Process for separating olefins from paraffins and molecular sieve adsorbent

Abstract

The application discloses a method for separating olefins and alkanes and a molecular sieve adsorbent, and relates to the field of molecular sieve adsorbents, and specifically relates to a method for separating olefins and alkanes and a molecular sieve adsorbent. The method comprises the following steps: feeding a Fischer-Tropsch synthesis oil raw material into a simulated moving bed reactor filled with the molecular sieve adsorbent to separate alkanes and olefins; the molecular sieve adsorbent is prepared by the following method: step S1, obtaining a formed molecular sieve; step S2, grinding the formed molecular sieve into powder and screening by using a sieve, and then washing and drying; step S3, adding deionized water and a surfactant into the molecular sieve to obtain a first mixed solution; step S4, adding an acid and a silicon source into the first mixed solution, adjusting the pH value, and obtaining a second mixed solution; crystallizing the second mixed solution, filtering, washing, drying and calcining the product to obtain the molecular sieve adsorbent. The method for separating olefins and alkanes provided by the application can improve the separation effect of alkanes and olefins with different carbon numbers by preparing a molecular sieve adsorbent with micropores and mesopores and using the molecular sieve adsorbent to separate alkanes and olefins in Fischer-Tropsch synthesis oil.

Description

[0001] This application claims priority to Chinese Patent Application No. 202511981577X, filed on December 25, 2025, entitled "Method for Separating Olefins and Alkanes and Molecular Sieve Adsorbent", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to the field of Fischer-Tropsch synthesis technology, specifically to a method for separating olefins and alkanes and a molecular sieve adsorbent. Background Technology

[0003] In the oil products produced by the Fischer-Tropsch synthesis process, the olefin component exhibits a wide carbon number distribution, mainly with α-olefin structure, and does not contain impurities such as sulfur, nitrogen, and aromatics. The alkane component has a very close boiling point to the olefin, and both are nonpolar molecules, resulting in highly similar physicochemical properties. This similarity makes the efficient and precise separation of olefins and alkanes from the complex Fischer-Tropsch synthesis oil a key factor restricting the high-value utilization of the product.

[0004] In existing technologies, the main separation methods for alkanes and alkenes include liquid-liquid extraction, distillation, and membrane separation. While liquid-liquid extraction has a relatively simple operation and low initial cost, traditional polar organic solvents are generally volatile and highly toxic, posing potential threats to the safety of the operating environment and human health. Novel extraction systems, such as ionic liquids and eutectic solvents, offer the advantage of designable molecular structures, but their preparation costs are significantly high, making them unsuitable for large-scale continuous industrial production. Distillation and its derivative processes, such as extractive distillation, can achieve a certain degree of separation, but their operation is energy-intensive, costly, and involves large solvent consumption and complex recovery processes, resulting in poor overall economic efficiency. Membrane separation is limited by the inherent defects of membrane materials, such as limited throughput, short lifespan, and difficult regeneration processes, making stable operation difficult in industrial applications, especially in large-scale Fischer-Tropsch synthesis oil processing scenarios, where its widespread adoption faces significant challenges.

[0005] Therefore, existing technologies have significant shortcomings in terms of separation efficiency, cost control, and industrial applicability. Summary of the Invention

[0006] This disclosure provides a method for separating olefins and alkanes and a molecular sieve adsorbent to address the problems existing in the prior art.

[0007] According to a first aspect of this disclosure, a method for separating olefins and alkanes is provided, comprising: passing a Fischer-Tropsch synthetic oil feedstock containing olefins and alkanes into a simulated moving bed reactor packed with a molecular sieve adsorbent for alkane-olefin separation, wherein the molecular sieve adsorbent in the simulated moving bed reactor is prepared by a method comprising the following steps:

[0008] Step S1: Add aluminum source and silicon source to alkaline solution and age at room temperature; after aging, crystallize at a predetermined temperature; the crystallized product is filtered, washed, and dried to obtain molecular sieve raw powder; the molecular sieve raw powder is shaped under the action of a forming agent and calcined to obtain the shaped molecular sieve.

[0009] Step S2: Take the molecular sieve formed in step S1, grind it into powder and sieve it. Wash and dry the sieved molecular sieve.

[0010] Step S3: Add deionized water and surfactant to the dried molecular sieve from step S2 to obtain the first mixture;

[0011] Step S4: Add acid and silicon source to the first mixture in step S3 and adjust the pH value to obtain a second mixture. Liquidize the second mixture, and after the reaction, filter, wash, dry, and calcine the product to obtain the molecular sieve adsorbent.

