An energy-saving pyridine coupling system and method for rectifying and separating 2,2'-bipyridine

Abstract

The application relates to the technical field of rectification separation and energy saving, in particular to an energy-saving pyridine coupling 2,2'-bipyridine rectification separation system and method. The rectification separation system provided by the application comprises a pre-fractionating tower system, a bipyridine light-removing tower, a bipyridine product tower, a piperidine-removing tower and a pyridine-removing tower system; the pre-fractionating tower system comprises a No.1 pre-fractionating tower, a No.2 pre-fractionating tower and a No.3 pre-fractionating tower; the pyridine-removing tower system comprises a No.1 pyridine-removing tower and a No.2 pyridine-removing tower; the top of the No.1 pre-fractionating tower is connected with the piperidine-removing tower and the pyridine-removing tower system through pipelines in sequence; the No.2 pre-fractionating tower is provided with a closed heat pump system; and the top of the No.3 pre-fractionating tower is connected with the pyridine-removing tower system through a pipeline. The separation method provided by the application is innovatively combined with differential pressure type heat coupling, heat pump rectification and double-effect rectification and other energy-saving technologies through unique material arrangement and rectification sequence comprehensive optimization, so that 2,2'-bipyridine products can be separated efficiently and with low energy consumption.

Description

Technical Field

[0001] This application relates to the technical field of distillation separation and energy saving, and in particular to an energy-saving distillation separation system and method for the coupling of pyridine to 2,2'-bipyridine. Background Technology

[0002] 2,2'-Bipyridine is a very important pyridine derivative, appearing as a white or light pink crystalline powder with a melting point of 69.7℃ and a boiling point between 272 and 273℃. As an important chemical intermediate, 2,2'-bipyridine is widely used in catalyst synthesis, electrochemical analysis, metal corrosion inhibitors, and the preparation of functional materials. Particularly in pesticide production and research, 2,2'-bipyridine can serve as a major raw material for the systemic contact herbicide diquat. Due to the increasing demand for 2,2'-bipyridine, green production technologies for 2,2'-bipyridine have significant industrial value and important social significance.

[0003] The main industrial production methods for 2,2'-bipyridine include the Ullmann coupling method and the pyridine coupling method. The Ullmann coupling method, however, has low atom utilization and generates significant amounts of difficult-to-treat solid waste, and has been gradually phased out in recent years. The pyridine coupling method uses pyridine as a raw material, directly coupling it to 2,2'-bipyridine under nickel-based catalysis. This method is the most atom-economical and environmentally friendly among various 2,2'-bipyridine preparation methods, and is also a relatively clean method for 2,2'-bipyridine production. However, this method has a low conversion rate, and the reaction products have a complex composition, mainly containing piperidine, pyridine (approximately 90%), 2-methylpyridine, bipyridine precursors, 2,2'-bipyridine (approximately 8%), the target product, and heavy bipyridine impurities, among other components.

[0004] Multicomponent distillation separation inevitably involves the selection of distillation sequences, and a superior sequence can effectively reduce energy consumption in chemical production processes. Separation sequence synthesis refers to systematically analyzing and synthesizing processes that can separate the desired product from the feed while minimizing total cost, given a specific feed composition and conditions. Taking the distillation separation of a three-component mixture as an example, if a conventional column is used, there are two distillation sequences—a direct sequence (light components are drawn off sequentially at the top of the column) and an indirect sequence (heavy components are drawn off sequentially at the bottom of the column). When the mixture to be separated contains more than R components, the number of feasible distillation sequences is S. R =[2(R-1)]! / [R!(R-1)]! as many as [2(R-1)]!.

[0005] Therefore, the selection of distillation sequence is of great significance for the economics of the separation process. Choosing a suitable distillation sequence can minimize the energy consumption of the distillation process.

[0006] However, the separation of pyridine coupling reaction products faces the following specific challenges:

[0007] (1) The product has a complex composition with no less than 6 important components that need to be separated; and some components, such as piperidine and pyridine, and 2-methylpyridine and water, exhibit azeotropic phenomena, which are difficult to effectively separate using conventional separation methods.

[0008] (2) Traditional separation sequences usually adopt the strategy of prioritizing the separation of the component with the highest content. However, the separation and recovery of a large amount of pyridine has a significant impact on energy consumption, and no effective measures have been taken to optimize the separation energy consumption of this part.

[0009] (3) Bipyridine products have a high boiling point at normal pressure (2,2'-bipyridine has a boiling point of about 273°C), which requires high heating equipment and steam quality, and is prone to decomposition or coking at high temperatures.

[0010] Therefore, developing an optimized distillation sequence for this specific system, combined with advanced energy-saving technologies, is of great significance for achieving efficient, energy-saving, and economical production of 2,2'-bipyridine. Summary of the Invention

[0011] This application provides an energy-saving distillation separation system and method for the production of 2,2'-bipyridine from pyridine coupling. The distillation separation system provided by this application can efficiently and with low energy consumption separate 2,2'-bipyridine from the complex mixture obtained from the pyridine coupling reaction.

