Method and system for integrating a methyl TERT-butyl ether production process with an isobutylene production process

Abstract

The present disclosure provides a method and system for integrating MTBE production with isobutylene production, the method including isomerizing a mixed hydrocarbon feed stream to form an isobutane stream; dehydrogenating the isobutane stream to form an isobutylene stream; reacting the isobutylene stream with methanol to form an MTBE product stream; separating at least a portion of impurities from the MTBE product stream to form a MTBE feed stream; decomposing MTBE in the MTBE feed stream to form a decomposed MTBE product stream; treating the decomposed MTBE product stream with water to form a wash water stream comprising methanol and a water-washed product stream comprising isobutylene; separating methanol from the wash water stream to form a methanol recovery stream; separating at least a portion of DME and metal ions from the methanol recovery stream to form a purified methanol stream; and feeding the purified methanol stream to the MTBE synthesis reactor.

Description

23 CHEM0042-WO-ORD1DESCRIPTIONMETHOD AND SYSTEM FOR INTEGRATING A METHYL TERT-BUTYL ETHER PRODUCTION PROCESS WITH AN ISOBUTYLENE PRODUCTION PROCESSTECHNOLOGICAL FIELD

[0001] The present disclosure relates to methods and systems for integrating the production of methyl tert-butyl ether (MTBE) with the production of isobutylene.BACKGROUND

[0002] MTBE is an organic compound that is used as an additive in gasoline to enhance the octane number of the gasoline. A common synthesis technique for MTBE involves etherification of isobutylene by reaction with methanol in the presence of an acidic catalyst. Generally, isobutylene and methanol are fed into a fixed bed reactor to produce an MTBE-containing effluent.

[0003] Isobutylene is an organic compound that is used as an additive, or as a precursor to synthesize an additive such as MTBE, and is found in a variety of products, including gasoline, sealants, and plastics. Isobutylene used for MTBE synthesis can be obtained from C4 hydrocarbon feed streams in a dehydrogenation unit where isobutane is dehydrogenated to isobutylene in the presence of a catalyst.

[0004] Integration of MTBE synthesis and isobutylene synthesis processes has been proposed. See, for example, US9422205 to Brianti et al. However, there remans a need to provide integrated synthesis processes that make efficient use of reagents while preserving the desired purity of the end products.BRIEF SUMMARY

[0005] Example implementations of the present disclosure are directed to methods and systems for enhancing both isobutylene production efficiency and MTBE production efficiency by, for example, using closed loop recycling of methanol generated as a byproduct of isobutylene production to an MTBE production unit. Recycling of methanol from isobutylene production to MTBE synthesis is challenging due to impurities typically present in the methanol that can adversely impact MTBE synthesis. The present disclosure provides an integrated system that addresses this challenge and produces high quality MTBE using such recycled methanol.

[0006] The present disclosure includes, without limitation, the following embodiments.

[0007] Embodiment 1 : A method of integrating methyl tert-butyl ether (MTBE) production with isobutylene production, the method comprising: i) isomerizing a mixed hydrocarbon feed stream comprising n-butane to form an isobutane feed stream comprising isobutane; ii)23 CHEM0042-WO-ORD2 dehydrogenating the isobutane in the isobutane feed stream in a dehydrogenation reactor to convert at least a portion of the isobutane to isobutylene and form an isobutylene stream comprising isobutylene and unconverted isobutane; iii) reacting the isobutylene stream with methanol from a purified methanol stream in an MTBE synthesis reactor to form an MTBE product stream comprising primarily MTBE and impurities; iv) separating at least a portion of the impurities from the MTBE product stream to form a MTBE feed stream comprising primarily MTBE; v) decomposing MTBE in the MTBE feed stream to form a decomposed MTBE product stream comprising primarily methanol, isobutylene, and MTBE; vi) treating the decomposed MTBE product stream with water to form a wash water stream comprising methanol, water, and MTBE and a water-washed product stream comprising isobutylene; vii) separating methanol from the wash water stream to form a methanol recovery stream comprising methanol, metal ions, and dimethyl ether (DME); viii) separating at least a portion of the DME and the metal ions from the methanol recovery stream to form the purified methanol stream; and ix) feeding the purified methanol stream to the MTBE synthesis reactor or in other words feeding the purified methanol stream to the MTBE synthesis reactor to step (iii).

[0008] Embodiment 2: The method of Embodiment 1, wherein the impurities of the MTBE product stream comprise unconverted isobutane, and the iv) separating step comprises separating at least a portion of the unconverted isobutane from the MTBE product stream to form an isobutane recycle stream.

[0009] Embodiment 3 : The method of Embodiment 2, further comprising treating the isobutane recycle stream in an oxygenate removal unit to remove at least a portion of oxygenates and forming a purified isobutane recycle stream, and feeding the purified isobutane recycle stream to the dehydrogenation reactor, optionally wherein the oxygenate removal unit comprises an adsorbent material.

