Low-catalytic-activity adsorbent for separating alkane from olefin as well as preparation method and application of low-catalytic-activity adsorbent

Abstract

The invention relates to a low-catalytic-activity adsorbent for separating alkane from olefin as well as a preparation method and application of the low-catalytic-activity adsorbent. The adsorbent comprises a molecular sieve and an active metal component, the ratio of # imgabs0 # acid to Lewis acid is smaller than or equal to 0.2, and the adsorbent only shows selective adsorption capacity on olefin and does not have catalytic isomerization, self-polymerization and other activities. The molecular sieve is an X-type or Y-type molecular sieve, and the active metal component is selected from alkaline earth metal or transition metal. The adsorbent modifies a molecular sieve through an ion exchange method, and adopts an alkali solution treatment and roasting process to ensure low catalytic activity and molecular sieve skeleton stability. The prepared adsorbent has high adsorption capacity and excellent selectivity, can be widely applied to adsorption separation of C6-C12 alpha-olefin and alkane, is especially suitable for separation of an alkane / olefin mixture in Fischer-Tropsch synthetic oil, is low in process energy consumption and stable in performance, and has important industrial value.

Description

Technical Field

[0001] The present invention relates to the technical field of adsorption separation, and particularly relates to a low-catalytic-activity adsorbent, a preparation method thereof, and an application in the separation of alkanes and alkenes. Background Art

[0002] Alkenes are important chemical raw materials and are widely used in the production of lubricants, surfactants, plastic additives, and other high-value-added chemicals. Industrially, alkenes usually coexist with alkanes, especially in alkane / alkene mixtures produced by processes such as petroleum cracking and Fischer-Tropsch synthesis. Separating high-purity alkenes is of great significance for improving the quality and added value of alkene products. However, due to the similar physical properties of alkanes and alkenes (such as boiling point, molecular weight, etc.), their separation is difficult, and traditional separation methods (such as distillation separation) have high energy consumption and low efficiency.

[0003] Adsorption separation is an efficient and low-energy alkane / alkene separation technology, and its core lies in the selectivity of the adsorbent. Existing adsorbents mainly modify molecular sieves with metal ions to improve the selective adsorption performance for alkenes. However, most modified molecular sieves will show a certain catalytic activity towards alkenes during the separation process, resulting in side reactions such as isomerization, self-polymerization, or double-bond migration of alkenes. This not only reduces the yield of the target product α-olefin but also increases the complexity of the separation process. In addition, some modification processes may lead to the destruction of the molecular sieve framework structure, thereby affecting the stability and service life of the adsorbent.

[0004] In addition, in order to improve the adsorption capacity and selectivity of the adsorbent, a single metal ion modification scheme is often used in the prior art. However, due to the uneven distribution or inaccurate regulation of acidic sites in the molecular sieve, it is often difficult to effectively balance the catalytic activity and adsorption performance. Therefore, how to develop an adsorbent with low catalytic activity, high adsorption selectivity, and stable structure has become an urgent problem to be solved in the current technical field. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a low-catalytic-activity adsorbent and a preparation method thereof. By precisely regulating the acid / Lewis acid ratio, it only shows selective adsorption ability for alkenes during the separation of alkanes and alkenes without catalytic activity, thereby improving the separation purity and yield of the target α-olefin. The adsorbent has a high adsorption capacity and selectivity, and a stable framework structure, and is suitable for various industrial alkane / alkene separation scenarios.

[0006] According to the first aspect of the present invention, there is provided a low-catalytic-activity adsorbent for the separation of alkanes and alkenes, which comprises:

[0007] Molecular sieve;

[0008] Active metal component;

[0009] After the molecular sieve is introduced with the active metal component by ion exchange, it is further modified by alkali treatment to reduce the acid content, so that the ratio of Brønsted acid to Lewis acid of the adsorbent is controlled below 0.2, so that only selective adsorption ability for olefins is exhibited during the separation process, without catalytic activity;

[0010] The active metal component is selected from alkaline earth metals, transition metals or combinations thereof, and the molecular sieve is X-type molecular sieve, Y-type molecular sieve or a composite thereof.

