Desorbent purification in a simulated moving bed separation process and device

Abstract

The present invention relates to a method and device for simulated moving bed separation comprising / using: a simulated moving bed adsorption separation unit (1) treating a feedstock (2) with a desorbent (3) to produce an extract (4) and a raffinate (5); an extract column (6) treating the extract to separate a product of interest (7) and desorbent; a raffinate column (8) treating the first raffinate to separate desorbent; and an adsorption separation unit (17) treating desorbent to produce purified desorbent (15) sent to the simulated moving bed separation unit. The present invention also relates to the modification of a pre-installed simulated moving bed separation unit. Figure 2 to be published

Description

Title of the invention: Purification of desorbent in a simulated moving bed separation process and device Technical field

[0001] The present invention relates to a device and a method for the simulated moving bed separation of a product of interest (such as paraxylene) from a mixture of products (such as xylenes) using a desorbent (such as paradiethylbenzene). In particular, the present invention relates to the purification of the desorbent. Prior art

[0002] [Fig. 1] proposes a reference scheme used for the separation in a simulated moving bed (sometimes abbreviated in the rest of the text LMS or SMB for “Simulated Moving Bed” according to the Anglo-Saxon terminology) of a product of interest (in this example paraxylene) from a mixture of products (in this example xylenes, aromatics with 8 carbon atoms, mixture called “A8”), in the case of the use of a heavy desorbent (in this example paradiethylbenzene). A desorbent is said to be “heavy” when its boiling point is higher than that of the product of interest to be separated. In particular, a simulated moving bed separation unit 1 makes it possible to separate a feed 2 (product mixture) with the desorbent 3 to produce an extract 4 containing the product of interest and desorbent, and a raffinate 5 containing the product mixture depleted in product of interest (in this example orthoxylene and metaxylene) and desorbent.

[0003] Current simulated moving bed separation technologies use LMS units that have a number of common features: - one or two separation columns (or adsorbers) each comprising a plurality of adsorption chambers arranged between a distribution channel and a collection channel, said adsorption chambers comprising a bed of adsorbent within which a fluid flows, - injection systems, in particular of the feedstock and desorbent, and withdrawal systems, in particular of the effluents produced called extract and raffinate, - collection and redistribution systems, known as inter-bed zones, to move from one bed to the next.

[0004] The extract 4 and the raffinate 5 are each directed towards a separation unit, typically by distillation, with the aim of separating the products from the desorbent: - the extract column 6 separates the product of interest 7 and a desorbent stream 3; - the raffinate column 8 separates a desorbent stream 3 and the mixture of products depleted in product of interest 9.

[0005] The product of interest 7 is often purified in a purification column 10 by distillation to produce a purified product of interest 11 and a light fraction 12.

[0006] The desorbent flow 3 recovered at the bottom of the two extract 6 and raffinate 8 columns is recycled to the inlet of the simulated moving bed separation unit 1 for obvious gains in desorbent consumption. A top-up is made regularly to compensate for the losses of desorbent which may be among the product mixture depleted in product of interest 9.

[0007] In practice, heavy compounds (in this example, compounds with at least 10 carbon atoms, so-called “C10+” compounds) may appear over time during operation of the process. To avoid accumulating heavy compounds in the desorbent stream 3, a distillation column 13 ensures extraction of heavy compounds 14 (e.g., continuous or periodic extraction) to produce purified desorbent 15.

[0008] In this example, the aromatic compounds with 9 carbon atoms (so-called A9 compounds) also tend to accumulate in the desorbent streams 3 over time and reduce its desorption capacity. For this reason, a distillation column called "Xylene rerun" can be placed upstream of the simulated moving bed separation unit 1 to ensure a feed 2 free of aromatic C9. Patent application US2009 / 326306 proposes in particular the addition of an adsorption separation unit for A9 on the desorbent recycle, with implementation in a fixed bed with adsorption / regeneration cycles or in a simulated moving bed. The authors claim an energy gain since the constraint on the C8-C9 separation can be largely relaxed.

[0009] The classic scheme recycles the desorbent with a purification based on a boiling point criterion (distillation column 13) which guarantees a recycle of the desorbent typically accompanied by compounds having the same number of carbon atoms as the desorbent (in this example aromatic compounds with 10 carbon atoms, so-called "A10" compounds), but which does not necessarily mean that these compounds will be good desorbents. Considering for example the desorbent paradiethylbenzene, orthodiethylbenzene and metadiethylbenzene appear over the years in the distillation cut of paradiethylbenzene and are never eliminated. Their contents can reach around ten percent in certain cases. These compounds generally have little or no desorption power (for example the "para" function of paradiethylbenzene is important to guarantee effective desorption). Summary of the invention

[0010] In the context previously described, a first object of the present description is to overcome the problems of the prior art and to provide a device and a method LMS separation to improve the separation of the extract, in particular by preserving the desorption power of the desorbent.

