Electrolyte and electrolysis method for electrolysis of acrylonitrile to adiponitrile

Abstract

The application provides an electrolyte for electrolysis of acrylonitrile to adiponitrile, which comprises acrylonitrile, modified quaternary ammonium salt and water, wherein the modified quaternary ammonium salt comprises functional groups shown in formula (a) and formula (b) simultaneously, the functional group shown in formula (b) is wherein R1-R4 in formula (a) are alkyl groups with carbon number of 0-6; formula (b) is an alkyl group with carbon number of n, n=1-20; the structure of the modified quaternary ammonium salt contains 2-4 functional groups shown in formula (a). A method for electrolysis of acrylonitrile to adiponitrile by using the electrolyte is also disclosed. The electrolyte for electrolysis of acrylonitrile to adiponitrile contains modified quaternary ammonium salt, thereby improving the conversion rate and selectivity of electrolysis of acrylonitrile to adiponitrile.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical synthesis, in particular to an electrolyte and an electrolysis method for synthesizing adiponitrile from acrylonitrile. BACKGROUND

[0002] Adiponitrile (ADN) is an important organic chemical intermediate, mainly used in the production of polyhexamethylene adipamide (nylon 66), 1,6-hexamethylene diisocyanate (HDI) and nylon 610 materials. According to statistics, about 90% of the global adiponitrile is used for the production of nylon 66 every year.

[0003] The technical barrier and investment threshold of adiponitrile are high, and the industry concentration is extremely high. Adiponitrile manufacturers all have supporting hexamethylene diamine production devices, most of the capacity is used for the production of hexamethylene diamine and nylon 66 of the company, only a few companies have some surplus adiponitrile for sale, and Invejos almost monopolizes the global supply of adiponitrile, and the global adiponitrile market is in a state of tension.

[0004] The industrial production process of adiponitrile includes adipic acid catalytic ammoniation (ADA), acrylonitrile electrolysis dimerization (AN) and butadiene cyanation (BD). The process technology is mainly monopolized by a few enterprises such as Invejos, BASF and Asahi Kasei. There is no adiponitrile production device in China at present, and the product is completely dependent on import.

[0005] The acrylonitrile electrolysis dimerization method was initially industrialized by Monsanto Company. This process uses acrylonitrile as raw material and uses electrochemical method to dimerize adiponitrile. The acrylonitrile electrolysis dimerization method for preparing adiponitrile has the characteristics of short process and high product quality. In the existing electrolysis acrylonitrile dimerization process for preparing adiponitrile, ionic liquid is used as supporting electrolyte to improve the yield and current efficiency of adiponitrile, which can greatly reduce the corrosion of anode material and crude product separation equipment, and the property of ionic liquid is stable, which can greatly reduce the loss of electrolyte. However, the molecular structure of the existing technology is not reasonable, which leads to low conversion rate and product selectivity of acrylonitrile, therefore, it is necessary to develop a more efficient synthesis method. SUMMARY

[0006] In order to improve the conversion rate and selectivity of electrolysis acrylonitrile for preparing adiponitrile, the present application provides an electrolyte and a preparation method for preparing adiponitrile from electrolysis acrylonitrile.

[0007] The present application provides an electrolyte for preparing adiponitrile from electrolysis acrylonitrile, which comprises acrylonitrile, modified quaternary ammonium salt and water, and the modified quaternary ammonium salt comprises functional groups represented by formula (a) and formula (b) at the same time:

[0008]

[0009] The functional group represented by formula (b) is

[0010] wherein R1 to R4 in formula (a) are each an alkyl group having a carbon number of 0 to 6; and formula (b) is an alkyl group having a carbon number of n, n = 1 to 20;

[0011] The modified quaternary ammonium salt contains 2 to 4 functional groups represented by formula (a) in its structure, when the modified quaternary ammonium salt contains 2 functional groups represented by formula (a) in its structure, the free ends of the 2 functional groups represented by formula (a) are connected by 2 free ends of a functional group represented by formula (b1); when the modified quaternary ammonium salt contains 3 functional groups represented by formula (a) in its structure, the free ends of the 3 functional groups represented by formula (a) are connected by 3 free ends of a functional group represented by formula (b2); and when the modified quaternary ammonium salt contains 4 functional groups represented by formula (a) in its structure, the free ends of the 4 functional groups represented by formula (a) are connected by 4 free ends of a functional group represented by formula (b3).