[0010] Embodiment 4: The method of any one of Embodiments 1 to 3, wherein the impurities of the MTBE product stream further comprise additional hydrocarbons having a molar mass higher and / or lower than MTBE, and the iv) separating step further comprises separating at least a portion of the additional hydrocarbons from the MTBE product stream.

[0011] Embodiment 5 : The method of any one of Embodiments 1 to 4, wherein the iv) separating step comprises one or more distillation columns.

[0012] Embodiment 6: The method of any one of Embodiments 1 to 5, wherein the viii) separating step comprises feeding the methanol recovery stream to a separation unit comprising one or more distillation columns to remove at least a portion of the DME and form a DME-23 CHEM0042-WO-ORD3 reduced methanol stream and treating the DME-reduced methanol stream with an ion exchange resin to remove at least a portion of the metal ions and form the purified methanol stream.

[0013] Embodiment 7 : The method of any one of Embodiments 1 to 6, further comprising decanting water from the methanol recovery stream.

[0014] Embodiment 8: The method of any one of Embodiments 1 to 7, wherein the purified methanol stream comprises about 98% molar fraction of methanol or higher and / or about 0.01 molar fraction of DME or lower, such as about 0.001 molar fraction of DME or lower.

[0015] Embodiment 9: A system for integrating methyl tert-butyl ether (MTBE) production with isobutylene production, the system comprising: one or more isomerization reactors in fluid communication with a mixed hydrocarbon feed stream comprising n-butane, the one or more isomerization reactors configured to convert at least a portion of the n-butane of the feed stream to isobutane, thereby forming an isobutane feed stream comprising isobutane; one or more dehydrogenation reactors in fluid communication with the isobutane feed stream and configured to produce an isobutylene stream, the isobutylene stream comprising isobutylene and unconverted isobutane; one or more MTBE synthesis reactors in fluid communication with the isobutylene stream and a purified methanol stream, the one or more MTBE synthesis reactors adapted to react isobutylene with methanol and produce an MTBE product stream comprising primarily MTBE and impurities; one or more purification units in fluid communication with the MTBE product stream and configured to separate at least a portion of the impurities from the MTBE product stream and produce an MTBE feed stream; one or more decomposition reactors in fluid communication with the MTBE feed stream and configured to decompose MTBE and produce a decomposed MTBE product stream comprising primarily methanol, isobutylene, and MTBE; a wash water treatment unit adapted to treat the decomposed MTBE product stream with water to form a wash water stream comprising methanol, water, and MTBE and a water-washed product stream comprising isobutylene; one or more separation units in fluid communication with the wash water stream and configured to separate the methanol from the wash water stream and produce a methanol recovery stream, the mixed methanol recovery stream comprising methanol, metal ions, and dimethyl ether (DME); and one or more distillation columns and one or more metal ion removal units in fluid communication with the methanol recovery stream and configured to separate at least a portion of the DME and at least a portion of the metal ions, respectively, from the methanol recovery stream and form the purified methanol stream, the purified methanol stream being in fluid communication with the one or more MTBE synthesis reactors.23 CHEM0042-WO-ORD4

[0016] Embodiment 10: The system of Embodiment 9, wherein the impurities of the MTBE product stream comprise one or more oxygenates and unconverted isobutane, and the one or more purification units in fluid communication with the MTBE product stream comprises at least one separation unit configured to separate at least a portion of the unconverted isobutane from the MTBE product stream and produce an isobutane recycle stream, the isobutane recycle stream being in fluid communication with the one or more dehydrogenation reactors.

[0017] Embodiment 11: The system of Embodiment 10, further comprising one or more oxygenate removal units in fluid communication with the isobutane recycle stream, the one or more oxygenate removal units configured to remove at least a portion of the oxygenates from the isobutane recycle stream and produce a purified isobutane recycle stream, the purified isobutane recycle stream being in fluid communication with the one or more dehydrogenation reactors, optionally wherein the one or more oxygenate removal units comprises a bed of adsorbent material.

[0018] Embodiment 12: The system of Embodiments 10 or 11, wherein the impurities of the MTBE product stream further comprise additional hydrocarbons having a molar mass higher and / or lower than MTBE, and the one or more purification units in fluid communication with the MTBE product stream comprise at least one fractionation column in fluid communication with the MTBE product stream configured to remove at least a portion of the additional hydrocarbons from the MTBE product stream.

[0019] Embodiment 13: The system of any one of Embodiments 9 to 12, further comprising a decanter in fluid communication with the methanol recover stream configured to remove water from the methanol recovery stream.

[0020] Embodiment 14: The system of any one of Embodiments 9 to 13, wherein the one or more distillation columns in fluid communication with the methanol recovery stream produces a bottoms stream having reduced DME content, and the bottoms stream is in fluid communication with the one or more metal ion removal units.

[0021] Embodiment 15: The system of any one of Embodiments 10 to 14, wherein the one or more metal ion removal units comprises a bed of ion exchange resin.

