CN110841716B - Catalyst for preparing citral through dehydrolinalool rearrangement reaction, preparation method of catalyst and method for preparing citral - Google Patents
Catalyst for preparing citral through dehydrolinalool rearrangement reaction, preparation method of catalyst and method for preparing citral Download PDFInfo
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- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/14—Phosphorus; Compounds thereof
- B01J27/186—Phosphorus; Compounds thereof with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
- B01J27/188—Phosphorus; Compounds thereof with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium with chromium, molybdenum, tungsten or polonium
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- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/14—Phosphorus; Compounds thereof
- B01J27/186—Phosphorus; Compounds thereof with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
- B01J27/188—Phosphorus; Compounds thereof with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium with chromium, molybdenum, tungsten or polonium
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- C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
- C07C45/51—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by pyrolysis, rearrangement or decomposition
- C07C45/511—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by pyrolysis, rearrangement or decomposition involving transformation of singly bound oxygen functional groups to >C = O groups
- C07C45/512—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by pyrolysis, rearrangement or decomposition involving transformation of singly bound oxygen functional groups to >C = O groups the singly bound functional group being a free hydroxyl group
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Abstract
The invention belongs to the technical field of organic synthesis, and particularly relates to a catalyst for preparing citral through a rearrangement reaction of dehydrolinalool, a preparation method thereof, and a method for preparing citral, wherein the catalyst is a solid acid catalyst and comprises an active component, a carrier and an optional auxiliary agent; the active component is selected from one or more of silicotungstic acid, phosphomolybdic acid and phosphotungstic acid, and the auxiliary agent is selected from one or more of gold trichloride, rhenium trichloride, indium trichloride and lanthanum trichloride. The method for preparing citral comprises: under the existence of a solvent and the solid acid catalyst, dehydrolinalool is used as a raw material, and the citral is prepared through a Meyer-Schuster rearrangement reaction. The solid acid catalyst is simple to prepare, low in cost and long in service life; when the catalyst is used in the process of preparing citral, the reaction yield and the conversion rate are improved, and the selectivity is good; in addition, the catalyst has long service life and can realize continuous large-scale operation.
Description
Technical Field
The invention belongs to the technical field of organic synthesis, and particularly relates to a catalyst for preparing citral through a dehydrolinalool rearrangement reaction, a preparation method of the catalyst, and a method for preparing citral.
Background
Citral is a very important open-chain monoterpene spice, has a strong lemon fragrance, can be directly added into soft drinks, chewing gum, ice cream, candies and baked foods as one of edible essences specified in China, and can also be used for preparing various fruit type edible essences, particularly is indispensable in essence with a citrus fragrance. In addition, citral is a very important organic synthesis intermediate, and can be used for synthesizing higher spices such as ionone and irone, as well as vitamin A, vitamin E, phytol, beta-carotene, isophytol, and the like.
The natural citral can be extracted from the granada oil by a plurality of methods such as reduced pressure distillation, steam distillation, molecular distillation and the like, but is limited by the raw material source and the production process efficiency and can not meet the market demand. At present, the artificial synthesis of citral has been developed rapidly, and six methods, such as an aldol condensation method, an isoprene method, an acetone method, a nitrogen oxide method, a geraniol gas-phase oxidation method, a dehydrolinalool rearrangement method and the like, appear.
The dehydrolinalool rearrangement method is characterized in that dehydrolinalool is used as a raw material and is subjected to Meyer-Schuster rearrangement under the action of a catalyst to directly generate citral. The method has the advantages of easily available raw materials, simple process and mild conditions, is a green synthetic method with atomic economy, simplifies reaction steps and production operation flows, can also improve the utilization rate of the raw materials, is easy to obtain the raw materials, has high yield, and is suitable for large-scale production.
However, in the course of the preparation of dehydrolinalool rearrangement reaction, the choice of citral catalyst is the key to the successful operation of this process. The research on the catalyst for preparing citral by rearrangement of dehydrolinalool starts in the 70 th century, and after decades of development, the field has made some progress and achievement, and the current catalyst for preparing citral by rearrangement of dehydrolinalool mainly comprises three major types of vanadium-based catalyst, molybdenum-based catalyst and titanium-based catalyst.
