Process and device for separating ethyl acetate and alkanes through azeotropic combined extractive distillation

Abstract

The invention belongs to the technical field of chemical separation, and discloses a process for separating ethyl acetate and alkanes by azeotropic combined extractive distillation, which comprises the following steps: S1, azeotropic distillation process: adding a raw material containing alkanes and ethyl acetate and an entrainer methanol into distillation equipment for azeotropic distillation; s2, an alkane crude product rectification process: returning the alkane crude product obtained in the step S1 to rectification equipment for rectification; s3, extractive distillation: returning the kettle liquid obtained in the step S1 to distillation equipment, and adding water as an extracting agent for extractive distillation; and S4, rectifying the crude ethyl acetate product, namely returning the crude ethyl acetate product obtained in the step S3 to rectifying equipment for rectifying. According to the present invention, the normal pressure azeotropic distillation and the normal pressure extractive distillation are combined to separate the ethyl acetate and the alkanes, especially the n-hexane or / and the n-heptane, such that the high-purity ethyl acetate and the high-purity alkanes are obtained, and the product yield is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical separation, and particularly relates to a process and device for separating ethyl acetate and alkanes by azeotropic combined extractive distillation. Background Art

[0002] Ethyl acetate and alkanes (n-hexane or n-heptane) are both important solvents and are widely used in fields such as medicine, rubber, and paint. In the final products, these solvents must be completely removed, thus forming waste organic solvent liquids. If these waste organic solvent liquids are discharged in large quantities without recovery, it will not only increase production costs and cause environmental pollution, but may also cause production accidents. Therefore, the recovery and utilization of these organic solvents has become an important issue.

[0003] Since ethyl acetate and n-hexane / n-heptane form an azeotrope under normal pressure, it is difficult to separate them by general distillation methods. Most pharmaceutical productions are carried out batchwise and have the characteristics of small batches. Drugs are usually obtained by reacting with many solvents as carriers. When n-hexane / n-heptane and ethyl acetate are used as the main solvents, various solvent impurities in the drugs are dissolved out. The contents of n-hexane / n-heptane and ethyl acetate obtained by conventional distillation methods are relatively low and cannot be returned to the pharmaceutical reaction section for use. The literature "Study on the Azeotropic Agent for the Batch Azeotropic Distillation of n-Hexane and Ethyl Acetate" (Petrochemical Technology, 2006, 35(1), 37) reported the azeotropic distillation with acetone as the azeotropic agent to separate ethyl acetate and n-hexane, and the yields of n-hexane and ethyl acetate obtained by atmospheric distillation and variable pressure distillation were 75.15% and 73.89% respectively. The literature "Simulation Calculation of the Extractive Distillation Process of Ethyl Acetate - n-Hexane" (Computers and Applied Chemistry, 2012, 29(8), 955) reported a method for continuously separating ethyl acetate and n-hexane by extractive distillation with DMF as the extractant. When the number of trays is 30, the feed tray of the raw material is 20, the feed tray of the extractant is 12, the solvent ratio is 3, and the reflux ratio is 4.5, ethyl acetate and n-hexane with purities of 99.0% are respectively obtained at the top of the two towers. The invention patent "System and Method for Separating the Azeotropic System of Ethyl Acetate and n-Hexane by Variable Pressure Distillation" with the application number CN201710244733.3 reported the method of separating ethyl acetate and n-hexane by variable pressure distillation, and the highest yields of ethyl acetate and n-hexane reached 73.89% and 75.15% respectively. However, the existing technology solutions have high energy consumption and unsatisfactory product yields. Summary of the Invention

[0004] In view of the above deficiencies of the existing technology, the present invention provides a process and device for separating ethyl acetate and alkanes by azeotropic combined extractive distillation, which can obtain high-purity ethyl acetate and alkanes, and at the same time improve the product yield.

[0005] The specific technical solutions are as follows:

[0006] One of the objectives of the present invention is to provide a process for separating ethyl acetate and alkanes by azeotropic combined extractive distillation, which comprises the following steps:

[0007] The specific technical solution is as follows:

[0008] One of the objectives of the present invention is to provide a process for separating ethyl acetate and alkanes by azeotropic combined extractive distillation, which comprises the following steps:

[0009] S1. Azeotropic distillation process

[0010] Adding the raw material containing alkanes and ethyl acetate and the azeotropic agent methanol into a distillation device for azeotropic distillation; obtaining a mixture of methanol and alkanes at the top of the distillation column, separating the phases of the mixture to obtain a methanol phase and a crude alkane product, and the crude alkane product is to be further distilled; the methanol phase is refluxed to the bottom of the column; the bottom liquid is a mixture of ethyl acetate and methanol, which is to be further distilled;

