PROCEDURE OF SEPARATION OF CRISOLS IN SIMULE MOBILE BED

Abstract

The present invention relates to a process for separating cresols by simulated moving bed using an agglomerated zeolitic adsorbent solid, and an optimized desorbent, chosen from 2 or 3-pentanol. Figure 1 to be published

Description

Title of the invention: METHOD FOR SEPARATING CRESOLS IN A SIMULATED MOVING BED Technical field

[0001] The present invention relates to the field of processes for separating cresols in a simulated moving bed (abbreviated as LMS).

[0002] The invention aims to improve the long-term productivity of existing processes by adjusting the choice of liquid allowing desorption, called desorbent.

[0003] Simulated moving bed separation is understood here in the broad sense, that is to say that one can be dealing with either a simulated counter-current process, or a simulated co-current process, or a so-called "varicol" process.

[0004] The common characteristic of this family of processes is that the adsorbent solid is implemented in a fixed bed, and that the liquid flows in contact with the adsorbent are managed either by means of a set of on / off valves, or by means of a single complex valve known as a rotary valve.

[0005] When the active element of the adsorbent solids used as adsorption agents in these processes is a zeolite, the latter, obtained in powder form, is preferably used on an industrial scale in the form of agglomerates. These zeolite adsorbents, agglomerated in the form of platelets, beads or extrudates, are generally made up of a zeolite powder, which constitutes the active element in the sense of adsorption and a binder intended to ensure the cohesion of the crystals in the form of grains. This binder also gives the grains sufficient mechanical strength to withstand the mechanical stresses to which they are subjected during their implementation within the units. These mechanical stresses are the cause of the formation of fines, which can induce a deterioration in performance during the operation of the process.

[0006] The process of separating cresols in a simulated moving bed (SMB) has undergone numerous technological improvements, particularly at the level of the fluid distribution trays, but in the case of cresols there has been relatively little development concerning the type of desorbent used.

[0007] The properties sought at the desorbent level are as follows: - selectivity towards the most adsorbed species (here para-cresol) close to 1. - high boiling point difference with respect to the products of the charge to be separated, to allow simple and inexpensive separation by distillation - good chemical stability of the compound and absence of reactivity with respect to the products to be separated, this liquid having to be made to rotate in a loop in the process during several years

[0008] The selectivity aA / H of the adsorbent for a component A with respect to a compound B is defined as the ratio of the concentrations of the compounds in the adsorbed phase divided by the ratio of the concentrations of the compounds in the non-adsorbed phase at equilibrium:

[0009] “a / B = Aads / Bads X Bliq / Aiiq

[0010] where Aads and Bads are the concentrations of compound A and compound B in the adsorbed phase respectively and Aiiq and Biiq are the concentrations of compound A and compound B in the fluid phase. Prior art

[0011] The prior art documents describing the chemical and microscopic characteristics of zeolite adsorbents used for the separation of paraxylene are particularly numerous, for example (US 3,558,730; US 3,663,638 (Neuzil); US 3,960,774 (Rosback); US 6,706,938 (Roeseler); US 7,820,869 (Priegnitz); US 7,812,208 (Cheng); US 6,410,815; US 6,884,918 (Plee); WO08 / 009845; WO09 / 081023 (Bouvier); US2011 / 105301 (Wang)).

[0012] The general teaching on the chemical characteristics of these adsorbent solids is that it is necessary to use a zeolite of faujasite structure (LSX, X or Y zeolite) exchanged with barium (at least 90%, expressed in exchange rate) or exchanged very predominantly with barium and to a minor extent with potassium (for example from 2 to 33%). For the separation of metaxylene, US 5,382,747 (Kulprathipanja) teaches the use of a sodium Y zeolite or a sodium Y zeolite partially exchanged with lithium.

[0013] In the process of separation of cresols by adsorption in a simulated moving bed, the zeolitic adsorbent solid is brought into contact with the feed liquid stream (charge) composed of the mixture of cresols, containing ortho-cresol, meta-cresol, para-cresol and possible traces of phenol.

[0014] In the case where the charge contains only traces of ortho-cresol, two flows are obtained, one mainly consisting of para-cresol, the other mainly consisting of meta-cresol.

[0015] By "predominantly constituted", we mean that said flows may contain a very small quantity of impurities, in particular ortho-cresol, up to 1% by volume.

[0016] By using a zeolite adsorbent based on zeolite of faujasite structure, preferably a faujasite zeolite with a Si / Al ratio of between 1 and 1.5 (LSX, X zeolite) exchanged with barium (at least 90% expressed in exchange rate) or exchanged very predominantly with barium and to a minor extent with potassium, the para-cresol is then adsorbed in the micropores of the zeolite preferentially compared to all other compounds present in the feed stream. The phase adsorbed in the micropores of the zeolite is then enriched in para-cresol compared to the initial mixture constituting the feed stream. The liquid phase is conversely enriched in compounds such as ortho-cresol and meta-cresol in a greater relative proportion than that characterizing the initial mixture constituting the feed stream.

[0017] The liquid phase is removed from contact with the adsorbent, thus forming a raffinate stream (rich in ortho- and meta-cresol compounds).

[0018] The adsorbed phase, enriched in para-cresol, is desorbed under the action of a flow of desorbent, and removed from contact with the adsorbent, thus forming a flow of extract.

[0019] In the case of the separation of cresols, the choice of the desorbent used has an impact on the selectivities between the products to be separated, meta-cresol and ortho-cresol on the one hand, and para-cresol on the other hand, but also on the ease of regenerating the adsorbent. The higher the selectivity between meta- and para-cresol, the easier the separation of the isomers is, in other words, the productivity (in kg of para-cresol separated / kg of sieve / h) of the sieve is increased. The selectivity between para-cresol and the desorbent must, on the other hand, be as close as possible to 1. A high selectivity induces a large quantity of desorbent for regeneration and therefore high energy consumption for the distillation columns used to separate the cresols from the desorbent which are located downstream of the simulated moving bed.On the contrary, a selectivity much lower than 1 can be problematic, because the desorbent tends to remain in the sieve after regeneration, limiting the productivity of the sieve for future cycles.

[0020] The type of desorbent that will be used will allow, depending on its properties, an extraction of the compound strongly adsorbed in the zeolite which will be more or less easy. The closer its relative selectivity to para cresol is to 1, the lower the quantity to be used will be, leading to lower distillation costs on the upstream recovery units. On the other hand, this desorbent will also have an influence on the capacity to separate the different isomers and therefore on the quantity of zeolite to be used. It is therefore advisable to choose it appropriately to optimize these two parameters as best as possible.