The vanadium catalyst is represented by taking trialkyl siloxy vanadium oxide as a main catalyst and taking trialkyl silanol as a sub-catalyst. For example, patent document US3912656A reports the synthesis of citral with a catalytic system consisting of trialkylsiloxovanadate oxide and trialkylsiloxol, with a yield of greater than 90%; patent document US3994936 reports the introduction of an electron-withdrawing group in trialkylsiloxovanadate oxide or trialkylsiloxol, further improving the activity of the catalyst. However, the trialkylsiloxovanadate oxide used as the main catalyst is easy to hydrolyze, has poor stability, needs strict anhydrous environment, and is not beneficial to large-scale production because a large amount of expensive trialkylsiloxy alcohol is used. Scientific literature Russian Chemical Bulletin,1988,37 (9): 1765-1768 reports that polymerized alkyl silicon oxygen vanadium oxide is used as a catalyst to catalyze the rearrangement synthesis of the citral by dehydrolinalool, and the catalyst is simple to prepare, good in stability and not easy to hydrolyze, but the yield of the obtained citral is not high and is only 70%. Patent document US4463196 reports that citral is synthesized at 120 to 220 ℃ using an alkyl alcohol having 7 to 11 carbon atoms and/or an alkyl alcohol having 12 to 18 carbon atoms instead of the expensive trialkyl alcohol, but the citral yield is only 20%. As described above, although the vanadium-based catalyst has been developed earlier, it is not practical due to its poor stability, high yield and high cost, and thus the method is difficult to be applied to industrial production.
The molybdenum-based catalyst is dialkyl or diaryl sulfoxide and MoO m X n (m is 2 or 3, n is 0 or 2, X is acetyl pyruvic acid or halide). For example, patent document US6198006 reports MoO 2 X 2 The preparation method for synthesizing the citral by catalytic dehydrogenation of linalool through rearrangement is simple to operate, the citral yield is 88%, but the reaction time is as long as 17h, the catalyst is easy to inactivate and difficult to separate and recycle, and the catalyst has unpleasant odor, so that the quality of the citral is seriously influenced. Patent document CN103694092A provides a solution for using alcohol ether high boiling point solvent to realize the application of catalyst molybdenum acetylacetonate. Trans formAfter the reaction is finished, the solvent and the raw materials are recovered by reduced pressure distillation, the catalyst of molybdenum acetylacetonate and organic acid are remained in the solvent, and the yield of the citral can reach 94% by repeated application, but the catalyst in the scheme has the input amount of 4-6% of the weight of the dehydrolinalool, the using amount is large, and by-products are accumulated along with the increase of application times, the activity of the catalyst is reduced, and the selectivity is reduced. Patent document CN101391942A reports that molybdenum dioxide diacetyl pyruvate is used as a catalyst, macroporous weakly acidic cation exchange resin is used as a cocatalyst, a solvent and dimethyl sulfoxide are added to catalyze dehydrolinalool to synthesize citral through rearrangement, the citral yield can reach 90.2% at most after 9h of reaction, but the catalyst is reused once, the reaction time needs to be prolonged to 12h, and the citral yield can be reduced to 86.7%. Patent document CN104387248A reports that molybdenum trioxide is used as a catalyst to catalyze dehydrogenation of linalool to synthesize citral through rearrangement, and meanwhile, stoichiometric organic acid and dimethyl sulfoxide are added, and toluene is used as a solvent, so that the yield of the citral is over 95%. In summary, the yield of the citral prepared by the rearrangement reaction of the molybdenum-based catalyst for catalyzing dehydrogenation linalool is better and can reach 95% at most, but the catalyst has low reaction activity and long reaction time, and the catalyst has low recycling utilization, so that the cost is high, and the catalyst is difficult to apply to industrial production.
The titanium catalyst is a catalyst system consisting of a titanium compound and a halide of copper or silver. For example, U.S. Pat. No. 4,196,196A first reported in 1984 that titanium tetrachloride or titanium tetrabutoxide was used as a main catalyst, and halides of copper or silver were used as a co-catalyst to catalyze the rearrangement of dehydrolinalool to produce citral; the process is simple, but the yield of the citral is low, only 64 percent, and the application to industrial production is difficult. Scientific and technological literature (rich roots, zhoushan flowers, dehydrolinalool catalytic rearrangement synthesis citral heuristic [ J ]. Perfume and essence cosmetics 2003, (1): 1-4) reports that the preparation of citral by dehydrolinalool catalytic rearrangement in the presence of adipic acid is explored by using butyl titanate and copper chloride as catalysts, the catalysts are simple and easy to obtain, the process operation is simple, but the reaction yield is only 73%. Scientific and technological literature (Zhao Ningbo, zhu Zhi Qing, iso-titanate catalyzes the synthesis of citral [ J ] by dehydrogenating linalool, chemical industry advances 2016,35 (4): 1203-1206) reports that the catalytic rearrangement of dehydrogenated linalool to prepare citral in the presence of p-methyl benzoic acid by using isopropyl titanate as a main catalyst and cuprous chloride as a cocatalyst, and the yield can reach 88.4% at most. The process has the advantages of mild reaction conditions, short reaction time and simple and convenient operation, but the product citral has poor stability in the system and high post-treatment requirement, which greatly limits the application of the catalyst in industry.
