WO2019116202A1

WO2019116202A1 - Mtbe process with improved specific c4 consumption

Info

Publication number: WO2019116202A1
Application number: PCT/IB2018/059833
Authority: WO
Inventors: Sunil Shivajirao DHUMAL; Sethuraman Balasubramaniyan; Arijit GANGULI; Vinod Sankaran Nair
Original assignee: Sabic Global Technologies B.V.
Priority date: 2017-12-11
Filing date: 2018-12-10
Publication date: 2019-06-20

Abstract

A method of producing methyl tertiary butyl is disclosed. The method involves removing n-butane and/or other light hydrocarbons from an isobutane stream separated from a C4 hydrocarbon stream such that the isobutane is of high purity. The purification of the isobutane stream can be carried out by molecular sieves. The highly purified isobutane stream is then dehydrogenated to form isobutylene. The isobutylene is reacted with methanol to produce MTBE.

Description

MTBE PROCESS WITH IMPROVED SPECIFIC C4 CONSUMPTION

CROSS REFERENCE TO RELATED APPLICATIONS

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

Application No. 62/597,398, filed December 11, 2017, which is hereby incorporated by reference in its entirety.

FIELD OF INVENTION

[0002] The present invention generally relates to the production of methyl tertiary butyl ether (MTBE). More specifically, the present invention relates to the production of MTBE in a process that includes utilizing molecular sieves to purify a feed stream to one of the reactor units used in the process.

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 by reacting isobutylene with methanol in the presence of an acidic catalyst. Global demand for MTBE has prompted several petrochemical companies to synthesize MTBE by isomerizing n-butane to form isobutane, followed by isobutane dehydrogenation to isobutylene and then isobutylene etherification. In this process, typically, a mixed C₄ stream (isobutane + n-butane + traces of light and heavy impurities) is fed to a deisobutanizer (DIB) column (single column with side draw or multiple columns) for separation of n-butane and other impurities from isobutane.

[0004] Complete separation of the components of the hydrocarbon mixture is not possible in practice due to column limitations as well as other process factors such as issues related to temperature and pressure control, isomerization section performance, variation in feed composition, condenser and reboiler performance, etc. The C₄ specific consumption of a MTBE production process is a ratio of mass of C₄ mixture/mass of MTBE produced from the mass of C₄ mixture. A theoretical specific consumption of mixed C₄ (n-butane + isobutane) per mass of MTBE produced is 0.6595. Achieving this specific consumption number is difficult and probably not achievable because of selectivity losses at each stage of the process. Achievable C₄ specific consumption is approximately 0.74 to 0.82 based upon the separation efficiencies and catalyst performance. One of the major factors that can cause an increase in C₄ specific consumption is n-butane slippage into the dehydrogenation section. When this happens, the n-butane gets coked and cracked into smaller molecules due to severe process conditions in the dehydrogenation section. [0005] In one conventional MTBE production method, a C₄ separation section separates a fresh C₄ mixture. Specifically, multiple distillation columns remove isobutane along with traces of light components and n-butane (the major impurity) as overhead and removes n-butane and other heavy components as bottom product. If a single column is used in the C₄ separation section, then n-butane is removed as a side draw whereas heavy components like Cs’s are removed as bottom product. The bottom product is fed to a recovery section. N-butane, which, as noted above, can be either removed as side draw or overhead product, is sent to an isomerization section where it is isomerized. The isomerized product goes through a separation process in a stabilizer column where light ends are removed as overhead product and used as fuel gas. Bottom product (isobutane and n-butane) from the stabilizer column is fed back to the C₄ separation section along with the fresh feed. Isobutane, removed as overhead product from the C₄ separation section, along with n-butane as the major impurity, is fed to a dehydrogenation section to synthesize isobutylene in the presence of Cr-Al or Pt-Al catalyst at a temperature of 500-650 °C.

