Guide to understand Octane and Reid Vapor Pressure as an operational requirement in blending services

 Gasoline blending is a refinery operation that blends different ingredient streams into different grades of gasoline. Typical grades include 83 octanes that are blended later with an oxygenated fuel like ethanol, regular 87 octanes, and premium 92 octanes.

The Reid Vapor Pressure (RVP) is always set according to several factors like the average temperature of the location, the gasoline will be used. It is quite evident that cold temperatures require higher RVP than warmer climates. These two features are the most important and they are ensured with each blend, to reduce the capability for octane giveaway.

While gasoline is obtained from crude oil for most of the decades since the evolution and in its current formulation it was usually a blend of oil-derived components forever. There are many gasoline blending consultant that are active in the industry. Blending biofuels into the gasoline pool is a contemporary development. Today gasoline that is sold in the US market should always meet the operational requirements of:

Modern combustion engines

Stringent environmental standards

Biofuel blending mandates

These three themes always govern gasoline blending.

Octane: An operational requirement

With the pace in the adoption of automobiles at the beginning of the twentieth century, the consumption of gasoline increased at a faster pace. In initial days, gasoline-powered automobiles had engines of low compression. Apparently, light naphtha or straight-run gasoline was enough. But the auto manufacturers hunted ways to accommodate the increasing demand for vehicle power quickly.

More power could be obtained if there is an increase in the number of cylinders in an engine; another way was to increase the compression of engines.

To diminish and eliminate knocking, straight-run gasoline required a thing to delay or prolong combustion.

RVP (Reid Vapor Pressure) and Seasonal Blending: Operational requirements

While the octane of a specific grade is the same throughout the year, the RVP specification changes as winter arrives. It is quite obvious that all gasoline produced for sale must meet all local environmental specifications and include set standards at the national level for blending in biofuels.

Blending advisory services suggests that a usual summer gasoline blend must consist of approximately 40% FCC gas, nearly 25% straight run gas, about 15% alkylate, near to 18% reformate, and some 2% butane.

The RVP of the gasoline blend depends on how much of each ingredient is present in the blend, and what the RVP is of each component.

Butane is a comparatively inexpensive component in gasoline, but it has the highest vapor pressure of approximately 52 psi. In a gasoline blend, each ingredient gives some contribution of a fraction to the overall RVP.

As evident, in the case of butane, if there is a 10% butane present as a component in the blend, it will give the contribution of around 5.2 psi (10% of 52 psi) to the overall blend.

This implies that in the summer, the butane fraction should be very less in the gasoline, or the overall RVP of the blend will be too much. That is the main difference between winter and summer gasoline blending services.

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