Method for preparing p-xylene adsorbent

Abstract

The invention relates to a method for preparing a p-xylene adsorbent, the method comprises the steps of forming, drying roasting treatment, pre-wetting, crystal transformation treatment, ion exchange treatment and activation dehydration treatment, NaX molecular sieve crystallization mother liquor is used for crystal transformation treatment, and the p-xylene adsorbent can be produced with low energy consumption, low material consumption and low emission.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of p-xylene adsorbent preparation, in particular, to a method for preparing a p-xylene adsorbent. BACKGROUND

[0002] P-xylene (PX) is an important raw material for producing polyester (PET), which can be used in the fields of textiles, fibers, plastics, building, automobile, electronics and pharmaceutical. P-xylene (PX) mainly exists in mixed C8 aromatics, and the mixed C8 aromatics include four isomers of p-xylene (PX), m-xylene (MX), o-xylene (OX) and ethylbenzene (EB), which have very small boiling point difference, especially the boiling points of p-xylene and m-xylene only differ by 0.6℃, so it is difficult to obtain high-purity p-xylene by distillation method, and the adsorption separation method is generally used in industry to produce high-purity p-xylene. The adsorption separation technology is composed of zeolite adsorbent and simulated moving bed continuous countercurrent separation process, and the high-performance adsorbent is the core technology of the process, and the production process of the adsorbent has important influence on the performance and cost of the adsorbent. How to reduce the wastewater discharge, energy and material consumption in the production process of PX adsorbent as much as possible is an important problem in the field. SUMMARY

[0003] The purpose of the present disclosure is to provide a method for preparing a p-xylene adsorbent, which can produce the p-xylene adsorbent with low energy consumption, low material consumption and low emission.

[0004] In order to achieve the above-mentioned purpose, the present disclosure provides a method for preparing a p-xylene adsorbent, which comprises the following steps: S1, mixing NaX molecular sieve, a binder and optional additives and molding to obtain first NaX molecular sieve particles; S2, drying and calcining the first NaX molecular sieve particles to obtain second NaX molecular sieve particles and first tail gas; S3, pre-wetting the second NaX molecular sieve particles to obtain third NaX molecular sieve particles; S4, contacting the third NaX molecular sieve particles with a NaX molecular sieve crystallization mother liquor to perform a crystal transformation treatment to obtain fourth NaX molecular sieve particles; S5, contacting the fourth NaX molecular sieve particles with an exchange solution containing a barium source and an optional potassium source to perform an ion exchange treatment to obtain fifth NaX molecular sieve particles and an ion exchange tail liquid; S6, performing an activation and dehydration treatment on the fifth NaX molecular sieve particles.

[0005] Optionally, in the NaX molecular sieve crystallization mother liquor, the concentration of NaOH is 15-160 g / L, the concentration of SiO2 is 6-20 g / L, and the concentration of KOH is 0-70 g / L.

[0006] Optionally, in step S1, the binder comprises kaolin and / or halloysite; The adjuvants include one or more of guar gum powder, starch and carboxymethyl cellulose; On a dry basis, relative to the total weight of the NaX molecular sieve and the binder, the amount of binder added is 5-20% by weight, and the amount of additives added is 0-6% by weight.

[0007] Optionally, in step S1, the silica-to-alumina ratio of the NaX molecular sieve is 2.0 to 2.7; The forming methods include ball forming and extrusion forming; The diameter of the first NaX molecular sieve particles is 0.2~1.5 mm.

[0008] Optionally, step S1 includes: mixing NaX molecular sieve, binder, optional additives and optional NaX molecular sieve fine powder and molding them to obtain the first NaX molecular sieve particles; The NaX molecular sieve fine powder includes NaX molecular sieve fine powder produced in one or more of steps S2, S3 and S4. On a dry basis, the amount of NaX molecular sieve fine powder added is 0-5% by weight relative to the total weight of the NaX molecular sieve and the binder. The diameter of the NaX molecular sieve fine powder is less than 0.3 mm.

[0009] Optionally, in step S2, the drying and calcining treatment is carried out at a temperature of 500~650℃ for 1~6 hours.

[0010] Optionally, step S3 includes: cooling the first exhaust gas to obtain cooled first exhaust gas; The cooled first tail gas is brought into contact with the second NaX molecular sieve particles to perform the pre-wetting, thereby obtaining the third NaX molecular sieve particles and the second tail gas. The pre-wetting time is 1 to 10 hours, and the gas-solid volume ratio of the cooled first tail gas to the second NaX molecular sieve particles is 500 to 5000. The water content of the third NaX molecular sieve particles is more than 20% by weight. The dew point of the second exhaust gas is below -20°C.

[0011] Optionally, the cooling includes: contacting the first exhaust gas with water at 0~40°C to obtain a cooled first exhaust gas; The temperature of the first exhaust gas after cooling is 20~50℃.

