A method for separating methyl acetal from crude propylene oxide

Abstract

The present application relates to a method for separating methyl acetal in crude propylene oxide, which uses ionic liquid extractant for extractive distillation, the ionic liquid extractant is 1-butyl-3-methyl imidazole tetrafluoroborate or 1-butyl-3-methyl imidazole triflate, the crude propylene oxide is fully contacted with the ionic liquid extractant in the extractive distillation column, and high-purity propylene oxide product is obtained at the top of the extractive distillation column. The method of the present application can stably obtain high-purity propylene oxide, has simple process, and the ionic liquid extractant is simple to recover and low in cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of propylene oxide purification, and particularly relates to a method for separating dimethyl acetal in crude propylene oxide. BACKGROUND

[0002] Propylene oxide, also known as propylene oxide, is a very important organic compound raw material, and is the third largest propylene derivative next to polypropylene and acrylonitrile. The most commonly used propylene oxide production process in the world is chlorohydrination and co-oxidation. The chlorohydrination process is relatively mature, but has the disadvantages of more wastewater and residue, and large investment in comprehensive treatment of three wastes. The co-oxidation process has a long process route, high energy consumption, high equipment requirements, and is restricted by the market of co-produced products. With the continuous promotion of the "double carbon" policy, the propylene oxide (PO) industry is facing transformation and upgrading, and green production and process change are becoming a trend. Hydrogen peroxide direct oxidation method for preparing propylene oxide (HPPO) is considered as a new green propylene oxide production process. The method has mild conditions and belongs to an environmentally friendly clean production system, representing the development direction of the industry.

[0003] The HPPO method uses methanol as a solvent, and hydrogen peroxide is used to directly epoxidize propylene under the catalysis of a molecular sieve catalyst. The crude propylene oxide product contains impurities such as acetaldehyde, dimethyl acetal, methanol, methyl formate and water. Since propylene oxide and dimethyl acetal can form an azeotrope, ordinary rectification method is not suitable for removing dimethyl acetal from the propylene oxide product. If it cannot be removed, it will continuously enrich in the system, affecting the quality of the product propylene oxide. SUMMARY

[0004] The present application is to solve the problem that dimethyl acetal in crude propylene oxide is not easy to separate when propylene oxide is prepared by the HPPO method in the prior art.

[0005] The method for separating dimethyl acetal in crude propylene oxide provided by the present application comprises that the crude propylene oxide is propylene oxide material containing dimethyl acetal, ion liquid extractant is used for extraction rectification, the ion liquid extractant is 1-butyl-3-methyl imidazole tetrafluoroborate or 1-butyl-3-methyl imidazole trifluoromethanesulfonate, the crude propylene oxide is fully contacted with the ion liquid extractant in the extraction rectification tower, the extraction rectification tower top obtains propylene oxide product, the extraction rectification tower bottom obtains a mixture of dimethyl acetal and ion liquid extractant, the mixture enters a flash tank for separation to obtain dimethyl acetal material and ion liquid extractant material, and the obtained ion liquid extractant material is refluxed to the extraction rectification tower for recycling.

[0006] In the process of preparing propylene oxide by HPPO method, the content of by-product methylal is high, and methylal and product propylene oxide are easy to form azeotrope, which leads to great difficulty in rectification and low purity of product propylene oxide. Therefore, the present application is not to solve the separation problem of all impurities in propylene oxide product, but to solve the separation problem of methylal and propylene oxide. The present application adopts the separation method of ionic liquid extractive distillation. On the one hand, ionic liquid is composed of anions and cations, and is a salt in liquid state at normal temperature. Compared with traditional organic solvents, ionic liquid has no odor, is non-flammable, has very low vapor pressure, low melting point, and has high thermal stability, chemical stability and structural designability, and other excellent physical and chemical properties.

[0007] In order to obtain better separation effect, the ionic liquid extractive agent preferably adopted by the present application is 1-butyl-3-methyl imidazole tetrafluoroborate ([Bmin][BF4]) or 1-butyl-3-methyl imidazole triflate ([Bmim][OTF]), which can effectively separate methylal in crude propylene oxide and obtain propylene oxide product with high purity. Moreover, the ionic liquid extractive agent of the present application is simple to recover and has low cost.

[0008] In an embodiment of the present application, the operating condition of the extractive distillation column is normal pressure, the feeding temperature of crude propylene oxide is 20-35℃, the feeding temperature of ionic liquid extractive agent is 40-90℃, the mass ratio of ionic liquid extractive agent to crude propylene oxide is 0.05-1, and the reflux ratio is 1-5.

[0009] In an embodiment of the present application, the number of plates of the extractive distillation column is 20-80.

