Production of high purity methanol using partition wall technology

Abstract

Methods and systems are provided for producing high purity methanol and isobutene from a crude MTBE feed using multiple partition wall columns. The method may include purifying MTBE, dissociating MTBE to produce isobutene and methanol, purifying isobutene, and recovering / purifying methanol.

Description

[0001] This application is a divisional application of the patent application with application number 201980059470.6 filed on September 11, 2019 and invention name “Using isolation wall technology to produce high-purity methanol”. Technical Field

[0002] Embodiments disclosed herein relate to methods and systems for co-producing isobutylene and a high purity methanol product stream. Background Art

[0003] As the demand for isobutylene increases, the dissociation of methyl tert-butyl ether (MTBE) to isobutylene using a suitable catalyst is a relatively clean process compared to the cold acid treatment by which high-purity isobutylene can be obtained. Therefore, the dissociation of MTBE is feasible and economical. In addition, the cold acid process not only requires a large amount of energy, but is also highly corrosive due to the use of sulfuric acid. The use of cationic resin catalysts or other catalysts (e.g., phosphoric acid supported on silica gel, alumina, supported metal sulfates) for dissociation requires less energy and is essentially corrosion-free.

[0004] The reaction to produce MTBE is known to be reversible, i.e., MTBE will dissociate to produce methanol and isobutylene, which originally combined to form MTBE. For example, U.S. Patent Nos. 3,121,124, 3,170,000, 3,634,534, 3,634,535, 4,232,177, and 4,320,232 disclose the use of ion exchange resin catalysts to dissociate alkyl tertiary alkyl ethers.

[0005] The use of acidic cation exchange resins for the dissociation of methyl tert-butyl ether has been demonstrated in the past, namely, U.S. Patent No. 3,121,124 (Verdol) using a gel-type catalyst (Dowex 50) and U.S. Patent No. 4,232,177 (Smith) using a macroreticular catalyst (Amberlyst 15) in a catalytic distillation process. The dissociation of MTBE will produce a stream containing isobutylene, methanol, and some oxygenates and polymer impurities. Summary of the Invention

[0006] As mentioned above, the product stream produced by the decomposition of MTBE includes various impurities. In addition, the products may form azeotropes. Each of these may make the desired separation into high-purity product streams more difficult.

[0007] Embodiments disclosed herein relate to systems and methods for co-producing a high purity methanol stream and a target isobutylene product.

[0008] In one aspect, embodiments disclosed herein relate to a system for producing isobutylene and a high-purity methanol product. The system may include a system for producing isobutylene, the method comprising: a first fractionation system receiving a feed stream comprising crude MTBE and producing an MTBE product stream comprising at least 94 wt% MTBE and a heavies stream; a first reactor configured to contact the MTBE product stream with a catalyst to provide an effluent comprising isobutylene and methanol; an extraction unit configured to contact the effluent comprising isobutylene and methanol with one or more extractants to produce an extractant / methanol stream and a mixed isobutylene stream; a second fractionation system receiving the mixed isobutylene stream and producing an isobutylene-containing stream comprising at least 95 wt% isobutylene; and a third fractionation system receiving the extractant / methanol stream and producing a methanol stream comprising at least 95 wt% methanol, a light fraction, and a heavy fraction comprising the extractant.

[0009] In one aspect, embodiments disclosed herein relate to a method for producing isobutylene and a high-purity methanol product. The method may be a method for co-producing isobutylene and high-purity methanol, comprising separating a feed stream comprising crude MTBE in a first fractionation system to recover an MTBE product stream comprising at least 94 wt% MTBE and recovering a heavy stream; contacting the MTBE product stream with a catalyst to provide an effluent comprising isobutylene and methanol; contacting the effluent comprising isobutylene and methanol with one or more extractants to produce an extractant / methanol stream and a mixed isobutylene stream; feeding the mixed isobutylene stream to a second fractionation system to recover an isobutylene-containing stream comprising at least 95 wt% isobutylene; and feeding the extractant / methanol stream to a third fractionation system to recover a light fraction, a methanol product stream comprising at least 95 wt% methanol, and a heavy fraction comprising the extractant.

[0010] In another embodiment, the process can be a process for co-producing isobutylene and high-purity methanol, comprising separating a feed stream comprising crude MTBE in a first fractionation system to recover an MTBE product stream comprising at least 94 wt% MTBE, and recovering a heavy stream; contacting the MTBE product stream with a catalyst to provide an effluent comprising isobutylene and methanol; contacting the effluent with one or more extractive agents to produce an extractive agent / methanol stream and a mixed isobutylene stream; feeding the mixed isobutylene stream to a second fractionation system to recover an isobutylene-containing stream comprising at least 95 wt% isobutylene; and feeding the extractive agent / methanol stream to a third fractionation system comprising a dividing wall distillation column to recover an overhead fraction, a methanol side draw product stream comprising at least 95 wt% methanol, and a bottoms stream comprising the extractive agent.

