WO2020144576A1

WO2020144576A1 - Process intensification of mtbe synthesis unit

Info

Publication number: WO2020144576A1
Application number: PCT/IB2020/050089
Authority: WO
Inventors: Srikant Vasant BADGANDI; Umesh Krishna Hasyagar; Vinod Sankaran Nair
Original assignee: Sabic Global Technologies B.V.
Priority date: 2019-01-07
Filing date: 2020-01-07
Publication date: 2020-07-16

Abstract

A method of making methyl tert-butyl ether (MTBE) and related systems are disclosed. The method can include supplying a C-4 hydrocarbon containing feed stream to a first distillation column to produce a first stream comprising isobutylene, reacting the first stream with methanol in at least one MTBE reactor to produce a second stream comprising MTBE, supplying the second stream to a second distillation column to produce a third stream comprising MTBE and a fourth stream comprising unreacted isobutylene, and supplying the fourth stream to the first distillation column.

Description

PROCESS INTENSIFICATION OF MTBE SYNTHESIS UNIT

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional

Application No. 62/789,172, filed January 7, 2019, the contents of which is incorporated into the present application in its entirety.

FIELD OF INVENTION

[0002] The present invention generally relates to a process for producing methyl tert- butyl ether (MTBE). More specifically, the present invention concerns a process that positions an MTBE synthesis reaction unit in between an upstream distillation column and a downstream distillation column. The downstream distillation column can be configured to recycle unreacted isobutylene to the upstream distillation column, which allows for increased efficiency and higher percentage yield of MTBE product.

BACKGROUND OF THE INVENTION

[0003] MTBE is an organic compound that is used as an additive in gasoline to enhance the octane number of the gasoline. Since about 1970, MTBE has been synthesized by etherification of isobutylene by reacting it with methanol in the presence of an acidic catalyst. After etherification, the MTBE product from the reactor is separated from the unreacted materials and other impurities.

[0004] An example of such a reaction process is provided in US patent publication

US2009/0112030. In this publication, a purified isobutylene stream is fed to an MTBE reactor. The resulting MTBE product stream is introduced to a first pressure column to remove unreacted isobutane, which is recycled back to a dehydrogenation unit. The purified MTBE product stream is then introduced to a second pressure column to remove unreacted methanol, which is recycled back to the MTBE reactor. One of the problems associated with this process is that it fails to maximize the use of any potential unreacted isobutylene. A second problem with this process is that it relies on multiple downstream separation columns to produce a purified MTBE product stream, which can add costs and complexities to the process.

[0005] There have been attempts to maximize the complete conversion of isobutylene during the MTBE reaction process. These attempts have primarily focused on positioning a second MTBE reactor downstream from a first reactor, as described by Syed N. Naqvi in the December 2012 paper titled,“IHS PEP Review No. 2012-07: Methyl Tertiary Butyl Ether Production from Steam Cracker C4 Stream.” A problem associated with this approach is the reliance on multiple MTBE reactors, which can increase the costs and complexities associated with operating multiple reactors. The presence of MTBE in the feed stream to the second reactor is also problematic because it limits the conversion rate by pushing the reaction toward the reactants.

[0006] Overall, while methods of producing MTBE via etherification of isobutylene exist, these methods suffer from cost and/or isobutylene conversion inefficiencies.

BRIEF SUMMARY OF THE INVENTION

[0007] A solution to at least some of the above-mentioned problems associated with producing MTBE via etherification of isobutylene has been discovered. The solution resides in the configuration of a MTBE system that maximizes isobutylene conversion. In particular, the solution includes positioning an MTBE reactor in between an upstream distillation column and a downstream distillation column, where the downstream distillation column is configured to provide unreacted isobutylene to the upstream distillation. Without wishing to be bound by theory, it is believed that this set-up allows for greater conversion of isobutylene and ultimately a more cost efficient MTBE production process. Further, while the MTBE process and system configuration of the present invention can use multiple upstream and/or downstream distillation columns or other separation units, in some aspects only two distillation columns (the upstream and downstream columns) may be used, which can increase the efficiency of the process from a cost and/or complexity perspective. Similarly, while the processes and systems of the present invention can use multiple MTBE reactors ( e.g ., reactors positioned parallel or in series with one another), in some aspects only one MTBE reactor may be used, which can also increase the efficiency of the process from a cost and/or complexity perspective. Additional non limiting advantages of the present invention can include increased MTBE production while (1) having a simplified and compact system configuration, (2) reducing capital and operating costs when compared with the aforementioned conventional MTBE processes, (3) efficiently using floor space in the MTBE plant, and/or (4) realizing enhanced equipment performance.

