Methyl TERT-butyl ether synthesis method with integraged feed pre-processing

Abstract

The present disclosure provides a method and system for producing an alkyl tert-butyl ether, the method including separating a mixed hydrocarbon stream into a C3-rich stream and a C4-rich stream; separating the C4-rich stream into an isobutane stream and an n-butane stream; dehydrogenating the isobutane in the isobutane stream to form an isobutene stream; compressing the isobutene stream to form a condensed liquid stream and a gaseous stream; treating the gaseous stream and the C3-rich stream in a low temperature recovery system to form a purified product stream and a light gas stream; separating at least a portion of the C3 impurities from the purified product stream and the condensed liquid stream to form a purified C4 stream; and reacting the purified C4 stream with an alkanol in a reactor to form an alkyl tert-butyl ether product stream.

Description

METHYL TERT-BUTYL ETHER SYNTHESIS METHOD WITH INTEGRAGED FEED PRE-PROCESSINGTECHNOLOGICAL FIELD

[0001] The present disclosure relates to methods and systems for producing methyl tert-butyl ether (MTBE).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. The effluent is optionally fed to a reaction column to react isobutylene remaining in the effluent with additional methanol to produce more MTBE.

[0003] Isobutylene used for MTBE synthesis can be obtained from C4 hydrocarbon process streams. One of the sources for the C4 hydrocarbons used in the MTBE production process can include liquefied petroleum gas, which includes primarily C4 and C3 hydrocarbons. The liquefied petroleum gas is processed in a dehydrogenation unit to produce isobutylene. If the feedstock for the dehydrogenation unit contains a relatively low content of isobutane, the feedstock is first processed in an isomerization unit upstream of the dehydrogenation unit. The effluent stream from the dehydrogenation unit(s) is then flowed to an MTBE synthesis unit to react with methanol for producing MTBE. However, the reaction efficiency in the isomerization unit(s) and / or dehydrogenation unit(s) is relatively low when liquefied petroleum gas is used as the feedstock, resulting in high production cost for MTBE. See, for example, the MTBE production processes set forth in WO2019 / 116202; WO2022 / 013836; and W02022 / 013840.BRIEF SUMMARY

[0004] Example implementations of the present disclosure are directed to processes and systems for enhancing MTBE production efficiency by, for example, use of a feed pre-processing unit that reduces C3 impurities in a mixed hydrocarbon feed stream and coupling the C3 impurity stream to a low temperature recovery unit downstream of a dehydrogenation reactor to recover C4 hydrocarbons from the C3 impurity stream, which reduces C4 losses in the system.

[0005] The present disclosure includes, without limitation, the following embodiments.

[0006] Embodiment 1 : A method of producing an alkyl tert-butyl ether, the method comprising: i) separating a mixed hydrocarbon stream into a C3-rich stream comprising primarily C3 hydrocarbons and a C4-rich stream comprising primarily C4 hydrocarbons; ii) separating the C4-rich stream into an isobutane stream comprising primarily isobutane and an n- butane stream comprising primarily n-butane; iii) dehydrogenating the isobutane in the isobutane stream in a dehydrogenation reactor to form an isobutene stream, the isobutene stream comprising primarily isobutene and isobutane; iv) compressing the isobutene stream to form a condensed liquid stream comprising a portion of the isobutene and isobutane and a gaseous stream comprising the remainder of the isobutene and isobutane, one or more C1-C3 hydrocarbons, one or more oxocarbons, and hydrogen; v) treating the gaseous stream and the C3- rich stream in a low temperature recovery system to separate light gases and form a purified product stream comprising primarily isobutene and isobutane and C3 impurities and a light gas stream comprising one or more C1-C3 hydrocarbons, one or more oxocarbons, and hydrogen; vi) separating at least a portion of the C3 impurities from the purified product stream and the condensed liquid stream to form a purified C4 stream comprising primarily isobutene and isobutane and a C3 off-gas stream; and vii) reacting the purified C4 stream with an alkanol in one or more reactors to form an alkyl tert-butyl ether product stream.

[0007] Embodiment 2: The method of Embodiment 1, further comprising separating the alkyl tert-butyl ether product stream into a purified alkyl tert-butyl ether product stream and a recycle stream comprising isobutane, and recycling the recycle stream to the iii) dehydrogenating step.