[0012] Optionally, in step S4, the conditions for the crystal transformation treatment include: a temperature of 85~150℃, a time of 1~4h, and a liquid-to-solid volume ratio of 2~10.

[0013] Optionally, in step S5, Ba in the exchange liquid 2+ The concentration is 0.1~1.0 mol / L, K + The concentration is 0~0.2mol / L; The ion exchange treatment is performed at a temperature of 55~99℃ for a time of 1~10h. The liquid-to-solid volume ratio of the exchange liquid to the fourth NaX molecular sieve particles is 5 to 40.

[0014] Optionally, step S6 includes: contacting the fifth NaX molecular sieve particles with an activation gas to perform the activation and dehydration treatment at a temperature of 200~300℃ for 0.5~2h, wherein the gas-to-solid volume ratio of the activation gas to the fifth NaX molecular sieve particles is 1000~4000. Optionally, the activating gas includes the second tail gas.

[0015] Through the above technical solution, the method disclosed herein uses the NaX molecular sieve crystallization mother liquor for the crystallization treatment step in the preparation of para-xylene adsorbent, eliminating the steps of preparing the crystallization solution and heating it. Without affecting the performance of the adsorbent, it reduces the discharge of waste liquid and the amount of raw materials used, and can save energy, producing para-xylene adsorbent with low energy consumption, low material consumption and low emissions.

[0016] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Detailed Implementation

[0017] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0018] This disclosure provides a method for preparing a p-xylene adsorbent, the method comprising the following steps: S1. Mix and shape the NaX molecular sieve, binder and optional additives to obtain the first NaX molecular sieve particles; S2. The first NaX molecular sieve particles are dried and calcined to obtain the second NaX molecular sieve particles and the first tail gas. S3. The second NaX molecular sieve particles are pre-wetted to obtain the third NaX molecular sieve particles. S4. The third NaX molecular sieve particles are brought into contact with the NaX molecular sieve crystallization mother liquor and subjected to crystallization treatment to obtain the fourth NaX molecular sieve particles. S5. The fourth NaX molecular sieve particles are contacted with an exchange solution containing a barium source and an optional potassium source to perform ion exchange treatment, thereby obtaining the fifth NaX molecular sieve particles and the ion exchange tail liquid. S6. The fifth NaX molecular sieve particles are activated and dehydrated.

[0019] The inventors of this disclosure unexpectedly discovered that the crystallization mother liquor of NaX molecular sieves can be directly used as a conversion liquid for preparing para-xylene adsorbents. The recycling of the crystallization mother liquor reduces waste liquid discharge during the molecular sieve synthesis process, eliminates the need for raw materials such as sodium hydroxide, water glass, and deionized water required for preparing the conversion liquid, saves the heat required for heating the conversion liquid, and does not affect the adsorption performance of the adsorbent.

[0020] Unless otherwise specified, pH in this disclosure refers to the test value under normal pressure at 25°C.

[0021] According to one embodiment of the present disclosure, the method for preparing p-xylene adsorbent further includes preparing NaX molecular sieve, using the prepared NaX molecular sieve in step S1, and using the crystallization mother liquor in step S4 as a crystallization solution; the method for preparing NaX molecular sieve is the conventional hydrothermal crystallization method in the art.

[0022] According to one embodiment of this disclosure, the NaX molecular sieve crystallization mother liquor can be derived from the crystallization step of preparing NaX molecular sieve. In the NaX molecular sieve crystallization mother liquor, the concentration of NaOH is 15~160 g / L, the concentration of SiO2 is 6~20 g / L, and the concentration of KOH is 0~70 g / L. The temperature of the NaX molecular sieve crystallization mother liquor is 80~99℃. The NaOH, SiO2, and KOH in the NaX molecular sieve crystallization mother liquor can be used as crystallization raw materials, realizing the full utilization of raw materials and heat, avoiding the discharge of waste liquid, and reducing the preparation cost of paraxylene adsorbent.

[0023] To ensure that the prepared adsorbent has good adsorption performance, according to one embodiment of this disclosure, the silicon-to-aluminum ratio of the NaX molecular sieve used in step S1 is 2.0 to 2.7. The silicon-to-aluminum ratio refers to the molar ratio of SiO2 to Al2O3. It can be commercially available or prepared using conventional methods in the art. The crystallization mother liquor generated during the preparation process is used for the crystallization treatment in step S4.

[0024] According to one embodiment of this disclosure, in step S1, the binder includes kaolin and / or halloysite; the additives include one or more of guar gum powder, starch and carboxymethyl cellulose; on a dry basis, relative to the total weight of the NaX molecular sieve and the binder, the amount of binder added is 5-20% by weight and the amount of additives added is 0-6% by weight.

