Simulated moving bed separation process and device with reduced number of valves

Abstract

PROCESS AND SEPARATION DEVICE IN SIMULATED MOBILE BED WITH REDUCED NUMBER OF VALVES The present invention relates to a simulated moving bed (SMB) separation device, which comprises a column, Ai adsorbent beds separated by Pi plates of single network of distribution and extraction of fluids, in particular charge F, desorbent D, refined R, and extract E, and a plurality of 2-way valves for the distribution of these fluids, these valves being limited in number in relation to the prior art. According to the invention, the column is divided into a plurality of Sk segments of 2 or 3 overlapping plates, each Sk segment comprising an external branch line Lk connected to each Pi plate of Sk by a tip comprising a Vi valve plate . Each Sk line comprises a controlled means of limiting its internal flow, and is connected to each of the fluid networks F, D, R, E via a single line comprising a single 2-way commanded isolating valve for the supply or sequential transfer of the corresponding fluid F, D, R or E to or from the considered Sk segment. The invention also relates to a separation process using that device, or to the use of that device notably for the separation of paraxylene or metaxylene from an aromatic C8 cut.

Description

Descriptive Report of the Invention Patent for "PROCESS "AND A SIMULATED MOBILE BED SEPARATION DEVICE WITH A REDUCED NUMBER OF VALVES." Domain of the Invention The present invention relates to the field of separations of natural or chemical products that can be difficult to separate by distillation. It utilizes a family of processes and associated devices, known as "chromatographic" separation processes or devices, or "simulated moving bed" processes or devices, or "simulated countercurrent" processes or devices, or "simulated co-current" processes, which will be referred to below as "SMB". The domains in question are notably, but not exclusively: - the separation between, on the one hand, normal paraffins and, on the other hand, branched paraffins, naphthenes, and aromatics, - the separation of olefins / paraffins, - the separation of paraxylene from other aromatic C8 isomers, - the separation of metaxylene from other aromatic C8 isomers, - the separation of ethylbenzene from other C8 aromatic isomers. Outside of refineries and petrochemical complexes, there are numerous other applications, including glucose / fructose separation, separation of cresol positional isomers, optical isomers, etc. Previous Technique SMB chromatographic separation is well known in the state of the art. As a general rule, a simulated moving bed comprises at least three chromatographic zones, advantageously four or five, each of these zones consisting of at least one bed or a column portion and comprised between two successive feed or transfer points. Typically, at least one feed F to be fractionated and a desorbent D (sometimes called eluent) are fed in, and at least one raffinate R and one extract E are transferred out. The feed and transfer points are modified over time, typically shifted to the bottom of a bed, and this is done synchronously. Several advantageous variants allow for improved operation of this type of unit by using asynchronous permutations. In simplified terms, these asynchronous permutations serve to compensate for the dead volume(s) of the recirculation pump(s), as indicated in US patent 5,578,215, to work with a constant recycling flow rate in the recirculation pump in order to eliminate sudden flow and pressure movements, as indicated in US patent 5,762,806, or finally to operate with at least two chromatographic zones, each equivalent to a non-integer number of adsorbent beds. This last variant, as indicated in US patents 6,136,198, 6,375,839, 6,712,973, and 6,413,419, is known as Varicol. Naturally, these three variants can be combined. It should be noted that a multi-way rotary valve that connects incoming and outgoing fluids on one side and the beds arranged in the adsorption column(s) on the other side only allows for synchronous exchange. For asynchronous exchanges, a plurality of on-off valves is indispensable. This technological aspect is discussed further below. The state of the art describes in detail different devices and processes that allow for the separation of loads on a simulated moving bed. Notably, 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, and US 5,316,821 can be cited. These patents also describe in detail the operation of a simulated moving bed. SMB devices typically comprise at least one column (and often two), adsorbent beds Ai arranged in that column, separated by plates Pi with distribution and / or extrusion chamber(s) Ci. Fluid traction into or from different adsorbent beds, and controlled means of sequential fluid distribution and extraction. Each Pi plate typically comprises a plurality of distributor, mixer, extractor, or "DME" panels fed by distribution / extraction lines or "spider" arrays. The plates can be of any type and geometry, notably with panels forming adjacent sectors of the column section, for example, panels with angled sectors as shown in US patent 6,537,471 figure 8, which are symmetrical feed, or parallel sectors such as those cut in a circumference, as indicated in published US patent application 03 / 0,127,394, which are asymmetrical feed. Preferably, the separation column comprises DME-type plates with parallel sectors and asymmetrical feeds. Also preferably, the adsorbent is installed in dense loading. This allows for the use of a greater quantity of adsorbent in a given column, and increases the purity of the desired product and / or the feed rate of the SMB. Distribution in each of the beds requires collecting the flow from the preceding bed (the main fluid circulating along the main axis of the column), the possibility of injecting an ancillary or secondary fluid while mixing these two fluids as well as possible, or even the possibility of removing a portion of the collected fluid, extracting it to send it outside the device, and also