A p-xylene adsorbent, its preparation method and application

Abstract

The present application relates to a kind of paraxylene adsorbent and its preparation method and application, it is related to mixed xylene separation technical field, the active component of the paraxylene adsorbent includes Silicalite-1 molecular sieve;The Silicalite-1 molecular sieve has hydrophobicity, there is no structural defect, contain mesoporous structure at 2.6nm and crystal is the flaky structure of preferential orientation growth along the direction of mass transfer benefit.This application uses this special crystal structure and the Silicalite-1 molecular sieve of morphology as active component, after rolling ball forming, paraxylene adsorbent of spherical shape is made, effectively solve the existing paraxylene adsorbent due to strong water absorption and lead to deactivation, slow adsorption speed and low paraxylene adsorption capacity and other technical problems.

Description

Technical Field

[0001] This application relates to the field of mixed xylene separation technology, and in particular to a p-xylene adsorbent, its preparation method and application. Background Technology

[0002] p-Xylene is an important organic chemical raw material, mainly used to synthesize terephthalic acid or dimethyl terephthalate, which is an indispensable raw material for the synthesis of polyester. With the surge in global polyester demand, the production of p-xylene will also grow rapidly. The main source of p-xylene is the separation of C8 aromatics, i.e., mixed xylenes, which are mixtures of xylene isomers of p-xylene (PX), m-xylene (MX), and o-xylene (OX) and ethylbenzene (EB).

[0003] Currently, the main methods for separating C8 aromatics include adsorption, distillation, cryogenic separation, and the newly developed integrated adsorption-crystallization separation method. Because the components of C8 aromatics have similar densities and small boiling point differences (e.g., the boiling point difference between PX and MX is only 0.75℃), they are difficult to separate using traditional distillation methods, which are energy-intensive, produce low-purity products, and are inefficient. Crystallization methods suffer from high energy consumption, low purity and recovery rates of individual components, significant raw material losses, and complex and expensive equipment. Adsorption methods utilize the different affinities of adsorbents for adsorbates to achieve separation. Due to its advantages such as flexible operation, high separation efficiency, energy saving, environmental friendliness, and wide applicability, it accounts for approximately 75% of the current industrial C8 aromatics separation market and is the most important separation method.

[0004] Industrially used p-xylene adsorbents mainly consist of X-type molecular sieves, Y-type molecular sieves, and KX-type molecular sieves (K... + Exchanged X-type molecular sieve), BaX-type molecular sieve (Ba 2+ Exchanged X-type molecular sieve), KBaX-type molecular sieve (K + and Ba 2+ The X-type molecular sieve after exchange and the MFI series molecular sieves. However, when used for the separation and adsorption of p-xylene in mixed xylenes, the active components of the existing p-xylene adsorbents reported above have problems such as deactivation due to strong water absorption, slow adsorption rate and low p-xylene adsorption capacity. Summary of the Invention

[0005] This application provides a p-xylene adsorbent, its preparation method, and its application, to solve the technical problems of existing p-xylene adsorbents, such as deactivation due to strong water absorption, slow adsorption rate, and low p-xylene adsorption capacity.

[0006] In a first aspect, this application provides a p-xylene adsorbent, wherein the active component of the p-xylene adsorbent includes Silicalite-1 molecular sieve;

[0007] The Silicalite-1 molecular sieve is hydrophobic, free of structural defects, contains mesoporous structures at 2.6 nm, and has a plate-like structure in which the crystals are preferentially oriented along directions that facilitate mass transfer.

[0008] Further, by weight percentage, the p-xylene adsorbent comprises the following components: 85-98% Silicalite-1 molecular sieve, 2-13% binder, 1-5% pore structure modifier, and 0.1-2% lubricant; wherein the pore structure modifier is an organic acid.

[0009] Further, by weight percentage, the p-xylene adsorbent comprises the following components: 88-95% Silicalite-1 molecular sieve, 5-8% binder, 1-5% pore structure modifier, and 0.1-2% lubricant.

[0010] Furthermore, the performance parameters of the p-xylene adsorbent include: specific surface area > 300 m². 2 / g, compressive strength of 50N / cm, and adsorption capacity of p-xylene >3.5wt%.

[0011] Secondly, this application provides a method for preparing the p-xylene adsorbent according to any one of the first aspects, the preparation method comprising the following steps:

[0012] The preparation method includes the following steps:

[0013] The Silicalite-1 molecular sieve was obtained;

[0014] The Silicalite-1 molecular sieve, binder, pore structure modifier and lubricant are first mixed, and then subjected to a first ball rolling process to obtain masterbatch;

[0015] The masterbatch, Silicalite-1 molecular sieve and molding aid are mixed for a second time, and then a second spherical rolling molding process is carried out to obtain a spherical intermediate product.

