Production of adiponitrile

Abstract

The present invention discloses a method for producing adiponitrile from acrylonitrile in an electrolytic cell. An aqueous electrolyte containing acrylonitrile is converted to adiponitrile in the presence of a solid anode and in the absence of a solid cathode. The cathode comprises a gas plasma.

Description

Technical Field

[0001] The present application relates to the production of adiponitrile from acrylonitrile. Background Art

[0002] Adiponitrile (ADN) is an important intermediate in the production of hexamethylenediamine (HMDA), one of the monomers used to produce nylon-6,6 (a copolymer of HMDA and adipic acid (AA)). Historically, nylon-6,6 has been used primarily in the formation of carpet fibers used in high-quality carpeting for residential applications and in fibers for clothing. More recently, nylon-6,6 has been used as an engineering resin in demanding automotive "under the hood" high-temperature applications, such as linings for hydraulic brake lines, insulation for cables and wires, and molded parts such as radiator housings.

[0003] One commercial route to produce adiponitrile that has been practiced for over 50 years involves the electrohydrodimerization of acrylonitrile. An early example of such a process is disclosed in US Pat. No. 4,306,949, in which a mixture of at least 0.1 wt. % acrylonitrile, at least 10 wt. % acrylonitrile, and at least 10 wt. % acrylonitrile is electrolyzed in an undivided reaction cell. -5 An aqueous electrolyte containing quaternary ammonium cations of gram-mole / liter directed salts and at least 0.1 weight percent conductive salt. The aqueous electrolyte is in contact with a cathode surface having a cathode potential sufficient to hydrodimerize acrylonitrile while incidentally forming oxygen at the anode surface. During electrolysis, an effective amount of a non-competitive gas such as nitrogen, helium, hydrogen, argon, and / or air is introduced into the electrolyte to reduce the oxygen concentration in the aqueous electrolyte and at the cathode surface, thereby reducing corrosion of the cathode surface. Typically, the cathode surface is cadmium and the anode surface is steel.

[0004] A newer iteration of the electrohydrodimerization of acrylonitrile to produce adiponitrile is disclosed in CN110016690A. Features include placing an electrolyte containing acrylonitrile in an undivided cell connected to a plasma gas on one side; conducting electrolysis while the plasma gas is introduced into the electrolyte; passing the electrolyzed liquid through a three-phase separator to separate an oil phase; and distilling the oil phase to produce an adiponitrile product. Because the plasma gas has absorbed high-frequency energy and has very high conductivity, it is effective not only in achieving the required mass transfer of the adiponitrile product from the cathode surface but also in increasing electrolysis efficiency, which can reduce the current density of the electrolyte and thereby reduce the energy consumption required for electrolysis. A suitable plasma gas is argon; the anode material is stainless steel or an insoluble titanium-based electrode, and the cathode material is cadmium or lead.

[0005] US8529749B2 relates to an electrochemical cell using a plasma source and also discloses a method for operating the electrochemical cell.

[0006] Problems with some technologies arise from the formation of organic bases and hydrogen. The cathode may become contaminated with iron. The cathode may lose cadmium due to corrosion. The organic base causes yield loss and must be separated from the adiponitrile product to maintain high product quality. The formation of hydrogen can lead to the presence of explosive waste gas mixtures containing both hydrogen and oxygen in the process, which poses a significant risk. These problems are discussed in "Electro-organic Synthesis and Product Recovery: An illustration using the EHD of acrylonitrile" by Chris J. H. King and Charles E. Cutchens, Solutia, Inc., 11 th It is well described in International Forum, Electrolysis in the Chemical Industry, Nov. 2-6 1997. Solutions to these problems are highly desirable.

[0007] Despite recent progress, there remains considerable interest in developing improved processes for the electrohydrodimerization of acrylonitrile to produce adiponitrile, and in particular in reducing or avoiding the need for periodic shutdowns to replace metal anodes and / or cathodes. Summary of the Invention

[0008] A method for converting acrylonitrile to adiponitrile in a cell having a plasma-forming gas in the absence of a metal cathode is disclosed. The method simplifies maintenance and reduces corrosion products. Reducing corrosion products can be particularly beneficial if the corrosion products are catalytically active in converting adiponitrile to undesirable byproducts.

