Process for separating C6-C9-aromatic hydrocarbons and isoprene using improved extractant

Abstract

The present invention relates to a process for separating one or more compounds selected from the group consisting of C6-C9 aromatic hydrocarbons, isoprene and any mixture thereof from a feed composition comprising said one or more compounds mixed with at least one other organic and / or inorganic compound, the process comprises at least one liquid-liquid extraction step using an extraction agent, where the extraction agent comprises i) sulfolane, ii) at least one co-solvent selected from the group consisting of 3-methylsulfolane and sulfones according to the general formula (I) R1R2SO2, where R1 and R2 are independently of each other C1-C4-alkyl groups, and iii) water.

Description

[0001] The present invention relates to a method for separating C6-C9-aromatic hydrocarbons and isoprene from a feed composition, said feed composition comprising one or more compounds mixed with at least one other organic and / or inorganic compound.

[0002] Separating one or more specific compounds from a mixture containing other chemical compounds is a crucial task in chemical processes. A variety of separation methods are available, such as distillation, extraction, absorption, adsorption, ion-exchange chromatography, and many others. A very common separation technique for separating mixtures of several organic compounds is distillation, which allows the separation of volatile organic compounds based on their different boiling points. During distillation, the mixture to be separated is heated, causing compounds with lower boiling points to evaporate and rise to the top of the distillation column, where they are removed as the overhead stream, condensed, and then further processed as needed. In contrast, compounds with higher boiling points do not evaporate but remain as liquids and flow down the distillation column to the bottom, where they are removed as the basal stream and then further processed as needed. However, distillation is not suitable for separating different chemical compounds with similar boiling points.

[0003] For separating mixtures containing different chemical compounds with similar or even the same boiling points, liquid-liquid extraction is a promising option. Extraction uses an extractant from which the chemical compound to be separated from the mixture has a significantly higher solubility than other (or one or more) chemical compounds in the mixture from which it will be separated. During operation, the mixture and extractant are introduced co-currently or counter-currently through an extraction column, where the two streams come into contact with each other. Due to its higher solubility in the extractant, most, or ideally almost all, of the chemical compounds to be separated from the mixture dissolve in the extractant, thus forming an extract composition, which is withdrawn from the extraction column separately from the remaining raffinate containing other (or one or more) chemical compounds. Extractive distillation, on the other hand, is a distillation process in which the extractant, in addition to the mixture, is also fed into a distillation column, where the extractant is selected such that it increases the relative volatility of the chemical compounds to be separated. Relative volatility is an indicator of the degree of separability or ease of separation of two or more chemical compounds from the mixture of these chemical compounds by distillation. An additional requirement for the extractant used in extractive distillation is that it has a boiling point significantly different from that of the chemical compounds to be separated.

[0004] Sulfolane and mixtures of sulfolane and water are commonly used to separate C6-C9 aromatic hydrocarbons, such as benzene and styrene, from non-aromatic compounds with very similar or even substantially the same boiling points. Even though sulfolane is a fairly suitable extractant, it is limited in terms of selectivity and solubility, even at relatively high levels (referring to the separation of C6-C9 aromatic hydrocarbons and isoprene from other chemical compounds with highly similar boiling points). Therefore, the use of sulfolane or mixtures of sulfolane and water requires a relatively large amount of energy to separate a predetermined volume of the mixture, which hinders the higher profitability of the separation method. Furthermore, it is currently desirable to minimize the energy requirements of the method for environmental reasons, and thus reduce carbon emissions associated with energy production.

[0005] In view of this, the object of the present invention is to provide a method for separating one or more compounds selected from C6-C9-aromatic hydrocarbons, isoprene, and any mixture thereof from a feed composition comprising the one or more compounds mixed with at least one other organic and / or inorganic compound, the method comprising at least one liquid-liquid extraction step utilizing an extractant having increased selectivity and, in particular, improved solubility for C6-C9-aromatic hydrocarbons and isoprene, such that the method is characterized by reduced energy requirements per unit of separated mixture, and thereby reduced carbon emissions associated with energy generation and increased method profitability.

[0006] According to the present invention, this objective is achieved by providing a method for separating one or more compounds selected from C6-C9-aromatic hydrocarbons, isoprene, and any mixtures thereof from a feed composition comprising the one or more compounds mixed with at least one other organic and / or inorganic compound, the method comprising at least one liquid-liquid extraction step using an extractant comprising i) sulfolane, ii) at least one cosolvent selected from 3-methylsulfolane and sulfones according to general formula (I) R1R2SO2, wherein R1 and R2 are independently C1-C4-alkyl groups, and iii) water.