[0008] Embodiment 3: The method of Embodiment 1 or 2, further comprising isomerizing the n-butane in the n-butane stream to form an isobutane-enriched stream and recycling the isobutane-enriched stream to the ii) separating step.

[0009] Embodiment 4: The method of any one of Embodiments 1 to 3, wherein the isobutene stream prior to compressing has a pressure of about 1 kg / cm2or less, such as about 0.2 kg / cm2to about 0.8 kg / cm2, and the gaseous stream after compressing has a pressure of about 12 kg / cm2or higher, such as about 14 kg / cm2to about 35 kg / cm2.

[0010] Embodiment 5: The method of any one of Embodiments 1 to 4, wherein the low temperature recovery system comprises at least one heat exchanger receiving a heat transfer medium having a temperature below 0 °C.

[0011] Embodiment 6: The method of any one of Embodiments 1 to 5, wherein the i) separating step comprises feeding the mixed hydrocarbon stream to a separation unit comprising one or more distillation columns; and / or wherein the ii) separating step comprises feeding the C4-rich stream to a separation unit comprising one or more distillation columns.

[0012] Embodiment 7: The method of any one of Embodiments 1 to 6, wherein: a) the mixed hydrocarbon stream comprises about 60 wt.% of n-butane or higher, such as about 60 wt.% to about 80 wt.% n-butane, about 20 wt.% isobutane or higher, such as about 20 wt.% to about 40 wt.% isobutane, and optionally up to about 5 wt.% of propane, such as about 0.1 wt.% to about 5 wt.% propane; b) or the C4-rich stream comprises about 0.5 wt.% or less of C3 hydrocarbons, such as about 0.01 wt.% to about 0.2 wt.% C3 hydrocarbons; c) or the isobutane stream separated from the C4-rich stream comprises about 95 wt.% isobutane or higher, such as about 98 wt.% to about 99.8 wt.% isobutane; d) or the C3 off-gas stream comprises about 1.8 wt.% or less of C4 hydrocarbons, such as about 0.1 wt.% to about 1.5 wt.% of C4 hydrocarbons; or e) a combination of two or more of the above.

[0013] Embodiment 8: A system for producing an alkyl tert-butyl ether, the system comprising: a first separation unit comprising one or more columns in fluid communication with a mixed hydrocarbon feed source, the first separation column producing a C3-rich stream comprising primarily C3 hydrocarbons and a C4-rich stream comprising primarily C4 hydrocarbons; a second separation unit comprising one or more columns in fluid communication with the C4-rich stream and producing an isobutane stream comprising primarily isobutane and an n-butane stream comprising primarily n-butane; a dehydrogenation reactor in fluid communication with the isobutane stream and producing an isobutene stream, the isobutene stream comprising primarily isobutene and isobutane; a compressor in fluid communication with the isobutene stream and suitable to perform a condensation of at least a portion of the isobutene and isobutane, the compressor producing a condensed liquid stream and a gaseous effluent; a low temperature recovery system in fluid communication with the gaseous effluent and the C3-rich stream and producing a purified product stream comprising primarily isobutene and isobutane and C3 impurities and a light gas stream comprising one or more C1-C3 hydrocarbons, one ormore oxocarbons, and hydrogen; a depropanizer unit comprising one or more columns in fluid communication with the purified product stream and the condensed liquid stream, the depropanizer unit producing a purified C4 stream comprising primarily isobutene and isobutane and a C3 off-gas stream; and one or more reactors in fluid communication with the purified C4 stream and a source of alkanol and suitable for allowing reaction of isobutene with alkanol and produce an alkyl tert-butyl ether product stream.

[0014] Embodiment 9: The system of Embodiment 8, further comprising at least one separation column in fluid communication with the alkyl tert-butyl ether product stream and suitable to separate the alkyl tert-butyl ether product stream into a purified alkyl tert-butyl ether stream and a recycle stream comprising isobutane, wherein the recycle stream is in fluid communication with the dehydrogenation reactor.

