Method and system for concentrating caprolactam aqueous solution

Abstract

The method comprises the following steps: (a) enabling the caprolactam aqueous solution to sequentially pass through an oximation reaction liquid heat exchanger, a primary rearrangement reaction liquid heat exchanger and a secondary rearrangement reaction liquid heat exchanger, heating the caprolactam aqueous solution by utilizing the heat of the cyclohexanone oximation reaction liquid, the primary rearrangement reaction liquid and the secondary rearrangement reaction liquid; (b) introducing the heated caprolactam aqueous solution into a second inlet of the distillation tower for connection, and separating and removing part of water through vacuum distillation to obtain a concentrated caprolactam solution; part of the concentrated solution is circulated and combined with the low-concentration caprolactam aqueous solution, and the rest of the concentrated solution is extracted to a downstream process; and (c) refluxing the water phase part extracted from the tower top of the distillation tower to the distillation tower, and extracting the other part to a downstream process for use. Through comprehensive utilization of waste heat and integrated innovation of the system, the system has remarkable advantages in the aspects of energy conservation, consumption reduction, cost control and environmental protection performance.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical industry, and in particular to a system and method for concentrating a caprolactam aqueous solution. Background Art

[0002] Caprolactam is an important organic chemical raw material, primarily used in the production of nylon-6. It is widely used in industries such as spinning, tires, and food packaging, and has a wide range of applications. Caprolactam production processes primarily include the cyclohexanone-hydroxylamine process, the toluene process, the cyclohexane photonitrosation process, and the cyclohexanone ammoximation process. The cyclohexanone ammoximation process offers advantages such as a simple process flow, mild reaction conditions, high reactant conversion rates, and high selectivity.

[0003] The cyclohexanone ammoximation method mainly includes two processes: cyclohexanone oximation and rearrangement reaction. The cyclohexanone oximation reaction refers to the process of producing cyclohexanone oxime by reacting cyclohexanone with ammonia under the action of hydrogen peroxide. This process generates high reaction heat. In common production processes, circulating water is usually used to remove the reaction heat, resulting in waste of low-level thermal energy and circulating water.

[0004] The rearrangement reaction in caprolactam production is a highly exothermic reaction that generates a large amount of heat. This heat is usually removed by circulating hot water. However, since the hot water temperature is generally 65-80°C, the temperature is relatively low and the temperature range varies greatly, the waste heat from this reaction is difficult to recycle. The industry generally removes this reaction heat by circulating cooling water, resulting in waste of low-level thermal energy and circulating water.

[0005] Patent CN 111013170A discloses an energy-saving evaporation system and method for caprolactam aqueous solution. While this method reduces evaporation energy consumption, it still relies on external steam and fails to fully integrate waste heat from the reaction. Furthermore, the traditional process operates separately from the concentration system, failing to achieve cascaded energy utilization and limiting overall energy efficiency.

[0006] Therefore, there is an urgent need to develop a caprolactam concentration system and concentration method that can efficiently utilize reaction waste heat, reduce cooling water demand and reduce external energy input, so as to achieve green and energy-saving optimization of the production process. Summary of the Invention

[0007] The purpose of the present application is to provide a system and method for concentrating a caprolactam aqueous solution that utilizes waste heat from the reaction to achieve high efficiency and energy saving.

[0008] To achieve the above experimental objectives, the present invention adopts the following technical solutions: First, the present invention provides a method for concentrating a caprolactam aqueous solution. Second, the present invention provides a system for concentrating a caprolactam aqueous solution.

[0009] A first aspect of the present application provides a method for concentrating a caprolactam aqueous solution, comprising the following steps: (a) passing the caprolactam aqueous solution through an oximation reaction liquid heat exchanger, a primary rearrangement reaction liquid heat exchanger, and a secondary rearrangement reaction liquid heat exchanger in sequence, and heating the caprolactam aqueous solution in multiple stages by utilizing the heat of the cyclohexanone oximation reaction liquid, the primary rearrangement reaction liquid, and the secondary rearrangement reaction liquid; (b) introducing the heated caprolactam aqueous solution into a distillation column, separating water in the distillation column by vacuum distillation to obtain a concentrated caprolactam solution; a portion of the concentrated solution is refluxed and combined with the low-concentration caprolactam aqueous solution, and the remaining portion is withdrawn to a downstream process; (c) The aqueous phase extracted from the top of the distillation tower is refluxed to the distillation tower, and the remaining portion is extracted and used in downstream processes.

