Problem 40 - Chemistry in Context

Question

Prior to 1990 , diesel fuel could contain as much as \(2 \%\) sulfur. New regulations have changed this, and today most diesel fuel is ultra-low sulfur diesel (ULSD) containing a maximum of \(15 \mathrm{ppm}\) sulfur. ULTRA-LOW SULFUR HIGHWAY DIESEL FUEL (15 ppm Sulfur Maximum) Required for use in all model year 2007 and later highway diesel vehicles and engines. Recommended for use in all diesel vehicles and engines. a. Express 15 ppm as a percent. Likewise, express \(2 \%\) in terms of ppm. How many times lower is the ULSD than the older formulation of diesel fuel? b. Write a chemical equation that shows how burning diesel fuel containing sulfur contributes to air pollution. c. Diesel fuel contains the hydrocarbon \(\mathrm{C}_{12} \mathrm{H}_{26}\). Write a chemical equation that shows how burning diesel adds carbon dioxide to the atmosphere. d. Comment on burning diesel fuel as a sustainable practice, both in terms of how things have improved and in terms of where they still need to go.

Step-by-Step Solution

Answer

a. 15 ppm = 0.0015%, 2% = 20,000 ppm, ULSD is ~1333 times lower. b. \( S + O_2 \rightarrow SO_2 \) c. \( 2C_{12}H_{26} + 37O_2 \rightarrow 24CO_2 + 26H_2O \) d. Progress in sulfur reduction, but need to reduce CO2 for better sustainability.

Step 1: Convert ppm to Percent

To express 15 ppm as a percentage, remember that ppm stands for 'parts per million.' This means that 15 ppm is equivalent to 15 parts per million. To convert this to a percentage, divide by 10,000 (since there are 1 million units in 100 percentives). Therefore, \( \frac{15}{10,000} = 0.0015\% \), so 15 ppm is 0.0015\%.

Step 2: Convert Percent to ppm

To express 2\% in ppm, we reverse the earlier calculation. Since 1\% is equivalent to 10,000 ppm, 2\% would be \(2 \times 10,000 = 20,000\) ppm.

Step 3: Compare Sulfur Levels

To find how many times lower ULSD (15 ppm) is compared to the older diesel formulation (20,000 ppm), divide 20,000 by 15. \( \frac{20,000}{15} \approx 1333.33 \). Therefore, ULSD is approximately 1333 times lower in sulfur content than the older formulation.

Step 4: Chemical Reaction of Sulfur Combustion

Burning sulfur in diesel fuel yields sulfur dioxide, which contributes to air pollution. The chemical equation is: \( S + O_2 \rightarrow SO_2 \).

Step 5: Chemical Reaction of Hydrocarbon Combustion

When diesel fuel (\( C_{12}H_{26} \)) is burned, it reacts with oxygen to produce carbon dioxide and water. The balanced chemical equation is: \( 2C_{12}H_{26} + 37O_2 \rightarrow 24CO_2 + 26H_2O \).

Step 6: Evaluation of Sustainable Practice

Burning diesel fuel is becoming more sustainable due to reductions in sulfur content, reducing sulfur dioxide emissions that contribute to air pollution. However, diesel combustion still emits carbon dioxide, a greenhouse gas, indicating that further improvements towards cleaner energy sources are necessary for greater sustainability.

Key Concepts

Ultra-Low Sulfur Diesel (ULSD)

Ultra-Low Sulfur Diesel (ULSD) is a type of diesel fuel that has significantly lower sulfur content compared to traditional diesel. Sulfur in fuel creates sulfur dioxide when burned, leading to pollution. ULSD contains a maximum of 15 parts per million (ppm) of sulfur, which is 0.0015% when converted to a percentage. This represents a dramatic reduction from diesel fuels used before 1990, which could have sulfur contents as high as 2%, equivalent to a staggering 20,000 ppm.

• ULSD is essential for new engines, particularly those manufactured from 2007 onwards, as it complies with stricter environmental regulations.
• The reduced sulfur levels help decrease emissions that contribute to acid rain and respiratory problems in humans.

Implementing ULSD has been a significant step forward in reducing the negative environmental impact associated with diesel fuels.

Sulfur Dioxide Emissions

Sulfur dioxide (SO₂) emissions are a primary concern when it comes to air pollution from burning sulfur-containing fuels. These emissions are a result of sulfur in fuel reacting with oxygen during the combustion process. The chemical equation representing this reaction is:\[ S + O_2 \rightarrow SO_2 \]Such emissions contribute to various environmental and health issues.

• Sulfur dioxide can lead to acid rain, which harms ecosystems and corrodes buildings.
• It also causes smog and respiratory problems, especially in sensitive groups like the elderly and children.

Efforts to curb these emissions through the use of ULSD are crucial in mitigating these adverse effects, making air cleaner and safer for everyone.

Hydrocarbon Combustion

Diesel engines primarily use hydrocarbons, like dodecane (\(\mathrm{C}_{12}\mathrm{H}_{26}\)), which combust in the presence of oxygen to produce carbon dioxide (CO₂) and water. The balanced chemical equation for this reaction is:\[ 2C_{12}H_{26} + 37O_2 \rightarrow 24CO_2 + 26H_2O \]While this reaction is essential for the energy production in diesel engines, it poses the challenge of CO₂ emissions, a significant greenhouse gas that contributes to climate change.

• Combustion of hydrocarbons is a major source of energy worldwide, but it comes with environmental costs.
• CO₂ contributes to the greenhouse effect, which leads to global warming.

Balancing energy needs with reducing emissions remains a key focus for achieving sustainable energy solutions.

Sustainable Energy Practices

Sustainable energy practices aim to reduce harmful emissions and promote cleaner alternatives. With the introduction of ULSD, the diesel industry took an important step toward sustainability by significantly cutting sulfur content, thus lowering sulfur-related emissions. While this is a progressive change, it is only a part of a larger puzzle.

• Theres's a need to further reduce CO₂ emissions from diesel combustion, as CO₂ significantly contributes to the greenhouse effect.
• Investing in alternative and renewable energy sources, such as electric vehicles and biofuels, is crucial.
• The adoption of energy-efficient technologies and practices can also help in reducing the carbon footprint.

Although strides have been made, the journey towards sustainability requires continuous innovation and commitment to cleaner energy practices. Integrating these practices can pave the way to a healthier and more sustainable future.