WO2016094249A2

WO2016094249A2 - Processes for adsorptive separation of benzene

Info

Publication number: WO2016094249A2
Application number: PCT/US2015/064022
Authority: WO
Inventors: James A. Johnson
Original assignee: Uop Llc
Priority date: 2014-12-12
Filing date: 2015-12-04
Publication date: 2016-06-16
Also published as: WO2016094249A3

Abstract

Processes for separating benzene from a stream with non-aromatics. The benzene is selectively adsorbed onto an adsorbent. The non-aromatics may be passed to a cracking section and a hot effluent from the cracking zone may be used to desorb the benzene from the adsorbent. Also hydrogen may be used to desorb the benzene. The adsorption section including the adsorbent may include two or more vessels being operated in alternating modes between adsorption and desorption.

Description

PROCESSES FOR ADSORPTIVE SEPARATION OF BENZENE

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 62/091,086 which was filed on December 12, 2014, the contents of which are hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention relates generally to the separation of benzene from a stream with non-aromatics and more particularly to an adsorptive separation of benzene from such a stream. BACKGROUND OF THE INVENTION

Conventional methods for co-producing paraxylene and benzene from a naphtha or reformate stream requires that the benzene be sent through liquid-liquid extraction or extractive distillation with a solvent such as sulfolane, in order to achieve benzene purity that is 99.9% or greater and less than 1000 ppm of non-aromatics. While sulfolane is typically the solvent, although other solvents such as ethers, glycols, NMF or morphyline or mixtures thereof can be used.

The liquid-liquid extraction or extractive distillation will produce high purity benzene, along with a non-aromatic raffmate that is often sent to a steam cracker to produce olefins. However, oftentimes, the liquid raffmate from these processes that is sent to the steam cracker is a relatively high molecular weight liquid. Therefore, the liquid will have a comparatively low selectivity for ethylene and propylene.

Additionally, the liquid-liquid extraction and extractive distillation technologies require significant capital to build and significant utilities to operate. The liquid-liquid extraction and extractive distillation equipment capital cost can be upwards of $25MM, and the utility cost to operate these types of units can be upwards of $15MM/yr. It would be desirable to provide a more economical alternative for the recovery of benzene compared to liquid-liquid extraction and extractive distillation, while still generating high purity benzene. It would further be desirable to have such an alternative that provides a by-product non-aromatic stream that would be suitable for feed to a steam cracker for light olefin production.

SUMMARY OF THE INVENTION

One or more processes have been invented in which benzene is separated from a stream containing non-aromatics by selectively adsorbing benzene on an adsorbent.

Therefore, in a first aspect of the present invention, the present invention may be broadly characterized as a process for separating a benzene from a stream by: selectively adsorbing benzene from a feed stream in an adsorption section comprising an adsorbent and configured to provide a by-product raffmate stream; hydrocracking the raffmate stream in a hydrocracking section comprising an acidic hydrocracking catalyst to provide a hydrocracked effluent; and, desorbing benzene from the adsorbent in the adsorption zone with the hydrocracked effluent in an extract stream.

In one or more embodiments, the process also includes separating the extract stream into a vapor stream and a liquid stream, the liquid stream comprising a benzene product stream.

In one or more embodiments, the process also includes purging voids of the adsorbent with a hydrogen stream. It is contemplated that at least a portion of the hydrogen stream used to purge voids of the adsorbent is passed to the cracking zone.

In one or more embodiments, the cracked effluent is rich in C₂ to C₄ hydrocarbons.

In one or more embodiments, the adsorption section comprises at least two vessels and the process further includes selectively adsorbing benzene from the feed stream in a first vessel in the adsorption section comprising an adsorbent and configured to provide a raffmate stream and selectively desorbing benzene from the feed stream in a second vessel in the adsorption section.

In a second aspect of the present invention, the invention may be broadly characterized as providing a process for separating benzene from a stream by: passing a feed stream to a first vessel of an adsorption section, wherein the feed stream comprises C₅ to C₇ non-aromatic hydrocarbons and benzene; selectively adsorbing benzene in the first vessel of the adsorption section with an adsorbent; selectively desorbing benzene from the adsorbent in the first vessel of the adsorption section; and, passing the feed stream to a second vessel of the adsorption section while the benzene is being selectively desorbed in the first vessel of the adsorption section.

