Process for refining a raw C4 hydrocarbon mixture

Abstract

The present invention relates to a process for purifying a feed C4 hydrocarbon mixture containing at least 2 wt.% isobutene, at least 23 wt.% butenes other than isobutene, less than 3 wt.% butadiene, at least 1.5 ppm by weight of a catalyst deactivator selected from the group of polar nitrogen-containing compounds and mixtures thereof, the sum of all components in the C4 hydrocarbon mixture being 100 wt.%, the process comprising the steps of: (d) contacting the feed C4 hydrocarbon mixture in a countercurrent flow with an aqueous stream in an extraction unit to obtain an intermediate C4 hydrocarbon mixture; (e) withdrawing at least a portion of the intermediate C4 hydrocarbon mixture from the extraction unit; (f) dehydrating the withdrawn intermediate C4 hydrocarbon mixture to obtain a purified C4 hydrocarbon mixture having a content of at most 1 ppm by weight of the catalyst deactivator. The invention further relates to a process for obtaining isobutene from an isobutene-containing C4-hydrocarbon mixture in a plant comprising an etherification unit, a first distillation unit, an ether cleavage unit and a second distillation unit.

Description

[Technical field]

[0001] The present invention relates to a process for purifying a feed C4-hydrocarbon mixture containing at least 2% by weight of isobutene, at least 23% by weight of butenes other than isobutene, less than 3% by weight of butadiene, at least 1.5 ppm by weight of a catalyst deactivator selected from the group of polar nitrogen-containing compounds and mixtures thereof. The present invention further relates to a process for obtaining isobutene from an isobutene-containing C4-hydrocarbon mixture in a plant comprising an etherification unit, a first distillation unit, an ether cleavage unit and a second distillation unit. [Background technology]

[0002] The C4 cut from a steam cracker or fluid catalytic cracker (FCC) unit consists essentially of butadiene, isobutene, 1-butene and 2-butene along with the saturated hydrocarbons isobutane and n-butane. The conventional work-up process used worldwide for such C4 cuts includes the following steps: First, most of the butadiene is removed. A hydrocarbon mixture called raffinate 1 remains, which contains saturated hydrocarbons along with isobutene, 1-butene and 2-butene. A possible way to remove isobutene from this mixture is to react it with a primary alcohol to form alkyl tert-butyl ethers. This leaves saturated hydrocarbons and linear butenes. The C4 mixture obtained after removal of butadiene and isobutene is called raffinate 2.

[0003] Document EP 0003305 discloses a method for removing isobutene from an isobutene-containing C4-hydrocarbon mixture, which comprises the steps of: (a) reacting the mixture with a primary alcohol in the presence of an acidic ion exchange resin to form an alkyl tert-butyl ether; (b) distilling the reaction mixture to obtain an overhead product comprising unconverted hydrocarbons and a bottom product comprising an alkyl tert-butyl ether; (c) feeding the bottom product to an ether cleavage unit to crack the alkyl tert-butyl ether to obtain isobutene and a primary alcohol; (d) distilling the mixture of isobutene and primary alcohol produced in step (c) to obtain an overhead product comprising isobutene and a bottom product comprising a primary alcohol; and (e) recycling the bottom product of step (d) to step (a).

[0004] The document CN1158228 discloses a method for producing isoolefins and / or tertiary alkyl ethers by reacting a mixed hydrocarbon stream containing isoolefins with an alcohol to obtain a tertiary alkyl ether product. The tertiary alkyl ether product is separated in a distillation column, and a high purity tertiary alkyl ether product is withdrawn as a side draw from the stripping section of the distillation column to reduce the equipment cost and energy consumption for preparing the tertiary alkyl ethers and / or isoolefins.

[0005] The document CN1239444 discloses a method for producing isoolefins, which includes the steps of (a) feeding an isoolefin-containing hydrocarbon mixture and alcohol to an etherification reactor; (b) separating the obtained product mainly containing tertiary alkyl ether in a first fractionator and a second fractionator; (c) heating the product with a heater and then feeding it to an ether decomposition reactor to obtain a product mainly containing unreacted tertiary alkyl ether, isoolefins, and alcohols; and (d) subjecting the product to high-boiling fraction removal in a third fractionator to obtain isoolefins.

[0006] The document US Patent No. 5,446,231 discloses a method for removing contaminants from a hydrocarbon stream, particularly a C5 hydrocarbon stream. The C5 hydrocarbon stream is washed countercurrently with a mixture containing 50% methanol and 50% water, and nitriles are extracted from the C5 hydrocarbons into a water-methanol mixture. Further, a method is disclosed for recovering methanol from the extraction stream by hydrogenating the nitriles to form amines.

[0007] The document US 2011 / 0282092 discloses a method for reducing nitrogen-containing Lewis bases in molecular sieve oligomerization, where nitrogen-containing Lewis bases act as poisons to molecular sieve catalysts. Reducing the presence of nitrogen-containing Lewis bases in the feedstock before contacting the molecular sieve extends the catalyst life.

[0008] Despite the existence of plant facilities for the reactive separation of isobutene from C4-hydrocarbon mixtures, several challenges remain when operating these plants with regard to their operating window, i.e. the range of process conditions that must be met to ensure stable operation of the plant. One problem encountered during the operation of such plants is the deactivation over time of the catalyst in the etherification reactor. As soon as the activity of the catalyst falls below a certain limit, it must be replaced, which requires a reactor shutdown and additional costs. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] European Patent No. 0003305 [Patent Document 2] Chinese Patent No. 1158228 [Patent Document 3] Chinese Patent No. 1239444 [Patent Document 4] U.S. Pat. No. 5,446,231 [Patent Document 5] US Patent Application Publication No. 2011 / 0282092 Summary of the Invention [Problem to be solved by the invention]

[0010] The object of the present invention was to provide a method for reactive separation of isobutene from a C4 hydrocarbon mixture via the formation and reverse cracking of alkyl tert-butyl ethers which is more robust against potential catalyst deactivation. [Means for solving the problem]

[0011] This object is achieved according to the invention by a method for purifying a feed C4-hydrocarbon mixture according to claim 1. This object is further achieved according to the invention by a method for obtaining isobutene from an isobutene-containing C4-hydrocarbon mixture according to claim 9. Advantageous variants of this method are presented in claims 2 to 8 and claim 10.

[0012] The first subject of the present invention is a process for purifying a feed C4-hydrocarbon mixture containing at least 2% by weight of isobutene, at least 23% by weight of butenes other than isobutene, less than 3% by weight of butadiene, at least 1.5 ppm by weight of a catalyst deactivator selected from the group of polar nitrogen-containing compounds and mixtures thereof, the sum of all components in the C4-hydrocarbon mixture being 100% by weight, The method further comprising: (a) contacting a feed C4 hydrocarbon mixture in a countercurrent manner with an aqueous stream in an extraction unit to obtain an intermediate C4 hydrocarbon mixture; (b) withdrawing at least a portion of the intermediate C4 hydrocarbon mixture from the extraction unit; (c) dehydrating the withdrawn intermediate C4 hydrocarbon mixture to obtain a refined C4 hydrocarbon mixture having a catalyst deactivator content of at most 1 ppm by weight; The method includes:

[0013] A second subject of the invention is a method for obtaining isobutene from an isobutene-containing C4-hydrocarbon mixture in a plant comprising an etherification unit, a first distillation unit, an ether cleavage unit and a second distillation unit, the method comprising the steps of: (i) contacting a C4 hydrocarbon mixture with a primary alcohol in an etherification unit and reacting the mixture with the primary alcohol in the presence of an acidic catalyst to form the corresponding alkyl tert-butyl ether; (ii) distilling the reaction mixture from the etherification unit in a first distillation unit to withdraw a C4-hydrocarbon raffinate as an overhead product and an alkyl tert-butyl ether as a liquid or vaporous bottom product, and vaporizing the bottom product if withdrawn as a liquid; (iii) reacting the vaporous bottoms in an ether cleavage unit in the presence of an acidic catalyst to obtain isobutene and a primary alcohol as reaction products; and (iv) distilling the reaction mixture from the ether cleavage unit in a second distillation unit to withdraw isobutene as an overhead product and primary alcohol as a bottom product for recycling to the etherification unit. Includes.

[0014] According to the present invention, the C4 hydrocarbon mixture fed to the etherification unit is obtained by pretreating a feed C4 hydrocarbon mixture containing a catalyst deactivator, the pretreatment comprising the steps of (a) contacting the feed C4 hydrocarbon mixture in a countercurrent flow with an aqueous stream in an extraction unit to obtain an intermediate C4 hydrocarbon mixture, (b) withdrawing at least a portion of the intermediate C4 hydrocarbon mixture from the extraction unit, and (c) dehydrating the withdrawn intermediate C4 hydrocarbon mixture to obtain a purified C4 hydrocarbon mixture having a content of at most 1 ppm by weight of the catalyst deactivator, the catalyst deactivator being selected from the group of amines, acetonitrile, ammonia, dimethylformamide, and mixtures thereof.

