Electrolytic byproduct conversion method based on online oxidative aromatization

Abstract

The invention belongs to the technical field of electro-catalysis and electrochemical engineering, and particularly relates to a method for converting electrolytic byproducts based on online oxidative aromatization. According to the method for converting the electrolytic by-product based on the online oxidative aromatization, on the basis of a process for electrolyzing p-methyl anisole to synthesize anisaldehyde, a ruthenium-supported catalyst is used, and the by-product 1, 4-trimethoxy-4-methyl-2, 5-cyclohexadiene generated in the electrolysis process is converted into pure p-methyl anisole through the online oxidative aromatization, so that the yield of the p-methyl anisole is increased, and the yield of the p-methyl anisole is increased. Therefore, the selectivity of electrochemical production of anisaldehyde is improved by 20%; and moreover, the generated pure p-methyl anisole is directly returned to an electrolysis system without being purified, so that the process flow is simplified, the cost is reduced, and the economic value is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of electrocatalysis and electrochemical engineering, and specifically relates to a method for converting electrolysis by-products based on online oxidation aromatization. Background Art

[0002] In the field of chemical engineering, especially in the field of electrochemical engineering and catalytic reactions, electrolysis is a commonly used technical means. In particular, in organic synthesis, the electrolysis process can be used to prepare various organic compounds. The electrolysis process for methyl anisole is a common reaction, which can be used to synthesize compounds such as anisaldehyde. However, due to the electron-rich nature of the benzene ring of methyl anisole, it is easy to produce by-products such as 1,4-trimethoxy-4-methyl-2,5-cyclohexadiene during the electrolysis process, thereby reducing the selectivity of the raw materials, which not only increases the process cost, but also limits the industrialization prospects of the technology.

[0003] At present, there is no literature report in the art that can reuse the above-mentioned byproducts produced in electrochemical oxidation. Usually, the byproducts can only be incinerated by means of external discharge, which not only increases the cost of three wastes treatment, but also reduces the selectivity of raw materials and the competitiveness of products. Therefore, how to reuse or convert the byproduct 1,4-trimethoxy-4-methyl-2,5-cyclohexadiene into high value-added products, and how to simplify the process of electrolysis while reducing costs and improving selectivity are problems that need to be solved in the art. Summary of the invention

[0004] To this end, the technical problem to be solved by the present invention is to provide a method for converting electrolysis by-products based on online oxidative aromatization, which greatly improves the selectivity of electrolysis products and helps to significantly reduce process costs.

[0005] In order to solve the above technical problems, the present invention discloses a method for converting electrolysis by-products based on online oxidative aromatization, which includes the steps of subjecting the electrolysis by-product 1,4-trimethoxy-4-methyl-2,5-cyclohexadiene to oxidative aromatization in the presence of a precious metal-supported catalyst, and the step of directly returning the obtained p-methylanisole to the electrolysis system.

[0006] Specifically, in the method for converting electrolysis by-products based on online oxidative aromatization, the precious metal includes metallic ruthenium and / or metallic rhodium.

[0007] Specifically, in the electrolysis by-product conversion method based on online oxidative aromatization, the noble metal loading of the catalyst is 0.1-1wt%, preferably 0.2-0.5wt%;

[0008] Preferably, the average particle size of the catalyst is 5-10 microns;

[0009] Preferably, the specific surface area of ​​the catalyst is 100-200m 2 / g.

[0010] Specifically, in the electrolysis by-product conversion method based on online oxidative aromatization, the carrier of the noble metal-supported catalyst includes a weakly alkaline carrier;

[0011] Preferably, the carrier comprises nano-microspheres or nano-particles of a weakly alkaline carrier;

[0012] Preferably, the carrier comprises at least one of nano-microspheres or nano-particles of alumina, silica gel or activated carbon;

[0013] Preferably, the diameter of the carrier is 5-100 nm, preferably 10-40 nm.

[0014] Specifically, the method for converting electrolysis by-products based on online oxidative aromatization, the oxidative aromatization reaction has the following characteristics:

[0015] The temperature of the oxidative aromatization reaction is 100-150° C.; and / or,

[0016] The reaction pressure of the oxidative aromatization reaction is 1-5 MPa; and / or,

[0017] The reaction time of the oxidative aromatization reaction is 1-5 hours.

[0018] Specifically, in the method for converting electrolysis by-products based on online oxidative aromatization, the oxidative aromatization reaction step includes the step of introducing the 1,4-trimethoxy-4-methyl-2,5-cyclohexadiene into a fixed bed reactor loaded with the ruthenium-supported catalyst.