[0022] These and other features, aspects, and advantages of the present disclosure will be apparent from a reading of the following detailed description together with the accompanying figures, which are briefly described below. The present disclosure includes any combination of two, three, four or more features or elements set forth in this disclosure, regardless of whether such features or elements are expressly combined or otherwise recited in a specific example23 CHEM0042-WO-ORD5 implementation described herein. This disclosure is intended to be read holistically such that any separable features or elements of the disclosure, in any of its aspects and example implementations, should be viewed as combinable, unless the context of the disclosure clearly dictates otherwise.

[0023] It will therefore be appreciated that this Brief Summary is provided merely for purposes of summarizing some example implementations so as to provide a basic understanding of some aspects of the disclosure. Accordingly, it will be appreciated that the above described example implementations are merely examples and should not be construed to narrow the scope or spirit of the disclosure in any way. Other example implementations, aspects and advantages will become apparent from the following detailed description taken in conjunction with the accompanying figures which illustrate, by way of example, the principles of some described example implementations.BRIEF DESCRIPTION OF THE FIGURES

[0024] Having thus described aspects of the disclosure in the foregoing general terms, reference will now be made to the accompanying figures, which are not necessarily drawn to scale, and wherein:

[0025] FIG. 1 is a schematic representation of a system that integrates the production of isobutylene with the production of MTBE, according to an example embodiment of the present disclosure;

[0026] FIG. 2 is a schematic representation of a system for processing a methanol recycle stream, according to an example embodiment of the present disclosure;

[0027] FIG. 3 is a schematic representation of a system for processing an isobutane recycle stream, according to an example embodiment of the present disclosure; and

[0028] FIG. 4 is a schematic representation of the processing system of EXPERIMENTAL Example 1.DETAILED DESCRIPTION

[0029] Some implementations of the present disclosure will now be described more fully hereinafter with reference to the accompanying figures, in which some, but not all implementations of the disclosure are shown. Indeed, various implementations of the disclosure may be embodied in many different forms and should not be construed as limited to the implementations set forth herein; rather, these example implementations are provided so that this23 CHEM0042-WO-ORD6 disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like reference numerals refer to like elements throughout.

[0030] Unless specified otherwise or clear from context, references to first, second or the like should not be construed to imply a particular order. A feature described as being above another feature (unless specified otherwise or clear from context) may instead be below, and vice versa; and similarly, features described as being to the left of another feature else may instead be to the right, and vice versa. Also, while reference may be made herein to quantitative measures, values, geometric relationships or the like, unless otherwise stated, any one or more if not all of these may be absolute or approximate to account for acceptable variations that may occur, such as those due to engineering tolerances or the like.

[0031] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other (e.g., ranges of “up to 25 wt. %, or, more specifically, 5 wt. % to 20 wt. %”, is inclusive of the endpoints and all intermediate values of the ranges of “5 wt. % to 25 wt. %,” etc.). “Combination” is inclusive of blends, mixtures, alloys, reaction products, and the like.

[0032] As used herein, unless specified otherwise or clear from context, the “or” of a set of operands is the “inclusive or” and thereby true if and only if one or more of the operands is true, as opposed to the “exclusive or” which is false when all of the operands are true. Thus, for example, “[A] or [B]” is true if [A] is true, or if [B] is true, or if both [A] and [B] are true. Further, the articles “a” and “an” mean “one or more,” unless specified otherwise or clear from context to be directed to a singular form.

[0033] Conventionally, MTBE can be produced by processing a C4 hydrocarbon mixture in an isomerization reactor and a dehydrogenation reactor, sequentially. The effluent from the dehydrogenation reactor comprising isobutylene is then fed into a MTBE synthesis reactor to react with methanol and produce an effluent comprising MTBE. To produce isobutylene, the MTBE effluent can be fed to a decomposition reactor where the MTBE is decomposed (dissociated, or chemically broken into fragments such as isobutylene and methanol). The effluent from the decomposition reactor comprising isobutylene, methanol, and MTBE is then washed with water to produce a wash water stream comprising methanol, water, and MTBE, and a water-washed product stream comprising isobutylene.

[0034] To increase the efficiency of isobutylene production and the MTBE production, it is desirous to recover each of MTBE and methanol from the wash water stream for recycling back into the production processes. For example, the MTBE can be recovered and recycled back to23 CHEM0042-WO-ORD7 the purification unit or the decomposition unit to improve the efficiency of isobutylene production. In the recovery of methanol, however, oftentimes impurities remain such as dimethyl ether (DME), water, and / or metal ions, which can damage the dehydrogenation catalyst and / or the MTBE synthesis catalyst and decrease the efficiency of the MTBE production process. In particular, the

[0035] According to the present disclosure, a system and method of integrating MTBE production with isobutylene production is provided. MTBE obtained at least partially from an MTBE production process is fed to an isobutylene production process to convert the MTBE to isobutylene and methanol. The methanol is then recovered from the isobutylene production process and fed to a methanol cleaning unit for recycling back to an MTBE synthesis unit in the MTBE production process. The recycled methanol includes reduced impurities, thereby increasing the efficiency of both the isobutylene production process and the MTBE production process.

