Preparation method of isobutyric anhydride

Abstract

The invention belongs to the technical field of organic synthesis, and provides a preparation method of isobutyric anhydride. The preparation method provided by the invention comprises the following steps: by taking isobutyric acid as a raw material and TiO2, gamma-Al2O3, SiO2, CuO, palladium-loaded silicon dioxide or triethyl phosphate as a catalyst, dehydrating to form isobutyric anhydride; the catalyst does not react with isobutyric acid, so that side reactions are few in the reaction process, the conversion rate of isobutyric acid and the selectivity of isobutyric anhydride are improved, and finally the yield of isobutyric anhydride is improved. Meanwhile, isobutyric anhydride can be separated from isobutyric acid and water through simple condensation, high-purity isobutyric anhydride is obtained, and continuous production can be achieved.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and in particular to a method for preparing isobutyric anhydride. Background Technology

[0002] Isobutyric anhydride (IBAN), also known as 2-methylpropionic anhydride, is an organic compound with the chemical formula C8H. 14 O3, with a molecular weight of 158.195, is a colorless, transparent liquid, slightly soluble in water, and miscible with ethanol and ether. Isobutyric anhydride is an important derivative of isobutyric acid, used in the synthesis of pesticide and pharmaceutical intermediates, the production of isobutyrate plasticizers, and fragrances and flavorings, making it an important organic chemical raw material. In organic synthesis, it is used as an acylation reagent to introduce isobutyryl groups (e.g., in pharmaceutical and fragrance intermediates). In the polymer industry, it participates in the synthesis of polymers or the modification of resins. In the laboratory, it can be used as a protecting agent for hydroxyl or amino groups.

[0003] Chinese patent CN202010804269 mentions that most of the isobutyric anhydride on the domestic market is imported from Eastman Chemical Company in the United States, while other sources are basically produced using intermittent production processes. The production process of isobutyric anhydride is rarely mentioned in literature or patents. Most of the existing information on butyric anhydride production involves the synthesis of isobutyric acid and ketene. However, the reaction to generate ketene in this method is difficult to control and involves many side reactions, resulting in a low yield of isobutyric anhydride. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a method for preparing isobutyric anhydride. The preparation method provided by the present invention has a high yield of isobutyric anhydride.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing isobutyric anhydride, comprising the following steps: Isobutyric acid is preheated to obtain isobutyric acid gas; Under catalytic conditions, the isobutyric acid gas is dehydrated to obtain a mixed gas containing isobutyric anhydride; The mixed gas containing isobutyric anhydride is condensed to obtain liquid isobutyric anhydride; The catalyst is TiO2, γ-Al2O3, SiO2, CuO, palladium-supported silica, or triethyl phosphate.

[0006] Preferably, the preheating temperature is 200~400℃.

[0007] Preferably, when the catalyst is TiO2, γ-Al2O3, SiO2, CuO, or palladium-supported silica, the dehydration of the isobutyric acid gas under the conditions of the catalyst includes: the isobutyric acid gas, carried by a carrier gas, comes into contact with the catalyst to undergo dehydration.

[0008] Preferably, the carrier gas is nitrogen and / or argon; the volume ratio of isobutyric acid gas to carrier gas is 1:100 to 1:10000; and the flow rate of the carrier gas is 0 to 10 L / min, and is not 0.

[0009] Preferably, when the catalyst is TiO2, γ-Al2O3, SiO2, CuO, or palladium-supported silicon oxide, the particle size of the catalyst is 10~1000 nm and the specific surface area is 100~1000 m². 2 / g.

[0010] Preferably, the catalyst is packed to a height of 2 to 10 cm.

[0011] Preferably, the residence time of the isobutyric acid gas on the catalyst is 1 to 2 seconds.

[0012] Preferably, when the catalyst is triethyl phosphate, the step of preheating isobutyric acid to obtain isobutyric acid gas; under the condition of the catalyst, the dehydration of the isobutyric acid gas includes: mixing isobutyric acid and the catalyst and then preheating to obtain a mixed gas; the mixed gas is then dehydrated.

[0013] Preferably, the temperature of the dehydration reaction is 400~600℃.

[0014] Preferably, the condensation temperature is 20~80℃.

[0015] This invention provides a method for preparing isobutyric anhydride.

