Method for preparing mu3-O trinuclear chromium propionic acid complex based on microchannel-microwave

Abstract

The invention discloses a method for preparing a mu3-O trinuclear chromium propionic acid complex based on microchannel-microwave, and relates to the technical field of organic synthesis.The method comprises the following steps that a chromium trioxide-propionic acid aqueous solution and an n-propyl alcohol aqueous solution are fed into a microchannel reactor to be subjected to a reaction, and a microchannel reaction solution is obtained; feeding the micro-channel reaction liquid into a microwave reactor, carrying out toluene azeotropic dehydration reaction, and obtaining microwave reaction liquid after dehydration is completed; carrying out reduced pressure distillation on the microwave reaction liquid at the pressure of 30 KPa and the temperature of 77-79 DEG C until no distillate exists, crystallizing, filtering and drying to obtain a mu3-O trinuclear chromium propionic acid complex; the method for preparing the mu3-O trinuclear chromium propionic acid complex has the characteristics of high raw material conversion rate, short reaction time, good product selectivity and no need of introducing additional inorganic acid, so that the yield and purity of the target product are high, no wastewater, waste gas or waste residue is generated, and the method is safer and more environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and specifically to a method for preparing μ3-O trinuclear chromium propionate complexes based on microchannel-microwave technology. Background Technology

[0002] Chromium propionate is a type of organic chromium widely used in feed additives, chemical catalysts, and oilfield chemical auxiliaries. As a feed additive, chromium propionate can effectively improve livestock and poultry growth performance; reduce carcass fat and backfat thickness, improving meat quality; enhance livestock and poultry immunity and stress resistance; and significantly increase farrowing and breeding rates, reduce newborn mortality, and improve animal reproduction when added to diets. In the oil extraction field, chromium propionate is mainly used for drilling fluid optimization, gel profile control, and sterilization. In drilling and fracturing fluids, it is primarily used to improve system stability and rheological control; it forms high-strength gels in high-permeability zones of reservoirs, blocking water flow channels and forcing subsequent injected fluids to divert to low-permeability oil layers, thereby increasing oil recovery; and by adjusting the pH of drilling or fracturing fluids, it reduces the corrosion of metal surfaces by hydrogen sulfide (H2S), lowering the risk of microbial induced corrosion (MIC) and indirectly extending equipment lifespan. In addition, chromium propionate, as a chemical catalyst, has shown great potential in organic synthesis, polymerization reactions and redox catalysis due to its tunable coordination structure and green chemistry properties.

[0003] Currently, there are few methods for preparing μ3-O trinuclear chromium propionate complexes. Most of the chromium propionate obtained is chromium propionate [Cr(C2H5COO)]3 in a 3:1 molar ratio, and there are two main preparation methods.

[0004] One method uses hexavalent chromium as the chromium source, which is reduced to trivalent chromium and then reacted with propionic acid, such as: Patent document CN86100694A discloses a method for preparing chromium propionate. In an aqueous propionic acid solution, an inorganic sulfur-based compound (such as acidic sulfites, sulfites, metabisulfites, and bisulfites of alkali metals or ammonium) is used to reduce dichromic acid or alkali metal or ammonium salts of chromic acid to trivalent chromium, further reacting to generate an aqueous solution of chromium propionate. This method does not further explain how to obtain a high content of chromium propionate, nor the structural form of chromium propionate. Patent document CN112209821A discloses a method for preparing chromium propionate. In this method, chromium oxide is added to an aqueous solution of propionic acid, amino acids, and ethanol, and the mixture is dried under reduced pressure to obtain chromium propionate containing amino acids. This method uses ethanol as a reducing agent to reduce chromium oxide to trivalent chromium, while the ethanol is oxidized to carbon dioxide, acetaldehyde, or acetic acid. The reaction is difficult to control, and pure chromium propionate is not obtained. Patent document CN103288622A discloses a method for preparing chromium propionate, which involves reacting propionic acid, chromium oxide, and hydrazine hydrate in an aqueous system and then crystallizing to obtain chromium propionate. This method uses a large amount of hydrazine hydrate, which is easily explosive, highly toxic, and carcinogenic, as an initiator, posing significant safety and occupational health risks. Patent document RU2694234 discloses a method for preparing chromium propionate. This method uses propylene glycol as a reducing agent, adding it in batches to a solution of propionic acid and sodium dichromate, reacting at 130°C to generate a chromium propionate solution, and then adsorbing it with an inert adsorbent material to obtain chromium propionate. This method does not yield pure chromium propionate; instead, it uses a carrier containing impurities such as sodium pyruvate (an oxidation product of propylene glycol), sodium carbonate, and sodium propionate to adsorb the chromium propionate. Patent document EP0897267 discloses a method for preparing chromium propionate. This method uses monosaccharides, disaccharides, polysaccharides, or glycols as reducing agents to reduce sodium dichromate or sodium chromate to trivalent chromium, which then reacts with propionic acid to generate chromium propionate. This method uses sugars or glycols as reducing agents, and the oxidation products are carbon dioxide and keto acids, which further generate their sodium salts. However, it does not further explain how to obtain pure chromium propionate. Patent document CN116332842A discloses a method for preparing chromium propionate. This method uses 2-pyridinecarboxaldehyde to reduce chromium trioxide, co-producing chromium 2-pyridinecarboxate and chromium propionate in a propionic acid solution. It boasts high atom economy and is environmentally friendly. However, the yields of chromium 2-pyridinecarboxate and chromium propionate in the co-production process are mutually influential. When market demand for one of the products changes, the flexibility in adjusting the yield of that product is poor due to the interconnectedness of production processes, and the yield of chromium propionate is less than 80%.

