Separation and purification process and device for methylal

Abstract

The invention provides a process and a device for separating and purifying methylal. The device mainly comprises an azeotropic distillation tower, an azeotropic distillation tower top condenser, a decanter, an entrainer phase pump, a methanol phase pump, a methylal product pump, an entrainer recovery tower, an entrainer recovery tower top condenser, an entrainer recovery tower top reflux tank, an entrainer recovery tower top reflux pump, a methanol product pump and the like. A methylal and methanol mixture is separated by adopting an azeotropic distillation process, the methylal and methanol mixture enters an azeotropic distillation tower from the middle part of the tower, a supplementary entrainer enters the tower from the upper part of the tower, tower top reflux enters the tower from the tower top, the entrainer and methanol are extracted from the tower top of the azeotropic distillation tower, and a high-purity methylal product is extracted from the tower kettle of the azeotropic distillation tower. A methanol material carrying part of the entrainer enters the entrainer recovery tower from the middle lower part, the entrainer containing a small amount of methanol is extracted from the top of the entrainer recovery tower, high-purity methanol is extracted from the bottom of the entrainer recovery tower, and the prepared methylal product is high in purity and low in energy consumption.

Description

Technical Field

[0001] The invention belongs to the field of chemical industry and relates to a chemical separation technology, in particular to a separation and purification process and device for methylal. Background Art

[0002] Dimethyl carbonate, also known as dimethoxymethane, is an important intermediate in the production process of polyacetal plastics. Methylal has good physical and chemical properties, low boiling point, good water solubility, etc. It is widely used in the production of cosmetics, pharmaceuticals, automotive industrial products, rubber and other fields. In addition, due to its good degreasing ability and volatility, methylal can be used as a cleaning agent to replace chlorine-containing and fluorine-containing solvents, reduce volatile organic compounds (VOCs) emissions, and reduce pollution to the atmosphere.

[0003] The preparation of methylal generally uses methanol and formaldehyde solution as raw materials, and is synthesized by reaction under the catalytic action of an acidic catalyst. The reaction is a reversible reaction, and the equilibrium conversion rate of formaldehyde is only about 60%. In industry, a reactive distillation process is usually used to separate the methylal generated by the reaction from the top of the reactive distillation tower in time, thereby improving the conversion rate of formaldehyde. Since methylal and methanol form an azeotrope, the purity of the methylal separated from the top of the reactive distillation tower is usually around 87% to 92%. The subsequent conventional distillation separation method can only obtain a product with a purity of about 92% to 94% of methylal, and the remaining 6 to 8% is methanol. With the development and upgrading of the manufacturing industry, the market demand for high-purity methylal is also increasing.

[0004] It is difficult to separate methylal-methanol azeotrope by ordinary distillation. In order to obtain high-purity methylal products, special separation processes such as pressure swing distillation, extractive distillation and azeotropic distillation are often required. Chinese patent CN104447240A discloses a method for preparing high-purity methylal by pressure swing distillation. The principle of different azeotropic compositions of methylal-methanol under different pressures is used. First, the azeotrope is sent to a pressure distillation tower, and the methylal-methanol azeotrope under pressure is distilled out from the top of the tower, and high-purity methylal is obtained at the bottom of the tower; the azeotrope at the top of the pressure distillation tower is sent to a normal pressure distillation tower, and the top of the tower is a methylal-methanol azeotrope under normal pressure, and the bottom of the tower is a high-concentration methanol. Pressure swing distillation is a common process for separating methylal-methanol azeotropes in industrial devices. The advantage is that no third component needs to be added, but the disadvantages are high energy consumption and large equipment investment.

[0005] In the method disclosed in patent CN104761430A, thermal coupling is performed between the pressure distillation tower and the atmospheric distillation tower, and the top gas of the pressure distillation tower is used as the heat source of the reboiler of the atmospheric distillation tower, which reduces the energy consumption of the pressure swing distillation process to a certain extent, but there are also disadvantages such as poor stability of thermal coupling operation and high pressure of the pressure distillation tower. The extractive distillation process is to select a suitable third component as an extractant, use the extractant to change the relative volatility of methylal and methanol, obtain a high concentration of methylal at the top of the extractive distillation tower, and send the extractant and methanol mixture at the bottom of the tower to the extractant recovery tower to separate methanol and extractant. Patent CN114591155A uses N,N-dimethylformamide as an extractant, CN101302143B uses ethylene glycol dimethyl ether as an extractant, CN102627536B uses polyols or dimethyl sulfoxide as an extractant, and CN108569952B uses 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid as an extractant. It can be seen that most of these extractants are toxic and harmful high-boiling point components, the product is easily contaminated by the extractant, and the heat source required for the recovery of the extractant is of high quality.

