STUDY OF PYROLYSIS OIL COMPOSITION AND ISOLATION OF NAPHTHALENE FROM ITS COMPOSITION

ABSTRACT

This research paper presents the results of studying the chemical composition of pyrolysis oil – a secondary product formed during the deep processing of natural gas – pyrolysis, as well as isolating and purifying naphthalene from it through fractional distillation. The naphthalene fraction was isolated by distillation of the pyrolysis oil at a temperature of 210-225 C. This fraction was re-distilled using steam and purified from naphthalene impurities by column chromatography. The composition and structure of naphthalene were confirmed by IR spectroscopy.

АННОТАЦИЯ

В данной исследовательской работе представлены результаты изучения химического состава пиролизного масла – вторичного продукта, образующегося в процессе глубокой переработки природного газа – пиролиза, а также выделения и очистки нафталина из него методом фракционной дистилляции. Нафталиновую фракцию выделяли путем перегонки пиролизного масла при температуре 210-225°С. Эту фракцию повторно перегоняли с использованием пара и очищали от примесей нафталина методом колоночной хроматографии. Состав и структура нафталина были подтверждены методом ИК-спектроскопии.

Keywords: Deep processing of natural gas, pyrolysis distillate, pyrolysis oil, distillation, fractionation, naphthalene, indene, polyaromatic hydrocarbons, IR spectrum.

Ключевые слова: Глубокая переработка природного газа, пиролизный дистиллят, пиролизное масло, дистилляция, фракционирование, нафталин, инден, полиароматические углеводороды, ИК-спектр.

Introduction. It is known that oil and natural gas are the most important raw material sources for the chemical industry worldwide. Based on them, various polymer-plastics, synthetic rubber and rubber products, synthetic fibers, dyes, chemical pesticides, growth regulators and stimulants, various medicinal substances and pharmaceutical preparations, and even some food products are manufactured. In the chemical industry, nearly waste-free technologies for the deep processing of oil and gas have been developed.

Recently, significant attention in scientific research has been directed towards obtaining important industrial products based on certain types of secondary products generated during oil and gas processing. In particular, in our Republic, the comprehensive utilization of oil and gas industry waste and the establishment of production for various products based on them is one of the urgent tasks [1-3].

In our country, enterprises engaged in the deep processing of natural gas, particularly "Uz-Kor Gas Chemical" LLC, which is focused on producing polymer-plastic products from natural gas feedstock, generate industrial wastes such as pyrolysis distillate, pyrolysis oil, and TAR products as a result of deep processing of natural gas. According to the official website data of the enterprise, about 8,000 tons of pyrolysis oil is produced as a secondary product. Analyzing the chemical composition of this product, reprocessing it, separating it into individual components, and establishing the production of various industrial products based on the obtained separate fractions is one of the main tasks [1-5].

Literature Review. According to the studied sources, pyrolysis oil consists of a mixture of indene and its homologs, tetralin, naphthalene and its homologs, diphenyl, fluorene, and other polyaromatic hydrocarbons.

Naphthalene C₁₀H₈ – consists of two condensed benzene rings, a colorless crystal with a characteristic odor. It is slightly soluble in water. It dissolves very well in organic solvents, particularly in diethyl ether, carbon disulfide, chloroform, benzene; it dissolves well in toluene, xylene, cyclohexane, hexane, methanol, and ethanol. Tₘ = 80.1 °C, Tᵦ = 218 °C, ρ = 1.145 g/cm³ (15.5 °C) [3-7].

Materials and methods of research

Isolation of Naphthalene from Pyrolysis Oil. To isolate naphthalene from pyrolysis oil by fractional distillation at atmospheric pressure, a 1000 ml distillation flask and a rectification distillation apparatus were used. 600 ml of pyrolysis oil and 3-4 g of boiling chips were placed in the distillation flask, and heating began in the distillation apparatus up to 150 °C. Then the temperature was gradually increased by 10 °C per minute; starting from 180-185 °C, the first fractionated products began to distill from the pyrolysis oil. During the distillation process, the fraction within the range of 180 °C to 210 °C was collected separately in a receiving flask. Then, the second fraction distilled from 210 °C to 220 °C was collected separately in another receiving flask. Fractions distilled within the temperature ranges of 220-250 °C and 250-300 °C, as well as the undistilled residue, were collected in separate flasks [5-8].

The second fraction obtained in the temperature range of 210-220 °C was redistilled using a steam distillation apparatus and then purified with water.

Results and discussion

According to the studied literature, 32-33% of pyrolysis oil corresponds to the fraction that can be isolated in the temperature range of 210-220 °C, and over 90% of this fraction consists of naphthalene, with the remaining part composed of its homologs. During the research, it was found that the fraction distilled in the temperature range of 210-220 °C was about 31% (by mass). The naphthalene fraction isolated by distillation at atmospheric pressure in the 210-220 °C range was further purified by steam distillation and then by column chromatography using a solvent system of benzene:ethanol = 5:2. The composition and structure of the obtained naphthalene were analyzed by IR spectroscopy (Figure 1 and Table 1).

Figure 1. IR spectrum of naphthalene

From the analysis of the IR spectrum of the isolated and purified naphthalene from pyrolysis oil, it can be seen that the valence vibrations of the C–H bond in the aromatic nucleus are observed in the regions of 2913.83 cm^-1 and 3050.12 cm^-1, deformation vibrations at 476.31 cm^-1 and 626.952 cm^-1, valence vibrations of the C=C bond at 1506.41 cm^-1 and 1599.66 cm^-1, and valence vibrations of the aromatic nucleus at 1506.41 cm^-1 and 1599.66 cm^-1.

Table 1.

Analysis of the IR Spectrum of Naphthalene

Conclusion

The composition of pyrolysis oil, one of the secondary products of a natural gas pyrolysis plant, has been studied. Various polyaromatic hydrocarbon fractions were separated from pyrolysis oil by distillation at atmospheric pressure. Naphthalene with 96% purity was isolated from the fraction of pyrolysis oil distilled in the temperature range of 210-225 °C. The structural composition of the obtained naphthalene was analytically studied using IR spectroscopy. The naphthalene that can be isolated from secondary pyrolysis oil provides the opportunity to obtain various products of industrial importance in organic synthesis.

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