Preparation method and application of isocyanate

Abstract

The invention relates to a preparation method and application of isocyanate, and belongs to the technical field of fine chemical engineering, the preparation method comprises the following steps: (1) carrying out salt forming reaction on an amine solution, fresh hydrogen chloride and hydrogen chloride recycle gas to obtain amine hydrochloride slurry and unreacted hydrogen chloride; (2) carrying out phosgenation reaction on the amine hydrochloride slurry obtained in the step (1) and phosgene to obtain isocyanate and photochemical gas phase exhaust gas; the unreacted hydrogen chloride in the step (1) and a part of the photochemical gas phase exhaust gas in the step (2) are used as hydrogen chloride recycle gas for the salt forming reaction; the content of isocyanate groups in the hydrogen chloride recycle gas is 100 to 10000 mg / L. According to the preparation method provided by the invention, less fresh hydrogen chloride is introduced, the salt forming time is greatly shortened, the salt forming rate is high, the purification difficulty of hydrogen chloride is reduced, the recycling of hydrogen chloride is realized, and the process economy is improved.

Description

Technical Field

[0001] The invention relates to the technical field of fine chemicals, and in particular to a preparation method of isocyanate and application thereof. Background Art

[0002] In the prior art, the phosgene method for preparing isocyanates by reacting organic primary amines with phosgene in an inert solvent is well known. The phosgene method can be divided into a direct method and a salt-forming method. When preparing isocyanates by using a salt-forming phosgenation reaction, the reaction is usually carried out in two steps. In the first step of the salt-forming reaction, the amine reacts with excess hydrogen chloride (or carbon dioxide) under solvent conditions to form a salt. If hydrogen chloride is insufficient, it is easy to cause problems such as a long salt-forming time and a low salt-forming rate. The second step of the hydrochloride (or carbonate) phosgenation reaction is to pass excess phosgene into the above hydrochloride solution to obtain a product containing the target isocyanate, and at the same time, a large amount of hydrogen chloride formed according to the stoichiometry of the chemical reaction on which it is based will be released.

[0003] The hydrogen chloride produced in the above reaction process is generally obtained directly from the crude reaction product in the form of gas after decompression, and then purified by low-temperature treatment. Various impurities such as trace amounts of phosgene, solvents, organic by-products and inert gases inevitably remain in the obtained hydrogen chloride, which seriously restricts the downstream application of hydrogen chloride.

[0004] At present, hydrogen chloride produced as a byproduct in the preparation of isocyanates generally has two important uses: one is to prepare hydrochloric acid through water absorption, and the other is to prepare chlorine through catalytic oxidation with oxygen. The purity requirement of hydrogen chloride used to prepare hydrochloric acid is relatively low, but the economic value of hydrochloric acid is not high, while hydrogen chloride used to prepare chlorine requires high purity and extremely low organic impurity content, and needs to undergo a complex and harsh pretreatment process.

[0005] For example, CN111548249A discloses a method for recovering chloroform and hydrogen chloride in the production process of methyl isocyanate. The production of methyl isocyanate includes synthesizing methylcarbamoyl chloride using phosgene and monomethylamine, and decomposing the methylcarbamoyl chloride into methyl isocyanate and tail gas containing chloroform and hydrogen chloride. The method comprises the following steps: 1) the tail gas containing chloroform and hydrogen chloride passes through a condenser, most of the chloroform gas is condensed into liquid and captured, and the remaining chloroform and hydrogen chloride gas are absorbed by a falling film absorber. Spraying is a hydrochloric acid mixture; 2) The hydrochloric acid mixture in step 1) is cooled to 20-60°C, and then fed into the stratifier along the tangential liquid inlet set on the side of the stratifier, and the baffles set inside the stratifier are deflected and rotated to make chloroform and hydrochloric acid settle and stratify, wherein the hydrochloric acid flows into the hydrochloric acid circulation tank along the overflow port set at the top of the stratifier, and the chloroform flows into the chloroform receiving kettle from the discharge port set at the bottom of the stratifier, and the remaining mixed liquid in the stratifier is re-sent into the stratifier along the discharge port and the tangential liquid inlet. Although it realizes the recovery of hydrochloric acid, it needs to adopt a specific stratifier device, which increases the production cost and reduces the economic value of hydrochloric acid.