[0019] Specifically, in the method for converting electrolysis by-products based on online oxidative aromatization, the fixed bed reactor is arranged between the light removal tower and the electrolysis concentration tank of the electrolysis process.

[0020] Specifically, the method for converting electrolysis byproducts based on online oxidative aromatization further comprises the steps of collecting the product of the oxidative aromatization reaction and separating p-methyl anisole;

[0021] Preferably, the separation device of the separation step comprises a distillation column and a condenser;

[0022] Preferably, the temperature of the distillation column is 100-150°C;

[0023] Preferably, the temperature of the condenser is 0-20°C.

[0024] Specifically, in the method for converting electrolysis by-products based on online oxidative aromatization, the electrolysis system includes an electrolysis system for the process of electrolyzing p-methylanisole to synthesize anisaldehyde.

[0025] The invention also discloses a process for synthesizing anisaldehyde based on the electrolysis of p-methylanisole, comprising the step of converting electrolysis byproducts according to the method.

[0026] Specifically, in the process for synthesizing anisaldehyde based on electrolysis of p-methylanisole, the electrolysis system of the electrolysis process comprises an anode, a cathode and an electrolyte; wherein:

[0027] The electrolyte comprises p-methylanisole, potassium-containing inorganic salt, water and alcohol solvent.

[0028] In the process for synthesizing anisaldehyde based on the electrolysis of p-methylanisole, direct current is passed through the anode and the cathode to obtain the target product after the reaction conversion rate is reached.

[0029] The method for converting electrolysis by-products based on online oxidative aromatization of the present invention is based on the process of synthesizing anisaldehyde by electrolysis of p-methylanisole, uses a noble metal-loaded catalyst such as ruthenium or rhodium, and converts the by-product 1,4-trimethoxy-4-methyl-2,5-cyclohexadiene generated in the electrolysis process into pure p-methylanisole through online oxidative aromatization, thereby improving the selectivity of electrochemical production of anisaldehyde by 20%; moreover, the generated pure p-methylanisole is directly returned to the electrolysis system without purification, which not only simplifies the process flow, but also reduces costs and improves economic value.

[0030] The method for converting electrolysis by-products based on online oxidative aromatization is used to obtain pure p-methylanisole from the by-product 1,4-trimethoxy-4-methyl-2,5-cyclohexadiene produced in the electrolysis through an online ruthenium / alumina nanosphere fixed bed catalysis, which basically realizes the full application of the original external discharge stream, greatly improves the selectivity of anisaldehyde generated by electrolysis, and greatly reduces the cost. The method does not need to significantly change the process flow, and only needs to add a fixed bed reactor between the light removal tower and the electrolysis concentration tank. The transformation is simple and the economic value generated is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0032] Figure 1 This is a process flow chart of electrolysis of p-methyl anisole;

[0033] Figure 2 is a flow chart of the online oxidative aromatization reaction;

[0034] Figure 3 It is a schematic diagram of the principle of the online oxidative aromatization reaction of the present invention. DETAILED DESCRIPTION

[0035] In order to solve the problem that there are many by-products in the electrolysis process, thereby affecting the product selectivity, the first aspect of the present application provides a method for converting electrolysis by-products based on online oxidative aromatization, the method comprising the steps of subjecting the electrolysis by-product 1,4-trimethoxy-4-methyl-2,5-cyclohexadiene to oxidative aromatization in the presence of a precious metal-supported catalyst, and the step of directly returning the obtained p-methylanisole to the electrolysis system.

[0036] In some possible embodiments, the noble metal includes ruthenium and / or rhodium.

[0037] In some feasible embodiments, the loading amount of the noble metal supported catalyst is 0.1-1wt%, preferably 0.2-0.5wt%. For example, the loading amount of noble metals such as ruthenium and / or rhodium in the catalyst can be adjusted to 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0wt%, etc., or any range between the above values.

[0038] In some feasible embodiments, the particle size of the noble metal supported catalyst such as ruthenium and / or rhodium is 5-10 microns, and the specific surface area is 100-200m 2 / g. For example, the particle size of the supported catalyst is controlled to be 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10 microns, etc., or any range between the above values. For example, the specific surface area of ​​the supported catalyst is controlled to be 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200m 2 / g, etc., or any range between the above values.

