CN116271907A - Green preparation method and system for hexamethylene diisocyanate - Google Patents

Abstract

The invention provides a method and a system for green preparation of hexamethylene diisocyanate, which are characterized in that a first thermal decomposition reaction device and a second thermal decomposition reaction device are connected in series; a bi-component heat carrier consisting of a low boiling point heat carrier and a high boiling point heat carrier is selected; the first and second dephlegmators are provided. The invention has the beneficial effects that: avoiding the product hexamethylene diisocyanate from staying at high temperature for too long, thereby avoiding further polymerization reaction; the byproduct methanol generated by the thermal decomposition reaction is carried out of the reaction system by the low-boiling point carrier, so that the thermal decomposition reaction is promoted to be continuously and positively carried out; avoiding the increase of isocyanate concentration caused by the massive loss of low boiling point heat carrier, which aggravates side reaction; the isocyanate concentration is effectively reduced, and the occurrence of polymerization side reaction is avoided.

Description

Green preparation method and system for hexamethylene diisocyanate

Technical Field

The invention belongs to the field of chemical synthesis, and particularly relates to a method and a system for green preparation of hexamethylene diisocyanate.

Background

Isocyanate is an important organic synthesis intermediate and is widely applied to the fields of medicines, dyes, adhesives, sealants and the like. Isocyanates are also important raw materials for the synthesis of polyurethane, with about 90% of the isocyanates produced annually being used for the synthesis of polyurethane materials. Currently, the global industrialization of isocyanates has reached 50 or more, among which the larger yields include phenylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polyphenylpolymethylene isocyanate (PAPI), hexamethylene diisocyanate, etc. Compared with TDI, MDI, PAPI, HDI belongs to aliphatic isocyanate, and has the advantages of excellent light stability, heat resistance, yellowing resistance, weather resistance and the like due to saturated molecular structure and smaller steric hindrance, so that the product has great market application value.

At present, HDI is mainly produced by a phosgene method in the world, and the method has the following problems although the synthetic process is mature, economical and reasonable: (1) the process flow is complex, and the reaction condition is harsh; (2) A large amount of highly toxic gas phosgene is needed in the production process, so that the raw materials are strictly limited in storage and transportation and use; (3) The byproduct hydrochloric acid with high corrosiveness is generated, so that equipment is easily corroded; (4) Residual chlorine in the product is difficult to remove, and the performance of the product is directly affected. Therefore, with the development of technology and the increasing environmental protection requirements of people, the phosgene method is gradually limited, and the simple, economic and environmental protection non-phosgene synthesis method is favored.

Many methods for synthesizing HDI with green non-phosgene are reported in the patent and literature, such as nitro compound carbonylation, hexamethylenediamine carbonylation, cyanidation, carbamate thermal decomposition, and the like. The carbamate thermal decomposition method has the advantages of clean process and environment-friendly raw materials, and is the process with the most industrialization potential. The process is mainly realized by a two-step method: (1) Preparing an intermediate Hexamethylene Dicarbamate (HDU); (2) The synthesized intermediate HDU is catalyzed and thermally decomposed to prepare HDI and byproduct methanol.

The preparation of HDI by thermal decomposition of HDU is the most important and difficult step in the process of preparing HDI by carbamate thermal decomposition, and the reaction condition not only affects the reaction rate, but also affects the yield and quality of the product HDI. The thermal decomposition process of HDU is mainly divided into two processes, and the energy required for thermal decomposition in the latter process is higher than that in the former process:

(1) HDU first pyrolyses methyl formate groups at one end to give the intermediate hexamethylene 1- (-6-carbamic acid methyl ester) isocyanate (HMI)

(2) Intermediate HMI thermally decomposes under further heat to form HDI

At present, this step mainly has the following problems: (1) The generated isocyanate is easy to react with the generated byproduct methanol again to generate methyl carbamate; (2) reacting the resultant HDI with a raw HDU to form a polymer; (3) HDI self-polymerizes under high temperature conditions to form a trimer.

