Solvent deasphalting
Increasing the oil refining depth and rational use of resources remain urgent tasks to the present day. This is because heavy oil residues make up a significant part of refineries products, but have low value. Therefore, it is important to explore processes that can increase production of light fractions and efficiently process the remaining heavy products.
A sufficient place among the processes that allow to increase the refining depth is occupied by solvent deasphalting.
The essence of the method is to perform sedimentary extraction using solvents, which are usually low-molecular-weight alkanes. This process takes place in a countercurrent extraction column at different pressures and temperatures, depending on the raw material and the solvent characteristics.
The target product is usually deasphalted oil – a part of the hydrocarbon components with no high-molecular-weight resinous-asphaltenic compounds. It is used in production of high-viscosity residual oils, and is also used as a component of feedstock for catalytic cracking and hydrocracking. [1]
The side product is de-oiled asphalt (bitumen). Under certain process conditions and composition of the raw material, it is possible to produce high-quality bitumen appropriate for the road construction industry. This solves the problem of disposing the heaviest part of the oil residues. A number of studies prove the potential of this technology in solving non-standard tasks - producing road bitumen from low-viscosity, low-sulfur feedstocks. [2–4]
Some of process parameters for a particular raw material can be determined by modeling. But the group composition of bitumen, as a product of de-asphalting, and especially its performance parameters are quite difficult to predict, so that it requires laboratory and pilot tests.
Production of petroleum road bitumen
The most widely used technologies of bitumen production are [5]:
- oxidation of heavy oil residues;
- deep-cut vacuum distillation of high-sulfur high resinous crude oils;
- blending of oxidized bitumen with heavy oil residues, or asphalt of propane-butane deasphalting with oil residues.
Bitumen blending technology expands the product range and improves the properties of petroleum bitumen. As a rule, oxidized bitumen and vacuum residues are mixed. Also, performance properties are improved by introducing various modifying agents to the blend.
The advantage of solvent deasphalting in the production of road bitumen is the ability to produce high-quality bitumen even from high-paraffin oils, which are of little use or unsuitable in traditionally used technologies. the method attracted the attention of specialists of INK when solving the problem of processing its own high-paraffin raw materials.
Bitumen in INK
The task of obtaining bitumen was driven by the need of the Irkutsk Oil Company to facilitate exploitation of fields and provide them with a high-quality roadbed. For this purpose, it was planned to use its own raw materials – atmospheric distillation residues – and process it into paving-grade bitumen. The first step to solving this problem was to assess the quality of raw materials (Table 1).
Table 1. Main characteristics of atmospheric distillation residues (fuel oil)
| Parameter | Test method | Value |
|
Group composition, %wt.:
- saturated - aromatic - resins - asphaltenes |
IP 469 |
55.2 |
| Sulfur content, %wt. | ASTM D 4294 | 0.211 |
| Carbon residue, %wt. | ASTM D 4530 | 1.25 |
| Density 15°C, kg/m3 | ASTM D 1298 | 889.1 |
According to the JSC "INHP", the suitability of raw materials for the production of bitumen can be estimated by the formula: A+R-2.5*P ≥ 8, where A, R, P – the content of asphaltenes, resins and paraffins, respectively [7,8]. The application of the formula for the evaluation of fuel oil of INK showed that the raw materials do not meet the requirements for processing into road bitumen. The main obstacles are the predominance of saturated compounds in the group composition and the low content of sulfur, which is necessary for the effective oxidation of vacuum bottoms and the production of oxidized bitumen. In this regard, the question arose about the adjustment of the group composition of atmospheric distillation residues.
The traditional method of bitumen production – the oxidation of oil residues – allows to increase the concentration of resins and asphaltenes. At the same time, the paraffin-naphthenic fraction also undergoes changes during oxidation, but the decrease in its concentration is insignificant. An alternative method for producing bitumen – solvent deasphalting – allows to adjust the group composition within large limits, especially in terms of reducing the concentration of saturated compounds. The conclusion was made about the advantage of solvent deasphalting over oxidation for available feedstock.
