Process and apparatus for rectification purification of chloroformates

Abstract

This invention provides a distillation purification process and equipment for chloroformate, relating to the field of fine chemical separation technology, specifically a distillation purification process and equipment for chloroformate. This application aims to solve the technical problems in existing chloroformate purification processes, such as the difficulty in separating impurities due to their similar relative volatility to the main product, and the ease with which the product undergoes thermal decomposition during distillation. The purification process of this application includes: mixing a synthesis liquid containing chloroformate and chloroalkane impurities with an azeotropic agent and feeding it into an azeotropic distillation column; performing azeotropic distillation at a pressure below atmospheric pressure; the azeotropic agent and chloroalkane impurities forming an azeotrope is collected from the top of the column; the bottom temperature is controlled at 70-80°C; and the chloroformate product is collected from the bottom of the column. The purification equipment of this invention includes an azeotropic distillation column, a pressure reducing device, and a heating device. The azeotropic distillation column is provided with a feed inlet, a top outlet, and a bottom outlet.

Description

Technical Field

[0001] This invention relates to the field of fine chemical separation technology, specifically to a distillation purification process and equipment for chloroformate. Background Technology

[0002] Chloroformates, especially long-chain alkyl esters represented by 2-ethylhexyl chloroformate, are high-end organic synthesis intermediates with significant applications in polymer initiators, pharmaceuticals, pesticides, and advanced materials. To obtain high-purity products meeting material-grade application requirements, a combined production process of phosgenation reaction and subsequent purification is typically employed. The mainstream preparation route uses fatty alcohols and phosgene as raw materials, esterifying them in a reactor to produce crude esters. After removing unreacted phosgene through photochemical treatment, the crude product is separated and purified.

[0003] However, existing technical solutions have limitations in practical applications. First, the crude ester system contains impurities with relative volatility close to the target product, resulting in low separation efficiency using conventional distillation. Second, chloroformates are heat-sensitive substances; increasing the temperature or extending the residence time during conventional distillation easily induces exothermic decomposition reactions, reducing product yield and generating new impurities that contaminate the bottom product. Furthermore, the traditional batch reactor combined with batch distillation production method suffers from low efficiency in unit operation integration, high overall energy consumption per unit product, and difficulty in controlling the stability of quality indicators between batches. Summary of the Invention

[0004] The present invention aims to solve the technical problems of low separation efficiency, easy thermal decomposition of products, high comprehensive energy consumption per unit product, and difficulty in controlling batch quality stability in the purification process of chloroformate in the prior art. The present invention provides a distillation purification process and equipment for chloroformate, so as to at least partially solve the problems mentioned in the background art.

[0005] The technical solution adopted by this invention is as follows: The first aspect provides a distillation and purification process for chloroformate, comprising the following steps: The synthesis solution containing chloroformate and chloroalkane impurities is mixed with an azeotropic agent to form a mixture to be separated; The mixture to be separated is fed into an azeotropic distillation column for azeotropic distillation, where the azeotropic agent forms an azeotrope with the chlorinated alkane impurities. Azeotropic distillation is carried out at a pressure below atmospheric pressure, and the bottom temperature of the azeotropic distillation column is controlled at 70-80°C. The light component containing the azeotrope and azeotropic agent is collected from the top outlet of the column, and the chloroformate product is collected from the bottom outlet of the column.

[0006] Furthermore, the synthesis solution is prepared by a two-step phosgenation reaction, which includes a low-temperature reaction at -5 to 25°C, followed by a high-temperature reaction at 30 to 70°C.

[0007] Furthermore, the azeotropic agent is N,N-dimethylformamide or toluene.

[0008] Furthermore, the mass ratio of the synthesis liquid to the azeotropic agent is 1:0.05 to 0.15, the operating pressure of the azeotropic distillation is 1 to 5 kPa, the theoretical number of plates in the azeotropic distillation column is 10 to 30, and the reflux ratio is 1 to 3:1.

[0009] Furthermore, it also includes: sending the light components containing azeotropic substances and azeotropic agents collected from the top outlet of the column into an azeotropic agent recovery column, and after rectification and separation, recycling the recovered azeotropic agent back to the azeotropic distillation column.

