Method and device for separating and purifying aromatic hydrocarbon, alkane and olefin

Abstract

The invention relates to the technical field of separation and purification, in particular to a method and a device for separating and purifying aromatic hydrocarbon, alkane and olefin, and the method combines liquid-liquid extraction and extractive distillation (namely, first extractive distillation and second extractive distillation), so that the liquid-liquid extraction and the extractive distillation are operated in respective dominant zones. In liquid-liquid extraction, heavy alkanes with small solubility are separated, light alkanes with high relative volatility are separated in first extractive distillation, olefins with high relative volatility are separated in second extractive distillation, aromatic hydrocarbons and solvents are separated in solvent recovery, and finally, the same solvent is used to realize efficient separation of aromatic hydrocarbons, alkanes and olefins.

Description

Technical Field

[0001] The invention relates to the technical field of separation and purification, and in particular to a method for separating and purifying aromatic hydrocarbons, alkanes and olefins and a device for separating and purifying aromatic hydrocarbons, alkanes and olefins. Background Art

[0002] With the rapid development of new energy, the growth rate of gasoline consumption has slowed down, and the structural overcapacity of refining has become increasingly serious. It is a general trend for refining enterprises to transform from producing gasoline and diesel to producing low-carbon olefins, aromatics and other chemical products. The targeted catalytic cracking (TCO) process with olefins as cracking raw materials has the advantages of strong olefin selectivity and high carbon and hydrogen utilization. The source of its olefin raw materials can be naphtha, reforming raffinate oil and other generated oils obtained by alkane dehydrogenation (PTOA) units, or olefin-rich catalytic cracking gasoline. If the aromatics, alkanes and olefins in the above raw materials are separated and purified at a lower cost, olefin-rich oil can be used as the raw material of the TCO unit, alkane-rich oil can be used as the raw material of the PTOA unit, and aromatics can be used as the product, so as to achieve the technical effect of simultaneously improving the yield of olefin products and aromatic products.

[0003] The separation of aromatics from cracking and hydrogenating gasoline or reforming oil is a mature technology in industry, which mainly includes two processes: liquid-liquid extraction and extractive distillation. The liquid-liquid extraction process separates aromatics and non-aromatic components based on the different solubility of solvents in aromatics and non-aromatic components; the extractive distillation process achieves distillation separation by adding selective solvents to change the relative volatility of non-aromatic and aromatic components. For narrow-fraction raw materials, the extractive distillation process has the advantages of simple process, low investment and low energy consumption.

[0004] However, the above technologies are unable to further separate alkanes and olefins from non-aromatic hydrocarbons. Existing studies on the separation of alkanes and olefins focus on the separation of ethylene / ethane, propylene / propane, C4 alkanes and α-olefins and normal alkanes with the same carbon number. For example, CN106966852A discloses a method for separating high-carbon normal alkanes and normal olefins by continuous extraction and distillation, which uses phthalate compounds as extractants and double-tower extraction and distillation to separate high-carbon normal alkanes and olefins with the same carbon number (C 10 -C 16 ) for separation. CN1170793C discloses a method for separating butane and butene by extractive distillation using a series of methyl ethyl ketone mixtures as solvents. CN86104676A discloses a method for separating C4 alkanes and C4 olefins by extractive distillation using anhydrous methyl ether.

[0005] Therefore, for multi-component, wide-range hydrocarbon mixtures, it is impossible to effectively separate the aromatic, alkane and olefin components in the raw materials. Summary of the invention

[0006] The purpose of the present invention is to overcome the above-mentioned technical problems and provide a method for separating and purifying aromatic hydrocarbons, alkanes and olefins and a device for separating and purifying aromatic hydrocarbons, alkanes and olefins. The method utilizes an organic combination of liquid-liquid extraction and extractive distillation processes to achieve the effect of simultaneously and efficiently separating aromatic hydrocarbons, alkanes and olefins in a hydrocarbon mixture.

[0007] In order to achieve the above object, the present invention provides a method for separating and purifying aromatic hydrocarbons, alkanes and olefins in a first aspect, the method comprising the following steps:

[0008] (1) contacting the hydrocarbon mixture with an extraction solvent and performing liquid-liquid extraction to obtain a first raffinate oil enriched in heavy alkanes and a first rich solvent enriched in light alkanes, olefins and aromatics;

[0009] (2) subjecting the first rich solvent to a first extractive distillation to obtain a second raffinate oil enriched in light alkanes and a second rich solvent enriched in olefins and aromatics;

[0010] (3) mixing the first raffinate oil and the second raffinate oil and washing with water to obtain an alkane-rich oil;

[0011] (4) subjecting the second rich solvent to a second extractive distillation to obtain a third rich solvent rich in olefin oil and aromatics;

[0012] (5) recovering the third rich solvent to obtain aromatic hydrocarbons and a lean solvent; wherein the lean solvent is divided into a first lean solvent, a second lean solvent and a third lean solvent, which are returned and subjected to the liquid-liquid extraction, the first extractive distillation and the second extractive distillation respectively.