[0025] According to one embodiment of this disclosure, in step S1, the forming method includes ball forming and extrusion forming, preferably ball forming. Ball forming can be carried out in a high-speed granulator, a sugar coating machine, a disc granulator, or other ball forming equipment. The mixed powder is placed into the ball forming equipment, and water is added to the material while it is rolling. At the same time, mixed powder is sprinkled into the material, causing the fine powder to agglomerate and become round, forming small granules.

[0026] According to one embodiment of this disclosure, the diameter of the NaX molecular sieve particles is 0.2~1.5 mm, preferably 0.30~0.80 mm.

[0027] According to one embodiment of this disclosure, step S1 includes: mixing and molding NaX molecular sieve, binder, optional additives and optional NaX molecular sieve fine powder to obtain the first NaX molecular sieve particles; the NaX molecular sieve fine powder includes one or more NaX molecular sieve fine powders generated in steps S2, S3 and S4; on a dry basis, the amount of NaX molecular sieve fine powder added is 0-5% by weight relative to the total weight of the NaX molecular sieve and the binder; the diameter of the NaX molecular sieve fine powder is less than 0.3 mm, preferably less than 0.2 mm; during the drying and calcination treatment, pre-wetting and crystallization treatment, particle friction and collision, liquid scouring, etc., will generate a certain amount of fine particles or powder. Direct emission of these substances will not only cause environmental burden but also increase material loss. This disclosure uses the above-mentioned fine powder for molding in step S1, which can avoid the environmental burden caused by its emission and reduce the preparation cost, while not affecting the performance of the adsorbent.

[0028] According to one embodiment of this disclosure, in step S2, the conditions for the drying and calcining treatment include: a temperature of 500~650℃ and a time of 1~6h. High-temperature calcination can transform the binder within the particles into a zeolite-forming precursor, i.e., a reactive amorphous aluminosilicate; it can also decompose the additives during calcination to form suitable pore structures within the particles, thereby improving the mass transfer performance of the adsorbent. The drying and calcining treatment can be carried out in a converter, mesh belt kiln, or roller kiln. For example, the drying and calcining treatment in a mesh belt kiln includes: feeding the third NaX molecular sieve particles from the kiln head of the mesh belt kiln; the mesh belt kiln consists of a low-temperature heating section, a high-temperature isothermal section, and a cooling section from the kiln head to the kiln tail; the temperature of the high-temperature isothermal section is 520~560℃; and the exhaust gas from the cooling section is fed into the heating section, which is the first exhaust gas.

[0029] According to one embodiment of this disclosure, step S3 includes: cooling the first tail gas to obtain a cooled first tail gas; contacting the cooled first tail gas with the second NaX molecular sieve particles to perform the pre-wetting, thereby obtaining the third NaX molecular sieve particles and the second tail gas; the pre-wetting time is 1~10h; the gas-solid volume ratio of the cooled first tail gas to the second NaX molecular sieve particles is 500~5000; the water content of the third NaX molecular sieve particles is 20% by weight or more; and the dew point of the second tail gas is below -20℃.

[0030] According to one embodiment of this disclosure, cooling includes: contacting the first tail gas with water at 0-40°C to obtain a cooled first tail gas; the temperature of the cooled first tail gas is 20-50°C. The above steps can recover the heat from the first tail gas obtained after drying and calcination, transferring it to cold water. The cooled first tail gas has a lower temperature and carries more water vapor, which comes into contact with the second NaX molecular sieve particles for pre-wetting. This prevents the NaX molecular sieve particles from violently exothermizing and exploding upon contact with water during subsequent crystallization, thus achieving heat recovery, saving on utility costs, and reducing production energy consumption.

[0031] According to one embodiment of this disclosure, in step S4, the conditions for the crystal transformation treatment include: a temperature of 85~150℃, preferably 90~99℃, a time of 1~4h, and a liquid-to-solid volume ratio of 2~10. The crystal transformation treatment can be carried out in a batch vessel or a column vessel.

[0032] According to one embodiment of this disclosure, the method further includes: after the crystallization treatment is completed, solid-liquid separation is performed to obtain crystallization mother liquor and fourth NaX molecular sieve particles, and the fourth NaX molecular sieve particles are washed with deionized water until the pH of the filtrate is less than 10. After the crystallization mother liquor and the washing liquid are filtered and the NaX molecular sieve fine powder is collected, it is contacted with the ion exchange tail liquid. The NaX molecular sieve fine powder can be used for molding in step S1.