redistributing fluid in the next bed. To achieve this, it is possible to use distribution chambers (injection / extraction) in a Pi plate, which can be separate or common with the mixing chambers. Pi plates with one or more chambers are known, either fed (or transferred) separately by different fluids at a given instant, or fed (or transferred) simultaneously and in parallel by the same fluid at a given instant. In the first case, the plate is said to have several distribution networks, while in the second case it has a single distribution network. The invention relates exclusively to a device comprising plates with a distribution network. single action. In general, it is possible either to have the entirety of the fluid or main flow pass through the column according to a scheme described in US patent 2,985,589, or to have a large part or all of that fluid exit to the outside according to a process described in US patent 5,200,075. A common problem with SMB devices is minimizing pollution generated by the liquid present in different zones and volumes of the fluid feed and transfer circuits of the trays, when changes to the feed and transfer points occur during SMB operation. In fact, when, during the operating sequence, a feed line, chamber, or zone of a Pi tray is no longer swept by a process fluid, it becomes a dead zone where the liquid stagnates, and is only set in motion again when another process fluid circulates within it. Since, due to the SMB operation, a different process fluid is then used, the liquid in the dead zone is necessarily displaced by a liquid of significantly different composition.The mixing, or circulation for a short period of time, of fluids of significantly different compositions therefore introduces a disturbance to the ideal operation, for which compositional discontinuities should be avoided. Another problem can arise from potential recirculation between different zones of the same tray, which then also induces a disruption in relation to optimal operation. To solve these problems related to recirculation and dead zones, different techniques are already known from the previous technique: a) It has already been proposed to perform a sweep (the English word "flush" is also frequently used) of the dead lines and zones with, notably, a relatively pure desorbent or the desired product. This technique effectively avoids contamination of the desired product during its extraction. However, since the sweeping liquid typically has a very different composition from the liquid it displaces, this in- This introduces compositional discontinuities that are detrimental to optimal functioning. This first variant of scanning typically performs "short-duration scans with a high concentration gradient." These scans are short in duration to limit the effects of compositional discontinuities. (b) Another solution, as described in US patent 5,972,224, consists of having a majority of the main fluid transit into the inside of the column and a minority of this flow to the outside, typically 2% to 20% of the flow, through external bypass lines between neighboring plates. This sweeping is typically performed most of the time or continuously, so that the lines and zones are no longer "dead" but swept. Such a system with sweeping via bypass lines is shown in Figure 1 of US patent 5,972,224 and reproduced in a simplified way in Figure 1 of the present application. As the bypass lines are designed for a small flow rate, they can consequently be of small diameter and include a small diameter valve, which reduces the cost of the system. A primary advantage of such a system is that the injection and withdrawal circuits of the secondary fluids are swept by liquid with a composition very close to that of the displaced liquid, since, on the one hand, the bypass originates from the neighboring plate, and on the other hand, the sweeping is not point-based but rather essentially continuous. Furthermore, the flow rates in the bypasses are preferably determined so that the transit velocity in each bypass is approximately the same as the velocity of the concentration gradient in the main flow of the SMB. Thus, on the one hand, the different lines and capacities are swept with a fluid that has a composition approximately identical to that of the liquid in them, and on the other hand, the liquid circulating in a bypass is reintroduced at a point where the composition of the main flow is approximately identical.This second variant therefore performs "long-duration scans with a low or zero concentration gradient". A second advantage of this long-duration scanning system (excluding injection or transfer periods) is that it allows for... to suppress the effects of possible recirculation between zones of the same tray, due to small differences in pressure losses. Regarding the operation of an SMB, the controlled means of fluid distribution and extraction in an SMB are typically of one of the following two main types of technology: - or, for each platter, a plurality of on-off controlled valves for the feeding or transfer of fluids, these valves typically being located in the immediate vicinity of the corresponding platter, and notably comprising, for each platter Pi, at least 4 on-off 2-way controlled valves for the feeding of fluids F and D and the transfer of fluids E and R, respectively. - or a multi-way rotary valve for feeding or transferring fluids within the tray assembly. The first technology uses 2-way valves, which allows for standard mass production leading to increased reliability and a relatively low unit cost. The second technology uses only a single valve, but this single valve is multi-way and necessarily of special construction, large size, and high complexity. Furthermore, this second technology excludes the possibility of asynchronous switching, as in Varicol devices. The invention relates to SMBs that use conventional 2-way valves, meaning they utilize the first of the two technologies described above. It refers specifically to an improved simulated moving bed separation device comprising a plurality of on-or-off 