[0012] In a first aspect, this application provides an energy-saving distillation and separation system for the coupling of pyridine to 2,2'-bipyridine, employing the following technical solution:

[0013] An energy-saving distillation and separation system for the coupling of pyridine to 2,2'-bipyridine, the distillation and separation system comprising a pre-separation column system, a bipyridine light-light-removal column, a bipyridine product column, a piperidine-removing column, and a pyridine-removing column system; the pre-separation column system comprises a pre-separation column #1, a pre-separation column #2, and a pre-separation column #3; the pyridine-removing column system comprises a pyridine-removing column #1 and a pyridine-removing column #2.

[0014] The top of the No. 1 pre-separation tower is connected in sequence to the piperidine removal tower, the No. 1 pyridine removal tower, and the No. 2 pyridine removal tower via pipelines; the bottom of the No. 1 pre-separation tower is connected in sequence to the No. 2 pre-separation tower, the No. 3 pre-separation tower, the bipyridine light removal tower, and the bipyridine product tower via pipelines.

[0015] The No. 2 pre-separation tower is equipped with a closed-loop heat pump distillation system; the top of the No. 3 pre-separation tower is connected to the pyridine removal tower system via a pipeline.

[0016] To address the shortcomings of existing technologies in the selection of multi-component distillation sequences and the problem of high energy consumption, this application innovatively combines energy-saving technologies such as differential pressure thermal coupling, heat pump distillation, and double-effect distillation through unique material arrangement and comprehensive optimization of distillation sequences. This maximizes the recovery and utilization of the internal energy of process materials and significantly reduces the consumption of external utilities, thereby enabling the efficient, low-energy, and continuous separation of 2,2'-bipyridine products from complex mixtures obtained from pyridine coupling reactions, minimizing process energy consumption.

[0017] Optionally, the composition range of the materials separated by the distillation separation system is as follows: piperidine 1~2%, water 0.3~1%, pyridine 70~90%, 2-methylpyridine 0.1~0.5%, light bipyridine 0.1~1%, 2,2'-bipyridine 5~10%, and heavy bipyridine 0.1~0.5%.

[0018] Optionally, the No. 1 pre-separation tower and the depiperidine tower are in a pressure differential thermal coupling relationship, and the gas phase at the top of the depiperidine tower provides a heat source for the bottom of the No. 1 pre-separation tower; a side-stream outlet is provided below the feed of the depiperidine tower, and the liquid phase pyridine material collected from the side-stream of the depiperidine tower provides heat for the feed of the depiperidine tower.

[0019] Optionally, the No. 2 pre-distillation tower adopts heat pump distillation, which introduces a heat pump compressor to provide heat source for its own bottom by using the heat of the steam at the top of the tower, so as to consume a small amount of electrical energy instead of expensive steam heat energy.

[0020] Optionally, the liquid pyridine product collected from the top of the No. 2 pre-separation tower exchanges heat with the feed to increase the feed temperature of the No. 2 pre-separation tower and reduce the load on the heat pump compressor.

[0021] Optionally, the No. 2 pre-separation tower adopts closed-loop heat pump distillation technology for energy saving, and the closed-loop circulation medium used is 105℃ hot water. The gas phase at the top of the No. 2 pre-separation tower exchanges heat with the 105℃ hot water and condenses in the heat pump heat exchanger. After the hot water absorbs heat and rises in temperature, it enters the heat pump gas-liquid separator to separate 105℃ steam. The steam is then pressurized and heated to 145℃ in the heat pump compressor to serve as the heat source for the heat pump reboiler. The liquid phase at the bottom of the No. 2 pre-separation tower absorbs heat and rises in temperature in the heat pump reboiler and returns to the bottom of the No. 2 pre-separation tower. The material at the heat source outlet of the heat pump reboiler enters the heat pump gas-liquid separator. The gas phase enters the heat pump compressor to rise in temperature and pressure, and the liquid phase is circulated by the heat pump water circulation pump to the heat pump heat exchanger to absorb heat and rise in temperature.

[0022] Optionally, the No. 1 depyridine column and the No. 2 depyridine column form a double-effect co-current distillation relationship, with the No. 1 depyridine column being a high-pressure column and the No. 2 depyridine column being a low-pressure column; the separated crude pyridine enters the No. 1 depyridine column, and the bottom material of the separated column is used as the feed for the No. 2 depyridine column; the top gas phase of the No. 1 depyridine column is used to provide a heat source for the bottom of the No. 2 depyridine column; high-purity pyridine products are collected from the top of both columns; 2-methylpyridine material is collected from the bottom of the No. 2 depyridine column.

[0023] Optionally, the pre-separation tower system, the bipyridine light removal tower, and the bipyridine product tower adopt a direct distillation sequence; the No. 1 pre-separation tower and the piperidine removal tower adopt an indirect distillation sequence.

[0024] Optionally, the No. 3 pre-separation tower, the bipyridine light removal tower, and the bipyridine product tower are all negative pressure operation systems. Except for the top of the No. 3 pre-separation tower and its auxiliary equipment, which are connected by pipelines, the others are connected by jacketed pipelines. The insulation medium of the jacketed pipeline is 90°C circulating hot water.

[0025] Optionally, the overall steam consumption of the system is reduced to 4.5~8t of steam per ton of product.