[0005] Another method involves a complexation reaction between propionic acid and trivalent chromium salts (chromium sulfate, chromium chloride, chromium nitrate, chromium phosphate, and chromium carbonate) in aqueous solution, such as: Patent document CN02351680A discloses a method for preparing chromium propionate. The method involves reacting trivalent chromium salts such as chromium sulfate, chromium nitrate, chromium chloride, and chromium phosphate with sodium hydroxide to obtain chromium hydroxide. After filtration and washing, the hydroxide is reacted with propionic acid, filtered, concentrated, and purified to obtain chromium propionate. This method generates large amounts of inorganic salt waste liquid containing chromium-containing sodium sulfate, sodium nitrate, and sodium chloride, and the separation of the generated hydrated chromium oxide is difficult. Patent document CN110054559A discloses a method for preparing chromium propionate, which uses ultrasound to promote the reaction of a mixture of basic chromium carbonate and chromium carbonate. However, the reaction time is long, which is not conducive to large-scale industrial production. Summary of the Invention

[0006] This invention aims to address the technical problems of existing methods for preparing chromium propionate, such as the use of large amounts of toxic reagents, failure to obtain pure chromium propionate, low yield and purity of chromium propionate, generation of large amounts of difficult-to-treat waste liquid, and long reaction time. The purpose is to provide a method for preparing μ3-O trinuclear chromium propionate complex based on microchannel-microwave technology. This method has a short reaction time, good product selectivity, complete reaction of raw materials, and does not require the introduction of additional inorganic acids. It results in high yield and purity of the target product and generates no wastewater, waste gas, or waste residue, making it safer and more environmentally friendly.

[0007] The present invention is achieved through the following technical solution.

[0008] The first objective of this invention is to provide a method for preparing μ3-O trinuclear chromium propionate complexes based on microchannel-microwave technology, comprising the following steps: Chromium trioxide-propionic acid aqueous solution and n-propanol aqueous solution were fed into a microchannel reactor to react and obtain microchannel reaction solution; The microchannel reaction solution was fed into a microwave reactor to carry out an azeotropic dehydration reaction of toluene. After dehydration, the microwave reaction solution was obtained. The microwave reaction solution was subjected to vacuum distillation until no distillate was obtained. The solution was then crystallized, filtered, and dried to yield the μ3-O trinuclear chromium propionate complex, with the following chemical structural formula: .

[0009] This invention uses chromium trioxide and n-propanol as raw materials. Chromium trioxide is reduced to trivalent hydrated chromium ions as the chromium source for the target product, and n-propanol is oxidized to propionic acid as the ligand for the target product. No other inorganic salts or byproducts, wastewater, waste gas, or waste residue are generated. Furthermore, this invention uses propionic acid as a solvent, which can provide hydrogen ions (H+) to enhance the oxidizing power of chromium trioxide. + The donor is also the ligand of the target product (C2H5COO). - This achieves two goals at once, without introducing other inorganic acids, resulting in higher product purity.