[0036] Referring to FIG. 1, a system 10 for integrating an MTBE production process 100 with an isobutylene production process 300 is schematically depicted, which begins with flowing a mixed hydrocarbon feed stream 110 into the MTBE production process 100. The mixed hydrocarbon feed stream 110 is a C4-rich stream, that primarily includes C4 hydrocarbons (e.g., n-butane and / or isobutane), and possibly small amounts of C1-C3 or C5+ hydrocarbons. An example mixed hydrocarbon feed stream comprises about 95% by weight of n-butane or higher, such as about 96% or more, about 97% or more, about 98% or more, or about 99% or more, and about 0.5% by weight or less of C1-C3 or C5+ hydrocarbons, such as about 0.1% to about 0.2%. The mixed hydrocarbon feed stream 110 source can be liquefied petroleum gas or derived from natural gas and oil extraction, oil refining, or waste or renewable vegetable oils.

[0037] According to embodiments of the present disclosure, the mixed hydrocarbon feed stream 110 is in fluid communication with one or more isomerization reactors 112. The one or more isomerization reactors 112 can be configured to isomerize at least a portion of n-butane of the mixed hydrocarbon feed stream 110 to produce isobutane feed stream 114 that primarily includes isobutane. The one or more isomerization reactors 112 can include a fixed bed reactor, a continuous catalytic converter, an adiabatic or a cooled isothermal converter reactor. In one implementation, the one or more isomerization reactors 112 includes two reactors serially connected. In one embodiment, the one or more isomerization reactors 112 may comprise a catalyst including, for example, Pt / AlCh / AhCE, Pt / AlCh / zeolite, Pt / SOf2-ZrO2, or any combination thereof.23 CHEM0042-WO-ORD8

[0038] According to embodiments of the present disclosure, the isobutylene feed stream 114 is in fluid communication with one or more dehydrogenation reactors 116, which are configured to dehydrogenate isobutane to produce isobutylene stream 118 primarily including isobutylene and unconverted (unreacted) isobutane. In some implementations, the one or more dehydrogenation reactors 116 comprise a plurality of fixed bed reactors serially connected. In one embodiment, the one or more dehydrogenation reactors 116 can comprise three or more parallel fixed bed reactors and a catalyst regeneration system.

[0039] When the fixed bed dehydrogenation reactor is in operation, one or more reactors are on line (in dehydrogenation mode), and one or more fixed bed reactors are in regeneration mode. In a typical fixed bed dehydrogenation process, an aliphatic hydrocarbon passes through a dehydrogenation catalyst bed and is dehydrogenated to a complementary olefin. The product (dehydrogenated hydrocarbon) of the fixed bed dehydrogenation unit may comprise, for example, isobutylene. The dehydrogenation reactions may include reactions (i) and / or (ii) as follows, where "n" in reactions (i) and (ii) is the number of carbon atoms in a hydrocarbon molecule, and "n" is less than 5:(i) CnH2n+2^CnH2n+H2, and / or(ii) CnH2n^CnH2n-2+H2.

[0040] A fixed bed reactor in dehydrogenation mode first dehydrogenates the hydrocarbon feed for a period of time. Then, the fixed bed reactor is purged with steam. In a subsequent regeneration mode, heated air is blown through to decoke the catalyst disposed in the fixed bed reactor. The reactor is in turn evacuated and the catalyst in the reactor undergoes reduction with hydrogen. After catalyst reduction, the reactor is placed back on line for dehydrogenation reaction. In certain embodiments, the reaction conditions during dehydrogenation include a reaction temperature of 520 to 640 °C, a reaction pressure of 0.36 to 1.2 bar, and / or a weight hourly space velocity in a range of 0.2 to 4.0 hr-1. In some implementations, the dehydrogenation reaction occurs in the presence of a catalyst including, for example, chromia / alumina.

[0041] According to embodiments of the present disclosure, the isobutylene stream 118 is in fluid communication with one or more MTBE synthesis reactors 120, where isobutylene is reacted with methanol to produce an MTBE product stream 122. The MTBE product stream 122 primarily includes MTBE and impurities, such as hydrocarbon compounds having a molar mass higher and / or lower than the molar mass of MTBE. In one implementation the impurities primarily include unconverted (unreacted) isobutane. In another implementation, the impurities23 CHEM0042-WO-ORD9 further include one or more oxygenates, such as DME, MTBE, methyl sec-butyl ether (MSBE), TBA, or combinations thereof.