In one or more embodiments, the process also includes passing a raffmate stream from the adsorption zone to a cracking zone being operated under conditions to crack non-aromatic hydrocarbons in the raffmate stream and provide an effluent stream and selectively desorbing benzene from the adsorbent of the adsorption section with the reaction section effluent stream into an extract stream. In one or more embodiments, the process also includes passing the extract stream into a separation zone to provide a benzene rich stream and a C₄- stream. It is contemplated that the process also includes purging non-aromatic hydrocarbons from the adsorbent with a purge stream before selectively desorbing the benzene. In one or more embodiments, the process also includes separating a raffmate stream from the adsorption section into a hydrogen rich stream and a liquid stream and selectively desorbing the benzene with the hydrogen rich stream. It is contemplated that the process also includes purging non-aromatic hydrocarbons from the adsorbent with a purge stream before selectively desorbing the benzene, wherein the purge stream comprises a cooled hydrogen stream. It is further contemplated that the process includes heating the hydrogen rich stream to provide a heated hydrogen stream and selectively desorbing the benzene with the heated hydrogen rich stream.

In one or more embodiments, the process also includes separating an extract stream from the adsorption section into a hydrogen stream and a benzene stream. It is further contemplated that the process includes selectively desorbing the benzene with the hydrogen stream.

In a third aspect of the present invention, the invention may be broadly characterized as providing a process for separating a benzene stream by: passing a feed stream to an adsorption section, wherein the feed stream comprises C₅ to C₇ paraffmic and naphthenic hydrocarbons and benzene and the adsorption section comprises at least two vessels; selectively adsorbing benzene in a first vessel of the adsorption zone with an adsorbent; selectively adsorbing benzene in a second vessel of the adsorption section with an adsorbent; selectively desorbing benzene from the adsorbent in the first vessel of the adsorption section; and selectively desorbing benzene from the adsorbent in the second vessel of the adsorption section. It is contemplated that the first vessel is adsorbing benzene when the second vessel is desorbing benzene and the second vessel is adsorbing benzene when the first vessel is desorbing benzene. In one or more embodiments, a desorbent used to desorb benzene comprises a heated stream. It is contemplated that the heated stream comprises an effluent stream from a cracking section. It is further contemplated that a feed stream to the cracking section comprises a raffmate stream from the adsorption section. It is also contemplated that the heated stream comprises a hydrogen stream from a separation zone.

Additional aspects, embodiments, and details of the invention are set forth in the following detailed description of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

In the drawings of the present invention, one or more embodiments are shown in which like numerals denote like elements and in which the Figure 1 shows a process flow diagram for one or more processes according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

One or more processes have been invented in which benzene from a feed stream is separated from non- aromatics in the feed stream by being selectively adsorbed onto an adsorbent. The processes according to the various embodiments of the present invention may provide a lower capital and utility cost for achieving a high purity benzene. Additionally, such processes may provide for the co-production of a byproduct stream that is suitable for feed to a steam cracker for olefin production.

With the foregoing general principals of the present invention in mind, one or more embodiments of the present invention will be described with the understanding that these embodiments are merely exemplary of the present invention and are not intended to be limiting.

With reference to the Figure, a feed stream 10, preferably comprising an effluent stream from a reforming reactor, is passed to a fractionation column 12. In a preferred embodiment, the fractionation column 12 is a depentanizer column or debutanizer column. Depending on the type and configuration of the fractionation column 12, a benzene rich vapor stream 14, which includes C₄-C₇ non-aromatics or, in some embodiments, C₅-C₇ non-aromatics, is produced by the fractionation column 12. In some embodiments the benzene rich vapor stream 14 may be a sidecut, while in other embodiments, benzene rich vapor stream 14 may comprise an overhead stream. A bottoms stream 16 from the fractionation column 12 may comprise toluene and heavy aromatic hydrocarbons and C₈+ non-aromatics and the further processing of this stream is not necessary to the understanding or practicing of the present invention.

