N-heptanoic acid prepared by oxidizing alcohol and preparation method of n-heptanoic acid

Abstract

The invention discloses n-heptanoic acid prepared by oxidizing alcohol and a preparation method of the n-heptanoic acid, sec-octanol is taken as a raw material, a copper oxide-zinc oxide supported catalyst is added into a caustic alkali aqueous solution, reaction is carried out under the conditions that the temperature is 160-240 DEG C and the pressure is 1.0-2 MPa to obtain n-heptanoate, and then the n-heptanoic acid is obtained through acidification. The catalyst is added to promote the dehydrogenation reaction of the octanol and accelerate the reaction rate, so that the problem that the reaction is slow when the reaction temperature is lower than 320 DEG C is solved, by controlling the addition amount of water and the reaction pressure, generation of a 2-methyl-2-octene byproduct caused by dehydration of a system can be prevented, and by adding the defoaming agent, the yield of the 2-methyl-2-octene is increased. The problem of mass transfer difficulty caused by a large amount of foam in the later reaction stage is solved. According to the method disclosed by the invention, the yield of the n-heptanoic acid is more than 70% at 160-240 DEG C, and the method does not need to depend on a large amount of potassium hydroxide and has remarkable industrial advantages.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical preparation, and more specifically, to n-heptanoic acid prepared by oxidizing alcohol and a preparation method thereof. Background Art

[0002] N-heptanoic acid is an important industrial raw material, which has a wide range of uses in many industries such as spices, pharmaceuticals, lubricants and plasticizers. N-heptanoic acid is an oily liquid with a faint aroma, insoluble in water and easily soluble in common organic solvents. N-heptanoic acid naturally exists in many plants such as Acorus calamus, Mentha arvensis and Violet leaves. Traditional synthesis methods of heptanoic acid, such as oxidation of heptaldehyde with KMnO4, air oxidation under a catalyst or oxidation with calcium hypochlorite, have disadvantages such as high raw material prices, large amounts of organic solvents used, high environmental protection pressure and complex post-treatment.

[0003] At present, Lawson et al. proposed a method for synthesizing heptanoic acid using sec-octanol under the condition of caustic alkali melting. This method uses sec-octanol obtained by cracking natural castor oil as a raw material, which has a great cost advantage. However, this method has high requirements for reaction equipment, harsh reaction conditions, requires a high temperature above 320 °C, and also relies on a large amount of potassium hydroxide, resulting in high raw material costs. In addition, there are many reaction by-products and low conversion rate, making it difficult to achieve industrial scale-up.

[0004] In view of this, the present application is specifically proposed. Summary of the Invention

[0005] The problems existing in the prior art are that the current method for preparing heptanoic acid using sec-octanol has problems such as high requirements for reaction equipment, harsh reaction conditions, the need to use a large amount of potassium hydroxide, many by-products and low conversion rate. In order to solve the above problems, the present invention provides n-heptanoic acid prepared by oxidizing alcohol and a preparation method thereof. By adding a catalyst and limiting the amount of water and high-pressure reaction conditions, the reaction temperature can be significantly reduced, the reaction selectivity can be improved, the conversion rate can be increased, the generation of by-products can be reduced, and the yield of n-heptanoic acid can be greatly improved.

[0006] The present invention is achieved by the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing n-heptanoic acid by oxidizing alcohol. Using sec-octanol as a raw material, a copper oxide-zinc oxide supported catalyst is added to an aqueous solution of caustic alkali, and the reaction is carried out under the conditions of a temperature of 160-240 °C and a pressure of 1.0-2 MPa to obtain a heptanoate, and then n-heptanoic acid is obtained by acidification.

[0008] In a specific embodiment, the addition amount of the copper oxide-zinc oxide supported catalyst is 0.4-0.6 wt% of the sec-octanol feed amount.

[0009] In a specific embodiment, the amount of water in the aqueous caustic solution is 20-40 wt% of the feeding amount of sec-octanol.

[0010] In a specific embodiment, the caustic used is sodium hydroxide, and the addition amount of sodium hydroxide is 31-35 wt% of the feeding amount of sec-octanol.

[0011] In a specific embodiment, the preparation method of the copper oxide-zinc oxide supported catalyst is as follows:

[0012] (1) Prepare copper ion and zinc ion solutions respectively, and transfer them to a reaction kettle;

[0013] (2) Slowly dropwise add an aqueous ammonia solution, and the solution gradually becomes turbid to form a precipitate;

[0014] (3) Add coarse pore microsphere silica gel, stir and react at high temperature, then cool to room temperature, stand, filter, wash, and collect the precipitate;

[0015] (4) Dry the precipitate and then put it into a muffle furnace for high temperature roasting to obtain the copper oxide-zinc oxide supported silica gel catalyst.

[0016] In a specific embodiment, the reaction system further includes an antifoaming agent, and the antifoaming agent used is AFE-0800.

[0017] In a specific embodiment, the preparation method of the antifoaming agent is as follows: Add a 10% NaOH solution to water and stir evenly, then add AFE-0800, stir evenly, and then add a 10% NaOH solution again and stir evenly to obtain the antifoaming agent.

[0018] In a specific embodiment, the reaction conditions are: temperature 180 °C, pressure 1.5 MPa.