[0021] Unexpectedly, the Applicant has demonstrated that a process for separating cresols in a simulated moving bed using a FAU type zeolite adsorbent and a desorbent chosen from alcohols with 5 linear carbon atoms, in particular 2-pentanol and 3-pentanol, offered a notable gain compared to the prior art in terms of selectivities in particular. Summary of the invention

[0022] The present invention thus proposes a process for separating cresols using an agglomerated zeolite adsorbent based on faujasite zeolite (structural type FAU) and a 2-pentanol or 3-pentanol desorbent, allowing in particular the production of high purity para-cresol and meta-cresol, with improved productivity.

[0023] The desorbent specifically chosen from 2-pentanol and 3-pentanol offers an excellent compromise between the quantity of adsorbent required and the solvent flow rate. Furthermore, these two desorbents have a regeneration selectivity close to 1, ensuring an energy gain during the distillation phase aimed at separating the para-cresol from the desorbent. The selectivities obtained between para-cresol / meta-cresol isomers also allow for better productivity of the separation process.

[0024] The invention relates to a process for separating cresols from a feedstock comprising cuts of aromatic hydrocarbon isomers containing an alcohol function with 7 carbon atoms, in a simulated moving bed, in the liquid phase or in the gas phase, by selective adsorption of an isomer of cresol in the presence of a desorbent chosen from 2-pentanol and 3-pentanol, using particles of agglomerated zeolitic adsorbent based on faujasite zeolite crystals with a number average diameter of less than or equal to 1.5 μm.

[0025] In one embodiment, the desorbent may be 2-pentanol.

[0026] In another embodiment, the desorbent may be 3-pentanol.

[0027] The process for separating cresols according to the invention can be implemented in a simulated mobile bed unit having the following characteristics: - number of beds between 4 and 24 - number of zones: at least 4.

[0028] The cycle time, corresponding to the time between two injections of desorbent on a given bed, is preferably between 2 and 18 min, inclusive.

[0029] The process for separating cresols according to the invention can operate at a temperature of 100°C to 200°C, inclusive, preferably at a temperature of 110°C to 180°C, inclusive, very preferably of 115°C to 145°C, inclusive, and at a pressure conditioned by maintaining the pentanol desorbent in the liquid phase at the process temperature and less than 3 MPa.

[0030] The ratio of the desorbent flow rates to the load may be between 0.5 and 4.0, preferably between 0.7 and 2.5, very preferably between 1.0 and 2.0, inclusive.

[0031] The process for separating cresols according to the invention may comprise the following steps: a) A step of bringing the load into contact, under suitable adsorption conditions, with a bed containing the selected adsorbent, so as to preferentially adsorb the para-cresol b) a step of bringing the adsorbent bed into contact with the desorbent under desorption conditions, c) a step of withdrawing from the adsorbent bed a flow containing the desorbent and the least selectively adsorbed feed products, d) a step of withdrawing from the adsorbent bed a flow containing the desorbent and the desired product, namely para-cresol e) a separation of the flow from step c) into a first flow containing the desorbent and a second flow containing the least selectively adsorbed feed products, namely meta-cresol and possibly ortho-cresol;

[0032] f) a separation of the flow from step d) into a first flow containing the desorbent and a second flow containing para-cresol at a purity level greater than or equal to 90%, preferably greater than or equal to 99%, and very preferably greater than or equal to 99.7%.

[0033] The number-average diameter of the agglomerated zeolite adsorbent particles may be between 300 pm and 700 pm, preferably between 400 pm and 600 pm, inclusive.

[0034] The number average diameter of the zeolite crystals may be between 0.1 pm and 1.5 pm, inclusive, preferably between 0.5 pm and 1.2 pm, inclusive.

[0035] In one embodiment, the cresol separation process operates by selective adsorption of para-cresol with an agglomerated zeolite adsorbent based on zeolite X or LSX having an Si / Al atomic ratio such that 1.0 < Si / Al < 1.5.

[0036] The agglomerated zeolite adsorbent may further comprise: i. A content of barium oxide BaO and a content of potassium oxide K2 O such that the ratio between the number of moles of the set barium oxide + potassium oxide (BaO+K2O) and the number of moles of the set (BaO+K2O+Na2O) is greater than 90%; ii. A potassium oxide K2O content such that the ratio between the number of moles of potassium oxide K2O and the number of moles of barium oxide BaO is less than 0.5; iii. and a total content of alkali or alkaline earth ion oxides other than barium and potassium preferably less than 5% relative to the total weight of the zeolite adsorbent.

[0037] In another embodiment, the cresol separation process operates by selective adsorption of para-cresol, with an agglomerated zeolite adsorbent based on zeolite Y having an Si / Al atomic ratio such that 1.5 < Si / Al < 6.

[0038] The agglomerated zeolite adsorbent may further comprise: i. A sodium oxide Na2O content and a lithium oxide Li2O content such that the ratio between the number of moles of sodium oxide and the number of moles of the sodium oxide + lithium oxide (Na2O+Li2O) assembly is greater than 65%. ii. And a total content of alkali or alkaline earth ion oxides other than sodium and lithium preferably less than 5% relative to the total weight of the zeolite adsorbent.

[0039] In the process for separating cresols according to the invention, the agglomerated zeolite adsorbent may have a grain density of between 1.1 and 1.4 g / mL, as measured by mercury intrusion (expressed relative to the dry mass of the zeolite adsorbent) and a total pore volume measured by mercury intrusion (pore volume contained in the macropores and mesopores with an apparent diameter greater than 4 nm) of between 0.20 and 0.35 mL / g (expressed relative to the dry mass of the zeolite adsorbent).

[0040] The process for separating cresols according to the invention can allow the production of high purity para-cresol.

[0041] The process for separating cresols according to the invention can allow the production of high purity meta-cresol. List of figures [Fig 1]

[0042] [Fig. 1] illustrates the invention and is presented without limitation.

[0043] [Fig. 1] represents the diagram of a multi-stage column operating in a moving bed simulated. Description of the embodiments

[0044] In the process for separating cresols by adsorption in a simulated moving bed, the zeolitic adsorbent solid is brought into contact with the feed liquid stream (charge) composed of the mixture of cresols, containing ortho-cresol, meta-cresol, para-cresol and possible traces of phenol. In the context of the invention, it is sought to recover ortho-cresol, para-cresol or meta-cresol, alone or as a mixture, preferably a stream comprising a mixture of meta-cresol and ortho-cresol and a stream of para-cresol.