[0010] This invention employs a microchannel reactor for the oxidation reaction of chromium trioxide and n-propanol, achieving efficient heat transfer, precise temperature control, and rapid and efficient reaction. Furthermore, the extremely low liquid holdup enhances mass transfer, preventing localized overheating that could lead to excessive oxidation of n-propanol to carbon dioxide and incomplete oxidation to n-propanal. This significantly improves product selectivity, thereby increasing the purity and yield of the target product.

[0011] This invention also employs a microwave reactor to assist the coordination reaction of propionic acid with trivalent hydrated chromium ions. Microwave irradiation accelerates the polymerization of trivalent hydrated chromium ions, promotes the entry of propionate ions into the inner sphere of the chromium complex, and promotes changes in the ratio and structure of the chromium propionate complex. This is because, in the microwave field, the chromium complex and propionate ligand, as polar and charged particles, are forced to oscillate under the influence of the high-frequency changing electromagnetic field, increasing the number of collisions between them and the probability of effective collisions. Therefore, the coordination reaction proceeds more thoroughly, thereby greatly improving the selectivity of the target product μ3-O trinuclear chromium propionate complex and resulting in a high product yield.

[0012] In summary, the method of this invention for preparing μ3-O trinuclear chromium propionic acid complex has a short reaction time, does not require the introduction of additional inorganic acids, has high yield and purity of the target product, and generates no wastewater, waste gas, or waste residue, making it safer and more environmentally friendly.

[0013] Furthermore, in the raw materials, the mass ratio of chromium trioxide to n-propanol is 40:18.

[0014] Furthermore, the reaction temperature in the microchannel reactor is 50-60℃.

[0015] Furthermore, the reaction residence time in the microchannel reactor is 60-150 s.

[0016] Furthermore, the power of the microwave reactor is 100-300W.

[0017] Furthermore, the temperature for the toluene azeotropic dehydration reaction is 86°C.

[0018] Furthermore, the microwave reaction solution was depressurized to 30±2 KPa and distilled at 77-79 °C.

[0019] Further, the crystallization method is as follows: add cyclopentyl methyl ether-methanol solution and cool to 0-5℃.

[0020] A second objective of this invention is to provide an apparatus for preparing μ3-O trinuclear chromium propionate complexes based on microchannel-microwave technology, characterized in that the method described above includes: A liquid preparation container for preparing aqueous solutions of chromium trioxide-propionic acid and n-propanol; A microchannel reactor, with its inlet connected to a liquid preparation container, is used for the reaction of chromium trioxide and n-propanol. The microwave reactor, with its inlet connected to the outlet of the microchannel reactor, is used for the coordination reaction of propionic acid with trivalent hydrated chromium ions.

[0021] In one specific embodiment, the liquid preparation container includes a liquid preparation container one and a liquid preparation container two, wherein the liquid preparation container one is used to prepare a chromium trioxide-propionic acid aqueous solution and is connected to the inlet of the microchannel reactor through a delivery pump one, and the liquid preparation container two is used to prepare a n-propanol aqueous solution and is connected to the inlet of the microchannel reactor through a delivery pump two.

[0022] Furthermore, the device also includes a water distributor and a condenser, the water distributor being connected to the outlet of the microwave reactor and the bottom of the condenser.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects.

[0024] 1. This invention uses chromium trioxide and n-propanol as raw materials. Chromium trioxide is reduced to trivalent hydrated chromium ions as the chromium source for the target product, and n-propanol is oxidized to propionic acid as the ligand for the target product. No other inorganic salts or byproducts, wastewater, waste gas, or waste residue are generated. Furthermore, this invention uses propionic acid as a solvent, which can enhance the hydrogen ion (H+) ion content of chromium trioxide's oxidation ability. + The donor is also the ligand of the target product, achieving two goals at once. No other inorganic acids are introduced, resulting in higher product purity.

[0025] 2. This invention employs a microchannel reactor for the oxidation reaction of chromium trioxide and n-propanol, achieving efficient heat transfer, precise temperature control, and rapid and efficient reaction. Furthermore, the extremely low liquid holdup enhances mass transfer, preventing localized overheating that could lead to excessive oxidation of n-propanol to carbon dioxide and incomplete oxidation to n-propanal. This significantly improves product selectivity, increases the purity and yield of the target product, and greatly enhances reaction safety.