[0012] In one embodiment of this disclosure, step S4 further includes: adjusting the pH value to 1-4, crystallizing in a high-pressure reactor for 10-20 hours, and crystallizing at a temperature of 100℃-160℃.

[0013] In one embodiment of this disclosure, the mass ratio of molecular sieve, surfactant and deionized water in the first mixture is 1:0.2:2 to 1:0.5:6.

[0014] In one embodiment of this disclosure, the mass ratio of acid, silicon source and molecular sieve in the second mixture is 1:2:2-1:8:10.

[0015] In one embodiment of this disclosure, the shaped molecular sieve obtained in step S1 is one or more of type A molecular sieve, type X molecular sieve, and type Y molecular sieve.

[0016] In one embodiment of this disclosure, the silicon source in step S4 is one or more of sodium silicate, silicon dioxide, tetraethyl orthosilicate, and silica.

[0017] In one embodiment of this disclosure, the acid in step S4 is one or more of hydrochloric acid, sulfuric acid, nitric acid, and acetic acid, with a concentration of 4 mol / L to 7 mol / L.

[0018] In one embodiment of this disclosure, the surfactant added in step S3 has a molecular weight range of 200-800, and the surfactant is one or more of hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, and alkylphenol polyoxyethylene ether.

[0019] According to a second aspect of this disclosure, a molecular sieve adsorbent is provided, which is prepared by the method described above.

[0020] In one embodiment of this disclosure, the total specific surface area of ​​the molecular sieve adsorbent is 800 m². 2 / g-1000m 2 / g; The specific surface area of ​​the micropores is 500m² 2 / g-600m 2 / g, the specific surface area of ​​the mesopores is 300m². 2 / g-400m 2 / g.

[0021] The present disclosure provides a method for separating α-olefins and alkanes, as well as a molecular sieve adsorbent. This method involves passing a Fischer-Tropsch synthetic oil feedstock containing olefins and alkanes into a simulated moving bed reactor filled with a molecular sieve adsorbent to separate olefins and alkanes. By preparing the molecular sieve adsorbent, the method effectively solves the problems of low separation efficiency, high operating environment risk, and insufficient cost control in the prior art.

[0022] Other features and advantages of the invention will become clear from the following detailed description of exemplary embodiments of the invention with reference to the accompanying drawings. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the present disclosure and, together with their description, serve to explain the principles of the present disclosure.

[0024] Figure 1 This is a flowchart of a method for preparing a molecular sieve adsorbent provided in one embodiment of this disclosure. Detailed Implementation

[0025] To make the inventive objectives, technical solutions, and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with specific embodiments. It should be understood that the embodiments described in this specification are merely illustrative and not intended to limit the scope of this application.

[0026] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an unspecified range.

[0027] In the description of this article, it should be noted that, unless otherwise stated, "above" and "below" include the number itself, and "several" in "one or more" means two or more.

[0028] The foregoing description of this invention is not intended to describe every disclosed embodiment or implementation. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are merely representative and should not be construed as exhaustive.

[0029] First, the nouns and terms used in one or more embodiments will be explained.

[0030] Simulated moving bed reactor: A highly efficient continuous separation device that simulates the movement of adsorbents in a bed to achieve continuous operation of adsorption, desorption, washing and regeneration, suitable for large-scale material separation and purification processes.

[0031] Confinement effect: refers to the phenomenon that when molecules or particles are confined in a small space at the nanoscale (such as the micropores of molecular sieves, the channels of mesoporous materials, etc.), their physicochemical behavior changes significantly due to the spatial limitation.

[0032] The Fischer-Tropsch synthesis produces alkenes with a wide carbon number distribution, mainly in olefin structure, and free of impurities such as sulfur, nitrogen, and aromatics. However, the alkanes produced by the Fischer-Tropsch synthesis have similar boiling points to alkenes and are both nonpolar molecules with highly similar physicochemical properties. Therefore, the efficient separation of alkenes and alkanes from the complex Fischer-Tropsch synthetic oil has become the key to its high-value utilization.

[0033] In existing technologies, the main separation methods for alkanes and alkenes include liquid-liquid extraction, distillation, and membrane separation. Among these, liquid-liquid extraction is simple to operate and inexpensive, but traditional polar organic solvents are generally volatile and toxic. Furthermore, ionic liquids and eutectic solvents are novel, designable extractants, but they are expensive and unsuitable for industrial production. Extractive distillation processes are very costly and energy-intensive, with large solvent consumption and difficult recovery. Membrane separation methods are limited in their industrial application due to the small processing capacity, short lifespan, and difficulty in regenerating membranes.