[0045] In the case where the charge contains only traces of ortho-cresol, two flows are obtained, one mainly consisting of para-cresol, the other mainly consisting of meta-cresol.

[0046] By predominantly constituted, it is meant that said flows may contain a very small quantity of ortho-cresol of up to 1% volume.

[0047] In the process of separating cresols by adsorption in a simulated moving bed, the zeolitic adsorbent solid is implemented in one or two multi-stage columns to be brought into contact with the liquid flow. A multi-stage column is a column consisting of a multiplicity of plates arranged along a substantially vertical, each tray supporting a bed of granular solid, and the different successive beds being crossed in series by the fluid(s) used in the column. Between two successive beds is located a fluid distribution device allowing each bed of granular solid to be fed.

[0048] In other words, in the process of separating cresols by adsorption in a simulated moving bed, the zeolite adsorbent is supported by trays forming successive beds of granular solid crossed in series by the fluid(s) used in the column. Between two successive beds is located a fluid distribution device making it possible to feed each bed of granular solid and most often, there is an empty space between the distribution device and the surface of the downstream bed of granular solid.

[0049] The trays can be cut into parallel panels (meridian panels) or radial panels (pie-cut panels). Each tray is delimited by a lower grid and an upper grid. A volume containing no adsorbent is located between the lower grid of a tray and the top of the bed placed below the tray in question. This volume is necessary to avoid any phenomenon of mechanical degradation of the adsorbent solid linked to the flexing of the tray.

[0050] Generally speaking, the operation of a simulated moving bed column can be described as follows:

[0051] A column comprises at least four zones, and possibly five or six, each of these zones being constituted by a certain number of successive beds, and each zone being defined by its position between a feed point and a withdrawal point. Typically, a CCS unit for the production of para-cresol or the production of meta-cresol is fed with at least one feed F to be fractionated (aromatic hydrocarbon feed consisting of isomers with 7 carbon atoms) and a desorbent D, sometimes called eluent (generally a linear alcohol with 4, 5 or 6 carbon atoms), and at least one raffinate R containing the least selectively adsorbed feed products and the desorbent and an extract E containing the most adsorbed feed product and the desorbent are withdrawn from said unit.

[0052] Other injection and withdrawal points can be added so as to rinse the distribution circuits, as described for example in US patent 7,208,651. The addition of these additional rinsing flows does not change the operating principle of the CCS in any way, for the sake of conciseness, we will not add these additional injection and withdrawal points in the description of the method according to the invention.

[0053] The feed and draw points are modified over time, shifted in the same direction by a value corresponding to a bed. The shifts of the different injection or withdrawal points can be either simultaneous or non-simultaneous as taught in US patent 6,136,198. The process according to this second mode of operation is called VARICOL.

[0054] Conventionally, 4 different chromatographic zones are defined in a column operating in simulated countercurrent (CCS). • Zone 1: desorption zone of the most adsorbed charge product, between the injection of desorbent D and the collection of extract E. • Zone 2: desorption zone for the least selectively adsorbed feed products, between the collection of extract E and the injection of the feed to be fractionated F. • Zone 3: adsorption zone of the most adsorbed feed product, between the injection of the feed and the withdrawal of raffinate R. • Zone 4: zone located between the withdrawal of raffinate R and the injection of desorbent D.

[0055] The attached [Fig.l] represents a multi-stage column with distributor trays operating in a simulated moving bed for the separation of cresols. This figure is provided for purely illustrative purposes.

[0056] The column in the enclosure (1) is divided into a certain number of granular beds (2). Between two successive granular beds, denoted upstream bed and downstream bed, is inserted a distributor tray (5) placed on beams (7). An upper grid (4) supports the granular medium (2) while allowing the fluid to enter inside the tray.

[0057] The distribution devices also comprise a distribution network (6) embedded in the granular medium (2), which makes it possible to inject or withdraw an auxiliary fluid into the tray. In the event of injection, the injected auxiliary fluid is thus mixed with the main fluid coming from the upstream bed.

[0058] The distributor tray (5) also comprises a lower grid (3) or perforated plate, or any other means for distributing the flow over the downstream granular bed. There is an empty space (8) between the lower grid (3) and the upper surface of the downstream granular bed.

[0059] Throughout the description, the value ranges are understood to include the limits, unless otherwise stated.

[0060] The invention relates to a process for separating cresols from a feedstock comprising cuts of aromatic hydrocarbon isomers with an alcohol function containing 7 carbon atoms, in a simulated moving bed, by selective adsorption of a cresol isomer in the presence of a desorbent, using agglomerated zeolite adsorbent particles of faujasite zeolite type (FAU structural type) preferably based on zeolite crystals with a number average diameter less than or equal to 1.5 pm, very preferably between 0.1 pm and 1.5 pm, in a manner even more preferred between 0.5 pm and 1.2 pm.

[0061] The number-average diameter of said adsorbent particles is preferably between 300 pm and 700 pm, preferably between 400 pm and 600 pm, and the mechanical strength measured by the Shell method SMS series 1471-74 adapted for agglomerates of size less than 500 pm is preferably greater than or equal to 2 MPa.

[0062] Preferably, the particle size distribution of said adsorbent particles is such that there are no particles smaller than 100 μm.

[0063] Maintaining the hydration of the zeolite at the desired value, for example a loss on ignition of 3% to 8% for zeolite X, can be adjusted by a person skilled in the art when implementing it in the cresol separation process according to the invention.

[0064] The cresol separation process can be carried out in a simulated moving bed unit having the following characteristics: • number of beds between 4 and 24 • number of zones: at least 4.

[0065] Advantageously, the cycle time, corresponding to the time between two injections of desorbent on a given bed, is between 2 and 18 min.

[0066] In said process for separating cresols, the desorbent is a linear alcohol with 5 carbon atoms, chosen from 2-pentanol and 3-pentanol.

[0067] Advantageously, the process for separating cresols operates at a temperature of 100°C to 200°C, preferably 110°C to 180°C, very preferably between 115°C and 145°C, and at a pressure conditioned by maintaining the pentanol desorbent in the liquid phase at the process temperature and less than 3 MPa.

