Method for preparing internal olefin by catalyzing dehydration isomerization of straight-chain fatty alcohol
Through the one-step dehydration and isomerization reaction of HMOR zeolite molecular sieve catalyst, the two-step method of converting long-chain fatty alcohols into internal olefins in the prior art was solved, and efficient and environmentally friendly internal olefin synthesis was achieved, avoiding expensive catalysts and liquid acids The use of alkali demonstrates excellent characteristics of high selectivity and high yield.
Patent Information
- Application Number
- CN202411342697.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-25
- Publication Date
- 2024-12-31
AI Technical Summary
In the prior art, the process of converting long-chain fatty alcohols into internal olefins requires a two-step process, and relying on expensive transition metal complexes and liquid acid-base catalysts, there are problems such as environmental pollution, high costs and difficult to recycle the catalyst.
Using cheap HMOR zeolite molecular sieve catalyst, the one-step dehydration isomerization reaction is performed to directly convert n-heptol into 2-heptene and 3-heptene, avoiding the use of transition metals and liquid acid and bases, and achieving easy recovery of the catalyst. and environmentally friendly, high selectivity and high yield synthesis.
It achieves easy operation, environmentally friendly high selectivity and high yield conversion, reduces production costs, and is easy to separate and reuse from the reaction system.
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Abstract
Description
Technical Field
[0001] The present invention focuses on the field of heterogeneous catalytic organic synthesis, and discloses a method for preparing internal olefins by catalyzing the dehydration isomerization of straight-chain fatty alcohols using a heterogeneous zeolite molecular sieve catalyst, such as a new method for directly synthesizing 2-heptene and 3-heptene in a one-step manner by catalyzing the tandem reaction of the dehydration isomerization of n-heptanol. Technical Background
[0002] As an important chemical raw material, long-chain olefins have a wide range of application values in many fields such as petrochemicals, medicine, light industry, pharmaceuticals and textiles. Compared with olefins with C=C double bonds at the end (terminal olefins), olefins with double bonds inside (internal olefins) often have special chemical properties and application prospects. This is because internal olefin compounds have lower hydrogenation saturation activity, especially good antibacterial, antioxidant and anti-free radical activities. Therefore, it is extremely important in the synthesis of some special chemicals. For example: it is used in the flavor and fragrance industry, pharmaceutical and cosmetic industries, and as an intermediate in organic and pharmaceutical synthesis for the synthesis of complex structured compounds. Therefore, the chemical process of selectively converting terminal olefins into internal olefins has extremely important scientific research value and practical application significance.
[0003] For example, the synthesis of internal olefins such as 2-heptene and 3-heptene is mainly prepared by catalyzing the isomerization of 1-olefins using transition metal complex catalysts (Angewandte Chemie International Edition, 2017, 56 (6): 1614-1618; Journal of the American Chemical Society, 2021, 143 (7): 2792-2800). Expensive transition metals are required, and additives need to be added to achieve the isomerization process. At the same time, there are certain difficulties in separating the catalyst and the product.
[0004] n-Heptanol is a cheap alcohol compound. If it is converted into internal olefin compounds such as 2-heptene and 3-heptene, its added value can be greatly improved. Existing research converts alcohols into internal olefins through a two-step process: first, the alcohol forms 1-olefins through a dehydration reaction under the action of a catalyst; then, the 1-olefin is isomerized into internal heptenes such as 2,3-olefins under the catalysis of other catalysts. The dehydration of alcohols to form terminal olefins can generally be achieved by using acid, base and transition metal complex catalysts. For example: J. Ahmad et al. reported the use of sulfuric acid to catalyze the dehydration of long-chain alcohols to prepare olefins, and studied its reaction kinetics (Langmuir, 1990, 6 (6): 1098-1101); Connor P. Nash ... Molecular sieve catalysts containing Lewis acid and Lewis acid catalyze the conversion of mixed alcohols such as ethanol, propanol, and butanol. The conversion rate was found to be greater than 98%. However, the activity of mesoporous materials containing Lewis acid was slightly poor, and a certain amount of ether compounds were produced (Applied Catalysis A: General, 2016, 510: 110-124). Olaf Nachtigall et al. used a transition metal complex catalyst [Fe(OTf)2(FOX)] to selectively convert 1-phenylethanol into styrene in good yield at moderate temperatures (American Chemical Society Catalysis, 2021, 11(17): 10885-91);
[0005] Regarding the second step double bond isomerization reaction pathway, although there have been many relevant literature reports, this process is mainly achieved by using a variety of transition metal complexes and homogeneous catalysts such as liquid acids and bases, specifically involving: cobalt metal complex catalysts (Journal of the American Chemical Society, 2014, 136 (3): 945-955); nickel metal complex catalysts (Nature catalysis, 2021, 4 (8): 674-683.) solid acid catalysts (Fuel, 2019, 254: 115593) liquid acids (The Journal of Organic Chemistry, 1990, 55 (20): 5520-5525; Journal of the American Chemical Society, 1953, 75 (7): 1631-1635) liquid bases (Organic letters, 2013, 15 (11): 2822-2825), etc.
