Recycling method of amide chloride aqueous solution

Abstract

The invention discloses a method for recycling an amide chloride aqueous solution, which belongs to the technical field of chemical engineering separation, and comprises the following steps: feeding the amide chloride aqueous solution into a heat pump rectifying tower from a feed port for heat pump rectification separation, and extracting amide / chloride and a small amount of water from the tower bottom; amide / chloride and a small amount of water enter a conventional rectifying tower for conventional rectifying separation, water is extracted from the tower top, an amide solvent is extracted from the tower side line, and an amide / chloride solution is extracted from the tower bottom; feeding the amide / chloride solution into a first filter for hot filtration, and separating out insoluble substances and filtrate; cooling the filtrate through a second condenser, crystallizing the filtrate in a crystallizer and secondarily filtering the filtrate through a second filter in sequence to obtain pure chloride, and feeding the remaining filtrate into an evaporator; and evaporating the remaining filtrate in an evaporator, further evaporating and condensing the amide solvent in the remaining filtrate, recovering, and discharging the residual liquid at the bottom of the kettle as tar.

Description

Technical Field

[0001] The invention relates to a separation process for recovering polymer solvent and cosolvent from aramid fiber coagulation liquid, belongs to the field of chemical engineering separation technology, and specifically relates to a method for recovering amide chloride aqueous solution. Background Art

[0002] Aramid is a special fiber with excellent performance. It is widely popular for its high strength, high temperature resistance, corrosion resistance, flame retardancy, dimensional stability and other characteristics that are different from conventional fibers. Aramid can be divided into meta-aramid and para-aramid. Meta-aramid refers to aramid 1313, and para-aramid mainly includes aramid 1414, aramid III, and Technora fiber. Aramid is formed by the condensation polymerization reaction of organic compound monomers in a solvent system, and then processed into fibers through a spinning process. The solvent system includes two substances: solvent and cosolvent. In the production process of aramid, the consumption of solvents and cosolvents is very large and must be recycled. Otherwise, the production cost is very high and the prepared aramid fiber has no market application prospects.

[0003] The solvents for producing aramid include N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAC), etc., and the cosolvents include lithium chloride, calcium chloride and other substances. The cosolvent is dissolved in the solvent to obtain the solvent system of the aramid polymer, that is, the amide / chloride solution. The monomer is polymerized to generate an aramid polymer, which is dissolved in the amide / chloride solvent system, and then the aramid polymer is prepared into aramid fiber through spinning technology. During the manufacturing process, the amide / chloride solvent system is dissolved in water to form a mixed solution of amide / chloride / water, and then the amide and chloride are separated and recovered from the water through solvent recovery technology, and then recycled repeatedly.

[0004] In industry, extraction technology is usually used to extract amide / chloride / water solution with chloroform and then separate the phases to obtain an extract phase solution and a raffinate phase solution. The extract phase solution is a mixed solution containing a large amount of chloroform, amide, and very small amounts of water and chloride. The raffinate phase solution is a mixed solution containing a large amount of water, a small amount of chloride, and very small amounts of chloroform and amide. For the extract phase solution, distillation technology is usually used to separate and obtain an amide solvent. For the recovery of chloride in the raffinate phase solution, it can be achieved by distillation technology from the top of the tower and the side line, or by stripping and evaporation technology. However, these two methods have a common disadvantage, that is, the energy consumption is large, especially the first method, the operating cost is high, which is not conducive to reducing production costs.

[0005] The above technical method has two defects: ① The environmental pollution problem caused by chloroform. With the progress of society, the country pays more and more attention to environmental protection, requiring the chloroform content in the exhaust gas to be less than 20ppm, and the chloroform content in the discharged wastewater to be less than 1ppm. The environmental pollution problem of chloroform requires considerable cost investment; ② The complex process leads to excessively high recovery costs of amides and chlorides. The above process route is relatively long, and the fixed asset investment and operating costs are high, which is not conducive to reducing the cost of fiber production and limits the application and promotion of fibers. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a method for recycling an amide chloride aqueous solution, wherein a mixed solution of amide / chloride / water is treated, amide and chloride are separated and recovered from water, and then recycled repeatedly. The present invention can reduce the production cost of heterocyclic aramid, avoid environmental pollution, and realize maximum recovery of amide solvent and lithium chloride co-solvent with economical investment cost.

