In recent years, there has been a greater understanding of the role of automotive emissions as environmental pollutants. Sulfur dioxide, nitrogen oxides, and carbon monoxide degrade the earth’s atmosphere and are health hazards. Carbon dioxide adds to the atmospheric buildup of greenhouse gases and in turn accelerates the process of global warming.
Sulfur is a particular problem as an environmental impact and emissions. It occurs naturally in various concentrations in petroleum, and it is difficult and costly to remove all of it. Distillation and cracking removes some, but small amounts survive the distillation and cracking processes and enter into the gasoline. The average level of sulfur in gasoline has not changed much since 1970, remaining at 300 parts per million (ppm) with a range between 30 and 1,000 ppm.
High levels of sulfur not only form dangerous oxides, but they also tend to poison the catalyst in the catalytic converter. As it flows over the catalyst in the exhaust system, the sulfur decreases energy conversion efficiency and limits the catalyst’s oxygen and hydrogen storage capacity. With the converter working at less than maximum energy efficiency, the exhaust entering the atmosphere contains increased concentrations, not only of the sulfur oxides but also, of hydrocarbons, nitrogen oxides, carbon monoxides, toxic metals, and particulate matter.
In the 1990s, the EPA began controlling sulfur through its reformulated gasoline reducing program. It developed regulations in 1999 that would sharply reduce the sulfur content in gasoline from 300 ppm to a maximum of 80 ppm.
The new regulations, scheduled to go into effect in 2004, are compelling certain refiners to purchase low-sulfur content (“sweet”) crude oil. This is the strategy being pursued by Japanese refiners. However, the Japanese are not major oil producers but import oil from other producing countries. U.S. refiners, in contrast, consume oil from a wide range of (“sour”) petroleum sources that have a high-sulfur content, including Venezuela, California, and parts of the Gulf Region. U.S. companies own and operate oil producing infrastructures (i.e., derricks, pipelines), within the United States and overseas. They are committed to working these oil fields, even if producing high-sulfur oil. U.S. refineries thus need to continue dealing with high-sulfur crude oil. Imported crude from the Middle East, while historically low in sulfur, is also becoming increasingly less sweet.
Petroleum refiners will have to reduce sulfur content at the refineries. This will require the costly retooling of some of their plant operations in order to achieve a suitable fuel mix. Removing additional amounts of sulfur at the refinery will entail installation of separate catalyst-based process such as hydro sulfurization. Another possible approach is the removal of sulfur in liquid oil or gasoline consumption by the use of both organic and inorganic scavenger agents added to the oil or gasoline to seek out, combine with, and precipitate out sulfur and its compounds. This will further reduce the number of automotive emissions.
