A method for purifying hexamethylenediamine with low energy consumption

Abstract

The present invention provides a method for purifying hexamethylenediamine with low energy consumption, comprising the following steps: 1) extracting hexamethylenediamine and impurities from water using ionic liquid from an aqueous reaction liquid coming out of a hexamethylenediamine reaction system to obtain an extraction mixture; 2) subjecting the extraction mixture obtained in step 1) to static stratification, discharging the aqueous phase as wastewater, and the organic phase being a mixture of ionic liquid, hexamethylenediamine and impurities; 3) separating the organic phase obtained in step 2), obtaining crude hexamethylenediamine at the top, and obtaining ionic liquid at the bottom and returning to step 1) for recycling of the extractant; 4) allowing the crude hexamethylenediamine obtained in step 3) to enter a bulkhead tower to remove light / heavy component impurities, and obtaining a hexamethylenediamine product with a purity greater than 99.9wt%. The method of the present invention removes water and light and heavy component impurities in the reaction liquid by means of ionic liquid extraction and bulkhead tower technology, which can greatly reduce energy consumption and equipment costs, and create higher economic benefits.

Description

Technical Field

[0001] The invention belongs to the technical field of separation and purification, and particularly relates to a method for purifying hexamethylenediamine with low energy consumption. Background Art

[0002] Hexamethylenediamine is an important bifunctional compound with two reactive functional groups in the molecule, which can generate a variety of important chemicals. Hexamethylenediamine is the main raw material for the manufacture of polyamide (nylon) fibers and resins, and is also the main raw material for high-grade polyurethane hexamethylene diisocyanate (HDI). It can also be used to manufacture curing agents and crosslinking agents for resins.

[0003] Among them, the refining process of hexamethylenediamine is very critical. At present, companies producing hexamethylenediamine such as DuPont in the United States, Asahi Kasei in Japan, and Henan Shenma all use conventional distillation equipment to produce hexamethylenediamine. Although this process has greater operational flexibility and can achieve the purity required by the market, it has disadvantages such as a long process flow, high equipment investment cost, and high energy consumption. In addition, conventional distillation and dehydration of the reaction liquid may cause salt to enter the crude hexamethylenediamine, blocking the downstream separation system.

[0004] Patent CN10423623B discloses a method for depolymerization and recovery of high-temperature resistant nylon poly(hexamethylene terephthalamide), wherein sodium hydroxide and water are added to a reactor, and after dissolving, crushed nylon PA6T is added to obtain an alkaline hydrolysis solution, which is passed through a filter into a separation and extraction section, and is extracted and separated with an aromatic hydrocarbon / alcohol mixed extractant to obtain a crude hexamethylenediamine extract and a sodium terephthalate salt extract. The crude hexamethylenediamine extract is distilled to obtain an extraction solvent and refined hexamethylenediamine, respectively. The patented process for recovering hexamethylenediamine will introduce a highly volatile, toxic and flammable extractant in actual industrial production, and the distillation process will also be relatively long and complicated.

[0005] Therefore, there is still a need for a new method for purifying hexamethylenediamine with low energy consumption. Summary of the invention

[0006] In view of the above problems existing in the prior art, the present invention provides a new method for purifying hexamethylenediamine with low energy consumption.

[0007] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solution:

[0008] A method for purifying hexamethylenediamine with low energy consumption comprises the following steps:

[0009] 1) extracting hexamethylenediamine and impurities from water using an ionic liquid as an extractant from the aqueous reaction liquid coming out of the hexamethylenediamine reaction system to obtain an extraction mixed liquid;

[0010] 2) the extraction mixture obtained in step 1) is allowed to stand for stratification, the aqueous phase is discharged as waste water, and the organic phase is a mixture of ionic liquid, hexamethylenediamine and impurities;

[0011] 3) separating the organic phase obtained in step 2) to obtain crude hexamethylenediamine at the top and ionic liquid at the bottom, which are then returned to step 1) for recycling of the extractant;

[0012] 4) The crude hexamethylenediamine obtained in step 3) enters a dividing wall tower to remove light and heavy impurities to obtain a hexamethylenediamine product with a purity greater than 99.9 wt %.

[0013] In a specific embodiment, the ionic liquid consists of two parts: a cation M+ and an anion N-; the cation M+ is an imidazole-type cation with a disubstituted group; the anion N- is hexafluorophosphate; preferably, the two substituent groups in the disubstituted group are different, one of which is a straight-chain alkenyl of C7 to C10, and the other is an alkyl of C1 to C2.

[0014] In a specific embodiment, the mass ratio of the ionic liquid used as the extractant in step 1) to the aqueous reaction liquid from the hexamethylenediamine reaction system is 0.1-3, preferably 0.3-1.

[0015] In a specific embodiment, step 1) and step 2) are completed in the same device or in two devices respectively; preferably, the same device is selected from any one of a packed extraction tower, a sieve plate extraction tower, a rotary disc extraction tower, a mixing and settling tank, and a centrifugal extractor; and the two devices are a stirred tank and a phase separation tank respectively.