[0010] Furthermore, in step (a), the initial concentration of the caprolactam aqueous solution is 30%-35% wt.

[0011] Furthermore, the heat source of the oximation reaction liquid heat exchanger is the oximation reaction circulating liquid, and the heat sources of the first-stage rearrangement reaction liquid heat exchanger and the second-stage rearrangement reaction liquid heat exchanger correspond to the first-stage rearrangement reaction circulating liquid and the second-stage rearrangement reaction circulating liquid respectively.

[0012] Furthermore, in step (b), the pressure at the top of the distillation tower of the vacuum distillation is controlled in the range of 5-50 kPa, and the concentration of the concentrated caprolactam solution is 40%-55% wt.

[0013] Furthermore, in step (b), the concentrated liquid is circulated to maintain the temperature control of the oximation reaction liquid heat exchanger, the first-stage rearrangement reaction liquid heat exchanger and the second-stage rearrangement reaction liquid heat exchanger.

[0014] Furthermore, in step (c), the downstream process refers to a caprolactam stripping process, that is, using an aqueous phase to strip caprolactam from the organic phase to the aqueous phase.

[0015] A second aspect of the present application provides a caprolactam aqueous solution concentration system for implementing the method, the caprolactam aqueous solution concentration system comprising an oximation reaction liquid heat exchanger, a primary rearrangement reaction liquid heat exchanger, a secondary rearrangement reaction liquid heat exchanger, a distillation tower, a caprolactam solution circulation pump, a condenser, a reflux tank, a vacuum pump, a condensate extraction pump, and a distillation tower bottom extraction pump; The caprolactam aqueous solution feed pipeline is connected to the inlet of the oximation reaction liquid heat exchanger through the caprolactam solution circulation pump, the outlet of the oximation reaction liquid heat exchanger is connected to the first rearrangement reaction liquid heat exchanger and the second rearrangement reaction liquid heat exchanger in sequence, the outlet of the second rearrangement reaction liquid heat exchanger is connected to the inlet of the distillation tower, the top outlet of the distillation tower is connected to the first inlet of the condenser, the outlet of the condenser is connected to the inlet of the reflux tank, the first outlet of the reflux tank is connected to the inlet of the vacuum pump, the second outlet of the reflux tank is connected to the inlet of the condensate extraction pump, the first outlet of the condensate extraction pump is connected to the second inlet of the distillation tower, the first bottom outlet of the distillation tower is connected to the second inlet of the caprolactam solution circulation pump, the outlet of the caprolactam solution circulation pump is connected to the inlet of the oximation reaction liquid heat exchanger, and the second bottom outlet of the distillation tower is connected to the inlet of the distillation tower kettle extraction pump.

[0016] Furthermore, the oximation reaction liquid heat exchanger, the first-stage rearrangement reaction liquid heat exchanger and the second-stage rearrangement reaction liquid heat exchanger are any one of a shell and tube heat exchanger, a coiled plate heat exchanger or a plate and frame heat exchanger.

[0017] Furthermore, the distillation tower is any one of a sieve plate tower, a packed tower or a floating valve tower. The system realizes the cascade utilization of the reaction waste heat by connecting multiple stages of heat exchangers in series.

[0018] Beneficial effects: The present invention has significant advantages in energy saving and consumption reduction, cost control, environmental friendliness and economic efficiency through comprehensive utilization of waste heat and system integration innovation, and is suitable for large-scale application of cyclohexanone ammoximation method to produce caprolactam.

[0019] Compared with the existing technology, the present invention has the following advantages: (1) Cascade utilization of waste heat: By connecting the heat exchangers for the oximation reaction liquid, the first-stage rearrangement reaction liquid, and the second-stage rearrangement reaction liquid in series, the waste heat from the multi-stage reaction is used to heat the caprolactam aqueous solution, completely replacing the external steam relied on in the traditional process. This is the first time that the deep integration of reaction waste heat and the concentration system has been achieved, breaking the traditional process's reliance on a single heat source.