[0026] 3. This invention employs a microwave reactor to assist the coordination reaction of propionic acid with trivalent hydrated chromium ions. Microwave irradiation accelerates the polymerization of trivalent hydrated chromium ions, promotes the entry of propionate ions into the inner sphere of the chromium complex, and promotes changes in the ratio and structure of the chromium propionate complex. This is because, in the microwave field, the chromium complex and propionate ligand, as polar and charged particles, are forced to oscillate under the influence of the high-frequency changing electromagnetic field, increasing the number of collisions between them and the probability of effective collisions. Therefore, the coordination reaction proceeds more thoroughly, thereby greatly improving the selectivity of the target product μ3-O trinuclear chromium propionate complex and resulting in a high product yield. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a schematic diagram of the device structure of the present invention; Figure 2 This is a diagram illustrating the reaction mechanism between propionic acid and trivalent hydrated chromium ions. Figure 3 Electron micrographs of the product of this invention; Figure 4 The HPLC chromatogram is for the standard. Figure 5 The HPLC spectrum of the product of this invention is shown below. Figure 6 Infrared spectrum of standard sample; Figure 7 The infrared spectrum of the product of this invention; Figure 8 The HPLC spectrum of the product of Comparative Example 1 is shown below. Figure 9 The HPLC spectrum of the product of Comparative Example 2 is shown below. Figure 10 The image shows the HPLC spectrum of the product from Comparative Example 3.

[0028] The attached diagram shows the markings and corresponding component names: 1-Liquid preparation container one, 2-Transfer pump one, 3-Liquid preparation container two, 4-Transfer pump two, 5-Microchannel reactor, 6-Microwave reactor, 7-Water separator, 8-Condenser. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0030] The following detailed description, with appropriate reference to the accompanying drawings, outlines an embodiment of the method for preparing μ3-O trinuclear chromium propionate complexes based on a microchannel-microwave approach according to the present invention. However, unnecessary details may be omitted. For example, detailed descriptions of well-known facts and repetitive descriptions may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art.

[0031] The "scope" disclosed in this invention is defined in the form of a lower limit and an upper limit. A given scope is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific scope. The scope defined in this way can include or exclude end values, and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a scope.

[0032] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0033] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0034] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other substances not listed may also be included, or that only the listed substances may be included.

[0035] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0036] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0037] It should be noted that, unless otherwise specified, the experimental methods used in the embodiments are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0038] Examples 1-4 An apparatus for preparing μ3-O trinuclear chromium propionate complexes based on microchannel-microwave technology, comprising: A solution preparation container is used to prepare chromium trioxide-propionic acid aqueous solution and n-propanol aqueous solution; the solution preparation container includes solution preparation container 1 and solution preparation container 2 3, wherein solution preparation container 1 is used to prepare chromium trioxide-propionic acid aqueous solution and is connected to the inlet of microchannel reactor 5 through transfer pump 2, and solution preparation container 2 3 is used to prepare n-propanol aqueous solution and is connected to the inlet of microchannel reactor 5 through transfer pump 2 4; Microchannel reactor 5, with its inlet connected to the liquid preparation container, is used for the oxidation reaction of n-propanol by chromium trioxide. The microwave reactor 6 is a microwave device with a built-in reaction vessel containing at least two ports. One port is connected to the outlet of the microchannel reactor 5, and the other port is connected to the bottom inlet of the water separator 7. It is used for the coordination reaction of propionic acid with trivalent hydrated chromium ions. Water distributor 7 and condenser 8, wherein the bottom of condenser 8 is connected to the top of water distributor 7.

[0039] It should be noted that the microchannel reactor 5 in this invention was provided by Shandong Jinde New Materials Co., Ltd.