[0015] Embodiment 10: The system of Embodiment 8 or 9, further comprising one or more isomerization reactors in fluid communication with the n-butane stream and suitable to isomerize the n-butane in the n-butane stream to form an isobutane-enriched stream, the isobutane-enriched stream in fluid communication with the second separation unit.

[0016] Embodiment 11 : The system of any one of Embodiments 8 to 10, wherein the low temperature recovery system comprises at least one heat exchanger receiving a heat transfer medium having a temperature below 0 °C.

[0017] Embodiment 12: The system of any one of Embodiments 8 to 11, wherein the compressor is a multi-stage compressor comprising at least one intercooler and at least one gas / liquid separator for separating a condensed liquid from a compressed gas.

[0018] Embodiment 13: The system of any one of Embodiments 8 to 12, wherein the first separation unit comprises one or more distillation columns; and / or wherein the second separation unit comprises one or more distillation columns.

[0019] Embodiment 14: The process operating a system according to any one of Embodiments 8 to 13, wherein: a) the mixed hydrocarbon stream obtained from the mixed hydrocarbon feed source, comprises about 60 wt.% of n-butane or higher, such as about 60 wt.% to about 80 wt.% n-butane, about 20 wt.% isobutane or higher, such as about 20 wt.% to about 40 wt.% isobutane, and optionally up to about 5 wt.% of propane, such as about 0.1 wt.% to about 5 wt.% propane; or b) the C4-rich stream comprises about 0.5 wt.% or less of C3 hydrocarbons, such as about 0.01 wt.% to about 0.2 wt.% C3 hydrocarbons; or c) the isobutanestream separated from the C4-rich stream comprises about 95 wt.% isobutane or higher, such as about 98 wt.% to about 99.8 wt.% isobutane; or d) the C3 off-gas stream comprises about 1.8 wt.% or less of C4 hydrocarbons, such as about 0.1 wt.% to about 1.5 wt.% of C4 hydrocarbons; or e) a combination of two or more of the above.

[0020] 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 example 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.

[0021] It will therefore be appreciated that this Brief Summary is provided merely for purposes of summarizing some example implementations 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 with the accompanying figures which illustrate, by way of example, the principles of some described example implementations.BRIEF DESCRIPTION OF THE FIGURE

[0022] Having thus described aspects of the disclosure in the foregoing general terms, reference will now be made to the accompanying figure, which is not necessarily drawn to scale, and wherein:

[0023] FIG. l is a schematic representation of a system for producing MTBE according to an example embodiment of the present disclosure.DETAILED DESCRIPTION

[0024] Conventionally, MTBE can be produced by processing a C3 and C4 hydrocarbon mixture in an isomerization unit and a dehydrogenation unit, sequentially. The effluent from thedehydrogenation unit comprising isobutene is then fed into a MTBE synthesis unit to produce MTBE. However, the C3 hydrocarbons and lighter hydrocarbons (e.g., methane and C2 hydrocarbons) in the hydrocarbon mixture are inert components that dilute the C4 hydrocarbon reactants in each of the reaction units, thereby reducing the reaction efficiency and increasing the energy consumption for producing MTBE.

[0025] According to the present disclosure, C3 and any lighter hydrocarbons are separated from a mixed hydrocarbon feed stream prior to processing the feed stream in an isomerization unit and / or a dehydrogenation unit, resulting in higher isobutene concentration in the feed to the MTBE synthesis unit. Any losses of C4 due to separation of the C3 impurity stream are reduced by directing the C3-rich stream to a recovery system, such as a recovery system including a Low Temperature Recovery System (LTRS) and depropanizer. Furthermore, in certain embodiments, unreacted C4 hydrocarbons are separated from synthesized MTBE and recycled back into the dehydrogenation unit, thereby increasing the utilization rate and the overall value of the C4 hydrocarbon mixture.

[0026] Some implementations of the present disclosure will now be described more fully hereinafter with reference to the accompanying figure, 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 this 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.

[0027] 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.

[0028] 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.

[0029] The term “about” is defined as being close to as understood by one of ordinary skill in the art. In one non -limiting embodiment, the terms are defined to be within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5%.

[0030] The terms “wt.%”, “vol.%”, or “mol.%” refer to a weight, volume, or molar percentage of a component, respectively, based on the total weight, the total volume of material, or total moles, that includes the component. In a non-limiting example, 10 grams of a component in 100 grams of the material is 10 wt.% of the component.

