Process and apparatus for separating methanol from other oxygenates

Abstract

We have discovered that the addition of water to a mixture of oxygenates increases their volatility relative to methanol. Methods and apparatus for separating methanol from other oxygenates are disclosed. Water is separated from a stream comprising water, methanol, and at least one other oxygenate to provide a water-rich stream and a methanol- and oxygenate-rich stream. The methanol- and oxygenate-rich stream and water are fed to a column to provide an oxygenate-rich stream and a methanol and water extract stream. The methanol and water can then be readily separated from each other.

Description

[0001] Priority Statement

[0002] This application claims priority to U.S. Application No. 16 / 805,431, filed February 28, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This field involves the separation of methanol from other oxygen-containing compounds, especially in the presence of water. Background Technology

[0004] A major part of the global petrochemical industry involves the production of light olefin materials and their subsequent use in the production of many important chemical products. This production and use of light olefin materials can involve a variety of well-known chemical reactions, including, for example, polymerization, oligomerization, and alkylation. Light olefins typically include ethylene, propylene, and mixtures thereof. These light olefins are an important component used in the modern petrochemical and chemical industries. In today's refining processes, the primary source of light olefins is the steam cracking of petroleum feedstocks. For various reasons, there is a need to source significant amounts of raw materials from sources other than petroleum to meet the demand for these light olefin materials.

[0005] The exploration of alternative materials for the production of light olefins has led to the use of oxygen-containing compounds such as alcohols, and more specifically, methanol, ethanol, and higher alcohols or their derivatives, or other oxygen-containing compounds such as dimethyl ether (DME) and diethyl ether. Molecular sieves such as microporous crystalline zeolites and non-zeolite catalysts, particularly aluminosilicate silicate (SAPO), are known to promote the conversion of oxygen-containing compounds into hydrocarbon mixtures, especially those composed primarily of light olefins. This method has been referred to as the oxygen-to-olefins (OTO) method and also as the methanol-to-olefins (MTO) method.

[0006] Such processing, where the feedstock containing oxygenated compounds is primarily methanol or a methanol-water combination, typically results in the release of significant amounts of water when seeking to convert such feedstock into light olefins. For example, such processing typically involves the release of approximately 2 moles of water per mole of ethylene formed and approximately 3 moles of water per mole of propylene formed.

[0007] The chosen reaction conditions for the methanol-to-olefins (MTO) process result in a high overall oxygen-containing compound feed conversion rate, exceeding 97%; however, unconverted reactants still exit the reactor as methanol and DME. To achieve the high overall yield of this method, it is necessary to recover the unconverted methanol and DME feed for recycling back to the MTO reactor. Besides olefins, the MTO process generates many other oxygen-containing compound byproducts, most notably acetone, acetaldehyde, and methyl ethyl ketone. Conventional methods for recovering and recycling methanol and DME also lead to the recycling of these oxygen-containing compound byproducts.

[0008] When recycled, these oxygen-containing byproducts are not readily converted on the MTO catalyst, and thus they can accumulate in the recycled stream. The high concentration of these oxygen-containing byproducts in the recycled stream can lead to operational difficulties and require greater capacity to recover and recycle them back into the reactor, which offers no advantage.

[0009] Seeking methods and equipment for separating oxygen-containing compounds from reactants and byproducts. Summary of the Invention

[0010] We have discovered that adding water to a mixture of oxygenated compounds increases their volatility relative to methanol. This invention discloses a method and apparatus for separating methanol from other oxygenated compounds. Water is separated from a feed stream containing water, methanol, and at least one other oxygenated compound to provide a water-rich feed stream and a methanol- and oxygenated compound-rich feed stream. This methanol- and oxygenated compound-rich feed stream, along with water, is fed into a column to provide an oxygenated compound-rich feed stream and a methanol- and water extract feed stream. The methanol and water can then be easily separated from each other.