[0042] The one or more MTBE synthesis reactors 120 can include an adiabatic or a cooled isothermal converter reactor. Whether the synthesis reaction is exothermic and the temperature rise in each reactor will depend, in part, on whether the reactor is adiabatic or isothermal. Example reaction conditions include a temperature range of 40 to 100 °C, a pressure of 5 to 8 bar, and a liquid hourly space velocity of 2 to 12 hr-1. In some implementations the synthesis reaction occurs in the presence of catalyst including, for example, cation exchange resins, polystyrene divinyl benzene mounted ion exchange resins, polymeric support mounted ion exchange resins, or combinations thereof. In some embodiments, the one or more MTBE reactors include a macroreticular, strongly acidic, cationic, polymeric resin catalyst, such as AMBERLYST™ 15, AMBERLYST™ 35, AMBERLYST™ CSP2 and AMBERLYST™ CSP3.

[0043] According to embodiments of the present disclosure, the MTBE product stream 122 is in fluid communication with one or more purification units 200 configured to separate at least a portion of the impurities from the MTBE product stream 122 and form MTBE feed stream 310. The one or more purification units 200 can be found in the MTBE production process 100, the isobutylene production process 300, or a combination thereof. In some implementations the one or more purification units 200 can include at least one separation unit configured to separate at least a portion of unconverted (unreacted) isobutane from the MTBE product stream 122, and produce an isobutane recycle stream 210. In one embodiment, the isobutane recycle stream 210 is in fluid communication with the one or more dehydrogenation reactors 116. The type of separation unit can vary, but will typically include at least one distillation column and / or an adsorption process.

[0044] In some implementations, the one or more purification units 200 further include at least one fractionation column. The at least one fractionation column can be configured to remove at least a portion of the hydrocarbon compounds having a higher and / or lower molar mass than the molar mass of MTBE from the MTBE product stream 122. In one embodiment, at least a portion of hydrocarbon compounds having a higher molar mass and lower molar mass are removed from the MTBE product stream 122 to form heavy stream 212 and light stream 214, respectfully.

[0045] According to embodiments of the present disclosure, the MTBE feed stream 310 is in fluid communication with one or more decomposition reactors 312, which are configured to produce decomposed MTBE product stream 314 through the cracking of MTBE in the presence23 CHEM0042-WO-ORD10 of a catalyst. The cracking of MTBE can occur in the vapor phase, at temperatures and pressures sufficient to decompose MTBE into isobutylene and methanol. The decomposed MTBE product stream 314 primarily includes MTBE, methanol, and isobutylene, and possibly smaller amounts of metal ions, dimethyl ether (DME), and water. Sources of metal ions can be, for example, sodium and calcium ions associated with fresh water or iron and chromium ions from pipe scaling erosion or corrosion.

[0046] The one or more decomposition reactors 312 decompose at least a portion of MTBE in the MTBE feed stream 310 into isobutylene and methanol by reaction (iii), and methanol reacts with itself to produce DME and water by reaction (iv):(iii) (CH3)3COCH3 (CH3)2C=CH2+ CH3OH;(iv) 2CH3OH^CH3OCH3 + H2O.

[0047] According to embodiments of the present disclosure, the decomposed MTBE product stream 314 is in fluid communication with a wash water treatment unit 316. The wash water treatment unit 316 is adapted to treat or wash the decomposed MTBE product stream 314 with water to form a wash water stream 318 primarily including methanol, water, and MTBE, and possibly smaller amounts of metal ions and DME. The wash water treatment unit 316 is also adapted to form a water-washed product stream 320 primarily including isobutylene. In some implementations, the water-washed product stream 320 is in fluid communication with one or more separation units, such as a fractionation column, where isobutylene is isolated with a concentration of over 99.9% isobutylene.

[0048] According to embodiments of the present disclosure, the wash water stream 318 is in fluid communication with one or more separation units 322. The one or more separation units 322 are configured to separate the methanol from the wash water stream 318, and produce methanol recovery stream 324 primarily including methanol and impurities. For example, in some implementations, the methanol recovery stream 324 comprises about 97% by molar percent of methanol and about 3% by molar percent of impurities. In some implementations, the one or more separation units 322 are further configured to separate at least a portion of MTBE from the wash water stream 318 and form MTBE recycle stream 326. In one embodiment, the MTBE recycle stream 326 is in fluid communication with at least one of the one or more purification units 200 such that the MTBE is ultimately recycled for reaction in the one or more decomposition reactors 312.

[0049] The impurities in the methanol recovery stream 324 primarily include DME, metal ions, and water. Even in trace amounts, the presence of impurities can hinder recycling efforts23 CHEM0042-WO-ORD11 back to the MTBE production process 100. For example, the presence of water in a recovered methanol stream recycled back to one of the one or more MTBE synthesis reactors 120 can lead to side reactions that decrease the efficiency of the MTBE production process 100 by decreasing the concentration of MTBE in the MTBE product stream 122. Rather than react with methanol to produce MTBE, at least some of the isobutylene will react with water when present and produce tert-butanol (TBA) by reaction (v):(v) (CH3)2CH=CH2 + H2O^(CH3)3OH.

