Development of highly active hydrodesulfurization (HDS) catalysts is one of the most urgent problems in the petroleum industry. Better characterization and understanding of the nature of HDS catalysts on the molecular scale are of great importance for the rational design of highly active HDS catalysts. Our approaches for this purpose involve the fabrication of model catalysts using metal carbonyls to overcome the difficulties caused by the heterogeneity of practical catalysts. One of our new approaches uses the synthesis of intrazeolite homogeneous Mo, Co and Co-Mo sulfide clusters with well defined structures. The local structure of intrazeolite Mo sulfide dimer clusters, Mo2S4, depends on the composition of the host zeolite. Thermally stabilized Co2Mo2S6 binary sulfide clusters, which show catalytic synergies between Co and Mo for thiophene HDS, with a thiocubane type structure are formed in zeolite. The intrinsic HDS activity of Co sulfide clusters depends on the host zeolite. The hydrode-selenium reaction of selenophene, combined with an extended X-ray absorption fine structure (EXAFS) study, over Mo2S4 and MoS2 clusters suggests a microscopic HDS reaction mechanism. More practical modeling of Co-Mo sulfide catalysts using a selective preparation method of CoMoS phases supported on refractory oxides is established to understand the nature of practical HDS catalysts. No effects of the support are found with the CoMoS phase supported on Al2O3, TiO2 and ZrO2, whereas the CoMoS phase supported on SiO2 shows a higher intrinsic activity. The fraction of the CoMoS phase accessible to NO adsorption is elucidated, based on the number of the CoMoS phase in the model catalyst, suggesting a new model of the CoMoS structure. The maximum potential HDS activity of Co(Ni)-Mo(W) catalysts is evaluated by using Co(CO)3NO as a probe molecule. Such model catalysts provide important information about the effects of the catalyst preparation and additives, the catalyst structure and the fundamental aspects of HDS catalysts such as microscopic reaction mechanisms and structure-reactivity relationship.
A new polymerization retarder was investigated as an alternative to highly toxic dinitrophenols for the styrene distillation process. Dodecylbenzenesulfonic acid (DBS) was found to reduce the initial rate of thermal radical polymerization of styrene. The molecular weight of polystyrene resulting from thermal polymerization was slightly higher in the presence of DBS than in the absence of DBS. 1-Phenyltetraline (1), obviously produced by isomerization of the initial Diels-Alder adduct of styrene (4), was also detected in the presence of DBS. These observations suggest that DBS behaves as an acid catalyst for the isomerization of 4 to 1. The retardation effect can be explained as the reduction of the concentration of initiate radicals generated from molecular assisted homolysis of 4 and monomeric styrene. Although only sulfonic acid cannot completely replace highly toxic and reactive dinitrophenols, it can reduce the amount of dinitrophenols required.
Bimetallic palladium-platinum catalyst supported on yttrium-modified ultrastable Y (USY) zeolite, Pd-Pt/Y-USY, showed high activity and stability for deep hydrodesulfurization (HDS) and hydrodearomatization (HDA) of diesel fuel. In model reactions, the HDS activity based on rate constant increased as much as 5.3 times and HDA activity increased as much as 1.9 times after yttrium modification. The deeper hydrogenation of 4, 6-dimethyldibenzothiophene (4, 6-DMDBT) allowed the following HDS reactions to be promoted over the Pd-Pt/Y-USY catalyst. The adsorptive interaction between Pd-Pt/Y-USY and basic tetralin was weaker than that between Pd-Pt/USY and tetralin. Under reaction conditions of P = 4.9 MPa, WHSV = 4 h-1 and T = 280°C for hydrotreating desulfurized gas oil feedstock, Pd-Pt/Y-USY successfully removed a large part of 4, 6-DMDBT and also almost all refractory alkyl-substituted sulfur compounds, which are supposed to be more difficult to hydrodesulfurize. The hydrotreated product after 216 h on stream contained 28 wtppm sulfur and 8 wt% aromatics. NH3 adsorption analyses showed that yttrium modification decreased the number of strong acidic sites with little change in the total acidic sites. This modification in acidity could help to minimize the excessive hydrocracking which causes carbonaceous deposits, and to increase the nitrogen tolerance. Scanning transmission electron microscopy (STEM) analyses clearly showed that yttrium modification suppressed the agglomeration of Pd-Pt phases, which might be linked to the high stability of the Pd-Pt/Y-USY catalyst. Therefore, Pd-Pt/Y-USY catalyst is quite promising as a second stage catalyst for the integrated two-stage reformulation of gas oils.
