CN116023204A - Method for separating dimethyl ether in process of preparing propylene from methanol - Google Patents

Abstract

The invention discloses a method for separating dimethyl ether in a process for preparing propylene from methanol, which comprises the following steps: (1) Introducing a raw material containing DME into an MTP reactor for propylene synthesis reaction, wherein an obtained product mixture contains unconverted DME; (2) Introducing the product mixture into a quenching absorption stabilization device, and separating to obtain liquefied gas, wherein the liquefied gas contains hydrocarbon with the carbon number of 1-6 and unconverted DME; (3) Rectifying and separating the liquefied gas through a depropanizer, a deethanizer and a propylene tower, wherein: separating hydrocarbon with 3 or less carbon atoms from the top of the depropanizer, and then further separating to obtain propylene products and propane products; separating hydrocarbon with 4 or more carbon atoms from the bottom of the depropanizer; the DME component mixture is withdrawn at a location below the liquefied gas feed inlet and above the bottom of the column of the depropanizer. The DME and propane can be separated efficiently by the method.

Description

Method for separating dimethyl ether in process of preparing propylene from methanol

Technical Field

The invention relates to the technical field of a process for preparing propylene (MTP) from methanol, in particular to a method for separating dimethyl ether (DME) in the process for preparing propylene (MTP) from methanol.

Background

The process for the production of propylene from methanol (MTP process) was successfully developed by Lurgi company, germany in the 90 s of the 20 th century. The process comprises the following steps: first, the refined methanol output from the methanol plant is sent to a dimethyl ether (DME) pre-reactor, where the refined methanol is converted to DME and water; the methanol, water, DME vapor is then fed to the MTP reactor along with the recycled olefins, vapors, with a substantial portion of the methanol, DME, being converted to hydrocarbons, primarily low carbon olefins (C2-C5 hydrocarbons, e.g., ethylene, propylene, ethane, propane, butane, butene, etc.), more primarily propylene, product mixtures. And cooling, separating, compressing, drying, rectifying, removing impurities and the like the product mixture flowing out of the MTP reactor to finally obtain various hydrocarbon products with higher purity. The process technology is used as an important supplementary means for preparing propylene, and the separation and purification flow is simpler and the propylene yield is higher because of relatively fewer byproducts.

The byproduct propane produced in the MTP process can be used as a raw material for propane dehydrogenation or light hydrocarbon cracking units, and can also be used as liquefied petroleum gas (mainly composed of hydrocarbon, mainly composed of propane, butane and other alkanes), etc.

However, in the propane product produced by this process, substantial amounts of DME are typically accumulated. This is because DME formed as an intermediate product of the MTP process is not completely converted in the MTP reactor and the stream comprising propane typically comprises DME because of the fact that the subsequent separation process is not where the oxygenate DME in the light hydrocarbon stream is not specifically removed. However, the propane dehydrogenation or light hydrocarbon cracking device has strict limit on the dimethyl ether content in the raw material propane, for example, the content of total oxides (including dimethyl ether, methanol, acetone and the like) in the raw material propane is required to be less than or equal to 30mg/kg; the national administration for quality supervision, inspection and quarantine makes regulations forbidding the blending of dimethyl ether into domestic liquefied petroleum gas (quality inspection special function (2008) No. 17, notification about gas cylinder filling about problems). Therefore, there is a need to find a suitable way to remove DME mixed in propane and to increase the purity of the propane product. Therefore, how to optimize the MTP process, obtain a higher purity propane product and a higher DME utilization is a constant concern for researchers.

Chinese patent CN203904242U discloses a method for removing and recycling DME in an MTP process, in which a bottom discharge port of a depropanizer is sequentially connected in series with an extraction separation tank, a methanol recovery tower, a DME reactor and an MTP reactor. The depropanizer is also provided with a methanol feed inlet, methanol is directly injected into the depropanizer, and DME products at the top of the depropanizer are simply and efficiently dissolved to be separated from propylene and C3, and DME/methanol is accumulated at the bottom of the depropanizer to be separated, so that the purity of propylene products is ensured. DME is recovered by a simple extractive separation process and returned to the reactor for reuse.

Disclosure of Invention

The invention aims to solve the technical problem of separating dimethyl ether simply and efficiently from an MTP reactor product stream of a propylene (MTP) process for preparing methanol.

