Dehydration method of raw material 1, 5-pentanediamine in PDI synthesis process by phosgenation method

Abstract

The invention discloses a dehydration method of a raw material 1, 5-pentanediamine in a PDI synthesis process by a phosgenation method, which is characterized by comprising the following steps: firstly, uniformly mixing the raw material 1, 5-pentanediamine and a solvent chlorobenzene according to a mass ratio of 1: 3; secondly, according to the azeotropic distillation principle, water in the mixed material is slowly enriched at the tower top through reduced pressure distillation and tower top total reflux operation modes; thirdly, passing through a tower top oil-water two-phase dynamic separator, and slowly and continuously extracting the enriched water phase (upper layer) from an overflow port at the upper end of the dynamic separator; and then continuously extracting the qualified mixed material dehydrated in the tower kettle from the tower kettle. According to the method, the moisture content of the mixture of the dehydrated raw material 1, 5-pentamethylene diamine and the solvent chlorobenzene is less than or equal to 50ppm, the dehydration efficiency is high, and the operation cost is low. The technical index requirements of a PDI synthesis process by a phosgenation method are completely met.

Description

Technical Field

[0001] This invention belongs to the field of chemical engineering, specifically relating to a dehydration method for 1,5-pentanediamine, a raw material in the phosgenation process for synthesizing PDI. Background Technology

[0002] 1,5-Pentanediamine, as a precursor compound, has a wider range of applications and broader market prospects due to its derivatives. The preparation of PDI using bio-based 1,5-pentanediamine can replace or supplement the three major isocyanates: HDI, MDI, and TDI. It can also be used with traditional polyols to prepare semi-bio-based or fully bio-based polyurethanes. There are generally two methods for producing pentanediamine: one is the chemical synthesis, using glutaronitrile as a raw material, which is first converted to 5-aminopentanilide under the action of a catalyst, and then to pentanediamine. However, the raw materials for this method are becoming increasingly scarce. The other method is the biological synthesis, using biomass such as straw and corn as raw materials, obtained through bio-fermentation. This method has been industrialized.

[0003] Currently, the production of 1,5-pentanediamine in China mainly adopts the biological method, and the production capacity has been scaled up. The biological synthesis process involves water and produces water as a byproduct. Moreover, aliphatic amines have a strong affinity for water, resulting in a high water content (around 1000 ppm) in industrial-grade bio-based 1,5-pentanediamine products. This leads to side reactions and adversely affects product indicators. Summary of the Invention

[0004] The purpose of this invention is to provide a 1,5-pentanediisocyanate raw material with qualified moisture content for the phosgenation synthesis of 1,5-pentanediisocyanate, which can effectively control the side reactions caused by excessive moisture in the raw material 1,5-pentanediisocyanate and the impact on product indicators.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: a method for dehydrating 1,5-pentanediamine, a raw material, in the phosgenation synthesis of PDI, characterized by the following specific steps: Step (1): Using a PDA high-level tank and a solvent high-level tank, the raw material 1,5-pentanediamine and the solvent chlorobenzene are mixed evenly in a mixing tank according to the specified ratio; Step (2): For the first start-up, fill the oil-water two-phase dynamic separator with solvent chlorobenzene until the liquid level is level with the U-shaped sealing line and there is obvious reflux at the top of the distillation column. Step (3): Establish negative pressure in the distillation column using a vacuum system, and stabilize the pressure at -56~-60 kPa; Step (4): Use medium-pressure steam to slowly heat the mixing vessel until a stable total reflux is established at the top of the distillation column; Step (5): After running the full reflux for 1.5~2.0h, take a sample from the mixing vessel to analyze the moisture content of the mixture. The process is complete when the moisture content is ≤50ppm. The dehydrated material is then slowly and continuously extracted from the mixing vessel. Step (6): While the mixing vessel is continuously pumping out the raw material, the PDA high-level tank and the solvent high-level tank are continuously fed into the mixing vessel to maintain a stable liquid level and achieve continuous operation of the dehydration of the raw material 1,5-pentanediamine.

[0006] In step (1), the moisture content of the raw material 1,5-pentanediamine is 800-1000 ppm; the moisture content of the solvent chlorobenzene is ≤50 ppm; the mass ratio of 1,5-pentanediamine to solvent chlorobenzene is 1:3; the dynamic liquid level of the mixture in the mixing vessel is controlled at 75-80%, and the stirring time is controlled at 30-40 min.

