Separation method of n-hexane
By using dimethylformamide and N-methylpyrrolidone as solvents and controlling process parameters, efficient separation of n-hexane at a lower agent-oil ratio is achieved, and the problems of high energy consumption and purity in the prior art are solved, reducing energy consumption costs and ensuring product quality.
Patent Information
- Application Number
- CN202510176555.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-18
- Publication Date
- 2025-05-02
AI Technical Summary
The existing n-hexane separation process is carried out under a high agent-oil ratio, resulting in higher energy consumption and it is difficult to achieve a n-hexane purity of more than 99% at a lower agent-oil ratio.
Dimethylformamide and N-methylpyrrolidone are used as solvents, and through specific mass ratios and process parameters, the distillation and rectification of n-hexane are achieved, the agent-oil ratio is reduced, and the mass content of methylcyclopentane is ensured between 10% and 15%.
The efficient separation of n-hexane is achieved at a lower agent-oil ratio, which reduces the energy consumption cost of the device and ensures the quality of the separated products.
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Abstract
Description
Technical Field
[0001] The invention relates to the technical field of petrochemical separation, in particular to a method for separating normal hexane. Background Art
[0002] The C6 fraction mainly contains isohexane, n-hexane, methylcyclopentane, cyclohexane and a small amount of heavy components above C6. Among them, n-hexane and methylcyclopentane are near-boiling systems with a boiling point difference of 2.8°C. It is difficult to obtain n-hexane with a purity of more than 99% by ordinary distillation. Therefore, the extractive distillation process is adopted. The extractive distillation operation is to add a liquid solvent (extractant) that is immiscible or partially miscible with the liquid mixture to be separated to form a two-phase system. The difference in solubility of each component in the raw material liquid in the extractant is used to achieve a certain degree of separation of each component in the raw material liquid. Because N-methylpyrrolidone (NMP) has many advantages such as good selectivity for methylcyclopentane, high solubility, easy separation from C6 hydrocarbons, low corrosiveness and relatively low toxicity, it is widely used. At present, N-methylpyrrolidone is generally used as the solvent for extractive distillation in domestic methylcyclopentane separation devices.
[0003] N-Methylpyrrolidone (NMP) is a polar solvent with strong selectivity and good stability. It has the advantages of low toxicity, high boiling point, strong solvency, non-flammability, biodegradability, recyclability, safety in use and suitability for a variety of formulations. The selectivity of NMP solvent: aromatics> olefins> cycloalkanes> alkanes. The solubility of NMP is higher than other solvents. Currently, NMP is widely used as a solvent for the extraction and distillation process of separating n-hexane and a series of new compound solvents have been developed.
[0004] The energy consumption of the extractive distillation process is relatively high because the solvent needs to be purified and regenerated at high temperature. However, with the severe energy crisis in recent years, how to optimize and reduce the energy consumption cost of the extractive distillation device has become a problem that needs to be solved. Summary of the invention
[0005] In view of this, the technical problem to be solved by the present invention is to provide a method for separating n-hexane. The separation method provided by the present invention can perform n-hexane distillation at a relatively low solvent-oil ratio, while ensuring that the mass content of methylcyclopentane in the separated n-hexane is 10% to 15%. On the one hand, the degree of separation is ensured, and on the other hand, the solvent loss of downstream customers due to low content is avoided, which increases the operating cost.
[0006] The present invention provides a method for separating n-hexane, comprising the following steps:
[0007] S1) separating the light component C5 oil and isohexane from the hydrogenated saturated aromatics and olefin reforming raffinate to obtain the remaining heavy components;
[0008] S2) using dimethylformamide and N-methylpyrrolidone in a mass ratio of 1:(10-15) as solvent, sequentially performing n-hexane distillation and n-hexane rectification on the remaining heavy components obtained in step S1) to obtain n-hexane; the n-hexane rectification is performed at a solvent-to-oil ratio of 3-5.