[0006] N-butane is consumed across the dehydrogenation section as it is converted to unwanted products like coke, light hydrocarbons, butenes, etc. Such loss of n-butane leads to higher C₄ specific consumption of the overall process. The dehydrogenated product goes through low temperature recovery section to remove light ends from the C₄ mixture. Light ends are used as a hydrogen (Eb) source as well as fuel gas source. The separated C₄ mixture (rich in isobutane and isobutylene) is then sent to an MTBE synthesis unit for selective removal of isobutylene by methanol etherification reaction. A raffinate stream (rich in isobutane) generated after MTBE synthesis is sent back to the isobutane storage vessel. Overall, in this conventional process, the cracking of n-butane to produce products with smaller molecules leads to losses in C₄ specific consumption as well as increased load on downstream operations. BRIEF SUMMARY OF THE INVENTION

[0007] A method has been discovered for producing MTBE in a process that controls n-butane slippage from the C₄ separation section, which supplies isobutane to the dehydrogenation section, into the dehydrogenation section.

[0008] Embodiments of the invention include a method of producing MTBE. The method includes separating a C₄ hydrocarbon stream that comprises primarily isobutane and n-butane collectively into (1) a first stream comprising primarily isobutane, where the first stream further includes n-butane and (2) a second stream comprising primarily n-butane. The method further includes separating the first stream, by molecular sieves, into a purified isobutane stream comprising 98 to 99.99 wt. % iso-butane and a purified n-butane stream comprising 90 to 100 wt. % n-butane, wherein 100 wt. % of the purified isobutane stream is a total wt. % of n-butane and isobutane in the purified isobutane stream and 100 wt. % of the purified n-butane stream is a total wt. % of n-butane and isobutane in the purified n-butane stream. The method also includes dehydrogenating the isobutane in the purified isobutane stream to form isobutylene and reacting the isobutylene with methanol under reaction conditions sufficient to form a product stream of MTBE.

[0009] Embodiments of the invention include a method of producing MTBE. The method includes separating a crude C₄ hydrocarbon stream that comprises primarily isobutane and n-butane collectively into (1) a first stream comprising primarily isobutane, where the first stream further includes n-butane and (2) a second stream comprising primarily n-butane. The method further includes separating the first stream, by molecular sieves, into a purified isobutane stream comprising 98 to 99.99 wt. % isobutane and a purified n-butane stream comprising 90 to 100 wt. % n-butane, wherein 100 wt. % of the purified isobutane stream is a total wt. % of n-butane and isobutane in the purified isobutane stream and 100 wt. % of the purified n-butane stream is a total wt. % of n-butane and isobutane in the purified n- butane stream. The separating includes adsorbing n-butane from the first stream onto the molecular sieves. The method also includes desorbing the molecular sieves to release the adsorbed n-butane into the purified n-butane stream. Additionally, the method includes isomerizing the n-butane in the purified n-butane stream to form additional isobutane. Further, the method includes dehydrogenating the isobutane in the purified isobutane stream to form isobutylene and reacting the isobutylene with methanol under reaction conditions sufficient to form a product stream of MTBE. [0010] The following includes definitions of various terms and phrases used throughout this specification.

[0011] 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%.

[0012] The terms“wt. %”,“vol.%” or“mol.%” refers 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.

[0013] The term“substantially” and its variations are defined to include ranges within

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

[0014] 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.

[0015] The term“effective,” as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.

[0016] The term“primarily,” as that term is used in the specification and/or claims, means greater than any of 50 wt. %, 50 mol. %, or 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, 50.1 vol. % to 100 vol. % and all values and ranges there between.

[0017] 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.”

[0018] 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.

[0019] The process of the present invention can“comprise,”“consist essentially of,” or“consist of’ particular ingredients, components, compositions, etc., disclosed throughout the specification.

[0020] 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

[0021] For a more complete understanding, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: [0022] FIG. 1 shows a system for producing MTBE, according to embodiments of the invention; and

[0023] FIG. 2 shows a method for producing MTBE, according to embodiments of the invention.

DETATEED DESCRIPTION OF THE INVENTION [0024] The effectiveness of the C₄ separation prior to isomerization and dehydrogenation is an important step in the on-purpose MTBE synthesis. Any operational or design issues in this step leads to higher C₄ specific consumption through n-butane slippage into the dehydrogenation section instead of getting used in the isomerization section to make isobutane. Slipped n-butane goes through coking and cracking reactions to form small molecules as well as coke. This can result in increased C₄ consumption per mass of MTBE synthesized. These side reactions can also increase the load on downstream units ( e.g ., separation, recycle, pumping, heating, cooling, etc.). The dehydrogenation catalyst also goes through sintering (deactivation) triggered by local higher temperatures during regeneration. Coke is one of the factors that cause local higher temperature to be generated during regeneration.