[0012] According to an embodiment of the present application, R1 to R4 in the functional group represented by formula (a) are each an alkyl group having a carbon number of 0 to 4, and n in the functional group represented by formula (b) is 4 to 6.

[0013] According to another embodiment of the present application, the anion of the modified quaternary ammonium salt is one or more of hydroxide, hydrogen sulfate, dihydrogen phosphate, acetate, nitrate.

[0014] According to another embodiment of the present application, the content of the modified quaternary ammonium salt is 0.1 to 10 wt%, preferably 0.5 to 5 wt%.

[0015] According to another embodiment of the present application, the electrolyte further contains 0.1 to 10 wt% of EDTA or its sodium salt or potassium salt, and 0.01 to 5 wt% of borax.

[0016] According to another embodiment of the present application, the electrolyte further contains 1 to 20 wt% of phosphate, which is at least one of potassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate.

[0017] According to another embodiment of the present application, the content of the acrylonitrile is 3 to 7 wt%.

[0018] The present application also provides a method for electrolyzing acrylonitrile to produce adiponitrile, which uses the above electrolyte for electrolysis reaction.

[0019] According to an embodiment of the present application, the cathode of the electrolysis reaction is Cd or Pb or an alloy thereof, and the anode is carbon steel or stainless steel.

[0020] According to another embodiment of the present application, the reaction temperature of the electrolysis reaction is 30 to 70°C, and the current density is 200 to 5000 A / m2 .

[0021] The electrolyte for electrolysis of propylene cyanide to adiponitrile of the present application comprises modified quaternary ammonium salt, thereby improving the conversion rate of propylene cyanide and the selectivity of adiponitrile. DETAILED DESCRIPTION

[0022] The present application will be described in detail below with specific embodiments.

[0023] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and any values are provided as approximate values, and the ranges and values are understood to encompass values approximately the same as the stated values. For numeric values, the endpoints of each range, the endpoints of each range and individual point values, and individual point values can be combined with each other to form one or more new numeric ranges, which are to be considered as specifically disclosed herein.

[0024] The electrolyte for electrolysis of propylene cyanide to adiponitrile of the present application comprises propylene cyanide, modified quaternary ammonium salt and water, and the modified quaternary ammonium salt comprises functional groups represented by formula (a) and formula (b) at the same time:

[0025]

[0026] The functional group represented by formula (b) is

[0027] wherein R1-R4 in formula (a) are alkyl groups with carbon number of 0-6 respectively; formula (b) is an alkyl group with carbon number of n, n = 1-20;

[0028] The modified quaternary ammonium salt contains 2-4 functional groups represented by formula (a) in its structure, when the modified quaternary ammonium salt contains 2 functional groups represented by formula (a) in its structure, the free ends of the 2 functional groups represented by formula (a) are connected by 2 free ends of the functional groups represented by formula (b1); when the modified quaternary ammonium salt contains 3 functional groups represented by formula (a) in its structure, the free ends of the 3 functional groups represented by formula (a) are connected by 3 free ends of the functional groups represented by formula (b2); when the modified quaternary ammonium salt contains 4 functional groups represented by formula (a) in its structure, the free ends of the 4 functional groups represented by formula (a) are connected by 4 free ends of the functional groups represented by formula (b3). The structure of the alkyl group in formula (b) is not limited to the form in the schematic diagram, but is an alkyl group composed of primary carbon, secondary carbon, quaternary carbon, tertiary carbon, etc. The alkyl group as a whole has 2-4 free ends, and the free ends are connected to the free ends of (a).

[0029] The functional group represented by formula (a) in the structure of the modified quaternary ammonium salt has a 4-valent N +The structural unit is an "inducer" of the acrylonitrile electrolytic dimerization reaction, which can form a hydrophobic layer on the electrode surface and increase the solubility of acrylonitrile on the electrode surface. R1-R4 are each an alkyl group with a carbon number of 0-6. When the carbon number of R1-R4 is greater than 6, the steric hindrance is large, which is not conducive to the formation of a hydrophobic layer on the electrode surface.

