Determination of composition of industrial cracked C4 by gas chromatography method

1. Introduction

The C4 fraction is widely used as a fuel and chemical raw material (see figure), and most of the C4 fractions used as fuel are divided into C4 alkanes. The storage and transportation of C4 alkanes are very convenient, not only as industrial fuels, but also for civilian use. In the petroleum refining industry, C4 alkanes are used as gasoline additives to increase gasoline vapor pressure and adapt to use in winter or cold regions; There are also some applications in non chemical utilization, but their usage is not large, such as as as refrigerants, heavy oil processing deasphalting solvents, oilfield wellbore dewaxing agents, resin foaming agents, and olefin polymerization solvents.

When hydrocarbons are cracked to produce ethylene and propylene, C4 hydrocarbons are also produced as by-products, commonly known as cracked C4 fractions. Their content (%) and composition vary depending on the cracking feedstock and conditions. Usually, when cracking naphtha or diesel, the by-product C4 fraction accounts for 8% to 10% (by mass) of the total raw material. The characteristic is that the content of olefins and dienes (%) is as high as 92-95, with butadiene content of 40-50 (or even higher), and the rest being isobutene 22-27, 1-butene 14-16, cis-2-butene 4.8-5.5, trans-2-butene 5.8-6.5, and butane (normal, iso) 3-5. Cracking C4 fraction is a convenient raw material for producing butadiene.

Refinery gas analyzerapplicationRange

This regulation is applicable to the determination of the composition of C4 hydrocarbons in the cracking of C4 raw materials and the extraction process of butadiene. It is mainly used for the determination of C4 olefin isomers and hydrocarbon impurities with a content of 0.01% (mass fraction) or more.

3 Normative References

SH/T 1142-2009 Industrial Cracking C4 Liquid Sampling Method

SH/T 1141-1992 Determination of Composition of Cracking C4 for Industrial Use Gas Chromatography Method

GB/T 3723-1999 General Safety Rules for Sampling of Industrial Chemical Products

GB/T 8170-2008 Numerical rounding rules and representation and determination of limit values

Summary of Method 4

The sample is injected through an injection device and carried into an alumina capillary column by a carrier gas, where it is separated into corresponding components. Then, it is detected by a FID detector and quantitatively calculated using the calibration area normalization method.

5 Reagents and Materials

5.1 Carrier gas

Nitrogen: purity greater than 99.995% (volume fraction).

5.2 Gas

Hydrogen gas: purity greater than 99.99% (volume fraction).

5.3 Auxiliary Gas

Air: dried and purified using silica gel or 5A molecular sieve.

5.4 Standard Samples

The mixture standard purchased from the certification agency contains component concentrations that are close to those in the measured sample.

Refinery gas analyzer

6.1 GC-7890/7900/9860 gas chromatograph, equipped with FID detector.

6.2 Automatic six way gas injection valve, with a quantitative tube of 0.5ml.

Analyze spectra: