Adsorbent having hierarchical structure
By designing adsorbent agglomerates with a graded structure, the problems of pressure drop and fluidization risks of existing adsorbents after reducing their size are solved, and more stable and efficient gas separation performance is achieved.
Patent Information
- Application Number
- CN202411191019.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-08-29
- Filing Date
- 2024-08-28
- Publication Date
- 2025-02-28
AI Technical Summary
After the size of existing adsorbents decrease, they lead to increased pressure drop and fluidization risks, and increase fragility, affecting processing operations and service life.
An adsorbent agglomerate is designed, which comprises an internal region and a superimposed adsorbent particle layer. Each adsorbent particle layer has a hierarchical structure, an average particle volume increases, and a standard deviation of particle volume is controlled between less than 20%, 10%, or 5%.
The adsorbent agglomerates in the graded structure reduce pressure drop and fluidization risks, improve the stability and service life of the adsorbent, while maintaining efficient gas separation performance.
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Figure CN119524819A_ABST
Abstract
Description
[0001] The invention is in the field of materials for separating gas mixtures into a highly adsorptive fraction and a less adsorptive fraction.
[0002] Adsorption is widely used for the purification or separation (fractionation) of gases. Examples include the fractionation of "normal" and "iso" paraffins, the fractionation of xylenes, the fractionation of alcohols, the production of nitrogen or oxygen from atmospheric air, and the removal of CO2 from flue gases and from blast furnace gases. In terms of purification, there are dryers, hydrogen or helium purging, methane-rich gas purging, adsorption of trace impurities in many fluids (rejection of mercury, NOx, sulfur products, etc.).
[0003] Improved efficiency and reduced costs of adsorption separation processes involve improvements in the adsorbents used in these processes and reduced cycle times. The need for reduced mass transfer zones in rapid adsorption cycles requires the use of smaller sized adsorbent agglomerates or smaller sized non-agglomerated adsorbent solids or crystals. However, reducing the size of the adsorbent results in an increased pressure drop through the adsorbent bed and a risk of fluidization of the bed. Since smaller sized adsorbents are also more fragile, they are likely to deteriorate during processing operations or by fluidization.
[0004] It would therefore be desirable to provide an adsorbent which alleviates these known disadvantages of the prior art.
[0005] The present invention therefore relates to an adsorbent agglomerate comprising an inner region and superimposed layers of adsorbent particles, said layers of adsorbent particles succeeding one another starting from said inner region, enclosing said inner region, each adsorbent particle having a volume referred to as particle volume, at least two layers of adsorbent particles constituting mutually graded layers, said at least two layers being the layers of adsorbent particles furthest from the inner region, in said adsorbent agglomerate, the average particle volume of the adsorbent particles constituting each of said graded layers before a subsequent graded layer is smaller than the average particle volume of the adsorbent particles constituting the subsequent graded layers, the standard deviation of the particle volume values of the adsorbent particles of each graded layer being less than 20%, preferably less than 10%, preferably less than 5% relative to the average particle volume of the adsorbent particles constituting the graded layer under consideration.
[0006] According to one embodiment, the graded layers are concentric. More particularly, the inner region is the central region of the adsorbent agglomerates.
[0007] According to one embodiment, the adsorbent agglomerate comprises at least 3 graded layers, preferably at least 4 graded layers.
[0008] According to one embodiment, the adsorbent agglomerate comprises 2 to 15 graded layers, inclusive, preferably 2 to 10 graded layers, inclusive.
[0009] According to one embodiment, the thickness of each graded layer is between 30 and 500 microns. More particularly, the thickness of the graded layer farthest from the inner region is between 30 and 300 microns. More particularly, the thickness of the graded layer preceding the subsequent graded layer farthest from the inner region is between 50 and 400 microns. More particularly, the thickness of the graded layer preceding the subsequent graded layer that itself precedes the graded layer farthest from the inner region is between 100 and 500 microns. More particularly, the graded layer farthest from the inner region, the graded layer preceding the subsequent graded layer farthest from the inner region, and the graded layer preceding the subsequent graded layer that itself precedes the graded layer farthest from the inner region have the same or substantially the same volume.
[0010] According to one embodiment, the ratio of the volume of each graded layer after the preceding graded layer to the volume of the preceding graded layer is between 100% and 350%, preferably between 150% and 250%. More particularly, the ratio of the volume of the graded layer farthest from the inner region to the volume of the graded layer before the subsequent graded layer farthest from the inner region is between 170% and 250%. More particularly, the ratio of the volume of the graded layer before the subsequent graded layer farthest from the inner region to the volume of the graded layer before the subsequent graded layer which itself precedes the subsequent graded layer farthest from the inner region is between 190% and 220%.
[0011] According to one embodiment, the ratio of the volume of the graded layer furthest from the inner region to the volume of the adsorbent agglomerates is between 20% and 90%, preferably between 35% and 75%, preferably between 45% and 65%.
[0012] The interparticle spaces of the one or more outermost graded layers overlying the one or more preceding graded layers are advantageously wider than the interparticle spaces of the one or more preceding graded layers.
[0013] According to one embodiment, the graded layers constitute at least 30%, preferably at least 50%, preferably at least 60% of all layers of the adsorbent agglomerate. The average volume of the adsorbent particles increases continuously between the graded layer closest to the inner region and the graded layer farthest from the inner region. The graded layer farthest from the inner region is not covered by any other layer of adsorbent particles.
[0014] According to one embodiment, the inner region comprises an aggregate of sorbent particles. More particularly, there is no hierarchy of sorbent particles within the aggregate.
[0015] According to one embodiment, the adsorbent agglomerates are substantially spherical.
[0016] According to one embodiment, the particle volume of each adsorbent particle contained in the graded layer is between 4 and 4000 microns. 3 Between 40 and 400 microns3 More specifically, the particle volume of each adsorbent particle in the graded layer farthest from the inner region is between 200 and 4000 microns. 3 More specifically, the particle volume of each adsorbent particle in the graded layer preceding the subsequent graded layer farthest from the inner region is between 60 and 1000 microns. 3 More specifically, the particle volume of each adsorbent particle in the graded layer preceding the subsequent graded layer that itself precedes the subsequent graded layer farthest from the inner region is between 30 and 500 microns. 3 between.
[0017] According to one embodiment, the adsorbent particles are substantially spherical and the average diameter of the adsorbent particles of each graded layer prior to constituting a subsequent graded layer thereafter is smaller than the average diameter of the adsorbent particles constituting the subsequent graded layer.
[0018] According to one embodiment, the adsorbent particles comprise one or more adsorbent crystals. More particularly, the adsorbent particles comprise a plurality of adsorbent crystals agglomerated together. In a particular embodiment, each adsorbent particle contained in a graded layer consists of a single adsorbent crystal. In this embodiment, the average volume of adsorbent crystals of each graded layer prior to constituting a subsequent graded layer thereafter is less than the average volume of adsorbent crystals constituting the subsequent graded layer.
[0019] According to one embodiment, the adsorbent particles contained in the graded layer comprise one or more amorphous solids. More particularly, the adsorbent particles comprise a plurality of agglomerated amorphous solids. Amorphous solids particularly include activated carbon, aluminum oxide or other metal oxides and / or silicon dioxide, such as silica gel. In a particular embodiment, each adsorbent particle contained in the graded layer consists of a single amorphous solid. In this embodiment, the average volume of amorphous solids of each of the graded layers before constituting the subsequent graded layer is less than the average volume of amorphous solids constituting the subsequent graded layer.
[0020] According to one embodiment, the sorbent particles comprise a binder, more particularly between 1 and 12 weight % (wt %) of binder, preferably between 4 and 10 wt % of binder.
[0021] According to one embodiment, the sorbent agglomerates comprise a binder between the sorbent particles, more particularly between 1 and 10 weight % (wt %) of binder.
[0022] According to one embodiment, the adsorbent agglomerates are zeolitic adsorbents, in particular FAU zeolites, in particular X, Y or A zeolites, more in particular calcium exchanged. Preferably, the adsorbent agglomerates are LSX type zeolites.
[0023] According to one embodiment, the adsorbent agglomerates have a tortuosity between 1 and 2.2.