[0016] The preparation method provided by this invention uses isobutyric acid as a raw material and TiO2, γ-Al2O3, SiO2, CuO, palladium-supported silica, or triethyl phosphate as a catalyst to form isobutyric anhydride through dehydration. The catalyst of this invention does not react with isobutyric acid, thus reducing side reactions during the reaction process, improving the conversion rate of isobutyric acid and the selectivity of isobutyric anhydride, and ultimately increasing the yield of isobutyric anhydride. Simultaneously, this invention allows for the simple separation of isobutyric anhydride from isobutyric acid and water through condensation, yielding high-purity isobutyric anhydride. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the preparation process for isobutyric anhydride according to the present invention; Figure 2 The total ion chromatogram of the liquid isobutyric anhydride obtained in Example 1; Figure 3 The mass spectrum of the liquid isobutyric anhydride obtained in Example 1; Figure 4 The total ion chromatogram of the liquid isobutyric anhydride obtained in Example 2; Figure 5 The mass spectrum of the liquid isobutyric anhydride obtained in Example 2; Figure 6 The total ion chromatogram of the liquid isobutyric anhydride obtained in Example 3; Figure 7 The mass spectrum of the liquid isobutyric anhydride obtained in Example 3; Figure 8 The total ion chromatogram of the liquid isobutyric anhydride obtained in Example 4; Figure 9 The mass spectrum of the liquid isobutyric anhydride obtained in Example 4; Figure 10 The total ion chromatogram of the liquid isobutyric anhydride obtained in Example 5; Figure 11 The mass spectrum of the liquid isobutyric anhydride obtained in Example 5; Figure 12 The total ion chromatogram of liquid isobutyric anhydride obtained in Comparative Example 1; Figure 13 The mass spectrum of the liquid isobutyric anhydride obtained in Comparative Example 1 is shown. Figure 14 The total ion chromatogram of the liquid isobutyric anhydride obtained in Example 6; Figure 15 This is the mass spectrum of the liquid isobutyric anhydride obtained in Example 6. Detailed Implementation

[0018] This invention provides a method for preparing isobutyric anhydride, comprising the following steps: Isobutyric acid is preheated to obtain isobutyric acid gas; Under catalytic conditions, the isobutyric acid gas is dehydrated to obtain a mixed gas containing isobutyric anhydride; The mixed gas containing isobutyric anhydride is condensed to obtain liquid isobutyric anhydride; The catalyst is TiO2, γ-Al2O3, SiO2, CuO, palladium-supported silica, or triethyl phosphate.

[0019] Unless otherwise specified, the raw materials used in this invention are preferably commercially available products.

[0020] This invention preheats isobutyric acid to obtain isobutyric acid gas.

[0021] In this invention, the purity of the isobutyric acid is preferably 99.9%.

[0022] In this invention, the feed rate for preheating isobutyric acid is preferably 0~10 mL / min, and not 0, specifically preferably 0.1 mL / min, 0.5 mL / min, 1 mL / min, 2 mL / min, 3 mL / min, 4 mL / min, 5 mL / min, 6 mL / min, 7 mL / min, 8 mL / min, 9 mL / min or 10 mL / min.

[0023] In this invention, the preheating temperature is preferably 200~400℃, and more specifically 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃ or 400℃.

[0024] In this invention, the preheating is preferably carried out in a preheating reactor.

[0025] In this invention, the preheating can convert liquid isobutyric acid into isobutyric acid gas.

[0026] After obtaining isobutyric acid gas, the present invention dehydrates the isobutyric acid gas under the condition of a catalyst to obtain a mixed gas containing isobutyric anhydride.

[0027] In this invention, when the catalyst is triethyl phosphate, the triethyl phosphate is preferably fed and preheated together with isobutyric acid. The feeding and preheating conditions are preferably consistent with the above-described technical solution and will not be repeated here. In this invention, the molar ratio of isobutyric acid to triethyl phosphate is preferably 45-50:1, specifically preferably 45:1, 46:1, 47:1, 48:1, 49:1, or 50:1.

[0028] In this invention, when the catalyst is TiO2, γ-Al2O3, SiO2, CuO, or palladium-supported silica, the dehydration of the isobutyric acid gas under catalytic conditions preferably includes: the isobutyric acid gas, carried by a carrier gas, contacting the catalyst for dehydration. In this invention, the carrier gas is preferably nitrogen and / or argon, more preferably nitrogen. In this invention, the volume ratio of isobutyric acid gas to carrier gas is preferably 1:100 to 1:10000, and more preferably 1:100, 1:200, 1:300, 1:400, 1:500, 1:600, 1:700, 1:800, 1:900, 1:1000, 1:2000, 1:3000, 1:4000, 1:5000, 1:6000, 1:7000, 1:8000, 1:9000, or 1:10000. In this invention, the flow rate of the carrier gas is preferably 0~10L / min, and not 0, specifically preferably 0.1L / min, 0.5L / min, 1L / min, 1.5L / min, 2L / min, 2.5L / min, 3L / min, 3.5L / min, 4L / min, 4.5L / min, 5L / min, 5.5L / min, 6L / min, 6.5L / min, 7L / min, 7.5L / min, 8L / min, 8.5L / min, 9L / min, 9.5L / min or 10L / min. In this invention, when the catalyst is TiO2, γ-Al2O3, SiO2, CuO, or palladium-supported silica, the particle size of the catalyst is preferably 10~1000 nm, specifically preferably 10 nm, 12.97 nm, 20 nm, 25 nm, 30 nm, 33 nm, 35 nm, 40 nm, 50 nm, 60 nm, 80 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, 850 nm, 900 nm, 950 nm, or 1000 nm; the specific surface area is preferably 100~1000 m². 2 / g, preferably 100m 2 / g、130m 2 / g, 150m 2 / g、160m 2 / g、170m 2 / g、200m 2 / g、250m 2 / g、300m 2 / g, 350m 2 / g、400m 2 / g、450m 2 / g、500m 2 / g、550m 2 / g、600m 2 / g、650m 2 / g、700m 2 / g、750m 2 / g、800m 2 / g、850m 2 / g、900m 2 / g、950m 2 / g or 1000m 2 / g.