To overcome the above problems, measures that can be taken are: (1) Discharging the methanol generated by the reaction out of the thermal decomposition system as soon as possible; (2) The high-efficiency catalyst is used for reducing the thermal decomposition temperature and time; (3) And a heat carrier (namely an inert solvent which does not react with raw materials and products) is added into the reaction system, so that the concentration of isocyanate is reduced, and side reactions are avoided.

Patent CN101530785a discloses a process for preparing HDI using a two-component inert solvent (composed of an inert solvent having a higher boiling point and an inert solvent having a lower boiling point), wherein the thermal decomposition reaction is promoted by bringing out alcohols as by-products by evaporation of the low boiling point solvent. However, evaporation of the low boiling point solvent causes an increase in the concentration of the substance, resulting in occurrence of side reactions.

Patent CN102964272a discloses a process for preparing HDI using a composite catalyst to catalyze thermal decomposition of HDU. The process has higher HDI yield which is more than 92%, but the generated alcohols are difficult to separate from the system in time due to the fact that only high-boiling-point heat carriers are used in the reaction, so that the purity of the HDI is lower.

Patent CN114456091a discloses an apparatus for preparing HDI by pyrolyzing HDU in a mixed solvent, and the patent realizes separation and collection of a product, a byproduct and a medium boiling point heat carrier by adding a product separator, but the product, the byproduct and the medium boiling point heat carrier need to enter the product separator in sequence according to a certain sequence, so that the production efficiency is low, and the product purity is low, which is only about 40%.

Disclosure of Invention

In view of the above, the present invention aims to provide a green efficient preparation system for hexamethylene diisocyanate, which solves the problems in the prior art.

In order to achieve the above purpose, the technical scheme of the invention is realized as follows:

the utility model provides a green preparation system of hexamethylene diisocyanate, includes batching jar, first thermal decomposition reaction unit, second thermal decomposition reaction unit, rectifying device, product tank, the batching jar is equipped with hexamethylene dicarbamate feed inlet, heat carrier feed inlet, catalyst feed inlet, batching jar discharge gate and first thermal decomposition reaction unit feed inlet intercommunication, first thermal decomposition reaction unit's liquid phase discharge gate and second thermal decomposition reaction unit's feed inlet intercommunication, second thermal decomposition reaction unit's liquid phase discharge gate and rectifying device's feed inlet intercommunication, rectifying device's discharge gate and product tank's feed inlet intercommunication.

Further, the first thermal decomposition reaction device and the second thermal decomposition reaction device are one or two of a closed reaction kettle, a fluidized bed reactor, a falling film evaporator and a thin film evaporator.

Further, the preparation system further comprises a first dephlegmator, a second dephlegmator and a byproduct tank, wherein the feed inlet of the first dephlegmator is communicated with the mixed steam discharge outlet of the first thermal decomposition reaction device, the feed inlet of the second dephlegmator is communicated with the mixed steam discharge outlet of the second thermal decomposition reaction device, and the feed inlets of the first dephlegmator and the second dephlegmator are communicated with the feed inlet of the byproduct tank.

Further, the preparation system also comprises a byproduct condenser, wherein the byproduct condenser is arranged between the first dephlegmator, the second dephlegmator and the byproduct tank, the discharge holes of the first dephlegmator and the second dephlegmator are communicated with the feed inlet of the byproduct condenser, and the discharge hole of the byproduct condenser is communicated with the feed inlet of the byproduct tank.

Further, the heat carrier discharge port of the rectifying device is communicated with the heat carrier feed port of the batching tank.

Further, the preparation system further comprises a product condenser, the product condenser is arranged between the rectifying device and the product tank, a discharge hole of the rectifying device is communicated with a feed hole of the product condenser, and a discharge hole of the product condenser is communicated with a feed hole of the product tank.