[0011] S2. Crude alkane distillation process

[0012] Returning the crude alkane product obtained in step S1 to the distillation device for distillation, successively obtaining a pre-fraction of a mixture of methanol and alkanes, a middle fraction of a mixture of alkanes and ethyl acetate, and a post-fraction of an alkane product; after phase separation of the pre-fraction, obtaining an alkane phase and a methanol phase, and the alkane phase is refluxed to the distillation device; the middle fraction is to be returned to the azeotropic distillation process; the bottom liquid is a mixture of alkanes and heavy-boiling substances, which is to be returned to the azeotropic distillation;

[0013] S3. Extractive distillation process

[0014] Returning the bottom liquid obtained in step S1 to the distillation device, adding water as an extractant for extractive distillation, and obtaining a mixture of ethyl acetate and water at the top of the distillation column; stopping adding water, and then distilling the bottom liquid, successively obtaining a pre-fraction of a mixture of ethyl acetate and methanol, a middle fraction of finished methanol, and a post-fraction of a mixture of methanol and water; after phase separation of the mixture of ethyl acetate and water, obtaining an aqueous phase and a crude ethyl acetate product; the pre-fraction is to be subjected to extractive distillation again;

[0015] S4. Crude ethyl acetate distillation process

[0016] Returning the crude ethyl acetate product obtained in step S3 to the distillation device for distillation, successively obtaining a pre-fraction of a mixture of ethyl acetate, methanol and water, a middle fraction of a mixture of ethyl acetate and water, and a post-fraction of a product of ethyl acetate; the pre-fraction is to be returned to the extractive distillation process; the middle fraction is to be returned to the distillation device for continuous distillation; the bottom liquid is a mixture of ethyl acetate and methanol, which is to be returned to the extractive distillation process.

[0017] Wherein, the distillation device includes a distillation column and a distillation kettle connected to the bottom of the distillation column.

[0018] The present invention adopts a method combining atmospheric azeotropic distillation and atmospheric extractive distillation to separate ethyl acetate from alkanes, especially n-hexane or / and n-heptane. There is a minimum azeotrope between ethyl acetate and the n-hexane or n-heptane material, and qualified ethyl acetate products and n-hexane or n-heptane products cannot be obtained by ordinary distillation methods. Methanol and n-hexane or n-heptane can form a lower-boiling azeotrope, and methanol and n-hexane / n-heptane will phase-separate in a low-temperature environment. Therefore, an atmospheric azeotropic extractive distillation process is designed to separate the ethyl acetate and n-hexane or n-heptane material. An azeotrope of methanol and n-hexane or n-heptane is obtained at the top of the column. The heavy-phase methanol after phase separation of methanol and n-hexane or n-heptane is fully refluxed, and the light-phase n-hexane or n-heptane crude product is taken out to a water-washing kettle and then returned to the kettle to obtain qualified n-hexane / n-heptane products through an atmospheric batch distillation process.

[0019] Further, the alkanes are preferably n-hexane or / and n-heptane.

[0020] Further, the content of ethyl acetate in the raw material is preferably 5 wt% to 65 wt%, more preferably 30 wt% to 50 wt%; the content of alkanes is preferably 35 wt% to 90 wt%, more preferably 50 wt% to 70 wt%.

[0021] Further, the raw material containing alkanes and ethyl acetate may also contain methanol. Since methanol is used as an azeotropic agent in the present invention, the presence of methanol in the raw material does not affect the separation of each component.

[0022] Further, the bottom liquid in step S1 is to be returned to the azeotropic distillation process for further distillation separation.

[0023] Further, in step S1, the mixture of methanol and alkanes is condensed and then phase-separated.

[0024] Further, in step S1, the mass ratio of the raw material to methanol in the feed is preferably (1 - 5):1.

[0025] Further, the azeotropic distillation in step S1 is carried out at atmospheric pressure.

[0026] Specifically, in step S1: the top temperature is preferably 40 - 50 °C, the bottom temperature is preferably 60 - 70 °C; the reflux ratio is preferably R = 0.5 - 4; the raw material is fed into the bottom of the column.

[0027] Further, in step S2, the bottom liquid after distillation is mainly alkanes and a small amount of heavy-boiling substances, and is to be returned to the azeotropic distillation process.

[0028] Further, in step S2, the pre-fraction is condensed and then phase-separated.

[0029] Further, the distillation in step S2 is carried out at atmospheric pressure.

[0030] Specifically, in step S2: the bottom temperature is preferably 70 - 100 °C; the reflux ratio is preferably R = 1 - 6; feed the bottom; when the top temperature rises to the azeotropic point or boiling point of the corresponding fraction, start to extract the corresponding fraction.

[0031] Furthermore, in step S3, send the methanol to the azeotropic distillation process as the azeotropic agent.