[0039] In some feasible embodiments, the carrier of the ruthenium and / or rhodium supported catalyst includes a weakly basic carrier, such as nano-microspheres or nano-particles of a weakly basic carrier. As an exemplary embodiment, the carrier includes nano-microspheres or nano-particles of alumina, silica gel or activated carbon;

[0040] In some feasible embodiments, the diameter of the carrier (nanosphere or nanoparticle) is 5-100nm, preferably 10-40nm. For example, the diameter of the carrier is selected to be 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100nm, etc., or the range between any of the above values.

[0041] In the following embodiments of the present invention, the preparation method of the precious metal loaded catalyst, such as ruthenium loaded catalyst or rhodium loaded catalyst can be completely prepared by conventional methods in the art, and those skilled in the art can prepare catalyst products with corresponding loading amounts according to conventional technical means.

[0042] As an exemplary embodiment, the method for preparing the supported catalyst in the art can be an impregnation method: an alumina support and a ruthenium chlorate solution are impregnated, and the catalyst is obtained after a high-temperature sintering treatment. A solvent with a suitable ratio is selected for impregnation according to the loading amount, and the high-temperature sintering temperature within the conventional range does not affect the performance of the catalyst.

[0043] As an exemplary embodiment, the method for preparing supported catalysts in the art may be a co-precipitation method: mixing a ruthenium / rhodium salt and an aluminum oxide salt solution, adjusting the pH value, and co-precipitating ruthenium and aluminum oxide to obtain the catalyst.

[0044] As an exemplary embodiment, the method for preparing supported catalysts in the art may be a sol-gel method: ruthenium / rhodium and an alumina precursor are formed into a sol in a solvent, the solvent is heated to obtain a gel, and then the catalyst is obtained after high-temperature calcination.

[0045] In some feasible embodiments, the temperature of the oxidative aromatization reaction is 100-150° C., the reaction pressure is 1-5 MPa, and the reaction time is 1-5 hours.

[0046] As an exemplary embodiment, the temperature of the aromatization reaction is adjusted to 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150° C., etc., or any range between the above values.

[0047] As an exemplary embodiment, the reaction pressure of the aromatization reaction is adjusted to 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 MPa, etc., or any range between the above values.

[0048] As an exemplary embodiment, the reaction time of the aromatization reaction is adjusted to 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 hours, etc., or any range between the above values.

[0049] In some feasible embodiments, the oxidative aromatization reaction step includes the step of introducing the 1,4-trimethoxy-4-methyl-2,5-cyclohexadiene into a fixed bed reactor containing the noble metal supported catalyst.

[0050] In some feasible embodiments, the fixed bed reactor is disposed between the lightness removal tower and the electrolysis concentration tank of the electrolysis process.

[0051] In some feasible embodiments, in the fixed bed reaction, the length-to-diameter ratio of the fixed bed reactor is (5-8):1, which can be adaptively selected according to the model of the fixed bed reactor.

[0052] In some feasible embodiments, in the fixed bed reaction, the loading structure of the supported catalyst is a sandwich structure, for example, from top to bottom, 2-4 mm hard alumina balls (bed height 5-15%), 0.3-0.8 mm hard quartz sand (bed height 5-15%), noble metal supported catalyst (bed height 50-70%), 0.3-0.8 mm hard quartz sand (bed height 5-15%) and 2-4 mm hard alumina balls (bed height 5-15%).

[0053] In some feasible embodiments, the electrolysis system includes a process for electrolyzing p-methylanisole to synthesize anisaldehyde.

[0054] In a second aspect, the present invention also discloses a process for synthesizing anisaldehyde based on the electrolysis of p-methylanisole, comprising the step of converting electrolysis by-products according to the method.

[0055] like Figure 1 The flow chart is a schematic diagram of the process of electrolyzing p-methylanisole to synthesize anisaldehyde. p-methylanisole and methanol are subjected to an electrolysis process in the presence of an anode, a cathode and an electrolyte. The electrolysis products are collected and passed through a light-removal tower to remove light components / electrolytes, and then anisaldehyde is prepared after hydrolysis.

[0056] like Figure 2-3 The flowchart and principle diagram shown in the present invention are Figure 1 Based on the process of synthesizing anisaldehyde from p-methylanisole electrolysis, a fixed bed reactor 2 is provided between the light removal tower 1 and the electrolysis concentration tank 3 of the electrolysis device, and the by-products produced in the electrolysis step are subjected to online oxidative aromatization to realize the conversion of the electrolysis by-products into raw materials. In the process, the electrolysis by-product 1,4-trimethoxy-4-methyl-2,5-cyclohexadiene is subjected to oxidative aromatization reaction in the presence of a ruthenium and / or rhodium supported catalyst, and the pure p-methylanisole obtained by the reaction is directly returned to the electrolysis system without purification.