In order to achieve the above object, the present invention provides a method for separating dimethyl ether (DME) in a process for preparing propylene (MTP) from methanol, comprising the steps of:

(1) Introducing a raw material containing DME into an MTP reactor for propylene synthesis reaction to obtain a product mixture, wherein the product mixture contains unconverted DME;

(2) Introducing the product mixture into quenching absorption stabilization equipment, and separating to obtain liquefied gas, wherein the liquefied gas contains hydrocarbon with 1-6 carbon atoms and unconverted DME;

(3) Rectifying and separating the liquefied gas through a depropanizer, a deethanizer and a propylene tower, wherein:

separating out hydrocarbon with 3 carbon atoms or hydrocarbon with less than 3 carbon atoms from the top of the depropanizer, and then further separating out propylene products and propane products;

separating hydrocarbon with 4 carbon atoms or more than 4 hydrocarbons from the bottom of the depropanizer;

the DME component mixture is withdrawn at a location below the liquefied gas feed inlet and above the bottom of the column of the depropanizer.

In the present invention, hydrocarbons having 3 or less carbon atoms are simply referred to as "C3-"; hydrocarbons having 3 carbon atoms are simply referred to as "C3"; hydrocarbons having 4 or more carbon atoms are simply referred to as "c4+"; hydrocarbons having 4 carbon atoms are simply referred to as "C4"; "C1", "C2", "C5", "C5+" have similar meanings, wherein "C" represents a carbon atom; the numbers 1, 2, 5, 5+ represent the number of carbon atoms.

In the present invention, "methyl tert-butyl ether" is abbreviated as MTBE.

In the present invention, the fraction of 3/10 to 5/10 of the "liquefied gas feed port is located at any one tray in the region of 3/10 to 5/10 from top to bottom" is understood as that the tray is installed inside the depropanizer column, the total height of the depropanizer column is regarded as 10 parts, and the liquefied gas feed port is located at any one tray in the region of 3/10 to 5/10 from top to bottom of the column.

Other scores used to describe some locations on the tower have similar meanings in the present invention.

In the process of the present invention, in step (1), the feedstock comprises water vapor in addition to DME.

In the process of the invention, in step (2), the product mixture is passed to a quench absorption stabilization device, from which water, gasoline (predominantly c5+ components) and dry gas (predominantly C1 components) are separated in addition to the liquefied gas. Wherein the C2-C4 components and unconverted DME are enriched in the liquefied gas and further separated by subsequent steps.

In the process of the present invention, in step (3), the liquefied gas may be subjected to rectification separation sequentially through a depropanizer, a deethanizer and a propylene tower. Specifically, the liquefied gas may be first introduced into a depropanizer for rectification; then sequentially introducing a first mixture obtained from the top of the depropanizer into a deethanizer and a propylene tower, separating to obtain C2-, propylene and propane products, and sequentially introducing a second mixture obtained from the bottom of the depropanizer into an MTBE reactor and an azeotropic tower to obtain MTBE and C4 products;

in the process of the present invention, in step (3), the liquefied gas may be further subjected to rectification separation in a deethanizer, a depropanizer and a propylene tower in this order. Specifically, the liquefied gas is firstly introduced into a deethanizer for separation, a C2-stream is obtained at the top of the deethanizer, and a C3+ stream is obtained at the bottom of the deethanizer; then, introducing C3+ material flow obtained from the bottom of the deethanizer into a depropanizer for rectification separation, introducing a first mixture obtained from the top of the depropanizer into the propylene tower for separation to obtain a propylene product and a propane product, and sequentially introducing a second mixture obtained from the bottom of the depropanizer into an MTBE reactor and an azeotropic tower to obtain MTBE and C4 products;

in the process of the present invention, in step (3), the DME component mixture is withdrawn at a location below the liquid gas feed to the depropanizer and above the bottom of the column. In the process of the present invention, the DME component mixture withdrawn in step (3) can be either a gaseous material or a liquid material, provided that the withdrawal point is below the liquid gas feed to the depropanizer and above the bottom of the column. Preferably, the gaseous DME component mixture is withdrawn in step (3) to achieve a better separation.

In the process of the present invention, in step (3), said DME component mixture is withdrawn which contains, in addition to DME, a total content of C3-, C4+, C3-, C4+ of less than 55V%.

