CN118908860A - Method and system for purifying terephthalyl isocyanate - Google Patents

Abstract

The invention provides a method and a system for purifying terephthalyl diisocyanate (PPDI), which are used for purifying photochemical liquid obtained by phosgene-based synthesis. The method comprises the following steps: and (3) feeding the PPDI photochemical solution into a degassing tower for degassing, centrifuging the degassed Bi Dafu feed liquid, removing insoluble solid impurities through centrifugation, feeding the centrifugate into a first crystallization purification device to obtain PPDI crystals, a first washing liquid and a first filtration mother liquor, feeding the filtration mother liquor into a desolventizing tower for desolventizing after adding a quantitative stabilizer into a configuration kettle, and feeding the tower kettle after removing most of the solvent into a second crystallization purification device to obtain PPDI crystals, a second washing liquid and a second filtration mother liquor. The method can avoid the problems of product deterioration, kettle blockage and the like caused by high-temperature rectification and purification of the traditional PPDI, has good safety and high product separation yield, and can be suitable for small-batch industrial production.

Description

A method and system for purifying p-phenylene diisocyanate

Technical Field

The invention belongs to the technical field of post-processing, purification or refining of p-phenylene diisocyanate, and specifically relates to a purification method and system for p-phenylene diisocyanate, and further to a purification method and system for p-phenylene diisocyanate synthesized by photochemical synthesis.

Background Art

P-phenylene diisocyanate (hereinafter referred to as PPDI) is a new high-performance special PU curing agent. Due to its excellent comprehensive performance and outstanding dynamic mechanical properties, its application value is increasingly recognized by people. PPDI products have the advantages of high technical content, great market potential, and outstanding performance. It occupies an important position in the field of fine chemical intermediates. There are two methods for synthesizing PPDI: phosgene method and non-phosgene method, among which the phosgene method is the traditional method for synthesizing p-phenylene diisocyanate. Specifically, using o-dichlorobenzene or chlorobenzene as a solvent, adding phosgene solution to p-phenylenediamine solution at 0℃～10℃, and then introducing phosgene, p-phenylenediamine and phosgene undergo photochemical reaction, and introducing nitrogen to drive off excess phosgene and HCl to obtain a crude product of p-phenylene diisocyanate.

During the production process, p-phenylene diisocyanate is easily oxidized in the air to form dimers, which causes the product to deteriorate. Therefore, the crude product obtained by synthesis needs to be purified. At present, p-phenylene diisocyanate is usually purified by separation and purification steps such as distillation, crystallization, centrifugation, and drying. The following problems exist in the traditional p-phenylene diisocyanate distillation and purification process: 1) The boiling point and melting point of PPDI under high vacuum are close or even inverted. Under this condition, PPDI is easily entrained and sublimated, resulting in blockage of the condenser and gas phase pipeline; 2) PPDI monomer is very easy to self-polymerize during repeated melting-crystallization, resulting in harsh storage and transportation conditions of PPDI in the traditional distillation process; 3) In the traditional intermittent distillation process of PPDI, the fluidity of the residue in the distillation tower is poor, resulting in the inability to discharge the material. A part of the PPDI product must be retained before the material can be discharged, resulting in an actual yield of only about 80%.

Summary of the invention

In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a method and system for purifying p-phenylene diisocyanate, which solves the problems of long heating time of materials, easy coking and clogging of the tower kettle, and low purification yield in the traditional distillation purification process.

The invention provides a method for providing p-phenylene diisocyanate, comprising: a phosgene removal tower, a centrifugal device, a first crystallization purification device, a stabilizer configuration kettle, a desolventizing tower, and a second crystallization purification device, which are connected in sequence, wherein PPDI photochemical liquid is transported to the phosgene removal tower, light components are extracted from the tower top, and the degassed liquid extracted from the tower bottom is transported to the centrifugal device, and the obtained centrifuged liquid is transported to the first crystallization purification device, and primary precipitated PPDI crystals, primary washing liquid and a first filtered mother liquor are obtained through cooling, crystallization and washing, and the filtered mother liquor is transported to a stabilizer configuration kettle, and the stabilizer-containing liquid obtained after adding a stabilizer is transported to the desolventizing tower, and the desolventized liquid obtained after removing most of the solvent is transported to the second crystallization purification device, and secondary precipitated PPDI crystals, secondary washing liquid and a second filtered mother liquor are obtained through cooling, crystallization and washing.