Specialists of INK together with RRT developed a work plan and performed tests, including vacuum distillation of atmospheric residues, and solvent deasphalting of resulting vacuum bottoms.
Laboratory tests in RRT
The testing of vacuum distillation and solvent deasphalting technologies was carried as a continuous process. Several experiments on vacuum distillation were carried out to produce a product with different boiling ranges. Tar (the residue of vacuum distillation) with a boiling point above 500 °C was selected as the raw material for solvent deasphalting. The density of the product was 929.2 kg/m3.
The next testing stage was the deasphalting of the tar. For this purpose, an appropriate solvent and starting technological conditions were determined [9, 10]. A number of experiments made it possible to select regime in which the lowest paraffin content in the product is achieved. The results obtained are shown in Table 2.
Table 2. The main characteristics of the residues of vacuum distillation and asphalt deasphalting
| Parameter | Test method | Tar | Asphalt |
|
Group composition, %wt.:
- saturated - aromatic - resins - asphaltenes |
IP 469 |
45.7 38.7 13.4 2.2 |
2.2 21.1 62.2 14.5 |
|
Density, kg/m3 |
ASTM D 1298 | 929.2 | 1024.5 |
Figure 1. a) – photo of raw materials (tar), b) – photo of the product of solvent deasphalting (asphalt).
The analysis of deasphalting product showed that the asphalt is characterized by a high ring and ball softening point – 75 °C (GOST 33142) and low ductility (the material is fragile), which indicates an insufficiency of the plasticizing component. In such cases, blending asphalt with vacuum distillation residues or oil production extracts is a good solution [5]. The relevant approaches are planned to be considered in the course of further work.
Conclusion
The study of solvent deasphalting in the column allowed to evaluate the key characteristics in the processing of INK raw materials: the type of solvent, its feed rate, the interval of optimal temperatures. The dynamics of changes in the group composition of feedstock depending on the conditions of the process, as well as some regularities in the physical and chemical properties of the resulting bitumen, were analyzed.
A crucial role in the work was played by RRT. They have experience in the processes and apparatus of petrochemistry and oil refining. Based on the results of testing the technology in the laboratory/pilot scale, a number of recommendations were made for the industrial implementation of the process.
In conclusion, it is worth noting that such a thorough scientific approach, including the study of processes in laboratory / pilot conditions, often becomes the only way to comprehensively analyze the object of research. It allows to get reliable and important data on the process, as well as to predict the yield and evaluate the necessary characteristics of the product.
References
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- Sultanov F. M. et al. Propane-butane tar deasphalting process of highly paraffinic crude in order to obtain feedstock for road bitumen production// World of petroleum products. 2016. Vol. 4. P. 9-11.
- Tong Y., Shen B., Fang, W., Liu J., Sun H. Optimization of solvent deasphalting of vacuum resid to produce bright stock and hard asphalt // Pet. Sci. Technol. 2018. V. 36. №1. pp. 55–61.
- Wang Y., Chen Z., Shen B. The dual-purpose of solvent deasphalting integrated with FCC for production of qualified pavement asphalt and FCC feedstock to realize its maximum potential // Energy Sources, Part A Recover. Util. Environ. Eff. 2012. V. 34. No. 13. pp. 1187-1195.
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- Kutin Yu. A., Telyashev E. G. Bitumens and bituminous materials. Standards, quality, technologies. GUP INKhP RB, 2018. 272 p.
- Akhmetova R. S., Fryazinov V. V. Classification of oils according to their suitability for the production of bitumen. High-sulfur oils and problems of their processing. Proceedings of the BashNII NP, Vol. VIII. Moscow: Khimiya, 1968. 296 p
- Vishnevsky A.V., Martynenko A. G., Potashnikov G. L., Martirosov R. A., Deasphaltation of tars with the help of liquefied gas, Chemistry and Technology of fuels and oils, No. 3, pp. 12-13, 1983.
- Akhmetov S. A., Technology of deep oil and gas processing. Ufa: “Gilem”, 2002.
- Kuvardina Evgeniya, INK LLC;
- Suprunov Mikhail, RRT Ltd.;
- Karmanovsky Andrey, RRT Ltd.