[0030] The functional group represented by formula (b) in the modified quaternary ammonium salt plays a role in connecting multiple functional groups of (a) in one molecular structure. In formula (b), n = 1-20. When n is greater than 20, the steric hindrance is large, which is not conducive to the formation of a hydrophobic layer on the electrode surface.

[0031] The modified quaternary ammonium salt containing formula (a) and formula (b) has multiple functional groups of (a) connected in one molecular structure, which enhances the induction of acrylonitrile electrolytic dimerization and increases the selectivity and conversion rate of the acrylonitrile electrolytic dimerization reaction.

[0032] In optional embodiments, R1-R4 in the functional group represented by formula (a) are each an alkyl group with a carbon number of 0-4, and n in the functional group represented by formula (b) is 4-6. Within the preferred range, the 4-valent N + The steric hindrance is smaller when exposed to the bulk of the electrolyte, which is conducive to increasing the selectivity and conversion rate of the acrylonitrile electrolytic dimerization reaction.

[0033] In optional embodiments, the anion (A - ) of the modified quaternary ammonium salt is one or more of hydroxide, bisulfate, dihydrogen phosphate, acetate, and nitrate.

[0034] In optional embodiments, the content of the modified quaternary ammonium salt is 0.1-10 wt%. When the content of the modified quaternary ammonium salt in the electrolyte is less than 0.1 wt%, the content of the modified quaternary ammonium salt is low, which is not sufficient to significantly affect the conversion rate and selectivity of the acrylonitrile electrolytic dimerization reaction; when it is greater than 10 wt%, the content of the modified quaternary ammonium salt is too high, resulting in high use cost. Those skilled in the art can select any value within the above range, such as but not limited to 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, etc. Preferably, the content of the modified quaternary ammonium salt in the electrolyte is 0.5-5 wt%.

[0035] In optional embodiments, in order to improve the electrolysis efficiency, the electrolyte can also contain 0.1-10 wt% of EDTA or its sodium salt or potassium salt, and 0.01-5 wt% of borax.

[0036] In an optional embodiment, the electrolyte can further contain 1-20 wt% of phosphate, and the phosphate is at least one of potassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, sodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate. The phosphate serves to adjust the pH value of the electrolyte, and the content of the phosphate can be selected according to the actual needs to achieve the desired pH value. For example, the concentration of the phosphate can be, but is not limited to, 1 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, etc.

[0037] In an optional embodiment, the content of acrylonitrile is 3-7 wt%. When the content of acrylonitrile in the electrolyte is less than 3 wt%, the production efficiency is relatively low; and the saturated solubility of acrylonitrile in the electrolyte is 7 wt%. Therefore, the content of acrylonitrile is preferably 3-7 wt%.

[0038] The present application also provides a method for electrolyzing acrylonitrile to produce adiponitrile, which comprises using the above electrolyte for electrolysis.

[0039] In an optional embodiment, the cathode of the electrolysis reaction is Cd or Pb or an alloy thereof, and the anode is carbon steel or stainless steel.

[0040] In an optional embodiment, the reaction temperature of the electrolysis reaction is 30-70℃, and the current density is 200-5000 A / m 2 . When the current density is less than 200 A / m 2 , the production efficiency is too low, and more electrolytic cells need to be invested to achieve the same production capacity; when the current density is greater than 5000 A / m 2 , the current heat production is large, and the side reactions increase.

[0041] After the electrolysis reaction, the electrolyte after electrolysis is mixed with the crude adiponitrile to absorb the unreacted acrylonitrile, and the mixture is subjected to oil-water separation to obtain an oil phase containing acrylonitrile, adiponitrile, and organic by-products, and a water phase, and the oil phase is subjected to distillation to obtain acrylonitrile, crude adiponitrile, and organic by-products.

[0042] The present application will be further described in detail through specific examples. However, these examples are merely exemplary and do not constitute any limitation on the protection scope of the present application. In the following examples and comparative examples, the reagents, materials, and instruments used are commercially available unless otherwise specified.