[0006] It is worth noting that these catalytic systems generally require the use of expensive transition metal complexes and require the addition of additives to achieve better results. Liquid acids and bases also have problems such as corrosion of equipment. At the same time, there are certain difficulties in the recovery of catalysts and the separation of products. Therefore, the current synthesis method has the following problems: ① Using alcohol as a raw material, it takes two steps to obtain 2-heptene and 3-heptene; ② It requires the use of liquid acids and bases, transition metal complex catalysts and corresponding additives or ligands, which are environmentally unfriendly, costly, and difficult to recycle catalysts.
[0007] As a solid acid, molecular sieves can achieve the dehydration of fatty alcohols and the skeletal isomerization of corresponding olefins (CN201610946837.4), and are generally suitable for the dehydration reaction of short-chain alcohols C<6 with smaller molecular structures. However, for long-chain alcohols C>6 with longer carbon chain structures, there are relatively few studies using solid acids such as molecular sieves as catalysts to achieve long-chain normal alcohols. A small number of studies have achieved the isomerization of α-hexadecene to prepare internal olefins under high temperature and high pressure conditions of 180-250°C and pressure of 0.5-2MPa (CN202210859593.1). It is worth noting that during the synthesis of molecular sieves, different raw material ratios will affect the acid strength and pore structure of the molecular sieve, which can greatly affect the selectivity of alcohol dehydration and olefin double bond isomerization.
[0008] In view of the problems existing in the reaction of generating 2-heptene and 3-heptene by n-heptanol, the present invention adopts a relatively cheap HMOR zeolite molecular sieve catalyst, and realizes a new process of directly converting n-heptanol into internal olefins such as 2-heptene and 3-heptene by a one-step method through a series reaction of dehydration isomerization without the participation of expensive transition metal complexes. The method of the present invention is simple to operate, environmentally friendly, and exhibits excellent characteristics of high selectivity and high yield. In addition, the heterogeneous catalyst in the present invention is easy to separate from the reaction system, and can be recycled and reused, and has a high application prospect. Summary of the invention
[0009] The present invention aims at the problems existing in the process of synthesizing linear internal olefins in existing research, and provides a new method for directly preparing linear internal olefins in one step by using only a heterogeneous catalyst to catalyze the dehydration isomerization of linear alkyl alcohols.
[0010] In order to achieve the above object, the technical solution adopted by the present invention is:
[0011] The present invention is applicable to C n H 2n+1 OH (n ≧ 7) alcohols are directly used to prepare internal olefins in one step. Linear fatty alcohols and HMOR zeolite catalysts are added to a reaction tube, and a solvent is added, and then placed in a heater for reaction. After the reaction is completed, the reaction liquid is separated and purified to obtain linear internal olefin compounds.
[0012]
[0013] Wherein R and R' are independently selected from alkyl groups. The total number of carbon atoms in the alkyl groups in R and R' is (n-2).
[0014] The following uses n-heptanol as an example.
[0015] The reaction steps are as follows: n-heptanol and HMOR zeolite catalyst are added to a reaction tube, a reaction solvent is added, and the tube is heated and stirred at 130-150° C. for 6-24 hours. After the reaction is completed, the reaction solution is centrifuged to collect the supernatant. After reduced pressure concentration, the obtained crude product is separated and purified by column chromatography to finally obtain 2-heptene and 3-heptene.
[0016] The preferred reaction temperature in the present invention is 150°C.