[0029] In this invention, when the catalyst is TiO2, the particle size of the catalyst is preferably 35 nm, and the specific surface area is preferably 150 m². 2 / g. In this invention, the preparation method of TiO2 preferably includes the following steps: mixing tetrabutyl titanate and ethanol to obtain a titanium source solution; mixing ethanol and water to obtain an ethanol-water solution; adding the ethanol-water solution dropwise to the titanium source solution to carry out a hydrolysis reaction to obtain TiO2. In this invention, the mixing of tetrabutyl titanate and ethanol is preferably carried out under stirring conditions, and the stirring time is preferably 30 min. In this invention, the volume concentration of the titanium source in the titanium source solution is preferably 40%. In this invention, the mixing of ethanol and water is preferably carried out under stirring conditions, and the stirring time is preferably 30 min. In this invention, the volume concentration of ethanol in the ethanol-water solution is preferably 50%. In this invention, the volume ratio of the titanium source solution to the ethanol-water solution is preferably 6:8 to 8:8, more preferably 7:8. In this invention, the dropwise addition is preferably dropwise addition. In this invention, the temperature of the hydrolysis reaction is preferably room temperature, i.e., neither additional heating nor additional cooling is required. In this invention, the hydrolysis reaction time is preferably 4 h; the hydrolysis reaction is preferably carried out under stirring conditions. After the hydrolysis reaction, the present invention preferably further includes: filtering the obtained hydrolysis reaction solution, drying the obtained filter residue, and obtaining the TiO2.

[0030] In this invention, when the catalyst is γ-Al₂O₃, the particle size of the catalyst is preferably 30 nm, and the specific surface area is preferably 160 m². 2 / g. In this invention, the preparation method of γ-Al2O3 preferably includes the following steps: dissolving aluminum sulfate and sodium hydroxide in water respectively to obtain aluminum sulfate solution and sodium hydroxide solution respectively; adding the aluminum sulfate solution dropwise to the sodium hydroxide solution to carry out a precipitation reaction to obtain aluminum hydroxide; calcining the aluminum hydroxide to obtain γ-Al2O3. In this invention, the dissolution of aluminum sulfate in water is preferably carried out under stirring conditions, and the stirring time is preferably 30 min. In this invention, the mass concentration of the aluminum sulfate solution is preferably 5~10%, specifically preferably 5%, 6%, 7%, 8%, 9% or 10%. In this invention, the dissolution of sodium hydroxide in water is preferably carried out under stirring conditions, and the stirring time is preferably 30 min. In this invention, the mass concentration of the sodium hydroxide solution is preferably 8~12%, specifically preferably 8%, 9%, 10%, 11% or 12%. In this invention, the volume ratio of the aluminum sulfate solution to the sodium hydroxide solution is preferably 1:1~1.2, specifically preferably 1:1, 1:1.1 or 1:1.2. In this invention, the dropwise addition method is preferably dropwise addition. In this invention, the precipitation reaction temperature is preferably room temperature, i.e., neither additional heating nor additional cooling is required; the precipitation reaction time is preferably 1 hour; the precipitation reaction is preferably carried out under stirring conditions. After the precipitation reaction, this invention preferably further includes filtering the obtained precipitation reaction solution and drying the resulting filter residue to obtain the aluminum hydroxide. In this invention, the calcination temperature is preferably 600°C, and the calcination time is preferably 2 hours.