[0040] Based on the above apparatus, a method for preparing μ3-O trinuclear chromium propionate complexes using a microchannel-microwave approach is provided, comprising the following steps: 40 g of chromium trioxide was dissolved in 70 mL of deionized water, and then 90 g of propionic acid was added to prepare solution A for later use; 18 g of n-propanol was dissolved in 14 g of deionized water to prepare solution B for later use; 100 g of toluene was added to a microwave reactor for later use. The microchannel reactor is heated and maintained at a reaction temperature T1. Solution A and solution B are simultaneously delivered to the microchannel reactor for reaction. After a reaction residence time t1, the microchannel reaction solution is obtained. The microchannel reaction solution was introduced into a microwave reactor. The microwave frequency was set to 915 MHz and the microwave power to 200 W. A microwave azeotropic dehydration reaction was carried out at 86-88℃ (86℃ at the start of dehydration and 88℃ at the end) for 15 min to obtain the microwave reaction solution. The reaction mechanism of propionic acid with trivalent hydrated chromium ions is shown in the diagram below. Figure 2 As shown; The microwave reaction solution was depressurized to 30±2 kPa and distilled at 77-79℃ (77℃ at the start of distillation and 79℃ at the end of distillation (no distillate)) until it became a slurry (no distillate). Then, 50% cyclopentyl methyl ether-methanol solution was added, the temperature was lowered to 0℃, and the solution was crystallized, filtered, and vacuum dried to obtain green crystals.

[0041] Table 1. Effects of microchannel reaction temperature and time on the products

[0042] As can be seen from the data in Table 1, when the microchannel reaction temperature is 50 ℃ and the reaction (residence) time is 150 s, and the microwave reaction temperature is 86 ℃ and the time is 20 min, the Cr content of the microchannel reaction solution is... 6+ The lowest content (not detected), highest product content and yield. When the microchannel reaction temperature is too low, the reaction shown in equation (1) may occur, causing Cr... 6+ If the residue is present and the temperature is too high, a reaction as shown in equation (2) may occur. Taking all factors into consideration, a reaction temperature of 50-60℃ and a residence time of 60-150s are selected. .

[0043] Examples 5-7 An apparatus for preparing μ3-O trinuclear chromium propionate complexes based on microchannel-microwave technology, comprising: A solution preparation container is used to prepare chromium trioxide-propionic acid aqueous solution and n-propanol aqueous solution; the solution preparation container includes solution preparation container 1 and solution preparation container 2 3, wherein solution preparation container 1 is used to prepare chromium trioxide-propionic acid aqueous solution and is connected to the inlet of microchannel reactor 5 through transfer pump 2, and solution preparation container 2 3 is used to prepare n-propanol aqueous solution and is connected to the inlet of microchannel reactor 5 through transfer pump 2 4; Microchannel reactor 5, with its inlet connected to the liquid preparation container, is used for the oxidation reaction of n-propanol by chromium trioxide. The microwave reactor 6 is a microwave device with a built-in reaction vessel containing at least two ports. One port is connected to the outlet of the microchannel reactor 5, and the other port is connected to the bottom inlet of the water separator 7. It is used for the coordination reaction of propionic acid with trivalent hydrated chromium ions. Water distributor 7 and condenser 8, wherein the bottom of condenser 8 is connected to the top of water distributor 7.

[0044] It should be noted that the microchannel reactor 5 in this invention was provided by Shandong Jinde New Materials Co., Ltd.

[0045] Based on the above apparatus, a method for preparing μ3-O trinuclear chromium propionate complexes using a microchannel-microwave approach is provided, comprising the following steps: 40 g of chromium trioxide was dissolved in 70 mL of deionized water, and then 90 g of propionic acid was added to prepare solution A for later use; 18 g of n-propanol was dissolved in 14 g of deionized water to prepare solution B for later use; 100 g of toluene was added to a microwave reactor for later use. The microchannel reactor is heated and maintained at a reaction temperature of 50 °C. Solutions A and B are simultaneously fed into the microchannel reactor to react. After a reaction (residence) time of 150 s, the microchannel reaction solution is obtained. The microchannel reaction solution enters container 3 of the microwave reactor. The microwave frequency is set to 915 MHz, the microwave power is set to P, and the microwave azeotropic dehydration reaction is carried out at a temperature of T2. After a certain time t2, no water is generated in the water separator, and the microwave reaction solution is obtained. The microwave reaction solution was depressurized to 30±2 kPa and 77-79℃ (77℃ at the start of distillation and 79℃ at the end of distillation (no distillate)). After distillation to a slurry (no distillate), 50% cyclopentyl methyl ether-methanol solution was added, the temperature was lowered to 0℃, crystallized, filtered, and vacuum dried to obtain dark green crystals.

[0046] Table 2. Effects of microwave power and reaction temperature on the products

[0047] Table 2 shows that increasing the microwave reaction power only shortens the microwave azeotropic dehydration reaction time, without significantly affecting the content and yield of the reaction products. Therefore, a microwave power of 100W-300W is suitable, with 300W being the optimal choice, as it results in a short dehydration time and avoids bumping.