[0020] (2) Resource conservation: Low-level heat recovery: The waste heat of 65-80℃ circulating hot water in traditional processes is effectively utilized to avoid heat energy waste and achieve energy system optimization.

[0021] (3) Low equipment investment: The system of the present invention does not require the addition of complex equipment: only a heat exchanger needs to be added, and the adaptability design is carried out according to the physical properties of the medium, and the pipeline connection is optimized. There is no need to add equipment such as a tower kettle and a large evaporator. Strong compatibility: It can be adapted to a variety of heat exchangers such as shell and tube, coiled plate, and plate, as well as distillation tower types such as sieve plate towers, packed towers, and float valve towers. The modification cost is low and it is easy to promote.

[0022] (4) Process stability: The present invention refluxes part of the concentrated solution to the front end and merges it with the low-concentration solution, providing a stable refrigerant flow to the oximation and rearrangement reactors, ensuring precise control of the reaction temperature. Avoiding temperature fluctuations: The risk of system downtime caused by heat fluctuations in traditional processes is significantly reduced, improving production continuity and product quality consistency.

[0023] (5) The present invention reduces carbon emissions: the significant reduction in steam usage directly reduces coal or gas consumption, reducing CO2 emissions. This meets the environmental protection requirements of green chemical industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0025] Figure 1 This is a process schematic diagram of the caprolactam aqueous solution concentration system of the present invention.

[0026] 1-oximation reaction liquid heat exchanger, 2-first-stage rearrangement reaction liquid heat exchanger, 3-second-stage rearrangement reaction liquid heat exchanger, 4-distillation tower, 5-caprolactam solution circulation pump, 6-condenser, 7-reflux tank, 8-vacuum pump, 9-condensate extraction pump, 10-distillation tower kettle extraction pump. DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0028] In this application, the term "and / or" describes the relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0029] In this application, "-at least one" means one or more, and "plurality" means two or more. "-at least one" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "-at least one of a, b, or c" or "-at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can each be single or plural.

[0030] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0031] The terms used in the embodiments of the present application are for the purpose of describing specific embodiments only and are not intended to limit the present application. The singular forms "a", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0032] The weights of the relevant components mentioned in the examples of this application may not only refer to the specific content of each component, but also represent the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally increased or decreased according to the examples of this application, it is within the scope disclosed in the examples of this application. Specifically, the mass described in the examples of this application may be a mass unit known in the chemical industry, such as μg, mg, g, kg, etc.

[0033] The terms "first" and "second" are used solely for descriptive purposes, to distinguish objects, such as substances, from one another. They should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the technical features being referred to. For example, a first XX could also be referred to as a second XX, and similarly, a second XX could also be referred to as a first XX, without departing from the scope of the embodiments of this application. Thus, features defined as "first" or "second" may explicitly or implicitly include one or more of such features.

[0034] A first aspect of the present application provides a method for concentrating a caprolactam aqueous solution, comprising the following steps: (a) passing the caprolactam aqueous solution through an oximation reaction liquid heat exchanger 1, a primary rearrangement reaction liquid heat exchanger 2, and a secondary rearrangement reaction liquid heat exchanger 3 in sequence, and heating the caprolactam aqueous solution in multiple stages using the heat of the cyclohexanone oximation reaction liquid, the primary rearrangement reaction liquid, and the secondary rearrangement reaction liquid; (b) introducing the heated caprolactam aqueous solution into a distillation column 4, separating water in the distillation column 4 by vacuum distillation to obtain a concentrated caprolactam solution; a portion of the concentrated solution is refluxed and combined with the low-concentration caprolactam aqueous solution, and the remaining portion is withdrawn to a downstream process; (c) The aqueous phase extracted from the top of the distillation tower 4 is refluxed to the distillation tower, and the remaining portion is extracted and used in the stripping system.

[0035] In some embodiments, in step (a), the initial concentration of the caprolactam aqueous solution is 30% wt.