[0015] It was found that pre-treating the feed C4 hydrocarbon mixture by washing out potential catalyst deactivators and reducing their content in the refined C4 hydrocarbon mixture to a value of up to 1 ppm significantly increases the catalyst life in the subsequent etherification reaction. Furthermore, the purification step prior to the etherification reaction makes it possible to use a feed C4 hydrocarbon mixture with a much higher content of potential catalyst deactivators than would be possible without the purification step. This allows a more flexible operation of the entire process, since it is possible to handle feedstocks with a higher and more varied content of catalyst deactivators.

[0016] Feedstock C4 hydrocarbon mixtures suitable for the process of the invention are obtained, for example, from thermal or catalytic cracking of petroleum products, from thermal cracking of liquefied petroleum gas (LPG), naphtha, diesel, etc., or from catalytic dehydrogenation of n-butane and / or n-butene. Generally, these C4 hydrocarbon mixtures contain, in addition to isobutene, olefins and paraffinic C4 hydrocarbons. They may also contain butadiene and acetylenes, such as 1-butyne and butenine. Butadiene-containing C4 hydrocarbon mixtures may be used as they are or after removal of butadiene from the C4 hydrocarbon mixture, for example by extraction with a selective solvent. Generally, isobutene-containing C4 hydrocarbon mixtures contain 2 to 77% by weight, preferably 10 to 70% by weight, in particular 20 to 60% by weight, of isobutene. Preferably, a C4 hydrocarbon mixture containing, in addition to isobutene, n-butane, isobutane, 1-butene, trans-2-butene and cis-2-butene with or without 1,3-butadiene is used. More preferably, a C4 hydrocarbon mixture without 1,3-butadiene, known as "raffinate-1", is used in the process of the present invention.

[0017] Preferably, the feed C4 hydrocarbon mixture contains less than 1 wt. % of components having less than 4 carbon atoms and less than 1 wt. % of components having at least 5 carbon atoms.

[0018] Such raw C4 hydrocarbon mixtures typically contain polar nitrogen compounds that can deactivate the acid catalysts used in the etherification of isobutene with primary alcohols. Catalyst deactivators present in raw C4 hydrocarbon mixtures are in particular amines, acetonitrile, ammonia, dimethylformamide, and mixtures thereof.

[0019] The primary alcohol suitable for the process of the present invention is one that can react with isobutene to form the corresponding alkyl tert-butyl ether. Preferably, the primary alcohol is selected from the group of methanol, ethanol, isopropyl alcohol and isobutanol. More preferably, the primary alcohol is isobutanol.

[0020] In a first embodiment of the second subject of the present invention, the primary alcohol is methanol and the alkyl tert-butyl ether is methyl tert-butyl ether (MTBE). A method for obtaining isobutene from an isobutene-containing C4-hydrocarbon mixture in a plant comprising an etherification unit, a first distillation unit, an ether cleavage unit and a second distillation unit comprises the following steps: i) contacting the C4 hydrocarbon mixture with methanol in an etherification unit and reacting the mixture with methanol in the presence of an acidic catalyst to form methyl tert-butyl ether (MTBE); ii) distilling in a first distillation unit the reaction mixture from the etherification unit, withdrawing a C4 hydrocarbon raffinate as an overhead product and MTBE as a liquid or vaporous bottom product, and vaporizing the bottom product if withdrawn as a liquid; iii) reacting the vaporous bottoms in an ether cleavage unit in the presence of an acidic catalyst to obtain isobutene and methanol as reaction products; and iv) distilling the reaction mixture from the ether cleavage unit in a second distillation unit to withdraw isobutene as an overhead product and methanol as a bottom product for recycling to the etherification unit; Includes The C4 hydrocarbon mixture fed to the etherification unit is obtained by pretreating a feed C4 hydrocarbon mixture, the pretreatment comprising the steps of: (a) contacting said feed C4 hydrocarbon mixture in a countercurrent flow with an aqueous stream in an extraction unit to obtain an intermediate C4 hydrocarbon mixture; (b) withdrawing at least a portion of the intermediate C4 hydrocarbon mixture from the extraction unit; and (c) dehydrating the withdrawn intermediate C4 hydrocarbon mixture to obtain a C4 hydrocarbon mixture having a catalyst deactivator content of at most 1 ppm by weight, the catalyst deactivator being selected from the group of amines, acetonitrile, ammonia, dimethylformamide, and mixtures thereof.

[0021] In a second embodiment of the second subject of the present invention, the primary alcohol is ethanol and the alkyl tert-butyl ether is ethyl tert-butyl ether (ETBE). A method for obtaining isobutene from an isobutene-containing C4-hydrocarbon mixture in a plant comprising an etherification unit, a first distillation unit, an ether cleavage unit and a second distillation unit, comprising the following steps: i) contacting a C4 hydrocarbon mixture with ethanol in an etherification unit and reacting the mixture with ethanol in the presence of an acidic catalyst to form ethyl tert-butyl ether (ETBE); ii) distilling in a first distillation unit the reaction mixture from the etherification unit, withdrawing a C4-hydrocarbon raffinate as an overhead product and ETBE as a liquid or vaporous bottom product, and vaporizing the bottom product if withdrawn as a liquid; iii) reacting the vapor stream of step (c) in the presence of an acidic catalyst in an ether cleavage unit to obtain isobutene and ethanol as reaction products; and iv) distilling the reaction mixture from the ether cleavage unit in a second distillation unit to withdraw isobutene as an overhead product and ethanol as a bottom product for recycling to the etherification unit; Includes The C4 hydrocarbon mixture fed to the etherification unit is obtained by pretreating a feed C4 hydrocarbon mixture, the pretreatment comprising the steps of: (a) contacting said feed C4 hydrocarbon mixture in a countercurrent flow with an aqueous stream in an extraction unit to obtain an intermediate C4 hydrocarbon mixture; (b) withdrawing at least a portion of the intermediate C4 hydrocarbon mixture from the extraction unit; and (c) dehydrating the withdrawn intermediate C4 hydrocarbon mixture to obtain a C4 hydrocarbon mixture having a catalyst deactivator content of at most 1 ppm by weight, the catalyst deactivator being selected from the group of amines, acetonitrile, ammonia, dimethylformamide, and mixtures thereof.

[0022] In a third embodiment of the second subject of the present invention, the primary alcohol is isopropyl alcohol and the alkyl tert-butyl ether is isopropyl tert-butyl ether (IPTBE). A method for obtaining isobutene from an isobutene-containing C4-hydrocarbon mixture in a plant comprising an etherification unit, a first distillation unit, an ether cleavage unit and a second distillation unit, comprising the following steps: i) contacting a C4 hydrocarbon mixture with isopropyl alcohol in an etherification unit and reacting the mixture with isopropyl alcohol in the presence of an acid catalyst to form isopropyl tert-butyl ether (IPTBE); ii) distilling in a first distillation unit the reaction mixture from the etherification unit, withdrawing a C4-hydrocarbon raffinate as an overhead product and IPTBE as a liquid or vaporous bottom product, and vaporizing the bottom product if withdrawn as a liquid; iii) reacting the vapor stream of step (c) in the presence of an acidic catalyst in an ether cleavage unit to obtain isobutene and isopropyl alcohol as reaction products; and iv) distilling the reaction mixture from the ether cleavage unit in a second distillation unit to withdraw isobutene as an overhead product and ethanol as a bottom product for recycling to the etherification unit; Includes The C4 hydrocarbon mixture fed to the etherification unit is obtained by pretreating a feed C4 hydrocarbon mixture, the pretreatment comprising the steps of: (a) contacting said feed C4 hydrocarbon mixture in a countercurrent flow with an aqueous stream in an extraction unit to obtain an intermediate C4 hydrocarbon mixture; (b) withdrawing at least a portion of the intermediate C4 hydrocarbon mixture from the extraction unit; and (c) dehydrating the withdrawn intermediate C4 hydrocarbon mixture to obtain a C4 hydrocarbon mixture having a catalyst deactivator content of at most 1 ppm by weight, the catalyst deactivator being selected from the group of amines, acetonitrile, ammonia, dimethylformamide, and mixtures thereof.