[0033] According to one embodiment of this disclosure, in step S5, the ion exchange treatment can be carried out in a batch vessel or a column vessel, preferably in a continuous manner in an exchange column. In the exchange solution, Ba... 2+ The concentration is 0.1~1.0 mol / L, K + The concentration of the ion exchange solution is 0~0.2 mol / L; the barium source includes BaCl2 and / or Ba(NO3)2; the potassium source includes KCl and / or KNO3; the ion exchange treatment temperature is 55~99℃, the time is 1~10h, and the liquid-to-solid volume ratio of the exchange solution to the fourth NaX molecular sieve particles is 5~40; the BaCl2 concentration of the fifth NaX molecular sieve particles .... 2+ Ions and K +The total ion exchange rate is 97-100%. After ion exchange treatment, at least some of the NaX molecular sieve particles are converted into BaX molecular sieve particles and optionally BaKX molecular sieve particles. After the ion exchange treatment, the molecular sieve particles are washed with deionized water. The washing liquid can be recycled for preparing the exchange solution, making full use of BaX. 2+ and K + The ion exchange tailings are contacted with the filtered crystallization mother liquor and washing solution obtained in step S4 to form BaSiO3 precipitate, and the Ba is recovered from it. 2+ This reduces waste liquid discharge.

[0034] According to one embodiment of this disclosure, step S6 includes: contacting the fifth NaX molecular sieve particles with an activation gas to perform the activation and dehydration treatment; the activation and dehydration treatment is carried out in a vibrating fluidized bed or a converter at a temperature of 200~300℃ for a time of 0.5~2h, and the gas-solid volume ratio of the activation gas to the fifth NaX molecular sieve particles is 1000~4000.

[0035] To fully utilize the system's heat and save energy, according to one embodiment of this disclosure, the activation gas includes the second tail gas; preferably, the activation gas is entirely the second tail gas. The third tail gas generated from the activation and dehydration treatment can be used for flash drying in the preparation of NaX molecular sieves.

[0036] The present invention will be described in detail below through embodiments, but is not limited to the following embodiments.

[0037] In the following embodiments and comparative examples: The method for determining the toluene adsorption capacity is as follows: Take 1g of sample and activate it at 500℃ for 2h. Cool it to room temperature in a desiccator. The net weight of the sample is M0. Then, saturate the sample with a mixture of nitrogen and toluene vapor at 35℃. The total pressure of the mixed gas is 0.1MPa, and the partial pressure of toluene vapor is 0.5 times the saturated vapor pressure of toluene at this temperature. The net weight of the sample after adsorption saturation is M1. Then, the toluene adsorption capacity of the sample (mg / g) = 1000×(M1-M0) / M0.

[0038] Mechanical strength is characterized by the compressive breakage rate of the small balls. The test method is as follows: Take an appropriate amount of adsorbent with constant weight in air, weigh it, and put it into a stainless steel cylinder with a closed bottom. Place a cylindrical pin that matches the stainless steel cylinder on top of the adsorbent, and then place it on a particle strength tester to pressurize the pin to 250N. After depressurization, take out the adsorbent, and sieve it with a 0.3mm mesh. Weigh the small balls that do not pass through the mesh. The percentage of the weight reduction compared to the weight of the sample before pressurization is the compressive breakage rate of the tested sample.

[0039] The weight percentages of SiO2 and Al2O3 in the sample were analyzed by X-ray fluorescence spectrometry (XRF), and the molar ratio of SiO2 to Al2O3 was calculated based on their molar masses.

[0040] In the examples, the weights of NaX molecular sieve, recovered NaX fine powder, and kaolin refer to their weight on ignition. The loss on ignition test conditions were calcination at 600°C for 2 hours. According to this method, the weight of NaX molecular sieve on ignition was 78% by weight, and the weight of kaolin on ignition was 72% by weight.

[0041] The testing methods for other parameters are standard practices in this field.

[0042] Example 1 (1) Synthesis of NaX molecular sieve Add 370 kg of sodium hydroxide (analytical grade), 10010 kg of water, and 2550 kg of sodium silicate (Na₂O 0.088 g / g, SiO₂ 0.281 g / g) to the reactor and stir until a clear and transparent solution is obtained. While stirring at high speed, add 2270 kg of sodium aluminate solution (Na₂O) to the reactor. A gel was formed from 0.22 g / g NaOH and 0.181 g / g Al2O3. The gel was aged at 70℃ for 12 h and then crystallized at 95℃ for 6 h. The gel was filtered using a belt filter to obtain a molecular sieve filter cake and 13274 kg of crystallization mother liquor A (NaOH concentration of 71.0 g / L, SiO2 concentration of 9.3 g / L, and temperature of NaX molecular sieve crystallization mother liquor A of 90℃). The molecular sieve filter cake was pulped and sent to a flash dryer to obtain NaX molecular sieve powder with a loss on ignition of 22% by weight, a toluene adsorption capacity of 235 mg / g, and a molar ratio of SiO2 to Al2O3 of 2.5. (2) Ball forming Take 900 kg of the above NaX molecular sieve powder, 100 kg of kaolin, and 20 kg of guar powder and mix them evenly. Then roll them into balls in a sugar coating pan and sieve to obtain 700 kg (dry basis) of the first NaX molecular sieve particles with a diameter of 0.3~0.8 mm. The toluene adsorption capacity is 212 mg / g. On a dry basis, the amount of kaolin added is 10% by weight and the amount of guar powder added is 2% by weight relative to the total weight of NaX molecular sieve and guar powder.