[0009] Disclosed is a method for converting acrylonitrile into adiponitrile, the method comprising:

[0010] a. flowing an aqueous electrolyte containing acrylonitrile to a cell having an anode in the absence of a solid cathode;

[0011] b. flowing a gas plasma cathode to the cell, wherein the gas plasma cathode is separated from the anode by an electrolyte; and

[0012] c. Recovering the adiponitrile-containing product from the tank.

[0013] The aqueous electrolyte may include at least one selected from the group consisting of:

[0014] a. ≥1 wt% to ≤8 wt% acrylonitrile;

[0015] b. ≥4 wt% to ≤21 wt% phosphate;

[0016] c. ≥0.2 wt% to ≤8 wt% EDTA; and

[0017] d. ≥0.1 wt% to ≤8 wt% of a quaternary ammonium salt.

[0018] The aqueous electrolyte may contain at least two selected from the immediately aforementioned group.

[0019] The pH of the electrolyte may be ≥6 and ≤9, for example, ≥6 and ≤8, ≥6.5 and ≤7.5.

[0020] EDTA may suitably be present in the electrolyte as the sodium or potassium salt of EDTA.

[0021] If the electrolyte contains phosphate, the phosphate may include one or more of sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, dipotassium hydrogen phosphate, and potassium dihydrogen phosphate.

[0022] The skilled person can adjust the process conditions to achieve a range of desired single-pass conversions, selectivities, and yields. Examples of suitable process conditions include electrolyte temperatures of ≥20°C to ≤50°C, a flow rate of ≥300 Amps / m 2 to ≤2000Amps / m 2 The current density and electrolysis voltage are ≥3 volts to ≤6 volts.

[0023] Suitable plasma gases include gases that are inert to the conversion of acrylonitrile to adiponitrile, such as argon.

[0024] The plasma gas may be generated outside the cell, for example in an external plasma generator.

[0025] The plasma gas may be delivered to the cell by vacuum.

[0026] The supply rate of plasma gas to the electrolytic cell can be adjusted to obtain the desired conversion, selectivity, and yield, for example, ≥ 0.2 liters / hour to ≤ 2 liters / hour per liter of electrolyte.

[0027] The anode of the cell comprises at least one of the following:

[0028] a. Stainless steel;

[0029] b. Carbon steel; and

[0030] c. Titanium-containing alloys.

[0031] The cell may optionally contain no solid anode.

[0032] The anode may include a gas, such as hydrogen.

[0033] The pool may be an undivided pool.

[0034] The method may further comprise:

[0035] a. recovering the electrolyzed liquid from the cell; and

[0036] b. Separating the organic phase containing adiponitrile from the recovered electrolyzed liquid.

[0037] The method may further include:

[0038] a. separating the aqueous phase from the recovered electrolyzed liquid; and

[0039] b. Recirculating at least a portion of the aqueous phase as electrolyte supplied to the cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a simplified schematic diagram of a process for preparing adiponitrile from acrylonitrile according to one embodiment of the present disclosure. DETAILED DESCRIPTION

[0041] The present disclosure provides a method and apparatus for preparing adiponitrile from acrylonitrile. Although not intending to limit the scope of the present invention by stating theory, the following summary may be useful for a skilled artisan to effectively select process conditions for the disclosed method.

[0042] The reaction mechanism of this process has been studied in detail. Although the theoretical mechanism is not fully understood, it is believed that in the first stage of the process, acrylonitrile [CH2=CHCN] is protonated to form a cyanoethyl anion [CH2CH2CN - ] by reacting with two electrons [e - ] and a proton [H + ] occurs in combination with:

[0043] CH2=CHCN+H + +2e - →CH2CH2CN - .

[0044] In the second stage, it is believed that the resulting cyanoethyl anion interacts with the second acrylonitrile molecule as follows:

[0045] CH2=CHCN+CH2CH2CN - →NCCH(CH2)3CN - .