[0011] According to a first aspect of the invention, the aforementioned objects, as well as other advantages, are obtained by a simulated moving bed separation process comprising the following steps: - treating a feed in a first simulated moving bed adsorption separation unit with a first desorbent stream to produce a first extract containing a product of interest and desorbent, and a first raffinate containing a mixture of products depleted in product of interest and first desorbent; - treating the first extract in a first extract column to separate the product of interest from the first desorbent stream; - treating the first raffinate in a raffinate column to separate from the first desorbent stream and a product mixture depleted in the product of interest; - sending at least a first portion of the first desorbent stream from the first extract column and / or the raffinate column into a second adsorption separation unit to produce a purified first desorbent; - send at least part of the first purified desorbent to the inlet of the first simulated moving bed adsorption separation unit.

[0012] According to one or more embodiments, the method comprises: - recycle a second part of the first desorbent flow from the first extract column and / or the raffinate column at the inlet of the first simulated moving bed adsorption separation unit.

[0013] According to one or more embodiments, the method comprises: - treating the product of interest in a first purification column to separate a purified product of interest.

[0014] According to one or more embodiments, the second adsorption separation unit is operated continuously or discontinuously.

[0015] According to one or more embodiments, the second adsorption separation unit is implemented in a fixed bed with adsorption / regeneration cycles or in a simulated moving bed.

[0016] According to one or more embodiments, the second adsorption separation unit is adapted to treat a first desorbent stream with a second desorbent stream to produce a second extract enriched in first desorbent and a second raffinate depleted in first desorbent.

[0017] According to one or more embodiments, the second extract is treated in a second extract column adapted to separate a first purified desorbent and the second desorbent stream, the first purified desorbent being sent to the inlet of the first simulated moving bed adsorption separation unit, the second desorbent flow being recycled to the inlet of the second adsorption separation unit.

[0018] According to one or more embodiments, the first simulated moving bed adsorption separation unit comprises at least one separation column, each separation column being divided into n adsorption chambers each comprising an adsorbent bed, the n adsorbent beds being separated by n trays for injecting the feed and the first desorbent flow and withdrawing the extract and the raffinate, the adsorbent beds being interconnected in a closed loop, the feed and withdrawal points in the at least one separation column being offset over time by a value corresponding to an adsorbent bed with a permutation period and determining a plurality of operating zones of the simulated moving bed separation device, including the following zones: - zone I of desorption of the product of interest (eg paraxylene) is included between the injection of the first desorbent flow and the withdrawal of the extract; - zone II of desorption of the isomers is included between the withdrawal of the extract and the injection of the charge; - zone III of adsorption of the product of interest is between the injection of the feedstock and the withdrawal of the raffinate; and - zone IV is between the raffinate withdrawal and the injection of the first desorbent flow.

[0019] According to one or more embodiments, the adsorbent beds of the first simulated moving bed adsorption separation unit are distributed in zones I to IV according to the following so-called a / b / c / d type configurations: - a is the number of beds in zone I; - b is the number of beds in zone II; - this is the number of beds in zone III; and - d is the number of beds in zone IV, and - a = (t * 0.2) * (1 ± 0.2); - b = (t * 0.4) * (1 ± 0.2); - c = (t * 0.27) * (1 ± 0.2); And - d = (t * 0.13) * (1 ± 0.2), and in which t is a natural integer between 6 and 24, preferably between 8 and 15.

[0020] According to one or more embodiments, the adsorbent beds of the first simulated moving bed adsorption separation unit are distributed in zones I to IV according to the following so-called a / b / c / d type configurations: - a is the number of beds in zone I; - b is the number of beds in zone II; - this is the number of beds in zone III; and - d is the number of beds in zone IV, and - a = (t * 0.17) * (1 ± 0.2); - b = (t * 0.42) * (1 ± 0.2); - c = (t * 0.25) * (1 ± 0.2); And - d = (t * 0.17) * (1 ± 0.2), and in which t is a natural integer between 6 and 24, preferably between 8 and 15.

[0021] According to one or more embodiments, the method comprises at least one of the following operating conditions for the first simulated moving bed adsorption separation unit: - the first desorbent is chosen from the group consisting of one or more isomers of diethylbenzene, diethyltoluene, isopropyltoluene, dipropylbenzene, naphthalene; - the adsorbent used comprises / consists of at least one Faujasite chosen from the group consisting of zeolites X and Y; - the charge is chosen from the group consisting of a mixture of essentially aromatic C8 compounds; - the temperature in the adsorbent beds is between 140°C and 189°C; - the pressure is controlled to remain in the liquid phase at all points of the device; - the ST permutation period is between 20 seconds and 90 seconds; and - the average circulation flow rate between the beds is between 1000 and 5000 m3 / h.

[0022] According to one or more embodiments, the second desorbent is selected from the group consisting of: toluene; benzene; naphthalene; a naphthalene derivative, preferably a naphthalene alkyl; a diethyltoluene; an ethylpropylbenzene; and a dipropylbenzene.

[0023] According to one or more embodiments, a stream comprising a mixture of aromatic compounds with at least 10 carbon atoms is introduced via a make-up line to the second adsorption separation unit.