[0009] The solvent-to-oil ratio of the present invention is the ratio of the amount of solvent flowing into the n-hexane distillation to the amount of solvent in the stripping gas phase of the n-hexane distillation. In certain embodiments of the present invention, the solvent flowing into the n-hexane distillation is a distillation regeneration liquid phase obtained by distilling and regenerating the stripping liquid phase obtained by the n-hexane distillation, and the solvent circulation ratio is the ratio of the amount of solvent in the distillation regeneration liquid phase to the stripping gas phase of the n-hexane distillation.
[0010] The inventors of the present application creatively discovered that after separating the light component C5 oil and isohexane from the hydrogenated saturated aromatics and olefin reforming raffinate oil, the obtained materials are sequentially subjected to n-hexane stripping and n-hexane rectification using dimethylformamide and N-methylpyrrolidone in a specific mass ratio as solvents, and n-hexane rectification can be performed at a lower agent-to-oil ratio, while ensuring that the mass content of methylcyclopentane in the separated n-hexane is 10% to 15%. Preferably, dimethylformamide and N-methylpyrrolidone in a mass ratio of 1:(10 to 12) are used as solvents. Preferably, the n-hexane rectification is performed at an agent-to-oil ratio of 3 to 4. The present invention also combines the control of the separation process parameters of n-hexane to better achieve the separation of n-hexane. The temperature of the n-hexane distillation of the present invention is 150°C~170°C, and the pressure is 100 KPa~120 KPa; the temperature of the n-hexane rectification is 70°C~85°C, the pressure is 10 KPa~80 KPa, and the reflux ratio is 2~6.
[0011] The hydrogenated saturated aromatic and olefin reforming raffinate oil of the present invention is obtained by hydrogenating the saturated aromatic and olefin reforming raffinate oil. In certain embodiments of the present invention, the saturated aromatic and olefin reforming raffinate oil from the tank area and the hydrogen from the pipeline network are subjected to hydrogenation reaction to remove aromatics and olefins to obtain the hydrogenated saturated aromatic and olefin reforming raffinate oil; the raw material index requirements after hydrogenation are: controlling the benzene content to be less than 1 ppm, the olefin content to be less than 1 ppm, and the total aromatic content to be less than 50 ppm.
[0012] The method for separating n-hexane provided by the present invention first separates light component C5 oil and isohexane from hydrogenated saturated aromatics and olefin reforming raffinate oil to obtain the remaining heavy component. Specifically, hydrogenated saturated aromatics and olefin reforming raffinate oil are sequentially subjected to light component C5 oil stripping and light component C5 oil rectification to separate the light component C5 oil. More specifically, hydrogenated saturated aromatics and olefin reforming raffinate oil are introduced into a light component C5 oil stripping tower for stripping to obtain a light component C5 oil stripping gas phase and a light component C5 oil stripping liquid phase; the light component C5 oil stripping gas phase is introduced into a light component C5 oil rectification tower for light component C5 oil rectification to obtain a light component C5 oil rectification gas phase and a light component C5 oil rectification liquid phase, wherein the light component C5 oil rectification gas phase escapes at the top of the tower and takes away the light component C5 oil, and the light component C5 oil rectification liquid phase refluxes to the bottom of the tower and is reintroduced into the light component C5 oil stripping tower. The tower bottom temperature of the light component C5 oil distillation of the present invention is 100°C~120°C, and the tower bottom pressure is 220 KPa~250 KPa; the tower top temperature of the light component C5 oil distillation of the present invention is 60°C~70°C, the tower top pressure is 150KPa~170KPa, and the reflux ratio is 9~12.