[0019] In a specific embodiment, the amount of water in the aqueous caustic solution is 25 wt% of the feeding amount of sec-octanol.

[0020] In a second aspect, the present invention provides n-heptanoic acid prepared by oxidizing an alcohol, which is obtained by the above method.

[0021] The present invention provides a method for preparing n-heptanoic acid from sec-octanol. Using sec-octanol as a raw material, adding 20-40% of water based on its feeding amount, using sodium hydroxide as an oxidant, heating the reaction system to 160-240 °C and pressurizing to 1.0-2 MPa, under the synergistic action of the copper oxide-zinc oxide supported catalyst and the base, sec-octanol is first oxidized to 2-octanone; subsequently, in an alkaline environment, 2-octanone is further oxidized to n-heptanoate, and through acidification treatment, the target product n-heptanoic acid can be obtained, and the process is as shown below.

[0022] The reaction mechanism of the present invention is as follows: Under the action of a catalyst, the catalyst activates the hydrogen atom on sec-octanol by providing active sites. The hydrogen atom is activated and freed, and the free hydrogen acts on the adjacent hydrogen atom to remove it to form a H2 molecule, forming a double bond. The base promotes the removal of CH4 through deprotonation to form heptanoate, as shown in Path 2 of the following reaction route. At the same time, under the action of the base, sec-octanol removes one molecule of H2 and then one molecule of CH4 to form heptanoate, as shown in Path 1 of the following reaction route. In this reaction, the catalyst and the base play a synergistic role to promote the progress of the reaction.

[0023] Among them, usually sec-octanol is prone to dehydration to produce the by-product 1-octene under the action of a catalyst, as shown in Reaction A in the following reaction route. However, after the catalyst is added in the present invention, the reaction selectivity is improved, and the reaction tends to produce the by-product 2-octanone. Under alkaline conditions, 2-octanone forms a tertiary alcohol. Since the carbocation formed by the dehydration of the tertiary alcohol is relatively stable, it is easy to undergo a dehydration reaction, as shown in Reaction D. To solve the above problems, the present invention controls the addition of a certain amount of water in the reaction system and controls the pressure to ensure that there is enough water in the reaction system to inhibit the dehydration of 2-octanone to produce by-products.

[0024]

[0025] In summary, the present invention promotes the dehydrogenation reaction of sec-octanol by adding a catalyst to accelerate the reaction rate, thereby solving the problem of slow reaction when the reaction temperature is lower than 320°C. At the same time, by controlling the addition amount of water and the reaction pressure, it is possible to prevent the formation of by-products of 2-methyl-2-octene caused by system dehydration. By adding an antifoaming agent, the problem of mass transfer difficulty caused by a large amount of foam in the later stage of the reaction is solved. The method of the present invention can achieve a n-heptanoic acid yield > 70% at 160 - 240°C, and does not need to rely on a large amount of potassium hydroxide, having significant industrial advantages.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0027] 1. A method for preparing n-heptanoic acid by oxidizing an alcohol provided in an embodiment of the present invention promotes the dehydrogenation reaction of sec-octanol by adding a catalyst to accelerate the reaction rate, thereby solving the problem of slow reaction when the reaction temperature is lower than 320°C, and overcoming the disadvantages such as the need for high temperature, a special reactor, and a special stirrer in the preparation process;

[0028] 2. The n-heptanoic acid prepared by oxidizing alcohol and its preparation method provided by the embodiments of the present invention improve the reaction selectivity through the synergistic effect of a catalyst and a base. The catalyst activates hydrogen atoms by providing active sites, and the hydrogen atoms are activated and freed. The free hydrogen then acts on adjacent hydrogen atoms, causing them to be removed as H2 molecules to form a double bond. The base promotes the removal of CH4 through deprotonation, and finally forms a heptanoate.

[0029] 3. The n-heptanoic acid prepared by oxidizing alcohol and its preparation method provided by the embodiments of the present invention can prevent the generation of 2-methyl-2-octene by-products caused by system dehydration by controlling the amount of water added to the reaction system and the reaction pressure, reduce by-products, and improve the product yield.

[0030] 4. The n-heptanoic acid prepared by oxidizing alcohol and its preparation method provided by the embodiments of the present invention have relatively low requirements for process preparation conditions. At the same time, without using potassium hydroxide, the price of sodium hydroxide is relatively low, reducing the raw material cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and thus should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0032] Figure 1 It is the gas phase diagram of the product prepared in Example 4 of the present invention;

[0033] Figure 2 It is the gas phase diagram of the distilled heptanoic acid provided by the present invention;

[0034] Figure 3 It is the gas phase diagram of the product prepared in Comparative Example 1 of the present invention;

[0035] Figure 4 It is the gas phase diagram of the product prepared in Comparative Example 2 of the present invention;

[0036] Figure 5 It is the gas phase diagram of the product prepared in Comparative Example 3 of the present invention;

[0037] Figure 6 It is the gas phase diagram of the product prepared in Comparative Example 4 of the present invention;

[0038] Figure 7 It is the gas phase diagram of the product prepared in Comparative Example 5 of the present invention;

[0039] Figure 8 It is the gas phase diagram of the product prepared in Comparative Example 6 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the embodiments and the accompanying drawings. The illustrative embodiments and descriptions thereof of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0041] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to those of ordinary skill in the art that: the present invention may be practiced without these specific details. In other embodiments, well-known materials or methods have not been described in detail in order to avoid obscuring the present invention.