Furthermore, the PPDI photochemical liquid is condensed in a tower top condenser to produce phosgene and hydrogen chloride gas, and the degassed material with a phosgene content of less than 1000 ppm is produced in the tower bottom. The operating pressure of the dephosgene tower is 0.5 bar to 2.0 bar, the theoretical number of plates is 5 to 15, and the tower bottom temperature is 80 to 120°C.

Furthermore, the first crystallization purification device and the second crystallization purification device include a cooling crystallization kettle and a plate and frame filter press.

Furthermore, in the first crystallization purification device, the starting point of the cooling crystallization temperature is 40-120°C and the end point is -20-0°C; in the second crystallization purification device, the starting point of the cooling crystallization temperature is 90-120°C and the end point is -20-0°C.

Furthermore, the mass ratio of the secondary precipitated PPDI crystals to the primary precipitated PPDI crystals is 10 to 20:1.

Furthermore, the purity of the first precipitated PPDI crystals is ≥99.5%, and the purity of the second precipitated PPDI crystals is ≥99.9%.

Furthermore, the stabilizer is selected from one or more of triphenyl phosphite, didodecyl phosphite, and diisooctyl phosphite, and the stabilizer is preferably triphenyl phosphite; the amount of the stabilizer added is 1wt% to 10wt% of the PPDI equivalent of the feed liquid, i.e., the first filtered mother liquor, preferably 1.5wt% to 3wt%. PPDI exists as a dimer as an aromatic isocyanate, and the dimer itself can be decomposed into monomers again in the subsequent high-temperature desolvation process, but the dimer is also easy to further react with active hydrogen and oxygen free radicals in the system at high temperature to generate irreversible urea-type insoluble impurities. The stabilizer such as triphenyl phosphite of the present invention can decompose active hydroperoxides, inhibit oxygen free radicals, and avoid the generation of insoluble impurities such as urea to the greatest extent.

Furthermore, the theoretical number of plates of the desolventizing tower is 10 to 20, the operating pressure of the desolventizing tower is 0.05 bar to 0.3 bar, preferably 0.05 bar to 0.1 bar, and the stabilizer-containing feed liquid is fed into the desolventizing tower from the 8th to 12th plates, and the feed liquid contains 10% to 25% solvent after desolventizing. If the amount of residual solvent is less than 10%, the soluble light component impurities in the washing liquid increase, resulting in a high level of impurities in the primary crystallized PPDI, and the fluidity of the desolventizing tower kettle becomes poor and difficult to transfer, and the temperature of the desolventizing tower kettle will increase, and the monomers are easy to polymerize. If the amount of residual solvent is higher than 25%, the yield of secondary crystallized PPDI decreases, the amount of PPDI online in the system increases, and the energy consumption is high.

Furthermore, part of the secondary washing liquid is applied to the first crystallization purification device as a detergent for the first crystallization purification device. Preferably, the detergent for the first crystallization purification device all comes from the secondary washing liquid. More preferably, when the heavy component impurities in the secondary washing liquid are ≥0.15%, the secondary washing liquid is discarded.

Furthermore, the mass ratio of the amount of detergent used in the second crystallization purification device to the second precipitated PPDI crystals is 2 to 8:1; the mass ratio of the amount of detergent used in the first crystallization purification device to the second precipitated PPDI crystals is 5 to 10:1.

Furthermore, the second filtered mother liquor is applied to the stabilizer preparation kettle.

