Improved aromatics extraction by integration of supplemental co-solvents

Abstract

Solvent mixtures for extractive distillation are described. A solvent mixture consists essentially of a first solvent having a higher octane to benzene relative volatility than sulfolane in a 90% benzene 10% octane feed mixture at 150 DEG C and a 24: 1 solvent to feed weight ratio; a second solvent having a higher relative volatility of octane to benzene than sulfolane in a 50% benzene and 50% octane feed mixture at 150 DEG C and a weight ratio of solvent to feed of 3: 1; and optionally an additive; wherein the solvent mixture has a higher octane to benzene relative volatility than sulfolane in the combined benzene and octane feed at 125 DEG C and a 3: 1 solvent to feed weight ratio wherein the benzene weight ratio is greater than 30%. Another solvent mixture consists essentially of: a base solvent selected from the group consisting of: sulfolane, N-methyl-pyrrolidone (NMP), N-formylmorpholine (NFM), dimethylformamide (DMF), a diol derivative, or a combination thereof; and a first co-solvent and a second co-solvent. Methods of extractive distillation are also described.

Description

[0001] Priority Claim

[0002] This application claims priority to U.S. Non - Provisional Patent Application Serial No. 18 / 528,858, filed Dec. 5, 2023, which claims priority to U.S. Provisional Patent Application Serial No. 63 / 477,421, filed Dec. 28, 2022, the entire contents of which are incorporated herein by reference. Background Art

[0003] Recovering benzene, toluene, and xylene (BTX) from an incoming feed stream (e.g., pyrolysis gas, reformate, etc.) is central to the success of an aromatics complex. Since aromatics and non - aromatics have overlapping boiling points, solvent - assisted liquid - liquid extraction (LLE) or extractive distillation (ED) is commonly used in this separation. In a typical aromatics complex, an ED sulfolane extraction unit takes the feed from the top of a reformate separator, removes non - aromatic compounds as a raffinate stream, and sends the extract stream to one or more benzene - toluene separation towers. Other feeds, including pyrolysis gas, can also be used. The name of the process comes from the sulfolane solvent used, and this solvent has remained the industry leader in BTX extraction for decades. Enhancing the separation of aromatics and non - aromatics by improving solvent performance can bring significant benefits to the aromatics complex and reduce overall utility. However, due to the changing process conditions within the extractive distillation column (EDC), it is a difficult task to evaluate the performance of the solvent, and thus improving solvent performance is challenging.

[0004] Accordingly, there is a need for improved solvents for aromatics extraction and improved aromatics extraction processes. Brief Description of the Drawings

[0005] Figure 1 Shows the relative volatility (RV) of octane to benzene for several conventional solvents from COSMO - RS modeling at 125 °C and a solvent:feed weight ratio of 3:1.

[0006] Figure 2 Shows the RV of octane to benzene from COSMO - RS modeling at 125 °C for various combinations of TMSO and DMSO with sulfolane at a total solvent:feed weight ratio of 3:1.

[0007] Figure 3 Is an illustration of the processing of COSMOtherm data.

[0008] Figure 4 Is a graph showing the variation of experimental RV with the benzene content in the feed mixture for different feed compositions. Detailed Description

[0009] At different stages of the EDC, the percentage of aromatics in each stage increases from the feed stage towards the bottom of the EDC tower to a maximum. An increase in the aromatics content in the liquid, an increase in the process temperature, or an increase in the solvent-to-feed ratio all directionally lead to the single-liquid-phase vapor-liquid equilibrium (VLE) condition in the ED tower. From the feed stage towards the top of the tower, the aromatics content drops sharply, which is also consistent with a sharp increase in the solvent-to-feed (S:F) ratio in the liquid phase. This complex situation highlights the fact that no assessment of the "better" solvent in the BTX ED process can be made based solely on the relative volatility (RV) of a specific composition under specific conditions, such as the feed composition under specific conditions. Aiming to maximize the RV under a selected condition, i.e., the single-liquid-phase (VLE) or two-liquid-phase vapor-liquid-liquid equilibrium (VLLE) condition, as is commonly done in patents and literature, can prove detrimental to the overall performance of the ED tower.

[0010] The development of a new solvent blend for BTX extraction in the aromatic complex stems from this understanding. In the stages below the feed stage, there is a single liquid phase in the EDC, where the percentage of aromatics is high. The aromatics content in the liquid above the feed stage gradually decreases, but the solvent-to-feed ratio also increases accordingly. Therefore, under the ED tower operating guidelines, in most cases, it is possible to maintain a single liquid phase above the feed stage. A solvent with a very high single-liquid-phase RV will more readily transition to the two-liquid-phase (VLLE) region, which results in reduced performance, especially at and above the feed stage and near the lean solvent injection stage, where the percentage of aromatics is significantly lower. Generally, in order to operate by themselves in the desired single-liquid-phase (VLE) scenario, due to the lower solubility of solvents with high RV, they may require additional solvents to increase the S:F ratio. For solvents with higher solubility, the opposite is true, which can prevent the formation of two phases in the EDC but at the cost of a reduced single-liquid-phase RV. This is manifested in the bottom stage of the EDC with a single liquid phase and high aromatics content, where in order to meet the product specifications, a lower selectivity requires additional solvents to increase the S:F ratio to compensate for the decrease in the single-liquid-phase RV. Therefore, solvents that are very selective at the expense of solubility or highly soluble at the expense of selectivity may be detrimental to the ED process.

