Selective solvent for extractive rectification
A mixed solvent of sulfolane and 3-methylsulfolane addresses the limitations of existing benzene extraction methods by enhancing selectivity and dissolving power, reducing energy costs and solvent use in benzene recovery from gasoline fractions.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- MNUSHKIN IGOR ANATOLEVICH
- Filing Date
- 2025-12-29
- Publication Date
- 2026-07-02
AI Technical Summary
Existing solvent systems for extracting benzene from gasoline fractions in reforming and pyrolysis processes are limited by narrow composition ranges, high solvent consumption, and inefficiencies in selectivity and dissolving power, leading to high energy costs and complex distillation requirements.
A mixed solvent composed of sulfolane and 3-methylsulfolane, with specific dipole moment and molecular weight ratios, is used for extractive rectification, allowing for high selectivity and dissolving capacity, and adaptable composition to varying feedstock concentrations.
The mixed solvent reduces energy costs and improves extraction efficiency, achieving higher benzene recovery with reduced solvent consumption and simplified equipment needs.
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Abstract
Description
[0001] SELECTIVE SOLVENT
[0002] FOR EXTRACTIVE RECTIFICATION TECHNICAL AREA
[0003] The solvent is designed for the selective extraction of aromatic hydrocarbons from gasoline fractions of reforming and pyrolysis processes by extractive rectification and can be used in the oil refining industry.
[0004] During the catalytic reforming of gasoline fractions, intense aromatization of the catalysate, which contains high levels of aromatic hydrocarbons (arenes)—benzene, toluene, xylenes, and other homologues—occurs. During the pyrolysis of hydrocarbon feedstock, in addition to the target lower olefins—ethylene and propylene—a significant amount of byproducts is formed, including pyrogasoline, which consists primarily of valuable aromatic compounds, particularly benzene. Arenes are valuable feedstocks for the petrochemical industry and are therefore extracted in significant quantities from the catalysate and pyrogasoline. However, when the catalysate is subsequently used as a high-octane component in motor gasoline, benzene must be almost completely removed in accordance with environmental safety requirements (the benzene content is limited to 1% vol.). Therefore, benzene is typically removed from narrow gasoline fractions with a boiling point between n.c. and n.c.(initial boiling point, individual for each fraction) - (90-100) °C, which, in addition to benzene, contain a small amount of toluene (up to traces). Since the narrow fractions contain, in addition to benzene, alkanes and cycloalkanes with similar boiling points, and benzene and cyclohexane form a binary azeotrope, to separate this fraction into sufficiently pure benzene and the remaining hydrocarbon mixture free of benzene, using distillation, it is necessary to use a set of distillation columns with several dozen theoretical plates in each. Therefore, extractive distillation using selective solvents is typically used to extract benzene from narrow fractions of catalysate or pyrogasoline.These solvents effectively and almost completely extract benzene from the feedstock, along with a small amount of alkanes and cycloalkanes, with only a small amount of benzene ending up in the raffinate. However, they also require high solvent consumption in the extractive distillation system. Further improvement of this separation method requires the use of a solvent with both high selectivity and high dissolving power.
[0005] PRIOR ART
[0006] A method is known for separating at least one aromatic hydrocarbon having 6-12 carbon atoms per molecule from at least one non-aromatic hydrocarbon at close boiling point, comprising extractive distillation of an initial mixture containing at least one aromatic hydrocarbon and at least one non-aromatic hydrocarbon in the presence of a mixture of solvents, wherein the extractive distillation process is carried out in an extractive distillation column, and the mixture of solvents is introduced into the extractive distillation column in a weight ratio of approximately 3 parts of the mixture of solvents per part of the initial mixture, wherein said initial mixture contains n-heptane and benzene, wherein the mixture of solvents contains approximately 10-25% by weight of sulfolane, and the remainder is 3-methylsulfolane (patent US 6,781,026, IPC C07C 7 / 00, C07C 7 / 17, C10G 7 / 00, C10G 7 / 08, declared 21.10.2002, published 06.03.2003).A disadvantage of the invention is the narrow range of variation of the recommended mixed solvent composition (10-25% by weight of the main solvent) with a wide range of aromatic hydrocarbon concentrations (20-80% by weight), whereas the composition of the feedstock in terms of the extracted target and non-target components requires the formation of a specific mixed solvent composition. From the given examples of calculating the relative volatility of a benzene-heptane mixture in a 1:1 ratio, it is unclear how the mixed solvent will behave at a benzene concentration in the feedstock of 5-10% by weight. Furthermore, there is no justification for replacing 3-methylsulfolane in the mixed solvent with N-methyl-2-pyrrolidone, acetophenone, isophorone, morpholine, and their mixtures.