[0007] In step (iii), while establishing negative pressure in the distillation column, a unified negative pressure system is simultaneously established in the mixing and stirring vessel, the column top condenser, the oil-water two-phase dynamic separator, and the aqueous phase slow storage tank, with a stable pressure of -56~-60 kPa.

[0008] The total recirculation involved in steps (iv) and (v) has a flow rate control of 120-150 kg / h.

[0009] The working principle of the oil-water two-phase dynamic separator is as follows: See Figure 2 The condensate (a mixture of water and chlorobenzene) from the top condenser slowly (120~150 kg / h) enters the oil-water two-phase dynamic separator from the oil-water mixed phase inlet. After being buffered and slowed by a first-stage baffle plate, the oil and water phases quickly separate: the aqueous phase slowly accumulates in the upper layer of the vertical cylinder of the oil-water two-phase dynamic separator, and when the liquid level rises to the aqueous phase overflow port, it will be continuously overflowed and collected; the oil phase (chlorobenzene) is then buffered by another first-stage baffle plate and will slowly flow out from the oil phase outlet, flowing back to the top of the tower via the U-shaped sealing pipeline Y (see...). Figure 1 This ensures that the lowest liquid level in the oil-water two-phase dynamic separator is above the horizontal line X, which is level with the Y phase of the inverted U-shaped sealing pipeline. The top of the tower operates stably in a full reflux state, enabling continuous enrichment of water in the system and its extraction from the aqueous phase overflow port.

[0010] The beneficial effects of this invention are as follows: By utilizing the solvent chlorobenzene and its feed ratio in the phosgenation synthesis reaction, the indirect dehydration of the raw material 1,5-pentanediamine is achieved through azeotropic distillation, resulting in a PDA water content ≤50ppm. This method boasts high dehydration efficiency, low cost, simple principle, and ease of control. It completely solves the problem of numerous side reactions in the phosgenation synthesis of 1,5-pentanediisocyanate caused by excessive moisture content in the industrial raw material 1,5-pentanediamine, as well as the impact on the acid value, hydrolyzed chlorine, and purity of PDI products. This lays a solid foundation for the industrialization of PDI products. It is suitable for industrial production and has strong practicality and applicability in the industry. Furthermore, it provides a feasible method for dehydrating the raw material PDA in pilot-scale or industrial production of phosgenation synthesis of 1,5-pentanediisocyanate. Attached Figure Description

[0011] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a schematic diagram showing the distribution and flow direction of the oil and water phases in the oil-water two-phase dynamic separator of the present invention.

[0012] In the diagram: 001 - Raw material PDA; 002 - Solvent chlorobenzene; 003 - Dehydrated mixture; 004 - Aqueous phase removed from the top of the column; 005 - Oil phase replacement port; 006 - Vacuum system; V1 - PDA high-level tank; V2 - Solvent high-level tank; V3 - Mixing and stirring vessel; T - Distillation column; E - Top condenser; V4 - Oil-water two-phase dynamic separator; V5 - Aqueous phase slow storage tank; X - Horizontal line; Y - U-shaped sealing pipeline. Detailed Implementation

[0013] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the method of the present invention and are not intended to limit the scope of application of the present invention. Example 1

[0014] See Figure 1 A method for dehydrating 1,5-pentanediamine, a raw material in the phosgenation synthesis of PDI, characterized by the following specific steps: Step (1): Using PDA high-level tank V1 and solvent high-level tank V2, the raw material 1,5-pentanediamine and solvent chlorobenzene are mixed evenly in a mixing vessel V3 at a mass ratio of 1:3; wherein the moisture content of the raw material 1,5-pentanediamine is 800-1000ppm; the moisture content of the solvent chlorobenzene is ≤50ppm; the dynamic liquid level of the mixture in mixing vessel V3 is controlled at 75-80%, and the stirring time is controlled at 30-40min.

[0015] Step (2): For the first start-up, fill the oil-water two-phase dynamic separator V4 with solvent chlorobenzene until the liquid level reaches the horizontal line X, which is level with the inverted U-sealing pipeline Y, and until there is obvious reflux at the top of the distillation column T.

