The interaction between hindered amine light stabilizers (HALS), and ultraviolet absorbers (UVA) was investigated, in order to clarify the reason why they generally show synergism, although UVA belong to kinds of phenols. A homolytic decomposition of cumene hydroperoxide (CHP) by amine-type HALS (HALS NH) in the presence of UVA is the antagonism bringing about autoxidation. This antagonism is found considerably weaker for UVA than that of 3,5-di-t-butyl-4-hydroxytoluene. This is based on a weak proton-donating ability of UVA to HALS due to their intramolecular hydrogen bond. Furthermore, a good relationship was found between the inhibition of photo-oxidation by UVA and the initial rate of homolytic decomposition of CHP by HALS in the presence of UVA, and a strong synergism of UVA with HALS was observed. As a result, UVA are able to exhibit an apparent synergism in a combination with HALS, because of no or little acceleration (antagonism) of homolytic hydroperoxide decomposition caused by the interaction with HALS, as well as the estimated regeneration (synergism) of new UVA from the corresponding quinoide-type compounds, even if formed, by the action of HALS or the derivatives.
The reason is discussed, why ultraviolet absorbers (UVA) having phenolic moiety show the synergism with HALS apparently, on the contrarily to phenolic antioxidants. A HALS nitrosonium is a substrate causing the useless oxidation of a phenol, and is formed from HALS more easily in the presence of a phenol. However, 2-hydroxybenzophenone (2-HBP) did not accelerate the formation of the nitrosonium so fast as 3,5-di-t-butyl-4-hydroxytoluene (BHT). A HALS nitrosonium, even if formed, did not oxidize 2-HBP so much as BHT. That is, 2-HBP can continue to work longer and more efficiently in the presence of HALS. This fact suggests a weak antagonism of 2-HBP and a strong antagonism of BHT with HALS. On the other hand, quinones, derived from 2-HBP and BHT as result of peroxy radical-catching, were reduced to the corresponding hydroquinones by the action of HALS derivatives, such as HALS hydroxylamine. This reaction occurs strikingly faster and more easily for 2-HBP than for BHT. This fact shows a strong synergism of 2-HBP and a weak synergism of BHT with HALS. The above-mentioned results well explain the apparent synergism of UVA (2-HBP) with HALS, contrarily to the apparent antagonism of BHT with HALS.
Catalytic features of supported and unsupported ruthenium containing polyoxomolybdate anion (Ru2Mo14) were evaluated using the methanol transformation reaction. Decomposition of methanol into hydrogen (H2) and carbon monoxide (CO) predominantly occurred over unsupported Ru2Mo14 whereas no acid-catalyzed reaction (formation of dimethyl ether, DME) occurred indicating that Ru2Mo14 had a weak acidity or had no acidity. Ru2Mo14 was homogeneously loaded up to ca. 40 wt% on silica and titania that had been chemically modified with N -(2-aminoethyl-3-aminopropyltrimethoxysilane. Ru2Mo14 catalysts supported on these modified supports exhibited higher conversion of methanol than Ru2Mo14 catalysts either unsupported or supported on unmodified supports, indicating that Ru2Mo14 was highly dispersed on the modified supports. Even in the presence of water vapor, no steam reforming of methanol or shift reaction of CO occurred over the supported Ru2Mo14 catalysts. Ru2Mo14 catalyst supported on modified alumina support converted methanol to DME by acid-catalyzed reaction together with the decomposition products, CO and H2, indicating that the Ru2Mo14 catalyst supported on modified alumina possessed strong acidity. FT-IR measurement of the methanol species adsorbed on Ru2Mo14 catalyst supported on modified alumina and the contact time dependency of this reaction suggested that methanol decomposition proceeded via formation of formaldehyde and subsequent decomposition into CO and H2.
Conventional simulations of hot water flooding processes are based on fully-implicit finite difference (FD) thermal models, which have been successfully applied to thermal simulation. However, these models require long computational times and may suffer from grid orientation effects. Streamline simulation offers a viable alternative to FD simulation if the reservoir heterogeneity and fluid mobility dominate the displacement mechanism. This paper describes the development and verification of a new streamline-based model, and applications to the simulation of hot water flooding processes in heavy oil reservoirs. For simplification of the modeling, heat was assumed to transfer only by convection, in the direction parallel with the flowing phases. This convective heat flow was solved implicitly along streamlines. An important extension of this method did not assume volumetric heat flux along streamlines as a constant but as a variable depending on the temperature and pressure. This variable was introduced as a sink or source in the streamline heat transport model. The developed model was applied to three case studies and the results were compared with those from the 5- and 9-point schemes of a commercial fully-implicit thermal simulator. The streamline results were closer to those of the 9-point scheme than the 5-point scheme. The results also demonstrated that the streamline-based model minimizes the grid orientation effects and requires less time than the FD thermal model.
