compounds in the fuels are converted to sulfur oxide, i.e. SOx, during their combustion. Therefore, amounts ... has several advantages compared with a classical.
OXIDATIVE DESULFURIZATION OF DIESEL FUELS BY MOLECULAR OXYGEN
+ 2 RCHO + 2 O2 S
Satoru Murata, Kazutaka Murata, Koh Kidena, and Masakatsu Nomura
+ 2 RCOOH
Introduction Deep desulfurization of petroleum-derived fuels is nowadays the most important technology in petroleum industry. Sulfur-containing compounds in the fuels are converted to sulfur oxide, i.e. SOx, during their combustion. Therefore, amounts of S-compounds were strictly limited. For example, regulation of sulfur amounts in diesel fuels in Japan is 500 wtppm, and the value will be reduced to 50 wtppm in 2005 and 10 wtppm in 2008. Petroleum-refining and catalyst-making companies, therefore, are trying to develop new and efficient desulfurization processes and highly active catalysts. In 1990s, an epoch making process was proposed, so-called, oxidative desulfurization (ODS). ODS consists of two processes: the former one is oxidation of sulfur-containing compounds in feeds and the latter is removal of oxidized S-compounds from the feeds. ODS has several advantages compared with a classical hydrodesulfurization process: (1) reaction conditions are very mild such as ambient pressures and temperatures, (2) there are high potentials for desulfurization of sterically hindered thiophene derevatives, and (3) expensive hydrogen is not required. Oxidants examined were peroxyacetic acid, hydrogen peroxide-acetic or formic acids, hydrogen peroxide-polyoxometalte, etc.1 Photoirradiation of DBT in the presence of sensitizer or catalyst under molecular oxygen was also examined.2 The authors are very interested in oxidation with peroxy carboxylic acids, because reaction proceeds rapidly and selectively. However, large scalestorage and usage of peroxide are somewhat dangerous. Transition metal-catalyzed co-oxidation of aldehydes and organic substrates with molecular oxygen may solve the above problems. Co-oxidation of aldehydes and alkenes are well known, and extensively studied by several authors. The reaction is believed to proceed via two steps, autoxidation of aldehydes to peroxy acids and oxidation of alkenes to oxyranes by peroxy acids produced in situ (eq .1).3
Cat.
O + RCOOH
(1)
Therefore, the authors examined the co-oxidation of aldehydes and Scontaining compounds such as dibenzothiophene (DBT) by molecular oxygen to develop a new system for deep desulfurization of petroleum-derived fuels. Experimental Typical procedure for oxidation of model compounds was as follows: A mixture of cobalt(II) acetate (0.05 mmol), n-octanal (4 mmol), DBT (1 mmol), and benzene (10 mL) was stirred at 40 oC under ambient pressure of oxygen. Time-profiles of DBT conversion was monitored by gas chromatographic analysis.
In order to check the stoichiometry of this reaction, the following experiments were conducted: A benzene solution containing cobalt acetate (0.05 mmol), DBT (1 mmol), and n-octanal (1 mmol) was stirred at 40 oC for 15 min under oxygen, GC-analysis of the products indicating formation of 1 mmol of n-octanoic acid and 0.5 mmol of DBT sulfone, and recovery of 0.5 mmol of DBT. In the absence of either cobalt catalyst or aldehyde, the reaction did not proceed and DBT was recovered almost quantitatively. These results indicate that the stoichiometry of the reaction obey the equation 2. Several metal salts and aldehydes were examined as catalysts and sacrificial materials for this reaction, respectively, the results being summarized in Table 1. This indicates that both cobalt(II) acetate and chloride are the most suitable catalysts among the metal salts employed and aliphatic aldehydes with 6-10 carbons and benzaldehyde could be used instead of n-octanal. Table 1. Oxidation of DBT with molecular oxygen in the presence of several transition metal salts and aldehydes. Conv. of Metal salt Aldehyde DBT (mol%) Co(OAc)2 n-octanal > 99 CoCl2 n-octanal > 99 Mn(OAc)2 n-octanal > 99 Ni(OAc)2 n-octanal 54 CuCl n-octanal 35 none n-octanal 0 Co(OAc)2 none 0 Co(OAc)2 n-hexanal > 99 Co(OAc)2 n-decanal 96 Co(OAc)2 benzaldehyde 93 Co(OAc)2 cinnamaldehyde 0 Then, the authors tried to desulfurization of commercial diesel oil by this method. The commercial oil (100 mL) was treated with cobalt acetate (0.1 mmol) and n-octanal (16 mmol) at 40 oC for 16 h under oxygen. Oxidized S-compounds were removed from the feed by adsorption with alumina. Concentration of sulfur could be reduced from 193 wtppm (in the original feed) to