[0016] In a specific embodiment, the pressure for separating the crude hexamethylenediamine and the ionic liquid in step 3) is 1 to 10 kPaA, preferably 3 to 6 kPaA.

[0017] In a specific embodiment, the equipment used for separation of crude hexamethylenediamine and ionic liquid in step 3) is selected from any one of a thin film evaporator, a falling film evaporator, a rising film evaporator and a distillation tower.

[0018] In a specific embodiment, the bulkhead tower for separating crude hexamethylenediamine in step 4) comprises: a main tower, a condenser, a reboiler and a baffle;

[0019] Preferably, the main column is divided into a rectification region, a stripping region, a pre-fractionation region, and a main fractionation region, and comprises at least one feed stream and at least three outlet streams;

[0020] The rectification region is mainly used to remove low-boiling point components, and the stripping region is mainly used to remove high-boiling point components;

[0021] The at least one feed stream is a crude product stream containing hexamethylenediamine, and the at least three discharge streams are a light component stream containing a small amount of hexamethylenediamine, a hexamethylenediamine product stream, and a heavy component stream containing a small amount of hexamethylenediamine.

[0022] In a specific embodiment, the crude product stream containing hexamethylenediamine enters the middle feed plate of the pre-fractionation zone, and the upper and lower parts of the feed plate of the pre-fractionation zone are connected;

[0023] A light component stream containing a small amount of hexamethylenediamine flows out from the top of the distillation area, and a heavy component stream containing a small amount of hexamethylenediamine flows out from the bottom of the stripping area;

[0024] The hexamethylenediamine product flow flows out from the middle discharge plate of the main fractionation area, and the upper and lower parts of the discharge plate of the main fractionation area are connected.

[0025] In a specific embodiment, the height of the partition is determined according to the number of plates required for the pre-fractionation zone and the main fractionation zone; preferably, the operating pressure of the dividing wall tower is 1 to 10 kPaA, preferably 2 to 5 kPaA.

[0026] In a specific embodiment, the crude product stream containing hexamethylenediamine includes: 0.5-10 wt% of light components of 1,3-diazocyclohexane, aminomethylcyclopentane, and aminopropanol, 80-99 wt% of hexamethylenediamine, and 0.5-10 wt% of heavy components of N-ethylhexamethylenediamine and 2-hexamethylenetriamine;

[0027] The hexamethylenediamine product logistics comprises: more than 99.9 wt % of hexamethylenediamine and less than 1000 ppmwt of light and heavy component impurities.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] In the method of the present invention, ionic liquid is used as an extractant to separate water and crude hexamethylenediamine, so that salt remains in the water phase. Compared with conventional distillation dehydration, the method can avoid the high energy consumption caused by distilling water for distilling hexamethylenediamine and water, and can also avoid the problem that salt in the water enters the crude hexamethylenediamine and blocks the downstream separation system. The method is also a green extraction process.

[0030] The method of the present invention utilizes ionic liquid to extract the aqueous solution of hexamethylenediamine, and further separates the extracted organic phase in combination with a dividing wall tower, thereby avoiding the defects of a long process flow, high equipment investment and high energy consumption of a conventional distillation process. The distillation of crude hexamethylenediamine by a dividing wall tower can greatly reduce energy consumption and equipment investment costs, and reduce process operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The figure is a schematic diagram of the process of purifying hexamethylenediamine according to the present invention.

[0032] Figure 2 The figure is a schematic diagram of the purification process of hexamethylenediamine according to another embodiment of the present invention.

[0033] Figure 3 This is a flow chart of the purification of hexamethylenediamine in Comparative Example 3 of the present application.

[0034] Among them, 1 is an ionic liquid extraction device, 2 is a stratification device, 3 is an ionic liquid separation device, 4 is a dividing wall tower, 5 is a reboiler, 6 is a condenser, 7 is a hexamethylenediamine dehydration tower, 8 is a desalination tower, 9 is a lightness removal tower, and 10 is a hexamethylenediamine refining tower. DETAILED DESCRIPTION

[0035] In order to better understand the technical solution of the present invention, the method and device provided by the present invention are further described below in conjunction with the accompanying drawings. However, the present invention is not limited to the listed embodiments, but also includes any other known changes within the scope of the claims of the present invention.

[0036] like Figure 1 As shown, the process of purifying hexamethylenediamine of the present invention is as follows: the hexamethylenediamine reaction liquid and the ionic liquid enter the ionic liquid extraction device 1 together, the ionic liquid extracts the crude hexamethylenediamine from the water, and the salt is left in the water, the logistics obtained by the ionic liquid extraction device 1 enters the stratification device 2, the water-oil two phases are statically stratified in the stratification device 2, the water phase is discharged as waste water, the oil phase enters the ionic liquid separation device 3, the crude hexamethylenediamine and the ionic liquid are separated in the ionic liquid separation device 3, the obtained ionic liquid is circulated to the ionic liquid extraction device 1, the obtained crude hexamethylenediamine enters the bulkhead tower 4 for refining hexamethylenediamine, the crude hexamethylenediamine enters the middle feed plate of the pre-fractionation area, and the upper and lower parts of the feed plate of the pre-fractionation area are connected. The light component containing a small amount of hexamethylenediamine is extracted from the top of the distillation area, and the heavy component containing a small amount of hexamethylenediamine is extracted from the bottom of the stripping area. The hexamethylenediamine product is extracted from the middle discharge plate of the main distillation area, and the upper and lower parts of the discharge plate of the main distillation area are connected.