[0024] According to a second aspect of the invention, the aforementioned objects, as well as other advantages, are obtained by a simulated moving bed separation device comprising the following units: - a first simulated moving bed adsorption separation unit adapted to treat a feed with a first desorbent stream to produce a first extract containing a product of interest and desorbent, and a first raffinate containing a mixture of products depleted in product of interest and first desorbent; - a first extract column adapted to treat the first extract to separate the product of interest from the first desorbent stream; - a raffinate column adapted to treat the first raffinate to separate from the first desorbent stream and a product mixture depleted in product of interest; - a second adsorption separation unit adapted to treat at least a first part of the first desorbent stream coming from the first extract column and / or the raffinate column, to produce a first purified desorbent, and to send the first purified desorbent to the inlet of the first adsorption separation unit in a simulated moving bed.

[0025] According to a third aspect, the aforementioned objects, as well as other advantages, are obtained by a method of modifying a simulated moving bed separation device, the simulated moving bed separation device comprising the following units: - a pre-installed simulated moving bed adsorption separation unit comprising a first separation column and a second separation column adapted to treat a feed with a stream of first desorbent to produce a first extract containing a product of interest and desorbent, and a first raffinate containing a mixture of products depleted in product of interest and first desorbent; - a first extract column adapted to treat the first extract to separate the product of interest from the first desorbent stream; - a raffinate column adapted to treat the first raffinate to separate from the first desorbent stream and a product mixture depleted in the product of interest, and the modification method comprising the following steps: - the first separation column is modified into a first simulated moving bed adsorption separation unit adapted to treat the feed with the first desorbent stream to produce the first extract containing the product of interest and the desorbent, and the first raffinate containing the product mixture depleted in the product of interest and the first desorbent; and - the second separation column is modified into a second adsorption separation unit adapted to treat at least a first portion of the first desorbent stream coming from the first extract column and / or the raffinate column, to produce a first purified desorbent, and to send the first purified desorbent to the inlet of the first simulated moving bed adsorption separation unit.

[0026] Other characteristics and advantages of the invention according to the aforementioned aspects will appear on reading the description below and non-limiting examples of embodiments, with reference to the figures appended and described below. List of figures

[0027] [Fig.l] schematically shows a reference LMS separation device.

[0028] [Fig.2] schematically shows a separation device in LMS according to a or more embodiments of the invention comprising a second simulated moving bed separation unit for separating the first desorbent. Description of the embodiments

[0029] The invention relates to a method and a device for simulated moving bed separation, for example for the separation of paraxylene.

[0030] Embodiments of the device and method according to the foregoing aspects will now be described in detail. In the following detailed description, numerous specific details are set forth in order to provide a more thorough understanding of the method. However, it will be apparent to those skilled in the art that the method can be implemented without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0031] In the present application, the term "comprise" is synonymous with (means the same as) "include" and "contain", and is inclusive or open and does not exclude other elements not recited. It is understood that the term "comprise" includes the exclusive and closed term "consist". Furthermore, in the present description, the terms "essentially" or "substantially" correspond to an approximation of ± 5%, preferably ± 1%, very preferably ± 0.5%. For example, an effluent essentially comprising or consisting of compounds A corresponds to an effluent comprising at least 95% by weight of compounds A. In the present description, the term "purified" means an increase in the content of the product under consideration, the content being able to be at least 98% by weight, preferably at least 99% by weight, very preferably at least 99.5% such as at least 99.9% by weight.

[0032] With reference to [Fig.2], the present invention can be defined as a method and a device for simulated moving bed separation, using / comprising: - a first simulated moving bed adsorption separation unit 1 adapted to be fed with a feed 2 (e.g. mixture of products, such as xylenes) with the flow of first desorbent 3 (e.g. first desorbent: paradiethylbenzene or toluene), and to produce a first extract 4 containing the product of interest (e.g. paraxylene) and the first desorbent, and a first raffinate 5 containing the mixture of products depleted in product of interest (e.g. orthoxylene and metaxylene) and the first desorbent; - a first extract column 6 adapted to treat the first extract and separate, eg by distillation, the product of interest 7 and (part of) the first desorbent flow 3; - a raffinate column 8 adapted to treat the first raffinate 5 and separate, e.g. by distillation, (a part) of the first desorbent stream 3 and a mixture of products depleted in product of interest 9; - optionally a first purification column 10 adapted to treat the product of interest 7 and separate (eg by distillation) a purified product of interest 11 and a light fraction 12 (in the case where the first desorbent is said to be “heavy”) or a heavy fraction (in the case where the first desorbent is said to be “light”); - preferably, a make-up line of fresh first desorbent (not shown in [Fig.2]) sent for example into the desorbent circuit (a line), or at the inlet of the first simulated moving bed adsorption separation unit 1, in particular to compensate for losses of first desorbent which may be among the product of interest 7 and / or among the mixture of products depleted in product of interest 9.

[0033] In practice during operation of a reference process, unwanted compounds may appear and contaminate the flow of first desorbent 3 returned to the first simulated moving bed adsorption separation unit 1 (for example compounds with at least 10 carbon atoms, so-called “C10+” compounds in paradiethylbenzene.