[0025] A method has been discovered for producing MTBE. The method involves a dehydrogenation reactor dehydrogenating isobutane that originates from a C₄ mixture, where the isobutane stream is purified prior to supplying it to the dehydrogenation reactor. The refining includes removing hydrocarbons, such as n-butane, from the isobutane stream. The removed n-butane can be isomerized to produce additional isobutane. According to embodiments of the invention, adsorption media removes n-butane and other light components from the isobutane stream prior to supplying the isobutane stream to the dehydrogenation unit. The n-butane is desorbed and reused in the isomerization section of the process. Table 1 shows the molecular sizes of all relevant hydrocarbons.

Table 1

Molecular size of hydrocarbon molecule

[0026] As can be seen from Table 1, isobutane’s molecular size is higher than all the other hydrocarbons listed and, thus, isobutane can be separated from those other hydrocarbons by adsorption. According to embodiments of the invention, a molecular sieve separation unit will separate the n-butane and other relevant light components from, for example, the C₄ separation overhead product of the conventional process described above. This can purify the isobutane stream significantly prior to its entry into the dehydrogenation section of the MTBE production process. Adsorption and desorption operations implemented by multiple beds can ensure n-butane removal along with other light components and bed regeneration for further adsorption takes place in a continuous manner. The separated n- butane stream along with other light components can be fed to the isomerization reactor unit as part of the isomerization unit’s regular feed stream. Light components can pass through the isomerization reactor unit as inert and can be separated in a stabilizer column located just after the isomerization reactor unit. Further, relevant light components (for example, propane) can also be recovered using the same principle or by some other means like connecting stabilizer gas output to a low temperature recovery section, etc.

[0027] Using the molecular sieves as described above can result in better C₄ specific consumption, reduction in downstream load and removal of catalyst deactivation events due to n-butane and other light components related failure modes, if any. The molecular sieve separation of embodiments of the invention can be operated either in vapor or liquid phase. Further, the molecular sieve separation unit can be operated as an optional unit in an MTBE production process based on operations requirements and with a bypass provision.

[0028] Embodiments of the invention can be implemented in refineries and petrochemical plants with C₄ separation units to recover C₄ being lost in those plants. Embodiments of the invention can also be used to recover C₄ from bottom streams as well. In embodiments of the invention, molecular sieves offer superior recovery when compared to other recovery methods such as recovery by distillation column, membrane separation, special distillation units like extractive distillation, etc.

[0029] FIG. 1 shows system 10 for producing MTBE, according to embodiments of the invention. FIG. 2 shows method 20 for producing MTBE, according to embodiments of the invention. Method 20 may be implemented by using system 10.

[0030] Method 20 as implemented by system 10 may begin at block 200, which includes feeding fresh C₄ mixture 100 to C₄ separation unit 103. According to embodiments of the invention, C₄ mixture 100 comprises primarily isobutane and n-butane collectively. According to embodiments of the invention, C₄ mixture 100 comprises 70.5 to 74 wt. % isobutane, 23 to 25.5 wt. % n-butane, 1.8 to 3 wt. % propane and 0.8 to 1.2 wt. % heavies (Cs’s). In embodiments of the invention, C₄ mixture 100 is a crude C₄ stream. A crude C₄ stream is a byproduct stream produced in a cracking process to produce olefins. The crude C₄ stream can comprise butadiene, isobutylene, 2-butene, l-butene, acetylene, isobutane, and n-butane.

[0031] C₄ separation unit 103 is adapted to separate C₄ mixture 100. In block 201, C₄ separation unit 103 separates C₄ mixture 100 into stream 104 (overhead stream), stream 105, and stream 106. According to embodiments of the invention, stream 105 comprises heavies that are sent to a recovery section. Stream 104 may include primarily isobutane with n- butane and propane as the major impurities (some amount of C₃’s (propane + propylene) may be present). Stream 104, according to embodiments of the invention, comprises 95 to 97.5 wt. % isobutane, 0.9 to 1.3 wt. % n-butane, and 1.8 to 3.5 wt. % lights components (C₃’s). Stream 106 comprises primarily n-butane. According to embodiments of the invention, stream 106 comprises 92.5 to 93.7 wt. % n-butane, 5 to 5.5 wt. % isobutane, and 0.8 to 2 wt. % heavies (Cs’s). If C₄ separation unit 103 is adapted for multiple distillation column separation, stream 106 can comprise n-butane along with other heavy products removed in a bottom stream. If C₄ separation unit 103 is adapted for single column separation, stream 106 can comprise n-butane removed as a side draw and heavy products removed as a bottom stream.

