Sulfur content of petroleum

The sulfur content of petroleum varies from less than 0.05 to more than 14 wt% but generally falls in the range 1 to 4 wt%. Petroleum with less than 1 wt% sulfur is referred to as low-sulfur, and that with more than 1 wt% sulfur is referred to as high-sulfur. The refining industry considers heavy oils, residua, and bitumen to be high-sulfur feedstocks. Hence they are the focus of many conversion and desulfurization scenarios. 

The sulfur content of petroleum varies from less than 0.05 to more than 14% wt. 

The hydrogenolysis of sulfur-containing compounds is also an important industrial process, known as hydrodesulfurization, in the field of petroleum refinery to reduce the sulfur content of petroleum fractions. The most commonly used catalyst is a mixture of either cobalt or nickel and molybdenum oxides supported on alumina, which is sulfided before use and usually employed at about 300-400°C and 1-7 MPa H2.128 The basic reactions involved in the hydrodesulfurization process are represented in eq. 13.60. 

The sulfur content of petroleum containing these compounds is usually quite low but it can be as high as 6% of the total. The more stable oxygen derivatives of hydrocarbons, such as the paraffinic acids, ketones, and phenols (Eq. 18.7), also occur in crude oils. 

Thus process units in a refinery require analytical test methods that can adequately evaluate feedstocks and monitor product quality. In addition, the high sulfur content of petroleum and regulations limiting the maximum sulfur content of fuels makes sulfur removal a priority in refinery processing. Here again, analytical methodology is key to the successful determination of the sulfur compound types present and their subsequent removal. 

The sulfur content of petroleum is an important property and varies widely within the rough limits 0.1% w/w to 3.0% w/w, and a sulfur content up to 8.0% w/w has been noted for tar sand bitumen. Compounds containing this element are among the most undesirable constituents of petroleum because they can give rise to plant corrosion and atmospheric pollution. Petroleum can evolve hydrogen sulfide during distillation as well as low-boUing sulfur compounds. 

Until recently, one of the most widely used methods for determination of total sulfur content has been combustion of a sample in oxygen to convert the sulfur to sulfur dioxide, which is collected and subsequently titrated iodometricaUy or detected by nondispersive infrared (ASTM D-1552). This method is particularly applicable to heavier oil and fractions such as residua that boil above 177°C (350°F) and contain more than 0.06% w/w sulfur. In addition, the sulfur content of petroleum coke containing up to 8% w/w sulfur can be determined. 

Numerous papers contradict and appear to refute the above claims. However, an examination of these papers indicates that they are less contradictory than they first appear. Many investigators considered coal tars and a variety of different petroleum fractions produced by different processes as equivalents. Others compared the natural sulfur content of petroleum with materials to which elemental sulfur had been added. However, not all of the contradictory evidence was explained, and in some cases investigators obtained different results even though they were attempting to duplicate each others efforts. Cases where the same investigator was unable to reproduce data are known also. 

Riazi, M.R., Nasimi, N., Roomi, Y. 1999. Estimating sulfur content of petroleum products and crude oils. Ind. Eng. Chem. Res. 38(11) 4507—4512. 

Knowledge of sulfur content in petroleum products is imperative the analytical methods are numerous and depend on both the concentration being measured and the material being analyzed. 

Over the years, larger quantities of sulfur have been recovered for a number of reasons. These iaclude iacreased petroleum refining and natural-gas processiag, more stringent limitations on sulfur dioxide emissions, and higher sulfur contents of the cmde oil refined. Another contributiag factor is the lower sulfur content limits set on petroleum-based fuels. 

The hydrogen content of petroleum fuels can be calculated from density with the following formula, with an accuracy of about 1 percent for petroleum liquids that contain no sulfur, water, or ash ... 

Assuming that demand for petroleum continues to increase at a rate of 1.2% per annum to 2010,37 and that all gasoline and diesel produced by U.S. refineries will have a sulfur content of less than 30 ppm, desulfurization of gasoline and diesel to these low levels will require extensive hydrotreating of both catalytic cracker feed and product of distillate. 

Sulfur dioxide is released during these operations when either coal or oil is burned. Coal and oil both naturally contain compounds of sulfur that, when burned, produce sulfur dioxide. The sulfur content of both coal and oil ranges from less than 1 percent to more than 7 percent, although refined petroleum tends to have lower concentrations of sulfur than do most forms of coal. Natural gas, by... 

The production of domestic sulfur values (elemental recovered sulfur and the sulfur content of acid) will total about 18 million long tons per year by the year 2000. By region (Petroleum Administration for Defense districts), except for the east coast (PAD I), there will be no deficit areas in the U. S. Major contributors are sour natural gas and the refining of heavier, sour, crude oil. Proximate, scenario dependent sources, are electric utilities and coal-based synfuels. Shale oil, domestic tar sands and heavy oil, and unconventional sources of natural gas will be small suppliers. 

Sulfur compounds form the largest group of nonhydrocarbons in petroleum. Crude oils vary considerably in their sulfur content. Some have extremely low sulfur contents with less than 0.1 weight percent of sulfur. However, high sulfur crudes can contain as much as five to seven weight percent sulfur. Since the sulfur atom is only a small part of a large molecule, a crude oil with a sulfur content of five weight percent may actually have sulfur atoms as a part of more than half of the total molecules. 

---