[0050] Similarly, the presence of metal ions in a recovered methanol stream recycled back to one of the one or more MTBE synthesis reactors 120 can act as a poison and decrease the efficiency of the MTBE production process 100 by decreasing the lifespan of the MTBE synthesis catalyst. For example, exposure of metal ions to an MTBE synthesis catalyst such as a sulfonic compound can lead to the breakdown of the catalyst by reaction (vi), where M is a metal ion such as iron, chromium, calcium or sodium:(vi): n(SO3H) + M" ^(SO3)nM + nH+

[0051] DME in a recovered methanol stream recycled back to one of the one or more MTBE synthesis reactors 120 does not have a significant impact on the concentration of MTBE in the MTBE product stream. However, the DME is not easily separable from isobutane, and can follow the isobutane to the one or more dehydrogenation reactors 116 through isobutane recycle stream 210 from the one or more purification units 200. When exposed to the catalyst in the one or more dehydrogenation reactors 116, the DME can act as a poison and decrease the efficiency of the MTBE production process 100 by decreasing the lifespan of the dehydrogenation catalyst. For example, exposure of DME to a dehydrogenation catalyst such as chromium alumina can decrease the lifespan of the catalyst by up to 20%.

[0052] According to embodiments of the present disclosure, the methanol recovery stream 324 flows to a methanol cleaning unit 400 to remove at least a portion of the impurities in the methanol recovery stream 324 and produce purified methanol stream 410. Referring to FIG. 2, in some implementations, the methanol cleaning unit 400 includes one or more distillation columns 402 in fluid communication with the methanol recovery stream 324. The type of distillation column(s) can vary, but will typically include at least one single column distillation column. The one or more distillation columns 402 can be configured to separate at least a portion of the impurities from the methanol recovery stream 324 to produce impurities stream 404 and a methanol recovery stream 324a having impurities. In one embodiment, the one or more distillation columns 402 are configured to separate at least a portion of DME from the methanol23 CHEM0042-WO-ORD12 recovery stream 324. In a single column example, at least a portion of DME is taken from the top of the column and the methanol recovery stream 324a having reduced DME content taken from the bottom of the column.

[0053] In some implementations, the methanol cleaning unit 400 further includes one or more metal ion removal units 406 in fluid communication with the methanol recovery stream 324a. The one or more metal ion removal units 406 can be configured to separate at least a portion of the metal ions from the methanol recovery stream 324a and produce purified methanol stream 410. The one or more metal ion removal units 406 can include a bed of ion exchange resin configured to capture at least a portion of metal ions from the methanol recovery stream 324a. In one embodiment, the ion exchange resin is anionic, with an example metal ion removal unit being a Protego® Plus purifier.

[0054] In some implementations, the methanol cleaning unit 400 includes a decanter 408 in fluid communication with the methanol recovery stream 324a. The decanter 408 can be configured to remove water from the methanol recovery stream 324a to produce methanol recovery stream 324b having reduced water content. In some embodiments, the methanol recovery stream 324b is further in fluid communication with the one or more metal ion removal units 406. In a preferred embodiment, the methanol recovery stream 324a passes through the decanter 408 to produce methanol recovery stream 324b having reduced water content, and the methanol recovery stream 324b passes through the one or more metal ion removal units 406 to produce purified methanol stream 410 having a reduced metal ion content.

[0055] Referring back to FIG. 1, the purified methanol stream 410 is in fluid communication with at least one of the one or more MTBE synthesis reactors 120, and can supply methanol for the MTBE synthesis reaction. In some implementations the purified methanol stream 410 includes about 98% by molar percent methanol or higher, such as about 99% or at least 99.5% (e.g., about 98% to about 99.9% molar fraction methanol). In some embodiments, the purified methanol stream 410 further includes about 0.01% by molar percent DME or lower, such as about 0.001% or lower (e.g., about 0.01% to about 0.0005 molar fraction DME).

[0056] In some implementations, to further limit the passing of trace amounts of oxygenates such as DME in the MTBE product stream 122 to the one or more dehydrogenation reactors 116, the isobutane recycle stream 210 can pass through one or more oxygenate removal units 500 prior to reaching the one or more dehydrogenation reactors 116. The one or more oxygenate removal units 500 can be in fluid communication with the isobutylene recycle stream 210, which can include an initial isobutane recycle stream 210a and a purified isobutane recycle stream23 CHEM0042-WO-ORD13210b. The one or more oxygenate removal units 500 can be configured to entrap at least a portion of the oxygenates as the isobutane recycle stream 210 passes therethrough. Referring to FIG. 3, the one or more oxygenate removal units 500 can include a bed 510 of at least one absorbent material, such as a zeolite material. The bed 510 can be configured to entrap at least a portion of oxygenates from the initial isobutane recycle stream 210a, and form the purified isobutane recycle stream 210b, which is in fluid communication with the one or more dehydrogenation reactors 116. In one implementation, two or more oxygenate removal units 500 can be used in parallel, such that one oxygenate removal unit is on-stream and at least one oxygenate removal unit is on stand-by or undergoing regeneration. Regeneration of a saturated oxygenate removal unit can be accomplished by passing an isobutane stream through the bed.