[0032] Method 20 may include, at block 202, flowing stream 104 to separation unit 107. In embodiments of the invention, separation unit 107 has molecular sieves for separating the isobutane of stream 104 from other components of stream 104. The molecular sieves may include zeolite molecular sieves. Thus, the separating can include adsorbing n-butane from stream 104 onto the molecular sieves at block 203. The separating at block 203 may be carried out at a temperature in the range 10 to 400 °C and all values and ranges there between including 10 to 50 °C, 50 to 100 °C, 100 to 150 °C, 150 to 200 °C, 200 to 250 °C, 250 to 300 °C, 300 to 350 °C, and 350 to 400 °C, an adsorption pressure in a range of 0.9 to 140 bara and all values and ranges there between including 0.9 to 20 bara, 20 to 40 bara, 40 to 60 bara, 60 to 80 bara, 80 to 100 bara, 100 to 120 bara, and 120 to 140 bara, and a desorption pressure in a range of 0.01 to 0.25 bara and all values and ranges there between including 0.01 to 0.05 bara, 0.05 to 0.10 bara, 0.10 to 0.15 bara, 0.15 to 0.20 bara, and 0.20 to 0.25 bara. Subsequently, the molecular sieves can be desorbed to release the adsorbed n- butane into stream 108 (the purified n-butane stream). The desorbing may be carried out at a temperature between 10 to 400 °C, an adsorption pressure in a range of 0.9 to 140 bara, and a desorption pressure in a range of 0.01 to 0.25 bara. Thus, according to embodiments of the invention, at block 203, separation unit 107 separates stream 104 into purified isobutane stream 109, comprising 98 to 99.99 wt. % isobutane, and a purified n-butane stream (stream 108), comprising 98 to 100 wt. % n-butane, wherein 100 wt. % of purified isobutane stream 109 is a total wt. % of n-butane and isobutane in purified isobutane stream 109 and 100 wt. % of purified n-butane stream 104 is a total wt. % of n-butane and isobutane in purified n- butane stream 104. At block 204, purified isobutane stream 109 is flowed to isobutane storage 116 and then to dehydrogenation reactors 118. In isobutane storage 116, purified isobutane stream 109 may be mixed with raffinate 127 from MTBE synthesis unit 126.

[0033] At block 205, dehydrogenation reactors 118 dehydrogenate isobutane of stream 117 (which may comprise purified isobutane stream 109 or purified isobutane stream 109 and raffinate 127) to form isobutylene. In embodiments of the invention, the dehydrogenation at block 205 includes a temperature in a range of 500 to 700 °C, a pressure in a range of 0.4 to 2 bar, and a weight hourly space velocity in a range of 0.8 to 2 hr ¹. The dehydrogenation at block 205 may take place in presence of either Cr-Al and/or Pt-Al catalyst. Dehydrogenating stream 117 includes dehydrogenating the isobutane in purified isobutane stream 109 to form isobutylene in dehydrogenation reactor effluent stream 119. In embodiments of the invention, dehydrogenation reactor effluent stream 119 comprises 42 to 47 wt. % isobutane, 49.5 to 52.5 wt. % isobutylene, and 1 to 1.75 wt. % C₃’s (propane+propy 1 ene) .

[0034] At block 206, according to embodiments of the invention, dehydrogenation reactor effluent stream 119 is flowed to low temperature recovery section 120, which removes lights ends from dehydrogenation reactor effluent stream 119 (comprising isobutylene) to form hydrogen and fuel gas stream 121 and form stream 122 (comprising isobutylene). At block 207, stream 122 (comprising isobutylene) is flowed to C3 recovery column 123, which recovers C3 hydrocarbons from stream 122 to form stream 125. Stream 125 may comprise 49.4 to 52.9 wt. % isobutylene and 42.3 to 46.7 wt. % isobutane.