[0011] In some technical solutions, the active metal component is selected from one or more of calcium, magnesium, zinc, nickel, copper, manganese, cobalt;

[0012] The molecular sieve is 13X molecular sieve and / or NaY molecular sieve.

[0013] In some technical solutions, the mass fraction of the active metal in the adsorbent is 0.1-20%, preferably 3-15%, and the mass fraction of the molecular sieve is 80-99.9%, preferably 85-97%.

[0014] In some technical solutions, the specific surface area of the adsorbent is 550-750 m 2 / g; the pore size is 0.3-0.5 cm 3 / g.

[0015] According to the second aspect of the present invention, a method for preparing the adsorbent as described above includes the following steps:

[0016] Mix the molecular sieve with the active metal salt solution and carry out an ion exchange reaction at a certain temperature;

[0017] Treat the ion-exchanged molecular sieve with an alkali solution;

[0018] Wash, dry and then calcine to obtain the adsorbent.

[0019] As a preferred solution, the concentration of the active metal salt solution is 0.1-3.0 mol / L, preferably 0.5-1.5 mol / L; the volume ratio of the active metal salt solution to the mass of the molecular sieve is 5-15 mL / g, preferably 10 mL / g;

[0020] The temperature of the ion exchange reaction is 20-80 °C, preferably 40-60 °C, the reaction time is 1-24 h, preferably 4-16 h, and the number of ion exchange times is 1-3 times.

[0021] As a preferred embodiment, the alkali solution is at least one of NaOH, KOH, NH3·H2O, and Ca(OH)2 solutions;

[0022] The concentration of the alkali solution is 0.1 - 2.0 mol / L, preferably 0.5 - 1.5 mol / L;

[0023] The ratio of the volume of the alkali solution to the mass of the adsorbent is 1 - 5 mL / g, preferably 2 - 3 mL / g;

[0024] The temperature for treating with the alkali solution is 20 - 80 °C, preferably 30 - 60 °C, and the alkali treatment time is 1 - 6 h, preferably 2 - 4 h.

[0025] As a preferred embodiment, the roasting temperature is 200 - 500 °C, preferably 300 - 400 °C, and the roasting time is 2 - 8 h, preferably 3 - 6 h.

[0026] As a preferred embodiment, the active metal salt solution is selected from one or more of nitrates, chlorides, carbonates, acetates, hydroxides, or oxides, preferably nitrates.

[0027] According to the third aspect of the present invention, there is further provided an application of a low catalytic activity adsorbent, and the adsorbent is prepared as described above or by the above preparation method;

[0028] Applied to the adsorption separation of alkane / alkene mixtures, and the alkene is one or more of C6 - C 12 α-olefins.

[0029] The present invention adopts the above technical solutions and has at least the following beneficial effects:

[0030] 1. Through the two-step modification process combining ion exchange and alkali treatment, the present invention realizes the precise regulation of the acidic sites of the molecular sieve, and controls the Brønsted acid / Lewis acid ratio to ≤0.2, effectively reducing the catalytic activity of the adsorbent towards alkenes. During the separation process, the adsorbent only shows selective adsorption ability towards the target α-olefin, without side reactions such as catalytic isomerization, self-polymerization, or double bond migration, thus significantly improving the purity and separation efficiency of the target product α-olefin. 2. The adsorbent of the present invention uses X-type molecular sieve and / or Y-type molecular sieve, and is modified with active metal components (such as calcium, magnesium, nickel, zinc, etc.). The adsorbent has a large specific surface area and a suitable pore size distribution, and these characteristics ensure that the adsorbent can show a high adsorption capacity and selectivity towards C6 - C

[0031] α-olefins, realizing efficient separation. 12 α-olefins, realizing efficient separation.