[0031] In this invention, when the catalyst is SiO2, the particle size of the catalyst is preferably 12.97 nm, and the specific surface area is preferably 450 m². 2 / g. In a specific embodiment of the present invention, the method for preparing SiO2 preferably includes the following steps: mixing anhydrous ethanol, tetraethoxysilane (TEOS), and sodium hydroxide solution, and stirring the mixture to obtain the silicon dioxide. In the present invention, the mass concentration of the sodium hydroxide solution is preferably 5%. In the present invention, the volume ratio of anhydrous ethanol, tetraethoxysilane, and sodium hydroxide solution is preferably 30:12:12. In the present invention, the temperature of the stirring reaction is preferably room temperature, i.e., neither additional heating nor additional cooling is required; the stirring reaction time is preferably 2 hours. After the stirring reaction, the present invention preferably further includes: filtering to collect the solid; washing and drying the solid sequentially to obtain the silicon dioxide. In the present invention, the washing reagent is preferably anhydrous ethanol. In the present invention, the drying time is preferably 12 hours.

[0032] In this invention, when the catalyst is CuO, the particle size of the catalyst is preferably 25 nm, and the specific surface area is preferably 130 m².2 / g. In this invention, the preparation method of CuO preferably includes the following steps: dissolving copper sulfate in water to obtain a copper sulfate solution; adding ammonia water dropwise to the copper sulfate solution to carry out a precipitation reaction to obtain copper hydroxide; calcining the copper hydroxide to obtain CuO. In this invention, the dissolution of copper sulfate in water is preferably carried out under stirring conditions, and the stirring time is preferably 30 min. In this invention, the mass concentration of the copper sulfate solution is preferably 5-10%, specifically preferably 5%, 6%, 7%, 8%, 9% or 10%. In this invention, the mass concentration of ammonia water is preferably 8-12%, specifically preferably 8%, 9%, 10%, 11% or 12%. In this invention, the volume ratio of the copper sulfate solution to ammonia water is preferably 1:1-1.2, specifically preferably 1:1, 1:1.1 or 1:1.2. In this invention, the dropwise addition method is preferably dropwise addition. In this invention, the temperature of the precipitation reaction is preferably 30℃, and the precipitation is preferably carried out under water bath heating conditions; the precipitation reaction time is preferably 3 h; the precipitation reaction is preferably carried out under stirring conditions. Following the precipitation reaction, the present invention preferably further includes filtering the obtained precipitation reaction solution and drying the resulting filter residue to obtain the copper hydroxide. In the present invention, the calcination temperature is preferably 400°C, and the calcination time is preferably 2 hours.

[0033] In this invention, the preferred method for preparing palladium-supported silica (Pd / SiO2) includes the following steps: pretreating silica to obtain pretreated silica; adding a palladium salt solution dropwise onto the pretreated silica under stirring to obtain a precursor; and sequentially drying (referred to as first drying), calcining, and reducing the precursor to obtain the palladium-supported catalyst. In this invention, the pretreatment method is preferably drying (referred to as second drying); the temperature of the second drying is preferably 110°C, and the time is preferably overnight. In this invention, the palladium salt in the palladium salt solution is preferably palladium chloride, and the mass concentration of the palladium salt solution is preferably 20-40%, specifically preferably 20%, 30%, or 40%. In this invention, the ratio of the pretreated silica to the palladium salt solution is preferably 4-6 g:10 mL, more preferably 5 g:10 mL. In this invention, the precursor is preferably a moist but non-liquid paste; the stirring time is not specifically limited, as long as a moist but non-liquid paste is obtained. In this invention, the temperature of the first drying is preferably 80-120°C, more preferably 90-110°C, and even more preferably 100°C; the time is preferably 5-7 hours, and even more preferably 6 hours; the first drying is preferably carried out in a drying oven. In this invention, the calcination temperature is preferably 350-450°C, more preferably 400°C, and the holding time is preferably 3-5 hours, and even more preferably 4 hours; the calcination is preferably carried out in an air atmosphere. In this invention, the reduction atmosphere is preferably hydrogen, the reduction temperature is preferably 250-350°C, more preferably 300°C; the time is preferably 1-3 hours, and even more preferably 2 hours.

[0034] In this invention, the loading height of the catalyst is preferably 2 to 10 cm, and more preferably 2 cm, 3 cm, 4 cm, 5 cm, 6 cm, 7 cm, 8 cm, 9 cm or 10 cm.

[0035] In this invention, the residence time of the isobutyric acid gas on the catalyst is preferably 1 to 2 seconds, and more preferably 1.42 seconds.

[0036] In this invention, the temperature of the dehydration reaction is preferably 450~550℃, specifically preferably 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃, or 550℃; the time is preferably 1~2s, specifically preferably 1.42s. In this invention, the dehydration reaction time preferably refers to the time during which the gas and catalyst contact and react at the dehydration reaction temperature.

[0037] In this invention, the mixed gas containing isobutyric anhydride includes isobutyric anhydride and water, and preferably also includes unreacted isobutyric acid.

[0038] After obtaining the mixed gas containing isobutyric anhydride, the present invention condenses the mixed gas containing isobutyric anhydride to obtain liquid isobutyric anhydride.