[0023] In a fourth embodiment of the second subject of the present invention, the primary alcohol is isobutanol and the alkyl tert-butyl ether is isobutyl tert-butyl ether (IBTBE). A method for obtaining isobutene from an isobutene-containing C4-hydrocarbon mixture in a plant comprising an etherification unit, a first distillation unit, an ether cleavage unit and a second distillation unit, comprising the following steps: i) contacting a C4 hydrocarbon mixture with isobutanol in an etherification unit and reacting the mixture with isobutanol in the presence of an acidic catalyst to form isobutyl tert-butyl ether (IBTBE); ii) distilling in a first distillation unit the reaction mixture from the etherification unit, withdrawing a C4-hydrocarbon raffinate as an overhead product and IBTBE as a liquid or vaporous bottom product, and vaporizing the bottom product if withdrawn as a liquid; iii) reacting the vapor stream of step (c) in the presence of an acidic catalyst in an ether cleavage unit to obtain isobutene and isobutanol as reaction products; and iv) distilling the reaction mixture from the ether cleavage unit in a second distillation unit to withdraw isobutene as an overhead product and isobutanol as a bottom product for recycling to the etherification unit; Includes The C4 hydrocarbon mixture fed to the etherification unit is obtained by pretreating a feed C4 hydrocarbon mixture, the pretreatment comprising the steps of: (a) contacting said feed C4 hydrocarbon mixture in a countercurrent flow with an aqueous stream in an extraction unit to obtain an intermediate C4 hydrocarbon mixture; (b) withdrawing at least a portion of the intermediate C4 hydrocarbon mixture from the extraction unit; and (c) dehydrating the withdrawn intermediate C4 hydrocarbon mixture to obtain a C4 hydrocarbon mixture having a catalyst deactivator content of at most 1 ppm by weight, the catalyst deactivator being selected from the group of amines, acetonitrile, ammonia, dimethylformamide, and mixtures thereof.

[0024] Purification Step In the extraction unit, the raw C4 hydrocarbon mixture is contacted with an aqueous stream in a countercurrent flow to obtain an intermediate C4 hydrocarbon mixture. The extraction unit may consist of any device known in the art that allows for the extraction of components from an organic phase to an aqueous phase by vigorous contact of the C4 hydrocarbon mixture with an aqueous stream. For example, the extraction unit may include a pipe equipped with a static mixer that allows for vigorous mixing of the phases, followed by a phase separation device, such as a settling tank.

[0025] In a preferred embodiment, the extraction unit comprises an extraction tower. The extraction tower may be equipped with internals such as trays or packing. Preferably, the feed C4 hydrocarbon mixture is fed to the lower part of the extraction tower, more preferably to the bottom of the internals or to the bottom of the tower. Preferably, the aqueous stream is fed to the upper part of the extraction tower, more preferably to the top of the internals or to the top of the tower. The countercurrent flow of the organic phase flowing upward and the aqueous phase flowing downward allows vigorous mixing of the two phases and transfer of catalyst deactivation components from the organic phase to the aqueous phase.

[0026] Preferably, the extraction column is operated at a pressure of 4 to 7 bar (absolute) and a temperature of 30 to 60°C.

[0027] The aqueous phase is concentrated in the lower part of the extraction tower and removed from the bottom outlet of the tower. In a preferred embodiment, a portion of the aqueous bottom outlet stream is recycled to the extraction tower. Preferably, 40-80 wt. % of the bottom stream withdrawn from the bottom of the extraction tower is recycled to the extraction tower, preferably to the upper part of the extraction tower. It is further preferred that a portion of the recycle stream is fed to a stripping unit, where organic components are removed from the recycle stream. Preferably, fresh water is added to the recycle stream or directly to the extraction tower in an amount corresponding to the amount of organic phase removed from the stripping unit.

[0028] The aqueous stream fed to the extraction unit preferably comprises 90% to 100% by weight water, more preferably the aqueous stream is water.

[0029] The extraction process obtains a water-containing intermediate C4 hydrocarbon mixture by extracting the catalyst deactivating components from the raw C4 hydrocarbon mixture into the aqueous phase. At least a portion of the intermediate C4 hydrocarbon mixture is withdrawn from the extraction unit. Preferably, the intermediate C4 hydrocarbon mixture is withdrawn completely from the extraction unit.

[0030] The withdrawn intermediate C4 hydrocarbon mixture is dehydrated to obtain a purified C4 hydrocarbon mixture. In a preferred embodiment, the intermediate C4 hydrocarbon mixture withdrawn from the extraction unit is fed to a phase separation unit for dehydration. The phase separation unit preferably comprises a filter, a coalescer and / or a phase separator. Depending on the physical properties of the organic-aqueous mixture of the intermediate C4 hydrocarbon mixture, a filter, a coalescer and a phase separator may be provided. For example, when the water droplets in the organic-aqueous dispersion are rather large, a phase separator is sufficient to remove the aqueous phase from the organic phase. When the droplets are rather small, it is advantageous to provide a filter-coalescer-phase separator sequence to first increase the size of the droplets before they are separated. It may also be advantageous to cool the intermediate C4 hydrocarbon mixture before entering the phase separation unit.

[0031] Etherification Unit The etherification is based on the selective reaction of primary alcohols with isobutene contained in an isobutene-containing C4-hydrocarbon mixture, for example, in raffinate 1. The products formed are the respective alkyl tert-butyl ethers. Other C4-hydrocarbons do not participate in the etherification reaction. The etherification may be carried out, for example, in one or more stirred tanks or in one or more fixed-bed reactors, the latter being preferred.

[0032] Diisobutene is formed as the main by-product during the etherification reaction. Tertiary butanol may be formed as a further by-product, especially when water and isobutene are present over an acidic catalyst.

[0033] The etherification reaction takes place in the presence of an acidic ion exchange resin acting as a heterogeneous etherification catalyst. The acidic ion exchange resin is a cation exchanger in acidic form. In one embodiment, the acidic ion exchange resin comprises a sulfonic acid or phosphoric acid ion exchange resin. Preferably, the acidic ion exchange resin comprises a macroreticular ion exchange resin. Examples of suitable ion exchange resins are sulfonated phenol-formaldehyde resins, sulfonated resins derived from coumarone-indene condensation products, and in particular sulfonated polystyrene resins. In a preferred embodiment, the acidic ion exchange resin comprises a copolymer of styrene and divinylbenzene, such as a crosslinked styrene-divinylbenzene copolymer functionalized with sulfonic acid groups.

[0034] In one embodiment, the acidic ion exchange resin can have a concentration of acidic ion exchange groups of at least about 1 milliequivalent of H+ per gram of dry resin. Typically, the amount of ion exchange resin is between 0.01 and 1 liter of bulk volume per liter of reactor volume.

[0035] The etherification reaction is an equilibrium reaction. Therefore, a certain residence time is required to reach equilibrium. However, from a practical point of view, it is preferable to carry out the etherification continuously, in which case the quotient of the volume (volume unit) of the reaction zone and the throughput in volume units per hour is generally 0.01 to 5 hours, preferably 0.02 to 1 hour, and particularly 0.03 to 1 hour.

[0036] Generally, the etherification reaction results in a conversion of at least 90%, preferably at least 95%, in particular at least 96%, of the isobutene contained in the C4-hydrocarbon mixture to alkyl tert-butyl ethers.

[0037] A molar excess of primary alcohol relative to isobutene is advantageous in reaching a high conversion of isobutene and suppressing the formation of isobutene oligomers. The conversion increases as the molar ratio of primary alcohol to isobutene increases. Preferably, the molar ratio of primary alcohol to isobutene contained in the C4 hydrocarbon mixture is 100:1 to 1:1, more preferably 20:1 to 1.2:1, in particular 4:1 to 1.3:1.

[0038] The etherification can be carried out under atmospheric pressure. However, it is advantageous to operate under overpressure, for example from 1.01 to 30 bar, in particular from 2 to 20 bar. Depending on the pressure and temperature, the isobutene-containing C4-hydrocarbon mixture can be used as a liquid or gas. Preferably, a liquid isobutene-containing C4-hydrocarbon mixture is used. To ensure that no vaporization occurs in the etherification unit, the pressure is maintained in the range of 12 to 20 bar.

[0039] Preferably, the outlet temperature of the reaction mixture from the etherification unit is between 25 and 65°C, preferably between 30 and 60°C, in particular between 30 and 50°C. Etherification is an exothermic reaction. Ether formation is favored at low temperatures. To achieve high reaction rates and high isobutene conversions with low by-product formation, the reactor system is preferably cascaded and temperatures below 70°C are applied. In one embodiment, multiple adiabatic fixed bed reactors are used in series, for example three adiabatic fixed bed reactors. Typical reactor inlet temperatures are in the range of 30 to 40°C. The conversion is highest in the first reactor, the second reactor converts the remaining isobutene, and the last reactor has a longer residence time to achieve equilibrium conditions for the etherification reaction.

[0040] As catalyst degradation progresses, the main contribution to the total conversion shifts from the first reactor to the second reactor. The inlet temperatures of the reactors are adjusted to achieve the intended conversion and depend on the activity of each of the catalysts. The inlet temperature of the third reactor is usually the lowest and is kept as low as possible while still achieving equilibrium conditions at the outlet of this reactor.

[0041] Generally, the catalyst in the first reactor is replaced more frequently than the catalyst in the second and third reactors because contaminants in the feedstock have a higher probability of deactivating the catalyst in the first reactor, and conversion is typically highest in the first reactor.

