CN116078293A - Tubular reactor suitable for preparing hexamethylene diisocyanate by gas phase method and application thereof - Google Patents

Abstract

The invention provides a tubular reactor suitable for preparing hexamethylene diisocyanate by a gas phase method and application thereof. The tubular reactor comprises a tubular reactor body with a tubular reaction chamber; the device comprises a body, a first air inlet, a gas outlet, a plurality of groups of second air inlets, a first air inlet, a second air inlet, a first air inlet and a second air inlet, wherein the first air inlet is arranged at one end of the body, the gas outlet is arranged at the other end of the body, a plurality of groups of second air inlets are further arranged on the side wall of the body between the first air inlet and the gas outlet according to the material flow sequence, each group comprises at least one second air inlet, the air inlet direction of the first air inlet is parallel to the axial direction of the body, and an acute angle is formed between the air inlet direction of the second air inlet and the air inlet direction of the first air inlet; the inside of the body is distributed with concave structures. The gas distributor is arranged in the tubular reactor body and close to the first gas inlet, a plurality of gas distribution holes are formed in the gas distributor, and the gas distribution direction of the gas distribution holes is parallel to the axial direction of the tubular reactor body.

Description

A tubular reactor suitable for preparing hexamethylene diisocyanate by gas phase method and its application

technical field

The invention relates to the technical field of fine chemicals, in particular to a tubular reactor suitable for preparing hexamethylene diisocyanate by a gas phase method and its application.

Background technique

Hexamethylene diisocyanate (HDI) is an aliphatic isocyanate (ADI) mainly used in coatings, adhesives, and food packaging. It has unique and excellent yellowing resistance, weather resistance, and chemical resistance. The isocyanate family belongs to the high-end product category. It is widely used in high-end coatings, adhesives, elastomers and military fields, especially in the fields of automotive paints, industrial protective paints, and wood paints. With the rapid development of the automobile industry, the demand for global HDI has increased significantly.

So far, more than 90% of isocyanate products in the world are produced by phosgene method. HDI phosgene production process is mature, economical and reasonable. According to the production process conditions, the phosgene method can be divided into liquid-phase phosgene method, salt-forming phosgene method and gas-phase phosgene method.

The liquid phase phosgene method refers to the method of generating HDI by the direct reaction of phosgene and hexamethylenediamine in the liquid phase. This method first adopts the one-step high-temperature phosgene method, that is, the hexamethylenediamine solution and the phosgene solution are directly synthesized under the catalysis of the catalyst. HDI. This method not only has many by-products, but also has a low yield of product HDI. After a lot of research, the researchers improved the one-step high-temperature phosgene method, and proposed the cold and hot two-step phosgene method that is currently used more. The reaction time of the method is short, and it is especially suitable for the phosgenation reaction of amine compounds with high boiling point, difficult vaporization and low reactivity. However, this method is easy to generate by-products such as urea compounds and monoisocyanate chloride Cl(CH ₂ ) ₆ NCO in the HDI synthesis reaction, and the generated urea compounds will further consume phosgene and form resinous tar compounds, seriously affecting the product. yield.

The salt-forming phosgene method is a widely used production method for the production of isocyanates, which overcomes the shortcomings of the liquid-phase phosgene method. In this process, hexamethylenediamine and hydrogen chloride first form hydrochloride, and then react with phosgene to obtain HDI. Compared with the liquid-phase phosgene method, the salt-forming phosgene method can better reduce by-products, but this method still has many disadvantages, such as a long reaction time, and the prepared HDI is easy to form tar-like substances after prolonged heating , reducing the yield. In addition, the salt formation rate is difficult to control, and the solubility of hydrochloride is small, and it is easy to precipitate to increase the viscosity of the feed liquid, resulting in problems such as uneven mixing of the feed liquid.

The gas-phase phosgene method is currently the mainstream method for producing HDI in the world. This method mixes gaseous amine compounds with inert solvent vapor or inert gas, and reacts with phosgene at a high temperature of 200-600°C to prepare isocyanate. The process has high reaction yield, less phosgene consumption, high production efficiency and good safety factor, but has high technical barriers. In gas phase phosgenation, efficient gas phase mixing reactor and reaction conditions are the core of the whole production process. Unoptimized reactor and process conditions In the process of producing HDI, a wide variety of by-products are formed, such as isocyanurate, biuret, allophanate, carbodiimide or urea. Although the concentration of these by-products is low, they are easy to deposit, block the pipeline, and affect the steady-state operation of the reaction.

Patent CN100475783C discloses a method for preparing (poly)isocyanates in the gas phase. A tubular reactor is provided, which has a clamped conduit extending along the center in the direction of the rotational axis of the tubular reactor, a concentric annular gap is formed between the inner wall and the outer wall of the clamped conduit, and the amine vapor is transported at a certain gas velocity The feed into the tubular reactor is via a concentric annular gap, while the phosgene is fed into the tubular reactor at a gas velocity from the remaining cross-section of the tubular reactor. Both generate HDI in a tubular reactor. The process can effectively improve the yield and purity of the product. However, after the amine materials in this process pass through the concentric annular gap, a continuous gas film and phosgene contact reaction will occur, resulting in incomplete reaction. After running for a long time, it is easy to accumulate by-products and cause blockage.