[0039] In this invention, the condensation temperature is preferably 20~80℃, more preferably 40~60℃, and specifically preferably 20℃, 30℃, 40℃, 45℃, 50℃, 55℃, 60℃, 70℃ or 80℃.

[0040] In this invention, the condensation is preferably carried out on a condenser.

[0041] In this invention, the mixed gas containing isobutyric anhydride includes isobutyric anhydride, isobutyric acid, and water, wherein the boiling point of isobutyric anhydride is 182°C, the boiling point of isobutyric acid is 152~155°C, and the boiling point of water is 100°C. Since isobutyric anhydride has the highest boiling point in the mixed gas containing isobutyric anhydride, it condenses first during the condensation process, forming liquid isobutyric anhydride, which is separated from isobutyric acid and water.

[0042] In this invention, the main component of the liquid isobutyric anhydride is isobutyric anhydride, and it contains few impurities.

[0043] Taking a solid catalyst as an example, the schematic diagram of the preparation process of isobutyric anhydride provided by this invention is as follows: Figure 1 As shown, Figure 1 As shown, isobutyric acid gas, carried by a carrier, enters the reactor and comes into contact with a solid catalyst in the reactor for dehydration, resulting in a mixed gas containing isobutyric anhydride; the mixed gas containing isobutyric anhydride is then condensed to obtain liquid isobutyric anhydride.

[0044] The preparation method of isobutyric anhydride provided by the present invention will be described in detail below with reference to the embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0045] Example 1 At room temperature, isobutyric acid (IBA) is introduced into a preheating reactor at 350℃ at a feed rate of 0.1 mL / min for preheating, whereby the isobutyric acid changes from a liquid to a gaseous state. The isobutyric acid gas, carried by a carrier gas N2 at a flow rate of 0.1 L / min (where the volume ratio of isobutyric acid gas to nitrogen is 1:1000), passes through a catalyst with a packing height of 2 cm (the catalyst is SiO2, with a particle size of 12.97 nm and a specific surface area of ​​450 m²). 2 / g); During this process, the residence time of isobutyric acid gas on the catalyst is 1.42 s. The dehydrated products (including isobutyric anhydride, isobutyric acid, and water) pass through a condenser and are cooled to about 50°C. The isobutyric anhydride, which has the highest boiling point, first becomes liquid, while the water is discharged as a gas, achieving gas-liquid separation and obtaining liquid isobutyric anhydride; the entire dehydration reaction takes 3 hours. The isobutyric acid conversion rate is 70%, the isobutyric anhydride selectivity is 99%, and the yield is 69.3%.

[0046] The preparation method of SiO2 is as follows: 30 mL of anhydrous ethanol, 12 mL of sodium hydroxide aqueous solution (mass concentration of 5%) and 12 mL of tetraethoxysilane (TEOS) are placed in a beaker, stirred for 2 h, filtered, and the resulting solid is washed with anhydrous ethanol several times and dried for 12 h.

[0047] Liquid isobutyric anhydride was detected using GC-MS, and the results are as follows: Figure 2 and Figure 3 As shown, Figure 2 The total ion chromatogram of the obtained liquid isobutyric anhydride is shown. Figure 3 The mass spectrum of the obtained liquid isobutyric anhydride is shown from... Figure 2 It can be seen that the peak position of isobutyric acid is at 3.120s, and the peak area of ​​isobutyric acid is 30% by peak integration. The peak position of isobutyric anhydride is at 4.272s, and the peak area of ​​isobutyric anhydride is 70%. In summary, the purity of the obtained liquid isobutyric anhydride is 70%.

[0048] Example 2 At room temperature, isobutyric acid (IBA) is introduced into a preheating reactor at 350℃ at a feed rate of 0.1 mL / min for preheating, whereby the isobutyric acid changes from a liquid to a gaseous state. The isobutyric acid gas, carried by a carrier gas N2 at a flow rate of 0.1 L / min (where the volume ratio of isobutyric acid gas to nitrogen is 1:1000), passes through a catalyst with a packing height of 2 cm (the catalyst is TiO2, with a particle size of 35 nm and a specific surface area of ​​150 m²). 2 / g). During this process, the residence time of isobutyric acid gas on the catalyst is 1.42 s. The dehydrated products (including isobutyric anhydride, isobutyric acid, and water) pass through a condenser and are cooled to approximately 50°C. The isobutyric anhydride, with the highest boiling point, becomes liquid, while the water is discharged as a gas, achieving gas-liquid separation and yielding liquid isobutyric anhydride. The entire dehydration reaction takes 3 hours. The isobutyric acid conversion rate is 60%, the isobutyric anhydride selectivity is 90%, and the yield is 54%.