[0031] 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.

[0032] FIG. 1 schematically illustrates an example implementation of the present disclosure. As shown, a system 100 for producing MTBE begins with a mixed hydrocarbon feed stream 10 that includes both C3 and C4 hydrocarbons, and possibly small amounts of C1-C2 or C5 hydrocarbons. An example mixed hydrocarbon feed stream comprises about 60 wt.% of n- butane or higher, such as about 60 wt.% to about 80 wt.% n-butane, and about 20 wt.% isobutane or higher, such as about 20 wt.% to about 30 wt.% isobutane, and up to about 5 wt.% of propane (e.g., about 0.1 wt.% to about 5 wt.% propane). Mixed hydrocarbon feed stream 10 source can be liquefied petroleum gas or derived from natural gas and oil extraction, oil refining, or waste or renewable vegetable oils.

[0033] System 100 includes a first separation unit 110 configured to separate mixed hydrocarbon feed stream 10 into a C3-rich stream 12 comprising primarily C3 hydrocarbons (e.g., propane) and a C4-rich stream 14 comprising primarily C4 hydrocarbons (e.g., n-butane and isobutane). In certain embodiments, C4-rich stream 14 comprises 95 wt.% or more of C4 hydrocarbons, such as 96 wt.% or more, or 97 wt.% or more, or 98 wt.% or more, or 99 wt.% or more, and comprises about 0.5 wt.% or less of C3 hydrocarbons, such as about 0.01 wt.% toabout 0.2 wt.% C3 hydrocarbons. The type of first separation unit 110 can vary, but will typically include at least one distillation column (e.g., a depropanizer column). Alternatively, an adsorption process could be used.

[0034] In some implementations, a bottom outlet of first separation unit 110 is in fluid communication with a second separation unit 120 such that C4-rich stream 14 flows from first separation unit 110 to second separation unit 120. Within second separation unit 120, C4-rich stream 14 is separated into an isobutane-rich stream 20 comprising primarily isobutane and an n- butane rich stream 14a comprising primarily n-butane. In certain embodiments, isobutane-rich stream 20 comprises about 97 wt.% or more of isobutane, such as about 98 wt.% or more, or about 99 wt.% or more (e.g., about 98 wt.% to about 99.8 wt.% isobutane). The type of second separation unit 120 can vary, but will typically include one or more distillation columns (e.g., a de-isobutanizer (DIB) column). In a single column example, isobutane-rich stream 20 is taken from the top of the column and n-butane rich stream 14a is separated in a side draw.Alternatively, two columns in series could be used, with isobutane-rich stream 20 taken from the top of the first column and the n-butane-rich stream 14a taken from the top of the second column. In another single column example, where no isomerization unit 130 (discussed below) is needed, isobutane-rich stream 20 is taken from the top of the column and n-butane rich stream 14a is taken from the bottom of the column and, for example, sent for further processing in a steam cracking unit (not shown).

[0035] In some embodiments, second separation unit 120 may be in fluid communication with an isomerization unit 130. Isomerization unit 130 can be configured to isomerize n-butane of n-butane rich stream 14a to produce an isomerization unit effluent stream 14b comprising isobutane, which is recycled back to second separation unit 120 to increase isobutane production. Isomerization unit 130 can include, for example, a fixed bed reactor, a continuous catalytic converter, an adiabatic or a cooled isothermal converter reactor. In one embodiment, isomerization unit 130 comprises two reactors serially connected. In some implementations, isomerization unit 130 may comprise a catalyst including, for example, Pt / AlCh / AhCh, Pt / AlCh / zeolite, Pt / SO42-ZrO2, SO^-ZrCh-AhCh, or any combination thereof.

[0036] According to embodiments of the disclosure, isobutane-rich stream 20 is in fluid communication with an inlet of a dehydrogenation system 140, which is configured to dehydrogenate isobutane to produce a dehydrogenation system effluent stream 40 comprisingprimarily isobutene and C4 impurities including unreacted isobutane, oxocarbon gases, light hydrocarbons, and hydrogen. In some embodiments, dehydrogenation system 140 includes a plurality of fixed bed reactors housing a dehydrogenation catalyst comprising, for example, chromia / alumina, Pt / alumina, or combinations thereof.