[0011] As detailed in Example 1, COSMO-RS modeling in the COSMOTherm software was used to initially screen a variety of solvents at 100 °C with an S:F ratio of 3:1 and weight ratios of benzene to non-aromatics of 90:10 and 50:50. The COSMO-RS modeling implemented in the COSMOTherm software will hereinafter be referred to as COSMOtherm simulation. Four systems were used to evaluate the solvent systems: benzene:cyclohexane, benzene:heptane, benzene:n-octane, and benzene:ethylcyclohexane. At a ratio of 90:10, most solvents form a single liquid phase (i.e., the single liquid phase (VLE) case), while at a ratio of 50:50, several solvents form two liquid phases (i.e., the two liquid phases (VLLE) case), and the other solvents remain in a single phase. Sulfolane is an established commercial solvent that transforms into two liquid phases (VLLE) at an S:F ratio of 3:1 and a feed ratio of 50:50 at 100 °C and can be considered an industry benchmark as an aromatic extraction solvent. For the single liquid phase case, there is a general correlation among the four systems tested, i.e., a good single liquid phase solvent for one system is also good for another system. The RV decreases as the aromatic content in the feed decreases, but they are strongly correlated with the systems that remain in a single liquid phase. For strongly selective systems (such as sulfolane) that transform into two liquid phases at 50:50, the decrease in RV is significant. Further, when operating in a VLLE scenario with reduced tray efficiency in a distillation column, there are significant challenges with mass transfer limitations.

[0012] Several solvents exhibit higher RVs than sulfolane in the two liquid phase (VLLE) region for sulfolane. These have higher non-aromatic solubility, as well as lower polarity and lower selectivity for aromatics, and can thus maintain a single liquid phase (VLE) for a wider range of non-aromatics in the feed at the same S:F ratio. These solvents have lower RVs in the single liquid phase (VLE region). However, their lower single liquid phase RVs reduce the resulting selectivity of the solvent blend for feeds in the single phase region where EDC is typically designed to operate.

[0013] Some solvents exhibit a strong affinity for aromatics, resulting in higher RVs at higher aromatics in the feed concentration. These solvents can transform into two liquid phases (VLLE) faster than sulfolane, and this transformation significantly reduces the resulting RV. The resulting blend will show poor solubility for lean aromatic feeds and will require a higher S:F ratio to maintain a single liquid phase (VLE) and prevent a severely reduced RV in the two liquid phase (VLLE) region. These solvents cannot take advantage of their high RVs and require a larger S:F than sulfolane in actual operation.

[0014] As Figure 1As shown, the solvents evaluated using COSMO-RS modeling do not have a consistently higher RV than sulfolane in the aromatic range of the feed, i.e., the better performance in the two-liquid phase region of sulfolane is accompanied by worse performance in the single-liquid phase region, and vice versa. Based on the aromatic content in the feed, the dividing line between the two liquid phases (VLLE) and one liquid phase (VLE) of sulfolane is shown by a dashed line.

[0015] However, the present invention has shown that by combining solvents with different properties having enhanced solubility and higher aromatic selectivity, in the entire aromatic range of the feed, the blend has a higher RV than sulfolane (i.e., the feed compositions that result in the two-liquid phase or single-liquid phase of sulfolane), significantly enhancing the extractive distillation solvent performance in BTX extraction.

[0016] One aspect of the present invention is a solvent mixture for extractive distillation of an aromatic-containing feed stream. In one embodiment, the solvent mixture consists essentially of: a first solvent which, according to COSMOTherm simulation, has a higher relative volatility of octane to benzene than sulfolane in a 90% benzene 10% octane feed mixture at 150 °C and a solvent-to-feed weight ratio of 24:1; a second solvent which, according to COSMOTherm simulation, has a higher relative volatility of octane to benzene than sulfolane in a 50% benzene 50% octane feed mixture at 150 °C and a solvent-to-feed weight ratio of 3:1; and an optional additive; wherein, according to COSMOTherm simulation, the solvent mixture has a higher relative volatility of octane to benzene than sulfolane in the combined benzene and octane feed at 125 °C and a solvent-to-feed weight ratio of 3:1, where the benzene weight ratio is higher than 30%.

[0017] Suitable first solvents include but are not limited to dimethyl sulfoxide (DMSO), 1,4-diformylpiperazine (DFP), dimethyl sulfone (DMS), ethyl-methyl sulfone (EMS), or combinations thereof.