2-way valves, but in a reduced number compared to the previous technique. It is usable for both synchronous and asynchronous permutation SMBs, for example, a Varicol. Simplified Description of the Invention The invention relates to an improved simulated moving bed separation device belonging to the broader technological type of SMBs, which utilizes a plurality of 2-way on / off controlled valves, typically standard, mass-produced valves with reduced cost. for a high level of quality (leak tightness / reliability) required. One of the essential objectives of the invention is to reduce the relative inconvenience of this type of SMB, which is the requirement for a large number of 2-way controlled valves. The invention makes it possible to reduce the number of these valves, while retaining the advantage of being able to perform an effective sweep of the "long-duration dead zones with low or zero concentration gradient" type. Another objective of the invention is to present a device that requires a reduced number of 2-way valves without increasing the opening / closing frequency of these valves compared to the prior art solution. Considering the reduced number of valves, this limits the statistical risks of malfunction and therefore increases the reliability of the system. Finally, a preferred variant of the device allows for a further reduction in the number of large-diameter valves that enable the circulation of the main fluids in the SMB at their nominal flow rate. The device according to the invention can be used in new installations but is also compatible with various existing installations in which it can be installed with limited modifications. It is also compatible with various types and geometries of Pi plates, for example, plates with angular sector panels or parallel sector panels, insofar as these plates (or most of them) are of the single distribution network type. A method was therefore discovered that allows for a significant reduction in the number of main controlled valves, which correspond to the inlets and outlets of the SMB process fluids: In the previous technique, there is at least one set of 4 main network valves for each tray for the feed / transfer of F, D, R, E. This number is further increased if there are more than 4 fluids, for example, if there are 2 refined fluids R1, R2 or if a reflux RE rich in the desired product is used. The small-diameter bypass lines in the previous technique are only attached lines that are not taken by the fluids F, D, R, E, (E1) (E2) (RE) in their normal flow rate. feeding or racking mine. According to the invention, the column, or the main part of that column, is grouped into superimposed Sk segments, each Sk segment comprising 2 or 3 adsorbent beds and 2 or 3 trays, and comprising a bypass line Lk. Contrary to the prior art, the Lk line is taken by the SMB fluids at their nominal flow rate, and a single set of main network valves (feed or transfer) is used per column segment (and not per tray as in the prior art), these valves being connected to the bypass line Lk in order to allow the circulation of these fluids via Lk. According to the invention, "tray valves" and means of limiting the bypass fluid flow rates are also provided, but the total number of valves remains significantly reduced, as will be explained below. The invention also relates to an SMB separation process that uses the device described above, notably for the separation of paraxylene or metaxylene from a load of aromatic hydrocarbons with 8 carbon atoms. The invention also relates to the use of the device thus described for separating an aromatic from a cut of aromatics having the same number of carbon atoms. Detailed Description of the Invention The invention will be better understood by reading the description that follows and by consulting Figures 1 (prior art) and Figures 2 and 3 (device according to the invention). To achieve one of the aforementioned objectives, therefore, a device is proposed according to the invention that allows the separation of at least one desired compound from a mixture comprising that compound by adsorption in a simulated moving bed comprising: at least one column divided into a plurality of adsorbent beds Ai separated by distributor / extractor plates Pi for the sequential feeding and extraction of at least two feed fluids: a feed F and a desorbent D, and at least two transfer fluids. of: a refined R and an extract E, Pi being placed between bed Ai and the immediately lower bed Ai+1, the device also comprising at least one F-Net feed network, one D-Net desorbent network, one R-Net raffinate network and one E-Net extract network, each of these networks being connected to the column by a plurality of intermediate lines comprising 2-way controlled shut-off valves, called network valves, for the sequential feeding or transfer of fluids F, D, R, E, in which the column is divided, at least for most of its height, into a plurality of adjacent superimposed segments Sk, each segment Sk consisting essentially of a group of at least 2 and at most 5 successive adsorbent beds and the distributor / extractor plates Pi that are arranged immediately below these successive adsorbent beds, Each of the Pi distribution / extraction plates in each of the Sk sectors uses a single common network for the sequential feeding and transfer of fluids F, D, R, E, The Pi plates of each Sk segment are connected to each other by an external branch line Lk connected to each Pi plate of Sk by a fitting comprising a unique 2-way controlled shut-off valve specific to the Pi plate, called the Vi plate valve, for the sequential feeding or transfer of fluids F, D, R, E into or from Pi. Each of said Lk bypass lines comprises at least one controlled means of limiting the flow circulating in Lk (such as a controlled valve + flow meter + valve control system assembly) that is either installed in the Lk line or bypassed around a Vi plate valve of a Sk Pi plate. in which the branch line Lk of each of the Sk segments is connected to each of the F-Net, D-Net, R-Net and E-Net networks via a single line comprising