Process for recovering alkali metals and sulfur from alkali metal sulfides and polysulfides

Abstract

Alkali metals and sulfur may be recovered from an oil desulfurization process which utilized alkali metal in an electrolytic process that utilizes an electrolytic cell having an alkali ion conductive membrane. An anolyte solution includes an alkali monosulfide, an alkali polysulfide, or a mixture thereof and a solvent that dissolves elemental sulfur. A catholyte includes molten alkali metal. Applying an electric current oxidizes sulfide and polysulfide in the anolyte compartment, causes alkali metal ions to pass through the alkali ion conductive membrane to the catholyte compartment, and reduces the alkali metal ions in the catholyte compartment. Liquid sulfur separates from the anolyte solution and may be recovered. The electrolytic cell is operated at a temperature where the formed alkali metal and sulfur are molten.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a continuation in part of, and claims priority to, U.S. patent application Ser. No. 14 / 210,891 (the “'891 application”), filed Mar. 14, 2014, which application claims the benefit of U.S. Provisional Patent Application No. 61 / 781,557, filed Mar. 14, 2013. The '891 application is also a continuation-in-part of U.S. application Ser. No. 12 / 576,977, filed Oct. 9, 2009, which claims the benefit of U.S. Provisional Patent Application No. 61 / 103,973, filed Oct. 9, 2008. These applications are incorporated by reference.GOVERNMENT LICENSE RIGHTS[0002]This invention was made with government support under Award No. DE-FE0000408 awarded by the United States Department of Energy. The government has certain rights in the invention.FIELD OF THE INVENTION[0003]The present invention relates to a process for removing nitrogen, sulfur, and heavy metals from sulfur-, nitrogen-, and metal-bearing shale oil, bitumen, heavy oil, or refinery ...

AI Technical Summary

Benefits of technology

[0025]Sulfur may be recovered in the liquid form when the temperature exceeds the melting point of sulfur and the sulfur content of the anolyte exceeds the solubility of the solvent. Most of the anolyte solvents have lower specific gravity compared to sulfur so the liquid sulfur settles to the bottom. This settling may occur within a settling zone in the cell where the sulfur may be drained through an outlet. Alternatively a portion of the anolyte solution may be transferred to a settling zone out of the cell where settling of sulfur may occur more effectively than in a cell.

[0026]The melting temperature of sulfur is near 115° C. so the cell is best operated above that temperature, above 120° C. At that temperature or above, the alkali metal is also molten if the alkali metal is sodium. Operation near a higher temperature, such as in the 125-150° C. range, allows the sulfur to fully remain in solution as it is formed from the polysulfide at the anode, then when the anolyte flows to a settling zone, within or external to the cell where the temperature may be 5-20° C. cooler, the declining solubility of the sulfur in the solvent results in a sulfur liquid phase forming which is has higher specific gravity and settles from the anolyte. Then when the anolyte flows back toward the anodes where sulfur is forming through electrochemical oxidation of polysulfide, the anolyte has solubility has the capacity to dissolve the sulfur as it is formed, preventing fouling and polarization at the anodes or at membrane surfaces.

Problems solved by technology

The hydrocarbon raw materials used to provide this energy, however, contain difficult to remove sulfur and metals that hinder their usage.

Sulfur can cause air pollution, and can poison catalysts designed to remove hydrocarbons and nitrogen oxide from motor vehicle exhaust.

As the price of crude oil rises, the resource becomes more attractive but technical issues remain to be solved.

Shale oil characteristically is high in nitrogen, sulfur, and heavy metals which makes subsequent hydrotreating difficult.

Heavy metals contained in shale oil pose a large problem to upgraders.

In order to remove sufficient sulfur from the bitumen for it to be useful as an energy resource, excessive hydrogen must be introduced under extreme conditions, which creates an inefficient and economically undesirable process.

As mentioned above, desulfurizing or denitrogenating using hydrogen without sodium or lithium is further complicated with the masking of catalyst surfaces from precipitating heavy metals and coke.

Although the effectiveness of the use of alkali metals such as sodium in the removal of sulfur has been demonstrated, the process is not commercially practiced because a practical, cost-effective method to regenerate the alkali metal has not yet heretofore been proposed.

Beta-alumina, however, is both expensive and fragile, and no significant metal production utilizes beta-alumina as a membrane separator.

Further, the cell utilizes a sulfur anode, which results in high polarization of the cell causing excessive specific energy requirements.

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