Method for separating 2-methyltetrahydrofuran and acetonitrile through extractive distillation

Abstract

The invention relates to a method for separating 2-methyltetrahydrofuran and acetonitrile through extractive distillation. The method comprises the following steps: respectively adding an extracting agent dimethyl sulfoxide and a raw material solution into an extractive distillation tower, and extracting 2-methyltetrahydrofuran from the tower top to obtain high-purity 2-methyltetrahydrofuran; a mixture of acetonitrile and dimethyl sulfoxide is obtained in the tower kettle and enters an extractant recovery tower, an acetonitrile product is extracted from the tower top, dimethyl sulfoxide is extracted from the tower kettle, and the mixture is cooled by a cooler and then enters the extractive distillation tower again. The method is simple in process, good in separation effect and low in energy consumption; and 2-methyltetrahydrofuran and acetonitrile with the product purity of 99.5 wt% or above can be obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of separation of 2-methyltetrahydrofuran and acetonitrile, and relates to a method for separating 2-methyltetrahydrofuran and acetonitrile by extractive distillation. Background Art

[0002] 2-Methyltetrahydrofuran has attracted much attention as an environmentally friendly solvent and is widely used in chemical reactions and extraction processes, especially in the pharmaceutical and chemical industries. It has good combustion characteristics and can be used as a candidate for renewable biofuels. Acetonitrile is an important organic intermediate that can be used to synthesize vitamin A. It is widely used as a solvent and reactant in organic synthesis and has the characteristics of low freezing point, low toxicity and low viscosity. As an important chemical product, both are widely used in the pharmaceutical industry. A large amount of mixture of the two will be produced during the production process. However, under normal pressure, 2-methyltetrahydrofuran and acetonitrile will form an azeotrope with an azeotropic composition of 70wt% 2-methyltetrahydrofuran and 30wt% acetonitrile, and an azeotropic temperature of 74°C. At present, there is no relevant research report on how to experimentally separate the binary azeotrope. Therefore, how to achieve efficient and energy-saving separation of 2-methyltetrahydrofuran and acetonitrile is one of the key directions of current research. Summary of the invention

[0003] The purpose of the present invention is to solve the problem that the conventional distillation requires high energy consumption and high equipment investment and has poor separation effect when separating 2-methyltetrahydrofuran and acetonitrile in the current industrial production, because 2-methyltetrahydrofuran and acetonitrile have the lowest azeotrope, and the vacancy of the azeotropic system separation technology of 2-methyltetrahydrofuran and acetonitrile is proposed. A method for separating 2-methyltetrahydrofuran and acetonitrile by extractive distillation is proposed. The method selects dimethyl sulfoxide as an extractant, adopts a double tower process of an extractive distillation tower and a solvent recovery tower, and can obtain 2-methyltetrahydrofuran and acetonitrile with a product purity of more than 99.5wt%; the process of the present invention is simple, the separation effect is good, and the energy consumption is low.

[0004] The technical solution of the present invention is:

[0005] A method for extractive distillation separation of 2-methyltetrahydrofuran and acetonitrile, the method comprising the following steps:

[0006] The extractant and the raw material liquid are added to the extractive distillation tower respectively, and 2-methyltetrahydrofuran is extracted from the top of the tower to obtain high-purity 2-methyltetrahydrofuran; the mixture of acetonitrile and dimethyl sulfoxide is obtained in the bottom of the tower, and enters the extractant recovery tower, and the acetonitrile product with a mass fraction of 99.7% is extracted from the top of the tower, and the bottom of the tower is dimethyl sulfoxide with a mass fraction of 99.99%, which is cooled by a cooler and then enters the extractive distillation tower again;

[0007] The extractant is dimethyl sulfoxide; the raw material liquid is a mixture of 2-methyltetrahydrofuran and acetonitrile, and the mass fraction of 2-methyltetrahydrofuran is 30-70%;

[0008] The mass flow ratio of the raw liquid and the extract is 1:2.5-3.0;

[0009] The extractive distillation tower is a plate tower with 49 to 52 plates; the reflux ratio is 1 to 5, and the feed positions are 5 to 6 and 30 to 33 respectively;

[0010] The top pressure of the extractive distillation tower is 1 bar, the top temperature is 79℃~79.5℃, and the bottom temperature is 121℃~143℃.