[0011] In other embodiments, the process can be a process for co-producing isobutylene and high-purity methanol, comprising separating a feed stream comprising crude MTBE, C4, C5, diisobutylene (DIB), tert-butyl alcohol (TBA), and 2-methoxybutane (MSBE) in a first fractionation system to recover an MTBE product stream comprising at least 94 wt% MTBE, and recovering a heavy stream comprising a mixture of MTBE, tert-butyl alcohol (TBA), and 2-methoxybutane (MSBE); contacting the MTBE product stream with a catalyst to provide an effluent comprising isobutylene, methanol, and residual MTBE; contacting the effluent with one or more extractants to produce The invention relates to a method for producing an extractive agent / methanol stream and a mixed isobutylene / MTBE stream; feeding the mixed isobutylene / MTBE stream to a second fractionation system to recover an isobutylene-containing stream comprising at least 94 weight percent isobutylene and a heavy stream comprising MTBE / isobutylene; recycling the heavy stream comprising MTBE / isobutylene to the first fractionation system; feeding the extractive agent / methanol stream to a third fractionation system comprising a dividing wall distillation column to recover an overhead fraction, a methanol side draw product stream comprising at least 95 weight percent methanol, and a bottoms stream comprising residual MTBE, methanol, and the extractive agent; and recycling the bottoms stream comprising residual MTBE, methanol, and the extractive agent to the first fractionation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a simplified process flow diagram of a method for an integrated reactor system according to embodiments disclosed herein.

[0013] Figure 2 is a simplified process flow diagram of a method for an integrated reactor system according to embodiments disclosed herein.

[0014] Figure 3 is a schematic diagram of a divided wall column (also referred to as a dividing wall column) according to embodiments disclosed herein.

[0015] Figure 4 is a schematic representation of a dividing wall column according to embodiments disclosed herein. DETAILED DESCRIPTION

[0016] In one aspect, a method and system for producing high-purity methanol from a crude MTBE feed using one or more dividing wall columns is provided. The method can include purifying the MTBE, dissociating the MTBE to produce isobutylene and methanol, purifying the isobutylene, and recovering / purifying the methanol.

[0017] The dividing wall tower herein can be used to separate a multi-component mixture into pure fractions. They are particularly suitable for obtaining high-purity medium-boiling fractions. In conventional distillation systems, separating a three-component mixture into its fractions requires a sequential system with at least two towers or a main tower with a side tower. Utilizing a dividing wall tower, only one fractionator is used to separate light distillates (lights) and heavy distillates (heavies) from medium-boiling products. A vertical wall is introduced in the middle portion of the tower, thereby forming a feed and discharge section in this portion of the tower. This arrangement saves a second tower. There is no need for a tower shell, internal components, reboiler, and condenser for the second tower.

[0018] As used herein, the term "dividing wall column" refers to any tower having a dividing wall suitable for separating a mixture containing two or more components with different boiling points. As used herein, the term "dividing wall" refers to any separator at least partially arranged in the inside of the tower to provide the first fractionating region at least on one side of the dividing wall and to provide the second fractionating region on the other side of the dividing wall. The dividing wall can be segmented or continuous. The dividing wall can be parallel or non-parallel relative to the longitudinal axis of the tower. The first fractionating region and the second fractionating region can have the same or different cross-sectional area and / or volume. The tower can have a circular cross section, and the dividing wall can be positioned or arranged in the tower to provide the first fractionating region and the second fractionating region with equal or unequal cross-sectional areas relative to each other. The dividing wall can extend completely or only partially from one side of the dividing wall column to the other side of the dividing wall column.

[0019] The dividing wall column according to the embodiments herein is, in principle, a system of thermally coupled distillation columns. In the dividing wall column herein, the dividing wall is located within the interior space of the column. The dividing wall column herein may employ either a chordal wall or an annular wall. The dividing wall is typically vertical. Two different mass transfer separations occur on either side of the dividing wall, which may have different operating pressures and temperatures, and the dividing wall may have to withstand pressure and / or temperature differences across the dividing wall.

[0020] Dividing wall columns herein may include internals, including trays, rotating trays, and random and / or structured packing. Useful trays include: trays with holes or slots; trays with slots or chimneys covered by bubble caps, covers, or shields; trays with holes covered by removable valves; and trays with specialized configurations. In columns with rotating internals, the reflux is sprayed onto the heated tube walls through a rotating funnel with the aid of a rotor or distributed as a thin film. The column may also include random packing of various shaped bodies.

[0021] A dividing wall column can have a common stripping section and a common rectifying section with a dividing wall in the middle. This design allows for different vapor and liquid paths on either side of the wall, thereby increasing product purity while minimizing the number of equipment units.

[0022] For example, can process methanol feed according to the embodiment of this paper, to produce the highest methanol concentration in the dividing wall tower, minimize the amount of the methanol leaving together with the bottoms product simultaneously.This causes in the distillate product and in the distillation zone, close to azeotropic concentration.Methanol must be separated from hydrocarbons, so that hydrocarbons can be used for gasoline blending and saving methanol.Separation can be realized by washing the hydrocarbon / methanol mixture with water.Methanol can be selectively absorbed in the aqueous phase, which is then fractionated to separate methanol.

