System and method for continuously synthesizing aromatic diisocyanate

Abstract

The invention discloses a system and a method for continuously synthesizing aromatic diisocyanate. The method comprises the following steps: continuously introducing an aromatic diamine solution and hydrogen chloride gas into a salifying kettle for reaction, and carrying out primary and secondary photochemical reactions on a liquid-phase material and phosgene after the salifying reaction to obtain a diisocyanate synthetic solution; the tail gas of the primary and secondary photochemical reactions is condensed by a condenser, the condensate returns to the photochemical kettle for continuous reaction, the uncondensed gas phase enters the absorption tower, the absorption liquid returns to the primary photochemical kettle for reaction, and the unabsorbed part of the gas phase enters the salifying kettle for reaction. The method can realize continuous synthesis of isocyanate, can effectively utilize synthesis tail gas, and reduces hydrogen chloride raw material cost and tail gas treatment cost; the phosgene is utilized to the maximum extent, the phosgene consumption is reduced, the product yield is improved, and the method has the advantages of low consumption of auxiliary raw materials and convenience in industrial implementation.

Description

Technical Field

[0001] The invention relates to the field of fine chemicals, and in particular to a system and method for continuously synthesizing aromatic diisocyanates. Background Art

[0002] Aromatic isocyanates are important intermediates for synthesizing high-performance polyurethane materials. Polyurethane materials based on aromatic isocyanates such as phenylene diisocyanate (PPDI) and 1,5-naphthalene diisocyanate (NDI) have the characteristics of high hardness, good resilience, excellent dynamic performance, good wear resistance, etc., and have very broad application prospects in large-scale machinery, new rail transportation equipment, new energy wind power, etc. With the upgrading of market consumption, the market has higher requirements for the tear strength, resilience, functionality and heat resistance of polyurethane elastomers, and traditional polyurethane elastomers synthesized from MDI are not enough to meet the special needs of some markets. In this context, the market demand for PPDI and NDI-based elastomers has a trend of increasing volume. Therefore, it is imperative to study the synthesis process of aromatic isocyanates, improve the yield and content, and reduce production costs.

[0003] Aromatic isocyanates are usually synthesized by the salt-forming phosgene process due to their special properties, that is, aromatic diamines are first reacted with hydrogen chloride or carbon dioxide to form aromatic diamine salts, and then the diamine salts are reacted with phosgene to form aromatic isocyanates, and finally the pure products are obtained through purification steps. The yields and production costs of different salt-forming phosgene processes vary greatly.

[0004] Patent GB1086782A discloses a method for preparing xylylene diisocyanate, wherein xylylene diamine reacts with hydrogen chloride at 0-60°C to form a salt, and then reacts with phosgene at 120-128°C, which can reduce the generation of by-products. In this process, the concentration of hydrochloride in the photochemical reaction stage is below 5.5wt%, resulting in a low time-space conversion rate of the photochemical reaction, and a large amount of solvent increases the cost during the distillation process.

[0005] Patent CN102070491B discloses a method for preparing xylylene diisocyanate. In this method, a jet reactor is set in a salt-forming reactor to enhance the mixing effect to improve the conversion rate of the salt-forming reaction. After the obtained amine hydrochloride is centrifuged and concentrated, it is subjected to high-pressure phosgenation and low-pressure phosgenation steps to obtain isocyanate. In order to solve the problem of jet reactor blockage, this process needs to be operated at a concentration of amine hydrochloride less than 8wt%, and the utilization rate of hydrogen chloride is low, and the overall energy consumption is high.

[0006] Patent CN111825572B discloses a method for preparing isocyanates by salt atomization phosgenation, which uses 2,4-diaminotoluene solution to react with hydrogen chloride to generate diamine hydrochloride, and then the diamine hydrochloride is atomized at 400°C, and enters the photochemical reactor together with high-temperature phosgene and nitrogen to react, and finally obtains 2,4-toluene diisocyanate solution through solvent absorption. This process can use a wide range of amine concentrations of 10-40wt%, has a short reaction residence time, is easy to scale up production, and has a high content. However, aromatic diisocyanates are very easy to coke when synthesized at high temperatures, which blocks the reactor and causes production stagnation, which is not conducive to continuous and stable production.

[0007] Patent CN111718282B discloses a method for preparing isocyanates with low chlorinated impurity content based on salt-forming phosgenation. The method uses an aromatic diamine and hydrogen chloride to react to generate a diamine hydrochloride with high particle size uniformity, and then reacts with phosgene at a molar ratio of 1:3 or more under pressure or normal pressure to synthesize an aromatic diisocyanate product. The product obtained by this process has high content and yield, simple operation, and is easy to implement. However, this process is an intermittent process, which is not conducive to large-scale production. At the same time, the tail gas phosgene of this process is not replenished, resulting in a large consumption of phosgene and increased production costs.