[0016] The spherical intermediate product is polished and then subjected to a first calcination to obtain the para-xylene adsorbent.

[0017] Furthermore, the steps for obtaining the Silicalite-1 molecular sieve include the following processes:

[0018] The organic structure directing agent and additives were dissolved in water, and then a silicon source was added and stirred to obtain the first mixed gel solution.

[0019] A second mixture was obtained by adding Silicalite-1 seed solution dropwise to the first mixed gel solution and stirring.

[0020] The second mixture is transferred into a polytetrafluoroethylene reactor and crystallized at 180–220°C for 15–25 days to obtain the third mixture.

[0021] The third mixture is filtered, washed, and then dried to obtain a solid.

[0022] The solid was subjected to a second calcination at 540–560°C for 1–3 hours to obtain the Silicalite-1 molecular sieve.

[0023] Furthermore, the organic structure directing agent is an organic ammonium base and a surfactant, the auxiliary agent is an amine compound, the silicon source includes at least one of fumed silica and solid silica gel, and the weight percentage concentration of the Silicalite-1 seed crystal is 5-15%.

[0024] Furthermore, the diameter of the spherical intermediate product is 1.6 to 2.5 mm, and the working parameters of the first roasting include: temperature of 540 to 560°C and time of 1 to 3 hours.

[0025] Thirdly, this application provides a p-xylene adsorbent as described in any one of the first aspects, and / or the p-xylene adsorbent prepared by any one of the preparation methods described in any one of the second aspects, for the separation of mixed xylenes.

[0026] The technical solutions provided in this application have at least the following advantages compared with the prior art:

[0027] This application provides a p-xylene adsorbent, wherein the active component of the p-xylene adsorbent is hydrophobic, has no structural defects, contains a mesoporous structure at 2.6 nm, and the crystals are sheet-like structures preferentially oriented along a direction conducive to mass transfer.

[0028] (1) The active component of PX adsorbent is Silicalite-1 molecular sieve, which is hydrophobic, has mild operating conditions, does not require pretreatment before use, and the adsorption effect of the adsorbent will not be affected by the raw materials and water in the air.

[0029] (2) The active component of the PX adsorbent does not have structural defects and will not form silanol defect sites due to the presence of Al atoms in the framework. Therefore, the sieving capacity of the adsorbent is improved, which is conducive to the selective adsorption of PX in C8 aromatics without adsorbing MX and OX, thus improving the PX separation selectivity.

[0030] (3) The PX adsorbent has a certain amount of mesopores at 2.6 nm, which is conducive to the rapid diffusion of molecules, resulting in better adsorption rate and higher p-xylene adsorption capacity.

[0031] (4) The active component crystal of PX adsorbent is a sheet-like structure that grows preferentially along the direction that is conducive to mass transfer. It has a linear ten-membered ring channel, which makes molecular diffusion smoother, the diffusion path shorter, the diffusion efficiency higher, and the C8 separation adsorption and recovery effect of PX better.

[0032] Therefore, this invention uses Silicalite-1 molecular sieve, which is hydrophobic, free of structural defects, contains mesoporous structure at 2.6 nm, and whose crystals are preferentially oriented along a direction conducive to mass transfer, as the active component. This effectively solves the technical problems of existing para-xylene adsorbents, such as deactivation due to strong water absorption, slow adsorption rate, and low para-xylene adsorption capacity. Attached Figure Description

[0033] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0034] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a schematic flowchart illustrating a method for preparing a p-xylene adsorbent, as provided in an embodiment of this application.

[0036] Figure 2 The diagram shows the adsorption-desorption isotherm results of PX adsorbents prepared in Examples 1, 1, and 2 of this application.

[0037] Figure 3 The diagram shows the mesopore size distribution of the PX adsorbents prepared in Examples 1, 1, and 2 of this application.

[0038] Figure 4 The image shows the XRD results of the PX adsorbent prepared in Example 1 of this application.

[0039] Figure 5 This is a SEM image of the PX adsorbent prepared in Example 1 of this application.

[0040] Figure 6 The image shows the SEM results of the PX adsorbent prepared for Comparative Example 2.

[0041] Figure 7 The Fourier transform infrared spectra of the PX adsorbents prepared in Examples 1 and Comparative Examples 1-3 of this application are shown. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0043] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0044] In a first aspect, this application provides a p-xylene adsorbent, wherein the active component of the p-xylene adsorbent includes Silicalite-1 molecular sieve;

[0045] The Silicalite-1 molecular sieve is hydrophobic, free of structural defects, contains a mesoporous structure at 2.6 nm, and has a plate-like structure with crystals preferentially oriented along a direction conducive to mass transfer.