[0006] Therefore, how to develop a method for preparing isocyanate with low hydrogen chloride dosage, short salt formation time, high salt formation efficiency, and easy reuse of hydrogen chloride has become a problem to be solved urgently. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a method for preparing isocyanate and its application. By forming a hydrogen chloride cycle and controlling the isocyanate content in the circulating gas, the salt formation time is greatly shortened, the salt formation reaction effect is improved, and the difficulty of hydrogen chloride reuse is significantly reduced, thereby improving the process economy.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing isocyanate, the preparation method comprising the following steps:

[0010] (1) an amine solution reacts with fresh hydrogen chloride and hydrogen chloride circulating gas to form a salt to obtain an amine hydrochloride slurry and unreacted hydrogen chloride;

[0011] (2) subjecting the amine hydrochloride slurry obtained in step (1) to a phosgenation reaction with phosgene to obtain the isocyanate and phosgene phase exhaust;

[0012] The unreacted hydrogen chloride in step (1) and part of the photochemical gas phase exhaust in step (2) are used as hydrogen chloride circulating gas for the salt-forming reaction;

[0013] The isocyanate content in the hydrogen chloride circulating gas is 100-10000 mg / L, for example, 200 mg / L, 500 mg / L, 1000 mg / L, 1500 mg / L, 2000 mg / L, 3000 mg / L, 5000 mg / L or 8000 mg / L, as well as specific values ​​between the above points. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific points included in the range.

[0014] The method for preparing isocyanate provided by the present invention comprises a salt-forming reaction in step (1) and a phosgenation reaction in step (2). In step (2), the phosgenation reaction of amine hydrochloride with introduced phosgene generates the target isocyanate and releases a large amount of hydrogen chloride gas formed by the stoichiometry of the chemical reaction. The present invention recycles the hydrogen chloride remaining from the salt-forming reaction and the hydrogen chloride tail gas produced as a byproduct in the phosgenation reaction process, and controls the content of isocyanate in the hydrogen chloride circulated to the salt-forming reaction by recycling the hydrogen chloride tail gas to the salt-forming process. Isocyanate reacts with amine to form macromolecular byproducts such as ureas in the salt-forming reaction, resulting in a rapid increase in the viscosity of the salt-forming reaction system, poor dispersibility of the hydrochloride, and easy agglomeration and wrapping, which affects the salt-forming of the amine and the hydrogen chloride. Therefore, it is advantageous that the isocyanate content in the circulating tail gas is extremely low, but a great additional processing cost is required. Therefore, it is necessary to control the content of isocyanate in the hydrogen chloride involved in the salt-forming reaction to a suitable value, which can not only greatly improve the chemical ratio of hydrogen chloride and amine under the condition of less fresh hydrogen chloride, but also greatly shorten the salt-forming time and improve the salt-forming rate. In addition, the difficulty of hydrogen chloride purification is reduced, the recycling of hydrogen chloride is achieved, and the process economy is improved.

[0015] The preparation method provided by the present invention, on the one hand, reduces the amount of fresh hydrogen chloride used, and at the same time achieves an excellent salt-forming reaction effect, thereby solving the problem in the prior art that a large amount of fresh hydrogen chloride needs to be introduced to achieve a good salt-forming reaction effect; on the other hand, it avoids the problem in the prior art that the hydrogen chloride gas obtained by the phosgenation reaction usually contains impurities such as phosgene, solvent, isocyanate, inert gas, etc., resulting in low purity and cannot be used directly, and usually needs to be purified before use, and the commonly used purification measures such as low-temperature condensation separation and low-temperature solvent absorption have higher economic costs for higher purity requirements of hydrogen chloride.

