Adsorbent for adsorbing n-alkanes from hydrocarbon mixture and preparation method thereof

Abstract

The invention provides an adsorbent for adsorbing n-alkanes from a hydrocarbon mixture and a preparation method of the adsorbent. The invention relates to an adsorbent for adsorbing n-alkanes from a hydrocarbon mixture. The adsorbent comprises the following components in percentage by weight: 85-95% of a high-silicon 5A molecular sieve, 5-15% of a binder, 1-5% of a pore structure modifier and 0.1-2% of a lubricant, wherein the molecular silicon-aluminum ratio of the high-silicon 5A molecular sieve is 3-5. The adsorbent provided by the invention has a high silica-alumina ratio and stronger repellency to polar isoparaffin and aromatic hydrocarbon, the obtained n-alkane has higher purity, and the high silica-alumina ratio has good high-temperature hydrothermal stability and high regeneration times.

Description

Technical Field

[0001] The invention relates to the field of adsorption separation, and in particular to an adsorbent for adsorbing normal alkanes from a hydrocarbon mixture and a preparation method thereof. Background Art

[0002] Separating normal alkanes from various petroleum products has important practical and economic value. For example, kerosene fractions, gasoline fractions and light diesel fractions containing normal alkanes are separated from isoalkanes, cycloalkanes and aromatic hydrocarbons by molecular sieve adsorbents to obtain high-purity normal alkanes, which can be used as raw materials, solvents for synthetic detergents and raw materials for sodium alkyl sulfonates.

[0003] The molecular sieve adsorbent is used for separation because the minimum cross-sectional diameter of normal alkanes is approximately The cross-sectional diameters of isoalkanes, cycloalkanes, and aromatic hydrocarbons are larger than Therefore, the aperture is The 5A molecular sieve only adsorbs normal alkanes, while isoalkanes, cycloalkanes and aromatic hydrocarbons are excluded from the micropores. When the molecular sieve reaches a certain adsorption capacity, the adsorbed normal alkanes can be desorbed by appropriate desorption methods, and the molecular sieve can continue to be used after desorption.

[0004] Chinese patent CN103170304B discloses a method for preparing 5A molecular sieve for adsorption of straight-chain alkanes using attapulgite. The method calcined and acid-treated attapulgite, and then crystallized under certain conditions to obtain 4A molecular sieve powder, and then calcium ion exchange was performed to obtain 5A molecular sieve. Although the 5A molecular sieve has a certain static saturated adsorption capacity (up to 0.072g / g and 0.123g / g, respectively) for n-decane and n-pentadecane, in actual application scenarios, in order to meet the pressure drop index of the adsorption tower, a certain amount of binder must be added to shape it, and the addition of a binder often reduces the adsorption capacity of the molecular sieve. Therefore, domestic and foreign experts have carried out a lot of research on improving the adsorption capacity of molecular sieves.

[0005] For example, Chinese patent CN111111609B discloses a 5A molecular sieve adsorbent and its preparation method and application. The 5A molecular sieve adsorbent first molds, dries and roasts the powder containing 4A molecular sieve and binder source to obtain matrix beads, and then converts the binder in the matrix beads into 4A molecular sieve under certain crystallization conditions to obtain 4A molecular sieve beads, and then washes the 4A molecular sieve beads with water and calcium exchanges to obtain 5A molecular sieve beads, and finally roasts the 5A molecular sieve beads to obtain the desired adsorbent, and the adsorbent obtained has the advantage of large adsorption of liquid wax (especially n-tetradecane). For another example, Chinese patent CN106861614A discloses a 5A molecular sieve adsorbent containing normal alkane distillate oil for adsorption and separation and its preparation method. The preparation method uses polyquaternary ammonium salt as a soft template for crystallization synthesis, and hydrothermally synthesizes a multi-level pore 4A molecular sieve with a microporous-mesoporous structure; after removing the soft template from the 4A molecular sieve, it is molded with a binder, and after drying and calcining, calcium ion exchange and activation are performed to obtain a 5A molecular sieve adsorbent with a microporous-mesoporous structure; the 5A molecular sieve synthesized by this method has multi-level pores, which improves the rate of adsorption and separation. However, the above patents usually use water vapor displacement desorption. Under this process, the service life of the adsorbent is only 4-6 months, which is far less than the normal service life of 3-5 years. The main reason is that water vapor damages the molecular sieve structure. None of the above patents have proposed an effective solution to this problem. Summary of the invention

[0006] The present invention aims at the problem of poor hydrothermal stability in the prior art and provides an adsorbent for adsorbing normal alkanes from a hydrocarbon mixture and a preparation method thereof.

[0007] The technical method of the present invention is as follows:

[0008] An adsorbent for adsorbing normal alkanes from a hydrocarbon mixture comprises, based on the total amount of the adsorbent, 85-95wt% of high-silicon 5A molecular sieve, 5-15wt% of a binder, 1-5wt% of a pore structure modifier and 0.1-2wt% of a lubricant; wherein the molecular silicon-to-aluminum ratio of the high-silicon 5A molecular sieve is 3-5.