[0023] According to one or more embodiments disclosed herein, a dividing wall column can be used, for example, in an existing integrated MTBE and isobutylene facility and can produce only high-purity isobutylene. Existing facilities can recycle all of the methanol produced from the isobutylene unit to the MTBE unit. In order to handle the additional imported MTBE and simultaneously produce export-quality commercial-grade methanol, a new methanol purification section would need to be installed in such a facility. Such a methanol purification section would likely require two distillation columns (a methanol topping column and a methanol tailing column) with associated equipment. The dividing wall column disclosed herein can be used to replace multiple separate conventional columns for producing commercial-grade methanol.

[0024] Additionally, an integrated MTBE and isobutylene process may not have the flexibility to produce commercial-grade methanol. To co-produce methanol by introducing an additional MTBE inlet into the isobutylene section, a methanol purification section may need to be integrated into the process. This methanol purification process may involve a dividing wall column or a series of distillation columns to achieve a methanol product that meets specifications while using minimal equipment. Furthermore, the reboil / condensation load of this process can be approximately 30% lower than that of a conventional two-column system. Finally, because a dividing wall column can use less equipment, it significantly saves on required land area and structure (pipe racks, foundations, etc.).

[0025] According to one or more embodiments disclosed herein is a dividing wall column or a series of distillation columns that can utilize the bottoms of an extraction column and separate one or more of MTBE, DIB, TBA, DME, MSBE, TAME, and water from methanol to produce an export-grade methanol product.

[0026] Now refer to Figure 1A method for producing high-purity isobutylene is described below. To purify MTBE, crude MTBE 1 is introduced into a fractionation column 5. Crude MTBE 1 can be obtained from an isobutylene-based C4 olefin mixture, such as a C4 cut from a steam cracker or FCC unit. Crude MTBE may also include methanol, sec-butyl alcohol (SBA), tert-butyl alcohol (TBA), 2-methoxybutane (MSBE), diisobutylene, tert-amyl methyl ether (TAME), and other high-boiling components.

[0027] In some embodiments, crude MTBE stream 1 may comprise 94-97 wt% MTBE, such as 95.9 wt% MTBE. Crude MTBE stream 1 may also contain small amounts of highly unsaturated compounds such as 1,3-butadiene, trans-1,3-pentadiene, cis-1,3-pentadiene, 2-methyl-1,3-butadiene, and the like. The feed stream may additionally comprise crude MTBE provided by an upstream etherification reaction zone and a make-up MTBE feed stream. Such a make-up MTBE feed stream may come from a separate facility, an OSBL, an upstream separation system, or other sources.

[0028] MTBE stream 1 can be introduced at an intermediate position in tower 5. Light hydrocarbon stream 2 can be withdrawn from or near the first end of tower 5, and side stream 3 can be withdrawn from an intermediate position of tower 5. Light hydrocarbon stream 2 can be recycled to the top of tower 5 as reflux. Light hydrocarbon stream 2 can be a mixture of MTBE, methanol, water and highly unsaturated compounds. Compared to MTBE feed stream 1, this side stream can be an MTBE stream with improved purity. This side stream can further include one or more impurities present in the feed stream. Heavy hydrocarbon stream 4 can be withdrawn from or near the lower end of dividing wall tower 5. Heavy hydrocarbon 4 can be a mixture of MTBE, tert-butyl alcohol (TBA), 2-methoxybutane (MSBE) and higher olefins.

[0029] The fractionation column 5 can be operated at a temperature in the range of about 45° C. to about 130° C. and a pressure in the range of about 0.1 to about 5 barg. The purification of MTBE 1 provides a side stream (MTBE) 3 having a composition of, for example, about 99.5 wt. % MTBE or higher, such as 99.8 wt. % MTBE or 99.9 wt. % MTBE. The MTBE side stream can be generated by fractionation in the fractionation system 5, thereby separating MTBE 1 into light hydrocarbons 2 comprising MTBE, methanol, water, and other low-boiling components and heavy hydrocarbons 4 comprising butene oligomers, TBA, and other high-boiling components, while withdrawing a high-purity MTBE side stream 3.

[0030] To produce isobutylene, the MTBE side stream 3 can be sent to a reactor 6 to produce isobutylene. Reactor 6 dissociates the high-purity MTBE 3 and produces a crude isobutylene stream 7 comprising isobutylene, methanol, and unreacted MTBE. In some embodiments, reactor 6 comprises a fixed bed operating at a reactor bed temperature in the range of about 90°C to about 160°C, and in other embodiments, in the range of about 120°C to about 150°C. The high-purity MTBE 3 can be fed at an inlet temperature of about 110°C to about 150°C in some embodiments, and about 115°C to about 145°C in other embodiments. Reactor 6 can have an LHSV (liquid hourly space velocity) in the range of about 7 to about 35, or about 10 to about 30, or about 14 to about 25. Reactor 6 can have a pressure drop across the fixed bed in the range of about 0.5 to about 50 psig and be at a reaction pressure in the range of about 0.5 to about 4 atmospheres.