[0032] 3. Through appropriate alkali treatment processes and calcination conditions, the present invention reduces the acidic sites of the molecular sieve while not damaging its framework structure, avoiding the problem of molecular sieve collapse caused by strong chemical treatment or high-temperature calcination. The adsorbent exhibits excellent stability and durability during multiple adsorption-desorption cycles and can be widely applied in industrial adsorption separation devices.

[0033] 4. The preparation method of the adsorbent of the present invention adopts a two-step modification process (ion exchange and alkali treatment), combined with a conventional calcination process, with simple operation and easy industrial scale-up. The ranges of process parameters (such as metal salt solution concentration, alkali solution concentration, temperature, and time, etc.) are clear, and the repeatability is strong, which can effectively reduce production costs and is suitable for large-scale preparation.

[0034] 5. The adsorbent of the present invention is not only applicable to the separation of C6-C 12 α-olefins and alkanes, but also can be widely applied to the separation of other complex alkane / olefin mixtures, especially suitable for the separation of alkanes / olefins in the Fischer-Tropsch synthesis oil system. By reasonably designing the metal components and molecular sieve types of the adsorbent, the present invention can meet various industrial separation requirements and has important practical application value in the production of high-value-added olefin products.

[0035] 6. The adsorbent of the present invention relies on the physical process of adsorption-desorption during the separation process, avoiding the high energy consumption of traditional distillation processes. At the same time, since there is no catalytic side reaction in the adsorbent, additional treatment steps and the generation of pollutants are reduced, thus having significant advantages in terms of environmental friendliness and separation cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is the pyridine infrared spectrum of 3 comparative examples, 2 examples, and 1 blank control sample provided by the present invention;

[0037] Figure 2 is the X-ray diffraction pattern of 3 comparative examples, 2 examples, and 1 blank control sample provided by the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0038] The following further elaborates the present invention in combination with specific examples. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application. All common reagents used in the examples are commercially available products.

[0039] The measurement method of the evaluation performance data of the adsorbent in the following examples is as follows:

[0040] The adsorption performance of the adsorbent was evaluated by static saturation adsorption experiments. Weigh 5 g of the sample, then add 10 mL of the prepared alkene mixture, and conduct static saturation adsorption in a 40 °C water bath. After 4 h, take a sample and send it for GC-MS analysis and characterization. Among them, the prepared alkene mixture is a mixture of 1-hexene, n-hexane, 1-octene, and n-octane, and their mass ratio is 1:1:1:1.

[0041] Pyridine infrared analysis and characterization: Use an FT-IR of the Nicolet 6700 model to measure the acids and Lewis acids of the sample, with a scanning range of 4000 - 400 cm -1 and a resolution of 0.09 cm -1 . The sample amount is 50 mg. Purge and dehydrate with helium at 200 °C for 60 min, cool to room temperature and adsorb pyridine for 30 min, heat up to 150 °C to remove the unadsorbed pyridine, and finally conduct an infrared scan at 200 °C.

[0042] GC-MS analysis and characterization: The chromatographic column is a 19091s-001 PONA analytical column, and the inlet temperature is 250 °C; the carrier gas is high-purity hydrogen, and the split ratio is 200:1; the chromatographic column temperature programming is as follows: the initial temperature is 35 °C, hold for 15 min, increase to 100 °C at 2 °C / min, and keep the temperature constant for 10 min; the injection volume is 0.2 μL. Mass spectrometry conditions: Electron impact ionization source (EI); ionization energy: 70 eV; ion source temperature is 230 °C; interface temperature is 280 °C; the spectral library is the NIST 2002 database.

[0043] Data calculation:

[0044] The calculation method of the liquid-phase apparent adsorption capacity q of the adsorbent for olefins is as follows:

[0045]

[0046] In the formula, ω1 and ω2 are the mass fractions of olefins in the liquid before and after adsorption respectively, ρ is the density of the added alkene mixture (0.7 g / ml), V is the volume of the added alkene mixture, and m a is the mass of the adsorbent used.