[0042] Throughout the specification, the reference to "one embodiment", "an embodiment", "one example" or "an example" means that a particular feature, structure or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present invention. Thus, the phrases "one embodiment", "an embodiment", "one example" or "an example" appearing throughout the specification do not necessarily all refer to the same embodiment or example. In addition, the particular features, structures or characteristics may be combined in any suitable combination and / or sub-combination in one or more embodiments or examples. The term "and / or" used herein includes any and all combinations of one or more of the associated listed items.

[0043] The "range" disclosed in this application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise specified, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. In addition, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. If there is no special instruction, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0044] At present, the method for synthesizing heptanoic acid by using sec-octanol under the condition of caustic alkali melting has high requirements for reaction equipment, harsh reaction conditions, requires a high temperature above 320 °C, and at the same time relies on a large amount of potassium hydroxide, with high raw material costs. In addition, there are many reaction by-products and low conversion rate, making it difficult to achieve industrial scale-up.

[0045] In order to solve the above technical problems,

[0046] In a first aspect, the present invention provides a method for preparing n-heptanoic acid by oxidizing an alcohol. Using sec-octanol as a raw material, adding a copper oxide-zinc oxide supported catalyst to an aqueous caustic alkali solution, reacting under the conditions of a temperature of 160-240 °C and a pressure of 1.0-2 MPa to obtain a n-heptanoate, and then acidifying to obtain n-heptanoic acid. [[ID=SI0]] [[ID=SI1]]

[0047] In a specific embodiment, the addition amount of the copper oxide-zinc oxide supported catalyst is 0.4-0.6 wt% of the sec-octanol feed amount.

[0048] In a specific embodiment, the amount of water in the aqueous solution of caustic alkali is 20-40 wt% of the feeding amount of sec-octanol.

[0049] In a specific embodiment, the caustic alkali is sodium hydroxide, and the addition amount of sodium hydroxide is 31-35 wt% of the feeding amount of sec-octanol.

[0050] In a specific embodiment, the preparation method of the copper oxide-zinc oxide supported catalyst is as follows:

[0051] (1) Prepare copper ion and zinc ion solutions respectively, and transfer them to a reaction kettle;

[0052] (2) Slowly dropwise add an aqueous ammonia solution, and the solution gradually becomes turbid to form a precipitate;

[0053] (3) Add coarse pore microsphere silica gel, stir and react at high temperature, then cool to room temperature, stand, filter, wash, and collect the precipitate;

[0054] (4) Dry the precipitate and then put it into a muffle furnace for high-temperature roasting to obtain the copper oxide-zinc oxide supported silica gel catalyst.

[0055] In a specific embodiment, the reaction system further includes an antifoaming agent, and the antifoaming agent is AFE-0800.

[0056] In a specific embodiment, the preparation method of the antifoaming agent is as follows: Add a 10% NaOH solution to water and stir evenly, then add AFE-0800, stir evenly, and then add a 10% NaOH solution again and stir evenly to obtain the antifoaming agent.

[0057] In a specific embodiment, the reaction conditions are: temperature 180 °C, pressure 1.5 MPa.

[0058] In a specific embodiment, the amount of water in the aqueous solution of caustic alkali is 25 wt% of the feeding amount of sec-octanol.

[0059] ] Second, the present invention provides n-heptanoic acid prepared by oxidizing an alcohol, which is obtained by the above method.

[0060] The present invention provides a method for preparing n-heptanoic acid from sec-octanol. Using sec-octanol as a raw material, adding 20-40% of water based on its feeding amount, using sodium hydroxide as an oxidant, heating the reaction system to 160-240 °C and pressurizing to 1.0-2 MPa. Under the synergistic action of the copper oxide-zinc oxide supported catalyst and the base, sec-octanol is first oxidized to 2-octanone; subsequently, in an alkaline environment, 2-octanone is further oxidized to n-heptanoate, and through acidification treatment, the target product n-heptanoic acid can be obtained. The process is as follows.

[0061] The reaction mechanism of the present invention is as follows: Under the action of a catalyst, the catalyst activates hydrogen atoms by providing active sites, and the hydrogen atoms are activated and dissociated. The free hydrogen then acts on adjacent hydrogen atoms, causing them to be removed to form H2 molecules and form a double bond. The base promotes the removal of CH4 through deprotonation to form heptanoate, as shown in Path 2 of the following reaction route. At the same time, under the action of the base, sec-octanol loses one molecule of H2 and then one molecule of CH4 to form heptanoate, as shown in Path 1 of the following reaction route. In this reaction, the catalyst and the base play a synergistic role to promote the progress of the reaction.