[0006] The azeotropic distillation process forms a new low-boiling azeotrope by introducing an azeotropic agent. A suitable azeotropic agent can also break the limitation of the distillation boundary by the principle of partial miscibility, thereby achieving efficient separation of the azeotropic agent. This patent proposes a process for separating methylal-methanol azeotropes by azeotropic distillation, screens out a suitable azeotropic agent, reduces energy consumption, and improves separation efficiency. Summary of the invention

[0007] In order to solve the technical problems of high power consumption, large equipment investment and low separation efficiency in the prior art, the present invention provides a separation and purification process and device for methylal.

[0008] The present invention provides a separation and purification process of methylal, comprising the following steps:

[0009] 1) Crude methylal containing methanol enters the azeotropic distillation tower from the middle of the tower, supplementary entrainer enters from the upper part of the tower, and the top reflux enters from the top of the tower. The bottom product is high-purity methylal. The top gas enters the decanter for separation after condensation and cooling, and the top product is methanol containing a small amount of entrainer;

[0010] 2) the entrainer phase separated from the decanter in step 1) is returned to the azeotropic distillation tower, and the methanol phase separated from the decanter is sent to the entrainer recovery tower for treatment;

[0011] 3) The methanol phase carrying part of the entrainer is separated by distillation in the entrainer recovery tower in step 2), the entrainer containing a small amount of methanol is extracted from the top of the entrainer recovery tower, and the high-purity methanol is extracted from the bottom of the entrainer recovery tower.

[0012] As an improved solution, the azeotropic agent is n-pentane.

[0013] As a further improved solution, the number of theoretical plates of the azeotropic distillation tower is 30 to 120, and the number of theoretical plates of the solvent recovery tower is 5 to 40.

[0014] As a further improved solution, the top pressure of the azeotropic distillation tower is 0.1-1.5 MPag, and the top pressure of the solvent recovery tower is 0.01-0.5 MPag.

[0015] As a further improved solution, the top temperature of the azeotropic distillation tower is 30°C to 80°C, and the top temperature of the solvent recovery tower is 10°C to 50°C.

[0016] As a further improved solution, the bottom temperature of the azeotropic distillation tower is 50°C to 120°C, and the bottom temperature of the solvent recovery tower is 50°C to 100°C.

[0017] The present invention also provides a device used in the separation and purification process of methylal, which includes an azeotropic distillation tower, an azeotropic distillation tower top condenser, a decanter, an azeotropic distillation tower reboiler, an entrainer phase pump, a methanol phase pump, a methylal product pump, an entrainer recovery tower, an azeotropic agent recovery tower top condenser, an entrainer recovery tower top reflux tank, an entrainer recovery tower top reflux pump, an entrainer recovery tower reboiler, and a methanol product pump; the top outlet of the azeotropic distillation tower is connected with the top condenser of the azeotropic distillation tower, the decanter, the entrainer phase pump, and the reflux inlet of the azeotropic distillation tower in sequence, the lower outlet of the azeotropic distillation tower is connected with the inlet of the azeotropic distillation tower reboiler, and the outlet of the azeotropic distillation tower reboiler is connected to the azeotropic distillation tower reboiler. Return to the azeotropic distillation tower; the bottom outlet of the azeotropic distillation tower is connected to the methylal product pump, and the product methylal is recovered by the methylal product pump; the inlet and outlet of the methanol phase pump are respectively connected to the decanter outlet and the inlet of the entrainer recovery tower, the top outlet of the entrainer recovery tower is connected to the entrainer recovery tower top condenser, the entrainer recovery tower top reflux tank, the entrainer recovery tower top reflux pump, and the reflux inlet of the entrainer recovery tower in sequence, the lower outlet of the entrainer recovery tower is connected to the inlet of the entrainer recovery tower reboiler, and returns to the entrainer recovery tower through the reboiler outlet of the entrainer recovery tower, and the bottom outlet of the entrainer recovery tower is connected to the methanol product pump and discharged through the methanol product pump.