[0013] The present invention separates the light component C5 oil from the hydrogenated saturated aromatics and olefin reforming raffinate oil, and then separates isohexane to obtain the remaining heavy components. Specifically, after the light component C5 oil is separated from the hydrogenated saturated aromatics and olefin reforming raffinate oil, the light component C5 oil distillation liquid phase in the light component C5 oil distillation tower is sequentially subjected to isohexane stripping and isohexane rectification to separate isohexane. More specifically, the light component C5 oil distillation liquid phase in the light component C5 oil distillation tower is introduced into the isohexane distillation tower for isohexane stripping to obtain an isohexane stripping gas phase and an isohexane distillation liquid phase; the isohexane stripping gas phase is introduced into the isohexane rectification tower for isohexane rectification to obtain an isohexane rectification gas phase and an isohexane rectification liquid phase, wherein the isohexane rectification gas phase escapes from the top of the tower and takes away isohexane, and the isohexane rectification liquid phase refluxes to the bottom of the tower and is reintroduced into the isohexane stripping tower. The tower bottom temperature of the isohexane distillation of the present invention is 90°C-110°C, and the tower bottom pressure is 100 KPa-130 KPa; the tower top temperature of the isohexane distillation is 70°C-80°C, the tower top pressure is 30 KPa-60 KPa, and the reflux ratio is 7-10.
[0014] After the remaining heavy components are obtained, the present invention uses dimethylformamide and N-methylpyrrolidone as solvents to sequentially perform n-hexane distillation and n-hexane rectification on the remaining heavy components to obtain n-hexane. Specifically, the remaining heavy components and the mixed solution of dimethylformamide and N-methylpyrrolidone are first subjected to n-hexane distillation to obtain a n-hexane distillation gas phase and a n-hexane distillation liquid phase. More specifically, the remaining heavy components and the mixed solvent of dimethylformamide and N-methylpyrrolidone are introduced into a n-hexane distillation tower for n-hexane distillation to obtain a n-hexane distillation gas phase and a n-hexane distillation liquid phase; wherein the n-hexane distillation gas phase contains a n-hexane component, which escapes from the top of the n-hexane distillation tower; the n-hexane distillation liquid phase contains C6 and above heavy components and solvent components such as N-methylpyrrolidone and dimethylformamide, which reflux to the bottom of the n-hexane distillation tower.
[0015] The present invention performs n-hexane distillation on the remaining heavy components to obtain a n-hexane distillation gas phase and a n-hexane distillation liquid phase, and then performs n-hexane rectification on the n-hexane distillation gas phase to obtain n-hexane. Specifically, the n-hexane distillation gas phase escaping from the top of the n-hexane distillation tower is introduced into the n-hexane distillation tower for n-hexane rectification to obtain a n-hexane distillation gas phase and a n-hexane distillation liquid phase; wherein the n-hexane distillation gas phase is the n-hexane product, which escapes from the top of the n-hexane distillation tower; and the n-hexane distillation liquid phase is refluxed to the bottom of the distillation tower. The present invention introduces the obtained n-hexane distillation liquid phase into the n-hexane distillation, and the n-hexane distillation is maintained at the aforementioned agent-to-oil ratio.
[0016] The present invention performs n-hexane distillation on the remaining heavy components to obtain a n-hexane distillation gas phase and a n-hexane distillation liquid phase, and then performs rectification and regeneration on the n-hexane distillation liquid phase to obtain a rectification and regeneration gas phase and a rectification and regeneration liquid phase, and then introduces the rectification and regeneration liquid phase into the n-hexane distillation. Specifically, the present invention performs n-hexane distillation on the remaining heavy components to obtain a n-hexane distillation gas phase and a n-hexane distillation liquid phase, and then introduces the rectification and regeneration liquid phase into the solvent regeneration tower for rectification and regeneration to obtain a rectification and regeneration gas phase and a rectification and regeneration liquid phase, wherein the rectification and regeneration gas phase contains heavy components above C6, which escape from the top of the solvent regeneration tower; the rectification and regeneration liquid phase contains solvent components such as dimethylformamide and N-methylpyrrolidone, which refluxes to the bottom of the solvent regeneration tower, and is introduced into the middle of the n-hexane distillation tower as the regenerated solvent for recycling, and the n-hexane distillation is maintained at the aforementioned agent-to-oil ratio. The tower top temperature of the distillation regeneration of the present invention is 70°C-80°C, the tower top pressure is 10 KPa-40 KPa, the tower bottom temperature is 190°C-230°C, the tower bottom pressure is 25 KPa-40 KPa, and the reflux ratio is 1-3.
