A system and method for reducing coking in a nitrilation reactor

Abstract

The present application relates to adiponitrile preparation technical field, disclose a kind of system and method for reducing coking of nitrilation reactor.The method for producing adiponitrile has many, but the high coking rate of reactor has been a problem, compared with the modification update on nitrilation reactor, the present application is more advantageous, the change of feed mode, opens a new production mode, and the cost required is greatly reduced, process flow is simple, easy to transform.Before reactor, steam is passed, solve the problem that two kinds of substances are not compatible, can make reactant better mixing, conversion rate increases.In the use of inert gas is also a breakthrough, although it increases the use cost of public works, but compared with the transportation of material, the benefit brought by the improved production efficiency and the increased device use cycle is far greater than the cost of nitrogen.Compared with similar device, the present application has good innovation, improves production efficiency, reduces cost, and has very broad application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of adiponitrile preparation, and provides a system and method for reducing coking of a nitrilation reactor. BACKGROUND

[0002] The ammoniation method of adipic acid is an important method for preparing adiponitrile at present. Adipic acid and excess ammonia are fed into a nitrilation reactor of adiponitrile in the presence of a catalyst such as phosphoric acid or its salt or ester, and the reaction is carried out at a temperature of 270-290℃ to generate diammonium adipate, which is then heated and dehydrated to generate crude adiponitrile, and the product is obtained through rectification. The main defects of the existing nitrilation reactor include that the mixture of ammonia liquid and adipic acid is not uniform, a long residence time is required, and the phenomena of coking on the inner wall of the reactor and deposition of materials in dead corners are prone to occur. Not only is the service life of the equipment greatly reduced, but also safety hazards exist, the cost of decoking is increased, the workload of the operating personnel is also increased, and the main problem of the device is the production, so a process for reducing the coking rate and maintaining long-period operation is urgently needed.

[0003] DAS1196179 discloses a convenient method for continuously preparing adiponitrile from adipic acid and ammonia uniformly passing through a catalyst at 250-550℃, which comprises introducing adipic acid in the form of a solid free-flowing powder into an ammonia stream, and introducing the gas stream containing adipic acid into a fluidized bed that has been heated to a reaction temperature under conditions of less than 50℃, and producing by passing the vaporized reaction mixture through condensation, separation of the organic layer, toluene extraction of the water layer, distillation and then fractional distillation of the organic phase. The method does not pass steam, and cannot uniformly mix ammonia and adipic acid.

[0004] CN204147839U discloses a design of an adiponitrile reactor, which comprises a tower body and an ammonia inlet pipe, the tower body is horizontally provided in three parts of upper, middle and lower parts, and is tightly connected with the inner wall, vertical columns connecting the spaces above and below the upper and lower pipe plates are arranged between the upper and lower pipe plates, and the columns are sealingly connected, the ammonia inlet pipe penetrates through the wall of the tower body, one end of the ammonia inlet pipe is located outside the tower body, and the other end of the ammonia inlet pipe is opened in the lower part of the space in the tower body, the lower part of the tower body is conical, and a feeding port is arranged at the bottom end. This method uses a modified reactor, which increases the cost of equipment, and the service life is not obviously increased, and the process flow needs to be modified, which is complex and high in cost. SUMMARY

[0005] In order to overcome the above-mentioned defects of the prior art, reduce coking and improve the yield, the present application adopts solid powder feeding of adipic acid, and directly feeds steam and a small amount of inert gas into the nitrilation reactor.

[0006] The application aims to provide a system and method for producing adiponitrile from adipic acid and ammonia, which can effectively reduce the coking of the nitrilation reactor, and in the method, the coking phenomenon of the nitrilation reactor can be greatly reduced even if a high ammonia to adipic acid ratio or a high conversion rate of adipic acid is used. Meanwhile, the process is simple, easy to operate, low in cost, protects the surrounding environment, prolongs the service life, greatly improves the benefit due to the novel and simple angle, and thus has a wide application prospect.