[0011] The extractant recovery tower is a plate tower with 30 to 39 plates; the reflux ratio is 0.8 to 1, the tower top pressure is 1 bar, the tower top temperature is 81°C to 82°C, the tower bottom temperature is 190°C to 191.5°C; the feed position is 20 to 28;

[0012] The extractive distillation tower produces a 2-methyltetrahydrofuran product with a mass fraction of 99.7% at the top, an acetonitrile product with a mass fraction of 99.9% at the top of the extractant recovery tower, and an extractant with a mass fraction of 99.99% at the bottom of the tower;

[0013] The beneficial effects of the present invention are:

[0014] The invention fills the gap in the separation technology of 2-methyltetrahydrofuran-acetonitrile azeotrope, proposes a method for separating the binary azeotrope by extractive distillation, and avoids the problem of resource waste caused by direct incineration of the waste liquid for the 2-methyltetrahydrofuran and acetonitrile mixture waste liquid generated in the chemical production process, and realizes the high-purity recovery of 2-methyltetrahydrofuran and acetonitrile, the purity of the recovered product can reach more than 99.5%, and the recovery rate can reach more than 99.7%. Different waste liquid compositions have different energy consumption, but the overall separation energy consumption is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0016] Figure 1 The schematic diagram of the device flow of the method for extractive distillation separation of 2-methyltetrahydrofuran and acetonitrile of the present invention is as follows:

[0017] Figure 2 is the vapor-liquid equilibrium diagram of dimethyl sulfoxide-2-methyltetrahydrofuran-acetonitrile;

[0018] Wherein, 1-extractive distillation tower; 2-extractant recovery tower; 3-cooler; 4-mixer; a-raw material (2-methyltetrahydrofuran-acetonitrile) feed; b-2-methyltetrahydrofuran product; c-acetonitrile and extractant mixture; d-acetonitrile product; e-extractant; f-supplementary extractant; g-extractant feed; DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0020] like Figure 1 As shown, the device system comprises an extractive distillation tower 1, an extractant recovery tower 2, a cooler 3 and a mixer 4; wherein the extractive distillation tower 1 is respectively provided with a raw material feed port and an extractant feed port; the mixer 4 is connected to the extractant feed port of the extractive distillation tower 1; a first condenser is provided at the top of the extractive distillation tower 1; the tower kettle is connected to the feed port of the extractant recovery tower 2 via a first reboiler; the tower top of the extractant recovery tower 2 is connected to the 2-methyltetrahydrofuran production outlet b via a second condenser; the tower kettle is connected to the hot flow stream inlet of the cooler 3 via the second reboiler, and then connected to the inlet of the mixer 4 via the hot flow stream outlet of the cooler 3;

[0021] The invention uses Aspen plus for separation, the raw materials 2-methyltetrahydrofuran and acetonitrile mixture (any ratio) are fed at a certain position of the extractive distillation tower, and the extractant is fed at the upper part of the extractive distillation tower, in the extractive distillation tower, 2-methyltetrahydrofuran is extracted from the tower top, acetonitrile and the extractant are extracted from the tower bottom and then enter the extractant recovery tower, in the extractant recovery tower, the acetonitrile product is extracted from the tower top, the extractant is extracted from the tower bottom and then cooled by a cooler and returned to the upper feed port of the extractive distillation tower for recycling, and the extractant is appropriately supplemented at the upper feed port of the extractive distillation tower, and finally the separation of the azeotropic system 2-methyltetrahydrofuran and acetonitrile is realized. The extractive distillation tower top extracts 99.9% of the 2-methyltetrahydrofuran product by mass fraction, the extractant recovery tower top extracts 99.7% of the acetonitrile product by mass fraction, and the tower bottom extracts 99.99% of the extractant by mass fraction. The extractant only needs to make up for the extractant lost from the top of the two distillation towers.