[0024] Another subject of the invention is an adsorber comprising an adsorbent bed comprising a plurality of adsorbent agglomerates as described above.
[0025] Another subject of the invention is a process for the adsorptive separation of gas mixtures using an adsorbent agglomerate as described above or an adsorber as described above. The process is in particular a pressure swing adsorption (PSA) process, more in particular a VSA or VPSA process. The process can also be a RPSA (rapid PSA) pressure swing adsorption process, in which the duration of the pressure cycle is generally less than 1 minute. The process is in particular an air separation process, for example for the production of oxygen.
[0026] Another subject of the invention is the use of an adsorbent agglomerate as described above or an adsorber as described above in a process for fractionating “normal” and “iso” paraffins, for fractionating xylenes, for fractionating alcohols or for purging hydrogen or helium.
[0027] Another subject of the present invention is a process for producing adsorbent agglomerates, in particular adsorbent agglomerates as described above, comprising the following steps:
[0028] - providing a plurality of adsorbent particles, each adsorbent particle having a volume referred to as a particle volume,
[0029] - forming at least two batches of adsorbent particles, each batch of adsorbent particles corresponding to a target average particle volume of the particles constituting it, the standard deviation of the particle volume values of each batch of adsorbent particles being less than 20%, preferably less than 10%, preferably less than 5% relative to the target average particle volume of said batch,
[0030] - an agglomeration step comprising the following sub-steps:
[0031] a) agglomerating the first batch of adsorbent particles into a first adsorbent particle layer,
[0032] b) agglomerating a next batch of adsorbent particles into a subsequent upper layer of adsorbent particles covering the first layer of adsorbent particles,
[0033] The target average particle volume of each batch before the next batch is smaller than the target average particle volume of the next batch.
[0034] In one embodiment, step b) is repeated until the last batch of adsorbent particles is agglomerated into a final adsorbent particle layer covering the previous adsorbent particle layer. The adsorbent agglomerate thus comprises at least three adsorbent particle layers.
[0035] According to one embodiment, the number of batches is between 2 and 15, inclusive, in particular between 2 and 10, inclusive.
[0036] According to one embodiment, the adsorbent particles provided have a particle size of 4 to 4000 microns. 3 Between 40 and 400 microns 3 More specifically, the first batch of adsorbent particles has a particle size of 4 to 10 microns. 3 More particularly, the particle size of the final batch of adsorbent particles is between 200 and 4000 microns. 3 More particularly, the particle size of the adsorbent particles of the batches before the last batch is between 60 and 1000 microns. 3 between.
[0037] According to one embodiment, the method comprises a step of providing an aggregate of adsorbent particles and a step of agglomeration of the formed batch of adsorbent particles occurring on the aggregate (agglomeration step). More particularly, there is no fractionation of the adsorbent particles in the aggregate.
[0038] According to one embodiment, the batches are formed by sieving the adsorbent particles.
[0039] According to one embodiment, the method comprises the step of feeding formed batches of adsorbent particles to an agglomeration step, said feeding being carried out from reservoirs of adsorbent particles, each reservoir containing one of the formed batches.
[0040] According to one embodiment, the agglomeration step is carried out in the presence of moisture or dry.
[0041] According to one embodiment, the agglomeration step comprises a sub-step of preparing each batch of adsorbent particles in the form of a dispersion of adsorbent particles. The dispersion comprises in particular a surfactant and a pore former.
[0042] According to one embodiment, the agglomeration step is performed by fluidization. More particularly, the agglomeration step comprises the following sub-steps:
[0043] a′) fluidized-bed spraying of a first prepared dispersion corresponding to the first batch until the adsorbent particles of the first dispersion agglomerate into a first adsorbent particle layer,
[0044] b′) fluidized bed spraying of a next prepared dispersion corresponding to a next batch until the adsorbent particles of the next dispersion agglomerate into a next adsorbent particle layer covering the first adsorbent particle layer.
[0045] According to one embodiment, b′) is repeated until the adsorbent particles corresponding to the last dispersion of the last batch are agglomerated into a last adsorbent particle layer covering the previous adsorbent particle layer.
