A process for separating C 6-C 9-aromatic hydrocarbons and isoprene using an improved extracting agent

Abstract

The present invention relates to a process for separating one or more compounds being selected from the group consisting of C6-C9-aromatic hydrocarbons, isoprene and arbitrary mixtures thereof from a feed composition including the one or more compounds in admixture with at least one other organic and / or inorganic compound comprising at least one liquid-liquid extraction step using an extracting agent, wherein the extracting agent comprises i) sulfolane, ii) at least one cosolvent selected from the group consisting of 3-methyl sulfolane and a sulfone according to the general formula (I) R1R2SO2, wherein R1 and R2 are independently from each other a C1-C4-alkyl radical, and iii) water.

Description

[0001] A process for separating Ce-Cs-aromatic hydrocarbons and isoprene using an improved extracting agent

[0002] The present invention relates to a process for separating Ce-Cg-aromatic hydrocarbons and isoprene thereof from a feed composition including the one or more compounds in admixture with at least one other organic and / or inorganic compound.

[0003] Separating one or more specific compounds from a mixture containing the one or more specific compounds in admixture with other chemical compounds is an important task in chemical processes. A plurality of separation methods is available, such as distillation, extraction, absorption, adsorption, ion exchange chromatography and many others. A very common separation technique used to separate a mixture of several organic compounds is distillation, which allows to separate volatile organic compounds based on their different boiling points. During the distillation, the mixture to be separated is heated, which causes that compounds with lower boiling points vaporize and rise to the top of the distillation column, where they are withdrawn as overhead stream, condensed and are then further processed according to the need. In contrast thereto, compounds with higher boiling points do not vaporize, but remain as liquid and flow down the distillation column to the bottom of the distillation column, where they are removed as bottom stream and are then further processed according to the need. However, distillation is not applicable to separate different chemical compounds having a similar boiling point.

[0004] For separating such mixtures comprising different chemical compounds having a similar or even identical boiling point, liquid-liquid extraction is a promising option. Extraction uses an extracting agent, in which the chemical compound to be separated from a mixture has a drastic higher solubility than the other chemical com- pound(s) of the mixture from which the chemical compound shall be separated. During the operation, the mixture and extracting agent are led, co-currently or counter-currently, through an extraction column, in which both streams are contacted with each other. On account of its higher solubility in the extracting agent, most or ideally virtually all of the chemical compound to be separated from the mixture is dissolved in the extracting agent, thus forming an extraction composition, which is withdrawn from the extraction column separately from the remaining raffinate, which contains the other chemical compound(s). In turn, extractive distillation is a distillation, in which an extracting agent is fed in addition to the mixture into the distillation column, wherein the extracting agent is so selected that it increases the relative volatility of the chemical compounds to be separated. Relative volatility is an indication of the degree of the separability or ease of separation, respectively, of two or more chemical compounds by distillation from a mixture of these chemical compounds. An additional requirement for the extracting agent being used in extractive distillation is that it has a significant different boiling point than the chemical compounds to be separated.

[0005] Sulfolane and mixtures of sulfolane and water are commonly used to separate Ce-Cg-aromatic hydrocarbons, such as benzene, styrene or the like, from nonaromatic compounds having a very similar or even essentially identical boiling point. Even if sulfolane is a quite suitable extracting agent, it is, even at a comparable high level, limited concerning the selectivity and solvency with regard to Ce-Cg-aromatic hydrocarbons and isoprene to be separated from other chemical compounds having a highly similar boiling point. Therefore, using sulfolane or a mixture of sulfolane and water, a relatively high amount of energy is required to separate a predetermined volume of the mixture, which avoids a higher profitability of the separation process. Furthermore, it is nowadays desired to reduce the energy demand for processes as much as possible for environmental reason and to reduce thereby carbon emissions being connected with the energy production. In view of this, the object underlying the present invention is to provide a process for separating one or more compounds being selected from the group consisting of Ce-Cg-aromatic hydrocarbons, isoprene and arbitrary mixtures thereof from a feed composition including the one or more compounds in admixture with at least one other organic and / or inorganic compound comprising at least one liquid-liquid extraction step making use of an extracting agent having an increased selectivity and in particular an improved solvency with regard to Ce-Cg-aromatic hydrocarbons and isoprene so that the process is characterized by a reduced energy demand, per unit of separated mixture, and thus by reduced carbon emissions being connected with the energy production and with an increased profitability of the process.

[0006] In accordance with the present invention, this object is satisfied by providing a process for separating one or more compounds being selected from the group consisting of Ce-Cg-aromatic hydrocarbons, isoprene and arbitrary mixtures thereof from a feed composition including the one or more compounds in admixture with at least one other organic and / or inorganic compound comprising at least one liquidliquid extraction step using an extracting agent, wherein the extracting agent comprises i) sulfolane, ii) at least one co-solvent selected from the group consisting of 3-methyl sulfolane and a sulfone according to the general formula (I) R1R2SO2, wherein R1 and R2 are independently from each other a Ci-C4-alkyl radical, and iii) water.