[0007] This solution is based on the surprising discovery that the mixture contains i) sulfolane, ii) at least one co-solvent selected from 3-methylsulfolane and a sulfone according to general formula (I) R1R2SO2, wherein R1 and R2 are independently C1-C4 alkyl groups, and iii) water. This mixture exhibits high selectivity, and particularly high solubility, for C6-C9 aromatic hydrocarbons and isoprene to be separated from other chemical compounds having highly similar boiling points compared to sulfolane alone or a mixture of sulfolane and water. More specifically, the inventors of this invention have surprisingly discovered that the addition of water to the mixture of i) sulfolane and ii) at least one co-solvent (selected from 3-methylsulfolane and a sulfone according to general formula (I)) further enhances the selectivity, and particularly the solubility, for C6-C9 aromatic hydrocarbons and isoprene (compared to other chemical compounds having highly similar boiling points).

[0008] This invention does not particularly limit the content and ratio of sulfolane, co-solvent, and water. However, tending to be, the higher the total amount of these components i), ii), and iii), the better the performance of the extractant. Particularly good results are obtained when the extractant contains, based on 100% by weight, at least 80% by weight, more preferably at least 90% by weight, and even more preferably at least 95% by weight of i) sulfolane, ii) at least one co-solvent selected from 3-methylsulfolane and a sulfone according to general formula (I), and iii) water.

[0009] According to a preferred embodiment of the invention, the extractant comprises or is at least substantially comprised of: i) sulfolane, ii) a cosolvent selected from 3-methylsulfolane and a sulfone according to general formula (I) and iii) water, i.e., the total amount of components i), ii) and iii) is at least 98% by weight, preferably at least 99% by weight, more preferably at least 99.5% by weight, and most preferably 100% by weight, based on 100% by weight of the extractant.

[0010] According to an alternative preferred embodiment of the invention, the extractant contains a large amount of components i) and ii), and additionally a considerable amount of water. Similarly, the inventors of the invention have surprisingly discovered that adding water, and particularly a relatively small amount of water, to the mixture of i) sulfolane and ii) at least one co-solvent selected from 3-methylsulfolane and a sulfone according to general formula (I) further increases the selectivity, and particularly the solubility, of C6-C9-aromatic hydrocarbons and isoprene (compared to other chemical compounds with highly similar boiling points). Preferably, in this embodiment, based on 100% by weight of the extractant, the extractant comprises a) 90 to 100% by weight, preferably 95 to 99% by weight, and more preferably 97 to 99% by weight of the sum of i) sulfolane and ii) at least one co-solvent selected from 3-methylsulfolane and a sulfone according to general formula (I), and b) 1 to 10% by weight, preferably 1 to 5% by weight, and more preferably 1 to 3% by weight of water. Furthermore, in this embodiment, the total amount of i) sulfolane, ii) at least one co-solvent selected from 3-methylsulfolane and a sulfone according to general formula (I) and iii) water is 100% by weight based on 100% by weight of the extractant.

[0011] As stated above, the present invention does not particularly limit the ratio of sulfolane to co-solvent in the extractant (i.e., the relative amounts of sulfolane and co-solvent). Particularly good results are obtained when the extractant contains approximately equal amounts of components i) and ii) or a higher amount of component i) than component ii). Therefore, it is preferred that, based on 100% by weight of the extractant, the extractant contains 40 to 90% by weight of i) sulfolane, 10 to 60% by weight of ii) at least one co-solvent selected from 3-methylsulfolane and sulfones according to general formula (I), and up to 100% by weight of the remaining portion of component iii). Specific favorable results are obtained when the extractant contains more than 50% to 90% i) sulfolane, 10% to less than 50% ii) at least one co-solvent selected from 3-methylsulfolane and sulfones according to general formula (I) and up to 100% of the remaining component iii) based on 100% by weight of the extractant, for example, 60 to 75% i) sulfolane, 25 to less than 40% ii) at least one co-solvent selected from 3-methylsulfolane and sulfones according to general formula (I), and up to 100% of the remaining component iii (preferably 1 to 3% by weight).

[0012] According to the present invention, the extractant comprises i) sulfolane, at least one co-solvent selected from 3-methylsulfolane and a sulfone according to general formula (I), and iii) water. Particularly good results are obtained when the extractant comprises i) sulfolane, ii) only one co-solvent selected from 3-methylsulfolane and a sulfone according to general formula (I) R1R2SO2, but without a mixture thereof, and iii) water.

[0013] According to the present invention, a sulfone of general formula (I) R1R2SO2, wherein R1 and R2 are independently C1-C4-alkyl groups.