[0062] Among them, usually sec-octanol is prone to dehydration to produce the by-product 1-octene under the action of a catalyst, as shown in Reaction A in the following reaction route. However, after the catalyst is added in the present invention, the reaction selectivity is improved, and the reaction tends to produce the by-product 2-octanone. Under alkaline conditions, 2-octanone forms a tertiary alcohol. Since the carbocation formed by the dehydration of the tertiary alcohol is relatively stable, it is prone to dehydration reaction, as shown in Reaction D. To solve the above problems, the present invention adds a certain amount of water to the reaction system and controls the pressure to ensure that there is enough water in the reaction system to inhibit the dehydration of 2-octanone to produce by-products.

[0063]

[0064] In summary, the present invention promotes the dehydrogenation reaction of sec-octanol by adding a catalyst to accelerate the reaction rate, thereby solving the problem of slow reaction when the reaction temperature is lower than 320 °C. By controlling the addition amount of water and the reaction pressure, it is possible to prevent the formation of by-products of 2-methyl-2-octene caused by system dehydration. By adding an antifoaming agent, the problem of mass transfer difficulty caused by a large amount of foam in the later stage of the reaction is solved. The method of the present invention can achieve a heptanoic acid yield > 70% at 160-240 °C and does not need to rely on a large amount of potassium hydroxide, having significant industrial advantages.

[0065] Preparation Example 1

[0066] Preparation of copper oxide-zinc oxide supported catalyst silica gel catalyst

[0067] Prepare a solution containing 0.5 mol / L of copper ions and zinc ions by mixing copper acetate and zinc acetate. Transfer the above solution to a reaction kettle, and slowly add 4 mol / L ammonia water solution dropwise. The solution gradually becomes turbid and forms a precipitate. Add the macroporous microsphere silica gel pretreated with deionized water. After stirring and reacting at 140 °C for 24 h, cool it to room temperature, let it stand for 10 h, filter, and wash and collect the precipitate with distilled water until the pH = 7. Then dry the silica gel impregnated with copper ion and zinc ion solutions at 80 °C for 12 h to remove the excess liquid. Put the dried precipitate into a muffle furnace and calcine it at 500 °C for 8 h to obtain a copper oxide-zinc oxide supported silica gel catalyst. After the calcination is completed, cool the catalyst to room temperature and store it in a desiccator for standby.

[0068] Preparation Example 2

[0069] Prepare an antifoaming agent

[0070] Add 0.45 wt% of 10% NaOH solution to 79.1 wt% of water and stir evenly. Add 20 wt% of XIAMETER AFE-0800 to the above solution, stir evenly, and then add 0.45 wt% of 10% NaOH solution and stir evenly to obtain an antifoaming agent.

[0071] Detection method

[0072] The experimental products were analyzed using a Shimadzu GC-2010Pro gas chromatograph. The instrument was equipped with a sk-5 capillary chromatographic column, and the stationary phase was 5% phenyl / 95% dimethyl polysiloxane with a specification of 25 m × 0.32 mm × 0.25 μm. Temperature program: The initial temperature was 100 °C, and it was heated to 205 °C at a rate of 5 °C per minute. Qualitative analysis was performed by comparing the gas chromatographic retention times of the experimental products and the reference substances, and the purity of crude heptanoic acid was determined by the area normalization method.

[0073] Example 1

[0074] An embodiment of the present invention provides a method for preparing n-heptanoic acid by oxidizing alcohol. Add sodium hydroxide (98%, 81.6 g, 2.0 mol), water (66.1 g, 25 wt%), copper oxide-zinc oxide supported catalyst (0.13 g, 0.5 wt%), and antifoaming agent (0.26 g, 1 wt%) into a 500 mL stainless steel pressure reactor. Replace with nitrogen three times, pressurize to 1.2 Mpa, stir and heat to 180 °C. While maintaining the reaction temperature, add sec-octanol (264.4 g, 98.5%, 2.0 mol) in batches slowly. Under the condition of maintaining the pressure, release the generated gas. After reacting for 3 hours, there is no obvious change in the pressure in the kettle. Then continue to stir and react for half an hour until no gas is generated. After the reaction is completed, cool to room temperature, add 300 mL of water to dissolve the mixed solution which is light yellow, filter to remove insoluble substances, separate the organic layer by liquid separation, acidify the aqueous layer with 50% sulfuric acid solution to pH = 2, separate by liquid separation, wash the organic layer with water and dry to obtain 241.3 g of a mixture. The purity of heptanoic acid is 80.56% by GC test, and the yield of n-heptanoic acid is 74.66%.

[0075] By vacuum distillation, 179.5 g of a colorless oily liquid is obtained, with a total yield of 68.95%. The purity of n-heptanoic acid is 99.46% by GC test.

[0076] Example 2

[0077] An embodiment of the present invention provides a method for preparing n-heptanoic acid by oxidizing alcohol. Add sodium hydroxide (98%, 81.6 g, 2.0 mol), water (66.1 g, 25 wt%), copper oxide-zinc oxide supported catalyst (0.13 g, 0.5 wt%), and antifoaming agent (0.26 g, 1 wt%) into a 500 mL stainless steel pressure reactor. Replace with nitrogen three times, pressurize to 1.0 Mpa, stir and heat to 180 °C. While maintaining the reaction temperature, add sec-octanol (264.4 g, 98.5%, 2.0 mol) in batches slowly. Under the condition of maintaining the pressure, release the generated gas. After reacting for 3 hours, there is no obvious change in the pressure in the kettle. Then continue to stir and react for half an hour until no gas is generated. After the reaction is completed, cool to room temperature, add 300 mL of water to dissolve the mixed solution which is light yellow, filter to remove insoluble substances, separate the organic layer by liquid separation, acidify the aqueous layer with 50% sulfuric acid solution to pH = 2, separate by liquid separation, wash the organic layer with water and dry to obtain 236.1 g of a mixture. The purity of heptanoic acid is 77.26% by GC test, and the yield of n-heptanoic acid is 70.06%.<https: / / patents.google.com / patent / US20190376773A1 / en?q=US20190376773A1&oq=US201903#