Patent CN106715385B discloses a method for preparing isocyanate in gas phase. The gaseous amine stream and the inert gas stream are mixed through a coaxial Kenics type static mixer, and then phosgene is injected into the gaseous amine stream after the static mixer to react to generate HDI. The introduced phosgene stream is relatively gaseous The direction of flow of the amine stream is at an angle of ≦90°. The invention describes the structure of the reactor in detail, as well as control conditions such as temperature and pressure. Through process improvements, the disadvantages of known methods can be avoided and high yields can be achieved, while extending device life. However, this process only solves the problem of mixing uniformity of amine substances and inert gas, and fails to further elaborate on the mixing uniformity of amine substances and phosgene. Whether the amines and phosgene are evenly mixed has a great influence on the formation of reaction impurities and steady-state operation.

In view of this, it is necessary to invent a high-efficiency tubular reactor that can effectively solve the problem of mixing uniformity and promote the smooth operation of the preparation reaction of hexamethylene diisocyanate.

Contents of the invention

The main purpose of the present invention is to provide a method for preparing hexamethylene diisocyanate in the gas phase, to solve the problem of hexamethylene diisocyanate caused by uneven distribution of amines and phosgene or phosgene itself in the prior art. The problem of low preparation yield and unstable reaction.

In order to achieve the above object, according to one aspect of the present invention, a kind of tubular reactor suitable for preparing hexamethylene diisocyanate by gas phase method is provided, the tubular reactor comprises a tubular reactor body, which has a tubular reaction chamber room; among them,

One end of the tubular reactor body has a first air inlet, and the other end has a gas extraction port. According to the flow sequence of the materials, there are also installed on the side wall of the tubular reactor body between the first air inlet and the gas extraction port. A plurality of sets of second air inlets, each group including at least one second air inlet, and the air inlet direction of the first air inlet is parallel to the axial direction of the tubular reactor body, and the air inlet direction of the second air inlet form an acute angle with the air intake direction of the first air inlet;

There are concave structures distributed inside the tubular reactor body;

The first gas inlet is used to feed 1,6-hexamethylenediamine gas, and a gas distributor is provided inside the tubular reactor body near the first gas inlet, and a plurality of gas distribution holes are arranged on the gas distributor. And the gas distribution direction of the gas distribution holes is parallel to the axial direction of the tubular reactor body;

The second air inlet is used to pass into the mixed gas of phosgene and chlorobenzene;

The gas extraction port is used to extract the mixed gas containing hexamethylene diisocyanate.

Further, the depth of the apex in the concave structure is 0.5-5 mm; preferably, the concave structure occupies an area of 30-60% of the total area of the side wall of the tubular reactor body; more preferably, the concave structure is an arcuate structure, more preferably Hemispherical structure.

Further, two groups of second gas inlets are arranged on the side wall of the tubular reactor body between the first gas inlet and the gas extraction port, and according to the direction away from the first gas inlet, the first group of second gas inlets are respectively Two air inlets and a second set of second air inlets;

Preferably, the aspect ratio of the tubular reactor body is (40-50):1;

Preferably, the distance between the first group of second gas inlets and the gas distributor is 2 to 5 times the diameter of the tubular reactor body;

Preferably, the distance between the second group of second gas inlets and the gas distributor is 20-25 times the diameter of the tube reactor body.

Further, in each group of second air inlets, a plurality of second air inlets are located on the same radial section of the tubular reactor body, preferably, a plurality of second air inlets are equally spaced along the circumference of the tubular reactor body Setting; most preferably, each group of second air inlets is further provided with gas nozzles corresponding to each second air inlet; the overall injection direction of the nozzles is preferably conically distributed, and the cone angle is 120- 150°;

Preferably, the air intake direction of the second air inlet is 30-60° from the air inlet direction of the first air inlet.

Further, the opening ratio of the air distribution holes in the gas distributor is 15-40%, preferably the diameter of the air distribution holes is 2-5 mm.

In order to achieve the above object, according to one aspect of the present invention, a kind of system suitable for preparing hexamethylene diisocyanate by gas phase method is provided, comprising:

The reactor is the above-mentioned tubular reactor;

The flash evaporator is connected to the gas extraction outlet of the reactor, the flash evaporator has a first gas phase outlet and a first liquid phase outlet, and the flash evaporator is used to flash the mixed gas containing hexamethylene diisocyanate to obtain the first part of hexamethylene diisocyanate The crude product of methyl diisocyanate and the first mixed gas;

The absorber is connected to the first gas phase outlet of the flasher, and the absorber has a chlorobenzene inlet, a second gas phase outlet and a second liquid phase outlet, and the absorber is used for component separation of the first mixed gas to obtain the second part six Methyl diisocyanate crude product and the second mixed gas;

The dephosphorization equipment is connected with the first liquid phase outlet and the second liquid phase outlet, and the dephosphorization equipment has a third liquid phase outlet, and the dephosphorization equipment is used to process the first part of hexamethylene diisocyanate crude product and the second part of hexamethylene diisocyanate The crude methyl diisocyanate is subjected to dephosgenation to obtain a chlorobenzene liquid containing hexamethylene diisocyanate.