[0043] (3) Drying and roasting treatment The first NaX molecular sieve granules are fed into a mesh belt kiln for drying and calcination. The kiln consists of a low-temperature heating section, a high-temperature calcination section, and a cooling section, arranged sequentially from the kiln head to the kiln tail. The temperature in the low-temperature heating section is 30–520°C, the high-temperature calcination section is 520°C, and the cooling section is 520–60°C. The feed rate of the first NaX molecular sieve granules is 0.3 t (dry basis) per hour. The high-temperature calcination time is 2 hours. The exhaust gas from the cooling section is fed into the heating section. The exhaust gas from the heating section is then cooled by contacting cold water at 30°C, resulting in cooled exhaust gas (at 40°C) and warm water at 60°C.

[0044] The sieve yielded NaX molecular sieve fine powder A with a diameter less than 0.3 mm and second NaX molecular sieve particles with a diameter greater than 0.3 mm. The water content was 3% by weight, the crushing rate at 250 N was 20% by weight, and the toluene adsorption capacity was 210 mg / g.

[0045] (4) Pre-wetting The second NaX molecular sieve granules are brought into contact with the cooled first tail gas obtained in step (3) for pre-wetting for 2 hours to obtain the third NaX molecular sieve granules (with a water content of 20% by weight) and NaX molecular sieve fine powder B with a diameter of less than 0.3 mm, as well as the second tail gas (with a dew point of -20℃). The gas-solid volume ratio of the cooled first tail gas to the second NaX molecular sieve particles is 2000:1.

[0046] (5) Crystal transformation treatment The crystallization mother liquor A was contacted with the third NaX molecular sieve particles (dry basis) at 90℃ for 3 hours with a liquid-to-solid volume ratio of 2:1. Then, solid-liquid separation was performed, and the solid particles were washed with warm water until the pH was below 10 to obtain the fourth NaX molecular sieve particles with a toluene adsorption capacity of 232 mg / g.

[0047] The mother liquor from the crystallization process and the washing liquid were filtered to obtain fine NaX molecular sieve powder C with a diameter of less than 0.3 mm and the filtrate.

[0048] (6) Ion exchange treatment 700 kg (dry basis) of fourth NaX molecular sieve particles were packed into a 1 m³ volume. 3 The exchange column was used, and 0.2 mol / L BaCl2 solution was injected from the bottom of the column as the exchange liquid. The liquid-to-solid volume ratio was 20:1, the temperature was 90℃, and the time was 5 h. The obtained spheres were washed with warm water, and the washing liquid was recovered and used to prepare BaCl2 solution, yielding fifth NaX molecular sieve spheres and ion exchange tailings.

[0049] (7) Activation and dehydration treatment The fifth NaX molecular sieve granules were fed into a vibrating fluidized bed. The second tail gas was heated to 270°C and sent to the bottom front section of the fluidized bed for drying for 1 hour. The gas-solid volume ratio of the second tail gas to the fifth NaX molecular sieve granules was 1000:1. The tail end of the fluidized bed was cooled by induced draft air to obtain paraxylene adsorbent with a loss on ignition of 5% by weight and a toluene adsorption capacity of 185 mg / g, as well as a third tail gas at 150°C.

[0050] (8) The filtered liquid obtained in step (5) is contacted with the ion exchange tail liquid to form BaSiO3 precipitate, and Ba is recovered. 2+ .

[0051] Example 2 (1) Synthesis of NaX molecular sieve NaX molecular sieves were prepared using the method described in Example 1, except that the third tail gas obtained in step (7) of Example 1 was used for flash drying. The loss on ignition of the NaX molecular sieve was 23% by weight, the toluene adsorption capacity was 235 mg / g, and the molar ratio of SiO2 to Al2O3 was 2.5.

[0052] (2) Ball forming The NaX molecular sieve fine powder A obtained in step (3) of Example 1, the NaX molecular sieve fine powder B obtained in step (4) and the NaX molecular sieve fine powder C obtained in step (5) are ground to fine powder with a diameter of less than 0.1 mm. 50 kg of the ground fine powder, 900 kg of NaX molecular sieve prepared in step (1), 50 kg of kaolin, and 10 kg of guar gum powder are mixed evenly and then rolled into balls in a sugar coating pan. 700 kg of the first NaX molecular sieve particles with a diameter of 0.3~0.8 mm (dry basis) are obtained by sieving. The toluene adsorption capacity is 218 mg / g. On a dry basis, relative to the total weight of NaX molecular sieve and kaolin, the amount of kaolin added is 5% by weight, the amount of guar gum powder added is 1% by weight, and the amount of fine powder added is 5% by weight.