[0042] Providing a reactor stage with parallel reactors allows for catalyst replacement without the need to shut down the entire etherification unit. Parallel connected reactors can be provided in any reactor stage, for example the two first reactors, the two second reactors and / or the two third reactors.

[0043] First distillation unit The reaction mixture withdrawn from the etherification unit contains alkyl tert-butyl ether, diisobutene, unconverted hydrocarbons and unreacted primary alcohol. The C4-hydrocarbons that did not participate in the etherification reaction are separated from the alkyl tert-butyl ether and excess primary alcohol in a first distillation unit. The top product removed is a C4-hydrocarbon raffinate that is substantially free of isobutene. In general, the isobutene content is less than or equal to 5% by weight, preferably less than or equal to 2.5% by weight, in particular less than or equal to 1.5% by weight. The isobutene content in the top product is determined by the conversion in the etherification unit and the initial composition of the isobutene-containing C4-hydrocarbon mixture, for example raffinate 1. The isobutene content in the overhead product can be reduced by recycling part of the overhead product to the etherification unit.

[0044] Preferably, the total amount of alkyl tert-butyl ethers and / or di-isobutyl ethers in the overhead product is less than or equal to 200 ppm by weight. The overhead product is also called "raffinate 2".

[0045] Preferably, a raffinate 2 product stream is withdrawn in a side draw at the top of the distillation column. Components having boiling points lower than those of the raffinate 2 components are preferably withdrawn as off-gas from the overhead condenser of the distillation column. These light components may include nitrogen, C3 hydrocarbons or potentially formed tertiary butanol.

[0046] The bottom product from the first distillation unit mainly comprises alkyl tert-butyl ethers and diisobutene, as well as components with a boiling point higher than that of alkyl tert-butyl ethers. The bottom product may or may not contain excess primary alcohols. Advantageously, a bottom product is taken off containing not more than 1,000 ppm by weight, preferably not more than 500 ppm by weight, in particular not more than 100 ppm by weight of C4-hydrocarbons.

[0047] Conveniently, the first distillation unit is operated under a pressure of about 4 to 8 bar and has a bottom temperature of 165 to 200°C, for example about 170°C.

[0048] In one embodiment of the process according to the invention, the alkyl tert-butyl ether-containing bottom product from the first distillation unit is withdrawn in the gas phase, for example as a vapor side draw from a distillation column.

[0049] In another embodiment, the alkyl tert-butyl ether-containing bottom product from the first distillation unit is withdrawn in liquid phase or as a two-phase gas-liquid stream. In this case, the bottom product is vaporized. Possible vaporizers are all conventional types of vaporizers, such as falling film evaporators, spiral tubes, thin film evaporators, natural convection evaporators with external or internal circulation, such as Robert evaporators, or forced circulation evaporators. Robert evaporators or falling film evaporators are preferred.

[0050] In a preferred variant of this embodiment, the bottom product from the first distillation unit is vaporized in an evaporator and a purge stream containing high-boiling components having a normal boiling point higher than that of the alkyl tert-butyl ether is withdrawn from the evaporator.

[0051] Additionally, it is preferred to superheat the vapor phase to prevent condensation on the ether cleavage catalyst due to endothermic reactions and pore condensation.

[0052] In a first preferred embodiment, the first distillation unit comprises a distillation column, the bottom product is withdrawn as a side stream from the distillation column at a stage below the feed stage, and a purge stream rich in high boiling components is withdrawn from the sump of the distillation column. The side stream may be withdrawn as a vapor or liquid. Withdrawing the bottom product as a side stream has the advantage that high boiling components that can lead to degradation of the ether cleavage process are dramatically reduced in the bottom product.

[0053] It is further preferred for this embodiment that the purge stream from the sump of the distillation column of the first distillation unit is fed to a by-product separation unit. The purge stream containing high boiling point components can be separated into valuable products in the by-product separation unit. This increases the overall efficiency of the isobutene separation process by reducing the loss of by-products.

[0054] In a second preferred embodiment, the bottom product from the first distillation unit is vaporized in an evaporator, and a purge stream containing high-boiling components having a normal boiling point higher than the boiling point of the alkyl tert-butyl ether is withdrawn from the evaporator. Removing the high-boiling components in the evaporator before the ether cleavage unit has the advantage that the potential accumulation of those high-boiling components in the closed process is prevented, resulting in an increase in the capacity of the isobutene separation process. In addition, the potential catalyst deactivation in the ether cleavage unit is prevented.

[0055] It is further preferred in this embodiment that the evaporator is a natural circulation evaporator, in particular a Roberts type evaporator, and the purge stream is withdrawn from the liquid phase at the bottom of the evaporator, which allows the high boiling point components to be easily and efficiently removed.

[0056] It is further preferred in this embodiment that the purge stream from the evaporator is fed to a by-product separation unit. The purge stream containing high boiling components can be separated into valuable products in the by-product separation unit. This increases the overall efficiency of the isobutene separation process by reducing by-product losses.

[0057] Ether Cleavage Unit In the ether cleavage unit, the alkyl tert-butyl ether is decomposed into isobutene and primary alcohol in the presence of an acid catalyst at high temperature. Preferably, the alkyl tert-butyl ether-containing bottom product from the first distillation unit is transferred to the ether cleavage unit without removing excess primary alcohol that may be present. Alternatively, it is possible to remove some or all of the primary alcohol.

[0058] The decomposition of alkyl tert-butyl ethers is carried out in the gas phase over an acid catalyst, which may be carried out batchwise but is preferably carried out continuously.

[0059] The ether cleavage reaction is an equilibrium reaction, with decomposition promoted at high temperatures. Typical conversions are greater than 90%. The ether cleavage reaction may be carried out in one or more reactors connected in series and / or parallel. Useful reactors include heated tubular reactors, such as steam heated tubular reactors, or two reactor systems consisting of a heated tubular reactor followed by a second heated tubular reactor or an adiabatic fixed bed reactor. Alternatively, the ether cleavage reaction may be carried out in a two-phase system using a two-phase reactor.

[0060] Examples of suitable acid catalysts are ion exchangers in the acid form, such as sulfonated coal, sulfonated phenol-formaldehyde resins, sulfonated resins derived from coumarone-indene condensation products, especially sulfonated polystyrene resins, such as sulfonated crosslinked styrene-divinylbenzene copolymers.

[0061] Another catalyst that can be advantageously used is a solid phosphoric acid catalyst, which comprises monophosphoric acid or preferably polyphosphoric acid on a solid support. Examples of supports suitable for phosphoric acid catalysts are alumina, silica, activated carbon, diatomaceous earth or pumice. Silica gel is a preferred support.

[0062] Other suitable acid catalysts are metal sulfates, such as sodium bisulfate, calcium bisulfate, aluminum sulfate, nickel sulfate, copper sulfate, cobalt sulfate, cadmium sulfate and strontium sulfate. These sulfates may be used unsupported, but are preferably used on a carrier. Examples of suitable carriers are silica gel, activated carbon, alumina and pumice.

[0063] Further suitable catalysts for the decomposition are silica gel or alumina itself.

[0064] In a further embodiment of the process according to the invention, metal phosphates, in particular metal hydrogen phosphates, are used as acid decomposition catalysts. These phosphates may also contain an excess of phosphoric acid, for example up to 65%, preferably 1-50%, in particular 10-20% excess, relative to the amount corresponding to the stoichiometric composition of the acid metal phosphate. Examples of such metal phosphates are magnesium phosphate, calcium phosphate, strontium phosphate, barium phosphate, manganese phosphate, nickel phosphate, copper phosphate, cobalt phosphate, cadmium phosphate, iron(II) phosphate, chromium phosphate, in particular aluminum phosphate. The metal phosphate catalysts can be used as such or on a support. Examples of suitable supports are alumina, silica, activated carbon and zinc oxide.

[0065] The amount of acid catalyst is generally about 0.01 to 1 kg, preferably about 0.03 to 0.3 kg per kg of alkyl tert-butyl ether passing through the reactor per hour. Preferably, a fixed bed reactor is used for the decomposition of alkyl tert-butyl ether.

[0066] The decomposition temperature of tertiary ethers varies depending on the nature of the acid catalyst and the contact time, but is generally 50° C. to 350° C., preferably 80° C. to 300° C., and particularly 100° C. to 250° C. When a metal phosphate or phosphoric acid catalyst is used as the decomposition catalyst, the decomposition is generally carried out at 80° C. to 350° C., preferably 90° C. to 260° C., and particularly 170° C. to 210° C.

[0067] The contact time of the vaporized alkyl tert-butyl ether is advantageously between 0.1 and 20 seconds, preferably between 1 and 10 seconds.

[0068] The decomposition of alkyl tert-butyl ethers can be carried out under atmospheric pressure, but is generally carried out under superatmospheric pressure, for example up to 30 bar, preferably up to 20 bar. Advantageously, the decomposition of alkyl tert-butyl ethers is carried out under a pressure of 2 to 15 bar, preferably 3 to 12 bar, in particular 4 to 12 bar. However, the decomposition can also be carried out under reduced pressure.

