A method for purifying n-butyl isocyanate

Abstract

The application discloses a purification method of n-butyl isocyanate and belongs to the technical field of purification and separation of organic compounds. The application comprises the following steps: n-butyl isocyanate synthesis liquid is subjected to tower continuous gas chasing under a certain temperature and nitrogen flow rate, and most of hydrogen chloride is removed; after the gas chasing, the material is subjected to negative pressure rectification, and the n-butyl isocyanate is at the top of the tower; the n-butyl isocyanate at the top of the tower is further subjected to continuous acid removal and impurity removal in a fixed bed containing modified molecular sieves under a certain temperature, and finally, the n-butyl isocyanate product with a purity greater than 99.5% and an acidity less than 50 ppm is obtained. According to the application, nitrogen is used to remove acid under high temperature in a tower, the intermediate is fully decomposed by using a higher acid removal temperature, most of the hydrogen chloride in the material liquid is removed in time by using nitrogen as incondensable gas, and the fixed bed of the modified molecular sieves is used to adsorb part of impurities and further remove acid, so that high-purity and low-acidity high-quality products are obtained, and the application value of the application is good.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of purification and separation of organic compounds, and particularly relates to a purification method of n-butyl isocyanate. BACKGROUND

[0002] N-butyl isocyanate is mainly used for synthesizing insecticides such as benomyl, and can also be used as a catalyst for synthesizing sulfonylurea herbicides. As an important chemical intermediate, n-butyl isocyanate has wide application in the fields of pesticides and fungicides. The main synthesis method of n-butyl isocyanate is that a n-butyl amine solution with a certain concentration is reacted with phosgene at a certain temperature to generate n-butyl isocyanate, and the by-product is hydrogen chloride. The hydrogen chloride and the product n-butyl isocyanate are easily combined to generate an intermediate n-butyl carbamoyl chloride at low temperature, and the n-butyl carbamoyl chloride can be decomposed into n-butyl isocyanate and release hydrogen chloride at a higher temperature. In the traditional rectification process, due to the high temperature of the tower kettle, the intermediate is decomposed into n-butyl isocyanate and hydrogen chloride, and during the condensation process of the material in the overhead condenser, the n-butyl isocyanate reacts with gaseous hydrogen chloride to generate n-butyl carbamoyl chloride, so that the acidity of the product is difficult to remove, and the finished product has high acidity.

[0003] The existing method for removing the acidity of n-butyl isocyanate is to carry out kettle gas chasing at a certain temperature, and the gas chasing effect is poor. In addition, since the synthesis liquid contains a large amount of solvent, as the content of the overhead product increases in the rectification process, the acidity is further enriched, resulting in high acidity of the finished product, which affects the downstream application.

[0004] Patent CN104447411B introduces a method for refining n-butyl isocyanate. Sodium hydroxide is used to neutralize the impurity acid in the n-butyl isocyanate to be refined under the action of aluminum chloride. The product is obtained by oil-water separation and rectification of the oil layer. The operation of this method is carried out at a temperature of-10℃ to-5℃. Since the wastewater generated by this process is large, the amount of three wastes is high. SUMMARY

[0005] In view of the defects of the prior art, the purpose of the present application is to provide a purification method of n-butyl isocyanate, so as to obtain n-butyl isocyanate with high purity and low acidity, and reduce the discharge of three wastes.

[0006] In order to solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0007] (1) The n-butyl isocyanate synthesis liquid with a certain concentration and acidity is subjected to continuous tower chasing under a certain temperature and nitrogen flow, and the chasing material flow direction is: the synthesis liquid is introduced into the top of the tower, nitrogen is introduced into the middle of the tower, the nitrogen and the material are countercurrently contacted, the tail gas enters a tail gas absorption device, and the chased material is introduced into the tower kettle for refining.

[0008] (2) After the gas is removed, the material is subjected to negative pressure rectification, and the top of the column is n-butyl isocyanate;

[0009] (3) The n-butyl isocyanate at the top of the column enters a fixed bed containing modified molecular sieves for further continuous deacidification and impurity removal, and the final product n-butyl isocyanate has an acidity of <50 ppm and a purity of >99%.

[0010] The n-butyl isocyanate synthesis solution is prepared by passing phosgene into an n-butylamine o-dichlorobenzene solution, and the product concentration is 5%-50% and the acidity is 1%-10%.

[0011] The reaction equation is as follows:

[0012] Main reaction:

[0013]

[0014] The n-butyl isocyanate and the by-product hydrogen chloride are generated by the phosgenation reaction of n-butylamine and phosgene.

[0015] Side reaction:

[0016]

[0017] The intermediate n-butyl carbamoyl chloride is generated by the reaction of n-butyl isocyanate and the by-product hydrogen chloride at low temperature, and the intermediate decomposes into the finished product and hydrogen chloride at higher temperature.