[0046] This application provides a p-xylene adsorbent. The active component of this p-xylene adsorbent is hydrophobic, free of structural defects, contains a mesoporous structure at 2.6 nm, and has a sheet-like structure with crystals preferentially oriented along a direction conducive to mass transfer. The active component of the PX adsorbent is a Silicalite-1 molecular sieve, which is hydrophobic, has mild operating conditions, requires no pretreatment, and the adsorption effect is not affected by water in the raw materials or air. The active component of the PX adsorbent has no structural defects and will not form silanol defect sites due to the presence of Al atoms in the framework. Therefore, the sieving capacity of the adsorbent is improved, which is beneficial for the selective adsorption of PX in C8 aromatics without adsorbing MX and OX, thus improving the PX separation selectivity. The PX adsorbent has a certain amount of mesopores at 2.6 nm, which is conducive to the rapid diffusion of molecules, resulting in better adsorption rate and higher p-xylene adsorption capacity. The active component of the PX adsorbent has a sheet-like structure with crystals preferentially oriented along a direction conducive to mass transfer and has linear ten-membered ring channels, which makes molecular diffusion smoother, the diffusion path shorter, the diffusion efficiency higher, and the C8 separation adsorption and recovery of PX better. Therefore, this invention uses Silicalite-1 molecular sieve, which is hydrophobic, free of structural defects, contains mesoporous structure at 2.6 nm, and whose crystals are preferentially oriented along a direction conducive to mass transfer, as the active component. This effectively solves the technical problems of existing para-xylene adsorbents, such as deactivation due to strong water absorption, slow adsorption rate, and low para-xylene adsorption capacity.

[0047] In one embodiment of this application, the Silicalite-1 molecular sieve has a sheet-like morphology.

[0048] In this application, the Silicalite-1 molecular sieve has a plate-like morphology, which is beneficial for mass transfer, that is, it facilitates the rapid adsorption of PX.

[0049] As one embodiment of this application, the p-xylene adsorbent comprises, by weight percentage: 85-98% Silicalite-1 molecular sieve, 2-13% binder, 1-5% pore structure modifier, and 0.1-2% lubricant; wherein the pore structure modifier is an organic acid.

[0050] By weight percentage, the purpose of controlling the content of Silicalite-1 molecular sieve (85-98%), binder (2-13%), pore structure modifier (1-5%), and lubricant (0.1-2%) in the p-xylene adsorbent described in this application is to ensure product strength while maximizing the content of active components. Insufficient Silicalite-1 molecular sieve reduces the adsorbent's PX adsorption performance, while excessive Silicalite-1 molecular sieve results in insufficient product strength.

[0051] In some specific embodiments, the Silicalite-1 molecular sieve is 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, etc., by weight percentage.

[0052] In some specific embodiments, the adhesive is not specifically limited or required and may be water or a commercially available organic adhesive commonly used in the art; the adhesive may be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, etc. by weight percentage.

[0053] In some specific embodiments, the pore structure modifier may be an organic acid such as citric acid or tartaric acid; by weight percentage, the pore structure modifier may be 1%, 2%, 3%, 4%, 5%, etc.

[0054] In some specific embodiments, the lubricant is, by weight percentage, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, and 2.0%, etc.

[0055] Preferably, the p-xylene adsorbent comprises, by weight percentage: 88-95% Silicalite-1 molecular sieve, 5-8% binder, 1-5% pore structure modifier, and 0.1-2% lubricant.

[0056] As one embodiment of this application, the performance parameters of the p-xylene adsorbent include: specific surface area > 300 m². 2 / g, compressive strength of 50N / cm, and adsorption capacity of p-xylene >3.5wt%.

[0057] The p-xylene adsorbent provided in this application has excellent performance, with a specific surface area >300 m². 2 / g, compressive strength of 50N / cm, and adsorption capacity of p-xylene >3.5wt%.

[0058] Secondly, based on a general inventive concept, this application provides a method for preparing the p-xylene adsorbent as described in any of the first aspects, such as... Figure 1 As shown, the preparation method includes the following steps:

[0059] The preparation method includes the following steps:

[0060] The Silicalite-1 molecular sieve was obtained;

[0061] The Silicalite-1 molecular sieve, binder, pore structure modifier and lubricant are first mixed, and then subjected to a first ball rolling process to obtain masterbatch;

[0062] The masterbatch, Silicalite-1 molecular sieve and molding aid are mixed for a second time, and then a second spherical rolling molding process is carried out to obtain a spherical intermediate product.

[0063] The spherical intermediate product is polished and then subjected to a first calcination to obtain the para-xylene adsorbent.

[0064] The method for preparing the p-xylene adsorbent provided in this application is simple to operate, requires no additional specific equipment, and is suitable for industrial production. Furthermore, this preparation method is based on the p-xylene adsorbent described in any of the first aspects above, and therefore possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated further here.

[0065] In some specific embodiments, both the first mixing and the second mixing can be carried out using conventional mixing methods in the art, as long as the raw materials are mixed evenly.