[0008] In the existing reports on the salt-forming phosgene method, the salt-forming reaction section generally has the problems of low spatiotemporal conversion rate of photochemical reaction under low concentration of amine hydrochloride, excessive viscosity of amine hydrochloride solution under high concentration, difficulty in transportation, and difficulty in achieving continuous production. The photochemical reaction section shows the characteristics of high phosgene consumption, large amounts of phosgene and hydrogen chloride gas in the tail gas, and heavy load on the tail gas treatment system. The hydrogen chloride gas in the tail gas can be used to produce aqueous hydrochloric acid solution, but further purification and separation of residual phosgene and solvent are required, which is costly. Summary of the invention

[0009] The present invention provides a system and method for continuously synthesizing aromatic diisocyanates to make up for the deficiencies of the prior art, which can improve the raw material conversion rate and realize the resource utilization of phosgene and hydrogen chloride gas in tail gas. The overall equipment is simple, the product yield is high, and the production cost is reduced.

[0010] The present invention provides a system for continuously synthesizing aromatic diisocyanates, comprising: a salt-forming kettle, a primary photochemical kettle, a secondary photochemical kettle, a tail gas condenser, and an absorption tower;

[0011] The salt forming kettle is provided with a diamine solution feed port, a hydrogen chloride feed port, and a salt forming solution discharge port. The salt forming kettle discharge port is connected to the first-stage photochemical kettle feed port, and the first-stage photochemical kettle discharge port is connected to the second-stage photochemical kettle feed port.

[0012] The first-stage photochemical reactor is also provided with a phosgene inlet, a first-stage tail gas outlet, a condensate feed inlet, and an absorption liquid feed inlet, and the first-stage tail gas outlet is connected to the feed inlet of the tail gas condenser;

[0013] The secondary photochemical reactor is also provided with a phosgene inlet, a secondary tail gas outlet, and a condensate feed inlet, and the secondary tail gas outlet is connected to the feed inlet of the tail gas condenser;

[0014] The tail gas condenser is also provided with a condensate discharge port and a non-condensable tail gas outlet. The number of tail gas condensers is one, which is used to condense the tail gas of the primary photochemical reactor and the secondary photochemical reactor, or the number of tail gas condensers is two, which are used to condense the tail gas of the primary photochemical reactor and the tail gas of the secondary photochemical reactor respectively;

[0015] The condensate discharge port is connected to the condensate feed port of the primary photochemical reactor and / or the secondary photochemical reactor, and is used to send the condensed phosgene back to the primary photochemical reactor and / or the secondary photochemical reactor; the non-condensable tail gas outlet is connected to the non-condensable tail gas feed port of the absorption tower, and is used to transport the non-condensable tail gas to the absorption tower;

[0016] The absorption tower is also provided with a solvent feed port, a tail gas outlet, and an absorption liquid discharge port. The tail gas outlet is connected to the hydrogen chloride feed port of the tail gas treatment system and / or the salt-forming kettle, and the absorption liquid discharge port is connected to the absorption liquid feed port of the primary photochemical kettle, so as to recycle the phosgene absorbed in the uncondensed tail gas to the primary photochemical kettle.

[0017] The present invention provides a method for continuously synthesizing aromatic diisocyanates, comprising the following steps:

[0018] (1) preheating the salting kettle, introducing an aromatic diamine solution and hydrogen chloride gas into the salting kettle at a certain flow rate to react and form a salting solution containing diamine hydrochloride (reaction 1), and after a certain residence time, continuously extracting the salting solution into a primary photochemical kettle;

[0019] (2) introducing phosgene into the primary photochemical reactor at a certain molar flow rate, causing a photochemical reaction with the salt-forming liquid at a certain reaction temperature and pressure to obtain a primary photochemical liquid (reaction 2), and continuously extracting the primary photochemical liquid into the secondary photochemical reactor;

[0020] (3) Phosgene is introduced into the secondary photochemical reactor at a certain molar flow rate to react with the primary photochemical liquid at a certain reaction temperature and pressure to obtain a diisocyanate synthesis liquid.

[0021] Reaction 1:

[0022] Reaction 2:

[0023] In the above formula, "R" is one of the following structures:

[0024]

[0025] Further, in step (1), the preheating temperature of the salting kettle is 110°C to 130°C, so that the aromatic diamine is completely dissolved; the aromatic diamine is selected from one of 1,5-naphthalene diamine, p-phenylenediamine, and diaminotoluene, the solvent is selected from aromatic hydrocarbons and halogenated aromatic hydrocarbons, preferably o-dichlorobenzene, the molar ratio of aromatic diamine to hydrogen chloride is 1:2 to 2.5, the mass concentration of the o-dichlorobenzene solution of aromatic diamine is 8% to 10%, the residence time of the salting liquid in the salting kettle is 0.5h to 1.5h, the salting rate of the aromatic diamine in the salting kettle is 99.5% to 99.9%, and the obtained salting liquid has good fluidity. Among them, the volume flow rate of the aromatic diamine solution is equal to the liquid volume in the salting kettle / the residence time of the salting liquid, so the residence time of the salting liquid can be controlled by adjusting the volume flow rate of the aromatic diamine introduced into the salting kettle. When the specified residence time is reached, the salt-forming solution can be continuously extracted into the primary photochemical reactor to maintain the liquid level balance in the salt-forming reactor. At this time, the molar flow rate of diamine hydrochloride in the extracted salt-forming solution is equal to the molar flow rate of the aromatic diamine solution entering the salt-forming reactor.