[0011] Further details and embodiments of this disclosure will become apparent from the following detailed description. Attached Figure Description

[0012] Figure 1 A schematic diagram of the disclosed method and apparatus. Detailed Implementation

[0013] DME has a volatility close to that of propane, making it easily separable from unreacted methanol and oxygen-containing byproducts. However, oxygen-containing byproducts such as acetone, acetaldehyde, and methyl ethyl ketone (MEK) have volatility close to that of methanol, making them difficult to separate from methanol. Surprisingly, we found that adding diluent water increased the volatility of acetone, acetaldehyde, and MEK relative to methanol.

[0014] The initial separation of olefin products from water produces an aqueous stream containing unreacted methanol and other oxygenated byproducts, such as acetone, acetaldehyde, and MEK. A distillation column separates the bottom stream, which is essentially free of methanol and oxygenated byproducts, from the top stream, which contains most of the methanol and oxygenated byproducts. The top stream is then fed to a second distillation column to separate the oxygenated byproducts from the unreacted methanol. In this second distillation column, stripping water from the first distillation column can be introduced at the top to facilitate the separation of oxygenated byproducts from methanol. Adding water to the second distillation column further separates methanol from the oxygenated byproduct impurities. Initial water separation is required to concentrate the hydrocarbon oxygenated compounds, making them more volatile by adding dilution water.

[0015] As used in this article, oxygenated compounds generally refer to hydrocarbon oxygenated compounds to distinguish them from water; hydrocarbon oxygenated compounds may be referred to as oxygenated compounds.

[0016] The term "tower" refers to one or more distillation columns used to separate one or more components with different volatility. Unless otherwise specified, each column includes a condenser at the top of the column for condensing a portion of the overhead feed and refluxing it back to the top of the column, and a reboiler at the bottom of the column for vaporizing a portion of the bottom feed and returning it to the bottom of the column. The feed to the column may be preheated. Top pressure is the pressure of the vapor at the top of the column at the vapor outlet. Bottom temperature is the liquid temperature at the bottom outlet of the column. Top and bottom lines refer to the net lines from any downstream reflux or reboiler to the column. Stripping columns may omit the reboiler at the bottom of the column and instead provide the heating requirement and power for separating from a fluidized inert medium (such as steam). Stripping columns typically feed from the top tray and remove the main product from the bottom.

[0017] The oxygen-containing compound separation disclosed herein can be used not only in oxygen-containing compound olefin production methods, such as the MTO method and apparatus, but also in other scenarios. However, this method and apparatus will be described herein in the context of the MTO method and apparatus 10.

[0018] Turning to the accompanying drawings of method and apparatus 10, a superheated feed stream in line 12 is fed into oxygenated compound conversion reactor 202, which reacts oxygenated compounds such as methanol or DME with a fluidized catalyst. A hot steam reactor effluent stream in line 14 is removed from oxygenated compound conversion reactor 202, which periodically or continuously recycles the fluidized catalyst to regeneration zone 200 in a conventional manner to maintain desired selectivity and conversion rates. Reactor 202 is maintained under optimal conditions for converting oxygenated compounds to produce light olefin products and oxygenated byproducts. The hot steam reactor effluent stream may contain light olefins, water, and oxygenated compounds.

[0019] The hot steam reactor effluent in line 14 can be pre-cooled in reactor effluent heat exchanger 15 to recover heat before being fed into quench tower 20. In quench tower 20, the steam reactor effluent is de-superheated, neutralized with organic acids, and clarified with catalyst particles through direct contact with a water stream supplied from line 19, which can be taken from the stripping water stream in line 21. The quench reactor effluent in line 22 exits from quench tower 20 and is fed to product separation tower 24. Product separation tower 24 can be connected downstream of MTO reactor 202.