In conclusion, the Meyer-Schuster rearrangement reaction is adopted to synthesize the citral, and the vanadium catalyst, the molybdenum catalyst or the titanium catalyst have respective obvious defects, so that the application of the citral in industrialization is limited.
The mechanism of the Meyer-Schuster rearrangement reaction is shown below: in the presence of acid, the hydroxyl group of propargyl alcohol (dehydrolinalool) is protonated, then a molecule of water is lost to form propargyl cation, which is a group of synthons with the allene cation, then the water carries out nucleophilic reaction on the allene cation to generate enol, and enol tautomerism is carried out to obtain alpha, beta-unsaturated aldehyde (citral). The specific reaction process is as follows:
acid catalysis is the key to the overall reaction, as can be seen from the mechanism by which dehydrolinalool generates citral via the Meyer-Schuster rearrangement.
Heteropoly acids are a general term for oxygen-containing polybasic acids consisting of a central atom (e.g., P, si, as, ge, etc.) and a coordinating atom (e.g., mo, V, W, etc.) bridged by an oxygen atom and a coordination. Heteropolyacids are very strong protonic acids both in the solid state and in the solution state, and are approximately one hundred times more acidic than sulfuric acid. Since there is little charge localization, protons can move freely, which makes heteropoly acids have strong bronsted acidity. Compared with traditional inorganic acid or organic acid, the heteropoly acid has the advantages of stability, no toxicity, high reaction activity and the like, and the solid acid catalyst formed by loading the heteropoly acid on the carrier with high specific surface area can further enhance the catalytic activity of the heteropoly acid, is easy to recover and can be recycled, so the heteropoly acid is called as a green catalyst.
Therefore, how to use the heteropoly acid in the reaction process of synthesizing citral by the Meyer-Schuster rearrangement reaction becomes an important research topic.
Disclosure of Invention
The invention aims to provide a catalyst for preparing citral by a rearrangement reaction of dehydrolinalool, a preparation method thereof and a method for preparing citral, aiming at the defects of the existing catalytic system for preparing citral by dehydrolinalool, wherein the catalyst has the advantages of simple preparation process, low cost and long service life; when the catalyst is used in the process of preparing citral, the reaction yield and the conversion rate are improved, and the selectivity is good; in addition, the catalyst has long service life, and can realize continuous large-scale operation of the citral preparation process.
In order to achieve the purpose, the technical scheme provided by the invention is as follows:
in one aspect, there is provided a catalyst for preparing citral by a rearrangement reaction of dehydrolinalool, the catalyst being a solid acid catalyst comprising: an active ingredient, a carrier and optionally an adjuvant;
the active component is heteropolyacid, is selected from one or more of silicotungstic acid, phosphomolybdic acid and phosphotungstic acid, and is preferably phosphomolybdic acid;
the carrier is selected from one or more of silicon dioxide, aluminum oxide and titanium dioxide, and is preferably titanium dioxide;
the auxiliary agent is one or more selected from gold trichloride, rhenium trichloride, indium trichloride and lanthanum trichloride, and is preferably gold trichloride.
According to the catalyst provided by the present invention, preferably, the content of the active component is 0.1wt% to 20wt% (e.g., 0.2wt%, 0.5wt%, 1wt%, 1.5wt%, 2.5wt%, 4wt%, 6wt%, 8wt%, 10wt%, 15 wt%) of the total weight of the solid acid catalyst, more preferably 2 to 5wt%.
Preferably, the promoter is present in an amount of 0 to 0.1wt% (e.g., 0.01wt%, 0.015wt%, 0.025wt%, 0.04wt%, 0.06wt%, 0.08 wt%), more preferably 0.02 to 0.05wt%, based on the total weight of the solid acid catalyst.
In some examples, the solid acid catalyst comprises: an active ingredient and a carrier; wherein the content of the active component accounts for 0.1-20 wt% of the total weight of the solid acid catalyst.
In some examples, the solid acid catalyst comprises: active ingredients, carriers and auxiliaries; wherein, the content of the active component accounts for 0.1wt% -20 wt% of the total weight of the solid acid catalyst, and the content of the auxiliary agent accounts for 0.02wt% -0.05 wt% of the total weight of the solid acid catalyst.
In some examples, the solid acid catalyst comprises: active ingredients, carriers and auxiliaries; wherein, the content of the active component accounts for 2 to 5 weight percent of the total weight of the solid acid catalyst, and the content of the auxiliary agent accounts for 0.02 to 0.05 weight percent of the total weight of the solid acid catalyst.
In some examples, the solid acid catalyst comprises, based on 100wt% total weight of the solid acid catalyst:
0.1-20 wt% of active component;
0.01 to 0.1 weight percent of auxiliary agent;
the balance being carriers.