[0008] In one aspect of the present invention, a method of producing MTBE is disclosed. The method can include supplying a C-4 containing feed stream to a first non- extractive distillation column operating at 25 °C to 100 °C to produce a first stream comprising isobutylene, reacting the first stream with methanol in at least one MTBE reactor to produce a second stream comprising MTBE, supplying the second stream to a second distillation column to produce a third stream comprising MTBE and a fourth stream comprising unreacted isobutylene, and supplying the fourth stream to the first distillation column. In a particular embodiment, the C-4 containing feed stream can be supplied from an isobutane dehydrogenation unit. In another embodiment, the C-4 containing feed stream can be supplied from a raffinate stream. In either instance, isobutylene can be present in the C-4 containing feed stream and can be considered an isobutylene enriched C-4 containing feed stream. The fourth stream can further comprise at least one of, any combination of, or all of isobutane, additional C-4 hydrocarbons other than isobutane and isobutylene, C-3 hydrocarbons, unreacted methanol, and/or MTBE. The first distillation column can further produce a fifth stream comprising isobutane. The fifth stream can be recycled to the isobutane dehydrogenation unit. In a particular aspect, the first and second distillation columns can each have a top portion and a bottom portion, wherein the fifth stream is produced in the top portion and the first stream is produced in the bottom portion of the first distillation column, and wherein the fourth stream is produced in the top portion and the third stream is produced in the bottom portion of the second distillation column.

[0009] In some instances, the pressure within the top portion of the upstream distillation column can be 1 bar to 20 bar, more preferably 5 bar to 10 bar, and most preferably 6 bar to 9 bar. The temperature within the top portion of the upstream distillation column can be 25 °C to 100 °C, more preferably 40 °C to 70 °C, and most preferably 45 °C to 50 °C. In some instances, the pressure within the bottom portion of the upstream distillation column can be 1 bar to 20 bar, more preferably 5 bar to 10 bar, and most preferably 6 bar to 9 bar. The temperature within the bottom portion of the upstream distillation column can be 25 °C to 100 °C, more preferably 45 °C to 80 °C, and most preferably 55 °C to 60 °C. In some instances, the pressure within the top portion of the downstream distillation column can be 1 bar to 20 bar, more preferably 5 bar to 10 bar and most preferably 6 bar to 9 bar. The temperature within the top portion of the downstream distillation column can be 25 °C to 150 °C, more preferably 50 °C to 100 °C, and most preferably 60 °C to 65 °C. In some instances, the pressure within the bottom portion of the downstream distillation column can be 1 bar to 20 bar, more preferably 5 bar to 10 bar and most preferably 6 bar to 9 bar. The temperature within the bottom portion of the downstream distillation column can be 50 °C to 200 °C, more preferably 100 °C to 170 °C, and most preferably 130 °C to 135 °C. As discussed in more detail below, pressures and temperatures outside these ranges for the first and second distillation columns are contemplated in the context of the present invention.

[0010] In some instances, the MTBE reactor can operate at 1 bar to 50 bar, more preferably 10 bar to 30 bar, and most preferably 15 bar to 20 bar. The MTBE reactor can operate at 25 °C to 100 °C, more preferably 30 °C to 70 °C, and most preferably 40 °C to 60 °C. As discussed in more detail below, pressures and temperatures outside these ranges for the MTBE reactor are contemplated in the context of the present invention. In some aspects, a second, third, fourth, or more MTBE reactors can be used. The additional reactors can be positioned in parallel with one another. Having the reactors positioned parallel to one another can be beneficial in instances where the primary MTBE reactor is shut down ( e.g . , to regenerate MTBE catalyst, to perform maintenance, etc.). In this situation, the secondary reactor(s) can be used to continue with the MTBE production process. It is also contemplated in the context of the present invention to have multiple reactors that are positioned downstream from one another. This can be beneficial to increase isobutylene conversion for any unreacted isobutylene coming out of the upstream MTBE reactor.

[0011] Also disclosed in the context of the present invention is a system for making

MTBE. The system can include an upstream distillation column that is configured to distill a C-4 feed stream to produce a first stream comprising isobutane and a second stream comprising isobutylene, at least one MTBE reactor that is configured to receive the second stream and produce a third stream comprising MTBE, and a downstream distillation column. The downstream distillation column can be configured to receive and distill the third stream to produce a fourth stream comprising MTBE and a fifth stream comprising unreacted isobutylene, and supply the fifth stream to the upstream distillation column. In one aspect, the system can include an isobutane dehydrogenation unit that is configured to supply the C-4 feed stream to the upstream distillation column. In another aspect, the C-4 feed stream can be supplied from a raffinate feed stream. In instances where the isobutane dehydrogenation unit is used, this unit can be configured to receive the first stream from the upstream distillation column. The system can include multiple MTBE reactors (e.g., second, third, fourth, or more) that can be positioned in parallel or in series to one another. The system can also include multiple upstream and/or multiple downstream distillation columns. [0012] The following includes definitions of various terms and phrases used throughout this specification.

[0013] 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%.

[0014] 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.

[0015] The term“substantially” and its variations are defined to include ranges within

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

[0016] The terms“inhibiting” or“reducing” or“preventing” or“avoiding” or any variation of these terms, when used in the claims and/or the specification, includes any measurable decrease or complete inhibition to achieve a desired result.

[0017] The term“effective,” as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.

[0018] 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.”

[0019] 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.