[0034] According to the present invention, a second adsorption separation unit 17, for example with a fixed bed implementation with adsorption / regeneration cycles or in a simulated moving bed, is arranged to treat at least a first part of the first desorbent flow 3 coming from the first extract column 6 and / or from the raffinate column 8. The second adsorption separation unit 17 makes it possible to produce a first purified desorbent 15 sent to the inlet of the first simulated moving bed adsorption separation unit 1. Advantageously, the second adsorption separation unit 17 makes it possible to avoid the accumulation of unwanted compounds in the first desorbent flow 3.According to one or more embodiments, a recycling line is arranged to recycle (directly) a second part of the first desorbent flow 3 from the first extract column 6 and / or from the raffinate column 8 at the inlet of the first simulated moving bed adsorption separation unit 1. Advantageously, the second adsorption separation unit 17 can treat the first desorbent flow 3 in part or in its entirety, continuously or discontinuously, such as periodically.

[0035] In the example of [Fig.2], the second adsorption separation unit 17 is a simulated moving bed separation unit. The second adsorption separation unit 17 produces a second extract 18 enriched in first desorbent (relative to the first desorbent stream 3 entering the second adsorption separation unit 17) and a second raffinate 19 depleted in first desorbent. For example, when the first desorbent is paradiethylbenzene, the second extract 18 is rich in para-adsorbed compounds, the desorption being able to be carried out by a second lighter desorbent stream 20 (eg comprising fewer carbon atoms) such as a toluene stream.

[0036] The second extract 18 is treated in a second extract column 21 adapted to separate (eg by distillation) a first purified desorbent 15 and the second desorbent flow 20, the first purified desorbent 15 being sent to the inlet of the first simulated moving bed adsorption separation unit 1, the second desorbent flow 20 being recycled to the inlet of the second adsorption separation unit 17.

[0037] The second raffinate 19 comprises second desorbent and unwanted compounds, for example compounds that do not have good adsorption properties and that accumulate in this part. The second raffinate 19 can be recycled to the second adsorption separation unit 17 and at least partly extracted continuously or periodically through a purge line 22. Optionally, the second raffinate 19 can be treated at least partly in a second purification column (not described in [Fig. 2]) adapted to separate a second purified desorbent (eg by distillation) from the unwanted compounds, and recycle the second purified desorbent to the inlet of the second adsorption separation unit 17.

[0038] In the example of [Fig.2], the second desorbent (e.g. toluene) is lighter than the first desorbent (e.g. paradiethylbenzene). In the case of a second desorbent heavier than the first desorbent, the first purified desorbent 15 is recovered at the top of the second extract column 21.

[0039] In the example of [Fig.2], the second adsorption separation unit 17 is arranged to treat the desorbent stream 3 coming from the raffinate column 8. It is understood that the second adsorption separation unit 17 can be arranged to treat the desorbent stream 3 coming from the first extract column 6 and / or from the raffinate column 8. Furthermore, the second adsorption separation unit 17 can be operated continuously or intermittently, for example when the content of unwanted compounds in the desorbent stream 3 reaches a predetermined value.

[0040] Advantageously, the second adsorption separation unit 17 makes it possible to reduce the rate of first desorbent consumed in the simulated moving bed separation process, also leading to energy savings. In addition, the method according to the present invention allows recycling of only the good first desorbent(s), since the compounds not adsorbed in the second adsorption separation unit 17 do not reach the second extract 18. For example, when paradiethylbenzene is used as a desorbent, orthodiethylbenzene and metadiethylbenzene are removed from the process by the second raffinate 19. Similarly, it is not necessary to separate certain compounds separated with the first desorbent in the second extract 20, because said certain compounds are by nature good desorbents and can be recycled with the first desorbent.

[0041] Advantageously, the second adsorption separation unit 17 makes it possible to improve the purity of the product of interest (e.g. paraxylene). The raffinate column 8 ensures the separation between the first desorbent and the mixture of products depleted in product of interest 9. The authorized content of compounds of said mixture in the first desorbent is very low to prevent these compounds from being injected with the first desorbent into the simulated moving bed adsorption separation unit 1 and directly polluting the first extract 4. In the case of the invention, these compounds of said mixture are separated by the second adsorption separation unit 17 and cannot contaminate the first extract 4, improving the purity of the product of interest. It is also possible to relax the specification of the contaminant content in the flow of first desorbent 3 leaving the raffinate column 8 in order to save energy.

[0042] Advantageously, the second adsorption separation unit 17 makes it possible to reduce the addition of fresh first desorbent. Since the separation of the raffinate column 8 is not always perfect, the product mixture depleted in product of interest 9 may include first desorbent which is then lost. To compensate for these losses, a regular addition of fresh first desorbent is carried out. With the method according to the invention, it is now possible to produce quality first desorbent and therefore to limit or even eliminate the introduction of fresh first desorbent. For example, in a xylene separation process, the bottom of the “Xylene rerun” distillation column is often separated in a second column called “heavy aromatics” (or “Heavy Aro” according to English terminology) to recover at the top the aromatic compounds with 9 or 10 carbon atoms (compounds A9-10).The bottom, called "Heavy Aro" and which comprises compounds with at least 10 carbon atoms (C10+) including aromatic compounds with at least 10 carbon atoms (A10+), is not recovered. This flow of heavy aromatics can be introduced as a supplement into the new unit according to the invention, for example via the supplement line 16, to produce a quality desorbent for the separation of xylenes. The first adsorption separation unit