[0018] Suitable second solvents include but are not limited to tetramethylene sulfoxide (TMSO), γ-butyrolactone (GBL), 2-furanone, N-formylmorpholine (NFM), δ-valerolactone (DVL), N-methyl-pyrrolidone (NMP), propylene carbonate, diethyl sulfone (DES), 3-methyl sulfolane (3-MS), or combinations thereof.

[0019] One or more first solvents may be present in the solvent mixture. For example, the first solvent may be a single solvent, or it may be a blend of two, three, four, or five of the listed first solvents. One or more second solvents may be present in the solvent mixture. For example, the second solvent may be a single solvent, or it may be a blend of two, three, four, five, six, seven, eight, or nine of the listed second solvents.

[0020] The amounts of the first and second solvents present in the solvent mixture vary depending on the specific solvents used. Generally, the first solvent is present in an amount of 25% to 95%, and the second solvent is present in an amount of 5% to 75%. Solvent ranges for specific solvent combinations are given in Table 1 below, and examples with TMSO and DMSO solvents are shown in Example 1 and Figure 2 are presented.

[0021] The solvent mixture may contain one or more additives commonly used in extractive distillation. Typical additives are known to those skilled in the art. Suitable additives include, but are not limited to, solubilizers, antifoaming agents, corrosion inhibitors, stabilizers, surfactants, radical inhibitors, or combinations thereof.

[0022] Table 1

[0023]

[0024] Another aspect of the present invention is a solvent mixture for extractive distillation of an aromatic-containing feed stream. In one embodiment, the solvent mixture consists essentially of: a base solvent selected from the group consisting of sulfolane, N-methyl-pyrrolidone (NMP), N-formylmorpholine (NFM), dimethylformamide (DMF), glycol derivatives, or combinations thereof; a first cosolvent that, according to COSMOtherm simulations, has a higher relative volatility of octane to benzene than sulfolane in a 90% benzene 10% octane feed mixture at 150 °C and a solvent-to-feed weight ratio of 24:1; a second cosolvent that, according to COSMOtherm simulations, has a higher relative volatility of octane to benzene than sulfolane in a 50% benzene 50% octane feed mixture at 150 °C and a solvent-to-feed weight ratio of 3:1; an optional additive; wherein, according to COSMOtherm simulations, the solvent mixture has a higher relative volatility of octane to benzene than the base solvent in a combined benzene and octane feed at 125 °C and a solvent-to-feed weight ratio of 3:1, where the benzene weight ratio is higher than 30%. Suitable glycol derivatives include branched or straight-chain saturated or unsaturated alkyl chain diols, but are not limited to ethylene glycol, triethylene glycol, and tetraethylene glycol.

[0025] Suitable first cosolvents include, but are not limited to, dimethyl sulfoxide (DMSO), 1,4-diformylpiperazine (DFP), dimethyl sulfone (DMS), ethyl-methyl sulfone (EMS), or combinations thereof.

[0026] Suitable second cosolvents include, but are not limited to, tetramethylene sulfoxide (TMSO), γ-butyrolactone (GBL), 2-furanone (furan), N-formylmorpholine (NFM), δ-valerolactone (DVL), N-methyl-pyrrolidone (NMP), propylene carbonate, diethyl sulfone (DES), 3-methyl sulfolane (3-MS), or combinations thereof.

[0027] One or more base solvents may be present in the solvent mixture. For example, the base solvent can be a single base solvent, or it can be a blend of two, three, four, or five of the listed base solvents. One or more first cosolvents may be present in the solvent mixture. For example, the first cosolvent can be a single cosolvent, or it can be a blend of two, three, four, or five of the listed first cosolvents. One or more second cosolvents may be present in the solvent mixture. For example, the second cosolvent can be a single cosolvent, or it can be a blend of two, three, four, five, six, seven, eight, or nine of the listed second cosolvents.

[0028] The amounts of the first and second cosolvents present in the solvent mixture vary depending on the specific solvents used. The weight ratio of the second cosolvent to the first cosolvent can range from 0.05:1 to 5:1 depending on the components, but is typically between 0.1:1 and 2:1, with the balance being the base solvent. The cosolvent weight ratios for specific cosolvent combinations are given in Table 2 below.

[0029] The solvent mixture may contain one or more additives commonly used in extractive distillation. Typical additives are known to those skilled in the art. Suitable additives include, but are not limited to, solubilizers, antifoaming agents, corrosion inhibitors, stabilizers, surfactants, free radical inhibitors, or combinations thereof.