[0046] According to one embodiment, the fluidized bed agglomeration step is carried out in a reactor, wherein the prepared dispersion is fed as a spray, in particular at a pressure of 1 to 10 bar absolute. The pressure in the reactor is in particular between 1 and 10 bar absolute.
[0047] According to one embodiment, fluidization is carried out by circulating a gas stream in the reactor, in particular at a temperature between 40 and 500°C.
[0048] Alternatively, the agglomeration step is performed by a rotating tray. More particularly, the agglomeration step comprises the following sub-steps: a") placing a first prepared dispersion corresponding to a first batch on a tray, and rotating the tray until the adsorbent particles of the first dispersion are agglomerated into a first adsorbent particle layer, a1") optionally transferring the agglomerated adsorbent particles from the tray to another tray, b") placing a next prepared dispersion corresponding to a next batch on the tray or another tray, and rotating the tray or another tray until the adsorbent particles of the next dispersion are agglomerated into a next adsorbent particle layer covering the first adsorbent particle layer.
[0049] All dispersions can be agglomerated on the same tray. Alternatively, the dispersions are each agglomerated on a different tray. The agglomeration step then comprises a transfer substep a1").
[0050] According to one embodiment, step b") and optional step a1") are repeated until and including the agglomeration of the adsorbent particles of the last dispersion corresponding to the last batch into a final layer covering the previous one.
[0051] According to one embodiment, the process comprises a discharge step and a step of activating the adsorbent agglomerates obtained.
[0052] Figure 1 represents an adsorbent agglomerate according to the present invention;
[0053] Figure 2 represents a first embodiment of a method of making adsorbent agglomerates;
[0054] Figure 3 and 4 Each represents a variation of the second embodiment of the production method.
[0055] An adsorbent agglomerate comprises an inner region 7 and superimposed layers of adsorbent particles 1, the layers of adsorbent particles being successive from the inner region 7 and enclosing the inner region 7, each adsorbent particle 1 having a volume referred to as a particle volume, at least two layers 2, 3, 4, 5 of adsorbent particles 1 constituting mutually graded layers, each graded layer consisting of a group of adsorbent particles 1 having a target average particle volume, the standard deviation of the particle volume values of each group of adsorbent particles 1 being less than 20%, preferably less than 10%, preferably less than 5% relative to the target average particle volume of the group of adsorbent particles 1, the at least two layers 2, 3, 4, 5 being the layers furthest from the inner region 7, characterised in that in each graded layer 2, 3, 4 covered by a subsequent graded layer 3, 4, 5, the target average particle volume is less than the target average particle volume of the group of adsorbent particles 1 constituting the subsequent graded layer 3, 4, 5.
[0056] The adsorbent agglomerate according to the invention comprises substantially spherical adsorbent particles 1 arranged in layers and an inner region 7, here the central region of the adsorbent agglomerate. Figure 1 In the embodiment of the invention, the layer 2 of adsorbent particles is covered by an upper subsequent layer 3 covering the lower layer 2, which itself is covered by an upper subsequent layer 4 covering the lower layer 3, which itself is covered by an upper subsequent layer 5 covering the lower layer 4. The layers 2, 3, 4 and 5 are at a certain distance from the inner region 7 and are the layers farthest from the inner region 7. The layer 5 is the layer farthest from the inner region 7, or the outermost layer of the adsorbent agglomerate. The layers 2, 3, 4 and 5 enclose the inner region 7. The layers 2, 3, 4 and 5 are successively from the inner region 7, that is, in the direction from the inner region to the outer surface of the adsorbent agglomerate, the layer 2 precedes the layer 3, the layer 3 precedes the layer 4, which itself precedes the layer 5 farthest from the inner region 7. In other words, the layer 5 follows the layer 4, which itself follows the layer 3, which itself follows the layer 2.
[0057] In the sense of the present invention, a layer immediately before another layer is referred to as a “previous layer”, and a layer immediately after another layer is referred to as a “subsequent layer”.