[0043] In the following examples, all reactions were carried out in an electrolytic cell with an electrode size of 100 mm*200 mm, the anode and cathode being parallel and opposite, the distance between the anode and cathode being 3 mm. The electrolyte was pumped and circulated, the linear velocity of the electrolyte in the electrolytic cell being 1 m / s. The current was passed according to the current density and electrode area, the reaction time was calculated according to the Faraday efficiency of 100%, and the electrolysis reaction was carried out according to the calculated current and reaction time. After the reaction was completed, the organic matter in the electrolyte was extracted using CH2Cl2 and weighed, the composition of the organic matter was analyzed by chromatography, and the conversion rate of acrylonitrile and the selectivity of adiponitrile were calculated. The pressures involved are all gauge pressures. The test results are shown in Table 1.

[0044] In which, the test conditions and the calculation method of the results are as follows:

[0045] Current = electrode area x current density;

[0046] Reaction time = (2 x acrylonitrile mass x Faraday constant) / (molar mass of acrylonitrile x current);

[0047] Conversion rate of acrylonitrile = (1 - mass of residual acrylonitrile / mass of added acrylonitrile) x 100%;

[0048] Yield of adiponitrile = (mass of actual adiponitrile received / theoretical mass of acrylonitrile completely converted into adiponitrile) x 100%;

[0049] The compounds of formula (A) to (D) described in the examples are as follows:

[0050]

[0051] Example 1

[0052] The electrolyte used contains 5wt% of EDTA sodium salt, 10wt% of sodium dihydrogen phosphate, 1wt% of borax, and 2wt% of the modified quaternary ammonium salt shown in formula (B). The pH of the electrolyte is adjusted to 8 by adding NaOH. The concentration of acrylonitrile in the electrolyte is 7wt%. The cathode is a Pb plate, the anode is a carbon steel plate, and the current density is 1000 A / m 2 .

[0053] Example 2

[0054] The electrolyte used contains 5wt% of EDTA sodium salt, 10wt% of sodium dihydrogen phosphate, 1wt% of borax, and 2wt% of the modified quaternary ammonium salt shown in formula (B). The pH of the electrolyte is adjusted to 8 by adding NaOH. The concentration of acrylonitrile in the electrolyte is 7wt%. The cathode is a Cd plate, the anode is a carbon steel plate, and the current density is 2000 A / m 2 .

[0055] Example 3

[0056] The electrolyte used contains 5wt% of EDTA sodium salt, 10wt% of sodium dihydrogen phosphate, 1wt% of borax, and 2wt% of modified quaternary ammonium salt shown in formula (C). The pH of the electrolyte is adjusted to 8 by adding NaOH. The concentration of acrylonitrile is 7wt%, the cathode used is Cd, the anode is carbon steel, and the current density is 1000 A / m 2 .

[0057] Example 4

[0058] The electrolyte used contains 5wt% of EDTA sodium salt, 10wt% of sodium dihydrogen phosphate, 1wt% of borax, and 2wt% of modified quaternary ammonium salt shown in formula (D). The pH of the electrolyte is adjusted to 8 by adding NaOH. The concentration of acrylonitrile is 7wt%, the cathode used is Cd, the anode is carbon steel, and the current density is 1000 A / m 2 .

[0059] Example 5

[0060] The electrolyte used contains 5wt% of EDTA sodium salt, 10wt% of sodium dihydrogen phosphate, 1wt% of borax, and 0.1wt% of modified quaternary ammonium salt shown in formula (D). The pH of the electrolyte is adjusted to 8 by adding NaOH. The concentration of acrylonitrile is 7wt%, the cathode used is Cd, the anode is carbon steel, and the current density is 1000 A / m 2 .

[0061] Example 6

[0062] The electrolyte used contains 5wt% of EDTA sodium salt, 10wt% of sodium dihydrogen phosphate, 1wt% of borax, and 10wt% of modified quaternary ammonium salt shown in formula (D). The pH of the electrolyte is adjusted to 8 by adding NaOH. The concentration of acrylonitrile is 7wt%, the cathode used is Cd, the anode is carbon steel, and the current density is 1000 A / m 2 .