[0034] This disclosure provides a method for separating olefins and alkanes and a molecular sieve adsorbent to address the problems existing in the prior art.

[0035] According to a first aspect of this disclosure, a method for separating olefins and alkanes is provided, comprising: passing a Fischer-Tropsch synthetic oil feedstock containing olefins and alkanes into a simulated moving bed reactor packed with a molecular sieve adsorbent for alkane-olefin separation, wherein the molecular sieve adsorbent in the simulated moving bed reactor is prepared by a method comprising the following steps, such as... Figure 1 As shown:

[0036] Step S1: Add aluminum source and silicon source to alkaline solution and age at room temperature; after aging, crystallize at a predetermined temperature; the crystallized product is filtered, washed, and dried to obtain molecular sieve raw powder; the molecular sieve raw powder is shaped under the action of a forming agent and calcined to obtain the shaped molecular sieve.

[0037] Step S2: Take the molecular sieve formed in step S1, grind it into powder and sieve it. Wash and dry the sieved molecular sieve.

[0038] Step S3: Add deionized water and surfactant to the dried molecular sieve from step S2 to obtain the first mixture;

[0039] Step S4: Add acid and silicon source to the first mixture in step S3 and adjust the pH value to obtain a second mixture. Liquidize the second mixture, and after the reaction, filter, wash, dry, and calcine the product to obtain the molecular sieve adsorbent.

[0040] Specifically, Fischer-Tropsch synthetic oil feedstock containing olefins and alkanes is fed into a simulated moving bed (SMB) reactor packed with molecular sieve adsorbent for alkane-olefin separation. The process is based on the difference in adsorption capacity of olefins and alkanes on the molecular sieve adsorbent, and efficient separation is achieved through continuous countercurrent operation of the simulated moving bed.

[0041] Furthermore, due to the presence of carbon-carbon double bonds in olefin molecules, their electron cloud density distribution is uneven, resulting in a higher molecular polarizability than that of alkanes with the same number of carbon atoms. The local electrostatic field or van der Waals force field generated by the molecular sieve framework of the molecular sieve adsorbent prepared in this disclosure has a stronger inductive effect on olefins with high polarizability, enabling them to exhibit higher adsorption affinity during adsorption. In addition, the microporous structure (pore size typically less than 2 nm) provides a strong confinement effect, enhancing the interaction between molecules and pore walls; while mesoporous structures (2–50 nm) are beneficial for macromolecular diffusion and mass transfer, thereby alleviating the micropore clogging problem and improving adsorption kinetic efficiency. When a mixture of olefins and alkanes in Fischer-Tropsch synthetic oil flows through this hierarchical porous molecular sieve adsorbent, olefins are preferentially adsorbed and retained in the pores due to stronger dispersion and inductive forces, while alkanes pass through the bed relatively faster, thus achieving preliminary separation in time or space.

[0042] In the preparation of molecular sieve adsorbents for simulated moving bed reactors, in step S1, aluminum and silicon sources are first added to an alkaline solution and aged at room temperature to allow the silicon and aluminum species to fully hydrolyze and undergo preliminary condensation, forming a uniform amorphous gel precursor, providing a structural basis for subsequent crystallization. After aging, the mixture is transferred to a predetermined temperature for hydrothermal crystallization. During this process, the gel rearranges in an alkaline environment and gradually crystallizes to form molecular sieve crystals with specific pore structures. After crystallization, the product is subjected to solid-liquid separation and washing to remove residual alkali and impurities, and then dried to obtain molecular sieve powder. This powder is usually a fine powder with low mechanical strength, making it difficult to use directly in industrial reactors such as fixed beds. Therefore, a forming agent (such as boehmite, kaolin, or organic binder) needs to be added to shape it through extrusion, tableting, or spraying to give it the required shape and mechanical strength. Finally, it is calcined to remove organic components introduced during the shaping process and to enhance the thermal stability and structural integrity of the particles, ultimately obtaining a shaped molecular sieve suitable for industrial catalysis.

[0043] The molecular sieve synthesized in step S1 can be of various types, such as X-type and Y-type. The molecular sieve is ground into fine powder using mechanical grinding equipment, such as a ball mill or an air jet mill, to increase its specific surface area and subsequent reaction activity. The ground powder is then sieved through a vibrating screen or an air jet screen to obtain molecular sieve particles with uniform particle size distribution. The sieved molecular sieve particles are washed multiple times with deionized water to remove surface impurities and soluble salts. The washed molecular sieve is then dried in an oven to remove moisture.