The present invention also provides a device for providing p-phenylene diisocyanate, comprising: a dephosgene tower, a centrifugal device, a first crystallization purification device, a stabilizer configuration kettle, a desolventizing tower, and a second crystallization purification device connected in sequence, wherein the tower bottom material outlet of the dephosgene tower is connected to the feed port of the centrifugal device, the material outlet of the centrifugal device is connected to the feed port of the first crystallization purification device, the discharge port of the first crystallization purification device is connected to the feed port of the stabilizer configuration kettle, the discharge port of the stabilizer configuration kettle is connected to the middle feed port of the desolventizing tower, and the bottom discharge port of the desolventizing tower is connected to the feed port of the second crystallization purification device.

The solvent of the PPDI photochemical liquid of the present invention is dichlorobenzene, and the index requires that the PPDI purity is ≥96.0%, and the content is between 4% and 9%, which generally contains a large amount of solvent, a small amount of phosgene, hydrogen chloride and other soluble and insoluble impurities. The insoluble impurities in the photochemical liquid mainly include PPDI polymer products and carbodiimide, urea, the reaction product of amine and PPDI, etc.; the soluble impurities are divided into light component impurities with a lower boiling point than PPDI and heavy component impurities with a higher boiling point, wherein the light component impurities are mainly dichlorobenzene and its isomers, and the heavy component impurities are mainly PPDI dimer uretdione and chloroisocyanate.

In order to avoid corrosion of subsequent equipment under the action of acidic gas, it is necessary to first remove phosgene and hydrogen chloride to obtain degassed feed liquid, and then the feed liquid enters the centrifugal device for centrifugal removal of insoluble impurities. This step is very critical. If the insoluble impurities are not removed completely, it will affect the crystallization purity and yield of the subsequent PPDI product. After centrifugation, the feed liquid enters the first crystallization purification device. The first and second crystallization purification devices mainly include a cooling crystallization kettle and a plate and frame filter press. The feed liquid enters the cooling crystallization kettle and crystallizes according to the program. The crystals precipitated once are PPDI. After washing with detergent, a PPDI flake product with a content of ≥99.5% is obtained.

The first filtered mother liquor enters the stabilizer preparation kettle and is added with stabilizer for uniform mixing. The stabilizer of the present invention has the following two functions.

First, the inventors experimentally observed that PPDI has phase change polymerization characteristics, that is, pure PPDI (melting point 92-96°C) or high-content PPDI will undergo self-polymerization reaction during one or more crystallization-melting processes. The present invention can avoid phase change polymerization of PPDI in the desolventizing tower kettle in subsequent processes by adding a specific stabilizer.

Second, PPDI, as an aromatic isocyanate, is very easy to polymerize at high temperatures. The present invention can reduce the polymerization rate of PPDI in the bottom of the desolventizing tower to a certain extent by adding a specific stabilizer. The method of the present invention does not need to remove the solvent completely as in the traditional distillation purification process of PPDI, because pulling out the solvent will inevitably increase the bottom temperature and thus accelerate the polymerization process of PPDI. The present invention controls the residual solvent in the bottom of the desolventizing tower to account for 10% to 25% of the total mass, thereby reducing the bottom temperature of the desolventizing tower and synergizing with the stabilizer to avoid the polymerization of PPDI in the bottom of the desolventizing tower.

The uniformly mixed feed liquid in the stabilizer configuration kettle enters the desolventizing tower for distillation and desolventizing, and the solvent is removed. After the material in the desolventizing tower kettle is taken out, it directly enters the second crystallization and purification device. The first and second crystallization and purification devices mainly include a cooling crystallization kettle and a plate and frame filter press. The feed liquid enters the cooling crystallization kettle and is cooled and crystallized according to the program. The secondary precipitated crystals are PPDI, and after washing with a detergent, a PPDI flake product with a content of ≥99.9% is obtained. The detergent used in the second crystallization and purification device is one or more of chloroform, dichloroethane, and carbon tetrachloride. Part of the washing liquid in the second crystallization and purification device is applied to the first crystallization and purification device for washing. The second filtered mother liquor contains stabilizers and a small amount of PPDI, and the mother liquor is applied to the stabilizer configuration kettle for repeated use.