In some examples, the solid acid catalyst comprises, based on 100wt% total weight of the solid acid catalyst:
0.1-20 wt% of active component;
0.02-0.05 wt% of assistant;
the balance being carriers.
In some examples, the solid acid catalyst comprises, based on 100wt% of the total weight of the solid acid catalyst:
2-5 wt% of active component;
0.01 to 0.1 weight percent of auxiliary agent;
the balance being carriers.
In another aspect, there is provided a method of preparing a catalyst as described above, comprising the steps of:
i) Preparing the carrier (e.g., silica powder, alumina powder, and titanium dioxide powder) into a slurry, followed by molding and granulation to obtain a molded carrier;
ii) dissolving the heteropoly acid as an active component in water to form a solution, and optionally adding the auxiliary agent to prepare an impregnation liquid; placing the formed carrier in the impregnation liquid, uniformly stirring, and then heating and stirring until all water is evaporated to dryness to obtain a crude product;
iii) And drying and roasting the obtained crude product to obtain the solid acid catalyst.
According to the preparation method provided by the present invention, in some examples, the preparation method of the solid acid catalyst comprises the following steps:
i) Preparing the carrier (e.g., silica powder, alumina powder, and titanium dioxide powder) into a slurry, followed by molding and granulating to obtain a molded carrier;
ii) dissolving the heteropoly acid serving as an active component in water to form a solution, and adding the auxiliary agent to prepare a dipping solution; placing the formed carrier in the impregnation liquid, uniformly stirring, and then heating and stirring until all water is evaporated to dryness to obtain a crude product;
iii) And drying and roasting the obtained crude product to obtain the solid acid catalyst.
According to the preparation method provided by the invention, in some examples, the preparation method of the solid acid catalyst comprises the following steps:
i) Preparing the carrier (e.g., silica powder, alumina powder, and titanium dioxide powder) into a slurry, followed by molding and granulating to obtain a molded carrier;
ii) dissolving the heteropoly acid used as an active component in water to form a solution, so as to prepare a dipping solution; placing the formed carrier in the impregnation liquid, uniformly stirring, and then heating and stirring until all water is evaporated to dryness to obtain a crude product;
iii) And drying and roasting the obtained crude product to obtain the solid acid catalyst.
According to the preparation method provided by the present invention, in some examples, the active component is used in an amount of 0.1wt% to 20wt% (e.g., 0.2wt%, 0.5wt%, 1wt%, 1.5wt%, 2.5wt%, 4wt%, 6wt%, 8wt%, 10wt%, 15 wt%), preferably 2 to 5wt%; the amount of the co-agent is 0 to 0.1wt% (e.g., 0.01wt%, 0.015wt%, 0.025wt%, 0.04wt%, 0.06wt%, 0.08 wt%), preferably 0.02wt% to 0.05wt%, based on the total weight of the solid acid catalyst.
The preparation method of the solid acid catalyst is an impregnation method, namely, the carrier is immersed in an impregnation liquid containing the active component. For example, the support used for the preparation of the catalyst is first shaped and then introduced into an impregnation liquor which is configured from the heteropolyacid and optionally auxiliaries.
According to the preparation method provided by the invention, in some examples, the shape of the shaped carrier in step i) is one or more of a sphere, a cylinder, a clover and a ring, preferably a sphere (which has better strength and wear resistance).
For example, the processes of grinding the carrier into powder, and then pulping, shaping and granulating are all conventional in the art and will not be described herein.
In some examples, the shaped support has a particle size in the range of 3 to 5mm and a BET specific surface area in the range of 50 to 150m 2 (iv) g. In some examples, the shaped support is calcined at a temperature of 500 to 1100 ℃ for 4 to 6 hours before use.
In the preparation method of the invention, the auxiliary agent can be one or more selected from gold trichloride, rhenium trichloride, indium trichloride and lanthanum trichloride heptahydrate. The heteropolyacid may be selected from one or more of silicotungstic acid, phosphomolybdic acid and phosphotungstic acid.
In some examples, the temperature of the heating and stirring in step ii) is 60 to 100 ℃ (e.g., 70 ℃, 80 ℃,90 ℃).
In some examples, in step iii), the drying process conditions include: the temperature is 80-120 deg.C (e.g., 90 deg.C, 100 deg.C, 110 deg.C), and the time is 1-6h (e.g., 2h, 4h, 5 h); the roasting process conditions comprise: the temperature is 400-500 deg.C (e.g., 450 deg.C, 480 deg.C), and the time is 2-4 h (e.g., 2.5h, 3h, 3.5 h).
