Process and system for separating and purifying 1-hexene, 1-heptene and 1-octene from a hydrocarbon-containing stream

Abstract

The present application relates to the field of separating and purifying hydrocarbon-containing streams, and discloses a method and system for separating and purifying 1-hexene, 1-heptene and 1-octene from a hydrocarbon-containing stream, comprising: cutting the hydrocarbon-containing stream into fractions to obtain a C5 ‑ fraction stream, a C6-C8 fraction stream, a C9 + fraction stream; contacting the C6-C8 fraction stream, a composite extractant and an aqueous phase to perform extraction separation to obtain an extract phase and a raffinate phase; performing rectification separation treatment, fine separation and heavy removal treatment and extractive rectification treatment on the raffinate phase in sequence to obtain 1-hexene, 1-heptene and 1-octene; wherein the extract phase, after solvent recovery, is recycled into the composite extractant to obtain a recovered extractant; the composite extractant comprises an extractant a and an extractant b, the extractant a is selected from N-methyl pyrrolidone and / or N,N dimethylacetamide, and the extractant b is selected from gamma-butyrolactone and / or N-formyl morpholine; and the composite extractant is used for extractive rectification treatment. The extractant is single, and the content of oxygen-containing compounds in the final Fischer-Tropsch synthesis oil is less than or equal to 10 ppm (mass).

Description

TECHNICAL FIELD

[0001] The present application relates to the field of separating and purifying high value-added chemicals from hydrocarbon-containing streams, and in particular to a method for separating and purifying 1-hexene, 1-heptene and 1-octene from a hydrocarbon-containing stream. BACKGROUND

[0002] Alpha-olefins are important organic raw materials and intermediate products, and are widely used. 1-butene, 1-hexene and 1-octene are used as comonomers for polyethylene (PE) resins to improve the performance of PE. Currently, the production of alpha-olefins in the industry is mainly obtained by ethylene oligomerization. The Fischer-Tropsch synthesis oil product contains olefins and alkanes. The olefins are mainly linear alpha-olefins, and the content of alpha-olefins in Fischer-Tropsch light oil can reach more than 50%. The alpha-olefins produced by ethylene oligomerization have high quality, and the production of alpha-olefins abroad mainly uses this method.

[0003] EP1835011 discloses a distillation treatment method of Fischer-Tropsch synthesis crude product and the obtained middle distillate oil. The main process is to cut the FTS crude product into naphtha and middle distillate oil. In 1994, the South African SASOL company developed a combined process route of "alkali washing-etherification-distillation-extraction" to realize the preparation of polymer-grade 1-hexene and 1-octene. However, this method involves chemical reactions, and the process route is complex and the cost is relatively high.

[0004] WO2020177235A1 proposes to use a simulated moving bed process to separate alkanes and olefins. The different adsorption capacities of molecular sieves for alkanes and olefins are used for separation, and the purity of olefin components can be more than 99.5%. This process requires a high content of oxygen-containing compounds in the raw material, and irreversible adsorption of oxygen-containing compounds by the adsorbent must be avoided.

[0005] CN102452888A discloses a method for purifying 1-hexene from Fischer-Tropsch synthetic oil products. Fischer-Tropsch synthetic light distillate oil is first fractionated to obtain a C6 fraction segment; then, organic oxygen-containing compounds in the C6 fraction are removed by extractive distillation; then, the alkanes and olefins in the C6 fraction segment are separated by extractive distillation; the C6 olefins obtained by extractive distillation are subjected to reactive distillation, and under the action of a catalyst, tertiary carbon olefins in the C6 olefins react with low-carbon alcohols to form high-boiling-point ethers, thereby removing the tertiary carbon olefins; then, liquid-liquid extraction is used to remove the ethanol remaining in the C6 olefins; finally, 1-hexene products that meet polymerization grade requirements are purified from the C6 olefins by precision distillation. The extractants used for extractive distillation of C6 alkanes and olefins are polar solvents such as ACN, NMP, or DMF. To improve the selectivity of the solvent, the preferred extractant is a binary mixed solvent consisting of ACN or NMP and water. Therefore, in the entire process, a solvent recovery tower and a dehydration tower are required during the solvent recovery process, which increases the complexity of the process. In addition, the polarity of water is too different from that of the solvent, making the entire process complicated and affecting the stability of the entire operation.

[0006] Therefore, there is an urgent need to provide a new method for separating α-olefins from hydrocarbon-containing streams. Summary of the Invention

[0007] The present invention aims to overcome the problems of low purification efficiency and product purity, low solvent recovery rate, complex process flow and high energy consumption in the existing method for separating and purifying multiple α-olefins from hydrocarbon streams, which use multiple extractants for deoxygenation and alkene separation respectively, and provide a method for separating and purifying 1-hexene, 1-heptene and 1-octene from hydrocarbon streams.

[0008] To achieve the above object, the present invention provides a method for separating and purifying 1-hexene, 1-heptene and 1-octene from a hydrocarbon-containing stream in a first aspect, comprising:

[0009] (I) Cutting the hydrocarbon-containing stream into fractions to obtain C5 - Distillate logistics, C6-C8 distillate logistics, C9 + distillate logistics;

[0010] (II) contacting the C6-C8 fraction stream, the composite extractant, and an aqueous phase for extraction and separation to obtain an extract phase and a raffinate phase containing a deoxygenated C6-C8 fraction;

[0011] (III) subjecting the raffinate phase to a distillation separation treatment, a fine fractionation and weight removal treatment, and an extractive distillation treatment to obtain 1-hexene, 1-heptene, and 1-octene;

[0012] wherein, after the extraction phase is recovered by solvent, the recovered extractant is circulated and added into the composite extractant;

[0013] The composite extractant comprises extractant a and extractant b, wherein the extractant a is selected from N-methylpyrrolidone and / or N,N-dimethylacetamide, and the extractant b is selected from γ-butyrolactone and / or N-formylmorpholine;

[0014] Furthermore, the composite extractant is also used in the extractive distillation process.

[0015] A second aspect of the present invention provides a system for separating and purifying 1-hexene, 1-heptene, and 1-octene from a hydrocarbon-containing stream, comprising:

[0016] Fraction cutting unit, extraction unit, separation and purification unit and composite extractant storage tank; among which,

[0017] The fraction cutting unit is used to cut the hydrocarbon-containing stream into fractions to obtain C5 - Distillate logistics, C6-C8 distillate logistics, C9 + distillate logistics;

[0018] The extraction unit is connected to the fraction cutting unit, the separation and purification unit and the composite extractant storage tank, and is used to extract and separate the C6-C8 fraction flow from water and the composite extractant from the composite extractant storage tank to obtain a raffinate phase containing a deoxygenated C6-C8 fraction;

[0019] The separation and purification unit is connected to the composite extractant storage tank and is used to successively perform distillation separation treatment, fine separation and weight removal treatment, and extractive distillation treatment in the presence of the composite extractant on the raffinate phase to obtain 1-hexene, 1-heptene and 1-octene, and to recover the composite extractant and return it to the composite extractant storage tank.

[0020] Through the above technical solution, the present invention can achieve the following beneficial effects:

[0021] (1) A single extractant is used to simultaneously achieve oxygenate removal and alkane-alkene separation. The extractant has a good deoxygenation effect, and the oxygen content in the raffinate phase can be reduced to below 10 mass ppm. The recovery rate of olefins and alkanes after oxygenate removal is preferably greater than 95%. At the same time, the extractant also has good selectivity for alkane-alkene separation, and can increase both the relative volatility of alkanes and the solubility of olefins, thereby reducing the energy consumption of the alkane-alkene separation unit. A single extractant is achieved that can be used to simultaneously extract and separate oxygenates from hydrocarbon streams and to separate C6-C8 alkenes and alkanes by extractive distillation.

