An extractive distillation method for separating isobutanol-isobutyl formate azeotrope by using ionic liquid

Abstract

This invention includes an extractive distillation method for separating isobutanol-isobutyl formate azeotrope using ionic liquids. The process flow is as follows: The mixture of isobutanol and isobutyl formate to be separated is preheated and then enters an extractive distillation column. The ionic liquid 1-butyl-3-methylimidazolium acetate ([BMIM][OAC]) enters from the top of the column. High-purity isobutyl formate product is collected from the top of the column, and the mixture of isobutanol and ionic liquid is collected from the bottom of the column. The mixture is subjected to a two-stage flash distillation process to recover the ionic liquid. The vapor streams from the two flash distillations are condensed to obtain the isobutanol product. The ionic liquid regenerated liquid obtained from the bottom of the second flash distillation is introduced from the top of the extractive distillation column as a circulating stream. This process features high product purity, low energy consumption, high thermal efficiency, and environmental friendliness. Furthermore, it requires less equipment, is simple to operate, and is easily applicable to industrial production.

Description

Technical Field

[0001] This invention relates to the field of azeotropic mixture separation technology, and specifically to an extractive distillation method for separating isobutanol-isobutyl formate azeotrope using [BMIM][OAC]. Background Technology

[0002] Isobutanol (IBA) and isobutyl formate (IBF), as important basic chemical raw materials and excellent solvents, readily form a lowest-boiling-point azeotrope under normal pressure during industrial esterification production and related solvent recovery processes. Due to the strong non-ideal nature of the system, conventional distillation techniques lose their driving force near the azeotropic point, making high-purity separation impossible.

[0003] Currently, industrial processes for treating such oxygen-containing organic azeotropic systems mostly employ pressure swing distillation or distillation processes using traditional volatile organic solvents (such as DMSO) as extractants. However, pressure swing distillation is limited by the large pressure differential requirements of the equipment and extremely high steam consumption; while traditional organic extractants not only have weak separation selectivity and require a large solvent ratio, but also, due to their certain saturated vapor pressure, are highly volatile, thus causing secondary contamination of high-purity products.

[0004] Ionic liquids, due to their extremely low saturated vapor pressure, excellent thermal stability, and designability, are ideal green separation media to replace traditional volatile solvents. However, for extractive distillation processes containing ionic liquids, conventional high-temperature distillation methods are not only energy-intensive but also prone to thermal decomposition of the ionic liquids. Therefore, there is an urgent need to develop an extractive distillation process for the isobutanol-isobutyl formate system that offers high selectivity and mild ionic liquid recovery conditions. Summary of the Invention

[0005] This invention provides an extractive distillation method for separating isobutanol-isobutyl formate azeotrope using [BMIM][OAC]. This method uses the ionic liquid 1-butyl-3-methylimidazolium acetate ([BMIM][OAC]) as the extractant. Because [OAC]... - The anion, acting as a strong hydrogen bond acceptor, can form a very strong hydrogen bond association with the hydroxyl group in isobutanol, in addition to [BMIM]. + The relatively long alkyl side chains provide excellent nonpolar space for separation, resulting in a sharp drop in the liquid phase activity coefficient of isobutanol (salt-in effect) and a dramatic increase in the relative volatility of isobutyl formate (salt-out effect). This invention combines the advantages of micro-extraction with a multi-stage flash evaporation recovery process, achieving high-purity separation of the two target products and low-energy regeneration of the extractant.

[0006] The apparatus of the method described in this invention mainly includes: an extractive distillation column (EDC), a primary flash evaporator (FLA1), a secondary flash evaporator (FLA2), and condensers (C1 and C2). The feed mixture flows into the middle of the extractive distillation column, and [BMIM][OAC] enters the upper part of the column. Isobutyl formate is collected from the top of the column. The bottom stream enters the primary and secondary flash evaporators for flash separation. The isobutanol-enriched vapor phase obtained from the flash vapor outlet is condensed and collected to obtain the isobutanol product. The regenerated ionic liquid obtained from the bottom of the secondary flash evaporator is recycled back to the extractive distillation column.

[0007] In this invention, the feed rate of isobutanol and isobutyl formate is 100 kmol / h, with isobutanol and isobutyl formate each accounting for 50 mol%; the feed temperature is 25-35℃, and the feed pressure is 100-150 kPa. The circulating ionic liquid [BMIM][OAC] enters the extractive distillation column at a temperature of 90-100℃, a pressure of 100-150 kPa, and a flow rate of approximately 35-40 kmol / h.

