N-BUTANE DEHYDROGENATION

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application No. 62/743,495, filed October 9, 2018, which is hereby incorporated by reference in its entirety.

FIELD OF INVENTION

[0002] The present invention generally relates to the production of 1 -butene. More specifically, the present invention relates to dehydrogenating butane to form a mixture comprising butene isomers and recovering 1 -butene from the mixture.

BACKGROUND OF THE INVENTION

[0003] 1 -Butene is normally used as a comonomer in polyethylene production. One method of producing 1 -butene is separating it from C ₄ refinery streams. These C ₄ refinery streams are formed during steam cracking or fluid catalytic cracking of hydrocarbon feed to produce ethylene. 1 -Butene is also produced by dehydrogenating n-butane to form isomers of butene, including 1 -butene, and one or more of iso-butene, trans-2 -butene, and cis-2- butene. After the dehydrogenating, the 1 -butene is separated from the other isomers. In production processes that involve the dehydrogenation of n-butane to form butenes, the separation of 1 -butene from the other butene isomers is a major hurdle to overcome, if a high quality 1 -butene product is to be achieved.

[0004] Separating 1 -butene from other butene isomers is very challenging because these materials all have boiling points that are close. Hence, traditional separation techniques, such as distillation, are relatively ineffective. Further, conversion rates of n- butane to 1 -butene, in these processes are relatively low, so it is difficult to achieve suitable production capacity for 1 -butene in existing refineries.

BRIEF SUMMARY OF THE INVENTION

[0005] With the above described issues associated with the production of 1 -butene in mind, a process has been developed that can achieve required 1 -butene production capacity at the desired purity. In this process, n-butane is dehydrogenated to form a mixture comprising butene isomers and unreacted n-butane. The mixture is separated by techniques that include extractive distillation and unreacted n-butane from this separation process is sent back as recycle to be dehydrogenated. Iso-butene and 1 -butene recovered from the separation process is routed to a membrane to separate the iso-butene from 1 -butene. A mixture of trans-2-butene and cis-2-butene from the separation process can be used as feedstock for an isomerization unit. In this isomerization unit, both trans-2-butene and cis-2-butene are converted to 1 -butene.

[0006] Embodiments of the invention include a method of producing 1 -butene. The method includes dehydrogenating n-butane to produce a first stream comprising 1 -butene, isobutene, trans-2-butene, cis-2-butene, and n-butane. The method further includes separating the first stream by extractive distillation to produce a second stream comprising primarily n-butane and a third stream comprising primarily 1 -butene, iso-butene, trans-2- butene, and cis-2-butene, collectively. Further yet, the method includes distilling, in a distillation column, the third stream to form a fourth stream comprising primarily iso-butene and 1 -butene, collectively and a fifth stream comprising primarily trans-2-butene and cis-2- butene, collectively. The method also involves separating the fourth stream to produce a sixth stream comprising primarily iso-butene and seventh stream comprising primarily 1- butene.

[0007] Embodiments of the invention include a method of producing 1 -butene The method includes dehydrogenating n-butane to produce a first stream comprising 1 -butene, isobutene, trans-2-butene, cis-2-butene, and n-butane. The method further includes separating the first stream by extractive distillation to produce a second stream comprising primarily n-butane and a third stream comprising primarily 1 -butene, iso-butene, trans-2- butene, and cis-2-butene, collectively. Further yet, the method includes distilling the third stream in a distillation column to form a fourth stream comprising primarily iso-butene and 1- butene, collectively and a fifth stream comprising primarily trans-2-butene and cis-2-butene, collectively. The method also involves separating the fourth stream to produce a sixth stream comprising primarily iso-butene and seventh stream comprising primarily 1 -butene, wherein the separating of the fourth stream is performed with a membrane. The method further includes isomerizing at least some of the trans-2-butene and at least some of the cis-2-butene of the fifth stream to form 1 -butene. [0008] The following includes definitions of various terms and phrases used throughout this specification.

[0009] The terms “about” or“approximately” are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment the terms are defined to be within 10%, preferably, within 5%, more preferably, within 1%, and most preferably, within 0.5%.

[0010] The terms“wt. %”,“vol. %” or“mol. %” refer to a weight, volume, or molar percentage of a component, respectively, based on the total weight, the total volume, or the total moles of material that includes the component. In a non-limiting example, 10 moles of component in 100 moles of the material is 10 mol.% of component.

[0011] The term“substantially” and its variations are defined to include ranges within

10%, within 5%, within 1%, or within 0.5%.

[0012] The terms“inhibiting” or“reducing” or“preventing” or“avoiding” or any variation of these terms, when used in the claims and/or the specification, include any measurable decrease or complete inhibition to achieve a desired result.