[0017] The present invention provides a method for separating n-hexane. After separating the light component C5 oil and isohexane from hydrogenated saturated aromatics and olefin reforming raffinate oil, the present invention sequentially performs n-hexane stripping and n-hexane rectification on the obtained materials using dimethylformamide and N-methylpyrrolidone in a specific mass ratio as solvents, and n-hexane rectification can be performed at a relatively low agent-to-oil ratio, while achieving a methylcyclopentane mass content of 10% to 15% in the separated n-hexane. The separation process parameters of n-hexane are also controlled to better achieve the separation of n-hexane, promote the n-hexane rectification at a relatively low agent-to-oil ratio to obtain n-hexane with an appropriate methylcyclopentane mass content, and greatly reduce the energy consumption cost of the device. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 The figure is a simplified flow chart of the separation of n-hexane according to the present invention. DETAILED DESCRIPTION
[0019] The present invention discloses a method for separating n-hexane. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve the above. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in the present invention. The method and application of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the method and application of this article without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.
[0020] The present invention will be further described below in conjunction with embodiments:
[0021] Example 1
[0022] according to Figure 1 The process shown is used to separate n-hexane. Figure 1 The present invention is a simplified flow chart of the separation of n-hexane, and the specific steps are as follows:
[0023] a) The raffinate oil from the tank farm is hydrogenated with hydrogen from the pipeline network to remove aromatics and olefins.
[0024] b) The raffinate oil of hydrogenated saturated aromatics and olefins is used to separate the light component C5 oil. The bottom temperature of the distillation tower T101A for separating the C5 light component is 112°C and the bottom pressure is 225KPa; the top temperature of the distillation tower T101B is 65.6°C, the top pressure is 158KPa, and the reflux ratio is 9.5.
[0025] c) After separation of C5 oil, C6 oil is introduced to separate isohexane, wherein the bottom temperature of the isohexane separation distillation tower T102A is 93°C, and the bottom pressure is 115KPa; the top temperature of the distillation tower T102B is 70.5°C, the top pressure is 40KPa, and the reflux ratio is 9.5.
[0026] d) After separating isohexane, the bottom oil of T102 and the new NMP composite solvent are separated to obtain normal hexane, wherein the bottom temperature of the distillation tower T103A for normal hexane separation is 158°C and the bottom pressure is 112KPa; the gas phase at the top of T103A enters T103B, and the gas phase at the top of T103A contains not only normal hexane products but also solvents, which involves the control of the agent-oil ratio of T03B tower; and the liquid phase at the bottom of T103A tower is distilled and regenerated, and the liquid phase at the bottom of T103A tower contains the bottom oil and solvent after separating normal hexane. The top temperature of the distillation tower T103B for normal hexane separation is 75°C, the top pressure of the distillation tower T103B for normal hexane separation is 30KPa, the reflux ratio is 3.5, and the agent-oil ratio of T103B is controlled to be 3.5. The novel NMP composite solvent is obtained by mixing dimethylformamide (DMF) and N-methylpyrrolidone (NMP) in a ratio of DMF:NMP=1:11.
[0027] e) After separation of n-hexane, the bottom oil and solvent of T103A are introduced into the solvent regeneration tower T104 for solvent regeneration. The top temperature of T104 is 78°C, the top pressure is 20KPa, the bottom temperature is 210°C, the bottom pressure is 35KPa, and the reflux ratio is 1.7. The heavy oil above C6 is separated from the top of T104, and the bottom solvent is introduced into the middle of T103B for recycling.
[0028] The methylcyclopentane content in the n-hexane separated above is 12.3% (assessment index 10-15%).
