Process for efficient production of bio-pure isobutene from renewable resources

Abstract

A process and system for converting bioethanol to high purity isobutene is provided, the system including a dehydration unit configured to receive a bioethanol-containing stream and convert the bioethanol to bioethylene to produce a bioethylene-containing stream, a dimerization unit configured to receive the bioethylene stream and dimerize the ethylene to produce an n-butene-containing stream, a skeletal isomerization unit configured to receive the n-butene-containing stream and convert the n-butenes to produce a skeletal isomerization stream comprising isobutene, isobutane, n-butenes, and n-butanes, and a catalyst separation unit configured to receive the skeletal isomerization stream and convert olefins and / or isoolefins contained therein to produce a converted skeletal isomerization reaction product and fractionate the skeletal isomerization reaction product to produce bioisobutene.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate generally to processes and systems for producing high purity isobutene from renewable feedstocks such as bio-based ethanol. Such reaction schemes may include dehydration, dimerization, skeletal isomerization, and reactive separations to achieve the desired conversion of bio-based ethanol to a high purity isobutene product. [Background technology]

[0002] High purity isobutene is an important component used in the production of polymers used in various applications such as tires and lubricants. High purity isobutene is a requirement for the production of many of these polymer systems. However, the production of high purity isobutene can be an energy-intensive process that utilizes non-renewable feedstocks. Thus, there is a continuing need to make chemicals such as high purity isobutene from renewable resources such as bioalcohol. Summary of the Invention

[0003] This Summary is provided to introduce a selection of concepts that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0004] In one aspect, embodiments disclosed herein relate to a system for converting bioethanol to high purity isobutene, the system including a dehydration unit configured to receive a bioethanol-containing stream and convert the bioethanol to bioethylene to produce a bioethylene-containing stream, a dimerization unit configured to receive the bioethylene stream and dimerize the ethylene to produce an n-butene-containing stream, a skeletal isomerization unit configured to receive the n-butene-containing stream and convert the n-butenes to produce a skeletal isomerization stream comprising isobutene, isobutane, n-butenes, and n-butanes, and a catalyst separation unit configured to receive the skeletal isomerization stream and convert olefins and / or isoolefins contained therein to produce a converted skeletal isomerization reaction product and fractionate the skeletal isomerization reaction product to produce bioisobutene.

[0005] In another aspect, embodiments disclosed herein relate to a method for producing high purity isobutene from bioethanol, the method including dehydrating bioethanol to produce bioethylene, dimerizing the bioethylene to form n-butenes, skeletal isomerizing the n-butenes to form a bio-C4 mixture comprising isobutene, isobutane, n-butenes, and n-butanes, reacting and fractionating the bio-C4 mixture to separate isobutene from unconverted n-butenes, and recovering the bioisobutene.

[0006] In another aspect, embodiments herein relate to a system for converting bioethanol to high purity bioisobutene, the system includes a dehydration unit configured to receive a bioethanol-containing stream and convert the bioethanol to bioethylene to produce a bioethylene-containing stream, a dimerization unit configured to receive the bioethylene-containing stream and dimerize the bioethylene to produce a bio-n-butene-containing stream, and an olefin skeletal isomerization unit configured to receive the bio-n-butene-containing stream and convert the n-butenes to produce a skeletal isomerized C4 olefin-containing stream comprising isobutene and n-butene. In some embodiments, the system further comprises a catalytic reaction / separation unit configured to receive the skeletal isomerized C4 olefin-containing stream, convert isobutene to one or more of methyl tert-butyl ether, ethyl tert-butyl ether, tertiary butyl alcohol, and isobutyl alcohol, separate n-butene from one or more of methyl tert-butyl ether, tertiary butyl alcohol, and isobutyl alcohol, backcrack one or more of methyl tert-butyl ether, tertiary butyl alcohol, and isobutyl alcohol to form isobutene and one or more of water and methanol, and separate isobutene from one or more of water and methanol to produce a bioisobutene product fraction. Alternatively, the catalytic reaction / separation unit is configured to receive the skeletal isomerized C4 olefin-containing stream, convert 1-butene contained in the n-butene to 2-butene, and separate 2-butene from isobutene to produce a 2-butene fraction and a bioisobutene product fraction.

[0007] Other aspects and advantages of the claimed subject matter will become apparent from the following description and the appended claims. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a block flow diagram of a system for producing high purity bioisobutene, according to one or more embodiments. [Figure 1A]FIG. 1 is a block flow diagram of a system for producing high purity bioisobutene, according to one or more embodiments. [Diagram 2] FIG. 1 is a block flow diagram of a bioethanol dehydration unit according to one or more embodiments. [Diagram 3] FIG. 1 is a block flow diagram of a bioethylene dimerization unit according to one or more embodiments. [Figure 4] FIG. 1 is a block flow diagram of a bioolefin skeletal isomerization unit according to one or more embodiments. [Diagram 5] FIG. 1 is a simplified flow diagram of a catalytic deisobutenization tower according to one or more embodiments. [Figure 6] FIG. 1 is a block flow diagram of a system for producing high purity bioisobutene, according to one or more embodiments. [Figure 7] FIG. 1 is a block flow diagram of a separation system useful for producing high purity bioisobutene, according to one or more embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Embodiments disclosed herein relate to processes and systems for producing high purity isobutene from bioethanol. For embodiments requiring appropriate "green" certification, all steps according to such embodiments may be certified with bio-based feedstocks or bio-based intermediates and do not include fossil-based feedstocks or intermediates.

[0010] In general, the process configuration of the embodiments herein includes four major unit operations. The first unit is an alcohol dehydration unit for producing ethylene. The alcohol dehydration unit may be used, for example, to dehydrate a bioethanol feedstock to form ethylene. Other alcohol and bioalcohol feeds may also be used. The second unit is a dimerization unit for dimerizing ethylene to form n-butenes. The third unit is a skeletal isomerization unit that produces an isobutene / isobutane / n-butane / n-butene mixture, with small amounts of C5+ by-products also being produced. In some embodiments, little or no isobutane may be formed in the skeletal isomerization unit. The fourth unit is a catalytic separation unit configured to receive the isobutene / isobutane / n-butane / n-butene mixture from the skeletal isomerization unit and convert the components in the stream to form a readily separable mixture and recover a high purity isobutene (HPIB) product.

[0011] In one or more embodiments of the present disclosure, the purity of the HPIB produced can be from the lower of any of 85%, 86%, 87%, 88%, or 89% on a weight percent basis, up to an upper limit of any of 90%, 91%, 92%, 93%, 94%, 95%, 98%, 98.5, 99.0, 99.5, 99.8, or 99.9% on a weight percent basis.

[0012] In some embodiments, the catalyst separation unit may be a catalytic deisobutenizer tower to receive an isobutene / isobutane / n-butane / n-butene mixture and convert 1-butene to 2-butene while simultaneously fractionating the mixture to produce a high purity isobutene product and recover some unconverted n-butene and n-butane. The n-butene produced in the fourth unit may be recycled to the third unit to produce additional isobutene, while the n-butane may act as a diluent to help control the reaction in the skeletal isomerization unit. In some cases, for example, when less n-butane by-product is formed, the amount of n-butane recycled back to the third unit is also less, and a saturation (hydrogenation) step may be required to form n-butane for use as a diluent during skeletal isomerization.