[0010] Furthermore, the azeotropic distillation column is a partitioned column, with vertical partitions inside to divide the column into a pre-separation section and a main separation section, and the chloroformate product is drawn out from the side stream outlet.

[0011] Furthermore, the azeotropic distillation column integrates a mechanical vapor recompression heat pump system, which compresses and heats the vapor at the top of the column to serve as the heat source for the reboiler in the bottom of the column.

[0012] Furthermore, azeotropic distillation is carried out in a supergravity distillation machine, which generates a supergravity field through rotor rotation to enhance the mass transfer process.

[0013] A second aspect of the present invention provides a distillation purification apparatus for chloroformate, comprising: an azeotropic distillation column, having an inlet for receiving a mixture formed by a synthesis liquid containing chloroformate and chloroalkane impurities and an azeotropic agent, a top outlet for collecting a light component containing the azeotrope and the azeotropic agent, and a bottom outlet for collecting the chloroformate product. A pressure reducing device, connected to the azeotropic distillation column, is used to maintain the azeotropic distillation column at a pressure below atmospheric pressure. A heating device is used to control the bottom temperature of the azeotropic distillation column to 70–80°C.

[0014] Furthermore, it also includes a mechanical vapor recompression heat pump system integrated with an azeotropic distillation column; Alternatively, the azeotropic distillation column may be a partitioned column, with vertical partitions inside and a side outlet for extracting chloroformate products. Alternatively, the equipment may include a gravity distillation unit, which replaces the azeotropic distillation column.

[0015] Beneficial effects: This invention addresses the challenge of separating chloroformate and chloroalkanes using conventional distillation by introducing an azeotropic agent into the chloroformate synthesis solution. This alters the relative volatility between the chloroalkane impurities and the target product, chloroformate, within the separation system. The azeotropic agent forms a low-boiling-point azeotrope with the chloroalkane impurities, allowing for effective distillation of the impurities as an azeotrope from the top of the column at temperatures significantly below the boiling point of chloroformate. This design effectively overcomes the technical difficulty of separating chloroformate and chloroalkanes by conventional distillation due to their similar relative volatility, resulting in a chloroformate product with material-grade purity.

[0016] On the other hand, since the entire azeotropic distillation process is carried out under reduced pressure and at a lower reboiler temperature, the risk of thermal decomposition of the target product chloroformate due to prolonged exposure to high temperatures is greatly avoided. This eliminates the vicious cycle caused by the generation of new impurities through decomposition and significantly improves the product yield and quality stability. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the chloroformate distillation and purification process of the present invention; Figure 2 This is a schematic diagram of the azeotropic distillation column structure of the present invention; Figure 3 This is a schematic diagram of the MVR heat pump integrated device of the present invention; Figure 4 This is a schematic diagram of the internal structure of the azeotropic distillation column (divider column) of the present invention; Figure 5 This is a schematic diagram of the cross-sectional structure of the supergravity distillation machine of the present invention.

[0018] The components are as follows: 1. Azeotropic distillation column; 2. Feed inlet; 3. Top outlet; 4. Bottom outlet; 5. Top condenser; 6. Reflux tank; 7. Reflux pump; 8. Bottom reboiler; 9. Heating device; 10. Pressure reducing device; 11. Static mixer; 12. Condenser; 13. Bottom liquid pump; 14. Vertical baffle; 15. Pre-separation section; 16. Main separation section; 18. Common rectification section; 19. Common stripping section; 20. Side stream outlet; 21. Compressor; 22. Evaporator-condenser heat exchanger; 23. Working fluid condenser; 24. Throttling valve; 25. Circulating working fluid loop; 26. High gravity distillation machine; 27. Casing; 28. Rotor; 29. ​​Liquid distributor; 30. Drive motor; 31. Azeotropic agent recovery column; 32. Phosgene reaction vessel; 33. Phosgene degassing column.

[0019] The accompanying drawings are provided to further understand the embodiments and form part of the specification. They are used together with the embodiments for explanation and do not constitute a limitation on the embodiments. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection.

[0021] In the description of the embodiments, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing the embodiments and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments.