[0013] The term“effective,” as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.

[0014] The use of the words“a” or“an” when used in conjunction with the term

“comprising,”“including,”“containing,” or“having” in the claims or the specification may mean“one,” but it is also consistent with the meaning of“one or more,”“at least one,” and “one or more than one.”

[0015] The words“comprising” (and any form of comprising, such as“comprise” and

“comprises”),“having” (and any form of having, such as“have” and“has”),“including” (and any form of including, such as“includes” and“include”) or“containing” (and any form of containing, such as“contains” and“contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0016] The process of the present invention can“comprise,”“consist essentially of,” or“consist of’ particular ingredients, components, compositions, etc., disclosed throughout the specification. [0017] The term“primarily,” as that term is used in the specification and/or claims, means greater than any of 50 wt. %, 50 mol. %, and 50 vol. %. For example,“primarily” may include 50.1 wt. % to 100 wt. % and all values and ranges there between, 50.1 mol. % to 100 mol. % and all values and ranges there between, or 50.1 vol. % to 100 vol. % and all values and ranges there between.

[0018] Other objects, features and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] For a more complete understanding, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: [0020] FIG. 1 is a system for producing 1 -butene, according to embodiments of the invention; and

[0021] FIG. 2 is a method of producing 1 -butene, according to embodiments of the invention.

DETATEED DESCRIPTION OF THE INVENTION [0022] A method has been discovered for producing 1 -butene at improved production capacity and purity as compared with conventional processes. In the discovered method, n- butane is dehydrogenated to form a mixture comprising butene isomers and unreacted n- butane. Unreacted n-butane is separated from this mixture. The unreacted n-butane from this separation process can be sent back as recycle to be dehydrogenated. The separation process can include the use of distillation, including extractive distillation. Iso-butene and 1- butene recovered from the separation process is routed to a membrane to separate the iso- butene from 1 -butene. A mixture of trans-2-butene and cis-2-butene from the separation process can be used as feedstock for an isomerization unit. In this isomerization unit, both trans-2-butene and cis-2-butene are converted to 1 -butene.

[0023] FIG. 1 shows system 10 for producing 1 -butene, according to embodiments of the invention. FIG. 2 shows method 20 for producing 1 -butene, according to embodiments of the invention. Method 20 may be implemented with system 10. In embodiments of the invention, the mass numbers for streams shown in FIG. 1 may vary and the mass number for each stream can include mass numbers in a range from 10% less than the mass number shown to 10% greater than the mass number shown, including all ranges and values therein.

[0024] Method 20, as implemented using system 10, may include, at block 200, flowing feed stream 100, which comprises primarily n-butane, to dehydrogenation reactor 110. In embodiments of the invention, feed stream 100 may be combined with recycle n- butane stream 102 to form combined stream 117, which is flowed to dehydrogenation reactor 110. Alternatively or additionally, feed stream 100 and recycle n-butane stream 102 may be provided to dehydrogenation reactor 110 separately. According to embodiments of the invention, feed stream 100 may be sourced from feedstock and may comprise 99 to 99.5 wt. % n-butane.

[0025] At block 201, method 20 may further involve dehydrogenating n-butane of feed stream 100, in dehydrogenation reactor 110, to produce reactor effluent stream 101. Reactor effluent stream 101, according to embodiments of the invention, is a mixture comprising one or more of 1 -butene, isobutene, trans-2-butene, cis-2-butene, and n-butane. Reactor 110, in embodiments of the invention, is operated to provide reaction conditions for feed stream 100 that includes a temperature in a range of 500 to 650 °C, a pressure in a range of 0 to 10 bar, and a GHSV in a range of 1000 to 5000 h ¹ . According to embodiments of the invention, reactor effluent stream 101 comprises 20 wt. % to 30 wt. % l-butene, 2 wt. % to 5 wt. % isobutene, 25 wt. % to 35 wt. % trans-2-butene, 20 wt. % to 30 wt. % cis-2-butene, and 30 wt. % -50 wt. % n-butane. Further, in embodiments of the invention, the dehydrogenation reaction that occurs in reactor 110 may be catalyzed by a catalyst that comprises platinum and/or tin. [0026] Method 20, according to embodiments of the invention, includes flowing reactor effluent stream 101 to extractive distillation unit 111, at block 202. Extractive distillation unit 111 can include solvent extraction column 111 A and solvent recovery column 111B. According to embodiments of the invention, reactor effluent stream 101 enters solvent extraction column 111A. Then, at block 203, in embodiments of the invention, solvent extraction column 111A carries out extractive distillation on reactor effluent stream 101 to produce recycle n-butane stream 102 and intermediate raffinate stream 115. According to embodiments of the invention, the conditions for carrying out the extractive distillation includes temperature in a range 10 to 50 °C, a pressure in a range of 0.01 to 1 MPa. And in embodiments of the invention, the solvent used for carrying out the extraction includes a selection from the list consisting of and combinations thereof. Recycle n-butane stream 102, in embodiments of the invention, comprises primarily n-butane and intermediate raffinate stream 115 comprising primarily isobutene, 1 -butene, trans-2 -butene and cis-2-butene, collectively. In embodiments of the invention, recycle n-butane stream 102 comprises 98 to 99 wt. % n-butane. According to embodiments of the invention, intermediate raffinate stream 115 comprises 20 to 30 wt. % l-butene, 2 to 5 wt. % isobutene, 25 to 35 wt. % trans-2- butene, 20 to 30 wt. % cis-2-butene, and 30 to 50 wt. % n-butane.