[0018] The ratio of nitrogen to feed material in step (1) is 0.1-1 Nm 3 / Kg, preferably 0.3-0.5 Nm 3 / Kg

[0019] The gas removal temperature in step (1) is 90°C-140°C, preferably 110°C-130°C;

[0020] The number of plates in the gas removal column in step (1) is 5-15, preferably 8-10;

[0021] The gas removal residence time (the time for the material to go from the top of the column to the column bottom) in step (1) is 0.5-3 h, preferably 1-2 h;

[0022] The gas removal in step (1) is carried out under micro-negative pressure, and the pressure is 95-101 KPa;

[0023] The rectification negative pressure in step (2) is 1 KPa-10 KPa, preferably 2 KPa-5 KPa;

[0024] The rectification column bottom temperature in step (2) is 90°C-120°C, preferably 100°C-110°C;

[0025] The number of plates in the rectifying column in step (2) is 10-20, preferably 15-18;

[0026] The reflux ratio in the rectifying column in step (2) is 1-5:1, preferably 2-3:1;

[0027] The active ingredient in the modified molecular sieve in step (3) is one of CaO or TiO2 or a combination of the two, wherein the CaO / TiO2 content is 5%-30% of the weight of the molecular sieve, preferably 20%-30%;

[0028] The temperature for removing acid and impurities in step (3) is 10-80°C, preferably 30-50°C;

[0029] The ratio of the amount of feed to the weight of the molecular sieve in step (3) is 500-1000:1;

[0030] The residence time for removing acid in step (3) is 0.5h-5h, preferably 1h-2h.

[0031] Compared with the traditional acid removal and purification process, the present application has the following beneficial effects:

[0032] (1) The present application provides a purification method for n-butyl isocyanate. Compared with the traditional kettle type batch acid removal, the present application uses a tower type continuous high temperature nitrogen gas to remove acid. The higher acid removal temperature allows the intermediate to be fully decomposed, and nitrogen gas as a non-condensable gas removes most of the hydrogen chloride in the system in a timely manner. The tower type continuous gas removal has high automation degree and good acid removal effect, and can remove most of the acidity.

[0033] (2) After acid removal, the material is purified by rectification, and the acidity is enriched in the top product, resulting in a certain increase in acidity. The modified molecular sieve in the fixed bed adsorbs part of the impurities and further reacts with the acid to remove it. The modified molecular sieve contains active ingredients such as CaO and TiO2, which can further react with the small amount of acid in the product to remove it.

[0034] (3) After treatment by the present application, the purity of n-butyl isocyanate can reach more than 99.5%, and the acidity is less than 50ppm, which is small for the corrosion of downstream equipment, meets the needs of high-end market, and has high product competitiveness. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The process flow diagram of the present application, in which the n-butyl isocyanate synthesis liquid enters the gas removal tower from the top of the gas removal tower, and nitrogen gas enters from the lower middle position of the gas removal tower at a certain flow rate. The synthesis liquid is dispersed by the packed tower and fully contacts with the nitrogen gas for gas removal. The top of the tower is the tail gas, and the bottom of the tower is the gas removal liquid. The gas removal liquid enters the rectifying column for rectification, the bottom of the tower is the solvent, and the top of the tower is n-butyl isocyanate. The top liquid enters the fixed bed reactor containing molecular sieve for continuous acid and impurity removal, and the outlet is the finished product. DETAILED DESCRIPTION

[0036] For the convenience of the technical solutions of the application, the following first explains some concepts involved in the present application.

[0037] Example 1

[0038] (1) The content of n-butyl isocyanate o-dichlorobenzene solution is 10%, and the acidity is 5%. The solution is continuously fed into a gas-removing tower for gas removal. The gas-removing tower has 10 plates, the top of the tower is fed with the synthetic solution, and nitrogen is fed into the middle of the tower. The weight ratio of nitrogen to feed is 0.3 Nm3 / Kg, the gas-removal temperature is 110°C, the gas-removal is carried out under a micro-negative pressure of 98 KPa, and the gas-removal residence time is 2 h. After the gas-removal, the acidity of the synthetic solution is reduced from 5% to 0.15%.

[0039] (2) The solution after the gas-removal is subjected to rectification. The rectification negative pressure is 5 KPa, the column bottom temperature is 101°C, the rectification tower has 15 plates, and the reflux ratio at the top of the tower is 2:1. During the rectification process, part of the hydrogen chloride combines with the n-butyl isocyanate condensed at the top of the tower to form an intermediate, n-butyl carbamoyl chloride, resulting in a higher acidity of the material at the top of the tower than the original material. The content of n-butyl isocyanate at the top of the tower is 99.12%, and the acidity is 0.34%.