[0020] Product separator 20 comprises two sections for separating the reactor effluent stream into a product olefin stream in top line 40, an intermediate liquid stream in intermediate line 28, and a water stream in bottom line 26. The first or lower section receives the quenched reactor effluent stream in line 22. In the lower section, most of the heat is removed from the quenched reactor effluent stream, while water in the quenched reactor effluent stream is partially condensed to generate a product water stream in bottom line 26, which contains a portion of the oxygenated byproducts from the quenched reactor effluent stream in line 22. A portion of the product water stream is cooled and pumped to the top of the first section of product separator 24 to cool the quenched reactor effluent stream in line 22. A second section of the second bottom stream 26 is fed into water stripper 30. Water reflux containing oxygenated compound byproducts can also be fed into water stripper 30, these byproducts originating from the compression section 80 in reflux line 32. Water stripper 30 can be connected downstream of product separation tower 24.

[0021] The vapor feed from the first section of product separator 24 is introduced into the second section or upper section of the product separator. The intermediate feed stream in line 28, containing hydrocarbons, oxygenated byproducts, and liquid water, is withdrawn at the bottom of the upper section. A portion of the intermediate feed stream in line 28 is cooled and fed as reflux to the top of the second section of product separator 24. The remaining portion of the intermediate feed stream in line 28 is fed into coalescer 29 to separate the hydrocarbon overhead stream from the aqueous feed stream in line 34, which is fed back into the product water stream and pumped in line 36 to water stripper 30. The overhead product stream, containing olefins from the product separation column in line 40, can be delivered to compression section 80.

[0022] The product water stream in line 36 contains diluted hydrocarbon oxygenated compounds such as DME, methanol, acetaldehyde, acetone, and MEK. The water stripper 30 separates or strips the oxygenated compounds to a methanol- and oxygenated compound-rich stream in the top line 44, which is rich in both methanol and at least one other oxygenated compound, and to a water-rich stream in the bottom line 46. As used herein, the term "rich component stream" refers to a rich stream exiting a container with a higher component concentration than the feed to that container, and preferably higher than all other streams exiting that container. As used herein, the term "lean component stream" refers to a lean stream exiting a container with a lower component concentration than the feed to that container, and preferably lower than all other streams exiting that container.

[0023] A portion of the water-rich feed in the bottom line is reboiled and refluxed to the water stripper 30. The net water-rich feed in the bottom line 46 can be divided into the extract feed in line 62 supplied to the extractive distillation column 60, the water-rich feed in the remaining bottom line 47, and the stripping water supply feed in water supply line 21, which is fed to the quencher 20 in line 19 and the oxygenated absorber in line 102. The oxygenated feed in the top line 44 can be cooled and partially condensed and fed to the receiver separator 45. As used herein, the term "separator" means a container having an inlet and at least one top vapor outlet and a bottom liquid outlet, and may also have an outlet for the water-rich feed from the boot.

[0024] It can purify uncondensed light hydrocarbons from the receiver tower top line, while the lean hydrocarbon, methanol-rich, and oxygen-containing compound streams can be removed in the bottom line 48, containing methanol, DME, acetaldehyde, acetone, and MEK. A portion of the lean hydrocarbon, methanol-rich, and oxygen-containing compound streams can be refluxed back to the water stripper 30.

[0025] In one embodiment, the temperature at the bottom of the steam stripper 30 can be from 115°C (239°F) to 150°C (302°F), and the pressure at the top of the steam stripper can be from 75 kPa gauge pressure (11 psig) to 345 kPa (50 psig).

[0026] The term "connection" refers to the operative permission for fluid flow between enumerated components, which can be characterized as "fluid connectivity". The term "downstream connectivity" means that in downstream connectivity, at least a portion of the fluid flowing toward the main body can operatively flow from the object with which it is fluidly connected.