[0046] The resulting dimerized anion then reacts with hydrogen ions to form adiponitrile:

[0047] NCCH(CH2)3CN - +H + →NC(CH2)4CN.

[0048] During the electrolysis reaction, an electrooxidation reaction occurs at the surface of the anode (i.e., the positively charged electrode) surrounded by the aqueous cell medium. This anode electrooxidation provides free electrons and protons for the electrochemistry. Specifically, protons [H + ] and free electrons [e - ]:

[0049] 2H2O→O2+4H + +4e -

[0050] In the continuous electrochemical dimerization process carried out in an undivided electrolytic cell, it has been found that protons subsequently migrate through the conductive medium and find an ionically charged gas-liquid interface serving as a cathode (or negatively charged electrode), where the above-mentioned protonation and dimerization reactions occur. Due to the introduction of an ionized plasma gas phase in the cell, a charged gas-liquid interface is present. At this interface, the olefin feed molecules [e.g., acrylonitrile] are protonated and further dimerized to form adiponitrile. The conductive medium promotes the continuous flow of protons and free electrons through the cell.

[0051] As described above, the hydrodimerization reaction continues, whereby the two protonated acrylonitrile molecules are further converted into adiponitrile [NC(CH2)4CN]. Other side electrochemical reactions can occur at the charged gas-liquid interface to form byproducts; propionitrile [CH3CH2CN] and acrylonitrile hydrogenated trimer [NC(CH2)3NCCH(CH2)3CN].

[0052] One possible mechanism of the disclosed process includes the following overall schematic reaction at a dispersed ionized gas-liquid interface:

[0053] 2CH2=CH-CN+2H2O+2e - →NC-(CH2)4-CN+2OH - ;

[0054] CH2=CH-CN+2H2O+2e - →CH3CH2CN+2OH - ;as well as

[0055] 3CH2=CH-CN+2H2O+2e - →NC(CH2)3NCCH(CH2)3CN+2OH - .

[0056] In the method and apparatus of the present invention, electrolysis is carried out in a cell containing an aqueous electrolyte comprising acrylonitrile and having an anode and cathode separated by the electrolyte. However, unlike existing methods, in the cell adopted in the inventive method, the conventional metal cathode surface is replaced by the gas plasma supplied to the electrolyte to provide a cathode during electrolysis. The anode of the cell adopted in the disclosed method can be metallic, for example stainless steel, carbon steel or a titanium alloy, such as an insoluble titanium-based alloy. The cell can be a single undivided cell, or can be a separated cell, in which the ionized plasma gas [serving as cathode] and the anode are maintained in different chambers, separated by an ion permeable membrane or a salt bridge.

[0057] In conventional electrolytic cells, it is very important to maintain high electrolytic conductivity, that is, the effective flow of current between the two electrodes while having a high current density at the electrodes. Traditionally, an aqueous electrolytic medium containing organic or inorganic salts, such as a mixture of quaternary ammonium salts and alkali metal salts, is used together with the olefin feed to be hydrodimerized. Such electrolytic cell systems contain a pair of electrodes (cathode and anode) for achieving the desired electrolytic activity.

[0058] However, in such systems, it is difficult to maintain electrolytic conductivity due to various factors such as multiphase media, flow restrictions due to cell size, operating conditions, accumulation of contaminants, electrodes and their surface characteristics, etc.

[0059] Unexpectedly, it was discovered that when a gas plasma is introduced into the cell medium as a highly dispersed ionized gas phase instead of the cathode, overall electrolytic conductivity is improved. Cathode corrosion is known to be common in such systems, and the resulting resistance to current flow and current density reduces overall performance.

[0060] The disclosed method eliminates the metal surface cathode. In addition, the ionized gas phase (plasma) can be well dispersed in the electrolyte cell medium so that uniform local electrochemical action occurs at the dispersed ionized gas-liquid interface. In previously known methods using metal cathodes, reactant mass transfer occurs from the bulk medium to the active charged surface; and is balanced by product mass transfer from the active charged surface back to the bulk. The disclosed method can improve the overall mass transfer of reactants and product species. The disclosed electrolytic cell can improve current efficiency while improving reactant conversion and product yield.

