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

Abstract

The present invention relates to the field of separation and purification of high value-added chemicals from hydrocarbon-containing streams, and discloses a method for separating 1-hexene, 1-heptene and 1-octene from hydrocarbon-containing streams, comprising: (I) fractionating the hydrocarbon-containing stream to obtain C6 ‑ Distillate streams, C6-C8 distillate streams, C9 and C9 + The method comprises the following steps: (i) removing oxygenated compounds from the C6-C8 fraction stream to obtain a deoxygenated C6-C8 fraction stream; (ii) subjecting the deoxygenated C6-C8 fraction stream to a distillation separation treatment, a fractionation deweighting treatment and an extractive distillation treatment, to obtain 1-hexene, 1-heptene and 1-octene. The method can effectively remove oxygenated compounds from the Fischer-Tropsch synthetic oil during the separation process, reduce the content of oxygenated compounds in the deoxygenated Fischer-Tropsch synthetic oil to less than 10 ppm (mass), and achieve an alpha-olefin retention rate of more than 99%; achieve a good separation effect of alkanes and olefins, and have a low energy consumption during the separation process; and achieve a product yield of more than 90% and a purity of more than 98.5%.

Description

Technical Field

[0001] The invention relates to the field of separation and purification of high value-added chemicals from hydrocarbon-containing logistics, and in particular to a method for separating 1-hexene, 1-heptene and 1-octene from hydrocarbon-containing logistics. Background Art

[0002] α-Olefins are an important organic raw material and intermediate product with a wide range of uses. 1-Butene, 1-hexene and 1-octene can be used as comonomers of polyethylene (PE) resin to improve the performance of PE. At present, the production of α-olefins in industry is mainly obtained by ethylene polymerization. Fischer-Tropsch synthetic oil products contain olefins and alkanes. Olefins are mainly linear α-olefins, and the content of α-olefins in Fischer-Tropsch light oil can reach more than 50%. The α-olefins produced by ethylene polymerization are of high quality. This method is mainly used in the production of α-olefins abroad. The domestic polymerization technology has developed relatively late. Only in recent years has an industrial device for producing 1-hexene by ethylene polymerization been built. The extraction method was developed by Sasol Company of South Africa from the separation of Fischer-Tropsch synthetic oil products. It separates and purifies linear α-olefins such as 1-hexene and 1-octene from high-temperature Fischer-Tropsch synthetic oil products. Compared with the polymerization method, this method has obvious cost advantages.

[0003] CN105777467B discloses a method for separating oxygenated compounds and 1-hexene from Fischer-Tropsch synthetic oil products, the method uses Fischer-Tropsch synthetic oil products as raw materials, cuts in a pre-cutting tower to obtain a C6 fraction stream, uses two extractants to feed and operate in an extraction tower to remove oxygenated compounds to obtain an oxygen-rich stream and a crude C6 hydrocarbon stream; then uses a third extractant to further remove oxygenated compounds in the crude C6 hydrocarbon stream, and then uses methanol to convert tertiary carbon olefins into corresponding ethers under the action of an etherification catalyst and removes them, and then further purifies by distillation, and then uses a fourth extractant and a fifth extractant to remove C6 isoparaffin components and cycloolefin components respectively, to obtain a 1-hexene product stream. In this method, deoxygenation is carried out by extraction and extractive distillation, and two extractants are used for extraction. The raffinate phase also needs to be further extracted and distilled to remove oxygenated compounds, and the steps are cumbersome. The separation of normal alkanes and 1-hexene uses a refiner with a high plate number (theoretical plate number is 60-160), a large reflux ratio (reflux ratio is 10-40), and a low recovery rate of 1-hexene (80% and below).

[0004] CN103360195B discloses a method for separating and purifying 1-octene from a hydrocarbon-oxygen mixture. The method requires two refinement towers (a refinement heavy removal tower and a refinement light removal tower). The theoretical number of plates of the two towers is 80-250, the reflux ratio is 10-40, and the energy consumption is relatively high.

[0005] CN102452886B discloses a method for purifying 1-octene from Fischer-Tropsch synthetic oil products, and an equipment system for implementing the method. The method uses Fischer-Tropsch synthetic light distillate oil as a raw material, uses secondary fraction cutting to obtain a C8 fraction segment, and then first uses azeotropic distillation to simultaneously remove organic acids and other oxygen-containing compounds in the C8 fraction using ethanol and water binary entrainers; then separates alkanes and olefins in the C8 fraction segment by extractive distillation; and further purifies the obtained C8 olefins by precise distillation to obtain a 1-octene product. The equipment system includes a 1# cutting tower, a 2# cutting tower, an azeotropic distillation tower, an extractive distillation tower, a precise distillation tower, and related supporting equipment. For this method, due to the wide variety of oxygen-containing compounds in Fischer-Tropsch synthetic oil products, some substances such as esters and ketones will form azeotropes with ethanol during the process of removing oxygen-containing compounds by azeotropic distillation, making it difficult to remove. In the extraction and distillation stage, a binary mixed solvent of NMP and water is preferably used as an extractant to separate alkanes and olefins. A solvent recovery tower and a dehydration tower are required in the solvent recovery process. In addition, the polarity of water is too different from that of the solvent, and the entire process is complicated to operate and has poor stability.

[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 purpose of the present invention is to overcome the problems of unsatisfactory deoxygenation effect, low product purity, low recovery rate, complex process flow and high energy consumption in the existing method for separating and purifying α-olefins from hydrocarbon streams, and to provide a method for separating 1-hexene, 1-heptene and 1-octene from hydrocarbon-containing streams.

[0008] In order to achieve the above object, the present invention provides a method for separating 1-hexene, 1-heptene and 1-octene from a hydrocarbon-containing stream, comprising:

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

[0010] (II) removing oxygen-containing compounds from the C6-C8 fraction stream to obtain a deoxygenated C6-C8 fraction stream;

[0011] (III) subjecting the deoxygenated C6-C8 fraction stream to a distillation separation treatment, a fractionation and deweighting treatment, and an extractive distillation treatment to obtain 1-hexene, 1-heptene, and 1-octene;

[0012] Wherein, the oxygen-containing compound removal treatment comprises:

[0013] (A) subjecting the C6-C8 fraction stream to countercurrent extraction with an extraction solvent containing a first composite extractant to obtain a first extract phase and a first raffinate phase;

[0014] (B) washing the first raffinate phase with water to obtain the deoxygenated C6-C8 fraction stream; recovering the first solvent from the mixture obtained at the same time, and / or returning the extraction solvent in step (A);

[0015] (C) recovering the first solvent from the first extraction phase, recycling the obtained solvent and adding it into the extraction solvent in step (A), stratifying the obtained aqueous organic matter, separating the bottom material obtained by stratification, and recycling the separated aqueous phase to step (B).

