SEPARATION OF C9 HYDROCARBON FRACTION FROM PYROLYSIS DISTILLATE USING RASCHIG RING PACKING

УДК 66.048.3.069.834

ABSTRACT

A pyrolysis distillate was fractionated at 170°C using a laboratory-scale distillation column packed with glass Raschig rings, providing stable vapor–liquid contact under atmospheric pressure. The collected fraction was subsequently characterized by gas chromatography–mass spectrometry (GC–MS) to determine its chemical composition. The analysis revealed that the fraction is predominantly composed of aromatic and polyaromatic compounds, with indene, naphthalene, azulene, and their derivatives as the main constituents. Quantitative evaluation indicated a significant contribution of C₁₀ compounds, demonstrating the enrichment of medium-boiling aromatic species. At 170 °C, high-purity C₉ hydrocarbons with a high content of aromatic hydrocarbons were obtained. At 159 °C, a decrease in the amount of carbonyl adducts and an increase in the amount of unsaturated hydrocarbons were observed, indicating partial oxidation.The results confirm the suitability of Raschig ring packing for the controlled fractionation of pyrolysis distillates and highlight the potential of the obtained fraction for further use as a chemical feedstock or intermediate for value-added products.

АННОТАЦИЯ

Пиролизный дистиллят был фракционирован при температуре 170°C с использованием лабораторной ректификационной колонны, заполненной стеклянной насадкой в виде колец Рашига, что обеспечило стабильный контакт пар-жидкость при атмосферном давлении. Полученная фракция была охарактеризована методом газовой хромато-масс-спектрометрии (ГХ–МС) с целью определения ее химического состава. Результаты анализа показали, что фракция преимущественно состоит из ароматических и полиароматических соединений, основными компонентами которых являются инден, нафталин, азулен и их производные. Количественная оценка выявила значительную долю соединений состава C₉, что свидетельствует об обогащении фракции среднекипящими ароматическими компонентами. При 170 °C были получены углеводороды C₉ высокой чистоты с большым количеством ароматических углеводородов. При 159 °C наблюдалось уменьшение количества карбонильных аддуктов и увеличение количества ненасыщенных углеводородов, что указывает на частичное окисление. Полученные результаты подтверждают эффективность применения насадки колец Рашига для контролируемого фракционирования пиролизных дистиллятов и указывают на перспективность использования выделенной фракции в качестве химического сырья или промежуточного продукта для получения материалов с добавленной стоимостью.

Keywords: pyrolysis distillate, raschig ring packing, fractionation, gas chromatography–mass spectrometry, hydrocarbons, C₉ fraction

Ключевые слова: пиролизный дистиллят, насадка кольца Рашига, фракционирование, газовая хромато-масс-спектрометрия, фракция C₉.

Introduction

Pyrolysis distillates represent a complex mixture of hydrocarbons formed during the thermal decomposition of polymeric and heavy hydrocarbon feedstocks [1]. Due to their wide boiling range and heterogeneous composition, effective fractionation and detailed compositional analysis of pyrolysis-derived products are essential for their rational utilization as fuels, chemical feedstocks, or functional additives [2]. In this context, distillation-based separation combined with advanced analytical techniques plays a key role in understanding the chemical nature of individual fractions [3].

Packed columns equipped with Raschig ring packing are widely applied in laboratory-scale fractionation due to their simple design, chemical inertness, and ability to provide efficient vapor–liquid contact with relatively low pressure drop [4]. The use of glass Raschig rings is particularly advantageous when separating thermally sensitive pyrolysis products, as they minimize secondary reactions and contamination while ensuring stable separation conditions. Fractionation at controlled temperatures allows the isolation of narrow boiling fractions suitable for subsequent analytical characterization [5]. Gas chromatography (GC) is one of the most powerful and reliable methods for analyzing complex hydrocarbon mixtures, enabling the identification and semi-quantitative determination of individual components within distillate fractions [6]. GC analysis provides valuable insight into the distribution of paraffinic, olefinic, naphthenic, and aromatic hydrocarbons, which directly influences the physicochemical properties and potential applications of the obtained fractions. In the present study, a pyrolysis distillate was fractionated at 170 °C using a laboratory column packed with glass Raschig rings, and the isolated fraction was subjected to gas chromatographic analysis. The aim of this work is to characterize the chemical composition of the 170 °C fraction and to evaluate the effectiveness of Raschig ring packing for the controlled separation of pyrolysis distillate.