[0037] The ionic liquid extraction device 1 and the stratification device 2 can be combined into one device or two devices, and the equipment used can be a packed extraction tower, a sieve plate extraction tower, a rotary disk extraction tower, a stirring kettle + phase separation tank, a mixing and settling tank, a centrifugal extractor and other extraction equipment.

[0038] When the ionic liquid extraction device 1 and the layer separation device 2 can be combined into one device, another embodiment of the present invention is as follows Figure 2As shown, the hexamethylenediamine reaction liquid and the ionic liquid enter the ionic liquid extraction device 1, the crude hexamethylenediamine is extracted from the water using the ionic liquid, while the salt remains in the water and stratification is achieved, the salt-containing wastewater obtained from the ionic liquid extraction device 1 is directly discharged, the ionic liquid and the crude hexamethylenediamine stream obtained from the ionic liquid extraction device 1 enter the ionic liquid separation device 3 to separate the ionic liquid and the crude hexamethylenediamine by distillation, the ionic liquid obtained at the bottom of the ionic liquid separation device 3 is returned to the extraction tower for recycling, the crude hexamethylenediamine obtained at the top of the tower enters the bulkhead tower 4 to purify the crude hexamethylenediamine, the light component is extracted from the top of the bulkhead tower 4, the hexamethylenediamine product is extracted from the tower, and the heavy component is extracted from the bottom of the tower.

[0039] The equipment used in the ionic liquid separation device 3 can be a thin film evaporator, a falling film evaporator, a rising film evaporator, a distillation tower or other distillation equipment.

[0040] The distillation device of the dividing wall tower includes: a dividing wall tower 4, a tower top condenser 6, and a tower bottom reboiler 5. The dividing wall tower 4 includes: a pre-fractionation area (left side of the partition), a main fractionation area (right side of the partition), a partition, a distillation area (top packing section), and a stripping area (bottom packing section).

[0041] In combination with the above-mentioned device system, a method for purifying hexamethylenediamine with low energy consumption of the present invention comprises the following steps:

[0042] 1) extracting hexamethylenediamine and impurities from water using an ionic liquid as an extractant from the aqueous reaction liquid coming out of the hexamethylenediamine reaction system to obtain an extraction mixed liquid;

[0043] 2) the extraction mixture obtained in step 1) is allowed to stand for stratification, the aqueous phase is discharged as waste water, and the organic phase is a mixture of ionic liquid, hexamethylenediamine and impurities;

[0044] 3) separating the organic phase obtained in step 2) to obtain crude hexamethylenediamine at the top and ionic liquid at the bottom, which are then returned to step 1) for recycling of the extractant;

[0045] 4) The crude hexamethylenediamine obtained in step 3) enters a dividing wall tower to remove light / heavy impurities to obtain a hexamethylenediamine product with a purity greater than 99.9 wt %.

[0046] The present invention uses ionic liquid as an extractant to separate water and crude hexamethylenediamine, so that salt remains in the water phase, and then performs phase separation and rectification operations to obtain high-purity hexamethylenediamine. Ionic liquid is a type of liquid composed of anions and cations, which is liquid at room temperature or near room temperature. As a new type of green solvent, ionic liquid has low melting point, low vapor pressure, non-flammability, good solubility, good thermal stability, and designability.

[0047] The ionic liquid designed in the present invention consists of two parts: a cation M+ and an anion N-;

[0048] The cation M+ is an imidazole type cation having a disubstituted group;

[0049] The anion N- is hexafluorophosphate.

[0050] Among them, the two substituent groups in the disubstituted group are different, one of which is a C7-C10 straight-chain alkenyl group, such as heptenyl, octenyl, nonenyl, etc.; the other substituent group is a C1-C2 alkyl group, such as methyl or ethyl; specifically, for example, preferably 1-octenyl-3-methylimidazolium hexafluorophosphate ionic liquid, 1-heptenyl-3-ethylimidazolium hexafluorophosphate ionic liquid, 1-decenyl-3-methylimidazolium hexafluorophosphate ionic liquid, etc., but not limited thereto.

