DE2338341B2 - Process for the production of adipic acid dinitrile - Google Patents

Description

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It has now been found that in a continuous Process for electrohydrodimerization

The invention relates to a method for producing _a5 of acrylonitrile to A ^ P '"» "^!" ^^ ¹ ^^ of adipic acid dinitrile by electrolysis of an acrylic suitable mixture of AcryIn.trilWas «» nitrile stream, which is produced by a non-divided electrolysis - the and catalyzing, salts / awake cell, which has a cathode and an anode, leads through electrodes through e.ne "^^" ί ^^, through periodic rinsing of the cathode and ^ \ ^άΐ

and the anode of the cell with a basic aqueous 30 the anode with insulating ^ g ^ Washing solution, which is a concentration of the basic, a smoother operation of a better compound in the range of about 1 to 20 weight lower voltage requirements and non-non-alcoholic can reach a considerable polarization.

The electrohydrodimerization (EHD) of acrylic by reacting an aqueous solution of a strong base nitrile to form adiponitrile has ₃₅ such as aqueous Ka humhydroxyd per.od.seh by d as shown economically attractive. Adipic acid cell leads to the deposits ν der ^ dinitril is a valuable precursor material for the removal and their surface again to re ^ nerem production of nylon fibers. The invention therefore relates to e, η method, / ur

In this method an aqueous electrolyte, producing Ad.p.nsaured.n.tn ^d "^ ^{h, E 'ektro1;} of a relatively large amount of a conductive inorganic, 0 a composite Acryln rilstrom, the ch du African salt. , like potassium phosphate, and a small non-divided electrolytic cell gefuh. ^ * ^ ^ amount of a catalytically active organic salt, a cathode and an anode ^a " ^fwe £;""f * ^e ! * ^e ™ like tetrabutylammonium phosphate, the supply of the acrylonitrile ^ rom is continuously interrupted under electrolysis conditions between two electrodes suitable for the cell and the node and cathode suitable electrodes are circulated. Acrylic with a basic aqueous washing solution is continuously added to this current, which is circulated in the cell for a period of time before about 5 to 30 μm, under such conditions that the basic compound becomes an emulsion in a concentration between the two electrodes from about 1 to 20 percent by weight of the forms. To the extent that the electrolysis takes place, contains solution and then the electrolysis starts again, a 50 is taken from the circulated emulsion.

small amount deducted. This material can be further embodiments objects and advantages

Settle, whereupon the organic phase, which the parts of the invention result from the following desires Contains adipic dinitrile product, for writing, the examples and the drawing. Isolation and recovery of adipic acid dinitrile In the drawing, the sequence of the invention

is deducted. The aqueous phase is then again 55 according to the method using the verzu added to the circulated emulsion. A turned device in a schematic manner darge feature of the method according to the invention consists. .

in that this is done using a non-dividing As can be seen from FIG

th cell is carried out, ie a cell which has no acrylonitrile charge material and the mitiialffl membrane or some other type of device added fresh water via the lines 10 or 1, which introduces the space between the electrodes into the line 12. Divided by the line U cathode compartment and an anode compartment. Flowing a guided circle emulsion that has in the use of such non-shared cell range of cells into one and ^{you "h} .. ^{d 'e} * ^s _{F |} j! ⁿ _t JL ^u ™ J the advantage of an uncomplicated structure and cell. The electrode contained in the cell a relatively low internal resistance of the cell 65 are generally arranged so that you ^wisclie ^ "-. Proceeds _vertically space between them, the emulsion

Although the operation of a non-divided cell is pre- ferred through this gap either from above In certain cases long-lasting, smooth downward or upward flow from antennas are external

Cell area 1 comprises one or more cells which are operated in dead conditions and which are suitable for the electrolytic conversion of acrylonitrile to adipic dinitrile. An aqueous solution of conductive inorganic salts, such as alkali metal phosphate salts, and a smaller amount of catalytically active tetraalkylene ammonium salts (TAA salts), such as tetrabutylammonium phosphate, flows through line 12. There are also organic products and by-products. The stream conveyed through line 12 is _{referred to below} as the "composite acrynitrile stream". ^R removed via line 13 w 'd of the cell region 1, an emulsified mixture that is passed through the filter 2 and introduced into the gas separator. 3 In this separator, gases, in particular oxygen, are discharged from the system via line 14. The essentially gas-free liquid stream is then introduced into the heating device 7 via the line 19 and then again into the cell area 1 via the line 12. The filter, the gas separator, the pumps, heating devices, filling openings etc. do not have to be arranged in the way they are shown in the diagram, but can also be in a different order.