[0058] Figure 1The adsorbent agglomerate thus comprises a superposition of concentric layers 2, 3, 4 and 5 of adsorbent particles 1, each of which has a volume referred to as particle volume. Each of the layers 2, 3, 4 and 5 corresponds to a target average particle volume for each of the adsorbent particles 1 contained therein, i.e. each of the adsorbent particles 1 contained in the layers 2, 3, 4 and 5 has a particle volume close to the target average particle volume, the particle volume being able to vary between the adsorbent particles 1 by a standard deviation of the particle volume values of the particles 1 of the layer, the controlled standard deviation being less than 20%, preferably less than 10%, preferably less than 5% relative to the target average particle volume of the layer. The layer is thus defined by the volume of the adsorbent particles 1 constituting it. The target average particle volume corresponds to the desired volume value for the layer design.
[0059] The layers 2, 3, 4 and 5 constitute so-called hierarchical layers. The hierarchical layers 2, 3, 4, 5 have a hierarchy between them by observing the following rule: the target average particle volume of the adsorbent particles 1 of the hierarchical layer 2, 3, 4, referred to as the lower layer, is strictly smaller than the target average particle volume of the adsorbent particles of the subsequent hierarchical layer 3, 4, 5 following the lower layer 2, 3, 4, which covers the lower layer 2, 3, 4.
[0060] The average particle volume of a graded layer is calculated by dividing the sum of the volumes of all adsorbent particles in the graded layer by the number of adsorbent particles in the graded layer. The standard deviation of the particle volume of particles in a graded layer corresponds to the spread of the particle volume values of particles in the graded layer around a target average particle volume of the graded layer.
[0061] exist Figure 1 In the embodiment of the invention, the inner region 7 is composed of a layered aggregate of adsorbent particles without a specific gradation between the layers. Layers 2, 3, 4 and 5 are arranged around the aggregate, thereby encapsulating the aggregate.
[0062] Optionally, a binder is used to agglomerate the adsorbent particles with one another.
[0063] In the embodiment shown, the adsorbent particles 1 are formed from a crystalline powder, which is agglomerated to form the adsorbent particles. Agglomeration here can also be performed using a binder. In another embodiment (not shown), the adsorbent particles are formed from a powder of an amorphous solid, which is agglomerated to form the adsorbent particles. The amorphous solid can consist of activated carbon or silica gel. Agglomeration here can also be performed using a binder.
[0064] When the adsorbent particles 1 comprising agglomerated amorphous solids or crystals are substantially spherical, they are also referred to as adsorbent beads. The adsorbent agglomerates with graded porosity according to the invention then comprise agglomerates of adsorbent beads arranged in concentric layers, each of said beads comprising an agglomerate of amorphous solids or crystals. In embodiments in which each adsorbent particle in the sense of the invention consists of a single adsorbent crystal, the adsorbent agglomerates with graded porosity comprise agglomerates of crystals arranged in layers. These layers are graded relative to one another, observing the following rule: the target average volume of the crystals of the underlying layer is smaller than the target average volume of the crystals of the subsequent layer covering said underlying layer.
[0065] The interparticle spaces 6 of the one or more layers farthest from the inner region 7 covering the one or more underlying layers are advantageously wider than the interparticle spaces of the one or more underlying layers. The interparticle spaces measure the space between the adsorbent particles 1. The interparticle spaces of the outermost layer are more particularly open to the outside on the pores of the adsorbent particles, in particular the network of mesopores and micropores. Thus, the diffusion rate of molecules between the adsorbent particles of the outermost layer is optimized. Since the outermost layer usually occupies a large part of the volume of the adsorbent agglomerate, the mass transfer is greatly improved. In the case of concentric graded layers, since the geometry of the adsorbent agglomerate follows the central symmetry, the mass transfer properties of the adsorbent are homogenized. The smaller particle volume of the underlying layer makes it possible to benefit from the higher adsorption rate characteristics of the small adsorbent particles and therefore benefit from the higher selectivity. Due to the high volume of the adsorbent agglomerate according to the present invention relative to the adsorbent particles 1 constituting it, the disadvantages associated with the increase of pressure loss and / or associated with fluidization brought about by the use of these small-sized adsorbent particles 1 known in the prior art are avoided. Thus a compromise between seemingly irreconcilable properties is found.