The benzene rich vapor stream 14 from the fractionation column 12 is passed to a separation section 18. The separation zone 18 comprises at least one adsorber vessel 20a. Preferably, the separation section 18 includes two swing-bed adsorber vessels 20a, 20b, each vessel 20a, 20b includes an adsorbent that is capable of selectively adsorbing vapor phase benzene, and only weakly holding the non- aromatics. More specifically, each adsorber vessel 20a, 20b includes one or more beds of adsorbent pellets with suitable bed support grids. The adsorbent pellets may comprise Ba-X, Na-X, K-X, Ba-Y, K-Y, Na-Y, other similar high capacity faujasite or any suitable adsorbent which has a very high affinity for the benzene. The adsorber vessels 20a, 20b may be capable of up-flow or down flow operation, with a switch- valve manifold 22 at the inlet and a second switch-valve manifold 24 at the outlet that allows for switching and purging operations, similar to what is done in the Total Isomerization Processes (TIP) as described for example in U.S. Pat. Nos. 6,008,427 and 5,292,987. It should be appreciated that in the Figure, the first adsorber vessel 20a is shown as being operated in an "absorption mode" while the second adsorber vessel 20b is shown being operated in a "desorption mode." As will be appreciated, the switch-valve manifolds 22, 24 will allow the two adsorber vessels 20a, 20b to continuously switch back and forth between the two modes, so that while one vessel is on the absorption mode, the other vessel is in the desorption mode. In the adsorber vessels 20a, 20b, when operated in an adsorbing mode, the benzene from the benzene rich vapor stream 14 will be selectively adsorbed using the working volume of the adsorbent. The non-aromatics in the benzene rich vapor stream 20 will have very low adsorption affinity and thus will mostly pass through the adsorbent, with some left in the interstitial voids. A raffmate stream 26 from the separation section may be combined with a hydrogen rich stream 28 heated to between 260° to 37 C (500° to 700° F) and passed into a cracking section 30. It is contemplated that the cracking section 30 comprises a hydrocracking zone. The cracking section 30 comprises at least one reactor 32 that contains a microporous acidic zeolite catalyst with some metal, such as Re on MFI, Mo on UZM-14 or mordenite, or any other suitable acidic/metal catalyst. In the cracking section 30, the non-aromatics in the raffmate stream 26 are cracked to predominantly C₂ to C₄ paraffins under suitably mild conditions able to accomplish simple mono-cracking of the non-aromatics. The cracking section 30 will provide a heated cracked effluent stream 34 comprising mostly C₄- hydrocarbons and hydrogen. Via the switch-valve manifolds 22, 24, the heated cracked effluent stream 34, or at least a portion thereof, may be sent to an adsorber vessel 20a, 20b in a direction that is counter-current to the flow direction of benzene rich vapor stream 14 into the adsorber vessel 20a, 20b. The heated cracked effluent stream 34 will sweep out the non-selective voids of residual non-aromatics. After which, again via the switch-valves manifolds 22, 24, the heated cracked effluent stream 34 can desorb the benzene. Although not depicted as such, hot hydrogen could be used for desorption in addition to the heated cracked effluent stream 34.

A benzene rich effluent stream 36 from the adsorption section 18 may be cooled and passed to a vapor-liquid separator 38 to separate the benzene rich effluent stream 36 into a purified benzene steam 40 which can be passed, for example, to a product tank (not shown). The vapor stream 42, comprising hydrogen and C₂ to C₄ hydrocarbons, from the vapor-liquid separator 38 may be passed to a steam cracker for olefins production. It is contemplated that the vapor stream 42 from the vapor-liquid separator 38 may be combined with a portion of the heated cracked effluent stream 34. Additionally, at least a portion of the vapor stream 42 from the vapor-liquid separator 38 may be used as the hydrogen rich stream 28 combined with the effluent 26 passed into the cracking zone 30. The vapor stream 42 can then be directed to the steam cracker (not shown). Alternatively, the vapor stream 42 from the vapor-liquid separator 38 may also be recovered as high purity ethane, propane, and butane for use as fuel or petrochemical feedstock.

Again, in a two vessel configuration, it is preferred that while the first vessel is being operated in a desorption mode, the second vessel, via the valves and switching manifolds, is operated in an adsorption mode in which the benzene from the benzene rich vapor stream is being adsorbed within the adsorber vessel.

Such processes provide economical methods for adsorption and separation of benzene from a stream with non-aromatics. Additionally, these processes may gain a thermal advantage by close-coupling the heat of reaction of cracking with enhanced desorption of the purified benzene. It is contemplated that the present invention is particularly useful if integrated in with the operation of a CCR reactor unit. As discussed above, the adsorptive separation instead of a liquid-liquid extraction or extractive distillation is believed to be a more economical solution, both from an initial capital cost aspect, as well as from an operational cost aspect. It is contemplated that the present invention could also be used for coprocessing of benzene and toluene in order to avoid sending both benzene and toluene to liquid-liquid extraction or extractive distillation. In this case the adsorption section 18 and the cracking section 30 would become larger; however, the underlying principle would be the same, with post- fractionation of purified benzene and toluene. Depending on the effectiveness of the cracking section 30, it may be possible to send only a slipstream of benzene or benzene/toluene into the adsorption section 18 and still make the required product purity.