[0009] The high-silicon 5A molecular sieve of the present invention is obtained by preparing a high-silicon 4A molecular sieve from a silicon source and an aluminum source and then undergoing calcium exchange for more than two times, and the calcium exchange degree is greater than 75%.

[0010] The binder of the present invention is a hydrophobic silica material; wherein the hydrophobic silica material includes hydrophobic colloidal silica and / or hydrophobic fumed silica.

[0011] The pore structure modifier of the present invention is an organic polymer; wherein the organic polymer includes one or more of polyvinyl alcohol, polyacrylic acid and polyacrylamide.

[0012] The lubricant of the present invention comprises one or more of sesbania powder, graphite and starch.

[0013] The present invention also provides a method for preparing an adsorbent for adsorbing normal alkanes from a hydrocarbon mixture, comprising: mixing high-silicon 5A molecular sieve, a binder, a pore structure modifier and a lubricant, drying and roasting to obtain the adsorbent for adsorbing normal alkanes from a hydrocarbon mixture.

[0014] The preparation steps of the high silicon 5A molecular sieve of the present invention include: S1, mixing an aluminum source, a template agent and a silicon source, aging, adding a mixture of tetramethylammonium chloride and sodium chloride, mixing, crystallizing, filtering, washing, drying and roasting to obtain a high silicon 4A molecular sieve raw powder; S2, treating the high silicon 4A molecular sieve raw powder with Ca 2+ The aqueous solution is subjected to ion exchange, filtration, washing, drying and roasting to obtain a high-silicon 5A molecular sieve with a calcium exchange degree greater than 75%, wherein the number of ion exchanges is ≥2 times.

[0015] In the above step S1, the silicon source is colloidal silica, the aluminum source is aluminum isopropoxide, and the template agent is tetraethylammonium hydroxide and dimethyldiethylammonium hydroxide. The crystallization temperature is 95-105°C, and the crystallization time is 10-15 days. The drying temperature is 80-110°C, and the drying time is 10-14h. The calcination temperature is 500-600°C, and the calcination time is 1-3h.

[0016] In the above step S2, the ion exchange temperature is 60-95°C and the ion exchange time is 2-10h. The drying temperature is 80-110°C and the drying time is 10-14h. The calcination temperature is 500-600°C and the calcination time is 1-3h. 2+ The aqueous solution is calcium chloride, calcium nitrate, calcium acetate or calcium formate solution, preferably calcium chloride solution, and the concentration of the calcium chloride solution is 0.2-0.8 mol / L.

[0017] The preparation steps of the adhesive of the present invention include: stirring and drying a hydrophobic agent and hydrophilic silicon dioxide to obtain the adhesive.

[0018] The beneficial effects of the present invention are:

[0019] 1. The adsorbent of the present invention has a high silicon-aluminum ratio, has a stronger repulsion to polar isoalkanes and aromatic hydrocarbons, and the obtained normal alkanes have a higher purity. The high silicon-aluminum ratio has good high-temperature hydrothermal stability and a high number of regeneration times.

[0020] 2. The adsorbent of the present invention has a high silicon-aluminum ratio and a high cation exchange degree, which can further improve the effective adsorption performance of normal alkanes with a minimum cross-sectional diameter of about 5 angstroms, while not adsorbing isoalkanes and aromatic hydrocarbons with a diameter greater than 5 angstroms and polarity.

[0021] III. The present invention uses hydrophobic silica as a binder, avoiding carbon polymerization at the acidic sites on the binder due to the high metal content of conventional binders, which produces undesirable oligomers and polymers (e.g., green oil and coke).

[0022] IV. The present invention adds an organic pore former, which not only increases the macropore content of the adsorbent, enabling the n-alkanes to be adsorbed more quickly, but also improves the strength of the adsorbent, resulting in a lower pressure drop during use.

[0023] V. The specific surface area of the adsorbent of the present invention is > 620 m 2 / g, the mesoporous specific surface area is > 120 m 2 / g, the average compressive strength is greater than 40 N. When used to adsorb n-alkanes in a hydrocarbon mixture, the purity of the obtained n-alkanes is greater than 98%, the contents of isoalkanes and aromatic compounds are both less than 0.5%, and the service life of the adsorbent is greater than 2 years. Detailed Embodiments

[0024] The technical solutions of the present invention will be described clearly and completely below. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the scope of protection of the present invention.

[0025] The present invention provides an adsorbent for adsorbing n-alkanes from a hydrocarbon mixture, and the composition by weight of the total amount of the adsorbent contains: 85 - 95 wt% of high-silica 5A molecular sieve, 5 - 15 wt% of binder, 1 - 5 wt% of pore structure modifier, and 0.1 - 2 wt% of lubricant; wherein, the silicon-aluminum ratio of the high-silica 5A molecular sieve is 3 - 5.

[0026] For example, the high-silica 5A molecular sieve of the present invention is preferably 88 - 92 wt%. The binder of the present invention can be preferably 8 - 12 wt%. The pore structure modifier can be 2 wt%, 4 wt%. The lubricant can be 0.5 wt%, 1.1 wt%, 1.5 wt%.