[0020] The process of the present invention can“comprise,”“consist essentially of,” or“consist of’ particular ingredients, components, compositions, etc., disclosed throughout the specification. With respect to the phrase“consisting essentially of,” a basic and novel characteristic of the present invention is the production of MTBE by using an MTBE reactor that is positioned such that it obtains a C-4 feed stream from an upstream distillation column and transfers its MTBE product stream to a downstream distillation column that is configured to recycle unreacted isobutylene to the upstream distillation column.

[0021] 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.

[0022] An MTBE reactor that is positioned“between” an upstream or first distillation column and a downstream or second distillation column refers to the upstream or first distillation column feeding the C-4 feed stream to the MTBE reactor and the MTBE reactor feeding its MTBE product stream to the downstream or second distillation column. In this context, positioned“between” does not refer to the physical positioning of the MTBE reactor such that it physically resides between the upstream and downstream reactors. It is contemplated in the context of the present invention that the MTBE reactor can be physically positioned such that it resides between the upstream or first and downstream or second distillation columns. It is also contemplated in the context of the present invention that the MTBE reactor may not be physically positioned between the upstream or first and downstream or second distillation columns. In the context of the present invention, the upstream distillation column can be referred to as the first distillation column, and vice versa. Similarly, the downstream distillation column can be referred to as the second distillation column, and vice versa.

[0023] The term“top” as that term is used in the specification and/or claims relating to a distillation column means the upper portion of the distillation column in which the products with lower boiling points and/or higher volatility are gathered and where those products exit the distillation column.

[0024] The term“bottom” as that term is used in the specification and/or claims relating to a distillation column means the lower portion of the distillation column in which the products with the higher boiling points and/or lower volatility are gathered and where those products exit the distillation column. [0025] 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

[0026] For a more complete understanding, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0027] FIG. 1 shows a schematic diagram of a system for producing MTBE, according to an embodiment of the invention where an MTBE reactor is positioned between an upstream distillation column and a downstream distillation column;

[0028] FIG. 2A shows a schematic diagram of another system for producing MTBE, according to an embodiment of the invention where two MTBE reactors are positioned between an upstream distillation column and a downstream distillation column and where the two MTBE reactors are positioned in series relative to one another; and

[0029] FIG. 2B shows a schematic diagram of another system for producing MTBE, according to an embodiment of the invention where two MTBE reactors are positioned between an upstream distillation column and a downstream distillation column and where the two MTBE reactors are positioned in parallel relative to one another.

DETAILED DESCRIPTION OF THE INVENTION

[0030] Currently, MTBE is produced by reacting isobutylene and methanol in a reactor and later separating the produced MTBE from the unreacted components and purging the unreacted components. However, this currently available method fails to utilize the unreacted isobutylene and/or relies on multiple downstream separation columns to optimize MTBE purification and production. These existing methods can be overly complicated, inefficient, and/or expensive.

[0031] It has been discovered in the context of the present invention that positioning an

MTBE reactor between an upstream distillation column and a downstream distillation column can improve the efficiency of the MTBE production process from a cost and/or complexity perspective. Without wishing to be bound by theory, it is believed that this set-up allows for a more efficient way to recycle unreacted isobutylene by transferring the unreacted isobutylene from the downstream distillation column back to the upstream distillation column.

[0032] These and other non-limiting aspects of the present invention are discussed in further detail in the following sections.

A. System for producing MTBE

[0033] In some embodiments of the invention, the system for producing MTBE includes an isobutane dehydrogenation unit, an upstream distillation column, an MTBE reactor, a downstream distillation column, and a recycle stream containing at least unreacted isobutylene. With reference to FIG. 1, a schematic diagram is shown of system 10 that is capable of producing MTBE with improved MTBE separation and/or reduced production cost compared to conventional methods. System 10 includes isobutane dehydrogenation unit 200, which feeds C-4 hydrocarbon feed stream 101 comprising isobutylene and isobutane to upstream distillation column 201. Dehydrogenation units remove hydrogen from organic molecules, which can result in the conversion of alkanes (e.g., isobutane) to olefins (e.g., isobutylene). By using an isobutane dehydrogenation unit, the feed stream 101 can contain a higher concentration of isobutylene. In an alternative embodiment of the invention, feed stream 101 can be supplied from a raffinate stream (not shown), which is a product stream from another process in which one or more components has been removed.

[0034] In some embodiments of the invention, feed stream 101 comprises 10 to 99 wt.

% isobutylene, preferably 30 to 50 wt. % isobutylene, and 1 to 90 wt. % isobutane, preferably 30 to 50 wt. % isobutane and any amounts in between. Other hydrocarbons including but not limited to 1,3 -butadiene, dimethyl ether (DME), isobutene, propane, propene, and/or any combination can be present in the C-4 hydrocarbon feed stream 101. Feed stream 101 can include 10 to 99 wt. % isobutylene, 10 to 90 wt. % isobutane, and 0 to 20 wt. % methanol, or combinations thereof. The composition of the feed stream 101 can include 20 to 40 wt. % isobutylene, 20 to 70 wt. % isobutane, 0 to 20 wt. % methanol, 0 to 20 wt. % MTBE, less than 5% C-3 isomers, and less than 0.5% water.