[0043] The first simulated moving bed adsorption separation unit 1 comprises at least one separation (or absorber) column, each separation column being divided into n adsorption chambers each comprising an adsorbent bed, the n adsorbent beds being separated by n inter-bed trays or zones (i.e., n distribution zones and n collection zones). The distribution and collection zones comprise collection and redistribution systems for transmitting the fluid passing through the separation column from one bed to the next bed. In the present application, it is considered that the first distribution zone of the first adsorbent bed and the last collection zone of the last adsorbent bed together form the same inter-bed zone.

[0044] Simulated moving bed separation is a well-known technique. As a general rule, the column operating in a simulated moving bed comprises at least three zones, generally four, and possibly five, each of these zones comprising a certain number of successive adsorbent beds (e.g. fixed beds), and each zone being defined by its position between a feed point and a draw-off point. The feed and draw-off points are modified over time, typically shifted in the same direction by a value corresponding to an adsorbent bed.

[0045] The state of the art describes in detail various devices for carrying out charge separation in a simulated moving bed. Mention may in particular be made of patents US 2,985,589, US 3,214,247, US 3,268,605, US 3,592,612, US 4,614,204, US 4,378,292, US 5,200,075, US 5,316,821.

[0046] According to one or more embodiments, the distribution and collection zones comprise injection systems, in particular for the feedstock, the desorbent and for withdrawing the extract and the raffinate. The controlled means for supplying and withdrawing fluids from a simulated moving bed separation device are, for example, one of the following two main types of technology: - either, for each tray, a plurality of on-off controlled valves (optionally with flow control elements) for supplying or withdrawing fluids, these valves typically being located in the immediate vicinity of the corresponding tray. Each tray typically comprises at least four two-way valves, controlled on-off, to respectively supply the feedstock and the desorbent and withdraw the extract and the raffinate; - or a multi-way rotary valve for supplying or withdrawing fluids on all the trays.

[0047] The present invention is particularly within the framework of columns operating in a simulated moving bed using a plurality of valves to ensure the supply and withdrawal of the different fluids.

[0048] According to one or more embodiments, the number of separation columns of the first simulated moving bed adsorption separation unit 1 is between 1 and 2. Preferably, the number of separation columns is 1. According to one or more embodiments, the number n of adsorbent beds per separation column is between 6 and 15, preferably between 8 and 12. According to one or more embodiments, the total number of adsorbent beds is between 6 and 24, preferably between 8 and 19, very preferably between 12 and 15.

[0049] In the rest of the text, we speak of a step to designate an operation or a group of similar operations carried out on a given flow at a certain point in the process. describes the process in its various stages taken in the order of flow of the streams or products.

[0050] The LMS separation method of the first simulated moving bed adsorption separation unit 1 comprises the following steps: the separation column(s) are fed with at least the feedstock and the desorbent, and at least the extract and at least the raffinate are withdrawn from said separation column(s), each separation column comprising n beds of an adsorbent solid interconnected in a closed loop (i.e., the last bed of the last column being adapted to send the flow circulating in the first bed of the first column), the feed and withdrawal points in said separation column(s) being offset over time by a value corresponding to an adsorbent bed with a permutation period (denoted ST) and determining a plurality of operating zones of the LMS device, and in particular the following main zones: By definition, each of the operating zones is designated by a number: - zone I of paraxylene desorption is between the injection of the desorbent and the withdrawal of the extract; - zone II of desorption of the isomers is included between the withdrawal of the extract and the injection of the charge; - paraxylene adsorption zone III is between the injection of the feedstock and the withdrawal of the raffinate; and - zone IV is between the raffinate withdrawal and the desorbent injection.

[0051] According to one or more embodiments, the feedstock of the first simulated moving bed adsorption separation unit 1 is chosen from the group consisting of a mixture of essentially C8 aromatic compounds (e.g. xylenes and optionally ethylbenzene). According to one or more embodiments, the mixture comprises at least 95%, preferably at least 97% (e.g. at least 99%) of essentially C8 aromatic compounds. According to one or more embodiments, the feedstock comprises at least 15% by weight of paraxylene and / or 30% by weight of metaxylene relative to the total weight of the feedstock.

[0052] An example of an LMS separation process of great industrial importance concerns the separation of aromatic C8 cuts in order to produce paraxylene of commercial purity, typically at least 99.7% by weight, and a raffinate rich in ethylbenzene, orthoxylene and metaxylene.

[0053] According to one or more embodiments, the first desorbent of the first simulated moving bed adsorption separation unit 1 is chosen from the group consisting of one or more isomers of diethylbenzene, diethyltoluene, isopropyltoluene, dipropylbenzene, naphthalene.

[0054] According to one or more embodiments, the adsorbent of the first simulated moving bed adsorption separation unit 1 used comprises / consists of at least one Faujasite chosen from the group consisting of X and Y zeolites.