[0068] Advantageously, the ratio of the desorbent flow rates to the load is between 0.5 and 4.0, preferably between 0.7 and 2.5, very preferably between 1.0 and 2.0.

[0069] The agglomerated zeolite adsorbent used in the cresol separation process according to the invention is based on zeolite of structural type FAU (faujasite).

[0070] In one embodiment, the agglomerated zeolite adsorbent is based on zeolite X or LSX having an atomic ratio Si / Al such that 1.0 < Si / Al < 1.5, preferably between 1.1 < Si / Al < 1.5, more preferably such that 1.2 < Si / Al < 1.3.

[0071] The agglomerated zeolite adsorbent may further comprise: • A content of barium oxide BaO and a content of potassium oxide K2 O such that the ratio between the number of moles of the barium oxide + potassium oxide (BaO+K2O) assembly and the number of moles of the (BaO+K2O+Na2O) assembly is greater than 90%; • A potassium oxide K2O content such that the ratio between the number of moles of potassium oxide K2O and the number of moles of barium oxide BaO is less than 0.5; • and a total content of alkali or alkaline-earth ion oxides other than barium and potassium preferably less than 5% and preferably ranging from 0 to 2% and advantageously ranging from 0 to 1% by weight relative to the total weight of the zeolite adsorbent.

[0072] In this case, the agglomerated zeolite adsorbent may have a grain density of between 1.1 and 1.4 g / mL, and preferably between 1.1 and 1.3 g / mL as measured by mercury intrusion (expressed relative to the dry mass of the zeolite adsorbent) and a total pore volume measured by mercury intrusion (pore volume contained in the macropores and mesopores with an apparent diameter greater than 4 nm) of between 0.20 and 0.35 mL / g (expressed relative to the dry mass of the zeolite adsorbent).

[0073] The process for separating para-cresol can be carried out at a temperature of 100°C to 200°C, preferably 110°C to 180°C, very preferably between 115°C and 145°C. The water content in the hydrocarbon effluents is preferably less than 1000 ppm.

[0074] In another embodiment, the invention relates to a process for separating meta-cresol or para-cresol by selective adsorption of para-cresol in which the agglomerated zeolite adsorbent is based on Y zeolite having an Si / Al atomic ratio such that 1.5 < Si / Al < 6, preferably such that 2.5 < Si / Al < 3.

[0075] In this case, the agglomerated zeolite adsorbent may further comprise: • A sodium oxide Na2O content and a lithium oxide Li2O content such that the ratio between the number of moles of sodium oxide and the number of moles of the sodium oxide + lithium oxide (Na2O+Li2O) assembly is greater than 65%. • And a total content of alkali or alkaline-earth ion oxides other than sodium and lithium preferably less than 5% and preferably ranging from 0 to 2% and advantageously ranging from 0 to 1% by weight relative to the total weight of the zeolite adsorbent.

[0076] The invention also relates to a method for producing high purity para-cresol or a method for jointly producing high purity para-cresol and high purity meta-cresol.

[0077] By “high purity” is meant a level of purity greater than or equal to 90%, preferably greater than or equal to 99%, and very preferably greater than or equal to 99.7%.

[0078] More particularly, the invention relates to a process for separating cresols from aromatic isomer cuts with an alcohol function containing 7 carbon atoms in a simulated moving bed (SMB) consisting of using a zeolitic adsorbent as an adsorbent solid selectively retaining at least one isomer of cresol. agglomerated and a desorbent of the linear alcohol type with 5 carbon atoms chosen from 2 and 3-pentanol, the zeolite adsorbent possibly also having particular particle size characteristics. The particles of agglomerated zeolite adsorbent solid used in the process according to the invention preferably have a mean diameter (in number) of the particles of between 300 pm and 700 pm, preferably of between 400 pm and 600 pm. Preferably, the particles have a particle size distribution such that there are no particles of a size less than 100 pm.

[0079] More particularly, to selectively adsorb the para-cresol, zeolitic adsorbents based on zeolite X or LSX, exchanged with barium (at least 90% expressed as the exchange rate on the final agglomerate, estimated by evaluating the ratio between the number of moles of barium oxide, BaO, and the number of moles of the whole (BaO+Na2O) of the final agglomerate), or exchanged very predominantly with barium, and in a minor way with potassium (the exchange rate by the barium and potassium ions being at least 90%, estimated by evaluating the ratio between the number of moles of the whole barium oxide + potassium oxide (BaO+K2O) and the number of moles of the whole (BaO+K2O+Na2O)) of the final agglomerate, or zeolitic adsorbents based on zeolite Y,sodium or exchanged with sodium and lithium such that the ratio between the number of moles of sodium oxide Na2O and the number of moles of the sodium oxide + lithium oxide (Na2O+Li2O) assembly of the final agglomerate is greater than 65%, ,

[0080] This adsorbent solid also has the particular characteristics of granulometry at the size level of zeolite adsorbents.

[0081] The process thus makes it possible to separate the isomers of cresol and to obtain a flow comprising mainly para-cresol as well as a flow comprising meta-cresol and possibly ortho-cresol.

[0082] The process therefore also allows, in the case where the feed no longer contains ortho-cresol, the production of high purity meta-cresol.

[0083] The method according to the present invention can be implemented both in the liquid phase and in the gas phase.

[0084] The invention relates more particularly to a process for separating high-purity para-cresol and / or meta-cresol (i.e. a purity greater than or equal to 90%) in a simulated moving bed from a feedstock of aromatic hydrocarbons containing isomers with 7 carbon atoms, comprising the following steps: a) A step of bringing the load into contact, under suitable adsorption conditions, with a bed containing the selected adsorbent, so as to preferentially adsorb the para-cresol b) a step of bringing the adsorbent bed into contact, under desorption conditions, with a desorbent, the desorbent being chosen from linear alcohols with 5 atoms of 2-pentanol and 3-pentanol carbon c) a step of withdrawing from the adsorbent bed a flow containing the desorbent and the least selectively adsorbed feed products d) a step of withdrawing from the adsorbent bed a flow containing the desorbent and the desired product, namely para-cresol e) a separation of the flow from step c) into a first flow containing the desorbent and a second flow containing the least selectively adsorbed feed products, namely meta-cresol and possibly ortho-cresol; f) a separation of the flow from step d) into a first flow containing the desorbent and a second flow containing para-cresol at a purity level greater than or equal to 90%, preferably greater than or equal to 99%, and very preferably greater than or equal to 99.7%.

