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.)−162 Synthesiology - English edition Vol.1 No.3 (2009) 2 Objectives and Outcomes of ResearchDiesel fuel is produced by the hydrodesulfurization process in which sulfur (1 to 1.5 wt%) in organic sulfur compounds contained in the gas oil is removed as a hydrogen sulfide by reacting it with hydrogen over a hydrodesulfurization catalyst, thereby converting it to hydrogen sulfide (Fig. 2). With the stringent regulation of sulfur content, the performance of hydrodesulfurization catalysts has gradually improved, resulting in a significant improvement in hydrodesulfurization activity over the past 10 years.In order to produce sulfur-free diesel under the same conditions as those for producing one-generation-older diesel fuel with a sulfur content below 50 ppm, a highly active catalyst (with about double the activity) is required; in other words, comparable hydrodesulfurization activity can be obtained even at a reaction temperature about 10 °C lower. In the hydrodesulfurization reaction, as the time on stream elapses, the desulfurization activity gradually decreases. Therefore, the quality of the diesel is compensated to ensure a sulfur content below 10 ppm by gradually increasing the reaction temperature; e.g., about 1 °C increase/month. However, carbon deposition on the catalyst surface and structural changes in the catalyst’s active components become significant at higher reaction temperatures. Therefore, there are limits to temperature compensation in the high-temperature range. Increasing hydrodesulfurization activity even under lower temperatures is essential for the stable production of sulfur-free diesel (expansion of the temperature compensation range). Hydrodesulfurization catalysts for sulfur-free diesel production have already been developed and commercialized by catalyst manufacturers such as Criterion Catalyst, Haldor Topsøe A/S, and Albemarle Catalyst, as well as oil companies such as Exxon Mobil, IFP/Axens, Cosmo Oil, and Nippon Oil. However, they may be subject to constraints in terms of gas oil types and the operating conditions of hydrodesulfurization facilities. Research and development of high-performance hydrodesulfurization catalysts, i.e., catalysts offering activity enhancement under lower reaction temperatures and longer life, is still ongoing.We considered that in developing hydrodesulfurization catalysts for sulfur-free diesel, the key to high performance would be the catalyst preparation technology, and conducted full research to refine the developed catalyst preparation technology into “a catalyst preparation technology that can be applied to existing hydrodesulfurization catalyst production lines without the need for modifications.” Specifically, the following research objectives were formulated as representative examples.Issues related to performance and use of hydrodesulfurization catalysts:(1) Hydrodesulfurization catalysts with an activity more than double that of conventional desulfurization catalysts (for diesel with a sulfur content below 50 ppm)(2)Hydrodesulfurization catalysts with a lifetime longer than two years (temperature compensation rate for catalyst deactivation: approx. <1 °C/month), comparable to that of conventional hydrodesulfurization catalysts(3)Desulfurization catalysts with handling characteristics and safety comparable to those of conventional hydrodesulfurization catalystsIssues related to production of hydrodesulfurization catalysts:(4)Upscalable catalyst preparation method (from a beaker scale of a few tens of grams to an industrial scale of tons per day) that can use inexpensive catalyst materials as with conventional hydrodesulfurization catalysts(5)Technique to identify and control determining factors in the catalyst preparation process (6)Industrial-scale production technology for the developed hydrodesulfurization catalystWe were not able to address all of the above issues by ourselves, and therefore focused on issues (1), (4), and (5), for which we possess strong research potential. In particular, we focused on issues (4) and (5) involving new preparation methods for hydrodesulfurization catalysts, and jointly developed other items with a catalyst manufacturer. The research outcomes include the commercialization of a new hydrodesulfurization catalyst for sulfur-free diesel and support for the supply of sulfur-free diesel to the market. The new hydrodesulfurization catalyst can indirectly contribute to the market penetration of diesel vehicles equipped with a high-performance exhaust-gas treatment catalyst. Such a shift to diesel engines can be expected to have a ripple effect leading to CO2 reduction in the transportation sector.3 Research Scenario to Achieve the ObjectivesAs shown by the GC-SCD chromatogram in Fig. 3, obtained by gas chromatography (GC) with sulfur chemiluminescence detector (SCD), gas oil contains various sulfur compounds (8)−Fig. 2 Schematic diagram of the hydrodesulfurization process in refineries.

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