[0031] The crude isobutylene stream 7 is sent for product purification. The crude isobutylene 7 can be sent to an extraction column 8 to extract methanol and unreacted MTBE from the isobutylene. The extraction column 8 uses an extractant 9 fed in countercurrent to the crude isobutylene 7, thereby producing a washed reactor effluent 10 as an overhead and a bottoms product 11. The washed reactor effluent 10 (which can include isobutylene, MTBE, and residual light components) can be fed to an isobutylene fractionation system 12, and the bottoms product 11 (which can include water, methanol, MTBE, and residual heavy components) can be fed to a methanol fractionation system 13. The extractant 9 can be water or another suitable extractant that can be used to separate methanol from isobutylene.

[0032] In various embodiments, at least a portion of the crude isobutylene 7 may be recycled to the first fractionation system 5 as additional reflux, collected as a product, and / or combined with the heavier hydrocarbons 4 and sent off-site as a by-product.

[0033] To recover isobutylene, similar to that described above for purifying MTBE, the process can include introducing the washed reactor effluent 10 into an isobutylene fractionation system 12. The washed reactor effluent 10 can be introduced at an intermediate location in the isobutylene fractionation column 12. A light ends overhead 14 can be withdrawn from the upper end of the isobutylene fractionation column 12 and can be discharged or recycled as reflux to the isobutylene fractionation system 12. A side stream 16 of high-purity isobutylene can be withdrawn from the intermediate location of the isobutylene fractionation column 12 and can be used in downstream processes or can be recovered as a product and sent off-site. Such a high-purity isobutylene stream can have an isobutylene purity of 95%, 97%, 98%, 99%, 99.5%, 99.6%, 99.7%, 99.8%, or even 99.85% by weight. Isobutylene column 12 may also produce bottoms product 15, which may be a mixture of isobutylene, MTBE, and / or water, which may be recycled to fractionation system 5. Isobutylene column 12 may operate at a temperature in the range of about 45° C. to about 150° C. and a pressure in the range of about 3 to about 15 barg.

[0034] To recover / purify the methanol product stream, the bottoms product 11 from the extraction column 8 can be fed to an intermediate position in the methanol fractionation system 13. The methanol fractionation system can be a series of fractionation columns, such as a methanol topping column followed by a methanol bottoms column, or can be a dividing wall column as described below. The methanol fractionation system 13 can provide a high-purity methanol product 17 withdrawn as a side stream from an intermediate position of the methanol column 13, a bottoms stream 18, and an overhead stream 19. The light overhead stream 19 can contain methanol and other light components and can be discharged or recycled as reflux to the methanol fractionation system 13. The bottoms 18 can include water, TBA, MTBE, and / or methanol. The bottoms 18 can be recycled to the extraction column 8 or the fractionation system 5. The methanol column 13 can be operated at a temperature in the range of about 45°C to about 180°C and a pressure in the range of about 0.1 to about 5 barg.

[0035] In relation to the embodiments disclosed herein, Figure 2 As shown, the first fractionation system 5 can recover MTBE in the overhead product. The overall process scheme will proceed similarly, wherein the remaining MTBE, water and isobutylene are recycled in the bottom stream 15. In addition, methanol, residual isobutylene and other light components can be recycled to the first fractionation system via flow line 19.

[0036] The overall processing scheme disclosed herein can be performed using a single fractionation column, a series of fractionation columns, or a dividing wall column. Advantages resulting from the use of a dividing wall column may include, among other advantages, reduced capital investment; eliminating or greatly reducing the need for multiple columns to provide the same level of product purity.

[0037] In one aspect, embodiments herein relate to the purposes of a dividing wall distillation column. The feed of the dividing wall column can come from a preceding tower or reactor in which less than all reactants react. The feed material contains reactants and products fed to the pre-fractionation section (pre-fraction section, or referred to as the pre-fractionation section) of the dividing wall column. Then, the rear fractionation section produces a methanol product as a side cut. Between the front fractionation section and the rear fractionation section is a common tower bottom section, which reclaims as much methanol as possible while concentrating water and TBA into the bottom product. The overhead of the tower is used to reflux the front fractionation section, serving as the feed / reflux for the rear fractionation section, and a portion is extracted as a tower overhead product, which can be sent back to the MTBE synthesis section. Supplementary materials can be added as needed. A common stripping section can be arranged below the isolated vertical section.

[0038] The front fractionation section is responsible for separating methanol / MTBE from water and TBA. This section can reflux so that separation is carried out between methanol and water / TBA. The rear fractionation section of the dividing wall tower can separate MTBE from a part of methanol. In addition, a side draw can extract a methanol product from the rear fractionation section. Enough reflux can be sent to this section to maximize the methanol recovery in the side draw product while minimizing the amount of impurities. The tower section below the dividing wall can include enough mass transfer fillers or catalysts to further reclaim methanol from the water / TBA at the bottom of the front fractionation section. The liquid from the front fractionation section and the rear fractionation section and collected in the common tower bottom section is used as the internal reflux of this part of the tower.