[0053] (3) Drying and roasting treatment The method was carried out according to step (3) of Example 1, except that the temperature of the high-temperature calcination section was 560°C, the water content of the second NaX molecular sieve particles was 2.4 wt%, the crushing rate of 250N was 18 wt%, and the toluene adsorption capacity was 216 mg / g.

[0054] (4) Pre-wetting The method of step (4) in Example 1 was followed, and the water content of the third NaX molecular sieve particles was 20.8% by weight, and the dew point of the second tail gas was -22°C.

[0055] (5) Crystal transformation treatment The crystallization mother liquor A was contacted with the third NaX molecular sieve particles (dry basis) at 95℃ for 4 hours with a liquid-to-solid volume ratio of 5:1. Then, solid-liquid separation was performed, and the solid particles were washed with warm water until the pH was below 10 to obtain the fourth NaX molecular sieve particles with a toluene adsorption capacity of 233 mg / g.

[0056] (6) Ion exchange treatment Following the method in step (6) of Example 1, the fifth NaX molecular sieve particles were obtained.

[0057] (7) Activation and dehydration treatment Following the method of step (7) in Example 1, a paraxylene adsorbent was obtained, with a 5% weight loss on ignition, a toluene adsorption capacity of 188 mg / g, and a third tail gas at 130°C.

[0058] (8) The filtered liquid obtained in step (5) is contacted with the ion exchange tail liquid to form BaSiO3 precipitate, and Ba is recovered. 2+ .

[0059] Example 3 (1) Synthesis of NaX molecular sieve Add 700 kg of sodium hydroxide (analytical grade), 710 kg of potassium hydroxide (analytical grade), 6120 kg of water, and 1890 kg of sodium silicate (Na₂O 0.088 g / g, SiO₂ 0.281 g / g) to the reactor and stir until a clear and transparent solution is obtained. While stirring at high speed, add 2270 kg of sodium aluminate solution (Na₂O) to the reactor. A gel was formed by adding 0.22 g / g of NaX molecular sieve and 0.181 g / g of Al2O3. The gel was aged at 70°C for 3 hours and then crystallized at 95°C for 6 hours. The gel was filtered using a belt filter to obtain a molecular sieve filter cake and 9349 kg of crystallization mother liquor B (NaOH concentration of 134.0 g / L, KOH concentration of 56.0 g / L, SiO2 concentration of 6.3 g / L, and temperature of NaX molecular sieve crystallization mother liquor B of 92°C). The molecular sieve filter cake was slurried and sent to a flash dryer. The third tail gas obtained in step (7) of Example 2 was used for flash drying. The loss on ignition of NaX molecular sieve was 22% by weight, the toluene adsorption capacity was 234 mg / g, and the molar ratio of SiO2 to Al2O3 was 2.0.

[0060] (2) Ball forming The NaX molecular sieve fine powder B obtained in step (3) of Example 2, the NaX molecular sieve fine powder B obtained in step (4) and the NaX molecular sieve fine powder C obtained in step (5) are ground to fine powder with a diameter of less than 0.1 mm. 40 kg of fine powder, 810 kg of NaX molecular sieve prepared in step (1), 150 kg of kaolin, and 40 kg of guar powder are mixed evenly and then rolled into balls in a sugar coating pot. 700 kg of the first NaX molecular sieve particles with a diameter of 0.3~0.8 mm (dry basis) are obtained by sieving. The toluene adsorption capacity is 200 mg / g. On a dry basis, relative to the total weight of NaX molecular sieve and kaolin, the amount of kaolin added is 16% by weight, the amount of guar gum powder added is 4% by weight, and the amount of fine powder added is 4% by weight.

[0061] (3) Drying and roasting treatment The method of step (3) in Example 1 was followed. The water content of the second NaX molecular sieve particles was 2.2% by weight, the crushing rate of 250N was 16% by weight, and the toluene adsorption capacity was 198 mg / g.

[0062] (4) Pre-wetting The method of step (4) in Example 1 was followed, and the water content of the third NaX molecular sieve particles was 20.2% by weight, and the dew point of the second tail gas was -23°C.

[0063] (5) Crystal transformation treatment The crystallization mother liquor A was contacted with the third NaX molecular sieve particles (dry basis) at 92℃ for 3 hours with a liquid-to-solid volume ratio of 10:1. Then, solid-liquid separation was performed, and the solid particles were washed with warm water until the pH was below 10 to obtain the fourth NaX molecular sieve particles with a toluene adsorption capacity of 232 mg / g.

[0064] (6) Ion exchange treatment Following the method in step (6) of Example 1, the fifth NaX molecular sieve particles were obtained.

[0065] (7) Activation and dehydration treatment Following the method of step (7) in Example 1, a para-xylene adsorbent with a loss on ignition of 4.8% by weight and a toluene adsorption capacity of 186 mg / g was obtained, along with a third tail gas at 140°C.