[0013] Preferably, the hydrocarbon mixture is selected from at least one of a C5-C7 fraction, a C5-C6 fraction and a C6 fraction.

[0014] Preferably, the extraction solvent is selected from at least one of amide compounds, glycol compounds, glycol ether compounds, lactone compounds and sulfone compounds.

[0015] Preferably, the water content in the extraction solvent is 0.1-3 wt %.

[0016] The second aspect of the present invention provides a device for separating and purifying aromatic hydrocarbons, alkanes and olefins, the device comprising: an extraction tower, a first extractive distillation tower, a second extractive distillation tower and a solvent recovery tower, and a water washing tower connected in sequence;

[0017] The bottom of the solvent recovery tower is connected to the extraction tower, the first extractive distillation tower and the second extractive distillation tower respectively;

[0018] The tops of the extraction tower and the first extraction tower are respectively connected to water washing towers.

[0019] Through the above technical scheme, the method provided by the present invention combines liquid-liquid extraction and extractive distillation (i.e., the first extractive distillation and the second extractive distillation) so that they operate in their respective advantageous areas. Specifically, heavy alkanes with lower solubility are separated in the liquid-liquid extraction, light alkanes with higher relative volatility are separated in the first extractive distillation, olefins with higher relative volatility are separated in the second extractive distillation, and aromatics and solvent are separated in solvent recovery, and finally the same solvent is used to achieve efficient separation of aromatics, alkanes and olefins.

[0020] At the same time, the method provided by the present invention can process multi-component, wide-fraction raw materials, especially C5-C7 fraction and / or C5-C6 fraction, to obtain alkane-rich oil, olefin-rich oil and aromatic products with high yield and high purity; the method also simplifies the process flow and is convenient for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The present invention provides a schematic diagram of the structure of a device for separating and purifying aromatic hydrocarbons, alkanes and olefins.

[0022] Description of Reference Numerals

[0023] I, extraction tower; II, first extraction distillation tower; III, water washing tower; IV, second extraction distillation tower; V, solvent recovery tower; VI, stripping tower; VII, white clay tower; VIII, benzene tower;

[0024] 1. Hydrocarbon mixture; 2. Extraction solvent; 3. First raffinate oil; 4. First rich solvent; 5. Second raffinate oil; 6. Second rich solvent; 7. Raffinate oil; 8. Alkane-rich oil; 9. Wash water; 10. Stripping gas; 11. Third rich solvent; 12. Lean solvent; 12-i. First lean solvent; 12-ii. Second lean solvent; 12-iii. Third lean solvent; 13. Stripping water; 14. Side-drawn liquid; 15. Olefin-rich oil; 16. Aromatics; 17. Refined aromatics; 18. Pure benzene. DETAILED DESCRIPTION

[0025] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0026] In the present invention, unless otherwise specified, "first", "second" and "third" do not indicate a sequence, nor do they limit the materials or steps, but are only used to distinguish and indicate that they are not the same material or step. For example, "first rich solvent", "second rich solvent" and "third rich solvent" are only used to distinguish and indicate that they are not the same rich solvent; or, "first" and "second" in "first extractive distillation" and "second extractive distillation" are only used to indicate that they are not the same extractive distillation.

[0027] In the present invention, unless otherwise specified, the "top" of a container refers to the position of 0-10% from top to bottom of the container; the "upper part" of a container refers to the position of 10-40% from top to bottom of the container; the "middle part" of a container refers to the position of 40-60% from top to bottom of the container; the "lower part" of a container refers to the position of 60-90% from top to bottom of the container; and the "bottom" of a container refers to the position of 90-100% from top to bottom of the container.

[0028] The first aspect of the present invention provides a method for separating and purifying aromatic hydrocarbons, alkanes and olefins, the method comprising the following steps:

[0029] (1) contacting the hydrocarbon mixture with an extraction solvent and performing liquid-liquid extraction to obtain a first raffinate oil enriched in heavy alkanes and a first rich solvent enriched in light alkanes, olefins and aromatics;

[0030] (2) subjecting the first rich solvent to a first extractive distillation to obtain a second raffinate oil enriched in light alkanes and a second rich solvent enriched in olefins and aromatics;

[0031] (3) mixing the first raffinate oil and the second raffinate oil and washing with water to obtain an alkane-rich oil;

[0032] (4) subjecting the second rich solvent to a second extractive distillation to obtain a third rich solvent rich in olefin oil and aromatics;

[0033] (5) recovering the third rich solvent to obtain aromatic hydrocarbons and a lean solvent; wherein the lean solvent is divided into a first lean solvent, a second lean solvent and a third lean solvent, which are returned and subjected to the liquid-liquid extraction, the first extractive distillation and the second extractive distillation respectively.