[0032] Furthermore, in step S3, reflux the aqueous phase obtained by phase separation to the rectification equipment.

[0033] Furthermore, in step S3, the mass ratio of the bottom liquid to be extractively distilled to water is preferably 1:(1 - 3).

[0034] Furthermore, in step S3, the water as the extractant is continuously added from the middle of the distillation column. Adding water for extractive distillation is a continuous process; water is continuously added. Since methanol is soluble in water, the azeotrope of methanol and ethyl acetate is destroyed at this stage, and ethyl acetate and water are first extracted from the top of the column.

[0035] Furthermore, the extractive distillation in step S3 is carried out under atmospheric pressure.

[0036] Specifically, in step S3: when adding water for extractive distillation, the top temperature is preferably 69.0 - 71.0 °C, and the bottom temperature is preferably 75 - 86 °C.

[0037] Specifically, in step S3: in the stage of rectifying the bottom liquid after stopping adding water, the bottom temperature is preferably 70 - 100 °C; when the top temperature rises to the azeotropic point or boiling point of the corresponding fraction, start to extract the corresponding fraction.

[0038] Specifically, in step S3: if the bottom liquid obtained in step S1 still contains a small amount of alkanes, pretreatment can be carried out to rectify and remove impurities; the impurity removal conditions are as follows: the top temperature is preferably 50 - 70 °C, and the bottom temperature is preferably 60 - 80 °C.

[0039] Specifically, in step S3: the reflux ratio is preferably R = 2 - 6; feed the bottom.

[0040] Furthermore, the rectification in step S4 is carried out under atmospheric pressure.

[0041] Specifically, in step S4: the bottom temperature is preferably 70 - 80 °C; the reflux ratio is preferably R = 0.5 - 3; feed the bottom; when the top temperature rises to the azeotropic point or boiling point of the corresponding fraction, start to extract the corresponding fraction.

[0042] Furthermore, in step S2, after washing the methanol phase obtained by phase separation, a methanol and water mixture is obtained, and methanol recovery is carried out.

[0043] Furthermore, after washing the methanol phase obtained by phase separation in step S2, methanol recovery is carried out.

[0044] Furthermore, the post-fraction methanol and water mixture obtained in step S3 is subjected to methanol recovery.

[0045] Specifically, the methanol recovery includes: returning the methanol and water mixture to the distillation equipment for distillation, withdrawing the pre-fraction for return to azeotropic distillation; the middle fraction is finished methanol; the post-fraction is a methanol and water mixture for re-distillation and recovery; the bottom liquid is water and is sent outside the battery limit. The methanol recovery conditions are preferably: the bottom temperature is 75 - 101 °C, and the reflux ratio is 1 - 5; when the top temperature rises to the azeotropic point or boiling point of the corresponding fraction, the corresponding fraction is withdrawn.

[0046] The second object of the present invention is to provide an apparatus for separating ethyl acetate and alkanes by azeotropic combined extractive distillation, and the above process can be completed using this apparatus. The apparatus includes a distillation equipment, a process water tank, an ethyl acetate / alkane mother liquor tank, and a tank for the ethyl acetate / methanol mixture to be recovered; the distillation equipment includes a distillation column and a reboiler connected to the bottom of the distillation column; the process water tank, the ethyl acetate / alkane mother liquor tank, and the tank for the ethyl acetate / methanol mixture to be recovered all lead to the distillation equipment; the reboiler leads to the tank for the ethyl acetate / methanol mixture to be recovered;

[0047] The top of the distillation column is sequentially connected to a condenser, a phase separator, and a water washing kettle, and the water washing kettle leads to the reboiler;

[0048] The condenser leads to an ethyl acetate / water phase separation tank, a pre-fraction tank, an alkane product tank, a methanol / water mixture tank to be recovered, an ethyl acetate product withdrawal tank, and a methanol finished product tank respectively. The ethyl acetate / water phase separation tank leads to the tank for the ethyl acetate / methanol mixture to be recovered, and the pre-fraction tank leads to the ethyl acetate / alkane mother liquor tank and the tank for the ethyl acetate / methanol liquid to be recovered respectively.

[0049] Furthermore, the water washing kettle leads to the methanol / water mixture tank to be recovered, and the methanol / water mixture tank to be recovered leads to the reboiler.

[0050] Furthermore, the condenser is two-stage, including a primary condenser and a secondary condenser.

[0051] Furthermore, the condenser is connected to a top trap. After passing through the condenser, the uncondensable tail gas enters the gas trap.

[0052] Furthermore, a top cooler is connected between the condenser and the phase separator.

[0053] Specifically, the apparatus of the present invention may further include pumps for controlling the flow of materials.