[0016] Through the above technical solution, the present invention can achieve the following beneficial effects:

[0017] (1) The oxygen-containing compounds are removed by extraction. Combined with the use of a specific composite extractant, the oxygen-containing compounds such as alcohols, ketones, aldehydes, acids and esters in the Fischer-Tropsch synthetic oil can be effectively removed. The content of oxygen-containing compounds in the deoxygenated Fischer-Tropsch synthetic oil is reduced to less than 10 ppm (mass), and the α-olefin retention rate can reach more than 99%;

[0018] (2) The method of combining separation and deweighting with extractive distillation is adopted, and an extractant with good selectivity is used in the extractive distillation stage, so that the olefins separated are of high purity and the energy consumption of the separation process is low;

[0019] (3) The product yield is greater than 90% and the purity is greater than 98.5%;

[0020] (4) The process is simple and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the process provided by the present invention.

[0022] Description of Reference Numerals

[0023] A. First distillation tower B. Second distillation tower C. Extraction tower

[0024] D, water washing tower E, first solvent recovery tower F, decantation tower

[0025] G, stripping tower H, third distillation tower I, first deweighting tower

[0026] J, first extractive distillation tower K, second solvent recovery tower L, fourth distillation tower

[0027] M, the second separation and deweighting tower N, the second extraction and distillation tower O, the third solvent recovery tower

[0028] P, the third separation and deweighting tower Q, the third extraction and distillation tower R, the fourth solvent recovery tower

[0029] 1. Fischer-Tropsch synthetic oil 2. C9 - Fraction Stream 3, C9 and C9 + Distillate logistics

[0030] 4. C6-C8 fraction logistics 5. C6 - Fraction Stream 6, First Raffinate Phase

[0031] 7. First extraction phase 8. A-share material at the bottom of water washing tower 9. B-share material at the bottom of water washing tower

[0032] 10. First circulating solvent 11. Recovered materials 12. Decantation tower top product

[0033] 13. Decantation tower bottom product 14. Circulating water 15. Oxygen-containing compounds

[0034] 16. Deoxygenated C6-C8 fraction logistics 17. C6 fraction logistics 18. C7-C8 fraction logistics

[0035] 19. Crude C6 hydrocarbon stream 20. n-hexane and isohexane 21. First mixed stream

[0036] 22. Second circulating solvent 23. 1-hexene 24. C7 fraction logistics

[0037] 25, C8 fraction stream 26, crude C7 hydrocarbon stream 27, n-heptane and isoheptane

[0038] 28. Second mixed stream 29. Third circulating solvent 30. 1-heptene

[0039] 31. Bottom product of the third fine separation and deweighting tower 32. Crude C8 hydrocarbon stream 33. n-octane and isooctane

[0040] 34. third mixed stream 35. fourth circulating solvent 36. 1-octene

[0041] 37. Bottom product of the first fine separation and deweighting tower 38. Bottom product of the second fine separation and deweighting tower DETAILED DESCRIPTION

[0042] 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.

[0043] The present invention provides a method for separating 1-hexene, 1-heptene and 1-octene from a hydrocarbon-containing stream, comprising:

[0044] (I) Cutting the hydrocarbon-containing stream into fractions to obtain C6 - Distillate stream, C6-C8 distillate stream, C9 and C9 + fraction logistics;

[0045] (II) removing oxygen-containing compounds from the C6-C8 fraction stream to obtain a deoxygenated C6-C8 fraction stream;

[0046] (III) subjecting the deoxygenated C6-C8 fraction stream to a distillation separation treatment, a fractionation and deweighting treatment, and an extractive distillation treatment to obtain 1-hexene, 1-heptene, and 1-octene;

[0047] Wherein, the oxygen-containing compound removal treatment comprises:

[0048] (A) subjecting the C6-C8 fraction stream to countercurrent extraction with an extraction solvent containing a first composite extractant to obtain a first extract phase and a first raffinate phase;

[0049] (B) washing the first raffinate phase with water to obtain the deoxygenated C6-C8 fraction stream; recovering the first solvent from the mixture obtained at the same time, and / or returning the extraction solvent in step (A);

[0050] (C) recovering the first solvent from the first extraction phase, recycling the obtained solvent and adding it into the extraction solvent in step (A), stratifying the obtained aqueous organic matter, separating the bottom material obtained by stratification, and recycling the separated aqueous phase to step (B).

[0051] In some embodiments of the present invention, the hydrocarbon-containing stream comprises alkanes, olefins and oxygenates. More specifically, the hydrocarbon-containing stream that can meet the requirement can be a naphtha fraction, typically preferably a condensate product of a Fischer-Tropsch synthesis reaction, and can 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 content of α-olefins is 40-70wt%, preferably 50-70wt%.

[0052] In some embodiments of the present invention, the oxygen-containing compound in the hydrocarbon-containing stream comprises at least one of alcohol, ketone, aldehyde, carboxylic acid and ester. Further, based on the total amount of the hydrocarbon-containing stream, the total content of the oxygen-containing compound in the hydrocarbon-containing stream is 0.1-10wt%. Further, among the oxygen-containing compounds, the main oxygen-containing compound is alcohol, and the content of alcohol is 0.04-9.9wt%; the total content of ketone and aldehyde can be determined by carbonyl oxygen content, which can be 0.05-1wt%, the content of ester can be 0.01-0.2wt%, and the content of carboxylic acid can be determined by acidity, which can be 30-100mg / 100mL KOH. The alkanes in the hydrocarbon-containing stream are mainly normal alkanes, and there are also a small amount of isoalkanes.

[0053] In some embodiments of the present invention, in step (I), the fraction cutting comprises:

[0054] (i) cutting the hydrocarbon-containing stream into a first fraction to obtain C9 - Distillate Streams and C9 and C9 + fraction logistics;

[0055] (ii) the C9 - The fraction stream is subjected to a second fraction cut to obtain C6 - Fraction and C6-C8 fraction logistics.

[0056] Preferably, the conditions for cutting the first fraction include: a reflux ratio of 2-5; a bottom temperature of 155-170° C.; and a top pressure of normal pressure.