[0013] In other embodiments, the catalytic separation unit may be an oxygenation / backcracking separation unit. As an alternative to a catalytic separation unit including a catalytic deisobutenizer tower for separating the C4 received from the skeletal isomerization unit, embodiments herein further contemplate feeding the skeletal isomerized C4 to a separation unit including an oxygenation reactor, a backcracking reactor, and a separation system. The backcracking separation unit according to embodiments herein may receive a mixed stream including isobutene from the skeletal isomerization unit, selectively react the isobutene with oxygenates such as water, methanol, ethanol, propanol, or isobutanol to form alcohols or ethers (oxygenated intermediates) to facilitate separation of the isobutene (as oxygenated isobutene intermediates) from other C4 components in the mixture, and then backcrack the oxygenated intermediates to recover isobutene essentially free of other C4 impurities such as n-butene and isobutane that may be produced and recovered with the dimerization and skeletal isomerization reactor effluent.

[0014] Although described above with respect to four main units, each unit may include reactors, heat exchangers, separators, feed handling, internal recycle, and other processing or support equipment and features to achieve the desired conversions and products. Not all aspects of the unit operations are described in detail herein, but one of ordinary skill in the art should understand the primary functions of each unit based on the description herein.

[0015] A block flow diagram of a system 100 according to one or more embodiments is shown in Figure 1. Composition ranges for each of the streams associated with each of the following process steps, according to certain embodiments herein, are provided below in Table 1. Generally, the system 100 may include an alcohol dehydration unit 102, an ethylene dimerization unit 104, a backbone olefin isomerization unit 106, and a separation unit 108.

[0016] The process may include a first step of dehydrating bioethanol to form bioethylene. A bio-derived alcohol, such as bioethanol stream 1, may be fed to an ethanol dehydration unit 102. The ethanol dehydration unit 102 may include one or more reactors containing a catalyst for dehydrating the ethanol (contained in feed stream 1) to produce ethylene (stream 2). Water and other impurities or by-products may be removed from the ethanol dehydration unit 102 via one or more flow streams 12.

[0017] After the ethanol is dehydrated, the process includes dimerization of ethylene to form n-butenes. The bioethylene stream 2 recovered from the ethanol dehydration unit 102 can be fed to an ethylene dimerization unit 104. The ethylene dimerization unit 104 can include one or more reactors containing a catalyst for dimerizing the bio-based ethylene to form bio-based butenes, which can include a mixture of both 1-butene and 2-butene. The bio-based butenes can be recovered via flow stream 3, while C5 and heavier by-products can be recovered from the dimerization unit 104 via one or more flow streams 13.

[0018] The process then includes skeletal isomerization of n-butenes to form a mixed C4 stream, which may be an isobutene / isobutane / n-butane / n-butene mixture. The bio-based butene stream 3 recovered from the ethylene dimerization unit 104 may be fed to a C4 skeletal olefin isomerization unit 106. The C4 skeletal olefin isomerization unit 106 includes one or more reactors containing a catalyst for the skeletal isomerization of the bio-based butenes to form bio-based isobutene. The reaction effluent, which may include unreacted n-butenes and isobutene, may be recovered via flow line 4, while the C3 and lighter reaction by-products may be recovered via flow line 13, and the C5 and heavier by-products may be recovered via flow line 14.

[0019] The final step involves a reactive separation, such as catalytic deisobuteneization, to fractionate isobutene from unconverted n-butenes and produce a high purity isobutene product. The bio-based C4 reaction effluent (Stream 4) can be fed to a catalytic deisobuteneization tower 108 along with hydrogen 20. The catalytic distillation unit includes one or more catalytic zones and distillation structures to positionally isomerize 1-butene to 2-butene while simultaneously fractionating the C4 mixture, producing a bottoms distillation product stream 5 containing 2-butene and any n-butanes, a vent gas stream 16, and a bio-based isobutene product stream 6. An embodiment of the separation unit 108 (deisobuteneization) can include an integrated isobutene stripper to remove traces of isobutane from the high purity isobutene product. Any unconverted n-butenes (Stream 5) can be recycled back to the skeletal isomerization unit 106 to produce additional isobutene (Stream 4). [Table 1]

[0020] A block flow diagram of a system 100A according to one or more embodiments is shown in FIG. 1A. In general, the system 100A may include an alcohol dehydration unit 102, an ethylene dimerization unit 104, a skeletal olefin isomerization unit 106, and a reactive separation unit 108A, where units 102, 104, and 106 are as described above with respect to FIG. 1. In this embodiment, a bio-based C4 reaction effluent (Stream 4) may be fed to the separation unit 108A along with oxygenates 20A, such as water, methanol, or ethanol. The separation unit 108A includes an internal process step (not shown) that selectively reacts isobutene to form alcohols or ethers, recovers the alcohols or ethers, and then back-cracks the separated alcohols or ethers to recover high purity isobutene stream 6 and one or more by-product streams 16. The N-butenes, isobutane, or n-butanes recovered in the reactive separation unit 108 may be recycled to the skeletal isomerization unit 106, as described above. Separation units 108 and 108A are described in further detail below with respect to FIGS.

[0021] Each of the four major units according to the embodiments herein includes a reactor (dehydration, dimerization, skeletal isomerization, reaction separation, etc., as shown in Figures 1 and 1A). Reactors useful in the embodiments disclosed herein may include conventional fixed bed reactors, boiling point reactors, and pulse flow reactors, where reactant and product flows may be cocurrent or countercurrent. Boiling point and pulse flow reactors may also provide continuous washing of the catalyst, in addition to capturing at least a portion of the heat of reaction through evaporation, allowing for improved reactor temperature profiles compared to conventional fixed bed reactors. The reactors useful in the embodiments disclosed herein may be used as stand-alone reactors or in combination with one or more reactors of the same or different types.

[0022] Any type of reactor can be used to carry out the reactions described herein. Examples of reactors suitable for carrying out the reactions of the embodiments herein include distillation column reactors, divided wall distillation column reactors, conventional tubular fixed bed reactors, bubble column reactors, slurry reactors with or without distillation columns, pulse flow reactors, catalytic distillation columns with slurry solid catalyst flowing through the column, conventional fixed bed reactors, or any combination of these reactors. Multiple reactor systems useful in the embodiments disclosed herein may include a series of the same type of reactors or reactors in parallel, or different types of reactors in series, in each reaction zone. Those skilled in the art will recognize that other types of reactors may also be used.

[0023] Bioethanol Dehydration Unit 102 The feed to the dehydration system can include, consist essentially of, or consist of bio-based ethanol. Fresh bio-based ethanol feedstock can be provided from any number of sources. The bio-based ethanol feedstock can be of high purity, such as greater than 50% by weight bio-based ethanol, greater than 70% by weight bio-based ethanol, greater than 80% by weight bio-based ethanol, greater than 90% by weight bio-based ethanol, greater than 95% by weight bio-based ethanol, or greater than 98% or 99% by weight bio-based ethanol. In some embodiments, the remainder of the feedstock can include additional bio-based hydrocarbons or inert diluents, such as nitrogen or paraffins.

