PRIORITY CLAIM OF EARLIER NATIONAL APPLICATION

This application claims the benefit of U.S. Provisional Application No. 62/091, 123 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 para-xylene from a mixture of aromatic hydrocarbons, and more particularly to separating a para-xylene stream coupled with an adsorptive separation process. B ACKGROUND OF THE INVENTION

Cg alky] aromatic hydrocarbons are generally considered to be valuable products, with the highest demand being for para-xylene. Major sources of para-xylene include mixed xylene streams that result from the refining of crude oil. Examples of such streams are those resulting from commercial xylene isomerization processes or from the separation of C« alkylaromatic hydrocarbon fractions derived from a catalytic reformate by liquid-liquid extraction and/or fractional distillation.

A simulated moving bed ("SMB") adsorption process is used commercially in a number of large scale petrochemical separations to recover high purity para-xylene from mixed xylenes. As used herein, "mixed xylenes" refers to a mixture of Cg aromatic isomers that includes ethylbenzene, para-xylene, meta-xylene and ortho-xylene. High purity para- xylene may be used for the production of polyester fibers, resins and films by converting para-xylene to terephthalic acid or dimethyl terephthalate, which is then reacted with ethylene glycol to form polyethylene terephthalate, and the raw material for most polyesters.

The general technique employed in the performance of SMB adsorptive separation processes is widely described and practiced. Generally, the process simulates a moving bed of adsorbent with continuous counter-current flow of a liquid feed over the adsorbent. Feed and products enter and leave adsorbent beds continuously, at nearly constant compositions. Separation is accomplished by exploiting the differences in affinity of the adsorbent for para- xylene relative to the other Cg aromatic isomers. More specifically, the adsorbent is selected for its initial affinity for para-xylene relative to the other Cs aromatic isomers.

In order to desorb the para-xylene, a desorbent is used for which the adsorbent has a higher affinity relative to para-xylene. One such desorbent is para-diethylbenzene, a heavy desorbent, and which is two carbon numbers heavier than the xylenes. It is also known to use toluene, a light desorbent, which is only one carbon number lighter than the xylene feed. As a desorbent, toluene is comparatively weaker than para-diethylbenzene, since toluene has only one carbon number difference from the xylenes. Since the toluene is weaker, it requires a higher desorbent to feed ratio (D/F) and more energy for separation in extract and raffinate fracti onati on column s .

In order to produce a high purity para-xylene stream from a typical reformate product, which includes a mixture of toluene, xylenes and C ₉ aromatic hydrocarbons, an adsorptive separation with a light desorbent may be coupled with a xylene isomerization and ethylbenzene dealkylation. Toluene may be used as the desorbent to allow co-processing of the C9 aromatic hydrocarbons in the adsorptive separation, which reduces the capital costs for the processor.

If the feed stream to the separation unit is a mixed xylene feed stream, there is no need to transalkylate toluene with heavier aromatics to produce more benzene and xylenes. As a result, the use of a light desorbent in the combined processing is less desirable due to the high D/F ratio as well as the high energy required for separation of the desorbent from the raffinate and the extract.

It has been generally suggested that benzene may be used as desorbent. Indeed, theoretically, since benzene is two carbon atoms lighter than para-xylene, using benzene as a desorbent in a para-xylene adsorptive separation process should allow for lower energy requirements for separation from xylenes by fractionation and lower D/F requirements due to higher affinity of the adsorbent for the benzene. However, empirical data and the state of the art has expressly stated that benzene should be avoided in para-xylene recovery processes. This conclusion is based upon benzene taking up capacity on the adsorbent and altering the various components' selectivity. See, U.S. Pat. No. 3,558,732.

Despite these findings, it would be desirable to provide para-xylene adsorptive separation processes which can effectively and efficiently utilize benzene as a desorbent. It would further be desirable for such a process to economically process a mixed xylene feed stream and even further desirable if such a process could produce some of the desorbent used in the process

SUMMARY OF THE INVENTION

One or more processes have been invented in which benzene is used as a desorbent in a para-xylene separation process.