[0039] In addition, the auxiliary equipment used for this tower can be similar to the auxiliary equipment used on any distillation tower. For example, the system can include a public overhead system, thereby reclaiming overheads from each of the front fractionation section and the back fractionation section of the dividing wall tower. The condenser can be a full condenser, which condenses the steam from the front fractionation section and the back fractionation section. The condensed overhead can then be directed to a reflux accumulator or a tower drum, and its effluent can be split between the overhead product and the reflux for this tower. Depending on the tower separation kinetics, reflux can be fed to the front fractionation, the back fractionation or both with equal or unequal amounts. The tower can use a single public reboiler to provide the boiling required for separation.

[0040] Additionally, the product stream withdrawn from the side draw may be fed to a product cooler, which brings the methanol to transport temperature.

[0041] According to one or more embodiments disclosed herein, a distillation column may have at least two vertical distillation sections, including a front fractionation section with an inlet feed and a rear fractionation section with a side draw. The dividing wall column may also have at least one wall separating the at least two vertical distillation sections. The wall may extend through the vertical portion of the distillation column, the wall extending less than the total height of the column. The dividing wall column may also be equipped with a common stripping section below the at least two vertical distillation sections. The common stripping section may be in fluid communication around the bottom vertical end of the wall. The wall extending through the vertical portion of the distillation column may extend from the top of the column to near the top of the stripping section.

[0042] In addition, the dividing wall column can have a common overhead condenser system. The common overhead condenser system can receive overhead products from the at least two vertical distillation sections and can feed the overhead distillate to a common overhead drum. The common overhead drum can be equipped with all necessary piping and valves to recycle the condensed overhead product to each of the at least two vertical distillation sections.

[0043] The front and rear fractionation sections can be located entirely or partially within the rectifying section of the distillation column. The dividing wall column can utilize a side draw from the rectifying section of the rear fractionation section and can be configured for product recovery. Alternatively, the dividing wall column can utilize a common bottom reboiler, which provides the entire heating load for boiling the individual bottom product streams. The overhead drum can also carry an overhead product stream.

[0044] Now refer to Figure 3 , the methanol purification process can be carried out in a dividing wall column and can generally be operated as follows.

[0045] Feedstock 102 (which may include one or more of MTBE, DIB, TBA, DME, MSBE, TAME, water, and methanol) is fed to pre-fractionation section A. As shown, pre-fractionation section A can separate one or more feed components to produce methanol. The liquid travels down the dividing wall column and enters a common stripping section C. Vapor exits the top of section A via overhead stream 104A and enters a common overhead condenser 106.

[0046] A first portion of the liquid in the common stripping section C is fed to a common reboiler 110 via the first bottom outlet 108. A second portion of the liquid in the common stripping section C is recovered via outlet 112. These two portions may include water, TBA, other heavy components, and some residual methanol. The upwardly traveling vapor portion from the common stripping section C may flow to the front fractionation section A and the rear fractionation section B.

[0047] In all cases, the vapor traveling upward in the column can be purposefully distributed at the lowermost end of the dividing wall at a predetermined ratio, as determined based on rigorous reactive-distillation simulations of the dividing wall configuration. Such flow distribution can be controlled to a specified value through engineering design methods incorporating active or passive devices. Similarly, such flow distribution can be maintained at a specified value using engineering design methods incorporating active or passive devices. Such devices include having a larger bottom opening in either section A or section B, an off-center dividing wall, or feeding a certain amount of reflux to section A or section B.

[0048] Post-fractionation section B may include a product side draw 114. The side draw product may be substantially pure methanol. As defined herein, substantially pure may be at least 95%, 97%, 98%, 99%, 99.5%, 99.6%, 99.7%, 99.8%, or even 99.85% by weight. The product methanol may be fed through a product cooler 115 in preparation for transport.

[0049] Like the front fractionation section, the rear fractionation section B can separate one or more feed components to produce methanol. The liquid travels down the dividing wall column and enters the common stripping section C. The vapor leaves the top of section B through overhead stream 104B and enters the common overhead condenser 106. Overhead streams 104A and 104B are combined to form common overhead stream 104.

[0050] The combined condensed overheads 116 may be fed to an overhead collection drum 118. The vapor portion 124 exiting the overhead drum may be used to un-deadhead the column and increase the vapor traveling through sections A, B, and C. If necessary, the vapor portion 124 may be recycled to an upstream or downstream process or flared.

[0051] The liquid portion 120 leaving the overhead drum 118 can be fed as reflux to the post-fractionation section B via stream 121, to the pre-fractionation section A via stream 122, or both. If necessary, the portion of the liquid portion 120 not fed as reflux can be recovered via stream 123 and recycled to an upstream process, a downstream process, or to a flare.