[0018] Preferably, a recovery entrainer pipeline is provided at the outlet of the reflux pump at the top of the entrainer recovery tower, and the recovery entrainer pipeline is connected to the decanter or the azeotropic distillation tower.

[0019] Preferably, the decanter may be replaced by a three-phase separator.

[0020] The present invention is applied in devices including but not limited to separating and purifying methylal.

[0021] The working principle of a separation and purification process and device for methylal provided by the present invention is as follows:

[0022] In the azeotropic distillation tower, a mixture containing methylal and methanol enters the azeotropic distillation tower from the middle of the tower, and the top reflux and supplementary entrainer enter from the top of the tower. After distillation separation, the entrainer and methanol are extracted from the top of the azeotropic distillation tower, and the high-purity methylal product is extracted from the bottom of the azeotropic distillation tower. The top material of the azeotropic distillation tower enters the decanter after condensation and cooling, and the entrainer phase separated by the decanter returns to the azeotropic distillation tower, and the methanol phase separated by the decanter is sent to the entrainer recovery tower for treatment. In the entrainer recovery tower, the methanol material carrying part of the entrainer enters the entrainer recovery tower from the middle and lower part of the tower, and after distillation separation, the entrainer containing a small amount of methanol is extracted from the top of the entrainer recovery tower, and the high-purity methanol is extracted from the bottom of the entrainer recovery tower.

[0023] The present invention has the following beneficial effects:

[0024] 1) The azeotropic distillation process is used to separate the methylal and methanol mixture, and the methylal product prepared has high purity.

[0025] 2) The entrainer used may be n-pentane, dimethyl sulfide or methyl iodide, preferably n-pentane. n-pentane is widely available, has a good entrainment effect as an entrainer, is less toxic than the extractant of extractive distillation, and requires less n-pentane.

[0026] 3) The preferred azeotropic agent n-pentane is partially miscible with methanol, and liquid-liquid separation can be achieved by a decanter, which simplifies the separation process and reduces separation energy consumption.

[0027] 4) By adjusting the operating pressure of the distillation tower, the quality and consumption of cold and hot utilities can be further optimized, which is beneficial to reducing the overall energy consumption of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the process flow of the present invention.

[0029] In the figure: 1-azeotropic distillation tower, 2-azeotropic distillation tower top condenser, 3-decanter, 4-entrainer phase pump, 5-methanol phase pump, 6-azeotropic distillation tower reboiler, 7-methylal product pump, 8-entrainer recovery tower, 9-azeotropic agent recovery tower top condenser, 10-azeotropic agent recovery tower top reflux tank, 11-azeotropic agent recovery tower top reflux pump, 12-entrainer recovery tower reboiler, 13-methanol product pump, 14-azeotropic agent recovery pipeline. DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with the accompanying drawings.

[0031] like Figure 1As shown, a separation and purification process and device for methylal, the device comprises an azeotropic distillation tower 1, an azeotropic distillation tower top condenser 2, a decanter 3, an entrainer phase pump 4, a methanol phase pump 5, a methylal product pump 7, an entrainer recovery tower 8, an entrainer recovery tower top condenser 9, an entrainer recovery tower top reflux tank 10, an entrainer recovery tower top reflux pump 11, and a methanol product pump 13; the top outlet of the azeotropic distillation tower 1 is connected to the azeotropic distillation tower top condenser 2, the decanter 3, the entrainer phase pump 4, and the top reflux port of the azeotropic distillation tower 1 in sequence, The bottom outlet of the azeotropic distillation tower 1 is connected to the methylal product pump 7, and the product methylal is recovered by the methylal product pump 7; the inlet and outlet of the methanol phase pump 5 are respectively connected to the outlet of the decanter 3 and the inlet of the entrainer recovery tower 8, and the top outlet of the entrainer recovery tower 8 is connected to the entrainer recovery tower top condenser 9, the entrainer recovery tower top reflux tank 10, the entrainer recovery tower top reflux pump 11, and the reflux inlet of the entrainer recovery tower 8 in sequence; the bottom outlet of the entrainer recovery tower 8 is connected to the methanol product pump 7 and is sent out by the methanol product pump 7.