[0085] More specifically, the object of the invention is to optimize the process for separating cresol isomers by adsorption in a simulated moving bed, to maximize the performance of this process. In general, the desired performance for the separation of a feedstock containing cresols is maximum productivity for a purity of the desired product in the extract stream at least equal to 99.5% and even 99.7% by weight. Advantageously, obtaining two high-purity streams is sought: namely a high-purity meta-cresol stream on the one hand, and a high-purity para-cresol stream on the other hand.

[0086] In the present invention, the adsorbent solid used is a zeolitic adsorbent based on zeolite crystals, preferably zeolite X, LSX or Y, and optionally non-zeolitic phase (i.e. residual binder, amorphous phase, crystalline phases such as quartz etc. after zeolitization, etc.), adsorbent in which the crystals have a number average diameter less than or equal to 1.5 pm, preferably between 0.1 pm and 1.5 pm, and preferably between 0.5 pm and 1.2 pm.

[0087] When the agglomerate according to the present invention is prepared from zeolite X or LSX, the Si / Al atomic ratio is between 1 and 1.5, preferably between 1.2 and 1.3, and the agglomerate comprises: i. A barium oxide BaO content and a potassium oxide K2 O content such that the ratio between the number of moles of the barium oxide + potassium oxide (BaO+K2O) assembly and the number of moles of the (BaO+K2O+Na2O) assembly is greater than 90%. ii. A potassium oxide K2O content such that the ratio between the number of moles of potassium oxide K2O and the number of moles of barium oxide BaO is less than 50%. iii. And a total content of alkali or alkaline earth ion oxides other than barium and potassium preferably less than 5% and preferably ranging from 0 to 2% and advantageously ranging from 0 to 1% by weight relative to the total weight of the anhydrous zeolite adsorbent.

[0088] When the zeolite adsorbent according to the present invention is prepared from zeolite Y, the Si / Al atomic ratio is between 1.5 and 6, preferably between 2.5 and 3, and the zeolite adsorbent comprises i. A sodium oxide Na2O content and a lithium oxide Li2O content such that the ratio between the number of moles of sodium oxide Na2O and the number of moles of the sodium oxide + lithium oxide (Na2 O+Li2O) assembly is greater than 65%. ii. And a total content of alkali or alkaline earth ion oxides other than sodium and lithium preferably less than 5% and preferably ranging from 0 to 2% and advantageously ranging from 0 to 1% by weight relative to the total weight of the anhydrous zeolite adsorbent.

[0089] The zeolite adsorbents according to the invention have a mean diameter (in number) of the particles advantageously between 300 pm and 700 pm, preferably between 400 pm and 600 pm and preferably with a particle size distribution such that there are no particles of size less than 100 pm.

[0090] When the zeolite adsorbents according to the present invention are prepared from zeolite X or LSX, they preferably have a grain density of between 1.1 and 1.4 g / mL, and preferably between 1.1 and 1.3 g / mL as measured by mercury intrusion (expressed relative to the dry mass of the zeolite adsorbent) and a pore volume measured by mercury intrusion (pore volume contained in the macropores and mesopores with an apparent diameter greater than 4 nm) of between 0.20 and 0.35 mL / g (expressed relative to the dry mass of the zeolite adsorbent).

[0091] The zeolite adsorbents used in the present invention are conventionally obtained according to a process comprising the following steps: 1 / mixing of zeolite X, LSX or Y crystals in powder of desired particle size, in the presence of water with at least one binder based on a clay or a mixture of clays, 2 / shaping of the mixture obtained in 1 / to produce agglomerates, possibly followed by a sieving and / or cycloning step, 3 / calcination of the agglomerates obtained in 2 / at a temperature ranging from 500°C to 600°C, 4 / (optionally) zeolitization of the binder by bringing the product resulting from 3 / into contact with a basic alkaline aqueous solution followed by washing; 5 / ion exchange of zeolite agglomerates based on zeolite X or LSX obtained in 3 / or in 4 / by barium ions alone or by barium ions and potassium ions and possibly partial ion exchange of zeolite agglomerates based on sodium Y zeolite obtained in 3 / or 4 / by lithium ions, followed by washing and drying of the product thus treated; 6 / activation of the product from step 5 at a temperature ranging from 200 to 300°C.

[0092] Step 2 / of shaping makes it possible to obtain zeolite agglomerates having sufficient mechanical resistance for their use in a process for separating cresols in a simulated moving bed. However, the presence of binder reduces the proportion of active material in the sense of adsorption (zeolite X, LSX or Y).

[0093] The optional step 4 / of zeolitization of the binder thus makes it possible to transform all or part of the binder into active material in the sense of adsorption (zeolite X, LSX or Y) in order to obtain binderless agglomerates, i.e. no longer comprising any non-zeolitic phase or in a quantity typically less than approximately 1% or "binderlow" agglomerates, i.e. comprising little non-zeolitized phase, i.e. generally non-zeolitized residual binder or any other amorphous phase after zeolitization, in a quantity typically between approximately 2% and 5% in the final agglomerate, while maintaining mechanical strength. The rate of non-zeolitic phase (i.e. non-zeolitized residual binder, amorphous phase, after zeolitization) in the final agglomerate can be quantified by reference to an adsorbent composed solely of zeolite, in powder form, from adsorption measurements or from DRX peak intensities.The reference zeolite is the zeolite used in step 1 / of the process for obtaining the adsorbent, and having undergone the same ion exchange.

[0094] The crystals of zeolites X, LSX or Y resulting from the zeolitization of the binder (transformation of the binder into zeolite) are generally of smaller diameters than the initial crystals. Consequently, in the final agglomerate, the crystals whose average diameter is less than or equal to 1.5 μm, preferably between 0.1 μm and 1.5 μm, and more preferably between 0.5 μm and 1.2 μm, conventionally have a monomodal particle size distribution, but it is not outside the scope of the invention if the distribution of the diameters of the crystals is multi-modal, and in particular bi-modal, due to the presence of the population of crystals resulting from the zeolitization of the binder.

[0095] The performance of the cresol separation process is influenced by various process parameters, including the characteristics of the zeolite adsorbents, as described above, the operating conditions, the composition of the feedstock, the water content and the type of desorbent.