[0014] According to a preferred embodiment of the invention, groups R1 and R2 in general formula (I) are identical. Therefore, in this embodiment, it is preferred that the extractant comprises dimethyl sulfone, diethyl sulfone, dipropyl sulfone, or dibutyl sulfone as a co-solvent (ii).

[0015] According to an alternative preferred embodiment of the invention, groups R1 and R2 in general formula (I) are different from each other. Suitable examples of cosolvents for this embodiment are methyl ethyl sulfone, methyl propyl sulfone, methyl butyl sulfone, ethyl propyl sulfone, and ethyl butyl sulfone. More preferably, in this embodiment, one of groups R1 and R2 in general formula (I) is hydrogen, while the other group is a C1-C4-alkyl group. Examples of cosolvents for this variant are methyl sulfone, ethyl sulfone, propyl sulfone, and butyl sulfone, with more preferred examples being n-propyl sulfone, isopropyl sulfone, n-butyl sulfone, and isobutyl sulfone.

[0016] According to a particular preferred embodiment of the invention, the extractant comprises 3-methylcyclobutane sulfone, dimethyl sulfone, diethyl sulfone, or n-propyl sulfone as a co-solvent ii). More preferably, the extractant comprises 3-methylcyclobutane sulfone, dimethyl sulfone, or n-propyl sulfone as a co-solvent ii), and most preferably, the extractant comprises dimethyl sulfone as a co-solvent ii).

[0017] In view of the above, it is particularly preferred that the extractant comprises more than 50 to 90% by weight i) sulfolane, 10 to less than 50% by weight ii) at least one co-solvent and 1% to 3% by weight water, based on 100% by weight of the extractant, wherein the co-solvent ii) is 3-methylsulfolane, dimethyl sulfone, diethyl sulfone or n-propyl sulfone, and more preferably dimethyl sulfone.

[0018] The present invention does not particularly limit the type of feed composition, as long as it contains one or more compounds selected from C6-C9-aromatic hydrocarbons, isoprene, and any mixture thereof, mixed with at least one other organic and / or inorganic compound. The method according to the invention is particularly applicable to feed compositions comprising, based on 100% by weight of the feed composition, 10 to 90% by weight, and preferably 60 to 90% by weight, of C6-C9-aromatic hydrocarbons and / or isoprene, and 10 to 90% by weight, and preferably 10 to 40% by weight, of at least one other organic compound.

[0019] In a further development of the inventive concept, it is proposed that the feed composition contains one or more C6-C9-aromatic hydrocarbons selected from the following: benzene, toluene, xylene, ethylbenzene, styrene, and any mixture thereof.

[0020] The at least one other organic compound may be selected, for example, from alkanes, cycloalkanes, alkenes, cycloolefins, and any mixture thereof. When the feed composition contains at least one selected from n-alkanes, isoalkanes, cycloalkanes, n-olefins, isoolefins, and C4-C... 10 Good results are particularly obtained with other organic compounds of cycloolefins.

[0021] For example, the feed composition can be pyrolytic gasoline, reformate, an oil mixture obtained from plastic recycling methods, or any other organic chemical stream rich in aromatic compounds, particularly C6-C9 aromatic compounds. Most preferably, the feed composition is pyrolytic gasoline or reformate.

[0022] According to the invention, the method includes at least one liquid-liquid extraction step. Preferably, the at least one liquid-liquid extraction step is carried out in at least one liquid-liquid extraction tower. If the method includes two or more subsequent liquid-liquid extraction steps, each liquid-liquid extraction step is carried out in one liquid-liquid extraction tower, such that the method is carried out in total in two or more subsequently arranged liquid-liquid extraction towers.

[0023] The present invention does not particularly limit the type of at least one liquid-liquid extraction tower used in the method. Therefore, all conventional liquid-liquid extraction towers can be used. Particularly good results are obtained when one or more compounds selected from C6-C9-aromatic hydrocarbons, isoprene, and any mixtures thereof are separated from the feed composition using at least one liquid-liquid extraction step with an extractant, wherein the at least one liquid-liquid extraction step is carried out in at least one spray extraction tower, in at least one pulse extraction tower (e.g., in a packed extraction tower or a sieve tray extraction tower), or in at least one stirred extraction tower (e.g., in a stirred countercurrent extraction tower). For example, a stirred extraction tower includes one or more rotating shafts, each rotating shaft including one or more agitators, said agitators preferably selected from discs, blades, paddles, turbine impellers, fins, and any combination of two or more of the aforementioned agitators.

[0024] In addition to at least one liquid-liquid extraction step, the method according to the invention may further include at least one extractive distillation step using the extractant mentioned above. The at least one extractive distillation step is preferably carried out in a distillation column, wherein the distillation column includes an inlet for the feed composition, an outlet for the feed composition, a top outlet, and a bottom outlet. If the method includes two or more subsequent extractive distillation steps, each extractive distillation step is carried out in a single distillation column.