[0024] The bio-based ethanol feed may be derived from a fermentation process, such as fermentation of renewable resources such as corn, corn stalks, corn cobs, lignocellulosics, sugarcane, sugar beet, and wheat, among others. Other types of bio-based ethanol may also be used. There are various alcohol dehydration techniques and methods known to those skilled in the art, which will not be described in detail here, other than to note that various reactor types, catalysts, and configurations may be used, and that operating conditions may be appropriately selected based on the type of reaction, catalyst, and overall feed composition to achieve the desired conversion of ethanol to ethylene. Dehydration of ethanol to form ethylene may be achieved, for example, using the processes described in US9181143 or US11260367, respectively, to Braskem. Other known processes may be used to dehydrate bio-based ethanol to form bio-based ethylene according to embodiments herein.

[0025] Bioethanol feeds useful in the embodiments disclosed herein may contain impurities such as water, among other impurities that may be present in fermentation broths or other sources of bio-based ethanol. For example, bioethanol feeds may contain a certain amount of water. Typically, water is removed from bioethanol. However, because water is also a by-product of the ethanol dehydration reaction, bio-based ethanol feeds used in the embodiments disclosed herein may contain water as an impurity. Water as an impurity in the feed may be tolerated in the systems described herein, although excess water in the feed may reduce the reactor conversion equilibrium and increase the reboiler load, as discussed below.

[0026] In some embodiments, the bioethanol feed may include an amount of water, such as up to 40 weight percent water, in other embodiments up to 30 weight percent water, in other embodiments up to 20 weight percent water, in other embodiments up to 10 weight percent water, in other embodiments up to 5 weight percent water, and in yet other embodiments up to 2 weight percent water. In other embodiments, the bioethanol feed may be substantially pure ethanol. The amount of water that may be used in the catalytic reaction zone may depend on (1) the reaction equilibrium constant and (2) the enthalpy balance for the conversion of ethanol to ethylene.

[0027] In a dehydration system, ethanol is dehydrated to produce ethylene by removing water from the ethanol. This process typically involves heating the ethanol in the presence of an acidic catalyst that facilitates the destruction of hydroxyl (-OH) groups and the formation of double bonds between carbon atoms. The resulting ethylene product can then be recovered and used to produce isobutene.

[0028] The dehydration reaction conditions may vary based on the feed mixture used. The dehydration temperature may range from 30° C. to 500° C. in some embodiments. The dehydration reaction may be carried out under pressures ranging from 1 bar to 22 bar (0 psig to 300 psig) in some embodiments. The temperatures and pressures used may depend on the type of reactor, reaction phase, and catalyst(s) used in the reaction and may vary widely.

[0029] Contacting ethanol with a dehydration catalyst under dehydration conditions as described herein can result in the production of ethylene, unreacted alcohol, and heavier ends, which can include by-product ethers, alcohols, and oligomers, such as dimers or trimers of the desired olefin products. In some embodiments, contacting a bio-derived ethanol feed with a catalyst as described herein can result in a conversion of ethanol of at least 99 weight percent, in other embodiments at least 95 weight percent, in other embodiments at least 90 weight percent, in other embodiments at least 80 weight percent, and in other embodiments at least 70 weight percent.

[0030] The dehydrated reaction effluent may then be fed to a separation system to separate water and other reaction by-products from the desired bioethylene product. The separation system may include membrane separation units, distillation units, extractive distillation units, and other means for separating the water-ethylene mixture and separating other impurities to provide a high purity bioethylene product (high purity being greater than 95%, greater than 98%, greater than 99%, greater than 99.5%, or greater than 99.9% by weight in various embodiments). In some embodiments, the separation system may include water scrubbers, wash columns, ethylene distillation columns, and strippers to recover a very pure ethylene product for a downstream dimerization step.

[0031] The exact configuration of the units and the process conditions used may vary depending on the particular process employed, the catalyst used, the production capacity, and the product quality requirements. The dehydration process may also include an internal recycle of unreacted ethanol.

[0032] A general process block flow diagram of an alcohol dehydration unit according to embodiments herein is shown in Figure 2. Biologically derived alcohol, such as bioethanol stream 1, is fed to an ethanol dehydration reactor 202. The ethanol dehydration reactor 202 may include a dehydration catalyst and may be operated at suitable conditions to dehydrate the ethanol (contained in feed stream 1) to produce ethylene and water. The dehydration reactor effluent is recovered from the dehydration reactor via flow stream 204 and fed to a separation unit 206 for separating the bioethylene product 2 from water and other impurities or by-products recovered via one or more flow streams 12.

[0033] Bioethylene Dimerization Unit 104 After the ethanol is dehydrated, the process includes dimerization of ethylene to form n-butenes. Various catalysts and reactor configurations may be used for the selective dimerization of ethylene to form butenes. One example is the Lummus Ethylene Dimerization process, which may selectively dimerize ethylene to butenes and selectively form 2-butene to 1-butene in a ratio of about 9:1. Advantageously, producing a high ratio of 2-butene to 1-butene may facilitate or mitigate the requirements of downstream units, including separation units, in producing a high purity isobutene stream with little or no 1-butene as an impurity. Another example of a dimerization reactor is the ALPHABUTOL process (Axens), which uses a titanium-based catalyst for the dimerization of ethylene to butenes. Other known processes may be used to dimerize bio-based ethylene to form bio-based butenes according to embodiments herein. By-products including C5 and heavier components, such as trimers, tetramers, or other oligomers, as well as by-products resulting from the reaction of ethylene with any reactive modifiers present, can result in a variety of C5 and heavier hydrocarbon species. After dimerization of ethylene to form biobutenes, the reaction effluent can be fed to a separation system to separate the desired C4 product stream from the C5 and heavier by-products.

[0034] A general process block flow diagram of an ethylene dimerization unit according to embodiments herein is shown in FIG. 3. Biogenic ethylene, such as bioethylene stream 2, may be fed to ethylene dimerization reactor 302. Ethylene dimerization reactor 302 may include a selective dimerization catalyst and may be operated at suitable conditions to dimerize ethylene (contained in stream 2) to produce n-butenes and various by-products. Ethylene dimerization reactor effluent may be recovered from the ethylene dimerization reactor via flow stream 304 and fed to separation unit 306 for separating crude biobutene product stream 3 from C5 and heavier impurities or by-products recovered via one or more flow streams 13. In some embodiments, for example, if the conversion of ethylene is incomplete, ethylene may be stripped from the produced butenes and purged or recycled to the dimerization reactor via flow line 23 for continued conversion. Separation unit 306 may include, for example, one or more distillation or extractive distillation columns to perform the desired separations.

[0035] Olefin Skeleton Isomerization Unit 106 The feed to the third unit (olefin skeletal isomerization) may include a mixed C4 stream or a mixed C4+ stream from the bio-ethylene dimerization unit. Depending on the feed to the bioethylene dimerization unit and the overall conversion in the ethylene dimerization unit, a catalytic deoiler may be present between the bioethylene dimerization unit and the olefin skeletal isomerization unit. The purpose of the catalytic deoiler is to remove at least a portion of the undesired C5+ by-products and to hydrogenate at least a portion of any by-product 1,3-butadiene formed in the bioethylene dimerization unit. Thus, the catalytic deoiler may serve to prepare the dimerization effluent for the skeletal isomerization unit.