In order to achieve the above object, according to one aspect of the present invention, a method for preparing hexamethylene diisocyanate by a gas phase method is provided, the method adopts the above-mentioned system, and the method includes the following steps:

S1, the mixed gas of phosgene and chlorobenzene is passed into the reactor through the second gas inlet, and the 1,6-hexamethylenediamine gas is passed into the reactor through the first gas inlet to carry out the synthesis reaction to obtain Mixed gas of methylene diisocyanate;

S2, flashing the mixed gas containing hexamethylene diisocyanate in a flasher to obtain a first gas phase and a first liquid phase;

S3, using chlorobenzene for absorption to absorb the first gas phase in the absorber to obtain a second liquid phase and a second gas phase;

S4, dephosphorizing the first liquid phase and the second liquid phase in the dephosphorization equipment to obtain the third liquid phase and the third gas phase; wherein, the third liquid phase is the chlorobenzene containing hexamethylene diisocyanate liquid.

Further, before the mixed gas of phosgene and chlorobenzene is passed into the reactor, the method also includes: preheating and pressurizing the mixed gas of phosgene and chlorobenzene; the temperature of the preferred preheating is 300- 400° C., the pressure of pressurized treatment is 0.1-0.5 MPa; more preferably, the gas flow rate of the mixed gas of phosgene and chlorobenzene into the reactor is 10-30 m/s. .

Further, before the 1,6-hexamethylenediamine gas is fed into the reactor, the method also includes: preheating and pressurizing the 1,6-hexamethylenediamine gas; the temperature of the preheating treatment is preferably 300- 400°C, the pressure of pressurized treatment is 0.15-0.55MPa; more preferably, the gas flow rate of 1,6-hexamethylenediamine gas into the reactor is 10-30m/s.

Further, the pressure of the pressurized 1,6-hexanediamine gas is 0.02-0.05 MPa higher than the pressure of the pressurized mixed gas of phosgene and chlorobenzene.

Further, the molar ratio of 1,6-hexanediamine, phosgene and chlorobenzene is 1:(4-7):(1.5-2.5).

Further, step S1 includes, passing the mixed gas of the first part of phosgene and chlorobenzene into the reactor through the first group of second gas inlets, and passing the mixed gas of the second part of phosgene and chlorobenzene through the second group of second gas inlets. The gas inlet leads into the reactor; preferably, the volume ratio of the first part of the mixed gas of phosgene and chlorobenzene to the second part of the mixed gas of phosgene and chlorobenzene is (60-70): (30-40).

Further, the synthesis reaction time is 1-5s, the pressure is 0.1-0.5MPa, and the temperature is 350-450°C.

Further, in step S2, the flashing treatment is carried out under normal pressure at a temperature of 150-250°C.

Further, in step S3, the temperature of chlorobenzene is 50-100° C.; preferably, the molar ratio of chlorobenzene to the gas obtained from the outlet of the first gas phase is (0.6-1.0):1.

Further, in step S4, the temperature of the dephosphorization treatment is 100-120°C.

Applying the technical scheme of the present invention, the structure of the tubular reactor is optimized, and the reaction gas is distributed through the gas distributor and multiple sets of second gas inlets, effectively solving the uneven mixing of hexamethylenediamine and phosgene and the uneven distribution of phosgene itself. average problem. In particular, the interior of the tubular reactor is also provided with a concave structure, which can increase the degree of gas turbulence and facilitate the uniform mixing of materials. It is determined by experiments that the HDI synthesis reaction carried out by using the tubular reactor of the present invention is stable after 336 hours of long-term operation, without clogging phenomenon, and the yield of HDI is high.

Description of drawings

The accompanying drawings constituting a part of the present application are used to provide a further understanding of the present invention, and the schematic embodiments and descriptions of the present invention are used to explain the present invention, and do not constitute an improper limitation of the present invention. In the attached picture:

Fig. 1 shows the tubular reactor side view that is suitable for preparing hexamethylene diisocyanate by gas phase method according to the present invention;

Fig. 2 shows the cross-sectional view of the junction of the second gas inlet and the tubular reactor according to the present invention;

Fig. 3 shows a system suitable for preparing hexamethylene diisocyanate by gas phase method according to the present invention.

Wherein, the above-mentioned accompanying drawings include the following reference signs:

10. Tubular reactor body; 101. First gas inlet; 102. Gas extraction outlet; 103. Second gas inlet; 11. Gas distributor;

A. Intake valve; B. Pipe wall; C. Nozzle;

1. Reactor; 2. Flash evaporator; 3. Absorber; 4. Dephosphorization equipment.

Detailed ways

It should be noted that, in the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and examples.

In order to solve the above-mentioned problems in the prior art, according to one aspect of the present invention, a tubular reactor suitable for preparing hexamethylene diisocyanate by a gas phase method is provided.

A typical HDI synthesis tubular reactor structure schematic diagram according to the present invention is as shown in Figure 1, and it comprises tubular reactor body 10, and it has tubular reaction chamber; Wherein, one end of tubular reactor body 10 has The first air inlet 101 has a gas extraction port 102 at the other end. According to the flow sequence of materials, multiple sets of first air inlets 101 and the gas extraction ports 102 are arranged on the side wall of the tubular reactor body 10. Two gas inlets 103, at least one second gas inlet 103 is included in each group, and the gas inlet direction of the first gas inlet 101 is parallel to the axial direction of the tubular reactor body 10, and the gas inlet of the second gas inlet 103 There is an acute angle between the gas direction and the gas inlet direction of the first gas inlet 101; the interior of the tubular reactor body 10 is distributed with a concave structure; the first gas inlet 101 is used to feed 1,6-hexamethylenediamine gas, And the inside of the tubular reactor body 10 is also provided with a gas distributor 11 near the first air inlet 101. The gas distributor 11 is provided with a plurality of air distribution holes, and the gas distribution direction of the air distribution holes is parallel to the tubular reactor body. Axial direction of 10; The second air inlet 103 is used to pass into the mixed gas of phosgene and chlorobenzene; The gas extraction port 102 is used to extract the mixed gas containing hexamethylene diisocyanate.

