Device for producing isocyanate by light solvent method and production method thereof

Abstract

The invention relates to a device for producing isocyanate by a light solvent method and a production method thereof, the device comprises a pre-fractionating tower and a main tower, the tower top of the pre-fractionating tower is communicated with the tower top of the main tower, and the tower kettle of the pre-fractionating tower is communicated with the tower kettle of the main tower; the method comprises the following steps: directly conveying an isocyanate photochemical reaction material prepared by a light solvent method into a pre-fractionating tower for primary separation, extracting phosgene and a solvent from the top of the pre-fractionating tower, and directly feeding the phosgene and the solvent into the top of a main tower; a solvent and isocyanate are extracted from a tower kettle of the pre-fractionating tower and then directly enter a tower kettle of the main tower, phosgene is separated from the tower top of the main tower, a liquid-phase solvent is extracted from a side line of the main tower, and an isocyanate crude product separated from the tower kettle of the main tower enters the next process; a phosgene removal tower for removing phosgene and a solvent in a photochemical reaction material and a first desolventizing tower are combined into a complex tower. Therefore, the process flow is optimized, the energy efficiency is improved, and the load and energy consumption for separating and purifying the isocyanate product are reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical recycling, and particularly relates to a device for producing isocyanate by a light solvent method and a production method thereof. Background Art

[0002] Toluene diisocyanate (TDI) has the molecular formula C 9 H 6 N 2 O 2 , which belongs to a kind of isocyanate. It is a transparent to light yellow liquid with high reactivity, especially with polyols to undergo an addition reaction to form polyurethane. It is easily soluble in benzene, toluene, ethyl acetate, acetone, methyl ethyl ketone, carbon tetrachloride, and is hardly soluble in organic solvents such as acetonitrile, polyethylene glycol, n-hexane, and petroleum ether. Its structure contains two isocyanate groups (-NCO) and a benzene ring, with relatively high non-polarity and certain polar characteristics. With its excellent reactivity and wide application fields, it has become a key raw material for producing high-performance materials, adhesives, and fibers. TDI is a fine chemical product recognized internationally as having "two bigs and one high", namely large engineering investment, high production control difficulty, and high technical content.

[0003] The phosgenation method for preparing TDI remains the mainstream process in industrial production. The synthesis reaction of TDI generally consists of five steps: (1) carbon monoxide reacts with hydrogen to form phosgene; (2) toluene reacts with nitric acid to form dinitrotoluene (DNT); (3) DNT reacts with hydrogen to form toluenediamine (TDA); (4) treated and dried TDA reacts with phosgene to form TDI; (5) purification of TDI.

[0004] However, the currently commonly used TDI production devices have high energy consumption, complex structures, and low energy utilization rates. To solve the above problems, the present invention provides a device for producing isocyanate by a light solvent method and a production method thereof. Summary of the Invention

[0005] To solve the above problems, the present invention provides a device for producing isocyanate by a light solvent method and a production method thereof, aiming to optimize the process flow and improve energy efficiency.

[0006] To achieve the above object, the present invention provides the following solution:

[0007] A device for producing isocyanate by a light solvent method includes a pre-fractionating tower for introducing the phosgenation reaction materials of isocyanate and a main tower for receiving phosgene, solvent, and isocyanate produced in the pre-fractionating tower. The top of the pre-fractionating tower is connected to the top of the main tower, and the bottom of the pre-fractionating tower is connected to the bottom of the main tower.

[0008] Preferably, it further includes a condenser disposed near the top of the main tower, and the condenser is in circulating communication with the top of the main tower.

[0009] Preferably, it further includes a reboiler disposed at the bottom of the main tower, and the reboiler is in circulating communication with the main tower.

[0010] Preferably, a side draw is provided on the main tower.

[0011] Preferably, the solvent includes one or more of benzene, toluene, xylene, chlorobenzene, and dichlorobenzene.

[0012] Preferably, the top of the pre-fractionation tower is in communication with the top of the main tower, and the bottom of the pre-fractionation tower is in communication with the bottom of the main tower through pipelines.

[0013] Preferably, there are two pipelines each between the top of the pre-fractionation tower and the top of the main tower, and between the bottom of the pre-fractionation tower and the bottom of the main tower.

[0014] A method for producing isocyanate includes the following steps:

[0015] Continuously introduce the isocyanate photochemical reaction material into the pre-fractionation tower,

[0016] The top of the pre-fractionation tower extracts phosgene and gaseous solvent and directly enters the top of the main tower for condensation and collection; the bottom of the pre-fractionation tower extracts liquid solvent and isocyanate and directly enters the bottom of the main tower for separation;

[0017] Extract a liquid solvent with a purity of not less than 99.5% through the side draw provided on the main tower and an isocyanate solution with a purity of not less than 99.6% from the bottom of the tower;

[0018] The isocyanate solution enters the next stage of the process flow for further purification.

[0019] Preferably, the isocyanate photochemical reaction material includes a reaction liquid containing isocyanate, phosgene, solvent, and reaction by-products, with the isocyanate concentration being 15% to 16%, the phosgene concentration being 41% to 42%, and the solvent concentration being 42% to 45%.