[0007] The above-mentioned purpose of the application is achieved by the following technical scheme:

[0008] A system for reducing the coking of a nitrilation reactor, wherein an adipic acid feeding device, a nitrogen gas input pipeline and a steam input pipeline are additionally arranged at the center pipe at the bottom of the nitrilation reactor.

[0009] A method for reducing the coking of a nitrilation reactor, which uses solid powder of adipic acid as the raw material, mixes the solid powder with ammonia liquid, simultaneously inputs steam and nitrogen gas, and then uniformly mixes and reacts in the nitrilation reactor.

[0010] Further, the particle size of the solid powder of adipic acid is 0.1-0.4mm.

[0011] Further, the molar ratio of the solid powder of adipic acid to the ammonia liquid is 1:(4-20).

[0012] Further, the flow rate of the steam is 5-15m 3 / h.

[0013] Further, the flow rate of the nitrogen gas is 0.1m 3 / h.

[0014] Further, the volume ratio of the nitrogen gas to the mixture of adipic acid and ammonia liquid is 0.1-2%, preferably 0.3-0.6%.

[0015] Further, the reaction temperature of the nitrilation reactor is 250-420℃, preferably 300-375℃.

[0016] The application has the following beneficial effects compared with the prior art:

[0017] There are many methods for producing adiponitrile, but the problem of high coking rate of the reactor has been difficult to solve. Compared with the modification and update of the nitrile reactor, the present application has more advantages. The change of the feeding mode opens up a new production mode, and the required cost is greatly reduced. The process flow is simple and easy to modify. Before the reactor, steam is introduced to solve the problem of the incompatibility of the two substances, which can make the reactants mix better and improve the conversion rate. It is also a breakthrough in the use of inert gas. Although it increases the cost of using public works, the benefits brought by the transportation of materials, improved production efficiency and increased device usage period are much greater than the cost of nitrogen. Compared with similar devices, the present application has good innovation, improves production efficiency, reduces cost, and has a wide application prospect.

[0018] Adopting solid powder feeding of adipic acid, the steam injected into the reaction bed is not after the reaction of adipic acid and ammonia but before entering the distillation column. In this way, when adding steam to the fluidized bed, the formation of circulating by-products prone to resinification can be reduced, and ammonia and adipic acid can be fully mixed. The required residence time is short, the reaction mixture is uniformly distributed, and the phenomenon of coking and material deposition on the inner wall of the nitrile reactor is not easy to occur. This method has many advantages such as simple process, low energy consumption, low equipment investment, easy operation, high conversion rate, long running period, etc., which improves economic benefits and reduces resource waste. BRIEF DESCRIPTION OF DRAWINGS

[0019] The present application will be further described below in combination with the drawings and examples.

[0020] Figure 1 is the feeding mode system diagram of the original production device;

[0021] Figure 2 is the feeding mode system diagram of the device of the present application.

[0022] In the figure: 1. center tube, 2. adipic acid feeding device, 3. nitrogen input pipeline, 4. steam input pipeline. DETAILED DESCRIPTION

[0023] The present application will be further described below in combination with the drawings and examples.

[0024] Example 1

[0025] As Figure 1As shown, in the prior art normal reaction process, liquid ammonia enters the bottom of the nitrilation reactor from the center tube 1 of the nitrilation reactor, and due to the extrusion of the surrounding molten adipic acid, the liquid ammonia flows upwards along the outer wall of the center tube, the contact area between the liquid phases is small, and the stirring effect is not ideal. Due to the relatively concentrated flow and the relatively large flow rate, the two fluids do not blend with each other, the material in the center portion of the column tube of the nitrilation reactor is not good for film formation, and is flushed out of the tube before being completely reacted, resulting in incomplete reaction, serious decomposition of adipic acid, partial material carbonization and coking due to overheating, and shortening of the service life of the nitrilation reactor. At the same time, the production process produces more by-products, consumes more raw materials, has serious coking, reduces the mass transfer and heat transfer efficiency, and the product quality is unstable and the operating parameters are not easy to control.