[0035] In embodiments of the invention, feed stream 101 is supplied to upstream distillation column 201, which can separate much of the isobutylene from the other C-4 hydrocarbons contained in the feed stream 101. In some embodiments of the invention, upstream distillation column 201 does not use extractive distillation. System 10 shows a fractionation distillation system for upstream distillation column 201, which includes condenser 202 and reboiler 203 in the reflux loop and boilup loop, respectively. Stream 102 (the“first stream”), generated as the bottom product from the upstream distillation column and comprising isobutylene, some isobutane, and some heavy hydrocarbons (C-5+ hydrocarbons), is sent to MTBE reactor 204. Stream 103, generated as the top product from the upstream distillation column and comprising isobutane, other C-4 hydrocarbons, and optionally methanol, is recycled back to the isobutane dehydrogenation unit 200. In some embodiments of the invention, stream 103 contains no methanol. In some embodiments of the invention, stream 103 is not recycled to the isobutane dehydrogenation unit (not shown). In some embodiments of the invention, stream 103 is recycled to the raffinate stream (not shown). In some embodiments of the invention, stream 103 is used as a product to send to other parts of the plant or to sell (not shown).

[0036] In some embodiments of the invention, the pressure within the top portion of the upstream distillation column 201 can be 1 bar to 20 bar, more preferably 5 bar to 10 bar, and most preferably 6 bar to 9 bar. The temperature within the top portion of the upstream distillation 201 column can be 25 °C to 100 °C, more preferably 40 °C to 70 °C, and most preferably 45 °C to 50 °C. In some embodiments of the invention, the pressure within the bottom portion of the upstream distillation column 201 can be 1 bar to 20 bar, more preferably 5 bar to 10 bar, and most preferably 6 bar to 9 bar. The temperature within the bottom portion of the upstream distillation column 201 can be 25 °C to 100 °C, more preferably 45 °C to 80 °C, and most preferably 55 °C to 60 °C. In some embodiments of the invention, the top portion of the upstream distillation 201 column operates at pressure and temperature ranges 6 bar to 9 bar and 45 °C to 50 °C, respectively, and the bottom portion the upstream distillation column 201 operates at pressure and temperature ranges 6 bar to 9 bar and 55 °C to 60 °C, respectively.

[0037] In the reflux loop, the more volatile compounds including most of the isobutane, other C-4 hydrocarbons in the feed, and a small amount of isobutylene exit the upstream distillation column 201 in overhead stream 103. Overhead stream 103 is fed to condenser 202, which condenses the heavier hydrocarbons in the overhead stream, such as the isobutylene in the stream, and sends the partially condensed overhead stream 103 to a reflux drum (not shown), which separates the condensed components of stream 103 from the gaseous components of stream 103. From the reflux drum, the condensed components of overhead stream 103 (the“reflux”) are pumped back into the upstream distillation column 201 for better fractionation and the remainder of overhead stream 103 exits the reflux loop as the top product, comprising isobutane and other C-4 hydrocarbons, and is recycled to the isobutane dehydrogenation unit 200. In some embodiments of the invention, overhead stream 103 comprises 95 to 99 wt. % isobutane, less than 3 wt. % isobutylene, and less than 2 wt. % propane, or combinations thereof. In some embodiments of the invention, the overhead stream does not include the reflux drum (not shown), but separation of the condensed portion of overhead stream 103 is still returned to upstream distillation column 201 for better fractionation than is achieved with no reflux loop.

[0038] In the boilup loop, the bottom stream 102, comprising most of the isobutylene, and some of the C-4 hydrocarbons, and some of the optional methanol, exits the column and is sent to reboiler 203. Reboiler 203 heats the bottom stream 102, separating the isobutylene in the stream 102 from the other C-4 hydrocarbons and methanol as the more volatile C-4 hydrocarbons and optional methanol evaporate. The vapor components of stream 102 return to the upstream distillation column 201 and the liquid isobutylene bottom product exits the boilup loop as the first stream, or bottom product stream 102 which is fed to the MTBE reactor 204. Like in the reflux loop, reintroducing the separated portion of stream 102 into the upstream distillation column 201 causes better fractionation than would be achieved without the boilup loop. In some embodiments of the invention, bottom stream 102 contains no methanol. In some embodiments of the invention, bottom product stream 102 comprises 40 to 60 wt. % isobutylene, 20 to 40 wt. % isobutane, 0 to 20 wt. % methanol, 0 to 20 wt. % MTBE, less than 0.5 wt. % C-3 isomers, and less than 0.5 wt. % water, or combinations thereof. In some embodiments of the invention, no boilup loop will be present (not shown), and the bottom product will exit the column 201 as stream 102, with no reentry to the column 201, to be sent to MTBE reactor 204. In some embodiments of the invention, a heater and/or heat exchanger will take the place of reboiler 203 (not shown). [0039] The upstream distillation column 201 is considered upstream of MTBE reactor

204 due to column 201 supplying bottom stream 102 containing isobutylene to the MTBE reactor 204. The“upstream” designation is not due to physical position. In some embodiments, MTBE reactor 204 will be physically positioned between upstream distillation column 201 and downstream distillation column 205. In some embodiments, MTBE reactor 204 will be physically positioned away from upstream distillation column 201 and/or downstream distillation column 205. In some embodiments of the invention, upstream distillation column 201 will be physically positioned between MTBE reactor 204 and downstream distillation column 205. In some embodiments of the invention, downstream distillation column 205 will be physically positioned between MTBE reactor 204 and upstream distillation column 201. Physical position may be altered as necessary for the plant construction or operation.