[0016] The isocyanate group (NCO) content in the hydrogen chloride circulating gas is tested by the following test method:

[0017] 1) Pass the hydrogen chloride circulating gas into 100 g of n-hexane absorption liquid at a rate of 6 L / h and absorb for 20 minutes;

[0018] 2) The NCO mass content in the n-hexane absorption liquid was obtained by gas chromatography and recorded as w%. The test method was as follows: The different retention times of the substances containing NCO structure in the gas chromatography were determined by gas chromatography-mass spectrometry, and the percentages were obtained by area normalization method. The analysis instrument was Agilent 7890B; the chromatographic column model was DB-5 (30m×0.25mm×0.25μm); the detector was FID detector; the injection port temperature was 260°C; the detector temperature was 300°C; the temperature program was from 50°C to 90°C at 10°C / min, maintained for 2min, increased to 180°C at 15°C / min, maintained for 2min, increased to 280°C at 20°C / min, maintained for 15min; the injection volume was 0.2μL;

[0019] 3) The NCO content in the hydrogen chloride circulating gas is calculated to be 100 g×w% / (6 / 3)=500 w mg / L.

[0020] Preferably, the amine in the amine solution is any one or a combination of at least two of aliphatic amines or alicyclic amines of C4-C15 (for example, C5, C6, C7, C8, C10, C12 or C14, etc.).

[0021] Preferably, the functionality of the amine in the amine solution is 1-3, for example, 1, 2 or 3.

[0022] The functionality described in the present invention refers to the number of amino groups in an amine. For example, an amine with a functionality of 1 means that one amine molecule contains one amino group.

[0023] Preferably, the solvent in the amine solution includes an aromatic hydrocarbon solvent.

[0024] Preferably, the solvent in the amine solution includes any one of toluene, xylene, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, methyl benzoate, ethyl benzoate, butyl benzoate, propyl benzoate, chlorobenzene, o-dichlorobenzene, p-chlorotoluene or bromobenzene, or a combination of at least two thereof.

[0025] Preferably, the mass concentration of amine in the amine solution is 5-30%, for example, it can be 8%, 10%, 15%, 20%, 25% or 28%, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0026] Preferably, the photochemical gas phase exhaust in the hydrogen chloride circulating gas is 5-100% of the total volume of the photochemical gas phase exhaust in step (2), for example, it can be 8%, 10%, 20%, 30%, 50%, 60% or 90%, and specific values ​​between the above points. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific points included in the range, and it is further preferably 20-100%.

[0027] Preferably, in the step (1), the molar ratio of the total amount of hydrogen chloride in the fresh hydrogen chloride and hydrogen chloride circulating gas to the amino group in the amine solution is (5-20):1, wherein the specific value of (5-20) can be, for example, 6, 7, 8, 10, 12, 15 or 18, as well as specific values ​​between the above values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively enumerates the specific values ​​included in the range, and is further preferably (8-12):1.

[0028] Preferably, the molar ratio of hydrogen chloride in the fresh hydrogen chloride to amino groups in the amine solution is (0.5-3):1, wherein the specific value of (0.5-3) can be, for example, 0.8, 1, 1.5, 2 or 2.5, as well as specific values ​​between the above values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific values ​​included in the range, and is further preferably (0.5-2):1.

[0029] Preferably, the isocyanate content in the hydrogen chloride circulating gas is 200-5000 mg / L, for example, 300 mg / L, 400 mg / L, 500 mg / L, 800 mg / L, 1000 mg / L, 1500 mg / L, 2000 mg / L, 3000 mg / L or 4000 mg / L, as well as specific values ​​between the above values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively enumerates the specific values ​​included in the range, and is further preferably 500-1000 mg / L, for example, 550 mg / L, 600 mg / L, 700 mg / L, 800 mg / L, 900 mg / L or 950 mg / L, etc.

[0030] Preferably, the amine in the amine solution includes any one or a combination of at least two of cyclohexylamine, 1,4-butanediamine, 1,3-cyclohexanedimethylamine, 1,6-hexanediamine, 1,5-pentanediamine, 1,4-diaminocyclohexane, 1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane, 4,4'-diaminodicyclohexylmethanediamine, m-xylylenediamine or triaminononane.