[0022] In the industrial production of chloroformates, taking 2-ethylhexyl chloroformate as an example, the crude synthesis liquid obtained after phosgenation and photocatalytic treatment typically contains approximately 1-1.5 wt% isooctane chloroformate, 0.2-0.5 wt% diisooctyl carbonate, and a small amount of unreacted isooctyl alcohol, in addition to the main product. The relative volatility of isooctane chloroformate and the main product 2-ethylhexyl chloroformate is close to 1. Conventional vacuum distillation requires extremely high theoretical plate numbers and large reflux ratios, leading to reboiler temperatures easily exceeding 90°C. Furthermore, 2-ethylhexyl chloroformate has poor thermal stability and is prone to decomposition at high temperatures, which not only reduces product yield but also increases the potential for environmental pollution due to the decomposition products. Therefore, this application provides a purification process that can effectively separate near-boiling point impurities and inhibit product thermal decomposition.

[0023] Specifically, such as Figures 1-5 As shown, a distillation purification process for chloroformate includes the following steps: mixing a synthesis liquid containing chloroformate and chloroalkane impurities with an azeotropic agent to form a mixture to be separated; feeding the mixture to be separated into an azeotropic distillation column 1 for azeotropic distillation, where the azeotropic agent and chloroalkane impurities form an azeotrope; under reduced pressure, controlling the bottom temperature of the azeotropic distillation column 1 to 70-80°C, collecting a light component containing the azeotrope and the azeotropic agent from the top outlet 3, and collecting the chloroformate product from the bottom outlet 4.

[0024] Specifically, the synthesis solution is prepared by reacting isooctyl alcohol and phosgene through a phosgenation reaction.

[0025] In this embodiment, the synthesis liquid is prepared by a two-step phosgenation reaction to reduce the initial content of chloroalkane impurities and alleviate the subsequent separation load. The azeotropic agent is selected from N,N-dimethylformamide or toluene. Taking toluene as an example, toluene and chloroisooctane can form a minimum azeotrope with an azeotropic point of approximately 40-46°C, which is significantly lower than the boiling point of the main product, 2-ethylhexyl chloroformate. In the mixing step, the mass ratio of the synthesis liquid to the azeotropic agent is controlled within the range of 1:0.05-0.15. For example, 100 kg of the synthesis liquid and 10 kg of toluene are thoroughly mixed in a static mixer 11 to form the mixture to be separated.

[0026] The mixture to be separated is fed into the central feed inlet 2 of the azeotropic distillation column 1 via a feed pump. The azeotropic distillation column 1 is a packed column structure, filled with corrugated metal wire mesh packing with a specific surface area of ​​800-1200 m² / m³ and a plate height as low as 0.2-0.4 m, which can effectively enhance the gas-liquid mass transfer process.

[0027] The tower body is equipped with a heating device 9 and a vacuum system connected to a pressure reducing device 10. During operation, the pressure reducing device 10 maintains the absolute pressure inside the tower within a pressure reduction range of 1–5 kPa. The heating device 9 regulates the flow rate of the heat transfer medium to stably control the liquid phase temperature at the bottom of the tower between 70 and 80°C. Under these operating conditions, the rising vapor and descending liquid exchange heat and mass on the surface of the packing material. Since the boiling point of the azeotrope formed by the azeotropic agent and chloroisooctane is much lower than that of the main product, the azeotrope preferentially vaporizes and accumulates at the top of the tower. After being condensed by the top condenser 5, a portion enters the reflux tank 6, while another portion is returned to the top of the tower as reflux liquid via the reflux pump 7. The reflux ratio is controlled at 1–3:1, and a portion is continuously collected as a light component.

[0028] The content of chloroisooctane in the liquid phase at the bottom of the column continuously decreases, and finally, high-purity chloroformate product is continuously collected from the bottom outlet 4 via the bottom liquid pump 13. Gas chromatography analysis shows that the product purity can consistently reach over 99%. Optimizing the production process effectively improves product purity and ensures product quality.

[0029] It should be noted that the working principle of this purification process is as follows: by using an azeotropic agent to form a minimum azeotrope with the difficult-to-separate chloroalkane impurities, the relative volatility relationship of the components to be separated is changed thermodynamically, so that the impurities that originally had a boiling point similar to the main product can be preferentially distilled out in the form of a low-boiling-point azeotrope in a lower temperature range.