[0096] The operating conditions of the simulated countercurrent industrial adsorption unit using the zeolite adsorbents as described above are typically as follows: - number of beds between 4 and 24 - number of zones: at least 4 - temperature: 100°C to 200°C, preferably 110°C to 180°C, very preferred between 115°C and 145°C - pressure between the pressure required to keep the pentanol desorbent in the liquid phase at the process temperature and 3 MPa - cycle time, corresponding to the time between two injections of desorbent on a given bed, between 2 and 18 min - ratio of desorbent flow rates to load 0.5 to 4.0, preferably 0.7 to 2.5.

[0097] The desorbent is a linear C5 alcohol, chosen from 2-pentanol and 3-pentanol, which offers an excellent compromise between the quantity of adsorbent required and the solvent flow rate. Furthermore, the desorbent according to the invention has a regeneration selectivity close to 1, ensuring an energy gain during the distillation phase aimed at separating the para-cresol from the desorbent. The selectivities obtained between para-cresol / meta-cresol isomers also allow for better productivity of the separation process.

[0098] Techniques for characterizing zeolite adsorbents

[0099] Estimating the number-average diameter of the adsorbent solids obtained from shaping step 2 / requires performing an analysis of the particle size distribution of an adsorbent sample by imaging according to standard ISO 13322 - 2: 2006 using a conveyor belt allowing the sample to pass in front of the camera lens.

[0100] The number average diameter is then calculated from the particle size distribution by applying the ISO 9276-2:2001 standard. In this document, the term "number average diameter" or "size" is used for the zeolite adsorbent particles. The accuracy is of the order of 10 μm for the size range of zeolite adsorbents of the invention.

[0101] The estimation of the number-average diameter of the zeolite X, LSX or Y crystals contained in the zeolite adsorbents is carried out by observation under a scanning electron microscope (SEM). In order to estimate the size of the zeolite crystals on the samples, a set of images is taken at a magnification of at least 5000. The diameter of at least 200 crystals is then measured using dedicated software, for example the Smile View software from the publisher LoGraMi). The number-average diameter is then calculated from the particle size distribution by applying the ISO 9276-2:2001 standard.

[0102] The term "number average diameter" or "size" is used for zeolite crystals. The accuracy is of the order of 3%.

[0103] Observation of zeolitic adsorbents by SEM also makes it possible to confirm the presence of a non-zeolitic phase comprising, for example, residual binder (not converted during the zeolitization step) or any other amorphous phase in the ag- glomerates.

[0104] An elementary chemical analysis of the adsorbent can be carried out by various analytical techniques known to those skilled in the art. Among these techniques, mention may be made of the X-ray fluorescence chemical analysis technique as described in standard NF EN ISO 12677: 2011 on a wavelength dispersive spectrometer (WDXRF), for example Tiger S8 from the company BRUKER.

[0105] X-ray fluorescence is a spectral technique that provides precise determination, both quantitative and qualitative, except for the lightest elements such as lithium, sodium or potassium present in very low concentrations. In this case, we will prefer atomic emission spectrometry with high-frequency inductively coupled plasma (ICP-AES) described in standard NF EN ISO 21079-3 on a device such as the Perkin Elmer 4300DV.

[0106] These elementary chemical analyses make it possible both to verify the Si / Al atomic ratio of the zeolite adsorbent, and to measure the contents of alkali or alkaline-earth ion oxides, in particular BaO, K2O, Na2O, Li2O.

[0107] Note that the contents of different oxides are given regardless of the technique in percent by weight relative to the total weight of the anhydrous adsorbent.

[0108] The mercury intrusion technique is used to characterize the intra-granular pore volume contained in pores with diameters greater than 3.6 nm of the adsorbent, and to measure its grain density. A mercury porosimeter type Autopore 9500 Mi-croméritics is used to analyze the distribution of the pore volume contained in macropores with pore diameters > 50 nm and in mesopores between 3.6 and 50 nm. The micropore volume within the zeolite crystals as well as the pore volume contained in small mesopores between 2 and 3.6 nm are not accessible with current porosimeters.The experimental method, described in the operating manual of the apparatus, consists of placing a sample of adsorbent (of known loss on ignition) previously weighed, in a cell of the porosimeter, then, after a preliminary degassing (evacuation pressure of 30 pm Hg for at least 10 min), to fill the cell with mercury at a given pressure (0.0036 MPa), and then to apply an increasing pressure in stages up to 400 MPa in order to gradually penetrate the mercury into the porous network of the sample. The relationship between the applied pressure and the pore diameter is established by assuming cylindrical pores, a contact angle between the mercury and the pore wall of 140° and a surface tension of the mercury of 485 dynes / cm.

[0109] The cumulative quantity of mercury introduced as a function of the applied pressure is recorded. The apparatus does not allow the inter-granular volume and the intra-granular volume to be differentiated: it is assumed that at approximately 0.2 MPa (corresponding to apparent pore diameters of 7 pm), the mercury fills all the inter-granular voids. granular, and that beyond this the mercury penetrates into the pores of the adsorbent. The grain density of the adsorbent is thus calculated by dividing the mass of the sample by the volume of the sample evaluated from the volume of mercury introduced at a pressure of 0.2 MPa.

[0110] The total pore volume of the adsorbent is then evaluated from the total volume of mercury introduced corrected for the volume of mercury introduced at a pressure of 0.2 MPa.

[0111] In this document, the grain density and pore volume of zeolite adsorbents measured by mercury intrusion are related to the mass of the anhydrous sample (by correction for the loss on ignition of the analyzed sample).

[0112] The technique for characterizing the mechanical strength representative of the crushing of the adsorbent within a bed or a reactor is the technique for characterizing the mechanical strength in a bed, as described in the Shell method series SMS1471-74 (Shell Method Series SMS1471-74 Determination of Bulk Crushing Strength of Catalysts. Compression-Sieve Method"), associated with the "BCS Tester" device marketed by the company Vinci Technologies. This method, initially intended for the characterization of catalysts of 3 to 6 mm, is based on the use of a 425 μm sieve which will in particular make it possible to separate the fines created during crushing. The use of a 425 μm sieve remains suitable for particles with a diameter greater than 1.6 mm, but must be adapted according to the particle size of the zeolite adsorbents that one seeks to characterize.ASTM D7084-04, which also describes a method for measuring crushing strength in catalyst beds ("Determination of Bulk Crush Strength of Catalysts and Catalyst Carriers"), defines the sieve passage to be used as being equal to half the diameter of the catalyst particles to be characterized. The method provides for a preliminary step of sieving the sample of catalysts or adsorbents to be characterized. If an amount equal to 10% by weight of the sample passes through the grid, a smaller sieve passage will be used.

