Sulfur, crude oil

For the refiner, the main problem is to meet the specifications for kinematic viscosity and sulfur content. Dilution by light streams such as home-heating oil and LCO, and selection of feedstocks coming from low-sulfur crude oils give him a measure of flexibility that will nevertheless lead gradually to future restrictions, most notably the new more severe antipollution rules imposing lower limits on sulfur and nitrogen contents. 

Thiophene as a compound is not found in high concentration in crude oil. However, benzothiophenes and other aromatic thiophenes are critical components of high-sulfur crude oil. Also, thiophenes are present in relatively high concentrations in oils containing increased percentages of aromatics, asphaltenes, and resins. 

Compounds such as H2S and mercaptans are not commonly found in finished fuels. However, the possibility of carryover of these compounds into finished fuels can occur if fuel processed from high-sulfur crude oil is not properly stripped, caustic washed, or sweetened through refining. If H2S and mercaptans are found in finished fuel, they can still be removed by the addition of chemical sweetening additives. 

Hydrogen sulfide is a by-product of many industrial operations, eg, coking and the hydrodesulfurization of crude oil and of coal. Hydrodesulfurization is increasing in importance as the use of high sulfur crude oil becomes increasingly necessary (see Petroleum, refinery processes). A large future source of hydrogen sulfide may result if coal liquefaction attains commercial importance (see Coal CONVERSION processes). 

Low-Sulfur Crude Oil—Crude oil containing low concentrations of sulfur-beanng compounds, Crude is usually considered to be in tire low-sulfur category if it contains less than 0,5% (weight) sulfur. Examples of low-sulfur crudes are offshore Louisiana. Libyan, and Nigerian crudes,... 

Nevertheless, it became evident that reforming processes instituted in many refineries were providing substantial quantities of by-product hydrogen, enough to tip the economic balance in favor of hydrodesulfurization processes. In fact, the need for such commercial operations has become more acute because of a shift in supply trends that has increased the amount of high-sulfur crude oils employed as refinery feedstocks. 

This process is suitable for the desulfurization of high-sulfur residua (atmospheric and vacuum) to produce low-sulfur fuel oils or catalytic cracking feedstocks. In addition, the process can be used, through alternate design types, to upgrade high-sulfur crude oils or bitumen that are not suitable for the more conventional refining techniques. 

The chemistry of sulfur in fossil fuels is of both practical and academic interest. The behavior of sulfur during processing high-sulfur crude oils, coals and natural gas to make environmentally acceptable fuels poses special... 

One area of intrigue relates to preliminary reports (78,86,111) of sulfur cross-linked polymers isolated from low maturity high-sulfur crude oils. Presumably, these materials are still being investigated, and further evaluation of their character and their significance can be expected. 

Microbial degradation of the aromatic nucleus of substituted thiophenes has been demonstrated by Amphlett and Calley (12). Dibenzothiophene is converted into a water-soluble form, 3-hydroxy-2-formylbenzothiophene which imparts an orange-red color in the culture broth. Finnerty ( 13) reported the use of microorganisms of the genus Acinetobacter and Micrococcus to convert dibenzothiophenes into water-soluble products that can be removed from high-sulfur crude oil. 

In summary, imports of foreign oil should increase rapidly in this decade. Much of the oil will probably be high sulfur crude oil from the Persian Gulf. Expected modifications of the oil import program will enable the refinery equipment that will process the oil to be located domestically. This would be beneficial to national security, trade balance, and the domestic economy. The ultimate effect such modifications in the oil import program would have on domestic refinery configurations would probably be slightly beneficial to the environment. 

To achieve higher outputs of light olefins, particularly propylene, the hydrogen content of the feedstock must be increased and the sulfur content reduced. This can be achieved by the utilization of low sulfur crude oils or using a higher performance feed hydrotreater upstream of the FCC unit. There are several commercial FCC processes currently employed with major differences in the method of catalyst handling. 

High-Sulfur Crude Oils in the United States. 

Kerosene from naphthenic oil or high-sulfur crude oil requires hydrotreating, acid treatment and water wash, or extraction with a solvent and caustic wash and clay brightening to remove undesirable aromatics or... 

Historically, physical properties such as boiling point, density (gravity), odor, and viscosity have been used to describe oils. Petroleum may be called light or heavy in reference to the amount of low-boiling constituents and the relative density (specific gravity). Likewise, odor is used to distinguish between sweet (low sulfur) and sour (high sulfur) crude oil. Viscosity indicates the ease of (or more correctly the resistance to) flow. 

High sulfur crude oil Ignition, flaming 0.58 1.2 Rogers et al. (1991)... 

As higher sulfur crude oils are refined, additional hydrogen for desulfurization to meet existing and more stringent future regulations will be required... 

Because of the unavailability of low-sulfur crude oils, heavy asphaltic crudes and synthetic crudes are now being utilized. These less desirable crudes contain... 

As a practical matter, the concentration of vanadium, nickel, and other inorganic matter in petroleum coke is largely a function of the source of the crude oil as is shown in Table 2.8. Sweet (low sulfur) crude oils not only contain less ash, but can ccmtain lower concentrations of vanadium, nickel, and other deleterious metals (see data from [4]). The vanadium content in the Venezuelan crude oil shown in Table 2.8 is particularly high, while the vanadium content in the Canadian crude oil is... 

Carbon-steel tubes and cast-iron shells are least expensive, but high-sulfur crude oils may justify the use of 5 per cent chromium or even 18-8-chrome nickel tubes" particularly in cracking service. Refer to Chap. 9, pages 276 to 284. For the acid corrosion produced by salt brine, admiralty metal or occasionally cupronickel tubes are justified. Ammonia is often used as a neutralizer for acid corrosion, and it attacks admiralty metal so rapidly that admiralty metal cannot be used for such a situation. The mechanical properties of this alloy are also impaired by temperatures above 500°F, although under favorable conditions it can be used up to tube-wall temperatures of 600 F. Recommendations are as follows ... 

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