[0044] In step S3, deionized water and surfactant are added to the dried molecular sieve from step S2 to obtain a first mixture. The dried molecular sieve powder, deionized water and surfactant are mixed in a certain proportion and thoroughly mixed by a stirring device to form a uniform slurry. This mixing process can be carried out at room temperature and pressure, and the stirring time can be adjusted according to the uniformity of the mixture.

[0045] In step S4, acid and a silicon source are added to the first mixture from step S3, and the pH value is adjusted to obtain a second mixture. The second mixture is then transferred to a high-pressure reactor for crystallization. The temperature and pressure inside the reactor are raised to preset values ​​and maintained under these conditions for a certain period of time. During the crystallization process, the molecular sieve framework structure gradually takes shape under the action of surfactants and silicon sources. After the reaction, the product is removed from the reactor and subjected to filtration, washing, drying, and calcination. Filtration can be performed using vacuum filtration or centrifugal filtration to separate the solid product from the mother liquor. The solid product is repeatedly washed with deionized water to remove residual surfactants, unreacted raw materials, and byproducts. The washed product is dried in an oven to remove moisture. Finally, the dried product is calcined in a high-temperature furnace to remove surfactants and expose the pore structure of the molecular sieve, thereby obtaining a molecular sieve adsorbent with adsorption properties.

[0046] In practical applications, Fischer-Tropsch synthesis feedstock containing olefins and alkanes enters a simulated moving bed reactor packed with molecular sieve adsorbents. Utilizing the selective adsorption capacity of molecular sieve adsorbents for olefins (especially α-olefins), olefins are preferentially adsorbed and subsequently eluted by the desorption liquid, exiting from the evacuation port to form a mixture containing olefins and the desorption liquid. Alkanes are not adsorbed at all and flow out with the liquid phase from the evacuation port, forming a mixture containing alkanes, a small amount of olefins, and the desorption liquid.

[0047] In one embodiment of this disclosure, step S4 further includes: adjusting the pH value to 1-4, crystallizing in a high-pressure reactor for 10-20 hours, and crystallizing at a temperature of 100℃-160℃.

[0048] Specifically, crystallization under acidic conditions helps control the dissolution and polymerization rate of the silicon source, thereby affecting the formation of the molecular sieve framework and crystal growth. Crystallization within a set time range of 10-20 hours ensures sufficient growth of the molecular sieve, forming a stable crystal structure, while avoiding over-crystallization or incomplete crystallization. The crystallization time can be controlled by setting the operating time of the high-pressure reactor or by periodically sampling and analyzing the crystallinity of the crystallization product. Crystallization within a temperature range of 100℃-160℃ promotes the formation of the molecular sieve framework while inhibiting the formation of impurity phases, thus ensuring the purity of the product.

[0049] In one embodiment of this disclosure, the mass ratio of molecular sieve, surfactant, and deionized water in the first mixture is 1:0.2:2 to 1:0.5:6. The molecular sieve serves as a framework precursor, the surfactant acts as a directing agent to participate in framework reconstruction and mesoporous structure formation, and the deionized water serves as a solvent and reaction medium. When these three components are mixed in a specific mass ratio, it ensures that the molecular sieve powder is well dispersed in the deionized water, while the surfactant can be uniformly dissolved or dispersed in the system, forming a homogeneous and stable reaction precursor. This avoids the subsequent formation of crystal defects or byproducts due to uneven local concentrations.

[0050] In another embodiment of this disclosure, the mass ratio of acid, silicon source, and molecular sieve in the second mixture is 1:2:2 to 1:8:10. The acid and the surfactant in the first mixture work together to guide the growth of the molecular sieve framework material around it, thereby forming mesopores. By controlling the mass ratio of acid, silicon source, and molecular sieve, the size, pore volume, and connectivity of the mesopores can be effectively controlled. The 1:2:2 to 1:8:10 ratio is determined through experimental optimization or theoretical calculation, which can construct the optimal mesoporous structure, thus endowing the adsorbent with excellent adsorption and separation performance.

[0051] In one embodiment of this disclosure, the shaped molecular sieve obtained in step S1 is one or more of type A molecular sieve, type X molecular sieve, and type Y molecular sieve.