Accordingly, in a first aspect of the invention, the invention may be broadly characterized as a process for separating para-xylene from a mixed xylene feed stream by: selectively dealkylating ethylbenzene in a dealkvlation section operated under dealkylation conditions and having a dealkylation catalyst to provide a dealkylation effluent; selectively adsorbing and purifying para-xylene in an adsorption section using an adsorbent; selectively desorbing para-xylene in the adsorption section into an extract stream with desorbent; separating the extract stream from the adsorption section into a para-xylene product and a desorbent; and, recycling at least a portion of the desorbent into the adsorption section, wherein the desorbent is benzene.

In at least one embodiment, the process further includes selectively isomerizing at least a portion of a raffinate stream depleted in para xylene from the adsorption section in an isomerization section into an isomerate effluent. It is contemplated that the process includes separating the isomerate effluent into a toluene stream, a heavy aromatic stream and para- xylene rich stream. It is also contemplated that the process further includes selectively adsorbing para-xylene from the xylene isomerate stream in the adsorption section. It is even further contemplated that the process includes separating the raffinate stream from the adsorption section into a benzene rich stream and a benzene lean stream. The benzene lean stream may be the portion of the raffinate stream comprising unrecovered C8 aromatics. It is contemplated that the process also includes recycling at least a portion of the benzene rich stream back into the adsorption section.

In one or more embodiments, the process includes selectively dealkylating ethylbenzene from the isomerate effluent in the dealkylation section.

In a second aspect of the present invention, the present invention may be broadly characterized as a process for separating a para-xylene stream by: passing a feed stream to a dealkylation section having a dealkylation catalyst being operated to provide a dealkylation effluent, the feed stream comprising xylenes; passing the dealkylation effluent to an adsorption section zone comprising an adsorbent and being operated to selectively adsorb para-xylene; and, passing a benzene stream into the adsorption zone to desorb the para- xylene. The benzene stream preferably comprises at least a portion of a benzene rich extract stream from the adsorption section, at least a portion of a benzene-rich raffmate stream from the adsorption zone, or both.

In at least one embodiment, the process includes passing the extract stream from the adsorption section to a separation zone to provide a para-xylene stream and a desorbent benzene stream, the desorbent benzene stream comprising the portion of the extract stream used for desorbing para-xylene.

In some embodiments, the process includes passing the raffmate stream from the adsorption section to a separation zone to provide a benzene lean raffmate stream and a benzene rich stream, the raffmate benzene rich stream comprising the portion of the raffmate stream used for purifying the para-xylene.

In one or more embodiments, the process includes passing the benzene lean raffmate stream to an isomerization section comprising an isomerization catalyst and configured to selectively isomerize the benzene lean raffmate stream and provide an isomerization effluent stream. It is contemplated that the process further includes passing a first portion of the isomerization effluent stream to the deaikyiation section, and passing a second portion of the isomerization effluent stream to a separation zone.

In some embodiments, the process includes passing the isomerization effluent stream to a separation zone and separating the isomerization effluent stream into at least a xylene rich stream. It is contemplated that the process also includes passing the xylene rich stream to the adsorption section. The separation zone may comprise a divided wall separation column. It is contemplated that the divided wall separation column separates the isomerization effluent stream into a xylene rich stream, a toluene rich stream and a C ₉ + aromatic rich stream.

In some embodiments, the isomerization zone is a liquid phase isomerization section. In at least one embodiment, the process includes recovering a benzene product stream. In a third aspect of the present invention, the invention may be broadly characterized as providing a process for separating a para-xylene stream by: passing a feed stream to a deaikyiation section having a deaikyiation catalyst being operated to provide a deaikyiation effluent, the feed stream comprising xylenes; passing the deaikyiation effluent to an adsorption section comprising an adsorbent and being operated to selectively adsorb para- xylene; passing a raffinate stream from the adsorption section to a separation zone to provide a benzene lean raffinate stream and a raffinate benzene rich stream; recycling at least a portion of the benzene rich raffinate stream to the adsorption section to desorb the para- xyiene into an extract stream; passing the extract stream from the adsorption section to a separation zone to provide a para-xylene stream and a desorbent rich benzene stream; and, passing the benzene lean raffinate stream to an isomerization section comprising an isomerization catalyst and configured to selectively isomerize the benzene lean raffinate stream and provide an isomerization effluent stream.

In some embodiments, the process includes passing the desorbent benzene stream into the adsorption section to desorb the para-xylene.

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

BRIEF 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:

Figure J shows a process flow diagram of a process according to one or more embodiments of the present invention; and,

Figure 2 shows a graphical comparison of benzene selectivity based upon moisture content of an adsorbent.