[0049] The preparation method of TiO2 is as follows: Tetrabutyl titanate and anhydrous ethanol were added to a beaker and stirred for 30 min to obtain a tetrabutyl titanate solution with a volume concentration of 40%. Anhydrous ethanol and deionized water were added to a beaker and stirred for 30 min to obtain an ethanol aqueous solution with a volume concentration of 50%. 40 mL of the ethanol aqueous solution was added dropwise to 35 mL of the tetrabutyl titanate solution, stirred at room temperature for 4 h, filtered and dried to obtain TiO2.

[0050] Liquid isobutyric anhydride was detected using GC-MS, and the results are as follows: Figure 4 and Figure 5 As shown, Figure 4 The total ion chromatogram of the obtained liquid isobutyric anhydride is shown. Figure 5 The mass spectrum of the obtained liquid isobutyric anhydride is shown from... Figure 4 It can be seen that the peak position of isobutyric acid is at 2.975s, and the peak area of ​​isobutyric acid is 40% by peak integration. The peak position of isobutyric anhydride is at 4.278s, and the peak area of ​​isobutyric anhydride is 60%. In summary, the purity of the obtained liquid isobutyric anhydride is 60%.

[0051] Example 3 At room temperature, isobutyric acid (IBA) is introduced into a preheating reactor at 350°C at a feed rate of 0.1 mL / min for preheating, whereby the isobutyric acid changes from a liquid to a gaseous state. The isobutyric acid gas, carried by a carrier gas N2 at a flow rate of 0.1 L / min (where the volume ratio of isobutyric acid gas to nitrogen is 1:1000), passes through a catalyst with a packing height of 2 cm (the catalyst is CuO, with a particle size of 25 nm and a specific surface area of ​​130 m²). 2 / g). During this process, the residence time of isobutyric acid gas on the catalyst is 1.42 s. The dehydrated products (including isobutyric anhydride, isobutyric acid, and water) pass through a condenser and are cooled to approximately 50°C. The isobutyric anhydride, with the highest boiling point, becomes liquid, while the water is discharged as a gas, achieving gas-liquid separation and yielding liquid isobutyric anhydride. The entire dehydration reaction takes 3 hours. The isobutyric acid conversion rate is 70%, the isobutyric anhydride selectivity is 70.14%, and the yield is 49%.

[0052] The preparation method of CuO is as follows: CuSO4 was dissolved in water and stirred for 30 min to obtain a copper sulfate solution with a mass concentration of 7%. Then, 100 mL of ammonia solution with a mass concentration of 12% was added dropwise to 100 mL of copper sulfate solution, and the mixture was heated in a water bath at 30 °C for 3 h. After filtration and drying, copper hydroxide was obtained. The copper hydroxide was calcined at 400 °C for 2 h to obtain CuO.

[0053] Liquid isobutyric anhydride was detected using GC-MS, and the results are as follows: Figure 6 and Figure 7 As shown, Figure 6 The total ion chromatogram of the obtained liquid isobutyric anhydride is shown. Figure 7 The mass spectrum of the obtained liquid isobutyric anhydride is shown from... Figure 6 It can be seen that the peak position of isobutyric acid is at 2.901s, and the peak area of ​​isobutyric acid is 30% by peak integration. The peak position of isobutyric anhydride is at 4.272s, and the peak area of ​​isobutyric anhydride is 70%. In summary, the purity of the obtained liquid isobutyric anhydride is 70%.

[0054] Example 4 At room temperature, isobutyric acid and triethyl phosphate (molar ratio of isobutyric acid to triethyl phosphate is 47:1) are fed together at a feed rate of 0.1 mL / min. After preheating in a preheating reactor at 350℃, isobutyric acid changes from liquid to gaseous isobutyric acid gas, and triethyl phosphate changes from liquid to gaseous triethyl phosphate gas. The isobutyric acid gas is carried by N2 carrier gas at a flow rate of 0.1 mL / min. During this process, the residence time of the isobutyric acid gas in the furnace chamber is 1.42 s. The dehydrated products (including isobutyric anhydride, isobutyric acid, and water) pass through a condenser and are cooled to about 50℃. When the isobutyric anhydride, which has the highest boiling point, becomes liquid, the water and other impurities are discharged in gaseous form, achieving gas-liquid separation, and isobutyric anhydride is obtained. The entire dehydration reaction takes 3 hours.

[0055] The conversion rate of isobutyric acid was 47.90%, the selectivity of isobutyric anhydride was 70%, and the yield was 33.53%.

[0056] Liquid isobutyric anhydride was detected using GC-MS, and the results are as follows: Figure 8 and Figure 9 As shown, Figure 8 The total ion chromatogram of the obtained liquid isobutyric anhydride is shown. Figure 9 The mass spectrum of the obtained liquid isobutyric anhydride is shown from... Figure 8 It can be seen that the peak position of isobutyric acid is at 2.980s, and the peak area of ​​isobutyric acid is 52.1% by peak integration. The peak position of isobutyric anhydride is at 4.267s, and the peak area of ​​isobutyric anhydride is 47.90%. In summary, the purity of the obtained liquid isobutyric anhydride is 47.90%.