[0007] Also known is a method for separating benzene from mixtures with non-aromatic hydrocarbons with simultaneous production of distillate by extractive rectification, characterized in that mixtures containing 30-50% by weight of a mixed solvent sulfolane-3 -methylsulfolane of the composition 89 / 11% by weight and 50-70% by weight of N-methylpyrrolidone are used as a selective solvent (patent RU 2568114, IPC C07C 7 / 08, C07C 15 / 04, filed on 13.03.2014, published on 10.11.2015). A disadvantage of the invention is the rigidity of the fixed composition of the solvent sulfolane-3 -methylsulfolane at the level of 89 / 11% by weight, in combination with a high consumption of the less effective solvent N-methylpyrrolidone, which does not allow varying the optimal composition of the solvent when changing the benzene composition of the raw material.
[0008] Also known is a method for producing benzene and a debenzened high-octane mixture from hydrocarbon mixtures containing at least aromatic and non-aromatic hydrocarbons having six or more carbon atoms, characterized in that the initial mixture is separated by rectification into a bottoms product containing no more than 3% by weight, preferably no more than 1% by weight, of benzene, and a distillate containing predominantly C6 hydrocarbons, in which no more than 5% by weight, preferably no more than 0.5% by weight, of toluene and no more than 36.6% by weight, preferably no more than 10% by weight, of non-aromatic C7 hydrocarbons, which is subjected to extractive rectification in the presence of a polar organic, aprotic, solvent having a ratio of the dipole moment to the square root of the molar volume of more than 0.3 dB / (cm 3 / g • mol), preferably more than 0.4 dB / (cm 3 / g • mol), and a boiling point of 150-250 °C, a stream containing predominantly non-aromatic hydrocarbons C6-Cg is withdrawn as a distillate, which is possibly combined with the still product of rectification, and a mixture of the said solvent with hydrocarbons is withdrawn as a still product, from which a stream containing predominantly benzene is then distilled, which is possibly further subjected to additional distillation from hydrocarbons with higher boiling points, while substances selected from N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, alk(C C2)oxypropionitrile, N-formylmorpholine, including mixtures thereof with water are used as a polar organic aprotic solvent (patent RU 2153485, IPC C07C 7 / 08, C07C 15 / 04, C10G 7 / 08, declared 01.07.1998, published 27.07.2000).The disadvantages of the invention are the use of a single-component solvent, which does not allow for varying its selectivity and dissolving capacity when changing the composition of the feedstock, as well as the rather low selectivity of the proposed solvents, associated with the low level of polarization of the solvent molecules.
[0009] DISCLOSURE OF THE INVENTION
[0010] The objective of the claimed invention is to develop, on the basis of the theory of solutions and intermolecular interactions, a selective solvent for extractive rectification of narrow gasoline fractions n.k. - (90-100) °C reforming and pyrolysis processes, which simultaneously has high selectivity and high dissolving capacity.
[0011] The stated problem is solved due to the fact that the selective solvent for extractive rectification for the extraction of aromatic hydrocarbons from gasoline fractions of reforming and pyrolysis processes by the extractive rectification method is a mixed solvent, each component of which has a dipole moment of at least 4.5 D, the ratio of the dipole moment to the molecular weight in the range of 0.03-0.04 D / a.m.u., and is one of the homologues of the class of cyclic sulfones, wherein the first component of the mixed solvent has higher selectivity and lower dissolving power for alkanes compared to the second component of the mixed solvent, and the ratio between the first and second components of the mixed solvent is in the range of (90-10) - (10-90) % by weight, wherein the water content in the mixed solvent is 0.1 -5.0 % by weight.
[0012] In industrial settings, the extraction of arenes from mixtures with alkanes and cycloalkanes is achieved using polar solvents. Among the diverse force characteristics of polar solvents, dipole moments occupy a special place. These moments characterize the molecular force field and are equal to the sum of the dipole moments of the molecule's bonds. The higher the level of asymmetry of the solvent molecule, the greater the dipole moment, expressed in debyes (D). The presence of a functional element in the organic molecule, such as a foreign atom (nitrogen, oxygen, sulfur, phosphorus) or functional groups (amine, hydroxyl, oxide), leads to an increase in the dipole moment.
