Canadian oil sands bitumen contains no naphtha, about 44% gas oils, and 56% vacuum bottoms, as well as many "nasty" materials such as sulfur, nitrogen, aromatics, carbon residue, metals, and asphaltenes. Therefore, the technologies to upgrade bitumen are unique. The upgraded product, synthetic crude oil (SCO), contains less naphtha, more middle distillates and gas oils than conventional crude oil, and no bottoms. SCO contains very low sulfur but relatively high aromatics; therefore, it has a low diesel cetane number and jet fuel smoke point. Improving SCO quality is an ongoing challenge. This paper reviews the properties of bitumen, research on bitumen upgrading, the quality of upgraded products, and implications of processing bitumen products in conventional oil refineries.
This selective review discusses nonhydrogenation desulfurization processes, particularly oxidative desulfurization, for the manufacture of ultra clean fuels. The environmental regulations for transportation fuels are becoming more and more severe, and the statutory sulfur content in various fuels was reduced to below 10 ppm in 2005, and will be lower in the near future. However, there is considerable doubt whether conventional hydrodesulfurization processes can provide fuels with sulfur content less than 5 ppm. This review describes recent advances in nonhydrogenation desulfurization processes, particularly oxidative desulfurization, as well as our latest research results. The review consists of three sections as follows. (I) The oxidation reactivities of various sulfur- containing compounds present in fuels, oxidation and oxidative mechanisms for various oxidant-catalyst systems are introduced. (II) The oxidation of various practical fuels such as light gas oil, kerosene, and vacuum gas oil, and others are described; and the potential of various oxidative desulfurization processes for the fuels are evaluated. (III) Removal methods of oxidized sulfur compounds in various fuels are described.
The present study evaluated 129Xe NMR spectroscopy for the analysis of Co-Mo/Al2O3 hydrodesulfurization catalyst. This study also reconsidered the conventional interpretation of 129Xe NMR spectroscopy that had been used for zeolite micropore analysis. The chemical shift δ of an observed 129Xe NMR peak varied nonlinearly against the amount of adsorbed xenon N for sulfided Mo/Al2O3 catalyst. In contrast, δ was almost constant against N for dried catalyst. This result suggests that the nonlinear variation of δ against N is mainly caused by electronic interactions between xenon and coordinatively unsaturated sites on the edge of MoS2 crystallites. In addition, the xenon diffusibility δ0 calculated from 129Xe NMR spectra gradually increased with sulfidation temperature and approached the maximum value at more than 673 K, indicating that δ0 is closely related to the formation of MoS2 crystallites on the surface. δ0 became gradually larger with the cobalt loading and reached the maximum value at 5.7 mass% for sulfided Co-Mo/Al2O3 catalyst. On the other hand, δ0 increased from 0 mass% to 2.4 mass% and was almost constant at more than 2.4 mass% for sulfided Co/Al2O3 catalyst. This observation is mainly caused by the differences in the magnetic susceptibility between Co-Mo/Al2O3 catalyst and Co/Al2O3 catalyst after sulfidation. In other words, the formation of the antiferromagnetic Co-Mo-S phase causes increased magnetic susceptibility that greatly affects δ0. The slight decrease of δ0 at 7.3 mass% for sulfided Co-Mo/Al2O3 catalyst is closely related to the formation of Co9S8 prior to that of the Co-Mo-S phase. These findings strongly suggest that δ0 obtained from 129Xe NMR spectroscopy is a sensitive indicator of the amount of the Co-Mo-S phase. Furthermore, the relative hydrodesulfurization activity of various Co-Mo/Al2O3 catalysts was roughly correlated with δ0. This result also demonstrates that 129Xe NMR spectroscopy is useful for analysis of the Co-Mo-S phase on Co-Mo/Al2O3 hydrodesulfurization catalyst.
Decomposition of methane over nickel catalyst supported on spherical alumina was investigated using a thermogravimetric apparatus. The reaction products were hydrogen and multi-walled carbon nanotubes. Initial rate of carbon formation increased with reaction temperature up to 680°C. However, the initial rate decreased at higher reaction temperatures, implying that the reaction had an apparent negative activation energy, although thermodynamic considerations suggest that higher temperatures should favor the decomposition of methane. The reaction order with respect to methane was ca. 1.4, irrespective of the reaction temperature, whereas the reaction order with respect to hydrogen changed from −1/2 to zero by increasing the reaction temperature from <700°C to >720°C. The kinetic expression based on the Langmuir-Hinshelwood mechanism suggested that the rate- determining step changed from the adsorption of methane, which is disturbed by surface hydrogen atoms at below 700°C, to the dissolution of carbon species into the bulk of nickel particles at above 720°C. The apparent negative activation energy is interpreted by the decrease of solubility of carbon species into the bulk of nickel particles.