[0036] Skeletal isomerization is the process of converting straight-chain alkenes to branched-chain alkenes, or vice versa. This reaction involves rearrangement of carbon-carbon double bonds within a molecule, resulting in different molecular structures and physical properties.

[0037] Skeletal isomerization processes typically involve the use of a catalyst, such as a transition metal catalyst, to facilitate rearrangement of carbon-carbon double bonds. Reaction conditions such as temperature, pressure, and catalyst type and concentration are carefully controlled to optimize reaction conversion and selectivity.

[0038] In the skeletal isomerization unit, the dimerization effluent and any n-butene-containing C4 feed recycled from the catalyst separation unit are mixed and vaporized. The combined feed stream, or selected feed streams, can be heated, such as via a reactor feed / effluent heat exchanger, and then further heated to reaction temperature and sent to the isomerization reactor.

[0039] Skeletal isomerization of normal butenes (1-butene and 2-butene) to isobutene can be carried out in a gas phase reactor over an olefin skeletal isomerization catalyst. A variety of skeletal isomerization techniques and methods exist, many using acidic catalysts. Olefin skeletal isomerization processes are known to those skilled in the art and will not be described in detail here other than to note that a variety of reactor types, catalysts, and configurations can be used, and that operating conditions can be appropriately selected based on the type of reaction, catalyst, and overall feed composition to achieve the desired conversion of normal butenes to isobutene.

[0040] In some embodiments, the skeletal isomerization reactor may use an acidic catalyst and may operate at a temperature range of 250-450°C where the chemical equilibrium provides sufficient driving force towards n-butenes. These processes may also operate at 1.0 bara to 2.5 bara. Embodiments herein may also use a dilution medium provided from a downstream catalyst separation unit to reduce the partial pressure of the olefins to limit dimerization and thus improve selectivity. The resulting ratio of isobutene to n-butenes in the reactor effluent may be from 0.70 to 1.2.

[0041] The resulting reaction effluent, including residual 1-butene, 2-butene, isobutene, and any butanes (i.e., n-butane and isobutane), may be lean in 1-butene. For example, depending on the stringency of the reaction conditions used, the product may contain less than 1 wt. % total 1-butene, in other embodiments less than 0.5 wt. % total, in other embodiments less than 0.1 wt. % total, and in still other embodiments less than 500 ppm total 1-butene.

[0042] The effluent from the skeletal isomerization reactor may then be separated to recover a mixed C4 stream including unreacted normal butenes (1-butene and 2-butene) and isobutene. The recovered C4 stream may, in some embodiments, include lighter hydrocarbon by-products. The reaction may also produce fractions including C5 and heavier hydrocarbon by-products. The isomerization reaction effluent in such an embodiment may be separated in a third unit, as illustrated in FIG. 1 and described above, to produce a C5+ fraction, a C4 fraction, and a light fraction. The C5+ by-products may, in some embodiments, be recovered as a fuel fraction or a gasoline blend fraction. The C4 effluent from the isomerization reaction zone may then be fed to a fourth unit, a catalytic deisobutenizer.

[0043] A general process block flow diagram of an olefin skeletal isomerization unit according to an embodiment of the present disclosure is shown in FIG. 4. Bio-based butenes, such as bio-based C4 stream 3, can be fed to an olefin skeletal isomerization reactor 402. The olefin skeletal isomerization reactor 402 can include a skeletal isomerization catalyst and can be operated at conditions suitable for skeletal isomerization of normal butenes (contained in feed stream 3) to produce isobutene. C3 and lighter by-products, and C5 and heavier by-products can also be produced. The skeletal isomerization reactor effluent can be recovered from the olefin skeletal isomerization reactor via flow stream 404 and then fed to a separation unit 406 for separating the bio-based C4 stream 4 from the light by-products recovered via one or more flow streams 14 and the C5 and heavier by-products recovered via one or more flow streams 15.

[0044] The separation system 406 may include multiple distillation columns in some embodiments. For example, a depropanizer may be used to remove C3 and lighter components from the C4+ hydrocarbons in the skeletal isomerization reaction effluent, and a debutanizer may be used to recover a C4 stream (including bio-derived butenes and isobutene) from the C5 and heavier by-products. Various other configurations may be used to recover one or more lighter or heavier fractions. The C5+ by-products may be recovered as a fuel fraction or a gasoline blending fraction in some embodiments. The isobutene-containing product from the skeletal isomerization unit is then fed to a fourth unit, the catalyst separation unit.

[0045] Catalyst Separation Unit: Catalytic Deisobutenization Tower Unit 108 As mentioned above, the final step involves a reactive (catalytic) separation, some embodiments of which include catalytic deisobutenization to fractionate the isobutene from the unconverted n-butenes and produce a high purity isobutene product.

[0046] Referring now to FIG. 5, a simplified process flow diagram of a catalytic deisobutenizer unit according to an embodiment of the present disclosure is shown. The first step is to feed a mixed C4 stream 4, such as the mixed C4 reaction effluent from the olefin backbone isomerization unit 106, to a deisobutenizer (catalytic distillation column) 510. In the catalytic distillation column 510, a mixed C4 stream containing 1-butene, isobutene, and n-butane, among other C4 components, is fed to the catalytic distillation column 510 near the bottom of a catalytic distillation section 512 (catalytic zone 512) that contains a hydroisomerization catalyst supported in the form of a catalytic distillation structure. Hydrogen may also be fed via flow line 20 introduced below the catalytic zone 12.

[0047] When the reaction feed contacts the catalyst, any butadiene in the feed is hydrogenated to butenes, with equilibrium amounts of 1-butene and 2-butene produced at the catalyst, and the 2-butene is distilled off as bottoms to drive the reaction at the catalyst sites towards the production of 2-butene.

[0048] The stripping section of the column may include conventional distillation structures such as bubble caps, sieve trays or inert packing to allow complete separation of the 2-butene product from the lower boiling isobutene and isobutane. Any normal butane present is also removed as bottoms. The 2-butene and normal butane may then be recovered from the catalytic distillation column 510 via flow line 5.

[0049] Overhead stream 516, comprising isobutene and any isobutane, is condensed in condenser 518. The condensed overheads are collected in receiver separator 520, where the liquid isobutene and isobutane are separated from the hydrogen and light materials vented via flow line 16. Optionally, hydrogen may be recycled to catalytic distillation column 510 (hydrogen recovery and recycle not shown). A portion of the condensed overhead product is recycled as reflux to catalytic distillation column 510 via flow line 524. Isobutene and isobutane are removed as overhead products via flow line 6.

[0050] The overhead product stream 6 may include isobutene and isobutane, such as may result from by-product hydrogenation in catalytic distillation column 510 or as a reaction by-product elsewhere in the overall system 100. In some embodiments, for example, if a higher purity isobutene product is desired, the overhead product stream 6 may be fed to a splitter (not shown) to separate isobutene from isobutane. For example, a small stripper may be required for removal of trace amounts of isobutane. In some embodiments, the deisobutenizer tower may be as described in US6242661 or US7982086. In other embodiments, an integrated isobutene (IB) stripper, such as described in US11053177, may be used to remove isobutane from isobutene to produce a higher purity bio-derived isobutene product.