[0048] Test case This test example involves relevant detection and analysis of the product prepared in Example 6.

[0049] (1) Electron micrographs of the product, such as Figure 3 As shown.

[0050] (2) The elemental analysis results of the products are shown in Table 3: Table 3. Elemental Analysis Results of Target Product

[0051] The results showed that the absolute error between the elemental analysis results of the target product and the theoretical value was less than 0.3%. It was preliminarily determined that the molecular composition of the tested sample was consistent with that of the target compound ([Cr3O(OOCC2H5)6H2O)3]·COOC2H5), and the elemental analysis value of the target product was consistent with the theoretical value.

[0052] (3) HPLC identification An Agilent ZORBAX SB-Aq column (4.6 mm × 250 mm) was used. Linear gradient elution was performed with 1% propionic acid-water solution (phase A) and 1% acetonitrile-water solution (phase B) as shown in the table below. The flow rate was 1.2 mL / min, the detection wavelength was 443 nm, and the injection volume was 10 μL. HPLC analysis was performed on the products and standards.

[0053] Table 4. Gradient elution conditions

[0054] HPLC chromatogram of standard as shown Figure 4 As shown, the HPLC chromatogram of the product of this invention is as follows. Figure 5 As shown in the figure. By comparing the spectra, it can be seen that the retention times of the product and the standard are consistent, and their relative deviation is within ±2.5% (+0.98%).

[0055] (4) Identification by infrared absorption spectroscopy The target product and standard were analyzed using a Fourier transform infrared spectrometer (Thermo Fisher Nicoleti S50, USA). After spectral matching, the infrared spectrum of the target product was displayed. Figure 7 Infrared spectrum compared with standard Figure 6 The two samples exhibit high consistency in the three key characteristics of peak position, wavenumber, and peak shape, indicating that they share the same main components and have similar purity.

[0056] Comparative Example 1 The traditional batch oxidation reaction + batch complexation reaction is adopted: 70 mL of deionized water and 40 g of chromium trioxide were added to a three-necked flask and stirred until the chromium trioxide was completely dissolved. Then, 90 g of propionic acid was added, followed by the slow dropwise addition of 18 g of n-propanol, maintaining the reaction temperature at 50 °C during the dropwise addition. After the dropwise addition was complete, the reaction was maintained at 50 °C for 1 h. 100 g of toluene was added, and the temperature was raised to 86 °C for reflux azeotropic dehydration. After 65 min, no water was formed. The mixture was then distilled under reduced pressure to 30 kPa and at 77-79 °C until a slurry was obtained (no distillate). A 50% cyclopentyl methyl ether-methanol solution was added, and the mixture was cooled to 0 °C. Crystallization, filtration, and vacuum drying yielded 84.40 g of dark green crystals, with a yield of 60.68% (HPLC chromatogram shown). Figure 2 ).

[0057] Comparative Example 2 The traditional microchannel oxidation reaction combined with a batch complexation reaction is employed. Dissolve 40 g of chromium trioxide in 70 mL of deionized water, then add 90 g of propionic acid to prepare solution A, and set aside for use; dissolve 18 g of n-propanol in 14 g of deionized water to prepare solution B, and set aside for use. The microchannel reactor is heated and maintained at a reaction temperature of 50 °C. Solutions A and B are simultaneously fed into the microchannel reactor to react. After a reaction (residence) time of 300 s, the microchannel reaction solution is obtained. 100 g of toluene was added to the microchannel reaction solution, and the mixture was heated to 86 °C for reflux azeotropic dehydration. After 65 min, no water was generated. The solution was then distilled under reduced pressure to 30 kPa and 77-79 °C until a slurry was obtained (no distillate). A 50% cyclopentyl methyl ether-methanol solution was added, and the mixture was cooled to 0 °C. The solution was crystallized, filtered, and dried under vacuum to obtain 82.66 g of dark green crystals, with a yield of 63.03% (HPLC chromatogram shown). Figure 3 ).