[0069] In one embodiment, the ether cleavage unit comprises a first ether cleavage reactor and a second ether cleavage reactor connected in series. Due to the high initial activity of the first ether cleavage reactor, almost complete conversion is achieved in this reactor. If there is no cleavable ether at the output of the first reactor, undesirable side reactions may occur in the second reactor, such as dehydration of primary alcohol to water and isobutene. When the activity of the first ether cleavage reactor decreases over time and the output of the first ether cleavage reactor contains a predetermined concentration of alkyl tert-butyl ether, the second ether cleavage reactor is started.

[0070] In a preferred embodiment, the first and second ether cleavage reactors are periodically alternated in sequence and / or flow direction through the first ether cleavage reactor and / or the second ether cleavage reactor is periodically changed. The possibility of switching between the two reactors and periodically changing the flow direction through the reactors can result in more uniform deactivation and better reaction control over the length of the reactor. Ultimately, the overall run time can be improved.

[0071] Second distillation unit The reaction mixture obtained from the ether cleavage unit contains isobutene and primary alcohols as reaction products and is fed to a second distillation unit, where the high-purity isobutene is separated by distillation from heavy components such as primary alcohols, unreacted alkyl tert-butyl ethers, and further heavy compounds such as diisobutene.

[0072] In a first embodiment of the subject of the present invention, when the primary alcohol is methanol and the alkyl tert-butyl ether is methyl tert-butyl ether (MTBE), the second distillation unit preferably comprises a methanol extraction unit and an isobutene purification column. The reaction mixture from the ether cleavage unit is fed to the methanol extraction unit, where it is countercurrently contacted with a solvent, preferably water as a solvent. A water- and methanol-rich stream is withdrawn from the bottom of the extraction unit for further processing and recycling to the methanol etherification unit. An isobutene-rich stream is withdrawn from the top of the extraction unit and fed to an isobutene purification column, where isobutene is separated from high-boiling components and withdrawn as the overhead product of the isobutene purification column. Preferably, an isobutene product stream is withdrawn in a side draw at the top of the isobutene purification column while the column is operated with total liquid reflux. Components with a boiling point lower than that of isobutene are preferably withdrawn as off-gas from the overhead condenser of the column. These light components may include nitrogen or C3 hydrocarbons.

[0073] In a second embodiment of the subject of the present invention, when the primary alcohol is ethanol and the alkyl tert-butyl ether is ethyl tert-butyl ether (ETBE), the second distillation unit preferably comprises an ethanol extraction unit and an isobutene purification column. The reaction mixture from the ether cleavage unit is fed to the ethanol extraction unit, where it is countercurrently contacted with a solvent, preferably water as a solvent. A water- and ethanol-rich stream is withdrawn from the bottom of the extraction unit for further processing and recycling to the ethanol etherification unit. An isobutene-rich stream is withdrawn from the top of the extraction unit and fed to an isobutene purification column, where isobutene is separated from high-boiling components and withdrawn as the overhead product of the isobutene purification column. Preferably, an isobutene product stream is withdrawn in a side draw at the top of the isobutene purification column while the column is operated with total liquid reflux. Components with a boiling point lower than that of isobutene are preferably withdrawn as off-gas from the overhead condenser of the column. These light components may include nitrogen or C3 hydrocarbons.

[0074] In a third embodiment of the subject of the present invention, when the primary alcohol is isopropyl alcohol and the alkyl tert-butyl ether is isopropyl tert-butyl ether (IPTBE), the second distillation unit preferably comprises an isopropyl alcohol extraction unit and an isobutene purification column. The reaction mixture from the ether cleavage unit is fed to the isopropyl alcohol extraction unit, where it is countercurrently contacted with a solvent, preferably water as a solvent. A stream rich in water and isopropyl alcohol is withdrawn from the bottom of the extraction unit for further processing and recycling to the ethanol etherification unit. An isobutene-rich stream is withdrawn from the top of the extraction unit and fed to an isobutene purification column, where isobutene is separated from high boiling components and withdrawn as the overhead product of the isobutene purification column. Preferably, an isobutene product stream is withdrawn in a side draw at the top of the isobutene purification column while the column is operated with total liquid reflux. Components with a boiling point lower than that of isobutene are preferably withdrawn as off-gas from the overhead condenser of the column. These light components may include nitrogen or C3 hydrocarbons.

[0075] In a fourth embodiment of the subject of the present invention, when the primary alcohol is isobutanol and the alkyl tert-butyl ether is isobutyl tert-butyl ether (IBTBE), the second distillation unit preferably comprises a distillation column fed with the reaction mixture from the ether cleavage unit. Isobutene is withdrawn from said column as overhead product, and isobutanol and diisobutene are withdrawn as bottom products and recycled to the etherification unit. The bottom temperature is preferably between 150°C and 200°C, and the pressure in the column is preferably between 4 and 8 bar. In a preferred variant, an isobutene product stream is withdrawn in a side draw at the top of the column while the column is operated with total liquid reflux. Components with a boiling point lower than that of isobutene are preferably withdrawn as off-gas from the overhead condenser of the column. These light components may comprise nitrogen or C3-hydrocarbons.

[0076] Advantageously, the overhead product contains at least 99.3% by weight, preferably at least 99.5% by weight, in particular at least 99.7% by weight of isobutene. Preferably, isobutene containing at most 500 ppm by weight, preferably at most 100 ppm by weight, in particular at most 50 ppm by weight of primary alcohol is removed as overhead product.

[0077] Preferably, a high purity isobutene product is taken from a side draw of the second distillation unit near the top of the column. Water, which may be produced as a by-product during the process, can be removed from the system, for example, in a reflux drum of the overhead condenser of the distillation column.

[0078] The bottom product contains mainly primary alcohols, alkyl tert-butyl ethers and diisobutene. Advantageously, the bottom product contains 80-85% by weight of primary alcohols, 8-10% by weight of alkyl tert-butyl ethers and 4-5% by weight of diisobutene. The majority of the bottom product is recycled to the etherification unit. If necessary, the recycle stream can be supplemented with fresh primary alcohol.

[0079] By-product Separation Unit According to the invention, the plant further comprises a by-product separation unit to which a portion of the bottom purge stream of the first distillation unit and / or the bottom product of the second distillation unit is fed. When a portion of the bottom product of the second distillation unit is fed to the by-product separation unit, the weight ratio of the bottom product led to the by-product separation unit to the bottom product recycled to the etherification unit is preferably in the range of 1:20 to 1:5, more preferably about 1:10.

[0080] By providing a by-product separation unit to which the purge stream of the first distillation unit and / or a portion of the bottom product of the second distillation unit is fed, the operating window of the plant for obtaining isobutene from the isobutene-containing C4-hydrocarbon mixture is significantly increased. By removing the purge stream of the first distillation unit and / or a portion of the bottom product of the second distillation unit, it is possible to continuously remove high-boiling impurities from the system. The removal of high-boiling components from the system can be achieved in various ways. In a preferred embodiment, the by-product separation unit is fed with the bottom purge stream of the first distillation unit. In another preferred embodiment, the by-product separation unit is fed with a portion of the bottom product of the second distillation unit. In another preferred embodiment, the by-product separation unit is fed with the bottom purge stream of the first distillation unit and a portion of the bottom product of the second distillation unit.

[0081] The process according to the invention is more robust against internal disturbances, such as the accumulation of impurities, as well as against external disturbances, such as fluctuations in the feed composition. Furthermore, the separation of the withdrawn portion of the bottom product of the second distillation unit into three different fractions allows for more specific reuse strategies, higher process integration and thus reduced operating costs. The valuable by-product diisobutene is easily recovered, in contrast to known processes where it is discharged.

[0082] It is further preferred that an alcohol product stream rich in primary alcohol is separated therein from the stream that is fed to a by-product separation unit.

[0083] More preferably, the primary alcohol is recycled to the etherification unit. Recycling of the primary alcohol increases the overall efficiency of the isobutene separation process by reducing the amount of fresh primary alcohol required for isobutene separation. In the prior art processes, the amount of primary alcohol contained in the purge stream removed from the second distillation unit is typically discharged.

[0084] In a further preferred embodiment, the mass fraction of primary alcohol in the alcohol product stream is at least 90 wt%, preferably at least 95 wt%. Recycling the second by-product stream to the etherification unit reduces the amount of fresh primary alcohol required for isobutene separation due to the high purity of the primary alcohol, improving the overall efficiency of the isobutene separation process.

[0085] In a preferred embodiment, the alkyl tert-butyl ether contained in the bottom product stream from the second distillation unit is separated in a by-product purification unit and recycled for evaporation to the evaporator, the ether cleavage unit or both the evaporator and the ether cleavage unit in step (c). Separating and recycling the alkyl tert-butyl ether contained in the bottom stream from the second distillation column reduces the loss of valuable product isobutene contained in the alkyl tert-butyl ether and improves the overall efficiency of the isobutene separation process. In prior art processes, the purge stream removed from the second distillation unit is typically discharged.