[0057] Preferably, the hydrocarbon-containing stream can be subjected to the first fraction cutting in the first distillation tower to obtain C9 and C9 at the bottom of the first distillation tower. + The fraction stream is C9 obtained at the top of the first distillation tower. - The fraction logistics, wherein the number of theoretical plates of the first distillation tower is 30-50, the feed position of the hydrocarbon-containing logistics is the 15th-25th theoretical plate from the bottom to the top, and the conditions for cutting the first fraction include: the reflux ratio is 2-5; the bottom temperature is 155-170°C; and the top pressure is normal pressure.

[0058] 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 normal pressure.

[0059] Preferably, the C9 - The fraction stream is subjected to the second fraction cutting in the second distillation tower, and a C6-C8 fraction stream is obtained at the bottom of the second distillation tower, and a C6-C8 fraction stream is obtained at the top of the second distillation tower. -The fraction flow, wherein the number of theoretical plates of the second distillation tower is 30-50, the C9 - The feed position of the distillate flow is the 15th to 25th theoretical plates from bottom to top, and the conditions for cutting the second distillate include: the reflux ratio is 2-5; the bottom temperature is 80-90° C.; and the top pressure is normal pressure.

[0060] In some embodiments of the present invention, in step (II), the oxygen-containing compound removal treatment is performed by extraction. In the oxygen-containing compound removal step (A), the first composite extractant can be used to remove the oxygen-containing compounds by extraction of the entire fraction of the hydrocarbon-containing flow. Preferably, the composite extractant is an ester compound. Preferably, the ester compound is selected from at least one of benzoate compounds, carbonate compounds, and lactone compounds; more preferably, the composite extractant can be specifically selected from at least one of dimethyl phthalate, ethylene glycol carbonate, and γ-butyrolactone.

[0061] In some embodiments of the present invention, in step (A), preferably, the extraction solvent further comprises water. Preferably, the water content in the extraction solvent is no more than 50wt%, preferably 0-20wt%. When the extraction solvent contains water, the selectivity of the composite extractant can be significantly improved.

[0062] In some embodiments of the present invention, in the conditions for achieving the countercurrent extraction in step (A), preferably, the weight ratio of the extraction solvent to the C6-C8 fraction stream is 0.5-4:1, preferably 0.8-2:1.

[0063] In some embodiments of the present invention, in step (A), preferably, the temperature of the countercurrent extraction is 10-50°C, preferably 20-50°C. The operation process of the countercurrent extraction can be a multi-stage countercurrent extraction method. Preferably, the theoretical number of stages of the multi-stage countercurrent extraction can be 5-15, preferably 8-12. The extraction can be carried out in an extraction tower, and a first raffinate phase is obtained at the top of the tower, and a first extraction phase is obtained at the bottom of the tower. The first extraction phase is rich in oxygen-containing compounds; the first raffinate phase is rich in hydrocarbon compounds and has a low content of oxygen-containing compounds.

[0064] According to the above method provided by the present invention, the first raffinate phase obtained in step (A) contains a small amount of the extraction solvent, and the extraction solvent can be washed away by water washing in step (B) to obtain a deoxygenated hydrocarbon phase, that is, the deoxygenated C6-C8 fraction flow. The water washing can be carried out by introducing the first raffinate phase into a water washing tower, and the hydrocarbon phase is drawn out as the top product of the tower. A mixture of water and a small amount of extraction solvent can be obtained at the bottom of the tower, which can be directly returned to the extraction solvent in step (A) for recycling, or it can enter the first solvent recovery tower for first solvent recovery treatment. Preferably, the conditions of the water washing include: the water washing temperature is 10-80°C, and the weight ratio of water to the first raffinate phase is 0.4-1:1.

[0065] In some embodiments of the present invention, in step (C), the first extraction phase is subjected to first solvent recovery, which can be achieved by distillation to recover the solvent, and oxygen-containing compounds and circulating solvent can be obtained, which can be carried out in the first solvent recovery tower. The circulating solvent is obtained at the bottom of the first solvent recovery tower, containing the first composite extractant, and can be returned to the extraction solvent in step (A) for recycling. In the present invention, the material obtained at the bottom of the water washing tower and the circulating solvent obtained at the bottom of the first solvent recovery tower can also be returned to step (A) together, added to the extraction solvent for recycling, and the water content in the obtained circulating solvent can be adjusted. In the present invention, the material obtained at the bottom of the water washing tower can also be introduced into the first solvent recovery tower together with the first extraction phase. The recovered material is obtained at the top of the first solvent recovery tower, which can contain oxygen-containing compounds, water and a small amount of hydrocarbons. Further, the recovered material is also subjected to static stratification after being drawn out, and can be introduced into a decantation tower for carrying out, and a water-insoluble organic phase is obtained at the top of the decantation tower, which is mainly oxygen-containing compounds and a small amount of hydrocarbons, and water and water-soluble oxygen-containing compounds are obtained at the bottom of the decantation tower. Preferably, the conditions for recovering the first solvent include: a temperature of 150-250° C., a pressure of -0.01 to 0.08 MPa, and a reflux ratio of 0.5 to 1. The reflux ratio refers to the weight ratio of the flow rate of the reflux liquid returned to the recovery tower to the flow rate of the recovered material at the top of the recovery tower. The temperature may refer to the temperature at the bottom of the recovery tower.

[0066] In some embodiments of the present invention, in step (C), the material obtained at the bottom of the decantation tower after standing and stratifying can be further separated to separate the organic phase and water. Preferably, the separation is distillation or stripping. Specifically, the material obtained from the bottom of the decantation tower can be introduced into a distillation tower or a stripping tower, and the organic phase of oxygen-containing compounds is mainly obtained at the top of the distillation tower or the stripping tower, and water is mainly obtained at the bottom of the tower; further, the obtained water is circulated to the water washing tower. In some embodiments of the present invention, preferably, the conditions of the stripping include: temperature of 100-120°C, pressure of normal pressure, and reflux ratio of 1-2; the conditions of the distillation include: temperature of 100-120°C, pressure of normal pressure, and reflux ratio of 1-2.

[0067] By removing oxygenated compounds in step (II) of the present invention, the recovery rate of olefins and paraffins in the deoxygenated C6-C8 fraction stream is preferably greater than 92%, while at least substantially maintaining the ratio of olefins / paraffins. Not only is the content of α-olefins in the Fischer-Tropsch synthetic oil maintained, but alcohols, ketones, aldehydes, acids and esters in the Fischer-Tropsch synthetic oil can also be effectively removed, and the content of oxygenated compounds in the deoxygenated C6-C8 fraction stream is reduced to less than 10 ppm (mass).

