An extractive distillation method for separating the formate-n-propanol azeotrope using [EMIM][AC].

Abstract

This invention relates to a homogeneous extractive distillation method for separating the formate-n-propanol azeotrope using [EMIM][AC], belonging to the field of special distillation technology containing ionic liquids. The method includes the following steps: a mixture of formate and n-propanol is fed into an extractive distillation column; the ionic liquid 1-ethyl-3-methylimidazolium acetate ([EMIM][AC]) is added from the top of the column, and extractive distillation is performed inside the column. Formate is obtained at the top of the column, and a mixture of n-propanol and the ionic liquid is obtained at the bottom. The bottom stream is sequentially fed into a primary flash tank and a secondary flash tank for fractional flash evaporation recovery. The n-propanol-rich vapor phases obtained from the tops of the primary and secondary flash tanks are condensed and then combined to obtain the n-propanol product. The regenerated ionic liquid obtained from the bottom of the secondary flash tank is recycled back to the extractive distillation column for reuse. This method has the advantages of simple process, high separation efficiency, and recyclability of the ionic liquid.

Description

Technical Field

[0001] This invention relates to the field of azeotropic mixture separation technology, and specifically to an extractive distillation method for separating the formate-n-propanol azeotrope using [EMIM][AC]. Background Technology

[0002] n-Propyl formate and n-propanol are important organic chemical raw materials and solvents, with wide applications in fine chemicals, pharmaceuticals, fragrances, and organic synthesis. A mixture of n-propyl formate and n-propanol is often formed during related production and use processes. Because n-propyl formate and n-propanol form an azeotrope or exhibit difficult-to-separate properties, conventional distillation methods are often insufficient for efficient separation, typically resulting in long processes, high energy consumption, and limited product purity.

[0003] Extractive distillation is an effective method for separating azeotropic and near-boiling substances. By introducing a suitable extractant, the relative volatility between components in the original system can be altered, thereby achieving the separation of the target component. Ionic liquids have advantages such as low vapor pressure, good thermal stability, high designability, and convenient recycling, and are therefore considered a class of green extractants with application potential in extractive distillation.

[0004] For extractive distillation processes involving ionic liquid systems, the recovery and regeneration of the ionic liquid remains a critical issue. Conventional high-temperature distillation methods often require high reboiler temperatures, resulting in high energy consumption and the potential for thermal decomposition of some ionic liquids, impacting their recyclability. Conversely, low-pressure distillation significantly increases the demand for a low-temperature cooling source at the condenser, raising cooling resource consumption and operating costs. Therefore, it is necessary to develop an extractive distillation method suitable for the formate-n-propanol azeotropic system, capable of achieving high-purity separation and facilitating the gentle recovery and regeneration of the ionic liquid. Summary of the Invention

[0005] This invention provides an extractive distillation method for separating the formate-n-propanol azeotrope using [EMIM][AC]. This method uses the ionic liquid 1-ethyl-3-methylimidazolium acetate ([EMIM][AC]) as the extractant, combining extractive distillation with multi-stage flash evaporation recovery to achieve efficient separation of formate and n-propanol, and to enable the recycling of the ionic liquid.

[0006] The apparatus of the method described in this invention mainly includes: an extractive distillation column (EDC), a primary flash tank (FL1), a secondary flash tank (FL2), a first condenser (C1), a second condenser (C2), and a circulation pump. The feed mixture flows into the lower part of the extractive distillation column, while [EMIM][AC] enters the upper part. Propyl formate is collected from the top of the column. The bottom stream flows into the primary and secondary flash tanks for flash separation. The propanol-enriched vapor phase obtained from the top of the flash tank is condensed and then combined and collected. The regenerated ionic liquid obtained from the bottom of the secondary flash tank is recycled back to the extractive distillation column.

[0007] In this invention, the feed rate of the mixture of n-propyl formate and n-propanol is 100 kmol / h, wherein the molar ratio of n-propyl formate to n-propanol is 1:1; the feed temperature is 25–45 °C, and the feed pressure is 1.1–1.3 atm. The temperature of the recirculated [EMIM][AC] before entering the extractive distillation column is 70–90 °C, and the pressure is 1.1–1.3 atm.

[0008] In this invention, the theoretical number of plates in the extractive distillation column is 30–36; the feed position of the feed mixture is on the 13th–16th plate; the feed position of [EMIM][AC] is on the 2nd plate; the reflux ratio is 0.90–2.00; and the flow rate of the circulating [EMIM][AC] entering the extractive distillation column is 45–50 kmol / h. Within this range, [EMIM][AC] can fully contact the feed mixture, which is beneficial to improving the separation effect of n-propyl formate and n-propanol. Similarly, existing ionic liquid extractive distillation patents usually also specify the theoretical number of plates, feed position, reflux ratio, and extractant dosage as ranges to form a more stable protection range.

