PROCEDURE OF SEPARATION OF CRISOLS IN SIMULE MOBILE BED

Abstract

The present invention relates to a simulated moving bed method for separating cresols using an agglomerated zeolite adsorbent and an optimized desorbent, selected from 2- or 3-pentanol. Figure 1 to be published

Description

Title of the invention: METHOD FOR SEPARING CRESOLS IN A SIMULATED MOVING BED technical field

[0001] The present invention relates to the field of simulated moving bed cresol separation processes (abbreviated as MBD).

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

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

[0004] The common characteristic of this family of processes is that the solid adsorbent 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 flakes, beads, or extrudates, generally consist of a zeolite powder, which constitutes the active element in terms of adsorption, and a binder intended to ensure the cohesion of the crystals in granular form. This binder also gives the grains sufficient mechanical strength to withstand the mechanical stresses to which they are subjected during their use in the processing units. These mechanical stresses lead to the formation of fines, which can induce a deterioration in performance over the course of the process operation.

[0006] The simulated moving bed (SMD) cresol separation process has undergone numerous technological improvements, particularly in the area of ​​fluid distribution trays, but in the case of cresols there has been relatively little evolution regarding the type of desorbent used.

[0007] The desired properties of the desorbent are as follows: - selectivity towards the most adsorbed species (here paracresol) close to 1. - a significant difference in boiling point compared to the products of the feed to be separated, to allow for simple and inexpensive separation by distillation - good chemical stability of the compound and absence of reactivity towards the products to be separated, this liquid being required to circulate 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. Previous technique

[0011] Prior art documents describing the chemical and microscopic characteristics of zeolitic 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 a zeolite with a faujasite structure (LSX, X, or Y zeolite) exchanged with barium (at least 90%, expressed as an exchange ratio) or exchanged predominantly with barium and to a lesser extent with potassium (for example, from 2 to 33%) must be used. 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 separating cresols by simulated moving bed adsorption, the zeolitic adsorbent solid is brought into contact with the feed liquid stream (charge) composed of the cresol mixture, 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 fluxes are obtained, one mainly consisting of paracresol, the other mainly consisting of meta-cresol.

[0015] By "mostly constituted", it is understood that said streams may contain a very small amount of impurities, in particular ortho-cresol, up to 1% by volume.

[0016] By using a zeolite adsorbent based on faujasite-structured zeolite, preferably a faujasite zeolite with a Si / Al ratio between 1 and 1.5 (LSX, X zeolite) exchanged with barium (at least 90% expressed as an exchange rate) or exchanged predominantly with barium and to a lesser extent with potassium, paracresol is then adsorbed into the micropores of the zeolite preferentially compared to all the other compounds present in the feed stream. The phase adsorbed in the micropores of the zeolite is then enriched in paracresol compared to the initial mixture constituting the feed stream. Conversely, the liquid phase is enriched in compounds such as orthocresol and metacresol 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 flow of raffinate (rich in ortho- and meta-cresol compounds).

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

[0019] In the case of cresol separation, the choice of desorbent used impacts the selectivities between the products to be separated—meta-cresol and ortho-cresol on the one hand, and paracresol on the other—but also the ease of regenerating the adsorbent. The higher the selectivity between meta- and paracresol, the easier the separation of the isomers; in other words, the productivity (in kg of paracresol separated / kg of sieve / h) of the sieve is increased. Conversely, the selectivity between paracresol and the desorbent should be as close as possible to 1. High selectivity results in 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.Conversely, a selectivity much lower than 1 can be problematic, as the desorbent tends to remain in the sieve after regeneration, limiting the sieve's productivity for future cycles.

[0020] The type of desorbent used will, depending on its properties, determine the ease or difficulty of extracting the compound strongly adsorbed in the zeolite. The closer its relative selectivity to paracresol is to 1, the smaller the quantity required, resulting in lower distillation costs for upstream recovery units. Furthermore, this desorbent will also influence the separation capacity of the different isomers, and therefore the quantity of zeolite needed. It is therefore important to choose the appropriate desorbent to optimize these two parameters.