[0078] Example 3

[0079] An embodiment of the present invention provides a method for preparing n-heptanoic acid by oxidizing alcohol. Add sodium hydroxide (98%, 81.6 g, 2.0 mol), water (66.1 g, 25 wt%), copper oxide-zinc oxide supported catalyst (0.13 g, 0.5 wt%), and defoamer (0.26 g, 1 wt%) into a 500 mL stainless steel pressure reactor. Replace with nitrogen three times, pressurize to 2.0 Mpa, stir and heat to 180 °C. While maintaining the reaction temperature, add 2-ethyl-1-hexanol (264.4 g, 98.5%, 2.0 mol) in batches slowly. Under the condition of maintaining the pressure, release the generated gas. After reacting for 3 hours, there is no obvious change in the pressure in the reactor. Then continue to stir and react for half an hour until no gas is generated. After the reaction is completed, cool to room temperature, add 300 mL of water to dissolve the mixed solution which is light yellow, filter to remove insoluble substances, separate the organic layer by liquid separation, acidify the aqueous layer with 50% sulfuric acid solution to pH = 2, separate by liquid separation, wash the organic layer with water and dry to obtain 246.3 g of a mixture. The purity of heptanoic acid is 80.92% by GC test, and the yield of n-heptanoic acid is 76.55%.

[0080] Example 4

[0081] An embodiment of the present invention provides a method for preparing n-heptanoic acid by oxidizing alcohol. Add sodium hydroxide (98%, 81.6 g, 2.0 mol), water (66.1 g, 25 wt%), copper oxide-zinc oxide supported catalyst (0.13 g, 0.5 wt%), and defoamer (0.26 g, 1 wt%) into a 500 mL stainless steel pressure reactor. Replace with nitrogen three times, pressurize to 1.5 Mpa, stir and heat to 180 °C. While maintaining the reaction temperature, add 2-ethyl-1-hexanol (264.4 g, 98.5%, 2.0 mol) in batches slowly. Under the condition of maintaining the pressure, release the generated gas. After reacting for 3 hours, there is no obvious change in the pressure in the reactor. Then continue to stir and react for half an hour until no gas is generated. After the reaction is completed, cool to room temperature, add 300 mL of water to dissolve the mixed solution which is light yellow, filter to remove insoluble substances, separate the organic layer by liquid separation, acidify the aqueous layer with 50% sulfuric acid solution to pH = 2, separate by liquid separation, wash the organic layer with water and dry to obtain 240.1 g of a mixture. The purity of heptanoic acid is 81.34% by GC test, and the yield of n-heptanoic acid is 75.01%.

[0082] Example 5

[0083] An embodiment of the present invention provides a method for preparing n-heptanoic acid by oxidizing alcohol. Add sodium hydroxide (98%, 81.6 g, 2.0 mol), water (105.76 g, 40 wt%), copper oxide-zinc oxide supported catalyst (0.13 g, 0.5 wt%), and antifoaming agent (0.26 g, 1 wt%) into a 500 mL stainless steel pressure reactor. Replace with nitrogen three times, pressurize to 1.5 Mpa, stir and heat to 180 °C. While maintaining the reaction temperature, add 2-ethylhexanol (264.4 g, 98.5%, 2.0 mol) in batches slowly. Under the condition of maintaining the pressure, release the generated gas. After reacting for 3 hours, there is no obvious change in the pressure in the kettle. Then continue to stir and react for half an hour until no gas is generated. After the reaction is completed, cool to room temperature, add 300 mL of water to dissolve the mixed solution, which is light yellow. Filter to remove insoluble substances, separate and remove the organic layer. Acidify the aqueous layer with 50% sulfuric acid solution to pH = 2, separate, wash the organic layer with water, and dry to obtain 232.7 g of a mixture. After GC testing, the purity of heptanoic acid is 78.93%, and the yield of n-heptanoic acid is 70.54%.

[0084] Example 6

[0085] An embodiment of the present invention provides a method for preparing n-heptanoic acid by oxidizing alcohol. Add sodium hydroxide (98%, 81.6 g, 2.0 mol), water (79.32 g, 30 wt%), copper oxide-zinc oxide supported catalyst (0.13 g, 0.5 wt%), and antifoaming agent (0.26 g, 1 wt%) into a 500 mL stainless steel pressure reactor. Replace with nitrogen three times, pressurize to 1.5 Mpa, stir and heat to 180 °C. While maintaining the reaction temperature, add 2-ethylhexanol (264.4 g, 98.5%, 2.0 mol) in batches slowly. Under the condition of maintaining the pressure, release the generated gas. After reacting for 3 hours, there is no obvious change in the pressure in the kettle. Then continue to stir and react for half an hour until no gas is generated. After the reaction is completed, cool to room temperature, add 300 mL of water to dissolve the mixed solution, which is light yellow. Filter to remove insoluble substances, separate and remove the organic layer. Acidify the aqueous layer with 50% sulfuric acid solution to pH = 2, separate, wash the organic layer with water, and dry to obtain 238.6 g of a mixture. After GC testing, the purity of heptanoic acid is 79.81%, and the yield of n-heptanoic acid is 73.14%.