[0066] In some specific embodiments, both the first molding process and the second molding process can be conventional molding processes in the art, which will not be described in detail in this application.

[0067] As one embodiment of this application, the steps for obtaining the Silicalite-1 molecular sieve include the following process:

[0068] The organic structure directing agent and additives were dissolved in water, and then a silicon source was added and stirred to obtain the first mixed gel solution.

[0069] A second mixture was obtained by adding Silicalite-1 seed solution dropwise to the first mixed gel solution and stirring.

[0070] The second mixture is transferred into a polytetrafluoroethylene reactor and crystallized at 180–220°C for 15–25 days to obtain the third mixture.

[0071] The third mixture is filtered, washed, and then dried to obtain a solid.

[0072] The solid was subjected to a second calcination at 540–560°C for 1–3 hours to obtain the Silicalite-1 molecular sieve.

[0073] In some specific embodiments, the second calcination temperature may be 540℃, 541℃, 542℃, 543℃, 544℃, 545℃, 546℃, 547℃, 548℃, 549℃, 550℃, 551℃, 552℃, 553℃, 554℃, 555℃, 556℃, 557℃, 558℃, 559℃, 560℃, etc.; preferably 550℃.

[0074] In some specific embodiments, the crystallization temperature may be 180℃, 181℃, 182℃, 183℃, 184℃, 185℃, 186℃, 187℃, 188℃, 189℃, 190℃, 191℃, 192℃, 193℃, 194℃, 195℃, 196℃, 197℃, 198℃, 199℃, 200℃, 201℃, 202℃, 203℃, 204℃, 205℃, 206℃, 207℃, 208℃, 209℃, 210℃, 211℃, 212℃, 213℃, 214℃, 215℃, 216℃, 217℃, 218℃, 219℃, 220℃, etc.

[0075] In one embodiment of this application, the organic structure directing agent is an organic ammonium base and a surfactant, the auxiliary agent is an amine compound, the silicon source includes at least one of fumed silica and solid silica gel, and the weight percentage concentration of the Silicalite-1 seed crystal is 5-15%.

[0076] In some specific embodiments, the organic structure directing agent is an organic ammonium base and a surfactant. The organic ammonium base is preferably tetrapropylammonium bromide, tetrabutylammonium bromide, and tetrapropylammonium hydroxide, and the surfactant is preferably dodecyltrimethylammonium bromide or a long-chain primary amine.

[0077] In some specific embodiments, the auxiliary agent is an amine, preferably ammonium fluoride.

[0078] In some specific embodiments, the silicon source is preferably fumed silica or solid silica gel.

[0079] As one embodiment of this application, the diameter of the spherical intermediate product is 1.6 to 2.5 mm, and the working parameters of the first roasting include: temperature of 540 to 560°C and time of 1 to 3 hours.

[0080] In some specific embodiments, the temperature of the first calcination can be 540℃, 541℃, 542℃, 543℃, 544℃, 545℃, 546℃, 547℃, 548℃, 549℃, 550℃, 551℃, 552℃, 553℃, 554℃, 555℃, 556℃, 557℃, 558℃, 559℃, 560℃, etc.; preferably 550℃.

[0081] Thirdly, based on a general inventive concept, this application provides a p-xylene adsorbent as described in any one of the first aspects, and / or the application of a p-xylene adsorbent prepared by any one of the preparation methods described in any one of the second aspects in the separation of mixed xylenes.

[0082] The p-xylene adsorbent provided in this application has the advantages of high PX adsorption capacity, fast adsorption rate, and mild operating conditions, and is suitable for the adsorption of PX in C8 aromatic hydrocarbons at room temperature and medium temperature.

[0083] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0084] Example 1

[0085] This embodiment provides a p-xylene adsorbent, the preparation method of which includes the following steps:

[0086] 1) Add 426g of tetrapropylammonium bromide, 3.27g of dodecyltrimethylammonium bromide and 30g of ammonium fluoride to 7200g of distilled water and stir until dissolved, denoted as a; add 1200g of fumed silica to a and stir until homogeneous; add 8% Silicalite-1 seed solution dropwise to the above mixture, stir for 30 min, then transfer to a polytetrafluoroethylene autoclave and crystallize at 200℃ for 18 days. After filtration and washing, dry at 100℃ for 12 h and calcine at 550℃ for 2 h to obtain sheet-like Silicalite-1 molecular sieve.

[0087] 2) Mix 460g of the obtained Silicalite-1 molecular sieve, 50g of citric acid, 10g of guar gum powder and 280g of water evenly to make a masterbatch with a certain particle size; place the masterbatch in the rolling disc of the ball rolling machine, add 300g of the molecular sieve raw powder and citric acid mixed powder in a ratio of 9:1 for ball rolling and forming into adsorbent balls of 1.6-2.5mm; polish the formed balls in a polishing machine and then calcine them at 550℃ for 2h to obtain the PX adsorbent product of Example 1, denoted as PX-A1.