a single network valve, respectively V F k, V Dk VRk,V Ek for the sequential feeding or transfer of the corresponding fluid F, D, R or E to or from the considered Sk segment, and in which each Pi plate of the Sk segment is uniquely connected to each of the F-Net, D-Net, R-Net and E-Net networks via the series connection comprising the Vi plate valve, and then at least a part of Lk, and then said single line comprising said single network valve, respectively V F k, V D k, V Rk ,VEk. Ideally, each Sk segment consists essentially of a group of 2 or 3 successive adsorbent beds. Variants with 4 or 5 successive beds actually lead to columns that have a higher total number of beds, in order to achieve different chromatographic zones. In contrast to the device according to the prior art, the device according to the invention allows the use of the Lk bypass line for the circulation of fluids F, D, R, E fed into the SMB and transferred from the SMB at the Sk segment level, via a single set of corresponding network valves, instead of a set of network valves per plate Pi as according to the prior art. This allows a significant reduction in the overall number of valves controlled, even considering the addition of supplementary valves, namely the Vi plate valves. The aforementioned controlled valves: network valves and Vi plate valves are typically high-quality valves (reliability, tightness, lifespan) that perform the sequential operation of the SMB. In general, all controlled valves ensure the sequential operation of the SMB: network valves, disc valves, and also valves of the controlled means of limiting the flow circulating in Lk should be considered according to the invention as the "main" valves of the SMB, connected to the column and controlled by the sequential operation control system of the SMB (computer, programmable logic controller or other equivalent system). Certain key valves in the sequential operation of the SMB have been previously mentioned as being unique according to the invention: Vi for each Pi plate; unique set of V network valves. F k, V D k, Vrk.Vek for each Sk segment. However, it would not fall outside the scope of the invention if other valves were used, such as secondary valves for occasional isolation, typically of much lower quality, controlled or not, but which do not participate in the sequential operation of the SMB and which allow, for example, the disassembly of any equipment: pump or main valve used for sequential operation, etc. Typically, the bypass line Lk, which is used for the transit of all fluids F, D, R, E at their nominal flow rate, is no longer, in the device according to the invention, a small attached line as in the prior art, but rather generally has an internal diameter at least equal to the largest opening diameter of the network valves connected to Lk, so as to be able to circulate fluids F, D, R, E without capacity limitation. Due to the use of Lk bypass lines designed to carry large flow rates, flow limiting control devices are advantageously used to perform bypass circulations with low flow rates (typically 2 to 20% of the flow circulating in the column). The term "bypass circulation" here means that a (small) fraction of the flow circulating in the column is transferred from one tray and reintroduced into another tray of the same Sk segment. The term controlled devices typically applies to a controlled valve, typically with the aid of a control chain, based on information provided by a flow meter. It is possible to use a flow control valve installed directly on the Lk line. This valve is then typically a progressive-opening valve and not an all-or-nothing controlled valve (which has only 2 possible positions: full opening and closed). However, according to a preferred variant of the invention, at least one, or preferably each of said Lk bypass lines, comprises a controlled flow limiting means circulating in Lk, which is not installed directly in Lk but rather bypassed around a disc valve Vi of a disc valve Pi of Sk, in a small secondary bypass / &. This means is generally a controlled valve vi of A valve with a smaller opening diameter than the opening diameter of Vi, for example, with an opening diameter at most equal to 60%, or 50% of the opening diameter of Vi, for example between 10% and 50% of the opening diameter of Vi. When it is desired to perform an internal bypass sweep of Lk and limit this internal bypass flow (which circulates from one Sk plate to another Sk plate), the Vi plate valve is left closed and the smaller bypass valve Vi is opened around Vi. Thus, the use of a small secondary bypass lk around one of the Vi plate valves (typically the Vi valve of the lower Sk Pi plate) allows the use of a valve with a smaller opening diameter than if the flow limitation means is a valve arranged in the main bypass line Lk, which is of relatively larger diameter due to the fact that Lk must allow the circulation of fluids F, D, R, E at their nominal flow rate. According to the invention, the tip comprising Vi should be interpreted as not comprising the small secondary derivation lk around Vi, nor the small valve vi arranged in l. k This nozzle therefore includes a single valve Vi that allows the circulation of the main fluids F, D, R, E. According to a first embodiment, at least one Sk segment (and frequently all Sk segments) consists of two adsorbent beds Aj, Aj+1 and the two distributor / extractor plates Pj, Pj+1 that are arranged immediately below these adsorbent beds, respectively. The segments are then of 2 beds and 2 plates Pi. According to a second embodiment, at least one Sk segment consists of three adsorbent beds Aj, Aj+1, Aj+2 and the three distributor / extractor plates Pj, Pj+1, Pj+2 that are arranged immediately below these adsorbent beds respectively. The segments are then of 3 beds and 3 plates Pi. The definition of a Sk segment must be precise in the case of the column bottom. In fact, there is typically no Ph plate beneath the Pn adsorbent bed arranged in the column bottom, as there is no need for it. distribute the fluids in an immediately