[0027] The adsorbent of the present invention has a high silicon-aluminum ratio, has stronger repellency to polar isoalkanes and aromatic hydrocarbons, obtains a higher purity of n-alkanes, and the high silicon-aluminum ratio has good high-temperature hydrothermal stability and a high regeneration times.

[0028] Specifically, the high-silicon 5A molecular sieve is obtained by preparing a high-silicon 4A molecular sieve from a silicon source and an aluminum source, and then undergoing calcium exchange for more than two times, and the calcium exchange degree is greater than 75%. The adsorbent of the present invention has a high silicon-aluminum ratio and a high cation exchange degree, and can further improve the effective adsorption performance of normal alkanes with a minimum cross-sectional diameter of about 5 angstroms, while not adsorbing isoalkanes and aromatic hydrocarbons with a diameter greater than 5 angstroms and polarity.

[0029] Specifically, the binder is a hydrophobic silica material; wherein the hydrophobic silica material includes hydrophobic colloidal silica and / or hydrophobic fumed silica.

[0030] Compared with the prior art, conventional binders such as kaolin, montmorillonite or bentonite cannot enhance the adsorption capacity of molecular sieves, and in fact usually reduce the adsorption capacity of molecular sieves and lead to the production of undesirable oligomers and polymers (green oil and coke). The present invention uses hydrophobic silica as a binder, avoiding the carbon polymerization at the acidic sites on the binder due to the high metal content of conventional binders, resulting in the production of undesirable oligomers and polymers (e.g., green oil and coke).

[0031] Specifically, the pore structure modifier is an organic polymer. Among them, the organic polymer includes one or more of polyvinyl alcohol, polyacrylic acid and polyacrylamide. Compared with the adsorbent prepared by crystallization of a binder in actual production, it still has the problem of low strength, for example, the adsorbent involved in Chinese patent CN111111609B. The addition of an organic pore-forming agent in the present invention not only increases the macropore content of the adsorbent, allowing normal alkanes to be adsorbed faster, but also increases the strength of the adsorbent, making it have a lower pressure drop when in use.

[0032] Specifically, the lubricant includes one or more of sesbania powder, graphite, and starch.

[0033] The specific surface area of ​​the adsorbent of the present invention is greater than 620m 2 / g, mesopore specific surface area>120m 2 / g, the average compressive strength is greater than 40N. When used to adsorb normal alkanes in hydrocarbon mixtures, the purity of the obtained normal alkanes is greater than 98%, the contents of isoalkanes and aromatic compounds are both less than 0.5%, and the service life of the adsorbent is greater than 2 years.

[0034] The present invention also provides a method for preparing an adsorbent for adsorbing normal alkanes from a hydrocarbon mixture, comprising: mixing high-silicon 5A molecular sieve, a binder, a pore structure modifier and a lubricant, drying and roasting to obtain the adsorbent for adsorbing normal alkanes from a hydrocarbon mixture.

[0035] Specifically, the mixing is performed using a kneader. The steps of mixing and molding include: putting high-silicon 5A molecular sieve, binder, pore structure modifier and lubricant into a kneader, adding water while stirring and mixing, and then extruding into strips using a mold.

[0036] Specifically, the drying adopts conventional equipment in the art. The drying temperature is 110-130°C. The preferred temperature is 120°C. The drying time is 10-14h, and the preferred time is 12h. The roasting adopts conventional equipment in the art. The roasting temperature is 500-600°C, and the preferred temperature is 55°C. The roasting time is 2-5h, and the preferred time is 4h.

[0037] The preparation steps of the high silicon 5A molecular sieve of the present invention include:

[0038] S1. Mix and age the aluminum source, template and silicon source, then add a mixture of tetramethylammonium chloride and sodium chloride, mix, crystallize, filter, wash, dry and calcine to obtain high-silicon 4A molecular sieve raw powder.

[0039] Specifically, the aluminum source (in Al 2 O 3 ), template, silicon source (in terms of SiO 2 The ratio of tetramethylammonium chloride to sodium chloride is 12-14:120-140:26-35:1.5-1.8:1. Here, the ratio of tetraethylammonium hydroxide to dimethyldiethylammonium hydroxide is 1.03-1.08:1. The mixture of tetramethylammonium chloride and sodium chloride includes water in addition to tetramethylammonium chloride and sodium chloride. The ratio of tetramethylammonium chloride, sodium chloride and water is 1.5-1.8:1:10-13.

[0040] Specifically, the silicon source is colloidal silicon dioxide, the aluminum source is aluminum isopropoxide, and the template agent is tetraethylammonium hydroxide and dimethyldiethylammonium hydroxide.