[0013] An increase in the dipole moment simultaneously enhances the solvent's dissolving power and the ability to selectively extract components of a specific structure from solutions. Table 1 lists the dipole moments of several typical industrial solvents that selectively extract benzene and contain various functional groups. As can be seen from the data in Table 1, sulfolane has a large dipole moment (4.68 D) as the first representative of a homologous series of cyclic sulfones in which the symmetry of the five-membered ring is disrupted by a hexavalent sulfur atom and two oxygen atoms. 3-Methylsulfolane has an even higher dipole moment—5.08 D—due to the methyl radical.It is obvious that the following homologues of ethyl and propyl sulfolane will have a dipole moment at the level of 5.5-5.6 D and these substances can become ideal extractants for the recovery of benzene from narrow fractions of reforming catalysates, and although they are not yet produced on an industrial scale, it is advisable to ensure a simple industrial synthesis of these products based on the Diels-Alder reaction.
[0014] The presence of a large dipole moment in adjacent but differently oriented solvent molecules in solution leads to their linear and rotational motion in situ, changing the position of the dissolved non-polar molecules of the extracted components. This creates localized mixing structures at the microscopic level, equalizing the concentration of the solute within the bulk of the liquid phase and at the interface with the vapor phase during extractive distillation, and, consequently, intensifies the process. As shown in Table 2, sulfolane has the highest selectivity compared to other selective solvents for benzene.
[0015] The solvent's dissolving power also depends on its molecular weight, and this relationship is conveniently expressed as the ratio of the dipole moment to the molecular weight (D / M). The higher this ratio, the lower the solvent's dissolving power. Sulfolane, despite its very high selectivity, has low dissolving power, which during extractive distillation can lead to the formation of a second liquid phase, impeding mass transfer.In order to avoid this negative phenomenon, it is proposed to use a mixed solvent in the form of a mixture of sulfolane and 3-methyl sulfolane, in which both components have high selectivity, but the second component of the solvent has greater solubility compared to the first, which prevents the formation of a second liquid phase, and both components of the solvent are homologues of thiophene dioxides, that is, both components of the solvent have the same nature and character of interaction with the extracted benzene, while a wide range of compositions of the mixed solvent with a ratio between the first and second components of the mixed solvent within (90-10) - (10-90) % by weight allows for the adaptation of the composition of the mixed solvent relative to the concentration of benzene in the feedstock.At the same time, the second component of the mixed solvent, 3-methylsulfolane, improves the performance of the mixed solvent, as sulfolane, despite all its advantages, has one significant drawback: its high pour point of 28°C requires plant lines and equipment to be equipped not only with high-quality thermal insulation but also with an expensive, nearly continuous electric heating system. Using a mixed solvent with a lower pour point will dramatically reduce these costs.
[0016] Thus, it is advisable to use sulfolane, which is characterized by complete solubility in benzene, as the first component of the mixed solvent, and 3-methylsulfolane as the second component of the mixed solvent.
[0017] The water content of the mixed solvent reduces its viscosity, reduces diffusion resistance in the liquid phase during extraction, and reduces hydraulic resistance in the extractive distillation unit pipelines. Furthermore, the water content of the mixed solvent reduces its freezing point. Specifically, the presence of 3% water in the mixed solvent lowers its freezing point from -4 to -14°C, reducing the risk of mixed solvent pumping failure during a short-term winter shutdown of the extractive distillation unit.
[0018] The use of the proposed mixed solvent for the extraction of benzene from a narrow fraction of reforming catalysate is possible at any extractive distillation unit for this purpose, with appropriate adjustments to the process mode and energy savings if necessary.
[0019] Thus, the claimed invention solves the problem of developing, on the basis of the theory of solutions and intermolecular interactions, a selective solvent for extractive rectification for the extraction of aromatic hydrocarbons, in particular benzene, from narrow gasoline fractions n.k. - (90-100) °C reforming and pyrolysis processes, which simultaneously has high selectivity and high dissolving capacity.
[0020] The technical result of the invention is a reduction in energy costs for extracting benzene from narrow gasoline fractions n.k. - (90-100) °C reforming and pyrolysis processes.
[0021] LIST OF DRAWINGS
[0022] Figure 1 - Evaluation of the solubility of sulfolane.