Applying the technical scheme of the present invention, the structure of the tubular reactor is optimized, and the reaction gas is distributed through the gas distributor and multiple sets of second gas inlets 103, effectively solving the uneven mixing of hexamethylenediamine and phosgene and the distribution of phosgene itself uneven problem. In particular, the interior of the tubular reactor is also provided with a concave structure, which can increase the degree of gas turbulence and facilitate the uniform mixing of materials. It is determined by experiments that the HDI synthesis reaction carried out by using the tubular reactor of the present invention is stable after 336 hours of long-term operation, without clogging phenomenon, and the yield of HDI is high.

In the present invention, while preparing HDI, HCl gas is also obtained as another product.

In a preferred embodiment, in order to further optimize the degree of gas turbulence, the depth of the apex in the concave structure is 0.5-5 mm; preferably, the area occupied by the concave structure is 30-60% of the total area of the side wall of the tubular reactor body 10; More preferably, the concave structure is an arcuate structure, more preferably a hemispherical structure. Setting the concave structure according to the above parameters can better make the reaction gas form a cyclone in the tubular reactor, thereby making the reaction more complete.

In a preferred embodiment, in order to further optimize the uniformity of gas distribution, two sets of second gas inlets are arranged on the side wall of the tubular reactor body 10 between the first gas inlet 101 and the gas extraction outlet 102 103, according to the direction away from the first air inlet 101, respectively the first group of second air inlets 103 and the second group of second air inlets 103; carry out the above preferred mixed gas inlet mode of phosgene and chlorobenzene , the so-called "two-stage" ventilation, so that the mixed gas of phosgene and chlorobenzene can form a certain concentration at a position closer to the first air inlet 101 and farther away from the first air inlet 101, so that it is the same as 1, The 6-hexamethylenediamine gas can be mixed evenly, so that the reaction is more complete, and the product yield and quality are high.

Preferably, the length-to-diameter ratio of the tubular reactor body 10 is (40-50): 1; this preferred length-to-diameter ratio is more conducive to keeping the mixed gas under the premise that the product selectivity and conversion rate meet the requirements. A certain flow rate ensures that less impurities are deposited in the tube, which promotes the steady-state operation of the reaction, and the reactor is easier to achieve engineering transformation;

Preferably, the distance between the first group of second gas inlets 103 and the gas distributor 11 is 2 to 5 times the pipe diameter of the tubular reactor body 10; the position of the first group of second gas inlets 103 is preferred, It is more conducive to making the jet gas react without blocking the gas injection port. If the distance is too close to the gas distributor, the generated impurities will gradually accumulate and easily block the distributor hole, which is difficult to deal with later; if the distance is too far, the aspect ratio needs to be increased. , it is more difficult for engineering transformation;

Preferably, the distance between the second group of second gas inlets 103 and the gas distributor 11 is 20 to 25 times the pipe diameter of the tubular reactor body 10. This position of the first group of second gas inlets 103 is preferred, and more It is conducive to the full reaction of unreacted hexamethylenediamine and supplemented phosgene to ensure the yield and content of the product. If it is too close to the distributor, it will be too close to the first group, which is not conducive to the full reaction of unreacted hexamethylenediamine If the distance is too far, the unreacted hexamethylene diamine and the generated hexamethylene diisocyanate will continue to react to generate impurities such as ureas, which will cause the yield to decrease, and the generated impurities will easily block the reactor. In order to further mix the reaction gases evenly, in a preferred embodiment, as shown in Figure 2 (A represents the inlet valve; B represents the pipe wall; C represents the nozzle), in each group of second gas inlets 103, A plurality of second air inlets 103 are located on the same radial section of the tubular reactor body 10, preferably, a plurality of second air inlets 103 are arranged at equal intervals along the circumference of the tubular reactor body 10; most preferably, each The group of second air inlets 103 is three. The air inlet is set according to the above method, so that the mixed gas of phosgene and chlorobenzene is sprayed into the tubular reactor body 10 from multiple angles, which is more conducive to promoting the uniform distribution of the reaction gas, so that the reaction is more complete and the product yield is obtained. with high quality.

In order to further optimize the way of air intake, in a preferred embodiment, each second air inlet 103 is provided with gas nozzles in one-to-one correspondence; the overall injection direction of the preferred nozzles is conical distribution, and the cone angle is 120-150°; preferably, the air-intake direction of the second air inlet 103 and the air-intake direction of the first air inlet 101 are 30-60°. Air intake according to the above-mentioned preferred method can make the distribution of the reaction gas more uniform.

In a preferred embodiment, the opening ratio of the air distribution holes in the gas distributor 11 is 15-40%, preferably the diameter of the air distribution holes is 2-5 mm. Preferably, the gas distributor 11 with the above structure is beneficial to make the 1,6-hexamethylenediamine gas distribution more uniform.