[0058] Comparative Example 3 The process employs a combination of traditional batch oxidation reaction and microwave complexation reaction. 70 mL of deionized water and 40 g of chromium trioxide were added to a three-necked flask and stirred until the chromium trioxide was completely dissolved. Then, 90 g of propionic acid was added, followed by the slow addition of 18 g of n-propanol. The reaction temperature was maintained at 50 °C during the addition process, and the reaction was carried out at 50 °C for 1 h after the addition was completed. Then, the mixture was placed in a microwave reactor and microwave azeotropic dehydration reaction was carried out at a microwave frequency of 915 MHz and a microwave power of 200 W for 15 min to obtain the microwave reaction solution. The microwave reaction solution was distilled under reduced pressure (30 kPa) and 77-79 °C until it reached a slurry state (no distillate). A 50% cyclopentyl methyl ether-methanol solution was then added, and the mixture was cooled to 0 °C. Crystallization, filtration, and vacuum drying yielded 72.80 g of dark green crystals, with a yield of 72.44% (HPLC chromatogram shown). Figure 4 ).

[0059] Table 5. Detection results of comparative product

[0060] As can be seen from the data in Table 5, when any one or two of the oxidation or complexation reactions are replaced with the traditional batch reaction, the yield and content are significantly reduced. This also proves that the method of the present invention for preparing μ3-O trinuclear chromium propionate complex has the advantages of more thorough reaction of raw materials, good product selectivity, and high product yield and content.

[0061] Finally, it should be noted that the above specific embodiments are only used to describe the purpose, technical solution, and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation of the present invention and is not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the foregoing specific embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions or improvements can be made to some or all of the technical features. These modifications, equivalent substitutions, and improvements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A process for the preparation of a μ3-0 trinuclear chromium propionate complex based on microchannel-microwave, characterized by, The method comprises the following steps: sending a chromium trioxide-propionic acid aqueous solution and a n-propanol aqueous solution to a micro-channel reactor for reaction to obtain a micro-channel reaction liquid; sending the micro-channel reaction liquid to a microwave reactor for toluene azeotropic dehydration reaction, and obtaining a microwave reaction liquid after dehydration; carrying out reduced pressure distillation on the microwave reaction liquid until no distillate is obtained, and then carrying out crystallization, filtration and drying to obtain the μ3-O trinuclear chromium propionic acid complex.

2. A process for the preparation of μ3-0 trinuclear chromium propionate complex based on microchannel-microwave as claimed in claim 1, wherein, In the raw material, the mass ratio of chromium trioxide to n-propanol is 40: (18-80).

3. A process for the preparation of μ3-0 trinuclear chromium propionate complex based on microchannel-microwave as claimed in claim 1, wherein, The reaction temperature in the micro-channel reactor is 50-60℃.

4. A process for the preparation of μ3-0 trinuclear chromium propionate complex based on microchannel-microwave as claimed in claim 1, wherein, The reaction residence time in the micro-channel reactor is 60-150s.

5. A method for the preparation of μ3-0 trinuclear chromium propionate complex based on microchannel-microwave as claimed in claim 1, wherein, The power of the microwave reactor is 100-300W.

6. A method for the preparation of μ3-0 trinuclear chromium propionate complex based on microchannel-microwave as claimed in claim 1, wherein, The temperature of the toluene azeotropic dehydration reaction is 85-88℃.

7. A method for the preparation of μ3-0 trinuclear chromium propionate complex based on microchannel-microwave according to claim 1, characterized in that, The distillation pressure of the microwave reaction liquid is 30±2 KPa, and the distillation temperature is 77-79℃.

8. A process for the preparation of μ3-0 trinuclear chromium propionate complex based on microchannel-microwave as claimed in claim 1, wherein, The crystallization method is: adding a cyclopentyl methyl ether-methanol solution and cooling to 0-5℃.

9. A device for the preparation of a μ3-0 trinuclear chromium propionate complex based on microchannels-microwaves, characterized by, The method is used in the method of claim 1, comprising: a liquid preparation container for preparing the chromium trioxide-propionic acid aqueous solution and the n-propanol aqueous solution; a micro-channel reactor, the inlet of which is connected with the liquid preparation container, for reaction of the chromium trioxide and the n-propanol; a microwave reactor, the inlet of which is connected with the outlet of the micro-channel reactor, for coordination reaction of the propionic acid and the trivalent hydrated chromium ion.

10. A device for the preparation of μ3-0 trinuclear chromium propionate complex based on microchannel-microwave according to claim 9, characterized in that, It also comprises a water separator and a condenser, the water separator is connected with the outlet of the microwave reactor, and the water separator is connected with the bottom of the condenser.

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