[0007] The objective of the present invention is achieved through the following technical solutions: A method for recycling an amide chloride aqueous solution comprises the following steps: Step A, the aqueous solution of amide chloride is fed into a heat pump distillation tower from a feed port for heat pump distillation separation, the heat pump distillation temperature is 60-80°C, water vapor is discharged from the top of the tower, and enters the second heater to heat the kettle liquid after being pressurized by a steam heat pump, and the heated water vapor is divided into two streams, one as the reflux liquid of the distillation tower, and the other as the heating medium of the feed stream of the heat pump distillation tower; amide / chloride and a small amount of water are extracted from the bottom of the tower; Step B, amide / chloride and a small amount of water enter a conventional distillation tower for conventional distillation separation, the temperature of conventional distillation separation is 70-95° C., water is produced from the top of the tower, amide solvent is produced from the side line of the tower, and amide / chloride solution is produced from the bottom of the tower; Step C, the amide / chloride solution is sent to a first filter for hot filtration to separate insoluble matter and filtrate; Step D: The filtrate is cooled in turn through the second condenser, and crystallized in the crystallizer. The temperature of the crystallizer is -5~5°C. The second filter performs secondary filtration to obtain pure chloride, and the remaining filtrate enters the evaporator; Step E: The remaining filtrate is evaporated in an evaporator at an operating temperature of 80-105° C. The amide solvent in the remaining filtrate is further evaporated and condensed and then recovered, and the residual liquid at the bottom of the kettle is discharged as tar.

[0008] Preferably, in the amide chloride aqueous solution, the amide includes any one of N-methylpyrrolidone and N,N-dimethylacetamide, and the chloride includes any one of lithium chloride and calcium chloride.

[0009] Preferably, in step A, the theoretical number of stages of the heat pump distillation tower is 35-50; the heat pump distillation tower adopts reduced pressure operation, and the operating pressure is 5-30 kPa; the operating reflux ratio of the heat pump distillation tower is 2-5. Heat pump distillation tower: The theoretical number of stages is greater than 50, the equipment investment is large, and it is not economical; the theoretical number of stages is less than 35, and the separation requirements cannot be met. The operating pressure is higher than 30 kPa, the bottom temperature of the tower is high, and the amide solvent is easily hydrolyzed and deteriorated under high temperature conditions; the operating pressure is less than 5 kPa, the vacuum degree is too high, the equipment hardware requirements are high, and it is not economically desirable. The reflux ratio is higher than 5, and the energy loss is large; the reflux ratio is lower than 2, the separation is incomplete, and the DMAC at the bottom of the tower will enter the gas phase flow at the top of the tower.

[0010] Preferably, in step A, the pressure of the steam heat pump after pressurization is 0.15-0.5 MPa. Heat pump distillation tower: when the pressure is higher than 0.5 MPa, the heat pump compression ratio is large, and the equipment is required to be high; when the pressure is lower than 0.15 MPa, the steam temperature is low and cannot provide enough heat to heat the bottom kettle liquid.

[0011] Preferably, in step B, the theoretical number of stages of the conventional distillation tower is 20-35; the conventional distillation tower adopts reduced pressure operation, and the operating pressure is 5-15 kPa; the operating reflux ratio of the conventional distillation tower is 1-3. Conventional distillation tower: The theoretical number of stages is greater than 35, the equipment investment is large, and it is not economical; the theoretical number of stages is less than 20, and the separation requirements cannot be met. The operating pressure is higher than 15 kPa, the bottom temperature of the tower is high, and the amide solvent is easy to deteriorate under high temperature conditions; the operating pressure is less than 5 kPa, and the vacuum pump and equipment sealing requirements are high, which is economically undesirable. The reflux ratio is higher than 3, and the energy loss is large; the reflux ratio is lower than 1, it is difficult to meet the separation requirements, and the purity of DMAC at the top of the tower is affected.

[0012] Preferably, in step C, the temperature of the amide / chloride solution is controlled at 60-90° C. When the temperature is higher than 90° C., on the one hand, the filter element has high temperature resistance requirements, and on the other hand, the solubility of impurities increases; when the temperature is lower than 60° C., chloride crystals may be precipitated, reducing the recovery rate of chloride.

