generation is concluded as the essence of synergism of UVA with HALS.
The interaction of benzoate-type ultraviolet absorbers (UVA) with hindered amine light stabilizers (HALS) was investigated. Benzoate-type UVA showed antagonism or synergism with HALS, depending on the chemical structures of the UVA. p-Aminobenzoates exhibited antagonism with HALS to accelerate the photo-oxidation, despite absorbing UV rays with considerably high absorption coefficients. In contrast, p-hydroxybenzoates showed synergistic photo-antioxidant activity with HALS, despite no or little absorption of ultraviolet rays. The synergism has been ascribed to conversion into benzophenone-type UVA by a photo-Fries rearrangement. This mechanism can explain the photo-antioxidant ability of substituted phenyl p-hydroxybenzoates, but not that of alkyl p-hydroxybenzoates not undergoing the photo-Fries rearrangement. This study proposes a new and comprehensive synergism in which the photo-antioxidant activity of p-hydroxybenzoate is due to the formation of a UV-absorbing intermediate and a photo-antioxidant compound with a catechol structure from the reaction of the benzoate with HALS nitrosonium.
In this study a simple and applicable scaling equation as a function of pressure, molecular weight, dilution ratio (solvent) and weight percent of precipitated asphaltene has been developed. This equation can be used to determine the weight percent of precipitated asphaltene in the presence of different precipitants (solvents) and the amount of solvent at onset point. Since increasing the pressure of crude oil decreases the amount of asphaltene precipitation, the effect of reservoir pressure has been taken into account in developing this equation. By considering the effect of reservoir pressure in developing the scaling equation and application of a genetic algorithm, the unknown parameters of the scaling equation are simultaneously and without any reservation obtained. The most important application of this unique equation is in the determination of critical point of asphaltene precipitation, known as onset point, and asphaltene precipitation in gas injection operations for enhanced oil recovery. The results predicted using the scaling equations are compared with literature precipitation data and it is shown that they are in good agreement with experimental data. The scaling equation can be used in the design of gas-injected reservoir to prevent precipitation of the asphaltene aggregates in the reservoir.
The vapor-liquid equilibria (VLE) data of systems including tetrahydropyran (THP) are impotant, as tetrahydropyran is a useful reaction solvent and separation solvent, but are scarce in the literature. The boiling points of three binary systems at six pressures from 40.00 to 98.66 kPa were measured using a hold-up compensable ebulliometer. The binary system consisting of THP + toluene was nonazeotropic, whereas THP + n-heptane and THP + water were azeotropic. Furthermore, the THP + water system formed heterogeneous mixtures. Measured boiling points were satisfactorily correlated using the NRTL (Non Random Two-Liquid) equation. The mean deviations between the experimental and calculated boiling points were 0.08 K for THP + n-heptane, 0.09 K for THP + toluene and 1.75 K for THP + water systems. The ASOG (Analytical Solution of Groups) group pair parameters for the CH2, ArCH, H2O, and pyran groups were determined. Infinite-dilution partial molar excess entropies and enthalpies were determined for THP and solvents.
The liquid-phase oxidation of benzene to phenol was investigated in the biphasic benzene-water system using VCl3 and molecular oxygen as the catalyst and oxidant, respectively. Benzene was dissolved in the aqueous catalyst phase and reacted with oxygen to form phenol. Phenol was preferentially extracted into the benzene phase, thus suppressing the formation of over-oxidized byproducts. During the reaction, the catalyst was oxidized and deactivated. To regenerate the catalyst, a regenerator was installed into the system. Hydrogen was fed to the regenerator to reduce the deactivated catalyst, but no significant improvement of the system performance was observed without the presence of a second catalyst. Pd sheet in the regenerator allowed the system to run very stably, and the system was easy to shut down and start up.