In the present invention, light component impurities are extracted from the top of the desolventizing tower without enrichment, and heavy component impurities are enriched in the washing liquid by applying the washing liquid. After the device circulates for a certain period, the washing liquid is regularly discharged without applying, so as to avoid affecting the purity of the PPDI product due to the enrichment of heavy component impurities. When the heavy component impurities in the washing liquid are ≥0.15% (the heavy component impurities are substances with a retention time greater than PPDI in the gas chromatography), the washing liquid is discarded.

The method and system of the present invention can avoid problems such as product deterioration and distillation tower kettle blockage caused by traditional PPDI high-temperature distillation purification, has good safety, high product separation yield, and can be suitable for small-batch industrial production.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 is a gas chromatogram of PPDI photochemical liquid.

FIG. 2 is a schematic flow chart of the implementation method provided by the present invention.

In the figure, 1-phosgene removal tower; 2-centrifugal device; 3-first crystallization purification device; 4-stabilizer configuration kettle; 5-solvent removal tower; 6-second crystallization purification device.

DETAILED DESCRIPTION

The method of the present invention is further described below through specific embodiments and drawings.

In order to more clearly illustrate the embodiments of the present invention, the PPDI photochemical liquids used in the examples and comparative examples are all materials from the same batch, and their gas chromatograms are shown in FIG1 , with an absolute PPDI content of 5.38% and a purity of 96.89%.

Table 1

Example 1

A device for providing p-phenylene diisocyanate, as shown in FIG1 , comprises: a phosgene removal tower 1, a centrifugal device 2, a first crystallization purification device 3, a stabilizer configuration kettle 4, a solvent removal tower 5, and a second crystallization purification device 6 connected in sequence.

In Figure 1, L represents PPDI photochemical synthesis liquid, a represents the material produced from the top of the degassing tower, b represents the feed liquid after degassing, c represents the feed liquid after centrifugation, d represents the first filtered mother liquor, e represents the feed liquid containing stabilizer, f represents the material produced from the top of the desolventizing tower, g represents the feed liquid after desolventizing, i represents fresh detergent, h represents the washing liquid of the second crystallization purification device, P1 represents the first precipitated PPDI crystals, P2 represents the second precipitated PPDI crystals, and M represents the produced detergent.

The purification method comprises: conveying 46 kg of PPDI photochemical liquid (containing 2.48 kg of PPDI) into a phosgene removal tower 1, extracting light components from the top of the tower, conveying the degassed liquid extracted from the bottom of the tower to a centrifugal device 2, conveying the obtained centrifuged liquid to a first crystallization purification device 3, obtaining primary precipitated PPDI crystals, washing liquid and a first filtered mother liquor through cooling, crystallization and washing, conveying the first filtered mother liquor to a stabilizer preparation kettle 4, conveying the obtained stabilizer-containing liquid to a desolventizing tower 5 after adding a stabilizer, conveying the obtained desolventizing liquid to a second crystallization purification device 6 after removing most of the solvent, obtaining secondary precipitated PPDI crystals, washing liquid and a second filtered mother liquor through cooling, crystallization and washing.

The operating pressure of the phosgene removal tower 1 is 0.9 bar, the theoretical plate number is 8, and the bottom temperature is 100° C. The PPDI photochemical liquid is condensed by the top condenser to produce phosgene and hydrogen chloride gas, and the bottom of the tower produces a degassed liquid with a phosgene content of less than 1000 ppm.

The centrifuge used in the embodiment is a HEINKEL chemical grade-H 630-1600C horizontal centrifuge.

The first crystallization purification device 3 and the second crystallization purification device 6 both include a cooling crystallization kettle and a plate-frame filter press (not shown), and the model of the plate-frame filter press is MSE-Filterpressen CHAMBER FILTER PRESS KFP 800. The cooling crystallization temperature starting point of the cooling crystallization kettle in the first crystallization purification device 3 is 120°C and the end point is 0°C; the cooling crystallization temperature starting point of the cooling crystallization kettle in the second crystallization purification device 6 is 100°C and the end point is -15°C.