[0008] In this invention, the extractive distillation column is a plate column with 20-25 theoretical plates. The raw material enters from the 13th-16th plate, and the circulating [BMIM][OAC] is added from the second plate of the extractive distillation column. The reflux ratio of the distillation column is 1.0-1.2, the top temperature is 95-105℃, the bottom temperature ranges from 140-150℃, and the pressure ranges from 110-130 kPa.

[0009] In this invention, the operating temperature of the first-stage flash tank is 135-145℃ and the operating pressure is 5-10 kPa; the operating temperature of the second-stage flash tank is -45~-35℃ and the operating pressure is 0.10-0.15 kPa.

[0010] In this invention, the molar concentration of isobutyl formate, the product at the top of the extractive distillation column, is not less than 0.999, the molar concentration of isobutanol is not less than 0.999, and the concentration of [BMIM][OAC] in the circulation is not less than 0.997.

[0011] In this invention, the preferred operating parameters are as follows: the theoretical number of plates in the extractive distillation column is 24, and the feed position of the raw material mixture is the 15th plate; when the feed rate of the isobutanol and isobutyl formate mixture is 100 kmol / h, the optimized flow rate of the circulating [BMIM][OAC] entering the extractive distillation column is 37 kmol / h.

[0012] By setting the vacuum and temperature gradient of the two-stage flash tank, the isobutanol in the bottom of the column is vaporized step by step, while the ionic liquid [BMIM][OAC] is regenerated under milder low-pressure conditions. This avoids the risk of thermal degradation caused by conventional high-temperature distillation recovery.

[0013] Compared with the prior art, the present invention has the following advantages: By utilizing the strong hydrogen bond acceptance and steric hindrance effect of [BMIM][OAC], the azeotropic point of isobutanol-isobutyl formate can be completely broken with a relatively low solvent ratio, and the selectivity is much higher than that of traditional organic solvents.

[0014] The near-zero vapor pressure of the ionic liquid fundamentally prevents the extractant from evaporating from the top of the column, ensuring the high purity of the isobutyl formate product at the top of the column and avoiding the emission of volatile organic solvents.

[0015] Combining two-stage flash evaporation to recover ionic liquids replaces the traditional high-energy-consuming solvent desorption tower, significantly reducing the latent heat of vaporization consumption of the reboiler. The process has high thermodynamic efficiency and excellent economic performance. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the extractive distillation process for separating isobutanol-isobutyl formate azeotrope using ionic liquids according to the present invention. In the diagram, EDC is the extractive distillation column, FLA1 is the primary flash tank, FLA2 is the secondary flash tank, C1 and C2 are condensers, C3 is a condenser, and PRE is a preheater; Feed is the feed stream of the isobutanol and isobutyl formate mixture, IL is the ionic liquid circulation stream, IBF is the top isobutyl formate product stream, W is the bottom liquid of the extractive distillation column, V1 and V2 are the isobutanol enriched vapor streams, L1 and L2 are the residual liquid phases of the primary and secondary flash tanks, respectively, and IBA is the isobutanol product stream. Detailed Implementation

[0017] Example 1 The feed flow rate of the mixture of isobutanol and isobutyl formate is 100 kmol / h, with each component contributing 50 kmol / h. The feed mixture is preheated to 100°C and 120 kPa before being fed into the extractive distillation column. Circulating ionic liquids [BMIM][OAC] enter from the top of the extractive distillation column at a feed flow rate controlled at 37 kmol / h, a temperature of 100°C, and a pressure of 110 kPa.

[0018] Under these feed conditions, the extractive distillation column had a theoretical plate number of 24. The feed stream entered from the 15th plate, the ionic liquid from the 2nd plate, the reflux ratio was 1.0, the top temperature was 98℃, the bottom temperature was 144℃, the top pressure was 100 kPa, and the overall pressure drop was 10 kPa. High-purity isobutyl formate was collected from the top of the extractive distillation column, with a molar concentration of 0.999.

[0019] The reboiler stream contains [BMIM][OAC] and extracted isobutanol, which is fed into a primary flash tank for low-pressure flash evaporation. After primary flash evaporation, the top yields isobutanol vapor, while the bottom, containing some residual isobutanol, is fed into a secondary flash tank for deep flash evaporation at an even lower pressure.