[0054] The beneficial effects of the present invention are as follows:

[0055] The present invention adopts a combination of atmospheric azeotropic distillation and atmospheric extractive distillation to separate ethyl acetate from alkanes, especially n - hexane or / and n - heptane. Methanol is used as the azeotropic agent in the present invention. Methanol is easy to recover, has good physical properties, and good economy. The azeotropic agent can be introduced from the outside or the methanol recovered within the system, achieving high - efficiency recovery and utilization of resources. Water is used as the extractant in the extractive distillation of ethyl acetate and methanol in the present invention. Water as the extractant is more environmentally friendly, has a large solubility, and after the separation of ethyl acetate, the remaining methanol and water are easier to separate, and the separation efficiency is high, and the technology is mature. The present invention can obtain n - hexane / n - heptane, ethyl acetate and methanol with relatively high purity, and products with n - hexane purity > 99.5%, n - heptane purity > 99.0%, ethyl acetate purity > 99.5%, and methanol purity > 99.5% can be obtained; the yield of alkanes in the present invention is not less than 85%, and the yield of ethyl acetate is not less than 80%. Ensure continuous feeding of the methanol azeotropic agent at the top of the tower until all n - hexane with a purity > 99.5% is distilled out. The present invention is an intermittent reaction, with advantages such as small production batch and low equipment investment. Description of the Drawings

[0056] Figure 1 It is a schematic diagram of the device and process for separating ethyl acetate from alkanes by azeotropic combined extractive distillation in the specific embodiment of the present invention;

[0057] In the figure: 1. Process water tank; 2. Process water feed pump; 3. Ethyl acetate / alkane mother liquor tank; 4. Mother liquor feed pump; 5. Ethyl acetate / methanol mixed liquid tank to be recycled; 6. Ethyl acetate / methanol feed pump; 7. Distillation column; 8. Distillation kettle; 9. Bottom product pump; 10. Primary condenser; 11. Secondary condenser; 12. Top cooler; 13. Phase separator; 14. Top trap; 15. Ethyl acetate / water phase separation tank; 16. Pre - fraction tank; 17. Alkane product tank; 18. Washing kettle; 19. Methanol feed pump; 20. Alkane product pump; 21. Methanol / water mixed liquid tank to be recycled; 22. Methanol / water transfer pump; 23. Ethyl acetate product tank; 24. Ethyl acetate product pump; 25. Washing kettle product pump; 26. Methanol product tank. Specific Embodiments

[0058] The principles and features of the present invention are described below in conjunction with examples. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0059] Example 1

[0060] An apparatus for separating ethyl acetate from alkanes by azeotropic combined extractive distillation, comprising distillation equipment, a process water tank 1, an ethyl acetate / alkane mother liquor tank 3, and an ethyl acetate / methanol mixed liquid tank 5 to be recycled;

[0061] The described rectification equipment includes a rectification column 7 and a rectification still 8 connected to the bottom of the rectification column; the process water tank 1, the ethyl acetate / alkane mother liquor tank 3, and the ethyl acetate / methanol mixed liquid tank 5 to be recycled all lead to the rectification equipment; the rectification still 8 leads to the ethyl acetate / methanol mixed liquid tank 5 to be recycled; a process water feed pump 2 is provided on the pipeline where the process water tank 1 leads to the rectification column 7, a mother liquor feed pump 4 is provided on the pipeline where the ethyl acetate / alkane mother liquor tank 3 leads to the rectification column 7, an ethyl acetate / methanol feed pump 6 is provided on the pipeline where the ethyl acetate / methanol mixed liquid tank 5 to be recycled leads to the rectification column 7, and a bottom draw pump 9 is provided on the pipeline where the rectification still 8 leads to the ethyl acetate / methanol mixed liquid tank 5 to be recycled;

[0062] The top of the described rectification column 7 is successively connected to a condenser, a top cooler 12, a phase separator 13, and a water washing still 18, and the water washing still 18 leads to the rectification still 8; the condenser successively includes a primary condenser 10 and a secondary condenser 11, both leading to the top cooler 12; a water washing still draw pump 25 is provided on the pipeline where the water washing still 18 leads to the rectification still 8; the water washing still 18 leads to the methanol / water mixed liquid tank 21 to be recycled, the methanol / water mixed liquid tank 21 to be recycled leads to the rectification still 8, and a methanol / water transfer pump 22 is provided on the pipeline where the methanol / water mixed liquid tank 21 to be recycled leads to the rectification still 8; the secondary condenser 11 is connected to a top trap 14;

