The emergence of smog has made people pay more attention to the protection of the atmospheric environment. Although the cause of smog is complicated, it is certain that motor vehicle is one of the major pollutant manufacturers. The olefin content in gasoline is one of the important indicators for the quality control of gasoline. In order to minimize environmental pollution, improving the quality standard of gasoline and diesel is an objective requirement and an inevitable measure for controlling automobile exhaust pollution. Although olefins in gasoline are high octane components, they are prone to gels and deposits during storage and combustion. In addition, olefins are exposed to ultraviolet rays from the sun to form ozone-based toxic photochemical smog. Therefore, it is important to have an in-depth understanding of olefinic compounds in gasoline, which can not only provide reference for process catalyst research and production process, but also an important means to measure the quality of gasoline.

Fluorescent Indicator Adsorption Method

Fluorescent indicator adsorption (FIA) is a classic liquid-solid adsorption chromatography method for determining the total amount of olefins in gasoline fractions. The method uses a specific size silica gel adsorption column to separate alkane, olefin and aromatics from gasoline, uses a fluorescent indicator to indicate the separation interface, and calculates the volume fraction of each hydrocarbon by the length of the region occupied by the different components on the silica gel column.

Multidimensional Gas Chromatography

Multi-dimensional gas chromatography (MGC) is based on the principle of chromatographic separation. It uses multiple columns of different polarities and combines valve switching technology to separate different components in gasoline to obtain sample composition information. AC Corporation of the Netherlands has commercialized multidimensional gas chromatography for the analysis of olefin-containing gasoline. ASTM also published in 1998 a method for determining the total amount of olefins in olefin-containing gasoline based on this analytical system. The basic principle of the standard is to separate the saturated hydrocarbons from the aromatic hydrocarbons in the gasoline by the polar separation column, and then use the coordination effect of π electrons on the olefin double bonds to chemically adsorb and desorb the olefins by using the olefin trapping material, so as to achieve the purpose of separating olefins and alkanes. After separation, the chromatographic peak area of each hydrocarbon group component was detected and recorded, and the total amount of olefins was calculated by a normalization method.

Other Gas Chromatography Methods

A high resolution capillary column was used to separate gasoline fractions. Combined with the existing database, the components of alkanes, olefins and aromatics were qualitatively analyzed, and the area normalization method was used for quantitative analysis. It is a widely used method for determining the composition of gasoline monomers. However, these methods are indicated to be unsuitable for the determination of olefin-containing gasoline or for the determination of olefin components.

Accurate qualitative analysis in chromatographic methods mostly depends on the comparison of standardized compounds and retention time, but it is impossible for all the compounds in gasoline fractions to have corresponding standard samples. The retention index is usually calculated by logarithmic interpolation based on the retention values of adjacent n-alkanes on both sides of the substance to be measured. Retention index is only related to stationary phase and column temperature, and it is an important qualitative index of chromatography.

After the gas chromatography is connected with the mass spectrometry detector, the accuracy of the identification of monomer compounds can be greatly improved by mass spectrometry assisted characterization of the target compound. When using GC-MS to identify olefin monomers, the unseparated chromatographic peaks can be qualitatively identified by selecting ions. This kind of method can give a lot of olefin monomer information, which is of great significance for the qualitative work of olefins.

In order to solve the problems of peak overlap and inaccurate qualitative determination of olefins in gasoline by capillary chromatography, olefins in gasoline can be pretreated or derivatized, and then combined with chromatographic methods to realize the characterization of olefin monomers. The double bonds in the molecular structure of olefins are easy to react with a variety of compounds, while alkanes and cycloalkanes remain inert, so olefins can be distinguished from other hydrocarbons by chemical reactions. Alfa Chemistry Testing Lab is the world's leading third-party testing company, which can provide one-stop gasoline analysis and testing solutions for manufacturers and consumers.