[0016] Step (3): A negative pressure is established for the distillation column T through the vacuum system 006; at the same time, a unified negative pressure system is established for the mixing and stirring vessel V3, the column top condenser E, the oil-water two-phase dynamic separator V4, and the aqueous phase slow storage tank V5, with a stable pressure of -56~-60KPa.

[0017] Step (4): Use medium-pressure steam to slowly heat the mixing vessel (V3) until a stable total reflux is established at the top of the distillation column (T), with the flow rate controlled at 120-150 kg / h.

[0018] Step (5): The flow rate is controlled at 120-150 kg / h. After running in full reflux for 1.5-2.0 h, the mixture is sampled from mixing vessel V3 and the moisture content is ≤50 ppm. The dehydrated material 003 is then slowly and continuously extracted from mixing vessel V3.

[0019] Step (6): While continuously extracting from the mixing tank V3, continuously feed the raw material into the mixing tank V3 through the PDA high-level tank V1 and the solvent high-level tank V2 to maintain the stable liquid level of the mixing tank V3 and realize the continuous operation of the dehydration of the raw material 1,5-pentanediamine.

[0020] Specific process parameters are shown in Table 1.

[0021] Examples 2-4 A dehydration method for 1,5-pentanediamine, a raw material, in the phosgenation synthesis of PDI is described, similar to that in Example 1. Specific process parameters are shown in Table 1.

[0022]

Claims

1. A method for dehydrating 1,5-pentanediamine, a raw material in the phosgenation synthesis of PDI, characterized in that, The specific steps are as follows: Step (1): Using the PDA high-level tank (V1) and the solvent high-level tank (V2), the raw material 1,5-pentanediamine and the solvent chlorobenzene are mixed evenly in a mixing and stirring vessel (V3) in proportion; Step (2): For the first start-up, fill the oil-water two-phase dynamic separator (V4) with solvent chlorobenzene until the liquid level reaches the horizontal line (X) and is level with the inverted U-shaped sealing line (Y), and until there is obvious reflux at the top of the distillation column (T); Step (3): Establish negative pressure in the distillation column (T) through the vacuum system (006), and stabilize the pressure at -56~-60KPa; Step (4): Use medium-pressure steam to slowly heat the mixing vessel (V3) until a stable total reflux is established at the top of the distillation column (T); Step (5): After running the full reflux for 1.5~2.0h, take a sample from the mixing vessel (V3) to analyze the moisture content of the mixture. When the moisture content is ≤50ppm, the dehydrated material (003) is slowly and continuously extracted from the mixing vessel (V3). Step (6): While the mixing vessel (V3) is continuously pumping out, the mixing vessel (V3) is continuously fed into the mixing vessel (V3) through the PDA high-level tank (V1) and the solvent high-level tank (V2) to maintain the stable liquid level in the mixing vessel (V3) and achieve continuous operation of the dehydration of the raw material 1,5-pentanediamine.

2. The dehydration method for 1,5-pentanediamine, a raw material in the phosgenation synthesis of PDI as described in claim 1, characterized in that: In step (1), the moisture content of the raw material 1,5-pentanediamine is 800-1000 ppm; the moisture content of the solvent chlorobenzene is ≤50 ppm.

3. The dehydration method for 1,5-pentanediamine, a raw material, in the phosgenation synthesis of PDI as described in claim 1, characterized in that: In step (i), the mass ratio of 1,5-pentanediamine to solvent chlorobenzene is 1:

3.

4. The method for dehydrating 1,5-pentanediamine, a raw material, in the phosgenation synthesis of PDI as described in any one of claims 1-3, characterized in that: In step (1), the dynamic liquid level of the mixture in the mixing vessel (V3) is controlled at 75-80%, and the stirring time is controlled at 30-40 min.

5. The method for dehydrating 1,5-pentanediamine, a raw material, in the phosgenation synthesis of PDI as described in claim 1, characterized in that: In step (3), while establishing negative pressure in the distillation column (T), a unified negative pressure system is simultaneously established in the mixing and stirring vessel (V3), the column top condenser (E), the oil-water two-phase dynamic separator (V4), and the aqueous phase slow storage tank (V5), with a stable pressure of -56~-60KPa.

6. The method for dehydrating 1,5-pentanediamine, a raw material, in the phosgenation synthesis of PDI as described in claim 1, characterized in that: The total recirculation involved in steps (iv) and (v) has a flow rate control of 120-150 kg / h.

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