The green preparation method of hexamethylene diisocyanate, which is applied to any one of the green preparation systems of hexamethylene diisocyanate, comprises the following steps:

s1: adding raw materials of hexamethylene dicarbamate, a heat carrier and a catalyst into a batching tank under the protection of nitrogen, uniformly mixing and preheating to obtain a mixed solution;

s2: conveying the mixed solution obtained in the step S1 to a first thermal decomposition reaction device for primary thermal decomposition reaction to obtain mixed solution;

s3: conveying the mixed solution obtained in the step S2 to a second thermal decomposition reaction device, and heating to perform a secondary thermal decomposition reaction to obtain a mixed solution containing a target product and a heat carrier;

s4: and (3) conveying the mixed liquid obtained in the step (S3) to a rectifying device for distillation, conveying the distilled product to a product tank, and conveying the distilled heat carrier back to the material mixing tank for recycling through a pipeline.

Further, the mass ratio of the hexamethylene dicarbamate to the heat carrier to the catalyst in the S1 is 1:1-20:0.01-0.5, and the preheating temperature is 70-120 ℃.

Further, the heat carrier in the S1 consists of a low-boiling-point heat carrier and a high-boiling-point heat carrier, and the mass ratio of the low-boiling-point heat carrier to the high-boiling-point heat carrier is 1:1-20;

preferably, the low-boiling-point heat carrier is a solvent which has an atmospheric boiling point of 100-200 ℃ and does not react with isocyanate and alcohol, and comprises toluene, xylene, o-chlorotoluene, p-chlorotoluene and p-dichlorobenzene;

preferably, the high boiling point heat carrier is a solvent having an atmospheric boiling point of more than 290 ℃ and not reacting with isocyanate and alcohol, including diethyl phthalate, diethyl terephthalate, dioctyl terephthalate, and dioctyl phthalate.

Further, the reaction temperature of the first thermal decomposition reaction in the step S2 is 150-200 ℃, the reaction pressure is-0.05-1.0 MPa, and the reaction time is 2-6h;

preferably, the reaction temperature of the second thermal decomposition reaction in S3 is 200-250 ℃, the reaction pressure is-0.05-1.0 MPa, and the reaction time is 0.5-2.5h.

Compared with the prior art, the method and the system for green preparation of hexamethylene diisocyanate have the following advantages:

(1) According to the invention, through the first thermal decomposition reaction device and the second thermal decomposition reaction device which are connected in series, raw material hexamethylene dicarbamate is subjected to preliminary decomposition at a lower temperature, and then is further decomposed at a higher temperature to completely prepare target product hexamethylene diisocyanate, so that the product hexamethylene diisocyanate can be prevented from staying for too long at a high temperature, and further polymerization reaction is prevented;

(2) The heat carrier consists of a double-component heat carrier consisting of a low-boiling-point heat carrier and a high-boiling-point heat carrier, so that byproduct methanol generated by the thermal decomposition reaction is carried out of a reaction system by the low-boiling-point heat carrier continuously, and the thermal decomposition reaction is promoted to be continuously and positively carried out;

(3) According to the invention, the first dephlegmator and the second dephlegmator are arranged, so that the low-boiling-point heat carrier with higher boiling point in the mixed steam in the thermal decomposition reaction device flows back to the thermal decomposition reaction device, and the byproduct methanol with lower boiling point is collected by the byproduct tank through the dephlegmator, thus the increase of isocyanate concentration caused by the massive loss of the low-boiling-point heat carrier can be avoided, and the side reaction is aggravated. Meanwhile, the high-boiling point heat carrier group always existing in the reaction system can effectively reduce the concentration of isocyanate and avoid polymerization side reaction.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention. In the drawings:

FIG. 1 is a schematic diagram of a connection structure of a green preparation system for hexamethylene diisocyanate according to an embodiment of the present invention;

FIG. 2 is a gas chromatogram of a hexamethylene diisocyanate product prepared by a green preparation method of hexamethylene diisocyanate according to the embodiment of the invention.