In at least one particular embodiment of the present invention, after 10 minutes of passing a feed stream to a first adsorber vessel (in adsorption mode), a set of switch- valves is actuated and the feed stream is diverted to a second adsorber vessel (which is now in adsorption mode). A stream of cool hydrogen may be introduced into the first vessel to purge out the non-selective voids and the interstitial volume. Then, after another time interval, a hot hydrogen stream (149 °C) is passed through the first vessel to desorb the high purity benzene. The benzene rich stream may be cooled, condensed, and separated from the hydrogen and recovered as high purity benzene liquid.

In the following example, it is demonstrated that 11 MT of adsorbent in two vessels could be used to recover as much as 52 KMTA of benzene from a feed stream. Using a light reformate (C₄-C₇) scut containing 51.9 KMTA of benzene along with 115.599 KMTA of nonaromatics. Two adsorption vessels, each loaded with 11 tons of adsorbent that has significant selectivity for benzene over non-aromatics in the vapor phase, could alternate between adsorption mode and desorption mode, with suitable switching valves and controllers. The non-aromatics hydrocarbons could be processed in a small cracking reactor containing 3.61 MT of acidic zeolite/metal catalyst at relatively mild conditions to bring about mono-cracking of the saturates to predominantly C₂ to C₄ hydrocarbons. The exothermic heat of reaction in the cracking reactor would be 10 kcal/mol and the temperature rise across the cracking reactor could be in the range of 93.3° C (200° F). The desorbent stream could be a combination of makeup hydrogen used to flush out the interstitial voids and nonselective void volume of the adsorbent, and hot cracking reactor effluent to desorb the benzene from the adsorbent. The catalytic conversion function would be limited to producing highly useful light alkanes for feed to a steam cracker, and recovering much of this heat for desorbing the high purity benzene from the adsorbers vessels.

It is believed that the present invention can be implemented into an integrated refinery-petrochemical complex. In this case, valuable benzene can be recovered for product sale in an economical and efficient manner.

It should be appreciated and understood by those of ordinary skill in the art that various other components such as valves, pumps, filters, coolers, etc. were not shown in the drawings as it is believed that the specifics of same are well within the knowledge of those of ordinary skill in the art and a description of same is not necessary for practicing or understanding the embodiments of the present invention.

While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary

embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims and their legal equivalents.

SPECIFIC EMBODIMENTS

While the following is described in conjunction with specific embodiments, it will be understood that this description is intended to illustrate and not limit the scope of the preceding description and the appended claims.

A first embodiment of the invention is a process for separating benzene from a stream with non-aromatics, the process comprising selectively adsorbing benzene from a feed stream in an adsorption section comprising an adsorbent and configured to provide a raffmate stream; cracking the raffmate stream in a cracking section comprising an acidic cracking catalyst to provide a cracked effluent; and, desorbing benzene from the adsorbent in the adsorption zone with the cracked effluent in an extract stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising separating the extract stream into a vapor stream and a liquid stream, the liquid stream comprising a benzene product stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising purging voids of the adsorbent with a hydrogen stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein at least a portion of the hydrogen stream used to purge voids of the adsorbent is passed to the cracking section. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the cracked effluent is rich in C₂ to C₄ hydrocarbons. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the adsorption section comprises at least two vessels and the process further comprising selectively adsorbing benzene from the feed stream in a first vessel in the adsorption section comprising an adsorbent and configured to provide a raffmate stream; and, selectively desorbing benzene from the feed stream in a second vessel in the adsorption section.