[0021] Unexpectedly, the Applicant highlighted that a simulated moving bed cresol separation process using a FAU-type zeolitic adsorbent and a desorbent chosen from among the 5-carbon linear alcohols, 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 method for separating cresols using an agglomerated zeolite adsorbent based on faujasite zeolite (structural type) FAU) and a 2-pentanol or 3-pentanol type desorbent, enabling in particular the production of high purity paracresol and meta-cresol, with improved productivity.

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

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

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

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

[0027] The cresol separation process according to the invention can be implemented in a simulated moving 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 cresol separation process 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, most preferably from 115°C to 145°C, inclusive, and at a pressure conditioned by maintaining the pentanol desorbent in liquid phase at the process temperature and less than 3 MPa.

[0030] The ratio of desorbent flow rates to charge can be between 0.5 and 4.0, preferably between 0.7 and 2.5, most preferably between 1.0 and 2.0, inclusive.

[0031] The cresol separation process according to the invention may include 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 paracresol b) a step of bringing the adsorbent bed into contact with the desorbent under desorption conditions, c) a step of removing from the adsorbent bed a stream containing the desorbent and the least selectively adsorbed feed products, d) a step of removing from the adsorbent bed a stream containing the desorbent and the desired product, namely paracresol e) a separation of the stream from step c) into a first stream containing the desorbent and a second stream containing the least selectively adsorbed charge products, namely meta-cresol and possibly ortho-cresol;

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

[0033] The number average diameter of the agglomerated zeolite adsorbent particles can 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 paracresol with an agglomerated zeolite adsorbent based on zeolite X or LSX having an atomic ratio Si / Al such that 1.0 < Si / Al < 1.5.

[0036] The agglomerated zeolitic adsorbent may further comprise: i. A content of barium oxide BaO and a content of potassium oxide K2O such that 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) 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 zeolitic adsorbent.

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

[0038] The agglomerated zeolitic adsorbent may further comprise: i. A sodium oxide (Na2O) content and a lithium oxide (Li2O) content such that the ratio of the number of moles of sodium oxide to the number of moles of the total sodium oxide + lithium oxide (Na2O+Li2O) 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 zeolitic adsorbent.

[0039] In the cresol separation process according to the invention, the agglomerated zeolitic adsorbent can 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 zeolitic 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 zeolitic adsorbent).

[0040] The cresol separation process according to the invention can enable the production of high-purity paracresol.

[0041] The cresol separation process according to the invention can enable the production of high-purity meta-cresol. List of figures [Fig 1]

[0042] [Fig. 1] illustrates the invention and is presented by way of non-limiting reference.

[0043] Figure 1 shows a diagram of a multi-stage column operating as a moving bed simulated. Description of the implementation methods

[0044] In the simulated moving bed adsorption process for separating cresols, the zeolitic adsorbent solid is brought into contact with the feed liquid stream (charge) composed of a cresol mixture containing orthocresol, metacresol, paracresol, and possibly traces of phenol. The aim of this invention is to recover orthocresol, paracresol, or metacresol, alone or in a mixture, preferably a stream comprising a mixture of metacresol and orthocresol and a stream of paracresol.

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

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

[0047] In the simulated moving bed adsorption process for separating cresols, the zeolitic adsorbent solid is placed in one or two multi-stage columns to be contacted with the liquid flow. A multi-stage column is defined as a column consisting of multiple trays arranged along a substantially In a vertical column, each tray supports a bed of granular solid, and the successive beds are traversed in series by the fluid(s) used in the column. Between two successive beds is a fluid distribution device that supplies each bed of granular solid.

[0048] In other words, in the simulated moving bed adsorption process for separating cresols, the zeolite adsorbent is supported by trays forming successive granular solid beds through which the fluid(s) used in the column flow in series. Between two successive beds is a fluid distribution device that feeds each granular solid bed, and most often, there is a gap between the distribution device and the surface of the downstream granular solid bed.