[0026] Furthermore, in step (2), the reaction temperature is 120°C to 140°C, the pressure is 0.1 to 0.6 MPa, the ratio of the molar flow rate of phosgene introduced into the primary photochemical reactor to the molar flow rate of diamine hydrochloride in the salt-forming liquid is 1.0 to 1.2:1, preferably 1.05 to 1.15; the residence time of the liquid phase material in the primary photochemical reactor is 3 to 4 hours. When the yield of the diisocyanate generated in the primary photochemical reactor accounts for 40% to 60% of the theoretical yield, the liquid phase material is continuously removed and transported to the secondary photochemical reactor, which is conducive to maintaining good fluidity of the liquid phase materials in the primary photochemical reactor and the secondary photochemical reactor, and the utilization rate of phosgene is high, which is conducive to large-scale production. The residence time can be calculated by the volume of liquid in the primary photochemical reactor / (the volume flow rate of the salt-forming liquid entering the primary photochemical reactor + the volume flow rate of the inert solvent injected from the top of the absorption tower), so the residence time of the liquid phase material in the primary photochemical reactor can be controlled by adjusting the volume flow rate of the inert solvent injected from the top of the absorption tower.

[0027] Furthermore, in step (3), the reaction temperature is 120°C to 140°C, the pressure is 0.1 to 0.6 MPa, and the pressure in the secondary photochemical reactor is equal to that in the primary photochemical reactor. The ratio of the molar flow rate of phosgene introduced into the secondary photochemical reactor to the molar flow rate of diamine hydrochloride in the primary photochemical liquid is 1.0 to 1.2:1, preferably 1.1 to 1.2; the residence time of the liquid phase material in the secondary photochemical reactor is 2 to 3 hours, and the yield of diisocyanate in the secondary photochemical reactor is 98% to 99%. The residence time of the liquid phase material in the secondary photochemical reactor can be controlled by opening the valve at the bottom of the secondary photochemical reactor. When the specified residence time is reached, the valve at the bottom of the secondary photochemical reactor is opened to keep the liquid level in the secondary photochemical reactor stable. At this time, the molar flow rate of diisocyanate extracted from the secondary reactor is equal to the molar flow rate of aromatic diamine entering the salt-forming reactor.

[0028] Furthermore, in step (2) and step (3), the tail gas of the primary photochemical reactor and the secondary photochemical reactor mainly includes phosgene, solvent o-dichlorobenzene, and hydrogen chloride gas, and the tail gas is extracted into a tail gas condenser, and the condensation temperature of the tail gas condenser is -25°C to -15°C. Most of the phosgene and o-dichlorobenzene are condensed and then reused in the primary photochemical reactor and / or the secondary photochemical reactor, and a small amount of phosgene and inert solvent gas are transported to the absorption tower. There is one tail gas condenser for condensing the tail gas of the primary photochemical reactor and the secondary photochemical reactor, or there are two tail gas condensers, which are respectively used to condense the tail gas of the primary photochemical reactor and the tail gas of the secondary photochemical reactor.

[0029] An inert solvent is injected into the top of the absorption tower to absorb the residual phosgene in the uncondensed tail gas, and the absorption liquid obtained at the bottom of the absorption tower flows into the primary photochemical reactor. The volume flow rate of the inert solvent injected into the top of the absorption tower is 10% to 30% of the volume flow rate of the salt-forming liquid entering the primary photochemical reactor. The inert solvent is selected from aromatic hydrocarbons and halogenated aromatic hydrocarbons, preferably o-dichlorobenzene. The tail gas extracted from the top of the absorption tower is almost pure hydrogen chloride gas. The molar flow rate is determined by adjusting the gas volume flow rate through a valve. Part of the tail gas enters the salt-forming reactor, and the excess gas enters the tail gas system for treatment. The molar flow rate of the absorption tower tail gas entering the salt-forming reactor is 2 to 2.5:1, preferably 2.1 to 2.4:1. It should be noted that once the hydrogen chloride content of the tail gas is ≥99.5%, the recovered hydrogen chloride can be used for the salt-forming process by adjusting the valve, and the original hydrogen chloride gas valve is closed at the same time, so as to achieve the purpose of tail gas utilization and cost reduction.

[0030] Compared with the processes commonly used in the industry, the method of the present invention has the advantages of high product yield, low consumption of auxiliary raw materials, and convenient industrial implementation, and the beneficial effects are as follows:

[0031] (1) The method of the present invention can realize continuous salt formation and photochemical reaction to synthesize diisocyanate, thereby improving the time-space yield and economic benefits of the reactor;

[0032] (2) The method of the present invention adopts a two-stage photochemical reaction in series, and when the yield of the diisocyanate generated in the first-stage photochemical reactor accounts for 40% to 60% of the theoretical yield, the liquid phase material is continuously removed and transported to the second-stage photochemical reactor, thereby avoiding the disadvantages of excessive slurry concentration in the photochemical reactor, difficult stirring, and low phosgene utilization rate caused by only using the first-stage reaction. The slurry in the first-stage photochemical reactor and the second-stage photochemical reactor of the present invention has low viscosity and good fluidity, which can greatly improve the phosgene utilization rate, is conducive to large-scale production, and is particularly suitable for the photochemical reaction of high-concentration salt-forming solutions;

[0033] (3) The method of the present invention can achieve a very high phosgene utilization rate. Most of the phosgene in the tail gas is condensed in the condenser and then reused. A small amount of phosgene is absorbed in the absorption tower and then returned to the kettle to continue to participate in the reaction. As long as the theoretical phosgene consumption is exceeded by 10% to 20%, a large phosgene concentration in the liquid phase of the kettle can be achieved, thereby promoting the photochemical reaction to be complete and improving the raw material conversion rate and selectivity.