[0051] There is no particular limitation on the preparation method of the ionic liquid in the present invention, and reference may be made to the prior art, for example, by the following method:

[0052] Taking 1-octenyl-3-methylimidazolium hexafluorophosphate as an example, the preparation is divided into two steps. The first step is to synthesize 1-octenyl-3-methylimidazolium bromide ([C 8 mim]Br), add 100g of freshly distilled N-methylimidazole and 300ml of trichloroethane into a round-bottom flask, add 200g of freshly distilled 8-bromo-1-octene dropwise at 60°C under strong stirring, the dropping time exceeds 2h, after the dropping is completed, reflux at 80°C for about 3h, the reaction phenomenon is that it is turbid at first and then turns into an orange-yellow viscous liquid, separate the ionic liquid through a separatory funnel, wash it with trichloroethane several times, and then vacuum dry it at 65°C for 48h to remove the residual solvent and water, and then [C 8 mim]Br; the second step is to synthesize 1-octenyl-3-methylimidazole hexafluorophosphate, 250g sodium hexafluorophosphate (NaPF 6 ) was dissolved in 500 mL of water, and then the [C 8 mim]Br, stirred for 36 h, then extracted with dichloromethane, and the organic layer was washed with water several times until AgNO was added dropwise to the removed aqueous phase. 3 The solution was stirred until no yellow precipitate appeared. The dichloromethane solvent was evaporated first, and then vacuum dried at 60°C for 24 hours to remove the residual solvent and water.

[0053] In the present invention, the interaction between hexamethylenediamine and the hydrophobic groups in the cation of the ionic liquid, and the hydrogen bonding between the H atoms in the organic molecules and the F atoms in the anions of the ionic liquid are the main driving forces for the extraction process. The introduction of the hydrophobic groups and the groups that are easy to form hydrogen bonds in the amine molecules can increase the distribution of hexamethylenediamine in the ionic liquid.

[0054] The mass ratio of the extractant ionic liquid to the reaction solution used in the present invention is 0.1-3, for example including but not limited to 0.1, 0.5, 1, 1.5, 2, 2.5, 3, preferably 0.3-1.

[0055] The hexamethylenediamine extraction step in the present invention can be completed in one step in the same equipment or in two steps in two equipments. The equipment used can be a packed extraction tower, a sieve plate extraction tower, a rotary disk extraction tower, a stirred tank + phase separation tank, a mixing and settling tank, a centrifugal extractor and other extraction equipment.

[0056] The organic phase obtained by standing and stratifying the extraction mixture is a mixture of ionic liquid, hexamethylenediamine and impurities, and then the ionic liquid and crude hexamethylenediamine are separated, and the equipment used for separation can be a distillation equipment such as a thin film evaporator, a falling film evaporator, a rising film evaporator, a distillation tower, etc. The pressure for separating crude hexamethylenediamine and ionic liquid is, for example, 1 to 10 kPaA, for example, including but not limited to 1 kPaA, 2 kPaA, 3 kPaA, 4 kPaA, 5 kPaA, 6 kPaA, 7 kPaA, 8 kPaA, 9 kPaA, 10 kPaA, preferably 3 to 6 kPaA.

[0057] The present invention adopts a dividing wall tower to purify hexamethylenediamine, and can achieve the effect of two distillation towers through one distillation tower. Compared with a conventional rectification device for purifying hexamethylenediamine, the present invention consumes less energy and has lower equipment cost.

[0058] like Figure 1 As shown, the dividing wall tower 4 comprises: a main tower 4, a condenser 6, a reboiler 5 and a partition. The main tower 4 is divided into a rectification region, a stripping region, a pre-fractionation region, and a main fractionation region, and comprises at least one feed stream and at least three outlet streams. The at least one feed stream is a crude product stream containing hexamethylenediamine, and the at least three outlet streams are a light component stream containing a small amount of hexamethylenediamine, a hexamethylenediamine product stream, and a heavy component stream containing a small amount of hexamethylenediamine.

[0059] The crude product stream containing hexamethylenediamine enters the middle feed plate of the pre-fractionation region, and the upper and lower parts of the feed plate of the pre-fractionation region are connected. The light component stream containing a small amount of hexamethylenediamine flows out from the top of the rectification region, and the heavy component containing a small amount of hexamethylenediamine flows out from the bottom of the stripping region. The hexamethylenediamine product stream flows out from the middle discharge plate of the main fractionation region, and the upper and lower parts of the discharge plate of the main fractionation region are connected. The height of the partition is determined according to the number of tower plates required for the pre-fractionation region and the main fractionation region.

[0060] The crude product stream containing hexamethylenediamine is, for example, 0.5-10 wt% of light components such as 1,3-diazocyclohexane, aminomethylcyclopentane, and aminopropanol, 80-99 wt% of hexamethylenediamine, and 0.5-10 wt% of heavy components such as N-ethylhexamethylenediamine and 2-hexamethylenetriamine.

[0061] The hexamethylenediamine product stream, for example, contains more than 99.9 wt % of hexamethylenediamine and less than 1000 ppmwt of light and heavy impurities.

[0062] Wherein, the operating pressure of the dividing wall tower is 1 to 10 kPaA, for example, including but not limited to 1 kPaA, 2 kPaA, 3 kPaA, 4 kPaA, 5 kPaA, 6 kPaA, 7 kPaA, 8 kPaA, 9 kPaA, 10 kPaA, preferably 2 to 5 kPaA.