[0040] (3) The n-butyl isocyanate at the top of the tower is continuously fed into a fixed-bed reactor containing modified molecular sieves. The molecular sieves are modified molecular sieves containing 30% CaO, the deacidification temperature is 70°C, the weight ratio of the feed to the molecular sieves is 500:1, and the residence time is 1 h. After the deacidification, the content of the product is 99.83%, and the acidity is 30 ppm.

[0041] Example 2

[0042] (1) The content of n-butyl isocyanate o-dichlorobenzene solution is 30%, and the acidity is 2%. The solution is continuously fed into a gas-removing tower for gas removal. The gas-removing tower has 10 plates, the top of the tower is fed with the synthetic solution, and nitrogen is fed into the middle of the tower. The weight ratio of nitrogen to feed is 0.5 Nm3 / Kg, the gas-removal temperature is 120°C, the gas-removal is carried out under a micro-negative pressure of 98 KPa, and the gas-removal residence time is 2 h. After the gas-removal, the acidity of the synthetic solution is reduced from 2% to 0.05%.

[0043] (2) The solution after the gas-removal is subjected to rectification. The rectification negative pressure is 10 KPa, the column bottom temperature is 105°C, the rectification tower has 15 plates, and the reflux ratio at the top of the tower is 2:1. The content of n-butyl isocyanate at the top of the tower is 99.23%, and the acidity is 0.13%.

[0044] (3) At the top of the column, n-butyl isocyanate continuously passes through a fixed-bed reactor containing a modified molecular sieve containing 20% ​​TiO2. The deacidification temperature is 80°C, the feed weight to molecular sieve weight ratio is 1000:1, and the residence time is 1 hour. The finished product after deacidification has a content of 99.91% and an acidity of 20 ppm.

[0045] Example 3

[0046] (1) A 50% n-butyl isocyanate-containing o-dichlorobenzene liquid with an acidity of 7% was continuously fed into a purge tower for purge. The purge tower had 10 trays, with the synthesis liquid fed to the top and nitrogen fed into the tower. The nitrogen to feed weight ratio was 1.0 Nm³ / kg, the purge temperature was 130°C, the purge was carried out at a slightly negative pressure of 98 kPa, and the purge residence time was 1.5 h. After purge, the acidity of the synthesis liquid was reduced from 7% to 0.25%.

[0047] (2) The liquid after degassing was distilled at a negative pressure of 3 kPa, a bottom temperature of 94°C, 10 plates, and a top reflux ratio of 3:1. The top n-butyl isocyanate content was 99.31%, and the acidity was 0.46%.

[0048] (3) At the top of the column, n-butyl isocyanate continuously passes through a fixed-bed reactor containing a modified molecular sieve containing 15% CaO and 10% TiO2. The deacidification temperature is 60°C, the feed weight to molecular sieve weight ratio is 1000:1, and the residence time is 3 hours. After deacidification, the finished product has a content of 99.93% and an acidity of 35 ppm.

[0049] Example 4

[0050] (1) A 5% n-butyl isocyanate-containing o-dichlorobenzene solution with an acidity of 1.5% was continuously fed into a purge tower for purge. The purge tower had 13 plates, with the synthesis liquid fed to the top and nitrogen fed into the tower. The nitrogen to feed weight ratio was 0.2 Nm³ / kg, the purge temperature was 110°C, the purge was carried out under a slight negative pressure of 100 kPa, and the purge residence time was 1 hour. After purge, the acidity of the synthesis liquid decreased from 1.5% to 0.03%.

[0051] (2) The liquid after degassing was distilled at a negative pressure of 2 kPa, a bottom temperature of 92°C, 20 plates, and a top reflux ratio of 3:1. The top n-butyl isocyanate content was 99.52%, and the acidity was 0.09%.

[0052] (3) At the top of the column, n-butyl isocyanate continuously passes through a fixed-bed reactor containing a modified molecular sieve containing 30% TiO2. The deacidification temperature is 30°C, the feed weight to molecular sieve weight ratio is 700:1, and the residence time is 2 hours. After deacidification, the finished product has a content of 99.96% and an acidity of 10 ppm.

[0053] Example 5

[0054] (1) The content of n-butyl isocyanate o-dichlorobenzene solution was 20%, and the acidity was 10%. The solution was continuously fed into a gas stripping column. The gas stripping column had 15 plates, and the synthetic liquid was fed into the top of the column, and nitrogen was fed into the middle of the column. The weight ratio of nitrogen to feed was 0.8 Nm3 / Kg, the gas stripping temperature was 140°C, the gas stripping was carried out under a micro negative pressure of 98 KPa, and the gas stripping residence time was 3 h. After the gas stripping, the acidity of the synthetic liquid was reduced from 10% to 0.42%.