[0026] Secondly, this application provides a distillation separation method utilizing the above-mentioned distillation separation system, employing the following technical solution:

[0027] A distillation separation method utilizing the above-mentioned distillation separation system, the distillation separation method specifically includes the following steps:

[0028] S1: The crude product of the reaction enters the No. 1 pre-separation tower, where piperidine, water light components and a small amount of pyridine in the crude product of the reaction are pre-separated, and the molar recovery rate of the pyridine component at the top of the tower is controlled to achieve thermal coupling with the depiperidine tower.

[0029] S2: The material in the bottom of the No. 1 pre-separation tower enters the No. 2 pre-separation tower, where most of the pyridine is separated at the top of the tower. The molar recovery rate of pyridine in the bottom of the tower is controlled so that the temperature difference between the bottom and the top of the No. 2 pre-separation tower is not higher than 15°C, so as to achieve energy saving by using heat pump distillation technology.

[0030] S3: The material in the bottom of the No. 2 pre-separation tower enters the No. 3 pre-separation tower, where all the remaining pyridine is removed at the top of the tower;

[0031] S4: The material in the bottom of the No. 3 pre-separation tower enters the bipyridine light impurity removal tower, where all the light impurities of bipyridine are removed at the top of the tower, and the bottom of the tower contains a mixture of 2,2'-bipyridine containing heavy impurities of bipyridine;

[0032] S5: The material at the bottom of the bipyridine light-removal tower enters the bipyridine product tower, and high-purity 2,2'-bipyridine product is separated at the top of the tower. The high-boiling-point substances at the bottom of the tower are intermittently discharged and directly incinerated.

[0033] S6: The material collected from the top of the No. 1 pre-separation tower enters the depiperidine tower for the separation of pyridine and piperidine; the azeotropic mixture of pyridine and piperidine collected from the top of the depiperidine tower is sent to an external unit; the pyridine product with qualified color and purity collected from the liquid phase side stream is returned to the pyridine feed tank after heat exchange and cooling with the feed material in the depiperidine tower; the pyridine in the tower bottom is sent to the subsequent depiperidine tower system for further separation due to color or small amount of impurities.

[0034] S7: The bottom material of the piperidine stripping tower is combined with the crude pyridine material from the top of the No. 3 pre-separation tower and enters the piperidine stripping tower system for further recovery of pyridine and 2-methylpyridine;

[0035] S8: In the pyridine removal tower system, the No. 1 pyridine removal tower and the No. 2 pyridine removal tower form a double-effect co-current distillation tower sequence, which reduces steam consumption and achieves energy saving;

[0036] S9: The pyridine product from the top of the No. 2 pre-separation tower, the pyridine product from the side stream of the depiperidine tower, and the pyridine product recovered from the top of the depiperidine tower system are combined and returned to the reaction section for recycling.

[0037] Optionally, the feed temperature of the No. 1 pre-separation tower is 55°C, the operating pressure is 20 kPaA, the top gas phase temperature is 58°C, and the bottom liquid phase exit temperature is 75°C; the molar recovery rate of the pyridine component at the top of the tower is controlled at 15~20%, and the content of the 2-methylpyridine component at the top of the tower is controlled at no more than 150 ppm.

[0038] Optionally, the feed temperature of the No. 2 pre-separation tower is 95°C, the operating pressure is 110 kPaA, the top gas phase temperature is 118°C, and the bottom liquid phase exit temperature is 130°C; the molar recovery rate of pyridine in the bottom of the tower is controlled at 15~20%, and the content of 2-methylpyridine in the pyridine product at the top of the tower is not higher than 100 ppm.

[0039] Optionally, the No. 3 pre-separation tower operates at a pressure of 10 kPaA, a top gas phase temperature of 51°C, a pressure controlled at 5 kPa, and a bottom temperature of 201°C, using 2.5 MPaG saturated steam for heating; the content of bipyridine light impurities at the top of the tower is controlled to be no higher than 20 ppm; and the content of pyridine and 2-methylpyridine at the bottom of the tower is controlled to be no higher than 20 ppm.

[0040] Optionally, the bipyridine light impurity removal tower operates at a pressure of 5 kPaA, a top vapor temperature of 163°C, a pressure controlled at 5 kPa, and a bottom temperature of 188°C, heated by 2.5 MPaG saturated steam; the bottom 2,2'-bipyridine mass recovery rate is controlled at 99%, and the bottom bipyridine light impurities are not higher than 50 ppm.

[0041] Optionally, the bipyridine product tower operates at a pressure of 3 kPaA, a top vapor temperature of 153°C, a pressure controlled at 2 kPa, and a bottom temperature of 215°C, heated by 3.0 MPaG saturated steam; the recovery rate of 2,2'-bipyridine at the top of the tower is controlled to be no less than 99.9%, and the purity of 2,2'-bipyridine is 99.9%.

[0042] Optionally, the feed temperature of the depiperidine tower is 115°C, the operating pressure is 300 kPaA, the top gas phase temperature is 127°C, and the bottom liquid phase exit temperature is 158°C; the side-stream flow rate / feed flow rate ratio is 0.6~0.7 kg / kg; the purity of the side-stream pyridine is 99.9 wt%; the side-stream pyridine product is cooled to 60°C by heat exchange with the feed material of the depiperidine tower.

