Vol.1 No.3 2009

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Research paper : Development of highly-active hydrodesulfurization catalyst for sulfur-free diesel production (Y. Yoshimura et al.)−166 Synthesiology - English edition Vol.1 No.3 (2009) (12)−The stability of activity of the developed catalyst is the most important element of an industrial catalyst. A lifetime test of the developed LX-NC1 catalyst using bench apparatus confirmed very high stability; i.e., during operation to produce diesel with a sulfur content of 7 ppm, the activity reduction rate was less than 1.0 °C/month after a time on stream of two months.6 Future PlansThe LX-NC1 catalyst for sulfur-free diesel, developed using a new design concept and an advanced catalyst preparation method, can reduce sulfur content from straight-run gas oil both economically and efficiently to produce sulfur-free diesel, and can adequately meet the requirements for sulfur-free diesel production by refineries both in Japan and overseas. It is expected that after the introduction of sulfur-free diesel in Japan and overseas, market introduction of new automotive technologies, including new exhaust post-treatment technologies with the problem of sulfur poisoning mitigated or solved, will be accelerated, resulting in reduced diesel exhaust-gas emissions and improved fuel consumption of diesel engines (reduced CO2 emissions).On the other hand, with the stringent regulation of sulfur in gasoline, sulfur-free gasoline was introduced in 2008 in Japan. The sulfur content of premium gasoline had been below 10 ppm, and the issue was to also reduce sulfur in regular gasoline to below 10 ppm.The main blending stock of regular gasoline is a high-octane gasoline obtained by fluid catalytic cracking of heavy oil, known as FCC gasoline. Most of the sulfur content in regular gasoline comes from FCC gasoline, and hydrodesulfurization technology was therefore required to both reduce sulfur in FCC gasoline and maintain the high octane number. The following hydrodesulfurization processes have been studied: (1) hydrodesulfurization in the fluid catalytic cracking unit; (2) a process in which deep hydrodesulfurization of FCC gasoline is prioritized (simultaneous deep hydrogenation of olefins) and the octane number loss is then compensated for by alkylation, etc.; (3) a selective hydrodesulfurization process in which the hydrogenation of olefins contained in FCC gasoline is minimized (minimization of octane number loss), and thiophenes and thiols are selectively hydrodesulfurized; and (4) an alkylation desulfurization process in which olefins and sulfur compounds contained in FCC gasoline are alkylated and the produced high-boiling-point sulfur compounds are removed by distillation. The hydrodesulfurization processes in (2) and (3) were commercialized. The hydrodesulfurization process in (3) was developed in Japan [10]. However, a study on the effect of the increased octane number of regular gasoline on fuel consumption improvement has also begun in Japan. The octane number may be increased to around 95 as in the European market (it is currently around 90 in Japan). Demand may therefore increase for hydrodesulfurization catalysts that minimize the hydrogenation of olefins (for example, olefin hydrogenation rate < 15 %) and provide high hydrodesulfurization activity.In order to improve the hydrodesulfurization selectivity of FCC gasoline, studies are mainly being conducted on the control of hydrogenation of olefins. These include the study of a method of controlling the hydrogenation and isomerization of olefins due to the movement of double bonds in olefins by controlling the acidity of the catalyst support [10], thereby weakening the adsorption of basic olefins. However, most of the conventional hydrodesulfurization catalysts contain the Type-I Co-Mo-S phase (Fig. 4), and are susceptible to hydrogen activation and the hydrogenation of double bonds even in the presence of hydrogen sulfide. Therefore, there is presumably a limit to control of the hydrogenation of olefins. The hydrodesulfurization selectivity of FCC gasoline is expected to further improve if hydrodesulfurization catalysts contain only the Type-II Co-Mo-S phase (or the Ni-Mo-S phase) and, in addition, if hydrodesulfurization activity per sulfur coordinatively unsaturated site can be improved and the solid acidity of the support can be optimized. In other countries, the sulfur concentration of FCC gasoline is a few hundred to a few thousand ppm (higher by one to two digits than the concentration in Japan), and the need for improved hydrodesulfurization selectivity is higher than in Japan. We plan to apply the preparation method for the developed gas oil hydrodesulfurization catalyst to the production of selective hydrodesulfurization catalysts for FCC gasoline [11][12] to develop applications for the developed technology.AcknowledgementsThe LX-NC1 hydrodesulfurization catalyst for sulfur-free diesel was developed for commercialization through joint research for patent commercialization with Catalysts & Fig. 10 Hydrodesulfurization performance of the jointly developed LX-NC1 industrial catalyst .

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