[0031] Preferably, in the step (1), the molar ratio of the total amount of hydrogen chloride in the fresh hydrogen chloride and hydrogen chloride circulating gas to the amino group in the amine solution is (6-15):1, wherein the specific value of (6-15) can be, for example, 7, 8, 9, 10, 11, 12, 13 or 14, as well as specific values ​​between the above values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific values ​​included in the range.

[0032] Preferably, the temperature of the salt-forming reaction is 10-120°C, for example, it can be 15°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C or 110°C, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range, and 15-100°C is further preferred.

[0033] Preferably, the salt-forming reaction time is 0.5-2.5 h, for example, it can be 0.5 h, 0.8 h, 1 h, 1.2 h, 1.5 h, 1.8 h, 2 h or 2.2 h, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range, and it is further preferably 0.5-2 h.

[0034] Preferably, the molar ratio of phosgene to amino group in the amine solution is (3-15):1, wherein the specific value of (3-15) can be, for example, 5, 6, 7, 8, 10 or 12, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range, and is further preferably (5-10):1.

[0035] Preferably, the temperature of the phosgenation reaction is 80-170°C, for example, it can be 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C or 160°C, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range, and it is further preferably 100-160°C.

[0036] Preferably, the phosgenation reaction time is 1-5 h, for example, it can be 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h or 4.5 h, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range, and it is further preferably 2-4 h.

[0037] Preferably, the phosgenation reaction further comprises a post-treatment step.

[0038] Preferably, the post-treatment includes dephosgene removal and refined separation.

[0039] Preferably, the preparation method comprises the following steps:

[0040] (1) reacting an amine solution with fresh hydrogen chloride and hydrogen chloride circulating gas at 15-100° C. for 0.5-2.5 h to obtain an amine hydrochloride slurry and unreacted hydrogen chloride;

[0041] (2) reacting the amine hydrochloride slurry obtained in step (1) with phosgene at 100-160° C. for 2-4 hours to obtain a photochemical reaction liquid and exhaust gas from the photochemical reaction liquid, dephosgenating the photochemical reaction liquid, and refining and separating the isocyanate;

[0042] The unreacted hydrogen chloride in step (1) and part of the photochemical gas phase exhaust in step (2) are used as hydrogen chloride circulating gas for the salt-forming reaction;

[0043] Wherein, the isocyanate content in the hydrogen chloride circulating gas is 500-1000 mg / L;

[0044] In the step (1), the molar ratio of the total amount of fresh hydrogen chloride and hydrogen chloride in the hydrogen chloride circulating gas to the amino group in the amine solution is (8-12):1, wherein the specific value of (8-12) can be, for example, 8.5, 9, 9.5, 10, 10.5, 11 or 11.5;

[0045] The molar ratio of the phosgene to the amino group in the amine solution is (5-10):1.

[0046] In a second aspect, the present invention provides an application of the preparation method described in the first aspect in household appliances, automobiles, buildings, furniture or packaging materials.

[0047] Compared with the prior art, the present invention has at least the following beneficial effects:

[0048] The isocyanate preparation method provided by the present invention recycles the hydrogen chloride remaining from the salt-forming reaction and the hydrogen chloride tail gas produced as a by-product in the phosgenation reaction process, and controls the isocyanate group content in the circulating gas, thereby increasing the excess ratio of hydrogen chloride to amine in the salt-forming process, significantly reducing the amount of fresh hydrogen chloride used, greatly shortening the salt-forming time, and increasing the salt-forming efficiency. At the same time, the difficulty of reusing hydrogen chloride is also greatly reduced, thereby increasing the process economy. DETAILED DESCRIPTION

[0049] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0050] In the following specific implementation of the present invention, the materials involved are as follows:

[0051] Hexamethylenediamine, industrial grade product purchased from INVISTA (Shanghai);

[0052] Phosgene was purchased from Wanhua Chemical Group Co., Ltd.;

[0053] Chlorobenzene, purchased from Aladdin, purity 99.5%;

[0054] Hydrogen chloride was purchased from Wanhua Chemical Group Co., Ltd.