[0030] Table 2

[0031]

[0032]

[0033] Another aspect of the present invention is a method for aromatic hydrocarbon extraction. In one embodiment, the method comprises: introducing a feed stream containing aromatic hydrocarbons into an extractive distillation column at a feed stage; introducing a solvent mixture into the extractive distillation column at a stage above the feed stage, the solvent mixture consisting essentially of: a first solvent which, according to COSMOTherm simulation, has a higher relative volatility of octane to benzene in a 90% benzene 10% octane feed mixture at 150 °C and a solvent-to-feed weight ratio of 24:1 than sulfolane; a second solvent which, according to COSMOTherm simulation, has a higher relative volatility of octane to benzene in a 50% benzene 50% octane feed mixture at 150 °C and a solvent-to-feed weight ratio of 3:1 than sulfolane; and an optional additive; recovering a bottoms stream containing a rich aromatic hydrocarbon stream; and recovering a tops stream containing a lean aromatic hydrocarbon stream.

[0034] The solvent mixture can be added at a single point above the feed stage or at multiple points above the feed stage, i.e., at two, three, four, etc. points above the feed stage.

[0035] The first solvent and the second solvent, their respective amounts and the additive are as described above.

[0036] Another aspect of the present invention is a method for aromatic hydrocarbon extraction. In one embodiment, the method comprises: introducing a feed stream containing aromatic hydrocarbons into an extractive distillation column at a feed stage; introducing a solvent mixture into the extractive distillation column above the feed stage, the solvent mixture consisting essentially of: a base solvent selected from the group consisting of: sulfolane, N-methyl-pyrrolidone (NMP), N-formylmorpholine (NFM), dimethylformamide (DMF), diols, diol derivatives or combinations thereof; a first cosolvent which, according to COSMOTherm simulation, has a higher relative volatility of octane to benzene in a 90% benzene 10% octane feed mixture at 150 °C and a solvent-to-feed weight ratio of 24:1 than sulfolane; a second cosolvent which, according to COSMOTherm simulation, has a higher relative volatility of octane to benzene in a 50% benzene 50% octane feed mixture at 150 °C and a solvent-to-feed weight ratio of 3:1 than sulfolane; and an optional additive; recovering a bottoms stream containing a rich aromatic hydrocarbon stream; and recovering a tops stream containing a lean aromatic hydrocarbon stream.

[0037] The solvent mixture can be added at a single point above the feed stage or at multiple points above the feed stage, i.e., at two, three, four, etc. points above the feed stage.

[0038] The base solvent, the first cosolvent and the second cosolvent, their respective amounts and the additive are as described above.

[0039] Example

[0040] The COSMO-RS modeling (Klamt, A. J. Phys. Chem. 99, 2224 (1995); Klamt, A.; Jonas, V.; Bürger, T.; Lohrenz, J. C. J. Phys. Chem. A 102, 5074 (1998); Eckert, F. and A. Klamt, AIChE Journal, 48, 369 (2002)) was carried out in the COSMOtherm program (COSMOtherm (software), released by BIOVIA COSMOtherm in 2022; Dassault Systèmes. http: / / www.3ds.com. available). All molecules were selected from the COSMOtherm database if they were available in the database or constructed from scratch, where the conformational isomers of each molecule were first explored with rational design and simple molecular dynamics simulations, and the simple molecular dynamics simulations were implemented in the MedeA software (MedeA 3.3; MedeA is a registered trademark of Materials Design, Inc., San Diego, USA.), and then optimized in the Gaussian package (Gaussian 09, Revision E.01, Frisch, M. J.; Trucks, G. W.; Schlegel, H. B. et al., Gaussian, Inc., Wallingford, CT, 2013) (DFT calculations using the B3LYP density functional and the 6-31g basis set). The most stable conformational isomer of each target molecule was selected, which had an energy cut-off value of 5% or less in the group relative to the most stable conformational isomer, and then re-optimized in the TMoleX software (TURBOMOLE V7.5 2020, a project jointly developed by the University of Karlsruhe and Forschungszentrum Karlsruhe GmbH, 1989 - 2007, TURBOMOLE GmbH since 2007; available from https: / / www.turbomole.org) (DFT calculations using the BP density functional and the def2-TZVPD basis set, with an energy change of 10 -6 Hartree or less, and a geometric energy gradient of 10 -3in atomic units or less), and then its ".cosmo" file was loaded into the COSMOtherm database. All COSMOtherm calculations were carried out at the TVZPD-FINE precision level, where all available conformational isomers were selected for each molecule. In COSMOtherm, liquid-liquid extraction was calculated by implementing liquid-liquid equilibrium (LLE) between two phases, where the convergence threshold was 10 -5 . The vapor-liquid equilibrium (VLE) was calculated using the liquid-phase composition determined from the liquid-liquid extraction calculation.

[0041] All COSMOtherm data were processed as Figure 3 shown, where the "extract" in the second solvent is the phase dominated by the solvent, always rich in the target solute for selective extraction, and then the "raffinate" is the residue in the original feed.

[0042] Selectivity reflects the relative enrichment of one substance "i" with respect to another substance "k".

[0043] For liquid-liquid partitioning (or LLE in the second solvent), the distribution coefficient D i = y i / x i , and the selectivity S(i / k) = D i / D k .