The oxidative dehydrogenation of propane to propylene was investigated over vanadate catalysts supported on calcium and strontium hydroxyapatites (VOx/CaHAp and VOx/SrHAp, respectively). Catalytic activities were improved by both CaHAp and SrHAp supports, but the improvement was greater for VOx/SrHAp than for VOx/CaHAp. The maximum yield of propylene observed for 5% VOx/SrHAp was comparable to that of Mg2V2O7, which is one of the most active catalysts for the oxidative dehydrogenation of propane. The combination of active sites for loading (VOx) and the OH groups of the support (CaHAp and SrHAp) resulted in the enhanced catalytic activity. Furthermore, the redox nature of the loading directly contributed to the enhancement of VOx/SrHAp activity. The effect of catalyst weight (5% VOx/SrHAp) relative to the feedstock flow rate on selectivities to propylene and COx suggested that oxidative dehydrogenation proceeded through a consecutive mechanism in which propylene was formed from the oxidative dehydrogenation of propane, followed by deep oxidation from propylene to COx, rather than the direct oxidation of propane.
A series of bimetallic palladium-platinum (molar ratio Pd : Pt=4 : 1) catalysts supported on ytterbium (Yb)-modified ultrastable Y (USY) zeolite, Pd-Pt/Yb-USY, were prepared and characterized to investigate the effect of Yb loading (0-10.0 wt%) on the catalytic activity. Yb loading of less than 5.0 wt% enhanced the dispersion of Pd-Pt particles as well as the catalytic activity for hydrogenation (HYD) of tetralin and hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene. Improvement of HYD of tetralin was more significant than that of HDS after Yb loading. Interestingly, Yb loading decreased the inhibitory effect of tetralin on HYD of tetralin. Acidity measurements of Pd-Pt/Yb-USY catalysts showed that Yb modification selectively decreased the number of strong acidic sites and increased the number of medium and/or weak acidic sites with little change in the total amounts of acidity compared with the Pd-Pt/USY catalyst. Dispersion measurement by CO adsorption at 50°C showed that Yb loading promoted sulfidation of the surface of Pd-Pt particles, but TPR (temperature programmed reduction) measurements of sulfided Pd-Pt/Yb-USY catalyst showed that the affinity of Pd-Pt metallic phase to S weakened after Yb modification beyond the reduction temperature of 200°C. Therefore, Pd-Pt/Yb-USY catalyst has high potential for aromatic hydrogenation of industrial feedstocks containing large amounts of aromatic compounds, because this catalyst is highly sulfur-tolerant and more aromatic-tolerant than Pd-Pt/USY catalyst under hydrogenation reaction conditions.
Carboxylation of 2-naphthol with carbon dioxide in anisole at high temperature yields 3-hydroxy-2-naphthoic acid and 6-hydroxy-2-naphthoic acid, which are difficult to synthesize by the Kolbe-Schmitt reaction. The synthesis of 6-hydroxy-2-naphthoic acid by the carboxylation of 2-naphthol with carbon dioxide in kerosene was investigated, in particular the influence of the reaction conditions, such as reaction time and reaction temperature, and the alkali metal cations of the naphthoxides. The yield of all hydroxynaphthoic acids from potassium 2-naphthoxide was higher than that from sodium 2-naphthoxide. Carboxylation of sodium 2-naphthoxide yielded small amounts of 6-hydroxy-2-naphthoic acid, whereas the potassium salt provided high selectivity for 6-hydroxy-2-naphthoic acid. Reaction conditions had little effect on product yield. In the temperature range of 513 K to 573 K, however, the yield of 3-hydroxy-2-naphthoic acid decreased and that of 6-hydroxy-2-naphthoic acid increased with higher temperature. Based on the results of thermal rearrangement and thermal decomposition profile of the product, the dependence of product selectivity on reaction temperature was primarily attributable to the thermostability of the product. This finding indicated that selective synthesis of 6-hydroxy-2-naphthoic acid could be successfully achieved by carboxylation of potassium naphthoxide in kerosene.