[0057] Example 5 At room temperature, isobutyric acid (IBA) is fed into a preheating reactor at 350°C at a rate of 0.1 mL / min. After preheating, the isobutyric acid changes from a liquid to a gaseous state. The gaseous isobutyric acid, carried by a carrier gas N2 at a flow rate of 0.1 L / min (where the volume ratio of isobutyric acid gas to nitrogen is 1:1000), passes through a catalyst with a packing height of 2 cm (the catalyst is γ-Al2O3, with a particle size of 30 nm and a specific surface area of ​​160 m²). 2 / g). During this process, the residence time of isobutyric acid gas on the catalyst is 1.42 s. The dehydrated products (including isobutyric anhydride, isobutyric acid, and water) pass through a condenser and are cooled to approximately 50°C. The isobutyric anhydride, with the highest boiling point, becomes liquid, while the water is discharged as a gas, achieving gas-liquid separation to obtain isobutyric anhydride. The entire dehydration reaction takes 3 hours. The isobutyric acid conversion rate is 67.04%, the isobutyric anhydride selectivity is 80%, and the yield is 53.62%.

[0058] The preparation method of γ-Al2O3 is as follows: Aluminum sulfate was dissolved in water and stirred for 30 min to obtain a 6% aluminum sulfate solution. NaOH was dissolved in water and stirred for 30 min to obtain a 10% sodium hydroxide solution. 100 mL of aluminum sulfate solution was added dropwise to 100 mL of sodium hydroxide solution, stirred for 1 h, filtered, and dried to obtain Al(OH)3. Al(OH)3 was calcined at 600 °C for 2 h to obtain γ-Al2O3.

[0059] Liquid isobutyric anhydride was detected using GC-MS, and the results are as follows: Figure 10 and Figure 11 As shown, Figure 10 The total ion chromatogram of the obtained liquid isobutyric anhydride is shown. Figure 11 The mass spectrum of the obtained liquid isobutyric anhydride is shown from... Figure 10 It can be seen that the peak position of isobutyric acid is at 2.977s, and the peak area of ​​isobutyric acid is 32.96% by peak integration. The peak position of isobutyric anhydride is at 4.320s, and the peak area of ​​isobutyric anhydride is 67.04%. The purity of the obtained liquid isobutyric anhydride is 67.04%.

[0060] Comparative Example 1 At room temperature, isobutyric acid (IBA) is introduced into a preheating reactor at 350°C at a feed rate of 0.1 mL / min for preheating, whereby the isobutyric acid changes from a liquid to a gaseous state. The isobutyric acid gas, carried by a carrier gas N2 at a flow rate of 0.1 L / min (where the volume ratio of isobutyric acid gas to nitrogen is 1:1000), passes through a catalyst with a packing height of 2 cm (the catalyst is MgO, with a particle size of 33 nm and a specific surface area of ​​170 m²). 2 / g). During this process, the residence time of isobutyric acid gas on the catalyst is 1.42 s. The dehydrated products (including isobutyric anhydride, isobutyric acid, and water) pass through a condenser and are cooled to approximately 50°C. The isobutyric anhydride, with the highest boiling point, becomes liquid, while the water is discharged as a gas, achieving gas-liquid separation to obtain isobutyric anhydride. The entire dehydration reaction takes 3 hours. The isobutyric acid conversion rate is 60%, the isobutyric anhydride selectivity is 78%, and the yield is 46.80%.

[0061] The preparation method of MgO is as follows: Magnesium chloride was dissolved in water and stirred for 30 min to obtain a 9% magnesium chloride solution. NaOH was dissolved in water and stirred for 30 min to obtain an 8% sodium hydroxide solution. 100 mL of magnesium chloride solution was added dropwise to 100 mL of sodium hydroxide solution and stirred for 1 h. The mixture was then filtered and dried to obtain Mg(OH)₂. Mg(OH)₂ was calcined at 350 °C for 2 h to obtain MgO.

[0062] Liquid isobutyric anhydride was detected using GC-MS, and the results are as follows: Figure 12 and Figure 13 As shown, Figure 12 The total ion chromatogram of the obtained liquid isobutyric anhydride is shown. Figure 13 The mass spectrum of the obtained liquid isobutyric anhydride is shown from... Figure 12 It can be seen that the peak position of isobutyric acid is at 3.120s, and the peak area of ​​isobutyric acid is 40% by peak integration. The peak position of isobutyric anhydride is at 4.300s, and the peak area of ​​isobutyric anhydride is 60%. In summary, the purity of the obtained liquid isobutyric anhydride is 60%.