[0061] The electrolyte used in the process of the present invention contains acrylonitrile, which is usually present in the aqueous base of the electrolyte in an amount of ≥1 wt. % to ≤8 wt. % of the total electrolyte, wherein the upper limit of about ≤8 wt. % is mainly determined by the solubility of acrylonitrile in water as part of the conductive medium.

[0062] In some embodiments, the electrolyte used herein may further include one or more phosphates, typically in an amount of ≥4 wt% to ≤21 wt% of the total electrolyte. Suitable phosphates include one or more of sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, dipotassium hydrogen phosphate, and potassium dihydrogen phosphate.

[0063] In some embodiments, the electrolytes employed herein may further comprise ethylenediaminetetraacetic acid (EDTA) or a salt thereof, which is typically present in an amount of ≥0.2 wt % to ≤8 wt % of the total electrolyte. Suitable EDTA salts include sodium and potassium salts and mixtures thereof.

[0064] In some embodiments, the electrolyte used herein may also include one or more quaternary ammonium salts or quaternary phosphonium salts, which are typically present in an amount of ≥0.1 wt % to ≤8 wt % of the total electrolyte. Suitable salts may include those containing only a pentavalent nitrogen or phosphorus atom, such as in various monovalent monoquaternary ammonium (e.g., tetraalkylammonium) or monoquaternary phosphonium (e.g., tetraalkylphosphonium) cations, but they may contain more than one such pentavalent atom, such as in various polyvalent polyquaternary ammonium or polyquaternary phosphonium cations, such as diquaternary ammonium or diquaternary phosphonium cations, such as polymethylenebis(trialkylammonium or trialkylphosphonium) cations. Mixtures of such monovalent and polyvalent quaternary ammonium and / or quaternary phosphonium cations may also be used. Suitable monoquaternary ammonium or monoquaternary phosphonium cations may be cyclic, as in the case of piperidinium, pyrrolidinium and morpholinium cations, but they are more typically of the type in which the pentavalent nitrogen or phosphorus atom is directly attached to a total of four monovalent organic groups, the monovalent organic groups preferably being free of ethylenic unsaturation and ideally selected from the group consisting of alkyl groups and aryl groups and combinations thereof. Suitable polyquaternary ammonium or polyquaternary phosphonium cations may likewise be cyclic, as in the case of piperazinium cations, and they are typically of the type in which the pentavalent nitrogen or phosphorus atoms are attached to one another via at least one divalent organic (e.g., polymethylene) group and are each further substituted with a monovalent organic group of the type just mentioned, the monovalent organic groups being sufficient in number (typically two or three) to satisfy four-fifths of the valences of each such pentavalent atom by such divalent and monovalent organic groups. As such monovalent organic groups, suitable aryl groups generally contain six to twelve carbon atoms and preferably contain only one aromatic ring, as for example in a phenyl group or a benzyl group, and suitable alkyl groups may be straight-chain, branched or cyclic, each generally containing one to twelve carbon atoms.

[0065] While quaternary ammonium or phosphonium cations containing such combinations of alkyl and aryl groups (eg, benzyltriethylammonium or phosphonium ions) may be used, many embodiments of the present process are preferably performed with quaternary cations having no ethylenic or aromatic unsaturation. Good results are generally obtained with tetraalkylammonium or tetraalkylphosphonium ions containing at least three C2 to C6 alkyl groups and a total of 8 to 24 carbon atoms in the four alkyl groups, such as tetraethylammonium or phosphonium cation, ethyltripropylammonium or phosphonium cation, ethyltributylammonium or phosphonium cation, ethyltripentylammonium or phosphonium cation, ethyltrihexylammonium or phosphonium cation, octyltriethylammonium or phosphonium cation, tetrapropylammonium or phosphonium cation, methyltripropylammonium or phosphonium cation, decyltripropylammonium or phosphonium cation, methyltributylammonium or phosphonium cation, tetrabutylammonium or phosphonium cation, pentyltributylammonium or phosphonium cation, tetrapentylammonium or phosphonium cation, tetrahexylammonium or phosphonium cation, ethyltrihexylammonium or phosphonium cation, diethyldioctylammonium or phosphonium cation. From an economic point of view, the most practical are generally those tetraalkylammonium ions in which each alkyl group contains two to five carbon atoms, such as diethyldipentylammonium, tetrapropylammonium, tetrabutylammonium and pentyltripropylammonium, tetrapentylammonium, and those C8 to C5 alkyl groups containing at least three C2 to C5 alkyl groups. 20 In some embodiments, the present invention provides the present invention relates to a method for the treatment of aqueous electrolysis ...