[0034] (4) In the method of the present invention, hydrogen chloride in the tail gas is utilized as a resource, which reduces the cost of raw materials and reduces the load of tail gas post-treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solution of the present application, the drawings required for use in the embodiments are briefly introduced below.

[0036] Figure 1 is a system schematic diagram of an embodiment of the present invention;

[0037] in:

[0038] Salt forming kettle a, primary photochemical kettle b, secondary photochemical kettle c, primary tail gas condenser d, secondary tail gas condenser e, absorption tower f, tail gas treatment system g;

[0039] Diamine solution 1, salt-forming solution 2, primary photochemical solution 3, diisocyanate synthesis solution 4, fresh hydrogen chloride 5, fresh phosgene 6, primary condensate 7, secondary condensate 8, primary tail gas 9, secondary tail gas 10, non-condensable tail gas 11, o-dichlorobenzene solvent 12, absorption liquid 13, absorption tower tail gas 14. DETAILED DESCRIPTION

[0040] Unless otherwise defined herein, scientific and technical terms used in conjunction with the present invention shall have the meanings commonly understood by those of ordinary skill in the art. The meaning and scope of the terms should be clear, however, in the case of any potential ambiguity, the definitions provided herein take precedence over any dictionary or external definitions. In this application, unless otherwise stated, the use of "or" means "and / or". In addition, the use of the term "including" and other forms is non-limiting.

[0041] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] Example 1

[0043] like Figure 1As shown, the system for continuously synthesizing aromatic diisocyanates provided in this embodiment includes a salting kettle a, a primary photochemical kettle b, a secondary photochemical kettle c, a primary tail gas condenser d, a secondary tail gas condenser e, an absorption tower f, and a tail gas treatment system g. The salting kettle a is provided with a diamine feed port, a hydrogen chloride feed port, and a salting liquid discharge port, and the discharge port of the salting kettle a is connected to the feed port of the primary photochemical kettle b, and the discharge port of the primary photochemical kettle b is connected to the feed port of the secondary photochemical kettle c. The first-stage photochemical reactor b is also provided with a phosgene inlet, a first-stage tail gas outlet, a condensate feed inlet, and an absorption liquid feed inlet. The first-stage tail gas outlet is connected to the feed inlet of the first-stage tail gas condenser d, and the condensate discharge port of the first-stage tail gas condenser d is connected to the condensate feed inlet of the first-stage photochemical reactor b, so as to return the condensed phosgene to the first-stage photochemical reactor b. The non-condensable tail gas outlet of the first-stage tail gas condenser d is connected to the absorption tower f, so as to transport the non-condensable tail gas to the absorption tower f. The absorption liquid discharge port at the bottom of the absorption tower f is connected to the absorption liquid feed inlet of the first-stage photochemical reactor b, so as to return the phosgene absorbed in the non-condensable tail gas to the first-stage photochemical reactor b. The secondary photochemical reactor c is also provided with a phosgene inlet, a secondary tail gas outlet, a condensate feed port, and a diisocyanate synthesis liquid discharge port. The secondary tail gas outlet is connected to the feed port of the secondary tail gas condenser e, and the condensate discharge port of the secondary tail gas condenser e is connected to the condensate feed port of the secondary photochemical reactor c, which is used to send the condensed phosgene back to the secondary photochemical reactor c. The non-condensable tail gas outlet of the secondary tail gas condenser e is connected to the absorption tower f, which is used to transport the non-condensable tail gas to the absorption tower f. The upper part of the absorption tower f is also provided with a solvent feed port and an absorption tower tail gas outlet. The absorption tower tail gas outlet material is divided into two streams, one of which is combined with fresh hydrogen chloride 5 and enters the salting kettle a through the hydrogen chloride feed port on the salting kettle a, and the other stream enters the tail gas treatment system g.

[0044] The method for continuously synthesizing aromatic diisocyanates provided in this embodiment comprises the following steps:

[0045] (1) Preheat the salting kettle a to 120°C, and continuously and synchronously introduce 9 wt% 1,5-naphthalenediamine o-dichlorobenzene solution and 80 g / h hydrogen chloride gas into the salting kettle a at 1760 g / h, react under normal pressure to form a salting liquid containing diamine hydrochloride, and control the retention time of the salting liquid to be 1 hour. After the reaction, the salting liquid is continuously withdrawn to the primary photochemical kettle b at 1.35 L / h, and the liquid level in the salting kettle a is kept stable. Sampling and analysis show that the concentration of diamine hydrochloride in the withdrawn salting liquid is 12.6 wt%, and the salting rate of the aromatic diamine in the salting kettle a is 99.7%.