[0088] Example 2

[0089] This embodiment provides a p-xylene adsorbent, the preparation method of which includes the following steps:

[0090] 1) Add 426g of tetrapropylammonium bromide, 3.27g of dodecyltrimethylammonium bromide and 30g of ammonium fluoride to 7200g of distilled water and stir until dissolved, denoted as b; add 1200g of solid silica gel to b and stir until homogeneous; add 10% of Silicalite-1 seed solution dropwise to the above mixture, stir for 30 min, then transfer to a polytetrafluoroethylene autoclave and crystallize at 210℃ for 17 days. After filtration and washing, dry at 100℃ for 12 h and calcine at 550℃ for 2 h to obtain sheet-like Silicalite-1 molecular sieve.

[0091] 2) Mix 460g of the obtained Silicalite-1 molecular sieve, 50g of kaolin, 10g of guar gum powder and 280g of water evenly to make a masterbatch with a certain particle size; place the masterbatch in the rolling disc of the ball rolling machine, add 300g of molecular sieve raw powder and kaolin mixed powder in a ratio of 9:1 and roll into adsorbent balls of 1.6-2.5mm; polish the formed balls in a polishing machine and then calcine them at 550℃ for 2h to obtain the PX adsorbent product of Example 2, denoted as PX-A2.

[0092] Example 3

[0093] This embodiment provides a p-xylene adsorbent, the preparation method of which includes the following steps:

[0094] 1) Add 426g tetrapropylammonium bromide, 3.27g dodecyltrimethylammonium bromide and 30g ammonium fluoride to 7200g distilled water and stir until dissolved, denoted as c; add 1200g silica sol to c and stir until homogeneous; add 8% Silicalite-1 seed solution dropwise to the above mixture, stir for 30 min, then transfer to a polytetrafluoroethylene autoclave and crystallize at 205℃ for 18 days. After filtration and washing, dry at 100℃ for 12 h and calcine at 550℃ for 2 h to obtain sheet-like Silicalite-1 molecular sieve.

[0095] 2) Mix 460g of the obtained Silicalite-1 molecular sieve, 50g of attapulgite, 10g of talc powder and 280g of water evenly to make a masterbatch with a certain particle size; place the masterbatch in the rolling disc of the ball rolling machine, add 300g of molecular sieve raw powder and attapulgite mixed powder in a ratio of 9:1 and roll into adsorbent balls of 1.6-2.5mm; polish the formed balls in a polishing machine and then calcine them at 550℃ for 2h to obtain the PX adsorbent product of Example 3, denoted as PX-A3.

[0096] Example 4

[0097] This embodiment provides a p-xylene adsorbent, the preparation method of which includes the following steps:

[0098] 1) Add 426g tetrapropylammonium bromide, 3.27g dodecyltrimethylammonium bromide and 29g ammonium chloride to 7200g distilled water and stir until dissolved, denoted as d; add 1200g fumed silica to d and stir until homogeneous; add 12% Silicalite-1 seed solution dropwise to the above mixture, stir for 30 min, then transfer to a polytetrafluoroethylene autoclave and crystallize at 190℃ for 22 days. After filtration and washing, dry at 100℃ for 12 h and calcine at 550℃ for 2 h to obtain sheet-like Silicalite-1 molecular sieve.

[0099] 2) Mix 460g of the obtained Silicalite-1 molecular sieve, 50g of ethylenediaminetetraacetic acid, 10g of guar gum powder and 280g of water evenly to prepare a masterbatch with a certain particle size; place the masterbatch in the rolling disc of a ball rolling machine, add 300g of molecular sieve raw powder and ethylenediaminetetraacetic acid mixed powder in a ratio of 9:1 for ball rolling and forming into adsorbent balls of 1.6-2.5mm; polish the formed balls in a polishing machine and then calcine them at 550℃ for 2h to obtain the PX adsorbent product of Example 4, denoted as PX-A4.

[0100] Example 5

[0101] This embodiment provides a p-xylene adsorbent, the preparation method of which includes the following steps:

[0102] 1) Add 413g tetrapropylammonium hydroxide, 4.03g octylamine and 31g urea to 7100g distilled water and stir until dissolved, denoted as e; add 1200g fumed silica to e and stir until homogeneous; add 10% Silicalite-1 seed solution dropwise to the above mixture, stir for 30 min, then transfer to a polytetrafluoroethylene autoclave and crystallize at 200℃ for 20 days. After filtration and washing, dry at 100℃ for 12 h and calcine at 550℃ for 2 h to obtain sheet-like Silicalite-1 molecular sieve.