[0063] After the condenser is connected to the top cooler 12, it then leads to an ethyl acetate / water phase separation tank 15, a fore-fraction tank 16, an alkane product tank 17, a methanol / water mixed liquid tank 21 to be recycled, an ethyl acetate product tank 23, and a methanol finished product tank 26 respectively. The ethyl acetate / water phase separation tank 15 leads to the ethyl acetate / methanol mixed liquid tank 5 to be recycled, and the fore-fraction tank 16 leads to the ethyl acetate / alkane mother liquor tank 3 and the ethyl acetate / methanol mixed liquid tank 5 to be recycled respectively; an alkane product draw pump 20 is provided on the output pipeline of the alkane product tank 17, and an ethyl acetate product draw pump 24 is provided on the output pipeline of the ethyl acetate product tank 23; the methanol finished product tank 26 leads to the rectification column 7, and a methanol feed pump 19 is provided on the pipeline where the methanol finished product tank 26 leads to the rectification column 7.

[0064] Using the above device, the process of the present invention is applied to separate the waste liquid containing n-hexane and ethyl acetate. The composition of the waste liquid to be recycled is as follows: n-hexane 56.2 wt%, ethyl acetate 43.6 wt%, and the balance is impurities 0.02 wt%.

[0065] The process steps are as follows:

[0066] S1. Azeotropic rectification process

[0067] The waste liquid raw material in the ethyl acetate / alkane mother liquor tank 3 is transported from the bottom of the distillation column to the distillation kettle 8, and methanol is added as an azeotropic agent from the top of the distillation column 7 for azeotropic distillation; the azeotropic distillation process is carried out under atmospheric pressure, the top temperature is 45 °C, the bottom temperature is 68 °C, and the reflux ratio is maintained at R = 1.5 ± 0.5; the raw material is fed into the bottom of the column; the mass ratio of the raw material to methanol in the feed is 4:1.

[0068] The top of the distillation column 7 is condensed in two stages to obtain a mixture of methanol and n-hexane. After cooling the mixture, it is phase-separated by the phase separator 13 to obtain a methanol phase and a crude n-hexane product; the phase separation temperature is maintained at 15 ± 5 °C; the methanol phase is refluxed to the bottom of the column, and the crude n-hexane product enters the water-washing kettle 18, and after water-washing, it is ready to be returned to the kettle for further distillation; the bottom liquid of the distillation kettle 8 is a mixture of ethyl acetate and methanol, which enters the ethyl acetate / methanol mixed liquid tank 5 to be recovered for further distillation.

[0069] S2. Refining process of crude alkane

[0070] The washed crude n-hexane obtained in step S1 is returned to the distillation kettle 8 for distillation; the distillation process is carried out under atmospheric pressure, the bottom temperature is 79 °C, and the reflux ratio is maintained at R = 5 ± 1; the raw material is fed into the bottom of the column; the top of the column successively obtains a pre-fraction methanol and alkane mixture, an intermediate fraction alkane and ethyl acetate mixture, and a post-fraction alkane product; when the top temperature reaches 58 °C, it enters the pre-fraction stage, and the reflux ratio is R = 5; when the top temperature reaches 65 °C, it enters the intermediate fraction stage, and the reflux ratio is R = 6; when the top temperature reaches 68 °C, it enters the post-fraction stage, and the reflux ratio is R = 4.

[0071] The pre-fraction is condensed, cooled and phase-separated to obtain a n-hexane phase and a methanol phase, and the phase separation temperature is maintained at 15 ± 5 °C; the n-hexane phase is refluxed into the distillation column 7, and the methanol phase enters the water-washing kettle 18, and after water-washing, it enters the methanol / water mixed liquid tank 21 to be recovered by distillation; the intermediate fraction first enters the pre-fraction tank 16, and then enters the ethyl acetate / alkane mother liquor tank 3, waiting to be returned to the azeotropic distillation process; the bottom liquid of the distillation kettle 8 is a mixture of n-hexane and ethyl acetate, which enters the ethyl acetate / alkane mother liquor tank 3 and waits to be returned to the azeotropic distillation; the post-fraction n-hexane product enters the alkane product tank 17 and is withdrawn.

[0072] S3. Extractive distillation process

[0073] The bottom liquid obtained in step S1 is returned to the bottom of the distillation column, and first undergoes pretreatment distillation to remove impurities, and the azeotrope of alkane and methanol is withdrawn from the top; the pretreatment distillation process is carried out under atmospheric pressure, the top temperature is 55 °C, the bottom temperature is 64 °C; the reflux ratio is maintained at R = 2.5 ± 0.5; the raw material is fed into the bottom of the column.

[0074] After impurity removal, water is added for extractive distillation, and a mixture of ethyl acetate and water is obtained at the top of the column. The extractive distillation process is carried out at atmospheric pressure, with the top temperature of 71 °C, the bottom temperature of 85 °C, and the reflux ratio maintained at R = 2.5 ± 0.5. The number of trays is 25, and water is continuously added as the extractant from the 10th tray. The mass ratio of the bottom liquid to be extractively distilled to water is 1:3.