[0020] Preferably, the operating pressures of both the pre-fractionation tower and the main tower are 3 bara.

[0021] The present invention has achieved the following technical effects compared with the prior art:

[0022] Compared with the prior art, the present invention combines the phosgene removal tower and the first stripping tower into one tower to form a coupling system, that is, the overhead of the pre-fractionation tower directly enters the overhead of the main tower after phosgene and solvent are withdrawn; the bottom of the pre-fractionation tower directly enters the bottom of the main tower after solvent and isocyanate are withdrawn. The main tower removes phosgene and solvent in the bottom liquid by adjusting the appropriate bottom temperature, and then adjusts the appropriate top temperature so that the top condensate is used as an absorbent for the phosgene recovery system. The liquid-phase solvent is withdrawn from the side line of the main tower, and the crude isocyanate product separated from the bottom of the main tower enters the next process. Compared with the traditional process, the device combines two towers into one tower, reducing one reboiler and one condenser, and avoiding the backmixing effect of intermediate components, reducing the mixing problem caused by the difference in the composition of the feed and the material flow on the feed plate, saving 20-30% of the energy consumption; the device is novel in design, simple in structure, and scientific in principle. By optimizing the process flow, it not only reduces the production cost, but also significantly improves the energy utilization efficiency, meeting the dual requirements of environmental protection and economy in modern chemical production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0024] Attached Figure 1 is a schematic structural diagram of the present invention;

[0025] Among them, 1. Pre-fractionation tower; 2. Main tower; 3. Condenser; 4. Reboiler; 5. Vapor return pipe; 6. Liquid return pipe. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0027] In order to solve the above problems, the present invention provides a device and a production method for producing isocyanate by a light solvent method, aiming to optimize the process flow and improve energy efficiency.

[0028] In order to make the above objects, features and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0029] Reference Figure 1, A device for producing isocyanate by a light solvent method, comprising a pre-fractionating tower for introducing the reactants of the isocyanate photochemical reaction and a main tower for receiving phosgene, solvent and isocyanate produced in the pre-fractionating tower. The top of the pre-fractionating tower is connected to the top of the main tower, and the bottom of the pre-fractionating tower is connected to the bottom of the main tower. In the present invention, the phosgene removal tower and the first solvent stripping tower are combined into one tower to form a coupling system, that is, the phosgene and solvent are directly taken out from the top of the pre-fractionating tower and then enter the top of the main tower; the solvent and isocyanate are directly taken out from the bottom of the pre-fractionating tower and then enter the bottom of the main tower. The main tower removes phosgene and solvent in the bottom liquid by adjusting the appropriate bottom temperature, and then adjusts the appropriate top temperature so that the top condensate is used as an absorbent for the phosgene recovery system. The liquid phase solvent is taken out from the side line of the main tower, and the crude isocyanate product separated from the bottom of the main tower enters the next process. Compared with the traditional process, the coupling system combines two towers into one tower, reducing one reboiler and one condenser, and avoiding the backmixing effect of intermediate components, reducing the mixing problem caused by the different compositions of the feed and the material flow on the feed plate, saving 20-30% of the energy consumption; the device has a novel design, simple structure and scientific principle. By optimizing the process flow, not only the production cost is reduced, but also the energy utilization efficiency is significantly improved, meeting the dual requirements of environmental protection and economy in modern chemical production.

[0030] Reference Figure 1 , It further includes a condenser arranged near the top of the main tower, and the condenser is in a circulating connection with the top of the main tower.

[0031] Reference Figure 1 , It further includes a reboiler arranged at the bottom of the main tower, and the reboiler is in a circulating connection with the main tower.

[0032] Reference Figure 1 , A side line draw is provided on the main tower.

[0033] Further, the solvent includes one or more of benzene, toluene, xylene, chlorobenzene and dichlorobenzene.

[0034] Reference Figure 1 , The top of the pre-fractionating tower is connected to the top of the main tower, and the bottom of the pre-fractionating tower is connected to the bottom of the main tower through pipelines.

[0035] Reference Figure 1 , There are two pipelines between the top of the pre-fractionating tower and the top of the main tower and between the bottom of the pre-fractionating tower and the bottom of the main tower.

[0036] A production method of isocyanate is illustrated below by two examples regarding toluene diisocyanate

[0037] Example 1:

[0038] The TDI reaction liquid containing toluene diisocyanate (abbreviated as TDI), phosgene, solvent and reaction by-products is continuously fed into the pre-fractionating column. Among them, the TDI concentration is 15.7%, the phosgene concentration is 41.3%, the solvent concentration is 42.96%, and the operating pressure of the column is 3 bara; after the phosgene and solvent are withdrawn from the top of the pre-fractionating column, they directly enter the top of the main column; after the solvent and TDI are withdrawn from the bottom of the pre-fractionating column, they directly enter the bottom of the main column. The operating pressure of the column is also 3 bara; the gas phase at the top of the main column enters the main column condenser, and the condensation temperature is 40 °C. The mixed gas such as the solvent and phosgene at the top of the column is condensed simultaneously to minimize or avoid phosgene entering the vacuum system. The condensate at the top of the column is used as an absorbent for the phosgene recovery system; a liquid-phase solvent with a purity of 99.5% (mass fraction) is withdrawn from the side line of the main column; the temperature at the bottom of the main column is 170 °C. The TDI content in the TDI reaction liquid obtained at the bottom of the column is 96.64%. Then, the TDI product directly enters the next stage of the process flow for further purification. The main column is connected to the rectifying section of the pre-fractionating column through a gas-phase reflux pipeline; and is connected to the stripping section of the pre-fractionating column through a liquid-phase reflux pipeline.