[0022] (2) The present application realizes the removal of isomeric olefins and the separation of alkene and olefin by the combination of fine separation and heavy removal and extractive rectification. The 2-olefins and a small amount of alkane are removed in the fine separation and heavy removal, and the normal alkane and isomeric alkane are removed in the extractive rectification, so that the target product normal olefin (1-hexene, 1-heptene and 1-octene) is separated and purified from the hydrocarbon-containing stream. This combination can not only achieve the purity of separation, but also reduce the energy consumption of the whole process.

[0023] (3) The separation method of the alpha-olefin provided by the present application can make the content of oxygen-containing compounds in the target product less than 10 mass ppm, and the individual yield of various alpha-olefins in the hydrocarbon-containing stream is ≥83%. Under the preferred conditions, the individual purity of various alpha-olefins is greater than 98.5%. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The present application provides a method and a flow diagram.

[0025] BRIEF DESCRIPTION OF DRAWINGS

[0026] A, first rectification tower B, second rectification tower C, extraction tower

[0027] D, fourth solvent recovery tower E, composite extractant storage tank F, third rectification tower

[0028] G, first fine separation and heavy removal tower H, fourth rectification tower I, second fine separation and heavy removal tower

[0029] J, third fine separation and heavy removal tower K, first extractive rectification tower L, first solvent recovery tower

[0030] M, second extractive rectification tower N, second solvent recovery tower O, third extractive rectification tower

[0031] P, third solvent recovery tower

[0032] 1, hydrocarbon-containing stream 2, C8 - mixed fraction 3, C9 + fraction stream

[0033] 4, C5 - fraction stream 5, C6-C8 fraction stream 6, raffinate phase

[0034] 8, stream containing oxygen-containing compounds and water

[0035] 7, extraction phase 9, first recovery line

[0036] 10, second recovery line 11, second extractant line 12, first extractant line

[0037] 13, C6 fraction stream 14, C7-C8 fraction stream 15, crude C6 hydrocarbon stream

[0038] 18. A mixture of 1-hexene enriched with complexing extractant

[0039] 16. First fine deheavering column bottoms stream 17. n-hexane and iso-hexane

[0040] 19. 1-hexene 20. C7 cut stream 21. crude C7 hydrocarbon stream

[0041] 24. A mixture of 1-heptene enriched with complexing extractant

[0042] 22. Second fine deheavering column bottoms stream 23. n-heptane and iso-heptane

[0043] 25. 1-heptene 26. C8 cut stream 27. crude C8 hydrocarbon stream

[0044] 30. A mixture of 1-octene enriched with complexing extractant

[0045] 28. Third fine deheavering column bottoms stream 29. n-octane and iso-octane

[0046] 31. 1-octene 32. water DETAILED DESCRIPTION

[0047] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and any values are provided as approximate values, and the ranges and values should be understood to encompass values approximately the same as the stated values. For example, a range from 1 to 10 should be interpreted to include values from 1 to 10, and also include values from 1.1 to 10.1, and so on.

[0048] In the present application, unless otherwise specified, "C5 - " means the number of carbon is 5 or less (including C5, C4, C3, C2, C1), "C8 - " means the number of carbon is 8 or less (including C8), "C9 + " means the number of carbon is 9 or more (including C9). "C6-C8" includes the number of carbon is 6, 7, 8; "C7-C8" includes the number of carbon is 7, 8.

[0049] The first aspect of the present application provides a method for separating and purifying 1-hexene, 1-heptene and 1-octene from a hydrocarbon-containing stream, comprising:

[0050] (I) fractionating the hydrocarbon-containing stream to obtain a C5 - cut stream, a C6-C8 cut stream, and a C9 + cut stream;

[0051] (II) contacting the C6-C8 fraction stream, the composite extractant, and an aqueous phase for extraction and separation to obtain an extract phase and a raffinate phase containing a deoxygenated C6-C8 fraction;

[0052] (III) subjecting the raffinate phase to a distillation separation treatment, a fine fractionation and weight removal treatment, and an extractive distillation treatment to obtain 1-hexene, 1-heptene, and 1-octene;

[0053] wherein, after the extraction phase is recovered by solvent, the recovered extractant is circulated and added into the composite extractant;

[0054] The composite extractant comprises extractant a and extractant b, wherein the extractant a is selected from N-methylpyrrolidone and / or N,N-dimethylacetamide, and the extractant b is selected from γ-butyrolactone and / or N-formylmorpholine;

[0055] Furthermore, the composite extractant is also used in the extractive distillation process.

[0056] The present invention is used to separate and purify the target products 1-hexene, 1-heptene and 1-octene from the mixture, and under the conditions of ensuring product purity and recovery rate, a single extractant system can be used to complete the removal of oxygenated compounds and achieve alkane-olefin separation. In some embodiments of the present invention, the hydrocarbon-containing stream is a mixture comprising alkanes, olefins and oxygenated compounds. The hydrocarbon-containing stream may contain various alkanes, olefins, oxygenated compounds and the like having a carbon number of 4 or more. More specifically, the hydrocarbon-containing stream that can meet the requirements may be a naphtha fraction, typically preferably a condensate product of a Fischer-Tropsch synthesis reaction, and may be a condensate product of a low-temperature or high-temperature Fischer-Tropsch reaction. More preferably, the hydrocarbon-containing stream is a Fischer-Tropsch synthetic oil, wherein the total content of α-olefins is 50-80wt%.

[0057] In some embodiments of the present invention, the oxygenated compounds in the hydrocarbon stream include at least one of alcohols, ketones, aldehydes, carboxylic acids, and esters. Furthermore, based on the total amount of the hydrocarbon stream, the total content of the oxygenated compounds in the hydrocarbon stream is 0.1-10 wt%. Furthermore, among the oxygenated compounds, the major oxygenated compound is alcohol, with an alcohol content of 0.04-9.9 wt%. The total content of ketones and aldehydes can be determined by carbonyl oxygen content, which can be 0.05-1 wt%. The carboxylic acid content can be determined by acidity, which can be 30-100 mg / 100 mL KOH. In the hydrocarbon stream, the alkanes are primarily normal alkanes, with a small amount of isoalkanes.

[0058] In the present application, the method can combine processes such as fractionation, extraction, extractive rectification, etc. to realize that the α-olefins of a specific carbon number in the composition of the hydrocarbon-containing stream, in particular 1-hexene, 1-heptene and 1-octene, can be separated and purified to obtain. It can include first cutting the hydrocarbon-containing stream into fractions to distinguish by carbon number, separating and extracting to obtain the C6-C8 fraction stream, which contains organic compounds such as alkanes, olefins and oxygen-containing compounds, etc.; then performing extraction separation to remove part of the oxygen-containing compounds in the C6-C8 fraction stream in an extraction manner, and the raffinate phase obtained is mainly hydrocarbon compounds rich in C6-C8 fraction (wherein "containing deoxygenated C6-C8 fraction" means that the C6-C8 fraction contained in the composition of the raffinate phase has removed part of the oxygen-containing compounds); further separated and purified, including a combination of rectification separation treatment, fine separation and heavy removal treatment and extractive rectification treatment, to obtain 1-hexene, 1-heptene and 1-octene from the raffinate phase. Among them, the rectification separation treatment realizes the separation of the raffinate phase into C6 fraction stream, C7 fraction stream and C8 fraction stream, and then the fine separation and heavy removal treatment can remove the high-boiling-point compounds in the C6 fraction stream, C7 fraction stream and C8 fraction stream, respectively, and then the remaining substances continue to be treated by extractive rectification to separate and purify 1-hexene, 1-heptene and 1-octene.