[0055] According to one or more embodiments, the adsorbent beds of the first simulated moving bed adsorption separation unit 1 are distributed in zones I to IV according to configurations known as a / b / c / d type, i.e. the distribution of the beds is as follows: - a is the number of beds in zone I; - b is the number of beds in zone II; - this is the number of beds in zone III; and - d is the number of beds in zone IV.

[0056] According to one or more embodiments: - a = (t * 0.2) * (1 ± 0.2); - b = (t * 0.4) * (1 ± 0.2); - c = (t * 0.27) * (1 ± 0.2); and - d = (t * 0.13) * (1 ± 0.2), and in which t is a natural integer between 6 and 24, preferably between 8 and 15 (eg 12).

[0057] According to one or more embodiments: - a = (t * 0.17) * (1 ± 0.2); - b = (t * 0.42) * (1 ± 0.2); - c = (t * 0.25) * (1 ± 0.2); And - d = (t * 0.17) * (1 ± 0.2), and in which t is a natural integer between 6 and 24, preferably between 8 and 15 (eg 12).

[0058] According to one or more embodiments, the temperature in the adsorbent beds of the first simulated moving bed adsorption separation unit 1 is between 140°C and 189°C and preferably between 155°C and 185°C, particularly preferably between 170°C and 180°C. The pressure is adjusted so that the liquid phase remains at all points in the process according to the invention. According to one or more embodiments, the pressure in the adsorbent beds of the first simulated moving bed adsorption separation unit 1 is between 1 MPa and 10 MPa, preferably between 2 MPa and 4 MPa, preferably between 2 MPa and 3 MPa. According to one or more embodiments, the ST permutation period (period between two successive permutations of the feeds / extractions) used in the first simulated moving bed adsorption separation unit 1 is between 20 seconds and 90 seconds.Preferably, the ST switching period employed is between 30 seconds and 70 seconds (eg 50 ±10 seconds). According to . one or more embodiments, the average circulation flow rate between the beds of the first simulated moving bed adsorption separation unit 1 is between 1000 m3 / h and 5000 m3 / h, preferably between 2000 m3 / h or 2500 m3 / h and 4000 m3 / h, very preferably between 3000 m3 / h and 4000 m3 / h. The second adsorption separation unit

[0059] The second adsorption separation unit 17 is not limited by a particular separation mode. Preferably, the second adsorption separation unit 17 is implemented in a fixed bed with adsorption / regeneration cycles or in a simulated moving bed.

[0060] According to one or more embodiments, the second adsorption separation unit 17 is implemented in an alternating fixed bed and comprises at least two adsorption / regeneration separation zones comprising at least one adsorption chamber comprising an adsorbent bed. The operation in alternating mode can be summarized as the parallel implementation of at least two separation zones. For example, when the first separation zone is used to adsorb the first desorbent stream 3 and produce the second extract 18, then the second separation zone is used to desorb with the second desorbent stream 20 and produce the second raffinate 19, the second separation zone is thus in the regeneration phase.Conversely, when the second separation zone is used to adsorb the flow of first desorbent 3 and produce the second extract 18, then the first separation zone is used to desorb with the flow of second desorbent 20 and produce the second raffinate 19. Advantageously, the alternating mode can approach continuous production.

[0061] According to one or more embodiments, the second adsorption separation unit 17 is placed in a simulated moving bed as described above for the first simulated moving bed adsorption separation unit 1. Preferably, the number of separation columns of the second adsorption separation unit 17 is between 1 and 2. Preferably, the number of separation columns is 1. According to one or more embodiments, the number n of adsorbent beds per separation column is between 6 and 15, preferably between 8 and 12.

[0062] According to one or more embodiments, the second desorbent is chosen from the group consisting of toluene, benzene, naphthalene, a naphthalene derivative such as a naphthalene alkyl, a diethyltoluene, an ethylpropylbenzene, a dipropylbenzene. According to one or more embodiments, the second desorbent is chosen from toluene.

[0063] According to one or more embodiments, the adsorbent of the second adsorption separation unit 17 used comprises / consists of at least one para-selective adsorbent, chosen for example from zeolites X and Y.

[0064] According to one or more embodiments, the temperature in the adsorbent beds of the second adsorption separation unit 17 is between 20°C and 300°C and preferably between 100°C and 200°C, preferably between 165°C and 185°C. The pressure is adjusted so that the liquid phase remains at all points in the process according to the invention. According to one or more embodiments, the pressure in the adsorbent beds of the second adsorption separation unit 17 is between 1 MPa and 10 MPa, preferably between 2 MPa and 4 MPa. According to one or more embodiments, the permutation period ST (period between two successive permutations of the feeds / extractions) used in the second adsorption separation unit 17 is between 10 seconds and 150 seconds.According to one or more embodiments, the average circulation flow rate between the beds of the second adsorption separation unit 17 is between 100 m3 / h and 5000 m3 / h. Examples Example 1: Reducing the solvent rate

[0065] Consider a process using paradiethylbenzene (p-DEB) as a desorbent and which, over the years, has accumulated 5% of a mixture of orthodiethylbenzene (o-DEB) and metadiethylbenzene (m-DEB). In the reference process, these compounds are not removed by the distillation column 13 and accumulate in the desorbent. Since the selectivity between paraxylene and m-DEB and paraxylene and o-DEB is equal to 3, the desorbent is less effective and more must be added to desorb the paraxylene. In the process according to the invention, the m-DEB and o-DEB are not recycled and therefore do not accumulate in the desorbent. The solvent level can therefore be reduced, leading to energy savings on the distillation columns. Table 1 below shows a higher requirement for first desorbent 3 flow for the reference process compared to the process according to the invention.