[0066] Typically, the pH of the electrolyte is ≥6 and ≤9. Cell media pH control is critical from the perspective of minimizing unwanted acid- and base-catalyzed byproduct reactions via cyanoethylation, hydrolysis, reductive hydrogenation, and combinations thereof. Conventional methods of pH control can be implemented, including pre-determined addition of pH adjusters, buffers, and the like. Such methods are well known in the industry, and it will be understood that such pH control additives remain inert to the electrochemistry employed herein.

[0067] In some embodiments, the gaseous feed for plasma gas generation is argon. Therefore, argon is not only readily available, but as an inert gas, argon does not participate in the electrochemical reaction in any shape or form. Other non-limiting examples of suitable gases for plasma feed are neon, helium, carbon dioxide, krypton, xenon, etc. The choice of plasma gas can depend on a techno-economic analysis, i.e., gas availability, ease of handling, and overall cell performance.

[0068] The plasma gas is suitably delivered to the electrolytic cell by vacuum, for example by a vacuum pump. Atmospheric delivery may also be suitable. Delivery of the plasma gas to the cell under pressure may also be achieved, for example, by using a compressor system.

[0069] The plasma gas is suitably recycled by removing a portion of the gas from the electrolytic cell, removing a gaseous purge stream or exhaust stream from the gas recycle stream, and returning a portion of the gas to the plasma generator. In some cases, the exhaust stream can allow a portion of the by-products to be removed from the system.

[0070] Plasma gas can be produced by a plasma generator. One end of the plasma generator is connected to a suitably dry gas supply unit, such as an argon gas supply unit. In specific applications, the gas supply unit primarily comprises a vacuum pump, which introduces argon gas stored in an external storage tank into the plasma generator to generate an argon gas stream. The plasma generator comprises a high-voltage power supply, a high-voltage electrode, and a discharge chamber. The high-voltage power supply is electrically connected to the high-voltage electrode. One end of the discharge chamber is provided with an inlet connected to the gas supply unit, and the other end of the discharge chamber is provided with an outlet connected to the electrolyte. The high-voltage electrode is placed in the discharge chamber, and the high-voltage power supply can excite the argon gas at the high-voltage electrode to ionize it into plasma gas. In specific applications, the high-voltage power supply is a high-voltage pulse generator that generates pulses with a frequency of no more than 100 kHz. The higher the frequency of the high-voltage pulse generator, the faster the plasma processing speed. The discharge chamber can be made of insulating materials such as glass and ceramic. The high-voltage electrode undergoes a high-voltage discharge in the gas channel of the discharge chamber to generate plasma gas. Argon gas in an external gas storage tank is continuously introduced into the discharge chamber under the action of a vacuum pump. After high-voltage ionization is completed in the discharge chamber, the vacuum pump drives the plasma gas into the electrolyte to contact the electrolyte.

[0071] In some embodiments, the intensity of the plasma gas flow for electrolyzing 1 liter of electrolyte solution is about 0.2 liters / hour to 2 liters / hour.

[0072] In some embodiments, the conditions of the electrolysis step of the method of the present invention are an electrolysis temperature of ≥20°C to ≤50°C, a flow rate of ≥300 amps / m 2 to ≤2000amps / m 2The current density and electrolysis voltage are ≥3 volts to ≤6 volts.