[0051] The catalytic material used in the isomerization reaction is preferably in a form for functioning as distillation packing in the form of conventional distillation packing such as Raschig rings, Pall rings, saddles, and other structures such as balls, irregulars, sheets, tubes, spirals, etc. (such as those described in US4242530, US4443559, US5189001, US5348710, and US5431890), packed in bags or other structures, plated on grills or screens, or is a reticulated polymer foam (the foam cell structure must be large enough so as not to cause a high pressure drop through the column, or otherwise arranged in large chunks or concentrated tubular, etc. to allow vapor flow). Similarly, catalysts may be used as palladium, platinum, or nickel supported on one-eighth inch alumina extrudates, either in bags or loosely packed in a column. In some embodiments, the catalyst may be included in a structure such as those disclosed in US5730843, US5266546, US4731229, and US5073236.

[0052] The catalyst contained in the reaction zone of the catalytic distillation column can be any catalyst suitable for isomerization or hydroisomerization of 1-butene to 2-butene. In some embodiments, the catalyst may include palladium, platinum, or nickel, and may be in the form of extrudates, for example. In hydroisomerization, if butadiene is included in the feed, hydrogen will be lost from the catalyst due to hydrogenation, so the hydrogen rate to the distillation column reactor must be sufficient to maintain the catalyst in the active (hydride) form. The hydrogen rate is sufficient to support the butadiene hydrogenation reaction and replace the hydrogen lost from the catalyst, but can be adjusted to fall below the hydrogen required for butene hydrogenation or cause flooding of the column. Generally, the molar ratio of hydrogen to C4 hydrocarbons fed to the bed of the catalytic distillation column ranges from about 0.01:1 to 0.60:1, preferably 0.01:1 to 0.10:1.

[0053] Embodiments herein may perform the catalytic distillation step in a catalyst packed column, which, like any distillation, may be understood to include a gas phase and some liquid phase. Since the reaction is carried out simultaneously with the distillation, the initial reaction products are removed from the reaction zone as soon as possible. Additionally, since all components are boiling, the reaction temperature is controlled by the boiling point of the mixture at the system pressure, which may vary from tray to tray. The heat of reaction simply causes more boiling, but not an increase in temperature. Additionally, the reaction has an increased driving force because the reaction products are being removed and cannot contribute to the back reaction. As a result, by adjusting the system pressure, the reaction rate and distribution of products can be greatly controlled. Also, the throughput (residence time = liquid hourly space velocity) can be controlled by adjusting the system pressure. -1 ) provides further control over product distribution and the degree of 1-butene to 2-butene conversion.

[0054] The temperature in a distillation column reactor is determined by the boiling point of the liquid mixture present at any given pressure. The temperature at the bottom of the column reflects the composition of the materials in that part of the column and will be higher than the overheads. That is, at constant pressure, a change in temperature of the system indicates a change in the composition of the column. To change the temperature, change the pressure. Thus, temperature control in the reaction zone is affected by changes in pressure; by increasing the pressure the temperature in the system increases and vice versa.

[0055] Catalytic distillation columns according to embodiments herein may be operated at overhead temperatures ranging from 32°C to 138°C and pressures ranging from 3 bara to 20 bara, keeping in mind the effect of pressure on temperature as discussed above. In other embodiments, catalytic distillation columns according to embodiments herein may be operated at overhead temperatures ranging from 85°C or 90°C to 130°C or 135°C and pressures ranging from 9 bara, 10 bara, or 11 bara to 16 bara, 18 bara, or 20 bara, any lower limit may be combined with any upper limit. In other embodiments, the overhead temperature of the catalytic distillation column may range from 32°C to about 80°C, e.g., from about 47°C to about 68°C, or from about 60°C to about 65°C. In yet other embodiments, the overhead temperature is at a lower limit of 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 85 or 90° C. to an upper limit of 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 85, 90, 100, 110, 120, 130, or 138° C., any lower limit may be combined with any upper limit. In some embodiments, the overhead pressure of the catalytic distillation column may be in the range of about 3 bara to about 12 bara, e.g., in the range of about 7 bara to about 10 bara. In yet other embodiments, the overhead pressure of the catalytic distillation column can range from a lower limit of about 9, 10, 11, 12, 13, 14, or 15 bara to an upper limit of about 14, 15, 16, 17, 18, 19, or 20 bara. The bottoms temperature of the catalytic distillation column corresponds to the boiling point of the higher boiling component at the operating conditions and in various embodiments can range from about 60° C. to about 180° C., such as from about 60° C. to about 100° C., or from about 65° C. to about 88° C., etc., but can be higher based on the desired overhead temperature and pressure.The operating temperature may also take into account the activity of the catalyst to promote the desired reaction of 1-butene to 2-butene.

[0056] In embodiments herein, the catalytic distillation column is operated under conditions, particularly temperature and pressure, that tend to displace 2-butene from contact with the catalyst while contacting 1-butene with the catalyst. Thus, as 1-butene is isomerized to 2-butene, it falls within the column away from the catalyst and is removed as bottoms. The column may include a reflux, and the reflux ratio may range, for example, from 0.5:1 to 33:1.

[0057] As described above, the mixed C4 from the olefin skeletal isomerization reaction zone is fed to a catalytic distillation column. In the catalytic distillation column, the C4 stream is further processed using a positional isomerization catalyst and a hydrogenation catalyst, along with a hydrogen feed, to convert 1-butene to 2-butene and selectively hydrogenate any butadiene that may be present from the dehydration unit and the upstream processing of the skeletal isomerization unit. Cofractionation, in some embodiments, results in two C4 product streams including a 2-butene and n-butane bottoms product and a high purity isobutene overhead product. Hydrogen-containing vent gas may also be recovered.

[0058] The isobutene product stream produced from the processing of the skeletal isomerized mixed C4 effluent through a catalytic distillation column may have an isobutene content of at least 80 wt.%. In various embodiments, a high purity isobutene product stream may be produced having a purity of at least 85 wt.%, at least 90 wt.%, at least 95 wt.%, at least 98 wt.%, at least 99 wt.%, at least 99.5 wt.%, or at least 99.9 wt.%.

[0059] In yet other embodiments, the catalytic distillation column herein may provide three C4 product streams including a 2-butene and n-butane bottoms product, an isobutane overhead product, and a high purity isobutene product. The high purity isobutene product may be recovered, for example, as a bottoms draw from a splitter, as described above, or in some embodiments, as a fraction of the side draw from the catalytic distillation column. The side draw may be located at a suitable elevation within the column to recover an isobutane / isobutene stream having an isobutane to isobutene ratio ranging from 0.001:1 to 2:1, for example, from 0.01:1 to 1:1.5, or from 0.1:1 to 1:1. The side draw may be located above the catalytic distillation reaction zone and the feed may be located below the catalytic distillation reaction zone to provide a side draw containing a relatively small amount of n-butenes, and a stream containing greater than 80%, greater than 95%, greater than 98%, or greater than 99%, or greater than 99.9% isobutene may be recovered. Sufficient trays and height to the column may also be provided to provide an overhead stream of primarily isobutane, such as greater than 95% or greater than 98% isobutane (wt %).