[0034] The inventors of the present invention have found that for hydrocarbon mixtures containing aromatics, alkanes and olefins at the same time, especially C5-C7 fractions and / or C5-C6 fractions, due to the complex raw material composition and wide distillation range, if the extractive distillation method is used for separation, the light olefin loss is large to ensure the purity of the olefin product, and the yield is difficult to ensure; if the liquid-liquid extraction method is used for separation, the solubility of heavy olefins and light alkanes is similar, and the purity of olefins and the yield of alkanes are difficult to ensure. Therefore, the present invention adopts the process of liquid-liquid extraction and extractive distillation to achieve efficient separation and purification of aromatics, alkanes and olefins from hydrocarbon mixtures at the same time.

[0035] Compared with the existing aromatic extraction or aromatic extraction distillation, the method provided by the present invention can further effectively separate the alkanes and olefins in the raffinate oil on the basis of separating the aromatics; compared with the existing alkane-olefin separation method, the method provided by the present invention does not need to set up aromatic separation separately, and can simultaneously and continuously separate aromatics, alkanes and olefins using a single solvent, thereby reducing the fixed investment and energy consumption of the device. In particular, compared with the existing separation method that only processes alkanes and olefins with the same carbon number, the method provided by the present invention does not need to perform pre-fractionation and cutting when processing wide-fraction raw materials, and obtains alkane-rich oil, olefin-rich oil and aromatics with high yield and high purity.

[0036] In the present invention, the type of the hydrocarbon mixture has a wide selection range, as long as the hydrocarbon mixture contains alkanes, olefins and aromatics. Preferably, the hydrocarbon mixture is selected from at least one of a C5-C7 fraction, a C5-C6 fraction and a C6 fraction.

[0037] In some embodiments of the present invention, preferably, the hydrocarbon mixture includes and is limited to a dehydrogenated C5-C6 fraction, a catalytic cracking gasoline C5-C7 fraction, a dehydrogenated C6 fraction, and the like.

[0038] In the present invention, the liquid-liquid extraction is intended to separate heavy alkanes with lower solubility in the aromatic mixture to obtain a first raffinate enriched in heavy alkanes and a first rich solvent enriched in light alkanes, olefins and aromatics. Preferably, in step (1), the conditions of the liquid-liquid extraction include: a tower top pressure of 0.1-1.6MPa, preferably 0.1-1MPa; a tower top temperature of 35-110°C, preferably 40-90°C; a first solvent ratio of 1-15, preferably 4-12; the first solvent ratio refers to the mass ratio of the extraction solvent and / or the first lean solvent to the hydrocarbon mixture. In the present invention, pressure parameters all refer to gauge pressure.

[0039] In the present invention, the contacting mode of the hydrocarbon mixture and the extraction solvent is preferably selected from countercurrent contacting of the hydrocarbon mixture and the extraction solvent.

[0040] In the present invention, the liquid-liquid extraction is carried out in an extraction tower, and the number of theoretical plates of the extraction tower is 8-30.

[0041] Compared with the prior art, the extraction solvent provided by the present invention has both high selectivity and high solubility, that is, when the hydrocarbon mixture is subjected to liquid-liquid extraction, the extraction solvent has high selectivity and high solubility for light alkanes, olefins and aromatics in the hydrocarbon mixture. Preferably, the extraction solvent is selected from at least one of amide compounds, glycol compounds, glycol ether compounds, lactone compounds and sulfone compounds.

[0042] In some embodiments of the present invention, preferably, the water content in the extraction solvent is 0.1-3 wt %. That is, the extraction solvent provided by the present invention is a water-soluble organic matter, and the purity of the water-soluble organic matter is 97-99.9 wt %.

[0043] In some embodiments of the present invention, preferably, the amide compound is selected from at least one of N,N-dimethylformamide, N-formylmorpholine, 1,3-dimethyl-2-imidazolidinone and N-methylpyrrolidone.

[0044] In some embodiments of the present invention, preferably, the glycol compound is selected from at least one of diethylene glycol, triethylene glycol and tetraethylene glycol.

[0045] In some embodiments of the present invention, preferably, the glycol ether compound is at least one of diethylene glycol monomethyl ether, triethylene glycol monomethyl ether and tetraethylene glycol monomethyl ether.

[0046] In some embodiments of the present invention, preferably, the lactone compound is selected from at least one of γ-butyrolactone, γ-valerolactone and δ-valerolactone.

[0047] In some embodiments of the present invention, preferably, the sulfone compound is selected from at least one of sulfolane, 3-methylsulfolane, dimethyl sulfone and dimethyl sulfoxide.