[0086] Example 7

[0087] An embodiment of the present invention provides a method for preparing n-heptanoic acid by oxidizing alcohol. Add sodium hydroxide (98%, 81.6 g, 2.0 mol), water (66.1 g, 25 wt%), copper oxide-zinc oxide supported catalyst (0.13 g, 0.5 wt%), and antifoaming agent (0.26 g, 1 wt%) into a 500 mL stainless steel pressure reactor. Replace the air with nitrogen three times, pressurize to 1.5 Mpa, stir and heat to 240 °C. While maintaining the reaction temperature, add 2-ethylhexanol (264.4 g, 98.5%, 2.0 mol) in batches slowly. Under the condition of maintaining the pressure, release the generated gas. After reacting for 3 hours, there is no obvious change in the pressure in the reactor. Then continue to stir and react for half an hour until no gas is generated. After the reaction is completed, cool to room temperature, add 300 mL of water to dissolve the mixed solution, which is light yellow. Filter to remove the insoluble substances, separate the organic layer by liquid separation. Acidify the aqueous layer with 50% sulfuric acid solution to pH = 2, separate by liquid separation, wash the organic layer with water and dry it to obtain 234.8 g of a mixture. The purity of heptanoic acid is 80.77% and the yield of n-heptanoic acid is 72.84% by GC test.

[0088] Example 8

[0089] An embodiment of the present invention provides a method for preparing n-heptanoic acid by oxidizing alcohol. Add sodium hydroxide (98%, 81.6 g, 2.0 mol), water (66.1 g, 25 wt%), copper oxide-zinc oxide supported catalyst (0.13 g, 0.5 wt%), and antifoaming agent (0.26 g, 1 wt%) into a 500 mL stainless steel pressure reactor. Replace the air with nitrogen three times, pressurize to 1.5 Mpa, stir and heat to 160 °C. While maintaining the reaction temperature, add 2-ethylhexanol (264.4 g, 98.5%, 2.0 mol) in batches slowly. Under the condition of maintaining the pressure, release the generated gas. After reacting for 3 hours, there is no obvious change in the pressure in the reactor. Then continue to stir and react for half an hour until no gas is generated. After the reaction is completed, cool to room temperature, add 300 mL of water to dissolve the mixed solution, which is light yellow. Filter to remove the insoluble substances, separate the organic layer by liquid separation. Acidify the aqueous layer with 50% sulfuric acid solution to pH = 2, separate by liquid separation, wash the organic layer with water and dry it to obtain 238.7 g of a mixture. The purity of heptanoic acid is 77.86% and the yield of n-heptanoic acid is 71.38% by GC test.

[0090] The reaction pressure, reaction temperature, amount of water added, and product analysis results of the preparation methods of Examples 1-8 are shown in Table 1.

[0091] Table 1

[0092]

[0093]

[0094] Comparative Example 1

[0095] This comparative example provides a method for preparing n-heptanoic acid by oxidizing alcohol. Add sodium hydroxide (98%, 81.6 g, 2.0 mol), water (66.1 g, 25 wt%), and antifoaming agent (0.26 g, 1 wt%) to a 500 mL stainless steel pressure reactor. Replace the air with nitrogen three times, pressurize to 1.2 Mpa, stir and heat to 180 °C. Slowly add sec-octanol (264.4 g, 98.5%, 2.0 mol) in batches. The reaction of sec-octanol is slow at this temperature. Keep stirring and reacting at 180 °C for 18 hours until no gas is produced, and then continue stirring and reacting for half an hour. After the reaction is completed, cool to room temperature, add 300 mL of water to dissolve. The mixed solution is light yellow. Filter to remove insoluble substances, separate the organic layer by liquid separation. Acidify the aqueous layer with 50% sulfuric acid solution to pH = 2, separate by liquid separation, wash the organic layer with water and dry to obtain 196.3 g of a mixture. The purity of heptanoic acid is 49.63% by GC test, and the yield of n-heptanoic acid is 37.42%.

[0096] Comparative Example 2

[0097] This comparative example provides a method for preparing n-heptanoic acid by oxidizing alcohol. Add sodium hydroxide (98.0%, 81.6 g, 2.0 mol) to a 1 L stainless steel reactor equipped with a stirring, condensation system, and thermometer. Under a nitrogen atmosphere, heat to 320 °C for the materials in the kettle. Smoke and dust are generated during the heating process. Slowly add sec-octanol. It is difficult for sec-octanol to stay in the kettle and is quickly flash-evaporated. The materials in the kettle are difficult to stir due to accumulation. Continuously add the remaining sec-octanol (total addition amount is 264.4 g, 98.5%, 2.0 mol). Keep reacting at this temperature until no gas is produced, and then continue stirring and reacting for half an hour. After the reaction is completed, cool to room temperature, add 300 mL of water to dissolve. The solution is carbon black, and there are a large number of tarry insoluble substances in the mixture. Filter the insoluble substances, separate the tarry liquid. Acidify the aqueous layer with 50% sulfuric acid solution to pH = 2, separate by liquid separation, wash the organic layer with water and dry. Obtain 103.01 g of a mixture. The purity of heptanoic acid is 16.95% by GC test, and the yield of n-heptanoic acid is 6.71%.