[0029] Comparative Example 1
[0030] The method of Example 1 was used to separate n-hexane, except that in d), the ratio of DMF to NMP in the novel NMP composite solvent was 1:8.
[0031] The methylcyclopentane content in the n-hexane separated above is 8.2% (assessment index 10-15%).
[0032] Comparative Example 2
[0033] The method of Example 1 was used to separate n-hexane, except that in d), the ratio of DMF to NMP in the novel NMP composite solvent was 1:18.
[0034] The methylcyclopentane content in the n-hexane separated above is 18.6% (assessment index 10-15%).
[0035] Comparative Example 3
[0036] The method of Example 1 was used to separate n-hexane, except that in d), the ratio of DMF:NMP in the novel NMP composite solvent was 0:1.
[0037] The methylcyclopentane content in the n-hexane separated above is 20.2% (assessment index 10-15%).
[0038] Comparative Example 4
[0039] The method of Example 1 was used to separate n-hexane, except that in d), the ratio of DMF to NMP in the novel NMP composite solvent was 1:0.
[0040] The methylcyclopentane content in the n-hexane separated above is 3.4% (assessment index 10-15%).
[0041] Example 2
[0042] The method of Example 1 was used to separate n-hexane, except that the catalyst-to-oil ratio of T103B in d) was 4.5.
[0043] The methylcyclopentane content in the n-hexane separated above is 10.7% (assessment index 10-15%).
[0044] Comparative Example 5
[0045] The method of Example 1 was used to separate n-hexane, except that in d), the ratio of DMF:NMP of the new NMP composite solvent was 1:12, and the solvent-to-oil ratio of T103B was 2.5.
[0046] The methylcyclopentane content in the n-hexane separated above is 21.6% (assessment index 10-15%).
[0047] Comparative Example 6
[0048] The method of Example 1 was used to separate n-hexane, except that in d), the ratio of DMF:NMP of the new NMP composite solvent was 1:12, and the solvent-to-oil ratio of T103B was 6.5.
[0049] The methylcyclopentane content in the n-hexane separated above is 7.4% (assessment index 10-15%).
[0050] Comparative Example 7
[0051] The method of Example 1 was used to separate n-hexane, except that in d), the ratio of DMF:NMP of the new NMP composite solvent was 1:14, and the solvent-to-oil ratio of T103B was 2.5.
[0052] The methylcyclopentane content in the n-hexane separated above is 16.7% (assessment index 10-15%).
[0053] Example 3
[0054] The method of Example 1 was used to separate n-hexane, except that in d), the temperature at the bottom of T103A was 165°C, the pressure at the bottom of T103A was 115 kPa; the temperature at the top of T103B was 82°C, the pressure at the top of T103B was 71 KPa, and the reflux ratio was controlled to 3.
[0055] The methylcyclopentane content in the n-hexane separated above is 13.4% (assessment index 10-15%).
[0056] Comparative Example 8
[0057] The method of Example 3 was used to separate n-hexane, except that in d), the temperature at the bottom of T103A was 130°C, and the pressure at the bottom of T103A was 80 kPa; the temperature at the top of T103B was 65°C, and the pressure at the top of T103B was 8 KPa.
[0058] The methylcyclopentane content in the n-hexane separated above is 6.5% (assessment index 10-15%).
[0059] Comparative Example 9
[0060] The method of Example 3 was used to separate n-hexane, except that in d) the temperature at the bottom of tower T103A was 190°C, the pressure at the bottom of tower T103A was 150 kPa; the temperature at the top of tower T103B was 92°C, the pressure at the top of tower T103B was 102 KPa.
[0061] The methylcyclopentane content in the n-hexane separated above is 28.4% (assessment index 10-15%).
[0062] Comparative Example 10
[0063] The method of Example 3 was used to separate n-hexane, except that the reflux ratio of the T103B tower in d) was 1.5.
[0064] The methylcyclopentane content in the n-hexane separated above is 19.3% (assessment index 10-15%).