[0052] Specifically, type A molecular sieves are synthetic zeolites with a cubic crystal structure, typically with small and uniformly distributed pore sizes, such as 3A, 4A, and 5A. Type X molecular sieves are synthetic zeolites with an octahedral zeolite framework structure, typically with larger pore sizes than type A molecular sieves, exhibiting a larger specific surface area and adsorption capacity. Type Y molecular sieves are isomers of type X molecular sieves, possessing even larger pore sizes and higher thermal stability; their framework structure is typically a supercage structure. The specific type of molecular sieve obtained in step S1 depends on parameters such as the ratio of silicon and aluminum sources, basicity, type of template agent, and crystallization conditions used in the synthesis process.

[0053] When preparing molecular sieve adsorbents, a single type of molecular sieve can be selected as the starting material according to the performance requirements of the adsorption target, or two or more different types of molecular sieves can be combined. By combining the characteristics of different molecular sieves, the synergistic optimization of adsorbent performance can be achieved.

[0054] In one embodiment of this disclosure, the silicon source in step S4 is one or more of sodium silicate, silicon dioxide, tetraethyl orthosilicate, and silica. The silicon source of this disclosure is a substance used to provide silicon elements to participate in the construction of the molecular sieve framework. For example, the silicon source can serve as a provider of silicon-oxygen tetrahedral units, forming the molecular sieve framework through hydrolysis and condensation reactions; or it can serve as a silicon species, deposited or modified on the surface or within the pores of the molecular sieve to alter its surface properties and adsorption selectivity.

[0055] In one embodiment of this disclosure, the acid in step S4 is one or more of hydrochloric acid, sulfuric acid, nitric acid, and acetic acid, with a concentration of 4 mol / L to 7 mol / L. In step 43, the main function of the acid is to adjust the pH value of the second mixture, thereby providing a suitable acidic environment for the crystallization of the molecular sieve and promoting the formation of the molecular sieve framework.

[0056] In one embodiment of this disclosure, the surfactant added in step S3 has a molecular weight range of 200-800, and is one or more of hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, and alkylphenol polyoxyethylene ether. The main role of surfactants in the preparation of molecular sieve adsorbents is as structure-directing agents or pore-forming agents, influencing the crystallization process, pore structure, grain size, and specific surface area of ​​the molecular sieve. By selecting different types of surfactants, the microstructure of the molecular sieve can be controlled, thereby optimizing its adsorption performance.

[0057] According to a second aspect of this disclosure, a molecular sieve adsorbent is provided, which is prepared by the method described above.

[0058] In one embodiment of this disclosure, the total specific surface area of ​​the molecular sieve adsorbent is 800 m². 2 / g-1000m 2 / g; The specific surface area of ​​the micropores is 500m² 2 / g-600m 2 / g, the specific surface area of ​​the mesopores is 300m². 2 / g-400m 2 / g.

[0059] Specifically, total specific surface area refers to the total surface area per unit mass of the adsorbent, and is an important indicator for measuring the adsorption capacity of the adsorbent. It can be determined by the nitrogen adsorption-desorption method (BET method). The molecular sieve adsorbent prepared in this disclosure has a total specific surface area of ​​800 m². 2 / g-1000m 2The concentration of 500 m² / g ensures that the molecular sieve adsorbent has sufficient adsorption sites to effectively capture target molecules. The specific surface area of ​​micropores refers to the surface area contributed by micropores with a pore size of less than 2 nm in the adsorbent. The specific surface area of ​​the micropores in the molecular sieve adsorbent prepared in this disclosure is 500 m² / g. 2 / g-600m 2 The microporous structure can be controlled by selecting different types of molecular sieves (such as type A, type X, and type Y) or adjusting the crystallization time. The specific surface area of ​​mesopores refers to the surface area contributed by mesopores with pore sizes between 2 nm and 50 nm in the adsorbent. Mesopores mainly act as rapid mass transfer channels during adsorption, effectively reducing the diffusion resistance of the adsorbate into the micropores, thereby improving the adsorption rate and the utilization efficiency of the adsorbent. The specific surface area of ​​the mesopores in the molecular sieve adsorbent prepared in this disclosure is 300 nm. 2 / g-400m 2 / g can balance adsorption capacity and mass transfer rate.

