Selective liquid-liquid extraction of oxidative desulfurization reaction products

Abstract

The present invention provides selective extraction of sulfoxides, or sulfoxides in combination with sulfones, from hydrocarbon mixtures containing these compounds. A significant advantage of the invention is that oxidation products resulting from oxidative desulfurization of hydrocarbon feedstocks are selectively extracted with minimum co-extraction of non-oxidized products such as valuable hydrocarbon fuel components.

Description

RELATED APPLICATIONS[0001]This application is a Continuation of co-pending U.S. patent application Ser. No. 13 / 627,606 filed Sep. 26, 2012, which claims the benefit of U.S. Provisional Patent Application No. 61 / 539,734 filed Sep. 27, 2011, the disclosures of which are hereby incorporated by reference in its entirety.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]This invention relates to a system and process for extraction of sulfoxides or a combination of sulfoxides and sulfones, and more particularly to a selective liquid-liquid system and method for the extraction of oxidative desulfurization reaction products from a hydrocarbon mixture.[0004]2. Description of Related Art[0005]It is well known that certain sources of crude oil known as “sour” crude contain significant amounts of sulfur. If chemically-combined sulfur, such as organosulfur compounds, is not removed from the resultant hydrocarbon products, including paraffins, olefins and aromatics, particularly gas...

AI Technical Summary

Benefits of technology

[0016]The process described herein is directed to selective extraction of sulfoxides, or sulfoxides in combination with sulfones, from hydrocarbon mixtures containing these compounds. A significant advantage of the process described herein is that oxidation products resulting from oxidative desulfurization of hydrocarbon feedstocks are selectively extracted with minimum co-extraction of non-oxidized products such as valuable hydrocarbon fuel components.

[0018]The liquid-liquid extraction process can be carried out in a batch reactor, a continuous flow reactor, a tubular flow reactor, and / or in a liquid-liquid separator. An advantage of the process described herein compared to prior art extraction processes relates to the use of a selective solvent formulation that minimizes co-extraction of valuable hydrocarbon compounds during the liquid-liquid extraction step.

[0019]Another advantage of the process described herein is facilitating extraction of sulfoxides, and / or sulfoxides combined with sulfones, resulting from oxidation of hydrocarbon feeds by using the selective solvent formulation, thereby reducing the complexity and overall number of extractive steps. In conventional approaches, pure solvent is required, and necessary steps include storage of large quantities of highly flammable solvent, recycling of large quantities of solvent with an evaporation unit and distillation unit with multiple stages of cooling towers with associated tanks to segregate the sulfoxides and sulfones from the co-extraction of aromatics along with untreated organosulfur compounds. However, the process described herein is selective to extract the oxidized sulfur, and the solvent is recycled and separated from oxidized sulfur. In addition, polishing of oxidant material can be accomplished by flashing water after extraction, which can eliminate acid, peroxide or solvent remaining in treated stream. Therefore, by employing the selective solvent formulations of the process described herein, the total sulfur will be reduced in a shorter time while minimizing the co-extraction of other valuable hydrocarbons.

[0020]A further advantage of certain embodiments of the process described herein is the reduction of the oxygen required and a reduction in the oxidation reaction time by promoting formation of sulfoxides rather than increasing the oxidation to the subsequent step of sulfone formation. Sulfoxides can be formed using existing oxidation methods of photo-oxidation, photochemical oxidation, ozonation, ionic liquid oxidation, electro-chemical oxidation, bio-desulfurization, or contacting with hydrogen peroxides, organic peracids, peroxomonophosphoric acid, nitrogen oxides and / or nitric acid. In general, sulfoxides are more easily extracted than sulfones. Sulfoxides alone can be extracted with less solvent formulation. Under oxidation conditions using peroxides as the oxidation agent at mild operating conditions such as temperatures of about 30° C. to about 40° C., both sulfoxides and sulfones are formed.

[0021]With appropriate oxidation conditions and / or catalysts, sulfoxide production can be favored. Using certain solvents, the formulation concentration can be increased to extract both sulfoxides and sulfones while minimizing or eliminating co-extraction of untreated organosulfur compounds.

Problems solved by technology

If chemically-combined sulfur, such as organosulfur compounds, is not removed from the resultant hydrocarbon products, including paraffins, olefins and aromatics, particularly gasoline, diesel or other fuels, its presence can cause corrosion of processing equipment and engine parts, as well as other deleterious effects, particularly when water is present.

Further, the discharge into the atmosphere of sulfur compounds during processing and end-use of the petroleum products derived from sour crude oil pose safety and environmental problems.

However, many existing hydroprocessing facilities, such as low pressure hydrotreaters, which represent substantial prior capital investment, were constructed before more stringent sulfur specifications were enacted.

It is very difficult to upgrade existing hydroprocessing systems because of the comparably more severe operational requirements (i.e., higher temperature and pressure) to obtain clean fuel production.

However, all retrofitting alternatives are limited by process economics and the basic existing hydrotreating system upon which they improve.

The addition of alkyl groups to the ring compounds increases the difficulty of hydrodesulfurization.

Dibenzothiophenes resulting from addition of another ring to the benzothiophene family are even more difficult to desulfurize, and the difficulty varies greatly according to their alkyl substitution, with di-beta substitution being the most difficult to desulfurize, thus justifying their “refractory” appellation.

Oxidation of certain sulfur-containing compounds increases their solubility in certain solvents.

It is likely that non-treated organosulfur compounds, other aromatics and other hydrocarbons are also co-extracted to a considerable degree, thereby detrimentally impacting product yield.

However, it is known that the polar solvent methanol has a significant affinity for non-treated sulfur compounds, aromatics and other hydrocarbons, thus reducing the overall product yield in a manner that may not be commercially acceptable.

While the processes described above can be effective to remove sulfoxides and / or sulfones from a hydrocarbon mixture, problems remain related to co-extraction of other valuable hydrocarbon components, thus reducing the overall hydrocarbon product yield.

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