[0049] The trays may have parallel (meridian panels) or radial (pie-cut panels) panel shapes. 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 that tray. This volume is necessary to prevent any mechanical degradation of the adsorbent solid due to tray deflection.

[0050] In general, the operation of a column in a simulated moving bed can be described as follows:

[0051] A column comprises at least four zones, and possibly five or six, each of these zones being made up of 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 paracresol or the production of metacresol is fed with at least one feed F to be fractionated (an aromatic hydrocarbon feed consisting of the 7-carbon isomers) and a desorbent D, sometimes called an eluent (generally a linear alcohol with 4, 5, or 6 carbon atoms), and at least one raffinate R containing the products of the least selectively adsorbed feed and desorbent and an extract E containing the product of the most adsorbed feed and desorbent are withdrawn from said unit.

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

[0053] The supply and withdrawal points are modified over time, shifted in the same direction by a value corresponding to one 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] Classically, 4 different chromatographic zones are defined in a column operating in simulated countercurrent (CCS). • Zone 1: desorption zone of the most adsorbed load product, located between the injection of desorbant D and the sampling of extract E. • Zone 2: desorption zone of the least selectively adsorbed products of the load, located between the sampling of extract E and the injection of the load to be fractionated F. • Zone 3: Adsorption zone of the most adsorbed product of the feed, located between the injection of the feed and the withdrawal of the raffinate R. • Zone 4: zone located between the withdrawal of raffinate R and the injection of the desorbent D.

[0055] The attached [Fig. 1] represents a multi-stage column with distribution trays operating in simulated moving bed mode for cresol separation. This figure is provided for illustrative purposes only.

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

[0057] The distribution devices also include a distribution network (6) embedded in the granular medium (2), which allows an auxiliary fluid to be injected or withdrawn from the tray. In the case of injection, the injected auxiliary fluid is thus mixed with the main fluid coming from the upstream bed.

[0058] The distribution tray (5) also includes a lower grid (3) or perforated plate, or any other means for distributing the flow onto the downstream granular bed. There is a gap (8) between the lower grid (3) and the upper surface of the downstream granular bed.

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

[0060] The invention relates to a method for separating cresols from a feed comprising sections 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 the faujasite zeolite type (structural type FAU), preferably based on zeolite crystals with an average diameter of 1.5 pm or less, most preferably between 0.1 pm and 1.5 pm, in such a way 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 resistance measured by the Shell series SMS 1471-74 method 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 pm.

[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 during its implementation in the cresol separation process according to the invention.

[0064] The cresol separation process can be implemented 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 cresol separation process the desorbent is a linear alcohol with 5 carbon atoms, chosen from 2-pentanol and 3-pentanol.

[0067] Advantageously, the cresol separation process operates at a temperature of 100°C to 200°C, preferably 110°C to 180°C, most preferably between 115°C and 145°C, and at a pressure conditioned by maintaining the pentanol desorbent in liquid phase at the process temperature and below 3 MPa.

[0068] Advantageously, the ratio of desorbent flow rates to charge is between 0.5 and 4.0, preferably between 0.7 and 2.5, most 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 structural FAU type zeolite (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, preferably still such that 1.2 < Si / Al < 1.3.

[0071] The agglomerated zeolitic adsorbent may further comprise: • A content of barium oxide BaO and a content of potassium oxide K2O such that 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) 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 zeolitic adsorbent.

[0072] In this case, the agglomerated zeolitic 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 zeolitic 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 zeolitic adsorbent).

[0073] The paracresol separation process can be carried out at a temperature of 100°C to 200°C, preferably 110°C to 180°C, most 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 method for separating meta-cresol or paracresol by selective adsorption of paracresol in which the agglomerated zeolite adsorbent is based on zeolite Y having an atomic ratio Si / Al such that 1.5 < Si / Al < 6, preferably such that 2.5 < Si / Al < 3.