[0030] The operating temperature of the distillation column is strictly controlled below 80℃, which is far below the temperature threshold for significant thermal decomposition of chloroformate—the boiling point of methyl chloroformate is 71.4℃. Furthermore, the triphosgene commonly used in the preparation of chloroformate is stable at room temperature, and only a small amount of decomposition occurs even when the melting point is close to 80℃. Therefore, thermal degradation of the product during the distillation process is effectively avoided.

[0031] Furthermore, in some embodiments, during the synthesis of chloroformate, the conventional one-step phosgenation reaction is usually carried out at a constant temperature, and the content of chloroalkanes generated by the side reaction is relatively high, which increases the separation burden and energy consumption of the subsequent distillation unit.

[0032] In this embodiment, a two-step phosgenation reaction is used to prepare the synthesis liquid. The method consists of two stages: the first stage is a low-temperature reaction, with the temperature controlled between -5 and 25°C; the second stage is a high-temperature reaction, with the temperature controlled between 30 and 70°C.

[0033] Specifically, in the first low-temperature reaction stage, a measured amount of isooctanol is added to the phosgenation reactor 32, phosgene is introduced, and the temperature of the reaction solution is controlled within the range of 15-20°C using chilled brine, and the reaction continues for 3-6 hours. The lower reaction temperature allows the main reaction (chloroformate formation reaction) to dominate the rate, while effectively suppressing the rate of the side reaction (chloroisooctane formation reaction). In the second high-temperature reaction stage, the temperature of the reaction solution is gradually increased to 30-70°C, and phosgene is introduced again, continuing the reaction for 1-7 hours to promote the complete conversion of the trace amounts of isooctanol remaining in the system. After the reaction is completed, nitrogen is introduced into the photocatalytic degassing tower 33 at 30-50°C for photocatalytic removal to remove dissolved unreacted phosgene from the system, yielding the synthesis solution to be purified.

[0034] This embodiment significantly reduces the initial content of chloroalkane impurities in the synthesis solution from the reaction source, simplifies the impurity composition of the subsequent azeotropic distillation system, and creates more favorable initial conditions for efficient purification.

[0035] Furthermore, in some embodiments, the selection of the azeotropic agent is one of the key factors in the success or failure of the azeotropic distillation process. In this embodiment, toluene can be selected as the azeotropic agent. Toluene has a boiling point of 110.6°C, and the azeotrope formed with isooctane has a boiling point of approximately 40–46°C. The main product, isooctyl chloroformate, has a boiling point of 106–107°C / 30 mmHg, which translates to a boiling point of approximately 220°C at atmospheric pressure. The difference between the azeotropic point and the boiling point of the main product exceeds 150°C, providing a sufficient temperature operating window for distillation separation.

[0036] Another azeotropic agent that can be used is N,N-dimethylformamide, which is suitable for material-grade applications with stringent requirements for aromatic hydrocarbon residues in the product. (This sentence is correct.)

[0037] Furthermore, in some embodiments, the mass ratio of the synthesis liquid to the azeotropic agent is 1:0.05 to 0.15, the operating pressure of the azeotropic distillation is 1 to 5 kPa, the theoretical number of plates in the azeotropic distillation column 1 is 10 to 30, and the reflux ratio is 1 to 3:1.

[0038] In other words, when the feed rate of the synthesis liquid is 1000 kg / h and the feed rate of the azeotropic agent toluene is 100 kg / h, the mass ratio is 1:0.1. With the operating pressure of azeotropic distillation column 1 maintained at approximately 2 kPa, the column is packed with structured packing equivalent to 20 theoretical trays, and the reflux ratio at the top is set to 2:1. Under these operating parameters, the measured top temperature is 38–42℃, and the bottom temperature is stable at 72–76℃.

[0039] Furthermore, in some embodiments, the process also includes an azeotropic agent recovery step: the light components collected from the top outlet 3 of the column are sent to the azeotropic agent recovery column 31, and after distillation separation, the recovered azeotropic agent is recycled back to the azeotropic distillation column 1.