[0013] Preferably, in the step D, the material temperature after cooling in the second condenser is -5 to 5° C. If the temperature is higher than 5° C., the crystallization of lithium chloride from DMAC is affected, and the recovery rate of lithium chloride is reduced; if the temperature is lower than -5° C., the load requirement of the refrigerator is high, which is not economical.

[0014] Preferably, the pore size of the filter screens of the first filter and the second filter are both in the range of 1 μm to 5 μm. If the pore size is too large, the fine crystals of lithium chloride cannot be filtered; if the pore size is too small, the filter screen is easily blocked.

[0015] Preferably, in step F, the evaporator is operated under reduced pressure, with an operating pressure of 5-15 kPa. Evaporator: When the operating pressure is higher than 15 kPa, the tower bottom temperature is high, the steam pressure requirement is high, and the amide solvent is easy to deteriorate under high temperature conditions; when the operating pressure is less than 5 kPa, the vacuum pump and equipment sealing requirements are high, which is not economically desirable.

[0016] The beneficial effects of this technical solution are as follows: 1. The present invention provides a method for recycling an aqueous solution of amide chloride, which significantly reduces the cost of recycling aramid amide solvents: The extraction method for recycling aramid amide solvents is the current mainstream production technology, which has a long process flow, many production equipment, and high steam consumption. The steam consumption per unit of the extraction method for recycling aramid amide solvents reaches 8.5t / m 3 The process and system of the present invention greatly reduce the steam consumption through heat pump distillation technology, and fully recover the amide solvent through conventional distillation tower and evaporator, which can reduce the steam consumption of aramid amide solvent to 2.6t / m 3 Reducing the amount of steam also brings another benefit, that is, it also reduces the load of the top condenser and reduces the amount of circulating water.

[0017] 2. The present invention provides a method for recycling an amide chloride aqueous solution, which effectively recycles chloride, a co-solvent for aramid polymers: the extractant used for recycling the aramid amide solvent by extraction is chloroform, and the chloride aqueous solution obtained by this method contains many impurities, including chloroform, amide solvent, and various chloride salts. These impurities are soluble in water and difficult to completely remove. Very complex processes and equipment are required to separate the impurities from the chloride to obtain a chloride co-solvent that can be recycled. In the method of the present invention, a chloride amide solution is obtained, in which the chloride impurities have very low solubility in the amide solvent and can be ignored, and can be removed by hot filtration. After hot filtration, an almost pure chloride amide solution is obtained, and then a chloride solid is obtained by cooling, crystallizing, and filtering. The obtained chloride can be directly recycled.

[0018] 3. The present invention provides a method for recycling an aqueous solution of amide chloride, which eliminates environmental pollution caused by chloroform: the extractant used to recover the aramid amide solvent by extraction is chloroform; the environmental protection standard has clear provisions on the emission of chloroform in the environment, requiring the exhaust gas emission concentration to be less than 20ppm and the wastewater emission concentration to be less than 1ppm. If the aramid amide solvent is recovered by extraction, additional environmental protection facilities must be built to treat the chloroform emissions in the exhaust gas and wastewater to meet the emission standards. In the method of the present invention, the extraction method is abandoned, and there is no chloroform, which completely eliminates the environmental pollution problem caused by chloroform from the process.

[0019] 4. The present invention provides a method for recycling an aqueous solution of amide chloride, which simplifies the solvent recovery process and reduces the construction cost of the device: the extraction method for recovering aramid amide solvents has a long process, including extraction, dechloroform, distillation, stripping, evaporation, crystallization, filtration, lithium chloride refining, waste gas treatment, wastewater treatment and other processes, with many production equipment and high construction costs. The method of the present invention fundamentally improves the recovery process of aramid amide solvents, with more advanced technology, simpler process, less equipment required, and significantly reduced construction costs of solvent recovery devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the process used in the present invention; Wherein: 100, heat pump distillation tower; 101, first heater; 102, second heater; 103, first centrifugal pump; 104, steam heat pump; 105, second centrifugal pump; 200, conventional distillation tower; 201, third heater; 202, first condenser; 203, third centrifugal pump; 204, fourth centrifugal pump; 205, first storage tank; 206, second condenser; 300, evaporator; 400, second storage tank; 500, first filter; 600, crystallizer; 700, second filter. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