[0086] In a further preferred embodiment, the bottom product of the second distillation unit, which is fed to the by-product separation unit, is split into at least three by-product streams, the first by-product stream being rich in diisobutene, the second by-product stream being an alcohol product stream rich in primary alcohols, and the third by-product stream being rich in components having normal boiling points above 110° C. The separation of the withdrawn portion of the bottom product of the second distillation unit into three different fractions allows for more specific reuse strategies, higher process integration and thus reduced operating costs. The valuable by-product diisobutene is easily recovered, in contrast to known methods where it is discharged.

[0087] Methanol / MTBE In a first embodiment of the present subject matter, when the primary alcohol is methanol and the alkyl tert-butyl ether is methyl tert-butyl ether (MTBE), the by-product separation unit preferably comprises at least two distillation columns.

[0088] In one embodiment, the first distillation column of the by-product separation unit is fed with the purge stream of the first distillation unit and / or a portion of the bottom product of the second distillation unit, which contains mainly methanol, MTBE and diisobutene. A second by-product stream rich in methanol is withdrawn from the top of the first column. This second by-product stream may further contain MTBE. The bottom product stream of the first column is fed to the second distillation column of the by-product separation unit. A first by-product stream rich in diisobutene is withdrawn from the top of the second column, and a third by-product stream rich in components having a normal boiling point above 110° C. is withdrawn from the bottom of the second column. The third by-product stream may contain high boiling components such as triisobutene.

[0089] In another preferred embodiment, the by-product separation unit comprises at least three distillation columns. The first distillation column of the by-product separation unit is fed with the purge stream of the first distillation unit and / or a portion of the bottom product of the second distillation unit, which mainly contains methanol, MTBE and diisobutene. A stream rich in MTBE is withdrawn from the top of the first column. Components having a normal boiling point higher than MTBE are withdrawn from the bottom of the first column and fed to the second distillation column of the by-product separation unit. A second by-product stream rich in methanol is withdrawn from the top of the second column. A bottom product stream of the second column is withdrawn and fed to the third distillation column of the by-product separation unit. A first by-product stream rich in diisobutene is withdrawn from the top of the third column, and a third by-product stream rich in components having a normal boiling point higher than 110 ° C is withdrawn from the bottom of the third column. The third by-product stream may contain higher boiling components such as triisobutene.

[0090] Ethanol / ETBE In a second embodiment of the present subject matter, when the primary alcohol is ethanol and the alkyl tert-butyl ether is ethyl tert-butyl ether (ETBE), the by-product separation unit preferably comprises at least two distillation columns.

[0091] In one embodiment, the first distillation column of the by-product separation unit is fed with the purge stream of the first distillation unit and / or a portion of the bottom product of the second distillation unit, which contains mainly ethanol, ETBE and diisobutene. A second by-product stream rich in ethanol is withdrawn from the top of the first column. This second by-product stream may further contain ETBE. The bottom product stream of the first column is fed to the second distillation column of the by-product separation unit. A first by-product stream rich in diisobutene is withdrawn from the top of the second column, and a third by-product stream rich in components having a normal boiling point above 110° C. is withdrawn from the bottom of the second column. The third by-product stream may contain high boiling components such as triisobutene.

[0092] In another preferred embodiment, the by-product separation unit comprises at least three distillation columns. The first distillation column of the by-product separation unit is fed with the bottom purge stream of the first distillation unit and / or a portion of the bottom product of the second distillation unit, which contains mainly ethanol, ETBE and diisobutene. The first distillation column is a prefractionation column, in which a stream rich in ETBE and ethanol is withdrawn from the top of the column and a stream rich in diisobutene and high boiling components is withdrawn from the bottom of the column. The overhead product stream is fed to the second distillation column of the by-product separation unit, a stream rich in ETBE is withdrawn from the top of the second column and a second by-product stream rich in ethanol is withdrawn from the bottom of the second column. The bottom product stream of the first column is fed to a third distillation column of the by-product separation unit, a first by-product stream rich in diisobutene is withdrawn from the top of the third column, and a third by-product stream rich in components having normal boiling points greater than 110° C. is withdrawn from the bottom of the third column. The third by-product stream may contain higher boiling components such as triisobutene.

[0093] Isopropyl alcohol / IPTBE In a third embodiment of the present subject matter, when the primary alcohol is isopropyl alcohol and the alkyl tert-butyl ether is isopropyl tert-butyl ether (IPTBE), the by-product separation unit preferably comprises at least two distillation columns.

[0094] In one embodiment, the first distillation column of the by-product separation unit is fed with the purge stream of the first distillation unit and / or a portion of the bottom product of the second distillation unit, which contains mainly isopropyl alcohol, IPTBE and diisobutene. A second by-product stream rich in isopropyl alcohol is withdrawn from the top of the first column. The bottom product stream of the first column is fed to the second distillation column of the by-product separation unit. A first by-product stream rich in diisobutene is withdrawn from the top of the second column. This first by-product stream may further contain IPTBE. A third by-product stream rich in components having a normal boiling point higher than 110° C. is withdrawn from the bottom of the second column. The third by-product stream may contain high boiling components such as triisobutene.

[0095] In another preferred embodiment, the by-product separation unit comprises at least three distillation columns. The first distillation column of the by-product separation unit is fed with the purge stream of the first distillation unit and / or a portion of the bottom product of the second distillation unit, which contains mainly isopropyl alcohol, IPTBE and diisobutene. The first distillation column is a prefractionation column, in which a stream rich in IPTBE and isopropyl alcohol is withdrawn from the top of the column and a stream rich in diisobutene and high boiling components is withdrawn from the bottom of the column. The overhead product stream is fed to the second distillation column of the by-product separation unit, a second by-product stream rich in isopropyl alcohol is withdrawn from the top of the second column and a stream rich in IPTBE is withdrawn from the bottom of the second column. The bottom product stream of the first column is fed to a third distillation column of the by-product separation unit, a first by-product stream rich in diisobutene is withdrawn from the top of the third column, and a third by-product stream rich in components having normal boiling points greater than 110° C. is withdrawn from the bottom of the third column. The third by-product stream may contain higher boiling components such as triisobutene.

[0096] Isobutanol / IBTBE In a fourth embodiment of the present subject matter, when the primary alcohol is isobutanol and the alkyl tert-butyl ether is isobutyl tert-butyl ether (IBTBE), the by-product separation unit preferably comprises at least two distillation columns.

[0097] In one embodiment, the first distillation column of the by-product separation unit is fed with the purge stream of the first distillation unit and / or a portion of the bottom product of the second distillation unit, which contains mainly isobutanol, IBTBE and diisobutene. The first by-product stream, which is rich in diisobutene, is withdrawn from the top of the first column. The bottom product stream of the first column is fed to the second distillation column of the by-product separation unit. The second by-product stream, which is rich in isobutanol, is withdrawn from the top of the second column, and the third by-product stream, which is rich in components having a normal boiling point higher than 110 ° C., is withdrawn from the bottom of the second column. The third by-product stream contains mainly IBTBE and may contain further high boiling components such as diisobutyl ether (DIBE) and / or triisobutene.

[0098] In an alternative embodiment with two columns, the first distillation column of the by-product separation unit is fed with the purge stream of the first distillation unit and / or a portion of the bottom product of the second distillation unit, which contains mainly isobutanol, IBTBE and diisobutene. A third by-product stream, rich in components having a normal boiling point higher than 110 ° C, is withdrawn from the bottom of the first column. The third by-product stream contains mainly IBTBE and may contain further high-boiling components such as diisobutyl ether (DIBE) and / or triisobutene. The overhead product stream of the first column is fed to the second distillation column of the by-product separation unit. The first by-product stream, rich in diisobutene, is withdrawn from the top of the second column, and the second by-product stream, rich in isobutanol, is withdrawn from the bottom of the second column.

[0099] In another alternative embodiment with two columns, the first distillation column of the by-product separation unit is fed with the purge stream of the first distillation unit and / or a portion of the bottom product of the second distillation unit, which contains mainly isobutanol, IBTBE and diisobutene. A third by-product stream, rich in components having a normal boiling point higher than 110 ° C, is withdrawn from the bottom of the first column. The third by-product stream contains mainly IBTBE and may contain further high boiling components such as diisobutyl ether (DIBE) and / or triisobutene. A second by-product stream, rich in isobutanol, is withdrawn as a side draw from the first column. The overhead product stream of the first column is fed to the second distillation column of the by-product separation unit. The first by-product stream, rich in diisobutene, is withdrawn from the bottom of the second column. The overhead product of the second column is recycled to the first column.

[0100] More preferably, the by-product separation unit comprises at least three distillation columns.