[0075] In this case, the agglomerated zeolitic 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 whole sodium oxide + lithium oxide (Na2O+Li2O) is greater than 65%. • And a total content of alkali or alkaline-earth 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 process for producing high-purity paracresol or a process for jointly producing high-purity paracresol and high-purity metacresol.

[0077] By "high purity" is meant a level of purity greater than or equal to 90%, preferably greater than or equal to 99%, and most preferably greater than or equal to 99.7%

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

[0079] More specifically, for selectively adsorbing paracresol, zeolite adsorbents based on zeolite X or LSX, exchanged with barium (at least 90% expressed as an 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 total (BaO+Na2O) of the final agglomerate), or exchanged predominantly with barium and to a lesser extent with potassium (the exchange rate by barium and potassium ions being at least 90%, estimated by evaluating the ratio between the number of moles of the total barium oxide + potassium oxide (BaO+K2O) and the number of moles of the total (BaO+K2O+Na2O) of the final agglomerate), or zeolite adsorbents based on zeolite Y,sodium or sodium- and lithium-exchanged such that the ratio between the number of moles of sodium oxide Na2O and the number of moles of the total sodium oxide + lithium oxide (Na2O+Li2O) in the final agglomerate is greater than 65%,

[0080] This solid adsorbent also having the particular characteristics of particle size of zeolitic adsorbents.

[0081] The process thus makes it possible to separate the isomers of cresol and to obtain a stream comprising mainly paracresol as well as a stream comprising metacresol and possibly orthocresol.

[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 process according to the present invention can be implemented in both liquid and gaseous phases.

[0084] The invention relates more particularly to a process for separating high-purity paracresol and / or metacresol (i.e., a purity greater than or equal to 90%) in a simulated moving bed from an aromatic hydrocarbon feed containing 7-carbon isomers, 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 paracresol 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 type carbon c) a step of removing from the adsorbent bed a stream containing the desorbent and the least selectively adsorbed feed products d) a step of removing from the adsorbent bed a stream containing the desorbent and the desired product, namely paracresol e) a separation of the stream from step c) into a first stream containing the desorbent and a second stream containing the least selectively adsorbed charge products, 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 paracresol at a purity level greater than or equal to 90%, preferably greater than or equal to 99%, and most preferably greater than or equal to 99.7%.

[0085] More precisely, the object of the invention is to optimize the process for separating cresol isomers by simulated moving bed adsorption, in order to maximize the performance of this process. In general, the desired performance for the separation of a feed containing cresols is maximum productivity for a purity of the desired product in the extract stream of at least 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 paracresol stream on the other.

[0086] In the present invention, the solid adsorbent 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 zeolithization...), adsorbent in which the crystals have an average number 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 content of barium oxide BaO and a content of potassium oxide K2O such that 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) 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 going from 0 to 2% and advantageously ranging from 0 to 1% by weight relative to the total weight of the anhydrous zeolitic 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 whole sodium oxide + lithium oxide (Na2 O+Li2O) is greater than 65%. ii. And a total content of alkali or alkaline-earth 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 an average diameter (in number) of 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 is no particle smaller 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 with respect to the dry mass of the zeolite adsorbent) and a 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 with respect to the dry mass of the zeolite adsorbent).

[0091] The zeolitic adsorbents used in the present invention are conventionally obtained by a process comprising the following steps: 1 / Mixture of zeolite crystals X, LSX or Y in powder form of the desired particle size, in the presence of water with at least one binder based on a clay or a mixture of clays, 2 / shaping 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 / (possibly) zeolithization of the binder by contacting the product resulting from 3 / with a basic alkaline aqueous solution followed by washing; 5 / Ionic exchange of zeolitic 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 ionic exchange of zeolitic agglomerates based on sodium zeolite Y 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 exhibiting sufficient mechanical strength for their use in a simulated moving bed cresol separation process. 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 zeolithization 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 containing a non-zeolithic phase or in a quantity typically less than about 1% or "binderlow" agglomerates, i.e. containing little non-zeolithic phase, i.e. generally residual non-zeolithized binder or any other amorphous phase after zeolithization, in a quantity typically between about 2% and 5% in the final agglomerate, while maintaining mechanical resistance. The non-zeolitic phase rate (i.e. non-zeolithized residual binder, amorphous phase, after zeolithization) in the final agglomerate can be quantified by reference to an adsorbent composed solely of zeolite, in powder form, from adsorption measurements or from XRD peak intensities.The reference zeolite is the zeolite used in step 1 / of the adsorbent production process, and having undergone the same ion exchange.