[0032] An azeotropic distillation tower reboiler 6 is arranged at the lower part of the azeotropic distillation tower 1, and the lower outlet of the azeotropic distillation tower 1 is connected to the inlet of the azeotropic distillation tower reboiler 6, and returns to the azeotropic distillation tower through the outlet of the azeotropic distillation tower reboiler 6.

[0033] An entrainer recovery tower reboiler 12 is arranged at the lower part of the entrainer recovery tower 8, and the lower outlet of the entrainer recovery tower 8 is connected to the inlet of the entrainer recovery tower reboiler 12, and returns to the entrainer recovery tower 8 through the outlet of the entrainer recovery tower reboiler 12.

[0034] An azeotropic agent recovery pipeline 14 is provided at the outlet of the azeotropic agent recovery tower top reflux pump 11 , and the azeotropic agent recovery pipeline 14 is connected to the decanter 3 .

[0035] The crude methylal raw material is introduced into the middle part of the azeotropic distillation tower 1, and the supplementary entrainer is introduced into the upper part of the azeotropic distillation tower 1. The gas phase at the top of the tower is condensed by the azeotropic distillation tower top condenser 2 and then enters the decanter 3 for liquid-liquid separation. The entrainer phase separated from the bottom of the decanter 3 is pressurized by the entrainer phase pump 4 and then returned to the azeotropic distillation tower 1 for treatment. The methanol phase separated from the bottom of the decanter 3 is pressurized by the methanol phase pump 5 and then sent to the entrainer recovery tower 8 for separation. The azeotropic distillation tower 1 is provided with an azeotropic distillation tower reboiler 6, and the tower bottom product is high-purity methylal, which is sent out by the methylal product pump 7. The gas phase at the top of the entrainer recovery tower 8 is condensed by the entrainer recovery tower top condenser 9 and enters the entrainer recovery tower top reflux tank 10. The liquid phase at the bottom of the entrainer recovery tower top reflux tank 10 is drawn out by the entrainer recovery tower top reflux pump 11 and is divided into two parts, one part of which returns to the top of the entrainer recovery tower top reflux pump 8 as reflux, and the other part returns to the decanter 3 through the entrainer recovery pipeline. The entrainer recovery tower 8 is provided with an entrainer recovery tower reboiler 12, and the tower bottom product is high-purity methanol, which is sent out through the methanol product pump 13.

[0036] The azeotropic agent is n-pentane.

[0037] The number of theoretical plates of the azeotropic distillation tower is 30 to 120, and the number of theoretical plates of the solvent recovery tower is 5 to 40.

[0038] The top pressure of the azeotropic distillation tower is 0.1-1.5 MPag, and the top pressure of the solvent recovery tower is 0.01-0.5 MPag.

[0039] The top temperature of the azeotropic distillation tower is 30°C to 80°C, and the top temperature of the solvent recovery tower is 10°C to 50°C.

[0040] The temperature of the kettle of the azeotropic distillation tower is 50°C to 120°C, and the temperature of the kettle of the solvent recovery tower is 50°C to 100°C.

[0041] The azeotropic agent recovery pipeline 14 at the top of the azeotropic agent recovery tower can be connected to the decanter 3 or to the azeotropic distillation tower 1 .

[0042] The supplementary entrainer can pass through the upper part of the azeotropic distillation tower 1 or can be introduced into the decanter 3 .

[0043] A device and process for separating and purifying methylal. The crude methylal comprises (by mass fraction): 88.0% methylal and 12.0% methanol. The device and process provided by the invention are used to separate the mixture.

[0044] The theoretical plate number of the azeotropic distillation tower is 60, the tower top pressure is 0.8 MPag, the tower top temperature is 50° C., and the tower bottom temperature is 70° C. The mass concentration of the methylal product in the tower bottom is 99%, and the recovery rate of the methylal product is 99.9%.

[0045] The theoretical plate number of the azeotropic agent recovery tower is 15, the tower top pressure is 0.1 MPag, the tower top temperature is 30° C., and the tower bottom temperature is 70° C. The quality purity of the methanol product in the tower bottom is greater than 99.5%.

[0046] The device has a simple process, is easy to operate, and is conducive to industrial application.

[0047] The above description is only a typical embodiment of the present invention, and does not impose any form of limitation on the present invention. Any changes or modifications made by any technician familiar with the profession, without departing from the scope of the technical solution of the present invention, using the above content should be regarded as equivalent examples of equivalent changes. Any equivalent changes made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are within the scope of the technical solution of the present invention.