[0066] [Tables 1] Process type Desorbent / load ratio Reference process 1.40 Process according to the invention 1.33

[0067] Example 2: Improving the quality of paraxylene

[0068] Consider a case of operation with 200 ppm by weight of orthoxylene and / or metaxylene at the bottom of the raffinate column 8. In the reference process, these compounds are reinjected with the first desorbent stream 3 into the simulated moving bed adsorption separation unit 1 and increase the amount of unwanted compounds, which deteriorates the purity of the first extract 4 and the desired product. In the process according to the invention, these compounds can be separated from the desorbent in the second adsorption separation unit 17, which does not degrade the purity of the first extract 4 and the desired product. Table 2 shows the gain in paraxylene purity in the case where all operating conditions are identical except for a content of 200 ppm by weight of orthoxylene and metaxylene in the first desorbent stream 3 for the reference process. The calculations are made by simulation of the simulated moving bed. The results show a gain of 0.05% for the process according to the invention, which is significant given the desire for high product purity (>99.80%).

[0069] [Tables2] Type of process Purity (% weight) of paraxylene Reference process 99.80 Process according to the invention 99.85 Example 3: Reduction of the PDEB charge

[0070] Let us consider an operation with a flow rate of first raffinate 5 of 1000 t / h at a p-DEB content of 55% and an annual process operating time of 8400 h / year. With reference to Table 3, 100 ppm by weight of p-DEB being lost in the product mixture depleted in product of interest 9 during the treatment of the first raffinate 5 in the raffinate column 8, the annual consumption of p-DEB amounts to 460 t / year. The process according to the invention makes it possible to treat a flow of aromatic compounds with at least 10 carbon atoms (A10+) introduced into the make-up line 16. This flow of A10+ typically amounts to 3.8 t / h, including approximately 0.4 t / h of compounds that can be recovered by desorbing, i.e. a production capacity greater than the requirement for fresh p-DEB. In this way the process is autonomous and produces its own consumption of first desorbent.

[0071] [Tables3] Process type Consumption of p-DEB Reference process 460 t / year Process according to the invention 0 t / year

Claims

Claims

1. A simulated moving bed separation method comprising the following steps: - treating a feedstock (2) in a first simulated moving bed adsorption separation unit (1) with a first desorbent stream (3) to produce a first extract (4) containing a product of interest and desorbent, and a first raffinate (5) containing a product mixture depleted in the product of interest and the first desorbent; - treating the first extract (4) in a first extract column (6) to separate the product of interest (7) from the first desorbent stream (3); - treating the first raffinate (5) in a raffinate column (8) to separate from the first desorbent stream (3) a product mixture depleted in the product of interest (9);- sending at least a first part of the first desorbent stream (3) from the first extract column (6) and / or the raffinate column (8) into a second adsorption separation unit (17) to produce a first purified desorbent (15); - sending at least part of the first purified desorbent (15) to the inlet of the first simulated moving bed adsorption separation unit (1).;

2. Method according to claim 1, comprising: - recycling a second part of the first desorbent flow (3) coming from the first extract column (6) and / or from the raffinate column (8) at the inlet of the first simulated moving bed adsorption separation unit (1).

3. A method according to claim 1 or claim 2, comprising: - treating the product of interest (7) in a first purification column (10) to separate a purified product of interest (11).

4. A method according to any preceding claim, wherein the second adsorption separation unit (17) is operated continuously or discontinuously.

5. A method according to any preceding claim, wherein the second adsorption separation unit (17) is operated in a fixed bed with adsorption / regeneration cycles or in a simulated moving bed.

6. A method according to any preceding claim, wherein the second adsorption separation unit (17) is adapted to treat a first desorbent stream (3) with a second desorbent stream (20) to produce a second extract (18) enriched in first desorbent and a second raffinate (19) depleted in first desorbent.

7. A method according to claim 6, wherein the second extract (18) is treated in a second extract column (21) adapted to separate a first purified desorbent (15) and the second desorbent stream (20), the first purified desorbent (15) being sent to the inlet of the first simulated moving bed adsorption separation unit (1), the second desorbent stream (20) being recycled to the inlet of the second adsorption separation unit (17).