[0103] 2) Mix 460g of the obtained Silicalite-1 molecular sieve, 50g of attapulgite, 10g of paraffin wax and 280g of water evenly to make a masterbatch with a certain particle size; place the masterbatch in the rolling disc of the ball rolling machine, add 300g of molecular sieve raw powder and attapulgite mixed powder with a ratio of 9:1, and roll into adsorbent balls of 1.6-2.5mm; polish the formed balls in a polishing machine, and then calcine them at 550℃ for 2h to obtain the PX adsorbent product of Example 5, denoted as PX-A5.

[0104] Example 6

[0105] This embodiment provides a p-xylene adsorbent, the preparation method of which includes the following steps:

[0106] 1) Add 413g tetrapropylammonium hydroxide, 4.03g octylamine and 29g ammonium chloride to 7200g distilled water and stir until dissolved, denoted as f; add 1200g silica sol to f and stir until homogeneous; add 15% Silicalite-1 seed solution dropwise to the above mixture, stir for 30 min, then transfer to a polytetrafluoroethylene autoclave and crystallize at 205℃ for 18 days. After filtration and washing, dry at 100℃ for 12 h and calcine at 550℃ for 2 h to obtain sheet-like Silicalite-1 molecular sieve.

[0107] 2) Mix 460g of Silicalite-1 molecular sieve, 50g of attapulgite, 10g of dry starch and 280g of water evenly to make a masterbatch with a certain particle size; place the masterbatch in the rolling disc of a ball rolling machine, add 300g of molecular sieve raw powder and attapulgite mixed powder in a ratio of 9:1 and roll into adsorbent balls of 1.6-2.5mm; polish the formed balls in a polishing machine and then calcine them at 550℃ for 2h to obtain the PX adsorbent product of Example 6, denoted as PX-A6.

[0108] Comparative Example 1

[0109] This example provides a p-xylene adsorbent, the preparation method of which includes the following steps:

[0110] 460g of commercially available Silicalite-1 molecular sieve, 50g of attapulgite, 10g of guar gum powder, and 280g of water were mixed evenly to form a masterbatch of a certain particle size. The masterbatch was placed in the rolling disc of a ball rolling machine, and 300g of commercially available Silicalite-1 molecular sieve raw powder and attapulgite mixed powder in a 9:1 ratio were added to form ball rolling, which resulted in adsorbent spheres of 1.6-2.5mm. The formed spheres were polished in a polishing machine and then calcined at 550℃ for 2 hours to obtain the PX adsorbent product of Comparative Example 1, denoted as PX-B1.

[0111] Comparative Example 2

[0112] This example provides a p-xylene adsorbent, the preparation method of which includes the following steps:

[0113] 460g of commercially available ZSM-5 molecular sieve (SAR=30), 50g of attapulgite, 10g of guar gum powder, and 280g of water were mixed evenly to form a masterbatch with a certain particle size. The masterbatch was placed in the rolling disc of a ball rolling machine, and 300g of commercially available ZSM-5 molecular sieve raw powder and attapulgite mixed powder in a ratio of 9:1 were added to form ball rolling, which resulted in adsorbent spheres of 1.6-2.5mm. The formed spheres were polished in a polishing machine and then calcined at 550℃ for 2 hours to obtain the PX adsorbent product of Comparative Example 3, denoted as PX-B2.

[0114] Comparative Example 3

[0115] This example provides a p-xylene adsorbent, the preparation method of which includes the following steps:

[0116] 460g of commercially available LiX molecular sieve, 50g of attapulgite, 10g of guar gum powder, and 280g of water were mixed evenly to form a masterbatch with a certain particle size. The masterbatch was placed in the rolling disc of a ball rolling machine, and 300g of commercially available all-silica LiX molecular sieve raw powder and attapulgite mixed powder in a 9:1 ratio were added for ball rolling to form adsorbent spheres of 1.6-2.5mm. The formed spheres were polished in a polishing machine and then calcined at 550℃ for 2 hours to obtain the PX adsorbent product of Comparative Example 3, denoted as PX-B3.

[0117] Test case

[0118] In this example, the PX adsorbents prepared in Examples 1-6 and Comparative Examples 1-3 were subjected to physical adsorption, XRD, and SEM tests. The results are shown in Table 1 and... Figure 2 , Figure 3 , Figure 4 , Figure 5 As shown.

[0119] Table 1. Specific surface area results of PX adsorbents prepared in Examples 1-6 and Comparative Examples 1-3.

[0120] project <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Mesoporous specific surface area (m 2 / g)]]> Example 1 379 73 Example 2 364 69 Example 3 381 71 Example 4 356 55 Example 5 328 52 Example 6 363 63 Comparative Example 1 386 12 Comparative Example 2 392 6 Comparative Example 3 523 8

[0121] As can be seen from Table 1, compared with the comparative examples, the PX adsorbents prepared in Examples 1-6 have a higher mesoporous specific surface area, which is beneficial to the rapid molecular mass transfer.