[0063] Example 6 At room temperature, isobutyric acid (IBA) is introduced into a preheating reactor at 350°C at a feed rate of 0.1 mL / min for preheating, whereby the isobutyric acid changes from a liquid to a gaseous state. The isobutyric acid gas, carried by a carrier gas N2 at a flow rate of 0.1 L / min (where the volume ratio of isobutyric acid gas to nitrogen is 1:1000), passes through a catalyst with a packing height of 2 cm (the catalyst is Pd / SiO2, with a particle size of 13 nm and a specific surface area of ​​470 m²). 2 / g). During this process, the residence time of isobutyric acid gas on the catalyst is 1.42 s. The dehydrated products (including isobutyric anhydride, isobutyric acid, and water) pass through a condenser and are cooled to approximately 50°C. The isobutyric anhydride, with the highest boiling point, becomes liquid, while the water is discharged as a gas, achieving gas-liquid separation to obtain isobutyric anhydride. The entire dehydration reaction takes 3 hours. The isobutyric acid conversion rate is 85%, the isobutyric anhydride selectivity is 80%, and the yield is 68%.

[0064] The preparation method of Pd / SiO2 is as follows: First, SiO2 was dried overnight at 110℃ to obtain pretreated silica. Palladium chloride (PdCl2) was weighed and dissolved in an appropriate amount of deionized water to obtain a 30% (w / w) palladium chloride solution. 10 mL of the palladium chloride solution was added dropwise to 5 g of pretreated silica while stirring to ensure uniform absorption by the carrier, ultimately forming a moist but non-liquid paste. The impregnated wet solid was dried in an oven at 100℃ for 6 h. The dried solid was then calcined in air at 400℃ for 4 h. The calcined sample (at which point palladium mainly exists as PdO) was reduced in a hydrogen atmosphere at 300℃ for 2 h to obtain Pd / SiO2.

[0065] Liquid isobutyric anhydride was detected using GC-MS, and the results are as follows: Figure 14 and Figure 15 As shown, Figure 14 The total ion chromatogram of the obtained liquid isobutyric anhydride is shown. Figure 15 The mass spectrum of the obtained liquid isobutyric anhydride is shown from... Figure 14 It can be seen that the peak position of isobutyric acid is at 2.960s, and the peak area of ​​isobutyric acid is 15% by peak integration. The peak position of isobutyric anhydride is at 4.290s, and the peak area of ​​isobutyric anhydride is 85%. In summary, the purity of the obtained liquid isobutyric anhydride is 85%.

[0066] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing isobutyric anhydride, characterized in that, Includes the following steps: Isobutyric acid is preheated to obtain isobutyric acid gas; Under catalytic conditions, the isobutyric acid gas is dehydrated to obtain a mixed gas containing isobutyric anhydride; The mixed gas containing isobutyric anhydride is condensed to obtain liquid isobutyric anhydride; The catalyst is TiO2, γ-Al2O3, SiO2, CuO, palladium-supported silica, or triethyl phosphate.

2. The preparation method according to claim 1, characterized in that, The preheating temperature is 200~400℃.

3. The preparation method according to claim 1, characterized in that, When the catalyst is TiO2, γ-Al2O3, SiO2, CuO, or palladium-supported silica, the dehydration of the isobutyric acid gas under the conditions of the catalyst includes: the isobutyric acid gas, carried by a carrier gas, comes into contact with the catalyst to undergo dehydration.

4. The preparation method according to claim 3, characterized in that, The carrier gas is nitrogen and / or argon; the volume ratio of isobutyric acid gas to carrier gas is 1:100 to 1:10000; the flow rate of the carrier gas is 0 to 10 L / min, and is not 0.

5. The preparation method according to claim 3, characterized in that, When the catalyst is TiO2, γ-Al2O3, SiO2, CuO, or palladium-supported silica, the particle size of the catalyst is 10~1000 nm and the specific surface area is 100~1000 m². 2 / g.

6. The preparation method according to claim 3, characterized in that, The catalyst is packed to a height of 2-10 cm.

7. The preparation method according to claim 3, characterized in that, The residence time of the isobutyric acid gas on the catalyst is 1~2 s.

8. The preparation method according to claim 1, characterized in that, When the catalyst is triethyl phosphate, the step of preheating isobutyric acid to obtain isobutyric acid gas; under the condition of the catalyst, the dehydration of the isobutyric acid gas includes: mixing isobutyric acid and the catalyst and then preheating to obtain a mixed gas; the mixed gas is then dehydrated.

9. The preparation method according to claim 1, characterized in that, The temperature of the dehydration reaction is 400~600℃.

10. The preparation method according to claim 1, characterized in that, The condensation temperature is 20~80℃.

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