Gasoline

Also known as: petrol, motor gasoline, mogas, benzine

Gasoline is one of the major petroleum products produced from processing crude oil in a petroleum refinery.

Gasoline is one of the higher-valued light products (along with jet fuel and diesel). It is used almost exclusively in the transportation sector, mostly as a fuel in automobiles and other light-duty vehicles. Demand for gasoline varies seasonally with the highest demand during the Northern Hemisphere summer. Summer is also when gasoline quality specifications (especially vapor pressure) tend to be tightest, resulting in generally higher prices in these months.

Generally, refiners will try to maximize their yield of gasoline, along with diesel, to maximize profit. Since the two products draw from different boiling range material, they are largely complementary. However, there are a few conversion units that favor one over the other, forcing refiners to make a call on which will be more value-creating. Most notably, FCCs will tend to upgrade VGO more toward gasoline, and hydrocrackers will upgrade VGO more toward diesel.

Gasoline product qualities

Gasoline-powered vehicles use Otto cycle (spark ignition) engines. To perform well and to minimize environmental impact, this requires gasoline to have specific product qualities. Some of the more important ones are:

• Octane - A measure of a fuel's resistance to auto-igniting (knocking) when compressed with air in a spark ignition engine
• Vapor pressure - A fuel's volatility or tendency to vaporize
• Distillation profile - How much gasoline (volume %) evaporates at different temperatures
• Vapor lock index - The tendency of gasoline to vaporize in the fueling system, causing vapor lock
• Driveability index - A measure of a fuel's performance at both cold start and warmed-up conditions
• Sulfur content - A measure of the sulfur remaining in the fuel
• Aromatics content - Aromatics compounds include high-octane materials such as benzene, toluene, and xylene
• Benzene content - A known carcinogen for humans, consequently limited to very small amounts in many grades of gasoline
• Olefins content - Have a tendency to form coatings on engine walls, reducing performance over time

Gasoline blending

Gasoline is typically a complex blend of many different refinery intermediate streams. The most common refinery-produced components in the gasoline pool are:

• FCC gasoline from the FCC unit - Good octane and vapor pressure, but often high in sulfur and olefins
• Reformate from the reformer - High octane and low vapor pressure, but high in aromatics
• Alkylate from the alkylation unit - Good octane and vapor pressure with no aromatics, olefins, or sulfur
• Isomerate from the isomerization unit - Moderately good octane, low aromatics, and low sulfur, but high vapor pressure
• Light straight run naphtha directly from the distillation tower - Low octane and high vapor pressure

Gasoline also often contains non-refinery-sourced blend components, either as octane enhancers or to satisfy a renewable fuels mandate. Typical non-refinery-sourced blendstocks include:

• Ethanol - High octane with no aromatics or sulfur, but high vapor pressure
• MTBE - High octane, no aromatics or sulfur, and low vapor pressure, but limited by environmental concerns related to storage and leakage to water reservoirs in some areas. It is banned across the US
• ETBE - High octane with no aromatics or sulfur, but high vapor pressure

Gasoline is also blended with a number of additives to improve engine performance such as detergents. In the past, the additive TEL (a compound including lead) was blended into gasoline to raise its octane level. This practice has almost universally been eliminated out of environmental concerns, but is the reason gasoline is still often referred to as "unleaded."