[0047] The calculation method of the catalytic activity I of the adsorbent for olefins is as follows:

[0048]

[0049] In the formula, ω A and ω B are the mass fractions of isomeric olefins in the alkene mixture after and before adsorption respectively. The smaller the I value, the lower the catalytic activity of the adsorbent for olefins.

[0050] Comparative Example 1

[0051] First, weigh 22.05 g of calcium chloride dihydrate, add 300 mL of deionized water, place it in an 80 °C water bath and stir to dissolve. Then pour 30 g of 13X molecular sieve into it and perform ion exchange for 6 h. After the reaction, wash it clean with deionized water and place it in an oven at 100 °C for overnight drying to obtain the CaX adsorbent. Refer to Figure 1-2 , the acid / Lewis acid of the CaX adsorbent is 0.45, the liquid-phase apparent adsorption capacity q for olefins is 86.3 mg / g, and the catalytic activity I is 14.34%, indicating a relatively high acid content will result in a relatively high catalytic activity of the adsorbent for olefins.

[0052] Comparative Example 2

[0053] Weigh 10 g of unmodified 13X molecular sieve, add 30 mL of 0.5 mol / L NaOH solution, and treat it in a 60 °C water bath for 2 h. After treatment, wash it clean with deionized water and place it in an oven at 100 °C for overnight drying to obtain the NaOH-13X adsorbent. Refer to Figure 1-2 , the acid / Lewis acid of the NaOH-13X adsorbent is 0, the liquid-phase apparent adsorption capacity q for olefins is 68.9 mg / g, and the catalytic activity I is 0. And according to XRD analysis, the lattice structure of the adsorbent remains intact and the molecular sieve framework does not collapse.

[0054] Comparative Example 3

[0055] Use the same operation as in Comparative Example 2, with the difference that: after obtaining the NaOH-13X adsorbent, weigh 22.05 g of calcium chloride dihydrate, add 300 mL of deionized water, react at 80 °C for 6 h, then wash it clean with deionized water, and dry it overnight in an oven at 100 °C to obtain the pre-alkali-treated NaOH-CaX adsorbent. Refer to Figure 1-2 , the acid / Lewis acid of the NaOH-CaX adsorbent is 0.29, the liquid-phase apparent adsorption capacity q for olefins is 114.3 mg / g, and the catalytic activity I is 4.58%, indicating that the adsorbent prepared by the preparation method of pre-alkali treatment followed by ion exchange modification still has a relatively high acid content and still has a relatively high catalytic activity for olefins.

[0056] Example 1

[0057] Use the same operation as in Comparative Example 1, with the difference that: weigh 10 g of the prepared CaX adsorbent, add 30 mL of 0.5 mol / L NaOH solution, and treat it in a 60 °C water bath for 2 h. After treatment, wash it clean with deionized water and place it in an oven at 100 °C for overnight drying to obtain the CaX-NaOH adsorbent. Refer toFigure 1-2 , the acid / Lewis acid of the CaX-NaOH adsorbent is 0.04, the apparent liquid-phase adsorption capacity q of olefins is 90.1 mg / g, and the catalytic activity I = 0. This shows that after alkali treatment, the acid content of the sample is significantly reduced and it no longer has catalytic activity for olefins. Moreover, according to XRD analysis, the lattice structure of the adsorbent remains intact and the molecular sieve framework does not collapse.