Claims

1. A method for separating one or more compounds selected from C6-C9-aromatic hydrocarbons, isoprene, and any mixture thereof from a feed composition, said feed composition comprising said one or more compounds mixed with at least one other organic and / or inorganic compound, the method comprising at least one liquid-liquid extraction step using an extractant, said extractant comprising i) sulfolane, ii) a co-solvent of at least one sulfone selected from 3-methylsulfolane and a sulfone according to general formula (I) R1R2SO2, wherein R1 and R2 are independently C1-C4-alkyl groups, and iii) water.

2. The method according to claim 1, wherein the total amount of i) sulfolane, ii) at least one co-solvent selected from 3-methylsulfolane and sulfones according to general formula (I) and iii) water in the extractant is at least 98% by weight, preferably at least 99% by weight, more preferably at least 99.5% by weight and most preferably 100% by weight, based on 100% by weight of the extractant.

3. The method according to claim 1, wherein the extractant comprises, based on 100% by weight, a) 90 to 99% by weight, preferably 95 to 99% by weight, and more preferably 97 to 99% by weight, of i) sulfolane and ii) at least one co-solvent selected from 3-methylsulfolane and a sulfone according to general formula (I), and b) 1 to 10% by weight, preferably 1 to 5% by weight, and more preferably 1 to 3% by weight, of iii) water, wherein the total amount of the sum of i) sulfolane, ii) at least one co-solvent selected from 3-methylsulfolane and a sulfone according to general formula (I), and iii) water is preferably 100% by weight based on 100% by weight of the extractant.

4. The method according to any one of the preceding claims, wherein the extractant comprises 40 to 90% by weight, preferably greater than 50 to 90% by weight, i) sulfolane, 10 to 60% by weight, preferably 10 to less than 50% by weight, ii) at least one co-solvent selected from 3-methylsulfolane and sulfones according to the general formula (I), and up to 100% by weight of the remainder iii) water.

5. The method according to any one of the preceding claims, wherein the extractant comprises a sulfone according to general formula (I)R1R2SO2 as a co-solvent ii).

6. The method according to any one of the preceding claims, wherein the extractant comprises dimethyl sulfone, diethyl sulfone, dipropyl sulfone or dibutyl sulfone as a cosolvent (ii).

7. The method according to any one of the preceding claims, wherein the extractant comprises n-propyl sulfone, isopropyl sulfone, n-butyl sulfone or isobutyl sulfone as a cosolvent ii).

8. The method according to any one of the preceding claims, wherein the extractant comprises 3-methylcyclobutane sulfone, dimethyl sulfone, diethyl sulfone or n-propyl sulfone as a co-solvent ii), preferably 3-methylcyclobutane sulfone, dimethyl sulfone or n-propyl sulfone, and more preferably dimethyl sulfone.

9. The method according to any one of the preceding claims, wherein the extractant comprises, based on 100% by weight, greater than 50 to 90% by weight i) sulfolane, 10 to less than 50% by weight ii) at least one co-solvent and 1 to 3% by weight water, wherein the co-solvent ii) is 3-methylsulfolane, dimethyl sulfone, diethyl sulfone or n-propyl sulfone and preferably dimethyl sulfone.

10. The method according to any one of the preceding claims, wherein the feed composition comprises 10 to 90 wt%, preferably 60 to 90 wt%, of C6-C9-aromatic hydrocarbons and / or isoprene, and 10 to 90 wt%, preferably 10 to 40 wt%, of at least one other organic compound based on 100 wt% of the feed composition.

11. The method according to any one of the preceding claims, wherein the C6-C9-aromatic hydrocarbon is selected from benzene, toluene, xylene, ethylbenzene, styrene, and any mixture thereof.

12. The method according to claim 11, wherein the at least one other organic compound is selected from alkanes, cycloalkanes, alkenes, cycloalkenes, and any mixture thereof.

13. The method according to any one of the preceding claims, wherein the feed composition is pyrolytic gasoline, reformate, an oil mixture obtained from a plastic recycling process, or any other organic chemical stream rich in C6-C9 aromatic hydrocarbons, and preferably pyrolytic gasoline or reformate.

14. The method according to any one of the preceding claims, wherein the liquid-liquid extraction is carried out in a spray extraction tower, a pulse extraction tower, or a stirred extraction tower.

15. The method according to any one of the preceding claims, wherein the liquid-liquid extraction is carried out in a stirred countercurrent extraction tower, a packed extraction tower, or a sieve plate extraction tower.