[0073] According to the condition adopted, electrolysis can be carried out to complete the theoretical electrolysis time required for reaction, and electrolysis product is supplied to separator afterwards, and this separator is at least effectively separated into organic phase and aqueous phase containing adiponitrile by electrolysis product.Contact time can comprise ≥1 minute to ≤10 hours, for example, ≥5 minutes to ≤5 hours, for example, ≥5 minutes to ≤1 hour.Then organic phase can be supplied to distillation separation mechanism, wherein any unreacted vinyl cyanide and by-product (being mainly dimer and trimer polymer of propionitrile, vinyl cyanide) can be separated with desired adiponitrile product.Aqueous phase can be preferably recycled back to the pond after purifying to remove pollutant such as metallic substance, residual organic matter etc. as a part for electrolyte. Adopt suitable purge stream to keep and control the conventional method of the accumulation of these pollutants is well known in industry.Can be fed for the fresh supplement of the electrolytic medium lost via cleaning to balance this process.Usually use suitable waste disposal method to handle pollutant purge stream.

[0074] Now referring to the drawings, Figure 1 In the process, the components of the electrolyte for electrohydrodimerizing acrylonitrile to adiponitrile are added to a mixing tank 11 via one or more supply lines, generally indicated by line 13. After mixing in tank 11, the resulting electrolyte is fed via line 15 to an electrolysis cell 17 having a metal anode (not shown) and an argon gas plasma cathode (not shown). When the electrolysis is complete, the electrolysis products are sent via line 19 to a separator 21 where they are separated into an organic phase and an aqueous phase.

[0075] Separator 21 may contain a gas-liquid separation section for separating gaseous components present in line 19. Non-limiting examples of gas components in line 19 may include gases used for ionizing plasma, oxygen generated by the anode reaction, hydrogen from proton activity, volatile organic compounds, etc. Figure 1 The detached gas lines are not shown.

[0076] Separator 21 may contain one or more conventional unit operations that are effective to separate the organic phase from the aqueous phase. Such unit operations are well known to chemical engineers skilled in the art of product separation.

[0077] The organic phase is collected in line 23 and sent to a distillation unit (not shown) for recovery of the adiponitrile product, while the aqueous phase is collected in line 25 and recycled to the mixing tank 11.

[0078] While the present invention has been described and illustrated by reference to particular embodiments, those skilled in the art will appreciate that the invention lends itself to variations not necessarily illustrated herein. Therefore, reference should be made solely to the appended claims for purposes of determining the true scope of the present invention.

[0079] Electrolytic cell - metal cathode and metal anode

[0080] Electrolytic cell unit 17 (in Figure 1 The cell (also known as a cell) comprises a container containing a liquid electrolyte and a reaction medium, into which two flat surfaces serving as electrodes (a cathode and an anode) are immersed. The cathode surface is made of cadmium (Cd), while the anode surface is made of stainless steel. The linear spacing between the two electrodes ranges from 1.25 mm to 2.5 mm and can be adjusted by moving the two electrodes closer or further apart. The cell contains an external power source, and the two electrodes are connected to complete a continuous current flow path.

[0081] Pool at 300amps / m 2 -2000amps / m 2 The cell is operated at a current density within the range of 0 psi to 10 psi (gauge pressure). The cell is operated at a temperature within the range of 20°C to 55°C. The cell contents are continuously circulated through the cell at a rate of about 3 ft / s to 6 ft / s or about 1 m / s to 2 m / s. Cell unit 17 ( Figure 1 ) feed line 15( Figure 1 ) is about 1%-10% organic phase and about 90%-99% aqueous phase (% are by weight).

[0082] Electrolytic cell - metal anode and plasma gas cathode :

[0083] The electrolytic cell, similar to the one described above and used in the comparative example, comprises a container containing a liquid electrolyte and a reaction medium, in which a flat surface is immersed and serves as an anode. The anode surface is made of stainless steel.

[0084] The cell is integrated with a gas plasma generation unit. A dry gas stream is fed to the plasma generation unit, and a highly ionized gas plasma stream is made available for feeding to the cell. Highly ionized (or charged) gas plasma is introduced and dispersed in an electrolyte medium. This dispersed gas plasma phase serves as a second electrode and current flows through the electrolyte and across the anode surface. This current flow through the electrolyte triggers the desired electrochemical reaction, which consumes the organic feed material present in the electrolyte medium.