[0059] In some embodiments of the present application, step (I) is used to cut the C6-C8 fraction stream from the hydrocarbon-containing stream by carbon number distinction. In step (I), the fraction cutting process includes:

[0060] (I-1) The hydrocarbon-containing stream is subjected to first fraction cutting to obtain a C9 + fraction stream, a C8 - mixed fraction;

[0061] (I-2) The C8 - mixed fraction is subjected to second fraction cutting to obtain a C5 - fraction stream and a C6-C8 fraction stream.

[0062] Preferably, the conditions of the first fraction cutting include: a reflux ratio of 2-5; a column bottom temperature of 155-170°C; and a column top pressure of normal pressure, preferably 1-1.02 bar.

[0063] Preferably, the hydrocarbon-containing stream can be subjected to the first fraction cutting in a first rectification column, and a C9 + fraction stream is obtained at the bottom of the first rectification column, and a C8 - fraction stream is obtained at the top of the first rectification column, wherein the first rectification column has a theoretical plate number of 30-50 plates, and the feed position of the hydrocarbon-containing stream is the 15th-25th plate from the bottom.

[0064] Preferably, the conditions for cutting the second fraction include: a reflux ratio of 2-5; a bottom temperature of 80-90° C.; and a top pressure of atmospheric pressure, preferably 1-1.02 bar.

[0065] Preferably, the C8 - The fraction stream is subjected to the second fraction cutting in the second distillation tower, and the C6-C8 fraction stream is obtained at the bottom of the second distillation tower, and the C5 - Distillate logistics, wherein the number of theoretical plates of the second distillation tower is 30-50, the C8 - The feed position of the distillate stream is the 15th to 25th theoretical plate from the bottom up.

[0066] In some embodiments of the present invention, step (II) is used to remove oxygenates from the C6-C8 fraction stream by extraction. Preferably, the C6-C8 fraction stream is subjected to oxygenate removal using an extraction solvent consisting of the composite extractant and water. Preferably, the weight ratio of the composite extractant to water is 1:0.1-1, more preferably 1:0.2-0.5, to achieve better removal results.

[0067] In some embodiments of the present invention, preferably, in the composite extractant, the content of the extractant a is 50-80 wt%, preferably 60-80 wt%. Correspondingly, the content of the extractant b is 20-50 wt%, preferably 20-40 wt%.

[0068] In some embodiments of the present invention, preferably, in step (II), the weight ratio of the total amount of the composite extractant and water to the C6-C8 fraction stream is 0.5-4:1, preferably 0.8-3:1.

[0069] In some embodiments of the present invention, preferably, the temperature of the extraction separation is 10-50°C, preferably 20-50°C.

[0070] In some embodiments of the present invention, preferably, the extraction and separation method is a multi-stage countercurrent extraction method. Preferably, the theoretical number of stages of the multi-stage countercurrent extraction can be 5-15 stages, preferably 8-12 stages. The extraction and separation can be carried out in an extraction tower, wherein the composite extractant and water are first mixed to form an extraction solvent, which is introduced into the extraction tower at or near the top of the tower, and the C6-C8 fraction stream is introduced into the extraction tower at or near the bottom of the tower, and then the C6-C8 fraction stream and the extraction solvent are subjected to multi-stage countercurrent extraction in the extraction tower; the raffinate phase is obtained at the top of the tower, and the extract phase is obtained at the bottom of the tower. The extraction phase contains a composite extractant, water, and oxygen-containing compounds, as well as a small amount of olefins and alkanes. Therefore, a fourth solvent recovery tower is introduced to perform the solvent recovery. The fourth solvent recovery tower can be a distillation tower with a theoretical plate number of 10-30, preferably 15-25. The conditions for solvent recovery are a reflux ratio of 0.5-2; a bottom temperature of 164-237°C; and a top pressure of atmospheric pressure, preferably 1-1.02 bar. The oxygen-containing compounds and water obtained at the top of the fourth solvent recovery tower are discharged, and the composite extractant obtained at the bottom of the fourth solvent recovery tower is recycled. The raffinate phase is rich in hydrocarbon compounds of the C6-C8 fraction and has a low content of oxygen-containing compounds. Preferably, the above-mentioned extraction and separation conditions can achieve a raffinate phase with an oxygen-containing compound content of less than 10 mass ppm and a total mass fraction of olefins and alkanes greater than 99%.

[0071] In some embodiments of the present invention, step (III) is used to separate and purify 1-hexene, 1-heptene, and 1-octene from the raffinate phase. Preferably, the distillation separation process can be performed to separate the raffinate phase and obtain a C6 fraction stream, a C7 fraction stream, and a C8 fraction stream. Preferably, the distillation separation process comprises the following conditions: a reflux ratio of 2-5; a tower bottom temperature of 105-130°C; and a tower top pressure of atmospheric pressure, preferably 1-1.02 bar.

[0072] In some embodiments of the present invention, preferably, the distillation separation process includes:

[0073] (III-1-1) subjecting the raffinate phase to a first distillation to obtain a C6 fraction stream and a C7-C8 fraction stream;

[0074] (III-1-2) The C7-C8 fraction flow is subjected to a second distillation to obtain a C7 fraction flow and a C8 fraction flow.

[0075] Preferably, the conditions of the first distillation include: a reflux ratio of 2-5; a tower bottom temperature of 105-115° C.; and a tower top pressure of normal pressure, preferably 1-1.02 bar.

[0076] Preferably, the raffinate phase can be subjected to the first distillation in a third distillation tower to obtain a C7-C8 fraction flow at the bottom of the third distillation tower, and a C6 fraction flow at the top of the third distillation tower, wherein the third distillation tower has 30-50 theoretical plates, and the feed position of the raffinate phase is at the 15th to 25th theoretical plate from the bottom up.

[0077] Preferably, the conditions of the second distillation include: a reflux ratio of 2-5; a bottom temperature of 120-130° C.; and a top pressure of atmospheric pressure, preferably 1-1.02 bar.

[0078] Preferably, the C7-C8 fraction stream can be subjected to the second distillation in a fourth distillation tower to obtain a C8 fraction stream at the bottom of the fourth distillation tower, and a C7 fraction stream is obtained at the top of the fourth distillation tower, wherein the fourth distillation tower has 30-50 theoretical plates, and the feed position of the C7-C8 fraction stream is the 15th to 25th theoretical plate from the bottom up.

[0079] In some embodiments of the present invention, preferably, the fractionation and deweighting treatment can further remove 2-olefins from the C6 fraction stream, the C7 fraction stream, and the C8 fraction stream, respectively. In the process of removing 2-olefins, the normal alkanes in the above fraction streams can also be partially separated and removed due to their higher boiling points, thereby reducing the energy consumption of the subsequent extractive distillation treatment steps.

[0080] In some embodiments of the present invention, the degassing treatment can be carried out by distillation. Preferably, the conditions of the degassing treatment include: a reflux ratio of 7-15; a bottom temperature of 69-135°C; a top pressure of atmospheric pressure; and a theoretical plate number of 80-150.