[0075] Stop adding water and rectify the bottom liquid. The rectification process is carried out at atmospheric pressure, with the bottom temperature ranging from 85 to 100 °C. At the top of the column, a mixture of ethyl acetate and methanol as the fore-fraction, pure methanol as the middle-fraction product, and a mixture of methanol and water as the after-fraction are obtained in sequence. When the top temperature reaches 62 °C and the bottom temperature reaches 85 °C, it enters the fore-fraction stage, with a reflux ratio of R = 3. When the top temperature reaches 63.2 °C and the bottom temperature reaches 90 °C, it enters the middle-fraction stage, with a reflux ratio of R = 2. When the top temperature reaches 64.8 °C and the bottom temperature reaches 100 °C, it enters the after-fraction stage, with a reflux ratio of R = 3.

[0076] The mixture of ethyl acetate and water is condensed and cooled, then enters the ethyl acetate / water phase separator 15 for phase separation to obtain the aqueous phase and crude ethyl acetate. The phase separation temperature is maintained at 15 ± 5 °C. The aqueous phase is refluxed, and the crude ethyl acetate enters the ethyl acetate / methanol mixed liquid tank 5 to be recovered for re-rectification. The fore-fraction is condensed and cooled, then enters the fore-fraction tank 16 to be re-entered into the extractive distillation process. The middle-fraction pure methanol is condensed and cooled, then enters the methanol product tank 26 and is sent to the azeotropic distillation process as the azeotropic agent. The after-fraction is condensed and cooled, then enters the methanol / water mixed liquid tank 21 to be recovered by rectification. The bottom liquid of the rectification still 8 is water and is sent out of the battery limit.

[0077] S4. Rectification process for crude ethyl acetate

[0078] Return the crude ethyl acetate obtained in step S3 to the bottom of the rectification tower 7 through the rectification still 8 for rectification. The rectification process is carried out at atmospheric pressure, with the bottom temperature ranging from 72 to 80 °C, and the reflux ratio maintained at R = 1.5 ± 0.5. Feed at the bottom of the column. At the top of the column, a mixture of ethyl acetate, methanol, and water as the fore-fraction, a mixture of ethyl acetate and water as the middle-fraction, and the product ethyl acetate as the after-fraction are obtained in sequence. When the top temperature reaches 53 °C and the bottom temperature reaches 72 °C, it enters the fore-fraction stage, with a reflux ratio of R = 2. When the top temperature reaches 71 °C and the bottom temperature reaches 75 °C, it enters the middle-fraction stage, with a reflux ratio of R = 2. When the top temperature reaches 77 °C and the bottom temperature reaches 80 °C, it enters the after-fraction stage, with a reflux ratio of R = 1.5.

[0079] The overhead fraction enters the overhead fraction tank 16 after condensation and cooling, and is to be returned to the extractive distillation process; the middle fraction is returned to the distillation equipment for continuous distillation after water washing; the bottom fraction product ethyl acetate enters the ethyl acetate product tank after condensation and cooling. The bottom liquid of the distillation kettle 8 is a mixture of ethyl acetate and methanol, which is sent to the ethyl acetate / methanol mixed liquid tank 5 to be recovered and returned to the extractive distillation process.

[0080] S5. Methanol / Water Distillation Process

[0081] The liquid in the methanol / water mixed liquid tank to be recovered is transported to the distillation tower kettle for distillation; the distillation process is under atmospheric pressure, the tower kettle temperature is 78 - 101 °C, and the reflux ratio is maintained at R = 2.5 ± 0.5; feeding at the tower kettle; the overhead fraction is drawn and sent to the ethyl acetate / alkane mother liquid tank 3 to be returned to the azeotropic distillation; the middle fraction is the finished methanol, which enters the methanol product tank 26 after condensation and cooling and is sent to the azeotropic distillation process as an azeotropic agent; the bottom fraction is a mixture of methanol and water, which enters the methanol / water mixed liquid tank 21 to be recovered and is to be distilled again; when the top temperature reaches 63 °C and the tower kettle temperature reaches 78 °C, it enters the overhead fraction stage with a reflux ratio of R = 3; when the top temperature reaches 65 °C and the tower kettle temperature reaches 90 °C, it enters the middle fraction stage with a reflux ratio of R = 2; when the top temperature reaches 71 °C and the tower kettle temperature reaches 101 °C, it enters the bottom fraction stage with a reflux ratio of R = 3. The bottom liquid of the distillation kettle 8 is water and is sent outside the battery limit.