[0048] In some embodiments of the present invention, further preferably, the extraction solvent is selected from a compound solvent of tetraethylene glycol and tetraethylene glycol monomethyl ether, and a compound solvent of N-methylpyrrolidone and sulfolane.

[0049] In the present invention, the first extractive distillation is intended to separate the light alkanes with relatively high volatility in the first rich solvent to obtain a second raffinate oil enriched in light alkanes and a second rich solvent enriched in olefins and aromatics. Preferably, in step (2), the conditions of the first extractive distillation include: a tower top pressure of 0.05-0.6MPa, preferably 0.15-0.4MPa; a tower top temperature of 45-90°C, preferably 70-90°C; a tower bottom temperature of 100-180°C, preferably 120-160°C; a second solvent ratio of 0.1-5, preferably 0.5-2; the second solvent ratio refers to the mass ratio of the second lean solvent to the hydrocarbon mixture.

[0050] In the present invention, the first extractive distillation is carried out in a first extractive distillation tower, and the number of theoretical plates of the first extractive distillation tower is 20-50.

[0051] In the present invention, the water washing is to mix the first raffinate oil and the second raffinate oil, and the obtained raffinate oil enriched in heavy alkanes and light alkanes is washed with water to obtain alkane-rich oil and washing water. Preferably, in step (3), the conditions of the water washing include: the tower top pressure is 0.1-1MPa, preferably 0.1-0.5MPa; the tower top temperature is 30-60°C, preferably 35-50°C.

[0052] In the present invention, the second extractive distillation is intended to separate the olefins with relatively high volatility in the second rich solvent to obtain olefin-rich oil and a third rich solvent enriched in aromatics. Preferably, in step (4), the conditions of the second extractive distillation include: a tower top pressure of 0.05-0.3MPa, preferably 0.1-0.2MPa; a tower top temperature of 45-85°C, preferably 50-70°C; a tower bottom temperature of 140-220°C, preferably 130-180°C; a third solvent ratio of 0.4-3, preferably 0.5-2; the third solvent ratio refers to the mass ratio of the third lean solvent to the hydrocarbon mixture.

[0053] In the present invention, the second extractive distillation is carried out in a second extractive distillation tower having a theoretical plate number of 20-50.

[0054] In the present invention, the solvent recovery is intended to separate the aromatic hydrocarbons and the solvent in the third rich solvent to obtain aromatic hydrocarbons and a lean solvent. Preferably, in step (5), the conditions for the solvent recovery include: a tower top pressure of 0.01-0.3 MPa, preferably 0.05-0.1 MPa; a tower top temperature of 30-90°C, preferably 40-60°C; a tower bottom temperature of 140-220°C, preferably 150-180°C; a reflux ratio of 0-1, preferably 0.3-0.6. In the present invention, the reflux ratio is the mass ratio of the reflux material to the produced material.

[0055] In the present invention, the solvent recovery is carried out in a solvent recovery tower having a theoretical plate number of 8-40.

[0056] In some embodiments of the present invention, preferably, in step (5), the solvent recovery process comprises: subjecting the third rich solvent to solvent recovery in the presence of water vapor as a stripping medium to obtain the aromatic hydrocarbons and the lean solvent.

[0057] In some embodiments of the present invention, preferably, the method further comprises: stripping the washing water obtained by the water washing, and the obtained stripping gas and stripping water are independently used as stripping media and returned to the solvent for recovery. This arrangement not only allows the water in the process to be recycled, but also maximizes the use of the heat of the lean solvent.

[0058] In some embodiments of the present invention, preferably, the method further comprises: returning the side-drawn liquid of the first extractive distillation to perform the liquid-liquid extraction to improve the purity of olefins in the olefin-rich oil and the yield of alkanes in the alkane-rich oil.

[0059] In some embodiments of the present invention, further preferably, the liquid-liquid extraction conditions further include: a backwash ratio of 0.1-0.8, wherein the backwash ratio refers to the mass ratio of the sideline liquid to the extracted hydrocarbons. The extracted hydrocarbons refer to the sum of the second raffinate oil, olefin-rich oil and aromatics.

[0060] The method provided by the present invention can effectively improve not only the yield of alkane-rich oil, olefin-rich oil and aromatics, but also the purity of alkane-rich oil, olefin-rich oil and aromatics.

[0061] In the present invention, in order to further improve the purity of aromatic hydrocarbons, preferably, the method further comprises: sequentially desorbing and distilling the aromatic hydrocarbons to obtain pure benzene. In the present invention, the desorption is intended to remove trace olefins in the aromatic hydrocarbons, and the distillation is intended to remove non-benzene components in the aromatic hydrocarbons to obtain pure benzene.