[0057] In general, embodiments of the disclosure may alternately comprise, consist of, or consist essentially of, any appropriate components herein disclosed. The embodiments of the disclosure may additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any components, materials, ingredients, adjuvants or species used in the prior art compositions or that are otherwise not necessary to the achievement of the function and / or objectives of the present disclosure.EXPERIMENTALExample 1 : Purification of Methanol Recycle Stream using DME Removal Column

[0058] An example DME removal column of the type useful in the present disclosure was modeled using Aspen Plus and is shown schematically in FIG. 4. The modeling showed that a methanol recycle stream can be successfully treated using the column to reduce DME concentration. The details of the modeled DME removal column and the related streams are set forth in Tables 1 and 2 below.TABLE 123 CHEM0042-WO-ORDTABLE 2Example 2: Comparing Grade A methanol with methanol recycled in accordance with the present disclosure

[0059] In order to determine the impact of using recycled methanol purified according to the present disclosure as compared to use of Grade A methanol for MTBE production, comparative experiments were conducted using the same MTBE production system. Grade A methanol typically has a purity on a dry basis of at least 99.85% w / w with maximum acetone concentration of 30 ppm, maximum ethanol concentration of 50 ppm, and maximum water concentration of 0.1% w / w.

[0060] The experiments were conducted using a jacketed lab reactor having a diameter of 10.5 mm and a catalyst bed length of 110 mm. The reactor was loaded with 0.5 g of AMBERLYST™ 15 catalyst divided into five parts and loaded into five layers with a catalyst bed height of about 11 cm. The catalyst particle diameter was about 0.9 mm. The reaction feed contained methanol and isobutylene with an isobutylene to methanol ratio of 1 : 1 and the feed rate was 57.6 ml / h. The reaction set temperature was 60 °C and the weight hourly space velocity (WHSV) was 72.49 kg-feed per kg-catalyst hour.

[0061] The results indicated that the recycled methanol purified according to the present disclosure resulted in the same MTBE selectivity and the same isobutylene conversion percentage as Grade A methanol.Example 3: Comparison of Grade A methanol with methanol recycled in accordance with present disclosure in different processing configurations

[0062] A purified recycled methanol stream produced in accordance with the process of FIG. 1 was fed to four different plant configurations for synthesizing MTBE and compared to use of Grade A methanol or a recycled methanol stream produced according to the general process of FIG. 1 but without purification. The processing configurations are depicted in TABLE 3 below. The purity of the MTBE produced was recorded and compared, with the results indicating that23 CHEM0042-WO-ORD15 the recycled methanol stream purified according to the present disclosure was able to achieve the same MTBE purity as Grade A methanol in all four plant configurations. In all cases, the MTBE purity achieved was 98% or higher by weight. In contrast, the recycled methanol stream produced according to the general process of FIG. 1, but without purification, was unable to produce high purity MTBE. Instead, the purity of the MTBE produced was less than 97%.TABLE 3

[0063] Many modifications and other implementations of the disclosure will come to mind to one skilled in the art to which this disclosure pertains having the benefit of the teachings presented in the foregoing descriptions and the associated figures. Therefore, it is to be understood that the disclosure is not to be limited to the specific implementations disclosed herein and that modifications and other implementations are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

23 CHEM0042-WO-ORD16CLAIMS1. A method of integrating methyl tert-butyl ether (MTBE) production with isobutylene production, the method comprising: i) isomerizing a mixed hydrocarbon feed stream comprising n-butane to form an isobutane feed stream comprising isobutane; ii) dehydrogenating the isobutane in the isobutane feed stream in a dehydrogenation reactor to convert at least a portion of the isobutane to isobutylene and form an isobutylene stream comprising isobutylene and unconverted isobutane; iii) reacting the isobutylene stream with methanol from a purified methanol stream in an MTBE synthesis reactor to form an MTBE product stream comprising primarily MTBE and impurities; iv) separating at least a portion of the impurities from the MTBE product stream to form a MTBE feed stream comprising primarily MTBE; v) decomposing MTBE in the MTBE feed stream to form a decomposed MTBE product stream comprising primarily methanol, isobutylene, and MTBE; vi) treating the decomposed MTBE product stream with water to form a wash water stream comprising methanol, water, and MTBE and a water-washed product stream comprising isobutylene; vii) separating methanol from the wash water stream to form a methanol recovery stream comprising methanol, metal ions, and dimethyl ether (DME); viii) separating at least a portion of the DME and the metal ions from the methanol recovery stream to form the purified methanol stream; and ix) feeding the purified methanol stream to the MTBE synthesis reactor; wherein the purified methanol stream comprises about 98% molar fraction of methanol or higher and / or about 0.01 molar fraction of DME or lower, such as about 0.001 molar fraction of DME or lower.

