PHYSICOCHEMICAL PROPERTIES OF PYROLYSIS DISTILLATE AND ITS FRACTIONS

ABSTRACT

The reliability and durability of oil and gas pipelines are largely determined by the effectiveness of corrosion protection, since metal corrosion is one of the main causes of accidents, leaks and premature decommissioning of pipeline systems. The impact of aggressive factors of the external and internal environment - moisture, soil electrolytes, dissolved salts, hydrogen sulfide, carbon dioxide, as well as temperature and pressure drops - significantly accelerates corrosion processes and reduces the operating characteristics of pipes. In this regard, there is a problem of creating new inexpensive but effective compositions of anti-corrosion coatings for protecting pipelines. The use of secondary resources, in particular pyrolysis residues and bitumen as modifiers in the development of anti-corrosion coatings for steel pipes is today considered one of the most promising methods in this direction. This article is devoted to the issue of improving the protective properties of anti-corrosion coatings for steel main pipes by developing effective compositions and the possibilities of their effective use.

АННОТАЦИЯ

Надёжность и долговечность нефтегазовых трубопроводов в значительной степени определяются эффективностью антикоррозионной защиты, поскольку коррозия металла является одной из основных причин аварий, утечек и преждевременного выхода трубопроводных систем из эксплуатации. Воздействие агрессивных факторов внешней и внутренней среды — влаги, почвенных электролитов, растворённых солей, сероводорода, углекислого газа, а также перепадов температуры и давления — существенно ускоряет коррозионные процессы и снижает эксплуатационные характеристики труб. В связи с этим возникает проблема создания новых недорогих, но эффективных составов антикоррозийных покрытий для защиты трубопроводов. Использование вторичных ресурсов, в частности остатков пиролиза и битума в качестве модификаторов при разработке антикоррозионных покрытий для стальных труб сегодня считается одним из наиболее перспективных методов в данном направлении. Настоящая статья посвящена вопросу улучшения защитных свойств антикоррозийных покрытий для стальных магистральных труб  путем разработки эффективных составов и  возможностях их эффективного применения.

Keywords: adhesion, anticorrosive protection, pyrolysis distillate, hydrophobicity, oil products.

Ключевые слова: адгезия, антикоррозийная защита, пиролизный дистиллят, гидрофобность, нефтепродукты.

Introduction

The reliability and durability of oil and gas pipelines are largely determined by the effectiveness of corrosion protection, since metal corrosion is one of the main causes of accidents, leaks and premature decommissioning of pipeline systems. The impact of aggressive factors of the external and internal environment - moisture, soil electrolytes, dissolved salts, hydrogen sulfide, carbon dioxide, as well as temperature and pressure drops - significantly accelerates corrosion processes and reduces the operating characteristics of pipes.

Numerous scientists have contributed to solving problems in the field of pipeline corrosion problems and modern protection methods. In particular, in the work of Russian scientists [1, p.160–162], the possibility of using elastomeric materials as anti-corrosion protective coatings and the main criteria for choosing materials were considered. According to the author [2, p. 279-306], the effectiveness of using elastomeric composites as protective coatings is determined by their technological characteristics, high chemical resistance, and barrier properties.

The purpose of these tests is to obtain objective and reproducible information on the protective effectiveness of anticorrosive coatings, their compliance with the requirements of regulatory documentation and the possibility of using secondary resources in the development of new inexpensive but effective anticorrosive coating compositions for oil and gas pipelines. The research results will optimize coating compositions and technologies, increase the reliability of pipeline systems and reduce the risks of accidents and economic losses.

Materials and methods

Pyrolysis distillate (PD) is a product of the thermal decomposition of hydrocarbon feedstock (oil, tar, petroleum coke, polymer waste, etc.) under oxygen-limited conditions. It is a complex mixture of aliphatic, aromatic, cycloaliphatic hydrocarbons, and oxygen-containing compounds [3, p. 34-37].

Composition and Fractional Composition:

The pyrolysis distillate consists of several fractions that differ in boiling temperature and molecular weight (Table 1):

Table 1.

Boiling Temperature and Molecular Weight of Pyrolysis Distillate [4]

Table 2.

Physicochemical Characteristics (Summary Table) [5]:

Thermogravimetric analysis (TGA) [6, p. 915-970]:

The pyrolysis distillate is characterized by a complex thermal degradation that occurs in several stages:

50-150 °C - evaporation of light fractions;

150-300 °C - thermal decomposition of aliphatic components;

300-500 °C - destruction of polycyclic and resinous structures;

500 °C - residual coking and formation of carbon residue.

Significance in corrosion protection [7, p. 1-20]:

Pyrolysis distillate and its heavy fractions exhibit important properties in coatings that ensure effectiveness:

Hydrophobicity and high adhesion, which help to isolate from moisture and aggressive ions;

Chemical inertness to most acids and bases;

Compatible with bitumen and polymers, which allows for its use as a modifier.