[0022] The above-mentioned distillation towers (extractive distillation tower, solvent recovery tower) are all operated at normal pressure, with a single plate pressure drop of 0.06 kPa.

[0023] The extractant is dimethyl sulfoxide with high boiling point and low volatility.

[0024] The inventors found through research that 2-methyltetrahydrofuran and acetonitrile form an azeotrope when the mass ratio is 7:3, and the azeotropic temperature is 74 degrees. After adding dimethyl sulfoxide, the azeotropic phenomenon disappears. Figure 2As shown, x represents the liquid phase and y represents the vapor phase. It can be seen that dimethyl sulfoxide has a good separation effect.

[0025] Example 1

[0026] like Figure 1 The extractive distillation tower has 51 plates, the reflux ratio is 1.5, the extractant is dimethyl sulfoxide, which is fed from the 5th plate (from the top to the bottom of the tower) with a flow rate of 2900kg / h; the raw liquid is a mixture of 2-methyltetrahydrofuran and acetonitrile with a mass fraction of 70% 2-methyltetrahydrofuran and 30% acetonitrile, which is fed from the 32nd plate with a flow rate of 1000kg / h. The extractive distillation tower has a top pressure of 1 bar, a top temperature of 79.33°C, a bottom temperature of 141.47°C, and a 2-methyltetrahydrofuran with a mass fraction of 99.9% is produced from the top of the tower, with a production volume of 700 kg / h; a mixture of acetonitrile and dimethyl sulfoxide is obtained in the bottom of the tower, with a production volume of 3200 kg / h, and enters the extractant recovery tower from the 28th plate. The extractant recovery tower has 39 plates, a reflux ratio of 0.8, a top pressure of 1 bar, a top temperature of 81.21°C, a bottom temperature of 190.26°C, and an acetonitrile product with a mass fraction of 99.7% is produced from the top of the tower, with a production volume of 300.24 kg / h; the extractant recovery tower bottom obtains the extractant dimethyl sulfoxide, with a purity of up to 99.99% by mass. The recovery rate of 2-methyltetrahydrofuran is 99.90%, and the recovery rate of acetonitrile is 99.77%.

[0027] Example 2

[0028] like Figure 1 The extractive distillation tower has 49 plates, the reflux ratio is 2.44, the extractant is dimethyl sulfoxide, which is fed from the 5th plate (from the top to the bottom of the tower) with a flow rate of 2800kg / h; a mixture of 2-methyltetrahydrofuran and acetonitrile, with a mass fraction of 50% 2-methyltetrahydrofuran and 50% acetonitrile, is fed from the 30th plate with a flow rate of 1000kg / h. The extractive distillation tower has a top pressure of 1 bar, a top temperature of 79.32°C, a bottom temperature of 128.57°C, and a 2-methyltetrahydrofuran with a mass fraction of 99.9% is produced from the top of the tower, with a production volume of 500kg / h; a mixture of acetonitrile and dimethyl sulfoxide is obtained in the bottom of the tower, with a production volume of 3300kg / h, and enters the extractant recovery tower from the 22nd plate. The extractant recovery tower has 30 plates, a reflux ratio of 0.8, a top pressure of 1 bar, a top temperature of 81.23°C, and a bottom temperature of 190.90°C. An acetonitrile product with a mass fraction of 99.8% is produced from the top of the tower, with a production volume of 500.507kg / h; the extractant recovery tower bottom obtains the extractant dimethyl sulfoxide, with a purity of up to 99.99% by mass. The recovery rate of 2-methyltetrahydrofuran is 99.90%, and the recovery rate of acetonitrile is 99.90%.

