Question

Describe two ways in which the octane number of a gasoline consisting of alkanes can be increased.

Short answer

Two ways to increase the octane number of a gasoline consisting of alkanes are: (1) increasing the concentration of branched isomers in the fuel through isomerization, as they have higher octane ratings due to smoother burning and resistance to knocking, and (2) adding anti-knock additives like ethanol, which is a renewable, biodegradable, and environmentally friendly option that enhances the octane number by reducing knocking in the engine.

Step-by-step solution

Method 1: Increasing the branched isomers concentration

One way to increase the octane number of gasoline containing alkanes is to increase the concentration of branched isomers in the fuel. Branched isomers are hydrocarbon molecules that have a different arrangement of carbon and hydrogen atoms, leading to a branched shape. They have a higher octane rating because they burn more smoothly and resist knocking – a phenomenon where fuel ignites prematurely, causing engine damage. To increase the branched isomers concentration, the gasoline manufacturing process can incorporate a process called isomerization. It rearranges the structure of straight-chain alkanes into branched isomers, which have higher octane numbers. This will lead to a gasoline with improved performance.

Method 2: Adding anti-knock additives

Another method to increase the octane number of gasoline containing alkanes is by adding anti-knock additives. These additives are chemicals that help reduce knocking and improve the performance of the engine. Some common anti-knock additives that can be used to increase the octane rating of gasoline include: 1. Tetraethyllead (TEL): Historically, TEL was the go-to choice for enhancing octane numbers. However, it is now mostly banned due to its toxic nature and harmful effects on the environment. 2. Methyl Tertiary Butyl Ether (MTBE): This additive has been used as a replacement for TEL in many countries. It reduces knocking and increases the octane number. However, it should be noted that the use of MTBE has raised environmental and health concerns. 3. Ethanol: As a renewable and biodegradable anti-knock agent, ethanol is blended with gasoline to increase the octane number. It is widely used in many countries, and it is both environmentally friendly and economically viable. By adopting one or both of the methods – increasing the branched isomers concentration and adding suitable anti-knock additives – the octane number of gasoline consisting of alkanes can be increased, resulting in better engine performance and efficiency.