Reference numerals illustrate:

1. a batching tank; 2. a first thermal decomposition reaction device; 3. a second thermal decomposition reaction device; 4. a rectifying device; 5. a product tank; 6. a first dephlegmator; 7. a second dephlegmator; 8. and a byproduct tank.

Detailed Description

It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other.

The invention will be described in detail below with reference to the drawings in connection with embodiments.

The utility model provides a green preparation system of hexamethylene diisocyanate, including batching jar 1, first thermal decomposition reaction unit 2, second thermal decomposition reaction unit 3, rectifying device 4, product jar 5, batching jar 1 is equipped with hexamethylene dicarbamate feed inlet, the heat carrier feed inlet, the catalyst feed inlet, batching jar 1 discharge gate and first thermal decomposition reaction unit 2 feed inlet intercommunication, the liquid phase discharge gate of first thermal decomposition reaction unit 2 and the feed inlet intercommunication of second thermal decomposition reaction unit 3, the liquid phase discharge gate of second thermal decomposition reaction unit 3 and the feed inlet intercommunication of rectifying device 4, the discharge gate of rectifying device 4 and the feed inlet intercommunication of product jar 5.

The first thermal decomposition reaction device 2 and the second thermal decomposition reaction device 3 are one or two of a closed reaction kettle, a fluidized bed reactor, a falling film evaporator and a thin film evaporator.

The green preparation system of hexamethylene diisocyanate still includes first dephlegmator 6, second dephlegmator 7, accessory product jar 8, and first dephlegmator 6 feed inlet communicates with the mixed steam discharge gate of first thermal decomposition reaction unit 2, and second dephlegmator 7 feed inlet communicates with the mixed steam discharge gate of second thermal decomposition reaction unit 3, and first dephlegmator 6, second dephlegmator 7 discharge gate all communicates with accessory product jar 8 feed inlet.

The green preparation system of hexamethylene diisocyanate still includes the accessory product condenser, and the accessory product condenser is located between first dephlegmator 6 and second dephlegmator 7 and accessory product jar 8, and first dephlegmator 6, second dephlegmator 7 discharge gate all communicate with accessory product condenser feed inlet, accessory product condenser discharge gate and accessory product jar 8 feed inlet intercommunication.

The heat carrier discharge port of the rectifying device 4 is communicated with the heat carrier feed port of the batching tank 1.

The green hexamethylene diisocyanate preparation system further comprises a product condenser, wherein the product condenser is arranged between the rectifying device 4 and the product tank 5, a discharge port of the rectifying device 4 is communicated with a feed port of the product condenser, and a discharge port of the product condenser is communicated with a feed port of the product tank 5.

The green preparation method of hexamethylene diisocyanate, which is applied to the green preparation system of hexamethylene diisocyanate, comprises the following steps:

s1: under the protection of nitrogen, adding raw materials of hexamethylene dicarbamate, a heat carrier and a catalyst into a batching tank 1, uniformly mixing and preheating to a certain temperature to obtain a mixed solution;

s2: conveying the mixed solution obtained in the step S1 to a first thermal decomposition reaction device 2, and heating to perform primary thermal decomposition reaction to obtain mixed solution;

s3: conveying the mixed solution obtained in the step S2 to a second thermal decomposition reaction device 3, and heating to perform a secondary thermal decomposition reaction to obtain a mixed solution containing a target product and a heat carrier;

s4: and (3) conveying the mixed liquor obtained in the step (S3) to a rectifying device (4) for distillation, conveying the distilled product to a product tank (5), and conveying the distilled heat carrier back to the batching tank (1) for recycling through a pipeline.

In S1, the mass ratio of the hexamethylene dicarbamate to the heat carrier to the catalyst is 1:1-20:0.01-0.5, and the preheating temperature is 70-120 ℃.