[0040] In this embodiment, the azeotropic agent recovery column 31 is a conventional distillation column, operating at atmospheric pressure. The light components collected from the top of the column are condensed by condenser 12 and then enter the middle of the azeotropic agent recovery column 31. Distillation separation is achieved by utilizing the approximately 70°C boiling point difference between the azeotropic agent and isooctane. High-purity azeotropic agent is distilled from the top of the column, and after condensation, part of it is refluxed, while the rest is continuously returned to the azeotropic distillation column 1 for recycling. The bottom of the column periodically collects the enriched isooctane byproduct. By adding a small amount of fresh azeotropic agent, the system's trace losses are compensated, and the recycling rate is improved.

[0041] Furthermore, in some embodiments, for ternary mixture systems containing light impurities, target products, and heavy components simultaneously, the use of a partitioned tower structure can further improve thermodynamic efficiency.

[0042] Specifically, the azeotropic distillation column 1 adopts a partitioned column structure, with vertical partitions 14 inside the column, dividing the column cavity into a pre-separation section 15 and a main separation section 16, and the chloroformate product is collected from the side stream outlet 20.

[0043] In this embodiment, a vertical baffle 14 is installed axially inside the partition column, dividing the column into a feed-side pre-separation section 15 and a product-side main separation section 16. The upper part of the column is a common rectification section 18, and the lower part of the column, after the baffle terminates, is a common stripping section 19. After the mixture to be separated is introduced into the pre-separation section 15, the low-boiling-point azeotrope formed by chloroisooctane and the azeotropic agent flows upward into the common rectification section 18, while the high-boiling-point diester and some chloroformate flow downward. In the main separation section 16, high-purity chloroformate is enriched and continuously collected through the side feed outlet 20. The light azeotrope component is collected from the top of the common rectification section 18, and the heavy component residue is discharged from the bottom of the common stripping section 19. Using a partition column instead of the traditional two-tower process not only saves equipment investment but also further reduces energy consumption.

[0044] Furthermore, in some embodiments, the azeotropic distillation column 1 is integrated with a mechanical vapor recompression heat pump system, which compresses and heats the vapor at the top of the column to serve as the heat source for the reboiler 8 at the bottom of the column.

[0045] Specifically, in this embodiment, an indirect mechanical vapor recompression heat pump system is used. The azeotropic vapor discharged from the top of the azeotropic distillation column 1 first passes through the evaporator-condenser heat exchanger 22, transferring heat to the closed-loop organic working fluid. After absorbing heat, the circulating working fluid vaporizes and then enters the compressor 21; after being compressed to a higher pressure by the compressor 21, the temperature of the gaseous working fluid rises to approximately 90°C to 100°C.

[0046] High-temperature, high-pressure working fluid vapor enters the working fluid condenser 23, where it releases heat to the liquid phase in the bottom of the column as a heating medium. After condensation, the working fluid is depressurized and cooled by the throttling valve 24, returning to the evaporator-condenser heat exchanger 22 to complete the cycle. The circulating working fluid loop 25 connects all the above-mentioned devices, forming a closed-loop system. By adopting an azeotropic distillation unit with this integrated system, the external heating steam consumption is reduced, and the operating energy cost of the distillation operation is significantly decreased.

[0047] Furthermore, in some embodiments, for highly heat-sensitive materials, a supergravity distillation unit 26 can be used instead of a traditional distillation column. Azeotropic distillation is carried out in the supergravity distillation unit 26, which generates a supergravity field through the rotation of the rotor 28 to enhance the mass transfer process.

[0048] Specifically, the supergravity distillation unit 26 includes a casing 27, a rotor 28, a liquid distributor 29, and a drive motor 30. The mixture to be separated is uniformly sprayed onto the central region of the rotor 28 through the liquid distributor 29. Under the influence of the supergravity field generated by the high-speed rotation of the rotor 28, the liquid is forcefully thrown to the outer edge of the rotor 28, forming an extremely thin liquid film and tiny droplets within the packing layer. Vapor flows radially inward from the outer edge of the rotor 28, making countercurrent contact with the liquid film within the packing layer. Under supergravity conditions, the mass transfer rate between the gas and liquid phases is increased by 1 to 2 orders of magnitude compared to a gravity field, and the residence time of the entire gas-liquid contact process is only 0.1 to 1.0 seconds.

[0049] The stripped steam is discharged from the center of rotor 28 and condensed to obtain the light azeotropic component; the separated liquid phase is collected at the bottom of casing 27 and discharged, finally yielding a high-purity chloroformate product.