[0057] The preparation method provided by the present invention is further described in detail below through examples, but the present invention is not limited thereto.

[0058] Example

[0059] like Figure 1-2The process flow chart shown in the present embodiment is a process for electrolyzing p-methylanisole to synthesize anisaldehyde, wherein the electrolysis system comprises an anode, a cathode and an electrolyte; wherein 1wt% of potassium fluoride is added to a methanol solution, and p-methylanisole raw material and water are added to form an electrolyte raw material solution, direct current is passed through the anode and cathode, and the target product is obtained after the reaction conversion rate is reached.

[0060] In order to convert the by-product 1,4-trimethoxy-4-methyl-2,5-cyclohexadiene produced during the electrolysis process into p-methylanisole raw material to improve the reaction efficiency, the method for converting the electrolysis by-products into raw materials by online oxidative aromatization described in this embodiment is achieved by arranging a fixed bed reactor 2 between the light removal tower 1 and the electrolysis concentration tank 3 of the electrolysis device, and loading the precious metal loaded catalyst.

[0061] As an exemplary scheme, the fixed bed reactor has a length-to-diameter ratio of 6:1, and a specific filling structure is a sandwich structure, which includes, from top to bottom, 3 mm hard alumina balls (10% of the bed height), 0.5 mm hard quartz sand (10% of the bed height), precious metal-loaded catalyst (60% of the bed height), 0.5 mm hard quartz sand (10% of the bed height), and 3 mm hard alumina balls (10% of the bed height).

[0062] In various embodiments of the present invention, different loading amounts of ruthenium or rhodium are used as active components loaded on appropriate carriers with different particle sizes as catalysts to form catalysts with different particle sizes and specific surface areas.

[0063] As an exemplary scheme, in the following examples of the present invention, the supported catalyst used is prepared by the following method: a selected nano-alumina carrier and a ruthenium chlorate solution with a selected loading amount are impregnated, and a catalyst with a predetermined loading amount is obtained by high-temperature sintering at 450° C. The rhodium supported catalyst is prepared by the same method.

[0064] The by-product 1,4-trimethoxy-4-methyl-2,5-cyclohexadiene produced during the electrolysis process is introduced into a fixed bed reactor equipped with a catalyst to carry out an online oxidative aromatization reaction, and the oxidative aromatization reaction is carried out under different reaction temperatures and reaction pressures.

[0065] After the reaction is completed, the obtained pure p-methylanisole product is directly returned to the electrolysis system without purification to continue to participate in the electrolysis reaction.

[0066] In the following embodiments of the present invention, the process parameters involved are detailed in Table 1 below.

[0067] Table 1 Process parameters

[0068]

[0069] Comparative Example 1

[0070] The process and apparatus for preparing anisaldehyde by electrolysis of p-methylanisole described in this comparative example are the same as those in Example 1, the only difference being that the fixed bed reactor is not added and an oxidative aromatization reaction is not required.

[0071] Comparative Example 2

[0072] The method for converting electrolysis by-products into raw materials by online oxidative aromatization described in this embodiment is the same as that in Embodiment 1, the only difference is that the catalyst is loaded with active elements and the specific loading method is the ruthenium loading method in Embodiment 1.

[0073] Experimental example

[0074] This experimental example is based on the quantitative test of electrolysis selectivity and current efficiency in the electrolysis system of methyl anisole in the aforementioned embodiment.

[0075] The purity of anisaldehyde was determined by gas chromatography (GC), and the yield of anisaldehyde was calculated, yield = actual yield × purity / theoretical yield × 100%.

[0076] Gas chromatograph model: Agilent 8890; Injector: automatic sampler; Detector: FID detector; Chromatographic column: HP-VOC (30m×0.25mm×0.25μm); Temperature program: 50°C for 5 minutes, increase the temperature to 300°C at 10°C / min, and hold for 10 minutes.

[0077] The electrolysis efficiency is also the current efficiency. Through Faraday's second law It=nZF, the percentage of theoretical power consumption to actual power consumption is determined, that is, the electrolysis efficiency is obtained.

[0078] The electrolytic performance results of each embodiment and comparative example tested in this experimental example are shown in Table 2 below.