[0068] In some embodiments of the present invention, in step (III), the distillation separation treatment can achieve cutting of the deoxygenated C6-C8 fraction stream to obtain a C6 fraction stream, a C7 fraction stream and a C8 fraction stream. The distillation separation treatment comprises: subjecting the deoxygenated C6-C8 fraction stream to a first distillation separation treatment to obtain a C6 fraction stream and a C7-C8 fraction stream; and then subjecting the C7-C8 fraction stream to a second distillation separation treatment to obtain a C7 fraction stream and a C8 fraction stream.

[0069] Preferably, the conditions of the first distillation separation treatment include: a reflux ratio of 2-5; a bottom temperature of 105-115° C.; and a top pressure of normal pressure.

[0070] Preferably, the deoxygenated C6-C8 fraction logistics can be subjected to the first distillation separation treatment in a third distillation tower to obtain a C7-C8 fraction logistics at the bottom of the third distillation tower, and a C6 fraction logistics is obtained at the top of the third distillation tower, wherein the third distillation tower has 30-50 theoretical plates, and the feed position of the deoxygenated C6-C8 fraction logistics is at the 15th to 25th theoretical plate from bottom to top, and the conditions for the first distillation separation treatment include: a reflux ratio of 2-5; a bottom temperature of 105-115°C; and a top pressure of normal pressure.

[0071] Preferably, the conditions of the second distillation separation treatment include: a reflux ratio of 2-5; a bottom temperature of 120-130° C.; and a top pressure of normal pressure.

[0072] Preferably, the C7-C8 fraction logistics can be subjected to the second distillation separation treatment in a fourth distillation tower to obtain a C8 fraction logistics at the bottom of the fourth distillation tower, and a C7 fraction logistics 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 logistics is the 15th to 25th theoretical plate from the bottom up, and the conditions for the second distillation separation treatment include: a reflux ratio of 2-5; a bottom temperature of 120-130°C; and a top pressure of normal pressure.

[0073] In some embodiments of the present invention, in step (III), the fine separation and deweighting treatment can remove 2-olefins in the C6 fraction stream, the C7 fraction stream and the C8 fraction stream. In the process of removing 2-olefins, the normal alkanes in the above fraction streams can also be partially separated and removed, thereby reducing the energy consumption of subsequent separation steps.

[0074] In some embodiments of the present invention, in step (III), the fractionation and degravity treatment may be carried out by distillation. Preferably, the fractionation and degravity treatment conditions include: a reflux ratio of 7-15; a bottom temperature of 69-135°C; a top pressure of normal pressure; and a theoretical number of plates of 80-150.

[0075] In the present invention, the fine separation and de-weighting treatment includes: subjecting the C6 fraction logistics to a first fine separation and de-weighting treatment to obtain a crude C6 hydrocarbon logistics, 2-hexene and a C6 component with a higher boiling point; subjecting the C7 fraction logistics to a second fine separation and de-weighting treatment to obtain a crude C7 hydrocarbon logistics, 2-heptene and a C7 component with a higher boiling point; subjecting the C8 fraction logistics to a third fine separation and de-weighting treatment to obtain a crude C8 hydrocarbon logistics, 2-octene and a C8 component with a higher boiling point.

[0076] Preferably, the conditions of the first fine separation and deweighting treatment include: a reflux ratio of 7-15; a bottom temperature of 69-75° C.; a top pressure of normal pressure; and a theoretical number of plates of 80-150.

[0077] Preferably, the C6 fraction flow can be subjected to the first fine separation and deweighting treatment in a first fine separation and deweighting tower, the C6 fraction flow enters from the lower part of the first fine separation and deweighting tower, 2-hexene and C6 components with higher boiling points are obtained at the bottom of the tower, and a portion of normal hexane is also distilled out with the bottom flow during the deweighting process, and a crude C6 hydrocarbon flow is obtained at the top of the tower, wherein the theoretical number of plates of the first fine separation and deweighting tower is 80-150, the feed position of the C6 fraction flow is at the 20th-60th theoretical plate from the bottom to the top, and the conditions of the first fine separation and deweighting treatment include: a reflux ratio of 7-15; a bottom temperature of 69-75°C; a top pressure of normal pressure; and a theoretical number of 80-150 plates.

[0078] Preferably, the conditions of the second fine separation and deweighting treatment include: a reflux ratio of 7-15; a bottom temperature of 99-105° C.; a top pressure of normal pressure; and a theoretical plate number of 80-150.

[0079] Preferably, the C7 fraction flow can be subjected to the second fine separation and deweighting treatment in the second fine separation and deweighting tower, the C7 fraction flow enters from the lower part of the second fine separation and deweighting tower, 2-heptene and C7 components with higher boiling points are obtained at the bottom of the tower, a portion of n-heptane is also distilled out with the bottom flow during the deweighting process, and a crude C7 hydrocarbon flow is obtained at the top of the tower, wherein the theoretical number of plates of the second fine separation and deweighting tower is 80-150, the feed position of the C7 fraction flow is at the 20th-60th theoretical plate from the bottom to the top, and the conditions of the second fine separation and deweighting treatment include: a reflux ratio of 7-15; a bottom temperature of 99-105°C; a top pressure of normal pressure; and a theoretical number of 80-150 plates.

[0080] Preferably, the conditions of the third fine separation and degravity treatment include: a reflux ratio of 7-15; a bottom temperature of 128-135° C.; a top pressure of normal pressure; and a theoretical number of plates of 80-150.

[0081] Preferably, the C8 fraction flow can be subjected to the third fine separation and deweighting treatment in a third fine separation and deweighting tower, the C8 fraction flow enters from the lower part of the third fine separation and deweighting tower, 2-octene and C8 components with higher boiling points are obtained at the bottom of the tower, a portion of n-octane is also distilled out with the bottom flow during the deweighting process, and a crude C8 hydrocarbon flow is obtained at the top of the tower, wherein the third fine separation and deweighting tower has a theoretical plate number of 80-150, the feed position of the C8 fraction flow is at the 20th to 60th theoretical plate from the bottom to the top, and the conditions of the third fine separation and deweighting treatment include: a reflux ratio of 7-15; a bottom temperature of 128-135°C; a top pressure of normal pressure; and a theoretical plate number of 80-150.

[0082] In some embodiments of the present invention, in step (III), the extractive distillation treatment is intended to remove the alkane stream in the crude C6 hydrocarbon stream, the crude C7 hydrocarbon stream and the crude C8 hydrocarbon stream. The second composite extractant used in the extractive distillation treatment is a mixture of extractant a and extractant b; 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. The use of the second composite extractant can take into account both the selectivity of the solvent and the solubility of the solvent.