[0055] Example 1

[0056] A method for preparing isocyanate, the preparation method comprising the following steps:

[0057] (1) continuously introducing a 20 wt % hexamethylenediamine chlorobenzene solution, fresh hydrogen chloride gas and hydrogen chloride circulating gas into a 10 L salt-forming reactor at 45° C. for a residence time of 0.3 h to perform a salt-forming reaction to obtain an amine hydrochloride slurry and unreacted hydrogen chloride;

[0058] During stable operation, the feed rate of hexamethylenediaminechlorobenzene solution is 33.3L / h, and the feed rate of fresh hydrogen chloride gas is 5.5m 3 / h, the hydrogen chloride circulating gas is the unreacted hydrogen chloride obtained from the salt-forming reaction 44.3m 3 / h and photochemical reaction gas exhaust recycling 5m 3 / h, at this time, the NCO content in the hydrogen chloride circulating gas is 117 mg / L, and the molar ratio of fresh hydrogen chloride and hydrogen chloride in the hydrogen chloride circulating gas to the amino group in hexamethylenediamine is 20:1; after the salt formation is completed, the number average particle size of the hydrochloride particles tested by electron microscopy is 9-16 μm.

[0059] (2) The hydrochloride was transported to the phosgenation reactor, the reaction temperature was 140°C, and the phosgene flow rate was 19.2 m 3 / h, residence time 3h, to obtain a reaction solution containing the isocyanate, the isocyanate reaction yield is 98.6%, and the final isocyanate product is obtained after post-treatment.

[0060] Example 2

[0061] A method for preparing isocyanate, the preparation method comprising the following steps:

[0062] (1) continuously introducing a 15 wt % hexamethylenediamine chlorobenzene solution, fresh hydrogen chloride gas and hydrogen chloride circulating gas into a 10 L salt-forming reactor at 45° C. for a residence time of 0.5 h to perform a salt-forming reaction to obtain an amine hydrochloride slurry and unreacted hydrogen chloride;

[0063] During stable operation, the feed rate of hexamethylenediaminechlorobenzene solution is 20L / h, and the feed rate of fresh hydrogen chloride gas is 1.9m 3 / h, the hydrogen chloride circulating gas is the unreacted hydrogen chloride obtained from the salt formation reaction 13.8m 3 / h and photochemical reaction gas exhaust recycling 3m 3 / h, at this time, the NCO content in the hydrogen chloride circulating gas is 975 mg / L, and the molar ratio of fresh hydrogen chloride and hydrogen chloride in the hydrogen chloride circulating gas to the amino group in hexamethylenediamine is 15:1; after the salt formation is completed, the number average particle size of the hydrochloride particles tested by electron microscopy is 12-18 μm.

[0064] (2) After the salt formation is completed, the hydrochloride is transported to the phosgenation reactor, the reaction temperature is 140°C, and the phosgene flow rate is 8.7m 3 / h, residence time 3h, to obtain the isocyanate reaction solution, the isocyanate reaction yield is 99.4%, and the final isocyanate product is obtained after post-treatment.

[0065] Example 3

[0066] A method for preparing isocyanate, the preparation method comprising the following steps:

[0067] (1) continuously introducing a 12 wt % hexamethylenediamine chlorobenzene solution, fresh hydrogen chloride gas and hydrogen chloride circulating gas into a 10 L salt-forming reactor at 45° C. for a residence time of 0.8 h to perform a salt-forming reaction to obtain an amine hydrochloride slurry and unreacted hydrogen chloride;

[0068] During stable operation, the feed rate of hexamethylenediaminechlorobenzene solution is 12.5L / h, and the feed rate of fresh hydrogen chloride gas is 0.8m 3 / h, the hydrogen chloride circulating gas is the unreacted hydrogen chloride obtained from the salt-forming reaction 5.4m 3 / h and photochemical reaction gas exhaust recovery 1.4m 3 / h, at this time, the NCO content in the hydrogen chloride circulating gas is 2421 mg / L, and the molar ratio of fresh hydrogen chloride and hydrogen chloride in the hydrogen chloride circulating gas to the amino group in hexamethylenediamine is 12:1; after the salt formation is completed, the number average particle size of the hydrochloride particles tested by electron microscopy is 17-26μm.