In one embodiment of the process of the present invention, in step (3), the depropanizer overhead operating temperature is from 30 to 70 ℃, the operating pressure is from 1.35 to 1.7MPa, the tower bottom operating temperature is from 85 to 95 ℃, and the operating pressure is from 1.35 to 1.8MPa; in step (3), the DME component mixture is withdrawn from any tray in the region of 6/10 to 8/10 from top to bottom under conditions where the total tray number of the depropanizer is 54 to 84 and the liquefied gas feed port is located at any tray in the region of 3/10 to 5/10 from top to bottom. In the process of the present invention, in step (3), the location of extraction of the DME component mixture is affected by the following factors: the composition, content, etc. of the feed, the operating parameters of the depropanizer, the total tray number of the depropanizer, the liquefied gas feed tray location, etc.

In a further embodiment of the process of the present invention, in step (3), the DME component mixture is withdrawn from any tray in the region of 7/10 to 8/10 from top to bottom under conditions such that the liquefied gas feed inlet is located at any tray in the region of 4/10 to 5/10 from top to bottom. The higher DME content of the mixture withdrawn at the tray location described above allows for more efficient separation of DME from C3 and C4.

In a further embodiment of the method of the invention, the method further comprises the steps of: (4a) The DME component mixture is recycled directly back to the MTP reactor via line. Because the DME concentration in the withdrawn mixture is significantly higher, recycling the DME component mixture back to the MTP reactor in step (4 a) can reuse the incompletely reacted DME, increasing feedstock conversion.

In a still further embodiment of the process of the present invention, in step (3), the flow rate of the DME component mixture withdrawn at a point below the liquefied gas feed port and above the bottom of the column does not exceed 1/3 of the flow rate of the DME feedstock entering the MTP reactor. In a still further embodiment of the process of the present invention, for example, the flow rates of the DME 8 feedstock and the water vapor feedstock are in the range of 20 to 30 tons/hour; in step (3), the flow rate of the DME component mixture withdrawn from a location below the liquefied gas feed to the depropanizer and above the bottom of the column is from 0 to 10 tons/hour.

In other words, the range of adjustability of the extraction of the DME component mixture is relatively wide. For example, fresh catalyst in the MTP reactor, when DME is more completely reacted, no unreacted DME is available, so that the extraction amount is 0; in the case that the catalyst in the MTP reactor is deactivated in a large amount, the catalytic conversion rate is low, and a large amount of DME is not reacted, the extraction amount of the DME component mixture can be increased until the propane product obtained from the bottom of the propylene tower is detected to be qualified.

In a further embodiment of the method of the present invention, the method may further comprise the steps of: (4b) Introducing the DME component mixture into a coupling tower, rectifying and separating again, and obtaining high-purity DME in the coupling tower; (6) recycling said high purity DME back to said MTP reactor. In the method of the invention, the depropanizer and the coupling tower are used for secondary rectification separation, and high-purity DME is obtained in the coupling tower. In the process of the present invention, high purity DME means that the DME concentration is greater than 99V%. After rectification and separation in the coupling tower, the non-oxygenated hydrocarbon component is recycled back to the depropanizer, and the high purity DME is recycled back to the MTP reactor. Thus, the possible adverse effects of recycling components other than DME into the MTP reactor can be avoided.

In a still further embodiment of the process of the present invention, in step (4 b), the liquid phase of any of trays 18-22 of the depropanizer is flowed into the first tray at the upper portion of the coupling tower, and the vapor phase of any of trays 40-56 of the depropanizer is flowed into the first tray at the lower portion of the coupling tower; the gas phase at the top of the coupling tower enters the tray of the depropanizer and flows out of the liquid phase, and the liquid phase at the bottom of the coupling tower enters the tray of the depropanizer and flows out of the gas phase; in step (6), high purity DME is withdrawn from the lower portion of the side stream of the coupled column. In the process of the present invention, there is no need to provide a condensing column (top) and reboiler (bottom) in the coupled column. The coupling tower is connected with the depropanizer in parallel, and the conditions of temperature difference, pressure difference and the like of different tray positions of the depropanizer are utilized to drive the coupling tower to operate, so that the DME component mixture is further rectified and separated.