[0043] Optionally, the operating pressure of the No. 1 pyridine removal tower is 300 kPaA, the top gas phase temperature is 157°C, and the bottom liquid phase extraction temperature is 158°C.

[0044] Optionally, the No. 2 pyridine removal tower operates at a pressure of 110 kPaA, a top gas phase temperature of 118°C, and a bottom liquid phase exit temperature of 126°C; the 2-methylpyridine content in the bottom of the tower is not less than 60 wt%.

[0045] Optionally, the pyridine product from the side stream of the piperidine stripping tower, the pyridine product from the top of the No. 2 pre-separation tower, and the pyridine products from the top of the No. 1 and No. 2 piperidine stripping towers all have a purity of not less than 99.9 wt% and a 2-methylpyridine content of not more than 100 ppm; the 2,2'-bipyridine product from the top of the bipyridine product tower has a purity of not less than 99.9 wt%.

[0046] In summary, this application includes at least one of the following beneficial technical effects:

[0047] This application achieves the cascade separation of pyridine through a three-tower pre-separation system: the No. 1 pre-separation tower separates light components and a small amount of pyridine, achieving thermal coupling with the depiperidine tower while reducing the load on the heat pump system of the No. 2 pre-separation tower; the No. 2 pre-separation tower is dedicated to processing the main pyridine components, and adopts heat pump distillation technology to significantly reduce energy consumption; the No. 3 pre-separation tower utilizes the dilution effect of residual pyridine to reduce the separation temperature and reduce the consumption of high-quality steam energy.

[0048] This application features overall sequence optimization, employing a distillation component segmentation strategy to sequentially separate light components, reducing the number of component vaporizations and lowering energy consumption. Unique material arrangement and side-stream extraction methods enable cascaded energy utilization and efficient recovery.

[0049] This application integrates multi-level energy-saving technologies, organically combining three advanced energy-saving technologies—differential pressure thermal coupling, heat pump distillation, and double-effect distillation—into a single separation system. This maximizes the recovery and utilization of the internal energy of process materials and significantly reduces the consumption of external utilities. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the energy-saving distillation and separation system for the production of 2,2'-bipyridine by pyridine coupling according to this application.

[0051] Figure 2 This is a schematic diagram of a closed-loop heat pump distillation system.

[0052] Figure reference numerals: T1, Pre-separation tower #1; T2, Pre-separation tower #2; T3, Pre-separation tower #3; T4, Bipyridine light component removal tower; T5, Bipyridine product tower; T6, Depiperidine tower; T7, Depiperidine tower #1; T8, Depiperidine tower #2; E1, Depiperidine tower feed preheater; E2, Pre-separation tower #2 feed preheater. Detailed Implementation

[0053] Before describing the embodiments of this application in detail, it should be understood that the terminology used herein is for the purpose of describing a particular embodiment only. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the term pertains.

[0054] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more.

[0055] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0056] In this application, the terms "comprising" or "including" are open-ended expressions, meaning they include the content specified in this application but do not exclude other aspects.

[0057] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0058] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products. Unless otherwise specified, standard atmospheric pressure is 100 kPa.

[0059] The present application will be further described in detail below with reference to the embodiments.

[0060] Example 1

[0061] This embodiment provides an energy-saving distillation and separation system for the coupling of pyridine to 2,2'-bipyridine.

[0062] like Figure 1 As shown, the system includes pre-separation towers T1 (1#), T2 (2#), and T3 (3#), a bipyridine light-removal tower T4 (T4), and a bipyridine product tower T5, all connected sequentially from the bottom to the top of the towers via pipelines. The top of pre-separation tower T1 is connected sequentially to piperidine removal towers T6 (1#), T7 (1#), and T8 (2#), with pipelines connecting all three from the bottom to the top. Simultaneously, the top of pre-separation tower T3 is connected to piperically to piperidine removal tower T7 (1#). Therefore, pre-separation towers T1, T2, and T3 constitute the pre-separation tower system; piperidine removal towers T7 and T8 constitute the piperidine removal tower system. Furthermore, piperidine removal tower T6 is connected to piperidine removal tower feed preheater E1 via a pipeline, and pre-separation tower T2 is connected to pre-separation tower feed preheater E2 via a pipeline.

[0063] The crude product from the reaction is first separated into pyridines in a pre-separation tower system, and then purified in the bipyridine light-light-removal tower T4 and the bipyridine product tower T5 to obtain the target product 2,2'-bipyridine. The top material of the pre-separation tower T1 and the hot material collected from the side stream of the piperidine stripping tower T6 exchange heat in the piperidine stripping tower feed preheater E1, which increases the feed temperature of the piperidine stripping tower T6, helps to reduce the steam consumption of the piperidine stripping tower T6, and also avoids vibration of the feed pipeline.

[0064] The bottom material of the piperidine stripper T6 and the top material of the pre-separation tower T3 are combined as raw materials for the pyridine stripper system, and pyridine is recovered and purified by the pyridine stripper T7 and the pyridine stripper T8.