[0083] Preferably, based on the weight of the second composite extractant, the content of the extractant a is 70-30wt%, preferably 40-65wt%; the content of the extractant b is 30-70wt%, preferably 35-60wt%.

[0084] In the present invention, the extractive distillation treatment is carried out in an extractive distillation tower. Preferably, the conditions of the extractive distillation treatment include: a reflux ratio of 1-4; a bottom temperature of 120-190° C.; a top pressure of normal pressure; and a theoretical number of 40-70 plates.

[0085] In some embodiments of the present invention, the extractive distillation treatment includes: subjecting the crude C6 hydrocarbon flow and the second composite extractant to a first extractive distillation treatment to obtain a first mixed flow rich in 1-hexene and the second composite extractant, as well as n-hexane and isohexane; subjecting the crude C7 hydrocarbon flow and the second composite extractant to a second extractive distillation treatment to obtain a second mixed flow rich in 1-heptene and the second composite extractant, as well as n-heptane and isoheptane; subjecting the crude C8 hydrocarbon flow and the second composite extractant to a third extractive distillation treatment to obtain a third mixed flow rich in 1-octene and the second composite extractant, as well as n-octane and isooctane.

[0086] Preferably, the conditions of the first extractive distillation treatment include: a reflux ratio of 1-4; a bottom temperature of 120-140° C.; a top pressure of normal pressure; and a theoretical number of plates of 40-70.

[0087] Preferably, the crude C6 hydrocarbon stream can be subjected to the first extractive distillation treatment in a first extractive distillation tower, the crude C6 hydrocarbon stream enters from the lower part of the first extractive distillation tower, and the second composite extractant enters from the upper part of the tower. The volume ratio of the second composite extractant to the crude C6 hydrocarbon stream is 4-10:1, preferably 4-7:1. The content of the extractant b in the second composite extractant is 30-60wt%, preferably 35-50wt%. A first mixed stream rich in 1-hexene and the second composite extractant is obtained at the bottom of the tower, and n-hexane and isohexane are obtained at the top of the tower. Among them, the number of theoretical plates of the first extractive distillation tower is 40-70, the feeding position of the crude C6 hydrocarbon flow is the 15th to 35th theoretical plates from the bottom to the top, the feeding position of the second composite extractant is the 3rd to 6th theoretical plates from the top to the bottom, and the conditions of the first extractive distillation treatment include: a reflux ratio of 1-4; a bottom temperature of 120-140°C; a top pressure of normal pressure; and a theoretical number of 40-70 plates.

[0088] Preferably, the conditions of the second extractive distillation treatment 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.

[0089] Preferably, the crude C7 hydrocarbon stream can be subjected to the second extractive distillation treatment in a second extractive distillation tower, wherein the crude C7 hydrocarbon stream enters from the lower part of the second extractive distillation tower, and the second composite extractant enters from the upper part of the tower. The volume ratio of the second composite extractant to the crude C7 hydrocarbon stream is 4-10:1, preferably 4-7:1. The content of the extractant b in the second composite extractant is 35-65wt%, preferably 45-55wt%. A second mixed stream rich in 1-heptene and the second composite extractant is obtained at the bottom of the tower, and n-heptane and isoheptane are obtained at the top of the tower. The number of theoretical plates of the second extractive distillation tower is 40-70, the feed position of the crude C7 hydrocarbon flow is the 15th to 35th theoretical plates from the bottom up, the feed position of the second composite extractant is the 3rd to 6th theoretical plates from the top down, and the conditions of the second extractive distillation treatment include: a reflux ratio of 1-4; a bottom temperature of 150-170° C.; a top pressure of normal pressure; and a theoretical number of 40-70 plates.

[0090] Preferably, the conditions of the third extractive distillation treatment 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.

[0091] Preferably, the crude C8 hydrocarbon stream can be subjected to the third extractive distillation treatment in a third extractive distillation tower, wherein the crude C8 hydrocarbon stream enters from the lower part of the third extractive distillation tower, and the second composite extractant enters from the upper part of the tower. The volume ratio of the second composite extractant to the crude C8 hydrocarbon stream is 4-10:1, preferably 4-7:1. The content of the extractant b in the second composite extractant is 40-70wt%, preferably 50-60wt%. A third mixed stream rich in 1-octene and the second composite extractant is obtained at the bottom of the tower, and n-octane and isooctane are obtained at the top of the tower. Among them, the theoretical number of plates of the third extractive distillation tower is 40-70, the feeding position of the crude C8 hydrocarbon flow is the 15th to 35th theoretical plates from the bottom to the top, the feeding position of the second composite extractant is the 3rd to 6th theoretical plates from the top to the bottom, and the conditions of the third extractive distillation treatment include: a reflux ratio of 1-4; a bottom temperature of 170-190°C; a top pressure of normal pressure; and a theoretical number of plates of 40-70.

[0092] In some embodiments of the present invention, after the extractive distillation treatment, the obtained mixed stream is subjected to a desolventizing treatment, including: subjecting the first mixed stream to a first desolventizing treatment to obtain 1-hexene; subjecting the second mixed stream to a second desolventizing treatment to obtain 1-heptene; subjecting the third mixed stream to a third desolventizing treatment to obtain 1-octene. The desolventizing treatment separates and removes the second composite extractant in the first mixed stream, the second mixed stream, and the third mixed stream to obtain 1-hexene, 1-heptene, and 1-octene, and returns the obtained circulating solvent (i.e., the regenerated second composite extractant) to the extractive distillation treatment step for recycling.

[0093] In some embodiments of the present invention, the desolventizing treatment is carried out in a solvent recovery tower. For example, the first mixed stream, the second mixed stream and the third mixed stream can be subjected to the first desolventizing treatment, the second desolventizing treatment and the third desolventizing treatment in the second solvent recovery tower, the third solvent recovery tower and the fourth solvent recovery tower, respectively. The solvent recovery tower is preferably a distillation tower having 15-30 theoretical plates, the feed position being the 10th to 15th theoretical plates from bottom to top, and the conditions of the desolventizing treatment include: a reflux ratio of 0.5-1, a bottom temperature of 150-250°C, and a top pressure of -0.01 to 0.08MPa.