In a still further embodiment of the process of the present invention, in step (4 b), the total number of trays in the coupled column is from 25 to 35, and high purity DME is withdrawn from any of the 15 th to 25 th trays in the side stream of the coupled column. In a coupling column having 25-35 trays in parallel with the above tray locations of the depropanizer, it is preferred to withdraw DME at any of the 18-22 trays at the side of the coupling column, where the purity of the withdrawn DME is higher.

In a still further embodiment of the process of the present invention, in step (4 b), the flow rate of the liquid phase from the depropanizer tray into the coupled column is from 1/4 to 3/4 of the flow rate of the original liquid phase in the depropanizer tray; the flow of the vapor phase from the depropanizer tray into the coupled column is from 1/4 to 3/4 of the flow of the vapor phase in the tray within the depropanizer. Thus, the need for efficient separation of DME from the depropanizer can be met.

In the method of the present invention, step (4 a) and step (4 b) are not performed simultaneously. In the process of the invention, after step (3), either step (4 a) or step (4 b) is optionally carried out.

Specifically, after step (3), optionally, step (4 a) is performed to recycle the DME back to the MTP reactor as a DME component mixture for re-reaction; alternatively, after step (3), steps (4 b) and (6) are optionally performed sequentially, with DME being recycled back to the MTP reactor as high purity DME for re-reaction.

In the process of the invention, the columns are rectification columns. The rectifying tower is, for example, a packed tower, the packing is folded into the number of trays, and the positions of the trays are unchanged.

In an embodiment of the process of the present invention, the MTP reactor is operated at a temperature of 400 ℃ to 520 ℃ and at a pressure (gauge) of 0.01MPa to 0.2MPa.

In a further embodiment of the process of the present invention, the MTP reactor is operated at a temperature of from 450 ℃ to 520 ℃ and at a pressure (gauge) of from 0.05MPa to 0.08MPa.

Compared with the prior art, the method for separating dimethyl ether in the process (MTP) for preparing propylene from methanol has the following advantages:

1. the method of the invention is to split three materials in a depropanizer, wherein the DME component mixture is the third material. Unexpectedly, the inventors have found that there is a mixture at a location within the depropanizer that has a DME concentration (greater than 45V%) that is much higher than that in the liquefied gas (about 2V%) and also much higher than that in the C3 product (about 10V%), referred to in the context of the present invention as a DME component mixture. By withdrawing the DME component mixture to substantially reduce the DME concentration of the remaining material, substantially DME-free propane is obtained without further DME separation, with a propane content of greater than 98.5V%.

2. The method can effectively and simultaneously separate the DME mixed in the C3-and/or C4+ by one extraction step through the coordinated adjustment of the temperature and the pressure at the top and the bottom of the depropanizer. For example, after the step of increasing the DME component mixture withdrawal, if DME is present at the top of the column, the depropanizer column top temperature is suitably reduced or the column top pressure is suitably increased; if DME is present at the bottom of the column, the bottom temperature is suitably increased or the bottom pressure is suitably decreased; if DME is present at both the top and bottom of the column, the reflux ratio is increased and the DME extraction is increased. Thus, the DME concentration in the first mixture at the top of the depropanizer (comprising predominantly C3-) and/or the second mixture at the bottom of the depropanizer (comprising predominantly C4+) can be regulated separately or simultaneously, reducing the DME concentration in the top and bottom streams to be sufficiently low (less than 0.009V%).

In addition, the method can recover all unreacted DME to the maximum extent by simultaneously regulating and controlling the DME concentration at the top and the bottom of the depropanizer, and has high recovery rate and simple steps.

In addition, the method can recycle the extracted DME for repeated reaction, and the utilization rate of the DME raw material is high.

3. The method can directly circulate the extracted DME component mixture to the MTP reactor, so that the flow is simple, the equipment investment cost is low, and the maintenance is convenient; the extracted DME component mixture can be fed into a newly added coupling tower for further separation, so that after the DME with high purity (more than 99 V%) is obtained, the DME is recycled to the MTP reactor, and therefore other hydrocarbon substances are not circularly carried into the MTP reactor, the single-pass treatment capacity of the MTP reactor is not affected, and the coupling tower is free from a condenser and a reboiler, and the energy consumption is unchanged.