[0065] like Figure 2As shown, pre-separation tower T2 is equipped with a closed-loop heat pump distillation system. The closed-loop circulation medium used is 105℃ hot water. The vapor phase at the top of pre-separation tower T2 exchanges heat with the 105℃ hot water and condenses in the heat pump heat exchanger. After the hot water absorbs heat and vaporizes, it enters the heat pump gas-liquid separator to separate 105℃ vapor. This vapor is then pressurized and heated to 145℃ in the heat pump compressor to serve as the heat source for the heat pump reboiler. The liquid phase at the bottom of pre-separation tower T2 absorbs heat and vaporizes in the heat pump reboiler, returning to the bottom of pre-separation tower T2. The material at the heat source outlet of the heat pump reboiler enters the heat pump gas-liquid separator. The vapor phase enters the heat pump compressor for pressurization and heating, while the liquid phase is circulated by the hot water circulation pump back to the heat pump heat exchanger for heat absorption and vaporization. The top product of pre-separation tower T2 and the feed are cooled by heat exchange in the feed preheater E2 of pre-separation tower T2. Increasing the feed temperature of pre-separation tower T2 helps to reduce the heat load of the heat pump compressor.

[0066] Example 2

[0067] This embodiment provides an energy-saving distillation separation method for the production of 2,2'-bipyridine via pyridine coupling. This separation method can achieve an annual production of 25,000 tons of 2,2'-bipyridine. The material balance for each column is shown in Tables 1 and 2.

[0068] The system used for distillation separation in this embodiment is as follows: 2,2'-bipyridine is prepared by pyridine coupling reaction using a near-isothermal reaction apparatus and method disclosed in CN 115430365 A. The crude product obtained has the following composition: piperidine 1.17%, pyridine 88.9%, water 0.58%, 2-methylpyridine 0.21%, neonicotinoid 0.14%, 2,2'-bipyridine 8.82%, and heavy impurities such as 4,4'-bipyridine 0.18%.

[0069] This embodiment utilizes the distillation separation system of Example 1. First, the crude product obtained from the above-mentioned pyridine coupling is pre-separated in a pre-separation tower system (pre-separation tower T1, pre-separation tower T2, and pre-separation tower T3) to separate the pyridine into stages. Second, neonicotinoids are removed in the bipyridine light removal tower T4. Finally, 2,2'-bipyridine product with a purity of not less than 99.9 wt% is obtained at the top of the bipyridine product tower T5.

[0070] Meanwhile, the crude pyridine containing piperidine collected from the top of pre-separation tower T1 in the pre-separation tower system is depiperidine-pyridine azeotrope removed from the top of depiperidine tower T6, and a pyridine product with a purity of 99.9 wt% is collected from the side stream; the crude pyridine from the bottom of depiperidine tower T6 and the crude pyridine collected from the top of pre-separation tower T3 are used together in the depiperidine tower system (depiperidine tower T7, depiperidine tower T8) to recover pyridine and 2-methylpyridine.

[0071] Table 1 Material Balance for Each Tower (Part 1)

[0072]

[0073] Table 2 Material Balance for Each Tower (Part Two)

[0074]

[0075] The above-mentioned energy-saving distillation separation method for the coupling of pyridine to 2,2'-bipyridine is as follows:

[0076] The crude product obtained from pyridine coupling is first separated into a small amount of crude pyridine in pre-separation column T1 (#1). The molar ratio of the top product to the feed in pre-separation column T1 is controlled at 0.1–0.2, and the operating pressure is 20–50 kPaA. This creates conditions for thermal coupling with the piperidine depiperidine column T6. The operating pressure of pre-separation column T1 is 20 kPaA, and the molar recovery rate of pyridine at the top is 0.17. The vapor temperature at the top of pre-separation column T1 is 55–80 °C, and the liquid temperature at the bottom is 70–100 °C. The 2-methylpyridine content in the liquid mixture collected from the top of pre-separation column T1 is no higher than 150 ppm. The bottom of pre-separation column T1 is heated by steam from the top of the piperidine depiperidine column T6, without consuming steam.

[0077] The top material of pre-separation column T1 is preheated to 115°C before entering depiperidine column T6. Because pyridine and piperidine are azeotropic, pyridine with a purity of 99.9 wt% is collected from the side stream of depiperidine column T6, and a pyridine-piperidine azeotrope is collected from the top. The mass composition of the azeotrope at the top of depiperidine column T6 is 40% pyridine, 40% piperidine, and 20% water. The operating pressure of depiperidine column T6 is 300 kPaA, the top vapor temperature is 127°C, and the cold source at the top is the bottom material of pre-separation column T1. The bottom temperature of depiperidine column T6 is 158°C, heated by 0.8 MPaG steam, with a steam consumption of 5504 kg / h after thermal coupling. The pyridine product from the side stream of depiperidine column T6 is cooled to 60°C after heat exchange with the feed before being sent to the pyridine feed tank.