[0094] According to a specific embodiment of the present invention, Figure 1As shown, a method for separating 1-hexene, 1-heptene and 1-octene from a hydrocarbon-containing stream. The method can be carried out in the following separation system, which includes: a first distillation tower, a second distillation tower, an extraction tower, a water washing tower, a first solvent recovery tower, a decantation tower, a stripping tower, a third distillation tower, a first clean deweighting tower, a first extractive distillation tower, a second solvent recovery tower, a fourth distillation tower, a second clean deweighting tower, a second extractive distillation tower, a third solvent recovery tower, a third clean deweighting tower, a third extractive distillation tower, and a fourth solvent recovery tower; wherein the first distillation tower is sequentially connected to the second distillation tower, and the lower discharge port of the second distillation tower is connected to the extraction tower; the extraction tower The top of the tower is connected to the water washing tower, and the bottom of the tower is connected to the first solvent recovery tower. The extraction tower is provided with a lower feed port for feeding the C6-C8 fraction logistics, and an upper feed port is provided for feeding the extraction solvent; the water washing tower is provided with a lower feed port for feeding the first raffinate phase, and an upper feed port is provided for feeding water. The water washing tower is also provided with a top outlet to discharge the obtained deoxygenated C6-C8 fraction logistics to the lower feed port of the third distillation tower, and a bottom outlet is provided to discharge the bottom material and connect to the upper feed port of the extraction tower; the first solvent recovery tower is provided with a recovery feed port connected to the bottom of the extraction tower and the water washing tower The bottom outlet of the tower is also provided, and a recovery outlet at the top of the tower and a bottom outlet of the tower are also provided and connected to the upper feed inlet of the extraction tower; the decantation tower is provided with a decantation feed inlet connected to the recovery outlet, an organic phase outlet at the top of the tower and a bottom outlet; the stripping tower is provided with a separation feed inlet connected to the bottom outlet of the decantation tower, a bottom outlet connected to the upper feed inlet of the water washing tower, and an organic phase outlet at the top of the stripping tower; the third distillation tower, the first deweighting tower, the first extractive distillation tower and the second solvent recovery tower are connected in sequence, and the bottom outlet of the second solvent recovery tower is connected to the upper Extractant feed port; the fourth distillation tower, the second fractionation and deweighting tower, the second extractive distillation tower and the third solvent recovery tower are connected in sequence, and the feed port of the fourth distillation tower is connected to the bottom discharge port of the third distillation tower, and the bottom discharge port of the third solvent recovery tower is connected to the upper extractant feed port of the second extractive distillation tower; the third fractionation and deweighting tower, the third extractive distillation tower and the fourth solvent recovery tower are connected in sequence, and the feed port of the third fractionation and deweighting tower is connected to the bottom discharge port of the fourth distillation tower, and the bottom discharge port of the fourth solvent recovery tower is connected to the upper extractant feed port of the third extractive distillation tower. The method provided by the present invention can be implemented in the above system, comprising the following steps:

[0095] The Fischer-Tropsch naphtha fraction is cut into fractions by passing through the first distillation tower and the second distillation tower to obtain C6 - Distillate stream, C6-C8 distillate stream, C9 and C9 + Distillate stream.

[0096] The C6-C8 fraction flow and the extraction solvent containing the first composite extractant are respectively introduced into the extraction tower through the lower feed port and the upper feed port, and multi-stage countercurrent extraction is performed to obtain the first extraction phase and the first raffinate phase.

[0097] The first raffinate phase is passed into a water washing tower to wash away a small amount of extraction solvent contained therein by water washing, and a deoxygenated C6-C8 fraction flow is drawn out from the top of the water washing tower, which contains more than 99wt% of olefins and alkanes, and less than 10ppm (mass) of oxygen-containing compounds; the mixture of water and a small amount of extraction solvent obtained at the bottom of the water washing tower can be divided into a stock A at the bottom of the water washing tower and a stock B at the bottom of the water washing tower, stock A returns to the extraction tower to add the extraction solvent, and stock B is mixed with the first extraction phase and enters the first solvent recovery tower; the first solvent recovery tower is subjected to rectification and recovery, and a recovered material is obtained from the top of the tower, comprising Oxygen-containing compounds, water and a small amount of olefins and alkanes, a circulating solvent (which may mainly contain the first composite extractant) is obtained from the bottom of the tower, which can be returned to the extraction solvent for recycling; in the present invention, the amount and composition of the A-share material at the bottom of the water washing tower and the circulating solvent returned when they are added to the extraction solvent are used to adjust the composition of the extraction solvent to meet the extraction process. For example, the A-share material at the bottom of the water washing tower and the circulating solvent can be mixed to prepare a suitable composition and added to the extraction solvent. If the water content is excessive, the mixture can be distributed to more B-share material at the bottom of the water washing tower, and even all the mixture obtained at the bottom of the water washing tower enters the first solvent recovery tower.

[0098] The recovered material obtained from the top of the first solvent recovery tower is introduced into a decantation tower for static separation, and the decantation tower top product is obtained at the upper part of the decantation tower, which may contain oxygen-containing compounds and a small amount of hydrocarbons, and the decantation tower bottom product obtained at the bottom of the decantation tower may be recovered water and a small amount of water-soluble oxygen-containing compounds; further, the decantation tower bottom product of the decantation tower is introduced into a stripping tower to separate water and oxygen-containing compounds, and oxygen-containing compounds are obtained at the top of the tower, and circulating water is obtained at the bottom of the tower, which is circulated back to the water washing tower.

[0099] The deoxygenated C6-C8 fraction flow enters the third distillation tower and the fourth distillation tower successively for distillation and separation treatment to obtain a C6 fraction flow, a C7 fraction flow and a C8 fraction flow. The C6 fraction logistics enters the first de-weighting tower, the first extractive distillation tower and the second solvent recovery tower in sequence, and performs the first de-weighting treatment, the first extractive distillation treatment (using the second composite extractant) and the first desolventizing treatment in sequence to obtain 1-hexene, and the obtained second circulating solvent is returned to the first extractive distillation tower for recycling; the C7 fraction logistics enters the second de-weighting tower, the second extractive distillation tower and the third solvent recovery tower in sequence, and performs the second de-weighting treatment, the second extractive distillation treatment (using the second composite extractant) and the second desolventizing treatment in sequence to obtain 1-heptene, and the obtained third circulating solvent is returned to the second extractive distillation tower for recycling; the C8 fraction logistics enters the third de-weighting tower, the third extractive distillation tower and the fourth solvent recovery tower in sequence, and performs the third de-weighting treatment, the third extractive distillation treatment (using the second composite extractant) and the third desolventizing treatment in sequence to obtain 1-octene, and the obtained fourth circulating solvent is returned to the third extractive distillation tower for recycling.