[0044] For vapor-liquid partitioning in the first or second solvent, the distribution coefficient D i = z i / y i and the selectivity RV(i / k) = D i / D k , where substance "i" is usually more volatile, and for a small vapor volume as the default assumption, "y i " is replaced by "f i " for better comparison with experiments.

[0045] Example 1

[0046] Tables 3A to 3D show the modeling results for the combinations of TMSO (second solvent) with DMSO (3A), DMS (3B), DFP (3C), and EMS (3D) (first solvents). The modeled observed ratios of benzene to octane in the feed stream were 30:70, 50:50, 70:30, and 90:10. The ratio of TMSO to the first solvent varied from 90:10 to 10:90 as shown. Combinations that perform better than sulfolane in the range of 30:70 to 90:10 of benzene to octane are shown in italics with asterisks.

[0047] Tables 3A to 3D. Combinations of TMSO with the first solvents. Solvents with an asterisk indicate that the solvent combinations perform better than sulfolane. The data in Table 3C (combinations of TMSO and DMSO) are presented visually in Figure 2 Although neither TMSO alone nor DMSO alone is superior to sulfolane in terms of RV across the entire range of benzene to octane in the feed that is of interest, Figure 2 highlighting the combination of these two solvents, several of which are favorable to sulfolane across the entire range of interest. A direct experimental verification of this system is provided later in Example 2.

[0048] Table 3A

[0049]

[0050]

[0051] Table 3B

[0052]

[0053] Table 3C

[0054]

[0055] Table 3D

[0056]

[0057]

[0058] For the other second solvents, modeling is also carried out in the same way as these first solvents. This modeling yields the combinations and blend ratios shown in Table 1 above.

[0059] Example 2

[0060] To study the effect of two supplementary co-solvents on the performance of sulfolane, in the following examples, the amount of sulfolane in the blend is fixed at 50% and 80%. Each of Tables 4 to 7 shows that, according to COSMOtherm simulations, at 125 °C and a solvent-to-feed weight ratio of 3:1, in a combined benzene and octane feed, the optimal weight ratios of various components give an RV equivalent to or improved over that of sulfolane, where the benzene weight ratio is higher than 30%, keeping the same single first co-solvent while varying the second co-solvent and the amount of sulfolane. Table 4 shows the modeling results when the first co-solvent is DMSO. In Table 5, the first co-solvent is DMS. In Table 6, the first co-solvent is DFP. The first co-solvent in Table 7 is EMS.

[0061] Table 4

[0062]

[0063]

[0064] Table 5

[0065]

[0066] Table 6

[0067]

[0068]

[0069] Table 7

[0070]

[0071] These tables provide examples of several systems having RV equivalent to or improved over sulfolane. However, other weight percentages of sulfolane can be used with similar ratios of the first and second cosolvents; however, this may not result in an increase in RV.

[0072] Example 2

[0073] In this experimental study, all the chemicals utilized were sourced from Sigma Aldrich, India. The solvent properties were verified using an Agilent HS-GC 7890A, which was incorporated with a G1888 headspace sampler. To maintain uniformity across all the trials, a consistent sample weight was carefully dispensed into the Agilent vials. For all the experiments, a constant sample volume based on weight was taken in the Agilent vials. After achieving sufficient equilibration time, the peak area of each component was recorded from the GC and the mass concentration was estimated using the appropriate response factor. While estimating the relative volatility, it was assumed that the equilibrium liquid composition was the same as the feed composition.

[0074] At 85 °C and a solvent-to-feed ratio of 3, a mixture of TMSO and DMSO solvents was equilibrated with a liquid hydrocarbon feed containing benzene and octane.

[0075] Figure 4 The relative volatility of different feed compositions of a binary feed system of benzene and octane is shown, where the X coordinate represents the benzene content within the feed mixture. Three solvents were studied in this example: 100% sulfolane, 80% DMSO - 20% TMSO mixture, and 85% DMSO - 15% TMSO mixture.

[0076] Examining the findings presented from the experiments, it is evident that across all benzene / octane ratios, the combined DMSO / TMSO solvent mixture is superior to the sulfolane solvent in terms of relative volatility, which is consistent with the conclusions from the COSMO-RS modeling.

[0077] Specific implementation

[0078] While the following is described in conjunction with specific embodiments, it should be understood that the description is intended to illustrate and not limit the scope of the foregoing description and the appended claims.