[0017] The reaction time in the present invention is 6 to 24 hours, preferably 14 hours.
[0018] The solvent in the present invention may be toluene, 1,2-dichloroethane (DCE), DMF, DMSO, acetonitrile and cyclohexane, preferably DCE.
[0019] The amount of the catalyst used in the present invention is 30-40 mg / 0.3 mmol of straight-chain alkyl alcohol.
[0020] The reaction involved is:
[0021]
[0022] The synthesis method of H-type MOR zeolite molecular sieve catalyst is as follows:
[0023] Aluminum source calculated as Al2O3, silicon source calculated as SiO2, cationic copolymer template and water are mixed, loaded into a kettle, filtered, washed, dried and calcined at high temperature to obtain MOR zeolite. The molar composition of each substance in the gel system is: 0.05~1Al2O3: 0.5~10Na2O: 10-30SiO2: 0.001~0.1RCC: 50~600H2O.
[0024] Then, ammonium chloride or ammonium nitrate aqueous solution is used for ammonium ion exchange, followed by drying at 120-200° C. for 10-24 hours, and then calcining at 400-600° C. to finally obtain HMOR zeolite.
[0025] The pore structure parameters of HMOR zeolite are: specific surface area S BET =499.5m 2 / g, micropore volume is V micro =0.1cm 3 / g, and the mesopore volume is 0.4cm 3 / g. The added cationic copolymer template RCC can greatly affect the pore structure of the synthesized zeolite molecular sieve.
[0026] The Si / Al ratio of HMOR zeolite is between 6 and 20. When the Si / Al ratio is greater than 20, the Al content is low, the zeolite acidity is weak, and dehydration is difficult. When the Si / Al ratio is less than 6, the Al content is high, the zeolite acidity is strong, and alcohol is easily dehydrated to form ether.
[0027] Compared with the prior art, the technical advantages of the present invention are:
[0028] The present invention innovatively proposes a method of using HMOR as a catalyst to catalyze the dehydration of straight-chain fatty alcohols to generate terminal olefins while accompanying the isomerization of terminal olefins, thereby obtaining straight-chain internal olefin compounds in one step and avoiding skeletal isomerization reactions. This technical strategy shows significant advantages over traditional methods for synthesizing internal olefins: it abandons the previous homogeneous catalytic system that relies on transition metals, complex ligands, co-catalysts, and liquid acids and bases, and instead relies only on cheap zeolite molecular sieve catalysts to achieve a one-step efficient synthesis of the target product. This synthetic route is cleverly designed, easy to operate, mild in reaction conditions, easy to recycle the catalyst, and the entire process is environmentally friendly. It is particularly worth mentioning that zeolite molecular sieves have a high specific surface area and contain abundant active sites, which makes the target product have a high yield and selectivity. In addition, the catalyst can be recycled and reused, which further reduces the production cost and is both economical and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Figure 1 The nuclear magnetic spectrum (1HNMR) of 2-heptene prepared in Example 1;
[0030] Figure 2 This is the 1H NMR spectrum of 3-heptene prepared in Example 1. Specific implementation plan
[0031] The technical solution of the present invention is described in detail below with a specific embodiment using n-heptanol as a substrate, but the scope thereof is not limited thereto.
[0032] The HMOR zeolite catalyst synthesis method in the embodiment is:
[0033] 8 g of diallylamine (99%), 50 g of dimethyldiallylammonium chloride (60%) aqueous solution, 15 g of deionized water and 5 g of methacrylic acid (98%) were mixed and stirred at room temperature for 30 minutes. Then, 10 g of ammonium persulfate aqueous solution (10%) was added dropwise under vigorous stirring. The solution was heated to 105°C and maintained for 4 hours and then cooled to room temperature. The resulting cationic copolymer was named RCC.
[0034] Mix 18.7 mL of water glass and 5.0 mL of 2.6 wt.% NaAlO2 aqueous solution. After stirring at room temperature for 20 minutes, slowly add 3.0 mL RCC under vigorous stirring. After continuous stirring for 90 minutes, add 10.8 mL of 7.7 wt.% Al2(SO4)3 aqueous solution. After stirring at room temperature for 90 minutes, transfer to a stainless steel autoclave and crystallize at 170°C for 2 days. Filter, wash, dry at 120°C overnight, and calcine in air at 550°C for 5 hours. The obtained sample is named NB-MOR, and its molar ratio is 1.0Al2O3:7.0Na2O:25SiO2:0.005RCC:580H2O.