[0060] The embodiments of the present invention will be described in detail below with reference to the examples. The molecular sieve adsorbents used in the following examples are all... Figure 1 The method shown is for obtaining the product; however, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified, specific conditions in the examples were performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0061] Example 1

[0062] An aluminum source and a silicon source were added to an alkaline solution, and the mixture was aged at room temperature. After aging, crystallization was performed, and the product was filtered, washed, and dried to obtain an X-type molecular sieve. 10 g of the X-type molecular sieve was ground into powder and sieved to a mesh size of 20-40. The sieved molecular sieve was then washed and dried. 20 mL of deionized water and 2 g of hexadecyltrimethylammonium bromide (CTAB) were added to the dried molecular sieve, and the mixture was stirred thoroughly. 5 mL of dilute hydrochloric acid (5 mol / L) and 10 g of sodium silicate were then added, and the mixture was stirred at 40 °C for 4 h. The pH was then adjusted to 1, and the solution was transferred to a high-pressure reactor for crystallization at 120 °C for 15 h. The product after the reaction was filtered, washed, dried, and calcined at 550 °C for 12 h to obtain the final microporous alkane-olefin separation molecular sieve adsorbent.

[0063] Example 2

[0064] An aluminum source and a silicon source were added to an alkaline solution, and the mixture was aged at room temperature. After aging, crystallization was performed, and the product was filtered, washed, and dried to obtain an X-type molecular sieve. 10 g of the X-type molecular sieve was ground into powder and sieved. The sieved molecular sieve was then washed and dried. 20 mL of deionized water and 2 g of sodium dodecyl sulfate (SDS) were added to the dried molecular sieve, and the mixture was stirred thoroughly. 5 mL of dilute hydrochloric acid (5 mol / L) and 10 g of sodium silicate were then added, and the mixture was stirred at 40 °C for 4 h. The pH was then adjusted to 1, and the solution was transferred to a high-pressure reactor for crystallization at 120 °C for 15 h. The product after the reaction was filtered, washed, dried, and calcined at 550 °C for 12 h to obtain the final microporous alkane-olefin separation molecular sieve adsorbent.

[0065] Example 3

[0066] An aluminum source and a silicon source were added to an alkaline solution, and the mixture was aged at room temperature. After aging, crystallization was performed, and the product was filtered, washed, and dried to obtain an X-type molecular sieve. 10 g of the X-type molecular sieve was ground into powder and sieved. The sieved molecular sieve was then washed and dried. 20 mL of deionized water and 2 g of alkylphenol polyoxyethylene ether (APEO) were added to the dried molecular sieve, and the mixture was stirred thoroughly. 5 mL of dilute hydrochloric acid (5 mol / L) and 10 g of sodium silicate were then added, and the mixture was stirred at 40 °C for 4 h. The pH was then adjusted to 1, and the solution was transferred to a high-pressure reactor for crystallization at 120 °C for 15 h. The product after the reaction was filtered, washed, dried, and calcined at 550 °C for 12 h to obtain the final microporous alkylene-separated molecular sieve adsorbent.

[0067] Example 4

[0068] An aluminum source and a silicon source were added to an alkaline solution, and the mixture was aged at room temperature. After aging, crystallization was performed, and the product was filtered, washed, and dried to obtain an X-type molecular sieve. 10 g of the X-type molecular sieve was ground into powder and sieved. The sieved molecular sieve was then washed and dried. 20 mL of deionized water and 2 g of a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer (P-123) were added to the dried molecular sieve, and the mixture was stirred thoroughly. 5 mL of dilute hydrochloric acid (5 mol / L) and 10 g of sodium silicate were then added, and the mixture was stirred at 40 °C for 4 h. The pH was then adjusted to 1, and the solution was transferred to a high-pressure reactor for crystallization at 120 °C for 15 h. The product after the reaction was filtered, washed, dried, and calcined at 550 °C for 12 h to obtain the final microporous alkane-olefin separated molecular sieve adsorbent.

[0069] Example 5

[0070] An aluminum source and a silicon source were added to an alkaline solution, and the mixture was aged at room temperature. After aging, crystallization was performed, and the product was filtered, washed, and dried to obtain a Y-type molecular sieve. 10 g of the Y-type molecular sieve was ground into powder and sieved. The sieved molecular sieve was then washed and dried. 20 mL of deionized water and 2 g of hexadecyltrimethylammonium bromide (CTAB) were added to the dried molecular sieve, and the mixture was stirred thoroughly. 5 mL of dilute hydrochloric acid (5 mol / L) and 10 g of sodium silicate were then added, and the mixture was stirred at 40 °C for 4 h. The pH was then adjusted to 1, and the solution was transferred to a high-pressure reactor for crystallization at 120 °C for 15 h. The product after the reaction was filtered, washed, dried, and calcined at 550 °C for 12 h to obtain the final microporous alkane-olefin separation molecular sieve adsorbent.

[0071] Comparative Example 1

[0072] An aluminum source and a silicon source are added to an alkaline solution, and the solution is aged at room temperature. After aging, the solution is crystallized, and the product is filtered, washed, and dried to obtain an X-type molecular sieve.