[0040] In embodiments of the invention, the first stream 102 is contacted with methanol stream 104 and fed into MTBE reactor 204 in the presence of an MTBE catalyst. In some embodiments of the invention, the first stream 102 entering the MTBE reactor 204 comprises 20 to 60 wt. % isobutylene, 20 to 40 wt. % isobutane, 0 to 20 wt. % MTBE, a constant methanol concentration such that the ratio of methanol to isobutylene is greater than 1, less than 0.5 wt. % C-3 isomers, and less than 0.5 wt. % water. In some embodiments of the invention, methanol stream 104 or another methanol stream may be added to feed stream 101 or added directly into the first upstream distillation column 201 (not shown). In some embodiments of the invention, methanol stream 104 is added to the MTBE reactor 204 before contacting with stream 102 (not shown). Increasing the concentration of reactants can create a higher yield and therefore greater production of MTBE. In some embodiments of the invention, methanol stream 104 comprises more than 99 wt. % methanol, less than 0.5 wt. % water, and less than 1 wt. % dimethyl ether (DME). In some embodiments of the invention, methanol stream 104 contains a concentration of methanol such that the mole ratio of methanol to isobutylene in the MTBE reactor 204 is greater than or equal to 1, preferably about 1: 1.

[0041] An MTBE catalyst that can be used with MTBE reactor 204 can be an acid catalyst including but not limited to one or more of the following, individually or in combination: Amberlyst 15/ 35 and CSP-3 are from Dow, CT-175 and CT-275 are from Purolite, K-2620 and K-2629 from Lanxess and SINOCATA S-600 (resin catalyst). The resin catalyst can have a particle size in a ranges of 0.5 to 0.9 mm, a surface area in a range of 20 to 55 m²/gm, and a pore volume in a range of 0.3 to 0.6 ml/gm Some non-limiting reactions that can take place in the MTBE reactor include reactions of isobutylene and methanol in the presence of a catalyst to produce MTBE (main reaction, also called MTBE Synthesis); isobutylene and water to form /-butyl alcohol (side reaction); methanol with itself to form DME and water (side reaction); and/or isobutylene with itself to form diisobutylene (side reaction). Stream 105 (the “second stream”) leaving the MTBE reactor 204 is a product stream comprising MTBE, unreacted isobutylene, and unreacted methanol. The second stream 105 is sent to downstream distillation column 205.

[0042] In some embodiments of the invention, the second stream 105 leaving the reactor comprises 50 to 70 wt. % MTBE, 20 to 40 wt. % isobutane, 0 to 10 wt. % unreacted isobutylene, less than 1 wt. % unreacted methanol, less than 0.5 wt. % C-3 isomers, and less than 0.5 wt. % water. In some embodiments of the invention, the MTBE reactor 204 can operate at 1 bar to 50 bar, more preferably 10 bar to 30 bar, and most preferably 15 bar to 20 bar. The MTBE reactor 204 can operate at 25 °C to 100 °C, more preferably 30 °C to 70 °C, and most preferably 40 °C to 60 °C. In some embodiments of the invention, the MTBE reactor

204 operates at pressure and temperature ranges 15 bar to 20 bar and 40 °C to 60 °C, respectively.

[0043] Downstream distillation column 205 will separate the MTBE from the remaining C-4 hydrocarbons, unreacted reactants, and side products. System 10 shows a fractionation distillation system for downstream distillation column 205, which includes condenser 206 and reboiler 207 in the reflux loop and boilup loop respectively. Stream 106 (the“third stream”), generated as the bottom product from the downstream distillation column

205 and comprising MTBE, some isobutylene, and some heavy hydrocarbons (C-5+ hydrocarbons), exits the boilup loop as a product stream. Stream 107 (the“fourth stream”) is generated as the top product from the downstream distillation column 205 and comprising unreacted isobutylene, some isobutane, other C-4 hydrocarbons, and methanol. In some embodiments of the invention, some or all of the fourth stream is recycled back to the C-4 hydrocarbon feed stream 101 to utilize the unreacted reactants and some of the fourth stream can be used as a purge stream to remove unwanted components from the process. Composition of feed stream 101 can change based on the amount and composition of stream 107 recycled to feed stream 101.