[0037] Generally, dehydrogenation system 140 comprises three or more parallel fixed bed reactors and a catalyst regeneration system. When the fixed bed dehydrogenation unit 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 (e.g., propane, isobutane, n-butane, 1 -butene, or isopentane) 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, propylene, isobutylene, pentene, isoprene, butadiene, or combinations thereof. 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.

[0038] 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 °C to 640 °C, a reaction pressure of 0.36 bar to 1.2 bar, and / or a weight hourly space velocity in a range of 0.2 hr to 4.0 hr .

[0039] Dehydrogenation system effluent stream 40 is compressed in a compressor 150 to form a condensed liquid stream comprising a major portion of the isobutene and isobutane, which is subsequently fed as liquid effluent 52 to a depropanizer column 170 described below, and a gaseous stream 50 comprising the remainder of the isobutene and isobutane, Cl -3 hydrocarbons, oxocarbon gases such as CO and CO2, as well as hydrogen, which is the main product (besides isobutene) of the dehydrogenation reactions noted above. In certain embodiments, dehydrogenation system effluent stream 40 upstream of compression has apressure of about 1 kg / cm2or less, such as about 0.2 kg / cm2to about 0.8 kg / cm2, and the gaseous stream 50 after compression has a pressure of about 12 kg / cm2or higher, such as about 14 kg / cm2to about 35 kg / cm2. The type of compressor 150 can vary, but is typically a multi-stage compressor comprising at least one intercooler and at least one gas / liquid separator for separating a condensed liquid from a compressed gas.

[0040] Gaseous stream 50 and C3-rich stream 12 are both treated in a low temperature recovery system (LTRS) 160 to separate light gases and form a purified product stream 62 comprising primarily isobutene and isobutane and C3 impurities and a light gas stream comprising Cl -3 hydrocarbons, oxocarbon gases such as CO and CO2, as well as hydrogen. LTRS 160 typically includes treatment in a series of heat exchangers including at least one heat exchanger using a refrigerant as heat transfer medium, and is adapted to separate light gases from condensable gases. Although LTRS 160 may vary, in one embodiment, LTRS 160 includes two parts. In the first part, the gaseous stream from the last compression stage is cooled from a temperature of about 40 °C -45 °C to a temperature of about 5 °C -15 °C in a cooler where the cooling media is typically a C3 hydrocarbon. As temperature is decreased, part of the feed is liquefied (mainly composed by C3 and C4 hydrocarbons) and is consequently separated from the gas stream by a gas / liquid separator. The liquid stream (forming a portion of purified product stream 62) is sent directly to a separation unit 170 discussed below.

[0041] The second part of LTRS 160 treats the gas stream from the gas / liquid separator and is composed of an HC1 adsorber followed by two dryers (working in alternate fashion) and a cold box exchanger, typically operating at temperatures below 0 °C. The second part of LTRS 160 also produces a liquid and a gas stream. The liquid (forming a portion of purified product stream 62) is sent to separation unit 170 discussed below while the off-gas stream 60, which is hydrogen-rich, is sent to, for example, a pressure swing adsorption unit for recovery of hydrogen, a process fuel network, and / or recycled back to dehydrogenation system 140 for use as a reducing gas.

[0042] Liquid effluent 52 and purified product stream 62 from compressor 150 and LTRS 160, respectively, are processed in separation unit 170. Separation unit 170 is configured to separate the feed stream into a C3-rich stream 70 comprising primarily C3 hydrocarbons (e.g., propane and propylene) and a C4-rich stream 72 comprising primarily isobutene and isobutane. C3-rich stream 70 typically comprises about 1.8 wt.% or less of C4 hydrocarbons, such as about0.1 wt.% to about 1.5 wt.% of C4 hydrocarbons. The type of separation unit 170 can vary, but will typically include at least one distillation column (e.g., a depropanizer column). Alternatively, an adsorption process could be used. In one embodiment, a single tower composed of two vertically-arranged distillation vessels (with different diameters) is used.

