Regan Brown
Sulfur compounds in fuels such as gasoline and diesel create air pollution when the fuel is burned. In the 1970s, campaigns were launched to eliminate sulfur dioxide emissions from industrial countries, and in 1993, the EPA began regulating sulfur in diesel fuel. However, the push to lower sulfur content in diesel fuel gained momentum in 2006, when the EPA began phasing in more stringent regulations, reducing the allowable sulfur content to 15 ppm. This fuel is known as ultra-low sulfur diesel (ULSD) and has become the market standard. The transition to ULSD has been challenging, with concerns about increased microbial contamination and reduced lubricity. However, the removal of sulfur has also brought significant benefits, including reduced harmful emissions and extended vehicle lifetimes. Today, researchers continue to develop new techniques to further reduce sulfur content in diesel fuel, aiming to minimize air pollution and improve engine performance.
| Characteristics | Values |
|---|---|
| Why remove sulfur from diesel fuel? | Sulfur compounds in fuels create air pollution when the fuel is burned. |
| How is sulfur removed from diesel fuel? | The removal of sulfur from diesel fuel is done by hydrotreating at the refinery level. |
| When did the removal of sulfur from diesel fuel begin? | The EPA began regulating diesel fuel sulfur levels in 1993. Beginning in 2006, the EPA began to phase in more stringent regulations to lower the amount of sulfur in diesel fuel to 15 ppm. |
| What is the impact of removing sulfur from diesel fuel? | The removal of sulfur from diesel fuel has both positive and negative impacts. On the positive side, it allows for the application of advanced emissions control technologies that substantially lower harmful emissions from diesel combustion. On the negative side, it increases the fuel's susceptibility to microbial contamination and reduces its lubricating properties. |
| What are the health effects of sulfur in diesel fuel? | Sulfur emissions have a harmful impact on human health and the environment. They contribute to increased asthma, heart disease, respiratory disease, and environmental pollution in the form of acidic aerosols that cause acid rain, snow, and fog. |
| What are the alternatives to sulfur in diesel fuel? | Premium options are available that do not contain sulfur, such as biodiesel blends and ultra-low sulfur diesel (ULSD) fuel. |
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What You'll Learn
Sulfur removal methods
The removal of sulfur from diesel fuel started in 1993 when the EPA began regulating diesel fuel sulfur levels. In 2006, the EPA began phasing in more stringent regulations to lower the sulfur content in diesel fuel to 15 ppm, known as ultra-low sulfur diesel (ULSD). This fuel became the market standard, with almost two decades of hindsight.
The removal of sulfur from diesel fuel is typically done through hydrotreating or hydrodesulfurization at the refinery level. While this method enables refineries to produce diesel fuel with a maximum sulfur level of 15 ppm, it is costly and demands high temperatures and pressures. As a result, adsorptive desulfurization using materials like Co/MCM-41 has emerged as a promising technique due to its moderate operating conditions, low cost, and high selectivity for thiophene compounds.
Scientists from Caltech have also developed a new method for potentially removing nearly all sulfur compounds from diesel fuel. This method, known as KOSi, uses Earth-abundant materials such as potassium, oxygen, and silicon to achieve extremely low sulfur levels of about 2 ppm. The process operates under mild conditions and has the potential to significantly reduce air pollution caused by burning sulfur compounds in diesel fuel.
Another approach, known as the potassium salt method, has been successfully tested by Toutov and colleagues from the Grubbs lab in partnership with BP. This method reduced sulfur levels in diesel fuel from 8 ppm to an extremely low 2 ppm. The potassium salt method can be used as an additional step in the oil refinement process to eliminate the final traces of sulfur in fuels.
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The impact of sulfur on microbes
Sulfur has historically been considered an inhibiting factor for microbes in fuel, with some describing it as a “natural biocide”. This perception led to concerns about the potential for fuel contamination when the EPA began regulating sulfur in diesel fuel in 1993. The regulatory change, which took full effect by 2010, lowered the on-road sulfur limit from 500 ppm to 15 ppm, resulting in ultra-low sulfur diesel fuel (ULSD).
However, the idea that sulfur acts as a natural biocide is not technically accurate. While microbes may not thrive in excessive amounts of sulfur, it is a macronutrient that organisms need to live. Sulfur-reducing bacteria, for example, utilize sulfur as electron acceptors to sustain essential activities such as respiration, energy conservation, and growth in the absence of oxygen. The final product of these processes, sulfide, has a significant influence on the chemistry of the environment and is used as an electron donor for various microbial metabolisms.
The removal of sulfur from diesel fuel did lead to an increase in microbial problems, but not due to the reduced sulfur levels alone. The new fuel regulations also capped aromatic content, and diesel fuels with lower aromatic content are more susceptible to microbial contamination. Additionally, ULSD has a greater affinity for water, which is an essential element for microbial growth. As a result, today's ultra-low sulfur diesel fuels require more attention and care than previous diesel fuels.
The presence of sulfur-oxidizing bacteria (SOB) can help regulate microbial growth. For instance, the presence of SOB such as Thiobacillus has been shown to decrease the growth of Streptomyces scabies and S. ipomea, which are pathogens of potato plants. SOB can also play a role in maintaining the pH of mining impoundment waters.
In summary, while sulfur was once believed to inhibit microbial growth in fuel, it is now understood that microbes require sulfur for various metabolic processes. The removal of sulfur from diesel fuel has indeed led to increased microbial issues, but this is due to a combination of factors, including reduced aromatic content and the hydrophilic nature of ULSD. The presence of certain sulfur-oxidizing bacteria can help manage microbial growth in specific contexts.
