High-sulfur crude oils, refinement

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. 

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. 

High-sulfur crudes, especially those with a sulfur content >0.5 wt%, complicate refining and are also more expensive to refine. Sulfur and some sulfur compounds are corrosive toward metals and can decrease the pH of the crude oil. The sulfur content of most crude oil varies from <0.1% to >5%. 

It has been determined that certain nitrogen-, oxygen-, and sulfur-containing aromatic compounds contained in crude oil can lead to darkening of refined fuels and oils. Often, these compounds are found in fuels refined from naphthenic crude oil or asphaltic, high-sulfur crudes. Compounds such as indoles, quinolines, and naphthenobenzothiophenes can lead to darkening of fuel. 

Heavy Crude Oils. Heavy crude oils are produced in California. Production problems have been related to air pollution from the generation of steam used for flooding and refining the heavy, high sulfur, crude. Additional development may, however, be expected following the decontrol of prices on crudes up to 20° API and the exemption of crudes of 16° API and under from the windfall profits tax. It is expected that output additions will be 65,000 b/d in 1981 and 130,000 b/d by 1983. The goal is to double output from... 

Crude oil represents the largest non-Frasch sulfur resource and this source has received added stimulus from the passage of air pollution control laws and increased refining of heavier, high sulfur crudes. Sulfur recovered from sour natural gas contibutes a third source of by-product sulfur. 

In most industrial centers air pollution has become a critical problem, and refiners are under pressure to produce lower sulfur fuel oils to meet local standards. This is true in two areas—the Caribbean and Japan —which are also centers of a burgeoning petrochemical industry. Starting with a high sulfur crude, production of low sulfur fuel oil is a costly operation which adversely affects the refiners economic position. Our studies have shown that significant savings can be realized by integrating fuel desulfurization with the production of petrochemical feedstocks. To illustrate, let us consider a desulfurization operation which might be located in Japan. 

Sulfur for commercial purposes is derived mainly from native elemental sulfur mined by the Frasch process. Large quantities of sulfur are also recovered from the roasting of metal sulfides and the refining of crude oil, i.e., from the sulfur by-products of purified sour natural gas and petroleum (the designation sour is generally associated with high-sulfur petroleum products). Reserves of elemental sulfur in evaporite and volcanic deposits and of sulfur associated with natural gas,... 

One of the most ubiquitous multiple-component contaminants that reaches the soil and deeper subsurface layers is crude oil and its refined products. In the subsurface, these contaminants are transformed differently by various mechanisms (Cozzarelli and Baber 2003). Crude oil contains a multitude of chemical components, each with different physical and chemical properties. As discussed in Chapter 4, the main groups of compounds in crude oils are saturated hydrocarbons (such as normal and branched alkanes and cycloalkanes without double bonds), aromatic hydrocarbons, resins, and asphaltenes, which are high-molecular-weight polycyclic compounds containing nitrogen, sulfur, and oxygen. 

Catalytic cracking, coking, visbreaking, and other high-temperature refining processes can liberate sulfur from crude oil or from a process stream. Once free, sulfur can react to form low-molecular-weight compounds such as hydrogen sulfide, methyl mercaptan, carbon disulfide, and others. 

Liquid products contain sulfur and nitrogen and must be hydroprocessed to improve quality. Separate hydroprocessing units for upgrading the naphtha, kerosene, and gas oil fractions can be used to optimize the overall process. Refined gas oil or diesel fuel is aromatic in character and contains more cycloparaffins than conventional crude oil. The resulting fuel is low in cetane number, high in density, and typically has very good low-temperature handling properties. 

We will examine three synthetic fuel scenarios and compare their implications regarding sulfur availability with the current and projected market for sulfur to the year 2000. The analysis will consider three production levels of synthetic fuels from coal and oil shale. A low sulfur Western coal will be utilized as a feedstock for indirect liquefaction producing both synthetic natural gas and refined liquid fuels. A high sulfur Eastern coal will be converted to naphtha and syncrude via the H-Coal direct liquefaction process. Standard retorting of a Colorado shale, followed by refining of the crude shale oil, will round out the analysis. Insights will be developed from the displacement of imported oil by synthetic liquid fuels from coal and shale. 

It is in the field of middle distillates and fuel oils that sulfur may confront some refiners with major problems that will grow as the production of higher sulfur crudes increases. It may be worth while to consider in some detail the case of high speed Diesel oil, for which discussion about sulfur content is controversial. Curiously enough it is in the United States, where low-sulfur material has been in relatively plentiful supply, that... 

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