[0041] In the above-mentioned S1 step, the mixing is vigorously stirred. The stirring time is 0.5-1.5h, for example, 0.7h, 1h. The aging temperature is 90-105°C, for example, the temperature is 95°C, 100°C, 102°C. The aging time is 10-14h, for example, the time is 11h, 12h, 13h. The crystallization temperature is 95-105°C, for example, the temperature is 97°C, 100°C, 102°C. The crystallization time is 10-15 days, for example, the time is 12 days, 13 days, 14 days. The purpose of filtration is to filter out the solid product. Washing is performed with deionized water. Drying is performed using conventional equipment in the art. The drying temperature is 80-110°C, for example, the temperature is 99°C, 100°C, 105°C. The drying time is 10-14h, for example, the time is 11h, 12h, 13h. Roasting uses conventional equipment in the art. The calcination temperature is 500-600° C., for example, the temperature is 530° C., 550° C., 590° C. The calcination time is 1-3 h, for example, the time is 1.5 h, 2 h.

[0042] S2, high silicon 4A molecular sieve raw powder with Ca 2+ The aqueous solution is subjected to ion exchange, filtration, washing, drying and roasting to obtain a high-silicon 5A molecular sieve with a calcium exchange degree greater than 75%, wherein the number of ion exchanges is ≥ 2 times. The number of ion exchanges can be 2, 3, 4 or 5 times.

[0043] Specifically, the solid-liquid ratio is 1:3-12, preferably 1:5-10. For example, the solid-liquid ratio is 1:6, 1:7, 1:8. 2+ The aqueous solution is calcium chloride, calcium nitrate, calcium acetate or calcium formate solution, preferably calcium chloride solution, and the concentration of the calcium chloride solution is 0.2-0.8 mol / L.

[0044] In the above-mentioned S2 step, the ion exchange adopts the conventional operation in the art. The temperature of ion exchange is 60-95°C, for example, the temperature is 75°C, 80°C, 85°C. The time of ion exchange is 2-10h, for example, the time is 4h, 6h, 8h. Drying adopts conventional equipment in the art. The drying temperature is 80-110°C, for example, the temperature is 90°C, 100°C, 105°C. The drying time is 10-14h, for example, the time is 11h, 12h, 13h. Roasting adopts conventional equipment in the art. The roasting temperature is 500-600°C, for example, the temperature is 530°C, 550°C, 590°C. The roasting time is 1-3h, for example, the time is 1.5h, 2h.

[0045] The preparation steps of the adhesive of the present invention include: stirring and drying a hydrophobic agent and hydrophilic silicon dioxide to obtain the adhesive.

[0046] Specifically, the hydrophobic agent is hexamethyldisilazane, the hydrophilic silica is hydrophilic colloidal silica, and the ratio of the hydrophobic agent to the hydrophilic silica is 1:30-35.

[0047] Specifically, the stirring temperature is 20-60°C, for example, the temperature is 25°C, 45°C, 55°C. The stirring time is 20-24h, for example, the time is 21h, 22h, 23h. Drying is performed using a blast drying oven. The drying temperature is 60-130°C, for example, the temperature is 70°C, 100°C, 120°C. The drying time is 10-20h, for example, the time is 13h, 15h, 17h.

[0048] The adsorbent prepared by the invention has the advantages of high hydrothermal stability, high strength, no generation of coke and green oil, high adsorption efficiency and long service life, and is suitable for adsorption of normal alkanes in hydrocarbon mixtures.

[0049] In the present invention, unless otherwise specified, all preparation raw materials are commercially available products well known to those skilled in the art.

[0050] The present invention is described in detail below by way of examples and experimental examples, but these are merely examples and do not limit the present invention in any form.

[0051] Example 1

[0052] Preparation of high-silicon 5A molecular sieve raw powder: weigh 308g of aluminum isopropoxide, 804g of tetraethylammonium hydroxide, 760g of dimethyldiethylammonium hydroxide and 944g of colloidal silica, stir vigorously for 1 hour, and then divide them into a polytetrafluoroethylene autoclave and age them at 95°C for 12h; dissolve the obtained product, 20g of tetramethylammonium chloride and 12g of sodium chloride in 132g of water, stir vigorously and mix homogenize for 0.5h, and charge the reaction mixture into a polytetrafluoroethylene autoclave; crystallize at 98°C for 13 days, recover the solid product by centrifugation, wash it with deionized water, and dry it at 95°C for 12h to obtain high-silicon 4A molecular sieve raw powder; weigh 320g of the obtained high-silicon 4A molecular sieve raw powder, add it to 3.2L of CaCl with a concentration of 0.5mol / L 2 The solution was ion exchanged at 80°C for 3h, filtered, washed, dried at 105°C for 12h, and calcined at 550°C for 2h to obtain high-silicon 5A molecular sieve powder with a Ca exchange degree of 70%; 320g of high-silicon 5A molecular sieve powder with a Ca exchange degree of 70% was weighed and added to 3.2L of CaCl 2 In the solution, after ion exchange at 80°C for 3 hours, filtration, washing, drying at 105°C for 12 hours, and calcination at 550°C for 2 hours, high-silicon 5A molecular sieve raw powder with a Ca exchange degree greater than 75% was obtained, and the molecular silicon-aluminum ratio of the molecular sieve raw powder was 3.1.

[0053] Preparation of hydrophobic silica binder: 3 g of hexamethyldisilazane was weighed and added directly to a flask containing 100 g of hydrophilic colloidal silica dispersion. The mixture was stirred and reacted at 25° C. for 22 h, and then placed in a forced air drying oven at 130° C. for 12 h to obtain hydrophobic silica.