DETAILED DESCRIPTION OF THE INVENTION

One or more processes have been invented in which benzene is used as a desorbent, and where the strength of the benzene for the adsorbent, which is relatively high, can be tempered by dilution with aliphatic paraffins, by operating temperature, by adsorbent moisture content (or loss of ignition "LOI"), by adsorbent cation balance, or a combination thereof. While, benzene has historically been viewed as a component that should be avoided in para-xylene recovery processes, it is believed that benzene can effectively and efficiently be used as a desorbent with the proper choice of adsorbent cation composition (Ba-K balance on faujasite zeolite "FAU"), adsorbent moisture content, operating conditions such as temperature and even dilution with aliphatic paraffins. According to various embodiments of the present invention, a separation unit is operated with benzene as the primary desorbent. It is contemplated that a Ba-K X FAU adsorbent is used in which the cation (Ba, K) ratio has been adjusted, that a moisture content of an adsorbent is adjusted, that temperature of the separation zone have been adjusted, or a combination thereof to allow benzene to be efficiently used as a desorbent. An inert diluent, such as normal hexane or normal heptane can also be used to reduce the desorbent strength.

For a mixed xylene feed stream, a selective ethylbenzene deaikyiation from the feed with a catalyst can be utilized to reduce the ethylbenzene concentration in the mixed xylene feed with minimal xylenes loss. The process will generate additional benzene which can be used as desorbent. Additionally, the selective ethylbenzene deaikyiation may minimize the chance for methyl-ethylbenzene isomers to be created elsewhere in the process. Finally, since a raffinate from the separation unit will be very low in ethylbenzene, a liquid phase isomerization may be used to increase the xylenes produced in the process. Since such a process would produce benzene, no inventory of desorbent is needed, and, in fact, it is believed that excess benzene may be produced and recovered as a valuable by-product. Additionally, the use of a liquid phase isomerization does not require a fired heater, a recycle gas compressor or a combined feed heat exchanger, providing a process with lower capital costs and requiring less utility consumption.

These and other benefits of the present invention will be appreciated by those of skill in the art based upon the following description, which is intended to be merely exemplary of the principles of the present invention, and not intended to be limiting.

As shown in FIG. 1 , a feed stream 10 may be charged in a heater 12 and passed to a reaction zone 14. The feed stream 10 typically comprises para-xylene, as well as other C8 aromatic compounds including meta-xylene, ortho-xylene, and, ethylbenzene. The feed stream 10 may be combined with a hydrogen rich gas stream 16, as well as a recycle aromatic hydrocarbon stream 17 (discussed below).

In various embodiments the reaction zone 14 comprises a deaikyiation zone 18. In the deaikyiation zone 18, the mixture of entering hydrocarbons is contacted with a solid catalyst under conditions sufficient to selectively dealkylate ethylbenzene. The conditions may be chosen to complete the staged conversion of ethylbenzene, with the ethylbenzene in this reaction zone being dealkylated to form benzene and ethane and ethylene. The deaikyiation zone effluent stream 20 may be cooled through the use of air or cooling water heat exchanger 22. Additionally, although not shown, the deaikyiation zone effluent stream 20 may further be cooled by indirect heat exchange against the feed stream 10 entering the reaction zone 14.

The deaikyiation zone effluent stream 20 is separated, for example, in a vapor-liquid separator 24 to produce a vapor phase hydrogen stream 26 and a liquid phase deaikyiation effluent stream 28. The vapor phase hydrogen stream 26 includes hydrogen and light hydrocarbons which ma be recycled and combined with the feed stream 10 as the hydrogen rich gas stream 16 described above. The liquid phase deaikyiation effluent stream 28 may be passed to a separation zone 30 to separate the para-xylene from the other components of the liquid phase deaikyiation effluent stream 28.