[0050] This application also provides a distillation purification apparatus for chloroformate, comprising: an azeotropic distillation column 1, which has an inlet 2 for receiving a mixture of synthesis liquid and azeotropic agent, a top outlet 3 for collecting the azeotrope, and a bottom outlet 4 for collecting the chloroformate product; a pressure reducing device 10 connected to the azeotropic distillation column 1 for maintaining a pressure-reduced operating environment inside the column; and a heating device 9 for controlling the bottom temperature of the azeotropic distillation column 1 to 70–80°C. This temperature range is determined based on the azeotropic characteristics and phase equilibrium principle of the system processed by the azeotropic distillation column 1, and is also comprehensively considered in conjunction with indicators such as column pressure and the content of light components in the bottom distillate. In actual operation, the heating capacity of the heating device 9 is adjusted to stabilize the bottom temperature within the set range to ensure the separation effect of the azeotrope.

[0051] Specifically, the azeotropic distillation column 1 is a vertical cylindrical structure made of stainless steel, filled with high-efficiency structured packing. The feed inlet 2 is located in the middle of the column and is connected to the static mixer 11 and the feed pump via a pipeline. The top outlet 3 is connected in sequence via a pipeline to the top condenser 5, the reflux tank 6, and the reflux pump 7. The bottom outlet 4 is connected to the product storage tank via the bottom liquid pump 13.

[0052] The pressure reducing device 10 includes a liquid ring vacuum pump unit, which is connected to the gas phase space at the top of the reflux tank 6 via a suction pipe. The heating device 9 is a shell-and-tube reboiler, with a regulating valve on the heat medium inlet pipeline, which is interlocked with the reboiler temperature transmitter to achieve precise automatic control of the reboiler temperature.

[0053] Furthermore, in some embodiments, the purification equipment also includes a mechanical vapor recompression heat pump system integrated with the azeotropic distillation column 1, the system comprising a compressor 21, an evaporator-condenser heat exchanger 22, a working fluid condenser 23, a throttle valve 24, and a circulating working fluid loop 25.

[0054] Alternatively, a partitioned column can be used to replace the azeotropic distillation column 1. This partitioned column is equipped with vertical partitions 14 and a side-stream outlet 20.

[0055] In some embodiments, a supergravity distillation unit 26 may be used instead of an azeotropic distillation column 1. The supergravity distillation unit 26 includes a casing 27, a rotor 28, a liquid distributor 29, and a drive motor 30.

[0056] To verify the beneficial effects of the technical solution of this application, the following specific embodiments and comparative experiments were conducted using 2-ethylhexyl chloroformate synthesis solution as raw material. It should be noted that the following embodiments and comparative examples are merely illustrative and do not constitute a limitation on the scope of protection of this application.

[0057] Comparative Example 1 Conventional vacuum distillation without azeotropic agents was employed. The feedstock was a chloroformate-2-ethylhexyl ester synthesis solution containing 1.3 wt% isooctane chloro, 0.4 wt% diisooctyl carbonate, and 0.2 wt% unreacted isooctyl alcohol. The operating pressure was 2 kPa, the azeotropic distillation column had 30 theoretical plates, and the reflux ratio was 5:1. The reboiler temperature was gradually increased to observe the separation effect. The results showed that significant enrichment of isooctane chloro only began to appear in the top product when the reboiler temperature reached above 95℃. At this point, the residual isooctane chloro in the product was still higher than 0.8%, and the product purity did not exceed 98.5%. Simultaneously, due to the reboiler temperature exceeding 90℃, significant thermal decomposition occurred in the product, resulting in a product yield of only 85%, a darker color, and the detection of low-boiling-point chloride decomposition products. Comparative Example 2 Without adding an azeotropic agent, the reboiler temperature was controlled at 75±2℃, the operating pressure at 2 kPa, the theoretical number of trays at 30, and the reflux ratio at 5:1. The results showed that, limited by the near-perfect relative volatility of chloroisooctane and chloroformate (approximately 1), effective separation was almost impossible at the reboiler temperature of 75℃. The main product content in the top product exceeded 40%, resulting in significant product loss. The residual chloroisooctane content in the reboiler product remained above 1.0%, and the product purity did not exceed 98.0%.

