Yukitaka Wada

Deep hydrodesulfurization process for diesel oil

Abstract In Japan, in late 1989, the Environmental Agencys Central Council for Environmental Pollution Control instituted an exhaust gas control program for diesel vehicles, setting forth the permissible emission levels. The program not only imposes a substantial curb on NOx emissions but also calls for the reduction of black soot exhaust gas, which is peculiar to diesel vehicles, and restricts it in terms of the particulate matter (PM) emission level. Oil companies, on the other hand, have been required to reduce diesel oils sulfur content, which corrodes the equipment and piping tubes and causes deterioration of the catalyst, from 0.4% (or 0.5% under the Japanese Industrial Standards) to 0.2% by 1993 and further to 0.05% by 1997. The overall performance of the deep hydrodesulfurization (HDS) process for diesel oil is advancing with both improvements in catalysis and developments in process design. The item most focused on in the process development is how to control the color of product diesel oil. Japanese consumers of diesel oil tend to object to the current color on grounds that it reminds them of erstwhile inferior-quality products. This market inclination has become an essential point of quality control. Some problems are also discussed concerning a scale up of reactor, reactor efficiency, reaction kinetics, catalyst life and hydrogen consumption.

A new concept for catalysts of asphaltene conversion

Abstract One must understand the mechanism of bottoms cracking in asphaltene conversion in order to design a catalyst to affect this change. Asphaltene molecules are big, multiple stacked, porphyrin structures containing high concentrations of heteroatoms. They readily deactivate catalysts. Until now, the first stage of asphaltene conversion has not been given much attention. This first stage, that of demetallization, has been regarded as a simple metal take-up zone which guards the subsequent hydrotreating portion of the catalyst from undue fouling by metal sulfides. Large pore size and good strength are more important for a demetallization catalyst than are hydrotreating activity. Supported sepiolite catalysts and modifications thereof are good candidates to meet these targets.

Distribution function model for deep desulfurization of diesel fuel

We attempt the optimum design of the ultra-deep hydrodesulfurization required in the future or for the hydrogenation of aromatics in diesel oil, as the conventional reaction model based on n-th order of desulfurization is no more accurate enough. A further buildup of reaction simulator for reactor design was attempted. Distribution Function Model is developed in the present study. In this model, the distribution of rate constants is expressed with a Γ function. It is clear that the predictions agreed well with the observed data, down to the ultra-deep desulfurization range. This model could also be applied for various kinds of oil fractions and wide desulfurization reaction conditions. The reactor sizes were estimated, compared with both the distribution function and n-th order reaction models, in order to obtain diesel oil of sulfur level required by European Auto-Oil II Program. The reactor size calculated by the Distribution Function Reaction Model is estimated as being smaller than that estimated by the conventional 1.7th order. It means that a more competitive design of the process will be provided by the new model and will allow more practical feasibility study and the plant design for ultra-deep desulfurization process.