In yet another aspect, there is provided a method of preparing citral, comprising: in the presence of a solvent and a solid acid catalyst, taking dehydrolinalool as a raw material, and carrying out a Meyer-Schuster rearrangement reaction to prepare the citral;
the solid acid catalyst is the catalyst as described above or the catalyst prepared by the preparation method as described above.
In some examples of the invention, the reaction scheme for making citral via the Meyer-Schuster rearrangement reaction is as follows:
in the method, the raw material dehydrolinalool may be purchased directly or prepared by itself, and the preparation of dehydrolinalool is a method conventionally used in the art, and the present invention has no particular limitation thereto. Dehydrolinalool can be prepared, for example, by reacting 6-methyl-5-hepten-2-one with acetylene in the presence of liquid ammonia and potassium hydroxide, or by reacting 6-methyl-5-hepten-2-one with ethynyl Grignard in tetrahydrofuran.
According to the method for preparing citral provided by the present invention, in some examples, the method for preparing citral employs a continuous process or a batch process, preferably a continuous process.
In some preferred embodiments, the reactor used in the continuous process is a fixed bed reactor.
In some examples, the solvent is selected from one or more of acetonitrile, chloroform, toluene, and ethanol, preferably toluene.
In some examples, the mass ratio of the dehydrolinalool to the solvent is 1 to 50 (e.g., 1.
In some examples, the liquid phase volume space velocity is 1-10 h -1 (e.g., 2 h) -1 、4h -1 、6h -1 、8 h -1 ) Preferably 3 to 5 hours -1 。
In some examples, the process conditions of the Meyer-Schuster rearrangement reaction include:
the reaction temperature is 20 to 100 ℃ (e.g., 30 ℃, 50 ℃,70 ℃,90 ℃), preferably 40 to 60 ℃; the reaction pressure is 0.1 to 1MPa (gauge pressure) (e.g., 0.2MPa, 0.3MPa, 0.45 MPa, 0.6MPa, 0.8 MPa), preferably 0.4 to 0.5MPa (gauge pressure).
In the method for preparing citral, after the feed is stabilized for 10h, an internal standard is sampled and added, and the conversion rate and selectivity of the reaction are analyzed by gas chromatography. The conversion rate is the conversion rate of dehydrolinalool, and the selectivity refers to the selectivity of citral.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
1) The solid acid catalyst has the advantages of simple preparation process, low raw material cost and long service life, and the production cost is obviously reduced;
2) In the whole reaction process for preparing the citral, the reaction condition is mild, the three wastes are less, and the energy consumption is low; the prepared solid acid catalyst not only can improve the reaction yield and the conversion rate, but also has good selectivity;
3) In the preferred embodiment, the citral is prepared by adopting a continuous reaction process, the space-time yield is obviously improved, the catalyst can be continuously used for a long time, and the continuous large-scale operation can be realized, so that the method is suitable for industrial large-scale production.
Drawings
FIG. 1 is a graph showing the trend of the selectivity and conversion rate of the reaction 20 days after the solid acid catalyst prepared in example 5 was used in the reaction for preparing citral.
Detailed Description
In order that the technical features and contents of the present invention can be understood in detail, preferred embodiments of the present invention will be described in more detail below. While the preferred embodiments of the present invention have been described in the examples, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein.
1. Main reagent sources of each example and comparative example
Dehydrolinalool, with purity of 98%, is prepared by a self-made method, and the preparation process comprises the following steps:
ammonia gas was introduced into a 5L autoclave for 3 times of replacement, the temperature in the autoclave was lowered to-10 ℃ and liquid ammonia (1443 g, 85mol) was added thereto, and stirring was started and acetylene (336L, 15.0 mol) was introduced thereinto. Adding 50wt% of potassium hydroxide aqueous solution, wherein the dosage of the potassium hydroxide aqueous solution is 3mol% of a substrate in a reaction kettle, adding methyl heptenone (378 g, 3mol), controlling the reaction temperature at 10 ℃, sampling at regular time, detecting the reaction by GC, stopping the reaction when the methyl heptenone conversion rate is more than 99%, and adding ammonium bicarbonate aqueous solution into the reaction kettle to neutralize potassium hydroxide (the addition amount is 1.2 times of the molar amount of the potassium hydroxide) by using a constant flow pump. And (3) decompressing the reaction kettle, discharging the reaction liquid, carrying out phase separation, washing an organic phase with saturated salt water for three times, drying with anhydrous sodium sulfate to obtain a crude dehydrolinalool product, and carrying out reduced pressure rectification on the crude product to obtain 420g of a pure dehydrolinalool product with the purity of 98% and the yield of 90.01%.