[0036] In some embodiments, in step (a), the initial concentration of the caprolactam aqueous solution is 35% wt.

[0037] In some embodiments, in step (a), the initial concentration of the caprolactam aqueous solution is 32% wt.

[0038] In some embodiments, in step (b), the pressure at the top of the distillation tower 4 of the vacuum distillation is controlled in the range of 5-50 kPa, and the concentration of the concentrated caprolactam solution is 40% wt.

[0039] In some embodiments, in step (b), the pressure at the top of the distillation tower 4 of the vacuum distillation is controlled in the range of 5-50 kPa, and the concentration of the concentrated caprolactam solution is 55% wt.

[0040] In some embodiments, in step (b), the pressure at the top of the distillation tower 4 of the vacuum distillation is controlled in the range of 5-50 kPa, and the concentration of the concentrated caprolactam solution is 47% wt.

[0041] In some embodiments, in step (b), the concentrated liquid is circulated to maintain temperature control of the oximation reaction liquid heat exchanger, the first-stage rearrangement reaction liquid heat exchanger, and the second-stage rearrangement reaction liquid heat exchanger.

[0042] In some embodiments, the heat source of the oximation reaction liquid heat exchanger is the cyclohexanone oximation reaction circulating liquid, and the heat sources of the first-stage rearrangement reaction liquid heat exchanger and the second-stage rearrangement reaction liquid heat exchanger correspond to the first-stage rearrangement reaction circulating liquid and the second-stage rearrangement reaction circulating liquid, respectively.

[0043] In some embodiments, in step (b), the concentrated liquid is circulated to maintain the temperature of the oximation reaction liquid heat exchanger 1 , the first-stage rearrangement reaction liquid heat exchanger 2 , and the second-stage rearrangement reaction liquid heat exchanger 3 .

[0044] A second aspect of the present application provides a caprolactam aqueous solution concentration system for implementing the method, the caprolactam aqueous solution concentration system comprising an oximation reaction liquid heat exchanger 1, a primary rearrangement reaction liquid heat exchanger 2, a secondary rearrangement reaction liquid heat exchanger 3, a distillation tower 4, a caprolactam solution circulation pump 5, a condenser 6, a reflux tank 7, a vacuum pump 8, a condensate extraction pump 9, and a distillation tower bottom extraction pump 10; The caprolactam aqueous solution feed pipeline is connected to the inlet of the oximation reaction liquid heat exchanger 1 through the caprolactam solution circulation pump 5. The outlet of the oximation reaction liquid heat exchanger 1 is connected to the first rearrangement reaction liquid heat exchanger 2 and the second rearrangement reaction liquid heat exchanger 3 in sequence. The outlet of the second rearrangement reaction liquid heat exchanger 3 is connected to the inlet of the distillation tower 4. The top outlet of the distillation tower 4 is connected to the first inlet of the condenser 6. The outlet of the condenser 6 is connected to the inlet of the reflux tank 7. The first outlet of the reflux tank 7 is connected to the inlet of the vacuum pump 8. The second outlet of the reflux tank 7 is connected to the inlet of the condensate extraction pump 9. The first outlet of the condensate extraction pump 9 is connected to the second inlet of the distillation tower 4. The first bottom outlet of the distillation tower 4 is connected to the second inlet of the caprolactam solution circulation pump 5. The outlet of the caprolactam solution circulation pump 5 is connected to the inlet of the oximation reaction liquid heat exchanger 1. The second bottom outlet of the distillation tower 4 is connected to the inlet of the distillation tower kettle extraction pump 10.

[0045] In some embodiments, the oximation reaction liquid heat exchanger 1, the first-stage rearrangement reaction liquid heat exchanger 2 and the second-stage rearrangement reaction liquid heat exchanger 3 are any one of a shell and tube heat exchanger, a coil heat exchanger or a plate and frame heat exchanger.

[0046] In some embodiments, the distillation tower 4 is a sieve plate tower. The system realizes the cascade utilization of the reaction waste heat by connecting multiple stages of heat exchangers in series.

[0047] In some embodiments, the distillation tower 4 is a packed tower. The system realizes the cascade utilization of the reaction waste heat by connecting multiple stages of heat exchangers in series.