[0079] A first embodiment of the present invention is a solvent mixture for extractive distillation of a hydrocarbon feed stream containing aromatics, the solvent mixture consisting essentially of: a first solvent which, according to COSMOtherm modeling, has a higher relative volatility of octane to benzene in a 90% benzene 10% octane feed mixture at 150 °C and a solvent-to-feed weight ratio of 24:1 than sulfolane; a second solvent which, according to COSMOtherm modeling, has a higher relative volatility of octane to benzene in a 50% benzene 50% octane feed mixture at 150 °C and a solvent-to-feed weight ratio of 3:1 than sulfolane; and an optional additive; wherein, according to COSMOtherm modeling, the solvent mixture has a higher relative volatility of octane to benzene in a combined benzene and octane feed at 125 °C and a solvent-to-feed weight ratio of 3:1 than sulfolane, wherein the benzene weight ratio is higher than 30%. Embodiments of the present invention are one, any, or all of the previous embodiments in this paragraph to the first embodiment in this paragraph, wherein the first solvent is present in an amount of 25% to 95%, and the second solvent is present in an amount of 5% to 75%. Embodiments of the present invention are one, any, or all of the previous embodiments in this paragraph to the first embodiment in this paragraph, wherein the first solvent is selected from the group consisting of dimethyl sulfoxide (DMSO), 1,4-diformylpiperazine (DFP), dimethyl sulfone (DMS), ethyl-methyl sulfone (EMS), or combinations thereof. Embodiments of the present invention are one, any, or all of the previous embodiments in this paragraph to the first embodiment in this paragraph, wherein the second solvent is selected from the group consisting of tetramethylene sulfoxide (TMSO), γ-butyrolactone (GBL), 2-furanone (furan), N-formylmorpholine (NFM), δ-valerolactone (DVL), N-methyl-pyrrolidone (NMP), propylene carbonate, diethyl sulfone (DES), 3-methyl sulfolane (3-MS), or combinations thereof. Embodiments of the present invention are one, any, or all of the previous embodiments in this paragraph to the first embodiment in this paragraph, wherein the additive is selected from the group consisting of solubilizers, antifoaming agents, corrosion inhibitors, stabilizers, surfactants, free radical inhibitors, or combinations thereof. Embodiments of the present invention are one, any, or all of the previous embodiments in this paragraph to the first embodiment in this paragraph, wherein the first solvent and the second solvent are present in the amounts specified in Table 1.

[0080] Table 1

[0081]

[0082] A second embodiment of the present invention is a solvent mixture for extractive distillation of an aromatic-containing stream, the solvent mixture consisting essentially of: a base solvent selected from the group consisting of sulfolane, N-methyl-pyrrolidone (NMP), N-formylmorpholine (NFM), dimethylformamide (DMF), glycol derivatives, or combinations thereof; a first cosolvent which, according to COSMOTherm simulations, has a higher relative volatility of octane to benzene in a 90% benzene 10% octane feed mixture at 150 °C and a solvent to feed weight ratio of 24:1 than sulfolane; a second cosolvent which, according to COSMOTherm simulations, has a higher relative volatility of octane to benzene in a 50% benzene 50% octane feed mixture at 150 °C and a solvent to feed weight ratio of 3:1 than sulfolane; an optional additive; wherein, according to COSMOTherm simulations, the solvent mixture has a higher relative volatility of octane to benzene in a combined benzene and octane feed at 125 °C and a solvent to feed weight ratio of 3:1 than the base solvent, wherein the benzene weight ratio is higher than 30%. Embodiments of the present invention are one, any, or all of the previous embodiments in this paragraph to the second embodiment in this paragraph, wherein the weight ratio of the second cosolvent to the first cosolvent ranges from 0.05:1 to 5:1, with the balance being the base solvent. Embodiments of the present invention are one, any, or all of the previous embodiments in this paragraph to the second embodiment in this paragraph, wherein the first cosolvent is selected from the group consisting of dimethyl sulfoxide (DMSO), 1,4-diformylpiperazine (DFP), dimethyl sulfone (DMS), ethyl-methyl sulfone (EMS), or combinations thereof. Embodiments of the present invention are one, any, or all of the previous embodiments in this paragraph to the second embodiment in this paragraph, wherein the second cosolvent is selected from the group consisting of tetramethylene sulfoxide (TMSO), γ-butyrolactone (GBL), 2-furanone (furan), N-formylmorpholine (NFM), δ-valerolactone (DVL), N-methyl-pyrrolidone (NMP), propylene carbonate, diethyl sulfone (DES), 3-methyl sulfolane (3-MS), or combinations thereof. Embodiments of the present invention are one, any, or all of the previous embodiments in this paragraph to the second embodiment in this paragraph, wherein the additive is selected from the group consisting of solubilizers, antifoaming agents, corrosion inhibitors, stabilizers, surfactants, radical inhibitors, or combinations thereof. Embodiments of the present invention are one, any, or all of the previous embodiments in this paragraph to the second embodiment in this paragraph, wherein the first cosolvent and the second cosolvent are present in the amounts specified in Table 2.