[0035] At block 208, methanol and stream 125 are flowed to MTBE synthesis unit

126. At block 209, the isobutylene of stream 125 is reacted with methanol 128 in MTBE synthesis unit 126. The reacting of the isobutylene with methanol takes place under reaction conditions sufficient to form MTBE product stream 129. In embodiments of the invention, the reaction conditions for the MTBE synthesis step include a temperature in a range of 40 to 85 ^°C, a pressure in a range of 5 to 16 bar, and a weight hourly space velocity in a range of 10 to 25 hr ¹.

[0036] Considering one of the other streams flowing from separation unit 107, in embodiments of the invention, at block 210, stream 106 (from C₄ separation unit 103) and stream 108 (from separation unit 107) are flowed to isomerization unit 111. Stream 106 and stream 108 may be flowed together to isomerization unit 111 as stream 110. Stream 106 and stream 108 may also be flowed separately to isomerization unit 111. At block 211, hydrogen is also flowed to isomerization unit 111. It should be noted that stream 106 is shown as the means of removing n-butane from C₄ separation unit 103 to isomerization unit 111, but it should be noted that n-butane could also be removed as a bottom stream to isomerization unit 111 in embodiments of the invention. At block 212, isomerization unit 111 isomerizes n- butane of stream 110 to form isobutane. In this way, there is isomerizing of the n-butane in stream 110 (stream 108 and/or stream 106) to form additional isobutane. The reaction conditions for the isomerizing at block 212 include a temperature in a range 140 to 240 °C, a pressure in a range of 25 to 32 bar, and a weight hourly space velocity in a range of 5 to 10 hr ¹. At block 213, stream 113, which comprises the formed isobutane may be flowed from isomerization unit 111 to stabilizer column 114. Stabilizer column 114 removes light ends as an overhead product, which is used as fuel gas 115, at block 214, at block 215. Stream 102 (stabilizer bottom product), which comprises primarily n-butane and isobutane, flows from stabilizer column 114 and can be fed back to C₄ separation unit 103 along with C₄ mixture 100. As illustrated by block 214 and block 215, embodiments of the invention include stream 102 (effluent from the isomerizing) being sent to the separating process carried out by C₄ separation unit 103.

[0037] Processing an isobutane stream derived from a C₄ hydrocarbon mixture, prior to sending the isobutane stream to further processing to produce MTBE, according to embodiments of the invention, provides certain advantages. For example, C₄ specific consumption can be improved. In embodiments of the invention, the C₄ specific consumption achieved in the production of MTBE is in a range of 0.73 to 0.85. Further, operations downstream the C₄ separation (e.g., recycle, pumping, heating, cooling, separation, etc.) will become easier due to a lower amount of cracked products. Further yet, catalyst performance may increase due to reduced coking through a reduction in local temperature during regeneration. [0038] 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.

[0039] As part of the disclosure of the present invention, specific examples are included below. The examples are for illustrative purposes only and are not intended to limit the invention. Those of ordinary skill in the art will readily recognize parameters that can be changed or modified to yield essentially the same results.

EXAMPLE

Table 2

Sample calculation for n-Butane recovery from C₄ stream

[0040] Table 2 shows sample calculations for n-butane recovery from C₄ stream with

50 tons per hour and 100 tons per hour overhead product scenarios. Table 2 illustrates the amount of MTBE produced from lost n-butane with its delta impact on C₄ specific consumption for different levels (wt. %) of n-butane presence in the C₄ separation unit overhead stream.