[0044] At startup, feed stream 101 will not combine with recycle stream 107 because no product has been produced. Until operating conditions are achieved, the composition of feed stream 101 can change as more of recycle stream 107 is added and equilibrium is achieved. During operation, stream 107 can be recycled to feed stream 101. In some embodiments of the invention, recycle stream 107 can be fed directly into upstream distillation column 201 without mixing with feed stream 101, such that feed stream 101 does not contain unreacted methanol (not shown). In some embodiments of the invention, recycle stream 107 can be recycled to the isobutane dehydrogenation unit 200 that supplies feed stream 101 (not shown). In some embodiments of the invention, no portion of product stream 107 is recycled (not shown).

[0045] In some embodiments of the invention, the pressure within the top portion of the downstream distillation column 205 can be 1 bar to 20 bar, more preferably 5 bar to 10 bar and most preferably 6 bar to 9 bar. The temperature within the top portion of the downstream distillation column 205 can be 25 °C to 150 °C, more preferably 50 °C to 100 °C, and most preferably 60 °C to 65 °C. In some embodiments of the invention, the pressure within the bottom portion of the downstream distillation column 205 can be 1 bar to 20 bar, more preferably 5 bar to 10 bar and most preferably 6 bar to 9 bar. The temperature within the bottom portion of the downstream distillation column 205 can be 50 °C to 200 °C, more preferably 100 °C to 170 °C, and most preferably 130 °C to 135 °C. In some embodiments of the invention, the top portion of the downstream distillation column 205 operates at pressure and temperature ranges 6 bar to 9 bar and 60 °C to 65 °C, respectively, and the bottom portion the downstream distillation column 205 operates at pressure and temperature ranges 6 bar to 9 bar and 130 °C to 135 °C, respectively. The downstream distillation column 205 is downstream of the MTBE reactor 204 because this system utilizes MTBE reactor 204 chronologically before downstream distillation column 205, not due to physical position, as with the upstream distillation column 201. Like with the upstream distillation column 201, the reflux loop and boilup loop as part of the downstream distillation process can be customized to the appropriate conditions for the process. In some embodiments of the invention, no reflux loop is used (not shown) and/or no boilup loop is used (not shown).

[0046] In the reflux loop, the more volatile compounds including most of the unreacted isobutylene, other C-4 hydrocarbons, methanol, and a small amount of MTBE exit the distillation column 205 in overhead stream 107. Overhead stream 107 is fed to condenser 206, which condenses the heavier hydrocarbons in the overhead stream 107, such as the MTBE in the stream, and sends the partially condensed overhead stream 107 to a reflux drum (not shown), which separates the condensed components of stream 107 from the gaseous components of stream 107. From the reflux drum, the condensed components of overhead stream 107 (the “reflux”) are pumped back into the distillation column 205 for better fractionation and the remainder of overhead stream 107 exits the reflux loop as the top product, also called the fourth stream, comprising isobutylene, other C-4 hydrocarbons, and methanol. In some embodiments of the invention, fourth stream 107 comprises 20 to 60 wt. % isobutane, 20 to 30 wt. % isobutylene, 0 to 0.5 wt. % propane, 0 to 20 wt. % MTBE, and 1 to 20 wt. % methanol, or combinations thereof. In some embodiments of the invention, the overhead stream does not include the reflux drum, but separation of the condensed portion of overhead stream 107 is still returned to distillation column 205 for better fractionation than is achieved with no reflux loop.

[0047] In the boilup loop, the bottom stream 106, comprising most of the MTBE, some of the C-4 hydrocarbons, and some of the methanol, exits the column and is sent to reboiler 207. Reboiler 207 heats the bottom stream 106, separating the MTBE in the stream 106 from the other C-4 hydrocarbons and methanol as the more volatile C-4 hydrocarbons and methanol evaporate. The vapor components of stream 106 return to the distillation column 205 and the liquid MTBE bottom product exits the boilup loop as the third stream, or bottom product stream 106. Like in the reflux loop, reintroducing the separated portion of stream 106 into the distillation column 205 causes better fractionation than would be achieved without the boilup loop. In some embodiments of the invention, bottom product stream 106 comprises more than 98 wt. % MTBE, less than 2 wt. % isobutylene, and less than 2 wt. % heavies (C-5+ hydrocarbons), or combinations thereof. In some embodiments of the invention, no boilup loop will be present, and the bottom product will exit the column as stream 106 including the MTBE product (not shown). In some embodiments of the invention, a heater and/or heat exchanger will take the place of reboiler 207 (not shown).

[0048] In embodiments of the invention, the C-4 hydrocarbon feed stream 101 flows through an isobutylene feed filter to reduce impurities therefrom (not shown). Methanol stream 104 can flow through a methanol filter to remove impurities including methane, ethane, ethanol, propane, propanol, other hydrocarbons, or combinations thereof (not shown). Filtration of impurities in the various streams helps to increase productivity in the process by reducing fouling of the catalyst. In embodiments of the invention, any of the streams can be heated or cooled to a predetermined temperature, which can be in a range of 20 to 250 °C and all ranges and values there between. [0049] In some embodiments of the invention, one or more distillation columns 201 and 205 will be a distillation without a condenser and reboiler system to increase fractionation (not shown). In some embodiments of the invention, the upstream 201 and/or the downstream 205 distillation columns will be part of a system of distillation columns or other separation units upstream and or downstream of the MTBE reactor 204, respectively, to create a better separation of components (not shown). In some embodiments of the invention, one or more distillation columns may be replaced with another type of separation unit, using techniques such as gas-liquid chromatography, fractionation with molecular sieve absorbents, and/or thermal diffusion (not shown).