[0054] Preparation of normal alkane adsorbent: Weigh 315g of high-silicon 5A molecular sieve powder with a Ca exchange degree greater than 75%, 35g of hydrophobic silica, 7g of polyvinyl alcohol and 3.5g of field sesbania powder in a kneader, add a total of 190g of water while stirring and mixing, and then extrude into strips using a 3.5mm die. After drying at 120°C for 12h, calcinate at 500°C for 4h to obtain the normal alkane adsorbent NA-A1 of Example 1.

[0055] Example 2

[0056] Preparation of high-silicon 5A molecular sieve raw powder: weigh 308g of aluminum isopropoxide, 804g of tetraethylammonium hydroxide, 760g of dimethyldiethylammonium hydroxide and 944g of colloidal silica, stir vigorously for 1 hour, and then divide them into a polytetrafluoroethylene autoclave and age them at 95°C for 12h; dissolve the obtained product, 20g of tetramethylammonium chloride and 12g of sodium chloride in 132g of water, stir vigorously and mix homogenize for 0.5h, and charge the reaction mixture into a polytetrafluoroethylene autoclave; crystallize at 100°C for 12 days, recover the solid product by centrifugation, wash it with deionized water, and dry it at 105°C for 12h to obtain high-silicon 4A molecular sieve raw powder; weigh 320g of the obtained high-silicon 4A molecular sieve raw powder, add it to 2.6L of CaCl with a concentration of 0.6mol / L 2 The solution was ion exchanged at 80°C for 5h, filtered, washed, dried at 100°C for 12h, and calcined at 550°C for 2h to obtain high silicon 5A molecular sieve powder with a Ca exchange degree of 70%; 320g of high silicon 5A molecular sieve powder with a Ca exchange degree of 70% was weighed and added to 2.6L of CaCl 2 In the solution, after ion exchange at 80°C for 5 hours, filtering, washing, drying at 100°C for 12 hours, and calcining at 550°C for 2 hours, high-silicon 5A molecular sieve raw powder with a Ca exchange degree greater than 75% was obtained, and the molecular silicon-aluminum ratio of the molecular sieve raw powder was 3.2.

[0057] Preparation of hydrophobic silica binder: 3 g of hexamethyldisilazane was weighed and added directly to a flask containing 100 g of hydrophilic colloidal silica dispersion. The mixture was stirred and reacted at 35° C. for 21 h, and then placed in a forced air drying oven at 120° C. for 15 h to obtain hydrophobic silica.

[0058] Preparation of normal alkane adsorbent: Weigh 308g of high-silicon 5A molecular sieve powder with a Ca exchange degree greater than 75%, 42g of hydrophobic silica, 8g of polyacrylamide and 3.5g of field sesbania powder in a kneader, add a total of 185g of water while stirring and mixing, and then extrude into strips using a 3.5mm die. After drying at 120°C for 8h, calcinate at 500°C for 4h to obtain the normal alkane adsorbent NA-A2 of Example 2.

[0059] Comparative Example 1

[0060] Preparation of normal alkane adsorbent: Weigh 315g of commercially available 5A molecular sieve powder (Ca exchange degree of 70%, Shanghai Jiuzhou Chemical Co., Ltd.), 35g of kaolin and 3.5g of sesbania powder in a kneader, add a total of 190g of water while stirring and mixing, and then extrude into strips using a 3.5mm die. After drying at 120°C for 12h, calcinate at 500°C for 4h to obtain the normal alkane adsorbent NA-B1 of Comparative Example 1.

[0061] Comparative Example 2

[0062] Preparation of 5A molecular sieve powder: Weigh 320g of commercially available 4A molecular sieve powder (Shanghai Jiuzhou Chemical Co., Ltd.) and add it to 3.2L of 0.3mol / L CaCl 2 The solution was ion exchanged at 80°C for 2h, filtered, washed, dried at 100°C for 12h, and calcined at 550°C for 2h to obtain 5A molecular sieve powder with a Ca exchange degree of 70%. 320g of 5A molecular sieve powder with a Ca exchange degree of 70% was weighed and added to 3.2L of 0.5mol / L CaCl 2 In the solution, after ion exchange at 80° C. for 3 h, the solution was filtered, washed, dried at 105° C. for 12 h, and calcined at 550° C. for 2 h to obtain 5A molecular sieve raw powder with a Ca exchange degree greater than 75%.

[0063] Preparation of normal alkane adsorbent: Weigh 315g of the above-prepared 5A molecular sieve powder with a Ca exchange degree greater than 75%, 35g of attapulgite and 3.5g of sesbania powder into a kneader, add a total of 190g of water while stirring and mixing, and then extrude into strips using a 3.5mm mold. After drying at 120°C for 12h, calcinate at 500°C for 4h to obtain the normal alkane adsorbent NA-B2 of Comparative Example 2.