[0063] The tower is divided into two parts on the left and right due to the effect of the partition. The left side of the partition is used as a pre-fractionation tower to pre-fractionate the light components and heavy components first. The right side of the partition is used as a main fractionation tower to further separate the light components, heavy components and products. This distillation method is consistent with the PETLYUK system in principle. The distillation curve in the distillation tower is similar to the equilibrium distillation curve, so the energy consumption is low, and it solves the problem of difficult pressure balance and difficult operation of the two towers of the PETLYUK system.

[0064] The pre-fractionation area plays the role of a pre-fractionation tower in a conventional distillation process, a crude product flow containing hexamethylenediamine enters the middle feed plate of the pre-fractionation area, steam from the stripping area and liquid from the distillation area enter the pre-fractionation area for gas-liquid mass transfer exchange, wherein steam rich in light components and a portion of the product (hexamethylenediamine) flows out from the top of the pre-fractionation area and enters the distillation area; liquid rich in heavy components and a portion of the product (hexamethylenediamine) flows out from the bottom of the pre-fractionation area and enters the stripping area.

[0065] The main fractionation region plays the role of the main fractionation tower in the conventional distillation process, the hexamethylenediamine product logistics flows out from the middle discharge plate of the main fractionation region, the light components and products are mainly separated above the discharge plate of the main fractionation region, and the heavy components and products are mainly separated below the discharge plate of the main fractionation region. The steam from the stripping region and the liquid from the rectification region enter the main fractionation region for gas-liquid mass transfer exchange, wherein the steam rich in light components and a small amount of products (hexamethylenediamine) flows out from the top of the pre-fractionation region and enters the rectification region; the liquid rich in heavy components and a small amount of products (hexamethylenediamine) flows out from the bottom of the pre-fractionation region and enters the stripping region.

[0066] The steam from the top of the pre-fractionation area and the top of the main fractionation area, both of which contain light components and products (hexamethylenediamine), enter the bottom of the distillation area. The steam from the distillation area enters the condenser for condensation. A part of the condensed liquid is used as reflux and enters the top of the distillation area, thus separating the light components from the products. The other part of the liquid after condensation in the condenser is extracted as the light component. The steam entering the bottom of the distillation area and the reflux liquid entering the top of the distillation area are exchanged for gas-liquid mass transfer. The liquid containing light components and products (hexamethylenediamine) flowing out from the bottom of the distillation area is divided into two streams and sent to the pre-fractionation area and the main fractionation area respectively. In order to achieve the desired separation effect, the distribution ratio of the two liquids needs to be controlled, which can be adjusted according to the reflux ratio on both sides of the partition.

[0067] The liquids from the bottom of the pre-fractionation area and the bottom of the main fractionation area, both of which contain heavy components and products (hexamethylenediamine), enter the top of the stripping area. A portion of the liquid from the bottom of the stripping area enters the reboiler to generate steam, and the steam enters the bottom of the stripping area, thus separating the heavy components from the products. Another portion of the liquid from the bottom of the stripping area is produced as the heavy component. The steam entering the bottom of the stripping area and the liquid entering the top of the stripping area undergo gas-liquid mass transfer exchange, and the steam containing the heavy components and the product (hexamethylenediamine) flowing out from the top of the fine stripping area is divided into two streams and sent to the pre-fractionation area and the main fractionation area respectively. The two streams of steam are distributed by the inherent pressure drop of the pre-fractionation area and the main fractionation area.

[0068] The present invention is further explained below by more specific examples, but does not constitute any limitation.

[0069] The main raw material sources of the following examples are as follows:

[0070] The hexamethylenediamine reaction liquid comes from the reaction unit of the hexamethylenediamine pilot plant;

[0071] The ionic liquid is prepared by the following preparation process:

[0072] 1-Octenyl-3-methylimidazolium hexafluorophosphate is prepared in two steps. The first step is to synthesize 1-octenyl-3-methylimidazolium bromide ([C 8 mim]Br), add 100g of freshly distilled N-methylimidazole and 300ml of trichloroethane in a round-bottom flask, add 200g of freshly distilled 8-bromo-1-octene dropwise at 60°C under strong stirring for more than 2h, reflux at 80°C for about 3h after the addition is complete, the reaction phenomenon is that the liquid is turbid first and then turns into an orange-yellow viscous liquid, the ionic liquid is separated by a separatory funnel, and after washing with trichloroethane several times, it is vacuum dried at 65°C for 48h to remove the residual solvent and water, and [C 8mim]Br; the second step is to synthesize 1-octenyl-3-methylimidazole hexafluorophosphate, 250g sodium hexafluorophosphate (NaPF 6 ) was dissolved in 500 mL of water, and then the [C 8 mim]Br, stirred for 36 h, then extracted with dichloromethane, and the organic layer was washed with water several times until AgNO was added dropwise to the removed aqueous phase. 3 The solution was stirred until no yellow precipitate appeared. The dichloromethane solvent was evaporated first, and then vacuum dried at 60°C for 24 hours to remove the residual solvent and water.