[0020] The primary flash tank operates at a pressure of 10 kPa and a temperature of 140℃; the secondary flash tank operates at a pressure of 0.13 kPa and a temperature of -40℃. Isobutanol vapor is further obtained from the top of the secondary flash tank, which merges and condenses with the vapor from the top of the primary flash tank to yield a high-purity isobutanol product with a molar concentration of 0.999. The [BMIM][OAC] at the bottom of the secondary flash tank has undergone efficient regeneration, with a molar concentration of 0.999. After being pressurized and cooled by a pump, it is returned to the top of the extractive distillation column as a circulating extractant.

Claims

1. An extractive distillation method for separating isobutanol-isobutyl formate azeotrope using ionic liquids, characterized by a feed preheater, an extractive distillation column, a primary flash tank, a secondary flash tank, a reboiler and condenser, and a vacuum system. The feed preheater is connected to the extractive distillation column via pipelines; the top product of the extractive distillation column is connected to the top condenser via pipelines; the top condenser is connected to its reflux tank via pipelines; the top reflux tank of the extractive distillation column is connected to the feed valves of both the extractive distillation column and the primary flash tank via pipelines; the vapor phase outlet of the primary flash tank is connected to the condenser via pipelines, and the liquid phase outlet is connected to the feed valve of the secondary flash tank via pipelines; the vapor phase outlet of the secondary flash tank is connected to the condenser via pipelines, and the liquid phase outlet is connected to a pump via pipelines; the pump outlet is connected to a cooler via pipelines; and the cooler outlet is connected to the feed inlet of the second tray of the extractive distillation column via pipelines. The process includes the following steps: S1. The mixture of butanol and isobutyl formate is preheated to the feed temperature and pressure of the extractive distillation column before entering the extractive distillation column for extractive distillation. The circulating ionic liquid [BMIM][OAC] is fed from the second tray as the extractant to complete the feeding process. After the S2 feedstock and extractant enter the extractive distillation column, once the system is running stably, the top product is high-purity isobutyl formate; the bottom product is a mixture of isobutanol and [BMIM][OAC], which is used as feed for the first-stage flash tank for the recovery of [BMIM][OAC]. After the liquid from the S3 reactor enters the primary flash tank for gas-liquid separation, the vapor phase is enriched with isobutanol, and the liquid phase is a mixture of isobutanol and [BMIM][OAC]. The liquid phase is used as feed for secondary flash evaporation to further recover [BMIM][OAC]. After gas-liquid separation in a two-stage flash evaporator, the vapor phase is enriched with isobutanol, and the liquid phase is [BMIM][OAC]. The vapor phases from both flash evaporations are condensed by condensers and then combined to form a high-purity isobutanol product. [BMIM][OAC] is cooled and then enters the extractive distillation column as a circulating material.

2. The process method according to claim 1, characterized in that isobutanol and isobutyl formate each account for 50 mol% in the raw materials. When the feed of the mixture is 100 kmol / h, the recycling rate of [BMIM][OAC] is 35-40 kmol / h.

3. The process method according to claim 1, characterized in that the extractive distillation column is a plate column with 20-25 theoretical plates, the raw material enters from the 13th-16th plate, the circulating [BMIM][OAC] is added from the top of the extractive distillation column, and the reflux ratio of the distillation column is 1.0-1.

2.

4. The process method according to claim 1, characterized in that both the primary flash tank and the secondary flash tank are operated under low pressure or vacuum conditions. By setting temperature and pressure gradients for the two-stage flash evaporation, isobutanol in the bottom liquid of the distillation column is vaporized, avoiding high-temperature decomposition of the ionic liquid; the absolute pressure of the primary flash evaporation is 100 kPa, the absolute pressure of the secondary flash evaporation is 0.13 kPa, the absolute pressure range of the feed is 120 kPa, and the pressure of the distillation column is 110 kPa.

5. The process method according to claim 1, characterized in that the feed temperature is 25°C, the top temperature of the distillation column is 95-105°C, the bottom temperature range is 130-140°C, the operating temperature of the first-stage flash tank is 135-145°C, and the operating temperature of the second-stage flash tank is -45 to -35°C.

6. The process method according to claim 1, characterized in that the molar purity of both isobutanol and isobutyl formate products is not less than 0.999, meeting the industrial high purity requirements.

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