Materials and methods

The pyrolysis distillate used in this study was obtained from the thermal decomposition of hydrocarbon-based feedstock under controlled pyrolysis conditions. Prior to fractionation, the distillate was filtered to remove suspended solid impurities and stored in sealed glass containers to prevent evaporation and oxidative degradation. Glass Raschig rings were employed as the column packing material. The rings were chemically inert, cylindrical in shape, and characterized by a height-to-diameter ratio of approximately 1:1, ensuring effective vapor–liquid contact during the fractionation process. Analytical-grade carrier gases and calibration standards were used for gas chromatographic analysis. All reagents and solvents applied in the analytical procedures were of chromatographic or analytical purity.

GC-MS Analysis. Mass chromatographic analysis of the 170 °C fraction was performed using a gas chromatograph equipped with a flame ionization detector (FID). Separation was achieved on a capillary column suitable for hydrocarbon analysis [7-8]. The carrier gas was supplied at a constant flow rate, and the injector was operated in split mode. The oven temperature program was optimized to ensure effective separation of light and medium hydrocarbon components. Detector and injector temperatures were maintained at levels sufficient to prevent condensation of high-boiling compounds. Chromatograms were processed using dedicated chromatographic software. Individual components were identified based on their retention times by comparison with reference standards and literature data. Semi-quantitative analysis was performed using peak area normalization.

Results and discussions

To evaluate the chemical composition of the fraction obtained at 170 °C by fractionation of the pyrolysis distillate using a column packed with Raschig rings, gas chromatography–mass spectrometry (GC–MS) analysis was performed. The analysis enabled the identification of individual hydrocarbon components and provided insight into the distribution of compound classes present in the selected fraction [9-10]. The obtained GC–MS results are presented in table 1, illustrating the chromatographic profile and corresponding mass spectral information of the 170 °C fraction.   

Table 1.

GC–MS analysis of the pyrolysis distillate fraction obtained at 170°C

GC–MS analysis of the fraction obtained at 170 °C using a Raschig ring packed column revealed a complex mixture dominated by aromatic and polyaromatic compounds. The identified components mainly include indene, naphthalene, azulene, and their oxygen- and nitrogen-containing derivatives, indicating the prevalence of medium-boiling aromatic species in the fraction. The presence of substituted aromatics and heteroatom-containing compounds reflects the typical chemical transformation pathways occurring during pyrolysis and confirms the effectiveness of the Raschig ring packing in achieving controlled fractionation under laboratory conditions.

From the identified compounds, the C₉ fractions were separated for quantitative evaluation and the calculated. According to the data presented in table 1, the total content of C₉ compounds in the fraction obtained at 170°C using a raschig ring packed column reaches 46.41%, indicating that this fraction is predominantly enriched with medium-boiling aromatic components.

The C₉ fraction is mainly composed of naphthalene and its derivatives, including 1-naphthalenol (13.91%), naphthalene (4.00%), azulene (5.68%), and 1,4-naphthalenedione (0.24%), which together confirm the dominance of condensed aromatic structures. In addition, indene and alkyl-substituted indene derivatives (approximately 8.5% in total) were detected, suggesting that cyclization and re-aromatization reactions actively occurred during the pyrolysis process.

The presence of oxygen- and nitrogen-containing C₉ compounds, such as naphthalenol, naphthalene dione, and azonaphthalene, reflects the complex chemical nature of the pyrolysis distillate and indicates that the fractionation was carried out under relatively mild conditions, limiting excessive thermal degradation. Overall, the obtained results demonstrate that the use of Raschig ring packing enables effective separation and concentration of C₉ aromatic fractions from pyrolysis distillates under laboratory conditions.

Conclusion

In this study, a pyrolysis distillate was successfully fractionated using a laboratory column packed with Raschig rings, and the fraction collected at 170 °C was systematically characterized by GC–MS analysis. The results demonstrated that the selected fraction is dominated by aromatic and polyaromatic compounds, confirming the effectiveness of the applied packing in providing stable vapor–liquid contact and controlled separation. Quantitative evaluation revealed that C₁₀ compounds constitute 46.41% of the 170 °C fraction, with naphthalene, azulene, indene, and their derivatives being the major components. The presence of oxygen- and nitrogen-containing C₉ species further reflects the complex chemical nature of pyrolysis products and indicates that fractionation was achieved without excessive secondary thermal degradation.

Overall, the findings confirm that Raschig ring packed columns are suitable for the selective isolation of medium-boiling aromatic fractions from pyrolysis distillates under laboratory conditions. The obtained C₉-rich fraction shows potential for further utilization as a chemical feedstock, solvent component, or intermediate for value-added products, supporting the rational upgrading of pyrolysis-derived materials.

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