[0027] A lean hydrocarbon, methanol-rich, and oxygen-containing compound stream can be fed to extractive distillation column 60 to separate methanol from at least one other oxygen-containing compound. However, the lean hydrocarbon, methanol-rich, and oxygen-containing compound stream contains DME that is easily separated from methanol. Therefore, the lean hydrocarbon, methanol-rich, and oxygen-containing compound stream can be fed to DME stripper 50 to easily remove DME. DME stripper 50 can be connected downstream of water stripper 30. DME stripper 50 can separate or strip DME into a DME-rich stream in overhead line 52 and provide a lean DME, methanol-rich, and oxygen-containing compound stream in bottom line 54. The DME-rich stream in overhead line 52 can be recycled as reactant feed to MTO reactor 202. A portion of the lean DME, methanol-rich, and oxygen-containing compound stream can be reboiled and recycled to DME stripper 50. The clean, lean DME, methanol-rich, and oxygen-containing feed stream from the bottom line 54 can be fed into the extractive distillation column 60. The extractive distillation column 60 can be downstream connected to the water stripper 30 and located upstream of any product separation column 24 to ensure that no inert oxygen-containing compounds accumulate in the compression section 60 in the absence of a pathway for reflux back to the water stripper 30. Alternatively, in one embodiment, the extractive distillation column can be downstream connected to the DME stripper 50.

[0028] In one embodiment, the temperature at the bottom of the DME stripper 50 can be from 85°C (185℉) to 120°C (248℉), and the pressure at the top of the column can be from 75 kPa gauge pressure (11 psig) to 414 kPa (60 psig). In addition to or replacing the overhead condenser and receiver 45 used in the water stripper 30, the DME stripper 50 can utilize the overhead condenser and receiver separator to remove light hydrocarbon purifiers. The overhead material from the DME stripper can be recycled to the MTO reactor 202.

[0029] A feed stream of lean DME, rich methanol, and oxygenated compounds can be fed into a distillation column to separate methanol from at least one other oxygenated hydrocarbon and preferably all other oxygenated hydrocarbons. This separation will be difficult because the other oxygenated hydrocarbons have lower volatility relative to methanol. However, we have found that adding water increases the volatility of the oxygenated hydrocarbons acetaldehyde, acetone, and MEK relative to methanol, while slightly reducing the still high relative volatility of DME relative to methanol. Therefore, an alternative is to remove DME before adding water, as just described.

[0030] In one aspect, methanol is separated from an initial mixture of oxygenated compounds, which contains water, methanol, and at least one other hydrocarbon oxygenated compound such as acetaldehyde, acetone, or MEK. A large amount of water can be separated from the initial mixture to provide a water-lean mixture containing methanol and the at least one other oxygenated compound. This large amount of water needs to be removed to concentrate the oxygenated compounds in the initial mixture. DME can be separated from the water-lean mixture to provide a mixture of water-lean and DME. Water is then added to the water-lean mixture containing methanol and at least one other oxygenated compound to provide a water-rich mixture that enhances the volatility of the at least one other oxygenated compound relative to methanol. The added water can be taken from the large amount of water initially removed from the initial mixture. Methanol and water are then more easily extracted from the at least one other oxygenated compound in the water-rich mixture.

[0031] Moving to method and apparatus 10, a feed stream of lean DME, rich methanol, and oxygenated compounds from the clean bottom line 54 can be fed into extractive distillation column 60 to separate methanol from at least one other hydrocarbon oxygenated compound and preferably all other hydrocarbon oxygenated compounds. Alternatively, an extractant stream of water can be fed into extractive distillation column 60 at a location (e.g., at the top quarter of the column) or at a location (e.g., at the middle quarter of the column) above the column, where a feed stream of lean DME, rich methanol, and oxygenated compounds is introduced into the column. The extractant stream can be provided in line 62, which can be taken from a water-rich stream in the bottom line 46 of a water stripper.

[0032] The flow rate of the water-extractable feed stream entering the extractive distillation column 60 should be 1.5 to 3 times the flow rate of the hydrocarbon-oxygenated feed stream (which may also contain a large amount of water) entering the extractive distillation column 60, and should also be 1 to 3 times the flow rate of the entire lean DME, methanol-rich, and oxygenated feed stream.