[0060] In some embodiments, due to the low production of 1-butene in the preceding units, coupled with the isomerization of 1-butene to 2-butene in the catalytic distillation column, the isobutene product stream produced herein can have a purity of at least 99.9%, 99.95%, or 99.99% by weight isobutene, based on the total amount of isobutene and 1-butene in the high purity isobutene product stream, whether overhead or side draw from the catalytic distillation column.

[0061] The addition of a diluent has been found to improve the operation of the skeletal isomerization unit. The n-butenes produced in the catalytic distillation column unit may be recycled to a third unit (olefin skeletal isomerization) to produce additional isobutene, while n-butane may act as a diluent to help control the reaction in the skeletal isomerization unit. In some cases, for example, in embodiments where less n-butane by-product is formed, the amount of n-butane recycled back to the third unit may also be less. In such an embodiment, and as shown in FIG. 6, a saturation (hydrogenation) reactor 110 may be used to react the n-butenes with hydrogen 22 to form the desired amount of n-butane for use as a diluent during skeletal isomerization.

[0062] If present in sufficient quantities, the isobutane product may be optionally dehydrogenated to form additional isobutene and hydrogen. The hydrogen may be recovered and used as feed to a catalytic distillation column or a hydrogenation reactor to produce n-butane diluent, while the C4 dehydrogenation effluent may be fed to a catalytic distillation column, an isobutene stripper, or otherwise processed to recover additional bio-derived isobutene.

[0063] Catalytic separation: Oxygenation-backcracking separation system 108A The oxygenation-backcracking separation system selectively converts isobutene in a skeletal isomerized mixed C4 product stream to one or more of methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), tertiary butyl alcohol (TBA), butyl-butyl ether, or isobutyl alcohol, among other possible oxygenated intermediates, separates the resulting ether or alcohol from lighter C4 n-olefins and paraffins, and then backcracking the ether or olefin to form the constituent isobutene and water or alcohol, allowing the isobutene to be readily separated from the water or alcohol and recovered as a high purity isobutene product stream. The recovered alcohol or water can then be returned to the reactor for selectively converting isobutene.

[0064] The reaction system may include one or more reactors and catalytic distillation reactors suitable for etherifying isobutene and one or more alcohols to form one or more C4 ethers, such as MTBE and / or ETBE. Alternatively, water may be used to convert isobutene to an alcohol, such as TBA or isobutyl alcohol.

[0065] C4 isoolefins may be processed according to embodiments herein to etherify or alcoholize the isoolefins. The catalysts used in the reactors and distillation column reactors according to embodiments herein may have functionality for selectively hydrogenating butadiene, for isomerizing olefins, and for etherifying or alcoholizing isoolefins.

[0066] Typical conditions for the oxygenation reaction include a catalyst bed temperature above about 60° C., an overhead pressure above about 5.5 barg, and a reaction time of about 1.0 to 2.0 hours for a catalytic distillation reactor. 1 An equivalent liquid hourly space velocity of 0.01 m / s may be used. The temperature in the column is determined by the boiling point of the liquid mixture present at any given pressure. The temperature at the bottom of the column reflects the composition of the material in that part of the column, which will be higher than the overheads. That is, at a constant pressure, a change in temperature indicates a change in the composition of the column. To change the temperature, the pressure in the column can be changed. Thus, temperature control in the reaction zone is controlled by pressure by adding enough heat (the reaction is exothermic) to cause more boiling. By increasing the pressure, the temperature increases and vice versa. Even if a distillation column reactor is used, some isoolefins may be unconverted and may leave the column with the overheads.

[0067] The ether products, which are the highest boiling materials, are removed from the distillation column reactor as bottoms, along with the dimers in the effluent from the upstream reactor. The overheads may include unreacted light alcohols, such as ethanol, used in the upstream reactor and / or reactants in the distillation column reactor, as well as isoolefins, along with light inerts, such as normal butenes and butanes.

[0068] The catalyst for etherification can be any of the known etherification catalysts, such as an acidic cation exchange resin, such as Amberlyst 15, supplied by DuPont Chemical Company. Suitable catalyst structures may be used herein, with the cation exchange resin particles disposed in a bed within a fixed bed reactor. Additionally, the temperature and pressure may be similar to those known in the art for carrying out the particular reaction.

[0069] In some embodiments, the oxygenation reaction system may include an unreacted n-butene effluent. The effluent containing unreacted n-butene from the oxygenation reaction unit may be fed to a C4 separation system. The C4 separation system may be used to produce a 1-butene product stream and a 2-butene recycle stream. The 2-butene recycle stream may return the separated 2-butene to the skeletal isomerization system. In some embodiments, the etherification reaction system may produce an ETBE product stream.

[0070] The oxygenated (ether or alcohol) effluent from the etherification reaction system is then fed to a backcracking unit.

[0071] The backcracking system produces high purity isobutene along with unreacted feed components and reaction by-products such as n-butene, tert-butyl alcohol (TBA), ethanol, unconverted MTBE, ETBE, and ethyl sec-butyl ether (ESBE), diethyl ether (DEE), dimethyl ether (DME), diisobutene (DIB), or butyl-butyl ether (BBE). The backcracking unit includes a distillation unit that separates the components in the reaction effluent to obtain high purity isobutene. The recovered alcohol or water may be returned to the oxygenation reaction system. In some embodiments, for example, when the oxygenate is bioethanol, the recovered ethanol may be returned to the oxygenation reaction system to reduce the production of bio-based ethanol from renewable resources. In such embodiments, no additional external ethanol supply is required.

[0072] Under cracking conditions, contacting the ether feed with a catalyst as described herein can result in the production of desired olefins and alcohols, as well as by-products that can include by-product ethers, alcohols, and oligomers, such as dimers or trimers of the desired olefin products. In some embodiments, contacting the ether feed with a catalyst as described herein can result in a conversion of at least 90% by weight of the ether, in other embodiments at least 85% by weight, in other embodiments at least 80% by weight, in other embodiments at least 75% by weight, and in other embodiments at least 70% by weight.

[0073] 7, a simplified block flow diagram of an oxygenation-backcracking separation system 108A according to an embodiment herein is shown. A bio-based mixed C4 stream 4 containing isobutene among other components as described above, and a stream 20A containing an oxygenated reactant, such as methanol, ethanol, isobutanol, water, or mixtures thereof, may be fed to an etherification reaction system 702. The etherification reaction system 702 may include one or more reactors for selectively reacting isobutene with water, methanol, or ethanol over a suitable catalyst to form one or more of MTBE, ETBE, TBA, butyl-butyl ether, or isobutyl alcohol. The reaction effluent 704 may then be fed to a separation system 706, which may include one or more distillation or extractive distillation columns, to separate MTBE, ETBE, TBA, butyl-butyl ether or isobutyl alcohol from the unreacted C4 components in the mixed feed stream 4, with MTBE, ETBE, TBA, butyl-butyl ether or isobutyl alcohol being recovered as effluent stream 708 and the lighter C4 components being recovered via one or more flow streams 14A. Unreacted water or alcohol and other etherification reaction by-products may be recovered via one or more streams 15A.