[0122] Depend on Figure 2 and Figure 3 As can be seen, compared with the comparative example, the PX adsorbent prepared in Example 1 has a certain amount of mesopores at 2.6 nm, which is beneficial to the rapid molecular mass transfer.

[0123] Depend on Figure 4-6 It can be seen that the intensity of the diffraction peak at the (200) crystal plane of the PX adsorbent prepared in Example 1 is significantly higher than that of other diffraction peaks, and it has a sheet-like structure, while the PX adsorbent prepared in Comparative Example 2 has a blocky structure. This indicates that the PX adsorbent prepared in Example 1 grows preferentially along the direction that is conducive to mass transfer, making the molecular diffusion path shorter and the diffusion efficiency higher.

[0124] Depend on Figure 7 It can be seen that the PX adsorbent prepared in Example 1 has a performance at 3000-4000 cm⁻¹ -1 There are no absorption peaks at this location, meaning there are no defect sites, resulting in higher adsorption capacity and selectivity for the adsorbent PX.

[0125] Examples 1-6 and Comparative Examples 1-3 were used to conduct C8 aromatic hydrocarbon adsorption and separation experiments with the PX adsorbents prepared in these examples. The experimental procedures were as follows:

[0126] (1) Take a certain amount of PX adsorbent prepared in Examples 1-6 and Comparative Examples 1-3 respectively, and pretreat it at 550℃ for 2h.

[0127] (2) Take a certain amount of PX adsorbent prepared in Example 1 and Comparative Example 3, without pretreatment;

[0128] (3) Prepare a 2wt% xylene / TIPB (1,3,5-triisopropylbenzene) solution;

[0129] (4) Add 1g of adsorbent to 5g of solution, adsorb for 30min under ultrasonic conditions, centrifuge after adsorption, and take the supernatant.

[0130] (5) The supernatant was subjected to gas chromatography to test the content of each component. The column type was HP-FFAP, the split ratio was 40:1, the temperature was programmed to 210℃ and held for 5 min.

[0131] Data processing should be performed according to the following formula:

[0132] ① Adsorption rate calculation formula (taking PX as an example):

[0133]

[0134] ② Formula for calculating adsorption capacity (taking PX as an example):

[0135]

[0136] ③ Formula for calculating the selectivity factor (the closer the selectivity factor is to 1, the less selectivity there is):

[0137]

[0138] The adsorption results are shown in Table 2.

[0139] Table 2. Results of C8 aromatic hydrocarbon adsorption experiments in Examples 1-6 and Comparative Examples 1-3

[0140]

[0141]

[0142] Table 2 shows that: 1) The active component of Comparative Example 1 is the commercially available Silicalite-1 molecular sieve. This molecular sieve does not contain mesopores and does not exhibit preferred orientation growth. In contrast, the active components in Examples 1-6 have a certain amount of mesopores at 2.6 nm and possess linear ten-membered ring channels, resulting in shorter molecular diffusion paths and faster diffusion rates. Therefore, the PX adsorption capacity of Comparative Example 1 in Table 2 is lower than that of Examples 1-6; 2) The active component of Comparative Example 2 is the commercially available ZSM-5 molecular sieve. This molecular sieve has structural defects, namely, it contains acidic sites, which cause desorption at high temperatures. Side reactions can occur. In Table 2, the PX adsorption capacity and selectivity of Comparative Example 2 are lower than those of Examples 1-6. 3) The active component of the adsorbent in Comparative Example 3 is Li-X molecular sieve. This molecular sieve has strong water absorption and contains acidic sites. It has harsh operating conditions and low adsorption effect. It must undergo strict dehydration treatment before use. The presence of water in the raw material will greatly reduce the adsorption effect of the adsorbent. As shown in Table 2, the PX adsorption capacity of the untreated adsorbent in Example 1 is still very high, while the PX adsorption capacity of the untreated adsorbent in Comparative Example 2 is significantly reduced and basically not adsorbed.

[0143] In summary, the embodiments of this application provide a p-xylene adsorbent, which has at least the following beneficial effects compared to the prior art:

[0144] (1) The PX adsorbent of the present invention is hydrophobic, has mild operating conditions, does not require pretreatment before use, and the water in the raw materials and air will not affect the adsorption effect of the adsorbent.

[0145] (2) The PX adsorbent of the present invention does not have structural defects and will not form silanol defect sites due to the presence of Al atoms in the framework. Therefore, the sieving capacity of the adsorbent is improved, which is beneficial to selectively adsorbing PX in C8 aromatics without adsorbing MX and OX, thus improving the PX separation selectivity.