[0010] In an embodiment of the present application, crude propylene oxide is fed from the middle position of the extractive distillation column, and ionic liquid extractive agent is fed from the upper position of the extractive distillation column. Preferably, ionic liquid extractive agent is fed from the 2nd to 5th plate of the extractive distillation column.

[0011] In an embodiment of the present application, the temperature of the column bottom of the extractive distillation column is 80-150℃. Preferably, the temperature of the column bottom of the extractive distillation column is 80-100℃.

[0012] In an embodiment of the present application, the operating pressure of the flash tank is 0.01-0.1 MPa absolute pressure, and the operating temperature is 65-165℃. Methylal material is obtained at the top of the flash tank, and ionic liquid extractive agent material is obtained at the bottom of the flash tank.

[0013] In an embodiment of the present application, the mass fraction of methylal in crude propylene oxide is 10%-50%.

[0014] In one embodiment of the present application, the propylene oxide product has a propylene oxide purity of at least 99.95% by mass.

[0015] In one embodiment of the present application, the dimethyl ether material has a dimethyl ether purity of at least 99.9% by mass.

[0016] Features of the present application:

[0017] 1. The method of the present application uses ionic liquid as an extractant to extract and rectify the crude propylene oxide, obtaining a high-purity propylene oxide product. The present application uses green and environmentally friendly ionic liquid as an extractant, avoiding environmental pollution caused by volatilization of ordinary organic solvents, and having better separation effect than conventional extractants.

[0018] 2. The preferred ionic liquid of the present application has stable chemical properties and is easy to recover, reducing costs. In addition, the process of the present application is simple and continuous, and the purity of the propylene oxide product can reach more than 99.95%. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a schematic diagram of one embodiment of the method for separating dimethyl ether from crude propylene oxide provided by the present application. DETAILED DESCRIPTION

[0020] The present application will be further described below in conjunction with the drawings, but the present application is not limited thereby.

[0021] Figure 1 is a schematic diagram of one embodiment of the method for separating dimethyl ether from crude propylene oxide provided by the present application, as shown in Figure 1 , crude propylene oxide 4 enters the extractive rectification column 1 and is fully contacted with the ionic liquid extractant in the extractive rectification column, and the extractive rectification column 1 obtains propylene oxide product 6 at the top, and a mixture of dimethyl ether and ionic liquid extractant 5 at the bottom, the mixture 5 enters the flash tank 2 for separation, obtaining dimethyl ether material 7 and ionic liquid extractant material 3, and the obtained ionic liquid extractant material 3 is refluxed to the extractive rectification column 1 for recycling.

[0022] The present application will be further described below in conjunction with the drawings, but the present application is not limited thereby.

[0023] In the examples and comparative examples, crude propylene oxide prepared by mixing dimethyl ether and propylene oxide was used for testing.

[0024] The purity of the propylene oxide product, the dimethyl ether material, and the ionic liquid extractant was detected by gas chromatography.

[0025] Example 1

[0026] In this example, the crude propylene oxide contains 10 wt% of methylal, and the extractive distillation column has 40 theoretical plates. The ionic liquid extractant [Bmim][BF4] is fed from the 2nd plate, the feed temperature is 60°C, and the flow rate is 50 kg / h; the crude propylene oxide is fed from the 28th plate, the feed temperature is 25°C, and the flow rate is 200 kg / h. The extractive distillation column is operated at atmospheric pressure, the column bottom temperature is 80°C, the reflux ratio is 1, and the overhead product is 180 kg / h. The propylene oxide product with a purity of more than 99.95% is obtained at the top of the column, and the mixture of methylal and ionic liquid [Bmim][BF4] is obtained at the bottom of the column. The mixture is fed into a flash tank, the operating pressure of the flash tank is 0.05 MPa, and the operating temperature is 90°C. The methylal material with a mass fraction of 99.9% of methylal is extracted from the top of the flash tank, and the ionic liquid extractant material with a mass fraction of 99.9% of [Bmim][BF4] is obtained at the bottom of the flash tank. The ionic liquid extractant is recycled back to the extractive distillation column for recycling.

[0027] Example 2

[0028] In this example, the crude propylene oxide contains 25 wt% of methylal, and the extractive distillation column has 55 theoretical plates. The ionic liquid extractant [Bmim][BF4] is fed from the 2nd plate, the feed temperature is 55°C, and the flow rate is 80 kg / h; the crude propylene oxide is fed from the 20th plate, the feed temperature is 35°C, and the flow rate is 550 kg / h. The extractive distillation column is operated at atmospheric pressure, the column bottom temperature is 80°C, the reflux ratio is 1.5, and the overhead product is 400 kg / h. The propylene oxide product with a purity of more than 99.95% is obtained at the top of the column, and the mixture of methylal and ionic liquid [Bmim][BF4] is obtained at the bottom of the column. The mixture is fed into a flash tank, the operating pressure of the flash tank is 0.08 MPa, and the operating temperature is 140°C. The methylal material with a mass fraction of 99.9% of methylal is extracted from the top of the flash tank, and the ionic liquid extractant material with a mass fraction of 99.9% of [Bmim][BF4] is obtained at the bottom of the flash tank. The ionic liquid extractant is recycled back to the extractive distillation column for recycling.

