Sulfur compounds in gasoline

Acid Extraction. Strong sulfuric acid not only reacts with many sulfur compounds in gasolines at room temperature, but also with aromatic and unsaturated compounds however, when the temperature is dropped to 15° to 20° F., the acid is capable of dissolving the sulfur compounds while its activity toward unsaturates and aromatics has been diminished considerably (113, 131), thus making a selective removal of the sulfur compounds feasible. Dilution of the acid with water regenerates the sulfur compounds however, these compounds may not necessarily be the same as were originally present in the naphtha, particularly if the acid treatment was not maintained at the low temperature. 

In this section, a summary of the chemical principles involved with membrane reactors for desulfurization are overviewed. The details will be covered in the following sections. Electrochemical desulfurization technologies assisted by membranes have been extensively explored for the removal of sulfur that exists in sulfur compounds in fossil fuels and in SO2 form in flue gas. In principle, SO2 can be absorbed by an aqueous electrolyte solution and then electrochemically converted into species such as sulfate, hydrogen sulfide, and sulfur, among others, by oxidation or reduction processes, whereas the sulfur compounds in fossil fuels can be similarly removed. The universal reaction mechanism of the electrochemical cathodic reduction of organic sulfur compounds in gasoline and diesel is shown in Eqn (14.1) (Lam et al., 2012) ... 

Transition metal-based sorbent Commercial diesel, gasoline, and jet fuel Organic sulfur compounds in gasoline, diesel, and jet fuel can be removed by the sorbent. 

Ma and coworicers recently synthesized various adsorbents including metals, metal halides, metal oxides, metal sulfides, and modified zeolites and evaluated their desulfurizing abiUties in their laboratory. Their approach aims at removing sulfur compounds in gasoline and jet fuels selectively by a direct sulfur-adsorbent interaction, rather than 7t-complexation [1,10,15,16]-... 

Quimby, Giarrocco, V. and Sullivan, J., Fast Analysis of Oxygen and Sulfur Compounds in Gasoline by GC-AED," Journal of High Resolution Chromatography, Vol. 15, November 1992, pp. 705-709. 

The distribution of mercaptan sulfur compounds in gasolines is indicated in Table 10- 2. The removal of mercaptans by the solution processes is governed by the following equation, which is.applied to each mercaptan present in the gasoline. 

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

The relative importance attached to sulfur compounds in petroleum may, at first, seem unwarranted, but the presence of sulfur compounds in any crude oil can only result in harmful effects. For example, the presence of sulfur compounds in finished petroleum products such as gasoline will cause corrosion of engine parts, especially under winter conditions when water containing sulfur dioxide (from the internal combustion) may collect in the crankcase. On the other hand, mercaptans cause the corrosion of copper and brass in the presence of air and also have an adverse effect on the color stability of gasoline and other liquid fuels. 

The sulfur compounds in the FCC gasoline typically comprise mercaptans, thiophene, C1.4 substituted thiophenes, thiophenol, C1.2 substituted thiophenols, tetrahydrothiophene and benzothiophene, and are best analyzed by a Gas Chromatograph (GC) equipped with an Atomic Emission Detector (AED), Figure 5.29. 

All commercially produced gasoline blends which are intended for vehicle use contain organo-sulfur compounds in concentrations ranging from several parts per million (ppm) to 1000 ppm [1]. These compounds are present in the crude oil feedstocks [2] and can be partially removed by a hydrodesulfurization process in refining [3,4]. Removal of nearly all of the sulfur from gasoline is not always economical due to a number of factors including the variability in feedstock properties and the cost of deep hydrodesulfurization (HDS)... 

As in the US, member nations of the European Community will introduce further specifications for transportation fuels over the next few years. Besides other components, the sulfur content of transportation fuels and gasoline in particular will be limited.FCC gasoline can contribute up to 90% of the sulfur in the gasoline pool. The parameters thatcontrol the sulfur levels in gasoline have been described by various authors in the past. The main determinant of sulfur levels in the FCC gasoline is the feedstock. Researchers found that the reactions that converted the feed sulfur compounds in the FCCU were kinetically controlled and were dominated more by catalyst contact time than by catalyst-to-oil ratio [1]. 

The effect of the GSR technology on the sulfur content of the LCO is illustrated in Figure 12. This shows a decrease of approximately 10% sulfur content over the whole conversion range. For this experiment the USY/Matrix system was used on the low sulfur feed. Unlike the gasoline, the LCO shows an increase in the sulfur level with conversion, which is most likely due to a concentration of stable aromatic sulfur compounds in the LCO. 

For desulfurization of sulfur species in gasoline, it is not difficult to remove the sulfur compounds in the... 

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. 

The copper strip test methods are used to determine the corrosiveness to copper of gasoline, diesel fuel, lubricating oil, or other hydrocarbons. Most sulfur compounds in petroleum are removed during refining. However, some residual sulfur compounds can have a corroding action on various metals. This effect is dependent on the types of sulfur compounds present. The copper strip corrosion test measures the relative degree of corrosivity of a petroleum product. 

ETBE s clean volume allows significant dilution of undesirable benzene, olefin, and sulfur compounds in reformulated gasoline. 

Sulfur compounds in crude oil sharply decreases the quality of fuels and oils produced from the crude oil. They cause corrosion of equipment during treatment, reduce activity of antidetonation additives and antioxidizing stability of gasoline, raise the propensity to form hard residues in cracking gasoline fractions, and result an environment pollution. 

Thiophenic compounds are naturally present in crude oil. Although hydrodesulfurization targets them and converts toward hydrocarbon and hydrogen sulfide [7] still significant quantities are present after this treatment. The reactivities of the 1- to 3-ring compounds decreases in the order thiophenes > benzothiophenes > dibenzothiophenes. In gasoline benzothiophenes are present, in jet fuel - benzothiophenes and dibenzothiophenes whereas in diesel fuel dibenzothiophenes and 4, 6-dimethyldibenzothiophene (4,6-DMDBT) are found. The latter is considered as the most refractory suffur compound towards HDS. The most common refractory sulfur compounds in liquid fuels are presented in Fig. 4. 

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. 

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