[0069] (2) After the salt formation is completed, the hydrochloride is transported to the phosgenation reactor, the reaction temperature is 140°C, and the phosgene flow rate is 4.4m 3 / h, residence time 3h, to obtain the isocyanate reaction solution, the isocyanate reaction yield is 99.1%, and the final isocyanate product is obtained after post-treatment.

[0070] Example 4

[0071] A method for preparing isocyanate, the preparation method comprising the following steps:

[0072] (1) continuously introducing a hexamethylenediaminechlorobenzene solution having a concentration of 8 wt %, fresh hydrogen chloride gas and hydrogen chloride circulating gas into a salt-forming reactor having a volume of 10 L at 45° C. for a residence time of 1 h to perform a salt-forming reaction to obtain an amine hydrochloride slurry and unreacted hydrogen chloride;

[0073] During stable operation, the feed rate of hexamethylenediaminechlorobenzene solution is 10L / h, and the feed rate of fresh hydrogen chloride gas is 0.34m 3 / h, the hydrogen chloride circulating gas is the unreacted hydrogen chloride obtained from the salt-forming reaction 2.12m 3 / h and photochemical reaction gas exhaust gas recovery 0.9m 3 / h, at this time, the NCO content in the hydrogen chloride circulating gas is 4971 mg / L, and the molar ratio of fresh hydrogen chloride and hydrogen chloride in the hydrogen chloride circulating gas to the amino group in hexamethylenediamine is 8:1; after the salt formation is completed, the number average particle size of the hydrochloride particles tested by electron microscopy is 27-36μm.

[0074] (2) After the salt formation is completed, the hydrochloride is transported to the phosgenation reactor, the reaction temperature is 140°C, and the phosgene flow rate is 2.94m 3 / h, residence time 3h, to obtain the isocyanate reaction solution, the isocyanate reaction yield is 99%, and the final isocyanate product is obtained after post-treatment.

[0075] Example 5

[0076] A method for preparing isocyanate, the preparation method comprising the following steps:

[0077] (1) continuously introducing a 6 wt % hexamethylenediamine chlorobenzene solution, fresh hydrogen chloride gas and hydrogen chloride circulating gas into a 10 L salt-forming reactor at 45° C. for a residence time of 1.5 h to perform a salt-forming reaction to obtain an amine hydrochloride slurry and unreacted hydrogen chloride;

[0078] During stable operation, the feed rate of hexamethylenediaminechlorobenzene solution is 6.7L / h, and the feed rate of fresh hydrogen chloride gas is 0.13m 3 / h, the hydrogen chloride circulating gas is the unreacted hydrogen chloride obtained from the salt-forming reaction 0.71m 3 / h and photochemical reaction gas exhaust gas recovery 0.5m 3 / h, at this time, the NCO content in the hydrogen chloride circulating gas is 9700 mg / L, and the molar ratio of fresh hydrogen chloride and hydrogen chloride in the hydrogen chloride circulating gas to the amino group in hexamethylenediamine is 6:1; after the salt formation is completed, the number average particle size of the hydrochloride particles tested by electron microscopy is 39-50 μm.

[0079] (2) After the salt formation is completed, the hydrochloride is transported to the phosgenation reactor, the reaction temperature is 140°C, and the phosgene flow rate is 1.57m 3 / h, residence time 3h, to obtain the isocyanate reaction solution, the isocyanate reaction yield is 98.3%, and the final isocyanate product is obtained after post-treatment.

[0080] Example 6

[0081] A method for preparing isocyanate, the preparation method differs from Example 1 only in that the NCO content in the hydrogen chloride circulating gas is controlled to be 3451 mg / L by adjusting the condensation temperature of the hydrogen chloride circulating gas, and the remaining material amounts, steps, etc. are the same as those in Example 1. After the salt formation is completed, the number average particle size of the hydrochloride particles is tested by electron microscopy to be 21-27 μm. After the phosgenation reaction, the reaction liquid of the isocyanate is obtained, and the target isocyanate reaction yield is 98.4%.