[0074] The effluent stream 708 may then be fed to a backcracking reaction system 710 to convert the MTBE, ETBE, TBA, butyl-butyl ether, or isobutyl alcohol back into the constituent molecules, isobutene and water, methanol, or ethanol. The backcracking reaction system 710 may include one or more reactors containing a suitable backcracking catalyst. The backcracked effluent 712 may then be recovered from the reactor and fed to a separation system 714, which may include one or more distillation or extractive distillation columns to recover the high purity isobutene product 6, any heavy reaction by-products 14B, and alcohol or water reactants 15B, which may be recycled upstream of the reaction system 702, if desired. Although not shown, embodiments herein contemplate the recovery of 1-butene, 2-butene, MTBE, ETBE, or other components as separate product streams from the various reaction effluents and separation schemes described above.

[0075] As briefly described above, embodiments can provide for the use of renewable feedstocks, which can include bioethanol or bioisobutanol, which can be derived from fermentation processes or bioethanol and bioisobutene, which can be produced within the process schemes outlined above. Thus, embodiments herein can internally generate the feedstock used in the etherification reaction, facilitating the use of bio-derived feedstocks to produce fully certifiable bio-derived products.

[0076] Because the formation of alcohols or ethers provides efficient separation of isobutene from the n-butenes and isobutane that may be included in the C4 skeletal isomerization product stream, separation zone 108A can be used to produce a high purity isobutene product similar to that described above for unit 108. EXAMPLES

[0077] In an exemplary logical embodiment, 400 KTA of bioethanol is fed to the first unit for dehydration. 162 KTA of by-products including water are produced, and 239 KTA of bioethylene is produced. The bioethylene is dimerized in the second unit to form 12 KTA of C5+ by-products, while 226 KTA of n-butene is produced. During skeletal isomerization, 3 KTA of C3 purge is lost, and 31 KTA of C5+ by-products are formed, while 994 KTA of n-butene, isobutene, and n-butane are produced. During catalytic distillation, 9 KTA of hydrogen and purge gas are lost, while 183 KTA of high-purity bioisobutene is isolated. 802 KTA of 2-butene (288 KTA) and n-butane (5 MKTA) are recycled back to the skeletal isomerization step.

[0078] Bio-based polymers and elastomers are expected to be high-value products. For proper green certification, it is often necessary to show that all steps are certified with bio-based intermediates rather than fossil-based intermediates, even if the composition is similar between fossil and bio-based intermediates. This bio-HPIB route allows manufacturers to green many products such as tires and lubricants. This route is unique because it uses readily available bio-sourced ethanol in high yields for HPIB production, with minimal by-product formation, without producing isobutane, which typically makes the HPIB process production intensive.

[0079] A unique feature of this application may include the use of an ethylene dimer pathway in the process to make high purity bioisobutene. Recycle from the catalytic distillation column (CDDelB) back to the isomerization unit allows for the accumulation of n-butane diluent required for the isomplus process. This is necessary to allow the dimer effluent to be used. The downstream IB stripper is small because very little isobutane (paraffin) is produced in the process.

[0080] Embodiments of the present disclosure may provide at least one of the following advantages: The disclosed process may provide advantages over conventional processes for producing high purity isobutene because it produces significantly less paraffinic isobutane, which requires energy-intensive processes to convert to isobutene. Additionally, unconverted n-butenes and n-butane diluent can be recycled back to the skeletal isomerization step, allowing n-butenes and n-butanes to efficiently accumulate for continued skeletal isomerization.

[0081] Although only a few exemplary embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without substantially departing from the invention, and all such modifications are therefore intended to be included within the scope of the present disclosure as defined in the following claims.

Claims

1. 1. A system for converting bioethanol into high purity bioisobutene, comprising: a dehydration unit configured to receive a bioethanol-containing stream and convert the bioethanol into bioethylene to produce a bioethylene-containing stream; a dimerization unit configured to receive the bioethylene-containing stream and dimerize the bioethylene to produce a bio-n-butene-containing stream; an olefin skeletal isomerization unit configured to receive the bio-n-butene-containing stream and convert the n-butenes to produce a skeletal isomerized C4 olefin-containing stream comprising isobutene and n-butenes; a catalyst separation unit configured to receive the skeletal isomerized C4 olefin-containing stream, convert olefins and / or isoolefins contained therein to produce a converted skeletal isomerization reaction product, and fractionate the converted skeletal isomerization reaction product to produce a bioisobutene product fraction.

2. 2. The system of claim 1, wherein the catalyst separation unit comprises a catalytic distillation column configured to receive the skeletal isomerized C4 olefins-containing stream, convert 1-butene contained in the n-butenes to 2-butenes, and fractionate isobutene from the 2-butenes to produce a 2-butene stream and the bioisobutene product fraction.

3. 2. The system of claim 1, wherein the catalyst separation unit comprises: an oxygenation reactor configured to react the isobutene with an alcohol or water to produce an alcohol intermediate or an ether intermediate; a separator configured to separate the n-butenes from the alcohol or ether intermediate; a backcracking reactor configured to convert the alcohol or ether intermediate to produce a reaction effluent comprising the isobutene and the alcohol or water; and a separation system configured to separate the reaction effluent to produce the bioisobutene product fraction.

4. The dehydration unit is a reaction zone comprising one or more dehydration reactors each comprising an ethanol dehydration catalyst configured to receive the bioethanol-containing stream, convert the bioethanol to bioethylene, and produce a dehydration reactor effluent comprising bioethylene and water; a separation zone configured to receive the dehydration reactor effluent, separate the bioethylene from the water, and produce the bioethylene-containing stream and a water stream.

5. The dimerization unit is a reaction zone comprising one or more dimerization reactors each comprising an ethylene dimerization catalyst configured to receive the bioethylene-containing stream, convert the bioethylene to bio-n-butenes, and produce a dimerization reactor effluent comprising bio-n-butenes and C5 and heavier hydrocarbons; 5. The system of claim 4, comprising: a separation zone configured to receive the dimerization reactor effluent, separate the bio-n-butenes from the C5 and heavier hydrocarbons, and produce the bio-n-butenes-containing stream and a stream comprising the C5 and heavier hydrocarbons.

6. The olefin skeletal isomerization unit is a reaction zone comprising one or more skeletal isomerization reactors each comprising an olefin skeletal isomerization catalyst configured to receive the bio-n-butene-containing stream, convert the bio-n-butenes to bio-isobutenes, and produce a skeletal isomerization reactor effluent comprising bio-C4 olefins, C3 and lighter hydrocarbons, and C5+ hydrocarbons, comprising bio-n-butenes and bio-isobutenes; a separation zone configured to receive the skeletal isomerization reactor effluent and separate the bio-C4 olefins from the C3 and lighter hydrocarbons and the C5 and heavier hydrocarbons to produce the skeletal isomerized C4 olefins-containing stream, the C3 and lighter hydrocarbons-containing stream, and the C5+ hydrocarbons-containing stream.

7. The catalyst separation unit is a catalytic deisobutenizer unit, 7. The system of claim 6, comprising a catalytic deisobutenizer unit comprising a catalytic distillation reactor comprising a positional isomerization reaction zone and a distillation structure configured to react 1-butene contained in the bio-n-butene to 2-butene, separate the 2-butene from the bioisobutene, and recover a 2-butene stream and the bioisobutene product fraction.

8. 3. The system of claim 2, comprising a hydrogenation reactor configured to hydrogenate a portion of the 2-butenes in the 2-butene stream to produce a hydrogenated effluent comprising 2-butenes and n-butanes.