lower bed. Also, according to the invention, it is considered in this case that the missing plate Pn is replaced by the lower outlet line of the column, typically connected either to the inlet of the same column, via a recirculation pump, or to the top of a second separation column. Preferably, the entire column (with the exception of the top plate, excluded by the chosen definition of the word segment) consists of the adjacent superimposed segments Sk. All Sk segments can then be constituted by two adsorbent beds and the two distributor / extractor plates that are arranged immediately below these adsorbent beds respectively (or the said lower outlet line assimilated to a lower plate). The column is then essentially constituted by segments of 2 beds and 2 plates. It can also essentially be constituted by segments of 3 beds and 3 plates or by an association of segments of 2 beds and 2 plates and segments of 3 beds and 3 plates. Finally, according to a non-preferred variant, it is also possible to use Sk segments according to the invention and one or more individual Pi plates fed according to the prior art, as notably represented in Figure 1. The invention, previously described in the case of 4 fluid networks F, D, R, E, is also similarly usable when there are not 4, but 5 or 6 fluid networks, for example using 2 refined fluids R1, R2 and / or a reflux RE of product rich in the desired product. There are then 5 or 6 network valves per segment Sk and line Lk. The invention also relates to a separation process that uses the device described above, in which, during a cycle, each of the Lk lines is sequentially used to circulate fluids F, D, R, and E at their nominal flow rate to or from each of the Sk Pi plates via a series connection between the Pi plate valve and one of the Vp network valves. k V Dk V Rk V Ek , where Lk is taken for each of the fluids F, D, R, E along their entire length during a cycle. Generally, an internal scan of at least [amount] is performed. A portion of each of the Lk branch lines is cut off when no network valve connected to Lk is open, and any internal sweep of Lk is interrupted when a network valve connected to Lk is open. Preferably, an internal sweep of Lk is performed from the upper Pi plate in Sk towards the lower Pi+1 or Pi+2 plate in Sk, at any time when Sk is not connected to one of the fluid networks, and immediately before a period when one of the network valves connected to Sk is open for feeding or transferring one of the fluids to or from the Pi plate. This internal sweep leads to the opening of Vi in the period preceding a feeding or transfer period of the Pi plate (which also requires the opening of Vi) and avoids an opening or closing movement of Vi between these consecutive periods. Reducing the number of valve movements reduces wear on these valves and increases the reliability of the device and the associated process. Generally, internal scans are performed on at least two, and often on all, of the Lk branch lines. Typically, the internal scan lasts for at least 20%, often at least 40%, or even at least 50% of the time. The invention allows for the performance of all kinds of chromatographic separations, and notably to carry out a separation process of para-xylene, as the desired product, from a load of aromatic hydrocarbons with 8 carbon atoms, or a separation process of meta-xylene, as the desired product, from a load of aromatic hydrocarbons with 8 carbon atoms. In general, it allows the use of the device described above for the separation of any aromatic hydrocarbon from a load of aromatic hydrocarbons that have the same number of carbon atoms. Description of the Figures and Functioning of the Devices Shown: The invention will be easily understood by following the description in the attached figures, in which: Figure 1 schematically represents a part of an SMB device according to the prior art, with the corresponding network valves. Figure 2 schematically represents a part of an SMB device according to the invention, comprising Sk segments of 2 beds and 2 plates, with corresponding network valves, plate valves and bypass flow limiting valves. Figure 3 schematically represents a part of an SMB device according to the invention, comprising Sk segments of 3 beds and 3 plates, with corresponding network valves, plate valves and bypass flow limiting valves. Figures 4a and 4b schematically represent, respectively, an intermediate segment and the column bottom segment of a device according to the invention in the case of the Sk segments with 2 beds and 2 plates. Figures 4c and 4d schematically represent, respectively, an intermediate segment and the bottom column segment of a device according to the invention in the case of the 3-bed, 3-part 5K segments. Figures 5a and 5b schematically represent, respectively, an intermediate Sk segment with 2 beds and 2 plates and a Sk segment with 3 beds and 3 plates, in the case where the flow limiting medium at Lk is a regulating valve located at Lk. Now, reference is made to Figure 1, which represents a section of a chromatographic column of an SMB according to the previous technique. Each of the adsorbent beds Ai-1, Ai, Ai+1, Ai+2, Ai+3, Ai+4 is arranged above a plate Pi-1, Pi, Pi+1, Pi+2, Pi+3, Pi+4, and each of these plates is connected by a line, respectively 3, 4, 5, 6, 7, 8, to each of the 4 fluid networks F, D, R, E by a valve (not referenced). There are, therefore, 4 main valves per plate. In addition, the plates are connected two by two by a bypass line 1a, 1b, 1c, which comprises a small-diameter valve, respectively 2a, 2b, 2c, to allow the passage of A limited bypass flow rate: 2% to 20% of the flow rate circulating in the column. In total, therefore, there are 4 main valves and on average 0.5 small diameter valves (one for every 2 plates) for each Pi plate, that is, on average 4.5 valves per plate. The operation of an SMB that uses such a column is well known to the professional. Typically, valve 2a, or 2b, or 2c of a bypass line is opened when no fluid F, D, R, E is fed or transferred from one of the 2 plates connected by