[0073] 1-Heptenyl-3-ethylimidazole hexafluorophosphate, the preparation method is similar to 1-octenyl-3-methylimidazole hexafluorophosphate, and is also prepared in two steps. The first step is to synthesize 1-heptenyl-3-ethylimidazole bromide ([C 7 mim]Br), except that the temperature for adding 7-bromo-1-heptene to the solution of N-methylimidazole and trichloroethane is 55° C.; the method for synthesizing 1-heptenyl-3-ethylimidazole hexafluorophosphate in the second step is the same as the method for synthesizing 1-octenyl-3-methylimidazole hexafluorophosphate.

[0074] 1-Decenyl-3-methylimidazole hexafluorophosphate, the preparation method is similar to 1-octenyl-3-methylimidazole hexafluorophosphate, and is also prepared in two steps. The first step is to synthesize 1-decenyl-3-methylimidazole bromide ([C 10 mim]Br), except that the temperature for adding 10-bromo-1-decene to the solution of N-methylimidazole and trichloroethane is 65° C.; the method for synthesizing 1-decenyl-3-methylimidazole hexafluorophosphate in the second step is the same as the method for synthesizing 1-octenyl-3-methylimidazole hexafluorophosphate.

[0075] 1-Hexenyl-3-ethylimidazole hexafluorophosphate, the preparation method is similar to 1-octenyl-3-methylimidazole hexafluorophosphate, and is also prepared in two steps. The first step is to synthesize 1-hexenyl-3-ethylimidazole bromide ([C 6 mim]Br), except that the temperature for adding 6-bromo-1-hexene to the solution of N-ethylimidazole and trichloroethane is 50°C; the method for synthesizing 1-hexenyl-3-ethylimidazole hexafluorophosphate in the second step is the same as the method for synthesizing 1-octenyl-3-methylimidazole hexafluorophosphate.

[0076] 1-n-butyl-3-methylimidazolium tetrafluoroborate is prepared in two steps similar to 1-octenyl-3-methylimidazolium hexafluorophosphate. The first step is to synthesize 1-n-butyl-3-methylimidazolium bromide ([C 4mim]Br), except that the temperature of adding 4-bromobutane to the solution of N-methylimidazole and trichloroethane was 52°C; the second step was to synthesize 1-n-butyl-3-methylimidazole tetrafluoroborate, and sodium tetrafluoroborate (NaBF 4 ) was dissolved in water, and then the [C 4 mim]Br, and the rest is the same as the method for synthesizing 1-octenyl-3-methylimidazolium hexafluorophosphate.

[0077] The analysis method of hexamethylenediamine content is as follows:

[0078] Gas chromatography analysis: main test conditions of hydrogen flame ionization detector (FID): chromatographic column: capillary column, column tube material: fused quartz; column length: 30m, column inner diameter: 0.32mm; carrier gas: nitrogen; vaporization chamber temperature: 150℃; detector temperature: 200℃.

[0079] Example 1

[0080] Reference Figure 2 The ionic liquid used is 1-octenyl-3-methylimidazolium hexafluorophosphate. The hexamethylenediamine reaction liquid and the ionic liquid enter the hexamethylenediamine extraction tower. The crude hexamethylenediamine is extracted from the water using the ionic liquid, while the salt remains in the water. The salt-containing wastewater obtained from the extraction tower is directly discharged. The ionic liquid and the crude hexamethylenediamine stream obtained from the extraction tower enter the ionic liquid recovery tower to distill and separate the ionic liquid and the crude hexamethylenediamine. The ionic liquid obtained in the bottom of the tower is returned to the extraction tower for recycling. The crude hexamethylenediamine obtained at the top of the tower enters the next-door tower to purify the crude hexamethylenediamine. The light component is extracted from the top of the tower, the hexamethylenediamine product is extracted from the tower, and the heavy component is extracted from the bottom of the tower.

[0081] The composition of the hexamethylenediamine reaction liquid is: 82.8wt% hexamethylenediamine, 15wt% water, 0.6wt% light components, 1.6wt% heavy components and trace salts, the feed flow rate is 1000kg / h, the temperature is 40°C, and the pressure is 3barg.

[0082] The flow rate of the ionic liquid was 650 kg / h.

[0083] The flow rate of the obtained product is 749 kg / h, and the product purity is >99.9 wt%.

[0084] The recovery rate of hexamethylenediamine was 90.4%.

[0085] Table 1 below shows the equipment operating conditions and Table 2 shows the heat consumption.

[0086] Table 1 Equipment operating conditions of Example 1

[0087]

[0088] Table 2 Heat consumption of equipment in Example 1

[0089]

[0090] Example 2

[0091] This embodiment is based on Figure 2 The process shown is the same as that of Example 1, except that the ionic liquid used is 1-heptenyl-3-ethylimidazole hexafluorophosphate.