[0101] In one embodiment having three columns, the first distillation column of the by-product separation unit is fed with the purge stream of the first distillation unit and / or a portion of the bottom product of the second distillation unit, which contains mainly isobutanol, IBTBE and diisobutene. A third by-product stream, rich in components having a normal boiling point higher than 110° C., is withdrawn from the bottom of the first column. The third by-product stream contains mainly high-boiling components such as triisobutene. The overhead product stream of the first column is fed to the second distillation column. The second by-product stream, rich in isobutanol, is withdrawn from the bottom of the second column. The overhead product stream of the second column is fed to the third distillation column, and the first by-product stream, rich in diisobutene, is withdrawn from the bottom of the column. The first by-product stream may contain IBTBE and / or diisobutyl ether (DIBE).

[0102] In a preferred embodiment, the first by-product stream is further split into at least two further by-product streams, the fourth by-product stream being rich in diisobutene and the fifth by-product stream being rich in alkyl tert-butyl ether. Providing a further split of the first by-product stream increases the flexibility of the isobutene separation process, for example with respect to process integration by recycling the stream to a dedicated process unit. Furthermore, the overall efficiency of the process is increased.

[0103] For processes in which the first by-product stream is further split into at least two further by-product streams, it is preferred that the mass fraction of diisobutene in the first by-product stream is at least 30 wt.%, and the mass fraction of diisobutene in the fourth by-product stream is at least 90 wt.%, more preferably at least 95 wt.%, most preferably at least 98 wt.%, especially at least 99 wt.%. Providing a by-product stream with high to very high purity diisobutene allows the component to be used in a variety of applications, thus increasing the overall efficiency of the isobutene separation process.

[0104] In the case of the process in which the first by-product stream is further divided into at least two additional by-product streams, it is preferred that the fifth by-product stream is at least partially recycled to the evaporator and / or ether cleavage unit for evaporation. By recycling the fifth product stream rich in alkyl tert-butyl ether, the loss of valuable product isobutene contained in the alkyl tert-butyl ether is reduced. This increases the overall efficiency of the isobutene separation process.

[0105] The invention will be explained in more detail below with reference to the drawings, which should be interpreted as illustrative and not as constituting any limitation of the invention, e.g., with respect to specific embodiments. [Brief description of the drawings]

[0106] [Figure 1]1 shows a process flowsheet of an embodiment for the purification of a feed C4 hydrocarbon mixture according to the present invention. [Diagram 2] 1 shows a block diagram of a first embodiment of a process for obtaining isobutene from an isobutene-containing C4 hydrocarbon mixture according to the present invention. [Diagram 3] 1 shows a block diagram of a second embodiment of a process for obtaining isobutene from an isobutene-containing C4 hydrocarbon mixture according to the present invention. [Figure 4] 1 shows a block diagram of a third embodiment of a process for obtaining isobutene from an isobutene-containing C4 hydrocarbon mixture according to the present invention. [Diagram 5] 4 shows experimental data according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0107] FIG. 1 shows a process flow sheet of an extraction unit 10 as an exemplary embodiment for purifying a feed C4 hydrocarbon mixture according to the present invention. The extraction unit 10 includes a phase separation unit 20, which is shown in a dashed box around each process unit. The extraction unit 10 further includes an extraction tower 11, which is equipped with a top inlet, a bottom inlet, an inlet between the top and bottom inlets, a top outlet and a bottom outlet. A feed C4 hydrocarbon stream 12 containing the feed C4 hydrocarbon mixture is fed to the extraction tower 11 through the bottom inlet. An aqueous stream 13 is fed to the extraction tower 11 from the top inlet. The feed C4 hydrocarbon mixture flowing upwards is countercurrently contacted with the aqueous stream in the extraction tower 11 to produce an intermediate C4 hydrocarbon mixture, which is withdrawn from the top of the tower as an intermediate C4 hydrocarbon stream 16.

[0108] The countercurrent flow of the upwardly flowing organic phase and the downwardly flowing aqueous phase allows vigorous mixing of the two phases and transfer of catalyst deactivating components from the organic phase to the aqueous phase, which is withdrawn through the bottom outlet. A portion of the aqueous stream withdrawn from the bottom of extraction column 11 is recycled to aqueous recycle stream 14 and fed to the column through an intermediate inlet. The remaining portion is withdrawn from extraction unit 10 as waste water in aqueous bottom stream 15.

[0109] Due to the intense contact between the organic and aqueous phases in the extraction column 11, the intermediate C4 hydrocarbon stream 16 contains water, which is removed in a phase separation unit 20, which includes a filter 21, a coalescer 22, and a phase separator 23. The intermediate C4 hydrocarbon stream 16 is fed to the filter 21, which removes very small droplets that cannot coalesce in subsequent units. The filtered droplets are removed from the filter 21 as a wastewater stream (not shown in FIG. 1).

[0110] The remaining portion of the intermediate C4 hydrocarbon stream is fed to an allesser 22 where the small droplets coalesce into larger droplets. The resulting mixture is fed to a phase separator 23 where the organic phase is separated from the aqueous phase. The aqueous phase is collected in the phase separator 23 and is continuously or discontinuously removed (aqueous stream not shown in FIG. 1). A purified C4 hydrocarbon stream 24 is withdrawn from the phase separator 23 and can be used in subsequent process steps.

[0111] Figure 2 shows a block diagram of a first embodiment of a method for obtaining isobutene from an isobutene-containing C4-hydrocarbon mixture according to the invention. In a first step, in an extraction unit 10, a raw C4-hydrocarbon mixture containing isobutene is pretreated to obtain a refined C4-hydrocarbon mixture. In the extraction unit 10, a raw C4-hydrocarbon stream 12 is countercurrently contacted with an aqueous stream 13 to obtain an intermediate C4-hydrocarbon mixture. At least a portion of this intermediate C4-hydrocarbon mixture is withdrawn from the extraction unit and dehydrated to obtain a refined C4-hydrocarbon mixture 24 stream. The remaining aqueous phase is withdrawn from the extraction unit as a wastewater bottom stream 15. The extraction unit 10 may be configured as a process as illustrated in Figure 1.

[0112] The purified isobutene-containing C4-hydrocarbon feed stream 24 and the primary alcohol feed stream 31 are fed to an etherification unit 30, which comprises at least one reactor with an acid catalyst, preferably an ion exchange resin. Advantageously, the etherification unit 30 comprises a fixed-bed reactor, such as a flow tube or a loop reactor, or a combination of both types. The C4-hydrocarbon mixture is contacted with a primary alcohol, and the mixture is reacted in the presence of an acid catalyst to form the corresponding alkyl tert-butyl ether. Diisobutene is obtained as a by-product.

[0113] The resulting reaction mixture 32 is fed to a first distillation unit 40. A C4-hydrocarbon raffinate stream 41 is withdrawn as an overhead product of the first distillation unit 40. A bottom product stream 42 withdrawn from the first distillation unit 40 mainly comprises alkyl tert-butyl ethers and diisobutene. Excess primary alcohols and heavy components, typically having a normal boiling point above 110° C., may also be present in the bottom product stream 42. The bottom product stream 42 is withdrawn as a liquid or vapor stream. If withdrawn as a liquid stream, it is vaporized in an evaporator. A purge stream 43 containing high-boiling components, having a normal boiling point higher than the boiling point of the alkyl tert-butyl ether, may be withdrawn from the first evaporation unit 40.

[0114] The vaporous alkyl tert-butyl ether stream 42 is fed to an ether cleavage unit 50 comprising at least one reactor with an acidic catalyst, preferably an ion exchange resin. Advantageously, at least one reactor in the ether cleavage unit 50 is a fixed bed reactor. Isobutene and primary alcohols are obtained as reaction products.

[0115] The resulting reaction mixture 51 is fed to a second distillation unit 60. A high purity isobutene product stream 61 is withdrawn as an overhead product of the second distillation unit 60. The bottom product withdrawn from the second distillation unit 60 comprises mainly primary alcohols and diisobutene. Heavy components, typically having normal boiling points above 110° C., may also be present in the bottom product. The bottom product of the second distillation unit 60 is recycled to the etherification unit 30 in a primary alcohol recycle stream 62. The recycle stream may be supplemented with fresh primary alcohol, if necessary.

[0116] Figure 3 shows a block diagram of a second embodiment of the method for obtaining isobutene from an isobutene-containing C4-hydrocarbon mixture according to the invention. In this embodiment, the main part of the bottom product of the second distillation unit 60 is recycled to the etherification unit 30 in a primary alcohol recycle stream 62, while the remaining smaller part of the bottom product of the second distillation unit 60 is fed to a by-product separation unit 70. In this unit, the by-product separation unit feed stream 63 is split into at least three by-product streams, preferably three interconnected distillation columns. The first by-product stream 71 is rich in diisobutene and is removed from the plant. The second by-product stream 72 is rich in primary alcohols and is recycled to the etherification unit 30. The third by-product stream 73 is rich in components having a normal boiling point higher than 110 ° C and is also removed from the plant.