[0058] Example 1 The synthesis solution and the azeotropic agent toluene were mixed at a mass ratio of 1:0.1 and then fed into an azeotropic distillation column. The operating pressure was 2 kPa, the bottom temperature was controlled at 75±2℃, the theoretical number of plates was 20, and the reflux ratio was 2:1. The azeotrope (boiling point 38~42℃) was collected from the top of the column, and 2-ethylhexyl chloroformate was collected from the bottom. The results showed that the product purity was 99.6%, the residual amount of chloroisooctane was reduced to 0.08%, the product yield was 94.5%, no thermal decomposition products were detected, and the product was a colorless and transparent liquid. Example 2 The synthesis solution was mixed with the azeotropic agent N,N-dimethylformamide (DMF) at a mass ratio of 1:0.1, and the operating conditions were the same as in Example 1. The results showed that the product purity was 99.5%, the residual chloroisooctane was reduced to 0.09%, the product yield was 93.8%, and no thermal decomposition products were detected. The product contained no aromatic hydrocarbon residues, making it particularly suitable for material-grade applications where aromatic hydrocarbon content is strictly limited.

[0059] Examples 3-5: Comparison of different azeotropic agent dosages Using toluene as an azeotropic agent, the mass ratio of the synthesis solution to toluene was 1:0.03, 1:0.10, and 1:0.18, respectively, and the operating conditions were the same as in Example 1. The effect of the amount of azeotropic agent on the separation effect was investigated.

[0060] Table 1: Comparison of Dosage of Different Azeotropic Agents

[0061] The results showed that when the mass ratio of the synthesis liquid to the azeotropic agent was less than 0.05 (Example 3), the amount of azeotropic agent was insufficient to fully carry away impurities, and the product purity was only 98.8%. When the mass ratio was in the range of 0.05 to 0.15 (Example 4), the separation effect was optimal, and the product purity reached 99.6%. When the mass ratio was greater than 0.15 (Example 5), the product purity improved slightly, but the energy consumption for azeotropic agent recovery increased significantly. Therefore, the preferred mass ratio of the synthesis liquid to the azeotropic agent is 1:0.05 to 0.15.

[0062] Examples 6-7: Comparison of different operating pressures Toluene was used as an azeotropic agent, the mass ratio of the synthesis liquid to toluene was 1:0.1, the operating pressures were 5 kPa and 1 kPa, the reboiler temperatures were controlled at 78±2℃ and 72±2℃, and the other conditions were the same as in Example 1. The effect of operating pressure on the separation effect was investigated.

[0063] Table 2: Comparison of Different Operating Pressures

[0064] The results show that effective separation with a product purity of over 99% can be achieved within a pressure range of 1-5 kPa. Lower pressure results in better separation and higher product purity, but also increases the requirements for the vacuum system. Considering both separation performance and industrial implementation costs, 1-5 kPa is the preferred operating pressure range.

[0065] Table 3: Summary and Comparison Table of Experimental Data

[0066] As can be seen from the above experimental data, Comparative Examples 1-2 and Examples 1-2 show that without the addition of an azeotropic agent, even under conditions of a high reflux ratio (5:1) and a high theoretical plate number (30 plates), the product purity is only up to 98.5%, and the residual impurities exceed 0.8%; when the temperature is controlled, the product purity is even lower (98.0%). After introducing the azeotropic agent, under conditions of a moderate theoretical plate number (20 plates) and a low reflux ratio (2:1), the product purity increases to over 99.5%, and the residual impurities decrease to below 0.1%. Simultaneously, the product yield increases from no more than 90% to over 93%, and no thermal decomposition products are detected. This fully demonstrates that the introduction of an azeotropic agent is the key to solving the problem of near-boiling point separation between chloroformates and chloroalkanes, significantly improving both yield and quality while obtaining a high-purity product. As can be seen from Examples 1-2, both toluene and DMF azeotropic agents can effectively separate impurities, and the purity of the products can reach more than 99.5%. The type of azeotropic agent can be flexibly selected according to the product application.

[0067] As shown in Examples 3-5, when the mass ratio of the synthesis solution to the azeotropic agent is less than 1:0.05, the removal of impurities is incomplete; when the mass ratio is in the range of 1:0.05 to 0.15, the separation effect is optimal. This verifies the rationality of the preferred mass ratio range.

