Mercaptans in gasoline

Zone sampling (see 7.2) can be exploited in some expert flow systems with LLE in order to improve their performance, as initially demonstrated by the determination of Ci—C5 n—mercaptans in gasoline [199] (see also 8.7). Another example is the determination of ammonium by exploiting ion pairing [200]. 

X — concentration of mercaptan in gasoline. y = concentration of mercaptan in alkaline solution. 

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. 

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

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. 

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. 

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

In addition to this comprehensive scheme, other determinations may be carried out by utilizing specific properties of the sulfur compound types (54, 72). Sulfur may be determined by removal with elemental mercury 51, 70), or by reaction with a mercaptan. In the latter case the sulfur determination is made by measurement of the excess mercaptan after the sample has been treated with litharge, sodium hydroxide, and a known excess of butyl mercaptan 78,81). A qualitative method of detecting elemental sulfur in gasoline is by the addition of sodium hydroxide to a pyridine solution of the gasoline which turns blue if sulfur is present 67). Free sulfur can also be determined polarographically 60). 

Mercaptan sulphur in gasoline, kerosene, aviation turbine and distillate fiiels (potentiometric method). ASTM D 3227-83. 

Mercaptan sulfur (R-SH) and hydrogen sulfide (H2S) (ASTM D-1219, IP 103, IP 104) are undesirable contaminants because, apart from their corrosive nature, they possess an extremely unpleasant odor. Such compounds should have been removed completely during refining but their presence and that of free sulfur are detected by application of the Doctor test (ASTM D-4952, IP 30). The action on copper of any free or corrosive sulfur present in gasoline may be estimated by a procedure (ASTM D-130, ASTM D-849, IP 154) in which a strip of polished copper is immersed in the sample, which is heated under specified conditions of temperature and time, and any staining of the copper is subsequently compared with the stains on a set of reference copper strips and thus the degree of corrosivity of the test sample determined. 

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. 

Doctor test n. Method for detecting the presence of mercaptan sulfur in gasolines, naphthas, and kerosenes. 

Mercaptans can be determined in gasoline by using the anodic wave, which corresponds to a mercury compound formation at the surface of the dropping mercury electrode. 

Successful results have been obtained with both simple and complex analytical problems, i.e., mercaptan sulfur in gasoline and "Bayer liquors."... 

When this process first was introduced, the TBA was of low value, so the TBA/PO ratio was kept to a minimum. Since that time, valuable uses have been found for the TBA. t-Butanol is used as an octane enhancer in gasoline, competing with methanol, ethanol, and MTBE. Dehydration of TBA yields high-purity isobutylene, which is converted primarily into MTBE, butyl elastomers, polyisobutylenes, and a variety of substituted phenols and cresols, mercaptans, and amines. More than 450 million lb of isobutylene is produced from TBA. 

This test method covers the determination of mercaptan sulfur in gasolines, kerosines, aviation turbine fuels, and distillate fuels containing from 0.0003 to 0.01 mass % of mercaptan sulfur (Note 4). Organic sulfur compounds such as sulfides, disulfides, and thiophene do not interfere. Elemental sulfur in amounts less than O.OOOS mass % does not interfere. Hydrogen sulfide will interfere, if not removed as described in 9.2. 

Titration Solvent—Low molecular weight mercap-tans, as usually found in gasoline, are readily lost from the titration solution if an acidic titration solvent is used. For the determination of the higher molecular weight mercaptan as normally encountered in kerosines, aviation turbine fuels and distillate fuels, the acidic titration solvent is used to achieve more rapid equilibrium between successive additions of the titrant. 

FIG. 2 Precision Curve for Mercaptan Sulfur in Gasolines, Kerosines, Aviation Turbine, and DistMato Fuels... 

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