The heat carrier in S1 consists of a low-boiling point heat carrier and a high-boiling point heat carrier, and the mass ratio of the low-boiling point heat carrier to the high-boiling point heat carrier is 1:1-20;

the low-boiling-point heat carrier is a solvent which has an atmospheric boiling point of 100-200 ℃ and does not react with isocyanate and alcohol, and comprises toluene, dimethylbenzene, o-chlorotoluene, p-chlorotoluene and p-dichlorobenzene;

the high boiling point heat carrier is a solvent which has an atmospheric boiling point of more than 290 ℃ and does not react with isocyanate and alcohol, and comprises diethyl phthalate, diethyl terephthalate, dioctyl terephthalate and dioctyl phthalate.

The reaction temperature of the first thermal decomposition reaction in S2 is 150-200 ℃, the reaction pressure is-0.05-1.0 MPa, and the reaction time is 2-6h.

The reaction temperature of the second thermal decomposition reaction in the S3 is 200-250 ℃, the reaction pressure is-0.05-1.0 MPa, and the reaction time is 0.5-2.5h.

Example 1

Experimental procedure as described above, wherein:

s1: the mass ratio of the raw materials of the hexamethylene dicarbamate to the heat carrier to the catalyst is 1:10:0.1, the preheating temperature is 100 ℃, and the mass ratio of the low-boiling-point heat carrier to the high-boiling-point heat carrier in the heat carrier is 1:4;

s2: the first thermal decomposition reaction temperature is 170 ℃, the reaction time is 2.5h, and the pressure is 0.2MPa;

s3: the second thermal decomposition reaction temperature is 230 ℃, the reaction time is 1h, and the pressure is 0.6MPa.

The reaction substrate and the product are qualitatively and quantitatively detected by gas chromatography, and the conversion rate of the raw material hexamethylene diisocyanate is calculated to be 100%, the selectivity of the product hexamethylene diisocyanate is 97.3%, and the purity of the product is 98.5%.

Example two

Experimental procedure as described above, wherein:

s1: the mass ratio of the raw materials of the hexamethylene dicarbamate to the heat carrier to the catalyst is 1:5:0.05, the preheating temperature is 120 ℃, and the mass ratio of the low-boiling-point heat carrier to the high-boiling-point heat carrier in the heat carrier is 1:20;

s2: the first thermal decomposition reaction temperature is 180 ℃, the reaction time is 2 hours, and the pressure is 0.2MPa;

s3: the second thermal decomposition reaction temperature is 240 ℃, the reaction time is 0.5h, and the pressure is 0.8MPa.

The reaction substrate and the product are qualitatively and quantitatively detected by gas chromatography, and the conversion rate of the raw material hexamethylene diisocyanate is calculated to be 100%, the selectivity of the product hexamethylene diisocyanate is 96.8%, and the purity of the product is 99.1%.

Example III

Experimental procedure as described above, wherein:

s1: the mass ratio of the raw materials of the hexamethylene dicarbamate to the heat carrier to the catalyst is 1:20:0.25, the preheating temperature is 100 ℃, and the mass ratio of the low-boiling-point heat carrier to the high-boiling-point heat carrier in the heat carrier is 1:9;

s2: the first thermal decomposition reaction temperature is 150 ℃, the reaction time is 5 hours, and the pressure is normal pressure;

s3: the second thermal decomposition reaction temperature is 220 ℃, the reaction time is 1.5h, and the pressure is 0.4MPa.

The reaction substrate and the product are qualitatively and quantitatively detected by gas chromatography, and the conversion rate of the raw material hexamethylene diisocyanate is calculated to be 100%, the selectivity of the product hexamethylene diisocyanate is 98.1%, and the purity of the product is 98.9%.

Comparative example one

Experimental procedure as described above, wherein:

s1: the mass ratio of the raw materials of the hexamethylene dicarbamate to the heat carrier to the catalyst is 1:10:0.1, the preheating temperature is 100 ℃, and the heat carrier is a single-component high-boiling-point heat carrier;

s2: the first thermal decomposition reaction temperature is 170 ℃, the reaction time is 2.5h, and the pressure is 0.2MPa;

s3: the second thermal decomposition reaction temperature is 230 ℃, the reaction time is 1h, and the pressure is 0.6MPa.