[0027] At block 204 of method 20, intermediate raffinate stream 115 is flowed to solvent recovery column 111B. Then, at block 205, solvent recovery column 111B removes solvent from intermediate raffinate stream 115 to produce recycle solvent stream 116 (comprising primarily solvent) and raffinate stream 103.

[0028] Method 20, according to embodiments of the invention, includes flowing raffinate stream 103 to distillation column 114, at block 206. Then, at block 207, in embodiments of the invention, distillation column 114 distills raffinate stream 103 to produce column overhead stream 104 and column bottoms stream 105. According to embodiments of the invention, the conditions for carrying out the distilling include an overhead boiling range of -7 to 0 °C, a reboiler boiling range of 1 to 5 °C, and a pressure in a range of 0.01 to 1 MPa. Column overhead stream 104, in embodiments of the invention, comprises primarily l-butene and isobutene, collectively and column bottoms stream 105 comprises primarily trans-2- butene and cis-2-butene, collectively.

[0029] At block 208, in embodiments of the invention, column overhead stream 104 is routed to membrane separation unit 112. According to embodiments of the invention, membrane separation unit 112 comprises a membrane adapted to separate hydrocarbon mixtures based on molecular size. In embodiments of the invention, at block 209, membrane separation unit 112 separates column overhead stream 104 into stream 107, comprising primarily 1 -butene, and stream 106, comprising primarily isobutene.

[0030] According to embodiments of the invention, the membrane of membrane separation unit 112 comprises crystalline microporous materials such as one or more zeolitic imidazolate framework (ZIF). ZIFs are structurally equivalent to zeolites and/or other crystalline materials, but with different building blocks. ZIFs typically have pore sizes of less than 2 nm. Their regular pore structure enables them to differentiate gas molecules based on their molecular size. ZIFs in this technology are developed and functionalized to be effective and stable membranes for gas separations, either in powder form or in a continuous membrane form. See US Patent Application No. 13/709,155. Preferably, column overhead

104 is fed to membrane separation unit 112 in a substantially gaseous phase. The separation process carried out by membrane separation unit 112 at block 209, in embodiments of the invention, can involve the separation of C2- hydrocarbons (e.g, hydrogen, methane, ethane, and ethylene) from C3+ hydrocarbons (e.g. , propane, propylene, butane, butylene, isobutene).

[0031] In embodiments of the invention, stream 106 comprises 98 wt. % to 99 wt. % isobutene. Stream 107, in embodiments of the invention, comprises 99 to 99.8 wt. % 1- butene.

[0032] Method 20, at block 210, can include flowing column bottoms stream 105 to isomerization unit 113. According to embodiments of the invention, column bottoms stream

105 comprises 50 wt. % to 60 wt. % trans-2-butene and 40 wt. % to 50 wt. % cis-2 -butene. Isomerization unit 113 is adapted to isomerize cis-2-butene and isobutene to form l-butene. So block 211, according to embodiments of the invention, comprises isomerizing at least some of the trans-2-butene and at least some of the cis-2-butene in column bottoms stream 105 to form l-butene. As shown in FIG. 1, such l-butene is comprised in isomerization unit effluent stream 108, which is flowed from isomerization unit 113, at block, 212, according to embodiments of the invention. According to embodiments of the invention, at block 211, isomerization unit 113 is operated to provide conditions for carrying out the isomerizing that includes a temperature in a range of 50 to 60 °C, a pressure in a range of 0 to 5 MPa, and a space velocity in a range of 1000 to 2000 h ¹ by using positional sulfocationic exchangers. In embodiments of the invention, isomerization unit effluent stream 108 comprises 99 wt. % to 99.8 wt. % l-butene.