[0046] (2) Preheat the primary photochemical reactor b to 130°C, control the pressure in the primary photochemical reactor b to 0.3MPa, introduce phosgene into the primary photochemical reactor b at a rate of 1.05mol / h to cause a photochemical reaction, and inject o-dichlorobenzene solvent into the top of the absorption tower f at a rate of 0.27L / h. The liquid phase material in the primary photochemical reactor b is withdrawn to the secondary photochemical reactor c after a residence time of 3.5h. The tail gas of the primary photochemical reactor b is condensed by the primary tail gas condenser d, and the condensate is refluxed to the primary photochemical reactor b, and the non-condensable tail gas enters the absorption tower f. The absorption liquid of the absorption tower f flows into the primary photochemical reactor b, and the tail gas of the absorption tower is recycled to the salting reactor a at a volume flow rate of 18.3L / h (the molar flow ratio of the 1,5-naphthalenediamine solution entering the salting reactor a is 2.25:1), and the remaining gas is sent to the tail gas treatment system g. The concentration of diamine isocyanate in the primary photochemical liquid sampled and analyzed was 4.65 wt %. The amount of diisocyanate generated in the primary photochemical reactor b was calculated to account for 48.6 % of the theoretical amount.

[0047] (3) Preheat the secondary photochemical reactor c to 130°C, control the pressure in the secondary photochemical reactor c to 0.3 MPa, introduce phosgene into the secondary photochemical reactor c at a flow rate of 1.2 mol / h to cause a photochemical reaction, and condense the tail gas of the secondary photochemical reactor c through the secondary tail gas condenser e to obtain a condensate that flows back to the secondary photochemical reactor c, and the non-condensable tail gas enters the absorption tower f for absorption, and the absorption liquid flows into the primary photochemical reactor b. The liquid phase material of the secondary photochemical reactor c is extracted from the secondary photochemical reactor c after 2.5 hours, i.e., a diisocyanate synthesis liquid is obtained.

[0048] 1h of diisocyanate synthesis liquid was collected from the secondary photochemical reactor c, totaling 2175.8g. After the gas removal process, a liquid material weighing 2162.8g was obtained. The sample was quantitatively analyzed by liquid chromatography, and the content of 1,5-naphthalene diisocyanate (NDI) was 9.56%. The product yield was calculated to be 98.36%.

[0049] Example 2

[0050] This embodiment adopts the same system as that of embodiment 1, except that the diamine is p-phenylenediamine and the feed concentration is 10wt%. The specific method is as follows:

[0051] (1) Preheat the salting kettle a to 120°C, and continuously and synchronously introduce 10 wt% p-phenylenediamine solution in o-dichlorobenzene and 80 g / h of hydrogen chloride gas into the salting kettle a at 1080 g / h, react under normal pressure to form a salting liquid containing diamine hydrochloride, and control the retention time of the salting liquid to be 1 hour. After the reaction, the salting liquid is continuously withdrawn to the primary photochemical kettle b at 0.85 L / h, and the liquid level in the salting kettle a is kept stable. Sampling and analysis show that the concentration of diamine hydrochloride in the withdrawn salting liquid is 15.67%, and the salting rate of the aromatic diamine in the salting kettle a is 99.81%.

[0052] (2) Preheat the primary photochemical reactor b to 130°C, control the pressure in the primary photochemical reactor b to 0.3MPa, introduce phosgene into the primary photochemical reactor b at a rate of 1.05mol / h to cause a photochemical reaction, and inject o-dichlorobenzene solvent into the top of the absorption tower f at a rate of 0.19L / h. The liquid phase material in the primary photochemical reactor b is withdrawn to the secondary photochemical reactor c after a residence time of 3.5h. The tail gas of the primary photochemical reactor b is condensed by the primary tail gas condenser d, and the condensate is refluxed to the primary photochemical reactor b, and the non-condensable tail gas enters the absorption tower f. The absorption liquid of the absorption tower f flows into the primary photochemical reactor b, and the tail gas of the absorption tower f is recycled to the salting reactor a at a volume flow rate of 18.3L / h (the molar flow ratio of the p-phenylenediamine solution entering the salting reactor a is 2.25:1), and the remaining gas is sent to the tail gas treatment system g. The concentration of diamine isocyanate in the primary photochemical liquid sampled and analyzed was 5.4 wt %. The amount of diisocyanate generated in the primary photochemical reactor b was calculated to account for 46.62% of the theoretical amount.

[0053] (3) Preheat the secondary photochemical reactor c to 130°C, control the pressure in the secondary photochemical reactor c to 0.3 MPa, introduce phosgene into the secondary photochemical reactor c at a flow rate of 1.2 mol / h to cause a photochemical reaction, and condense the tail gas of the secondary photochemical reactor c through the secondary tail gas condenser e to obtain a condensate that flows back to the secondary photochemical reactor c, and the non-condensable tail gas enters the absorption tower f for absorption, and the absorption liquid flows into the primary photochemical reactor b. The liquid phase material of the secondary photochemical reactor c is extracted from the secondary photochemical reactor c after 2.5 hours, i.e., a diisocyanate synthesis liquid is obtained.