[0113] The zeolite adsorbents of the present invention are in the form of beads or extrudates, and have a number average diameter ranging from 300 pm to 700 pm, and preferably ranging from 400 pm to 600 pm. Preferably, no particle has a size less than 100 pm. Therefore, a 100 pm sieve will be used instead of the 425 pm sieve mentioned in Shell standard method SMS 1471-74.

[0114] The method is carried out as follows: a 20 cm3 sample of agglomerated adsorbents, previously sieved with the appropriate sieve (100 μm) and previously dried in an oven for at least 2 hours at 250°C (instead of 300°C mentioned in the standard Shell method SMS 1471-74), is placed in a metal cylinder of known internal section. An increasing force is imposed in stages on this sample by means of a piston, through a bed of 5 cm3 of steel balls in order to better distribute the force exerted by the piston on the agglomerates of adsorbents (use of 4 mm diameter beads for the analysis of all types of extrudates and spherical particles with a diameter >1.6 mm, and 2 mm diameter beads for spherical particles of diameter <1.6 mm). The fines obtained at the different pressure levels are separated by sieving (adapted 100 μm sieve) and weighed. The bed crushing strength is determined by the pressure in mega Pascals (MPa) for which the quantity of cumulative fines passing through the sieve amounts to 0.5% by weight of the sample. This value is obtained by plotting on a graph the mass of fines obtained as a function of the force applied to the adsorbent bed and interpolating to 0.5% by mass of cumulative fines. The mechanical resistance to bed crushing is typically between a few hundred kPa and a few tens of MPa and generally between 0.3 and 3.2 MPa.

[0115] The accuracy is typically less than 0.1 MPa. Examples

[0116] This example implements a process for separating cresols with several desorbents, comparative and according to the invention. The adsorbent chosen consists of Faujasite X type zeolites exchanged at 96% with barium and having a super-micronic crystal size (crystallite diameter). They are shaped into beads with an average diameter of 660 μm. The characteristics of the adsorbents are summarized in the following Table 1:

[0117] [Tableauxl] ADSORBENT Loss on ignition [%] 5.53 0 (beads) [mm] 0.66 0 (crystallite) [pm] 1.36 Crushing strength [MPa] 2.48 SPECIFIC VOLUMES Microporous volume: VLI DR (N2) [cmVg] 0.239 Macro- and mesoporous volume: Vmacro.meso (Hg) [cmVg dry] 0.235 Mesoporous volume Vmeso (Hg) [cmVg dry] 0.013 DENSITIES DT (packed density) [g / cm3] 0.883 DT dried [g / cm3] 0.835 Dry density [g / cm3] 1.278 POROSITIES Bed porosity e; bed [%] 34.9

[0118] To measure the selectivity of desorbent potentials, three piercing and piercing tests, each using three desorbents, are carried out (seven different desorbents in total). The performances obtained for the selectivities: para-cresol selectivity over meta-cresol, and paracresol selectivity over desorbent, are summarized in Table 2. The tests are carried out at a temperature of 130°C with a loss on ignition of the adsorbent of approximately 5.5%. The desorbent to charge ratio is equal to 1.68.

[0119] Table 2 below shows the drilling (adsorption) and drilling (regeneration) performances, except for comparative test 2 for which only the drilling data could be used.

[0120] [Tables2] LOAD CQMPQSmQN [% weight] SELECTED Candidate desorbents Desorbent. m- Cresot- 70 Tracer âp-C / $2 Q. § OR 1-hexano! >1} 20 30 10 1.46 3.39 1.38 3.05 Drilling 1-pentanoi 20 1.25 2.94 1.12 2.94 Stripping 4-methyl-2-pentanoi [3) 20 CM 2 $ ag O Ô 1-hexanol 20 30 10 — — —■ — 11 $ "O & 1-pentahoi (2) 20 127 3.41 1.37 0.72 s & Phenol & 20 Comparative 3 1-buianol 0V 20 30 10 1.63 072 1.40 1.62 Œ là kQ fO cydohexanol 20 171 073 1.45 1.74 Drilling o-cresoi 0 20

[0121] Several lessons can be learned from these first tests: Among linear alcohols, we observe a paracresol selectivity on desorbent ap.C / des increasing with the length of the carbon chain

[0122] [Math.l] Qp-C / C4 < 3p-C / C5 < Sp-C / CS

[0123] The best results are obtained with a chain comprising five carbon atoms (C5) (Comparison 1 and Comparison 2, desorbent (2)).

[0124] It should be noted that C5 branched alcohol desorbents exhibit a much higher paracresol selectivity on desorbent than C5 linear alcohols. (Comparison 1, desorbent (3)).

[0125] Among the cyclic alcohols, the aromaticity of the cycle accentuates the interaction between the desorbent and the adsorbent, which makes the use of phenol unfavorable due to a selectivity much lower than 1 (Comparison 2, desorbent (3)).

[0126] Therefore, the first tests indicate that the best candidate is 1-pentanol, a linear alcohol with the empirical formula C5Hi2O. Another test is carried out with the isomers of pentanol. Here, only one desorbent is used for each test and the results of selectivities observed in pC / mC and in regeneration using C5 alcohols are summarized in Table 3.

[0127] [Tables3] COMPOSITION OF THE LOAD [% weight] SELECTIVITIES Desorbent Des. m-Cres ol-70 Tracer ^pC / mC OpC / DES Comparative 1-pentanol 45 45 10 1.86 2.43 1.79 2.38 According to the invention 2-pentanol 45 45 10 2.04 1.54 1.87 1.50 According to the invention 3-pentanol 45 45 10 1.79 1.11 1.72 1.13 Comparative 2-methyl-1 -butanol 45 45 10 2.14 2.39 1.98 2.33

[0128] It emerges from these latest tests that 2-pentanol and especially 3-pentanol have a regeneration selectivity close to 1, as such their use guarantees an energy gain during the distillation phase aimed at separating the para-cresol from the desorbent. From the point of view of selectivities between para-cresol / meta-cresol isomers, they are comparable to 1-pentanol, or even higher for 2-pentanol, which can result in better productivity.

[0129] Once the selectivities have been obtained in the laboratory, it is therefore necessary to use a numerical model capable of predicting the operation of the adsorbent / load / desorbent system in LMS (Simulated Moving Bed) operation. This type of model is based on a dynamic simulation of the flows and transfers of material. It is thus possible to obtain an evaluation of the quantities of adsorbents required and the flow rates circulating in the unit to obtain the desired purity and yield on the products. para cresol and meta cresol.