[0082] The purity of n - hexane obtained by the above process is 99.8%, the purity of ethyl acetate is 99.8%, the purity of methanol is 99.9%, the recovery rate of n - hexane is 92.8%, and the recovery rate of ethyl acetate is 88.3%.

[0083] Example 2

[0084] Using the device in Example 1, the process of the present invention is applied to separate the waste liquid containing n - heptane and ethyl acetate. The composition of the waste liquid to be recovered is as follows: n - heptane 65.10 wt%, ethyl acetate 34.87 wt%, and 0.03 wt% is impurities.

[0085] The process steps refer to Example 1, and n - hexane in the process step description of Example 1 is replaced by n - heptane.

[0086] In step S1, the specific parameters are as follows: under atmospheric pressure operation, the top temperature is 50 °C, the tower kettle temperature is 63.5 °C; the reflux ratio is maintained at R = 2.5 ± 0.5, feeding at the tower kettle of the raw material; the mass ratio of the raw material to methanol is 1.5:1; the phase separation temperature is maintained at 15 ± 5 °C.

[0087] In step S2, the specific parameters are as follows: operating at atmospheric pressure, reflux ratio maintained at R = 3.0 ± 0.5; the temperature of the bottom of the column is 72 - 99 °C, and feeding at the bottom of the column; when the top temperature reaches 60 °C and the bottom temperature is 72 °C, entering the pre-fraction stage, reflux ratio R = 3.5; when the top temperature reaches 77 °C and the bottom temperature is 88 °C, entering the middle-fraction stage, reflux ratio R = 3; when the top temperature reaches 97 °C and the bottom temperature is 99 °C, entering the post-fraction stage, reflux ratio R = 2.5; the phase separation temperature is maintained at 15 ± 5 °C.

[0088] In step S3, the specific parameters are as follows:

[0089] The process of rectification for impurity removal is carried out at atmospheric pressure, with the top temperature of 65 °C and the bottom temperature of 70 °C; the reflux ratio is maintained at R = 4.0 ± 0.5; the bottom liquid obtained in step S1 is fed from the bottom of the column;

[0090] For the extractive rectification process with water addition, the top temperature is 70 °C, the bottom temperature is 77 °C, and the reflux ratio is maintained at R = 4.0 ± 0.5; the number of trays is 25, and water is continuously added as the extractant from the 10th tray; the mass ratio of the bottom liquid to be extractively rectified to water is 1:1;

[0091] The process of rectifying the bottom liquid after stopping water addition is carried out at atmospheric pressure, with the bottom temperature of 70 - 100 °C; the top fraction is successively obtained as a mixture of ethyl acetate and methanol, the middle fraction is the finished product methanol, and the post-fraction is a mixture of methanol and water; when the top temperature reaches 62 °C and the bottom temperature is 70 °C, entering the pre-fraction stage, reflux ratio R = 4; when the top temperature reaches 63.8 °C and the bottom temperature is 77 °C, entering the middle-fraction stage, reflux ratio R = 2; when the top temperature is 65 °C and the bottom temperature is 100 °C, entering the post-fraction stage, reflux ratio R = 3.5; the phase separation temperature is maintained at 15 ± 5 °C.

[0092] In step S4, the specific parameters are as follows: operating at atmospheric pressure, the bottom temperature is 73 - 77 °C; the reflux ratio is maintained at R = 1.5 ± 0.5; feeding at the bottom of the column; when the top temperature reaches 60 °C and the bottom temperature is 73 °C, entering the pre-fraction stage, reflux ratio R = 2; when the top temperature reaches 71 °C and the bottom temperature is 75 °C, entering the middle-fraction stage, reflux ratio R = 1.5; when the top temperature reaches 76 °C and the bottom temperature is 77 °C, entering the post-fraction stage, reflux ratio R = 1.

[0093] In step S5, the specific parameters are as follows: operating at atmospheric pressure, the column bottom temperature is 75 - 101 °C; the reflux ratio is maintained at R = 4 ± 0.5; when the top temperature reaches 63 °C and the column bottom temperature is 75 °C, it enters the pre-fraction stage with a reflux ratio of R = 3.5; when the top temperature reaches 65 °C and the column bottom temperature is 90 °C, it enters the middle fraction stage with a reflux ratio of R = 3.5; when the top temperature reaches 71 °C and the column bottom temperature is 101 °C, it enters the post-fraction stage with a reflux ratio of R = 4.0.

[0094] The obtained n-heptane purity is 99.5%, ethyl acetate purity is 99.8%, methanol purity is 99.9%, n-heptane recovery rate is 91.3%, and ethyl acetate recovery rate is 86.4%.