[0022] like Figure 1 As shown, a recycling system for an amide chloride aqueous solution includes a heat pump distillation tower 100, a conventional distillation tower 200, a first filter 500, a second storage tank 400, a second condenser 206, a crystallizer 600, a second filter 700 and an evaporator 300 connected in sequence, wherein a steam heat pump 104 is arranged on the steam outlet pipe at the upper end of the heat pump distillation tower 100, and the steam outlet pipe is also connected to the heat pump distillation tower 100 through a second heater 102 and a reflux pipe; the second heater 102 is connected to the bottom of the heat pump distillation tower 100; a first condenser 202 and a first storage tank 205 are arranged on the steam outlet pipe at the upper end of the conventional distillation tower 200, the first storage tank 205 is connected to a water outlet pipe and a water reflux pipe, the reflux pipe is connected to the conventional distillation tower 200, and a first amide outlet pipe is also arranged on the side wall of the conventional distillation tower 200; a second amide outlet pipe and a tar outlet pipe are respectively arranged at the upper and lower ends of the evaporator 300.

[0023] Preferably, a fourth centrifugal pump 204 is provided between the second storage tank 400 and the second condenser 206 .

[0024] Preferably, a third centrifugal pump 203 is provided between the conventional distillation tower 200 and the first filter.

[0025] Preferably, a second centrifugal pump 105 is provided between the heat pump distillation tower 100 and the conventional distillation tower 200 .

[0026] Preferably, a first centrifugal pump 103 is provided on the reflux pipe.

[0027] Preferably, the reflux pipe is connected to the first heater 101 through a branch pipe, the first heater 101 is arranged on the amide salt water inlet pipe, and the amide salt inlet pipe is connected to the heat pump distillation tower 100.

[0028] Preferably, a chloride outlet pipe is also provided at the lower end of the second filter 700 .

[0029] Examples 1 to 5 all adopt the above-mentioned system for recycling an aqueous solution of amide chloride.

[0030] Example 1 A method for recycling an aqueous solution of amide chloride, the specific process steps are as follows: Step A. Feeding a mixed solution of N-methylpyrrolidone (NMP) / calcium chloride / water from a feed port into a heat pump distillation tower 100 for heat pump distillation separation, the heat pump distillation temperature is 80° C., the theoretical stage is 35, the operating pressure is 5 kPa, the operating reflux ratio is 2.9, water vapor is discharged from the top of the tower, and after being pressurized to 0.4 MPa by a steam heat pump 104, enters the second heater 102 to heat the kettle liquid, and the heated water vapor is divided into two streams, one as the reflux liquid of the heat pump distillation tower 100, and the other as the heating medium of the feed stream of the heat pump distillation tower 100, and NMP / calcium chloride and a small amount of water are extracted from the bottom of the tower; Step B. The NMP / calcium chloride / water solution produced from the bottom of the heat pump distillation tower 100 enters a conventional distillation tower 200 for conventional distillation separation, wherein the conventional distillation temperature is 95° C., the theoretical number of stages is 20, the operating pressure is 15 kPa, and the operating reflux ratio is 2; water is produced from the top of the conventional distillation tower 200, NMP solvent (DMAC content is required to be greater than 99.5%) is produced from the side line of the tower, and NMP / calcium chloride solution is produced from the bottom of the tower; Step C. sending the NMP / calcium chloride solution extracted from the bottom of the conventional distillation tower 200 to the first filter 500 for hot filtration at a filtration temperature of 90° C. and a filter element pore size of 5 μm to separate insoluble matter and filtrate; Step D. Cool the filtrate after filtering in step C to -5°C, so that calcium chloride is crystallized into solid in NMP solvent, and the operating temperature of the crystallizer 600 is -5°C; filter with a second filter 700 with a filter mesh size of 5 μm to obtain recovered calcium chloride, and the filtrate enters the evaporator 300; Step E. Treat the calcium chloride filtrate in the evaporator 300, the operating temperature in the evaporator 300 is 105°C; the NMP solvent in the filtrate is further evaporated and condensed and then recovered, and the residual liquid at the bottom of the kettle is discharged as tar. The operating pressure of the evaporator 300 is 5kPa.

[0031] In this embodiment, NMP and calcium chloride are recovered from a mixed solution of NMP / calcium chloride / water. The recovery rate of NMP is 99.1%, and the recovery rate of calcium chloride is 95.5%.