[0026] As shown in Figure 2 The present application adds an adipic acid feeding device 2 to the center tube 1, and adipic acid powder prying blocks are directly added to the center tube 1 from the adipic acid feeding device 2 to mix with the ammonia liquid flow, and nitrogen gas input pipelines 3 and steam input pipelines 4 are additionally provided, nitrogen gas is introduced from the nitrogen gas pipeline network and enters the center tube 1 through the nitrogen gas input pipelines 3 to mix with the ammonia liquid flow, and steam is introduced from the steam pipeline network and enters the center tube 1 through the nitrogen gas input pipelines 3 to mix with the ammonia liquid flow.

[0027] The present application uses solid powder adipic acid instead of molten adipic acid, and the adipic acid is sent into the reaction zone as powder, with a particle size of up to 0.5 mm, although larger particles can be used, but the pneumatic transportation of large particle powder to the reaction chamber becomes more and more difficult. Commercially produced adipic acid with a water content of 0.1 to 0.2% can also be used, and intermediate drying is unnecessary. Introduce the adipic acid into the ammonia stream heated to 50°C, and if a small amount of inert gas such as nitrogen is present, the effect is better. The use concentration of inert gas is 0.001 to 0.02 parts, 0.003 to 0.006 parts per part of ammonia, and the corresponding ammonia use volume ratio is 0.1 to 2%, and more preferably 0.3 to 0.6%. Because of the liquid ammonia flow, the powder adipic acid can be brought into the nitrilation reactor, solving the problem of difficult transportation of solid powder materials. At the same time, the solid powder can achieve a better flow state in the nitrilation reactor, and the adipic acid can be fully mixed with the liquid ammonia, reducing the probability of coking in the nitrilation reactor.

[0028] The amount of ammonia liquor required during the transport of adipic acid depends to some extent on the nature of the adipic acid, and if necessary, a larger amount of ammonia liquor is used, but is controlled within a certain range, otherwise it will increase the side reactions, resulting in coking of the nitrile reactor. The production is more convenient through the fluidized bed of ammonia liquor stream itself. The amount of ammonia used is at least 2 moles per mole of adipic acid. Generally, the use of ammonia is in excess, for example, 4 to 20 moles of ammonia per mole of adipic acid. The reaction temperature range is 250°C to 420°C, better still is 300°C to 375°C. The process is usually carried out at ambient pressure. However, the process can be carried out under reduced pressure and increased pressure, for example, 1.2 times atmospheric pressure, if necessary.

[0029] Since the adipic acid remains in a fluidized state during the course of the reaction, the particle diameter is more effective in the range of 0.1 to 0.4 mm. The amount of adipic acid used is determined by the required ammonia flow rate, and when the fluidized bed is formed, the adipic acid and adiponitrile remain in the reaction chamber for 3 to 6 seconds depending on the reaction conditions. The present invention uses solid particles with a particle diameter of 0.1 to 0.4 mm for feeding, reduces the degradation of the reactants, uses the liquid ammonia liquor stream to transport the raw materials, solves the problem of difficult transportation of solid materials, and enhances the driving force by introducing nitrogen through nitrogen inlet pipe 3, but not too much, so as to reduce the residence time of the reactants in the reactor.

[0030] At the same time, steam can be directly introduced through steam inlet pipe 4 at the inlet of the nitrile reactor, the steam can increase the flowability of adipic acid powder and ammonia liquor, accelerate the mixing of liquid materials and solid materials, better carry out the reaction, and increase the inlet temperature of the nitrile reactor. In the presence of steam, adipic acid and ammonia can be dissolved in steam at the same time, increase the contact area, accelerate the reaction between the two, improve the conversion rate, and are beneficial to maintaining the temperature of the nitrile reactor. It greatly reduces the degradation of adipic acid and other by-products of organic matter, and reduces the amount of coking of the nitrile reactor. Such a design not only reduces the heating link of adipic acid feed, but also reduces the heating amount of the nitrile reactor, and increases the service life of the nitrile reactor.