As shown in Figure 1, the xylene deaikyiation effluent stream 28 is passed the separation zone 30 which comprises an adsorption zone 32 in which the para-xylene is separated from xylene mixture using a SMB unit. The SMB process is a commercial adsorptive separation process using several adsorption beds and moving the inlet streams and outlet streams between the beds, where a process stream comprising para-xylene is passed through the beds. The adsorption beds comprise an adsorbent for preferentially adsorbing the para-xylene and later desorbing the para-xylene using a desorbent as the process stream. As is known in the art, SMB technology is an established commercial technology wherein beds of the adsorbent are held in place in one or more typically cylindrical adsorbent chambers and the positions at which the streams involved in the process enter and leave the chambers are slowly shifted along the length of the chambers. Normally, there are at least four streams (feed, desorbent, extract, and raffinate) employed in this procedure and the location at which the feed and desorbent streams enter the chamber via individual bedlines and the extract and raffinate streams leave the chamber via other bedlines are simultaneously shifted in the same direction at set intervals. Each shift in location of these transfer points delivers or removes liquid from a different bed within the adsorbent chamber. This shifting could be performed using a dedicated bedline for each stream at the entrance to each bed. However, a large scale simulated moving bed technology process unit will normally have at least eight separate beds, or at least twelve separate beds, or at least sixteen separate beds or as many as twenty-four separate beds. Employing a separate bedline for each stream at each bed would greatly increase the cost of the process and therefore the bedlines are reused with each bedline carrying one of the four process streams at some point in the cycle and a valve, such as a rotary valve controlling the flow of the four streams throughout the unit.

A SMB process produces at least two effluent streams: an extract stream containing a compound which was selectively retained on the adsorbent; and, a raffmate stream containing compounds not strongly adsorbed. Both the extract and the raffinate streams will also contain the desorbent. The concentration of the desorbent in the extract and raffinate stream will vary somewhat with time during each incremental shifting of the process bed lines. The extract and raffinate streams typically are passed into extract and raffinate fractionation columns, in which the desorbent is separated from the extract and raffmate compounds, respectively. The desorbent is in this way recovered, and it may be then recycled to the adsorption zone as a process stream referred to herein as the desorbent stream. Each bed will include an adsorbent, discussed in more detail below.

The adsorbent in the adsorption section 32 will preferentially adsorb para-xylene while permitting meta-xylene, ortho-xyiene, and ethyibenzene to essentially pass through the adsorption zone 32 in an unchanged condition and become part of a raffinate stream 34. Thereafter, the adsorbed para-xylene is desorbed from the adsorbent by passing a desorbent through the adsorbent bed, forming an extract stream 36. The desorbent material is commonly also used to flush non-adsorbed materials from the void spaces around and within the adsorbent. Both the raffinate stream 34 and the extract stream 36 contain the desorbent compound(s) and may be fractionated to recover the desorbent, discussed below.

The adsorption and desorption steps can be performed in a single large bed of adsorbent or in several parallel beds on a swing bed basis. However, it has been found that simulated moving bed adsorptive separation provides several advantages, such as high purity and recovery. Therefore, many commercial scale petrochemical separations, especially those for the separation of xylenes and mixed normal paraffins are performed using SMB technology. Further details on equipment and techniques for using in an SMB process may be found in US 3,208,833; US 3,214,247; US 3,392, 113; US 3,455,815; US 3,523,762; US 3,617,504; US 4,006, 197, US 4, 133,842; US 4,434,051; and other patents. A different type of SMB operation which can be performed using similar equipment, adsorbent and conditions but which simulates co-current flow of the adsorbent and liquid in the adsorption chambers is described in US 4,402,832 and US 4,498,991. In the various embodiments of the invention, the desorbent used in the adsorptive separation process is benzene. As discussed above, while it has been suggested to utilize benzene in the prior art, it has not been shown how benzene can be an efficient and effective desorbent to recover para-xylene from an adsorbent. In the various processes of the present invention, the high strength of the benzene is lowered by dilution with an aliphatic hydrocarbon, by proper operating temperature, by adjusting adsorbent moisture content, by selecting proper adsorbent cation balance, or a combination thereof. For example, in various embodiments, the adsorbent is an X FAU zeolite or a Y FAU zeolite that has been ion exchanged with metals, specifically at least barium (Ba) and preferably also potassium (K). For an X FAU zeolite it is believed that the ratio of K to Ba on the adsorbent is preferably in the range of 0 to 1 for use with a benzene desorbent. For a Y FAU zeolite it is preferred that the ratio of to Ba is in the range of 0 to 500 for use with a benzene desorbent. Separately, or in addition to using the X FAU zeolite or Y FAU zeolite, it is also believed that by controlling one or more operating parameters, benzene can be used successfully as a desorbent. For example, the strength of the benzene can be lowered by diluting it with one or more aliphatic paraffins, such as n-hexane or n-heptane. It is believed that a ratio of benzene to the aliphatic paraffins is in the range of 1.0 to 0,25 for use with a benzene desorbent. Additionally, adjusting or controlling the moisture content on the adsorbent is believed to allow benzene to be utilized as a desorbent in such a process. More specifically, a moisture content (LOI) of the adsorbent is preferably between 1.0 and 6.0 wt%. Indeed, as shown in the attached Figure 2, by adjusting the moisture content of the adsorbent, the selectivity of the adsorbent to benzene increased. Thus, a range of moisture content is believed to provide an appropriate selectivity for the adsorbent to benzene. Finally, it is also believed that by controlling or maintain a temperature of the adsorption zone in an operating range of between 80° to 177°C will also allow for the use of benzene as a desorbent in the adsorptive separation process. In various embodiments, these different factors may be combined together. However, it is not required for the practicing of the present invention that such occur.