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The cost of ultra-low sulfur diesel
The transition to ultra-low sulfur diesel (ULSD) has incurred substantial costs. The removal of sulfur from diesel fuel is done through hydrotreating at the refinery level, which reduces the sulfur content to a maximum of 15 parts per million (ppm). This process also reduces the fuel's lubricating properties, as sulfur combines with the nickel content in metal alloys to increase lubricity. The decrease in lubricity can cause wear and damage to the engine's fuel injection system. ASTM International has adopted a lubricity specification, ASTM D975, to manage this change and protect engines.
Another cost associated with ULSD is the increased susceptibility to microbial contamination. While it was initially believed that the reduced sulfur content alone caused this issue, it is now understood to be a combination of factors, including the lower aromatic content of ULSD and its greater affinity for water. These factors create an environment conducive to microbial growth, requiring more attention and maintenance for diesel engines using ULSD.
The transition to ULSD has also resulted in a minor decrease in the energy content of diesel fuel, by approximately 1%. This reduction may lead to slightly lower peak power and fuel economy, impacting the performance and efficiency of diesel engines.
Additionally, the cost of implementing ULSD infrastructure and technology has been significant. Engine manufacturers and regulatory bodies have had to invest in advanced emissions control technologies to meet the new standards. While these technologies have successfully reduced harmful emissions from diesel combustion, they come with financial implications for both manufacturers and consumers.
The adoption of ULSD has also involved tax incentives and subsidies to encourage the use of lower-sulfur fuels. For example, Hong Kong reduced the tax on ULSD from HK$2.89 to $2.00 per liter during the transition period. Similarly, Sweden offered tax incentives for low aromatic, low sulfur fuel, which helped achieve a 98-99% penetration of the Swedish diesel fuel market. These tax measures carry financial costs for governments and impact fuel prices for consumers.
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$63.64
The environmental impact of sulfur
Sulfur compounds in fuels, such as gasoline and diesel, are a significant source of air pollution when burned. These sulfur compounds create sulfur dioxide (SO2) when released into the atmosphere, which is a highly reactive gas and a potent air pollutant. SO2 emissions contribute to the formation of particulate matter (PM) pollution, which can penetrate deeply into the lungs and cause serious health issues, particularly for children and individuals with asthma. The Environmental Protection Agency (EPA) in the United States has been regulating sulfur levels in diesel fuel since 1993, recognizing the harmful effects of sulfur emissions.
In 2006, stricter regulations were implemented to lower the sulfur content in diesel fuel to 15 parts per million (ppm), resulting in what is known as ultra-low sulfur diesel (ULSD) fuel. This change aimed to reduce emissions from on-road and non-road diesel sources by more than 90%. While effective in reducing sulfur emissions, ULSD fuel faced challenges with increased susceptibility to microbial contamination. This issue arose due to the reduced sulfur content and lower aromatic levels, as well as ULSD's greater affinity for water, which is essential for microbial growth.
The removal of sulfur from diesel fuel has had a significant impact on air quality and public health. By reducing sulfur emissions, the formation of particulate sulfur pollutants, such as fine sulfate particles, is mitigated. This, in turn, helps to improve air quality and protect sensitive individuals from the harmful respiratory effects of sulfur exposure. Additionally, the reduction of sulfur in diesel fuel contributes to the preservation of the natural environment. Sulfur dioxide is a key component of acid rain, which can cause deforestation, and harm trees and plants by damaging foliage and impeding growth.
While the elimination of sulfur from diesel fuel has been a positive step towards improving environmental conditions, it is important to continuously monitor and address any emerging challenges, such as the microbial issues observed with ULSD fuel. Furthermore, it is worth noting that other industrial processes, such as metal extraction and the operation of locomotives, ships, and heavy equipment, also contribute to SO2 emissions, underscoring the need for comprehensive emissions reduction strategies across various sectors.
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The health impact of sulfur
Sulfur compounds in fuels such as gasoline and diesel create air pollution when the fuel is burned. Before global efforts to improve air quality and remove sulfur from fuel, high levels of detergent additives were a necessary component of engine oil to protect engine parts from the damage caused by sulfur. Detergents were so important that a common way to interpret engine oil performance or oil life was by measuring the level of detergents in an oil by the total base number (TBN).
Regulations to reduce vehicle emissions over the past several decades have dramatically reduced the allowable sulfur content in diesel fuel. Today, sulfur content in diesel fuel in both the United States and Mexico is 97% lower than seen throughout most of the 20th century. In 2006, the EPA began to phase in more stringent regulations to lower the amount of sulfur in diesel fuel to 15 ppm, known as ultra-low sulfur diesel (ULSD).
The combustion of sulfur in diesel fuel creates sulfuric acid, which causes corrosive wear on the metal surfaces of an engine. Corrosion of a surface within a dynamic system, such as the cylinder wall/liner, can lead to corrosive wear; surface corrosion layers are removed through sliding or abrasion. All acids formed within the engine have the potential to cause corrosion, but the risk depends on their acidity. Sulfur acids are strong acids that form from the combustion of fuel containing sulfur.
The removal of sulfur from diesel fuel has also been linked to microbial contamination. However, this is not because of the reduced sulfur levels, but because of the effects that the regulations had on limiting aromatic content. Both gasoline and diesel fuels are made up of molecules that can be divided into two classes: aromatics and aliphatics. Aromatic molecules, when burned, contribute to air pollution.
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Frequently asked questions
The elimination of sulfur from diesel fuel began in 1993 when the EPA started regulating diesel fuel sulfur levels.
Removing sulfur from diesel fuel helps to reduce harmful emissions from diesel combustion. However, it also reduces the fuel's lubricating properties and increases its susceptibility to microbial contamination.
ULSD is diesel fuel with a substantially lowered sulfur content, typically containing a maximum of 15 ppm of sulfur. Since 2006, ULSD has been the market standard in Europe and North America.
