关键词: 乙烯, 烃类杂质, 气相色谱, PLOT柱, 高效分离, 微量检测

Abstract: As a core basic raw material in the petrochemical industry, the purity level of industrial ethylene and the contents of trace hydrocarbon impurities directly determine the molecular structure, mechanical properties and processing characteristics of downstream polymer products. Therefore, it is crucial to establish an efficient, accurate and stable detection technology system for trace impurities in ethylene. Aiming at the problems existing in the current impurity analysis methods for ethylene, such as low separation efficiency, insufficient resolution of key components, long analysis cycle and limited detection sensitivity, this study adopted gas chromatography （GC） and took 18 hydrocarbon impurities in the range of C₁-C₅ in industrial ethylene as the detection targets to systematically carry out the screening and optimization of chromatographic analysis conditions. In this experiment, an Al₂O₃/KCl PLOT column with a film thickness of 10 μm was employed as the separation carrier. By scientifically regulating the key operating conditions such as column temperature program, valve temperature parameters, split ratio and carrier gas flow rate, the effective separation of 18 target impurities from the ethylene matrix was successfully achieved when helium （He） or nitrogen （N₂） was used as the carrier gas. At the same time, the single sample analysis cycle was significantly shortened, solving the technical bottlenecks of impurity peak overlap and low analysis efficiency in traditional detection methods. The performance verification results showed that the limits of detection （LODs） of the chromatographic columns with 10 μm film thicknesses was 0.2-0.5 mL/m³, and the limits of quantification （LOQs） was 0.7-1.7 mL/m³, respectively. Superior detection sensitivity is achieved with this method, which fulfills the industrial requirement for accurate trace impurity detection. Compared with the traditional national standard method, the LODs and LOQs of the optimized method are significantly reduced, which solves the problem that the traditional method cannot accurately detect trace C₅ hydrocarbons and other impurities. Two quantitative methods, corrected area normalization method and external standard method, were used for verification. The recoveries of all target analytes ranged from 93.0% to 105.6%, with the relative standard deviations （RSDs） of six replicate determinations all less than 4.5%. To further improve the applicability of the method, a systematic comparative study on the adaptability of different chromatographic columns was carried out. The results showed that： when the Al₂O₃/KCl PLOT column was used in series with the methyl polysiloxane column, it not only significantly prolonged the analysis time, but also did not produce a gain effect on the separation effect; the Al₂O₃ column deactivated by Na₂SO₄ had a strong adsorption effect on propadiene, resulting in a significantly lower detection sensitivity than the KCl-deactivated column; the Al₂O₃/KCl PLOT columns of the same specification produced by different manufacturers could all achieve effective separation of 18 impurities after fine-tuning the initial column temperature, reducing the actual application cost of the method. In addition, the method was verified on three different models of gas chromatographs （Agilent 7890A, Agilent 7890B and Agilent 8890）, and the results showed that the correction factors of each component had good consistency, proving the strong universality of the method. The method established in this study extends the detection range of impurities in industrial ethylene, optimizes the separation and quantification conditions, and significantly improves the detection sensitivity and analytical efficiency. Compared with the existing standard analysis methods, it has obvious improvements in separation effect, analysis speed and number of analytes detected. It can provide reliable technical support for the quality control of industrial ethylene, process optimization and the production of downstream high-end polymers, and has both academic innovation and industrial practicality.

Key words: ethylene, hydrocarbon impurities, gas chromatography （GC）, PLOT column, high-efficiency separation, trace detection