[0032] In this embodiment, 1m 3 The solvent NMP consumes 3.2 tons of steam. Compared with the extraction recovery method, the steam consumption of the amide solvent is reduced by 62% (1-3.2 / 8.5=62%).

[0033] Example 2 A method for recycling an aqueous solution of amide chloride, the specific process steps are as follows: Step A. Feeding a mixed solution of N-methylpyrrolidone (NMP) / lithium chloride / water from a feed port into a heat pump distillation tower 100 for heat pump distillation separation, the heat pump distillation temperature is 70° C., the theoretical stage is 42, the operating pressure is 15 kPa, the operating reflux ratio is 2, water vapor is discharged from the top of the tower, and after being pressurized to 0.5 MPa by a steam heat pump 104, enters the second heater 102 to heat the kettle liquid, and the heated water vapor is divided into two streams, one of which is used as the reflux liquid of the heat pump distillation tower 100, and the other is used as the heating medium of the feed stream of the heat pump distillation tower 100, and NMP / lithium chloride and a small amount of water are extracted from the bottom of the tower; Step B. The NMP / calcium chloride / water solution produced from the bottom of the heat pump distillation tower 100 enters the conventional distillation tower 200 for rail distillation separation, and the conventional distillation temperature is 83° C., the theoretical stage is 26, the operating pressure is 10 kPa, and the operating reflux ratio is 1. Water is produced from the top of the conventional distillation tower 200, NMP solvent (DMAC content is required to be greater than 99.5%) is produced from the side line of the tower, and NMP / lithium chloride solution is produced from the bottom of the tower; Step C. sending the NMP / lithium chloride solution extracted from the bottom of the conventional distillation tower 200 to the first filter 500 for hot filtration at a filtration temperature of 60° C. and a filter element pore size of 1 μm to separate insoluble matter and filtrate; Step D. Cool the filtrate after filtering in step C to 0° C. to allow lithium chloride to crystallize into a solid in the NMP solvent. The operating temperature of the crystallizer 600 is 0° C. The filtrate is filtered by a second filter 700 with a mesh size of 1 μm to obtain recovered lithium chloride. The filtrate enters the evaporator 300; Step E: The lithium chloride filtrate is treated in the evaporator 300. The operating temperature of the evaporator 300 is 95° C. The NMP solvent in the filtrate is further evaporated and condensed and then recovered. The residual liquid at the bottom of the kettle is discharged as tar. The operating pressure of the evaporator 300 is 15 kPa.

[0034] In this embodiment, NMP and lithium chloride are recovered from a mixed solution of NMP / lithium chloride / water. The recovery rate of NMP is 98.9%, and the recovery rate of lithium chloride is 93.7%.

[0035] In this embodiment, 1m 3 The solvent NMP consumes 2.6 tons of steam. Compared with the extraction recovery method, the steam consumption of the amide solvent is reduced by 69% (1-2.6 / 8.5=69%).

[0036] Example 3 A method for recycling an aqueous solution of amide chloride, the specific process steps are as follows: Step A. Feeding a mixed solution of N,N-dimethylacetamide (DMAC) / calcium chloride / water from a feed port into a heat pump distillation tower 100 for heat pump distillation separation, the heat pump distillation temperature is 60° C., the theoretical number of stages is 50, the operating pressure is 30 kPa, the operating reflux ratio is 5, water vapor is discharged from the top of the tower, and after being pressurized to 0.15 MPa by a steam heat pump 104, it enters the reboiler of the distillation tower to heat the kettle liquid. The heated water vapor is divided into two streams, one of which is used as the reflux liquid of the heat pump distillation tower 100, and the other is used as the heating medium of the feed stream of the heat pump distillation tower 100. DMAC / calcium chloride and a small amount of water are extracted from the bottom of the tower; Step B. The DMAC / calcium chloride / water solution produced from the bottom of the heat pump distillation tower 100 enters the conventional distillation tower 200 for conventional distillation separation. The conventional distillation temperature is 70° C., the theoretical stage is 35, the operating pressure is 5 kPa, and the operating reflux ratio is 3. Water is produced from the top of the conventional distillation tower 200, the DMAC solvent is produced from the side line of the tower (the DMAC content is required to be greater than 99.5%), and the DMAC / calcium chloride solution is produced from the bottom of the tower; Step C. sending the DMAC / calcium chloride solution extracted from the bottom of the conventional distillation tower 200 to the first filter 500 for hot filtration at a filtration temperature of 80° C. and a filter element pore size of 3 μm to separate insoluble matter and filtrate; Step D. Cool the filtrate after filtering in step C to 5° C. to allow calcium chloride to crystallize into a solid in the DMAC solvent, and filter it with a second filter 700 with a filter mesh size of 3 μm to obtain recovered calcium chloride, and the filtrate enters the evaporator 300; Step E: treating the calcium chloride filtrate in an evaporator 300, the operating temperature of the evaporator 300 is 80°C; the DMAC solvent in the filtrate is further evaporated and condensed and then recovered, and the residual liquid at the bottom of the kettle is discharged as tar, and the operating pressure of the evaporator 300 is 12 kPa.