[0052] The allocation of how much reflux goes to zone A versus how much goes to zone B can be intentionally designed and controlled. Appropriate valves can be used to vary the amount of reflux fed to zone A or zone B at any given time. For example, the dividing wall column can be operated so that none of the vapor portion 124 is removed, and all of the reflux can be fed to zone A or zone B. Alternatively, the dividing wall column can be operated so that none of the vapor portion 124 is removed, and all of the reflux can be fed to zone A and zone B in equal or unequal amounts. Alternatively, the dividing wall column can be operated so that the vapor portion 124 is removed, and all of the liquid reflux can be fed to zone A or zone B. Or alternatively, the dividing wall column can be operated so that the vapor portion 124 is removed, and all of the liquid reflux can be fed to zone A and zone B in equal or unequal amounts.

[0053] In one or more embodiments herein, the light components can be concentrated and purged as an overhead product.The light distillate purge is required to control the temperature in the catalytic distillation column.

[0054] Section A is parallel to section B and is fed via liquid reflux from the overhead condenser system and vapor from stripping section C and the reboiler. Active or passive engineering devices can be used to intentionally control the vapor split between sections A and B to a specified level.

[0055] In another embodiment disclosed herein, a distillation column can have at least two vertical distillation sections, including a front fractionation section with an inlet feed and a rear fractionation section with a side draw. The dividing wall column can also have at least one wall separating the at least two vertical distillation sections. The wall can extend through the middle of the distillation column, extending less than the total height of the column. The dividing wall column can also be equipped with a common stripping section below the at least two vertical distillation sections. The common stripping section can be in fluid communication around the bottom vertical end of the wall.

[0056] In addition, the dividing wall column can have a common overhead condenser system. The common overhead condenser system can receive overhead products from at least two vertical distillation sections and can feed the overhead distillate to a common overhead drum. The common overhead drum can be equipped with all necessary piping and valves to recycle the condensed overhead product to the top tray of each of the at least two vertical distillation sections.

[0057] The front and rear fractionation sections can be located entirely or partially within the rectifying section of the distillation column. The dividing wall column can utilize a side draw from the rectifying section of the rear fractionation section and can be configured for product recovery. Additionally, the dividing wall column can utilize a common bottom reboiler, which provides the entire heating duty for boiling the individual bottom product streams. The overhead drum can also receive an overhead product stream.

[0058] Now refer to Figure 4 , the methanol purification process can be carried out in a dividing wall column and can generally be operated as follows.

[0059] Feedstock 202 (which may include one or more of MTBE, DIB, TBA, DME, MSBE, TAME, water, and methanol) is fed to pre-fractionation section A. As shown, pre-fractionation section A can separate one or more feed components to produce methanol. The liquid travels down the dividing wall column and enters a common stripping section C. Vapor exits the top of section A via overhead stream 204 and enters a common overhead condenser 206.

[0060] The first portion of the liquid in the common stripping section C is fed to a common reboiler 210 via the first bottom outlet 208. The second portion of the liquid in the common stripping section C is recovered via outlet 212. These two portions may be water, TBA, other heavy components, and some residual methanol. The vapor portion that travels upward from the common stripping section C may flow into the front fractionation section A and the rear fractionation section B.

[0061] In all cases, the vapor traveling upward in the column can be purposefully distributed at the lowermost end of the dividing wall at a predetermined ratio, as determined based on rigorous reactive-distillation simulations of the dividing wall configuration. Such flow distribution can be controlled to a specified value through engineering design methods incorporating active or passive devices. Similarly, such flow distribution can be maintained at a specified value using engineering design methods incorporating active or passive devices. Such devices include having a larger bottom opening in either section A or section B, an off-center dividing wall, or feeding a certain amount of reflux to section A or section B.

[0062] Post-fractionation section B may include a product side draw 214. The side draw product may be substantially pure methanol. As defined herein, substantially pure may be at least 95%, 97%, 98%, 99%, 99.5%, 99.6%, 99.7%, 99.8%, or even 99.85% by weight. The product methanol may be fed through a product cooler 215 in preparation for transport.

[0063] Like the front fractionation section, the rear fractionation section B can separate one or more feed components to produce methanol. The liquid travels down the dividing wall column and enters the common stripping section C. The vapor leaves the top of section B through the overhead stream 204 and enters the common overhead condenser 206.

[0064] The combined condensed overheads 216 may be fed to an overhead collection drum 218. The vapor portion 224 exiting the overhead drum may be used to de-head the column and increase the vapor traveling through sections A, B, and C. The vapor portion 224 may be recycled to an upstream process, a downstream process, or flared, if necessary.

[0065] The liquid portion 220 leaving the overhead collection drum 218 can be fed as reflux via stream 221 to an area near the top tray in the rear fractionation section B, via stream 222 to an area near the top tray in the front fractionation section A, or both. If necessary, the portion of the liquid portion 220 not fed as reflux can be recovered via stream 223 and recycled to an upstream process, a downstream process, or to a flare.