The reaction substrate and the product are qualitatively and quantitatively detected by gas chromatography, and the conversion rate of the raw material hexamethylene diisocyanate is calculated to be 100%, the selectivity of the product hexamethylene diisocyanate is 86.5%, and the purity of the product is 93.3%.

Comparative example two

Experimental procedure as described above, wherein:

s1: the mass ratio of the raw materials of the hexamethylene dicarbamate to the heat carrier to the catalyst is 1:10:0.1, the preheating temperature is 100 ℃, and the mass ratio of the low-boiling-point heat carrier to the high-boiling-point heat carrier in the heat carrier is 1:4;

s3: the mixed solution in S1 is directly input into a second thermal decomposition reaction device without passing through the first thermal decomposition reaction device, the second thermal decomposition reaction temperature is 220 ℃, the reaction time is 3.5h, and the pressure is 0.6MPa.

The reaction substrate and the product are qualitatively and quantitatively detected by gas chromatography, and the conversion rate of the raw material hexamethylene diisocyanate is 98.4 percent, the selectivity of the product hexamethylene diisocyanate is 82.6 percent and the purity of the product is 92.8 percent.

Comparative example three

Experimental procedure as described above, wherein:

s1: the mass ratio of the raw materials of the hexamethylene dicarbamate to the heat carrier to the catalyst is 1:10:0.1, the preheating temperature is 100 ℃, and the mass ratio of the low-boiling-point heat carrier to the high-boiling-point heat carrier in the heat carrier is 1:4;

s2: the first thermal decomposition reaction temperature is 170 ℃, the reaction time is 2.5h, the pressure is 0.2MPa, and the connection between the first thermal decomposition reaction device and the first dephlegmator is closed;

s3: the second thermal decomposition reaction temperature is 230 ℃, the reaction time is 1h, the pressure is 0.6MPa, and the connection between the second thermal decomposition reaction device and the second condenser is closed.

The reaction substrate and the product are qualitatively and quantitatively detected by gas chromatography, and the conversion rate of the raw material hexamethylene diisocyanate is calculated to be 96.5%, the selectivity of the product hexamethylene diisocyanate is 84.5%, and the purity of the product is 89.7%.

In the above examples and comparative examples, the conversion of hexamethylene diisocyanate, the selectivity for hexamethylene diisocyanate and the purity of the product were all calculated by an area normalization method by referring to the requirements of annex A of national standard GB/T37042-2018, and by measuring them by a gas chromatograph.

TABLE 1

	Conversion%	Selectivity%	Purity%
				Example 1	100	97.3	98.5
Example two	100	96.8	99.1
				Example III	100	98.1	98.9
Comparative example one	100	86.5	93.3
				Comparative example two	98.4	82.6	92.8
Comparative example three	96.5	84.5	89.7

Comparative example one and comparative example one can be seen: the use of the bi-component heat carrier can obviously improve the selectivity and the quality of the product;

as can be seen from comparative example one and comparative example two: the two-step thermal decomposition process has better effect than the one-step thermal decomposition process;

comparative example one and comparative example three can be seen: the byproduct methanol is timely removed by means of a dephlegmator, so that higher raw material conversion rate, product selectivity and product purity can be obtained.

The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the invention.

Claims (10)

1. A green preparation system of hexamethylene diisocyanate is characterized in that: including batching jar, first thermal decomposition reaction unit, second thermal decomposition reaction unit, rectifying device, product jar, the batching jar is equipped with hexamethylene dicarbamate feed inlet, heat carrier feed inlet, catalyst feed inlet, batching jar discharge gate and first thermal decomposition reaction unit feed inlet intercommunication, first thermal decomposition reaction unit's liquid phase discharge gate and second thermal decomposition reaction unit's feed inlet intercommunication, second thermal decomposition reaction unit's liquid phase discharge gate and rectifying device's feed inlet intercommunication, rectifying device's discharge gate and product jar's feed inlet intercommunication.