[0037] This embodiment recovers DMAC and calcium chloride from a DMAC / calcium chloride / water mixed solution. The DMAC recovery rate is 98.5%, and the calcium chloride recovery rate is 96.8%. In this embodiment, 1m 3 The solvent DMAC consumes 3.5t of steam. Compared with the extraction recovery method, the steam consumption of the amide solvent is reduced by 59% (1-3.5 / 8.5=59%).

[0038] Example 4 A method for recycling an aqueous solution of amide chloride, the specific process steps are as follows: Step A. Feeding a mixed solution of N,N-dimethylacetamide (DMAC) / lithium chloride / water from a feed port into a heat pump distillation tower 100 for heat pump distillation separation, with a theoretical stage of 45, an operating pressure of 20 kPa, and an operating reflux ratio of 2.5. The water vapor is discharged from the top of the tower, pressurized to 0.25 MPa by a steam heat pump 104, and then enters the second heater 102 to heat the kettle liquid. The cooled water vapor is divided into two streams, one of which is used as a reflux liquid of the heat pump distillation tower 100, and the other is used as a heating medium for the feed stream of the heat pump distillation tower 100. DMAC / lithium chloride and a small amount of water are extracted from the bottom of the tower; Step B. The DMAC / lithium chloride / water solution produced from the bottom of the heat pump distillation tower 100 enters the conventional distillation tower 200 for conventional distillation separation, with a theoretical stage of 30, an operating pressure of 10 kPa, and an operating reflux ratio of 1. Water is produced from the top of the conventional distillation tower 200, DMAC solvent is produced from the side line of the tower, and DMAC / lithium chloride solution is produced from the bottom of the tower; Step C. sending the DMAC / lithium chloride solution extracted from the bottom of the conventional distillation tower 200 to the first filter 500 for hot filtration at a filtration temperature of 60° C. and a filter element pore size of 3 μm to separate insoluble matter and filtrate; Step D. Cool the filtrate after filtering in step C to 0° C. to allow lithium chloride to crystallize into a solid in the DMAC solvent, and filter it with a second filter 700 with a filter mesh size of 3 μm to obtain recovered lithium chloride. The filtrate enters the evaporator 300; Step E: The lithium chloride filtrate is treated in the evaporator 300, and the DMAC solvent in the filtrate is further evaporated and condensed and then recovered, and the residual liquid at the bottom of the kettle is discharged as tar. The operating pressure of the evaporator 300 is 5 kPa.

[0039] In this embodiment, DMAC and lithium chloride are recovered from a DMAC / lithium chloride / water mixed solution. The DMAC recovery rate is 99.1%, and the lithium chloride recovery rate is 97.1%.

[0040] In this embodiment, 1m 3 The solvent DMAC consumed 2.8 tons of steam. Compared with the extraction recovery method, the steam consumption of the amide solvent was reduced by 67% (1-2.8 / 8.5=67%).

[0041] Example 5 The difference between this embodiment and embodiment 4 is that the reflux ratio of the conventional distillation tower 200 in step B is 3, and the filtrate in step D is cooled to 5°C.

[0042] In this embodiment, DMAC and lithium chloride are recovered from a DMAC / lithium chloride / water mixed solution. The DMAC recovery rate is 98.3%, and the lithium chloride recovery rate is 94.6%.