The applicability of liquefied dimethyl ether (DME) was evaluated as an extractant for phenol, a polar substance, in water. The phenol extraction ratio was 79% from 5.45 wt% phenol solution, and 67% from 0.11 wt% phenol solution using a liquefied DME/water volume ratio of 1.5 : 1. Phenol could be isolated from the DME phase by extraction with a water phase containing an initial phenol concentration of 1.09 wt% or more. Based on these results, a concept of the extraction process was constructed with a pressure swing method for recycling the DME extractant.
An immobilized 12-tungstophosphoric acid on an anion exchange resin (TPA/AER) catalyzes the oxidation of dibenzothiophene and 4, 6-dimethyldibenzothiophene with H2O2 in acetonitrile (MeCN) to give the corresponding sulfones as the major product. The oxidation rates increased with increasing amounts of H2O2 and TPA/AER. TPA/AER is reusable since the catalytic activity was not reduced even during the fifth cycle of use. TPA/AER acts as a catalyst for the oxidation of dibenzothiophenes in an octane/MeCN biphasic system as well. The major oxidation products were also the sulfones, which were mainly distributed in the MeCN phase. In TPA/AER-catalyzed oxidative desulfurization of diesel oil containing 330 ppm sulfur, the reduction of the sulfur content was enhanced with increasing amounts of immobilized TPA per unit weight of AER and the sulfur content was reduced to below 50 ppm. The sulfur content was further decreased by solvent extraction with MeCN.
The combinatorial approach is a successful tool for material development and for heterogeneous catalyst development. Combinatorial tools were developed consisting of a high-throughput screening reactor using a 96-well microplate, activity mapping by a neural network and optimization by a genetic algorithm. The tools were designed and manufactured to optimize Cu-based oxide catalyst for methanol synthesis. Escape from local optima in the search space is easy by GA, but the efficiency of search is not so high. Instead of GA, a more straight-forward method was applied: all 230, 000 activities of all possible combinations of catalyst components with 5% resolution were predicted by a neural network. These activities were visualized by mapping using two parameters, such as Cu and Zn composition, to find the global optimum.
Cu-Zn oxide catalyst for methanol synthesis was optimized using an activity map by neural network method. The catalyst composition was determined randomly and the training data were measured in a high-pressure HTS reactor using a 96-well microplate system. In this case, the data around the optimum were usually scattered with increasing parameters, despite 95 datasets causing low accuracy of the prediction. To obtain effective datasets for training, design of experiment was employed. After 18 datasets of catalyst composition-activity were designed and measured, a variety of neural networks were constructed. Each maximum was determined by the activity-envelope method and the best neural network was compared with that constructed from the 94 datasets. Design of experiment combined with the neural network was useful to determine the optimum catalyst composition.
Sulfur dioxide can be removed from exhaust gases by oxidation to sulfuric acid over an activated carbon catalyst in the presence of water. A manufacturing method for activated carbon was developed based on the steaming of wood at relatively low temperature. The catalytic activity of the activated carbon produced from wood for the oxidation of sulfur dioxide was compared with those of commercially available activated carbons. The carbon produced from wood showed high activity, but it was lower than that of a highly developed catalyst such as activated carbon fiber. However, the potential utilization of waste wood as an environmental catalyst was clearly demonstrated.
A mathematical model for miscible displacement in fractured porous media is developed. The model takes into account advective, gravitational and crossflow mechanisms of mass exchange between fracture and matrix. The model is normalized by using the dimensionless parameters which characterize the process, and the analytical solutions of the resulting system of equations are provided by utilizing the method of characteristics. The model developed has been compared with experimental results and with previous model, which includes only crossflow between fracture and matrix. There is very good agreement between experiments and this model prediction.