[0062] The second aspect of the present invention provides a schematic diagram of a device for separating and purifying aromatic hydrocarbons, alkanes and olefins. Figure 1 As shown by Figure 1 It can be seen that the device comprises: an extraction tower I, a first extractive distillation tower II, a second extractive distillation tower IV and a solvent recovery tower V, and a water washing tower III connected in sequence;

[0063] The bottom of the solvent recovery tower V is connected to the extraction tower I, the first extractive distillation tower II and the second extractive distillation tower IV respectively;

[0064] The tops of the extraction tower I and the first extraction tower II are respectively connected to the water washing tower III.

[0065] In the present invention, unless otherwise specified, Figure 1 As shown, the sequentially connected extraction tower I, the first extractive distillation tower II, the second extractive distillation tower IV and the solvent recovery tower V mean that the bottom of the extraction tower I is connected to the first extractive distillation tower II, the bottom of the first extractive distillation tower II is connected to the second extractive distillation tower IV, and the bottom of the second extractive distillation tower IV is connected to the solvent recovery tower V.

[0066] In the present invention, the extraction tower is used to contact the hydrocarbon mixture with the extraction solvent and perform liquid-liquid extraction, and a first raffinate oil enriched in heavy alkanes is obtained at the top of the tower, and a first rich solvent enriched in light alkanes, olefins and aromatics is obtained at the bottom of the tower; the first extractive distillation tower is used to perform a first extractive distillation on the first rich solvent, and a second raffinate oil enriched in light alkanes is obtained at the top of the tower, and a second rich solvent enriched in olefins and aromatics is obtained at the bottom of the tower; the water washing tower is used to mix the first raffinate oil and the second raffinate oil, and the obtained raffinate oil is washed with water, and alkane-rich oil is obtained at the top of the tower, and washing water is obtained at the bottom of the tower; the second extractive distillation tower is used to perform a second extractive distillation on the second rich solvent, and olefin-rich oil is obtained at the top of the tower, and a third rich solvent enriched in aromatics is obtained at the bottom of the tower; the solvent recovery tower is used to perform solvent recovery on the third rich solvent, and aromatics are obtained at the top of the tower. The lean solvent obtained at the bottom of the tower is divided into a first lean solvent, a second lean solvent and a third lean solvent, which are respectively recycled and used in the extraction tower, the first extractive distillation tower and the second extractive distillation tower.

[0067] In some embodiments of the present invention, Figure 1 As shown, the extraction tower I is used to contact the hydrocarbon mixture 1 and the extraction solvent 2 and perform liquid-liquid extraction, and a first raffinate oil 3 enriched in heavy alkanes is obtained at the top of the tower, and a first rich solvent 4 enriched in light alkanes, olefins and aromatics is obtained at the bottom of the tower; the first extractive distillation tower II is used to perform a first extractive distillation on the first rich solvent 4, and a second raffinate oil 5 enriched in light alkanes is obtained at the top of the tower, and a second rich solvent 6 enriched in olefins and aromatics is obtained at the bottom of the tower; the water washing tower III is used to mix the first raffinate oil 3 and the second raffinate oil 5, and the obtained raffinate oil 7 is washed with water, and the alkane-rich solvent 7 is obtained at the top of the tower. The second extractive distillation tower is used for performing a second extractive distillation on the second rich solvent 6, and olefin-rich oil 15 is obtained at the top of the tower, and a third rich solvent 11 enriched in aromatics is obtained at the bottom of the tower; the solvent recovery tower V is used for performing solvent recovery on the third rich solvent 11, and aromatics 16 are obtained at the top of the tower. The lean solvent 12 obtained at the bottom of the tower is divided into a first lean solvent 12-i, a second lean solvent 12-ii and a third lean solvent 12-iii, which are respectively recycled to the extractive tower I, the first extractive distillation tower II and the second extractive distillation tower IV.

[0068] In the present invention, Figure 1 As shown, preferably, the device further comprises: a stripping tower VI connected to the water washing tower III and the solvent recovery tower V, and the top and bottom of the stripping tower VI are connected to the bottom of the solvent recovery tower V respectively.

[0069] In the present invention, Figure 1 As shown, the stripping tower VI is used to strip the wash water 9, and the stripping gas 10 obtained at the top of the tower and the stripping water 13 obtained at the bottom of the tower are each independently used as a stripping medium and returned to the solvent recovery tower V.

[0070] In the present invention, if Figure 1 As shown, preferably, the side line outlet of the first extractive distillation tower II is connected to the extractive tower I, so as to recycle the side line draw liquid 14 of the first extractive distillation back to the extractive tower I.

[0071] In the present invention, if Figure 1 As shown, preferably, the device also includes: a kaolin tower VII and a benzene tower VIII connected to the top of the solvent recovery tower V in sequence.

[0072] In the present invention, if Figure 1 As shown, the bleaching clay tower VII is used to desorb the aromatic hydrocarbons 16 to obtain refined aromatic hydrocarbons 17; the benzene tower VIII is used to distill the refined aromatic hydrocarbons 17 to obtain pure benzene 18.