[0078] The feed to pre-separation tower T2 is the same as the material from the bottom of pre-separation tower T1 (pre-separation tower 1). The pyridine molar recovery rate in the bottom of pre-separation tower T2 is controlled at 0.17, and most of the pyridine product with a purity of 99.9% is collected from the top of the tower. Pre-separation tower T2 operates at atmospheric pressure, with a top temperature of 118℃ and a bottom temperature of 130℃. The top product is cooled by heat exchange with the feed, and the feed to T2 is preheated to 95℃. Pre-separation tower T2 utilizes heat pump energy-saving technology, with a compressor power consumption of 1445kW and a steam energy consumption of 0.

[0079] The material from the bottom of pre-separation tower T2 is used to extract residual crude pyridine in pre-separation tower T3. Pre-separation tower T3 operates at a pressure of 10 kPaA; the content of light impurities like bipyridine at the top is controlled to be no higher than 20 ppm; the content of pyridine and 2-methylpyridine at the bottom is controlled to be no higher than 20 ppm. The top temperature of pre-separation tower T3 is 51℃, cooled by circulating water. Because the main component of the material in the bottom of pre-separation tower T3 is 2,2'-bipyridine and its heavy impurities, and the mixture has a high melting and boiling point, the bottom of pre-separation tower T3 is insulated with steam coil heating. The bottom and equipment are connected by a jacketed pipeline, and the jacket insulation medium is 90℃ hot water. Furthermore, pre-separation tower T3 uses high-efficiency packing with low pressure drop, controlled at 5 kPa, and the bottom temperature is no higher than 200℃. It is heated with 2.5 MPaG saturated steam, with a steam consumption of 1637 kg / h.

[0080] The bottom material of pre-separation tower T3 is separated into neonicotinoids and bipyridine by the bipyridine light residue removal tower T4. Because neonicotinoids and bipyridine are difficult to separate, the recovery rate of 2,2'-bipyridine in the bottom of the bipyridine light residue removal tower T4 is controlled to be no less than 99%, and the bipyridine light residue in the bottom of the tower is controlled to be no more than 50 ppm. The operating pressure of the bipyridine light residue removal tower T4 is 5 kPaA, the top temperature is 163℃, and 120℃ hot water is used for condensation. The bipyridine light residue removal tower T4 uses high-efficiency packing with low pressure drop, controlled at 5 kPa, and the bottom temperature is 188℃. It is heated by 2.5 MPaG saturated steam, with a steam consumption of 2732 kg / h. The bipyridine light residue removal tower T4 is connected to its auxiliary equipment by a jacketed pipeline, and the jacket insulation medium is 90℃ hot water.

[0081] The bottom material of the bipyridine light component removal tower T4 is separated into the target product 2,2'-bipyridine in the bipyridine product tower T5. The recovery rate of 2,2'-bipyridine at the top of the bipyridine product tower T5 is controlled to be no less than 99.9%, and the purity of 2,2'-bipyridine is controlled to be 99.9%. The bipyridine product tower T5 is operated under high vacuum at an operating pressure of 3 kPaA; the top temperature is 154℃, and 120℃ hot water is used for condensation; T5 uses low-pressure-drop, high-efficiency packing, with the pressure drop controlled at 2 kPa, and the bottom temperature not exceeding 215℃, heated by 3.0 MPaG saturated steam; steam consumption is 1287 kg / h.

[0082] The bottom feed from the piperidine stripping tower T6 and the pyridine product from the top of the pre-separation tower T3 are mixed and then fed into the piperidine stripping tower T7 (No. 1). The operating pressure of piperidine stripping tower T7 is 300 kPaA; the top temperature is 157°C, and the bottom temperature is 158°C. The top product is pyridine with a purity of 99.9 wt%. The crude pyridine from the bottom of piperidine stripping tower T7 is fed into piperidine stripping tower T8 (No. 2). The top product is pyridine with a purity of 99.9 wt%, and the bottom product is 2-methylpyridine with a purity of not less than 60 wt%. The operating pressure of piperidine stripping tower T8 is 110 kPaA; the top temperature is 118°C, and the bottom temperature is 126°C. The reboiling heat source for the bottom of piperidine stripping tower T8 is the vapor phase from the top of piperidine stripping tower T7 (No. 1). Piperidine stripping tower T7 is heated using 0.8 MPaG saturated steam, and its steam consumption is 3348 kg / h.

[0083] Based on the above, the total feed flow rate of the crude product is 35816 kg / h, the total steam consumption is 14602.6 kg / h, and the power consumption is 1445 kW. The production rate of qualified 2,2-bipyridine is 3107 kg / h, with a steam consumption of 4.7 t / t of product.