[0066] The particle volume in the sense of the present invention corresponds to the macroscopic volume of the adsorbent particles 1 which can be observed and measured under a microscope, that is to say including the interstices between the constituent elements of the adsorbent particles, in particular the spaces between crystals or between amorphous solids. The volume of the adsorbent agglomerates in the sense of the present invention corresponds to the macroscopic volume of the adsorbent agglomerates, that is to say including the interparticle spaces 6. The average volume of the adsorbent particles 1 of the underlying layer is smaller than the average volume of the adsorbent particles 1 of the subsequent layer covering the underlying layer. In other words, the average characteristic size of the adsorbent particles 1 of the underlying layer is smaller than the average characteristic size of the adsorbent particles 1 of the subsequent layer.
[0067] The adsorbent agglomerates according to the invention may be zeolitic adsorbents, in particular FAU zeolites, preferably zeolite X. For example, zeolite X has a silica / alumina ratio of less than 1.15, preferably less than 1.1 or substantially equal to 1.0.
[0068] exist Figure 1In an embodiment of the invention, it is a calcium (Ca) exchanged faujasite adsorbent suitable for use in an adsorbent bed of an adsorber for a VSA type pressure swing adsorption separation process after activation. However, the adsorbent agglomerates according to the invention can be used in any adsorption process, such as pressure swing adsorption (PSA), more particularly a VSA (vacuum pressure swing adsorption or VPSA) process. The process can also be a RPSA (rapid PSA) pressure swing adsorption process, in which the duration of the pressure cycle is generally less than 1 minute.
[0069] Figure 2 is a schematic diagram of one example of a method for producing adsorbent agglomerates having graded porosity according to the present invention by fluidized bed agglomeration.
[0070] A certain amount of adsorbent particles 1 is provided and the adsorbent particles are distributed according to their particle volume to constitute batches S1, S2, S3, ... Sn. The adsorbent particles 1 contained in each batch S1, S2, S3, ... Sn all have similar particle volumes close to the target average particle volume, which is characteristic of the batch under consideration. The standard deviation of the particle volume values of the adsorbent particles 1 of each batch S1, S2, S3, ... Sn formed is controlled to be less than 20%, or even less than 10%, or even less than 5% relative to the target average particle volume. The rest of the manufacturing method includes agglomerating the adsorbent particles 1 distributed in batches in such a graded manner. The batches S1, S2, S3, ... Sn are sorted in this order by increasing the average target particle volume.
[0071] exist Figure 2 In the example of , batches S1, S2, S3, ... Sn are prepared with surfactants and pore formers in the form of dispersions d1, d2, d3, ..., dn. The dispersions d1, d2, d3, ..., dn thus prepared are then sequentially fed into a spraying device, such as a fluidized reactor or tank, wherein the dispersions d1, d2, d3, ..., dn are sprayed in a fluidized bed.
[0072] The first dispersion d1 is sprayed in the fluidized bed for the time required for the adsorbent particles 1 contained in the first spray dispersion d1 to agglomerate together to form a first layer 2 of adsorbent agglomerates. The agglomeration of the first layer 2 can be carried out on the aggregates. Next, the second dispersion d2 is then sprayed in the fluidized bed for the time required for the adsorbent particles 1 contained in the second spray dispersion d2 to agglomerate into a second layer 3 covering the first layer 2. This continues until the particles of the last dispersion agglomerate into a last layer 5 covering the previous layer 4. The last layer 5 constitutes the outer layer (or outermost layer) of the adsorbent aggregate. Thereby, adsorbent agglomerates in the form of concentric layers of adsorbent particles are obtained, in which the volume of the particles steadily decreases from the outer layer to the inner layer.
[0073] Figure 3Schematic diagram of another example of a method for producing adsorbent agglomerates with graded porosity according to the present invention by rotating disk agglomeration. Figure 2 The method is similar to that of the method of the invention, but differs in that the dispersions d1, d2, d3, ..., dn are fed successively in the same order onto one or more rotating disks for agglomeration. The one or more rotating disks rotate for the time required for the particles of a given dispersion to agglomerate into a layer (which, where appropriate, covers the previous layer). All batches S1, S2, S3, ... Sn can be fed as follows: Figure 3 In the example of FIG. 1 , the batches S1, S2, S3, ... Sn can be agglomerated on the same turntable, or the batches S1, S2, S3, ... Sn can be agglomerated on the same turntable. Figure 4 , . . . P_tournant n), with a step A1 , A2 of transferring the adsorbent particles 1 previously agglomerated on a given turntable to the next turntable, if necessary.