According to another aspect of the present invention, a kind of system suitable for preparing hexamethylene diisocyanate by gas phase method is provided, as shown in Figure 3, it comprises:

Reactor 1 is the above-mentioned tubular reactor;

Flash evaporator 2 is connected to the gas extraction outlet 102 of reactor 1, and flash evaporator 2 has a first gas phase outlet and a first liquid phase outlet, and flash evaporator 2 is used for flashing the mixed gas containing hexamethylene diisocyanate to Obtain the first part of hexamethylene diisocyanate crude product and the first mixed gas;

The absorber 3 is connected to the first gas phase outlet of the flasher 2. The absorber 3 has a chlorobenzene inlet, a second gas phase outlet and a second liquid phase outlet. The absorber 3 is used to separate the components of the first mixed gas to obtain The second part of hexamethylene diisocyanate crude product and the second mixed gas;

The dephosphorization device 4 is connected with the first liquid phase outlet and the second liquid phase outlet, the dephosphorization device 4 has a third liquid phase outlet, and the dephosphorization device 4 is used for the first part of hexamethylene diisocyanate crude product and the second Part of the crude hexamethylene diisocyanate is subjected to dephosgenation treatment to obtain a chlorobenzene liquid containing hexamethylene diisocyanate.

Applying the system of the present invention to carry out the HDI synthesis reaction, the reaction gas is distributed through the gas distributor and multiple sets of second gas inlets 103, which effectively solves the problems of uneven mixing of hexamethylenediamine and phosgene and uneven distribution of phosgene itself. The time run was stable and the yield of HDI was high. A flash evaporation process is set in the process flow of the present invention, which can preliminarily separate the target product and phosgene, reduce the absorption volume of chlorobenzene in the subsequent absorption process, and help reduce energy consumption and solvent consumption.

The above-mentioned first mixed gas mainly includes HDI, phosgene and HCl gas; the above-mentioned second mixed gas mainly includes phosgene and HCl gas.

In actual operation, optionally, the dephosphorization device 4 in the above system also includes a third gas phase outlet for discharging the third mixed gas; the above system also preferably includes a mixed gas re-separation device for processing the second mixed gas and a third mixed gas.

According to another aspect of the present invention, there is also provided a method for preparing hexamethylene diisocyanate by gas phase method, the method adopts the above-mentioned system, and the method comprises the following steps:

S1, the mixed gas of phosgene and chlorobenzene is passed into the reactor 1 through the second gas inlet 103, and the 1,6-hexamethylenediamine gas is passed into the reactor 1 through the first gas inlet 101 to carry out the synthesis reaction , to obtain a mixed gas containing hexamethylene diisocyanate;

S2, flashing the mixed gas containing hexamethylene diisocyanate in the flasher 2 to obtain the first gas phase and the first liquid phase;

S3, using chlorobenzene for absorption to absorb the first gas phase in the absorber 3 to obtain a second liquid phase and a second gas phase;

S4, dephosphorizing the first liquid phase and the second liquid phase in the dephosphorizing device 4 to obtain a third liquid phase and a third gas phase; wherein, the liquid phase is a chlorobenzene liquid containing hexamethylene diisocyanate.

The HDI is prepared according to the method of the invention, the reaction operation is stable, the side reaction is few, and the yield is high. After the long run experiment by technicians, there is no solid deposition in the reactor.

In actual operation, technicians can continue to process the chlorobenzene solution containing hexamethylene diisocyanate through desolvation, light removal, and rectification to obtain pure HDI. The specific parameter setting of the above process is the process setting well known to those skilled in the art.

In order to better promote the synthesis reaction, in a preferred embodiment, before the mixed gas of phosgene and chlorobenzene is passed into the reactor 1, the above-mentioned method also includes: pre-processing the mixed gas of phosgene and chlorobenzene Heat treatment and pressure treatment; the temperature of the preheating treatment is preferably 300-400°C, and the pressure of the pressure treatment is 0.1-0.5MPa; more preferably, the mixed gas of phosgene and chlorobenzene is passed into the gas in the reactor 1 The flow rate is 10-30m/s. Preheating and prepressurizing the reaction gas in advance is more conducive to the full reaction.

In a preferred embodiment, before step S1, before the 1,6-hexamethylenediamine gas is passed into the reactor 1, the above method further includes: preheating the 1,6-hexamethylenediamine gas and Pressure treatment; the temperature of the preheating treatment is preferably 300-400°C, and the pressure of the pressure treatment is 0.15-0.55MPa; more preferably, the gas flow rate of 1,6-hexamethylenediamine gas into the reactor 1 is 10 ~30m/s. The reaction gas is preheated and prepressurized in advance to make it evenly distributed after passing through the gas distributor 11, which is conducive to sufficient reaction.

In order to better distribute the reaction gas evenly, in a preferred embodiment, the pressure of the pressurized 1,6-hexanediamine gas is 0.02 higher than the pressure of the pressurized mixed gas of phosgene and chlorobenzene ~0.05MPa. The above-mentioned pressure difference is preferred, which is more conducive to the uniform mixing of the two reaction gases and the sufficient reaction.

In a preferred embodiment, the molar ratio of 1,6-hexanediamine, phosgene and chlorobenzene is 1:(4-7):(1.5-2.5). The above-mentioned feed ratio is preferred, which is more conducive to obtaining high-yield HDI.

In order to further distribute the reaction gas evenly, in a preferred embodiment, step S1 includes, passing the mixed gas of the first part of phosgene and chlorobenzene into the reactor 1 through the first group of second gas inlets 103, and feeding the first part of the mixed gas of phosgene and chlorobenzene into the reactor 1, The mixed gas of two parts of phosgene and chlorobenzene is passed into reactor 1 through the second group of the second gas inlet 103; Preferably, the mixed gas of the first part of phosgene and chlorobenzene is mixed with the second part of phosgene and chlorobenzene The gas volume ratio is (60-70): (30-40). Make the mixed gas of phosgene and chlorobenzene pass in more near the first air inlet 101, and pass in less at a position farther away from the first air inlet 101, which is more conducive to making its concentration distribution uniform, It is also beneficial to make it evenly mixed with 1,6-hexanediamine gas, so that the reaction is more complete, and the product yield and quality are high.

