RESEARCH CHEMICAL COMPOSITION, STRUCTURE AND PROPERTIES OF OIL BITUMENS

ABSTRACT

The main purpose of this article is to determine the chemical composition and basic properties of petroleum bitumen using modern methods and to develop production lines for high–quality construction bitumen based on them. This article presents the results of a study on the selection of optimal conditions for the technological process of obtaining high-quality petroleum bitumen based on petroleum raw materials.

АННОТАЦИЯ

Основная цель данной статьи – определение химического состава и основных свойств нефтяных битумов с использованием современных методов и разработка направлений производства высококачественных строительных битумов на их основе. В данной статье представлены результаты исследования по выбору оптимальных условий технологического процесса получения высококачественного нефтяного битума на основе нефтяного сырья.

Keywords: oil, bitumen, tar, oxidation, hydrocarbon, paraffin

Ключевые слова: нефт, битум, гудрон, окисления, углеводород, парафин

Основная цель данной статьи – определение химического состава и основных свойств нефтяных битумов с использованием современных методов и разработка направлений производства высококачественных строительных битумов на их основе. В данной статье представлены результаты исследования по выбору оптимальных условий технологического процесса получения высококачественного нефтяного битума на основе нефтяного сырья.

Introduction. Modern research conducted to improve the quality and durability of road bitumen is aimed at finding economically sound and least expensive ways to improve the production of petroleum oxidized bitumen with specified physicochemical and operational characteristics.

The chemical composition of bitumen and its structure are characterized to a greater extent by the types of hydrocarbon compounds that form bitumen, as well as the quantitative content of the elements included in the compounds: carbon, hydrogen, oxygen, sulfur and nitrogen [1-5]. The composition of petroleum bitumen includes from 70 to 85% carbon, the amount of hydrogen does not exceed 15%. The sulfur content in the distillation residues of various depths of selection of oil fractions obtained from domestic and foreign oils from various fields varies within the range: 0.2-8% [6]. Bitumen contains very small amounts (traces) of some metals: vanadium, nickel, cobalt, iron in the form of complex compounds called porphyrin complexes. The elemental and hydrocarbon composition of bitumen is different and changes over a wide range depending on the oil field, its nature and physicochemical properties, as well as on the technology of obtaining bitumen [7].

Due to the complexity of the composition, it is not possible to isolate individual components of bitumen with sufficient purity, therefore, three main groups are distinguished: asphaltenes, resins, oils, the properties of which have been studied in detail by such scientists as R.B. Gun, A.S. Kolbanovskaya, D.A. Rosenthal, S.R. Sergienko, Z.I. Sunyaev and others.

Numerous methods have been developed to determine the chemical composition of bitumen, based on the different ability of bitumen components to dissolve in different solvents and be sorbed by various sorbents. The components obtained using different methods do not always have the same composition and properties, and comparing the chemical composition of bitumen determined by different methods is difficult [7].

In addition to the main groups of hydrocarbons, carbenes and carboids are distinguished [4,5]. Sometimes acidic compounds are also distinguished - asphaltogenic acids and their anhydrides [1].

Oils are the lightest part of bitumen. It is the composition of the oil component of tar that changes most significantly with a change in the depth of selection of distillate fractions during the distillation of oil [3]. The group of oils includes paraffin-naphthenic compounds, combining solid high-melting paraffins and naphthenic hydrocarbons, as well as aromatic compounds.

Materials and methods. High-melting paraffins are normal and branched alkanes with a number of carbon atoms of 26 or more. Aromatic compounds are arenes with one or more benzene rings. Mono-, bi-, and polycyclic aromatic hydrocarbons are distinguished. In aromatic compounds, when passing from mono- to polycyclic, the side aliphatic chains are shortened. Monocyclic aromatic compounds are, as a rule, molecules with one benzene nucleus and more or less long side alkyl chains. They can contain from one to three naphthene rings, as well as heteroorganic compounds including sulfur atoms, less often nitrogen and oxygen [5]. Resins do not have a uniform character and cannot be assigned the same chemical structure [7,8]. Resins are a polycyclic system consisting mainly of condensed aromatic rings with aliphatic side chains. According to the elemental composition, resins are characterized by a content of about 79-87% carbon, 8.5-9.5% hydrogen, 1-10% oxygen, 1-10% sulfur, about 2% nitrogen, as well as other elements, including metals. Asphaltenes are a high-molecular fraction of bitumen, insoluble in light alkanes (n-pentane, n-hexane, n-heptane, petroleum ether, etc.), soluble in benzene, its homologues, carbon disulfide and carbon tetrachloride. Asphaltenes are considered a product of resin compaction. The density of asphaltenes is more than 1 g / cm³. They consist of 80-84% carbon, 7.5-8.5% hydrogen, sulfur - 4.6-8.3, oxygen - up to 6, nitrogen - 0.1 [1,3,7].

Results and discussion. Carbenes and carboids are high-carbon products of high-temperature processing of oil and its residues. Carbenes do not dissolve in carbon tetrachloride, carboids do not dissolve in carbon disulfide.

According to the concepts of colloid chemistry, bitumens can be considered as solutions of high-molecular compounds, which are a two-phase system: maltenes-asphaltenes. Maltenes are solvents and plasticizers for asphaltenes [3,4]. Asphaltene macromolecules are distributed in the maltene part. The equilibrium between the phases strongly depends on temperature. The better the equilibrium between the phases is maintained with a change in temperature, the more stable the bitumen [2].

Bitumens, according to the most applicable classification of A.S. Kolbanovskaya, classified into three types, depending on the content and ratio of the main structure-forming components: oils, resins and asphaltenes [6]:

Type I structure is a coagulation network-framework of asphaltenes located in a dispersion medium weakly structured by resins, which consists of a mixture of paraffin-naphthenic and aromatic hydrocarbons. Such a structure is formed when the asphaltene content is higher than 25%, resins less than 4% and oils more than 50%.

Type II structure is a stabilized diluted suspension of asphaltenes in a dispersion medium strongly structured by resins. Such a structure is typical for bitumens containing less than 18% asphaltenes, more than 36% resins and less than 48% oils.

Type III structure is intermediate between the structures of types 1 and 11. In it, individual asphaltene aggregates are in a dispersed medium structured by resins to a lesser extent than the type II medium, but to a greater extent than the type I medium. Type III bitumens contain 21-23% asphaltenes, over 30% resins and up to 49% oils.

The composition and properties of petroleum bitumens depend on the nature of the oil, the composition of the feedstock (oil residues) and the production technology.

Road bitumens must have the following set of properties:

a) have structural and mechanical properties in a wide range of operating temperatures, heat resistance at high and deformability at low temperatures;

b) have good adhesion (adhesion) to the surface of various mineral materials;

c) be resistant to thermal-oxidative aging under the influence of weather and climate changes and automobile traffic [7].

Conclusion. The study of the main physicochemical properties of bitumen serves as the basis for choosing the optimal conditions for the use of raw materials and the production processes necessary for its production.

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