When we talk about oil and gas production in this blog, we often refer to oil in a general sense, but there are many different kinds of crude oil. Crude oil is valued according to characteristics such as density and sulfur content, which is described as sweet or sour. Sulfur content in petroleum products can be determined using Wavelength Dispersive X-ray Fluorescence (WDXRF).
The web site petroleum.co.uk explains that early prospectors would taste oil to determine its quality because low sulfur oil actually tastes sweet. It defines sweet and sour sulfur content as follows:
Crude is currently considered sweet if it contains less than 0.5% sulfur. Sweet crude is easier to refine and safer to extract and transport than sour crude. Because sulfur is corrosive, light crude also causes less damage to refineries and thus results in lower maintenance costs over time.
Sour crude oil will have greater than 0.5% sulfur and some of this will be in the form of hydrogen sulfide. Sour crude also contains more carbon dioxide. Most sulfur in crude is actually bonded to carbon atoms, nevertheless, high quantities of hydrogen sulfide in sour crude can pose serious health problems or even be fatal.
The U.S. Energy Administration (EIA) defines sulfur as “A yellowish nonmetallic element, sometimes known as brimstone. It is present at various levels of concentration in many fossil fuels whose combustion releases sulfur compounds that are considered harmful to the environment.” According to the EIA website, light, sweet crude oils are usually priced higher than heavy, sour crude oils, partly because gasoline and diesel fuel can usually be more easily and cheaply produced using light, sweet grades, which can be processed with far less sophisticated and energy-intensive processes/refineries.
Low-sulfur oil is also desirable from an environmental standpoint. The U.S. Environmental Protection Agency’s Heavy-Duty Highway Diesel rule (the “2007 Highway Rule”) required a 97% reduction in the sulfur content of highway diesel fuel, from 500 parts per million (ppm), to 15 ppm, beginning with the 207 model year in order to reduce smog-causing nitrogen oxide emissions and particulate matter from diesel engines.
Following the EPA’s lead, new regulations to require lower-sulfur heating oil are emerging in the Northeastern United States. According to the National Oil Heat Research Alliance web site, Connecticut, Delaware, Maine, Massachusetts, New Jersey, New York, Rhode Island and Vermont all are requiring a dramatic reduction in the amount of sulfur present in heating oil, to no more than 15 PPM sulfur; Maryland and Pennsylvania have mandated a reduction to 500 PPM sulfur. Each state has set its own time table for the transition; the latest date is July 2018.
Because the operational efficiency and environmental safety of petroleum products depends on the sulfur concentration, precise testing must be done to meet regulatory guidelines that limit the amount of sulfur in fuel. Read Analysis of Sulfur in Oils according to ASTM D2622 Method to see test results in which a Wavelength Dispersive X-ray Fluorescence (WDXRF) instrument was used to demonstrate the analysis of sulfur in oil using a calibration curve prepared according to ASTM Standard D2622 .