[0094] The zeolite crystals X, LSX or Y resulting from the zeolithization of the binder (transformation of the binder into zeolite) are generally smaller in diameter than the initial crystals. Consequently, in the final agglomerate, crystals with an 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, classically exhibit a unimodal particle size distribution, but it does not depart from the scope of the invention if the crystal diameter distribution is multimodal, and in particular bimodal, due to the presence of the population of crystals resulting from the zeolithization of the binder.

[0095] The performance of the cresol separation process is influenced by various process parameters, including the characteristics of the zeolitic 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 counter-current adsorption industrial unit implementing zeolitic 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, in a very Preferred temperature range: 115°C to 145°C - pressure between the pressure required to maintain the pentanol desorbent in liquid phase at the process temperature and 3 MPa - cycle time, corresponding to the time between two injections of desorbent onto a given bed, ranging from 2 to 18 minutes - ratio of desorbent flow rates to charge 0.5 to 4.0, preferably 0.7 to 2.5.

[0097] The desorbent is a linear C5 alcohol, selected from 2-pentanol and 3-pentanol, which offers an excellent compromise between the amount of adsorbent required and the solvent flow rate. Furthermore, the desorbent according to the invention exhibits a regeneration selectivity close to 1, ensuring energy savings during the distillation phase aimed at separating the paracresol from the desorbent. The selectivities obtained between paracresol / metacresol isomers also allow for improved productivity of the separation process.

[0098] Techniques for characterizing zeolitic adsorbents

[0099] Estimating the number average diameter of the adsorbent solids obtained at the end of step 2 / of shaping requires performing an analysis of the granulometric distribution of an adsorbent sample by imaging according to 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 ISO 9276-2:2001. In this document, the terms "number-average diameter" or "size" are used for zeolite adsorbent particles. The accuracy is on the order of 10 µm for the size range of zeolite adsorbents of the invention.

[0101] The number-average diameter of zeolite X, LSX, or Y crystals contained in zeolite adsorbents is estimated by scanning electron microscopy (SEM). To estimate the size of the zeolite crystals in the samples, a series of images are taken at a magnification of at least 5000x. The diameter of at least 200 crystals is then measured using dedicated software, for example, 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 on the order of 3%.

[0103] Observation of zeolitic adsorbents by SEM also confirms the presence of a non-zeolitic phase including, for example, residual binder (not converted during the zeolithization step) or any other amorphous phase in the ag- glomerates.

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

[0105] X-ray fluorescence is a spectral technique that offers precise determination, both quantitative and qualitative, except for the lightest elements such as lithium, sodium, or potassium, which are present in very small concentrations. In this case, inductively coupled plasma atomic emission spectrometry (ICP-AES), as described in standard NF EN ISO 21079-3, is preferred on an instrument such as the Perkin Elmer 4300DV.

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

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

[0108] The mercury intrusion technique is used to characterize the intragranular pore volume contained in pores with diameters greater than 3.6 nm in the adsorbent, and to measure its grain density. An Autopore 9500 Mi-cromeritics type mercury porosimeter 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 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 instrument's operating manual, consists of placing a pre-weighed sample of adsorbent (with known loss on ignition) into a porosimeter cell. After initial degassing (evacuation pressure of 30 pm Hg for at least 10 min), the cell is filled with mercury at a given pressure (0.0036 MPa). A progressively increasing pressure is then applied up to 400 MPa to gradually force the mercury into the sample's porous network. The relationship between the applied pressure and the pore diameter is established assuming cylindrical pores, a contact angle between the mercury and the pore walls of 140°, and a mercury surface tension of 485 dynes / cm.