[0085] Pool at 300amps / m 2 -2000amps / m 2The cell is operated at a current density within the range of 0 psi to 10 psi (gauge pressure). The cell operating temperature is within the range of 20° C. to 55° C. The cell contents are continuously circulated through the cell at a rate of about 3 ft / s to 6 ft / s or about 1 m / s to 2 m / s. The cell feed is about 1% to 10% organic phase and about 90% to 99% aqueous phase (% by weight).

[0086] In the examples of the present disclosure, the yield of adiponitrile is defined as yield %=(moles of adiponitrile produced) / (moles of adiponitrile expected based on the amount of acrylonitrile fed)×100.

[0087] As used herein, the term "hydrodimerize" or "hydrodimerized" or "hydrodimerization" refers to an organic reaction that couples two olefin molecules with the addition of hydrogen to produce a symmetrical hydrocarbon called a dimer. As an example, two acrylonitrile molecules undergo hydrodimerization to form adiponitrile according to the following scheme:

[0088] 2CH2=CH-CN+2e - +2H + →NC-CH2-CH2-CH2-CH2-CN.

[0089] The term "electrodimerization" or "electrohydrodimerization" refers to the dimerization process described above being carried out in an electrolytic cell.

[0090] EDTA is ethylenediaminetetraacetic acid.

[0091] Chemical composition analysis can be performed using standard gas chromatography (GC) or liquid chromatography (LC) methods.

[0092] In the following gas plasma cathode example, the adiponitrile product is at least 99.0 wt% pure, with the combined amount of succinonitrile, MGN, CPI, acrylonitrile, HOPN, MCPA, BCE, and other trace impurities being <1.0 wt%.

[0093] MGN is 2-methylglutaronitrile.

[0094] CPI is 2-cyanocyclopentylideneimine.

[0095] HOPN is hydroxypropionitrile.

[0096] MCPA is monocyanopropylamine.

[0097] BCE is bis-(cyanoethyl)-ether.

[0098] EDTA is ethylenediaminetetraacetic acid.

[0099] Example

[0100] Example 1 :

[0101] To the above and Figure 1 A conventional undivided electrolytic cell of the type described in

[0015] was charged with a feed stream 15 containing 1 wt. % acrylonitrile and an aqueous electrolyte medium containing 4 wt. % disodium hydrogen phosphate, 0.2 wt. % ethylenediaminetetraacetic acid (EDTA), 0.5 wt. % quaternary ammonium salt (hexamethylenebisethyldibutylammonium p-toluenesulfonate), and the balance water. The cell was continuously circulated, maintained at a constant temperature of 25°C, and operated at 500 amps / m. 2 The cell was operated at a current density of 100 nm. The cell was operated using a carbon steel anode separated by 2 mm from the cadmium cathode. The solution was electrolyzed in the cell at an electrolysis voltage of 5 volts. After electrolysis, the electrolyzed effluent stream 19 was conveyed to a separator 21. The organic phase 23 containing the adiponitrile product was further processed using distillation separation. The yield of adiponitrile was determined to be 84.4% by gas chromatographic analysis.

[0102] Example 2 :

[0103] Example 1 was repeated except that the cell was operated using a carbon steel anode spaced 2 mm from the cadmium cathode and an ionized argon gas plasma additionally fed to the cell.After electrolysis and separation / purification, the yield of adiponitrile was determined to be 95.2%.

[0104] Example 3 :

[0105] Example 1 was repeated, except that the electrolyte cell was operated using a carbon steel anode and the cathode was replaced by an ionized argon gas plasma fed into the cell. The dispersed ionized argon gas phase in the electrolyte medium served as the cathode. After electrolysis and separation / purification, the yield of adiponitrile was determined to be 95.7%.

[0106] Example 4 :

[0107] Example 1 was repeated, except that the cell was operated using a carbon steel anode and the cathode was replaced by an ionized neon gas plasma fed into the cell. The dispersed ionized neon gas phase in the electrolyte medium served as the cathode. After electrolysis and separation / refining, the yield of adiponitrile was determined to be 94.1%.