[0095] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A process for separating ethyl acetate and alkanes by azeotropic combined extractive distillation, characterized in that: The steps include: S1. Azeotropic distillation process The raw material containing alkanes and ethyl acetate and the azeotropic agent methanol are added to the distillation equipment for azeotropic distillation; a mixture of methanol and alkanes is obtained at the top of the distillation tower, and the mixture is phase-separated to obtain a methanol phase and a crude alkane product, and the crude alkane product is to be further distilled; the methanol phase is refluxed to the bottom of the tower; the bottom liquid is a mixture of ethyl acetate and methanol, which is to be further distilled; S2. Alkane crude product distillation process The crude alkane product obtained in step S1 is returned to the distillation equipment for distillation to obtain a front fraction of methanol and alkane mixture, an intermediate fraction of alkane and ethyl acetate mixture, and a rear fraction of alkane product in sequence; after the front fraction is phase-separated, an alkane phase and a methanol phase are obtained, and the alkane phase is refluxed to the distillation equipment; the intermediate fraction is returned to the azeotropic distillation process; S3. Extraction and distillation process The bottom liquid obtained in step S1 is returned to the distillation equipment, and water is added as an extractant for extractive distillation, and a mixture of ethyl acetate and water is obtained at the top of the distillation tower; the addition of water is stopped, and the bottom liquid is distilled again to obtain a front fraction of ethyl acetate and methanol mixture, an intermediate fraction of finished methanol, and a rear fraction of methanol and water mixture in sequence; after the mixture of ethyl acetate and water is phase-separated, an aqueous phase and a crude ethyl acetate are obtained; the front fraction is to be extracted and distilled again; S4. Ethyl acetate crude product distillation process The crude ethyl acetate obtained in step S3 is returned to the distillation equipment for distillation to obtain the front fraction ethyl acetate, a mixture of methanol and water, the middle fraction ethyl acetate and water, and the rear fraction product ethyl acetate in sequence; the front fraction is to be returned to the extraction distillation process; the middle fraction is to be returned to the distillation equipment for further distillation; the kettle liquid is a mixture of ethyl acetate and methanol, which is to be returned to the extraction distillation process.

2. The process according to claim 1, characterized in that The alkanes are n-hexane and / or n-heptane.

3. The process according to claim 1, characterized in that The raw material containing alkanes and ethyl acetate also contains methanol.

4. The process according to claim 1, characterized in that The kettle liquid in step S1 is to be returned to the azeotropic distillation process.

5. The process according to claim 1, characterized in that In step S3, methanol is sent to the azeotropic distillation process as an azeotropic agent.

6. The process according to claim 1, characterized in that In step S3, the aqueous phase obtained by phase separation is refluxed to the distillation equipment.

7. The process according to claim 1, characterized in that The methanol phase obtained by phase separation in step S2 is washed with water and then methanol is recovered; The methanol and water mixture in the rear fraction obtained in step S3 is subjected to methanol recovery.

8. The process according to claim 7, characterized in that The methanol recovery includes: returning the methanol and water mixture to the distillation equipment for distillation, taking out the front fraction to be returned for azeotropic distillation; the middle fraction is the finished methanol; and the rear fraction is the methanol and water mixture to be distilled and recovered again.

9. A device for separating ethyl acetate and alkanes by azeotropic combined extraction and distillation, characterized in that: The invention comprises a distillation device, a process water tank (1), an ethyl acetate / alkane mother liquid tank (3) and an ethyl acetate / methanol mixed liquid tank (5) to be recovered; the distillation device comprises a distillation tower (7) and a distillation kettle (8) connected to the bottom of the distillation tower; the process water tank (1), the ethyl acetate / alkane mother liquid tank (3) and the ethyl acetate / methanol mixed liquid tank (5) to be recovered all lead to the distillation device; the distillation kettle (8) leads to the ethyl acetate / methanol mixed liquid tank (5) to be recovered; The top of the distillation tower (7) is connected to a condenser, a phase separator (13) and a water washing kettle (18) in sequence, and the water washing kettle (18) leads to the distillation kettle (8); The condenser is connected to an ethyl acetate / water phase tank (15), a fore fraction tank (16), an alkane product tank (17), a methanol / water mixed liquid tank (21) to be recovered, an ethyl acetate product tank (23) and a methanol finished product tank (26) respectively; the ethyl acetate / water phase tank (15) is connected to an ethyl acetate / methanol mixed liquid tank (5) to be recovered; and the fore fraction tank (16) is connected to an ethyl acetate / alkane mother liquid tank (3) and an ethyl acetate / methanol mixed liquid tank (5) to be recovered respectively.

10. The device according to claim 9, characterized in that The water washing kettle (18) leads to the methanol / water mixed liquid tank (21) to be recovered, and the methanol / water mixed liquid tank (21) to be recovered leads to the distillation kettle (8).

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