Acetonitrile, chloroform, toluene, ethanol and other organic solvents with the purity of more than 98 percent, and chemical industry of the west longas;
gold trichloride, rhenium trichloride, indium trichloride and lanthanum trichloride heptahydrate, the purity is more than 99 percent, and the sigma-aldrich is obtained;
silicon dioxide (particle size of 5 μm), titanium dioxide, aluminum oxide (particle size of 5 μm), and an avadin reagent;
molybdenum trioxide, acetic acid and dimethyl sulfoxide, wherein the purity is more than 98 percent, and an avastin reagent;
silicotungstic acid, phosphomolybdic acid, phosphotungstic acid, AR, avastin reagent;
the content of effective substances in solid phosphoric acid is more than 98 percent, and the Jining Huicheng chemical company Limited.
2. The gas chromatography test conditions adopted by the invention are as follows
The instrument model is as follows: agilent 7890B;
sample introduction volume: 1 microliter;
sample inlet temperature: 240 ℃; pressure: 12.659psi; total flow rate: 30ml/min;
the split ratio is as follows: 30/1;
a chromatographic column: agilent 19091N-113, 30m × 250 μm × 0.25 μm;
flow rate of the chromatographic column: 2ml/min; pressure: 8.51psi; linear velocity: 33.3cm/sec;
temperature rising procedure: the initial temperature is 80 ℃, the temperature is raised to 100 ℃ at the speed of 5 ℃/min, and the temperature is kept for 1min; heating to 150 deg.C at 5 deg.C/min, and maintaining for 1min; heating to 250 deg.C at 30 deg.C/min, and keeping for 5min;
detector temperature: 260 ℃; air flow rate: 400ml/min; hydrogen flow rate: 40ml/min; nitrogen flow rate: 25ml/min.
3. Preparation of solid acid catalyst
Examples 1 to 20 and comparative examples 1 to 2
The spherical carrier is prepared by a method well known to a person skilled in the art, and the specific process is as follows: after grinding the carriers (e.g., silicon dioxide, aluminum oxide and titanium dioxide) into powder, adding the powder into water, uniformly stirring to form carrier slurry, and then molding and granulating to obtain spherical carriers (e.g., spherical silicon dioxide, spherical aluminum oxide and spherical titanium dioxide). Roasting at 500-1100 deg.c for 4-6 hr to obtain particle size of 3-5 mm and BET specific surface area of 50-150 m 2 Per g of spherical support.
The solid acid catalyst is prepared by adopting an impregnation method, and the specific process is as follows: the heteropolyacid (such as silicotungstic acid, phosphomolybdic acid or phosphotungstic acid) and an optional auxiliary agent (such as gold trichloride, rhenium trichloride, indium trichloride or lanthanum trichloride heptahydrate) are dissolved in water to form an impregnation solution, then the spherical carrier prepared in the above way is placed in the impregnation solution and stirred uniformly, the stirring is carried out under the condition of 80 ℃ water bath until the water is completely evaporated to dryness, then the drying is carried out for 4h at 120 ℃, and the roasting is carried out for 2h at 400 ℃ to prepare the solid acid catalyst.
In each example and comparative example, a series of solid acid catalysts with different active components and auxiliary agent loading amounts can be obtained by changing the types and the dosage ratios of the heteropoly acid and the auxiliary agent. The types and contents of the active components and the auxiliary agents, and the types of the carriers in the catalysts obtained in the examples and comparative examples are shown in table 1:
table 1 solid acid catalyst composition prepared
4. Screening of the catalyst
Examples 23 to 50 and comparative examples 3 to 4
The 24 types of solid acid catalysts prepared in the examples 1-22 and the comparative examples 1-2 are selected for screening, and the method comprises the following steps: the catalyst reaction performance was examined with a fixed bed reactor from the top down, which was a stainless steel tube with an inner diameter of 20mm and a length of 800 mm. The catalyst loading was 5g and diluted to 20ml with glass beads. Each of the catalysts prepared in examples 1 to 22 and comparative examples 1 to 2 was packed in a fixed bed reactor, and each catalyst was activated under nitrogen protection at 400 ℃ for 2 hours. Then cooled to below 40 ℃ and the nitrogen purge was stopped. Mixing dehydrolinalool and a solvent according to a certain mass ratio, then passing a liquid phase through a catalyst bed layer, adjusting the fixed bed reactor to the temperature required by the reaction under the condition of continuously introducing nitrogen, adjusting the nitrogen pressure to maintain proper reaction conditions, and carrying out the rearrangement of the dehydrolinalool to prepare the citral. The specific reaction conditions for the preparation of citral are shown in Table 2.
TABLE 2 relationship between reaction conditions and raw material amounts for citral preparation
After the reaction was stabilized for 10 hours, the amount of the rearrangement reaction product produced per unit time was measured, and the composition of the reaction solution was analyzed by gas chromatography to calculate the conversion of dehydrolinalool and the selectivity of citral (the reaction yield equals to the selectivity multiplied by the conversion), and the results are shown in Table 3.