[0054] 1394.2 g of diisocyanate synthesis liquid was collected from the secondary photochemical reactor c for 1 hour. After the gas removal process, a liquid material weighing 1381.4 g was obtained. The content of p-phenylene diisocyanate (PPDI) was 11.36 wt % by liquid chromatography quantitative analysis. The product yield was calculated to be 98.08%.

[0055] Example 3

[0056] This embodiment adopts the same system as that of embodiment 1, except that the diamine is diaminotoluene, and the specific method is as follows:

[0057] (1) Preheat the salting kettle a to 120°C, and continuously and synchronously introduce 9 wt% diaminotoluene o-dichlorobenzene solution and 80 g / h hydrogen chloride gas into the salting kettle a at 1356 g / h, react under normal pressure to form a salting liquid containing diamine hydrochloride, and control the retention time of the salting liquid to be 1 hour. After the reaction, the salting liquid is continuously withdrawn to the primary photochemical kettle b at 1.05 L / h, and the liquid level in the salting kettle a is kept stable. Sampling and analysis show that the concentration of diamine hydrochloride in the withdrawn salting liquid is 13.63 wt%, and the salting rate of the aromatic diamine in the salting kettle a is 99.85%.

[0058] (2) Preheat the primary photochemical reactor b to 130°C, control the pressure in the primary photochemical reactor b to 0.3MPa, introduce phosgene into the primary photochemical reactor b at a rate of 1.05mol / h to cause a photochemical reaction, and inject o-dichlorobenzene solvent into the top of the absorption tower f at a rate of 0.21L / h. The liquid phase material in the primary photochemical reactor b is extracted into the secondary photochemical reactor c after a residence time of 3.5h. The tail gas of the primary photochemical reactor b is condensed by the primary tail gas condenser d, and the condensate is refluxed to the primary photochemical reactor b, and the non-condensable tail gas enters the absorption tower f. The absorption liquid of the absorption tower f flows into the primary photochemical reactor b, and the tail gas of the absorption tower f is recycled to the salting reactor a at a volume flow rate of 18.3L / h (the molar flow ratio of the diaminotoluene solution entering the salting reactor a is 2.25:1), and the remaining gas is sent to the tail gas treatment system g. The concentration of diamine isocyanate in the primary photochemical liquid sampled and analyzed was 5.33 wt %. The amount of diisocyanate generated in the primary photochemical reactor b was calculated to account for 52.3 % of the theoretical amount.

[0059] (3) Preheat the secondary photochemical reactor c to 130°C, control the pressure in the secondary photochemical reactor c to 0.3 MPa, introduce phosgene into the secondary photochemical reactor c at a flow rate of 1.2 mol / h to cause a photochemical reaction, and condense the tail gas of the secondary photochemical reactor c through the secondary tail gas condenser e to obtain a condensate that flows back to the secondary photochemical reactor c, and the non-condensable tail gas enters the absorption tower f for absorption, and the absorption liquid flows into the primary photochemical reactor b. The liquid phase material of the secondary photochemical reactor c is extracted from the secondary photochemical reactor c after 2.5 hours, i.e., a diisocyanate synthesis liquid is obtained.

[0060] 1696 g of diisocyanate synthesis liquid was collected from the secondary photochemical reactor b for 1 hour. After the gas removal process, a liquid material weighing 1681.1 g was obtained. The sample was quantitatively analyzed by liquid chromatography and the toluene diisocyanate content was 10.16 wt %. The product yield was calculated to be 98.16%.

[0061] Comparative Example 1

[0062] This comparative example provides a method for preparing aromatic diisocyanate. The system of this comparative example refers to the system of Example 1, with the only difference being that no absorption tower f is provided, and the non-condensable tail gas from the primary photochemical reactor b and the secondary photochemical reactor c directly enters the tail gas treatment system g.

[0063] The specific method of this comparative example is as follows:

[0064] (1) Preheat the salt forming kettle a to 120° C., continuously and synchronously introduce 9 wt % 1,5-naphthalenediamine o-dichlorobenzene solution and 80 g / h hydrogen chloride gas into the salt forming kettle a at a rate of 1760 g / h, react under normal pressure to form a salt forming solution containing diamine hydrochloride, and control the residence time of the salt forming solution to be 1 h. After the reaction, the salt forming solution is continuously withdrawn to the primary photochemical kettle b at a rate of 1.35 L / h to keep the liquid level in the salt forming kettle a stable.

[0065] (2) Preheat the primary photochemical reactor b to 130°C, control the pressure in the primary photochemical reactor b to 0.3 MPa, and introduce phosgene into the primary photochemical reactor b at a rate of 1.05 mol / h to cause a photochemical reaction. The liquid phase material in the primary photochemical reactor b is withdrawn to the secondary photochemical reactor c after a residence time of 3.5 hours. The tail gas of the primary photochemical reactor b is condensed by the primary tail gas condenser d, and the condensate is refluxed to the primary photochemical reactor b, and the non-condensable tail gas enters the tail gas treatment system g.