[0043] In this embodiment, 1m 3 The solvent DMAC consumed 3.7 tons of steam. Compared with the extraction recovery method, the steam consumption of the amide solvent was reduced by 56% (1-3.7 / 8.5=56%).

[0044] The experimental conditions and results of Comparative Example 4 and Example 5 are listed in the following Table 1.

[0045] Table 1 As a comparative example, Example 5 is adjusted on the basis of Example 4, the reflux ratio of the conventional distillation tower 200 in step B is increased from 1 to 3, the cooling temperature of the filtrate in step D is increased from 0° C. to 5° C., and the other process parameters remain unchanged.

[0046] After the adjustment, the recovery rate of lithium chloride is reduced, and the recovery rate of DMAC is also reduced. This is because after the cooling temperature of the filtrate in step D is increased from 0°C to 5°C, the amount of lithium chloride crystallized in the filtrate is reduced, resulting in a decrease in its recovery rate. At the same time, the amount of lithium chloride entering the evaporator 300 is increased, which increases the boiling point of the bottom liquid of the evaporator 300, resulting in a decrease in the recovery rate of DMAC.

[0047] In addition, the unit consumption of DMAC solvent vapor increased after the parameter adjustment. This is because the reflux ratio increased, the amount of liquid vaporization in the distillation tower increased, and the required heat increased.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for recycling an amide chloride aqueous solution, characterized in that: The following steps are involved: Step A, the aqueous solution of amide chloride is fed into a heat pump distillation tower from a feed port for heat pump distillation separation, water vapor is discharged from the top of the tower, and enters the second heater to heat the kettle liquid after being pressurized by a steam heat pump, and the heated water vapor is divided into two streams, one as the reflux liquid of the distillation tower, and the other as the heating medium of the feed stream of the heat pump distillation tower; amide / chloride and a small amount of water are extracted from the bottom of the tower; Step B, amide / chloride and a small amount of water enter a conventional distillation tower for conventional distillation separation, water is produced from the top of the tower, amide solvent is produced from the side line of the tower, and amide / chloride solution is produced from the bottom of the tower; Step C, the amide / chloride solution is sent to a first filter for hot filtration to separate insoluble matter and filtrate; Step D: the filtrate is cooled in turn by the second condenser, crystallized in the crystallizer, and filtered twice by the second filter to obtain pure chloride, and the remaining filtrate enters the evaporator; Step E: The remaining filtrate is evaporated in an evaporator, the amide solvent in the remaining filtrate is further evaporated and condensed and then recovered, and the residual liquid at the bottom of the kettle is discharged as tar.

2. The method for recycling an amide chloride aqueous solution according to claim 1, characterized in that: In the amide chloride aqueous solution, the amide includes any one of N-methylpyrrolidone and N,N-dimethylacetamide, and the chloride includes any one of lithium chloride and calcium chloride.

3. The method for recycling an amide chloride aqueous solution according to claim 1, characterized in that: In the step A, the theoretical number of stages of the heat pump distillation tower is 35-50; the heat pump distillation tower adopts reduced pressure operation, and the operating pressure is 5-30 kPa; the operating reflux ratio of the heat pump distillation tower is 2-5.

4. The method for recycling an amide chloride aqueous solution according to claim 1, characterized in that: In the step A, the pressure of the steam heat pump after pressurization is 0.15-0.5 MPa.

5. The method for recycling an amide chloride aqueous solution according to claim 1, characterized in that: In the step B, the theoretical number of stages of the conventional distillation tower is 20-35; the conventional distillation tower adopts reduced pressure operation, and the operating pressure is 5-15 kPa; the operating reflux ratio of the conventional distillation tower is 1-3.

6. The method for recycling an amide chloride aqueous solution according to claim 1, characterized in that: In the step C, the temperature of the amide / chloride solution is controlled at 60-90°C.

7. The method for recycling an amide chloride aqueous solution according to claim 1, characterized in that: In the step D, the temperature of the material after cooling by the second condenser is -5~5°C.

8. The method for recycling an amide chloride aqueous solution according to claim 1, characterized in that: The filter mesh apertures of the first filter and the second filter are both in the range of 1 μm to 5 μm.

9. The method for recycling an amide chloride aqueous solution according to claim 1, characterized in that: In the step F, the evaporator is operated under reduced pressure, and the operating pressure is 5-15 kPa.

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