[0092] The composition of the hexamethylenediamine reaction liquid is: 80.75wt% hexamethylenediamine, 15wt% water, 1.7wt% light components, 2.55wt% heavy components and trace salts, the feed flow rate is 1000kg / h, the temperature is 40°C, and the pressure is 3barg.

[0093] The flow rate of the ionic liquid was 300 kg / h.

[0094] The flow rate of the obtained product is 719 kg / h, and the product purity is >99.9 wt%.

[0095] The recovery rate of hexamethylenediamine was 89%.

[0096] Table 3 below shows the equipment operating conditions and Table 4 shows the heat consumption.

[0097] Table 3 Equipment operating conditions of Example 2

[0098]

[0099] Table 4 Heat consumption of equipment in Example 2

[0100]

[0101] Example 3

[0102] This embodiment is based on Figure 2 The process shown is the same as that of Example 1, except that the ionic liquid used is 1-decenyl-3-methylimidazolium hexafluorophosphate.

[0103] The hexamethylenediamine reaction liquid is composed of 83.725wt% hexamethylenediamine, 15wt% water, 0.425wt% light components, 0.85wt% heavy components and trace salts, with a feed flow rate of 1000kg / h, a temperature of 40°C and a pressure of 3barg.

[0104] The flow rate of the ionic liquid was 1000 kg / h.

[0105] The flow rate of the obtained product is 754 kg / h, and the product purity is >99.9 wt%.

[0106] The recovery rate of hexamethylenediamine was 90%.

[0107] Table 5 below shows the equipment operating conditions and Table 6 shows the heat consumption.

[0108] Table 5 Equipment operating conditions of Example 3

[0109]

[0110] Table 6 Heat consumption of equipment in Example 3

[0111]

[0112] Comparative Example 1

[0113] The comparison is based on Figure 2 The process shown is the same as that of Example 1, except that the ionic liquid used is 1-hexenyl-3-ethylimidazole hexafluorophosphate.

[0114] The composition of the hexamethylenediamine reaction liquid is: 81.2wt% hexamethylenediamine, 15wt% water, 1.5wt% light components, 2.3wt% heavy components and trace salts, the feed flow rate is 1000kg / h, the temperature is 40°C, and the pressure is 3barg.

[0115] The flow rate of the ionic liquid was 1500 kg / h.

[0116] The flow rate of the obtained product is 652 kg / h, and the product purity is >99.9 wt%.

[0117] The recovery rate of hexamethylenediamine was 80.2%.

[0118] Table 7 below shows the equipment operating conditions and Table 8 shows the heat consumption.

[0119] Table 7 Comparative Example 1 Equipment Operating Conditions

[0120]

[0121] Table 8 Heat consumption of equipment in comparative example 1

[0122]

[0123] Comparative Example 2

[0124] The comparison is based on Figure 2 The process shown is the same as that of Example 1, except that the ionic liquid used is 1-n-butyl-3-methylimidazolium tetrafluoroborate.

[0125] The composition of the hexamethylenediamine reaction liquid is: 82.8wt% hexamethylenediamine, 15wt% water, 0.6wt% light components, 1.6wt% heavy components and trace salts, the feed flow rate is 1000kg / h, the temperature is 40°C, and the pressure is 3barg.

[0126] The flow rate of the ionic liquid was 650 kg / h.

[0127] The flow rate of the obtained product is 663 kg / h, and the product purity is >99.9 wt%.

[0128] The recovery rate of hexamethylenediamine was 80%.

[0129] Table 9 below shows the equipment operating conditions and Table 10 shows the heat consumption.

[0130] Table 9 Comparative Example 2 Equipment Operating Conditions

[0131]

[0132] Table 10 Heat consumption of equipment in comparative example 2

[0133]

[0134] Comparative Example 3

[0135] like Figure 3 , the hexamethylenediamine reaction liquid enters the hexamethylenediamine dehydration tower 7, the wastewater is discharged from the tower top, and the crude hexamethylenediamine is obtained in the tower bottom. The crude hexamethylenediamine enters the desalting tower 8, the salt and part of the heavy components are discharged from the tower bottom, and the crude hexamethylenediamine without salt is obtained at the tower top. The crude hexamethylenediamine without salt enters the light removal tower 9, the light components are discharged from the tower top, and the hexamethylenediamine containing heavy components is obtained in the tower bottom. The hexamethylenediamine containing heavy components enters the hexamethylenediamine refining tower 10, the product hexamethylenediamine is obtained at the tower top, and the heavy components are discharged from the tower bottom.

[0136] The composition of the hexamethylenediamine reaction liquid is: 82.8wt% hexamethylenediamine, 15wt% water, 0.6wt% light components, 1.6wt% heavy components and trace salts, the feed flow rate is 1000kg / h, the temperature is 40°C, and the pressure is 3barg.

[0137] The flow rate of the obtained product is 748 kg / h, and the product purity is >99.9 wt%.

[0138] The yield of hexamethylenediamine was 90.3%.

[0139] Table 11 below shows the equipment operating conditions and Table 12 shows the heat consumption.