[0073] According to a particularly preferred embodiment of the present invention, a method for separating and purifying aromatic hydrocarbons, alkanes and olefins comprises the following steps:

[0074] (1) contacting the hydrocarbon mixture with an extraction solvent and performing liquid-liquid extraction to obtain a first raffinate oil enriched in heavy alkanes and a first rich solvent enriched in light alkanes, olefins and aromatics;

[0075] (2) subjecting the first rich solvent to a first extractive distillation to obtain a second raffinate oil enriched in light alkanes and a second rich solvent enriched in olefins and aromatics;

[0076] (3) mixing the first raffinate oil and the second raffinate oil and washing them with water to obtain alkane-rich oil and washing water; stripping the washing water, and returning the obtained stripping gas and stripping water to the solvent recovery independently as stripping media;

[0077] (4) subjecting the second rich solvent to a second extractive distillation to obtain a third rich solvent rich in olefin oil and aromatics;

[0078] (5) recovering the third rich solvent to obtain aromatic hydrocarbons and a lean solvent; and sequentially desorbing and distilling the aromatic hydrocarbons to obtain pure benzene;

[0079] wherein the lean solvent is divided into a first lean solvent, a second lean solvent and a third lean solvent, which are returned and subjected to the liquid-liquid extraction, the first extractive distillation and the second extractive distillation respectively;

[0080] The water content of the extraction solvent is 0.1-3wt%; the extraction solvent is selected from a compound solvent of tetraethylene glycol and tetraethylene glycol monomethyl ether, and a compound solvent of N-methylpyrrolidone and sulfolane.

[0081] The present invention will be described in detail below through examples.

[0082] Example 1

[0083] Devices such as Figure 1 As shown, the device comprises: an extraction tower I, a first extraction distillation tower II, a second extraction distillation tower IV, a solvent recovery tower V, a clay tower VII and a benzene tower VIII which are connected in sequence, and a water washing tower III which is respectively connected to the top of the extraction tower I and the first extraction distillation tower II, and a stripping tower VI which is connected to the water washing tower III and the solvent recovery tower V;

[0084] Among them, the side line outlet of the first extractive distillation tower II is connected to the extractive tower I; the top and bottom of the stripping tower VI are respectively connected to the bottom of the solvent recovery tower V; the bottom of the solvent recovery tower V is respectively connected to the extractive tower I, the first extractive distillation tower II and the second extractive distillation tower IV.

[0085] The method is carried out in the above-mentioned device, comprising:

[0086] (1) The dehydrogenated C5-C6 fraction (specific composition is shown in Table 1) and an extraction solvent (water content is 1 wt%; a composite solvent of N-methylpyrrolidone and sulfolane, and the weight ratio of N-methylpyrrolidone to sulfolane is 0.7:0.3) are countercurrently contacted in an extraction tower and liquid-liquid extraction is performed (process parameters are shown in Table 2), and a first raffinate oil is obtained at the top of the tower, and a first rich solvent is obtained at the bottom of the tower;

[0087] (2) the first rich solvent is introduced into a first extractive distillation tower for first extractive distillation (process parameters are shown in Table 2), a second raffinate oil is obtained at the top of the tower, a second rich solvent is obtained at the bottom of the tower, and the side-line liquid of the first extractive distillation tower is recycled to the extractive tower;

[0088] (3) The first raffinate oil and the second raffinate oil are mixed, and the obtained raffinate oil is sent to a water washing tower for water washing (process parameters are shown in Table 2), and alkane-rich oil S1 is obtained at the top of the tower, and washing water is obtained at the bottom of the tower;

[0089] (4) the second rich solvent is introduced into a second extractive distillation tower for second extractive distillation (process parameters are shown in Table 2), and olefin-rich oil P1 is obtained at the top of the tower, and a third rich solvent is obtained at the bottom of the tower;

[0090] (5) stripping the wash water, and the obtained stripping gas and stripping water are used as stripping media and enter the solvent recovery tower, and the third rich solvent enters the solvent recovery tower for solvent recovery (see Table 2 for process parameters), and the aromatics obtained at the top of the tower enter the white clay tower and the benzene tower in turn for desorption and distillation, respectively, to obtain pure benzene Q1, and the lean solvent is obtained at the bottom of the tower;

[0091] The above-mentioned lean solvent is divided into a first lean solvent, a second lean solvent and a third lean solvent, which are returned and subjected to the above-mentioned liquid-liquid extraction, the first extractive distillation and the second extractive distillation respectively.

[0092] Among them, the purity and yield of the above-mentioned alkane-rich oil S1, olefin-rich oil P1 and pure benzene Q1 are listed in Table 5.