[0083] Table 2

[0084]

[0085]

[0086] A third embodiment of the present invention is an aromatic extraction method, which includes introducing a feed stream containing aromatics into an extractive distillation column in a feed stage; introducing a solvent mixture into the extractive distillation column at a stage above the feed stage, the solvent mixture consisting essentially of: a first solvent, which, according to COSMOTherm simulation, has a higher relative volatility of octane to benzene than sulfolane in a 90% benzene 10% octane feed mixture at 150 °C and a solvent-to-feed weight ratio of 24:1; a second solvent, which, according to COSMOTherm simulation, has a higher relative volatility of octane to benzene than sulfolane in a 50% benzene 50% octane feed mixture at 150 °C and a solvent-to-feed weight ratio of 3:1; and an optional additive, the optional additive recovering a bottom stream containing an aromatic-rich stream; and recovering a top stream containing an aromatic-lean stream. Embodiments of the present invention are one, any, or all of the previous embodiments in this paragraph to the third embodiment in this paragraph, wherein the first solvent is present in an amount of 25% to 95%, and the second solvent is present in an amount of 5% to 75%. Embodiments of the present invention are one, any, or all of the previous embodiments in this paragraph to the third embodiment in this paragraph, wherein the first solvent is selected from the group consisting of: dimethyl sulfoxide (DMSO), 1,4-diformylpiperazine (DFP), dimethyl sulfone (DMS), ethyl-methyl sulfone (EMS), or a combination thereof; or wherein the second solvent is selected from the group consisting of: tetramethylene sulfoxide (TMSO), γ-butyrolactone (GBL), 2-furanone, N-formylmorpholine (NFM), δ-valerolactone (DVL), N-methyl-pyrrolidone (NMP), propylene carbonate, diethyl sulfone (DES), 3-methyl sulfolane (3-MS), or a combination thereof; or both. Embodiments of the present invention are one, any, or all of the previous embodiments in this paragraph to the third embodiment in this paragraph, wherein the additive is selected from the group consisting of: solubilizers, antifoaming agents, corrosion inhibitors, stabilizers, surfactants, free radical inhibitors, or a combination thereof.

[0087] A fourth embodiment of the present invention is an aromatic extraction method, which includes introducing a feed stream containing aromatics into an extractive distillation column in a feed stage; introducing a solvent mixture into the extractive distillation column at a stage above the feed stage, the solvent mixture consisting essentially of: a base solvent selected from the group consisting of: sulfolane, N-methyl-pyrrolidone (NMP), N-formylmorpholine (NFM), dimethylformamide (DMF), diols, diol derivatives, or combinations thereof; a first co-solvent which, according to COSMOTherm simulation, has a higher relative volatility of octane to benzene than sulfolane in a 90% benzene 10% octane feed mixture at 150 °C and a solvent-to-feed weight ratio of 24:1; a second co-solvent which, according to COSMOTherm simulation, has a higher relative volatility of octane to benzene than sulfolane in a 50% benzene 50% octane feed mixture at 150 °C and a solvent-to-feed weight ratio of 3:1; and an optional additive; recovering a bottoms stream containing an aromatic-rich stream; and recovering a tops stream containing an aromatic-lean stream. Embodiments of the present invention are one, any, or all of the previous embodiments in this paragraph to the fourth embodiment in this paragraph, wherein the weight ratio of the second co-solvent to the first co-solvent is in the range of 0.05:1 to 5:1, with the balance being the base solvent. Embodiments of the present invention are one, any, or all of the previous embodiments in this paragraph to the fourth embodiment in this paragraph, wherein the first co-solvent is selected from the group consisting of: dimethyl sulfoxide (DMSO), 1,4-diformylpiperazine (DFP), dimethyl sulfone (DMS), ethyl-methyl sulfone (EMS), or combinations thereof; or wherein the second co-solvent is selected from the group consisting of: tetramethylene sulfoxide (TMSO), γ-butyrolactone (GBL), 2-furanone (furan), N-formylmorpholine (NFM), δ-valerolactone (DVL), N-methyl-pyrrolidone (NMP), propylene carbonate, diethyl sulfone (DES), 3-methyl sulfolane (3-MS), or combinations thereof; or both. Embodiments of the present invention are one, any, or all of the previous embodiments in this paragraph to the fourth embodiment in this paragraph, wherein the additive is selected from the group consisting of: solubilizers, antifoaming agents, or corrosion inhibitors, stabilizers, surfactants, radical inhibitors, or combinations thereof.

[0088] Although no further elaboration is provided, it is believed that those skilled in the art can make the most of the present invention by using the foregoing description and can easily determine the basic features of the present invention without departing from the essence and scope of the present invention to make various changes and modifications thereto and adapt it to various uses and conditions. Therefore, the foregoing preferred specific embodiments should be construed as merely illustrative and not in any way limiting the remainder of the disclosure, and are intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0089] In the foregoing, all temperatures are shown in degrees Celsius and all parts and percentages are by weight unless otherwise indicated.