[0043] C4-rich stream 72 is used as a feed stream for an etherification unit 180, wherein isobutene is reacted with an alkanol in the presence of a catalyst under reaction conditions sufficient to produce alkyl tert-butyl ether in an etherification unit effluent stream 80. Nonlimiting examples of the alkanol include methanol and ethanol. Non-limiting examples of the alkyl tert-butyl ether include MTBE and ethyl tert-butyl ether (ETBE). The etherification catalyst may include cation exchange resins, polystyrene divinyl benzene mounted ion exchange resins, polymeric support mounted ion exchange resins, or combinations thereof. The reaction is exothermic and the temperature rise in the reactor will depend, in part, on whether the reactor is adiabatic or isothermal. Example reaction conditions include a temperature range of 40 °C to 100 °C, a pressure of 5 bar to 8 bar, and a liquid hourly space velocity of 2 hr to 12 hr-1. Etherification unit 180 can include a separation unit to separate the desired etherification unit effluent stream 80 from a recycle stream 82 comprising primarily isobutane, which can be recycled back to dehydrogenation system 140. In certain embodiments, the alkyl tert-butyl ether is MTBE and product stream 80 comprises 98 wt.% to 99.5 wt.% MTBE.

[0044] In general, the invention may alternately comprise, consist of, or consist essentially of, any appropriate components herein disclosed. The invention 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 invention.

[0045] 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

CLAIMS:

1. A method of producing an alkyl tert-butyl ether, the method comprising: i) separating a mixed hydrocarbon stream into a C3-rich stream comprising primarily C3 hydrocarbons and a C4-rich stream comprising primarily C4 hydrocarbons; ii) separating the C4-rich stream into an isobutane stream comprising primarily isobutane and an n-butane stream comprising primarily n-butane; iii) dehydrogenating the isobutane in the isobutane stream in a dehydrogenation reactor to form an isobutene stream, the isobutene stream comprising primarily isobutene and isobutane; iv) compressing the isobutene stream to form a condensed liquid stream comprising a portion of the isobutene and isobutane and a gaseous stream comprising the remainder of the isobutene and isobutane, one or more C1-C3 hydrocarbons, one or more oxocarbons, and hydrogen; v) treating the gaseous stream and the C3-rich stream in a low temperature recovery system to separate light gases and form a purified product stream comprising primarily isobutene and isobutane and C3 impurities and a light gas stream comprising one or more C1-C3 hydrocarbons, one or more oxocarbons, and hydrogen; vi) separating at least a portion of the C3 impurities from the purified product stream and the condensed liquid stream to form a purified C4 stream comprising primarily isobutene and isobutane and a C3 off-gas stream; and vii) reacting the purified C4 stream with an alkanol in one or more reactors to form an alkyl tert-butyl ether product stream.

2. The method of claim 1, further comprising separating the alkyl tert-butyl ether product stream into a purified alkyl tert-butyl ether product stream and a recycle stream comprising isobutane, and recycling the recycle stream to the iii) dehydrogenating step.

3. The method of claim 1, further comprising isomerizing the n-butane in the n-butane stream to form an isobutane-enriched stream and recycling the isobutane-enriched stream to the ii) separating step.

4. The method of claim 1, wherein the isobutene stream prior to compressing has a pressure of about 1 kg / cm2or less, such as about 0.2 kg / cm2to about 0.8 kg / cm2, and the gaseous stream after compressing has a pressure of about 12 kg / cm2or higher, such as about 14 kg / cm2to about 35 kg / cm2.

5. The method of claim 1, wherein the low temperature recovery system comprises at least one heat exchanger receiving a heat transfer medium having a temperature below 0 °C.

6. The method of any one of claims 1 to 5, wherein the i) separating step comprises feeding the mixed hydrocarbon stream to a separation unit comprising one or more distillation columns; and / or wherein the ii) separating step comprises feeding the C4- rich stream to a separation unit comprising one or more distillation columns.