[0009] In this invention, the operating temperature of the first-stage flash tank FL1 is 140–160 °C, and the operating pressure is 5–10 kPa; the operating temperature of the second-stage flash tank FL2 is 170–180 °C, and the operating pressure is 0.04–0.05 kPa. By setting a temperature and pressure gradient between the two flash tanks, the n-propanol in the bottom stream is vaporized and recovered in stages, while the ionic liquid is regenerated under milder conditions and returned to the extractive distillation column. This avoids the risk of thermal decomposition and high energy consumption associated with high-temperature distillation for recovering ionic liquids.

[0010] In this invention, the molar purity of the formate product obtained from the top of the extractive distillation column is 0.999, and the molar purity of the n-propanol product is 0.999; the molar fraction of [EMIM][AC] in the circulating ionic liquid obtained from the bottom of the secondary flash tank is 0.995 to 0.997; and the flow rate of the fresh [EMIM][AC] added is 0.01 to 0.10 kmol / h.

[0011] Compared with the prior art, the present invention has the following beneficial effects: Using [EMIM][AC] as an extractant can significantly improve the separation effect of the formate-n-propanol azeotropic system, achieving high-purity separation of the two target products.

[0012] By employing a process that combines extractive distillation with two-stage flash evaporation, the regeneration and recycling of ionic liquids can be achieved while ensuring separation efficiency.

[0013] Compared to high-temperature distillation for recovering ionic liquids, this invention helps reduce the risk of thermal decomposition of ionic liquids and reduces system energy consumption.

[0014] The present invention has a simple process and requires a low amount of extractant, and has good prospects for industrial application. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of an extractive distillation process for separating the formate-n-propanol azeotrope using [EMIM][AC] according to the present invention. In the diagram, EDC is the extractive distillation column, FL1 is the first-stage flash tank, FL2 is the second-stage flash tank, C1 and C2 are condensers, FEED is the feed stream, IL is the ionic liquid feed stream, D1 is the formate product stream, D2 and D3 are the n-propanol enriched vapor phase streams, W1 is the bottom stream of the extractive distillation column, W2 is the bottom stream of the first-stage flash tank, and W3 is the bottom circulating stream of the second-stage flash tank. Detailed Implementation

[0016] Example 1: The feed flow rate is 100 kmol / h, and the feedstock is a mixture of n-propyl formate and n-propanol, with each component at 50 kmol / h. The feedstock enters the extractive distillation column EDC via a FEED stream at a feed temperature of 35 °C and a feed pressure of 1.2 atm. Recycled ionic liquid and replenished fresh ionic liquid are mixed and then enter the extractive distillation column via an IL stream at a temperature of 80 °C and an inlet pressure of 1.2 atm.

[0017] The extractive distillation column EDC has a theoretical number of 33 plates. The feed stream FEED enters from the 14th plate, and [EMIM][AC] enters from the 2nd plate, with a reflux ratio of 0.987. The circulating [EMIM][AC] flow rate is 49.5 kmol / h. The total flow rate of stream IL is 49.686 kmol / h, of which [EMIM][AC] is 49.5 kmol / h and n-propanol is 0.186 kmol / h. Stream D1, collected from the top of the extractive distillation column EDC, is the n-propyl formate product stream, with a total flow rate of 50.05 kmol / h, of which n-propyl formate is 50 kmol / h and n-propanol is 0.05 kmol / h, resulting in a n-propyl formate mole fraction of 0.999. Stream W1, collected from the bottom of the extractive distillation column EDC, is sent to the first-stage flash tank FL1. The total flow rate of stream W1 was 99.636 kmol / h, of which [EMIM][AC] was 49.5 kmol / h and n-propanol was 50.136 kmol / h.

[0018] The operating temperature of the primary flash evaporator FL1 is 160 °C, and the operating pressure is 10 kPa. After primary flash evaporation, stream D2 is obtained from the top, and stream W2 is obtained from the bottom. The total flow rate of stream D2 is 39.056 kmol / h, and the mole fraction of n-propanol is 0.999. The total flow rate of stream W2 is 60.58 kmol / h, of which [EMIM][AC] is 49.5 kmol / h, n-propanol is 11.08 kmol / h, and the mole fraction of [EMIM][AC] is 0.817. Stream W2 from the bottom of the primary flash evaporator FL1 enters the secondary flash evaporator FL2.