2. The green preparation system of hexamethylene diisocyanate according to claim 1, wherein: the first thermal decomposition reaction device and the second thermal decomposition reaction device are one or two of a closed reaction kettle, a fluidized bed reactor, a falling film evaporator and a thin film evaporator.

3. The green preparation system of hexamethylene diisocyanate according to claim 1, wherein: the device comprises a first thermal decomposition reaction device, a second thermal decomposition reaction device, a first dephlegmator, a second dephlegmator, a byproduct tank, a first dephlegmator feed port, a second dephlegmator feed port, a byproduct tank and a byproduct tank, wherein the first dephlegmator feed port is communicated with the mixed steam discharge port of the first thermal decomposition reaction device, the second dephlegmator feed port is communicated with the mixed steam discharge port of the second thermal decomposition reaction device, and the first dephlegmator feed port and the second dephlegmator feed port are both communicated with the byproduct tank feed port.

4. The green preparation system of hexamethylene diisocyanate according to claim 1, wherein: the device comprises a byproduct tank, a first dephlegmator, a second dephlegmator, a byproduct condenser, a byproduct tank, a byproduct condenser feeding port, a byproduct condenser discharging port and a byproduct tank feeding port, wherein the byproduct condenser is arranged between the first dephlegmator, the second dephlegmator and the byproduct tank, and the first dephlegmator and the second dephlegmator discharging port are both communicated with the byproduct condenser feeding port.

5. The green preparation system of hexamethylene diisocyanate according to claim 1, wherein: and the heat carrier discharge port of the rectifying device is communicated with the heat carrier feed port of the batching tank.

6. The green preparation system of hexamethylene diisocyanate according to claim 1, wherein: still include the product condenser, the product condenser is located between rectifying device and the product jar, rectifying device discharge gate and product condenser feed inlet intercommunication, product condenser discharge gate and product jar feed inlet intercommunication.

7. A green preparation method of hexamethylene diisocyanate is characterized in that: use of a green preparation system of hexamethylene diisocyanate according to any of the claims 1-6, comprising the steps of:

s1: adding raw materials of hexamethylene dicarbamate, a heat carrier and a catalyst into a batching tank under the protection of nitrogen, uniformly mixing and preheating to obtain a mixed solution;

s2: conveying the mixed solution obtained in the step S1 to a first thermal decomposition reaction device for primary thermal decomposition reaction to obtain mixed solution;

s3: conveying the mixed solution obtained in the step S2 to a second thermal decomposition reaction device, and heating to perform a secondary thermal decomposition reaction to obtain a mixed solution containing a target product and a heat carrier;

s4: and (3) conveying the mixed liquid obtained in the step (S3) to a rectifying device for distillation, conveying the distilled product to a product tank, and conveying the distilled heat carrier back to the material mixing tank for recycling through a pipeline.

8. The green preparation method of hexamethylene diisocyanate according to claim 7, wherein: in S1, the mass ratio of the hexamethylene dicarbamate to the heat carrier to the catalyst is 1:1-20:0.01-0.5, and the preheating temperature is 70-120 ℃.

9. The green preparation method of hexamethylene diisocyanate according to claim 7, wherein: the heat carrier in S1 consists of a low-boiling point heat carrier and a high-boiling point heat carrier, and the mass ratio of the low-boiling point heat carrier to the high-boiling point heat carrier is 1:1-20.

10. The green preparation method of hexamethylene diisocyanate according to claim 7, wherein: the reaction temperature of the first thermal decomposition reaction in S2 is 150-200 ℃, the reaction pressure is-0.05-1.0 MPa, and the reaction time is 2-6h;

preferably, the reaction temperature of the second thermal decomposition reaction in S3 is 200-250 ℃, the reaction pressure is-0.05-1.0 MPa, and the reaction time is 0.5-2.5h.

Images