[0146] (3) The PX adsorbent of the present invention has a certain amount of mesopores, which is conducive to the rapid diffusion of molecules, and has better adsorption speed and higher p-xylene adsorption capacity.

[0147] (4) The active component crystal of the PX adsorbent of the present invention grows preferentially along the direction that is conducive to mass transfer, and has a linear ten-membered ring channel, which makes molecular diffusion smoother, diffusion path shorter, diffusion efficiency higher, and C8 separation adsorption and recovery of PX better.

[0148] (5) The PX adsorbent of the present invention has no aluminum defect sites, that is, it does not contain acidic sites. When regenerated at high temperature, it does not have catalytic activity for PX, that is, no side reaction will occur. Moreover, the molecular sieve does not contain acidic sites, so it will not protonate the aromatic ring to form strong chemical bonds, thus the adsorption rate is faster and the desorption time is shorter at low temperature.

[0149] The active component of the PX adsorbent has a plate-like structure with crystals preferentially oriented along a direction conducive to mass transfer. It possesses linear ten-membered ring channels, which facilitates smoother molecular diffusion, shorter diffusion paths, and higher diffusion efficiency, resulting in better C8 separation, adsorption, and recovery of PX. Therefore, this invention uses Silicalite-1 molecular sieve, which is hydrophobic, free of structural defects, contains mesoporous structures at 2.6 nm, and has crystals preferentially oriented along a direction conducive to mass transfer, as the active component. This effectively solves the technical problems of existing p-xylene adsorbents, such as deactivation due to strong water absorption, slow adsorption rate, and low p-xylene adsorption capacity.

[0150] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0151] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0152] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A para-xylene adsorbent, characterized by, The active component of the p-xylene adsorbent comprises Silicalite-1 molecular sieve; the Silicalite-1 molecular sieve has hydrophobicity, no structural defects, contains mesoporous structure at 2.6 nm and the crystal is a sheet structure which grows along the direction favorable to mass transfer, and the active component crystal grows along the b-axis direction, The p-xylene adsorbent comprises the following components in percentage by weight: Silicalite-1 molecular sieve 85-98%, binder 2-13%, pore structure modifier 1-5% and lubricant 0.1-2%, and the sum of all components is 100%; the pore structure modifier is organic acid.

2. The para-xylene adsorbent according to claim 1, wherein, The p-xylene adsorbent comprises the following components in percentage by weight: Silicalite-1 molecular sieve 88-95%, binder 5-8%, pore structure modifier 1-5% and lubricant 0.1-2%, and the sum of all components is 100%.

3. The para-xylene adsorbent according to any one of claims 1 to 2, characterized in that, The performance parameters of the p-xylene adsorbent include: specific surface area > 300 m 2 / g, compressive strength of 50 N / cm, and p-xylene adsorption capacity > 3.5 wt%.

4. A method for producing the p-xylene adsorbent according to any one of claims 1 to 2, characterized by, The preparation method comprises the following steps: The Silicalite-1 molecular sieve is obtained; The Silicalite-1 molecular sieve, binder, pore structure modifier and lubricant are first mixed, and then a first ball-rolling forming process is performed to obtain a master batch; The master batch, Silicalite-1 molecular sieve and forming aid are second mixed, and then a second ball-rolling forming process is performed to obtain a spherical intermediate product; The spherical intermediate product is polished, and then a first calcination is performed to obtain the p-xylene adsorbent.

5. The preparation method according to claim 4, characterized in that, The step of obtaining the Silicalite-1 molecular sieve comprises the following process: An organic structure directing agent and an aid are added to water for dissolution, and then a silicon source is added for stirring to obtain a first mixed gel solution; A Silicalite-1 seed solution is added dropwise into the first mixed gel solution, and then stirring is performed to obtain a second mixture; The second mixture is moved into a polytetrafluoroethylene kettle, and then crystallization is performed at a temperature of 180-220 ℃ for 15-25 days to obtain a third mixture; The third mixture is filtered and washed, and then dried to obtain a solid; The solid is subjected to a second calcination at a temperature of 540-560 ℃ for 1-3 hours to obtain the Silicalite-1 molecular sieve.

6. The preparation method according to claim 5, characterized in that, The organic structure directing agent is an organic ammonium base and a surfactant, the aid is an amine compound, the silicon source comprises at least one of fumed silica and solid silica gel, and the weight percentage concentration of the Silicalite-1 seed is 5-15%.

7. The preparation method according to claim 5, characterized in that, The diameter of the spherical intermediate product is 1.6-2.5 mm, and the working parameters of the first calcination comprise a temperature of 540-560 ℃ and a time of 1-3 hours.

8. Use of the p-xylene adsorbent of any one of claims 1-3 and / or the p-xylene adsorbent prepared by the preparation method of any one of claims 4-7 in separating mixed xylene.

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