[0019] The operating temperature of the secondary flash evaporator FL2 is 180.000 ℃, and the operating pressure is 0.045 kPa. After secondary flash evaporation, stream D3 is obtained from the top, and stream W3 is obtained from the bottom. Stream D3 has a total flow rate of 10.936 kmol / h, of which n-propanol is 10.894 kmol / h, [EMIM][AC] is 0.043 kmol / h, and the mole fraction of n-propanol is 0.996. Stream W3 has a total flow rate of 49.644 kmol / h, of which [EMIM][AC] is 49.457 kmol / h, n-propanol is 0.186 kmol / h, and the mole fraction of [EMIM][AC] is 0.996. This stream is pumped and cooled before being returned to the front-end process as a circulating ionic liquid.

[0020] The top stream D2 from the first-stage flash evaporator FL1 enters the first condenser C1 for condensation. After condensation, a liquid stream and a tail stream are obtained. The total liquid flow rate in the first condenser is 39.051 kmol / h, of which n-propanol is 39.047 kmol / h, with a n-propanol mole fraction of 0.999. The top stream D3 from the second-stage flash evaporator FL2 enters the second condenser C2 for condensation. After condensation, a liquid stream and a tail stream are obtained. The total liquid flow rate in the second condenser is 10.938 kmol / h, of which n-propanol is 10.894 kmol / h, [EMIM][AC] is 0.043 kmol / h, with a n-propanol mole fraction of 0.996.

[0021] The liquid product streams from the first condenser C1 and the second condenser C2 merge to form the final n-propanol product stream 13. The total flow rate of stream 13 is 49.989 kmol / h, of which n-propanol is 49.941 kmol / h, [EMIM][AC] is 0.043 kmol / h, and the mole fraction of n-propanol is 0.999. The bottom stream W3 from the secondary flash evaporator FL2 forms a circulating ionic liquid stream via a subsequent circulation unit, and is replenished with fresh [EMIM][AC] to form stream IL, which re-enters the extractive distillation column EDC. The total flow rate of the circulating ionic liquid stream is 49.644 kmol / h, [EMIM][AC] is 49.457 kmol / h, and the replenished fresh [EMIM][AC] flow rate is 0.043 kmol / h.

[0022] Under the above operating conditions, the molar purity of both n-propyl formate product stream D1 and n-propanol product stream 13 reached above 0.999.

[0023] In this embodiment, both the primary flash tank FL1 and the secondary flash tank FL2 operate under low-pressure conditions. By combining extractive distillation with two-stage flash evaporation, high-purity separation of n-propyl formate and n-propanol is achieved, and the recycling of [EMIM][AC] is realized.

Claims

1. An extractive distillation method for separating the formate-n-propanol azeotrope using [EMIM][AC], characterized in that, The process includes the following steps: A mixture of n-propyl formate and n-propanol is fed into an extractive distillation column. An ionic liquid, 1-ethyl-3-methylimidazolium acetate ([EMIM][AC]), is fed into the upper part of the extractive distillation column for extractive distillation. The top of the column yields n-propyl formate, and the bottom yields a mixture of n-propanol and [EMIM][AC]. The bottom mixture is fed into a primary flash evaporator for flash separation. The top of the primary flash evaporator yields a propanol-enriched vapor phase, and the bottom yields a mixture containing [EMIM][AC] and n-propanol. The bottom mixture from the primary flash evaporator is fed into a secondary flash evaporator for further flash separation. The top of the secondary flash evaporator yields a propanol-enriched vapor phase, and the bottom yields regenerated [EMIM][AC]. The propanol-enriched vapor phases obtained from the tops of the primary and secondary flash evaporators are condensed and then combined to obtain the n-propanol product. The regenerated [EMIM][AC] obtained from the bottom of the secondary flash evaporator is returned to the extractive distillation column for recycling.

2. The method according to claim 1, characterized in that: The feed flow rate of the mixture of n-propyl formate and n-propanol is 100 kmol / h, with 50 kmol / h of each (n-propyl formate and n-propanol), a feed temperature of 35 °C, and a feed pressure of 1.2 atm. The feed flow rate of the circulating [EMIM][AC] is 49.5 kmol / h, the feed temperature is 80 °C, the pressure is 1.2 atm, and the fresh [EMIM][AC] added is 0.043 kmol / h.

3. The method according to claim 1, characterized in that: The extractive distillation column has 33 theoretical plates. The feed mixture enters from the 14th plate, and the recycle [EMIM][AC] enters from the 2nd plate, with a reflux ratio of 0.

987.

4. The method according to claim 1, characterized in that: The operating temperature of the first-stage flash tank is 160 °C and the operating pressure is 10 kPa. The operating temperature of the second-stage flash tank is 180 °C and the operating pressure is 0.045 kPa. The mole fraction of [EMIM][AC] in the circulating ionic liquid obtained at the bottom of the second-stage flash tank is 0.

996.

5. The method according to claim 1, characterized in that: The molar purity of the n-propyl formate product is not less than 0.999, and the molar purity of the n-propanol product is not less than 0.999.

Images