[0066] (3) Preheat the secondary photochemical reactor c to 130°C, control the pressure in the secondary photochemical reactor c to 0.3 MPa, introduce phosgene into the secondary photochemical reactor c at a flow rate of 1.2 mol / h to cause a photochemical reaction, and condense the tail gas of the secondary photochemical reactor c through the secondary tail gas condenser e to obtain a condensate that flows back to the secondary photochemical reactor c, and the non-condensable tail gas enters the tail gas treatment system g. The liquid phase material of the secondary photochemical reactor c is extracted from the secondary photochemical reactor c after 2.5 hours, and the diisocyanate synthesis liquid is obtained.

[0067] From the secondary photochemical reactor c, 1820.8 g of diisocyanate synthesis liquid was extracted for 1 hour. After the gas removal process, the liquid phase material weighed 1812.3 g. The NDI content of the sample was 10.37 wt % by liquid chromatography quantitative analysis. The product yield was calculated to be 89.4%. The main reason why the product yield of Comparative Example 1 was lower than that of Example 1 was that the phosgene in the non-condensable tail gas was not collected, resulting in an improper phosgene ratio and incomplete reaction of some hydrochloride, resulting in a reduced product yield.

[0068] Comparative Example 2

[0069] This comparative example provides a method for preparing aromatic diisocyanate. The system of this comparative example refers to the system of Example 1, with the only difference being that it only includes a primary photochemical reaction and the liquid phase material stays in the primary photochemical reactor for a long time.

[0070] The specific method of this comparative example is as follows:

[0071] (1) Preheat the salt forming kettle a to 120° C., continuously and synchronously introduce 9 wt % 1,5-naphthalenediamine o-dichlorobenzene solution and 80 g / h hydrogen chloride gas into the salt forming kettle a at a rate of 1760 g / h, react under normal pressure to form a salt forming solution containing diamine hydrochloride, and control the residence time of the salt forming solution to be 1 h. After the reaction, the salt forming solution is continuously withdrawn to the primary photochemical kettle b at a rate of 1.35 L / h to keep the liquid level in the salt forming kettle a stable.

[0072] (2) Preheat the primary photochemical reactor b to 130°C, control the pressure in the primary photochemical reactor b to 0.3 MPa, introduce phosgene into the primary photochemical reactor b at a rate of 2.25 mol / h to cause a photochemical reaction, and inject o-dichlorobenzene solvent into the top of the absorption tower f at a rate of 0.27 L / h. The liquid phase material in the primary photochemical reactor b is extracted from the system after a residence time of 6 hours. The tail gas of the primary photochemical reactor b is condensed by the primary tail gas condenser d, and the condensate is refluxed to the primary photochemical reactor b, and the non-condensable tail gas enters the absorption tower f. The absorption liquid of the absorption tower f flows into the primary photochemical reactor b, and the tail gas of the absorption tower f is recycled to the salting reactor a at a volume flow rate of 18.3 L / h (the molar flow ratio of the 1,5-naphthalenediamine solution entering the salting reactor is 2.25:1), and the remaining gas goes to the tail gas treatment system g.

[0073] From the first-stage photochemical reactor b, 2181.8 g of diisocyanate synthesis liquid was extracted for 1 h. After the gas removal process, the liquid phase material weighed 2166.7 g. The sample was quantitatively analyzed by liquid chromatography, and the content of 1,5-naphthalene diisocyanate (NDI) was 8.14 wt %. The product yield was calculated to be 83.19%. The main reason why the product yield of Comparative Example 2 was lower than that of Example 1 was that the viscosity of the material in the first-stage photochemical reactor was relatively large, and the residence time of 6 h was not conducive to the full reaction of the salt-forming liquid and phosgene, resulting in a reduced product yield.

[0074] It can be seen from the above embodiments and comparative examples that the present invention arranges a two-stage photochemical reaction, and the slurry in the first-stage photochemical reaction kettle is promptly moved out to the second-stage photochemical reaction kettle. The liquid phase material in the two-stage photochemical reaction kettle has good fluidity, which improves the utilization rate of phosgene and is conducive to large-scale production. A condenser is further arranged on the top of the two-stage photochemical reaction kettle, and the phosgene in the tail gas is condensed in the condenser and then refluxed, and the phosgene and hydrogen chloride tail gas in the non-condensable tail gas are further separated in the absorption tower and reused in the photochemical kettle and the salt-forming kettle respectively. The above tail gas recycling method significantly improves the raw material conversion rate and selectivity, reduces the consumption of phosgene and hydrogen chloride, and reduces the load of tail gas post-treatment.