[0064] Comparative Example 3:

[0065] Preparation of high-silicon 5A molecular sieve raw powder: weigh 308g of aluminum isopropoxide, 804g of tetraethylammonium hydroxide, 760g of dimethyldiethylammonium hydroxide and 944g of colloidal silica, stir vigorously for 1 hour, and then divide them into a polytetrafluoroethylene autoclave and age them at 95°C for 12h; dissolve the obtained product, 20g of tetramethylammonium chloride and 12g of sodium chloride in 132g of water, stir vigorously and mix homogenize for 0.5h, and charge the reaction mixture into a polytetrafluoroethylene autoclave; crystallize at 98°C for 13 days, recover the solid product by centrifugation, wash it with deionized water, and dry it at 95°C for 12h to obtain high-silicon 4A molecular sieve raw powder; weigh 320g of the obtained high-silicon 4A molecular sieve raw powder, add it to 3.2L of CaCl with a concentration of 0.5mol / L 2 In the solution, after ion exchange at 80°C for 3 hours, the solution was filtered, washed, dried at 105°C for 12 hours, and calcined at 550°C for 2 hours to obtain high-silicon 5A molecular sieve raw powder with a Ca exchange degree of 70%;

[0066] Preparation of normal alkane adsorbent: Weigh 315g of the high-silicon 5A molecular sieve powder prepared above, 35g of montmorillonite and 3.5g of sesbania powder in a kneader, add a total of 190g of water while stirring and mixing, and then extrude into strips using a 3.5mm die. After drying at 120°C for 12h, calcinate at 500°C for 4h to obtain the normal alkane adsorbent NA-B3 of Comparative Example 3.

[0067] Comparative Example 4

[0068] Preparation of high-silicon 5A molecular sieve raw powder: weigh 308g of aluminum isopropoxide, 804g of tetraethylammonium hydroxide, 760g of dimethyldiethylammonium hydroxide and 944g of colloidal silica, stir vigorously for 1 hour, and then divide them into a polytetrafluoroethylene autoclave and age them at 95°C for 12h; dissolve the obtained product, 20g of tetramethylammonium chloride and 12g of sodium chloride in 132g of water, stir vigorously and mix homogenize for 0.5h, and charge the reaction mixture into a polytetrafluoroethylene autoclave; crystallize at 98°C for 13 days, recover the solid product by centrifugation, wash it with deionized water, and dry it at 95°C for 12h to obtain high-silicon 4A molecular sieve raw powder; weigh 320g of the obtained high-silicon 4A molecular sieve raw powder, add it to 3.2L of CaCl with a concentration of 0.5mol / L 2 The solution was ion exchanged at 80°C for 3h, filtered, washed, dried at 105°C for 12h, and calcined at 550°C for 2h to obtain high-silicon 5A molecular sieve powder with a Ca exchange degree of 70%; 320g of high-silicon 5A molecular sieve powder with a Ca exchange degree of 70% was weighed and added to 3.2L of CaCl 2 In the solution, after ion exchange at 80°C for 3 hours, filtering, washing, drying at 105°C for 12 hours, and calcining at 550°C for 2 hours, high silicon 5A molecular sieve raw powder with a Ca exchange degree greater than 75% was obtained;

[0069] Preparation of normal alkane adsorbent: Weigh 315g of high-silicon 5A molecular sieve powder with a Ca exchange degree greater than 75%, 35g of attapulgite and 3.5g of sesbania powder in a kneader, add a total of 190g of water while stirring and mixing, and then extrude into strips using a 3.5mm mold. After drying at 120°C for 12h, calcinate at 500°C for 4h to obtain the normal alkane adsorbent NA-B4 of Comparative Example 4.

[0070] Comparative Example 5

[0071] Preparation of high-silicon 5A molecular sieve raw powder: weigh 308g of aluminum isopropoxide, 804g of tetraethylammonium hydroxide, 760g of dimethyldiethylammonium hydroxide and 944g of colloidal silica, stir vigorously for 1 hour, and then divide them into a polytetrafluoroethylene autoclave and age them at 95°C for 12h; dissolve the obtained product, 20g of tetramethylammonium chloride and 12g of sodium chloride in 132g of water, stir vigorously and mix homogenize for 0.5h, and charge the reaction mixture into a polytetrafluoroethylene autoclave; crystallize at 98°C for 13 days, recover the solid product by centrifugation, wash it with deionized water, and dry it at 95°C for 12h to obtain high-silicon 4A molecular sieve raw powder; weigh 320g of the obtained high-silicon 4A molecular sieve raw powder, add it to 3.2L of CaCl with a concentration of 0.5mol / L 2 The solution was ion exchanged at 80°C for 3h, filtered, washed, dried at 105°C for 12h, and calcined at 550°C for 2h to obtain high-silicon 5A molecular sieve powder with a Ca exchange degree of 70%; 320g of high-silicon 5A molecular sieve powder with a Ca exchange degree of 70% was weighed and added to 3.2L of CaCl 2 In the solution, after ion exchange at 80°C for 3 hours, filtering, washing, drying at 105°C for 12 hours, and calcining at 550°C for 2 hours, high-silicon 5A molecular sieve raw powder with a Ca exchange degree greater than 75% was obtained.