In practical implementation, the staff can select according to the needs, and the industrial application range of the method is wide and the practicability is high.

Drawings

FIG. 1 is a flow chart of a prior art process for producing propylene (MTP) from DME.

Fig. 2 is a flow chart of a method of separating dimethyl ether (DME) in an MTP process according to an embodiment of the present invention.

Fig. 3 is a flow chart of a method of separating dimethyl ether (DME) in an MTP process according to another embodiment of the present invention.

Reference numerals illustrate:

MTP reactor-1; quenching absorption stabilization equipment-2; a depropanizer-3; deethanizer-4; propylene tower-5; methyl tert-butyl ether (MTBE) reactor-6; an azeotropic column-7; DME-8; steam-9; product mixture-10; dry gas-11; liquefied gas-12; gasoline-13; water-14; c3 to 15; c4+ -16; c2-product-17; c3-18; c4 product-19; propylene product-20; propane product-21; MTBE product-22; methanol-23; DME component mixture-24; high purity DME-25; coupled to tower-26.

Detailed Description

The invention will be further described with reference to specific embodiments, and advantages and features of the invention will become apparent from the description. These examples are merely exemplary and do not limit the scope of the invention in any way. It will be understood by those skilled in the art that various changes and substitutions of details and forms of the technical solution of the present invention may be made without departing from the spirit and scope of the present invention, but these changes and substitutions fall within the scope of the present invention.

FIG. 1 is a flow chart of a prior art process for producing propylene (MTP) from DME.

As shown in FIG. 1, first, in step (1), DME 8 raw material and steam 9 were introduced into an MTP reactor 1 at a flow rate of 25 tons/hr, and a reaction for synthesizing propylene was carried out at a temperature of 460℃and a pressure of 0.06MPa, to obtain a product mixture 10.

Then, in step (2), the product mixture 10 is passed into a quench absorption stabilization device 2. In the quenching absorption stabilization device 2, the product mixture 10 is separated into dry gas 11, liquefied gas 12, gasoline 13 and water 14.

Then, in step (3), the liquefied gas 12 is introduced into the depropanizer 3 through a liquefied gas feed port formed in a side wall of the depropanizer 3, and is subjected to rectification separation. The total tray number of the depropanizer 3 is 69, and the liquefied gas 12 enters the depropanizer 3 from a 30 th tray. The operation temperature of the top of the depropanizer 3 is 50 ℃ and the operation pressure is 1.5MPa; the operating temperature at the bottom of the column was 90℃and the operating pressure was 1.55MPa.

In step (3), as the rectification separation proceeds, a first stream of mixture C3- (C3 and lower hydrocarbons below C3) 15, obtained from the top of the depropanizer 3, is withdrawn from C3-15 and fed into deethanizer 4 for the rectification separation of the C2-and C3 components. C2-product 17 is obtained at the top of deethanizer 4 and C3 18 is obtained at the bottom. Then the C3 18 material is introduced into a propylene tower 5, and propylene products 20 and 21 are obtained through rectification and separation. A second mixture c4+ (lower hydrocarbons below C4 and C4) 16 is obtained from the bottom of the depropanizer 3, c4+16 is withdrawn and fed into the MTBE reactor 6 for synthesis reaction with methanol 23, and the resulting mixture containing product MTBE is then passed into the azeotropic column 7 for separation to obtain MTBE product and C4 product.

Wherein in step (1) unconverted DME starts to appear in the product mixture 10, even more and more, as the MTP reactor 1 is run longer and the catalyst activity is reduced. Accordingly, the liquefied gas 12 may contain unconverted DME in addition to C3-, c4+, and the amount of unconverted DME may dynamically vary with time, as shown in table 1, and the DME content in the liquefied gas 12 is 1.7969V%.

TABLE 1 integration ratio of various streams (V%)

(in Table 1 above-indicates that no detection is made)

In step (3), after such liquefied gas 12 is fed to the depropanizer 3, the DME component typically appears in the rectifying column to be slightly heavier than propane and lighter than C4 and closer to propane under the conventional operating conditions described above for the depropanizer 3, so that DME is more easily mixed with propane and exits the overhead of said depropanizer 3 and is less prone to separation. In step (3), after the rectification separation in deethanizer 4 and propylene tower 5, DME is further enriched in propane, at a higher concentration up to about 10V%, rendering propane product 21 unacceptable. As shown in table 1 above and tables 2, 3 and 4 below.