[0007] This solution bases on the surprising finding that a mixture comprising i) sulfolane, ii) at least one co-solvent selected from the group consisting of 3-methyl sulfolane and a sulfone according to the general formula (I) R1R2SO2, wherein R1 and R2 are independently from each other a Ci-C4-alkyl radical, and iii) water has a higher selectivity and in particular a higher solvency with regard to Ce-Cg-aromatic hydrocarbons and isoprene to be separated from other chemical compounds having a highly similar boiling point than sulfolane alone or than a mixture of sulfolane and water. More specifically, it has been surprisingly found by the inventors of the present invention that the addition of water to a mixture of i) sulfolane and ii) at least one co-solvent selected from the group consisting of 3-methyl sulfolane and a sulfone according to the general formula (I) even further increases the selectivity and in particular the solvency with regard to Ce-Cg-aromatic hydrocarbons and isoprene in comparison to other chemical compounds having a highly similar boiling point.

[0008] The present invention is not particularly limited concerning the contents and ratios of sulfolane, the co-solvent and water. However, in tendency, the higher the total amount of these components i), ii) and iii), the better the performance of the extracting agent. Good results are in particular obtained, when the extracting agent comprises, based on 100% by weight of the extracting agent, at least 80% by weight, more preferably at least 90% by weight and still more preferably at least 95% by weight of sum i) sulfolane, ii) at least one co-solvent selected from the group consisting of 3-methyl sulfolane and a sulfone according to the general formula (I) and iii) water.

[0009] In accordance with a preferred embodiment of the present invention, the extracting agent consists or at least essentially consists of a mixture of i) sulfolane, ii) at least one co-solvent selected from the group consisting of 3-methyl sulfolane and a sulfone according to the general formula (I) and iii) water, i.e. the total amount of the components i), ii) and iii) is, based on 100% by weight of the extracting agent, at least 98% by weight, preferably at least 99% by weight, still more preferably at least 99.5% by weight and most preferably 100% by weight.

[0010] In accordance with an alternative preferred embodiment of the present invention, the extracting agent contains high amounts of the components i) and ii) and in addition thereto a comparable small amount of water. Again, it has been surprisingly found by the inventors of the present invention that the addition of water and in particular of a comparable small amount of water to a mixture if i) sulfolane and ii) at least one co-solvent selected from the group consisting of 3-methyl sulfolane and a sulfone according to the general formula (I) even further increases the selectivity and in particular the solvency with regard to Ce-Cg-aromatic hydrocarbons and isoprene in comparison to other chemical compounds having a highly similar boiling point. It is preferred in this embodiment that the extracting agent comprises, based on 100% by weight of the extracting agent, a) 90 to 100% by weight, preferably 95 to 99% by weight and more preferably 97 to 99% by weight of sum of i) sulfolane and of ii) at least one co-solvent selected from the group consisting of 3- methyl sulfolane and a sulfone according to the 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, it is preferred in this embodiment that the total amount of sum of i) sulfolane, of ii) at least one co-solvent selected from the group consisting of 3-methyl sulfolane and a sulfone according to the general formula (I) and of iii) water is, based on 100% by weight of the extracting agent, 100% by weight.

[0011] As set out above, the present invention is not particularly limited concerning the ratios of sulfolane and the co-solvent, i.e. regarding the relative amounts of sulfolane and the co-solvent, in the extracting agent. Good results are in particular obtained, when the extracting agent contains about equal amounts of the components i) and ii) or a higher amount of component i) than of component ii). Accordingly, it is preferred that the extracting agent comprises, based on 100% by weight of the extracting agent, 40 to 90% by weight of i) sulfolane, 10 to 60% by weight of ii) at least one co-solvent selected from the group consisting of 3-methyl sulfolane and a sulfone according to the general formula (I) and remainder to 100% by weight of component iii). Particular good results are obtained, when the extracting agent comprises, based on 100% by weight of the extracting agent, more than 50 to 90% by weight of i) sulfolane, 10 to less than 50% by weight of ii) at least one co-solvent selected from the group consisting of 3-methyl sulfolane and a sulfone according to the general formula (I) and remainder to 100% by weight of component iii), such as 60 to 75% by weight of i) sulfolane, 25 to less than 40% by weight of ii) at least one co-solvent selected from the group consisting of 3-methyl sulfolane and a sulfone according to the general formula (I) and remainder to 100% by weight, which is preferably 1 to 3% by weight, of component iii).