[0130] As an example, the comparative characteristics of an LMS using 1-pentanol, 2-pentanol or 3-pentanol as desorbent can be cited here. The example describes the treatment of the same load (composition and flow rate), operating conditions of temperature and pressure which are also identical and the option of the same specifications for the products.

[0131] Table 4 shows the impact of the desorbent on the quantitative requirements for sieve and desorbent, X representing a quantity of sieve in kg and Y representing a flow rate of desorbent in kg / h.

[0132] [Tables4] Desorbent 1-pentanol 2-pentanol 3-pentanol Amount of adsorbent X 1.1X 1.2X Desorbent flow rate 2Y 1.1Y Y

[0133] As can be seen, 2-pentanol and 3-pentanol offer a much more favorable compromise between adsorbent quantity and solvent flow rate than 1-pentanol.

[0134] It can therefore be concluded that it is the desorbents according to the invention: 2-pentanol and 3-pentanol which offer the best compromise between quantity of adsorbent and solvent flow rate.

[0135] Furthermore, these two desorbents have a regeneration selectivity close to 1, ensuring an energy gain during the distillation phase aimed at separating the para-cresol from the desorbent. The selectivities obtained between para-cresol / meta-cresol isomers also allow for better productivity.

Claims

Claims

1. Process for separating cresols from a feedstock comprising fractions of aromatic hydrocarbon isomers containing an alcohol function with 7 carbon atoms, in a simulated moving bed, in the liquid phase or in the gas phase, by selective adsorption of an isomer of cresol in the presence of a desorbent chosen from 2-pentanol and 3-pentanol, using particles of agglomerated zeolite adsorbent based on faujasite zeolite crystals with a number average diameter less than or equal to 1.5 pm.

2. A process for separating cresols according to claim 1, wherein the desorbent is 2-pentanol.

3. A process for separating cresols according to claim 1, wherein the desorbent is 3-pentanol.

4. Method for separating cresols according to one of claims 1 to 3 implemented in a simulated moving bed unit having the following characteristics: - number of beds between 4 and 24 - number of zones: at least 4.

5. Process for separating cresols according to claim 4 in which the cycle time, corresponding to the time between two injections of desorbent on a given bed, is between 2 and 18 min, limits included.

6. Process for separating cresols according to one of claims 1 to 5 operating at a temperature of 100°C to 200°C, inclusive, preferably at a temperature of 110°C to 180°C, inclusive, very preferably of 115°C to 145°C, inclusive, and at a pressure conditioned by maintaining the pentanol desorbent in the liquid phase at the temperature of the process and less than 3 MPa.

7. Process for separating cresols according to one of the preceding claims, in which the ratio of the desorbent flow rates to the feedstock is between 0.5 and 4.0, preferably between 0.7 and 2.5, very preferably between 1.0 and 2.0, limits included.

8. Process for separating cresols according to one of claims 1 to 7 comprising the following steps: a) A contacting step, under adsorption conditions suitable, of the load with a bed containing the selected adsorbent, so as to preferentially adsorb the para-cresol b) a step of bringing the adsorbent bed into contact, under desorption conditions, with the desorbent, c) a step of withdrawing from the adsorbent bed a flow containing the desorbent and the least selectively adsorbed products of the load, d) a step of withdrawing from the adsorbent bed a flow containing the desorbent and the desired product, namely para-cresol e) a separation of the flow from step c) into a first flow containing the desorbent and a second flow containing the least selectively adsorbed products of the load, namely meta-cresol and possibly ortho-cresol;f) a separation of the stream from step d) into a first stream containing the desorbent and a second stream containing para-cresol at a purity level greater than or equal to 90%, preferably greater than or equal to 99%, and very preferably greater than or equal to 99.7%.;

9. Process for separating cresols according to one of the preceding claims, in which the number-average diameter of the agglomerated zeolite adsorbent particles is between 300 pm and 700 pm, preferably between 400 pm and 600 pm, limits included.

10. Process for separating cresols according to one of claims 1 to 9 in which the number average diameter of the zeolite crystals is between 0.1 pm and 1.5 pm, limits inclusive, preferably between 0.5 pm and 1.2 pm, limits inclusive.

11. Process for separating cresols according to one of claims 1 to 10 by selective adsorption of para-cresol in which the agglomerated zeolite adsorbent is based on zeolite X or LSX having an atomic ratio Si / Al such that 1.0 < Si / Al < 1.

5.

12. A method for separating cresols according to claim 11 wherein the agglomerated zeolite adsorbent further comprises: i. A barium oxide BaO content and a potassium oxide K2O content such that the ratio between the number of moles of the barium oxide + potassium oxide assembly (BaO+K2O) and the number of moles of the assembly (BaO+K2 O+Na2O) is greater than 90%; ii. A potassium oxide K2O content such that the ratio between the number of moles of potassium oxide K2O and the number of moles of barium oxide BaO is less than 0.5; iii. and a total content of oxides of alkali or alkaline earth ions other than barium and potassium preferably less than 5% relative to the total weight of the zeolitic adsorbent.

13. Process for separating cresols according to one of claims 1 to 10 by selective adsorption of para-cresol, in which the agglomerated zeolitic adsorbent is based on Y zeolite having an Si / Al atomic ratio such that 1.5 < Si / Al < 6.

14. A method for separating cresols according to claim 13 wherein the agglomerated zeolite adsorbent further comprises: i. A sodium oxide Na2O content and a lithium oxide Li2O content such that the ratio between the number of moles of sodium oxide and the number of moles of the sodium oxide + lithium oxide (Na2O+Li2O) assembly is greater than 65%. ii. And a total content of alkali or alkaline earth ion oxides other than sodium and lithium preferably less than 5% relative to the total weight of the zeolite adsorbent.

15. A method for separating cresols according to claim 11 to 14 wherein the agglomerated zeolite adsorbent has a grain density of between 1.1 and 1.4 g / mL, as measured by mercury intrusion (expressed relative to the dry mass of the zeolite adsorbent) and a total pore volume measured by mercury intrusion (pore volume contained in macropores and mesopores with an apparent diameter greater than 4 nm) of between 0.20 and 0.35 mL / g (expressed relative to the dry mass of the zeolite adsorbent).

Images