8. A method according to any one of the preceding claims, wherein the first simulated moving bed adsorption separation unit (1) comprises at least one separation column, each separation column being divided into n adsorption chambers each comprising an adsorbent bed, the n adsorbent beds being separated by n trays for injecting the feedstock (2) and the first desorbent stream (3) and withdrawing the extract (4) and the raffinate (5), the adsorbent beds being interconnected in a closed loop, the feed and withdrawal points in the at least one separation column being shifted over time by a value corresponding to an adsorbent bed with a permutation period and determining a plurality of operating zones of the simulated moving bed separation device,including the following zones: - zone I of desorption of the product of interest is between the injection of the first desorbent flow (3) and the withdrawal of the extract (4); - zone II of desorption of the isomers is between the withdrawal of the extract (4) and the injection of the feed (2); - zone III of adsorption of the product of interest is between the injection of the feed (2) and the withdrawal of the raffinate (5); and - zone IV is between the withdrawal of the raffinate (5) and the injection of the first desorbent flow (3).,

9. The method of claim 8, wherein the adsorbent beds of the first simulated moving bed adsorption separation unit (1) are distributed in zones I to IV according to the following configurations known as type a / b / c / d: - a is the number of beds in zone I; - b is the number of beds in zone II; - c is the number of beds in zone III; and - d is the number of beds in zone IV, and - a = (t * 0.2) * (1 + 0.2); - b = (t * 0.4) * (1 + 0.2); - c = (t * 0.27) * (1 + 0.2); and -d = (t*0.13) * (1 ±0.2), and in which t is a natural whole number between 6 and 24, preferably between 8 and 15.

10. A method according to claim 8, wherein the adsorbent beds of the first simulated moving bed adsorption separation unit (1) are distributed in zones I to IV according to the following so-called a / b / c / d type configurations: - a is the number of beds in zone I; - b is the number of beds in zone II; - c is the number of beds in zone III; and - d is the number of beds in zone IV, and - a = (t * 0.17) * (1+0.2); - b = (t * 0.42) * (1 + 0.2); - c = (t * 0.25) * (1 + 0.2); and -d = (t*0.17) * (1+0.2), and wherein t is a natural integer between 6 and 24, preferably between 8 and 15.

11. A method according to any one of claims 8 to 10, comprising at least one of the following operating conditions for the first simulated moving bed adsorption separation unit (D: - the first desorbent is selected from the group consisting of one or more isomers of diethylbenzene and toluene; - the adsorbent used comprises / consists of a Faujasite selected from the group consisting of zeolites X and Y; - the feedstock is selected from the group consisting of a mixture of essentially C8 aromatic compounds; - the temperature in the adsorbent beds is between 140°C and 189°C; - the pressure is controlled to remain in the liquid phase at all points in the device; - the ST permutation period is between 20 seconds and 90 seconds; and - the average circulation flow rate between the beds is between 1000 and 5000 m3 / h.

12. A method according to any preceding claim, wherein the second desorbent is selected from the group consisting of: toluene; benzene; naphthalene; a naphthalene derivative, preferably a naphthalene alkyl; diethyltoluene; ethylpropylbenzene; and dipropylbenzene.

13. A method according to any preceding claim, wherein a stream comprising a mixture of aromatic compounds with at least 10 carbon atoms is introduced via a make-up line (16) to the second adsorption separation unit (17).

14. A simulated moving bed separation device comprising the following units: - a first simulated moving bed adsorption separation unit (1) adapted to treat a feedstock (2) with a first desorbent stream (3) to produce a first extract (4) containing a product of interest and desorbent, and a first raffinate (5) containing a product mixture depleted in product of interest and first desorbent; - a first extract column (6) adapted to treat the first extract (4) to separate the product of interest (7) and the first desorbent stream (3); - a raffinate column (8) adapted to treat the first raffinate (5) to separate from the first desorbent stream (3) and a product mixture depleted in product of interest (9);- a second adsorption separation unit (17) adapted to treat at least a first part of the first desorbent stream (3) coming from the first extract column (6) and / or from the raffinate column (8), to produce a first purified desorbent (15), and to send the first purified desorbent (15) to the inlet of the first simulated moving bed adsorption separation unit (1).;

15. Method of modifying a simulated moving bed separation device, the simulated moving bed separation device comprising the following units: - a pre-installed simulated moving bed adsorption separation unit comprising a first separation column and a second separation column adapted to treat a feed with a first desorbent stream to produce a first extract containing a product of interest and desorbent, and a first raffinate containing a mixture of products depleted in product of interest and first desorbent; - a first extract column (6) adapted to treat the first extract (4) to separate the product of interest (7) and the first desorbent stream (3); - a raffinate column (8) adapted to treat the first raffinate (5) to separate from the first desorbent stream (3) and a product mixture depleted in product of interest (9), and the modification process comprising the following steps: - the first separation column is modified into a first simulated moving bed adsorption separation unit (1) adapted to treat the feedstock (2) with the first desorbent stream (3) to produce the first extract (4) containing the product of interest and the desorbent, and the first raffinate (5) containing the mixture of products depleted in the product of interest and the first desorbent; and - the second separation column is modified into a second adsorption separation unit (17) adapted to treat at least a first part of the first desorbent stream (3) coming from the first extract column (6) and / or the raffinate column (8), to produce a first purified desorbent (15), and to send the first purified desorbent (15) to the inlet of the first simulated moving bed adsorption separation unit (1).

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