[0048] In some embodiments, the distillation tower 4 is a floating valve tower. The system realizes the cascade utilization of the reaction waste heat by connecting multiple stages of heat exchangers in series. Example 1

[0049] A method for concentrating a caprolactam aqueous solution of the present invention comprises the following steps: (a) A caprolactam aqueous solution is sequentially passed through an oximation reaction liquid heat exchanger 1, a primary rearrangement reaction liquid heat exchanger 2, and a secondary rearrangement reaction liquid heat exchanger 3, where the caprolactam aqueous solution is heated in multiple stages using the heat from the cyclohexanone oximation reaction liquid, the primary rearrangement reaction liquid, and the secondary rearrangement reaction liquid. The initial concentration of the caprolactam aqueous solution is 35% wt. The heat source for the oximation reaction liquid heat exchanger is the oximation reaction circulating fluid, while the heat sources for the primary rearrangement reaction liquid heat exchanger 2 and the secondary rearrangement reaction liquid heat exchanger 3 correspond to the primary rearrangement reaction circulating fluid and the secondary rearrangement reaction unit circulating fluid, respectively.

[0050] (b) The heated caprolactam aqueous solution is introduced into distillation column 4, where water is separated by vacuum distillation to obtain a concentrated caprolactam solution. A portion of the concentrated solution is refluxed and combined with the low-concentration caprolactam aqueous solution, while the remainder is withdrawn to downstream processes. The pressure at the top of distillation column 4 during vacuum distillation is controlled within a range of 8 kPa, resulting in a concentrated caprolactam solution with a concentration of 47.2% wt. The reflux of the concentrated solution is used to maintain the temperatures of oximation reaction liquid heat exchanger 1, primary rearrangement reaction liquid heat exchanger 2, and secondary rearrangement reaction liquid heat exchanger 3.

[0051] (c) The aqueous phase extracted from the top of the distillation tower is refluxed to the distillation tower, and the remaining portion is extracted and used in the stripping system.

[0052] In Example 1, a solution with an initial concentration of 35% wt was heated to 47.4% wt through multiple stages without the need for additional steam. This increased power consumption by only 559 kW / h, equivalent to 0.0688 Tce / h of standard coal, was achieved. This compares to a conventional triple-effect evaporation process that consumes 26 t / h of steam (26 tons per hour, equivalent to 2.45 Tce / h of standard coal), resulting in a 97.2% reduction in overall energy consumption. Example 2

[0053] The difference between Example 2 and Example 1 is that in step (a), the initial concentration of the caprolactam aqueous solution is 30% wt. In step (b), the pressure at the top of the vacuum distillation column 4 is controlled within a range of 10 kPa, and the concentration of the concentrated caprolactam solution is 40% wt. Example 3

[0054] Example 3 differs from Example 1 in that in step (a), the initial concentration of the caprolactam aqueous solution is 32% wt. In step (b), the pressure at the top of the vacuum distillation column 4 is controlled within a range of 5 kPa, and the concentration of the concentrated caprolactam solution is 55% wt. Example 4

[0055] The present invention provides a caprolactam aqueous solution concentration system for implementing the method, the caprolactam aqueous solution concentration system comprising an oximation reaction liquid heat exchanger 1, a primary rearrangement reaction liquid heat exchanger 2, a secondary rearrangement reaction liquid heat exchanger 3, a distillation tower 4, a caprolactam solution circulation pump 5, a condenser 6, a reflux tank 7, a vacuum pump 8, a condensate extraction pump 9, and a distillation tower bottom extraction pump 10; The caprolactam aqueous solution feed pipeline is connected to the inlet of the oximation reaction liquid heat exchanger 1 through the caprolactam solution circulation pump 5. The outlet of the oximation reaction liquid heat exchanger 1 is connected to the first rearrangement reaction liquid heat exchanger 2 and the second rearrangement reaction liquid heat exchanger 3 in sequence. The outlet of the second rearrangement reaction liquid heat exchanger 3 is connected to the inlet of the distillation tower 4. The top outlet of the distillation tower 4 is connected to the first inlet of the condenser 6. The outlet of the condenser 6 is connected to the inlet of the reflux tank 7. The first outlet of the reflux tank 7 is connected to the inlet of the vacuum pump 8. The second outlet of the reflux tank 7 is connected to the inlet of the condensate extraction pump 9. The first outlet of the condensate extraction pump 9 is connected to the second inlet of the distillation tower 4. The first bottom outlet of the distillation tower 4 is connected to the second inlet of the caprolactam solution circulation pump 5. The outlet of the caprolactam solution circulation pump 5 is connected to the inlet of the oximation reaction liquid heat exchanger 1. The second bottom outlet of the distillation tower 4 is connected to the inlet of the distillation tower kettle extraction pump 10.