Table 3 conversion and selectivity in citral preparation for each example and comparative example
A series of supported heteropolyacid catalysts with different active components, auxiliary agent types and contents are prepared by adopting an impregnation method, and the conversion rate and selectivity of the supported heteropolyacid catalysts for preparing the citral by dehydrogenating linalool through rearrangement are investigated. From the tables it can be seen that:
examples 23 to 44 mainly examine the influence of different catalysts on the rearrangement reaction, and catalysts having different active components have a relatively large influence on the selectivity of the reaction. The results of examples 23-34 show that the selectivity of the reaction is generally 90% using phosphotungstic acid as the active component, whereas the selectivity of the reaction is around 94% and 97% using silicotungstic acid and phosphomolybdic acid as the active component, so that the preferred active component is phosphomolybdic acid. Meanwhile, for the same active component, gold trichloride is adopted as an auxiliary agent, which is more favorable for the conversion rate and selectivity of the reaction, so that the gold trichloride is preferably adopted as the auxiliary agent of the catalyst. The results of examples 35-37 show that the selectivity of the reaction is most favored when titanium dioxide is used as the support for the catalyst when the active component, the promoter, phosphomolybdic acid and gold trichloride, respectively, are used. The results of examples 38-44 show that the difference in the active ingredient and adjuvant loadings has a greater effect on the conversion and selectivity of the reaction, the active ingredient content increases, the conversion of the reaction increases but is detrimental to the selectivity of the reaction, conversely, the active ingredient decreases, the conversion of the reaction decreases but the selectivity of the reaction is as high as 99% at best, and therefore, the amount of active ingredient needs to be controlled within a reasonable range to balance the activity and selectivity of the reaction. The results of examples 40-42 show that the catalyst can achieve selectivity of about 90% without supporting the promoter, but is significantly lower than supported heteropolyacid catalysts containing the promoter.
Examples 45-50 were conducted to examine the reaction conditions and the influence of the solvent on the reaction when the optimum catalyst (i.e., the catalyst prepared in example 5) was selected, and finally the optimum space velocity was determined to be 3-5 h -1 The optimal reaction temperature is 40-60 ℃, and the optimal reaction solvent is toluene.
5. Examination of other comparative catalysts
Comparative example 5
100g of dehydrolinalool, 0.1g of silicotungstic acid and 400g of toluene are put into a 1000ml three-necked flask equipped with a stirrer, a thermometer and a condenser.
Fully stirring the added raw materials, heating to reflux, preserving heat for reaction, controlling the reaction temperature at 30 ℃ for reaction, tracking and detecting the reaction process by using gas chromatography, reacting for 1h until the content of dehydrolinalool is less than 0.5%, and stopping the reaction. Sampling, adding an internal standard, and analyzing the conversion rate of the dehydrolinalool of the reaction by GC to be 99.73 percent and the selectivity of the citral to be 81.23 percent.
Silicotungstic acid is directly used as a catalyst for preparing citral by dehydrogenating linalool through rearrangement, the reaction selectivity is general, and the separation of the silicotungstic acid needs to remove a solvent and a product in a system due to the adoption of an intermittent process; and the silicotungstic acid exists in heavy components in the rectifying tower kettle, so that tar and high-boiling point byproducts are coated on the surface of the catalyst, and the catalyst is difficult to recycle.
Comparative example 6
A fixed bed reactor from the top down, a stainless steel tube having an inner diameter of 20mm and a length of 800mm was used. Solid phosphoric acid as a catalyst, its loading was 5g, and diluted to 20ml with glass beads, the catalyst was activated under nitrogen, 400 ℃ for 2 hours. Then cooled to below 40 ℃ and the nitrogen purge was stopped.
Mixing dehydrolinalool and toluene according to the mass ratio of 1 -1 And carrying out rearrangement of dehydrolinalool to prepare citral. After the stable reaction for 10 hours, the output of the rearrangement reaction product in unit time is measured, and the composition of the reaction solution is analyzed by gas chromatography, the conversion rate of the dehydrolinalool is 99.67 percent, and the selectivity of the citral is 85.83 percent.
Solid phosphoric acid is used as a catalyst for preparing citral by dehydrolinalool rearrangement, and the selectivity of the reaction is general. Further, by examining the life of the solid phosphoric acid catalyst, it was found that the catalyst began to run off and the reaction activity gradually decreased with the long-term use of the catalyst (the use time exceeded 72 hours).