The stabilizer used in the stabilizer configuration kettle 4 is triphenyl phosphite, and the amount of the stabilizer added is 2.8% of the PPDI weight of the feed liquid, that is, 1.29 kg.

The theoretical plate number of the desolventizing tower 5 is 18, the operating pressure of the desolventizing tower 5 is 0.2 bar, and the stabilizer-containing feed liquid is fed into the desolventizing tower 5 from the 10th plate. The desolventizing feed liquid contains 10% of the solvent, and the solvent is dichlorobenzene.

The secondary washing liquid of the second crystallization purification device 6 is partially applied to the first crystallization purification device 3 as the washing agent of the first crystallization purification device 3. In this embodiment, the washing agent of the first crystallization purification device 3 comes entirely from the secondary washing liquid. The light component impurities are extracted from the top of the desolventizing tower without enrichment, and the heavy component impurities are enriched in the washing liquid by the washing liquid application. After the device circulates for a certain period of time, the washing liquid (M in the figure) is regularly discharged without application to avoid the enrichment of heavy component impurities affecting the purity of the PPDI product; when the heavy component impurities in the washing liquid h are ≥0.15% (the heavy component impurities are substances with a retention time greater than PPDI in the gas chromatography), the washing liquid is discarded. The new washing agent i is only added to the second crystallization purification device 6 and enters the washing liquid cycle. Ethylene dichloride is used as the washing agent.

The mass ratio of the amount of detergent used in the second crystallization purification device 6 to the second precipitated PPDI crystals is 5:1; the mass ratio of the amount of detergent used in the first crystallization purification device 3 to the second precipitated PPDI crystals is 8:1.

The second filtered mother liquor of the second crystallization purification device 6 is applied to the stabilizer preparation kettle 4 to improve the recovery rate of PPDI.

Example 2

This embodiment is the same as Embodiment 1 except for the following features:

The stabilizer selected is a mixture of triphenyl phosphite and didodecyl phosphite, the mixing mass ratio of which is 5:1, and the added amount of the mixed stabilizer is 1.5% of the PPDI weight of the feed liquid, that is, 0.69 kg.

Example 3

This embodiment is the same as Embodiment 1 except for the following features:

After desolventization, the feed solution contained 23% solvent.

Comparative Example 1

This comparative example is the same as Example 1 except for the following features:

No stabilizer is used, and there is no stabilizer configuration kettle. The first filtered mother liquor of the first crystallization purification device directly enters the desolventizing tower (not shown).

Comparative Example 2

This comparative example is the same as Example 1 except for the following features:

In the desolventizing tower, the feed liquid contains 5% solvent after desolventizing.

The analytical method used for PPDI of the present invention is:

The quality and purity of the primary precipitated PPDI crystals and the secondary precipitated PPDI crystals obtained in the above embodiments and comparative examples are shown in the following table.

Table 2

Compared with the examples, in Comparative Example 1, no stabilizer was used, and the bottom material produced urea impurities at high temperature, resulting in excessive solid impurities in P2 (secondary precipitated PPDI crystals), which was unqualified in quality, and only the yield of P1 (primary precipitated PPDI crystals) was calculated. In Comparative Example 2, due to the low amount of residual solvent in the desolventizing tower, the bottom fluidity was too poor to discharge the material, and the impurity content of P2 could not be detected, and only the yield of P1 could be calculated.

Claims (14)