[0081] In some embodiments of the present invention, preferably, the process of the fine separation and de-weighting treatment includes:

[0082] (III-2-1) subjecting the C6 fraction stream to a first fine separation and degravity removal tower to obtain a first fine separation and degravity removal tower top stream and a first fine separation and degravity removal tower bottom stream;

[0083] (III-2-2) subjecting the C7 fraction stream to a second fine separation and degravity removal process to obtain a second fine separation and degravity removal tower top stream and a second fine separation and degravity removal tower bottom stream;

[0084] (III-2-3) The C8 fraction stream is subjected to a third fine separation and degravity removal to obtain a third fine separation and degravity removal tower top stream and a third fine separation and degravity removal tower bottom stream.

[0085] Preferably, the first fine deheavy treatment conditions include: reflux ratio of 7-15; column bottom temperature of 69-75℃; column top pressure of normal pressure; and theoretical plate number of 80-150.

[0086] Preferably, the C6 fraction stream can be subjected to the first fine deheavy treatment in a first fine deheavy column, the C6 fraction stream is fed from the middle lower part of the first fine deheavy column, the first fine deheavy column bottom stream obtained at the bottom comprises 2-hexene and C6 components with higher boiling points, and part of n-hexane is also distilled out with the column top stream during the deheavy treatment, the first fine deheavy column top stream obtained at the top is a crude C6 hydrocarbon stream, which can be a mixture containing 1-hexene and a complex extractant; wherein the theoretical plate number of the first fine deheavy column is 80-150, and the feeding position of the C6 fraction stream is the 20th-60th plate from the bottom in the first fine deheavy column.

[0087] Preferably, the second fine deheavy treatment conditions include: reflux ratio of 7-15; column bottom temperature of 99-105℃; column top pressure of normal pressure; and theoretical plate number of 80-150.

[0088] Preferably, the C7 fraction stream can be subjected to the second fine deheavy treatment in a second fine deheavy column, the C7 fraction stream is fed from the middle lower part of the second fine deheavy column, the second fine deheavy column bottom stream obtained at the bottom comprises 2-heptene and C7 components with higher boiling points, and part of n-heptane is also distilled out with the column bottom stream during the deheavy treatment, the second fine deheavy column top stream obtained at the top is a crude C7 hydrocarbon stream, which can be a mixture containing 1-heptene and a complex extractant; wherein the theoretical plate number of the second fine deheavy column is 80-150, and the feeding position of the C7 fraction stream is the 20th-60th plate from the bottom in the second fine deheavy column.

[0089] Preferably, the third fine deheavy treatment conditions include: reflux ratio of 7-15; column bottom temperature of 128-135℃; column top pressure of normal pressure; and theoretical plate number of 80-150.

[0090] Preferably, the C8 fraction stream can be subjected to the third fine de-heavy processing in a third fine de-heavy column, the C8 fraction stream enters from the middle lower part of the third fine de-heavy column, a third fine de-heavy column bottom stream obtained at the bottom of the third fine de-heavy column comprises 2-octene and C8 components with higher boiling points, and a part of n-octane is also distilled out with the column bottom stream in the de-heavy process, a third fine de-heavy column top stream obtained at the top of the third fine de-heavy column is a crude C8 hydrocarbon stream, which can be a mixture containing 1-alkene and the complex extractant; wherein the number of theoretical plates of the third fine de-heavy column is 80-150, and the feeding position of the C8 fraction stream is the 20th-60th plate from the bottom in the third fine de-heavy column.

[0091] In some embodiments of the present application, the first fine de-heavy column bottom stream, the second fine de-heavy column bottom stream and the third fine de-heavy column bottom stream are all discharged.

[0092] In some embodiments of the present application, the extractive distillation processing can remove alkanes in the crude C6 hydrocarbon stream, the crude C7 hydrocarbon stream and the crude C8 hydrocarbon stream respectively, realize alkene-alkane separation and obtain olefin products. The extractive distillation processing also uses the complex extractant, which can take into account selectivity and solubility. The same complex extractant is used in the extractive separation and the extractive distillation processing, which can provide good deoxygenation effect when separating and purifying the hydrocarbon-containing stream, and the recovery rate of 1-hexene, 1-heptene and 1-octene obtained is high; at the same time, the process is simplified, and the energy consumption of the system for running this method is reduced.

[0093] In the present application, the extractive distillation processing is carried out in an extractive distillation column, preferably, the conditions of the extractive distillation processing include: a reflux ratio of 1-4; a column bottom temperature of 120-190°C; a column top pressure of normal pressure; and a number of theoretical plates of 40-80.

[0094] In some embodiments of the present application, the process of the extractive distillation processing comprises:

[0095] (III-3-1) subjecting the first fine de-heavy column top stream and the complex extractant to first extractive distillation to obtain a 1-hexene and complex extractant mixture, and subjecting the mixture to first solvent recovery to obtain 1-hexene;

[0096] (III-3-2) subjecting the second fine de-heavy column top stream and the complex extractant to second extractive distillation to obtain a 1-heptene and complex extractant mixture, and subjecting the mixture to second solvent recovery to obtain 1-heptene;

[0097] (III-3-3) subjecting the third fine de-heavy column top stream and the complex extractant to third extractive distillation to obtain a 1-octene and complex extractant mixture, and subjecting the mixture to third solvent recovery to obtain 1-octene.

[0098] Meanwhile, the first extractive rectification also obtains n-hexane and iso-hexane; the second extractive rectification also obtains n-heptane and iso-heptane; and the third extractive rectification also obtains n-octane and iso-octane.

[0099] Preferably, the conditions of the first extractive rectification include: a reflux ratio of 1-4; a bottom temperature of 120-140°C; a top pressure of normal pressure; and a theoretical plate number of 40-70.

[0100] Preferably, the first extractive rectification can be performed on the first fine fraction-deheavy overhead stream in a first extractive rectification column, the first fine fraction-deheavy overhead stream being fed from a lower part of the first extractive rectification column, and the composite extractant being fed from an upper part of the first extractive rectification column. The volume ratio of the composite extractant to the first fine fraction-deheavy overhead stream is 4-12:1, preferably 5-8:1. A mixture rich in 1-hexene and the composite extractant is obtained at the bottom of the column, and n-hexane and iso-hexane are obtained at the top of the column. The theoretical plate number of the first extractive rectification column is 40-70, the feeding position of the first fine fraction-deheavy overhead stream is the 15th-35th plate from the bottom, and the feeding position of the composite extractant is the 3rd-6th plate from the top.

[0101] Preferably, the conditions of the second extractive rectification include: a reflux ratio of 1-4; a bottom temperature of 150-170°C; a top pressure of normal pressure; and a theoretical plate number of 40-70.

[0102] Preferably, the second extractive rectification can be performed on the second fine fraction-deheavy overhead stream in a second extractive rectification column, the second fine fraction-deheavy overhead stream being fed from a lower part of the second extractive rectification column, and the composite extractant being fed from an upper part of the second extractive rectification column. The volume ratio of the composite extractant to the second fine fraction-deheavy overhead stream is 4-12:1, preferably 5-8:1. A mixture rich in 1-heptene and the composite extractant is obtained at the bottom of the column, and n-heptane and iso-heptane are obtained at the top of the column. The theoretical plate number of the second extractive rectification column is 40-70, the feeding position of the second fine fraction-deheavy overhead stream is the 15th-35th plate from the bottom, and the feeding position of the composite extractant is the 3rd-6th plate from the top.

[0103] Preferably, the conditions of the third extractive rectification include: a reflux ratio of 1-4; a bottom temperature of 170-190°C; a top pressure of normal pressure; and a theoretical plate number of 40-70.