A second embodiment of the invention is a process for separating a benzene from non-aromatics, the process comprising passing a feed stream to a first vessel of an adsorption section, wherein the feed stream comprises C₅ to C₇ paraffmic hydrocarbons and benzene; selectively adsorbing benzene in the first vessel of the adsorption section with an adsorbent; selectively desorbing benzene from the adsorbent in the first vessel of the adsorption section; and, passing the feed stream to a second vessel of the adsorption section while the benzene is being selectively desorbed in the first vessel of the adsorption section. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising passing a raffmate stream from the adsorption section to a cracking section being operated under conditions to crack non- aromatic hydrocarbons in the raffmate stream and provide an effluent stream; and, selectively desorbing benzene from the adsorbent of the adsorption section with the effluent stream into an extract stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising passing the extract stream into a separation section to provide a benzene rich stream and a C₄- stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising purging non-aromatic hydrocarbons from the adsorbent with a purge stream before selectively desorbing the benzene. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising separating a raffmate stream from the adsorption section into a hydrogen rich stream and a liquid stream; selectively desorbing the benzene with the hydrogen rich stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising aromatic hydrocarbons from the adsorbent with a purge stream before selectively desorbing the benzene, wherein the purge stream comprises a cooled hydrogen stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising heating the hydrogen rich stream to provide a heated hydrogen stream; and, selectively desorbing the benzene with the heated hydrogen rich stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising separating an extract stream from the adsorption zone into a hydrogen stream and a benzene stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising selectively desorbing the benzene with the hydrogen stream. A third embodiment of the invention is a process for separating a benzene from a stream with non-aromatics, the process comprising passing a feed stream to a an adsorption section, wherein the feed stream comprises C₅ to C₇ paraffmic hydrocarbons and benzene and the adsorption section comprises at least two vessels; selectively adsorbing benzene in a first vessel of the adsorption section with an adsorbent; selectively adsorbing benzene in a second vessel of the adsorption section with an adsorbent; selectively desorbing benzene from the adsorbent in the first vessel of the adsorption section; selectively desorbing benzene from the adsorbent in the second vessel of the adsorption section; and, wherein the first vessel is adsorbing benzene when the second vessel is desorbing benzene and the second vessel is adsorbing benzene when the first vessel is desorbing benzene. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph wherein a desorbent used to desorb benzene comprises a heated stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph wherein the heated stream comprises an effluent stream from a cracking section. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph wherein a feed stream to the cracking section comprises a raffmate stream from the adsorption section. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph wherein the heated stream comprises a hydrogen stream from a separation section.

Without further elaboration, it is believed that using the preceding description that one skilled in the art can utilize the present invention to its fullest extent and easily ascertain the essential characteristics of this invention, without departing from the spirit and scope thereof, to make various changes and modifications of the invention and to adapt it to various usages and conditions. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limiting the remainder of the disclosure in any way whatsoever, and that it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.

Claims

CLAIMS What is claimed is:

1. A process for separating benzene from a stream with non-aromatics, the process comprising:

selectively adsorbing benzene from a feed stream (10) in an adsorption section

(18) comprising an adsorbent and configured to provide a raffmate stream (26);

cracking the raffmate stream (26) in a cracking section (34) comprising an acidic cracking catalyst to provide a cracked effluent; and,

desorbing benzene from the adsorbent in the adsorption zone (18) with the cracked effluent (34) in an extract stream (36).

2. The process of claim 1 further comprising: separating the extract stream (36) into a vapor stream (42) and a liquid stream (40), the liquid stream (40) comprising a benzene product stream.

3. The process of claim 1 further comprising: purging voids of the adsorbent with a hydrogen stream.

4. The process of claim 3 wherein at least a portion of the hydrogen stream used to purge voids of the adsorbent is passed to the cracking section.

5. The process of claim 1 wherein the cracked effluent (34) is rich in C₂ to C₄ hydrocarbons.

6. The process of any one of claims 1 to 5 wherein the adsorption section

(18) comprises at least two vessels (20a, 20b) and the process further comprising: selectively adsorbing benzene from the feed stream (10) in a first vessel (20a) in the adsorption section (18) comprising an adsorbent and configured to provide a raffmate stream (26); and,

selectively desorbing benzene from the feed stream (10) in a second vessel

(20b) in the adsorption section (18).

7. The process of any one of claims 1 to 5 wherein the feed stream comprises C₅ to C₇ paraffmic hydrocarbons and benzene.

8. The process of any one of claims 1 to 5 further comprising:

removing non-aromatic hydrocarbons from the adsorbent with a purge stream before selectively desorbing the benzene, wherein the purge stream comprises a cooled hydrogen stream.

9. The process of claim 8 further comprising:

heating the hydrogen rich stream to provide a heated hydrogen stream; and, selectively desorbing the benzene with the heated hydrogen rich stream.

10. The process of claim 9 further comprising:

separating an extract stream from the adsorption zone into a hydrogen stream and a benzene stream.