1. A method for providing p-phenylene diisocyanate, characterized in that it comprises: a phosgene removal tower (1), a centrifugal device (2), a first crystallization purification device (3), a stabilizer preparation kettle (4), a desolventizing tower (5), and a second crystallization purification device (6) which are connected in sequence; PPDI photochemical liquid is transported to the dephosgene removal tower (1), light components are extracted from the tower top, and the degassed liquid extracted from the tower bottom is transported to the centrifugal device (2), and the obtained centrifuged liquid is transported to the first crystallization purification device (3), and after cooling, crystallization and washing, primary precipitated PPDI crystals, primary washing liquid and a first filtered mother liquor are obtained, and the first filtered mother liquor is transported to the stabilizer preparation kettle (4), and after adding a stabilizer, the obtained stabilizer-containing liquid is transported to the desolventizing tower (5), and after removing most of the solvent, the obtained desolventized liquid is transported to the second crystallization purification device (6), and after cooling, crystallization and washing, secondary precipitated PPDI crystals, secondary washing liquid and a second filtered mother liquor are obtained. 2. The method according to claim 1 is characterized in that the operating pressure of the phosgene removal tower (1) is 0.5 bar to 2.0 bar, the number of theoretical plates is 5 to 15, and the bottom temperature is 80 to 120°C. 3. The method according to claim 1 is characterized in that the first crystallization purification device (3) and the second crystallization purification device (6) both include a cooling crystallization kettle and a plate and frame filter press. 4. The method according to claim 1 is characterized in that in the first crystallization purification device (3), the starting point of the cooling crystallization temperature is 40-120°C and the end point is -20-0°C; in the second crystallization purification device (6), the starting point of the cooling crystallization temperature is 90-120°C and the end point is -20-0°C. 5. The method according to claim 1, characterized in that the mass ratio of the secondary precipitated PPDI crystals to the primary precipitated PPDI crystals is 10 to 20:1. 6. The method according to claim 1, characterized in that the purity of the first precipitated PPDI crystals is ≥ 99.5%, and the purity of the second precipitated PPDI crystals is ≥ 99.9%. 7. The method according to claim 1, characterized in that the stabilizer is selected from one or more of triphenyl phosphite, didodecyl phosphite, and diisooctyl phenyl phosphite, and the amount of the stabilizer added is 1wt% to 10wt% of the PPDI content in the first filtered mother liquor; Preferably, the stabilizer is triphenyl phosphite, and the amount of the stabilizer added is 1.5 wt% to 3 wt% of the PPDI equivalent in the first filtered mother liquor. 8. The method according to claim 1 is characterized in that the theoretical number of plates of the desolventizing tower (5) is 10 to 20, the operating pressure of the desolventizing tower (5) is 0.05 bar to 0.3 bar, and the stabilizer-containing liquid is fed into the desolventizing tower (5) from the 8th to 12th plates. 9. The method according to claim 1, characterized in that the feed liquid after desolventization contains 10% to 25% of solvent. 10. The method according to claim 1, characterized in that the secondary washing liquid is partially applied to the first crystallization purification device (3) as a washing agent for the first crystallization purification device (3); Preferably, the washing agent of the first crystallization purification device (3) is entirely from the secondary washing liquid. 11. The method according to claim 1, characterized in that when the heavy component impurities in the secondary washing liquid are ≥ 0.15%, the secondary washing liquid is discarded. 12. The method according to claim 1 is characterized in that the mass ratio of the amount of detergent used in the second crystallization purification device (6) to the second precipitated PPDI crystals is 2 to 8:1; the mass ratio of the amount of detergent used in the first crystallization purification device (3) to the second precipitated PPDI crystals is 5 to 10:1. 13. The method according to claim 1, characterized in that the second filtered mother liquor is applied to the stabilizer preparation kettle (4). 14. A device for providing p-phenylene diisocyanate, characterized in that it comprises: a dephosgene tower (1), a centrifugal device (2), a first crystallization purification device (3), a stabilizer configuration kettle (4), a desolventizing tower (5), and a second crystallization purification device (6) connected in sequence, wherein the bottom material outlet of the dephosgene tower (1) is connected to the feed port of the centrifugal device (2), the material outlet of the centrifugal device (2) is connected to the feed port of the first crystallization purification device (3), the discharge port of the first crystallization purification device (3) is connected to the feed port of the stabilizer configuration kettle (4), the discharge port of the stabilizer configuration kettle (4) is connected to the middle feed port of the desolventizing tower (5), and the bottom discharge port of the desolventizing tower (5) is connected to the feed port of the second crystallization purification device (6).