Claims
1. An adsorbent agglomerate comprising an inner region (7) and superimposed layers of adsorbent particles (1), the layers of adsorbent particles (1) being successive from the inner region (7) and enclosing the inner region (7), each adsorbent particle (1) having a volume referred to as particle volume, at least two layers of adsorbent particles (1) constituting mutually graded layers (2, 3, 4, 5), the at least two layers being layers of adsorbent particles (1) being farthest from the inner region (7), in the adsorbent agglomerate, the average particle volume of the adsorbent particles (1) of each graded layer (2, 3, 4) before constituting a subsequent graded layer (3, 4, 5) is smaller than the average particle volume of the adsorbent particles (1) constituting the subsequent graded layer (3, 4, 5), the standard deviation of the particle volume values of the adsorbent particles (1) of each graded layer being less than 20%, preferably less than 10%, preferably less than 5%, relative to the average particle volume of the adsorbent particles (1) constituting the graded layer.
2. Adsorbent agglomerate according to the preceding claim, wherein the graded layers (2, 3, 4, 5) are concentric.
3. The adsorbent agglomerate according to claim 1, comprising at least 3 graded layers (2, 3, 4, 5), preferably at least 4 graded layers (2, 3, 4, 5).
4. The adsorbent agglomerate according to claim 1, wherein the graded layers (2, 3, 4, 5) constitute at least 30%, preferably at least 50%, preferably at least 60% of all layers of the adsorbent agglomerate.
5. The adsorbent agglomerate according to claim 1, wherein the inner region (7) comprises aggregates of adsorbent particles (1) in which no classification of the adsorbent particles (1) exists.
6. The adsorbent agglomerate according to any one of the preceding claims, wherein the adsorbent agglomerate is substantially spherical.
7. Adsorbent agglomerate according to any of the preceding claims, wherein each adsorbent particle (1) contained in the graded layers (2, 3, 4, 5) consists of a single adsorbent crystal or a single amorphous solid.
8. The adsorbent agglomerate according to claim 1, wherein the adsorbent agglomerate is a zeolitic adsorbent, in particular a FAU zeolite, in particular zeolite X, Y or A.
9. An adsorber comprising an adsorbent bed, the bed comprising a plurality of adsorbent agglomerates according to any one of the preceding claims.
10. Process for the adsorptive separation of gas mixtures, wherein an adsorbent agglomerate according to one of claims 1 to 8 or an adsorber according to claim 9 is used.
11. The separation process according to the preceding claim, wherein the process is an air separation process.
12. Use of the adsorbent agglomerate according to one of claims 1 to 8 or the adsorber according to claim 9 in a process for fractionating "normal" and "iso" paraffins, for fractionating xylenes, for fractionating alcohols, for purging hydrogen or helium.
13. A method for producing adsorbent agglomerates comprising the steps of: - providing a plurality of adsorbent particles (1), each adsorbent particle (1) having a volume referred to as particle volume, - forming at least two batches of adsorbent particles (1), each batch of adsorbent particles (1) corresponding to a target average particle volume of the particles constituting it, the standard deviation of the particle volume values of each batch of adsorbent particles being less than 20%, preferably less than 10%, preferably less than 5% relative to the target average particle volume of said batch, - an agglomeration step comprising the following sub-steps: a) agglomerating a first batch of adsorbent particles (1) into a first layer (2) of adsorbent particles (1), b) agglomerating a next batch of adsorbent particles (1) into a subsequent upper layer (3) of adsorbent particles (1) covering the first layer of adsorbent particles (1), The target average particle volume of each batch before the next batch is smaller than the target average particle volume of the next batch.
14. Manufacturing process according to the preceding claim, wherein the agglomeration step is carried out by fluidization or by a rotating disk.