[0066] (8) The filtered liquid obtained in step (5) is contacted with the ion exchange tail liquid to form BaSiO3 precipitate, and Ba is recovered. 2+ .

[0067] Example 4 (1) Synthesis of NaX molecular sieve NaX molecular sieves were prepared using the method described in Example 3, except that the third tail gas obtained in step (7) of Example 3 was used for flash drying. The loss on ignition of the NaX molecular sieve was 23% by weight, the toluene adsorption capacity was 234 mg / g, and the molar ratio of SiO2 to Al2O3 was 2.0.

[0068] (2) Ball forming The NaX molecular sieve fine powder B obtained in step (3) of Example 3, the NaX molecular sieve fine powder B obtained in step (4) and the NaX molecular sieve fine powder C obtained in step (5) are ground to fine powder with a diameter of less than 0.1 mm. 40 kg of fine powder, 900 kg of NaX molecular sieve prepared in step (1) and 60 kg of kaolin are mixed evenly, and then rolled into balls in a sugar coating pot. 700 kg of the first NaX molecular sieve particles with a diameter of 0.3~0.8 mm (dry basis) are obtained by sieving. The toluene adsorption capacity is 220 mg / g. On a dry basis, the amount of kaolin added is 6% by weight and the amount of fine powder added is 4% by weight relative to the total weight of NaX molecular sieve and kaolin.

[0069] (3) Drying and roasting treatment The method of step (3) in Example 3 was followed, and the water content of the second NaX molecular sieve particles was 2.8% by weight, the crushing rate of 250N was 21% by weight, and the toluene adsorption capacity was 218 mg / g.

[0070] (4) Pre-wetting The method of step (4) in Example 3 was followed, and the water content of the third NaX molecular sieve particles was 22.0% by weight, and the dew point of the second tail gas was -23°C.

[0071] (5) Crystal transformation treatment Following the method of step (5) in Example 3, the toluene adsorption capacity of the fourth NaX molecular sieve particles was 233 mg / g.

[0072] (6) Ion exchange treatment Following the method in step (6) of Example 3, the fifth NaX molecular sieve particles were obtained.

[0073] (7) Activation and dehydration treatment Following the method of step (7) in Example 3, a para-xylene adsorbent with a loss on ignition of 4.6% by weight and a toluene adsorption capacity of 186 mg / g was obtained, along with a third tail gas at 155°C.

[0074] (8) The filtered liquid obtained in step (5) is contacted with the ion exchange tail liquid to form BaSiO3 precipitate, and Ba is recovered. 2+ .

[0075] Comparative Example 1 (1) Synthesis of NaX molecular sieve NaX molecular sieves were prepared using the method of Example 1, with a loss on ignition of 22% by weight, a toluene adsorption capacity of 235 mg / g, and a molar ratio of SiO2 to Al2O3 of 2.5. (2) Ball forming The spheroidization was carried out according to the method of step (2) in Example 1, and 700 kg (dry basis) of the first NaX molecular sieve particles with a diameter of 0.3~0.8 mm were obtained by sieving. The toluene adsorption capacity was 212 mg / g.

[0076] (3) Drying and roasting treatment The first NaX molecular sieve granules are fed into a mesh belt kiln for drying and calcination. The kiln consists of a low-temperature heating section, a high-temperature calcination section, and a cooling section, arranged sequentially from the kiln head to the kiln tail. The temperature in the low-temperature heating section is 30–540°C, the high-temperature calcination section is 540°C, and the cooling section is 540–60°C. The feed rate of the first NaX molecular sieve granules is 0.3 t (dry basis) per hour, and the high-temperature calcination time is 2 hours.

[0077] The second NaX molecular sieve particles with a diameter of 0.3 mm or more were obtained by sieving, with a water content of 2.7 wt%, a crushing rate of 19 wt% at 250 N, and a toluene adsorption capacity of 210 mg / g.

[0078] (4) Pre-wetting The second NaX molecular sieve granules were pre-wetted in a water tank with a volume ratio of 20 to water to obtain the third NaX molecular sieve granules (with a water content of 45% by weight).

[0079] (5) Crystal transformation treatment A crystallization solution was prepared using NaOH and sodium silicate (NaOH concentration 71.0 g / L, SiO2 concentration 9.3 g / L). The crystallization solution was then contacted with third NaX molecular sieve particles (dry basis) at a liquid-to-solid volume ratio of 5:1, a temperature of 95℃, and a time of 4 h. Solid-liquid separation was then performed, and the solid particles were washed with warm water until the pH was below 10 to obtain fourth NaX molecular sieve particles with a toluene adsorption capacity of 232 mg / g.

[0080] (6) Ion exchange treatment Following step (6) of Example 1, the fourth NaX molecular sieve particles were subjected to ion exchange to obtain the fifth NaX molecular sieve particles.