[0056] The oximation reaction liquid heat exchanger 1, the first-stage rearrangement reaction liquid heat exchanger 2 and the second-stage rearrangement reaction liquid heat exchanger 3 are shell and tube heat exchangers.

[0057] The distillation tower 4 is a sieve plate tower.

[0058] The condenser 6 at the top of the distillation tower works in conjunction with the vacuum pump 8 to maintain negative pressure in the system. The system achieves cascade utilization of the reaction waste heat through the series connection of multiple stages of heat exchangers. Example 5

[0059] The difference between Example 5 and Example 4 is that the oximation reaction liquid heat exchanger 1, the first-stage rearrangement reaction liquid heat exchanger 2 and the second-stage rearrangement reaction liquid heat exchanger 3 are coiled plate heat exchangers.

[0060] The distillation tower 4 is a packed tower. Example 6

[0061] The difference between Example 6 and Example 4 is that the oximation reaction liquid heat exchanger 1 is a tubular heat exchanger, the first-stage rearrangement reaction liquid heat exchanger 2 and the second-stage rearrangement reaction liquid heat exchanger 3 are plate heat exchangers, and the distillation tower 4 is a floating valve tower. Test Example 1

[0062] In a caprolactam production process, the initial concentration of the caprolactam aqueous solution is 35% wt., with a flow rate of 192 t / h. This solution is sequentially passed through an oximation reaction liquid heat exchanger, a primary rearrangement reaction liquid heat exchanger, and a secondary rearrangement reaction liquid heat exchanger. Heat from the cyclohexanone oximation reaction liquid, the primary rearrangement reaction liquid, and the secondary rearrangement reaction liquid is utilized to heat the caprolactam aqueous solution in a three-stage process, reaching a temperature of 80-95°C. After vacuum distillation in a distillation tower, the caprolactam aqueous solution concentration is increased to 55.0% wt. The process of this invention does not require additional steam consumption, but only increases power consumption by 644 kW, equivalent to 0.0792 Tce / h of standard coal. Comparative Example 1

[0063] The process conditions of the caprolactam aqueous solution are the same as those of Experimental Example 1. This comparative example adopts a three-stage reduced pressure evaporation process to provide the caprolactam aqueous solution. In order to increase the concentration of the caprolactam aqueous solution to 55.0%wt, the steam required is 33.3t / h, which is equivalent to 3.14Tce / h of standard coal.

[0064] From the comparison between the above-mentioned Test Example 1 and Comparative Example 1, it can be seen that under the same process conditions, the comprehensive energy consumption of the technology of the present invention is reduced by 97.5%. Comparative Example 2

[0065] Patent CN 107556213 B discloses a process for the ammoximation of cyclohexanone and a process for producing caprolactam. This patent utilizes the reaction heat of the subsequent rearrangement reaction to separate the extractant, thereby reducing energy consumption.

[0066] The heat energy of benzene distillation in Comparative Example 2 is less than that of the distillation of the caprolactam aqueous solution, and the heat of oximation reaction and rearrangement reaction cannot be fully utilized.

[0067] It can be seen from the above test examples that, compared with the organic system of this comparative example, the heating temperature of the caprolactam aqueous solution is higher (85°C), the temperature difference with the heat source is smaller, and the thermal energy utilization efficiency is higher.

[0068] The basic principles, main features and advantages of the present invention are shown and described above. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and improvements may be made to the present invention without departing from the spirit and scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims, the description and their equivalents.