[0098] Comparative Example 3

[0099] This comparative example provides a method for preparing n-heptanoic acid by oxidizing alcohol. Sodium hydroxide (98.0%, 40.8 g, 1.0 mol) and potassium hydroxide (85.0%, 65.9 g, 1.0 mol) were added to a 1 L stainless steel reactor equipped with a stirrer, a condensing system, and a thermometer. Under a nitrogen atmosphere, the temperature was raised to 320 °C for the materials in the kettle. A large amount of soot was generated during the heating process. Secondary octanol was slowly added. It was difficult for secondary octanol to stay in the kettle and was quickly flash-evaporated. It was difficult to stir the materials in the kettle, so the stirring was stopped. The remaining secondary octanol was continuously added (total addition amount was 264.4 g, 98.5%, 2.0 mol). The reaction was continued at this temperature until no gas was generated, and then the stirring reaction was continued for half an hour. After the reaction was completed, it was cooled to room temperature to obtain a viscous black mixture. 300 mL of water was added for dilution. The solution was carbon black, and there were black insoluble substances in the mixture. The insoluble substances were filtered, and the organic layer was separated by liquid separation. The aqueous layer was acidified to pH = 2 with 50% sulfuric acid solution, separated by liquid separation, and the organic layer was washed with water and dried. 116.8 g of the mixture was obtained. The purity of heptanoic acid was 21.16% by GC test, and the yield of n-heptanoic acid was 9.49%.

[0100] Comparative Example 4

[0101] This comparative example provides a method for preparing n-heptanoic acid by oxidizing alcohol. Sodium hydroxide (98%, 81.6 g, 2.0 mol), water (26.4 g, 10 wt%), copper oxide-zinc oxide supported catalyst (0.13 g, 0.5 wt%), and antifoaming agent (0.26 g, 1 wt%) were added to a 500 mL stainless steel pressure reactor. It was purged with nitrogen three times, pressurized to 1.5 Mpa, stirred and heated to 180 °C. Under the condition of maintaining the reaction temperature, secondary octanol (264.4 g, 98.5%, 2.0 mol) was added in batches slowly. Under the condition of maintaining the pressure, the generated gas was released. After the reaction for 3 hours, there was no obvious change in the pressure in the kettle. Then the stirring reaction was continued for half an hour until no gas was generated. After the reaction was completed, it was cooled to room temperature. 300 mL of water was added to dissolve the mixed solution, which was light yellow. The insoluble substances were filtered off, the organic layer was separated by liquid separation. The aqueous layer was acidified to pH = 2 with 50% sulfuric acid solution, separated by liquid separation, and the organic layer was washed with water and dried. 206.3 g of the mixture was obtained. The purity of heptanoic acid was 52.77% by GC test, and the yield of n-heptanoic acid was 41.81%.

[0102] Comparative Example 5

[0103] This comparative example provides a method for preparing n-heptanoic acid by oxidizing alcohol. Add sodium hydroxide (98%, 81.6 g, 2.0 mol), water (132.2 g, 50 wt%), copper oxide-zinc oxide supported catalyst (0.13 g, 0.5 wt%), and antifoaming agent (0.26 g, 1 wt%) into a 500 mL stainless steel pressure reactor. Replace the air with nitrogen three times, pressurize to 1.5 Mpa, stir and heat to 180 °C. While maintaining the reaction temperature, add 2-ethylhexanol (264.4 g, 98.5%, 2.0 mol) in batches slowly. Under the condition of maintaining the pressure, release the generated gas. After reacting for 3 hours, there is no obvious change in the pressure in the reactor. Then continue to stir and react for half an hour until no gas is generated. After the reaction is completed, cool to room temperature, add 300 mL of water to dissolve the mixed solution, which is light yellow. Filter to remove the insoluble substances, separate the organic layer by liquid separation, acidify the aqueous layer with 50% sulfuric acid solution to pH = 2, separate by liquid separation, wash the organic layer with water and dry it to obtain 214.3 g of a mixture. The purity of heptanoic acid is 61.19% and the yield of n-heptanoic acid is 50.36% by GC test.