[0073] Comparison Column 2

[0074] An aluminum source and a silicon source were added to an alkaline solution, and the mixture was aged at room temperature. After aging, crystallization was performed, and the product was filtered, washed, and dried to obtain an X-type molecular sieve. 10 g of the X-type molecular sieve was ground into powder and sieved. The sieved molecular sieve was then washed and dried. 20 mL of deionized water and 2 g of hexadecyltrimethylammonium bromide (CTAB) were added to the dried molecular sieve, and the mixture was stirred thoroughly. 5 mL of dilute hydrochloric acid (5 mol / L) and 10 g of sodium silicate were then added, and the mixture was stirred at 40 °C for 4 h. The pH was then adjusted to 1, and the solution was transferred to a high-pressure reactor for crystallization at 120 °C for 8 h. The product after the reaction was filtered, washed, dried, and calcined at 550 °C for 12 h to obtain the final molecular sieve adsorbent.

[0075] Comparison Column 3

[0076] An aluminum source and a silicon source were added to an alkaline solution, and the mixture was aged at room temperature. After aging, crystallization was performed, and the product was filtered, washed, and dried to obtain an X-type molecular sieve. 10 g of the X-type molecular sieve was ground into powder and sieved. The sieved molecular sieve was then washed and dried. 20 mL of deionized water and 2 g of hexadecyltrimethylammonium bromide (CTAB) were added to the dried molecular sieve, and the mixture was stirred thoroughly. 5 mL of dilute hydrochloric acid (5 mol / L) and 10 g of sodium silicate were then added, and the mixture was stirred at 40 °C for 4 h. The pH was then adjusted to 1, and the solution was transferred to a high-pressure reactor for crystallization at 120 °C for 15 h. The product after the reaction was filtered, washed, dried, and calcined at 550 °C for 6 h to obtain the final molecular sieve adsorbent.

[0077] Comparative Example 4

[0078] An aluminum source and a silicon source were added to an alkaline solution, and the mixture was aged at room temperature. After aging, crystallization was performed, and the product was filtered, washed, and dried to obtain an X-type molecular sieve. 10 g of the X-type molecular sieve was ground into powder, and 20 mL of deionized water and 2 g of hexadecyltrimethylammonium bromide (CTAB) were added, followed by thorough mixing. 5 mL of dilute hydrochloric acid (5 mol / L) and 10 g of sodium silicate were then added, and the mixture was stirred at 40 °C for 4 h. The pH was then adjusted to 1, and the solution was transferred to a high-pressure reactor for crystallization at 120 °C for 15 h. The product after the reaction was filtered, washed, dried, and calcined at 550 °C for 12 h to obtain the final molecular sieve adsorbent.

[0079] Comparative Example 5

[0080] An aluminum source and a silicon source were added to an alkaline solution, and the mixture was aged at room temperature. After aging, crystallization was performed, and the product was filtered, washed, and dried to obtain an X-type molecular sieve. 10 g of the X-type molecular sieve was ground into powder and sieved to a mesh size of 20-40. The sieved molecular sieve was then washed and dried. 20 mL of deionized water and 10 g of sodium silicate were added to the dried molecular sieve, and the mixture was stirred thoroughly. 5 mL of dilute hydrochloric acid (5 mol / L) and 2 g of hexadecyltrimethylammonium bromide (CTAB) were then added, and the mixture was stirred at 40 °C for 4 h. The pH was then adjusted to 1, and the solution was transferred to a high-pressure reactor for crystallization at 120 °C for 15 h. The product after the reaction was filtered, washed, dried, and calcined at 550 °C for 12 h to obtain the final microporous alkane-olefin separation molecular sieve adsorbent.

[0081] Comparative Example 6

[0082] An aluminum source and a silicon source were added to an alkaline solution, and the mixture was aged at room temperature. After aging, crystallization was performed, and the product was filtered, washed, and dried to obtain an X-type molecular sieve. 10 g of the X-type molecular sieve powder was added to 20 mL of deionized water and 2 g of hexadecyltrimethylammonium bromide (CTAB), and the mixture was stirred thoroughly. 5 mL of dilute hydrochloric acid (5 mol / L) and 10 g of sodium silicate were then added, and the mixture was stirred at 40 °C for 4 h. The pH was then adjusted to 1, and the solution was transferred to a high-pressure reactor for crystallization at 120 °C for 15 h. The product after the reaction was filtered, washed, dried, and calcined at 550 °C for 12 h to obtain the final microporous alkane-olefin separated molecular sieve adsorbent.