[0063] Comparative Example 1

[0064] The electrolyte used contains 5wt% of EDTA sodium salt, 10wt% of sodium dihydrogen phosphate, 1wt% of borax, and 2wt% of tetrabutylammonium hydroxide. The pH of the electrolyte is adjusted to 8 by adding NaOH. The concentration of acrylonitrile in the electrolyte is 7wt%. The cathode is a Pb plate, the anode is a carbon steel plate, and the current density is 1000 A / m 2 .

[0065] Comparative Example 2

[0066] The electrolyte used contains 5wt% of EDTA sodium salt, 10wt% of sodium dihydrogen phosphate, 1wt% of borax, and 2wt% of modified quaternary ammonium salt shown in formula (A). The pH of the electrolyte is adjusted to 8 by adding NaOH. The concentration of acrylonitrile in the electrolyte is 7wt%. The cathode is a Pb plate, and the anode is a carbon steel plate. The current density is 1000 A / m 2 .

[0067] Table 1

[0068] % conversion of acrylonitrile % yield of adiponitrile Example 1 93 91 Example 2 94 92 Example 3 92 90 Example 4 93 92 Example 5 88 76 Example 6 93 92 Comparative Example 1 87 76 Comparative Example 2 92 80

[0069] From the results in Table 1, it can be seen that the conversion of acrylonitrile and the selectivity of adiponitrile are improved by using the preparation method of the present application compared with the prior art.

[0070] The preferred embodiments of the present application disclosed above are only used to help explain the present application. The preferred embodiments do not describe all the details and limit the present application to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of the present specification. The present specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present application, so that those skilled in the art can well understand and utilize the present application. The present application is limited only by the claims and their full scope and equivalents.

Claims

1. An electrolyte for the electrolytic production of adiponitrile from propylene nitrile, characterized in that The electrolyte comprises acrylonitrile, modified quaternary ammonium salt and water, wherein the modified quaternary ammonium salt comprises functional groups represented by formula (a) and formula (b) simultaneously. The functional group represented by formula (b) is In formula (a), R1-R4 are alkyl groups with carbon number of 0-4; formula (b) is an alkyl group with carbon number of n, n=4-6. The modified quaternary ammonium salt comprises 2-3 functional groups represented by formula (a), when the modified quaternary ammonium salt comprises 2 functional groups represented by formula (a), the free ends of the 2 functional groups represented by formula (a) are connected by 2 free ends of functional groups represented by formula (b1); when the modified quaternary ammonium salt comprises 3 functional groups represented by formula (a), the free ends of the 3 functional groups represented by formula (a) are connected by 3 free ends of functional groups represented by formula (b2). The anion of the modified quaternary ammonium salt is one or more of hydroxide, hydrogen sulfate, dihydrogen phosphate, acetate and nitrate.

2. The electrolyte according to claim 1, characterized in that, The content of the modified quaternary ammonium salt is 0.1-10wt%.

3. The electrolyte according to claim 2, characterized in that, The content of the modified quaternary ammonium salt is 0.5-5wt%.

4. The electrolyte of claim 1, wherein The electrolyte further comprises 0.1-10wt% of EDTA or its sodium salt or potassium salt, and 0.01-5wt% of borax.

5. The electrolyte of claim 1, wherein The electrolyte further comprises 1-20wt% of phosphate, wherein the phosphate is at least one of potassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, sodium phosphate, disodium hydrogen phosphate and sodium dihydrogen phosphate.

6. The electrolyte of claim 1, wherein The content of the acrylonitrile is 3-7wt%.

7. A process for the electrolytic production of adiponitrile from acrylonitrile, characterized in that, The electrolyte of any one of claims 1-6 is used for electrolysis.

8. The method of claim 7, wherein, The cathode of the electrolysis is Cd or Pb or alloy thereof, and the anode is carbon steel or stainless steel.

9. The method of claim 7, wherein, The reaction temperature of the electrolysis reaction is 30-70℃, and the current density is 200-5000 A / m 2 .

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