Returning to Figure 1 , at least a portion of the extract stream 36 is passed to a separation zone 38 having a fractional distillation column 40. Likewise, at least a portion of the raffinate stream 34 is passed to a second separation zone 42 also having a fractional distillation column 44. In each of the fractional distillation columns 40, 44, at least a portion of the desorbent is recovered in a desorbent stream 46, 48. At least a portion of the desorbent streams 46, 48 from the fractional distillation columns 40, 44 may be recycled to the adsorption section 32 as desorbent stream 50. Additionally, since the reaction section 14 will be producing benzene, a benzene product stream 52 may also be recovered and, for example stored, or sold as by-product.

The fractional distillation column 40 which receives the extract stream 36 will also provide an extract product stream 54. Concomitantly, the fractional distillation column 44 which receives the raffinate stream 34 will provide a raffmate product, stream 56. The terms "extract product stream" and "raffinate product stream" mean streams produced by the process containing, respectively, an extract component and a raffinate component in higher concentrations than those found in the extract stream 36 and the raffmate stream 34 withdrawn from the adsorption section 32. The extract stream 36 will be rich in the para- xylene. The term "rich" is intended to indicate a concentration of the indicated compound or class of compounds greater than 50 mole percent. The extract product stream 54 will be para-xylene which can be processed further as desired. The raffinate product stream 56, lean in benzene, will comprise, for example, ortho-xylene and other aromatic hydrocarbons which may be passed to an isomerization section 58 to be isomerized into more desirable aromatics, including para-xylene.

As mentioned at the outset since the raffinate product stream 56 will be lean in ethylbenzene, the raffmate product stream 56, may be passed to a liquid phase isomerization section 60. In the liquid phase isomerization zone 60, the raffinate product stream 56 may be contacted with a suitable catalyst o in liquid phase. Contacting may be effected using the catalyst system in a fixed-bed system, a moving-bed system, a fluidized-bed system, slurry system or ebullated-bed system or in a batch-type operation.

Although not depicted as such, the raffinate product stream 56 may be preheated by suitable heating means as known in the art to the desired reaction temperature and passed in liquid phase in the substantial absence of hydrogen into a reactor containing a fixed bed or beds of the isomerization catalyst. The term "substantial absence of hydrogen" means that no free hydrogen is added to the feed mixture and that any dissolved hydrogen from prior processing is substantially less than 0.05 moles/mole of feed, frequently less than 0.01 moles/mole, and possibly not detectable by usual analytical means. The reactor in the liquid phase isomerization zone 60 may comprise a single reactor or two or more separate reactors with suitable means there between to ensure that the desired isomenzation temperature is maintained at the entrance to each reactor. The reactants may be contacted with the catalyst bed in upward-, downward-, or radial-flow fashion to obtain an isomerized product which contains aikyiaromatic isomers in a ratio which differs from that of the feed mixture.

Suitable isomerization conditions include temperature ranging from 100° to 500°C, and preferably from 200° to 400° C. The pressure should be sufficient to maintain the feed mixture in liquid phase, generally from 500 kPa to 5 MPa absolute. The reactor should contains a sufficient volume of catalyst to provide a liquid hourly space velocity with respect to the feed mixture of from 0.5 to 50 hr ^~l , and preferably 0.5 to 20 hr ^"1 .