[0065] Comparative Example 11
[0066] The method of Example 3 was used to separate n-hexane, except that the reflux ratio of the T103B tower in d) was 7.5.
[0067] The methylcyclopentane content in the n-hexane separated above is 3.7% (assessment index 10-15%).
[0068] Some process parameters and product indicators of the above embodiments and comparative examples are listed in Table 1 and Table 2:
[0069] Table 1
[0070]
[0071] Table 2
[0072]
[0073] From the above implementation cases, it can be seen that the mixing ratio of NMP and DMF directly affects the solvent's agent-oil ratio. At a lower agent-oil ratio, the process operation requirements and product index requirements can be met. However, a too high DMF mixing ratio affects the separation of methylcyclopentane and n-hexane too thoroughly, resulting in a low methylcyclopentane content. Therefore, the appropriate composite solvent mixing ratio can effectively reduce the agent-oil ratio while ensuring the quality of n-hexane products, thereby reducing the energy consumption of the device.
[0074] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.
Claims
1. A method for separating n-hexane, characterized in that: The following steps are involved: S1) separating the light component C5 oil and isohexane from the hydrogenated saturated aromatics and olefin reforming raffinate to obtain the remaining heavy components; S2) using dimethylformamide and N-methylpyrrolidone in a mass ratio of 1:(10-15) as solvent, sequentially performing n-hexane distillation and n-hexane rectification on the remaining heavy components obtained in step S1) to obtain n-hexane; the n-hexane rectification is performed at a solvent-to-oil ratio of 3-5.
2. The separation method according to claim 1, characterized in that In step S2), the temperature of the n-hexane distillation is 150° C. to 170° C., and the pressure is 100 KPa to 120 KPa.
3. The separation method according to claim 1, characterized in that In step S2), the temperature of the n-hexane distillation is 70° C. to 85° C., and the pressure is 10 KPa to 80 KPa.
4. The separation method according to claim 3, characterized in that In step S2), the reflux ratio of the n-hexane distillation is 2-6.
5. The separation method according to claim 1, characterized in that In step S1), the hydrogenated saturated aromatics and olefin reforming raffinate oil is subjected to light component C5 oil stripping and light component C5 oil rectification to separate the light component C5 oil; The tower bottom temperature of the light component C5 oil distillation is 100°C~120°C, and the tower bottom pressure is 220 KPa~250 KPa; The tower top temperature of the light component C5 oil distillation is 60°C~70°C, and the tower top pressure is 150KPa~170KPa.
6. The separation method according to claim 5, characterized in that The reflux ratio of the light component C5 oil distillation is 9-12.
7. The separation method according to claim 1, characterized in that In step S1), after the hydrogenated saturated aromatics and olefin reforming raffinate oil are separated into light component C5 oil, isohexane stripping and isohexane rectification are performed; The tower bottom temperature of the isohexane distillation is 90°C to 110°C, and the tower bottom pressure is 100 KPa to 130 KPa; The tower top temperature of the isohexane distillation is 70°C to 80°C, and the tower top pressure is 30 KPa to 60 KPa.
8. The separation method according to claim 7, characterized in that The reflux ratio of the isohexane distillation is 7-10.
9. The separation method according to any one of claims 1 to 8, characterized in that After the n-hexane is stripped, a n-hexane stripping gas phase and a n-hexane stripping liquid phase are obtained, and the n-hexane stripping gas phase is subjected to the n-hexane rectification; the n-hexane stripping liquid phase is subjected to rectification and regeneration, and the liquid phase obtained by the rectification and regeneration is returned to the n-hexane rectification; The tower top temperature of the distillation regeneration is 70°C to 80°C, the tower top pressure is 10 KPa to 40 KPa, the tower bottom temperature is 190°C to 230°C, and the tower bottom pressure is 25 KPa to 40 KPa.
10. The separation method according to claim 9, characterized in that The reflux ratio of the distillation regeneration is 1-3.