In order to further promote uniform gas distribution, in a preferred embodiment, the molar ratio of phosgene to 1,6-hexamethylenediamine contained in the first part of the mixed gas of phosgene and chlorobenzene is (2.4～2.9):1 . Controlling the ratio of phosgene and 1,6-hexanediamine according to the above conditions is more conducive to the uniform reaction in the tubular reactor.

In order to better promote the reaction, in a preferred embodiment, the synthesis reaction time is 1-5 s, the pressure is 0.1-0.5 MPa, and the temperature is 350-450°C.

In order to better complete the preliminary separation of HDI and gas phase, in a preferred embodiment, in step S2, the flashing treatment is carried out under normal pressure at a temperature of 150-250°C. The so-called atmospheric pressure is about one atmospheric pressure, about 101.3KPa. There are some differences in the average atmospheric pressure in various places, and the specific atmospheric pressure of the location shall prevail.

In order to better complete the further separation of HDI and the gas phase, in a preferred embodiment, in step S3, the temperature of chlorobenzene is 50-100°C; The ratio is (0.6～1.0):1.

In a preferred embodiment, in step S4, the temperature of the dephosphorization treatment is 100-120°C.

The present application will be described in further detail below in conjunction with specific examples, and these examples should not be construed as limiting the scope of protection claimed in the present application.

Example 1

The mixed gas of phosgene and chlorobenzene under specified conditions (temperature: 350° C., absolute pressure: 0.4 MPa) was sprayed into the tubular reactor at a flow rate of 12 m/s. Among them, phosgene with 3.2 times the molar equivalent of hexamethylenediamine is injected from the mixed gas inlet pipe closer to the distributor, and the rest of the mixed gas is injected from the mixed gas inlet pipeline farther from the distributor.

The gaseous 1,6-hexamethylenediamine gas (temperature: 350°C, absolute pressure: 0.45MPa) is passed into the upper chamber of the tubular reactor, distributed by the gas distributor, and sprayed into the tubular reactor for reaction. The molar ratio of hexamethylenediamine: phosgene: chlorobenzene is 1:5:2.

The chemical reaction equation is:

After the mixed gas containing HDI stays in the reactor for 1-2s, it is extracted from the bottom of the tubular reactor. It is determined by experiments that after the process runs for 336 hours, when the tubular reactor is disassembled, there is no solid deposition inside.

In this embodiment, the specific structure of the tubular reactor used is:

The aspect ratio is 45:1, the distance between the first group of second air inlets 103 and the first air inlet 101 is 4 times the pipe diameter, and the distance between the second group of second air inlets 103 and the first air inlet 101 is 22 times the pipe diameter;

There are three second air inlets 103 in each group;

The air inlet direction of the second air inlet and the air inlet direction of the first air inlet are 45°, and the cone angle of the nozzle in the second air inlet is 135°;

The opening rate of the gas distributor 11 is 25%, and the aperture of the gas distribution hole is 4mm;

The inner concave structure of the tubular reactor body 10 is hemispherical, the depth of the apex is 4 mm, and the area occupied by the concave structure is 45% of the total area of the side wall of the tubular reactor body 10 .

The side view of the HDI synthesis tubular reactor is shown in FIG. 1 .

Flash evaporation and absorption process: After the mixed gas containing HDI is extracted, it is flashed by a flash evaporator at 190°C under normal pressure, and the liquid phase is collected into a container, and the gas phase is partially absorbed by chlorobenzene at 60°C. The ratio of the number of moles of chlorobenzene used for absorption to the number of moles of gas obtained by flash evaporation is 0.8:1.

Degassing process: Combine the absorbed chlorobenzene liquid with the aforementioned liquid phase feed, control the temperature of the material to 110°C and remove phosgene, and obtain HDI chlorobenzene liquid at the bottom of the tank, wherein the phosgene content is 0.03%.

The schematic diagram of the system of the present invention is as shown in FIG. 2 .

Part of the degassed HDI chlorobenzene solution was desolvated, lightened, and rectified to obtain pure HDI (content: 99.63%, yield: 96.25%).

Example 2

The difference from Example 1 is that the phosgene of 2.5 times the molar equivalent of hexamethylenediamine is sprayed into the gas mixture inlet pipe closer to the distributor, and the rest of the gas mixture is injected from the gas mixture inlet pipeline farther away from the distributor. Squirt into.

Other reaction conditions and equipment parameter are identical with embodiment 1.

. Subsequent treatment process is identical with embodiment 1.

Pure HDI was obtained (content: 99.6%, yield 95.47%).

Example 3

The difference with embodiment 1 is that the concrete structure of used tubular reactor is:

The aspect ratio is 40:1, the distance between the first group of second air inlets 103 and the first air inlet 101 is twice the pipe diameter, and the distance between the second group of second air inlets 103 and the first air inlet 101 is 20 times the pipe diameter;

There are three second air inlets 103 in each group;

The short-term direction of the second air inlet and the air inlet direction of the first air inlet are 30°, and the cone angle of the nozzle in the second air inlet is 120°;

The opening ratio of the gas distributor 11 is 20%, and the aperture of the gas distribution hole is 2.5mm;

The inner concave structure of the tubular reactor body 10 is hemispherical, the depth of the apex is 2 mm, and the area occupied by the concave structure is 40% of the total area of the side wall of the tubular reactor body 10 .