[0012] In accordance with the present invention, the extracting agent comprises i) sulfolane, at least one co-solvent selected from the group consisting of 3-methyl sulfolane and a sulfone according to the general formula (I) and iii) water. Good results are in particular obtained, when the extracting agent comprises i) sulfolane, ii) (only) one co-solvent selected from the group consisting of 3-methyl sulfolane and a sulfone according to the general formula (I) R1R2SO2, but no mixture thereof, and iii) water.

[0013] In accordance with the present invention, the sulfone according to the general formula (I) R1R2SO2, in which R1 and R2 are independently from each other a Ci-C4-alkyl radical.

[0014] In accordance with a preferred embodiment of the present invention, the radicals R1 and R2 in the general formula (I) are the same. Accordingly, it is in this embodiment preferred that the extracting agent comprises as co-solvent ii) dimethylsulfone, diethylsulfone, dipropylsulfone or dibutylsulfone.

[0015] In accordance with an alternatively preferred embodiment of the present invention, the radicals R1 and R2 in the general formula (I) are the different to each other. Suitable examples for co-solvents of 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 the radicals R1 and R2 in the general formula (I) is hydrogen, whereas the other radical is a Ci-C4-alkyl radical. Examples for the co-solvent of this variant are methylsulfone, ethylsulfone, propyl- sulfone and butylsulfone, wherein more preferred examples are n-propylsulfone, iso-propylsulfone, n-butylsulfone and iso-butylsulfone.

[0016] In accordance with a particular preferred embodiment of the present invention, the extracting agent comprises as co-solvent ii) 3-methyl sulfolane, dimethylsulfone, diethylsulfone or n-propylsulfone. Still more preferably the extracting agent comprises as co-solvent ii) 3-methyl sulfolane, dimethylsulfone or n-propylsulfone and most preferably the extracting agent comprises as co-solvent ii) dimethylsulfone.

[0017] In view of the above, it is particularly preferred that the extracting agent comprises, based on 100% by weight of the extracting agent, more than 50 to 90% by weight of i) sulfolane, 10 to less than 50% by weight of ii) at least one co-solvent and 1 to 3% by weight of water, wherein the co-solvent ii) is 3-methyl sulfolane, dimethylsulfone, diethylsulfone or n-propylsulfone and more preferably dimethylsulfone.

[0018] The present invention is not particularly restricted concerning the kind of feed composition, as long as it contains one or more compounds being selected from the group consisting of Ce-Cg-aromatic hydrocarbons, isoprene and arbitrary mixtures thereof in admixture with at least one other organic and / or inorganic compound. The process in accordance with the present invention is in particular suitable for a feed composition, which comprises, based on 100% by weight of the feed composition, 10 and 90% by weight and preferably 60 and 90 % by weight of Ce-Cg-aromatic hydrocarbons and / or isoprene and 10 to 90% by weight and preferably 10 and 40 % by weight of at least one other organic compound.

[0019] In a further development of the idea of the present invention, it is suggested that the feed composition contains one or more Ce-Cg-aromatic hydrocarbons being selected from the group consisting of benzene, toluene, xylenes, ethylbenzene, styrene and arbitrary mixtures thereof. The at least one other organic compound may be for instance selected from the group consisting of paraffins, cycloalkanes, olefins, cycloolefins and arbitrary mixtures thereof. Good results are in particular obtained, when the feed composition contains at least one other organic compound being selected from the group consisting of normal paraffins, iso-paraffins, cycloalkanes, normal olefins, iso-olefins and C4-Cio-cycloolefins.

[0020] For instance, the feed composition may be a pyrolysis gasoline, a reformate, an oil mixture obtained from a plastic recycle process or any other organic chemical stream being rich in aromatics and in particular being rich in Ce-Cg-aromatics. Most preferably, the feed composition is a pyrolysis gasoline or a reformate.

[0021] In accordance with the present invention, the process comprises at least one liquid-liquid extraction step. Preferably, the at least one liquid-liquid extraction step is performed in at least one liquid-liquid extraction column. If the process comprises two or more subsequent liquid-liquid extraction steps, each liquid-liquid extraction step is performed in one liquid-liquid extraction column, so that the process is in total performed in two or more subsequently arranged liquid-liquid extraction columns.

[0022] The present invention is not particularly limited concerning the kind of the at least one liquid-liquid-extraction column used for the process. Thus, all conventional liquid-liquid-extraction columns may be used. Good results are in particular obtained, when the one or more compounds being selected from the group consisting of Ce-Cg-aromatic hydrocarbons, isoprene and arbitrary mixtures thereof are separated from the feed composition by at least one liquid-liquid extraction step using the extracting agent, wherein the at least one liquid-liquid extraction step is performed in at least one spray extraction column, in at least one pulsed extraction column, such as in a packed extraction column or in a in a sieve tray extraction column, or in at least one agitated extraction column, such as in an agitated coun- ter-current extraction column. For instance, the agitated extraction column comprises one or more rotating shafts, each of which comprising one or more agitators being preferably selected from the group consisting of discs, blades, paddles, turbine impellers, fins and arbitrary combinations of two or more of the aforemen- tioned agitators.