[0093] Example 2

[0094] According to the device of embodiment 1;

[0095] According to the method of Example 1, the difference is that

[0096] In step (1), the type of extraction solvent is replaced with a composite solvent of tetraethylene glycol and tetraethylene glycol monomethyl ether, and the weight ratio of tetraethylene glycol to tetraethylene glycol monomethyl ether is 0.4:0.6;

[0097] In steps (1)-(5), the process parameters of the above-mentioned liquid-liquid extraction, first distillation extraction, water washing, second distillation extraction and solvent recovery are listed in Table 2, and the other conditions are the same to obtain alkane-rich oil S2, olefin-rich oil P2 and aromatics Q2.

[0098] Among them, the purity and yield of the above-mentioned alkane-rich oil S2, olefin-rich oil P2 and pure benzene Q2 are listed in Table 5.

[0099] Example 3

[0100] According to the device of embodiment 1;

[0101] The method of Example 1 is followed, except that the type of raw material is replaced by catalytic cracking gasoline C5-C7 fraction. The specific composition is shown in Table 3.

[0102] In steps (1)-(5), the process parameters of the liquid-liquid extraction, the first distillation extraction, the water washing, the second distillation extraction and the solvent recovery are listed in Table 2. The other conditions are the same, and the alkane-rich oil S3, the olefin-rich oil P3 and the aromatics Q3 are obtained.

[0103] Among them, the purity and yield of the above-mentioned alkane-rich oil S3, olefin-rich oil P3 and pure benzene Q3 are listed in Table 5.

[0104] Example 4

[0105] According to the device of embodiment 1;

[0106] The method of Example 1 is followed, except that the raw material is a dehydrogenated C6 fraction, and the specific composition is shown in Table 4.

[0107] In steps (1)-(5), the process parameters of the above-mentioned liquid-liquid extraction, first distillation extraction, water washing, second distillation extraction and solvent recovery are listed in Table 2, and the other conditions are the same to obtain alkane-rich oil S4, olefin-rich oil P4 and aromatics Q4.

[0108] Among them, the purity and yield of the above-mentioned alkane-rich oil S4, olefin-rich oil P4 and pure benzene Q4 are listed in Table 5.

[0109] Comparative Example 1

[0110] According to the method of Example 1, the difference is that only the extractive distillation process is used, that is,

[0111] (1) extracting and distilling the dehydrogenated C5-C6 fraction and an extraction solvent (a composite solvent of N-methylpyrrolidone and sulfolane with a water content of 1 wt % and a weight ratio of N-methylpyrrolidone to sulfolane of 0.7:0.3) to obtain a raffinate oil rich in alkanes and olefins at the top of the tower and a rich solvent rich in aromatics at the bottom of the tower;

[0112] (2) The rich solvent is subjected to solvent recovery, and the aromatic hydrocarbons obtained at the top of the tower are sequentially fed into a white clay tower and a benzene tower for desorption and distillation, respectively, to obtain pure benzene DQ1, and the lean solvent obtained at the bottom of the tower is returned to the above-mentioned extractive distillation.

[0113] Among them, the purity and yield of the above pure benzene DQ1 are listed in Table 5.

[0114] Table 1

[0115]

[0116] Table 2

[0117]

[0118]

[0119] Table 3

[0120]

[0121] Table 4

[0122]

[0123] Table 5

[0124]

[0125]

[0126] It can be seen from the results in Tables 1-5 that, compared with Comparative Example 1, Examples 1-4 using the method provided by the present invention can achieve efficient separation of aromatics, alkanes and olefins in a hydrocarbon mixture.

[0127] Compared with Example 1, Comparative Example 1 adopts the extractive distillation process to obtain only aromatic products, and is unable to further separate alkanes and olefins.

[0128] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for separating and purifying aromatic hydrocarbons, alkanes and olefins, characterized in that: The method comprises the following steps: (1) contacting the hydrocarbon mixture with an extraction solvent and performing liquid-liquid extraction to obtain a first raffinate oil enriched in heavy alkanes and a first rich solvent enriched in light alkanes, olefins and aromatics; (2) subjecting the first rich solvent to a first extractive distillation to obtain a second raffinate oil enriched in light alkanes and a second rich solvent enriched in olefins and aromatics; (3) mixing the first raffinate oil and the second raffinate oil and washing with water to obtain an alkane-rich oil; (4) subjecting the second rich solvent to a second extractive distillation to obtain a third rich solvent rich in olefin oil and aromatics; (5) recovering the third rich solvent to obtain aromatic hydrocarbons and a lean solvent; wherein the lean solvent is divided into a lean solvent, a second lean solvent and a third lean solvent, which are returned and subjected to the liquid-liquid extraction, the first extractive distillation and the second extractive distillation respectively.

2. The method according to claim 1, wherein: The hydrocarbon mixture is selected from at least one of a C5-C7 fraction, a C5-C6 fraction and a C6 fraction; And / or, the hydrocarbon mixture is selected from at least one of a dehydrogenated C5-C6 fraction, a catalytic cracking gasoline C5-C7 fraction and a dehydrogenated C6 fraction.