[0104] Comparative Example 6

[0105] This comparative example provides a method for preparing n-heptanoic acid by oxidizing alcohol. Add sodium hydroxide (98%, 81.6 g, 2.0 mol), water (66.1 g, 25 wt%), copper oxide-zinc oxide supported catalyst (0.26 g, 1.0 wt%), and antifoaming agent (0.26 g, 1 wt%) into a 500 mL stainless steel pressure reactor. Replace the air with nitrogen three times, pressurize to 1.5 Mpa, stir and heat to 180 °C. While maintaining the reaction temperature, add 2-ethylhexanol (264.4 g, 98.5%, 2.0 mol) in batches slowly. Under the condition of maintaining the pressure, release the generated gas. After reacting for 3 hours, there is no obvious change in the pressure in the reactor. Then continue to stir and react for half an hour until no gas is generated. After the reaction is completed, cool to room temperature, add 300 mL of water to dissolve the mixed solution, which is light yellow. Filter to remove the insoluble substances, separate the organic layer by liquid separation, acidify the aqueous layer with 50% sulfuric acid solution to pH = 2, separate by liquid separation, wash the organic layer with water and dry it to obtain 242.6 g of a mixture. The purity of heptanoic acid is 78.23% and the yield of n-heptanoic acid is 71.77% by GC test.

[0106] The comparison results of the corresponding products of Example 4 and Comparative Examples 1-6 are shown in Table 2, and the gas chromatograms of the products are as Figure 1-8 shown.

[0107] Table 2

[0108]

[0109] It can be seen from Comparative Example 1 that although it adopts high-pressure and low-temperature conditions and can retain water and reactants in the system, it lacks a catalyst and cannot promote the reaction rate and reaction selectivity. The yield of n-heptanoic acid is significantly lower than that of Example 4 of the present invention. It can be seen from Comparative Example 2 that it adopts high-temperature, catalyst-free and atmospheric-pressure conditions. Although high temperature accelerates the reaction, a large amount of water and raw materials volatilize under atmospheric pressure, resulting in a decrease in the concentration of reactants. At the same time, side reactions intensify at too high temperatures, and the yield of n-heptanoic acid is only 6.71%. Comparative Example 3 also adopts high-temperature, catalyst-free and atmospheric-pressure conditions, and then most of the sodium hydroxide is replaced with potassium hydroxide, which is the existing conventional preparation method. Although the presence of potassium hydroxide can retain a part of water in the system, due to too high temperature and lack of a catalyst, the conversion rate is still very low. It can be seen from Comparative Examples 4-5 that too much or too little water addition will affect the reaction process and cause a decrease in yield. This is because excessive water will lead to a weakening of the alkalinity of the system, poor reaction selectivity, and an increase in by-products. Too little water cannot effectively inhibit the generation of by-products such as 2-methyl-1-octene, affecting reaction selectivity and thus affecting yield. Comparative Example 6 shows that an excessive amount of catalyst does not increase the yield, indicating that a 0.5 wt% catalyst has reached the best effect, and an excessive amount does not further promote the reaction.

[0110] The specific embodiments described above further elaborate on the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing n-heptanoic acid by oxidizing alcohol, characterized in that: With 2-octanol as raw material, copper oxide-zinc oxide supported catalyst is added to caustic alkali aqueous solution, and the reaction is carried out at a temperature of 160-240°C and a pressure of 1.0-2MPa to obtain n-heptanoate, which is then acidified to obtain n-heptanoic acid.

2. The method for preparing n-heptanoic acid by oxidizing alcohol according to claim 1, wherein The amount of the copper oxide-zinc oxide supported catalyst added is 0.4-0.6 wt% of the amount of the secondary octanol added.

3. The method for preparing n-heptanoic acid by oxidizing alcohol according to claim 1, wherein The amount of water in the caustic alkali aqueous solution is 20-40 wt% of the amount of secondary octanol added.

4. The method for preparing n-heptanoic acid by oxidizing alcohol according to claim 1, wherein The caustic soda is sodium hydroxide, and the amount of sodium hydroxide added is 31-35 wt% of the amount of secondary octanol added.

5. The method for preparing n-heptanoic acid by oxidizing alcohol according to claim 1, wherein: The preparation method of the copper oxide-zinc oxide supported catalyst is as follows: (1) preparing copper ion and zinc ion solutions respectively and transferring them into a reaction kettle; (2) Slowly add ammonia solution, the solution gradually becomes turbid and a precipitate forms; (3) adding coarse-porous microsphere silica gel, stirring the reaction at high temperature, cooling to room temperature, standing, filtering, washing, and collecting the precipitate; (4) After drying the precipitate, place it in a muffle furnace and calcine it at high temperature to obtain a copper oxide-zinc oxide supported silica gel catalyst.

6. The method for preparing n-heptanoic acid by oxidizing alcohol according to claim 1, characterized in that: The reaction system also includes a defoaming agent, and the defoaming agent is AFE-0800.

7. The method for preparing n-heptanoic acid by oxidizing alcohol according to claim 6, characterized in that: The defoaming agent is prepared as follows: 10% NaOH solution is added to water and stirred evenly, then AFE-0800 is added and stirred evenly, and 10% NaOH solution is added again and stirred evenly to obtain the defoaming agent.

8. The method for preparing n-heptanoic acid by oxidizing alcohol according to claim 1, wherein: The reaction conditions are: temperature 180°C and pressure 1.5 MPa.

9. The method for preparing n-heptanoic acid by oxidizing alcohol according to claim 3, wherein: The amount of water in the caustic alkali aqueous solution is 25 wt% of the amount of secondary octanol fed.

10. A method of preparing n-heptanoic acid by oxidizing an alcohol, characterized in that: The method is prepared by any one of claims 1 to 9.

Images