Claims

1. A separation and purification process for methylal, characterized in that: The process includes the following steps: 1) Crude methylal containing methanol enters the azeotropic distillation tower from the middle of the tower, supplementary entrainer enters from the upper part of the tower, and the top reflux enters from the top of the tower. The bottom product is high-purity methylal. The top gas enters the decanter for separation after condensation and cooling, and the top product is methanol containing a small amount of entrainer; 2) the entrainer phase separated from the decanter in step 1) is returned to the azeotropic distillation tower, and the methanol phase separated from the decanter is sent to the entrainer recovery tower for treatment; 3) The methanol phase carrying part of the entrainer is separated by distillation in the entrainer recovery tower in step 2), the entrainer containing a small amount of methanol is extracted from the top of the entrainer recovery tower, and the high-purity methanol is extracted from the bottom of the entrainer recovery tower.

2. The separation and purification process of methylal according to claim 1, characterized in that: The azeotropic agent is n-pentane.

3. The separation and purification process of methylal according to claim 1, characterized in that: The number of theoretical plates of the azeotropic distillation tower is 30 to 120, and the number of theoretical plates of the solvent recovery tower is 5 to 40.

4. The separation and purification process of methylal according to claim 1, characterized in that: The top pressure of the azeotropic distillation tower is 0.1-1.5 MPag, and the top pressure of the solvent recovery tower is 0.01-0.5 MPag.

5. The separation and purification process of methylal according to claim 1, characterized in that: The top temperature of the azeotropic distillation tower is 30°C to 80°C, and the top temperature of the solvent recovery tower is 10°C to 50°C.

6. The separation and purification process of methylal according to claim 1, characterized in that: The temperature of the kettle of the azeotropic distillation tower is 50°C to 120°C, and the temperature of the kettle of the solvent recovery tower is 50°C to 100°C.

7. The device used for the separation and purification process of methylal according to claim 1, characterized in that: The device comprises an azeotropic distillation tower, an azeotropic distillation tower top condenser, a decanter, an azeotropic distillation tower reboiler, an entrainer phase pump, a methanol phase pump, a methylal product pump, an entrainer recovery tower, an azeotropic agent recovery tower top condenser, an entrainer recovery tower top reflux tank, an entrainer recovery tower top reflux pump, an entrainer recovery tower reboiler, and a methanol product pump; the top outlet of the azeotropic distillation tower is connected with the top condenser of the azeotropic distillation tower, the decanter, the entrainer phase pump, and the reflux inlet of the azeotropic distillation tower in sequence, the lower outlet of the azeotropic distillation tower is connected with the inlet of the azeotropic distillation tower reboiler, and returns to the azeotropic distillation tower through the outlet of the azeotropic distillation tower reboiler; the azeotropic distillation tower top outlet is connected with the azeotropic distillation tower top condenser, the decanter, the entrainer phase pump, and the reflux inlet of the azeotropic distillation tower in sequence, the lower outlet of the azeotropic distillation tower is connected with the inlet of the azeotropic distillation tower reboiler, and returns to the azeotropic distillation tower through the outlet of the azeotropic distillation tower reboiler; The bottom outlet of the distillation tower is connected to the methylal product pump, and the product methylal is recovered by the methylal product pump; the inlet and outlet of the methanol phase pump are respectively connected to the decanter outlet and the inlet of the entrainer recovery tower; the top outlet of the entrainer recovery tower is connected to the top condenser of the entrainer recovery tower, the top reflux tank of the entrainer recovery tower, the top reflux pump of the entrainer recovery tower, and the reflux inlet of the entrainer recovery tower in sequence; the lower outlet of the entrainer recovery tower is connected to the inlet of the reboiler of the entrainer recovery tower, and returns to the entrainer recovery tower through the reboiler outlet of the entrainer recovery tower; the bottom outlet of the entrainer recovery tower is connected to the methanol product pump, and is discharged through the methanol product pump.

8. The device used in the separation and purification process of methylal according to claim 7, characterized in that: A recovery entrainer pipeline is arranged at the outlet of the reflux pump at the top of the entrainer recovery tower, and the recovery entrainer pipeline is connected to the decanter or the azeotropic distillation tower.

9. The device used for the separation and purification process of methylal according to claim 7, characterized in that: The decanter was replaced by a three-phase separator.

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