[0055] (2) The stripped solution was subjected to rectification under a negative pressure of 8 KPa, a column bottom temperature of 103°C, 20 plates of the rectification column, and a reflux ratio of 5:1 at the top of the column. The content of n-butyl isocyanate at the top of the column was 99.32%, and the acidity was 0.58%.

[0056] (3) The n-butyl isocyanate at the top of the column was continuously fed into a fixed bed reactor containing modified molecular sieves. The molecular sieves were modified molecular sieves containing 15% CaO+15% TiO2, the deacidification temperature was 60°C, the weight ratio of feed to molecular sieves was 600:1, and the residence time was 4 h. After the deacidification, the content of the product was 99.89%, and the acidity was 32 ppm.

[0057] Example 6

[0058] (1) The content of n-butyl isocyanate o-dichlorobenzene solution was 15%, and the acidity was 3%. The solution was continuously fed into a gas stripping column. The gas stripping column had 5 plates, and the synthetic liquid was fed into the top of the column, and nitrogen was fed into the middle of the column. The weight ratio of nitrogen to feed was 0.1 Nm3 / Kg, the gas stripping temperature was 90°C, the gas stripping was carried out under a micro negative pressure of 98 KPa, and the gas stripping residence time was 3 h. After the gas stripping, the acidity of the synthetic liquid was reduced from 3% to 0.08%.

[0059] (2) The stripped solution was subjected to rectification under a negative pressure of 10 KPa, a column bottom temperature of 105°C, 10 plates of the rectification column, and a reflux ratio of 4:1 at the top of the column. The content of n-butyl isocyanate at the top of the column was 99.41%, and the acidity was 0.15%.

[0060] (3) The n-butyl isocyanate at the top of the column was continuously fed into a fixed bed reactor containing modified molecular sieves. The molecular sieves were modified molecular sieves containing 5% CaO, the deacidification temperature was 60°C, the weight ratio of feed to molecular sieves was 1000:1, and the residence time was 5 h. After the deacidification, the content of the product was 99.96%, and the acidity was 15 ppm.

Claims

1. A method for purifying n-butyl isocyanate, characterized in that the steps include: (1) The n-butyl isocyanate synthesis liquid is driven out of the tower: the synthesis liquid is fed into the top of the tower, and nitrogen is fed into the tower. The nitrogen and the material are in countercurrent contact to form a tail gas containing hydrogen chloride and discharged; the feed material ratio of nitrogen to synthesis liquid is 0.1-1Nm 3 / Kg, the gas removal temperature is 90℃-140℃; the gas removal is carried out under negative pressure, the pressure is 95-101KPa; (2) distilling the synthetic liquid after degassing, and condensing the top of the tower to obtain crude n-butyl isocyanate; the distillation is a negative pressure distillation, the distillation negative pressure is 1KPa-10KPa, the distillation tower bottom temperature is 90°C-120°C, the number of distillation tower plates is 10-20, and the distillation reflux ratio is 1-5:1; (3) using molecular sieves to remove acid and impurities from crude n-butyl isocyanate to obtain pure n-butyl isocyanate; the molecular sieves contain one or two active ingredients of CaO or TiO2, and the content of the active ingredients is 5%-30% of the weight of the molecular sieves; wherein the temperature required for the acid and impurity removal is 10-80°C.

2. The method for purifying n-butyl isocyanate according to claim 1, wherein In the step (1), the n-butyl isocyanate synthesis liquid is prepared by introducing phosgene into an n-butylamine o-dichlorobenzene solution for reaction.

3. The method for purifying n-butyl isocyanate according to claim 1, wherein The tower in step (1) is a packed tower.

4. The method for purifying n-butyl isocyanate according to claim 1, wherein The feed material ratio of nitrogen to synthetic liquid in step (1) is 0.3-0.5Nm 3 / Kg.

5. The method for purifying n-butyl isocyanate according to claim 1, wherein: The gas-driving temperature in step (1) is 110°C-130°C.

6. The method for purifying n-butyl isocyanate according to claim 1, wherein: The distillation negative pressure in step (2) is 2KPa-5KPa.

7. The method for purifying n-butyl isocyanate according to claim 1, wherein: In the step (2), the temperature of the distillation tower kettle is 100° C.-110° C., and / or the number of distillation tower plates is 15-18, and / or the distillation reflux ratio is 2-3:

1.

8. The method for purifying n-butyl isocyanate according to claim 1, wherein: In the step (3), the weight ratio of the feed amount to the molecular sieve is 500-1000:

1.

9. The method for purifying n-butyl isocyanate according to claim 1, wherein: The active ingredient content is 20%-30% of the molecular sieve weight.

10. The method for purifying n-butyl isocyanate according to claim 1, wherein: The residence time of the acid removal in step (3) is 0.5h-5h.

Images