[0035] Then, the ion exchange step was performed. In a 250 mL round-bottom flask, 10 g of the synthesized MOR zeolite was added to 100 ml of 1 mol / L NH4Cl solution and stirred at 80°C for 6 hours. After the reaction was completed, the reactor was cooled to room temperature and the reaction mixture was separated by filtration. The obtained solid sample was washed with deionized water, dried at 100°C for 10 hours, and finally calcined in air at 500°C for 5 hours to obtain HMOR molecular sieve; the measured Si / Al ratio of the HMOR zeolite used in the present invention was 7.1. Specific embodiment 1:
[0037] In a 10mL Schlenk reaction tube, n-heptanol (0.3mmol, 42μL), 30mg HMOR, and 1.0mL DCE were added in sequence. After the operation was completed, the tube was placed in a heater, the reaction temperature was controlled at 150°C, and the reaction was stirred for 14h. After the reaction was completed, the tube was cooled to room temperature, the reaction system was centrifuged, filtered, the supernatant was collected, and the crude product was concentrated under reduced pressure. Column chromatography separation and purification were performed to obtain 2-heptene and 3-heptene. The yields were 42.4% and 50.1%, respectively, and the total yield of linear internal olefins was 92.5%.
[0038]
[0039] Specific embodiments 2, 3:
[0040] Compared with Example 1, the difference between Examples 2 and 3 is that the reaction temperature of 150°C in Example 1 is replaced by 140°C and 130°C, and the remaining operations are the same as those in Example 1.
[0041] Table 1: Comparison of the reaction results of Examples 2 and 3 with those of Example 1
[0042]
[0043] As shown in Table 1, when the reaction temperature is changed to 130 or 140°C, the yield is significantly reduced, preferably 150°C. Specific Examples 4-6:
[0044] Compared with Example 1, Examples 4-6 differ in that the amount of the catalyst in Example 1 is 30 mg, which is replaced by 20 mg, 40 mg, and 50 mg. The remaining operations are the same as those in Example 1.
[0045] Table 2: Reaction results of Examples 4-6
[0046]
[0047] As can be seen from Table 2, when the amount of catalyst is replaced with 20 mg, 40 mg, and 50 mg, the yield changes, and 40 mg is preferred for synthesizing 2-heptene and 3-heptene.
[0048] Specific embodiments 7-11:
[0049] The difference between Examples 7-11 and Example 1 is that the solvent DCE in Example 1 is replaced by toluene, cyclohexane, acetonitrile, DMSO, and DMF, and the remaining operations are the same as those in Example 1.
[0050] Table 3: Reaction results of Examples 7-11
[0051] catalyst Solvent 2-Heptene yield (%) 3-Heptene yield (%) Yield (%) Example 7 HMOR Toluene 10.9 9.7 20.6 Example 8 HMOR Cyclohexane 10.2 8.3 18.5 Example 9 HMOR Acetonitrile - - 0 Example 10 HMOR DMSO - - 0 Embodiment 11 HMOR DMF - - 0
[0052] It can be seen from Table 3 that when the reaction system solvent is replaced with toluene, cyclohexane, acetonitrile, DMSO, and DMF, the yield is significantly reduced, and DCE is preferred.
[0053] Specific examples 12-16:
[0054] The difference between Examples 12-16 and Example 1 is that the reaction time of Example 1 is replaced with 6h, 8h, 10h, 12h and 16h, and the remaining operations are the same as Example 1.
[0055] Table 4: Reaction results of Examples 12-16
[0056]
[0057] It can be seen from Table 4 that the catalytic activity is significantly reduced when the reaction time is replaced by 6 h, 8 h, 10 h, 12 h and 16 h, and the preferred reaction time is 14 h.
[0058] Specific embodiments 17-20:
[0059] Compared with Example 1, Examples 17-20 differ in that the catalyst HMOR in Example 1 is replaced by USY, HBeta, HZSM-5, and MOR (ie, the NB-MOR prepared as described above), and the remaining operations are the same as those in Example 1.