[0109] The cumulative quantity of mercury introduced as a function of the applied pressure is recorded. The device does not allow differentiation between the intergranular and intragranular volumes: it is assumed that at approximately 0.2 MPa (corresponding to apparent pore diameters of 7 pm), the mercury fills all the intergranular voids granular, and beyond which the mercury penetrates 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 based on the volume of mercury introduced at a pressure of 0.2 MPa.

[0110] The total porous 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 zeolitic adsorbents measured by mercury intrusion are referred to the mass of the anhydrous sample (by correction of the loss on ignition of the analyzed sample).

[0112] The technique for characterizing the mechanical resistance representative of the crushing of the adsorbent within a bed or reactor is the bed mechanical resistance characterization technique, as described in the Shell Method series SMS1471-74 (Determination of Bulk Crushing Strength of Catalysts. Compression-Sieve Method), associated with the "BCS Tester" apparatus marketed by Vinci Technologies. This method, initially intended for the characterization of catalysts from 3 to 6 mm in diameter, is based on the use of a 425 µm sieve, which notably allows for the separation of 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 distribution of the zeolitic adsorbents being characterized.ASTM D7084-04, which also describes a method for measuring the bed crush strength of catalysts ("Determination of Bulk Crush Strength of Catalysts and Catalyst Carriers"), defines the sieve passage size to be equal to half the diameter of the catalyst particles to be characterized. The method includes a preliminary step of sieving the sample of catalysts or adsorbents to be characterized. If 10% wt of the sample passes through the sieve, a smaller passage size sieve should 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 µm to 700 µm, and preferably from 400 µm to 600 µm. Preferably, no particle size is less than 100 µm. Therefore, a 100 µm sieve will be used instead of the 425 µm sieve mentioned in the standard Shell method SMS 1471-74.

[0114] The method proceeds as follows: a 20 cm³ sample of agglomerated adsorbents, previously sieved with the appropriate sieve (100 µm) and previously oven-dried for at least 2 hours at 250°C (instead of the 300°C mentioned in the standard Shell method SMS 1471-74), is placed in a metal cylinder of known internal cross-section. An increasing force is applied in steps to this sample by means of a piston, through a 5 cm³ bed of steel balls in order to better distribute the force exerted by the piston on the adsorbent agglomerates (using 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 (using a suitable 100 µm sieve) and weighed. The bed crushing strength is determined by the pressure in megapascals (MPa) at which the quantity of cumulative fines passing through the sieve reaches 0.5% by weight of the sample. This value is obtained by plotting 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 bed crushing strength 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 classically 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 chosen adsorbent consists of Faujasite X type zeolites, 96% barium exchanged, with a super-micron crystal size (crystallite diameter). They are shaped into beads with an average diameter of 660 pm. The characteristics of the adsorbents are summarized in Table 1 below:

[0117] [Tables] ADSORBENT Loss on ignition [%] 5.53 (beads) [mm] 0.66 (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 (dry) [g / cm3] 0.835 Dry density [g / cm3] 1.278 POROSITIES Bed porosity [%] 34.9

[0118] To measure the selectivity of desorbent potentials, three piercing and depiercing tests, each using three desorbents, are performed (seven different desorbents in total). The performance obtained for the selectivities of paracresol on metacresol, and paracresol on desorbent, is 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 1.68.

[0119] Table 2 below shows the drilling (adsorption) and drilling (regeneration) performance, except for comparative test 2 for which only 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-pentanoyl 20 1.25 2.94 1.12 2.94 Drilling 4-methyl-2-pentanoyl [3) 20 CM 2 $ ag O Ô 1-hexanol 20 30 10 — — —■ — 11 $ "O & 1-pentanoyl (2) 20 127 3.41 1.37 0.72 s & Phenol & 20 Comparative 3 1-butanol OV 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 initial 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) (Comparative 1 and Comparative 2, desorbent (2)).