[0081] (7) Activation and dehydration treatment The fifth NaX molecular sieve granules were fed into a vibrating fluidized bed. Air with a dew point of -23°C was heated to 270°C and fed into the bottom front section of the fluidized bed for drying for 1 hour. The gas-solid volume ratio of the second tail gas to the fifth NaX molecular sieve granules was 1000:1. The tail section of the fluidized bed was cooled by induced draft air to obtain paraxylene adsorbent. The loss on ignition was 5% by weight, and the toluene adsorption capacity was 185 mg / g.

[0082] As can be seen from the above, the method disclosed herein can improve the utilization rate of raw materials and energy while maintaining the adsorption performance of the p-xylene adsorbent.

[0083] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0084] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0085] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A process for preparing a p-xylene adsorbent, characterized in that, The method comprises the following steps: S1, mixing and shaping NaX molecular sieve, binder and optional additives to obtain first NaX molecular sieve particles; S2, drying and calcining the first NaX molecular sieve particles to obtain second NaX molecular sieve particles and first tail gas; S3, pre-wetting the second NaX molecular sieve particles to obtain third NaX molecular sieve particles; S4, contacting the third NaX molecular sieve particles with a NaX molecular sieve crystallization mother liquor to perform a crystal transformation treatment to obtain fourth NaX molecular sieve particles; S5, contacting the fourth NaX molecular sieve particles with an exchange solution containing a barium source and an optional potassium source to perform an ion exchange treatment to obtain fifth NaX molecular sieve particles and ion exchange tail liquid; S6, activating and dehydrating the fifth NaX molecular sieve particles.

2. The method of claim 1, wherein, In the NaX molecular sieve crystallization mother liquor, the concentration of NaOH is 15-160 g / L, the concentration of SiO2 is 6-20 g / L, and the concentration of KOH is 0-70 g / L.

3. The method of claim 1, wherein, In step S1, the binder comprises kaolin and / or halloysite; The additives comprise one or more of amaranth powder, starch and carboxymethyl cellulose; The amount of the binder added is 5-20% by weight based on the total weight of the NaX molecular sieve and the binder, and the amount of the additives added is 0-6% by weight.

4. The method of claim 1, wherein, In step S1, the Si / Al ratio of the NaX molecular sieve is 2.0-2.7; The shaping method comprises ball rolling and extrusion; The diameter of the first NaX molecular sieve particles is 0.2-1.5 mm.

5. The method of claim 1, wherein, In step S1, the NaX molecular sieve, the binder, the optional additives and the optional NaX molecular sieve fine powder are mixed and shaped to obtain the first NaX molecular sieve particles; The NaX molecular sieve fine powder comprises the NaX molecular sieve fine powder produced in one or more of steps S2, S3 and S4; The amount of the NaX molecular sieve fine powder added is 0-5% by weight based on the total weight of the NaX molecular sieve and the binder; The diameter of the NaX molecular sieve fine powder is less than 0.3 mm.

6. The method of claim 1, wherein, In step S2, the drying and calcining treatment is performed at a temperature of 500-650°C for 1-6 h.

7. The method of claim 1, wherein, In step S3, the first tail gas is cooled to obtain cooled first tail gas; The cooled first tail gas is contacted with the second NaX molecular sieve particles to perform the pre-wetting to obtain the third NaX molecular sieve particles and second tail gas; The pre-wetting is performed for 1-10 h, and the gas-solid volume ratio of the cooled first tail gas to the second NaX molecular sieve particles is 500-5000; The water content of the third NaX molecular sieve particles is 20% by weight or more; The dew point of the second tail gas is -20°C or lower.

8. The method of claim 7, wherein, The cooling comprises contacting the first tail gas with water at 0-40°C to obtain cooled first tail gas; The temperature of the cooled first tail gas is 20-50°C.

9. The method of claim 1, wherein, In step S4, the conditions of the crystal transformation treatment comprise a temperature of 85-150°C, a time of 1-4 h, and a liquid-solid volume ratio of 2-10.

10. The method of claim 1, wherein, In step S5, the concentration of Ba 2+ in the exchange solution is 0.1-1.0 mol / L, and the concentration of K + is 0-0.2 mol / L. The ion exchange treatment is performed at a temperature of 55-99℃ for 1-10 hours; The liquid-solid volume ratio of the exchange liquid to the fourth NaX molecular sieve particles is 5-40.

11. The method of claim 7, wherein, The step S6 comprises: contacting the fifth NaX molecular sieve particles with an activating gas to perform the activating dehydration treatment, at a temperature of 200-300℃ for 0.5-2 hours, and the gas-solid volume ratio of the activating gas to the fifth NaX molecular sieve particles is 1000-4000. Optionally, the activating gas comprises the second tail gas.