the bypass line (bypass temporarily in service). Conversely, valve 2a, or 2b, or 2c of a bypass line is closed when one of the fluids F, D, R, E is fed or transferred from one of the 2 plates connected by the bypass line (bypass temporarily out of service). Figure 2 represents a column section of a device according to the invention comprising 3 segments Sk, Sk+1, Sk+2, each comprising 2 adsorbent beds and 2 plates located immediately below. The 2 plates of each segment are connected by a branch line, respectively Lk, Lk+1, Lk+2, which is suitable for the circulation of fluids F, D, R, E at their nominal flow rate. Each branch line is connected to a set of 4 network valves for feeding and transferring the fluids. Unlike the prior art, this set of 4 valves feeds not 1, but 2 plates. So, for the first Sk segment, there are 4 Vp network valves. k V Dk V Rk V Ek which simultaneously feed Pi-1 and Pi. Each platter is, on the other hand, connected to the corresponding branch line Lk, or Lk+1, or Lk+2 by a ferrule (corresponding to the horizontal line in the figure) comprising a unique 2-way controlled shut-off valve specific to the platter, called the platter valve: Vi-1, Vi, Vi+1, Vi+2, Vi+3, Vi+4. Each lower platter valve of a segment: Vi, Vi+2, Vi+4, on the other hand, has a small secondary branch line l. k , l k+1 i k+ 2 equipped with a typically small diameter valve: vi, vi+2, vi+4. In total, for each 2-plate segment, there are 4 network valves. 2 plate valves, and one small diameter valve in secondary bypass, that is 7 valves, and therefore on average 3.5 valves per plate. The device works as follows: For example, in segment Sk, when it is desired to feed or transfer one of the fluids F, D, R, E onto plate Pi-1 during a given period, the corresponding network valve V is opened. Fk V D k, V R k, or V Ek as well as the Vi-1 plate valve. The other network valves in the Sk segment are then closed, as are Vi and the small secondary bypass valve vi. When it is desired, at another time, to feed or transfer one of the fluids F, D, R, E onto the Pi plate, the corresponding network valve Vpk, V is opened. Dk V Rk or Vgk as well as the disc valve Vi. The other network valves in the Sk segment are then closed, as is Vi-1. The small secondary bypass valve Vi can remain closed. When, in a third period, it is desired not to feed or transfer any of the fluids F, D, R, E onto the Pi-1 and Pi trays, the network valves V are closed. F k, V D k, V Rk and VEk A limited flow rate is then circulated through the Lk line (transferred from Pi-1 and injected into Pi) by opening Vi-1, closing Vi, and opening the small secondary bypass valve vi. This makes it possible to ensure via l k a small bypass flow. Vi is typically a regulating valve (progressive opening) controlled by flow regulation from a flow meter not shown. The other sectors, Sk+1 and Sk+2, function similarly. Figure 3 represents a column section of a device according to the invention comprising 2 segments Sk, Sk+1, each comprising 3 adsorbent beds and 3 plates located immediately below. The 3 plates of each segment are connected by a branch line, respectively Lk, Lk+1, which is suitable for the circulation of fluids F, D, R, E at their nominal flow rate. Each branch line is connected to a set of 4 network valves for feeding and transferring the fluids. Unlike the prior art, this set of 4 valves feeds not 1, but 3 plates. So, for the first Sk segment, there are 4 V network valves. F k, Vdk, V Rk V Ek which simultaneously power Pi-1, Pi, and Pi+1. Each plate, as in the device shown in Figure 2, is connected to the corresponding branch line by a ferrule comprising a plate valve. Each lower plate valve of a segment: Vi+1, Vi+4, has on the other hand a small secondary branch line equipped with a typically small diameter valve: vi+1, vi+4. The device works as follows: For the upper segment, for example, when it is desired, within a given period, to feed or transfer one of the fluids F, D, R, E onto the Pi-1 plate, the corresponding network valve V is opened. F k, V D k, V Rk or V Ek as well as the Vi-1 plate valve. The other network valves in the Sk segment are then closed, as are Vi, Vi+1 and the small secondary bypass valve vi. When it is desired, at another time, to feed or transfer one of the fluids F, D, R, E onto the Pi plate, the corresponding network valve V is opened. Fk Vok, VRk or V Ek as well as the disc valve Vi. The other network valves in the Sk segment are then closed, as are Vi-1 and Vi+1. The small secondary bypass valve Vi can remain closed. When, in a third period, it is desired not to feed or transfer any of the fluids F, D, R, E onto the Pi-1 and Pi trays, the network valves V are closed. Fk V Dk V Rk , and V Ek A limited flow rate is then introduced through the Lk line. Two options are then possible: - It is possible to transfer a small flow from Pi-1 and inject it into Pi+1 by opening Vi-1, closing Vi and Vi+1, and opening the small secondary bypass valve Vi+1. - It is also possible to transfer a small flow rate via a bypass from Pi and inject it into Pi+1, by opening Vi, closing Vi-1 and Vi+1, and then opening the small secondary bypass valve Vi+1. Frequently, the plate (Pi-1, Pi) from which the bypass flow is transferred is alternately varied, in order to sweep as many plates as possible. Preferably, the last bypass sweep period (before feeding or transferring fluid F, D, R, E) is completed by transferring through the upper plate Pi-1. In this case, valve Vi-1 is open during this period, and there is no need for valve movement at the beginning of the following period in which Pi-1 will be fed or transferred through Vi-1, since this valve is already open. The other sectors, Sk+1 and Sk+2, function similarly. An example of the operation of a 3-bed, 3-plate Sk sector (as shown in Figure 3) is, for example, the following, in which the valves for the Sk operation that are open are mentioned, and the valves not mentioned are closed. Period 1: shunt sweep from Pi-1 to Pi+1. Valves open: Vi-1, vi+1. Period 2: Desorbent injection at Pi-1. Valves open: Vi-1, V D k-Period 