Desulfurizing Diesel with Ionic Liquids at Room Temperature

22 May 2009

Researchers at the Chinese Academy of Sciences (CAS) have demonstrated that ionic liquids are effective for the selective removal of aromatic heterocyclic sulfur compounds from diesel at room temperature. A paper describing their work was published in the current issue of the ACS journal Energy & Fuels.

Combustion of sulfur compounds in gasoline and diesel fuel results in emission of SO_x and sulfate particulate matter which contribute to air pollution and create acid rain. Hydrodesulfurization (HDS) is the conventional method used by refiners to remove sulfur from their fuels to meet increasingly stirngent low-sulfur regulations worldwide.

However, HDS is a high-temperature (>300 °C), high-pressure (>4 MPa), high-energy process that requires a source of hydrogen and has diffulty in removing aromatic heterocyclic sulfur compounds, such as dibenzothiophene (DBT) and its derivatives.

Accordingly, a number of alternative deep desulfurizaiton processes have been under investigation, including biodesulfurization, adsorption, oxidation, and extractive desulfurization. Recent studies have shown various ionic liquids (ILs) can be used as extractants for the removal of sulfur compounds from the fuel because of their unique chemical and physical properties, such as negligible vapor pressure, high chemical and thermal stabilities, and ability to dissolve a wide range of organic and inorganic compounds. The CAS team had earlier shown good extractive desulfurizaiton performance for fuel from a set of pyridinium-based ionic liquids (IL).

To have a better insight into the structure-property relationship of this series of ILs and design a promising extractant, the structure of the cation of pyridinium-based ILs was altered.

—Gao et al.

Results of their testing suggest that these new 3-methylpyridinium-based ILs have better extractive desulfurization performance than in the group’s earlier research. The new ILs were applied to the desulfurization of diesel fuel containing sulfur content of 97 ppm, and resulted in a sulfur reduction of 60.4%, bringing sulfur content down to 38.4 ppm. Because the ILs can be recycled, the researchers noted, deep desulfurization could be obtained.

The results suggest, they said, that the 3-methylpyridinium-based ILs are competitive and feasible for extractive desulfurization applications, and could be used at least as a complementary process to conventional hydrodesulfurization (HDS).

Resources

• Hongshuai Gao, Yuguang Li, Yong Wu, Mingfang Luo, Qiang Li, Jianmin Xing and Huizhou Liu (2009) Extractive Desulfurization of Fuel Using 3-Methylpyridinium-Based Ionic Liquids. Energy Fuels, 23 (5), pp 2690–2694 doi: 10.1021/ef900009g