TABLE 2 detection of the composition of propane products (2022, 4, 13:10)

Component name	Content (V%)
		Methane	0.0072
Ethane (ethane)	0.1873
		Ethylene	0.0144
Propane	68.5372
		Propylene	1.4334
Isobutane	1.2317
		N-butane	0.2305
N/trans-butene	0.2593
		Maleic anhydride	0.0792
Isobutene (i-butene)	0.0432
		Butadiene	0.0005
Dimethyl ether	27.9700
		C5	0.0061

TABLE 3 results of component measurements for propane products (2022, 4, 11, 16:04)

(in Table 3 above-indicates that no detection is made)

TABLE 4 detection of the composition of propane products (2022, 4, 12, 10:17)

Component name	Content (V%)
		Methane	0
Ethane (ethane)	0
		Ethylene	0
Propane	90.77
		Propylene	0.41
Isobutane	0.52
		N-butane	0.29
N/trans-butene	0.36
		Maleic anhydride	0.004
Isobutene (i-butene)	0.018
		Butadiene	0.001
Dimethyl ether	7.6
		C5	0.004

The chromatographic data of the propane products in tables 2, 3 and 4 show that the DME content in propane product 21 is relatively high, 27.97V%, 7.86V% and 7.6V%, respectively.

The data of table 1 above were obtained by software calculations. Further observations were made of the variation in DME content data in the prior art process shown in Table 1, wherein the DME content in the liquefied gas 12 entering the depropanizer 3 was 1.7969V%, the DME content in the first mixture obtained at the top of the depropanizer was 3.8902V%, and the DME content in the second mixture obtained at the bottom of the depropanizer was 0V%. It can be seen that during the production of the prior art MTP process, DME is substantially enriched in the overhead (to 3.8902V%) in the effluent of the depropanizer 3. Based on such apparent data, one would prefer to withdraw DME from the top of the column and conduct post-processing, such as separating the DME.

Example 1

Fig. 2 is a flow chart of a method of separating dimethyl ether (DME) from an MTP process according to an embodiment of the present invention.

In this example 1, the process for producing propylene (MTP) from DME is similar to that of the prior art hereinabove, except that in step (3) a third stream of mixture, gaseous DME component mixture 24, is withdrawn at tray 50 of the depropanizer 3, and DME is separated by this operation. Then, in step (4 a), the gaseous DME component mixture 24 is recycled directly back to the MTP reactor 1 via line, recycling the incompletely reacted DME, increasing the conversion of the feedstock.

In this example 1, the flow rate of the gaseous DME component mixture withdrawn in step (3) can be dynamically adjusted, typically not exceeding 1/3 of the flow rate of the DME feedstock entering MTP reactor 1, in other words, the flow rate of the gaseous DME component mixture withdrawn can be dynamically adjusted in real time in the range of 0-8 tons/hour at a feed rate of 25 tons/hour for the DME feedstock while the MTP system is operating, with the aim of ensuring that the DME content in the propane product 21 obtained from the bottom of the propylene column 5 is detected as acceptable.

For example, when fresh catalyst is used in the MTP reactor and the DME reaction is relatively complete, the extraction flow rate is 0 ton/hr without the need to extract the unreacted DME. In the case of gradual deactivation of the catalyst in the MTP reactor, gradual reduction of the catalytic conversion and gradual increase of unreacted DME, the withdrawal flow of the gaseous DME component mixture can be correspondingly increased. The withdrawal flow of the gaseous DME component mixture can also be used in conjunction with the operating temperatures, pressures at the top and bottom of the depropanizer 3. During the withdrawal, if DME is present at the top of the column, the depropanizer column top temperature is suitably reduced or the column top pressure is suitably increased; if DME is present at the bottom of the column, the bottom temperature is suitably increased or the bottom pressure is suitably decreased; if DME appears at the top and bottom of the tower, the extraction amount of DME is increased, and the reflux ratio is increased, so that the operating temperature of the top of the tower is ensured to be maintained at 30-70 ℃, the pressure is ensured to be maintained at 1.35-1.7MPa, the operating temperature of the bottom of the tower is maintained at 85-95 ℃, and the pressure is maintained at 1.35-1.8MPa.