[0072] Preparation of hydrophobic silica binder: 3 g of hexamethyldisilazane was weighed and added directly to a flask containing 100 g of hydrophilic colloidal silica dispersion. The mixture was stirred and reacted at 25° C. for 22 h, and then placed in a forced air drying oven at 130° C. for 12 h to obtain hydrophobic silica.

[0073] Preparation of normal alkane adsorbent: Weigh 315g of high-silicon 5A molecular sieve powder with a Ca exchange degree greater than 75%, 17g of hydrophobic silica, 18g of kaolin and 3.5g of sesbania powder in a kneader, add a total of 190g of water while stirring and mixing, and then extrude into strips using a 3.5mm mold. After drying at 120°C for 12h, calcinate at 500°C for 4h to obtain the normal alkane adsorbent NA-B5 of Comparative Example 5.

[0074] Comparative Example 6

[0075] Preparation of high-silicon 5A molecular sieve raw powder: weigh 308g of aluminum isopropoxide, 804g of tetraethylammonium hydroxide, 760g of dimethyldiethylammonium hydroxide and 944g of colloidal silica, stir vigorously for 1 hour, and then divide them into a polytetrafluoroethylene autoclave and age them at 95°C for 12h; dissolve the obtained product, 20g of tetramethylammonium chloride and 12g of sodium chloride in 132g of water, stir vigorously and mix homogenize for 0.5h, and charge the reaction mixture into a polytetrafluoroethylene autoclave; crystallize at 98°C for 13 days, recover the solid product by centrifugation, wash it with deionized water, and dry it at 95°C for 12h to obtain high-silicon 4A molecular sieve raw powder; weigh 320g of the obtained high-silicon 4A molecular sieve raw powder, add it to 3.2L of CaCl with a concentration of 0.5mol / L 2 The solution was ion exchanged at 80°C for 3h, filtered, washed, dried at 105°C for 12h, and calcined at 550°C for 2h to obtain high-silicon 5A molecular sieve powder with a Ca exchange degree of 70%; 320g of high-silicon 5A molecular sieve powder with a Ca exchange degree of 70% was weighed and added to 3.2L of CaCl 2 In the solution, after ion exchange at 80°C for 3 hours, filtering, washing, drying at 105°C for 12 hours, and calcining at 550°C for 2 hours, high silicon 5A molecular sieve raw powder with a Ca exchange degree greater than 75% was obtained;

[0076] Preparation of hydrophobic silica binder: 3 g of hexamethyldisilazane was weighed and added directly to a flask containing 100 g of hydrophilic colloidal silica dispersion. The mixture was stirred and reacted at 25° C. for 22 h, and then placed in a forced air drying oven at 130° C. for 12 h to obtain hydrophobic silica.

[0077] Preparation of normal alkane adsorbent: Weigh 315g of high-silicon 5A molecular sieve powder with a Ca exchange degree greater than 75%, 35g of hydrophobic silica and 3.5g of field sesbania powder in a kneader, add a total of 190g of water while stirring and mixing, and then extrude into strips using a 3.5mm mold. After drying at 120°C for 12h, calcine at 500°C for 4h to obtain the normal alkane adsorbent NA-B6 of Comparative Example 6.

[0078] In order to illustrate the effect of the normal alkane adsorbent provided by the present application, the following experiment was conducted:

[0079] Physical adsorption tests were performed on the n-alkane adsorbents prepared in Examples 1-2 and Comparative Examples 1-6. The results are shown in Table 1.

[0080] Table 1 Specific surface area results of n-alkane adsorbent prepared by Examples 1-2 and Comparative Examples 1-6

[0081]

[0082]

[0083] It can be seen from Table 1 that, compared with the comparative example, the normal alkane adsorbent prepared in Example 1-2 has a higher mesoporous specific surface area, which is conducive to the rapid molecular mass transfer.

[0084] The n-alkane adsorbents prepared in Examples 1-2 and Comparative Examples 1-6 were subjected to a hydrothermal aging experiment. The experimental steps were as follows: a certain amount of n-alkane adsorbent was placed in a crucible, placed in a hydrothermal aging device, and treated at 500° C. for 24 hours under a water vapor content of 100%; the adsorbents before and after the treatment were subjected to strength and XRD tests, and the results are shown in Table 2.

[0085] Table 2 Strength and relative crystallinity results of n-alkane adsorbents prepared in Examples 1-2 and Comparative Examples 1-6

[0086]

[0087] It can be seen from Table 2 that, compared with the comparative example, the normal alkane adsorbent prepared in Example 1-2 has the least decrease in strength and molecular sieve crystallinity after hydrothermal aging treatment, indicating that the normal alkane adsorbent prepared in Example 1-2 has better hydrothermal stability and a longer actual service life.