[0058] Example 2

[0059] Using the same operation as in Comparative Example 1, the difference is that: the metal salt used is changed to 43.62 g of Ni(NO3)2·6H2O to prepare the NiX adsorbent. Then, 10 g of this adsorbent is weighed, 30 mL of 0.5 mol / L NaOH solution is added, and it is treated in a water bath at 60 °C for 2 h. After treatment, it is washed clean with deionized water and placed in an oven at 100 °C overnight to dry to obtain the NiX-NaOH adsorbent. Refer to Figure 1-2 , the acid / Lewis acid of the NiX-NaOH adsorbent is 0.19, the apparent liquid-phase adsorption capacity q of olefins is 60.7 mg / g, and the catalytic activity I = 0. This shows that after alkali treatment, the acid content of the sample is significantly reduced and it no longer has catalytic activity for olefins. Moreover, according to XRD analysis, the lattice structure of the adsorbent remains intact and the molecular sieve framework does not collapse.

[0060] Table 1. Specific surface area and pore volume data of 3 comparative examples, 2 examples and 1 blank control sample provided by the present invention

[0061] Sample Name <![CDATA[S BET / m 2 ·g -1 > <![CDATA[Pore volume / cm 3 ·g -1 > 13X 678 0.36 NaOH-13X 728 0.39 NaOH-CaX 701 0.37 CaX 641 0.36 CaX-NaOH 573 0.42 NiX-NaOH 597 0.46

[0062] The above embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation to the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

1. A low catalytic activity adsorbent for separation of alkanes and olefins, characterized in that: The adsorbent includes: Molecular sieves; Active metal components; After the molecular sieve is introduced with active metal components by ion exchange, it is further modified by alkali treatment to reduce The acid content of the adsorbent The ratio of acid to Lewis acid is controlled below 0.2; The active metal component is selected from alkaline earth metals, transition metals or a combination thereof, and the molecular sieve is an X-type molecular sieve, a Y-type molecular sieve or a composite thereof.

2. The low catalytic activity adsorbent according to claim 1, characterized in that: The active metal component is selected from one or more of calcium, magnesium, zinc, nickel, copper, manganese and cobalt; The molecular sieve is 13X molecular sieve and / or NaY molecular sieve.

3. The low catalytic activity adsorbent according to claim 1, characterized in that: The mass fraction of active metal in the adsorbent is 0.1-20%, and the mass fraction of molecular sieve is 80-99.9%.

4. The low catalytic activity adsorbent according to claim 1, characterized in that: The specific surface area of ​​the adsorbent is 550 to 750 m 2 / g; pore size: 0.3~0.5cm 3 / g.

5. A method for preparing the adsorbent according to any one of claims 1 to 4, characterized in that: The following steps are involved: The molecular sieve is mixed with an active metal salt solution to carry out an ion exchange reaction at a certain temperature; Treating the ion-exchanged molecular sieve with an alkaline solution; After washing, drying and calcining, the adsorbent is obtained.

6. The preparation method according to claim 5, characterized in that: The concentration of the active metal salt solution is 0.1 to 3.0 mol / L; the ratio of the volume of the active metal salt solution to the mass of the molecular sieve is 5 to 15 mL / g; The temperature of the ion exchange reaction is 20 to 80° C., the duration is 1 to 24 hours, and the number of ion exchanges is 1 to 3 times.

7. The preparation method according to claim 5, characterized in that: The alkaline solution is at least one of NaOH, KOH, NH3·H2O, and Ca(OH)2 solution; The concentration of the alkaline solution is 0.1-2.0 mol / L; The ratio of the volume of the alkaline solution to the mass of the adsorbent is 1 to 5 mL / g; The temperature of the alkaline solution treatment is 20-80° C., and the alkaline treatment time is 1-6 hours.

8. The preparation method according to claim 5, characterized in that: The calcination temperature is 200-500° C., and the calcination time is 2-8 hours.

9. The preparation method according to claim 5, characterized in that: The active metal salt solution is selected from one or more of nitrates, chlorides, carbonates, acetates, hydroxides or oxides.

10. An application of a low catalytic activity adsorbent, characterized in that: The adsorbent is prepared according to any one of claims 1 to 4 or according to any one of claims 5 to 9; Applied to the adsorption separation of alkane / olefin mixtures, wherein the olefins are C6~C 12 One or more α-olefins.

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