Flash evaporation and absorption process: After the mixed gas containing HDI is extracted, it is flashed by a flash evaporator at 190°C under normal pressure, and the liquid phase is collected into a container, and the gas phase is partially absorbed by chlorobenzene at 60°C. The ratio of the number of moles of chlorobenzene used for absorption to the number of moles of gas obtained by flash evaporation is 0.8:1.

Degassing process: Combine the absorbed chlorobenzene liquid with the aforementioned liquid phase feedstock, control the material temperature to 110°C and remove phosgene, and obtain HDI chlorobenzene liquid at the bottom of the tank, wherein the phosgene content is 0.032%.

Subsequent treatment process is identical with embodiment 1.

Pure HDI was obtained (content: 99.59%, yield 94.32%).

Comparative example 1

The difference from Example 1 is that there is no concave structure inside the tubular reactor used in this comparative example. Subsequent treatment process is identical with embodiment 1.

Pure HDI (content: 99.6%, yield 88.23%) was obtained.

Analyzing the composition of the sample of the distillation still residue, which contains more isocyanurate and other urea substances, it can be determined that because there is no concave structure, the local mixing effect of raw materials and products is reduced, resulting in the formation of a certain amount of by-products, causing Yield decreased. After the tubular reactor had been running for 252 hours, the tubular reactor was disassembled, and some solids were deposited on the tube wall.

Comparative example 2

The difference from Example 1 is that in this comparative example, no two-stage feed is used, so that phosgene and chlorine are all passed into the reactor at a distance of 4 times the pipe diameter from the first gas inlet. Subsequent treatment process is identical with embodiment 1.

Pure HDI was obtained (content: 99.61%, yield 80.56%).

Analyzing the composition of the sample of the distillation still residue, it contains more urea substances, which can be determined to be uneven distribution of phosgene, insufficient conversion of hexamethylenediamine, and a certain amount of urea substances are formed after reacting with the product. After the tubular reactor had been running for 118 hours, the tubular reactor was disassembled, and some solids were deposited on the tube wall.

From the above description, it can be seen that the above-mentioned embodiments of the present invention have achieved the following technical effects:

The invention provides a high-efficiency tubular reactor, which can effectively solve the problem of mixing uniformity of hexamethylenediamine, phosgene and phosgene itself, promote stable reaction, less side reactions, and high HDI yield.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (17)

1. A tubular reactor suitable for the gas phase preparation of hexamethylene diisocyanate, characterized in that it comprises a tubular reactor body (10) having a tubular reaction chamber; wherein,,

one end of the tubular reactor body (10) is provided with a first air inlet (101), the other end of the tubular reactor body is provided with a gas extraction outlet (102), a plurality of groups of second air inlets (103) are further arranged on the side wall of the tubular reactor body (10) between the first air inlet (101) and the gas extraction outlet (102) according to the material flow sequence, each group comprises at least one second air inlet (103), the air inlet direction of the first air inlet (101) is parallel to the axial direction of the tubular reactor body (10), and an acute angle is formed between the air inlet direction of the second air inlet (103) and the air inlet direction of the first air inlet (101);

the inside of the tubular reactor body (10) is distributed with a concave structure;

the first air inlet (101) is used for introducing 1, 6-hexamethylenediamine gas, a gas distributor (11) is further arranged inside the tubular reactor body (10) and close to the first air inlet (101), a plurality of gas distribution holes are formed in the gas distributor (11), and the gas distribution direction of the gas distribution holes is parallel to the axial direction of the tubular reactor body (10);

the second air inlet (103) is used for introducing mixed gas of phosgene and chlorobenzene;

the gas extraction port (102) is used for extracting mixed gas containing hexamethylene diisocyanate.

2. The tubular reactor of claim 1, wherein the depth of the peaks in the concave structures is 0.5-5 mm; preferably, the occupied area of the concave structure is 30-60% of the total area of the side wall of the tubular reactor body (10); more preferably, the concave structure is a cambered surface structure, and still more preferably a hemispherical structure.

3. A tubular reactor according to claim 1 or 2, characterized in that two sets of said second gas inlets (103) are provided on the side wall of said tubular reactor body (10) between said first gas inlet (101) and said gas outlet (102), respectively a first set of said second gas inlets (103) and a second set of said second gas inlets (103) in a direction away from said first gas inlet (101);

preferably, the aspect ratio of the tubular reactor body (10) is (40-50): 1, a step of;

preferably, the distance between the first group of the second gas inlets (103) and the gas distributor (11) is 2-5 times the pipe diameter of the pipe reactor body (10);

preferably, the distance between the second gas inlets (103) and the gas distributor (11) of the second group is 20-25 times the pipe diameter of the pipe reactor body (10).

4. A tubular reactor according to any one of claims 1 to 3, wherein in each set of said second gas inlets (103), a plurality of said second gas inlets (103) are located at the same radial cross section of said tubular reactor body (10), preferably a plurality of said second gas inlets (103) are equally spaced circumferentially along said tubular reactor body (10); most preferably, each group of the second air inlets (103) is three.

