Gasoline mercaptans

Although there is no ASTM specification for gasoline mercaptan or hydrogen sulfide levels, a copper corrosion specification does exist. Since mercaptans and hydrogen sulfide attack copper and copper-containing alloys such as brass and bronze, it is important to minimize fuel mercaptans and hydrogen sulfide concentrations. 

Precaution Combustible Uses Antiozonant in polyunsat. elastomers antioxidant, antiozonant for gasoline, mercaptans, synthetic rubber (NR, IR, BR, SBR) antioxidant/antiozonant in food-contact rubber articles for repeated use Regulatory FDA 21CFR 177.2600 Manuf./Distrib. ChemService http //WWW. chemservice. com] Crompton/Uniroyal... 

Term used for natural gas or a gasoline contaminated with odor-causing sulfur compounds. In natural gas, the contaminant is usually hydrogen sulfide (HjS) and can be fatal in high concentrations in gasoline, mercaptans are usually the source. 

Since the original cmde oils contain some sulfur compounds, the resulting products and gasolines also contain sulfur compounds, including hydrogen sulfide, mercaptans, sulfides, disulfides, and thiophenes. The processes used to sweeten, ie, desulfurize, the products depend on the type and amount of the sulfur compounds present and the specifications of the finished gasoline or other stocks. 

Oxidation or "sweetening" is used on gasoline and distillate fractions. A common oxidation process is also a Merox process that uses a solid catalyst bed. Air and a minimum amount of alkaline caustic ("mini-alky" operation) is injected into the hydrocarbon stream. As the hydrocarbon passes through the Merox catalyst bed, sulfur mercaptans are oxidized to disulfide. In the sweetening Merox process, the caustic is not regenerated. The disulfide can remain with the gasoline product, since it does not possess the objectionable odor properties of mercaptans hence, the product has been sweetened. 

Refiners use sweetening processes to remove mcr-captans that give a vei y unpleasant odor to gasolines and middle distillates (the skunk uses mercaptans to protect itself). This is done by washing the hydrocarbon stream with a caustic solution followed by a wash with water to remove die caustic. 

The gas plant products, namely fuel gas, Cfs, 4, and gasoline, contain sulfur compounds that require treatment. Impurities in the gas plant products are acidic in nature. Examples include hydrogen sulfide (HjS), carbon dioxide (COj), mercaptan (R-SH), phenol (ArOH), and naphthenic acids (R-COOH). Carbonyl and elemental sulfur may also be present in the above streams. These compounds are acidic. 

Sweetening of the FCC gasoline is usually sufficient to meet its sulfur specifications. However, in areas where reformulated gasoline is marketed, sulfur specifications in the gasoline may require more treatment. The mercaptans in the LPG need to be extracted to protect the downstream processes, such as alkylation. Sulfur increases acid consumption and produces undesirable by-products. 

The sulfur compounds in FCC gasoline consist of C -C mercaptan and various thiophenes. 

Caustic extraction can remove mercaptan sulfur in light fractions, but not higher carbon number mercaptans or other types of sulfur molecules that are in the FCC gasoline. 

Catalyst additives can reduce FCC gasoline sulfur by about 15%. They work by converting mercaptan, thiophene, etc., to H S. A secondary benefit of the additives is an approximate 10% reduction in the LCO sulfur. 

If refined products, such as gasoline, diesel, jet fuel, or kerosene, are transported in a pipeline, where otherwise sour hydrocarbon fluids are transported, there may be an undesired enrichment of sulfur in the refined products. This can be avoided if the oxygen level of the transportant is maintained at below 20 ppm [570]. The dissolved oxygen level in the hydrocarbon product is controlled by reducing the amount of air injection employed in mercaptan or disulfide reduction or by the use of oxygen scavengers prior to the introduction of the refined hydrocarbon product into the pipeline. 

Caustic washing. Here, caustic solution 5-15% strength is reacted with liquid gasoline or gaseous hydrocarbons. This interacts with H2S and lower molecular-weight mercaptans and they are thus removed. 

Unisol process. In this process, mixture of caustic soda and methanol removes mercaptans from gasoline. 

Odorization. Natural gas is odorized so that leaks can be detected, whereas gasoline is normally smelly. Odorization of natural gas is a prudent although not entirely effective safety measure. Hydrogen as an industrial gas or fuel cell vehicle fuel is not odorized because sulfur-containing substances (mercaptans) contaminate the catalysts of a fuel cell. 

Dualayer Gasoline A process for extracting mercaptans and other organic sulfur compounds from petroleum distillates by solvent extraction with aqueous sodium or potassium hydroxide and a proprietary solubilizer. 

Locap A process for removing mercaptans from gasoline by catalytic oxidation to disulfides, using a fixed bed of catalyst that is continuously treated with aqueous sodium sulfide. Commercialized by Petrolite Corporation in 1963. 

Sweetening Treatment Catalytic Remove H2S, convert mercaptan Untreated distillate/gasoline High-quality distillate/gasoline... 

Present formula gasolines contain approximately 300 ppm. No. 2 fuel oil contains 2,200 to 2,600 ppm by weight of sulfur. Even pipeline gas contains sulfur-containing odorants (mercaptans, disulfides, or commercial odorants) for leak detection. Metal catalysts in the fuel reformer can be susceptible to sulfur poisoning and it is very important that sulfur in the fuel reformate be removed. Some researchers have advised limiting the sulfur content of the fuel in a stream reformer to less than 0.1 ppm, but noted the limit may be higher in an autothermal... 

Thermal and catalytically cracked gasoline fractions can contain significant concentrations of phenols, low-molecular-weight organic acids, and alkyl and aryl mercaptans. All of these compounds can initiate gum formation in gasoline. Caustic treatment readily removes these compounds. 

This process is used frequently to sweeten gasoline and light distillate streams. In the first phase of Merox processing, mercaptans are extracted from the fuel with caustic. A sweetening process follows and involves sparging a caustic/fuel mixture with air in the presence of a catalyst. Remaining mercaptans then react to form... 

Mercaptan Sulfur in Gasoline, Kerosene, Aviation Turbine, and Distillate Fuels (Potentiometric Method)... 

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