The inventors have found that, surprisingly, a higher concentration of DME (45V%) is enriched in the gas phase near the 50 th tray of the depropanizer 3 (rather than at a location above the feed inlet) under normal operating conditions of the overall MTP system, as shown in tables 5, 6, 7 and 8 below.

TABLE 5 detection of gaseous DME component mixtures (2022, 4, 19, 16:01)

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TABLE 6 detection of gaseous DME component mixtures (2022, 4, 30, 12:00)

Component name	Content (V%)
		Methane	0.0008
Ethane (ethane)	0.0015
		Ethylene	0.0021
Propane	17.77
		Propylene	19
Isobutane	10.7
		N-butane	1.29
N/trans-butene	1.5
		Maleic anhydride	0.5
Isobutene (i-butene)	2.46
		Butadiene	0.01
Dimethyl ether	46.31
		C5	0.51

TABLE 7 detection of gaseous DME component mixtures (2022, 10, 26, 8:00)

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TABLE 8 detection of gaseous DME component mixtures (2022, 10, 26, 16:00)

Component name	Content (V%)
		Methane	0.00
Ethane (ethane)	0.00
		Ethylene	0.00
Propane	0.97
		Propylene	4.11
Isobutane	22.57
		N-butane	3.49
N/trans-butene	7.45
		Maleic anhydride	2.12
Isobutene (i-butene)	11.3917
		Butadiene	0.042
Dimethyl ether	48.01
		C5	0.07

Chromatographic analysis data for the gaseous DME component mixtures of tables 5, 6, 7 and 8 show that the DME content in the gaseous DME component mixture withdrawn in step (3) of this invention is 79.25V%, 46.31V%, 45.03V% and 48.01V%, respectively, all 45V% or more, at a concentration much higher than that in propane product 21 (10V%).

The inventive process reduces the DME content of the second mixture obtained at the bottom of the depropanizer 3 to below 0.009V% by the gaseous DME component mixture withdrawn at step (3), and the DME content of the first mixture obtained at the top of the depropanizer 3 to below 0.009V%, and further the DME content of the propane product to below 0.4V%, thus positively achieving an efficient separation of DME, as shown in tables 9, 10, 11 and 12 below.

TABLE 9 integration ratio of various streams (V%)

(in Table 9 above-indicates that no detection is made)

Table 10 results of the component measurements of propane products (2022, 4, 19, 0:08)

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TABLE 11 results of the component measurements of propane products (2022, 10, 26, 16:00)

Component name	Content (V%)
		Methane	0.002
Ethane (ethane)	0.0089
		Ethylene	0.0039
Propane	97.11
		Propylene	1.65
Isobutane	0.79
		N-butane	0.0042
N/trans-butene	0.01
		Maleic anhydride	0.0009
Isobutene (i-butene)	0.03
		Butadiene	0.0015
Dimethyl ether	0.4
		C5	0.0031

Table 12 results of the component measurement of propane product (2022, 10, 26, 20:00)

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The chromatographic data in tables 9, 10, 11 and 12 show that the DME content of propane product 21 after separation of DME by the process of the present invention is relatively low, at 0.0242V%, 0.05V%, 0.4V% and 0.34V%, respectively.

Thus, by withdrawing the gaseous DME component mixture at tray 50 of the depropanizer 3, good DME separation is achieved and propane product 21 having a DME content that meets the operating requirements is obtained without further separation processing.

Example 2

Fig. 3 is a flow chart of a method of separating dimethyl ether (DME) from an MTP process according to another embodiment of the present invention.

The process for separating dimethyl ether (DME) from an MTP process of this example 2 is similar to the process of example 1 described above, except that: in step (4 b), introducing 1/2 of the liquid phase in the 20 th tray of the depropanizer 3 into the 1 st tray at the upper part of the coupling tower 27, introducing 1/2 of the gas phase in the 50 th tray of the depropanizer 3 into the 1 st tray at the lower part of the coupling tower 27, and performing rectification separation; and the top vapor phase of the coupling column 27 is directed back to tray 20 of the depropanizer 3 and the bottom liquid phase of the coupling column 27 is directed back to tray 50 of the depropanizer 27. In step (6), high purity DME 25 is withdrawn from tray 20 of the coupled column 27 and recycled back to MTP reactor 1.