Suitable catalysis comprising molecular sieves for xylene isomerization are known in the art. U.S. Pat. No. 3,856,872, for example, teaches xylene isomerization and ethylbenzene conversion with a catalyst containing ZSM-5 (MFI-type), ZSM-12 (MTW-type (IUPAC Commission on Zeolitic Nomenclature)), or ZSM-21 zeolite. U.S. Pat, No, 4,899,011 discloses isomerization of Cs aromatics using two zeolites such as ZSM-5 with different crystal sizes, each of which is associated with a strong hydrogenation metal. U.S. Pat. No. 4,939,1 10 discloses a catalyst for isomerization using two metals and a pentasii zeolite, which includes ZSM-12 (MTW-type) zeolite, U.S. Pat. No, 6,222,086 and U.S. Pat. No. 6,576,581 disclose a dual catalyst system for aromatics isomerization using at least one non-zeolitic molecular sieve and one zeolitic alurainosilicate, U.S. Pat, No. 6,448,459 discloses a liquid phase isomerization stage and a gas phase isomerization stage with EUO-type zeolite. U.S. Pat, No. 4,962,258 discloses a process for liquid phase xylene isomerization over gallium- containing, crystalline silicate molecular sieves as an improvement over alurainosilicate zeolites ZSM-5, ZSM-12 (MTW-type), and ZSM-21 as shown in U.S. Pat. No. 3,856,871. The '258 patent refers to borosilicate work, as exemplified in U.S. Pat. No. 4,268,420, and to zeolites of the large pore type such as faujasite or mordenite.

Returning to Figure 1, an isomerized effluent 62 from the liquid phase isomerization zone 60 may be passed to a fractionation zone 64 having, for example, a column 66, preferably a split shell column.

In the column 66 of the fractionation zone 64, the isomerized effluent 62 may be separated into a xylene stream 70, a toluene stream 72, and a C9+ aromatic hydrocarbon (or a heavy aromatic) stream 80, The C9+ aromatic hydrocarbon stream 80 and the toluene stream 72 can be processed further as is known in the art. By using benzene as a desorbent in the separation zone, the separation of a high purity xylene stream from a mixed xylene stream with can be efficiently and effectively achieved. By including an ethylbenzene dealkylation, the desorbent can be produced within the process, thus not requiring the additional costs typically associated with maintaining a supply of desorbent. Additionally, since the raffinate from the adsorptive separation has a low concentration of ethylbenzene, the raffinate can be processed with a liquid phase isomerization, which is less costly than alternatives. Thus, the various embodiments provide processes for the production and separation of a high purity para-xylene stream that are economical and effective for refiners and processors. EXAMPLES

The concept of using benzene a desorbent for Cg Aromatic isomer separations was evaluated using a dynamic pulse test apparatus, such as described in US 4,886,929, In this case the chosen temperature was 135°C and benzene was used as the desorbent, with a 70 cc volume of adsorbent. In this particular test a faujasite adsorbent with a 2.5 Si/Al ₂ was used. The adsorbent had been ion exchanged to contain barium and potassium in a 75/25 ratio as oxide. A range of barium and potassium ratios could be used for optimization, as well as a range of adsorbent moisture contents. In this case the moisture content as measured by loss on ignition (LOT) at 900°C was 4.6 wt%. A feed pulse blend that contained n~C ₉ , EB, Px, MX, OX and p-DEB was prepared. N-C9 is a non-adsorbed species and typically is used as a tracer. It is the first component to exit the adsorbent column. At the outlet of the adsorbent column and online GC or fraction collector for offline GC will collect samples at prescribed time intervals. The test procedure has the following key steps;

1. Desorbent flow is established through the column containing the adsorbent.

2. The feed pulse is introduced to the column, followed by the resumption of desorbent flow.

3. Online GC or liquid fractions are collected at the outlet and analyzed.

4. From the analyses, component selectivities can be calculated, relative to a key component such as PX.

In this particular example, the following component selectivities were measured as shown in Table 1 : TABLE 1

When another sample of the faujasite adsorbent was ion-exchanged to have a 58/42 ratio of Ba and K as oxides, the following component seiectivities were measured as shown in Table 2

TABLE 2

These results illustrate that the purification and recover)-' of high purity PX can be accomplished with a faujasite adsorbent containing Ba and K cations, when used in a simulated moving bed process such as the UOP Parex Process, and employing benzene as the desorbent. Those who are expert in the art will recognize that by optimizing the Si/Al?. the Ba and K and the LOI, that a most optimal set of seiectivities will be found. The performance of this separation in the presence of benzene desorbent is novel and can be used for economical recover}' of pX in an industrial process.