2. The method of claim 1 , wherein the impurities of the MTBE product stream comprise unconverted isobutane, and the iv) separating step comprises separating at least a portion of the unconverted isobutane from the MTBE product stream to form an isobutane recycle stream.

3. The method of claim 2, further comprising treating the isobutane recycle stream in an oxygenate removal unit to remove at least a portion of oxygenates and forming a purified23 CHEM0042-WO-ORD17 isobutane recycle stream, and feeding the purified isobutane recycle stream to the dehydrogenation reactor, optionally wherein the oxygenate removal unit comprises an adsorbent material.

4. The method of claims 2 or 3, wherein the impurities of the MTBE product stream further comprise additional hydrocarbons having a molar mass higher and / or lower than MTBE, and the iv) separating step further comprises separating at least a portion of the additional hydrocarbons from the MTBE product stream.

5. The method of any one of claims 1-4, wherein the iv) separating step comprises one or more distillation columns.

6. The method of any one of claims 1 to 5, wherein the viii) separating step comprises feeding the methanol recovery stream to a separation unit comprising one or more distillation columns to remove at least a portion of the DME and form a DME-reduced methanol stream and treating the DME-reduced methanol stream with an ion exchange resin to remove at least a portion of the metal ions and form the purified methanol stream.

7. The method of any one of claims 1-6, further comprising decanting water from the methanol recovery stream.

8. A system for integrating methyl tert-butyl ether (MTBE) production with isobutylene production, the system comprising: one or more isomerization reactors in fluid communication with a mixed hydrocarbon feed stream comprising n-butane, the one or more isomerization reactors configured to convert at least a portion of the n-butane of the feed stream to isobutane, thereby forming an isobutane feed stream comprising isobutane; one or more dehydrogenation reactors in fluid communication with the isobutane feed stream and configured to produce an isobutylene stream, the isobutylene stream comprising isobutylene and unconverted isobutane; one or more MTBE synthesis reactors in fluid communication with the isobutylene stream and a purified methanol stream, the one or more MTBE synthesis reactors adapted to react isobutylene with methanol and produce an MTBE product stream comprising primarily MTBE and impurities;23 CHEM0042-WO-ORD18 one or more purification units in fluid communication with the MTBE product stream and configured to separate at least a portion of the impurities from the MTBE product stream and produce an MTBE feed stream; one or more decomposition reactors in fluid communication with the MTBE feed stream and configured to decompose MTBE and produce a decomposed MTBE product stream comprising primarily methanol, isobutylene, and MTBE; a wash water treatment unit adapted to treat the decomposed MTBE product stream with water to form a wash water stream comprising methanol, water, and MTBE and a water-washed product stream comprising isobutylene; one or more separation units in fluid communication with the wash water stream and configured to separate the methanol from the wash water stream and produce a methanol recovery stream, the mixed methanol recovery stream comprising methanol, metal ions, and dimethyl ether (DME); and one or more distillation columns and one or more metal ion removal units in fluid communication with the methanol recovery stream and configured to separate at least a portion of the DME and at least a portion of the metal ions, respectively, from the methanol recovery stream and form the purified methanol stream, the purified methanol stream being in fluid communication with the one or more MTBE synthesis reactors.

9. The system of claim 8, wherein the impurities of the MTBE product stream comprise one or more oxygenates and unconverted isobutane, and the one or more purification units in fluid communication with the MTBE product stream comprises at least one separation unit configured to separate at least a portion of the unconverted isobutane from the MTBE product stream and produce an isobutane recycle stream, the isobutane recycle stream being in fluid communication with the one or more dehydrogenation reactors.

10. The system of claim 9, further comprising one or more oxygenate removal units in fluid communication with the isobutane recycle stream, the one or more oxygenate removal units configured to remove at least a portion of the oxygenates from the isobutane recycle stream and produce a purified isobutane recycle stream, the purified isobutane recycle stream being in fluid communication with the one or more dehydrogenation reactors, optionally wherein the one or more oxygenate removal units comprises a bed of adsorbent material.23 CHEM0042-WO-ORD1911. The system of claims 9 or 10, wherein the impurities of the MTBE product stream further comprise additional hydrocarbons having a molar mass higher and / or lower than MTBE, and the one or more purification units in fluid communication with the MTBE product stream comprise at least one fractionation column in fluid communication with the MTBE product stream configured to remove at least a portion of the additional hydrocarbons from the MTBE product stream.

12. The system of any one of claims 8-11, further comprising a decanter in fluid communication with the methanol recover stream configured to remove water from the methanol recovery stream.

13. The system of any one of claim 8-12, wherein the one or more distillation columns in fluid communication with the methanol recovery stream produces a bottoms stream having reduced DME content, and the bottoms stream is in fluid communication with the one or more metal ion removal units.

14. The system of any one of claims 9-13, wherein the one or more metal ion removal units comprises a bed of ion exchange resin.

Images