[0033] At block 213, in embodiments of the invention, method 20 involves combining stream 174 with isomerization unit effluent stream 108 to form combined product stream 109. According to embodiments of the invention, combined product stream 109 comprises 99 wt. % to 99.8 wt. % l-butene.

[0034] Although embodiments of the present invention have been described with reference to blocks of FIG. 2, it should be appreciated that operation of the present invention is not limited to the particular blocks and/or the particular order of the blocks illustrated in FIG. 2. Accordingly, embodiments of the invention may provide functionality as described herein using various blocks in a sequence different than that of FIG. 2.

[0035] In the context of the present invention, at least the following 19 embodiments are described. Embodiment 1 is a method of producing l-butene. The method includes dehydrogenating n-butane to produce a first stream containing l-butene, isobutene, trans-2- butene, cis-2-butene, and n-butane. The method further includes separating the first stream by extractive distillation to produce a second stream containing primarily n-butane and a third stream containing primarily l-butene, iso-butene, trans-2-butene, cis-2-butene, collectively. The method even further includes distilling, in a distillation column, the third stream to form a fourth stream containing primarily iso-butene and l-butene, collectively and a fifth stream containing primarily trans-2-butene and cis-2-butene, collectively. The method also includes separating the fourth stream to produce a sixth stream containing primarily iso butene and seventh stream containing primarily l-butene. Embodiment 1 is the method of embodiment 1, wherein conditions for carrying out the dehydrogenating include a temperature in a range of 500 to 650 °C, a pressure in a range of 0 to 10 bar, and a GHSV in a range of 1000 to 5000 h ¹ . Embodiment 3 is the method of either of embodiments 1 or 2, wherein the dehydrogenating is catalyzed by a catalyst containing platinum and/or tin. Embodiment 4 is the method of either of embodiments 1 or 2, wherein the separating of the fourth stream is performed with a membrane. Embodiment 5 is the method of embodiment 4, wherein the membrane contains zeolitic imidazolate framework (ZIF). Embodiment 6 is the method of any of embodiments 1 to 5, further including isomerizing at least some of the trans-2-butene and at least some of the cis-2-butene of the fifth stream to form l-butene contained in an eighth stream. Embodiment 7 is the method of embodiment 6, wherein conditions for carrying out the isomerizing include a temperature in a range of 50 to 60 °C, a pressure in a range of 0 to 5 MPa, and a space velocity in a range of 1000 to 2000 h ¹ . Embodiment 8 is the method of any of embodiments 1 to 7, wherein the fourth stream contains 90 wt. % to 95 wt. % 1 -butene and 5 wt. % to 10 wt. % isobutene. Embodiment 9 is the method of any of embodiments 1 to 8, wherein the sixth stream contains 98 wt. % to 99 wt. % isobutene. Embodiment 10 is the method of any of embodiments 1 to 9, wherein the seventh stream contains 99 to 99.8 wt. % 1 -butene. Embodiment 11 is the method of any of embodiments 1 to 10, wherein first stream contains 20 wt. % to 30 wt. % 1 -butene, 2 wt. % to 5 wt. % isobutene, 25 wt. % to 35 wt. % trans-2-butene, 20 wt. % to 30 wt. % cis-2-butene, and 30 wt. % to 50 wt. % n-butane. Embodiment 12 is the method of any of embodiments 1 to 11, wherein the second stream is recycled to a dehydrogenation reactor that is carrying out the dehydrogenating. Embodiment 13 is the method of any of embodiments 1 to 12, wherein the second stream contains 98 to 99 wt. % n-butane. Embodiment 14 is the method of any of embodiments 1 to 13, wherein the third stream contains 30 wt. % to 40 wt. % 1 -butene and 2 wt. % to 5 wt. % iso-butene, 30 wt. % to 40 wt. % trans-2 -butene, and 20 wt. % to 30 wt. % cis-2-butene. Embodiment 15 is the method of any of embodiments 1 to 14, wherein the conditions for carrying out the distilling include an overhead boiling range of -7 to 0 °C, a reboiler boiling range of 1 to 5 °C, and a pressure in a range of 0.01 to 1 MPa. Embodiment 16 is the method of any of embodiments 1 to 15, wherein the fifth stream contains 50 wt. % to 60 wt. % trans-2 -butene, and 40 wt. % to 50 wt. % cis-2-butene. Embodiment 17 is the method of any of embodiments 1 to 16, wherein the eighth stream contains 99 wt. % to 99.8 wt. % 1 -butene. Embodiment 18 is the method of any of embodiments 1 to 16, further including combining the seventh stream and the eighth stream to form a ninth stream. Embodiment 19 is the method of embodiment 18, wherein the ninth stream contains 99 wt. % to 99.8 wt.% 1 -butene.

[0036] Although embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the above disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.