[0108] Example 5 :

[0109] Example 1 was repeated, except that the cell was operated using a carbon steel anode and the cathode was replaced by an ionized carbon dioxide gas plasma fed to the cell. The dispersed ionized carbon dioxide gas phase in the electrolyte medium served as the cathode. After electrolysis and separation / refining, the yield of adiponitrile was found to be 91.9%.

[0110] The embodiment provided has been described and used the electrochemical coupling of gas plasma electrolysis for acrylonitrile to obtain the effectiveness of adiponitrile.Data display, with respect to the traditional system that uses two conventional electrodes to operate, the productive rate that the system based on plasma that eliminates the metal surface cathode shows that the adiponitrile product forms increases.Example 2 and 3 comparison shows that argon gas and neon are both basically equally effective as plasma source gases, and similarly, embodiment 4 explanation, when using carbon dioxide as plasma gas, with respect to the adiponitrile productive rate that obtains by the conventional pond of embodiment 1, can obtain improved adiponitrile productive rate.

Claims

1. A method for converting acrylonitrile into adiponitrile, the method comprising: a) flowing an aqueous electrolyte comprising acrylonitrile to a cell having an anode in the absence of a solid cathode; b) flowing a gas plasma cathode to the cell, wherein the gas plasma cathode is separated from the anode by the electrolyte; and c) recovering a product containing adiponitrile from the tank.

2. The method according to claim 1, wherein the aqueous electrolyte further comprises at least one selected from the group consisting of: a) ≥1% to ≤8% by weight of acrylonitrile; b) ≥4% to ≤21% by weight of phosphates; c) ≥ 0.2 wt% to ≤ 8 wt% EDTA; and d) ≧0.1% to ≦8% by weight of a quaternary ammonium salt.

3. The method according to claim 2, wherein the aqueous electrolyte comprises at least two selected from the group consisting of. The method according to claim 1 , wherein the pH of the electrolyte is ≥6 and ≤9.

5. The method of claim 2, wherein the EDTA is present in the electrolyte as a sodium salt or a potassium salt of EDTA.

6. The method according to any one of claims 2 to 5, wherein the phosphate comprises one or more of sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, dipotassium hydrogen phosphate and potassium dihydrogen phosphate.

7. The method of claim 1, wherein the conditions include an electrolyte temperature of ≥20°C to ≤50°C, a flow rate of ≥300 Amps / m 2 to ≤2000Amps / m 2 At least one of a current density of ≥3 volts to ≤6 volts and an electrolysis voltage of ≥3 volts to ≤6 volts. The method of claim 1 , wherein the plasma gas comprises argon.

9. The method of claim 1, further comprising generating the plasma gas in a plasma generator external to the cell.

10. The method of claim 1, further comprising delivering plasma gas to the cell via a vacuum.

11. The method of claim 1 , further comprising delivering plasma gas to the cell at atmospheric pressure.

12. The method of claim 1, further comprising recycling a portion of the plasma gas for reuse in the method.

13. The method of claim 12, further comprising incorporating the vent stream or purge stream into a gas recycle system.

14. The method according to claim 1, wherein the rate of supplying plasma gas to the electrolyte is 0.2 liters / hour to 2 liters / hour per liter of electrolyte.

15. The method of claim 1, wherein the anode of the cell comprises at least one of: a) stainless steel; b) carbon steel; and c) Titanium-containing alloys.

16. The method of claim 1, wherein the cell does not contain a solid anode. The method of claim 16 , wherein the anode comprises a gas.

18. The method of claim 17, wherein the gas comprises hydrogen.

19. The method of claim 1, wherein the cell is an undivided cell.

20. The method according to claim 1, further comprising: a) recovering the electrolyzed liquid from the cell; as well as b) separating the adiponitrile-containing organic phase from the recovered electrolyzed liquid.

21. The method according to claim 20, further comprising: a) separating the aqueous phase from the recovered electrolyzed liquid; as well as b) recycling at least a portion of the aqueous phase as electrolyte supplied to the cell.

Images