[0084] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. An energy-saving distillation and separation system for the coupling of pyridine to 2,2'-bipyridine, characterized in that, The rectification separation system comprises a pre-fractionation column system, a bipyridine light-removing column (T4), a bipyridine product column (T5), a piperidine-removing column (T6), and a pyridine-removing column system; The pre-fractionation column system comprises a 1st pre-fractionation column (T1), a 2nd pre-fractionation column (T2), and a 3rd pre-fractionation column (T3); The pyridine-removing column system comprises a 1st pyridine-removing column (T7) and a 2nd pyridine-removing column (T8); The top of the 1st pre-fractionation column (T1) is connected to the piperidine-removing column (T6), the 1st pyridine-removing column (T7), and the 2nd pyridine-removing column (T8) in sequence through pipelines; the bottom of the 1st pre-fractionation column (T1) is connected to the 2nd pre-fractionation column (T2), the 3rd pre-fractionation column (T3), the bipyridine light-removing column (T4), and the bipyridine product column (T5) in sequence through pipelines; The 2nd pre-fractionation column (T2) is provided with a closed heat pump rectification system; the closed heat pump rectification system comprises a heat pump heat exchanger, a heat pump gas-liquid separation tank, a heat pump compressor, a heat pump reboiler, and a heat pump water circulating pump; the closed heat pump rectification system uses 105℃ hot water as a closed loop circulating medium; the gas phase at the top of the 2nd pre-fractionation column (T2) exchanges heat with the 105℃ hot water in the heat pump heat exchanger to condense; the hot water absorbs heat to increase temperature and vaporize to enter the heat pump gas-liquid separation tank to separate out 105℃ steam; the steam is pressurized and heated to 145℃ in the heat pump compressor to serve as a heat source of the heat pump reboiler; the liquid phase at the bottom of the 2nd pre-fractionation column (T2) absorbs heat to vaporize and return to the bottom of the 2nd pre-fractionation column (T2); the material at the outlet of the heat source of the heat pump reboiler enters the heat pump gas-liquid separation tank; the gas phase enters the heat pump compressor to be pressurized and heated; and the liquid phase is circulated to the heat pump heat exchanger by the heat pump water circulating pump to absorb heat and vaporize. The top of the 3rd pre-fractionation column (T3) is connected to the pyridine-removing column system through a pipeline.

2. The rectifying separation system of claim 1, wherein, The 1st pre-fractionation column (T1) and the piperidine-removing column (T6) form a differential pressure heat coupling relationship; the gas phase at the top of the piperidine-removing column (T6) provides a heat source for the bottom of the 1st pre-fractionation column (T1); the piperidine-removing column (T6) is provided with a side line tapping outlet below the feed inlet; and the liquid phase pyridine material tapped from the piperidine-removing column (T6) provides heat for the feed of the piperidine-removing column (T6).

3. The rectifying separation system of claim 1, wherein, The 2nd pre-fractionation column (T2) uses heat pump rectification; the heat of the steam at the top of the column is introduced into the heat pump compressor to provide a heat source for the bottom of the column to consume a small amount of electric energy instead of expensive steam heat energy.

4. The rectifying separation system of claim 1, wherein, The liquid phase pyridine product tapped from the top of the 2nd pre-fractionation column (T2) exchanges heat with the feed to increase the temperature of the feed of the 2nd pre-fractionation column (T2) and reduce the load of the heat pump compressor.

5. The rectifying separation system of claim 1, wherein, The 1# pyridine removal column (T7) and the 2# pyridine removal column (T8) constitute a double-effect counter-current rectification relationship, the 1# pyridine removal column (T7) is a high-pressure column, and the 2# pyridine removal column (T8) is a low-pressure column; the separated crude pyridine enters the 1# pyridine removal column (T7), and the separated column bottom material is used as the feed of the 2# pyridine removal column (T8); the gas phase at the top of the 1# pyridine removal column (T7) is used as the heat source for the column bottom of the 2# pyridine removal column (T8); the high-purity pyridine product is collected at the top of the two columns; and the 2-methylpyridine material is collected from the column bottom of the 2# pyridine removal column (T8).

6. The rectifying separation system of claim 1, wherein, The pre-fractionating column system and the bipyridyl light component removal column (T4) and the bipyridyl product column (T5) adopt a direct rectification sequence; the 1# pre-fractionating column (T1) and the piperidine removal column (T6) adopt an indirect rectification sequence.

7. The rectifying separation system of claim 1, wherein, The overall steam consumption of the system is reduced to 4.5-8 t of steam per ton of product.