6. Investigation of catalyst Life
The solid acid catalyst prepared in example 5 was selected for life span examination in a continuous reaction process, and the reactor was a fixed bed reactor having an inner diameter of 20mm and a length of 800 mm. The catalyst loading was 5g and diluted to 20ml with glass beads.
After the solid acid catalyst prepared in example 5 was packed in a fixed bed reactor, the catalyst was activated under nitrogen protection and activated at 400 ℃ for 2 hours. Then cooled to below 40 ℃ and the nitrogen purge was stopped. Mixing dehydrolinalool and toluene according to a mass ratio of 1 -1 The results of the catalyst life test are shown in FIG. 1.
In fig. 1, the service life of the catalyst on the abscissa in hours, it can be seen that the selectivity of the reaction remains unchanged after 20 days of use of the solid acid catalyst, and the conversion of citral slightly decreases, possibly due to a small loss of catalyst. Also, after the solid acid catalysts prepared in the other examples were used for 20 days in the reaction for preparing citral, the reaction selectivity and conversion rate trend varied similarly to the catalyst effect of example 5. The solid acid catalyst prepared by the invention has long service life and is suitable for industrial continuous production.
While embodiments of the present invention have been described above, the above description is illustrative, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.
Claims (15)
1. A method of making citral, comprising: in the presence of a solvent and a solid acid catalyst, taking dehydrolinalool as a raw material, and carrying out a Meyer-Schuster rearrangement reaction to prepare the citral;
the solid acid catalyst comprises: an active ingredient, a carrier and optionally an auxiliary agent; the content of the active component accounts for 0.1-20 wt% of the total weight of the solid acid catalyst, and the content of the auxiliary agent accounts for 0-0.1 wt% of the total weight of the solid acid catalyst;
the active component is heteropoly acid and is selected from one or more of silicotungstic acid, phosphomolybdic acid and phosphotungstic acid;
the carrier is selected from one or more of silicon dioxide, aluminum oxide and titanium dioxide;
the auxiliary agent is one or more selected from gold trichloride, rhenium trichloride, indium trichloride and lanthanum trichloride.
2. The method according to claim 1, wherein in the solid acid catalyst,
the active component is phosphomolybdic acid;
the carrier is titanium dioxide;
the auxiliary agent is gold trichloride.
3. The method according to claim 1, wherein in the solid acid catalyst,
the content of the active component accounts for 2-5 wt% of the total weight of the solid acid catalyst;
the content of the auxiliary agent accounts for 0.02wt% -0.05 wt% of the total weight of the solid acid catalyst.
4. The method of claim 1, wherein the method of preparing the solid acid catalyst comprises the steps of:
i) Preparing the carrier into slurry, and then molding and granulating to obtain a molded carrier;
ii) dissolving the heteropoly acid as an active component in water to form a solution, and optionally adding the auxiliary agent to prepare an impregnation liquid; placing the formed carrier in the impregnation liquid, uniformly stirring, and then heating and stirring until all water is evaporated to dryness to obtain a crude product;
iii) And drying and roasting the obtained crude product to obtain the solid acid catalyst.
5. The method according to claim 4, wherein in the preparation method of the solid acid catalyst, the temperature for heating and stirring in the step ii) is 60-100 ℃;
in step iii), the drying process conditions include: the temperature is 80-120 ℃, and the time is 1-6h; the roasting process conditions comprise: the temperature is 400-500 ℃ and the time is 2-4 h.
6. The method of claim 4, wherein the shaped support is one or more of spherical, cylindrical, clover-leaf, and toroidal in shape.
7. The method of claim 6, wherein the shaped carrier is spherical in shape.
8. The method according to claim 1, wherein the method for preparing citral employs a continuous process or a batch process.
9. The method of claim 8, wherein the method of preparing citral employs a continuous process;
the reactor used in the continuous process is a fixed bed reactor.
10. The method according to claim 1, wherein the solvent is selected from one or more of acetonitrile, chloroform, toluene and ethanol.
11. The method of claim 10, wherein the solvent is toluene.
12. The method according to any one of claims 1 to 11, wherein the mass ratio of the dehydrolinalool to the solvent is 1;
the liquid phase volume space velocity is 1-10 h -1 。
13. The method according to claim 12, wherein the mass ratio of the dehydrolinalool to the solvent is 1;
the liquid phase volume space velocity is 3 to 5 hours -1 。
14. The process of any one of claims 1 to 11, wherein the process conditions of the Meyer-Schuster rearrangement reaction comprise:
the reaction temperature is 20-100 ℃; the gauge pressure of the reaction is 0.1-1 MPa.
15. The process according to claim 14, wherein the process conditions of the Meyer-Schuster rearrangement reaction comprise:
the reaction temperature is 40-60 ℃; the gauge pressure of the reaction is 0.4-0.5 MPa.
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