[0104] Preferably, the third precise deweighting tower overhead stream can be subjected to the third extractive distillation in a third extractive distillation tower, wherein the third precise deweighting tower overhead stream enters from the lower part of the third extractive distillation tower, and the composite extractant enters from the upper part of the tower. The volume ratio of the composite extractant to the third precise deweighting tower overhead stream is 4-12:1, preferably 5-8:1. A mixture rich in 1-octene and the composite extractant is obtained at the bottom of the tower, and n-octane and isooctane are obtained at the top of the tower. The number of theoretical plates of the third extractive distillation tower is 40-70, the feed position of the third precise deweighting tower overhead stream is the 15th to 35th theoretical plate from the bottom up, and the feed position of the composite extractant is the 3rd to 6th theoretical plate from the top down.

[0105] In some embodiments of the present invention, the extractive distillation treatment may be carried out in a multi-stage countercurrent manner. For example, in a first extractive distillation column, the composite extractant is in countercurrent contact with the overhead stream of the first fractionation and weight removal column; in a second extractive distillation column, the composite extractant is in countercurrent contact with the overhead stream of the second fractionation and weight removal column; and in a third extractive distillation column, the composite extractant is in countercurrent contact with the overhead stream of the third fractionation and weight removal column.

[0106] Preferably, the first solvent recovery, the second solvent recovery, and the third solvent recovery respectively recover the composite extractant to obtain the final target products: 1-hexene, 1-heptene, and 1-octene. Simultaneously, the recovered extractants I, II, and III are added back to the composite extractant for recycling.

[0107] In some embodiments of the present invention, the first solvent recovery, the second solvent recovery, and the third solvent recovery can be performed in a first solvent recovery tower, a second solvent recovery tower, and a third solvent recovery tower, respectively. The first solvent recovery tower, the second solvent recovery tower, and the third solvent recovery tower can each preferably be a rectification tower having 15 to 30 theoretical plates, and a feed position at the 10th to 15th theoretical plate from the bottom up. The solvent recovery conditions include: a reflux ratio of 0.5 to 1, a tower bottom temperature of 150 to 250° C., and a tower top pressure of -0.01 to 0.08 MPa.

[0108] According to a particularly preferred embodiment of the present invention, a method for separating and purifying 1-hexene, 1-heptene and 1-octene from a hydrocarbon-containing stream comprises:

[0109] (I) Cutting the hydrocarbon-containing stream into fractions to obtain C5 - Distillate logistics, C6-C8 distillate logistics, C9 + distillate logistics;

[0110] (II) contacting the C6-C8 fraction stream, the composite extractant, and an aqueous phase for extraction and separation to obtain an extract phase and a raffinate phase containing a deoxygenated C6-C8 fraction;

[0111] (III) subjecting the raffinate phase to a distillation separation treatment, a fine fractionation and weight removal treatment, and an extractive distillation treatment to obtain 1-hexene, 1-heptene, and 1-octene;

[0112] wherein, after the extraction phase is recovered by solvent, the recovered extractant is circulated and added into the composite extractant;

[0113] The composite extractant comprises extractant a and extractant b, wherein the extractant a is selected from N-methylpyrrolidone and / or N,N-dimethylacetamide, and the extractant b is selected from γ-butyrolactone and / or N-formylmorpholine;

[0114] The composite extractant is also used in the extraction and distillation process;

[0115] The hydrocarbon-containing stream comprises alkanes, olefins and oxygenates; the hydrocarbon-containing stream is a naphtha fraction, preferably a condensate product of a Fischer-Tropsch synthesis reaction; the oxygenates comprise at least one of alcohols, ketones, aldehydes, carboxylic acids and esters; based on the total amount of the hydrocarbon-containing stream, the content of the oxygenates in the hydrocarbon-containing stream is 0.1-10 wt%, and the content of α-olefins in the hydrocarbon-containing stream is 50-80 wt%;

[0116] Wherein, in step (II), the weight ratio of the composite extractant to water is 1-10:1, preferably 2-5:1;

[0117] Wherein, in the composite extractant, the content of the extractant a is 50-80wt%, preferably 60-80wt%; the content of the extractant b is 20-50wt%, preferably 20-40wt%;

[0118] Wherein, in step (II), the weight ratio of the total amount of the composite extractant and water to the C6-C8 fraction stream is 0.5-4:1, preferably 0.8-3:1;

[0119] Wherein, during the extractive distillation process, the volume ratio of the composite extractant to the first fine separation and weight removal tower top stream, the second fine separation and weight removal tower top stream and the third fine separation and weight removal tower top stream is 4-12:1, preferably 5-8:1;

[0120] Other conditions are as described above.

[0121] The second aspect of the present invention provides a system for separating and purifying 1-hexene, 1-heptene and 1-octene from a hydrocarbon-containing stream using the aforementioned method of the present invention, such as Figure 1 Shown, including:

[0122] a fraction cutting unit, an extraction unit, a separation and purification unit, and a composite extractant storage tank E; wherein,

[0123] the fraction cutting unit is configured to cut the hydrocarbon-containing stream 1 into a C5 - a fraction stream 4, a C6-C8 fraction stream 5, a C9 + a fraction stream 3; wherein the fraction cutting unit comprises a first rectifying tower A and a second rectifying tower B connected in sequence, a raw material inlet for introducing the hydrocarbon-containing stream 1 is arranged at the lower part of the first rectifying tower A, an intermediate material outlet is arranged at the upper part (different side from the raw material inlet) of the first rectifying tower A to obtain a C8 - a fraction stream 2, a discharge outlet is arranged at the bottom of the first rectifying tower A to obtain a C9 + a fraction stream 3; a feed inlet for introducing the C8 - a mixed fraction 2, a discharge outlet is arranged at the upper part (different side from the feed inlet) of the second rectifying tower B to obtain a C5 - a discharge outlet of the fraction stream 4, a discharge outlet of the C6-C8 fraction stream 5 is arranged at the lower part (different side from the feed inlet) of the second rectifying tower B;

[0124] the extraction unit is connected to the fraction cutting unit, the separation and purification unit, and the composite extractant storage tank E, and is configured to extract and separate the C6-C8 fraction stream 5 with water and the composite extractant from the composite extractant storage tank E to obtain a raffinate phase 6 containing deoxygenated C6-C8 fractions; wherein the extraction unit comprises an extraction tower C and a fourth solvent recovery tower D, the extraction tower C is connected to the second rectifying tower B, the composite extractant storage tank E (the extraction tower C and the composite extractant storage tank E are connected by a first extractant pipeline 12, wherein the first extractant pipeline 12 is used to transport the composite extractant), and the separation and purification unit, the C6-C8 fraction stream 5, water 32, and the composite extractant are contacted to perform the extraction and separation to obtain the raffinate phase 6 and an extract phase 7; the fourth solvent recovery tower D is connected to the extraction tower C and the composite extractant storage tank E, and is configured to recover the extract phase 7 to obtain a stream 8 containing oxygen-containing compounds and water, and the recovered extractant is introduced into the composite extractant storage tank E through a first recovery pipeline 9;