[0033] Extractive distillation column 60 produces an oxygen-rich feed stream in its overhead line 64, which contains at least one other oxygenated hydrocarbon compound (such as acetone, acetaldehyde, MEK, and DME), and a methanol- and water-rich extract feed stream in its bottom line 66. A portion of the methanol- and water-rich feed stream in the bottom line 66 can be reboiled and refluxed back to extractive distillation column 60. The oxygen-rich feed stream in the overhead line 64 can be cooled and partially condensed before being fed to receiver separator 65. Uncondensed light hydrocarbons from the receiver overhead line can be purified, while a lean, oxygen-rich feed stream containing DME, acetaldehyde, acetone, and MEK can be removed in the receiver bottom line 68. A portion of the lean, oxygen-rich feed stream can be refluxed back to extractive distillation column 60 as reflux at a location above where the extract feed stream is added. The purified light hydrocarbons can be fed to the light olefin recovery section.

[0034] At least 99% by weight, and preferably at least 99.5% by weight, of hydrocarbon oxygenated compounds, other than the methanol fed into the extractive distillation column 60, can be recovered from the oxygen-rich feed stream in the top line 64 of the extractive distillation column 60 and the lean-hydrocarbon, oxygen-rich feed stream in the bottom line 68 of the extractive receiver 65. At least 90% by weight, and preferably at least 95% by weight, of methanol can be recovered from the methanol- and water-rich feed stream in the clean bottom line 66.

[0035] The extractive distillation column 60 may have the following operating conditions: a bottom temperature ranging from 75°C (167℉) to 150°C (302℉) and a top pressure ranging from 75 kPa gauge pressure (11 psig) to 200 kPa gauge pressure (29 psig). The extractive distillation column 60 may be connected downstream of the top line 44 of the water stripping column 30 and downstream of the bottom line 46 of the water stripping column.

[0036] The recovered methanol is an MTO reactant that can be recycled back to the MTO reactor 202, but it is undesirable to recycle water along with the methanol. Therefore, the methanol-rich and water-rich stream from the clean bottom line 66 can be fed to the methanol stripper 70 to separate the methanol-rich stream from the final water-rich stream in the top line 72 from the final water-rich stream in the bottom line 74. Then, in the absence of inert oxygen-containing compounds, the methanol-rich stream from the top line 72 can be recycled back to the MTO reactor 202, where these inert oxygen-containing compounds do not react and may otherwise accumulate in the method and apparatus 10. A portion of the final water-rich stream in the bottom line 74 can be reboiled and recycled back to the methanol stripper 70. The final water-rich stream from the clean bottom line 74, along with the unrecycled portion of the remaining water-rich stream from the bottom line 47 of the water stripper bottom line 46, can be sent to the water treatment section in line 75.

[0037] The product olefin stream returning in the product overhead line 40 carries valuable olefin products that must be recovered. The compression section 80 increases the pressure of the product olefin stream required for downstream processing, such as for conventional light olefin recovery units. The compression section 80 may include a first separation drum 82 that separates the product olefin stream into a pressurized first olefin-rich stream in the overhead line 83 and an oxygen-rich, water-containing stream in the bottom line 84. The olefin-rich stream in the overhead line 83 can be fed to a compressor 85 for cooling and directed to a second separation drum 86. The water-containing stream in the bottom line 84 is pumped via manifold 76 to a reflux line 32, which returns the water stream, along with the product water stream in the bottom line 36, to the water stripper 30.

[0038] The compression section 80 may include a second separation drum 86 that separates the pressurized first olefin-rich stream into a second pressurized olefin-rich stream in the overhead line 87 and a second oxygen-rich aqueous stream in the bottom line 88. The second olefin-rich stream in the overhead line 87 may be fed to a compressor 89 for cooling and directed to a third separation drum 90. The aqueous stream in the bottom line 88 is pumped via a manifold 76 to a reflux line 32, which returns the aqueous stream, along with the product aqueous stream in the bottom line 36, to the water stripper 30.

[0039] The compression section 80 may include a third separation drum 90, which separates the pressurized second olefin-rich stream into a third pressurized olefin-rich stream in the top line 91 and a third oxygen-rich aqueous stream in the bottom line 92. The third olefin-rich stream in the top line 91 may be fed to the oxygen-rich absorber 100. The aqueous stream in the bottom line 92 is pumped via manifold 76 to the reflux line 32, which returns the aqueous stream, along with the product aqueous stream in the bottom line 36, to the water stripper 30.