Claims

1. A method for concentrating a caprolactam aqueous solution, characterized in that The steps include: (a) passing the caprolactam aqueous solution through an oximation reaction liquid heat exchanger (1), a primary rearrangement reaction liquid heat exchanger (2), and a secondary rearrangement reaction liquid heat exchanger (3) in sequence, and heating the caprolactam aqueous solution in multiple stages by utilizing the heat of the cyclohexanone oximation reaction liquid, the primary rearrangement reaction liquid, and the secondary rearrangement reaction liquid; (b) introducing the heated caprolactam aqueous solution into a distillation tower (4), separating the water in the distillation tower (4) by vacuum distillation to obtain a concentrated caprolactam solution; a portion of the concentrated solution is refluxed and combined with the low-concentration caprolactam aqueous solution, and the remaining portion is withdrawn to a downstream process; (c) The aqueous phase extracted from the top of the distillation tower (4) is refluxed to the distillation tower, and the remaining portion is extracted and used in the downstream process.

2. The concentration method according to claim 1, wherein: In step (a), the initial concentration of the caprolactam aqueous solution is 30%-35% wt.

3. The concentration method according to claim 1, wherein: The heat source of the oximation reaction liquid heat exchanger is the oximation reaction circulating liquid, and the heat sources of the primary rearrangement reaction liquid heat exchanger and the secondary rearrangement reaction liquid heat exchanger correspond to the primary rearrangement reaction circulating liquid and the secondary rearrangement reaction circulating liquid respectively.

4. The concentration method according to claim 1, wherein: In step (b), the pressure at the top of the distillation tower of the vacuum distillation is controlled in the range of 5-50 kPa, and the concentration of the concentrated caprolactam solution is 40%-55%wt.

5. The concentration method according to claim 1, wherein: In step (b), the concentrated liquid is circulated to maintain the temperature of the oximation reaction liquid heat exchanger, the first-stage rearrangement reaction liquid heat exchanger, and the second-stage rearrangement reaction liquid heat exchanger.

6. A system for concentrating a caprolactam aqueous solution for implementing the method according to any one of claims 1 to 5, characterized in that: The caprolactam aqueous solution concentration system includes an oximation reaction liquid heat exchanger, a primary rearrangement reaction liquid heat exchanger, a secondary rearrangement reaction liquid heat exchanger, a distillation tower, a caprolactam solution circulation pump, a condenser, a reflux tank, a vacuum pump, a condensate extraction pump, and a distillation tower kettle extraction pump; the caprolactam aqueous solution feed pipeline is connected to the inlet of the oximation reaction liquid heat exchanger through the caprolactam solution circulation pump, the outlet of the oximation reaction liquid heat exchanger is connected to the primary rearrangement reaction liquid heat exchanger and the secondary rearrangement reaction liquid heat exchanger in sequence, and the outlet of the secondary rearrangement reaction liquid heat exchanger is connected to the inlet of the distillation tower. The top outlet of the distillation tower is connected to the first inlet of the condenser, the outlet of the condenser is connected to the inlet of the reflux tank, the first outlet of the reflux tank is connected to the inlet of the vacuum pump, the second outlet of the reflux tank is connected to the inlet of the condensate extraction pump, the first outlet of the condensate extraction pump is connected to the second inlet of the distillation tower, the first bottom outlet of the distillation tower is connected to the second inlet of the caprolactam solution circulation pump, the outlet of the caprolactam solution circulation pump is connected to the inlet of the oximation reaction liquid heat exchanger, and the second bottom outlet of the distillation tower is connected to the inlet of the distillation tower kettle extraction pump.

7. The system according to claim 6, characterized in that: The oximation reaction liquid heat exchanger (1), the first-stage rearrangement reaction liquid heat exchanger (2), and the second-stage rearrangement reaction liquid heat exchanger (3) are any one of a shell and tube heat exchanger, a coiled plate heat exchanger, or a plate heat exchanger.

8. The system according to claim 6, characterized in that: The distillation tower (4) is any one of a sieve plate tower, a packed tower or a floating valve tower.

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