[0041] In the context of the present invention, embodiments 1-14 are described. Embodiment 1 is a method of producing methyl tertiary butyl ether (MTBE). The method includes separating a C₄ hydrocarbon stream that includes primarily isobutane and n- butane collectively, into a first stream comprising primarily isobutane, the first stream further comprising n-butane, and a second stream comprising primarily n-butane. The method further includes separating the first stream, by molecular sieves, into a purified isobutane stream comprising 98 to 99.99 wt. % isobutane and a purified n-butane stream comprising 90 to 100 wt. % n-butane, wherein 100 wt. % of the purified isobutane stream is a total wt. % of n-butane and isobutane in the purified isobutane stream and 100 wt. % of the purified n- butane stream is a total wt. % of n-butane and isobutane in the purified n-butane stream, and dehydrogenating the isobutane in the purified isobutane stream to form isobutylene, then reacting the isobutylene with methanol under reaction conditions sufficient to form a product stream of MTBE. Embodiment 2 is the method of embodiment 1, wherein the C₄ hydrocarbon stream is a crude C₄ hydrocarbon stream. Embodiment 3 is the method of embodiment 2, wherein the crude C4 hydrocarbon stream includes butadiene, isobutylene, 2- butene, 1 -butene, acetylene, isobutane, and n-butane. Embodiment 4 is the method of any of embodiments 1 to 3, wherein the separating includes adsorbing n-butane from the first stream onto the molecular sieves, and desorbing the molecular sieves to release the adsorbed n- butane into the purified n-butane stream. Embodiment 5 is the method of any of embodiments 1 to 4, further including isomerizing the n-butane in the purified n-butane stream to form additional isobutane. Embodiment 6 is the method of embodiment 5, wherein reaction conditions for the isomerizing include a temperature in a range 140 to 240 °C, a pressure in a range of 25 to 32 bar, and a weight hourly space velocity in a range of 5 to 10 hr-l. Embodiment 7 is the method of any of embodiments 5 and 6, wherein effluent from the isomerizing is sent to a separating unit that does the separating of the C₄ hydrocarbon stream. Embodiment 8 is the method of any of embodiments 1 to 7, wherein the molecular sieves include zeolite molecular sieves. Embodiment 9 is the method of any of embodiments 1 to 8, wherein conditions of the separating by the molecular sieves include a temperature in a range 10 to 400 °C, an adsorption pressure in a range of 0.9 to 140 bara, and a desorption pressure in a range of 0.01 to 0.25 bara. Embodiment 10 is the method of any of embodiments 1 to 9, wherein reaction conditions for the dehydrogenating of the isobutane includes a temperature in a range of 500 to 700 °C, a pressure in a range of 0.4 to 2 bar, and a weight hourly space velocity in a range of 0.8 to 2 hr-l. Embodiment 11 is the method of any of embodiments 1 to 10, wherein the dehydrogenating of the isobutane is carried out in presence of a catalyst comprising Cr-Al and/or Pt-Al. Embodiment 12 is the method of any of embodiments 1 to 11, wherein the reaction conditions for the reacting of the isobutylene with the methanol include a temperature in a range of 40 to 85 °C, a pressure in a range of 5 to 16 bar, and a weight hourly space velocity in a range of 10 to 25 hr-l. Embodiment 13 is the method of any of embodiments 1 to 12, wherein C₄ specific consumption of the method is in a range of 0.73 to 0.85, wherein the C₄ specific consumption is the total mass of C₄ consumed per unit mass of MTBE produced in the method. [0042] Embodiment 14 is a method of producing methyl tertiary butyl ether

(MTBE). The method includes separating a crude C4 hydrocarbon stream that includes primarily isobutane and n-butane collectively, into a first stream comprising primarily isobutane, the first stream further comprising n-butane, and a second stream comprising primarily n-butane. The method further includes separating the first stream, by molecular sieves, into a purified isobutane stream comprising 98 to 99.99 wt. % isobutane and a purified n-butane stream including 90 to 100 wt. % n-butane, wherein 100 wt. % of the purified isobutane stream is a total wt. % of n-butane and isobutane in the purified isobutane stream and 100 wt. % of the purified n-butane stream is a total wt. % of n-butane and isobutane in the purified n-butane stream, wherein the separating includes adsorbing n-butane from the first stream onto the molecular sieves, desorbing the molecular sieves to release the adsorbed n-butane into the purified n-butane stream, isomerizing the n-butane in the purified n-butane stream to form additional isobutene, dehydrogenating the isobutane in the purified isobutane stream to form isobutylene, and reacting the isobutylene with methanol under reaction conditions sufficient to form a product stream of MTBE.

[0043] 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.