[0088] The normal alkane adsorbents prepared in Examples 1-2 and Comparative Examples 1-6 were subjected to a normal alkane adsorption experiment. The specific experimental steps are as follows:

[0089] A hexane solution with a normal hexane content of 20 wt% (cyclohexane content of 40 wt%, the rest is isohexane) is prepared as an adsorption stock solution;

[0090] Take a certain amount of n-alkane adsorbent, crush it into 60-80 mesh, pre-treat it at 550℃ for 2h, weigh 1g and load it into a stainless steel adsorption column;

[0091] After preheating, the adsorption stock solution is pumped into the raw material heating tank by a pump, heated to 350°C and then flows into the adsorption column at a flow rate of 25ml / min. The pressure of the adsorption column is 1MPa, and the adsorption lasts for 5min. The adsorbed liquid is collected in the adsorption residual liquid tank.

[0092] Steam purge removes the adsorption liquid on the surface of the adsorbent and collects it in the adsorption residual liquid tank;

[0093] The normal alkanes adsorbed on the adsorbent are purged out by means of decompression and desorption gas purging and collected in a product tank;

[0094] Weigh the mass of the samples in the adsorption residual liquid tank and the product tank, and use the PONA analyzer to analyze the concentration of n-hexane in the residual liquid tank and the product tank;

[0095] The adsorbent was removed after adsorption, and after being calcined at 500°C for 2 h, the carbon content in the sample was tested using an element analyzer.

[0096] The calculated yield and purity of normal alkanes and the carbon content in the adsorbent are shown in Table 3.

[0097] Table 3 Adsorption effect and carbon content of normal alkane adsorbent prepared by Examples 1-2 and Comparative Examples 1-6

[0098]

[0099] It can be seen from Table 3 that, compared with the comparative example, the purity and yield of the normal alkane adsorbent prepared in Example 1-2 are very high, and the amount of carbon deposits in the adsorbent after regeneration is very low, indicating that the polymerization of hydrocarbons on the adsorbent surface can be delayed during actual use, the production of coke and green oil can be reduced, and the adsorbent life can be extended.

[0100] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An adsorbent for adsorbing normal alkanes from a hydrocarbon mixture, characterized in that: The composition, calculated based on the total amount of the adsorbent, contains: 85-95wt% of high-silicon 5A molecular sieve, 5-15wt% of a binder, 1-5wt% of a pore structure modifier and 0.1-2wt% of a lubricant; wherein the molecular silicon-aluminum ratio of the high-silicon 5A molecular sieve is 3-5.

2. The adsorbent according to claim 1, characterized in that The high-silicon 5A molecular sieve is obtained by preparing a high-silicon 4A molecular sieve from a silicon source and an aluminum source, and then undergoing calcium exchange for more than two times, and the calcium exchange degree is greater than 75%.

3. The adsorbent according to claim 1, characterized in that The binder is a hydrophobic silica material; wherein the hydrophobic silica material includes hydrophobic colloidal silica and / or hydrophobic fumed silica.

4. The adsorbent according to claim 1, characterized in that The pore structure modifier is an organic polymer; wherein the organic polymer includes one or more of polyvinyl alcohol, polyacrylic acid and polyacrylamide.

5. The adsorbent according to claim 1, characterized in that The lubricant includes one or more of sesbania powder, graphite, and starch.

6. A method for preparing an adsorbent for adsorbing normal alkanes from a hydrocarbon mixture as claimed in any one of claims 1 to 5, characterized in that: include: The high-silicon 5A molecular sieve, a binder, a pore structure modifier and a lubricant are mixed, molded, dried and calcined to obtain an adsorbent for adsorbing normal alkanes from a hydrocarbon mixture.

7. The preparation method according to claim 6, characterized in that: The preparation steps of the high silicon 5A molecular sieve include: S1, mixing an aluminum source, a template and a silicon source, aging, adding a mixture of tetramethylammonium chloride and sodium chloride, mixing, crystallizing, filtering, washing, drying and calcining to obtain a high-silicon 4A molecular sieve raw powder; S2, high silicon 4A molecular sieve raw powder with Ca 2+ The aqueous solution is subjected to ion exchange, filtration, washing, drying and roasting to obtain a high-silicon 5A molecular sieve with a calcium exchange degree greater than 75%, wherein the number of ion exchanges is ≥2 times.

8. The preparation method according to claim 7, characterized in that: The silicon source is colloidal silicon dioxide, the aluminum source is aluminum isopropoxide, and the template agent is tetraethylammonium hydroxide and dimethyldiethylammonium hydroxide.

9. The preparation method according to claim 7, characterized in that: In the step S1, the crystallization temperature is 95-105°C, the crystallization time is 10-15 days, the drying temperature is 80-110°C, the drying time is 10-14 hours, the calcination temperature is 500-600°C, and the calcination time is 1-3 hours; In the step S2, the ion exchange temperature is 60-95°C, the ion exchange time is 2-10h, the drying temperature is 80-110°C, the drying time is 10-14h, the calcination temperature is 500-600°C, the calcination time is 1-3h, and Ca 2+ The aqueous solution is calcium chloride, calcium nitrate, calcium acetate or calcium formate solution, preferably calcium chloride solution, and the concentration of the calcium chloride solution is 0.2-0.8 mol / L.

10. The preparation method according to claim 6, characterized in that: The preparation steps of the binder include: stirring and drying a hydrophobic agent and hydrophilic silicon dioxide to obtain the binder.

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