3: Desorbent injection at Pi. Valves open: Vi, V Dk -Period 4: Desorbent injection at Pi+1. Valves open: Vi+1, V Dk . Period 5: Raffinate transfer from Pi-1. Open valves: Vi-1, V Rk . Period 6: Pi refinery racking. Open valves: Vi, V Rk . Period 7: Pi+1 raffinate racking. Open valves: Vi+1, V Rk . Period 8: Derivative sweep from Pi to Pi+1. Valves open: Vi, vi+1. Period 9: shunt sweep from Pi-1 to Pi+1. Valves open: Vi-1, vi+1. Period 10: Derivative sweep from Pi to Pi+1. Valves open: Vi, vi+1. Period 11: shunt sweep from Pi-1 to Pi+1. Valves open: Vi-1, vi+1. Period 12: Load injection at Pi-1. Valves open: Vi-1, V Fk Period 13: Load injection at Pi. Valves open: Vi, V Fk . Period 14: Load injection at Pi+1. Valves open: Vi+1, V Fk . Period 15: Derivative sweep from Pi to Pi+1. Valves open: Vi, vi+1. Period 16: shunt sweep from Pi-1 to Pi+1. Valves open: Vi-1, vi+1. Period 17: Derivative sweep from Pi to Pi+1. Valves open: Vi, vi+1. Period 18: shunt sweep from Pi-1 to Pi+1. Valves open: Vi-1, vi+1. Period 19: Derivative sweep from Pi to Pi+1. Valves open: Vi, vi+1. Period 20: shunt sweep from Pi-1 to Pi+1. Valves open: Vi-1, vi+1. Period 21: Transfer of Pi-1 extract. Valves open: Vi-1, V Rk . Period 22: Transfer of Pi extract. Valves open: Vi, V RkPeriod 23: Transfer of Pi+1 extract. Valves open: Vi+1, V Rk . Period 24: shunt sweep from Pi to Pi+1. Valves open: Vi, vi+1. The principles that allow establishing the preferred sequencing in the case of 3-bed, 3-plate adsorbent segments are as follows: 1) Each time one of the main fluids (F, D, R, E) is withdrawn or injected using a network valve in a bypass line Lk, this network valve remains open three times in succession (during 3 successive periods). The first time, the upper plate valve allows connection to the upper plate Pi-1, and the lower plate valves as well as the small bypass fluid control valve are closed. The second time, the intermediate plate valve allows connection to the intermediate plate Pi, and the upper and lower bed valves as well as the small bypass fluid control valve are closed. The third time, the lower plate valve allows connection to the lower plate Pi+1, and the upper plate valves as well as the small bypass fluid control valve are closed. 2) Outside the injection or transfer periods of the main fluids (F, D, R, E), a bypass flow rate of Lk is circulated. The valve The lower plate Vi+1 is closed, and the small control valve vi+1 located in a secondary bypass around Vi+1 regulates the bypass flow rate via the secondary bypass Vi+1, this flow rate coming alternately from the upper plate Pi-1 and the intermediate plate Pi. During the last period in which a bypass fluid circulates in Lk prior to the feeding or transfer of one of the main fluids, the upper plate valve Vi-1 (connected to the plate Pi-1) preferably opens, and can thus remain open during the following period. Figures 4a and 4b schematically represent a segment of 2 beds and 2 plates. Figure 4b shows such a segment at the bottom of a column. According to the invention, the referenced line Pi+1 replaces, by definition, the plate located below bed Ai+1, this plate being absent at the bottom of a column. Similarly, Figures 4c and 4d schematically represent a segment of 3 beds and 3 plates. Figure 4d shows such a segment at the bottom of a column. According to the invention, the referenced line Pi+2 replaces, by definition, the plate located below bed Ai+2, this plate being absent at the bottom of the column. Figures 5a and 5b represent, respectively, a Sk segment with 2 beds and 2 plates, and a Sk segment with 3 beds and 3 plates in which the flow limitation means does not comprise a secondary bypass with a valve vi, but rather a larger diameter valve 9 arranged in the Sk line itself (with the associated flow measurement means, not shown). Best Way to Do It: The best embodiment of the invention is an SMB in which the column(s) are essentially made up of Sk segments of 3 beds and 3 plates. In such a device, for example with 24 beds and 24 plates (for example, 2 loop columns of 12 beds and 12 plates each), only 24 plate valves are needed for the control of the SMB, and 4 x 8 = 32 network valves (4 for each of the 8 Sk segments required), i.e., 56 main valves to which 8 small valves must be added. regulation (in secondary derivation), that is, 64 valves in total, which represents an average of 2.67 valves per platter. In the prior art corresponding to Figure 1, the equivalent SMB requires 4 x 24 = 96 main valves (4 valves per plate) and 12 reduced-diameter valves, or 108 valves in total, and 4.5 valves per plate. The device according to the invention as described can be used for any chromatographic separation process, notably for the separation of an aromatic hydrocarbon from a load of aromatics that essentially have 8 carbon atoms and that comprise that hydrocarbon. In particular, it can be used for the separation of paraxylene from an aromatic cut essentially composed of C8 hydrocarbons, using toluene or paradiethylbenzene as a desorbent and a zeolite as an adsorbent, as described, for example, in patent FR 2,789,914. It can also be used for the separation of metaxylene from a C8 aromatic cut, using toluene or tetralin as a desorbent and an adsorbent, as described, for example, in US patent 5,900,523 and in patent applications FR 05 / 52,485 and FR 05 / 52,486. It can also be used for the separation of one or more normal paraffins (separated from the rest of the hydrocarbons) from a mixture of hydrocarbons, notably paraffinic or paraffinic and naphthenic, for example using normal butane or normal pentane as a desorbent (possibly isooctane as an inert diluent) and a zeolite 5A as an adsorbent. It can ultimately be used for the separation of at least one olefin from a hydrocarbon cut comprising such a hydrocarbon, according to conditions known from the prior art, for example, using a calcium-exchanged zeolite X. The invention is not limited to the preceding description, and the practitioner may use any other technical feature known in the state of the art for its implementation.