3. The method according to claim 1 or 2, wherein: In step (1), the conditions of the liquid-liquid extraction include: a tower top pressure of 0.1-1.6 MPa, preferably 0.1-1 MPa; a tower top temperature of 35-110° C., preferably 40-90° C.; a first solvent ratio of 1-15, preferably 4-12; the first solvent ratio refers to the mass ratio of the extraction solvent and / or the first lean solvent to the hydrocarbon mixture; and / or, the extraction solvent is selected from at least one of amide compounds, glycol compounds, glycol ether compounds, lactone compounds and sulfone compounds; And / or, the water content in the extraction solvent is 0.1-3 wt %.

4. The method according to claim 3, wherein: The amide compound is selected from at least one of N,N-dimethylformamide, N-formylmorpholine, 1,3-dimethyl-2-imidazolidinone and N-methylpyrrolidone; And / or, the glycol compound is selected from at least one of diethylene glycol, triethylene glycol and tetraethylene glycol; and / or, at least one of the glycol ether compounds diethylene glycol monomethyl ether, triethylene glycol monomethyl ether and tetraethylene glycol monomethyl ether; And / or, the lactone compound is selected from at least one of γ-butyrolactone, γ-valerolactone and δ-valerolactone; And / or, the sulfone compound is at least one selected from sulfolane, 3-methylsulfolane, dimethyl sulfone and dimethyl sulfoxide; And / or, the extraction solvent is selected from a compound solvent of tetraethylene glycol and tetraethylene glycol monomethyl ether, and a compound solvent of N-methylpyrrolidone and sulfolane.

5. The method according to any one of claims 1 to 4, wherein: In step (2), the conditions of the first extractive distillation include: a tower top pressure of 0.05-0.6 MPa, preferably 0.15-0.4 MPa; a tower top temperature of 45-90° C., preferably 70-90° C.; a tower bottom temperature of 100-180° C., preferably 120-160° C.; a second solvent ratio of 0.1-5, preferably 0.5-2; the second solvent ratio refers to the mass ratio of the second lean solvent to the hydrocarbon mixture; And / or, in step (3), the water washing conditions include: the tower top pressure is 0.1-1MPa, preferably 0.1-0.5MPa; the tower top temperature is 30-60°C, preferably 35-50°C; And / or, in step (4), the conditions of the second extractive distillation include: the tower top pressure is 0.05-0.3MPa, preferably 0.1-0.2MPa; the tower top temperature is 45-85°C, preferably 50-70°C; the tower bottom temperature is 140-220°C, preferably 130-180°C; the third solvent ratio is 0.4-3, preferably 0.5-2; the third solvent ratio refers to the mass ratio of the third lean solvent to the hydrocarbon mixture; And / or, in step (5), the conditions for solvent recovery include: top tower pressure of 0.01-0.3 MPa, preferably 0.05-0.1 MPa; top tower temperature of 30-90°C, preferably 40-60°C; bottom tower temperature of 140-220°C, preferably 150-180°C; reflux ratio of 0-1, preferably 0.3-0.

6.

6. The method according to any one of claims 1 to 5, wherein: In step (5), the solvent recovery process includes: recovering the third rich solvent in water vapor as a stripping medium to obtain the aromatic hydrocarbons and the lean solvent; And / or, the method further comprises: stripping the washing water obtained from the water washing, and the obtained stripping gas and stripping water are each independently used as stripping media and returned to the solvent for recovery.

7. The method according to any one of claims 1 to 6, wherein: The method further comprises: returning the sideline liquid of the first extractive distillation to perform the liquid-liquid extraction; Preferably, the liquid-liquid extraction conditions also include: a backwash ratio of 0.1-0.

8.

8. The method according to any one of claims 1 to 7, wherein: The method further comprises: sequentially desorbing and distilling the aromatic hydrocarbons to obtain pure benzene.

9. A device for separating and purifying aromatic hydrocarbons, alkanes and olefins, characterized in that: The device comprises: an extraction tower, a first extractive distillation tower, a second extractive distillation tower and a solvent recovery tower, and a water washing tower connected in sequence; The bottom of the solvent recovery tower is connected to the extraction tower, the first extractive distillation tower and the second extractive distillation tower respectively; The tops of the extraction tower and the first extraction tower are respectively connected to water washing towers.

10. The device according to claim 9, wherein: The device further comprises: a stripping tower connected to the water washing tower and the solvent recovery tower, wherein the top and bottom of the stripping tower are respectively connected to the bottom of the solvent recovery tower; and / or, the side line outlet of the first extractive distillation tower is connected to the extractive tower; And / or, the device further comprises: a kaolin tower and a benzene tower which are sequentially connected to the top of the solvent recovery tower.

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