[0140] Table 11 Equipment operating conditions of comparative example 3

[0141]

[0142] Table 12 Heat consumption of equipment in comparative example 3

[0143] equipment 1 4 7 10 Heat consumption / KW 259 99 885 265

[0144] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as limiting the present invention. Those skilled in the art will appreciate that, under the guidance of this specification, some modifications or adjustments may be made to the present invention. These modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A method for purifying hexamethylenediamine with low energy consumption, characterized in that: The following steps are involved: 1) Using an ionic liquid as an extractant in the aqueous reaction liquid from the hexamethylenediamine reaction system to extract hexamethylenediamine and impurities from water to obtain an extraction mixed liquid; 2) the extraction mixture obtained in step 1) is allowed to stand for stratification, the aqueous phase is discharged as waste water, and the organic phase is a mixture of ionic liquid, hexamethylenediamine and impurities; 3) Separating the organic phase obtained in step 2) to obtain crude hexamethylenediamine at the top and ionic liquid at the bottom, which is then returned to step 1) for recycling of the extractant; 4) The crude hexamethylenediamine obtained in step 3) enters a dividing wall tower to remove light / heavy impurities to obtain a hexamethylenediamine product with a purity greater than 99.9 wt%; The ionic liquid consists of two parts: a cation M+ and an anion N-; the cation M+ is an imidazole-type cation with a double-substituted group; the anion N- is a hexafluorophosphate; the two substituent groups in the double-substituted group are different, one of which is a C7-C10 straight-chain alkenyl group, and the other is a C1-C2 alkyl group.

2. The method according to claim 1, characterized in that In step 1), the mass ratio of the ionic liquid used as the extractant to the aqueous reaction liquid from the hexamethylenediamine reaction system is 0.1-3.

3. The method according to claim 2, characterized in that In step 1), the mass ratio of the ionic liquid used as the extractant to the aqueous reaction liquid from the hexamethylenediamine reaction system is 0.3-1.

4. The method according to claim 1, characterized in that: Step 1) and step 2) are completed in the same device or in two separate devices.

5. The method according to claim 1, characterized in that The same equipment is selected from any one of a packed extraction tower, a sieve plate extraction tower, a rotary disc extraction tower, a mixing and settling tank, and a centrifugal extractor; the two equipments are a stirred kettle and a phase separation tank respectively.

6. The method according to claim 1, characterized in that In step 3), the pressure for separating the crude hexamethylenediamine and the ionic liquid is 1 to 10 kPaA.

7. The method according to claim 6, characterized in that In step 3), the pressure for separation of crude hexamethylenediamine and ionic liquid is 3-6 kPaA.

8. The method according to claim 1 or 6, characterized in that: In step 3), the equipment used for separation of crude hexamethylenediamine and ionic liquid is selected from any one of a thin film evaporator, a falling film evaporator, a rising film evaporator and a distillation tower.

9. The method according to claim 1, characterized in that: The bulkhead tower for separating crude hexamethylenediamine in step 4) comprises: a main tower, a condenser, a reboiler and a baffle; The main column is divided into a rectification region, a stripping region, a pre-fractionation region, and a main fractionation region, and includes at least one feed stream and at least three discharge streams; The rectification region is used to remove low boiling point components, and the stripping region is used to remove high boiling point components; The at least one feed stream is a crude product stream containing hexamethylenediamine, and the at least three discharge streams are a light component stream containing a small amount of hexamethylenediamine, a hexamethylenediamine product stream, and a heavy component stream containing a small amount of hexamethylenediamine.

10. The method according to claim 9, characterized in that The crude product stream containing hexamethylenediamine enters the middle feed plate of the pre-fractionation zone, and the upper and lower parts of the feed plate of the pre-fractionation zone are connected; A light component stream containing a small amount of hexamethylenediamine flows out from the top of the distillation area, and a heavy component stream containing a small amount of hexamethylenediamine flows out from the bottom of the stripping area; The hexamethylenediamine product flow flows out from the middle discharge plate of the main fractionation area, and the upper and lower parts of the discharge plate of the main fractionation area are connected.

11. The method according to claim 9, characterized in that The height of the partition is determined according to the number of plates required for the pre-fractionation zone and the main fractionation zone.

12. The method according to claim 11, characterized in that The operating pressure of the dividing wall tower is 1-10 kPaA.

13. The method according to claim 11, characterized in that The operating pressure of the dividing wall tower is 2-5 kPaA.

14. The method according to claim 6 or 7, characterized in that: The crude product stream containing hexamethylenediamine includes: 0.5-10 wt % of light components of 1,3-diazocyclohexane, aminomethylcyclopentane, and aminopropanol, 80-99 wt % of hexamethylenediamine, and 0.5-10 wt % of heavy components of N-ethylhexamethylenediamine and 2-hexamethylenetriamine; The hexamethylenediamine product logistics comprises: more than 99.9 wt % of hexamethylenediamine and less than 1000 ppmwt of light and heavy component impurities.

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