[0050] In some embodiments of the invention, more than one MTBE reactor is present.

The multiple reactors can be positioned in series or parallel. With reference to FIG. 2A, system 20 shows two MTBE reactors 204 and 208 are positioned in series relative to one another. Having the reactors 204 and 208 positioned in this manner can lead to a greater yield of MTBE by having greater conversion of isobutylene. Stream 105A exiting the MTBE reactor 204 comprises MTBE, unreacted isobutylene, and unreacted methanol, and is fed to second MTBE reactor 208, which produces stream 105B (the“second stream”). More methanol from stream 104 can be added to the second MTBE reactor 208. In some embodiments of the invention, methanol is added to the feed stream 105A. In some embodiments of the invention, no methanol is added to the second reactor and only the unreacted methanol in the feed stream 105A is used (not shown). In some embodiments of the invention, at least one reactor is a batch reactor and methanol is added to the reactor prior to supplying the feed to the reactor (not shown). Stream 105B also comprises MTBE, unreacted isobutylene, and unreacted methanol. In some embodiments, no methanol and/or no isobutylene will be present in stream 105B. Stream 105B comprises a higher yield of MTBE than stream 105A.

[0051] With reference to FIG. 2B, system 30 shows two MTBE reactors 204 and 208 that are positioned in parallel relative to one another. In some embodiments of the invention, the first stream 102 will be sent to both MTBE reactors 204 and 208, which operate at the same time. In some embodiments of the invention, one reactor is in use at a time, and the use of each reactor can be alternated for cleaning, smoother operation, maintenance, and/or batch operation. In some embodiments of the invention, methanol can be fed directly to both reactors, mixed with the first stream 102, and/or placed in the reactors operating as batch reactors. In some embodiments of the invention, the multiple reactors can be in both parallel and series (not shown).

B. Method of producing MTBE

[0052] A method of producing MTBE has been discovered that is capable of reducing waste of key components of the process and/or increasing MTBE production rate compared to conventional methods. Embodiments of the invention include a method for producing MTBE by implementing systems 10, 20, or 30 from FIG. 1, FIG. 2A, or FIG. 2B, respectively, or from utilizing the system variations described in Section A.

[0053] Although embodiments of the present invention have been described with reference to systems of FIG. 1, FIG. 2A, and FIG. 2B, it should be appreciated that operation of the present invention is not limited to the particular systems and/or the particular order of the systems illustrated in the figures. Accordingly, embodiments of the invention can provide functionality as described herein using various steps in a sequence different than that of the figures.

[0054] 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 can be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

EXAMPLES

[0055] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results.

Example 1

(Production of MTBE with One Reactor and Two Distillation Columns)

[0056] MTBE production from a reaction between methanol and isobutylene was simulated using ASPEN PLUS V10 software, including custom membrane models developed using Aspen Custom Modeler. FIG. 1 is a schematic that was used in the simulation. In the simulation, an upstream distillation column 201, an MTBE reactor 204, and a downstream distillation column 205 were used. First, a C-4 hydrocarbon feed stream 101 was mixed with a recycle stream 107 from the top product stream of the downstream distillation column 205, and the resulting mixed stream was supplied to the upstream distillation column 201. The upstream distillation column 201 separated the feed 101 into an overhead stream 103 containing isobutane and other C-4 hydrocarbons and a bottom product stream 102 containing isobutylene. The isobutylene bottom product stream 102 was pumped to the MTBE reactor 204, and mixed with a methanol feed stream 104 before entering the MTBE reactor 204. The reacted product stream 105 exited the MTBE reactor and was supplied to the downstream distillation column 205. The downstream distillation column 205 separated the unreacted isobutylene, unreacted methanol, isobutane, and side products from the MTBE into the overhead stream 107 and bottom product 106 streams, respectively. A portion of the overhead stream 107 containing isobutylene, methanol was used as a recycle stream, which was recycled back to the C-4 hydrocarbon feed 101 and the remainder as a purge stream. Each distillation column in the model used a reflux loop and a boilup loop.

[0057] For the simulation, the following assumptions were made: (1) the C-4 feed stream 101 was fixed at a rate of 77.5 tons/hr with isobutylene and isobutane in a ratio of 50 wt.% each; (2) the mol. ratio of methanol to isobutylene used in the MTBE reactor 204 was approximately 1; (3) isobutylene conversion is varied from 85 to 95% using RStoic reactor model in ASPEN PLUS V10 software; and (4) the upstream distillation column 201 had 50 to 200 trays, a reflux ratio of 10 to 30, and a feed injection point corresponding to tray number in the range of 40 to 190, and the downstream distillation column 205 had 15 to 35 trays, a reflux ratio of 1 to 5, and a feed injection point corresponding to tray number in the range of 8 to 15. The upstream 201 and downstream 205 distillation columns can be optimized to obtain maximum purity of MTBE and isobutylene, respectively, as in this example. Based on the simulation of the proposed scheme in FIG. 1, the results in Table 1 are obtained.