5. A tubular reactor according to claim 4, wherein gas nozzles are provided at each of the second gas inlets (103) in one-to-one correspondence; preferably, the whole spraying direction of the nozzle is in conical distribution, and the cone angle of the nozzle is 120-150 degrees;

preferably, the air inlet direction of the second air inlet (103) is 30-60 degrees with the air inlet direction of the first air inlet (101).

6. A tubular reactor according to any one of claims 1 to 5, characterized in that the open area of the gas distribution holes in the gas distributor (11) is 15-40%, preferably the pore size of the gas distribution holes is 2-5 mm.

7. A system for preparing hexamethylene diisocyanate by a gas phase process comprising:

a reactor (1) being a tubular reactor according to any one of claims 1 to 6;

the flash evaporator (2) is connected with the gas extraction outlet (102) of the reactor (1), the flash evaporator (2) is provided with a first gas phase outlet and a first liquid phase outlet, and the flash evaporator (2) is used for flashing the mixed gas containing hexamethylene diisocyanate to obtain a first part of hexamethylene diisocyanate crude product and a first mixed gas;

an absorber (3) connected to the first gas phase outlet of the flash evaporator (2), the absorber (3) having a chlorobenzene inlet, a second gas phase outlet and a second liquid phase outlet, the absorber (3) being configured to perform component separation of the first mixed gas to obtain a second portion of crude hexamethylene diisocyanate product and a second mixed gas;

and the phosgene removing device (4) is connected with the first liquid phase outlet and the second liquid phase outlet, the phosgene removing device (4) is provided with a third liquid phase outlet, and the phosgene removing device (4) is used for performing the phosgene removing treatment on the first part of hexamethylene diisocyanate crude product and the second part of hexamethylene diisocyanate crude product so as to obtain chlorobenzene liquid containing hexamethylene diisocyanate.

8. A process for the preparation of hexamethylene diisocyanate by gas phase method, characterized in that it employs the system according to claim 7, comprising the steps of:

s1, introducing the mixed gas of phosgene and chlorobenzene into a reactor (1) through the second air inlet (103), and introducing the 1, 6-hexamethylenediamine gas into the reactor (1) through the first air inlet (101) to perform a synthesis reaction to obtain the mixed gas containing hexamethylene diisocyanate;

s2, carrying out flash evaporation treatment on the mixed gas containing hexamethylene diisocyanate in a flash evaporator (2) to obtain a first gas phase and a first liquid phase;

s3, absorbing the first gas phase in an absorber (3) by utilizing chlorobenzene for absorption to obtain a second liquid phase and a second gas phase;

s4, performing dephosgene treatment on the first liquid phase and the second liquid phase in a dephosgene device (4) to obtain a third liquid phase and a third gas phase; wherein the third liquid phase is chlorobenzene liquid containing hexamethylene diisocyanate.

9. The method according to claim 8, characterized in that before introducing the phosgene and chlorobenzene mixed gas into the reactor (1), the method further comprises: preheating and pressurizing the mixed gas of phosgene and chlorobenzene; preferably, the temperature of the preheating treatment is 300-400 ℃, and the pressure of the pressurizing treatment is 0.1-0.5 MPa; more preferably, the gas flow rate of the mixed gas of phosgene and chlorobenzene into the reactor (1) is 10-30 m/s.

10. The method according to claim 8 or 9, characterized in that before passing the 1, 6-hexamethylenediamine gas into the reactor (1), the method further comprises: preheating and pressurizing the 1, 6-hexamethylenediamine gas; preferably, the temperature of the preheating treatment is 300-400 ℃, and the pressure of the pressurizing treatment is 0.15-0.55 MPa; more preferably, the gas flow rate of the 1, 6-hexamethylenediamine gas introduced into the reactor (1) is 10 to 30m/s.

11. The method according to claim 9 or 10, wherein the pressure of the 1, 6-hexamethylenediamine gas after pressurization is 0.02 to 0.05MPa higher than the pressure of the mixed gas of phosgene and chlorobenzene after pressurization.

12. The process according to any one of claims 8 to 11, characterized in that the molar ratio of 1, 6-hexamethylenediamine, phosgene and chlorobenzene is 1: (4-7): (1.5-2.5).

13. The method according to any one of claims 8 to 12, wherein step S1 comprises introducing a first portion of the mixed gas of phosgene and chlorobenzene into the reactor (1) through a first set of the second gas inlets (103) and introducing a second portion of the mixed gas of phosgene and chlorobenzene into the reactor (1) through a second set of the second gas inlets (103); preferably, the volume ratio of the mixed gas of the phosgene and the chlorobenzene of the first part to the mixed gas of the phosgene and the chlorobenzene of the second part is (60-70): (30-40).

14. The method according to any one of claims 8 to 13, wherein the synthesis reaction is carried out for a period of time ranging from 1 to 5s, at a pressure ranging from 0.1 to 0.5MPa and at a temperature ranging from 350 to 450 ℃.

15. The method according to any one of claims 8 to 14, wherein in step S2 the flash treatment is carried out at atmospheric pressure at a temperature of 150 to 250 ℃.

16. The process according to any one of claims 8 to 15, characterized in that in step S3, the chlorobenzene is at a temperature of 50-100 ℃; preferably, the molar ratio of chlorobenzene to gas obtained at the first gas phase outlet is (0.6-1.0): 1.

17. the method according to any one of claims 8 to 16, wherein in step S4, the temperature of the dephosgenation treatment is 100 to 120 ℃.

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