[0023] Figure 2 - Evaluation of the solubility of 3-methylsulfolane for alkanes.
[0024] Figure 3 - Physicochemical properties of polar solvents (Table 1).
[0025] Figure 4 - Selectivity of some polar solvents for benzene in the separation of binary mixtures of hydrocarbons and reforming catalysates in a single extraction (Table 2).
[0026] BRIEF DESCRIPTION OF DRAWINGS
[0027] The effectiveness of the claimed invention is confirmed by the following examples.
[0028] Example 1. When replacing triethylene glycol with the proposed mixed solvent in an extractive distillation unit, while maintaining the same temperature process conditions, a higher degree of extraction and purity of the obtained benzene will be achieved with a 35.8% energy saving due to the difference in the heat capacity of the solvents (for ethylene glycol it is 2.09 kJ / (kg-K), for the mixed solvent - 1.34 kJ / (kg-K)). Example 2. When replacing triethylene glycol with the proposed mixed solvent in an extractive distillation unit, while maintaining the degree of extraction and purity of the obtained benzene and reducing the consumption of a more effective mixed solvent by 10% compared to triethylene glycol and maintaining the same temperature process conditions, a 40.9% energy saving will be achieved due to the difference in the heat capacity of the solvents (for ethylene glycol - 2.09 kJ / (kg-K), for the mixed solvent - 1.34 kJ / (kg-mK)) and a reduction in the consumption of circulating solvent.
[0029] Example 3. A comparative analysis of the solubility of sulfolane (Figure 1) and 3-methylsulfolane (Figure 2) for alkanes (isooctane and heptane) was performed. At 30°C, 3-methylsulfolane has a solubility three times higher than sulfolane, with a virtually identical effect of increasing temperature on solubility: the slope of the solubility versus temperature curve is 0.041 for sulfolane and 0.040 for 3-methylsulfolane, which allows the use of a proportional control law to control the temperature regime of the distillation column.
[0030] Example 4. 100 ml of a mixed solvent were prepared, for which 50.27 g of sulfolane (40 ml) and 70.98 g of 3-methylsulfolane (60 ml) were taken. A mixture of 82.43 g of heptane and 21.13 g of benzene was extracted with the mixed solvent. After stirring and settling, 131.21 g of extract and 93.53 g of raffinate solutions were obtained. After removing the solvent, the raffinate in an amount of 90.4 g had a refractive index at 25 °C of 1.3950, which corresponds to 12.8% by weight of benzene. In the extract weighing 10.03 g with a refractive index of 1.4830, the benzene concentration was 91.32% by weight. The degree of benzene recovery in a single extraction (one theoretical plate) was 43.0%.
[0031] Example 5. 100 ml of a mixed solvent were prepared, for which 76.06 g of sulfolane (60 ml) and 46.71 g of 3-methylsulfolane (40 ml) were taken. A mixture of 80.65 g of heptane and 21.31 g of benzene was extracted with the mixed solvent. After stirring and settling, 133.65 g of extract and 91.08 g of raffinate solutions were obtained. After removing the solvent, the raffinate in an amount of 90.4 g had a refractive index at 25 °C of 1.3950, which corresponds to 12.8% by weight of benzene. In the extract weighing 10.5 g, the benzene concentration was 88.79% by weight. The degree of benzene recovery in a single extraction (one theoretical plate) was 43.7%.
Claims
CLAUSES OF THE INVENTION 1. A selective solvent for extractive rectification for the extraction of aromatic hydrocarbons from gasoline fractions of reforming and pyrolysis processes by the extractive rectification method, characterized in that it is a mixed solvent, each component of which has a dipole moment of at least 4.5 D, a ratio of the dipole moment to the molecular weight in the range of 0.03-0.04 D / a.m.u., and is one of the homologues of the class of cyclic sulfones, wherein the first component of the mixed solvent has higher selectivity and lower dissolving power for alkanes compared to the second component of the mixed solvent, and the ratio between the first and second components of the mixed solvent is in the range of (90-10) - (10-90) wt.%, wherein the water content in the mixed solvent is 0.1-5.0 wt.%.
2. The solvent according to paragraph 1, characterized in that sulfolane, characterized by complete solubility in benzene, is used as the first component of the mixed solvent.
3. The solvent according to claim 1, characterized in that 3-methyl sulfolane is used as the second component of the mixed solvent.