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 a para-xylene stream, the process comprising selectively dealkylating ethylbenzene in a dealkylation section operated under dealkylation conditions and having a dealkylation catalyst to provide a dealkylation effluent; selectively adsorbing para-xylene in an adsorption section having an adsorbent; selectively desorbing para-xylene in the adsorption section into an extract stream with desorbent; separating the extract stream from the adsorption section into a para-xylene product and a desorbent; recycling at least a portion of the desorbent into the adsorption section, wherein the desorbent is benzene. 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 selectively isomerizing at least a portion of a raffinate stream from the adsorption section in an isomer! zation section into an isomerate effluent. 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 isomerate effluent into a toluene stream, a heavy aromatic stream and para-xylene rich 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 selectively adsorbing para-xylene from the xylene rich stream in the adsorption section. An embodiment of the invention is one, any or ail of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising separating the raffinate stream from the adsorption section into a benzene rich stream and a benzene lean stream, wherein the benzene lean stream is the portion of the raffinate stream isomerizing in the isomerization section. An embodiment of the invention is one, any or ail of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising recycling at least a portion of the benzene rich stream into the adsorption 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 further comprising selectively dealkylating ethylbenzene from the isomerate effluent in the dealkylation section.

A second embodiment of the invention is a process for separating a para-xylene stream, the process comprising passing a feed stream to a dealkylation section having a dealkylation catalyst being operated to provide a dealkylation effluent, the feed stream comprising xylenes, passing the dealkylation effluent to an adsorption section comprising an adsorbent and being operated to a selectively adsorbing para-xylene; and, passing a benzene stream into the adsorption section to desorb the para-xylene, wherein the benzene stream comprises at least a portion of an extract stream from the adsorption section, at least a portion of a raffinate stream from the adsorption section, or both. 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 from the adsorption section to a separation zone to provide a para-xylene stream and a desorbent benzene stream, the desorbent benzene stream comprising the portion of the extract stream used for desorbing para-xylene. 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 raffinate stream from the adsorption section to a separation zone to provide a benzene lean raffinate stream and a raffinate benzene stream, the raffinate benzene stream comprising the portion of the raffinate stream used for desorbing para-xylene. 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 benzene lean raffinate stream to an isomerization section comprising an isomerization catalyst and configured to selectively isomerize the benzene lean raffinate stream and provide an isomerization effluent 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 a first portion of the isomerization effluent stream to the dealkylation section; and, passing a second portion of the isomerization effluent stream to a separation zone. An embodiment of the invention is one, any or ail of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising passing the i somen zati on effluent stream to a separation zone; separating the isomerization effluent stream into at least a xylene 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 passing the xylene rich stream to 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 wherein the separation zone comprises a divided wall separation column. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the divided wall separation column separates the isomerization effluent stream into a xylene rich stream, a toluene rich stream and an C ₉ + aromatic rich stream. An embodiment of the invention is one, any or ail of prior

embodiments in this paragraph up through the second embodiment in this paragraph wherein the isomerization section is a liquid phase isomerization 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 recovering a benzene product stream.

A third embodiment of the invention is a process for separating a para-xylene stream, the process comprising passing a feed stream to a dealkylation section having a dealkylation catalyst being operated to provide a dealkylation effluent, the feed stream comprising xylenes; passing the dealkylation effluent to an adsorption section comprising an adsorbent and being operated to a selectively adsorbing para-xylene; passing a raffmate stream from the adsorption section to a separation zone to provide a benzene lean raffmate stream and a raffmate benzene stream, recycling at least a portion of the benzene raffinate stream to the adsorption section to desorb the para-xylene into an extract stream; passing the extract stream from the adsorption section to a separation zone to provide a para-xylene stream and a desorbent benzene stream; passing the benzene lean raffmate stream to an isomerization section comprising an isomerization catalyst and configured to selectively isomerize the benzene lean raffinate stream and provide an isomerization effluent stream. An embodiment of the invention is one, any or all of pri or embodiments in this paragraph up through the third embodiment in this paragraph further comprising passing the desorbent benzene stream into the adsorption section to desorb the para-xylene.

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, ail parts and percentages are by weight, unless otherwise indicated.