[0066] The allocation of how much reflux goes to zone A versus how much goes to zone B can be intentionally designed and controlled. Appropriate valves can be used to vary the amount of reflux fed to zone A or zone B at any given time. For example, the dividing wall column can be operated so that none of the vapor portion 224 is removed, and all of the reflux can be fed to zone A or zone B. Alternatively, the dividing wall column can be operated so that none of the vapor portion 224 is removed, and all of the reflux can be fed to zone A and zone B in equal or unequal amounts. Alternatively, the dividing wall column can be operated so that the vapor portion 224 is removed, and all of the liquid reflux can be fed to zone A or zone B. Or alternatively, the dividing wall column can be operated so that the vapor portion 224 is removed, and all of the liquid reflux can be fed to zone A and zone B in equal or unequal amounts.

[0067] In one or more embodiments herein, the light components can be concentrated and purged as an overhead product.The light distillate purge is required to control the temperature in the catalytic distillation column.

[0068] Section A is parallel to Section B and is fed by liquid reflux from the overhead condenser system and vapor from stripping section C and the reboiler. Active or passive engineering devices can be used to intentionally control the vapor split between Sections A and B at a specified level. Control of the reflux to Sections A and B can be above the top tray of each section or can be controlled by internal components within the column.

[0069] In conventional distillation column reactors, a reflux of the condensed overhead product is often present to facilitate separation of more volatile unreacted components from the product. In the case of methanol purification, the overhead product may contain methanol, as well as other lighter materials that may be present in the feed. The condensable overhead product is recovered and can be washed with water to separate the methanol from the hydrocarbons, selectively removing the methanol in the aqueous phase. The methanol and water can then be refluxed, and the methanol can be further separated in the distillation column.

[0070] Furthermore, in other embodiments, the methanol distillation column may be a series of distillation columns operated in parallel so that a high purity methanol stream may be obtained.

[0071] While this disclosure includes a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the present disclosure. Accordingly, the scope should be limited only by the terms of the appended claims.

Claims

1. A method for co-producing isobutylene and high-purity methanol, the method comprising: a. separating a feed stream comprising crude methyl tert-butyl ether (MTBE) in a first fractionation system to recover an MTBE product stream comprising at least 94 wt% MTBE, and recovering a heavy stream; wherein the feed stream comprises crude MTBE provided from an etherification reaction zone and a make-up MTBE feed stream; b. contacting the MTBE product stream with a catalyst in a first reactor to provide an effluent comprising isobutylene and methanol; c. contacting the effluent comprising isobutylene and methanol with one or more extractants to produce an extractant / methanol stream and a mixed isobutylene stream; d. feeding the mixed isobutylene stream to a second fractionation system to recover an isobutylene-containing stream comprising at least 95 wt% isobutylene and having less than 100 wppm normal C4 and less than 30 wppm C5, and recovering a stream comprising MTBE / isobutylene; e. feeding the extractive agent / methanol stream to a third fractionation system to recover a light fraction, a methanol product stream comprising at least 95 wt% methanol, and a heavy fraction comprising the one or more extractive agents; f. recycling the MTBE / isobutylene to the first fractionation system; g. recycling at least a first portion of the light fraction from the third fractionation system to the first fractionation system; h. recycling at least a second portion of the light fraction from the third fractionation system as reflux to the third fractionation system; i. feeding at least a third portion of the light fraction from the third fractionation system to the etherification reaction zone; The third fractionation system comprises a dividing wall distillation column, and the dividing wall distillation column comprises: at least two vertical distillation sections; at least one wall separating the at least two vertical distillation sections, the wall extending through a vertical portion of the dividing wall distillation column, the vertical portion having a height less than the total height of the column; wherein the dividing wall distillation column has a common overhead condenser system for receiving overhead products from the at least two vertical distillation sections and feeding the condensed overhead products to a common overhead drum, the common overhead drum being equipped with piping and valves for recycling the condensed overhead products to each of the at least two vertical distillation sections; wherein the third fractionation system operates at a temperature between 45°C and 130°C and a pressure between 0.1 and 5 barg; wherein the first reactor is operated at a reactor temperature between 90°C and 160°C; wherein the feed stream is fed at a temperature between 110°C and 150°C; wherein the first reactor is operated at a liquid hourly space velocity of 7 to 35; wherein the first reactor operates at a pressure drop between 0.5 and 50 psig and a reaction pressure between 0.5 and 4 atmospheres.

2. The method of claim 1, further comprising feeding the light fraction from the third fractionation system to the etherification reaction zone.

3. The process of claim 1 , wherein the feed stream further comprises C4, C5, diisobutylene (DIB), tert-butyl alcohol (TBA), and 2-methoxybutane (MSBE).

4. The method of claim 1, wherein the one or more extractants comprise water.

5. The process of claim 1, wherein the first fractionation system and the second fractionation system each comprise a dividing wall distillation column.

6. The process of claim 1, wherein the methanol stream comprises at least 99.8 wt% methanol.

7. The process of claim 1, wherein the at least two vertical distillation sections have a common stripping section below the at least two vertical distillation sections, the common stripping section being in fluid communication about the bottom vertical end of the wall.