Table 1

(Typical Mass Balance)

[0058] The compositions of each stream listed in Table 1 are provided in Table 2.

Table 2: Composition of Each Stream by Percentage Weight

Claims

1. A method of making methyl tert- butyl ether (MTBE), the method comprising:

(a) supplying a C-4 containing feed stream to a first distillation column to produce a first stream comprising isobutylene;

(i) wherein the first distillation column operates at 25 °C to 100 °C; and

(ii) wherein the first distillation column does not use extractive distillation;

(b) reacting the first stream with methanol in at least one MTBE reactor to produce a second stream comprising MTBE;

(c) supplying the second stream to a second distillation column to produce a third stream comprising MTBE and a fourth stream comprising unreacted isobutylene; and

(d) supplying the fourth stream to the first distillation column.

2. The method of claim 1, wherein the C-4 containing feed stream is supplied from an isobutane dehydrogenation unit.

3. The method of any one of claims 1 to 2, wherein the fourth stream further comprises at least one of isobutane, additional C-4 hydrocarbons other than isobutane and isobutylene, C-3 hydrocarbons, unreacted methanol, or MTBE.

4. The method of claim 2, wherein the first distillation column further produces a fifth stream comprising isobutane, and wherein the fifth stream is recycled to the isobutane dehydrogenation unit.

5. The method of claim 4, wherein the first and second distillation columns each have a top portion and a bottom portion, wherein the fifth stream is produced in the top portion and the first stream is produced in the bottom portion of the first distillation column, and wherein the fourth stream is produced in the top portion and the third stream is produced in the bottom portion of the second distillation column.

6. The method of claim 5, wherein the pressure and temperature within the top portion of the first distillation column is 6 bar to 9 bar and 45 °C to 50 °C, respectively, and the pressure and temperature within the bottom portion the first distillation column is 6 bar to 9 bar and 55 °C to 60 °C, respectively.

7. The method of claim 5, wherein the pressure and temperature within the top portion of the second distillation column is 6 bar to 9 bar and 60 °C to 65 °C, respectively, and the pressure and temperature within the bottom portion of the second distillation column is 6 bar to 9 bar and 130 °C to 135 °C, respectively.

8. The method of any one of claims 1 to 2, wherein the pressure and temperature in the at least one MTBE reactor is 15 bar to 20 bar and 40 °C to 60 °C, respectively.

9. The method of any one of claims 1 to 2, wherein step (b) is performed in the presence of an MTBE catalyst.

10. The method of any one of claims 1 to 2, further comprising a second MTBE reactor that is positioned in parallel with the at least one MTBE reactor.

11. The method of any one of claims 1 to 2, further comprising a second MTBE reactor that is positioned in series with the at least one MTBE reactor.

12. The method of any one of claims 1 to 2, wherein the first stream comprises 30 to 50% by weight of isobutylene, 30 to 50% by weight of isobutane, 0 to 15% by weight of C- 4 isomers other than isobutene or isobutylene, less than 2% by weight of 1,3 butadiene, less than 1% by weight of dimethoxyethane, less than 1% by weight of C-3 hydrocarbons, and less than 1% by weight of heavy hydrocarbons.

13. The method of any one of claims 1 to 2, wherein the second stream comprises at least 50% by weight of MTBE.

14. The method of any one of claims 1 to 2, wherein the third stream comprises at least 90%, preferably at least 95%, or more preferably at least 98 % by weight of MTBE.

15. The method of any one of claims 1 to 2, wherein the fourth stream comprises 20 to 60% by weight of isobutane, 20 to 30% by weight of isobutylene, 0 to 20% by weight of MTBE, 0 to 20% by weight of methanol, and 0 to 0.5% by weight of propane.

16. A system for making methyl tert- butyl ether (MTBE), the system comprising:

(a) an upstream distillation column that is configured to distill a C-4 feed stream to produce a first stream comprising isobutane and a second stream comprising isobutylene;

(b) at least one MTBE reactor that is configured to receive the second stream and produce a third stream comprising MTBE; and

(c) a downstream distillation column that is configured to:

(i) receive and distill the third stream to produce a fourth stream comprising MTBE and a fifth stream comprising unreacted isobutylene; and

(ii) supply the fifth stream to the upstream distillation column.

17. The system of claim 16, further comprising an isobutane dehydrogenation unit that is configured to supply the C-4 feed stream to the upstream distillation column.

18. The system of claim 17, wherein the isobutane dehydrogenation unit is configured to receive the first stream from the upstream distillation column.

19. The system of any one of claims 16 to 17, further comprising a second MTBE reactor that is positioned in parallel with the at least one MTBE reactor.

20. The system of any one of claims 16 to 18, further comprising a second MTBE reactor that is positioned in series with the at least one MTBE reactor.