[0040] Suitable compressor types may include centrifugal, positive displacement, reciprocating, diaphragm, screw, etc. In one embodiment, compressors 85 and 89 in compression section 80 are centrifugal compressors. The final discharge pressure may be between 1,000 kPa gauge pressure (145 psig) and 2,000 kPa gauge pressure (290 psig). The compressor discharge can be cooled to approximately ambient temperature using conventional heat transfer methods.

[0041] As shown in the accompanying drawings and according to a preferred embodiment, at least a portion of the compressed product stream via the top line 91 is contacted and cooled in the oxygenated compound absorber 100 under conditions that effectively absorb at least a certain amount of effluent oxygenated compounds. This cooled lean water stream is introduced via line 102 and taken from the rich water stream in the bottom line 46 of the water stripper, wherein water is not directly taken from the product separation tower 20 without prior removal of oxygenated compounds. The contact in the oxygenated compound absorber 100 produces an olefin-rich stream in the top line 104 and an olefin-rich water stream in the bottom line 106 containing a certain amount of effluent oxygenated compounds. The olefin-rich stream in the top line 104 can be fed to a third compressor 108, where it is partially condensed by cooling and fed to the absorber separator 110. The stream from the olefin recovery section in line 120 can be fed together with the compressed olefin-rich stream in line 104 to the absorber separator 110. The water-rich feed stream in the bottom pipeline 106 can be fed to the return pipeline 32 via the manifold 76, which allows the water stream to return to the water stripper 30 together with the product water stream in the bottom pipeline 36 of the separation tower.

[0042] The oxygen-containing compound absorber 100 may have the following operating conditions: a bottom temperature range of 30°C (86℉) to 50°C (122℉) and a top pressure range of 1,500 kPa gauge pressure (217 psig) to 2,000 kPa gauge pressure (290 psig).

[0043] The absorber separator 110 separates the pressurized olefin-rich feed stream into a light gas stream in line 112 (which can be fed to the scrubber for acid gas removal), a condensed olefin-rich feed stream in bottom line 114 (which can be sent to the olefin recovery section), and a water-containing guide stream in guide line 116. The water-containing guide stream in guide line 116 can be pumped to reflux line 32 via manifold line 76, which returns the water-containing guide stream and the product water stream in bottom line 36 of the separator to the water stripper 30.

[0044] Method and apparatus 10 provides the recovery of reactant oxygenated compounds for recycling back to MTO reactor 202 without recycling inert oxygenated compounds that would accumulate in the system without recovery. This is achieved by removing the inert oxygenated compounds from the reactive oxygenated compounds in the water stream prior to recycling to MTO reactor 202. Additionally, water is added back to the inert oxygenated compounds, which improves and facilitates the separation of these inert oxygenated compounds from the reactant oxygenated compounds and methanol.

[0045] Example

[0046] The relative volatility of a mixture of methanol with a large amount of water and a small amount of hydrocarbon oxygenated compounds was calculated. The relative volatility of the same mixture was then recalculated after dilution with more water than methanol at 0.45 MPa and 43.3 °C. The results are shown in Table 1. The K value is the ratio of the molar fractions in the gas phase to the molar fractions in the liquid phase, commonly referred to as "y / x".

[0047] Table 1

[0048]

[0049] Adding dilution water increases the relative volatility of acetaldehyde, acetone, and MEK compared to methanol, thus making their separation from methanol easier. The relative volatility of DME relative to methanol is negatively affected by water dilution. However, the relative volatility of DME relative to methanol remains very high, and there are no separation challenges, especially compared to the advantages gained from increased relative volatility of other oxygenated hydrocarbons.