[0039] Example 2

[0040] This example is the same as Example 1 except for the following features:

[0041] The TDI reaction liquid containing toluene diisocyanate (abbreviated as TDI), phosgene, solvent and reaction by-products is continuously fed into the pre-fractionating column. Among them, the TDI concentration is 16%, the phosgene concentration is 42%, the solvent concentration is 44%, and the operating pressure of the column is 3.2 bara; after the phosgene and solvent are withdrawn from the top of the pre-fractionating column, they directly enter the top of the main column; after the solvent and TDI are withdrawn from the bottom of the pre-fractionating column, they directly enter the bottom of the main column. The operating pressure of the column is also 3.2 bara; the gas phase at the top of the column enters the main column condenser, and the condensation temperature is 42 °C. The mixed gas such as the solvent and phosgene at the top of the column is condensed simultaneously to minimize or avoid phosgene entering the vacuum system. The condensate at the top of the column is used as an absorbent for the phosgene recovery system; a liquid-phase solvent with a purity of 99.8% (mass fraction) is withdrawn from the side line of the dividing wall column; the temperature at the bottom of the main column is 175 °C. The TDI content in the TDI reaction liquid obtained at the bottom of the column is 97.74%. Then, the TDI product directly enters the next stage of the process flow for further purification. The main column is connected to the rectifying section of the pre-fractionating column through a gas-phase reflux pipeline; and is connected to the stripping section of the pre-fractionating column through a liquid-phase reflux pipeline.

[0042] Adaptations made according to actual needs are all within the scope of protection of the present invention.

[0043] It should be noted that for those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the invention. Any reference signs in the claims should not be construed as limiting the claims involved.

Claims

1. A device for producing isocyanate by a light solvent process, characterized in that: It comprises a pre-fractionation tower for introducing isocyanate photochemical reaction materials and a main tower for receiving phosgene, solvent and isocyanate produced in the pre-fractionation tower, the top of the pre-fractionation tower is connected with the top of the main tower, and the bottom of the pre-fractionation tower is connected with the bottom of the main tower.

2. The device for producing isocyanate by light solvent method according to claim 1, characterized in that: It also includes a condenser arranged near the top of the main tower, and the condenser is cyclically connected to the top of the main tower.

3. The device for producing isocyanate by light solvent method according to claim 2, characterized in that: It also includes a reboiler arranged at the bottom of the main tower, and the reboiler is cyclically connected to the main tower.

4. The device for producing isocyanate by light solvent method according to claim 1, characterized in that: The main tower is provided with a side line production.

5. The device for producing isocyanate by light solvent method according to claim 1, characterized in that: The solvent includes one or more of benzene, toluene, xylene, chlorobenzene and dichlorobenzene.

6. The device for producing isocyanate by light solvent method according to claim 1, characterized in that: The top of the pre-fractionation tower and the top of the main tower, as well as the bottom of the pre-fractionation tower and the bottom of the main tower are all connected through pipelines.

7. The device for producing isocyanate by light solvent method according to claim 6, characterized in that: There are two pipelines between the top of the pre-fractionation tower and the top of the main tower, and between the bottom of the pre-fractionation tower and the bottom of the main tower.

8. A method for producing isocyanate, characterized in that: The device for producing isocyanate by a light solvent method according to any one of claims 1 to 7 comprises the following steps: The isocyanate photochemical reaction materials are continuously introduced into the pre-fractionation tower. The phosgene and gaseous solvent produced from the top of the pre-fractionation tower directly enter the top of the main tower and are condensed and collected; the liquid solvent and isocyanate produced from the bottom of the pre-fractionation tower directly enter the bottom of the main tower and are separated; A liquid phase solvent with a purity of not less than 99.5% is extracted through a side line arranged on the main tower, and an isocyanate solution with a purity of not less than 99.6% is extracted from the bottom of the tower; The isocyanate solution enters the next stage of the process for further purification.

9. The method for producing isocyanate according to claim 8, characterized in that The isocyanate photochemical reaction material comprises a reaction solution containing isocyanate, phosgene, solvent and reaction by-products. The isocyanate concentration is 15% to 16%, the phosgene concentration is 41% to 42%, and the solvent concentration is 42% to 45%.

10. The method for producing isocyanate according to claim 8, characterized in that: The operating pressure of the pre-fractionation tower and the main tower are both 3 bara.

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