Claims

1. A method of producing methyl tertiary butyl ether (MTBE), the method comprising:

separating a C₄ hydrocarbon stream that comprises primarily isobutane and n- butane collectively, into a first stream comprising primarily isobutane, the first stream further comprising n-butane, and a second stream comprising primarily n-butane; separating the first stream, by molecular sieves, into a purified isobutane stream comprising 98 to 99.99 wt. % isobutane and a purified n-butane stream comprising 90 to 100 wt. % n-butane, wherein 100 wt. % of the purified isobutane stream is a total wt. % of n-butane and isobutane in the purified isobutane stream and 100 wt. % of the purified n-butane stream is a total wt. % of n-butane and isobutane in the purified n-butane stream; dehydrogenating the isobutane in the purified isobutane stream to form isobutylene; and reacting the isobutylene with methanol under reaction conditions sufficient to form a product stream of MTBE.

2. The method of claim 1, wherein the C₄ hydrocarbon stream is a crude C₄ hydrocarbon stream.

3. The method of claim 2, wherein the crude C₄ hydrocarbon stream comprises butadiene, isobutylene, 2-butene, 1 -butene, acetylene, isobutane, and n-butane.

4. The method of any of claims 1 to 3, wherein the separating comprises adsorbing n- butane from the first stream onto the molecular sieves; and desorbing the molecular sieves to release the adsorbed n-butane into the purified n- butane stream.

5. The method of any of claims 1 to 3, further comprising the step of isomerizing the n- butane in the purified n-butane stream to form additional isobutane.

6. The method of claim 5, wherein reaction conditions for the isomerizing include a temperature in a range 140 to 240 °C, a pressure in a range of 25 to 32 bar, and a weight hourly space velocity in a range of 5 to 10 hr ¹.

7. The method of claim 5, wherein effluent from the isomerizing is sent to a separating unit that does the separating of the C₄ hydrocarbon stream.

8. The method of any of claims 1 to 3, wherein the molecular sieves comprise zeolite molecular sieves.

9. The method of any of claims 1 to 3, wherein conditions of the separating by the molecular sieves includes a temperature in a range 10 to 400 °C, an adsorption pressure in a range of 0.9 to 140 bara, and a desorption pressure in a range of 0.01 to 0.25 bara.

10. The method of any of claims 1 to 3, wherein reaction conditions for the dehydrogenating of the isobutane includes a temperature in a range of 500 to 700 °C, a pressure in a range of 0.4 to 2 bar, and a weight hourly space velocity in a range of 0.8 to 2 hr ¹.

11. The method of any of claims 1 to 3, wherein the dehydrogenating of the isobutane is carried out in presence of a catalyst comprising Cr-Al and/or Pt-Al.

12. The method of any of claims 1 to 3, wherein the reaction conditions for the reacting of the isobutylene with the methanol include a temperature in a range of 40 to 85 ^°C, a pressure in a range of 5 to 16 bar, and a weight hourly space velocity in a range of 10 to 25 hr ¹.

13. The method of any of claims 1 to 3, wherein C₄ specific consumption of the method is in a range of 0.73 to 0.85, wherein the C₄ specific consumption is the total mass of C₄ consumed per unit mass of MTBE produced in the method.

4. A method of producing methyl tertiary butyl ether (MTBE), the method comprising: separating a crude C₄ hydrocarbon stream that comprises primarily isobutane and n-butane collectively, into a first stream comprising primarily isobutane, the first stream further comprising n-butane, and a second stream comprising primarily n- butane;

separating the first stream, by molecular sieves, into a purified isobutane stream comprising 98 to 99.99 wt. % isobutane and a purified n-butane stream comprising 90 to 100 wt. % n-butane, wherein 100 wt. % of the purified isobutane stream is a total wt. % of n-butane and isobutane in the purified isobutane stream and 100 wt. % of the purified n-butane stream is a total wt. % of n-butane and isobutane in the purified n-butane stream, wherein the separating comprises:

adsorbing n-butane from the first stream onto the molecular sieves; and desorbing the molecular sieves to release the adsorbed n-butane into the purified n-butane stream; isomerizing the n-butane in the purified n-butane stream to form additional isobutane;

dehydrogenating the isobutane in the purified isobutane stream to form isobutylene; and reacting the isobutylene with methanol under reaction conditions sufficient to form a product stream of MTBE.