Claims

1. A system for continuous synthesis of aromatic diisocyanates, characterized in that: include: Salt forming kettle, primary photochemical kettle, secondary photochemical kettle, tail gas condenser, absorption tower; The salt-forming kettle is provided with a diamine feed port, a hydrogen chloride feed port, and a salt-forming solution discharge port, the salt-forming solution discharge port is connected to the feed port of the primary photochemical kettle, and the discharge port of the primary photochemical kettle is connected to the feed port of the secondary photochemical kettle; The first-stage photochemical reactor is also provided with a phosgene inlet, a first-stage tail gas outlet, a condensate feed inlet, and an absorption liquid feed inlet, and the first-stage tail gas outlet is connected to the feed inlet of the tail gas condenser; The secondary photochemical reactor is also provided with a phosgene inlet, a secondary tail gas outlet, and a condensate feed inlet, and the secondary tail gas outlet is connected to the feed inlet of the tail gas condenser; The tail gas condenser is also provided with a condensate discharge port and a non-condensable tail gas outlet. The number of the tail gas condenser is one, which is used to condense the tail gas of the primary photochemical reactor and the secondary photochemical reactor. The condensate discharge port of the tail gas condenser is connected to the condensate feed port of the primary photochemical reactor and / or the secondary photochemical reactor, and is used to send the condensed phosgene back to the primary photochemical reactor and / or the secondary photochemical reactor. Or the number of the tail gas condensers is two, which are respectively connected to the first-stage photochemical reactor and the second-stage photochemical reactor; The non-condensable tail gas outlet is connected to the non-condensable tail gas feed port of the absorption tower, and is used to transport the non-condensable tail gas to the absorption tower; The absorption tower is also provided with a solvent feed port, an absorption tower tail gas outlet, and an absorption liquid discharge port. The absorption tower tail gas outlet is connected to the hydrogen chloride feed port of the salt forming kettle, and the absorption liquid discharge port is connected to the absorption liquid feed port of the primary photochemical kettle.

2. A method for continuously synthesizing aromatic diisocyanates using the system of claim 1, characterized in that: The following steps are involved: (1) preheating a salt forming kettle, introducing aromatic diamine and hydrogen chloride into the salt forming kettle at a certain flow rate to react and form a salt forming solution containing diamine hydrochloride, and after a certain residence time, continuously extracting the salt forming solution into a primary photochemical kettle; (2) introducing phosgene into the primary photochemical reactor at a certain flow rate to cause a photochemical reaction with the salt-forming solution at a certain reaction temperature and pressure to obtain a primary photochemical liquid, and continuously extracting the primary photochemical liquid into the secondary photochemical reactor; (3) introducing phosgene into the secondary photochemical reactor at a certain flow rate to cause a photochemical reaction with the primary photochemical liquid at a certain reaction temperature and pressure to obtain a diisocyanate synthesis liquid.

3. The method according to claim 2, characterized in that: In the step (1), the preheating temperature of the salt-forming kettle is 110° C. to 130° C.; the aromatic diamine is selected from one of 1,5-naphthalene diamine, p-phenylenediamine, and diaminotoluene; the molar ratio of the aromatic diamine to hydrogen chloride is 1:2 to 2.5; the mass concentration of the aromatic diamine solution is 8% to 10%; and the residence time of the salt-forming solution in the salt-forming kettle is 0.5 h to 1.5 h.

4. The method according to claim 2, characterized in that: In the step (2), the reaction temperature is 120° C. to 140° C., the pressure is 0.1 to 0.6 MPa, the ratio of the molar flow rate of phosgene introduced to the molar flow rate of diamine hydrochloride in the salt-forming solution is 1.0 to 1.2:1; and the residence time of the liquid phase material in the first-stage photochemical reactor is 3 to 4 hours.

5. The method according to claim 2, characterized in that: In the step (3), the reaction temperature is 120°C to 140°C, the pressure is 0.1 to 0.6 MPa, the ratio of the molar flow rate of phosgene introduced to the molar flow rate of diamine hydrochloride in the primary photochemical liquid is 1.0 to 1.2:1; and the residence time of the liquid phase material in the secondary photochemical reactor is 2 to 3 hours.

6. The method according to claim 2, characterized in that: The proportion of the generated amount of diisocyanate in the primary photochemical reactor to the theoretical generated amount is 40% to 60%, and the yield of diisocyanate in the secondary photochemical reactor is 98% to 99%.

7. The method according to any one of claims 2 to 6, characterized in that: In the step (2) and the step (3), the tail gas of the primary photochemical reactor and the secondary photochemical reactor is extracted into a tail gas condenser, the condensate is recycled to the primary photochemical reactor and / or the secondary photochemical reactor, the non-condensable tail gas is transported to an absorption tower, an inert solvent is injected into the absorption tower, the obtained absorption liquid flows into the primary photochemical reactor, and the tail gas of the absorption tower is recycled to the salt-forming reactor; Wherein, the condensation temperature of the tail gas condenser is -25°C to -15°C.

8. The method according to claim 7, characterized in that: The volume flow rate of the inert solvent is 10% to 30% of the volume flow rate of the salt-forming solution entering the primary photochemical reactor, and the inert solvent is o-dichlorobenzene; the molar flow rate of the absorption tower tail gas entering the salt-forming reactor and the molar flow rate of the aromatic diamine solution are in a ratio of 2 to 2.5:

1.

9. The method according to claim 7, characterized in that: In the step (2), the residence time of the liquid phase material in the primary photochemical reactor is adjusted by the liquid volume in the primary photochemical reactor / (the volume flow rate of the salt-forming solution entering the primary photochemical reactor+the volume flow rate of the inert solvent injected into the absorption tower).

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