[0125] The separation and purification unit is connected to the composite extractant storage tank E and is used to sequentially perform distillation separation treatment, weight removal treatment, and extractive distillation treatment on the raffinate phase 6 to obtain 1-hexene, 1-heptene, and 1-octene, and recover the composite extractant and return it to the composite extractant storage tank E. The separation and purification unit includes: a distillation separation treatment group, a weight removal treatment group, and an extractive distillation treatment group; the distillation separation treatment group includes: a third distillation tower F and a fourth distillation tower H, wherein the third distillation tower F is used to perform a first distillation on the raffinate phase 6 to obtain a C6 fraction stream 13 from the top of the third distillation tower F and a C7-C8 fraction stream 14 from the bottom of the third distillation tower F; the fourth distillation tower H is used to perform a second distillation on the C7-C8 fraction stream 14 to obtain a C7 fraction stream 20 from the top of the fourth distillation tower H and a C8 fraction stream 26 from the bottom of the fourth distillation tower H;

[0126] The said fine separation and de-weighting treatment group comprises: a first fine separation and de-weighting tower G, a second fine separation and de-weighting tower I and a third fine separation and de-weighting tower J connected in parallel, wherein the first fine separation and de-weighting tower G is used to carry out a first fine separation and de-weighting of the C6 fraction stream 13 fed from the middle and lower part of the first fine separation and de-weighting tower, obtain a first fine separation and de-weighting tower bottom stream 16 from the bottom of the first fine separation and de-weighting tower G, and obtain a crude C6 hydrocarbon stream 15 (i.e., a first fine separation and de-weighting tower top stream) from the top of the first fine separation and de-weighting tower G; the second fine separation and de-weighting tower I is used to carry out a first fine separation and de-weighting of the C7 fraction stream 13 fed from the middle and lower part of the second fine separation and de-weighting tower The distillate stream 20 is subjected to a second fine separation and deweighting process, and a second fine separation and deweighting tower bottom stream 22 is obtained from the bottom of the second fine separation and deweighting tower I, and a crude C7 hydrocarbon stream 21 (i.e., a second fine separation and deweighting tower top stream) is obtained from the top of the second fine separation and deweighting tower I; the third fine separation and deweighting tower J is used to perform a third fine separation and deweighting process on the C8 distillate stream 26 fed from the middle and lower parts of the third fine separation and deweighting tower, and a third fine separation and deweighting tower bottom stream 28 is obtained from the bottom of the third fine separation and deweighting tower J, and a crude C8 hydrocarbon stream 27 (i.e., a third fine separation and deweighting tower top stream) is obtained from the top of the third fine separation and deweighting tower J;

[0127] The extractive distillation treatment group includes: a first extractive distillation group, a second extractive distillation group, and a third extractive distillation group connected in parallel, wherein the first extractive distillation group includes a first extractive distillation tower K and a first solvent recovery tower L connected in sequence, the second extractive distillation group includes a second extractive distillation tower M and a second solvent recovery tower N connected in sequence, and the third extractive distillation group includes a third extractive distillation tower O and a third solvent recovery tower P connected in sequence; wherein the first extractive distillation tower K, the second extractive distillation tower M, and the third extractive distillation tower O are all connected to the composite extractant storage tank E through a second extractant pipeline 11, and the second extractant pipeline 11 is used to transport the composite extractant from the composite extractant storage tank E;

[0128] The lower part of the first extractive rectifying tower K is provided with a feed inlet connected to the top of the second fine fractionation tower G for introducing the crude C6 hydrocarbon stream 15, while the upper part of the first extractive rectifying tower K is provided with a liquid inlet connected to the composite extractant storage tank E for introducing the composite extractant, and the crude C6 hydrocarbon stream 15 and the composite extractant are subjected to first extractive rectification in the first extractive rectifying tower K, the material outlet provided at the upper part of the first extractive rectifying tower K obtains a stream 17 containing n-hexane and iso-hexane, and the material outlet provided at the lower part of the first extractive rectifying tower K obtains a mixture 18 rich in 1-hexene and the composite extractant, which continues to enter the lower part of the first solvent recovery tower L for first solvent recovery, and the material outlet provided at the upper part of the first solvent recovery tower L obtains 1-hexene 19, while the liquid outlet provided at the lower part of the first solvent recovery tower L obtains recovered extractant-I;

[0129] The lower part of the second extractive rectifying tower M is provided with a feed inlet connected to the top of the third fine fractionation tower J for introducing the crude C7 hydrocarbon stream 21, while the upper part of the second extractive rectifying tower M is provided with a liquid inlet connected to the composite extractant storage tank E for introducing the composite extractant, and the crude C7 hydrocarbon stream 20 and the composite extractant are subjected to second extractive rectification in the second extractive rectifying tower M, the material outlet provided at the upper part of the second extractive rectifying tower M obtains a stream 23 containing n-heptane and iso-heptane, and the material outlet provided at the lower part of the second extractive rectifying tower M obtains a mixture 24 rich in 1-heptene and the composite extractant, which continues to enter the lower part of the second solvent recovery tower N for second solvent recovery, and the material outlet provided at the upper part of the second solvent recovery tower L obtains 1-heptene 25, while the liquid outlet provided at the lower part of the second solvent recovery tower M obtains recovered extractant-II.

[0130] The lower part of the third extractive rectifying tower O is provided with a feed inlet connected to the top of the third fine fractionation tower J for introducing the crude C8 hydrocarbon stream 27, while the upper part of the third extractive rectifying tower O is provided with a liquid inlet connected to the composite extractant storage tank E for introducing the composite extractant, and the crude C8 hydrocarbon stream 27 and the composite extractant are subjected to third extractive rectification in the third extractive rectifying tower O, the material outlet provided at the upper part of the third extractive rectifying tower O obtains a stream 29 containing n-octane and iso-octane, and the material outlet provided at the lower part of the third extractive rectifying tower O obtains a mixture 30 rich in 1-octene and the composite extractant, which continues to enter the lower part of the third solvent recovery tower P for third solvent recovery, and the material outlet provided at the upper part of the third solvent recovery tower P obtains 1-octene 31, while the liquid outlet provided at the lower part of the third solvent recovery tower P obtains recovered extractant-III.

[0131] The first solvent recovery tower, the second solvent recovery tower N and the third solvent recovery tower P are respectively connected to the composite extractant storage tank E, and the recovered extractant-I, the recovered extractant-II and the recovered extractant-III are combined and returned to the composite extractant storage tank E through the second recovery pipeline 10.

[0132] The method provided by the present application can be implemented in the system as above.

[0133] The present application will be described in detail below through examples.

[0134] Yield % of product (1-hexene, 1-heptene or 1-octene) = mass of product (1-hexene, 1-heptene or 1-octene) / (amount of feed of Fischer-Tropsch synthetic oil × percentage content of 1-hexene, 1-heptene or 1-octene) × 100%

[0135] The content of each component in the Fischer-Tropsch synthetic naphtha is measured by chromatography, wherein the content of alcohol in the oxygen-containing compound is measured by chromatography, the content of carbonyl oxygen (aldehyde, ketone) is measured according to GB / T6324.5-2008, the content of hydrocarbon compound component is measured according to SH / T1797-2015; the acidity is measured according to GB / T 264;

[0136] The content of each component in the product (1-hexene, 1-heptene or 1-octene) is measured by chromatography, wherein the content of oxygen-containing compound is measured by chromatography;

[0137] The composition and content of the raw material Fischer-Tropsch synthetic naphtha are shown in Table 1.

[0138] Table 1

[0139] Raw material composition Content (wt%) α-olefins 70 normal alkanes 23.8 2-Olefins 1.3 Isoalkanes 2.1 Isoolefins 0.3 alcohol 2.2 carbonyl oxygen 0.3

[0140] Example 1

[0141] (I) The Fischer-Tropsch synthetic naphtha (composition shown in Table 1) is subjected to first fraction cutting in the first rectifying column A to obtain C8 - mixed fraction and C9 + fraction stream, and then the C8 - mixed fraction is subjected to second fraction cutting in the second rectifying column B to obtain C5 - fraction stream and C6-C8 fraction stream, and the specific operation conditions are shown in Table 2.