9. 9. The system of claim 8, further comprising a flow line for supplying said hydrogenation effluent to said olefin skeletal isomerization unit.

10. 2. The system of claim 1, wherein the bioisobutene product fraction comprises isobutane, and the system comprises a splitter to separate at least a portion of the isobutane from the bioisobutene and recover a bioisobutane stream and a bioisobutene stream enriched in bioisobutene.

11. A method for producing high purity isobutene from bioethanol, comprising the steps of: Dehydrating the bioethanol to produce bioethylene; dimerizing the bioethylene to form bio-n-butene; skeletal isomerization of the bio-n-butenes to form a bio-C4 mixture comprising isobutene, isobutane, n-butenes, and n-butane; reacting and fractionating the bio-C4 mixture to separate bio-isobutene from unconverted n-butene; recovering the bioisobutene; and and recycling said unconverted n-butenes to said skeletal isomerization step.

12. 12. The process of claim 11, comprising hydrogenating a portion of the unconverted n-butenes to form a mixture comprising n-butanes, and recycling said mixture to the skeletal isomerization step.

13. Dehydrating the bioethanol to produce bioethylene, feeding the bioethanol-containing stream to a dehydration reaction zone comprising one or more dehydration reactors, each of which contains an ethanol dehydration catalyst; contacting bioethanol with the ethanol dehydration catalyst under reactive conditions to convert the bioethanol to bioethylene; recovering a dehydration reaction effluent from the dehydration reaction zone, the dehydration reaction effluent comprising the bioethylene and water; and separating the dehydration reaction effluent to recover a stream comprising the bioethylene and a water stream.

14. dimerizing the bioethylene to form bio-n-butene; feeding said stream comprising said bioethylene to a dimerization reaction zone comprising one or more dimerization reactors each containing an ethylene dimerization catalyst; contacting the bioethylene with the ethylene dimerization catalyst under reactive conditions to convert the bioethylene to biobutene; recovering a dimerization reaction effluent from said dimerization reaction zone comprising said bio-n-butenes and C5 and heavier reaction by-products; and separating the dimerization reaction effluent to recover a stream comprising the bio-n-butenes and a stream comprising the C5 and heavier reaction by-products.

15. skeletal isomerization of the bio-n-butenes to form a bio-C4 mixture; feeding said stream containing said bio-n-butenes to a skeletal isomerization reaction zone comprising one or more skeletal isomerization reactors each containing a skeletal isomerization catalyst; contacting the bio-n-butenes with the skeletal isomerization catalyst under reactive conditions to convert the n-butenes to isobutene; recovering a skeletal isomerization reaction effluent comprising said bio-C4 mixture, C3 and lighter reaction by-products, and C5+ reaction by-products; and separating the skeletal isomerization reaction effluent to recover a stream comprising the bio-C4 mixture, a stream comprising the C3 and lighter reaction by-products, and a stream comprising the C5+ reaction by-products.

16. The fractionating step comprises: feeding the stream comprising the bio-C4 mixture to a catalytic distillation reactor comprising a positional isomerization catalyst; In the catalytic distillation reactor, Converting 1-butene in the bio-C4 mixture to 2-butene; separating the isobutane and bioisobutene from the 2-butene and n-butane; recovering an overhead fraction comprising said isobutane and bioisobutene; recovering a bottom fraction comprising said 2-butene and n-butane; and separating the overhead fraction to recover an isobutane fraction and a bioisobutene fraction having a concentration of at least 95 wt% bioisobutene.

17. 17. The process of claim 16 comprising recycling said bottoms fraction to said skeletal isomerization reaction zone.

18. 18. The process of claim 17, comprising hydrogenating a portion of the 2-butenes in said bottoms fraction to form additional n-butanes prior to recycling said bottoms fraction to said skeletal isomerization reaction zone.

19. 1. A system for converting bioethanol into high purity bioisobutene, comprising: a dehydration unit configured to receive a bioethanol-containing stream and convert the bioethanol into bioethylene to produce a bioethylene-containing stream; a dimerization unit configured to receive the bioethylene-containing stream and dimerize the bioethylene to produce a bio-n-butene-containing stream; an olefin skeletal isomerization unit configured to receive the bio-n-butene-containing stream and convert the n-butenes to produce a skeletal isomerized C4 olefin-containing stream comprising isobutene and n-butenes; A catalytic reaction / separation unit comprising: receiving the skeletal isomerized C4 olefin-containing stream; converting isobutene to one or more of methyl tert-butyl ether, ethyl tert-butyl ether, tertiary butyl alcohol, and isobutyl alcohol; separating the n-butene from one or more of methyl tert-butyl ether, tertiary butyl alcohol, and isobutyl alcohol; back-cracking the one or more of methyl tert-butyl ether, tertiary butyl alcohol, and isobutyl alcohol to form isobutene and one or more of water and methanol; a catalytic reaction / separation unit configured to separate the isobutene from one or more of the water and methanol to produce a bioisobutene product fraction; or A catalytic reaction / separation unit comprising: receiving the skeletal isomerized C4 olefin-containing stream; converting 1-butene contained in the n-butene into 2-butene; a catalytic reaction / separation unit configured to separate the 2-butene from the isobutene to produce a 2-butene fraction and a bioisobutene product fraction.

20. 20. The system of claim 19, further comprising recovering one or more of a methyl tert-butyl ether product stream, an ethyl tert-butyl ether product stream, and a 1-butene product stream from the catalytic reaction / separation unit.

21. The dehydration unit is a reaction zone comprising one or more dehydration reactors each comprising an ethanol dehydration catalyst configured to receive the bioethanol-containing stream, convert the bioethanol to bioethylene, and produce a dehydration reactor effluent comprising bioethylene and water; a separation zone configured to receive the dehydration reactor effluent, separate the bioethylene from the water, and produce the bioethylene-containing stream and a water stream.

22. The dimerization unit is a reaction zone comprising one or more dimerization reactors each comprising an ethylene dimerization catalyst configured to receive the bioethylene-containing stream, convert the bioethylene to bio-n-butenes, and produce a dimerization reactor effluent comprising bio-n-butenes and C5 and heavier hydrocarbons; and a separation zone configured to receive the dimerization reactor effluent, separate the bio-n-butenes from the C5 and heavier hydrocarbons, and produce the bio-n-butenes-containing stream and a stream comprising the C5 and heavier hydrocarbons.

23. The olefin skeletal isomerization unit is a reaction zone comprising one or more skeletal isomerization reactors each comprising an olefin skeletal isomerization catalyst configured to receive the bio-n-butene-containing stream, convert the bio-n-butenes to bio-isobutenes, and produce a skeletal isomerization reactor effluent comprising bio-C4 olefins, C3 and lighter hydrocarbons, and C5+ hydrocarbons, comprising bio-n-butenes and bio-isobutenes; a separation zone configured to receive the skeletal isomerization reactor effluent and separate the bio-C4 olefins from the C3 and lighter hydrocarbons and the C5 and heavier hydrocarbons to produce the skeletal isomerized C4 olefins-containing stream, the C3 and lighter hydrocarbons-containing stream, and the C5+ hydrocarbons-containing stream.

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