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Combustion of alkanes
explain why sulfur dioxide can be removed from flue gases using calcium oxide or calcium carbonate.
Alkanes are used as fuels.
Combustion of alkanes and other organic compounds can be complete or incomplete.
The internal combustion engine produces a number of pollutants including NOx, CO, carbon and unburned hydrocarbons.
These gaseous pollutants from internal combustion engines can be removed using catalytic converters.
Combustion of hydrocarbons containing sulfur leads to sulfur dioxide that causes air pollution.
Alkanes are a class of hydrocarbons that are composed of carbon and hydrogen atoms. When alkanes react with oxygen, a chemical reaction known as combustion occurs, which releases a large amount of energy.
This reaction is exothermic and produces carbon dioxide and water as products. The general equation for the combustion of alkanes is:
alkane + oxygen → carbon dioxide + water + energy
For example, the combustion of methane (the simplest alkane) is as follows:
CH4 + 2O2 → CO2 + 2H2O + energy
This equation represents the complete combustion of methane, where there is a sufficient supply of oxygen for the reaction to occur. The energy released by the combustion of alkanes is used to generate electricity, heat homes, and power transportation.
However, if there is an insufficient supply of oxygen during the combustion of alkanes, incomplete combustion occurs. Incomplete combustion produces carbon monoxide, carbon, and water as products, along with less energy than complete combustion. The equation for the incomplete combustion of methane is as follows:
2CH4 + 3O2 → 2CO + 4H2O + energy
Incomplete combustion can also occur due to low temperatures or incomplete mixing of the fuel and air.
Sulfur is a common impurity in fuels that can lead to several problems during combustion. Sulfur-containing fuels produce sulfur dioxide as a product during combustion, which can cause environmental and health problems. Sulfur dioxide can react with water in the atmosphere to form acid rain, which can harm plants, aquatic life, and buildings.
Furthermore, sulfur dioxide can cause respiratory problems in humans, especially in people with pre-existing conditions like asthma. To prevent these problems, sulfur-containing fuels are treated with desulfurizing agents to remove the sulfur impurities before combustion.
One way to remove sulfur dioxide from flue gases is through a process called flue gas desulfurization (FGD). Calcium oxide (CaO) and calcium carbonate (CaCO3) are two commonly used materials in FGD to remove sulfur dioxide. Here's how it works:
Calcium Oxide - Calcium oxide is also known as quicklime and is a highly reactive material. In the FGD process, flue gas containing sulfur dioxide is passed through a reactor where it comes into contact with a slurry of calcium oxide and water. The sulfur dioxide reacts with the calcium oxide to form calcium sulfite (CaSO3), which is a solid that can be easily removed from the flue gas. The reaction is as follows:
SO2 + CaO + H2O → CaSO3 + H2O
The calcium sulfite can then be further oxidized to form calcium sulfate (CaSO4), which is a solid that can be disposed of safely.
Calcium Carbonate - Calcium carbonate is also known as limestone and is a naturally occurring mineral. In the FGD process, flue gas containing sulfur dioxide is passed through a reactor where it comes into contact with a slurry of calcium carbonate and water. The sulfur dioxide reacts with the calcium carbonate to form calcium sulfite, which is then further oxidized to form calcium sulfate. The reaction is as follows:
SO2 + CaCO3 + H2O → CaSO3 + CO2 + H2O
CaSO3 + 1/2O2 → CaSO4
Calcium carbonate is cheaper than calcium oxide but it requires a higher amount of material to remove the same amount of sulfur dioxide.
A catalytic converter is a device installed in the exhaust system of vehicles to reduce the amount of pollutants that are released into the atmosphere. The catalytic converter works by using a catalyst to facilitate a chemical reaction that converts harmful pollutants into less harmful substances.
Here's how various pollutants are adapted using a catalytic converter:
Carbon Monoxide (CO)
Carbon monoxide is a poisonous gas that is produced when fuels are burned. The catalytic converter uses a catalyst (usually platinum or palladium) to convert carbon monoxide into carbon dioxide (CO2), which is a less harmful gas.
The reaction is as follows: CO + O2 → CO2
Hydrocarbons are a group of pollutants that are produced when fuel is burned incompletely. The catalytic converter uses a catalyst (usually platinum, palladium, or rhodium) to convert hydrocarbons into carbon dioxide and water vapour.
The reaction is as follows: HC + O2 → CO2 + H2O
Nitrogen Oxides (NOx)
Nitrogen oxides are pollutants that are produced when fuels are burned at high temperatures. The catalytic converter uses a catalyst (usually platinum or rhodium) to convert nitrogen oxides into nitrogen gas (N2) and water vapor.
The reaction is as follows: 2NOx → xO2 + N2
Particulate Matter (PM)
Particulate matter is a group of tiny particles that are released into the air when fuels are burned. The catalytic converter uses a filter to trap these particles and prevent them from being released into the atmosphere.
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