Formulas (generalized structures):

Aliphatic hydrocarbon chain:

                                          (1)

Aromatic ring (benzene type):

                                                         (2)

Polynuclear aromatic hydrocarbon:

Naphthalene:                                           

                                                            (3)

The use of hydrocarbon feedstock, pyrolysis waste, and bitumen as modifying components is considered one of the promising directions in the development of anti-corrosion coatings for steel pipes. These technogenic products possess a number of physical and chemical properties that can be effectively used to improve the performance characteristics of protective coatings with proper processing and stabilization [8].

Pyrolysis residues: composition and properties

The pyrolysis of hydrocarbon feedstock (oil, gas, rubber, plastic) leads to the formation of distillate and heavy residual fractions, which include the following:

• aromatic hydrocarbons,

• resin-asphaltic compounds,

• technical carbon (soot),

• volatile organic compounds.

For coating modification, fractions containing high-molecular weight aromatic-resinous compounds that provide adhesion, hydrophobicity, and plasticity are particularly valuable [9, p. 417-422].

Bitumen is widely used as a matrix in composite anticorrosive coatings due to its moisture resistance, chemical inertness, and ability to fill metal pores. However, its main disadvantages—brittleness at low temperatures and aging under UV and oxygen exposure—can be overcome by introducing pyrolysis modifiers [10, p. 136-148].

Advantages of modifying bitumen with pyrolysis distillate:

Advantages of modifying bitumen with a pyrolysis distillate:

• Increasing the coating's elasticity at low temperatures;

• Increased adhesion to steel surfaces;

• Increased thermoxidation stability;

• Reduced crack formation;

• Improved ingress capability due to low viscosity [11, p. 43-45].

Modification Mechanism

When mixing bitumen with pyrolysis residues (e.g., in a 85:15 or 70:30 ratio), a physicochemical interaction occurs between the resinous components and the bitumen fractions. This stabilizes the coating's colloidal structure and ensures the formation of a more robust interfacial layer at the “coating-metal” boundary.

Implementation potential:

• Use of inexpensive secondary raw materials;

• Recycling of environmentally hazardous waste into a functional material;

• Extend the service life of protective coatings on pipelines;

• The ability to create hybrid composite coatings based on bitumen, pyrolysis distillate, and mineral fillers (technocarbon, ash, IES waste, etc.).

Examples of successful solutions:

• Using pyrolysis distillate as a plasticizer in the production of bitumen-polymer mastics;

• Obtaining sealing compositions for flanged joints with high resistance to aggressive environments (H₂S, CO₂);

• Development of cold coatings for hard-to-reach areas of pipelines.

Figure 1. The comparative IR spectra of the unmodified and modified bitumen

Figure 1 shows the comparative IR spectra of the unmodified and modified bitumen:

-2920 cm⁻¹ (CH₂) - an increase in the stretching band of the methylene groups is observed after modification.

- 1450 cm⁻¹ (CH₃) - the intensity decreases, indicating the redistribution of alkyl groups.

- 1600 cm⁻¹ (C = C) - a new line characteristic of aromatic compounds appears from the pyrolysis distillate.

Results and discussion

Thus, polymer, bituminous and composite coatings show high efficiency, especially when modifying bitumen with additives obtained from pyrolysis of hydrocarbon feedstocks. Such modifiers allow increasing thermal and chemical resistance of protective materials, reducing conductivity, improving adhesion to metal. Pyrolysis wastes and heavy oil residues demonstrate high potential in the development of new protective compositions, which is due to the presence of aromatic, resinous and hydrocarbon components that can effectively modify the bitumen matrix. Infrared spectroscopy, term gravimetry, prediction and modeling of the properties of coatings and protective compositions based on thermodynamic and kinetic models using computer calculations are becoming an integral part of research aimed at creating new generations of anti-corrosion materials. The advantages of this method are the use of inexpensive secondary raw materials, the processing of environmentally hazardous waste into a functional material, the extension of the service life of protective coatings on pipelines, the possibility of creating hybrid composite coatings based on bitumen, pyrolysis distillate and mineral fillers.

Conclusion

As a result of the studies, six variants of compositions of anticorrosive coatings based on bitumen, alkyd-urethane and alkyd varnishes, hydrocarbon solvents and mineral fillers were developed. The effect of temperature on the drying time of each formulation is almost halved, which is important for optimizing the coating process. The corrosion resistance, water resistance and adhesion tests performed have shown high resistance of the compositions to moisture and aggressive media. All ingredients used are available on the domestic market of Uzbekistan at relatively low prices, which ensures the economic feasibility of creating local anti-corrosion coatings and reduces dependence on imported raw materials. The conducted set of studies makes it possible to recommend optimal compositions for practical use on oil and gas pipelines, taking into account operational conditions and technological requirements, and also serves as a basis for the further development of new modified coatings.

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