[0023] In addition to the at least one liquid-liquid extraction step, the process in accordance with the present invention may additionally comprise at least one extractive distillation step being performed by using the aforementioned extracting agent. The at least one extractive distillation step is preferably performed in one distillation column, wherein the distillation column comprises an inlet for the feed composition, an inlet for the feed composition, an overhead outlet and a bottom outlet. If the process comprises two or more subsequent extractive distillation steps, each extractive distillation step is performed in one distillation column.

Claims

Claims:1 . A process for separating one or more compounds being selected from the group consisting of Ce-Cg-aromatic hydrocarbons, isoprene and arbitrary mixtures thereof from a feed composition including the one or more compounds in admixture with at least one other organic and / or inorganic compound comprising at least one liquid-liquid extraction step using an extracting agent, wherein the extracting agent comprises i) sulfolane, ii) at least one co-solvent selected from the group consisting of 3-methyl sulfolane and a sulfone according to the general formula (I) R1R2SO2, wherein R1 and R2 are independently from each other a Ci-C4-alkyl radical, and iii) water.

2. The process in accordance with claim 1 , wherein the total amount of i) sulfolane, ii) the at least one co-solvent selected from the group consisting of 3-methyl sulfolane and a sulfone according to the general formula (I) and iii) water in the extracting agent is, based on 100% by weight of the extracting agent, at least 98% by weight, preferably at least 99% by weight, still more preferably at least 99.5% by weight and most preferably 100% by weight.

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

4. The process in accordance with any of the preceding claims, wherein the extracting agent comprises, based on 100% by weight of the extracting agent, 40 to 90% by weight and preferably more than 50 to 90% by weight of i) sulfolane, 10 to 60% by weight and preferably 10 to less than 50% by weight of ii) at least one co-solvent selected from the group consisting of 3- methyl sulfolane and a sulfone according to the general formula (I) and remainder to 100% by weight of iii) water.

5. The process in accordance with any of the preceding claims, wherein the extracting agent comprises as co-solvent ii)a sulfone according to the general formula (I) R1R2SO2.

6. The process in accordance with any of the preceding claims, wherein the extracting agent comprises as co-solvent ii) dimethylsulfone, diethylsulfone, dipropylsulfone or dibutylsulfone.

7. The process in accordance with any of the preceding claims, wherein the extracting agent comprises as co-solvent ii) n-propylsulfone, isopropylsulfone, n-butylsulfone or iso-butylsulfone.

8. The process in accordance with any of the preceding claims, wherein the extracting agent comprises as co-solvent ii) 3-methyl sulfolane, dimethylsulfone, diethylsulfone or n-propylsulfone, preferably 3-methyl sulfolane, dimethylsulfone or n-propylsulfone and more preferably dimethylsulfone.

9. The process in accordance with any of the preceding claims, wherein the extracting agent comprises, based on 100% by weight of the extracting agent, more than 50 to 90% by weight of i) sulfolane, 10 to less than 50% by weight of ii) at least one co-solvent and 1 to 3% by weight of water, wherein the co-solvent ii) is 3-methyl sulfolane, dimethylsulfone, diethylsulfone or n-propylsulfone and preferably dimethylsulfone.

10. The process in accordance with any of the preceding claims, wherein the feed composition comprises, based on 100% by weight of the feed composition, 10 and 90% by weight and preferably 60 and 90 % by weight of Cs-Cg-aromatic hydrocarbons and / or isoprene and 10 to 90% by weight and preferably 10 and 40 % by weight of at least one other organic compound.11 . The process in accordance with any of the preceding claims, wherein the Ce-Cg-aromatic hydrocarbons are selected from the group consisting of benzene, toluene, xylenes, ethylbenzene, styrene and arbitrary mixtures thereof.

12. The process in accordance with claim 11 , wherein the at least one other organic compound is selected from the group consisting of paraffins, cycloalkanes, olefins, cycloolefins and arbitrary mixtures thereof.

13. The process in accordance with any of the preceding claims, wherein the feed composition is a pyrolysis gasoline, a reformate, an oil mixture obtained from a plastic recycle process or any other organic chemical stream being rich in Ce-Cg-aromatics and preferably a pyrolysis gasoline or a reformate.

14. The process in accordance with any of the preceding claims, wherein the liquid-liquid extraction is performed in a spray extraction column, in a pulsed extraction column or in an agitated extraction column.

15. The process in accordance with any of the preceding claims, wherein the liquid-liquid extraction is performed in an agitated counter-current extraction column, in a packed extraction column or in a in a sieve tray extraction column.