[0083] The adsorbents obtained above were subjected to specific surface area analysis and separation degree determination. The analysis results are shown in Table 1.

[0084] Table 1. Specific surface area and separation degree of the adsorbent

[0085]

[0086] Separation degree was determined using a fixed-bed reactor. The procedure for determining separation degree using a deoxidized Fischer-Tropsch synthesis C8-C10 distillate as feedstock, with an olefin content of 77% and an alkane content of 23%, and an desorption solution consisting of 30% dodecene and 70% dodecane, is described below:

[0087] Step 1: At room temperature, fill the adsorption column with the desorption solution and then apply a back pressure of 0.5 MPa.

[0088] Step 2: Take out the effluent from the outlet, and wait until the composition of the effluent is consistent with that of the desorbed liquid before introducing the raw material sample.

[0089] Step 3: Switch the pump inlet to the feed solution and inject 1.5 mL.

[0090] Step 4: After the raw material liquid is injected, switch the pump inlet to the desorption liquid and take samples at time intervals.

[0091] Step 5: After sampling, analyze the sample on a PONA chromatograph and plot the resolution curve based on the chromatographic results.

[0092] The formula for calculating the separation degree is as follows:

[0093]

[0094] Where R represents the resolution; t(R1) represents the time of peak height of alkane peak; t(R2) represents the time of peak height of olefin peak; W1 represents the peak width of alkane peak; and W2 represents the peak width of olefin peak.

[0095] The present disclosure provides a method for separating α-olefins and alkanes, as well as a molecular sieve adsorbent. This method involves passing a Fischer-Tropsch synthetic oil feedstock containing olefins and alkanes into a simulated moving bed reactor filled with a molecular sieve adsorbent to separate olefins and alkanes. By preparing the molecular sieve adsorbent, the method effectively solves the problems of low separation efficiency, high operating environment risk, and insufficient cost control in the prior art.

[0096] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, and are not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein. The scope of the invention is defined by the appended claims.

Claims

1. A method for separating olefins and alkanes, characterized in that, include: A Fischer-Tropsch synthesis feedstock containing olefins and alkanes is passed into a simulated moving bed reactor packed with molecular sieve adsorbent for alkane-olefin separation. The molecular sieve adsorbent in the simulated moving bed reactor is prepared by the following method, including the following steps: Step S1: Add aluminum source and silicon source to alkaline solution and age at room temperature; after aging, crystallize at a predetermined temperature; the crystallized product is filtered, washed, and dried to obtain molecular sieve raw powder; the molecular sieve raw powder is shaped under the action of a forming agent and calcined to obtain shaped molecular sieve; the shaped molecular sieve obtained in step S1 is one or more of type A molecular sieve, type X molecular sieve, and type Y molecular sieve. Step S2: Take the shaped molecular sieve from step S1, grind it into powder, and sieve it to a density of 20 μm. The molecular sieve after sieving is washed and dried using a 40-mesh screen. Step S3: Add deionized water and surfactant to the dried molecular sieve from step S2 to obtain a first mixture. The mass ratio of molecular sieve, surfactant, and deionized water in the first mixture is 1:0.2:2-1:0.5:

6. The molecular weight range of the surfactant added in step S3 is 200-800, and the surfactant is one or more of hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, and alkylphenol polyoxyethylene ether. Step S4: Add acid and silicon source to the first mixture in step S3, and adjust the pH value to obtain a second mixture. Crystallize the second mixture, and after the reaction, filter, wash, dry, and calcine the product to obtain the molecular sieve adsorbent. Adjust the pH value to 1-4, and crystallize in a high-pressure reactor for 10-20 hours at a crystallization temperature of 100℃-160℃. The mass ratio of acid, silicon source, and molecular sieve in the second mixture is 1:2:2-1:8:

10.

2. The method according to claim 1, characterized in that, The silicon source in step S4 is one or more of sodium silicate, silicon dioxide, tetraethyl orthosilicate, and silica.

3. The method according to claim 1, characterized in that, The acid in step S4 is one or more of hydrochloric acid, sulfuric acid, nitric acid, and acetic acid, with a concentration of 4 mol / L to 7 mol / L.

4. The method according to claim 1, characterized in that, The total specific surface area of ​​the molecular sieve adsorbent in step S4 is 800 m². 2 / g-1000m 2 / g; The specific surface area of ​​the micropores is 500m² 2 / g-600m 2 / g, the specific surface area of ​​the mesopores is 300m². 2 / g-400m 2 / g.

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