Dimethyl ether (DME) synthesis via the reforming of methane (CH4) by carbon dioxide (CO2) and steam (H2O) was investigated using a model synthesis gas obtained by the reforming of CH4. Reforming of CH4 over Ni/α-Al2O3, Ru/α-Al2O3, Ni/MgO-Al2O3 and Ru/MgO-Al2O3 catalysts showed that CH4 conversion was strongly affected by temperature, but not by CO2/CH4 and H2O/CH4 molar ratios. CO2 conversion was strongly affected by temperature, and CO2/CH4 and H2O/CH4 molar ratios. M value [H2/(2CO + 3CO2) molar ratio] was strongly affected by temperature and CO2/CH4 molar ratio, but not by H2O/CH4 molar ratio. Using Ni/MgO-Al2O3 and Ru/MgO-Al2O3 catalysts, CH4 conversion almost reached equilibrium in 800 h durability tests, and carbon deposition on the catalyst was very low. DME synthesis was investigated using the model synthesis gas obtained by the reforming of CH4 by CO2 and H2O through two reactions, the one-step reaction with a hybrid catalyst structure and the two-step reaction with separated catalysts. The 2000 h durability tests showed that (methanol + DME) yield through the one-step reaction was higher in the first stage than through the two-step reaction, and decreased gradually with time. However, the (methanol + DME) yield hardly decreased through the two-step reaction for the whole test time. DME selectivity was stable in both one-step and two-step reactions for 2000 h. Moreover, the two-step reaction gave 20% or more higher (methanol + DME) yield and DME selectivity from the model gas containing CO compared to those from the mixed gas of H2 and CO2 not containing CO.
Poisoning by very small amounts of nitrogen compounds was investigated for the catalysts for two types of hydrocracking processes. Nitrogen-free vacuum gas oil was used as feedstock with carbazole and tributyl amine as the model nitrogen compounds. Carbazole is abundant in hydrotreated oil as carbazole is difficult to remove. Tributyl amine is easily converted to ammonia in the reactor. Vacuum gas oils containing various amounts of carbazole were passed over the main hydrocracking catalyst of the two-stage hydrocracking process. Strong effects on both hydrocracking activity and middle distillate selectivity were observed, especially if nitrogen content was less than 2 wtppm. The nitrogen poisoning effect was stronger on the catalyst with higher activity than on the catalyst with lower activity. Poisoning of the main hydrocracking catalyst of the single-stage hydrocracking process, which is affected by both organic nitrogen compounds and ammonia, was evaluated with several ratios of combinations of carbazole and tributyl amine, maintaining total nitrogen concentration at 300 wtppm. Increased carbazole ratio lowered the hydrocracking activity and increased the middle distillate selectivity especially if the concentration of nitrogen as carbazole was less than 20 wtppm. These experimental results indicate that there is an optimum range of nitrogen concentration in the effluent to the main hydrocracking reactor to maximize middle distillate selectivity without severely affecting the hydrocracking activity.
MFI-type titanosilicate zeolite TS-1 is synthesized via a newly developed mechanochemical route, and the effects of mechanochemical reaction conditions on the physical and chemical properties are investigated. In the mechanochemical route, titania and silica powders are ground by using a planetary ball mill to yield a silica-titania composite powder, which is converted into TS-1 through hydrothermal treatment. TS-1 samples are characterized by powder X-ray diffractometry and UV-visible spectroscopy, and their catalytic activities in the alkene oxidation reaction are evaluated. Several parameters of the mechanochemical reaction such as the disk rotation speed, the grinding time, and the molar ratio of silica and titania are changed to evaluate their effects on the properties of resulting materials. It is demonstrated that these parameters have significant effects on the physical and chemical properties of the final product.
Hydrodesulfurization (HDS) of thiophene over silica-modified alumina-supported platinum (Pt/SiO2-Al2O3) catalysts was examined. The HDS activity of a Pt/Al2O3 catalyst was enhanced by silica modification. However, the optimal silica loading for HDS activity could not be identified. The dispersion of platinum on alumina, as measured by the hydrogen adsorption method, was enhanced by silica modification and the optimal silica loading for platinum dispersion was 10 to 40 wt%. The acidity of SiO2-Al2O3 was evaluated by 2-propanol dehydration (200°C) and cumene cracking (400°C). The optimal silica loading for the acidity of SiO2-Al2O3 was 90 wt%. Furthermore, the presence of Brönsted acid sites on SiO2-Al2O3 was confirmed by a pyridine adsorption method with FT-IR spectroscopy. The high HDS activity of the Pt/SiO2-Al2O3 catalyst is caused by both high Pt dispersion and formation of Brönsted acid sites.
Ru-SiO2 catalysts with uniform structure were prepared by the alkoxide method using various Ru precursors, and used to catalyze the Fischer-Tropsch (F-T) synthesis in the slurry phase under the reaction conditions of T = 503 K, P = 1 MPa, H2/CO = 2/1, and W/F = 5 g-catal.h/mol. All catalysts showed stable activity during the F-T reaction for 40 h. The CO conversion was relatively low over the catalyst prepared from ruthenium chloride, because of the trace amounts of residual Cl on the surface. The catalysts prepared from ruthenium nitrosyl nitrate and ruthenium acetylacetonate showed high activity, with suppression of CH4 and CO2 formation. The CO conversion linearly increased with the loading amounts of Ru, indicating identical dispersion of Ru regardless of the amount. The olefin/paraffin ratio of the products could be explained in terms of the electronic state of Ru on the catalysts.