[0142] (II) The C6-C8 fraction stream is subjected to multi-stage countercurrent extraction with a composite extractant and water in an extraction tower C to obtain an extract phase and a raffinate phase; wherein the composite extractant is N-methylpyrrolidone and γ-butyrolactone (each in an amount of 70 wt% / 30 wt%), the weight ratio of the composite extractant to water is 4:1, the countercurrent extraction temperature is 25°C, the feed rate of the C6-C8 fraction stream is 15 g / min, the feed rate of the composite extractant is 18 g / min (the weight ratio of (composite extractant + water): C6-C8 fraction stream is 1.2:1), and the theoretical number of extraction stages is 12; an extract phase and a raffinate phase are obtained. The extract phase at the bottom of the extraction tower C is introduced into a fourth solvent recovery tower D, and the regenerated composite extractant is withdrawn from the bottom of the tower after rectification and returned to the composite extractant storage tank E;

[0143] The raffinate phase at the top of extraction tower C is introduced into a third distillation tower F for a first distillation. The C6 fraction stream obtained at the top of the tower is then introduced into a first clean de-weighting tower G for a first clean de-weighting. The first clean de-weighting tower overhead stream (crude C6 hydrocarbon stream) obtained at the top of the tower is introduced into a first extractive distillation tower K for a first extractive distillation with a composite extractant from a composite extractant storage tank E (the volume ratio of the first clean de-weighting tower overhead stream: the composite extractant is 1:7). The 1-hexene and composite extractant mixture obtained at the bottom of the tower is introduced into a first solvent recovery tower L for a first solvent recovery to obtain 1-hexene. Simultaneously, the recovered extractant-I is returned to the composite extractant storage tank E. The purity of the 1-hexene is 99.1 wt%, the content of oxygenates is 4 ppm, and the yield of 1-hexene is 87.1%.

[0144] The C7-C8 fraction stream obtained from the bottom of the third distillation tower F is introduced into the fourth distillation tower H for secondary distillation, and the C7 fraction stream is obtained at the top of the tower and the C8 fraction stream is obtained at the bottom of the tower;

[0145] The C7 fraction stream is introduced into a second fine separation and weight removal tower I for a second fine separation and weight removal. The second fine separation and weight removal tower overhead stream (crude C7 hydrocarbon stream) obtained at the tower top enters a second extractive distillation tower M for a second extractive distillation with a composite extractant from a composite extractant storage tank E (volume ratio of the second fine separation and weight removal tower overhead stream: composite extractant = 1:7). The 1-heptene and composite extractant mixture obtained at the bottom of the tower enters a second solvent recovery tower N for a second solvent recovery to obtain 1-heptene. Simultaneously, the recovered extractant-II is returned to the composite extractant storage tank E. The purity of the 1-heptene is 98.9 wt%, the content of oxygenated compounds is 4 ppm, and the yield of 1-heptene is 88.2%.

[0146] The C8 fraction stream is introduced into a third fine separation and deweighting tower J for third fine separation and deweighting. The third fine separation and deweighting tower overhead stream (crude C8 hydrocarbon stream) obtained at the top of the tower enters a third extractive distillation tower O and undergoes third extractive distillation with a composite extractant from a composite extractant storage tank E (volume ratio of third fine separation and deweighting tower overhead stream: composite extractant = 1:7). The 1-octene and composite extractant mixture obtained at the bottom of the tower enters a third solvent recovery tower P for third solvent recovery to obtain 1-octene. Simultaneously, the recovered extractant-III is returned to the composite extractant storage tank E. The purity of the 1-octene is 98.8 wt%, the content of oxygenated compounds is 5 ppm, and the yield of 1-octene is 88.3%.

[0147] The material balance of the 100-min operation of the apparatus and method was performed, and 1390.7 g of the deoxygenated C6-C8 fraction stream was obtained, with a recovery rate of 88.1% for the deoxygenated C6-C8 fraction stream;

[0148] Gas chromatography revealed that the deoxygenated C6-C8 fraction contained 71.3 wt% α-olefins and 5 ppm oxygen-containing compounds. The oxygen-containing compounds contained 0 ppm alcohol and 4 ppm carbonyl oxygen, respectively, and had an acidity of 0.37 mg / 100 mL KOH.

[0149] Table 2

[0150]

[0151] Examples 2-5

[0152] The method of Example 1 was followed, except that the composition and usage of the composite extractant were as shown in Table 3.

[0153] Purification and separation were performed to obtain 1-hexene, 1-heptene and 1-octene respectively; the results are shown in Table 3.

[0154] The results of 100 minutes of operation of the device and method were used for material balance to obtain the recovery rate of the deoxygenated C6-C8 fraction stream. The content of α-olefins, the content of oxygen-containing compounds, the alcohol content in the oxygen-containing compounds, the content of carbonyl oxygen, and the acidity in the deoxygenated C6-C8 fraction stream were detected by gas chromatography, and the results are shown in Table 3.

[0155] Table 3

[0156]

[0157]

[0158] Table 3 (continued)

[0159]

[0160] Comparative Example 1-2

[0161] The method of Example 1 was followed, except for the composition and amount of the complex extractant used, as shown in Table 4.

[0162] Purification and separation were performed to obtain 1-hexene, 1-heptene and 1-octene, respectively. The results are shown in Table 4.

[0163] Material balance was performed based on the results of the 100 min device and method, to obtain the recovery of the deoxygenated C6-C8 fraction stream, the content of a-olefins in the deoxygenated C6-C8 fraction stream, the content of oxygen-containing compounds, the content of alcohol in the oxygen-containing compounds, the content of carbonyl oxygen, and the acidity results, as shown in Table 4.

[0164] Table 4

[0165]

[0166] As can be seen from the data of the examples, comparative examples and Tables 2-4, using the method of the present application, only one complex extractant is used, and under the control conditions of deoxygenation (extraction separation) and alkene separation (extractive distillation), a plurality of a-olefins, i.e. 1-hexene, 1-heptene and 1-octene, can be separated and purified from a hydrocarbon stream. The method simplifies the process flow, and can maintain the content of a-olefins during the removal of oxygen-containing compounds, so that the content of oxygen-containing compounds in the deoxygenated Fischer-Tropsch synthesis oil is reduced to less than 10 ppm, and the yield of the separated products 1-hexene, 1-heptene and 1-octene is greater than 83%, and the purity is greater than 98.5%.

[0167] The composition of the complex extractant in Comparative Example 1 is not within the preferred range of the present application, the weight ratio of (complex extractant + water) to hydrocarbon (C6-C8 fraction stream) in the deoxygenation process in Comparative Example 2 is not within the preferred range of the present application, and the volume ratio of the complex extractant to the refined de-removal column top stream in the alkene separation (extractive distillation) process in Comparative Example 3 is not within the preferred range of the present application, so that the content of oxygen-containing compounds in the deoxygenated Fischer-Tropsch synthesis oil, the yield and purity of the obtained products 1-hexene, 1-heptene and 1-octene cannot simultaneously achieve the effects obtained by the present application.

[0168] The preferred embodiments of the present application have been described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application, and all fall within the protection scope of the present application.