[0029] Example 3

[0030] like Figure 1 The extractive distillation tower has 52 plates, the reflux ratio is 4.50, the extractant is dimethyl sulfoxide, which is fed from the 6th plate (from the top to the bottom of the tower) with a flow rate of 2700kg / h; a mixture of 2-methyltetrahydrofuran and acetonitrile, with a mass fraction of 30% 2-methyltetrahydrofuran and 70% acetonitrile, is fed from the 33rd plate with a flow rate of 1000kg / h. The extractive distillation tower has a top pressure of 1 bar, a top temperature of 79.25°C, a bottom temperature of 121.31°C, and a 99.7% mass fraction of 2-methyltetrahydrofuran is produced from the top of the tower, with a production rate of 300 kg / h; a mixture of acetonitrile and dimethyl sulfoxide is obtained in the bottom of the tower, with a production rate of 3400 kg / h, and enters the extractant recovery tower from the 25th plate. The extractant recovery tower has 36 plates, a reflux ratio of 0.9, a top pressure of 1 bar, a top temperature of 81.22°C, and a bottom temperature of 191.04°C. An acetonitrile product with a mass fraction of 99.8% is produced from the top of the tower, with a production rate of 700.501 kg / h; the extractant recovery tower bottom obtains the extractant dimethyl sulfoxide, with a purity of up to 99.99% mass fraction. The recovery rate of 2-methyltetrahydrofuran is 99.90%, and the recovery rate of acetonitrile is 99.87%.

[0031] Table 1 Energy consumption of all reboilers in the whole process of each embodiment

[0032] Example 1 2 3 Energy consumption (kW) 514.14 621.62 717.72

[0033] According to three examples with different feed compositions, the method of the present invention has no requirements on the feed composition of the raw materials, and the purity and recovery rate of the obtained 2-methyltetrahydrofuran and acetonitrile are both above 99.5%, and the separation effect is very good.

[0034] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the specification of the present invention, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

[0035] Matters not covered by the present invention are known technologies.

Claims

1. A method for separating 2-methyltetrahydrofuran and acetonitrile by extractive distillation, characterized in that: The method comprises the following steps: The extractant and the raw material liquid are added to the extractive distillation tower respectively, and 2-methyltetrahydrofuran is extracted from the top of the tower to obtain high-purity 2-methyltetrahydrofuran; the mixture of acetonitrile and dimethyl sulfoxide is obtained in the bottom of the tower, and enters the extractant recovery tower, and the acetonitrile product with a mass fraction of 99.7% is extracted from the top of the tower, and the bottom of the tower is dimethyl sulfoxide with a mass fraction of 99.99%, which is cooled by a cooler and then enters the extractive distillation tower again; The extractant is dimethyl sulfoxide; the raw material liquid is a mixture of 2-methyltetrahydrofuran and acetonitrile, and the mass fraction of 2-methyltetrahydrofuran is 30-70%; The mass flow ratio of the raw liquid to the extract is 1:2.5-3.

0.

2. The method for extractive distillation separation of 2-methyltetrahydrofuran and acetonitrile as claimed in claim 1, characterized in that: The extractive distillation tower is a plate tower with 49 to 52 plates; the reflux ratio is 1 to 5; the feed position of the extractant is 5 to 6 plates, and the feed position of the raw liquid is 30 to 33 plates; The top pressure of the extractive distillation tower is 1 bar, the top temperature is 79℃~79.5℃, and the bottom temperature is 121℃~143℃. The extractant recovery tower is a plate tower with 30 to 39 plates; the reflux ratio is 0.8 to 1, the top pressure is 1 bar, the top temperature is 81°C to 82°C, the bottom temperature is 190°C to 191.5°C; the feed position is 20 to 28 plates.

3. The method for extractive distillation separation of 2-methyltetrahydrofuran and acetonitrile as claimed in claim 1, characterized in that: The extractive distillation tower produces a 2-methyltetrahydrofuran product with a mass fraction of 99.7% at the top, an acetonitrile product with a mass fraction of 99.9% at the top of the extractant recovery tower, and an extractant with a mass fraction of 99.99% at the bottom.

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