Claims

CLAIMS 1. A device that allows the separation of at least one desired compound from a mixture comprising that compound by adsorption in a simulated moving bed comprising: at least one column divided into a plurality of adsorbent beds Ai separated by distributor / extractor plates Pi for the sequential feeding and extraction of at least two feed fluids: a feed fluid F and a desorbent D, and at least two transferred fluids: a raffinate R and an extract E, Pi being arranged between bed Ai and the immediately lower bed Ai+1, the device also comprising fluid networks, namely at least one F-Net feeder network, one D-Net desorbent network, one R-Net raffinate network and one E-Net extract network, each of these networks being connected to the column by a plurality of lines comprising 2-way controlled shut-off valves, called network valves, for the sequential feeding or transfer of said fluids, in which the column is divided, at least for most of its height, into a plurality of adjacent superimposed segments Sk, each segment Sk consisting essentially of a group of at least 2 and at most 5 successive adsorbent beds and the distributor / extractor plates Pi that are arranged immediately below these successive adsorbent beds, Each of the Pi distribution / extraction plates in each of the Sk sectors is a single common network for the sequential feeding and transfer of fluids F, D, R, E, The Pi plates of each Sk segment are connected to each other by an external branch line Lk connected to each Pi plate of Sk by a fitting comprising a unique 2-way controlled shut-off valve specific to the Pi plate, called the Vi plate valve, for the sequential feeding or transfer of fluids F, D, R, E into or from Pi. each of the said Lk branch lines comprises at least one controlled means of limiting the flow circulating in Lk, which is or installed in the Lk line or in a branch around a Vi plate valve of a Pi plate of Sk, in which the branch line Lk of each of the Sk segments is connected to each of the F-Net, D-Net, R-Net and E-Net networks via a single line comprising a single network valve, respectively Vp. k V D k, V Rk V Ekfor the sequential feeding or transfer of the corresponding fluid F, D, R or E to or from the considered Sk segment, and in which each Pi plate of the Sk segment is uniquely connected to each of the F-Net, D-Net, R-Net and E-Net networks via a series connection to the terminal comprising the Vi plate valve, and then at least a portion of Lk, and then said single line comprising said single network valve, respectively V F k, V Dk V R k,V Ek .

2. Device according to claim 1, wherein each Sk segment essentially consists of a group of 2 or 3 successive adsorbent beds.

3. Device according to one of claims 1 and 2, in which the branch line Lk has an internal diameter at least equal to the largest opening diameter of the network valves connected to Lk.

4. Device according to one of claims 1 to 3, in which at least one segment Sk consists of two adsorbent beds Aj, Aj+1 and two distributor / extractor plates Pj, Pj+1 which are arranged immediately below these adsorbent beds respectively.

5. Device according to one of claims 1 to 4, in which at least one segment Sk consists of three adsorbent beds Aj, Aj+1, Aj+2 and the three distributor / extractor plates Pj, Pj+1, Pj+2 that are arranged immediately below these adsorbent beds respectively.

6. Device according to one of the preceding claims, in which the entire column consists of adjacent superimposed segments Sk, the column comprising a lower outlet line assimilated to a plate Pn corresponding to the lower adsorbent bed An.

7. Device according to one of claims 4 and 6, in which all Sk segments consist of two adsorbent beds and the two distributor / extractor plates that are disposed immediately below these adsorbent beds respectively, or said assimilated lower outlet line.

8. Device according to one of the preceding claims, in which each of said Lk bypass lines comprises at least one controlled means of limiting the flow circulating in Lk, which is installed in bypass around a disc valve Vi of the disc valve Pi of Sk.

9. Device according to claim 8, in which said flow limiting means circulating in Lk installed in bypass around said disc valve Vi comprises a controlled valve with a smaller opening diameter than the opening diameter of Vi.

10. Device according to claim 5, in which, for each three-plate segment Sk Pj, Pj+1, Pj+2, the branch line Lk comprises a first means for limiting the flow circulating between Pj and Pj+1, and a second means for limiting the flow circulating between Pj+1 and Pj+2.

11. A process for separating a product using a device as defined in any of the preceding claims, in which, during a cycle, each of the lines Lk is sequentially used for the circulation at its nominal flow rate of fluids F, D, R, E, to or from each of the plates Pi of Sk via a series plate valve Pi and one of the network valves Vn<, Vdr, Vrk, Ver, and in which Lk is taken by each of the fluids F, D, R, E along its entire length during a cycle.

12. Process according to claim 11, in which an internal scan of at least a portion of each of the Lk branch lines is performed when no network valve connected to Lk is open and any internal scan of Lk is interrupted when a network valve connected to Lk is open.

13. A process according to one of claims 11 and 12, in which an internal sweep of Lk is performed from plate Pi located in the upper position in Sk towards plate Pi+1 or Pi+2 located in the lower position in Sk, at any time when Sk is not connected to one of said fluid networks and which is immediately before a time when one of the network valves connected to Sk is open for feeding or transferring one of the fluids to or from plate Pi.

14. Process according to one of claims 11 to 13, in which scans of at least 2 Lk derivation lines are performed.

15. Process according to one of claims 11 to 14, in which asynchronous permutations of the feed and transfer points of fluids F, D, R, E in the column are performed.

16. Process according to claim 15, in which the device is used with chromatographic zones of which at least certain are equivalent to an integer number of adsorbent beds.

17. Process according to one of claims 11 to 15, for separating an aromatic hydrocarbon from a load of aromatics having essentially 8 carbon atoms and comprising that hydrocarbon.

18. Process according to claim 17, for separating paraxylene from a load of aromatic hydrocarbons having essentially 8 carbon atoms.

19. Process according to claim 17, for separating metaxylene from a load of aromatic hydrocarbons having essentially 8 carbon atoms.

20. A process for separating at least one normal-paraffin hydrocarbon from a hydrocarbon feedstock comprising such a hydrocarbon, using a device as defined in any one of claims 1 to 10.

21. A process for separating at least one olefinic hydrocarbon from a hydrocarbon feedstock comprising such a hydrocarbon, using a device as defined in any of the of claims 1 to 10.