8. A rectification separation method using the rectification separation system according to any one of claims 1 to 6, characterized by, The rectification separation method specifically comprises the following steps: S1: the reaction crude product enters the 1# pre-fractionating column (T1), the piperidine and water light components and a small amount of pyridine in the reaction crude product are pre-fractionated, the recovery rate of the pyridine component at the top of the column is controlled to realize thermal coupling with the piperidine removal column (T6); S2: the column bottom material of the 1# pre-fractionating column (T1) enters the 2# pre-fractionating column (T2), most of the pyridine is separated at the top, the pyridine recovery rate at the column bottom is controlled so that the temperature difference between the column top and the column bottom of the 2# pre-fractionating column (T2) is not higher than 15 ℃, to realize energy saving by using heat pump rectification technology; S3: the column bottom material of the 2# pre-fractionating column (T2) enters the 3# pre-fractionating column (T3), and all the remaining pyridine is removed at the top; S4: the column bottom material of the 3# pre-fractionating column (T3) enters the bipyridyl light component removal column (T4), all the bipyridyl light impurities are removed at the top, and the column bottom is a 2,2'-bipyridyl mixture containing bipyridyl heavy impurities; S5: the column bottom material of the bipyridyl light component removal column (T4) enters the bipyridyl product column (T5), the high-purity 2,2'-bipyridyl product is separated at the top, and the column bottom high-boiling substance is intermittently discharged and directly incinerated; S6: the material collected at the top of the 1# pre-fractionating column (T1) enters the piperidine removal column (T6) to separate pyridine and piperidine; the azeotropic mixture of pyridine and piperidine collected at the top of the piperidine removal column (T6) is sent to an external device; the pyridine product with qualified color and purity is collected from the liquid phase side line and returned to the pyridine raw material tank after heat exchange cooling with the feed material in the piperidine removal column (T6); the pyridine at the column bottom is sent to a subsequent pyridine removal column system for further separation due to color or a small amount of impurities; S7: the column bottom material of the piperidine removal column (T6) is combined with the crude pyridine material at the top of the 3# pre-fractionating column (T3), and enters the pyridine removal column system for further recovery of pyridine and 2-methylpyridine; S8: in the pyridine removal column system, the 1# pyridine removal column (T7) and the 2# pyridine removal column (T8) constitute a double-effect counter-current rectification column sequence, to reduce steam consumption and realize energy saving. S9: The pyridine product from the top of the 2# pre-fractionating tower (T2), the pyridine product from the side line of the de-piperidine tower (T6), and the pyridine product recovered from the top of the de-pyridine tower system are combined and returned to the reaction section for recycling.

9. The rectification separation method according to claim 8, characterized in that, The feed temperature of the 1# pre-fractionating tower (T1) is 55°C, the operating pressure is 20 kPaA, the top gas phase temperature is 58°C, and the bottom liquid phase extraction temperature is 75°C; the mass recovery rate of the pyridine component at the top is controlled to be 15-20%, and the content of the 2-methylpyridine component at the top is not higher than 150 ppm.

10. The rectification separation method of claim 8, wherein, The feed temperature of the 2# pre-fractionating tower (T2) is 95°C, the operating pressure is 110 kPaA, the top gas phase temperature is 118°C, and the bottom liquid phase extraction temperature is 130°C; the mass recovery rate of the pyridine at the tower bottom is controlled to be 15-20%, and the content of the 2-methylpyridine in the pyridine product at the top is not higher than 100 ppm.

11. The rectification separation method of claim 8, wherein, The operating pressure of the 3# pre-fractionating tower (T3) is 10 kPaA, the top gas phase temperature is 51°C, the pressure is controlled to be 5 kPa, the tower bottom temperature is 201°C, and 2.5 MPaG saturated steam is used for heating; the content of the bipyridyl light impurities at the top is controlled to be not higher than 20 ppm; the contents of the pyridine and 2-methylpyridine at the tower bottom are not higher than 20 ppm.

12. The rectification separation method of claim 8, wherein, The operating pressure of the bipyridyl light fractionation tower (T4) is 5 kPaA, the top gas phase temperature is 163°C, the pressure is controlled to be 5 kPa, the tower bottom temperature is 188°C, and 2.5 MPaG saturated steam is used for heating; the mass recovery rate of the 2,2'-bipyridyl at the tower bottom is controlled to be 99%, and the content of the bipyridyl light impurities at the tower bottom is not higher than 50 ppm.

13. The rectification separation method of claim 8, wherein, The operating pressure of the bipyridyl product tower (T5) is 3 kPaA, the top gas phase temperature is 153°C, the pressure is controlled to be 2 kPa, the tower bottom temperature is 215°C, and 3.0 MPaG saturated steam is used for heating; the mass recovery rate of the 2,2'-bipyridyl at the top is controlled to be not lower than 99.9%, and the mass purity of the 2,2'-bipyridyl is 99.9%.

14. The rectification separation method of claim 8, wherein, The feed temperature of the de-piperidine tower (T6) is 115°C, the operating pressure is 300 kPaA, the top gas phase temperature is 127°C, and the bottom liquid phase extraction temperature is 158°C; the side line extraction flow rate / feed flow rate ratio is 0.6-0.7 kg / kg; the purity of the pyridine extracted from the side line is 99.9 wt%; The side line pyridine product is heat-exchanged and cooled to 60°C with the feed material of the de-piperidine tower (T6).

15. The rectification separation method of claim 8, wherein, The operating pressure of the 1# de-pyridine tower (T7) is 300 kPaA, the top gas phase temperature is 157°C, and the bottom liquid phase extraction temperature is 158°C.

16. The rectification separation method of claim 8, wherein, The operating pressure of the 2# de-pyridine tower (T8) is 110 kPaA, the top gas phase temperature is 118°C, and the bottom liquid phase extraction temperature is 126°C; the content of the 2-methylpyridine at the tower bottom is not lower than 60 wt%.

17. The rectification separation method of claim 8, wherein, The pyridine product taken out from the side line of the de-piperidine column (T6), the pyridine product at the top of the 2# pre-fractionating column (T2), and the pyridine products taken out at the top of the 1# de-pyridine column (T7) and the 2# de-pyridine column (T8) all have a purity of not less than 99.9wt%, and a 2-methylpyridine content of not higher than 100ppm; the 2,2'-bipyridine product taken out at the top of the bipyridine product column (T5) has a purity of not less than 99.9wt%.

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