[0060] Table 5: Reaction results of Examples 17-20
[0061] catalyst Time(h) 2-Heptene yield (%) 3-Heptene yield (%) Yield (%) Embodiment 17 USY 14 9.7 11.4 21.1 Embodiment 18 HBeta 14 - 5.1 5.1 Embodiment 19 HZSM-5 14 5.2 3.8 9.0 Embodiment 20 MOR 14 54.8 22.1 76.9
[0062] It can be seen from Table 5 that the catalytic activity of other catalysts such as HZSM-5, USY, HBeta and MOR is inferior to the catalytic yield of HMOR, and HMOR is preferred.
[0063] Specific embodiments 21-23:
[0064] Compared with Example 1, Examples 21-23 differ in that the catalyst HMOR in Example 1 is further subjected to acid treatment for dealumination to obtain HMOR zeolites with different Si / Al ratios (different acidity), and the catalytic reaction is the same as that in Example 1.
[0065] Table 6: Reaction results of Examples 21-23
[0066] Acid treatment concentration (mM) Si / Al ratio Time(h) Yield (%) Embodiment 21 0.15 8.5 14 24.1 Embodiment 22 0.3 9.4 14 13.8 Embodiment 23 0.5 10.2 14 13.2
[0067] It can be seen from Table 6 that after acid treatment, the Si / Al ratio increases and the acidity weakens, and the HMOR catalyst in Example 1 is preferred. Specific embodiment 24:
[0069] Compared with Example 1, Example 24 differs in that n-heptanol in Example 1 is replaced with n-dodecyl alcohol, and other reaction conditions remain unchanged, and internal dodecene is obtained with a yield of 69.3%. This indicates that under the same experimental conditions, as the carbon chain length increases, the yield of internal olefins decreases significantly.
[0070]
[0071] The above describes the optional embodiments of the present invention to teach those skilled in the art how to implement and reproduce the present invention. The raw materials and equipment used in the present invention, unless otherwise specified, are all commonly used raw materials and equipment in the art; the methods used in the present invention, unless otherwise specified, are all conventional methods in the art. In order to teach the scheme of the present invention, some conventional technical aspects have been simplified and omitted. Those skilled in the art should understand that variations derived from this aspect are all within the scope of protection of the present invention.
Claims
1. A method for preparing internal olefins by catalytic dehydration isomerization of straight-chain fatty alcohols, characterized in that: The preparation method is: A straight-chain fatty alcohol and an HMOR zeolite catalyst are added to a reaction tube, and a solvent is added, and then placed in a heater for reaction. After the reaction is completed, the reaction liquid is separated and purified to obtain an internal olefin compound; The reaction formula is: R and R' are independently selected from alkyl groups; the total number of carbon atoms in the alkyl groups in R and R' is (n-2).
2. The method for preparing internal olefins by catalytic dehydration isomerization of straight-chain fatty alcohols according to claim 1, characterized in that: The reaction temperature is 130-150°C.
3. The method for preparing internal olefins by catalytic dehydration isomerization of straight-chain fatty alcohols according to claim 1, characterized in that: The reaction time is 6 to 24 hours.
4. The method for preparing internal olefins by catalytic dehydration isomerization of straight-chain fatty alcohols according to claim 1, characterized in that: The reaction solvent is one or a mixture of toluene, 1,2-dichloroethane and cyclohexane.
5. The method for preparing internal olefins by catalytic dehydration isomerization of straight-chain fatty alcohols according to claim 4, characterized in that: The reaction solvent is 1,2-dichloroethane.
6. The method for preparing internal olefins by catalytic dehydration isomerization of straight-chain fatty alcohols according to claim 1, characterized in that: The Si / Al ratio of HMOR zeolite is between 6 and 20.
7. The method for preparing internal olefins by catalytic dehydration isomerization of straight-chain fatty alcohols according to claim 6, characterized in that: The molar composition of each substance in the gel system used to synthesize MOR zeolite is: 0.05-1Al2O3: 0.5-10Na2O: 10-30SiO2: 0.001-0.1RCC: 50-600H2O; the MOR zeolite is subjected to ammonium ion exchange using ammonium chloride or ammonium nitrate aqueous solution, and is dried at 120-200°C for 10-24 hours; and then calcined at 400-600°C to obtain HMOR zeolite.