7. The method of any one of claims 1 to 5, wherein: a) the mixed hydrocarbon stream comprises about 60 wt.% of n-butane or higher, such as about 60 wt.% to about 80 wt.% n-butane, about 20 wt.% isobutane or higher, such as about 20 wt.% to about 30 wt.% isobutane, and optionally up to about 5 wt.% of propane, such as about 0.1 wt.% to about 5 wt.% propane; or b) the C4-rich stream comprises about 0.5 wt.% or less of C3 hydrocarbons, such as about 0.01 wt.% to about 0.2 wt.% C3 hydrocarbons; or c) the isobutane stream separated from the C4-rich stream comprises about 97 wt.% isobutane or higher, such as about 98 wt.% to about 99.8 wt.% isobutane; or d) the C3 off-gas stream comprises about 1.8 wt.% or less of C4 hydrocarbons, such as about 0.1 wt.% to about 1.5 wt.% of C4 hydrocarbons; or e) a combination of two or more of the above.

8. A system for producing an alkyl tert-butyl ether, the system comprising: a first separation unit comprising one or more columns in fluid communication with a mixed hydrocarbon feed source, the first separation column producing a C3-rich stream comprising primarily C3 hydrocarbons and a C4-rich stream comprising primarily C4 hydrocarbons;a second separation unit comprising one or more columns in fluid communication with the C4-rich stream and producing an isobutane stream comprising primarily isobutane and an n-butane stream comprising primarily n-butane; a dehydrogenation reactor in fluid communication with the isobutane stream and producing an isobutene stream, the isobutene stream comprising primarily isobutene and isobutane; a compressor in fluid communication with the isobutene stream and suitable to perform a condensation of at least a portion of the isobutene and isobutane, the compressor producing a condensed liquid stream and a gaseous effluent; a low temperature recovery system in fluid communication with the gaseous effluent and the C3-rich stream and producing a purified product stream comprising primarily isobutene and isobutane and C3 impurities and a light gas stream comprising one or more C1-C3 hydrocarbons, one or more oxocarbons, and hydrogen; a depropanizer unit comprising one or more columns in fluid communication with the purified product stream and the condensed liquid stream, the depropanizer unit producing a purified C4 stream comprising primarily isobutene and isobutane and a C3 off-gas stream; and one or more reactors in fluid communication with the purified C4 stream and a source of alkanol and suitable for allowing reaction of isobutene with alkanol and produce an alkyl tert-butyl ether product stream.

9. The system of claim 8, further comprising at least one separation column in fluid communication with the alkyl tert-butyl ether product stream and suitable to separate the alkyl tert-butyl ether product stream into a purified alkyl tert-butyl ether stream and a recycle stream comprising isobutane, wherein the recycle stream is in fluid communication with the dehydrogenation reactor.

10. The system of claim 8, further comprising one or more isomerization reactors in fluid communication with the n-butane stream and adapted to isomerize the n-butane in the n-butane stream to form an isobutane-enriched stream, the isobutane-enriched stream in fluid communication with the second separation unit.

11. The system of claim 8, wherein the low temperature recovery system comprises at least one heat exchanger receiving a heat transfer medium having a temperature below 0 °C.

12. The system of claim 8, wherein the compressor is a multi-stage compressor comprising at least one intercooler and at least one gas / liquid separator for separating a condensed liquid from a compressed gas.

13. The system of any one of claims 8 to 12, wherein the first separation unit comprises one or more distillation columns; and / or wherein the second separation unit comprises one or more distillation columns.

14. The process operating a system according to any one of claims 8 to 13, wherein: a) the mixed hydrocarbon stream obtained from the mixed hydrocarbon feed source, comprises about 60 wt.% of n-butane or higher, such as about 60 wt.% to about 80 wt.% n-butane, about 20 wt.% isobutane or higher, such as about 20 wt.% to about 30 wt.% isobutane, and optionally up to about 5 wt.% of propane, such as about 0.1 wt.% to about 5 wt.% propane; or b) the C4-rich stream comprises about 0.5 wt.% or less of C3 hydrocarbons, such as about 0.01 wt.% to about 0.2 wt.% C3 hydrocarbons; or c) the isobutane stream separated from the C4-rich stream comprises about 97 wt.% isobutane or higher, such as about 98 wt.% to about 99.8 wt.% isobutane; or d) the C3 off-gas stream comprises about 1.8 wt.% or less of C4 hydrocarbons, such as about 0.1 wt.% to about 1.5 wt.% of C4 hydrocarbons; or e) a combination of two or more of the above.

Images