8. A method for co-producing isobutylene and high-purity methanol, the method comprising: a. separating a feed stream comprising crude methyl tert-butyl ether (MTBE) in a first fractionation system to recover an MTBE product stream comprising at least 94 wt% MTBE, and recovering a heavy stream; b. contacting the MTBE product stream with a catalyst to provide an effluent comprising isobutylene and methanol; c. contacting the effluent with one or more extractants to produce an extractant / methanol stream and a mixed isobutylene stream; d. feeding the mixed isobutylene stream to a second fractionation system to recover an isobutylene-containing stream comprising at least 95 wt% isobutylene and having less than 100 wppm normal C4 and less than 30 wppm C5, and recovering a stream comprising MTBE / isobutylene; e. feeding the extractive agent / methanol stream to a third fractionation system comprising a dividing wall distillation column to recover an overhead fraction, a methanol side draw stream comprising at least 95 wt % methanol, and a bottoms stream comprising the one or more extractive agents; f. recycling the MTBE / isobutylene to the first fractionation system; g. recycling at least a first portion of the overhead fraction from the third fractionation system to the first fractionation system; h. recycling at least a second portion of the overhead fraction from the third fractionation system as reflux to the third fractionation system; The third fractionation system comprises a dividing wall distillation column, and the dividing wall distillation column comprises: at least two vertical distillation sections; at least one wall separating the at least two vertical distillation sections, the wall extending through a vertical portion of the dividing wall distillation column, the vertical portion having a height less than the total height of the column; wherein the dividing wall distillation column has a common overhead condenser system for receiving overhead products from the at least two vertical distillation sections and feeding the condensed overhead products to a common overhead drum, the common overhead drum being equipped with piping and valves for recycling the condensed overhead products to each of the at least two vertical distillation sections; wherein the third fractionation system operates at a temperature between 45°C and 130°C and a pressure between 0.1 and 5 barg.

9. The process of claim 8, wherein the feed stream comprises crude MTBE provided from the etherification reaction zone and a make-up MTBE feed stream.

10. The process of claim 9, further comprising feeding the condensed overhead fraction from the third fractionation system to the etherification reaction zone.

11. The process of claim 8, wherein the feed stream further comprises C4, C5, diisobutylene (DIB), tert-butyl alcohol (TBA), and 2-methoxybutane (MSBE).

12. The method of claim 8, wherein the one or more extractants comprise water.

13. The method of claim 8, wherein the first fractionation system and the second fractionation system each comprise a dividing wall distillation column.

14. The process of claim 8, wherein the methanol stream comprises at least 99.8 wt% methanol.

15. The process of claim 8, wherein the at least two vertical distillation sections have a common stripping section below the at least two vertical distillation sections, the common stripping section being in fluid communication about the bottom vertical end of the wall.

16. A method for co-producing isobutylene and high-purity methanol, the method comprising: a. separating a feed stream comprising crude methyl tert-butyl ether (MTBE), C4, C5, diisobutylene (DIB), tert-butyl alcohol (TBA), and 2-methoxybutane (MSBE) in a first fractionation system to recover an MTBE product stream comprising at least 94 wt% MTBE, and recovering a heavy stream comprising a mixture of MTBE, tert-butyl alcohol (TBA), and 2-methoxybutane (MSBE); b. contacting the MTBE product stream with a catalyst to provide an effluent comprising isobutylene, methanol, and residual MTBE; c. contacting the effluent with one or more extractants to produce an extractant / methanol stream and a mixed isobutylene / MTBE stream; d. feeding the mixed isobutylene / MTBE stream to a second fractionation system to recover an isobutylene-containing stream comprising at least 95 wt% isobutylene and having less than 100 wppm normal C4 and less than 30 wppm C5 and a heavy stream comprising MTBE / isobutylene; e. recycling the heavy stream comprising MTBE / isobutylene to the first fractionation system; f. feeding the extractant / methanol stream to a third fractionation system comprising a dividing wall distillation column to recover an overhead fraction, a methanol side draw stream comprising at least 95 wt% methanol, and a bottoms stream comprising residual MTBE, methanol, and the one or more extractants; and g. recycling the bottom stream comprising residual MTBE, methanol and the one or more extractive agents to the first fractionation system; h. recycling at least a first portion of the overhead fraction from the third fractionation system to the first fractionation system; i. recycling at least a second portion of the overhead fraction from the third fractionation system as reflux to the third fractionation system; The third fractionation system comprises a dividing wall distillation column, and the dividing wall distillation column comprises: at least two vertical distillation sections; at least one wall separating the at least two vertical distillation sections, the wall extending through a vertical portion of the dividing wall distillation column, the vertical portion having a height less than the total height of the column; wherein the dividing wall distillation column has a common overhead condenser system for receiving overhead products from the at least two vertical distillation sections and feeding the condensed overhead products to a common overhead drum, the common overhead drum being equipped with piping and valves for recycling the condensed overhead products to each of the at least two vertical distillation sections; wherein the third fractionation system operates at a temperature between 45°C and 130°C and a pressure between 0.1 and 5 barg.

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