[0082] Comparative Example 1

[0083] A method for preparing isocyanate, the preparation method differs from Example 2 only in that the NCO content in the hydrogen chloride circulating gas is controlled to be 11452 mg / L by adjusting the condensation temperature of the hydrogen chloride circulating gas, and the remaining material amounts, steps, etc. are the same as those in Example 2. After the salt formation is completed, the number average particle size of the hydrochloride particles is tested by electron microscopy to be 920-1241 μm. After the phosgenation reaction, the reaction liquid of the isocyanate is obtained, and the target isocyanate reaction yield is 92.1%.

[0084] Comparative Example 2

[0085] A method for preparing isocyanate, the preparation method comprising the following steps:

[0086] (1) continuously introducing a 6 wt % hexamethylenediamine chlorobenzene solution and fresh hydrogen chloride gas into a 10 L salt-forming reactor at 45° C. for a residence time of 5.5 h to perform a salt-forming reaction to obtain an amine hydrochloride slurry and unreacted hydrogen chloride;

[0087] During stable operation, the feed rate of hexamethylenediaminechlorobenzene solution is 6.7L / h, and the feed rate of fresh hydrogen chloride gas is 0.56m 3 / h; after the salt formation, the number average particle size of the hydrochloride particles was tested by electron microscopy and found to be 72-80 μm.

[0088] (2) After the salt formation is completed, the hydrochloride is transported to the phosgenation reactor, the reaction temperature is 140°C, and the phosgene flow rate is 1.57m 3 / h, residence time 4.5h, to obtain the isocyanate reaction solution, the target isocyanate reaction yield 96.8%, after post-treatment to obtain the final isocyanate product.

[0089] In the present invention, the post-treatment is a conventional post-treatment operation in the art and can be adjusted according to the requirements of the isocyanate product.

[0090] The salt-forming effects of the above-mentioned embodiments and comparative examples were tested by observing the particle size of the hydrochloride obtained by the salt-forming reaction using an electron microscope for characterization. The smaller the particle size, the better the salt-forming effect.

[0091] The test results are summarized in Table 1.

[0092] Table 1

[0093]

[0094] It can be seen from the test results that the present invention recycles the residual hydrogen chloride from the salt-forming reaction and the by-product hydrogen chloride tail gas in the phosgenation reaction process, and controls the isocyanate content in the circulating gas, thereby increasing the excess ratio of hydrogen chloride to amine in the salt-forming process, significantly reducing the amount of fresh hydrogen chloride, and achieving a salt-forming time of ≤1.5h, a small particle size of the obtained hydrochloride, a high reaction salt-forming rate, and an obtained isocyanate yield of ≥98.3%, thereby achieving the reuse of hydrogen chloride and having excellent process economy.

[0095] By comparing Examples 1 to 6, it can be seen that the present invention can significantly increase the ratio of hydrogen chloride to amine while reducing fresh hydrogen chloride by further controlling the isocyanate content in the circulating hydrogen chloride, thereby shortening the reaction time while ensuring the salt-forming reaction effect, and obtaining the target isocyanate product in high yield.

[0096] By comparing Example 2 with Comparative Example 1, it can be seen that the present invention can obtain good salt-forming effect and product yield by controlling the isocyanate content in the circulating hydrogen chloride, while when its content is too low, it will lead to a significant increase in processing costs and no reuse value, and when the current index is too high, it will significantly affect the salt-forming reaction effect, resulting in a decrease in product yield. Comparative Example 2 is a situation when there is no hydrogen chloride reuse, wherein the molar ratio of hydrogen chloride to amine is 2.5:1, at this time, the amount of fresh hydrogen chloride is increased, the salt-forming time is long, and the salt-forming effect is poor, and the problem of removal of tail gas cannot be solved.