[0050] We simulated the operation of a water stripper column with 30 ideal stages and a top-feed stage (15 stages). The reflux rate was 15,440 kg / h, with a top pressure of 329 kPa (gauge pressure) (48 psig) and a bottom temperature of 134 °C (273 °F). The reboiler load was 23.2 GJ / h, and the condenser load was -15.2 GJ / h. In a second simulation, an additional 14,875.9 g of water was added to the top stage of the column. The results with and without water addition are shown in Table 2.

[0051] Table 2

[0052]

[0053] Adding dilution water to an extractive distillation column significantly reduces the amount of hydrocarbon oxygenated compounds in the bottom stream, except for methanol, which is the component that needs to be separated at the bottom. Most of the methanol still flows out at the bottom along with water, while almost all other hydrocarbon oxygenated compounds flow out in the top stream. Adding dilution water allows at least 99.7% by weight of hydrocarbon oxygenated compounds to be recovered from the methanol at the top and at least 95% of the methanol reactants to be recovered at the bottom. The simple addition of dilution water in the separation process unexpectedly produces remarkable results.

[0054] Specific implementation plan

[0055] While the following description is presented in conjunction with specific embodiments, it should be understood that the description is intended to illustrate, and not limit, the scope of the foregoing description and the appended claims.

[0056] A first embodiment of the present invention is a method for separating methanol from other oxygen-containing compounds. The method includes separating water from a feed stream containing water, methanol, and at least one other oxygen-containing compound to provide a water-rich feed stream and a methanol- and oxygen-containing compound-rich feed stream; feeding the methanol- and oxygen-containing compound-rich feed stream and water into an extractive distillation column to provide an oxygen-rich feed stream and a methanol- and water extract feed stream. An embodiment of the present invention is any one or all of the embodiments described above to the first embodiment described above, wherein the at least one other oxygen-containing compound includes dimethyl ether, and the method further includes separating the dimethyl ether from the oxygen-rich feed stream to provide a dimethyl ether-rich feed stream and a dimethyl ether-lean, methanol- and oxygen-containing compound-rich feed stream, and feeding the DME-lean, methanol- and oxygen-containing compound-rich feed stream into the extractive distillation column. An embodiment of the present invention is any one or all of the embodiments described above to the first embodiment described above, wherein the method further includes feeding the dimethyl ether-rich feed stream into an oxygen-containing compound conversion reactor. The embodiments of the present invention are one, any, or all of the embodiments described above to the first embodiment described above in this paragraph, wherein the water fed to the extractive distillation column is taken from a water-rich stream. The embodiments of the present invention are one, any, or all of the embodiments described above to the first embodiment described above in this paragraph, wherein the method further includes separating methanol from water to provide a water-rich stream and a methanol-rich stream. The embodiments of the present invention are one, any, or all of the embodiments described above to the first embodiment described above in this paragraph, wherein the method further includes feeding the methanol-rich stream to an oxygen-containing compound conversion reactor. The embodiments of the present invention are one, any, or all of the embodiments described above to the first embodiment described above in this paragraph, wherein the mixture of water, methanol, and at least one other oxygen-containing compound further comprises light hydrocarbons, and the method further includes separating the light hydrocarbons from the methanol-rich and oxygen-containing compound stream. The embodiments of the present invention are one, any, or all of the embodiments described above to the first embodiment described above in this paragraph, wherein the mixture of water, methanol, and at least one other oxygen-containing compound further comprises light hydrocarbons, and the method further includes separating the light hydrocarbons from the oxygen-rich compound stream. The embodiments of the present invention are one, any, or all of the embodiments described above to the first embodiment described above in this paragraph, wherein these other oxygen-containing compounds include one of acetaldehyde, acetone, and methyl ethyl ketone. The embodiments of the present invention are one, any, or all of the embodiments described above to the first embodiment described above in this paragraph, wherein water in the extractive distillation column increases the volatility of the other oxygen-containing compounds relative to methanol.The embodiments of the present invention are one, any, or all of the embodiments described above to the first embodiment described above in this paragraph, wherein the feed stream containing water, methanol, and at least one other oxygen-containing compound is provided by the bottom feed stream of the product separation tower. The embodiments of the present invention are one, any, or all of the embodiments described above to the first embodiment described above in this paragraph, wherein the feed stream containing water, methanol, and at least one other oxygen-containing compound is provided by the bottom feed stream of the oxygen-containing compound absorption tower.