[0117] 4 shows a block diagram of a third embodiment of the method for obtaining isobutene from an isobutene-containing C4-hydrocarbon mixture according to the invention. In this embodiment, the first by-product stream 71 is further divided into at least two further by-product streams, a fourth by-product stream 74 rich in diisobutene and a fifth by-product stream 75 rich in alkyl tert-butyl ethers. The fifth by-product stream 75 is at least partially recycled to the ether cleavage unit 50. The first distillation unit 30 comprises a distillation column, the bottom product 42 is withdrawn as a side stream from the distillation column at a stage below the feed stage, and a purge stream 43 rich in high boiling components is withdrawn from the sump of the distillation column. The high boiling purge stream 43 from the sump of the distillation column of the first distillation unit 30 is fed to the by-product separation unit 70.

[0118] Working Example The feed C4 hydrocarbon mixture was refined and further processed in a plant according to Figures 1 and 2. The feed C4 hydrocarbon mixture was a raffinate 1 stream of varying composition over time having the following main components (values ​​in weight percent):

[0119] [Table 1]

[0120] The feed C4 hydrocarbon mixture contained catalyst deactivators up to 3 ppm, with an average of more than 1.5 ppm over time. The main component of the catalyst deactivators was amines.

[0121] The raw C4 hydrocarbon mixture 12 was fed to the bottom of the extraction column 11 with a mass flow rate of 17000-20000 kg / h. An aqueous stream 13 containing 99-100% by weight water was fed to the top of the extraction column 11 with a mass flow rate of 2000 kg / h. The extraction column was operated with a pressure of 4 bar (absolute) at the top of the column. The pressure at the bottom of the column was 6.5 bar (absolute) and the temperature was 38.2°C. An aqueous recycle stream 14 was recycled from the bottom of the column to the intermediate feed point with a mass flow rate of 5800-6000 kg / h.

[0122] An intermediate C4 hydrocarbon stream 16 was withdrawn from the top of the extraction column 11 and fed to a phase separation unit 20 including a filter 21, a coalescer 22 and a phase separator 23. The dehydrated purified C4 hydrocarbon stream 24 was fed to an etherification unit 30 where it was contacted with isobutanol to form isobutyl ethers. The catalyst deactivator content was less than 1 ppm by weight, averaging less than 0.5 ppm by weight over time. Amines made up the majority of the catalyst deactivation components, measured at less than 0.9 ppm by weight, averaging less than 0.4 ppm by weight over time.

[0123] FIG. 5 shows the conversion of isobutene over time in the first reactor of the etherification unit 30. At the time indicated by "t_start", the extraction unit 10 was put into operation. Prior to this time, the raw C4 hydrocarbon mixture was fed to the etherification unit without purification. As can be seen from FIG. 5, the removal of catalyst deactivators in the purification process according to the invention allows the etherification unit to operate more robustly and stably. The life of the etherification catalyst was extended from 3 months before the start-up of the extraction unit to more than 23 months after the start-up. [Explanation of symbols]

[0124] 10 Extraction Unit 11 Extraction tower 12 Feed C4 Hydrocarbon Stream 13 Aqueous flow 14 Aqueous recirculation flow 15 Aqueous bottom flow 16 Intermediate C4 Hydrocarbon Streams 20 Phase Separation Unit 21 Filters 22 Coalescer 23 Phase separator 24 Refined C4 Hydrocarbon Streams 30 Etherification Unit 31 Primary alcohol feed stream 32 Reaction mixture flow 40 First distillation unit 41 C4 Hydrocarbon Raffinate Stream 42 Alkyl tert-butyl ether bottom stream 43 High boiling point purge stream 50 Ether Cleavage Units 51 Reaction mixture flow 60 Second Distillation Unit 61 Isobutene product stream 62 Primary alcohol recycle stream 63 By-product separation unit feed stream 70 By-product Separation Unit 71 First by-product stream 72 Second by-product stream 73 Third by-product stream 74 Fourth by-product stream 75 Fifth by-product stream

Claims

1. at least 2% by weight of isobutene, at least 23% by weight of butenes other than isobutene, less than 3% by weight of butadiene, at least 1.5 ppm by weight of a catalyst deactivator selected from the group of polar nitrogen-containing compounds and mixtures thereof; A method for refining a feed C4 hydrocarbon mixture, comprising: the sum of all components in the C4 hydrocarbon mixture is 100 wt.%, The method further comprising: (a) contacting said feed C4 hydrocarbon mixture (12) in a countercurrent manner with an aqueous stream (13) in an extraction unit (10) to obtain an intermediate C4 hydrocarbon mixture (16); (b) withdrawing at least a portion of the intermediate C4 hydrocarbon mixture (16) from the extraction unit; (c) dehydrating the withdrawn intermediate C4 hydrocarbon mixture to obtain a refined C4 hydrocarbon mixture (24) having at most 1 ppm by weight of the catalyst deactivator; A method comprising:

2. 2. The method according to claim 1, wherein the extraction unit (10) comprises an extraction tower (11), the feed C4 hydrocarbon mixture (12) being fed to a lower part of the extraction tower (11) and the aqueous stream (13) being fed to an upper part of the extraction tower (11).

3. 3. The process according to claim 2, wherein the extraction column (11) is operated at a pressure of 4 to 7 bar (absolute) and at a temperature of 30 to 60°C.

4. 4. The process according to claim 2 or 3, wherein 40 to 80 wt. % of the bottoms stream withdrawn from the bottom of the extraction column is recycled to the extraction column (11), preferably to the upper part of the extraction column (11).

5. The method according to any one of claims 1 to 4, wherein the aqueous stream (13) of step (a) comprises from 90% to 100% by weight water.

6. 6. The method according to any one of claims 1 to 5, wherein the intermediate C4 hydrocarbon mixture (16) withdrawn from the extraction unit (10) is fed to a phase separation unit (20) comprising a filter (21), a coalescer (22) and / or a phase separator (23).

7. 7. The method of claim 1, wherein the feed C4 hydrocarbon mixture (12) comprises less than 1 wt. % of components having less than 4 carbon atoms and less than 1 wt. % of components having at least 5 carbon atoms.

8. 8. The method of any one of claims 1 to 7, wherein the catalyst deactivator is selected from the group of amines, acetonitrile, ammonia, dimethylformamide, and mixtures thereof.

9. A method for obtaining isobutene from an isobutene-containing C4-hydrocarbon mixture (24) in a plant comprising an etherification unit (30), a first distillation unit (40), an ether cleavage unit (50) and a second distillation unit (60), said method comprising the steps of: (i) contacting the C4 hydrocarbon mixture (24) with a primary alcohol (31) in the etherification unit (30) and reacting the C4 hydrocarbon mixture with the primary alcohol in the presence of an acidic catalyst to form the corresponding alkyl tert-butyl ether; (ii) distilling in the first distillation unit (40) the reaction mixture (32) from the etherification unit (30) to withdraw a C4-hydrocarbon raffinate as an overhead product (41) and the alkyl tert-butyl ether as a liquid or vaporous bottom product (42) and vaporizing the bottom product (42) if withdrawn as a liquid; (iii) reacting the vaporous bottoms (42) in the presence of an acidic catalyst in the ether cleavage unit (50) to obtain isobutene and the primary alcohol as reaction products; (iv) distilling the reaction mixture (51) from the ether cleavage unit (50) in the second distillation unit (60) and withdrawing isobutene as the overhead product (61) and the primary alcohol as the bottom product (62) for recycling to the etherification unit (30). Including, 1. The method of claim 1, wherein the C4 hydrocarbon mixture (24) fed to the etherification unit (30) is obtained by pretreating a feed C4 hydrocarbon mixture (12) containing a catalyst deactivator, the pretreatment comprising the steps of: (a) contacting the feed C4 hydrocarbon mixture (12) in a countercurrent flow in an extraction unit (10) with an aqueous stream (13) to obtain an intermediate C4 hydrocarbon mixture; (b) withdrawing at least a portion of the intermediate C4 hydrocarbon mixture from the extraction unit (10); and (c) dehydrating the withdrawn intermediate C4 hydrocarbon mixture to obtain the C4 hydrocarbon mixture (24) having a content of at most 1 ppm by weight of the catalyst deactivator, the catalyst deactivator being selected from the group of amines, acetonitrile, ammonia, dimethylformamide, and mixtures thereof.

10. The feed C4 hydrocarbon mixture is at least 2% by weight of isobutene, at least 23% by weight of butenes other than isobutene, less than 3% by weight of butadiene, at least 1.5 ppm by weight of said catalyst deactivator; Including, 10. The method of claim 9, wherein the sum of all components in the feed C4 hydrocarbon mixture is 100 wt.%.

11. 11. The method of claim 9 or 10, wherein the primary alcohol is isobutanol and the alkyl tert-butyl ether is isobutyl tert-butyl ether (IBTBE).

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