[0029] Example 3

[0030] In this example, the crude propylene oxide contains 10 wt% of methylal, and the extractive distillation column has 30 theoretical plates. The ionic liquid extractant [Bmim][OTF] is fed from the 2nd plate, the feed temperature is 65°C, and the flow rate is 30 kg / h; the crude propylene oxide is fed from the 15th plate, the feed temperature is 25°C, and the flow rate is 150 kg / h. The extractive distillation column is operated at normal pressure, the column bottom temperature is 80°C, the reflux ratio is 1.3, and the overhead product is 135 kg / h. The propylene oxide product with a purity of more than 99.95% is obtained at the top of the column, and the mixture of methylal and ionic liquid [Bmim][OTF] is obtained at the bottom of the column. The mixture is fed into a flash tank, the operating pressure of the flash tank is 0.03 MPa, and the operating temperature is 80°C. The methylal material with a mass fraction of 99.9% of methylal is obtained at the top of the flash tank, and the ionic liquid extractant material with a mass fraction of 99.9% of [Bmim][OTF] is obtained at the bottom of the flash tank. The ionic liquid extractant is recycled to the extractive distillation column for recycling use.

[0031] Comparative Example 1

[0032] In this comparative example, the ionic liquid extractant used is [Bmim][Br] (1-butyl-3-methylimidazolium bromide), and the crude propylene oxide, the extractive distillation column, and the remaining operating conditions are the same as in Example 1. The purity of the propylene oxide obtained at the top of the extractive distillation column is 94.1%, which does not meet the product purity requirement.

[0033] Comparative Example 2

[0034] In this comparative example, the ionic liquid extractant used is [Bmim][SCN] (1-butyl-3-methylimidazolium thiocyanate), and the crude propylene oxide, the extractive distillation column, and the remaining operating conditions are the same as in Example 1. The purity of the propylene oxide obtained at the top of the extractive distillation column is 93.6%, which does not meet the product purity requirement.

Claims

1. A method of separating methyl acetal from crude propylene oxide, characterized by, The crude propylene oxide is an propylene oxide material containing methylal, and is subjected to extractive distillation using an ionic liquid extractant, the ionic liquid extractant being 1-butyl-3-methylimidazolium tetrafluoroborate or 1-butyl-3-methylimidazolium trifluoromethanesulfonate, the crude propylene oxide being subjected to sufficient contact with the ionic liquid extractant in an extractive distillation column, propylene oxide product being obtained at the top of the extractive distillation column, and a mixture of methylal and ionic liquid extractant being obtained at the bottom of the extractive distillation column, the mixture being subjected to separation in a flash tank to obtain a methylal material and an ionic liquid extractant material, the obtained ionic liquid extractant material being refluxed to the extractive distillation column for recycling.

2. The method of claim 1, wherein, The operating conditions of the extractive distillation column are normal pressure, the feed temperature of the crude propylene oxide being 20-35℃, the feed temperature of the ionic liquid extractant being 40-90℃, the mass ratio of the ionic liquid extractant to the crude propylene oxide being 0.05-1, and the reflux ratio being 1-5.

3. The method of claim 1, wherein, The number of plates of the extractive distillation column is 20-80, the crude propylene oxide being fed from the middle position of the extractive distillation column, and the ionic liquid extractant being fed from the upper position of the extractive distillation column.

4. The method of claim 3, wherein, The ionic liquid extractant is fed from the 2nd to 5th plate of the extractive distillation column.

5. The method of claim 1, wherein, The column bottom temperature of the extractive distillation column is 80-150℃.

6. The method of claim 1, wherein, The column bottom temperature of the extractive distillation column is 80-100℃.

7. The method of claim 1, wherein, The operating pressure of the flash tank is 0.01-0.1MPa absolute, and the operating temperature is 65-165℃, methylal material being obtained at the top of the flash tank, and ionic liquid extractant material being obtained at the bottom of the flash tank.

8. The method of claim 1, wherein, In the crude propylene oxide, the mass fraction of methylal is 10%-50%.

9. The method of claim 1, wherein, The purity of the propylene oxide in the obtained propylene oxide product is at least 99.95% by mass.

10. The method of claim 1, wherein, The purity of the methylal in the obtained methylal material is at least 99.9% by mass.

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