[0057] A second embodiment of the present invention is an apparatus for recovering oxygen-containing compounds, comprising: a product separation tower connected downstream of an MTO reactor; a water stripping tower connected downstream of the product separation tower; and an extractive distillation tower connected downstream of the water stripping tower, the water stripping tower being located upstream of the product separation tower in any communication. An embodiment of the present invention is one, any one, or all of the embodiments described above to the second embodiment described above in this paragraph. The apparatus further includes a DME stripping tower connected downstream of the water stripping tower, and the extractive distillation tower is connected downstream of the DME stripping tower. An embodiment of the present invention is one, any one, or all of the embodiments described above to the second embodiment described above in this paragraph, wherein the extractive distillation tower is connected downstream of both the top and bottom pipelines of the water stripping tower.

[0058] A third embodiment of the present invention is a method for separating methanol from an initial mixture of oxygenated compounds, the initial mixture comprising water, methanol, and at least one other oxygenated compound. The method includes: separating water from the initial mixture to provide a water-lean mixture comprising methanol and the at least one other oxygenated compound; adding water to the water-lean mixture comprising methanol and the at least one other oxygenated compound to provide a water-rich mixture; and extracting methanol and water from the at least one other oxygenated compound in the water-rich mixture. Embodiments of the present invention are any one or all of the embodiments described above to the third embodiment in this paragraph, and the method further includes separating dimethyl ether from the water-lean mixture. Embodiments of the present invention are any one or all of the embodiments described above to the third embodiment in this paragraph, wherein the water added to the water-lean mixture is taken from water separated from the initial mixture.

[0059] Although no further detailed description has been provided, it is believed that those skilled in the art will be able to make full use of the invention by employing the foregoing description and will be able to readily identify the essential features of the invention without departing from its spirit and scope, and to make various changes and modifications to adapt it to various uses and situations. Therefore, the foregoing preferred embodiments should be understood as illustrative only and not as limiting the remainder of this disclosure in any way, and are intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0060] In the foregoing, all temperatures are expressed in degrees Celsius, and all portions and percentages are by weight unless otherwise specified.

Claims

1. A method for separating methanol from other oxygen-containing compounds, the method comprising: The effluent from the oxygen-containing compound conversion reactor is separated into a product olefin stream, an intermediate liquid stream, and a water stream in a product separator; The water stream containing water, methanol and at least one other oxygenated compound is separated in a water stripper to provide a water-rich stream and a methanol- and oxygenated compound-rich stream, wherein the other oxygenated compound includes at least one of acetaldehyde, acetone and methyl ethyl ketone. The methanol-rich and oxygen-containing compound stream and the water-rich stream are fed into the extraction tower to provide an oxygen-rich stream and a methanol and water extraction stream.

2. The method of claim 1, wherein the at least one other oxygen-containing compound comprises dimethyl ether, and the method further comprises separating the dimethyl ether from the oxygen-rich stream to provide a dimethyl ether-rich stream and a dimethyl ether-lean, methanol-rich, and oxygen-containing compound-rich stream, and feeding the dimethyl ether-lean, methanol-rich, and oxygen-containing compound-rich stream to the extraction tower.

3. The method according to claim 2, further comprising feeding the dimethyl ether-rich stream into the reactor.

4. The method according to claim 1, further comprising feeding the methanol-rich feed stream into a reactor.

5. The method of claim 1, wherein the water stream comprising water, methanol and at least one other oxygen-containing compound further comprises light hydrocarbons, and the method further comprises separating the light hydrocarbons from the methanol- and oxygen-containing compound-rich stream.

6. The method of claim 1, wherein the water stream comprising water, methanol and at least one other oxygen-containing compound further comprises light hydrocarbons, and the method further comprises separating the light hydrocarbons from the oxygen-rich stream.

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