After the treatment by the method of this example 2, the propane product 21 was sampled and analyzed, and the detection results are shown in table 13 below.

TABLE 13 integration ratio of various streams (V%)

(in Table 13 above-indicating undetected)

The data in Table 13 shows that the dimethyl ether content in propane product 21 was greatly reduced to 0.0172V% and that the DME concentration in high purity DME 25 was 99.5V%.

Claims (9)

1. A method for separating dimethyl ether (DME) in a process for producing propylene (MTP) from methanol, comprising the steps of:

(1) Introducing a raw material containing DME into an MTP reactor for propylene synthesis reaction to obtain a product mixture, wherein the product mixture contains unconverted DME;

(2) Introducing the product mixture into quenching absorption stabilization equipment, and separating to obtain liquefied gas, wherein the liquefied gas contains hydrocarbon with 1-6 carbon atoms and unconverted DME;

(3) Rectifying and separating the liquefied gas through a depropanizer, a deethanizer and a propylene tower, wherein:

separating out hydrocarbon with 3 carbon atoms or hydrocarbon with less than 3 carbon atoms from the top of the depropanizer, and then further separating out propylene products and propane products;

separating hydrocarbon with 4 carbon atoms or more than 4 hydrocarbons from the bottom of the depropanizer;

the DME component mixture is withdrawn at a location below the liquefied gas feed inlet and above the bottom of the column of the depropanizer.

2. The method of claim 1, wherein the step of determining the position of the substrate comprises,

in the step (3), the operation temperature of the top of the depropanizer is 30-70 ℃, the operation pressure is 1.35-1.7MPa, the operation temperature of the bottom of the depropanizer is 85-95 ℃, and the operation pressure is 1.35-1.8MPa;

in step (3), the DME component mixture is withdrawn from any tray in the region of 6/10 to 8/10 from top to bottom under conditions where the total tray number of the depropanizer is 54 to 84 and the liquefied gas feed port is located at any tray in the region of 3/10 to 5/10 from top to bottom.

3. The method of claim 2, wherein the step of determining the position of the substrate comprises,

in step (3), the DME component mixture is withdrawn from any tray in the region of 7/10 to 8/10 from top to bottom under conditions where the liquefied gas feed inlet is located at any tray in the region of 4/10 to 5/10 from top to bottom.

4. A method according to any one of claims 1-3, further comprising the step of:

(4a) The DME component mixture is recycled directly back to the MTP reactor via line.

5. The method of claim 4, wherein the step of determining the position of the first electrode is performed,

in step (3), the flow rate of the DME component mixture withdrawn at a point below the liquefied gas feed port and above the bottom of the column does not exceed 1/3 of the flow rate of the DME feedstock entering the MTP reactor.

6. A method according to any one of claims 1-3, further comprising the step of:

(4b) Introducing the gaseous DME component mixture into a coupling tower, rectifying and separating again, and obtaining high-purity DME in the coupling tower;

(6) Recycling the high purity DME back to the MTP reactor.

7. The method of claim 6, wherein the step of providing the first layer comprises,

in the step (4 b), the liquid phase of any one of the trays 18 to 22 of the depropanizer flows into a first tray at the upper part of the coupled rectifying tower, and the gas phase of any one of the trays 40 to 56 of the depropanizer flows into a first tray at the lower part of the coupled rectifying tower;

the gas phase at the top of the coupling tower enters the tray of the depropanizer and flows out of the liquid phase, and the liquid phase at the bottom of the coupling tower enters the tray of the depropanizer and flows out of the gas phase;

in step (6), high purity DME is withdrawn from the lower portion of the side stream of the coupled column.

8. The process of claim 7 wherein in step (4 b) the total number of trays in the coupling column is from 25 to 35, and high purity DME is withdrawn from any of the 15 th to 25 th trays in the side stream of the coupling column.

9. The process of claim 6 wherein in step (4 b) the amount of liquid phase flowing from the depropanizer tray into the coupled column is 1/4 to 3/4 of the amount of liquid phase in the tray within the depropanizer; the amount of vapor phase flowing from the depropanizer tray into the coupled column is from 1/4 to 3/4 of the amount of vapor phase in the tray within the depropanizer.

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