[0100] The present invention will be described in detail below through examples.

[0101] Recovery rate of deoxygenated C6-C8 fraction stream % = mass of deoxygenated naphtha obtained from the top of the water scrubber / [feed amount of C6-C8 fraction stream in the extraction tower × (1-content of oxygen-containing compounds %)] × 100%

[0102] Yield of product (1-hexene, 1-heptene or 1-octene) % = mass of product (1-hexene, 1-heptene or 1-octene) / (feed amount of Fischer-Tropsch oil × percentage content of 1-hexene, 1-heptene or 1-octene) × 100%

[0103] The content of each component in Fischer-Tropsch naphtha was measured by chromatography, among which the content of alcohol and ester in oxygen-containing compounds was determined by chromatography, the content of carbonyl oxygen was determined according to GB / T 6324.5-2008, and the acidity was determined according to GB / T264;

[0104] 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 compounds is determined by chromatography;

[0105] The composition and content of raw material Fischer-Tropsch synthesis naphtha are shown in Table 1.

[0106] Table 1

[0107] Raw material composition Content (wt%) α-Olefins 70 Normal alkanes 23.8 2-Olefin 1.3 Isoalkanes 2.1 Isoolefins 0.3 alcohol 2.2 Carbonyl oxygen 0.3

[0108] Example 1

[0109] (I) Fischer-Tropsch naphtha (composition shown in Table 1) is subjected to first fraction cutting in the first distillation tower to obtain C9 - Fractions and C9 and C9 + The fraction stream is then - The fraction stream is cut into the second fraction in the second distillation tower to obtain C6 - The specific operating conditions of the fractions and C6-C8 fraction logistics are shown in Table 2;

[0110] (II) subjecting the C6-C8 fraction stream and an extraction solvent containing a first composite extractant to multi-stage countercurrent extraction in an extraction tower to obtain a first extraction phase and a first raffinate phase; wherein the first composite extractant is dimethyl phthalate and γ-butyrolactone (80% / 20%), the extraction solvent contains 5% water, 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 extraction solvent is 18 g / min (the weight ratio of the extraction solvent: the C6-C8 fraction stream is 1.2:1), and the theoretical number of extraction stages is 12;

[0111] The first raffinate phase at the top of the extraction tower is introduced into a water washing tower, and the extraction solvent is washed away by water washing. The water washing temperature is 50°C, and the weight ratio of water to the first raffinate phase is 0.5:1. A deoxygenated C6-C8 fraction flow is obtained at the top of the water washing tower and drawn out; the mixture (containing dimethyl phthalate, γ-butyrolactone and water) obtained at the bottom of the water washing tower is divided into a stock A at the bottom of the water washing tower and a stock B at the bottom of the water washing tower. The stock A at the bottom of the water washing tower can be directly returned to the extraction tower for recycling. The stock B at the bottom of the water washing tower and the first extraction phase are introduced into the first solvent recovery tower for distillation recovery. The first solvent recovery conditions are: : The temperature is 200-205°C, the pressure is -0.08MPa, and the reflux ratio is 0.5; the first circulating solvent obtained at the bottom of the first solvent recovery tower is returned to the extraction tower for recycling as the extraction solvent; the recovered material obtained at the top of the first solvent recovery tower is introduced into the decantation tower for static separation, and the decantation tower top product obtained at the top is mainly oxygen-containing compounds; the decantation tower bottom product obtained at the bottom is introduced into the stripping tower to separate water and water-soluble oxygen-containing compounds, and the stripping conditions include: the temperature is 100-105°C, the pressure is normal pressure, the reflux ratio is 1.5, and the circulating water obtained is reused to the water washing tower;

[0112] 100 min was taken for material balance, and 1390.7 g of deoxygenated C6-C8 fraction logistics was obtained, and the recovery rate of the deoxygenated C6-C8 fraction logistics was 95.1%;

[0113] By gas chromatography, the content of α-olefins in the deoxygenated C6-C8 fraction stream was 71.3 wt%, and the content of oxygen-containing compounds was 5 ppm; the content of alcohol in the oxygen-containing compounds was 0 ppm (weight), the content of carbonyl oxygen was 3 ppm (weight), and the acidity was 0.37 mg / 100 mL KOH;

[0114] (III) subjecting the deoxygenated C6-C8 fraction stream to a first distillation separation treatment in a third distillation tower to obtain a C7-C8 fraction stream at the bottom of the tower and a C6 fraction stream at the top of the tower; subjecting the C7-C8 fraction stream to a second distillation separation treatment in a fourth distillation tower to obtain a C8 fraction stream at the bottom of the tower and a C7 fraction stream at the top of the tower; the specific operating conditions are shown in Table 2;

[0115] The C6 fraction stream is introduced into the first fine separation and deweighting tower for the first fine separation and deweighting treatment, the C7 fraction stream is introduced into the second fine separation and deweighting tower for the second fine separation and deweighting treatment, and the C8 fraction stream is introduced into the third fine separation and deweighting tower for the third fine separation and deweighting treatment, and a crude C6 hydrocarbon stream, a crude C7 hydrocarbon stream and a crude C8 hydrocarbon stream are obtained at the top of the tower respectively; and corresponding 2-olefins, higher boiling point components and part of normal alkanes are obtained at the bottom of the tower respectively; the specific operating conditions are shown in Table 2;

[0116] The crude C6 hydrocarbon stream is introduced into a first extractive distillation tower and a second composite extractant (the content of N-methylpyrrolidone is 55wt%, the content of γ-butyrolactone is 45wt%) for a first extractive distillation treatment (wherein the volume ratio of the second composite extractant to the crude C6 hydrocarbon stream is 6:1), and the crude C7 hydrocarbon stream is introduced into a second extractive distillation tower and a second composite extractant (the content of N-methylpyrrolidone is 50wt%, the content of γ-butyrolactone is 50wt%) for a second extractive distillation treatment (wherein the volume ratio of the second composite extractant to the crude C6 hydrocarbon stream is 6:1). The crude C8 hydrocarbon stream is introduced into a third extractive distillation tower and a second composite extractant (the content of N-methylpyrrolidone is 50wt%, the content of γ-butyrolactone is 50wt%) for a third extractive distillation treatment (wherein the volume ratio of the second composite extractant to the crude C8 hydrocarbon stream is 6:1), and a first mixed stream, a second mixed stream and a third mixed stream are obtained at the bottom of the tower respectively; and corresponding normal alkanes and isoalkanes are obtained at the top of the tower respectively; the specific operating conditions are shown in Table 2;

[0117] The first mixed stream is introduced into a second solvent recovery tower for a first desolventizing treatment, the second mixed stream is introduced into a third solvent recovery tower for a second desolventizing treatment, and the third mixed stream is introduced into a fourth solvent recovery tower for a third desolventizing treatment, and 1-hexene product (denoted as S1), 1-heptene product (denoted as P1) and 1-octene product (denoted as X1) are obtained at the top of the tower, respectively, and the second circulating solvent, the third circulating solvent and the fourth circulating solvent obtained at the bottom of the tower are respectively returned to the first extractive distillation tower, the second extractive distillation tower and the third extractive distillation tower for recycling.