Claims

1. A solvent mixture for extractive distillation of a hydrocarbon feed stream containing aromatics, said solvent mixture consisting essentially of: A first solvent which has a higher relative volatility of octane to benzene than sulfolane in a 90% benzene 10% octane feed mixture at 150 °C and a solvent-to-feed weight ratio of 24:1; A second solvent which has a higher relative volatility of octane to benzene than sulfolane in a 50% benzene 50% octane feed mixture at 150 °C and a solvent-to-feed weight ratio of 3:1; and An optional additive; Wherein said solvent mixture has a higher relative volatility of octane to benzene than sulfolane in a combined benzene and octane feed at 125 °C and a solvent-to-feed weight ratio of 3:1, wherein the benzene weight ratio is higher than 30%.

2. A solvent mixture for extractive distillation of a feed stream containing aromatics, said solvent mixture consisting essentially of: A base solvent selected from the group consisting of: sulfolane, N-methyl-pyrrolidone (NMP), N-formylmorpholine (NFM), dimethylformamide (DMF), glycol derivatives, or combinations thereof; A first cosolvent which has a higher relative volatility of octane to benzene than sulfolane in a 90% benzene 10% octane feed mixture at 150 °C and a solvent-to-feed weight ratio of 24:1; A second cosolvent which has a higher relative volatility of octane to benzene than sulfolane in a 50% benzene 50% octane feed mixture at 150 °C and a solvent-to-feed weight ratio of 3:1; An optional additive; Wherein said solvent mixture has a higher relative volatility of octane to benzene than said base solvent in a combined benzene and octane feed at 125 °C and a solvent-to-feed weight ratio of 3:1, wherein the benzene weight ratio is higher than 30%.

3. The solvent mixture according to any one of claims 1 to 2, wherein said first solvent or said first cosolvent is selected from the group consisting of: dimethyl sulfoxide (DMSO), 1,4-diformylpiperazine (DFP), dimethyl sulfone (DMS), ethyl-methyl sulfone (EMS), or combinations thereof.

4. The solvent mixture according to any one of claims 1 to 2, wherein said second solvent or said second cosolvent is selected from the group consisting of: tetramethylene sulfoxide (TMSO), γ-butyrolactone (GBL), 2-furanone, N-formylmorpholine (NFM), δ-valerolactone (DVL), N-methyl-pyrrolidone (NMP), propylene carbonate, diethyl sulfone (DES), 3-methyl sulfolane (3-MS), or combinations thereof.

5. The solvent mixture according to claim 1, wherein said first solvent and said second solvent are present in the amounts specified in Table 1 Table 1 。 6. The solvent mixture according to claim 2, wherein said first cosolvent and said second cosolvent are present in the amounts specified in Table 2 Table 2 7. A method for aromatic extraction, said method comprising: Introducing a hydrocarbon feed stream containing aromatics into an extractive distillation column in a feed stage; Introduce a solvent mixture into the extractive distillation column at a stage above the feed stage, the solvent mixture consisting essentially of: A first solvent which has a higher relative volatility of octane to benzene than sulfolane in a 90% benzene 10% octane feed mixture at 150 °C and a solvent to feed weight ratio of 24:1; A second solvent which has a higher relative volatility of octane to benzene than sulfolane in a 50% benzene 50% octane feed mixture at 150 °C and a solvent to feed weight ratio of 3:1; and Optional additives: Recover a bottoms stream comprising an aromatic-rich stream; and Recover a tops stream comprising an aromatic-lean stream.

8. A method for extracting aromatics, the method comprising: Introduce an aromatic-containing feed stream into an extractive distillation column at a feed stage; Introduce a solvent mixture into the extractive distillation column at a stage above the feed stage, the solvent mixture consisting essentially of: A base solvent selected from the group consisting of sulfolane, N-methyl-pyrrolidone (NMP), N-formylmorpholine (NFM), dimethylformamide (DMF), diols, diol derivatives, or combinations thereof; A first cosolvent which has a higher relative volatility of octane to benzene than sulfolane in a 90% benzene 10% octane feed mixture at 150 °C and a solvent to feed weight ratio of 24:1; A second cosolvent which has a higher relative volatility of octane to benzene than sulfolane in a 50% benzene 50% octane feed mixture at 150 °C and a solvent to feed weight ratio of 3:1; and Optional additives; Recover a bottoms stream comprising an aromatic-rich stream; and Recover a tops stream comprising an aromatic-lean stream.

9. The method according to any one of claims 7 to 8, wherein the first solvent or the first cosolvent is selected from the group consisting of dimethyl sulfoxide (DMSO), 1,4-diformylpiperazine (DFP), dimethyl sulfone (DMS), ethyl-methyl sulfone (EMS), or combinations thereof.

10. The method according to any one of claims 7 to 8, wherein the second solvent or the second cosolvent is selected from the group consisting of tetramethylene sulfoxide (TMSO), γ-butyrolactone (GBL), 2-furanone, N-formylmorpholine (NFM), δ-valerolactone (DVL), N-methyl-pyrrolidone (NMP), propylene carbonate, diethyl sulfone (DES), 3-methyl sulfolane (3-MS), or combinations thereof.

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