[0097] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing isocyanate, characterized in that: The preparation method comprises the following steps: (1) an amine solution reacts with fresh hydrogen chloride and hydrogen chloride circulating gas to form a salt to obtain an amine hydrochloride slurry and unreacted hydrogen chloride; (2) subjecting the amine hydrochloride slurry obtained in step (1) to a phosgenation reaction with phosgene to obtain the isocyanate and phosgene phase exhaust; The unreacted hydrogen chloride in step (1) and part of the photochemical gas phase exhaust in step (2) are used as hydrogen chloride circulating gas for the salt-forming reaction; The isocyanate content in the hydrogen chloride circulating gas is 100-10000 mg / L.

2. The preparation method according to claim 1, characterized in that: The amine in the amine solution is any one or a combination of at least two of a C4-C15 aliphatic amine or alicyclic amine; Preferably, the functionality of the amine in the amine solution is 1-3; Preferably, the solvent in the amine solution includes any one of toluene, xylene, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, methyl benzoate, ethyl benzoate, butyl benzoate, propyl benzoate, chlorobenzene, o-dichlorobenzene, p-chlorotoluene or bromobenzene, or a combination of at least two thereof; Preferably, the mass concentration of amine in the amine solution is 5-30%.

3. The preparation method according to claim 1, characterized in that: The photochemical gas phase exhaust in the hydrogen chloride circulating gas is 5-100% of the total volume of the photochemical gas phase exhaust in step (2); Preferably, in step (1), the molar ratio of the total amount of fresh hydrogen chloride and hydrogen chloride in the hydrogen chloride circulating gas to the amino group in the amine solution is (5-20):1; Preferably, the molar ratio of hydrogen chloride in the fresh hydrogen chloride to amino groups in the amine solution is (0.5-3):

1.

4. The preparation method according to claim 1, characterized in that: The isocyanate content in the hydrogen chloride circulating gas is 200-5000 mg / L; Preferably, the amine in the amine solution includes any one or a combination of at least two of cyclohexylamine, 1,4-butanediamine, 1,3-cyclohexanedimethylamine, 1,6-hexanediamine, 1,5-pentanediamine, 1,4-diaminocyclohexane, 1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane, 4,4'-diaminodicyclohexylmethanediamine, m-xylylenediamine or triaminononane; Preferably, in step (1), the molar ratio of the total amount of fresh hydrogen chloride and hydrogen chloride in the hydrogen chloride circulating gas to the amino group in the amine solution is (6-15):

1.

5. The preparation method according to claim 1, characterized in that: The temperature of the salt-forming reaction is 10-120°C; Preferably, the salt-forming reaction time is 0.5-2.5 h.

6. The preparation method according to claim 1, characterized in that: The molar ratio of the phosgene to the amino group in the amine solution is (3-15):

1.

7. The preparation method according to claim 1, characterized in that: The temperature of the phosgenation reaction is 80-170°C; Preferably, the phosgenation reaction time is 1-5 h.

8. The preparation method according to claim 1, characterized in that: The phosgenation reaction also includes a post-treatment step; Preferably, the post-treatment includes dephosgene removal and refined separation.

9. The preparation method according to claim 1, characterized in that: The preparation method comprises the following steps: (1) reacting an amine solution with fresh hydrogen chloride and hydrogen chloride circulating gas at 15-100° C. for 0.5-2.5 h to obtain an amine hydrochloride slurry and unreacted hydrogen chloride; (2) reacting the amine hydrochloride slurry obtained in step (1) with phosgene at 100-160° C. for 2-4 hours to obtain a photochemical reaction liquid and exhaust gas from the photochemical reaction liquid, dephosgenating the photochemical reaction liquid, and refining and separating the isocyanate; The unreacted hydrogen chloride in step (1) and part of the photochemical gas phase exhaust in step (2) are used as hydrogen chloride circulating gas for the salt-forming reaction; Wherein, the isocyanate content in the hydrogen chloride circulating gas is 500-1000 mg / L; In the step (1), the molar ratio of the total amount of hydrogen chloride in the fresh hydrogen chloride and hydrogen chloride circulating gas to the amino group in the amine solution is (8-12):1; The molar ratio of the phosgene to the amino group in the amine solution is (5-10):

1.

10. Use of the preparation method according to any one of claims 1 to 9 in household appliances, automobiles, construction, furniture or packaging materials.

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