[0118] Table 2

[0119]

[0120]

[0121] Comparative Example 1

[0122] The method of Example 1 is followed, except that ethylene glycol is used to replace the first composite extractant in step (II), and N-methylpyrrolidone is used to replace the second composite extractant in step (III). Other conditions are the same as those of Example 1. A 1-hexene product (denoted as D-S1), a 1-heptene product (denoted as D-P1) and a 1-octene product (denoted as D-X1) are obtained.

[0123] After testing, the purity of 1-hexene in product S1 is 99.1wt%, the content of oxygen-containing compounds is 4ppm, and the yield of 1-hexene is 92%; the purity of 1-heptene in product P1 is 98.9wt%, the content of oxygen-containing compounds is 4ppm, and the yield of 1-heptene is 93%; in product X1, the purity of 1-octene is 98.6wt%, the content of oxygen-containing compounds is 5ppm, and the yield of 1-octene is 94%.

[0124] The purity of 1-hexene in product D-S1 is 98.1wt%, the content of oxygen-containing compounds is 20ppm, and the yield of 1-hexene is 89%; the purity of 1-heptene in product D-P1 is 97.4wt%, the content of oxygen-containing compounds is 25ppm, and the yield of 1-heptene is 90%; in product D-X1, the purity of 1-octene is 97.0wt%, the content of oxygen-containing compounds is 28ppm, and the yield of 1-octene is 90%.

[0125] In summary, by adopting the method of the present invention, the content of α-olefins can be maintained during the process of removing oxygen-containing compounds, so that the content of oxygen-containing compounds in the Fischer-Tropsch synthetic oil after deoxygenation and refining is reduced to below 10 ppm, and the yield of the separated products 1-hexene, 1-heptene, and 1-octene is greater than 90%, and the purity is greater than 98.5%.

[0126] 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 1-hexene, 1-heptene and 1-octene from a hydrocarbon-containing stream, comprising: (I) Cutting the hydrocarbon-containing stream into fractions to obtain C6 - Distillate stream, C6-C8 distillate stream, C9 and C9 + fraction logistics; (II) removing oxygen-containing compounds from the C6-C8 fraction stream to obtain a deoxygenated C6-C8 fraction stream; (III) subjecting the deoxygenated C6-C8 fraction stream to a distillation separation treatment, a deweighting treatment and an extractive distillation treatment to obtain 1-hexene, 1-heptene and 1-octene; Wherein, the oxygen-containing compound removal treatment comprises: (A) subjecting the C6-C8 fraction stream to countercurrent extraction with an extraction solvent comprising a first composite extractant and water to obtain a first extract phase and a first raffinate phase; (B) washing the first raffinate phase with water to obtain the deoxygenated C6-C8 fraction stream; recovering the first solvent from the mixture obtained at the same time, and / or returning the extraction solvent in step (A); (C) recovering the first solvent from the first extraction phase, recycling the obtained solvent and adding it into the extraction solvent in step (A), stratifying the obtained aqueous organic matter, separating the bottom material obtained by stratification, and recycling the separated aqueous phase to step (B); The first composite extractant is an ester compound; the ester compound is selected from at least one of benzoate compounds, carbonate compounds, and lactone compounds; The second composite extractant used in the extractive distillation treatment is a mixture of extractant a and extractant b; 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.

2. The method according to claim 1, wherein: The hydrocarbon-containing stream comprises alkanes, olefins and oxygen-containing compounds; 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 %.

3. The method according to claim 2, wherein: The hydrocarbon-containing stream is a naphtha fraction.

4. The method according to claim 2, wherein: The hydrocarbon-containing stream is a condensate product of the Fischer-Tropsch synthesis reaction.

5. The method according to claim 1, wherein: The ester compound is selected from at least one of dimethyl phthalate, ethylene glycol carbonate and γ-butyrolactone; And / or, the water content in the extraction solvent is no more than 50 wt %.

6. The method according to claim 5, wherein: The water content in the extraction solvent is 5-20wt%.

7. The method according to any one of claims 1 to 4, wherein: The weight ratio of the extraction solvent to the C6-C8 fraction stream is 0.5-4:

1.

8. The method according to claim 7, wherein: The weight ratio of the extraction solvent to the C6-C8 fraction stream is 0.8-2:

1.

9. The method according to any one of claims 1 to 4, wherein: The temperature of the countercurrent extraction is 10-50°C.

10. The method according to claim 9, wherein: The temperature of the countercurrent extraction is 20-50°C.

11. The method according to any one of claims 1 to 4, wherein: The conditions for recovering the first solvent include: temperature of 150-250°C, pressure of -0.01 to 0.08 MPa, and reflux ratio of 0.5-1; And / or, the separation is distillation or stripping; And / or, the stripping conditions include: temperature of 100-120° C., pressure of normal pressure, and reflux ratio of 1-2; the distillation conditions include: temperature of 100-120° C., pressure of normal pressure, and reflux ratio of 1-2.

12. The method according to any one of claims 1 to 4, wherein: Based on the weight of the second composite extractant, the content of the extractant a is 70-30wt%; the content of the extractant b is 30-70wt%; And / or, after the extractive distillation treatment, the obtained mixed stream is subjected to a desolventizing treatment.

13. The method according to claim 12, wherein: Based on the weight of the second composite extractant, the content of the extractant a is 40-65wt%; the content of the extractant b is 35-60wt%.

14. The method according to any one of claims 1 to 4, wherein: The conditions of the fine separation and deweighting treatment include: a reflux ratio of 7-15; a tower bottom temperature of 69-135° C.; a tower top pressure of normal pressure; and a theoretical tower plate number of 80-150.

15. The method according to any one of claims 1 to 4, wherein: 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 normal pressure; and a theoretical tower plate number of 40-70.

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