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

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

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

[0127] [Tables3] CHARGE COMPOSITION [% 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] These latest tests show that 2-pentanol and especially 3-pentanol exhibit a regeneration selectivity close to 1; as such, their use guarantees an energy saving during the distillation phase aimed at separating paracresol from the desorbent. From the point of view of the selectivities between paracresol / metacresol isomers, they are comparable to 1-pentanol, or even higher with regard to 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 / filler / desorbent system in LMS (Simulated Moving Bed) operation. This type of model is based on a dynamic simulation of flows and mass transfer. 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 of the products. para cresol and meta cresol.

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

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

[0132] [Tables4] Desorbent 1-pentanol 2-pentanol 3-pentanol Adsorbent Quantity 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 the desorbents according to the invention: 2-pentanol and 3-pentanol which offer the best compromise quantity of adsorbent on solvent flow rate.

[0135] Furthermore, these two desorbents exhibit a regeneration selectivity close to 1, ensuring an energy saving during the distillation phase aimed at separating the paracresol from the desorbent. The selectivities obtained between paracresol / metacresol isomers also allow for improved productivity.

Claims

Demands

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

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

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

4. A cresol separation method according to any 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. A method for separating cresols according to claim 4 wherein the cycle time, corresponding to the time between two injections of desorbent onto a given bed, is between 2 and 18 min, inclusive.

6. A process for separating cresols according to any 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, most preferably from 115°C to 145°C, inclusive, and at a pressure conditioned by maintaining the pentanol desorbent in liquid phase at the process temperature and less than 3 MPa.

7. A method for separating cresols according to any one of the preceding claims wherein the ratio of desorbent flow rates to charge is between 0.5 and 4.0, preferably between 0.7 and 2.5, most preferably between 1.0 and 2.0, inclusive.

8. A method for separating cresols according to any 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 paracresol b) a step of bringing the adsorbent bed into contact with the desorbent under desorption conditions, c) a step of removing from the adsorbent bed a stream containing the desorbent and the least selectively adsorbed load products, d) a step of removing from the adsorbent bed a stream containing the desorbent and the desired product, namely paracresol e) a separation of the stream from step c) into a first stream containing the desorbent and a second stream containing the least selectively adsorbed load products, 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 paracresol at a purity level greater than or equal to 90%, preferably greater than or equal to 99%, and most preferably greater than or equal to 99.7%.;

9. A method for separating cresols according to any one of the preceding claims wherein the number-average diameter of the agglomerated zeolite adsorbent particles is between 300 pm and 700 pm, preferably between 400 pm and 600 pm, inclusive.

10. A method for separating cresols according to any one of claims 1 to 9 wherein the number-average diameter of the zeolite crystals is between 0.1 pm and 1.5 pm inclusive, preferably between 0.5 pm and 1.2 pm inclusive.

11. A method for separating cresols according to any one of claims 1 to 10 by selective adsorption of paracresol 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 cresol separation process 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 of the number of moles of the barium oxide + potassium oxide mixture (BaO+K2O) to the number of moles of the mixture (BaO+K2O+Na2O) is greater than 90%; ii. A potassium oxide (K2O) content such that the ratio 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 zeolitic adsorbent.

13. A method for separating cresols according to any one of claims 1 to 10 by selective adsorption of paracresol, wherein the agglomerated zeolite adsorbent is based on zeolite Y having an atomic ratio Si / Al such that 1.5 < Si / Al < 6.

14. A cresol separation process 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 of the number of moles of sodium oxide to the number of moles of the total sodium oxide + lithium oxide (Na2O+Li2O) is greater than 65%. ii. And a total content of alkali or alkaline earth ions other than sodium and lithium, preferably less than 5% by weight of the total zeolite adsorbent.

15. A method for separating cresols according to claims 11 to 14 wherein the agglomerated zeolitic 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 zeolitic 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 zeolitic adsorbent).

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