[0031] Example 2

[0032] The reaction temperature is 350°C, the molten adipic acid is used for feeding, the ammonia liquor is introduced in an amount of ammonia liquor to adipic acid molar ratio of 4:1, the steam flow is 10 m 3 / h, the nitrogen flow is 0.1 m 3 / h, after two months of use, coking phenomenon can be clearly seen.

[0033] Example 3

[0034] The reaction temperature is 350°C, the solid adipic acid powder is used for feeding, the ammonia liquor is introduced in an amount of ammonia liquor to adipic acid molar ratio of 4:1, the steam flow is 10 m 3 / h, nitrogen flow 0.1 m 3 / h, after two months, no obvious coking in the nitrile reactor.

[0035] Example 4

[0036] The reaction temperature was 350℃, solid adipic acid powder was used as the feed, the ammonia liquid was introduced in the amount of 4:1 molar ratio of ammonia liquid to adipic acid, and the steam flow was 0 m 3 / h, nitrogen flow 0.1 m 3 / h, after two months, a small amount of coking was produced in the nitrile reactor.

[0037] Example 5

[0038] The reaction temperature was 350℃, solid adipic acid powder was used as the feed, the ammonia liquid was introduced in the amount of 1:1 molar ratio of ammonia liquid to adipic acid, and the steam flow was 10 m 3 / h, nitrogen flow 0.1 m 3 / h, after two months, coking was obviously produced.

[0039] From the data of the above several working conditions, it can be seen that the nitrogen flow of 0.1 m 3 / h can achieve the effect of assisting production. There is a big difference in coking in the nitrile reactor between solid powder feed and molten state feed of adipic acid. The molar ratio of ammonia liquid to adipic acid of 4:1 is sufficient to inhibit coking. The presence of steam also makes the amount of coking in the nitrile reactor less.

[0040] Example 6

[0041] Before the application is used, the nitrile reactor cokes seriously, the production cost is high, the average coking is cleaned once every 95 days, which affects the device benefit. After the application is used, the reactor does not coke obviously, and is cleaned once every time of major overhaul, the operation cycle is greatly lengthened, the cost is reduced and the benefit is increased, and the benefit is ensured.

[0042] This set of process only needs to pass in a small amount of nitrogen and low flow steam, which reduces the coking probability and prolongs the production cycle of the device, and changes from cleaning coking once every 95 days to once every half year.

[0043] The above-described embodiments are only preferred embodiments of the present application, and not all the embodiments that can be implemented by the present application. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present application should be considered to be included in the protection scope of the claims of the present application.

Claims

1. A method of reducing coking in a nitrile synthesis reactor characterized by The center pipe (1) at the bottom of the nitrile reactor is additionally provided with an adipic acid feeding device (2), a nitrogen input pipeline (3) and a steam input pipeline (4), solid powder of adipic acid is fed, mixed with ammonia liquid, steam and nitrogen are simultaneously input, and the mixture is uniformly mixed and then reacted in the nitrile reactor; The particle size of the solid powder of adipic acid is 0.1-0.4 mm; The flow rate of the steam is 5-15 m 3 / h; The flow rate of the nitrogen gas is 0.1 m 3 / h; The volume ratio of the nitrogen to the volume of the mixture of adipic acid and ammonia liquid is 0.1-2%.

2. A method of reducing coking in a nitrile synthesis reactor as claimed in claim 1, characterized in that, The molar ratio of the solid powder of adipic acid to ammonia liquid is 1:(4-20).

3. A method of reducing coking in a nitrile synthesis reactor as defined in claim 1, wherein, The volume ratio of the nitrogen to the volume of the mixture of adipic acid and ammonia liquid is 0.3-0.6%.

4. The method of reducing coking in a nitrile reactor of claim 1, wherein, The reaction temperature of the nitrile reactor is 250-420℃.

5. The method of reducing coking in a nitrile reactor of claim 1, wherein, The reaction temperature of the nitrile reactor is 300-375℃.

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