Claims

1. A method for separating and purifying 1-hexene, 1-heptene and 1-octene from a hydrocarbon-containing stream, comprising: (I) Cutting the hydrocarbon-containing stream into fractions to obtain C5 - Distillate logistics, C6-C8 distillate logistics, C9 + distillate logistics; (II) contacting the C6-C8 fraction stream, the composite extractant and the aqueous phase for extraction and separation to obtain an extract phase and a raffinate phase containing the deoxygenated C6-C8 fraction; (III) subjecting the raffinate phase to a distillation separation treatment, a fine fractionation and a weight removal treatment, and an extractive distillation treatment to obtain 1-hexene, 1-heptene, and 1-octene; wherein, after the extraction phase is recovered by solvent, the recovered extractant is circulated and added into the composite extractant; The composite extractant comprises extractant a and extractant b, wherein the extractant a is selected from N-methylpyrrolidone and / or N,N-dimethylacetamide, and the extractant b is selected from γ-butyrolactone and / or N-formylmorpholine; Furthermore, the composite extractant is also used in the extractive distillation process.

2. The method according to claim 1, wherein The hydrocarbon-containing stream comprises alkanes, olefins and oxygenates.

3. The method according to claim 1 or 2, wherein: The hydrocarbon-containing stream is a naphtha fraction; and / or, the oxygen-containing compound comprises at least one of an alcohol, a ketone, an aldehyde, a carboxylic acid, and an ester; And / or, based on the total amount of the hydrocarbon-containing stream, the content of the oxygen-containing compound in the hydrocarbon-containing stream is 0.1-10 wt%, and the content of α-olefin is 50-80 wt%.

4. The method according to claim 3, wherein: The hydrocarbon-containing stream is a condensate product of the Fischer-Tropsch synthesis reaction.

5. The method according to claim 1 or 2, wherein: In step (I), the fraction cutting process includes: (I-1) cutting the hydrocarbon-containing stream into a first fraction to obtain C9 + Distillate logistics, C8 - Mixed fraction; (I-2) the C8 - The mixed fraction was cut into the second fraction to obtain C5 - fraction stream and C6-C8 fraction stream.

6. The method according to claim 1 or 2, wherein: In step (II), the weight ratio of the composite extractant to water is 1-10:

1.

7. The method according to claim 6, wherein: In step (II), the weight ratio of the composite extractant to water is 2-5:

1.

8. The method according to claim 1 or 2, wherein: In the composite extractant, the content of the extractant a is 50-80wt%; And / or, in step (II), the weight ratio of the total amount of the composite extractant and water to the C6-C8 fraction stream is 0.5-4:

1.

9. The method according to claim 1 or 2, wherein: In the composite extractant, the content of the extractant a is 60-80wt%; And / or, in step (II), the weight ratio of the total amount of the composite extractant and water to the C6-C8 fraction stream is 0.8-3:

1.

10. The method according to claim 1 or 2, wherein: The temperature of the extraction separation is 10-50°C; And / or, the extraction and separation method is multi-stage countercurrent extraction, and the theoretical number of stages of the multi-stage countercurrent extraction is 5-15 stages.

11. The method according to claim 10, wherein: The temperature of the extraction separation is 20-50°C; And / or, the extraction and separation method is multi-stage countercurrent extraction, and the theoretical number of stages of the multi-stage countercurrent extraction is 8-12 stages.

12. The method according to claim 1, wherein The distillation separation process includes: (III-1-1) performing a first distillation on the raffinate phase to obtain a C6 fraction stream and a C7-C8 fraction stream; (III-1-2) subjecting the C7-C8 fraction stream to a second distillation to obtain a C7 fraction stream and a C8 fraction stream; And / or, the conditions for the distillation separation treatment include: a reflux ratio of 2-5; a tower bottom temperature of 105-130° C.; and a tower top pressure of normal pressure.

13. The method according to claim 12, wherein: The conditions of the distillation separation treatment include: a tower top pressure of 1-1.02 bar.

14. The method according to claim 1, wherein The process of the fine separation and de-weighting treatment includes: (III-2-1) subjecting the C6 fraction stream to a first fine separation and degravity removal column to obtain a first fine separation and degravity removal column top stream and a first fine separation and degravity removal column bottom stream; (III-2-2) subjecting the C7 fraction stream to a second fine separation and degravity removal tower to obtain a second fine separation and degravity removal tower top stream and a second fine separation and degravity removal tower bottom stream; (III-2-3) subjecting the C8 fraction stream to a third fine separation and degravity removal tower to obtain a third fine separation and degravity removal tower top stream and a third fine separation and degravity removal tower bottom stream; And / or, the conditions of the fine separation and degraviation treatment include: a reflux ratio of 7-15; a tower bottom temperature of 69-135° C.; a tower top pressure of atmospheric pressure; and a theoretical plate number of 80-150.

15. The method according to claim 1, wherein The process of the extractive distillation treatment comprises: (III-3-1) subjecting the overhead stream of the first weight-removal column and the composite extractant to a first extractive distillation, and recovering the resulting mixture of 1-hexene and the composite extractant through a first solvent recovery step to obtain 1-hexene; (III-3-2) subjecting the second fractionation and weight removal tower overhead stream and the composite extractant to a second extractive distillation, and subjecting the resulting mixture of 1-heptene and the composite extractant to a second solvent recovery to obtain 1-heptene; (III-3-3) subjecting the top stream of the third weight-removal column and the composite extractant to a third extractive distillation, and recovering the resulting mixture of 1-octene and the composite extractant through a third solvent recovery step to obtain 1-octene; And / or, the conditions of the extractive distillation treatment include: a reflux ratio of 1-4; a tower bottom temperature of 120-190° C.; a tower top pressure of atmospheric pressure; and a theoretical plate number of 40-80; And / or, the volume ratio of the composite extractant to the first fine separation and weight removal tower top stream, the second fine separation and weight removal tower top stream and the third fine separation and weight removal tower top stream is 4-12:1 respectively.

16. The method according to claim 15, wherein The volume ratio of the composite extractant to the first fine separation and weight removal tower top stream, the second fine separation and weight removal tower top stream and the third fine separation and weight removal tower top stream is 5-8:

1.

17. The method according to claim 15, wherein: The first extractive distillation, the second extractive distillation and the third extractive distillation further comprise obtaining n-hexane, n-heptane and n-octane respectively; And / or, the first solvent recovery, the second solvent recovery and the third solvent recovery further include returning the respectively obtained recovered extractant-I, recovered extractant-II and recovered extractant-III to the composite extractant.

18. A system for separating and purifying 1-hexene, 1-heptene, and 1-octene from a hydrocarbon-containing stream, comprising: Fraction cutting unit, extraction unit, separation and purification unit and composite extractant storage tank; among which, The fraction cutting unit is used to cut the hydrocarbon-containing stream into fractions to obtain C5 - Distillate logistics, C6-C8 distillate logistics, C9 + distillate logistics; The extraction unit is connected to the fraction cutting unit, the separation and purification unit and the composite extractant storage tank, and is used to extract and separate the C6-C8 fraction flow from water and the composite extractant from the composite extractant storage tank to obtain a raffinate phase containing a deoxygenated C6-C8 fraction; The separation and purification unit is connected to the composite extractant storage tank and is used to successively perform distillation separation treatment, fine separation and weight removal treatment on the raffinate phase and perform extractive distillation treatment in the presence of the composite extractant to obtain 1-hexene, 1-heptene and 1-octene, and recover the composite extractant and return it to the composite extractant storage tank; The composite extractant comprises extractant a and extractant b, wherein the extractant a is selected from N-methylpyrrolidone and / or N,N-dimethylacetamide, and the extractant b is selected from γ-butyrolactone and / or N-formylmorpholine.

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