[0079] Table 2 Electrolysis reaction performance results

[0080] serial number Product selectivity Current efficiency Example 1 97％ 95％ Example 2 94％ 93％ Example 3 95％ 91％ Example 4 92％ 90％ Example 5 94％ 92％ Example 6 95％ 90％ Comparative Example 1 65％ 70％ Comparative Example 2 73％ 75％

[0081] The method for converting electrolysis by-products based on online oxidative aromatization of the present invention is based on the process of synthesizing anisaldehyde by electrolysis of p-methylanisole, uses a noble metal-loaded catalyst such as ruthenium or rhodium, and converts the by-product 1,4-trimethoxy-4-methyl-2,5-cyclohexadiene produced in the electrolysis process into pure p-methylanisole through online oxidative aromatization, thereby further improving the selectivity of electrochemical production of anisaldehyde by more than 20% and significantly improving the current efficiency.

[0082] In summary, the present invention uses ruthenium loaded on alumina microspheres as a catalyst, which can not only efficiently generate p-methylanisole raw materials and directly return them to the electrolysis system without purification, thereby improving the selectivity of electrochemical production of anisaldehyde and solving the problem of low raw material selectivity; at the same time, by converting the by-product 1,4-trimethoxy-4-methyl-2,5-cyclohexadiene produced in the electrolysis into pure p-methylanisole, the full utilization of the original external discharge stream is achieved, thereby reducing costs and improving economic value.

[0083] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for converting electrolysis by-products based on online oxidative aromatization, characterized in that: The method comprises the steps of subjecting the electrolysis byproduct 1,4-trimethoxy-4-methyl-2,5-cyclohexadiene to oxidative aromatization reaction in the presence of a noble metal supported catalyst, and directly returning the obtained p-methylanisole to the electrolysis system.

2. The method for converting electrolysis by-products based on online oxidative aromatization according to claim 1, characterized in that: The noble metal includes metallic ruthenium and / or metallic rhodium.

3. The method for converting electrolysis by-products based on online oxidative aromatization according to claim 1 or 2, characterized in that: The noble metal loading of the catalyst is 0.1-1wt%, preferably 0.2-0.5wt%; Preferably, the average particle size of the catalyst is 5-10 microns; Preferably, the specific surface area of ​​the catalyst is 100-200m 2 / g.

4. The method for converting electrolysis by-products based on online oxidative aromatization according to any one of claims 1 to 3, characterized in that: The carrier of the noble metal-loaded catalyst comprises a weakly alkaline carrier; Preferably, the carrier comprises nano-microspheres or nano-particles of a weakly alkaline carrier; Preferably, the carrier comprises at least one of nano-microspheres or nano-particles of alumina, silica gel or activated carbon; Preferably, the diameter of the carrier is 5-100 nm, preferably 10-40 nm.

5. The method for converting electrolysis by-products based on online oxidative aromatization according to any one of claims 1 to 4, characterized in that: The oxidative aromatization reaction has the following characteristics: The temperature of the oxidative aromatization reaction is 100-150° C.; and / or, The reaction pressure of the oxidative aromatization reaction is 1-5 MPa; and / or, The reaction time of the oxidative aromatization reaction is 1-5 hours.

6. The method for converting electrolysis by-products based on online oxidative aromatization according to any one of claims 1 to 5, characterized in that: The oxidative aromatization reaction step comprises the step of introducing the 1,4-trimethoxy-4-methyl-2,5-cyclohexadiene into a fixed bed reactor loaded with the ruthenium-supported catalyst; Preferably, the fixed bed reactor is arranged between the lightness removal tower and the electrolysis concentration tank of the electrolysis process.

7. The method for converting electrolysis by-products based on online oxidative aromatization according to any one of claims 1 to 6, characterized in that: The method further comprises the steps of collecting the product of the oxidative aromatization reaction and separating p-methylanisole.

8. The method for converting electrolysis by-products based on online oxidative aromatization according to any one of claims 1 to 7, characterized in that: The electrolysis system comprises an electrolysis system for the process of electrolyzing p-methylanisole to synthesize anisaldehyde.

9. A process for synthesizing anisaldehyde based on electrolysis of p-methylanisole, characterized in that: The method comprises the step of converting electrolysis by-products according to the method according to any one of claims 1 to 8.

10. The process for synthesizing anisaldehyde based on electrolysis of p-methylanisole according to claim 9, characterized in that: The electrolysis system of the electrolysis process comprises an anode, a cathode and an electrolyte; wherein the electrolyte comprises p-methylanisole, a potassium-containing inorganic salt and an alcohol solvent.

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