[0068] Examples 1, 6, and 7 demonstrate that effective separation with a product purity exceeding 99% can be achieved within an operating pressure range of 1–5 kPa, and the reboiler temperature is consistently controlled below 80°C, effectively preventing product thermal decomposition. This verifies the rationality of the optimized operating pressure range.

[0069] In summary, the technical solution of this application, through the synergistic combination of azeotropic distillation and low-temperature vacuum operation, successfully solves the problem of chloroformate purification in the prior art, and achieves simultaneous improvement in product purity, yield and stability.

[0070] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0071] The embodiments have been described above, and such description is not restrictive. The figures shown are only one embodiment, and the actual structure is not limited to this. In short, if a person skilled in the art is inspired by this description and designs a similar structure and embodiment without departing from the inventive spirit, such design should fall within the scope of protection.

Claims

1. A distillation purification process for chloroformate, characterized in that, Includes the following steps: The synthesis solution containing chloroformate and chloroalkane impurities is mixed with an azeotropic agent to form a mixture to be separated; The mixture to be separated is fed into an azeotropic distillation column for azeotropic distillation, where the azeotropic agent forms an azeotrope with the chlorinated alkane impurities. Azeotropic distillation is carried out at a pressure below atmospheric pressure, and the bottom temperature of the azeotropic distillation column is controlled at 70-80°C. The light component containing the azeotrope and azeotropic agent is collected from the top outlet of the column, and the chloroformate product is collected from the bottom outlet of the column.

2. The distillation purification process for chloroformate according to claim 1, characterized in that, The synthesis solution was prepared by a two-step phosgenation reaction, which included a low-temperature reaction at -5 to 25°C, followed by a high-temperature reaction at 30 to 70°C.

3. The distillation purification process for chloroformate according to claim 1, characterized in that, Azeotropic agents include N,N-dimethylformamide or toluene.

4. The distillation purification process for chloroformate according to claim 1, characterized in that, The mass ratio of the synthesis liquid to the azeotropic agent is 1:0.05 to 0.15, the operating pressure of the azeotropic distillation is 1 to 5 kPa, the theoretical number of plates in the azeotropic distillation column is 10 to 30, and the reflux ratio is 1 to 3:

1.

5. The distillation purification process for chloroformate according to claim 1, characterized in that, Also includes: The light components containing azeotropic substances and azeotropic agents collected from the top outlet of the column are sent to the azeotropic agent recovery column. After distillation separation, the recovered azeotropic agent is recycled back to the azeotropic distillation column.

6. The distillation purification process for chloroformate according to claim 1, characterized in that, The azeotropic distillation column is a partitioned column, which is equipped with vertical partitions to divide the column into a pre-separation section and a main separation section. The chloroformate product is drawn out from the side stream outlet.

7. The distillation purification process for chloroformate according to claim 1, characterized in that, The azeotropic distillation column is integrated with a mechanical vapor recompression heat pump system, which compresses and heats the vapor at the top of the column and uses it as a heat source for the reboiler in the bottom of the column.

8. The distillation purification process for chloroformate according to claim 1, characterized in that, Azeotropic distillation is carried out in a supergravity distillation machine, which generates a supergravity field through rotor rotation to enhance the mass transfer process.

9. A distillation and purification apparatus for chloroformate, characterized in that, include: An azeotropic distillation column is provided with a feed inlet for receiving a mixture of a synthesis liquid containing chloroformate and chloroalkane impurities and an azeotropic agent, a top outlet for collecting light components containing the azeotrope and the azeotropic agent, and a bottom outlet for collecting the chloroformate product. A pressure reducing device, connected to the azeotropic distillation column, is used to maintain the azeotropic distillation column at a pressure below atmospheric pressure. A heating device is used to control the bottom temperature of the azeotropic distillation column to 70–80°C.

10. The distillation and purification apparatus for chloroformate according to claim 9, characterized in that, It also includes a mechanical vapor recompression heat pump system integrated with an azeotropic distillation column; Alternatively, the azeotropic distillation column may be a partitioned column, with vertical partitions inside and a side outlet for extracting chloroformate products. Alternatively, the equipment may include a gravity distillation unit, which replaces the azeotropic distillation column.

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