The cell area 1 is operated under conditions that are: a temperature of 32.2 to 65.6 C, a pressure of atmospheric pressure or almost atmospheric pressure. a linear speed of the emulsion of 1.52 to 182.9 cm / sec, an emulsion with a content of organic materials of 2 to 12 percent by weight, based on the total liquid flow, suitable electrodes made of lead, a lead alloy, graphite, nickel, mercury , Platinum or the like, a current density of 5.38 to 43.6 Λ cm ² , a pH value of the emulsion of 6 to 12, a concentration of the inorganic conductive salts of 0.1 to 3n (normality), a concentration of Catalytic Salts (TAA) from 0.001 to 0.2N (normality), an aeryl nitrile conversion per throughput of up to 10 ',, and a total acrylonitrile conversion of biv 11 90/0.

[ ι a small part of the stream passed through the line! ·) is withdrawn according to the desired acrylonitrile conversion and transferred via line 15 to the cooling zone 4, in which this part of the emulsion is cooled to a temperature using a conventional cooling device , which is suitable for the separation of the emulsion into separate liquid phases. The cooled emulsion is then drawn off from the cooling zone 4 via the line 16 and transferred to the separation column 5. Any suitable device or combination of devices capable of separating an emulsified stream into organic and inorganic layers can be employed as the separation column of this type. The lower aqueous phase is withdrawn from the separation column 5 via line 18 and added again to the material flowing in the circuit in line 19. The organic phase is drawn off from the separation column 5 via the line 20 and transferred to the isolation zone 6.

The isolation zone 6 can generally have more than one separation unit, such as a series of fractionation devices for the separation, isolation and recovery of the products and the organic by-products, have and is usually also structured in this way. In addition to the distillation devices Other devices such as extraction units and absorption units can also be used will.

The adipic dinitrile product is over the line 21 withdrawn from the isolation zone 6, while the other organic by-products, such as propiononitrile and the like, can be removed from the isolation zone 6 via the line 22. The unconverted Acrylonitrile is discharged from the isolation zone via line 23 and is carried along in line 19 the circulated emulsion combined. Similarly, recirculated water and both organic and inorganic salts are withdrawn from isolation zone 6 via line 24 and combined again with the emulsion circulated in line 19. The united in line 19 Materials are supplied with fresh acrylonitrile via line 19 and with fresh acrylonitrile via line 11 Fresh water and fresh salts are added to form a mixture, which is via line 12 and the heating device 7, in which the mixture is heated to the desired cell temperature, in the Cell area 1 introduced.

At periodic time intervals, e.g. B. when necessary to maintain a given cell current Cell voltage increases by about 0.5 volts above the normally applied voltage, the The conveyance of the emulsion through the cell area 1 is interrupted, whereupon the cell is emptied and valves 25 and 26 are closed. Then valves 27 and 28 are opened, whereupon one contained in zone 8 Washing solution is conveyed with the aid of the pump 29 through the cell area 1 in the circuit. the Washing solution flows from the storage zone 8 via the line 30 into the cell area 1 and is via the line 31 returned to the storage zone 8. The circulating washing solution is enriched with it solid particulate material from cell area 1. This solid particulate material is discharged from zone 8 either continuously or intermittently via line 32. About the In line 33, the solution storage zone 8 is charged with fresh aqueous basic solution.

In the method of the invention, any cell and electrode configuration that includes a continuous guidance of a liquid flow between electrodes can be applied. the Cell can be made of any suitable material compatible with the electrolyte and that is not attacked or under the operating conditions normally used in the cell is corroded or only slightly corroded.

Preferred cathode materials are materials with a relatively high hydrogen overvoltage, d. H. with a hydrogen overvoltage greater than that of copper. Examples of materials of this Types include lead, graphite, nickel, silver, gold, lead alloys and the like.

Examples of materials suitable for making the anode include lead, lead alloys, Platinum, gold, nickel, iron and the like

Materials containing lead, such as metallic lead, lead alloys or lead dioxide, are used to manufacture the anode, preferred. Similarly, lead or lead alloys are also used to make the cathode preferred.

At periodic intervals or when the cell voltage is about 0.5 volts or more above the normal

Mal voltage has risen, the cell and the electrodes according to the invention with an aqueous base flushed. In general, the electrohydrodimerization process is used interrupted at intervals of only 10 to 100 hours, usually 20 to 50 hours.

Flushing is done simply by temporarily interrupting the flow of the emulsion through the cell and replacing this material with a stream of aqueous base. The circulation of the aqueous basic Irrigation solution through the cell is carried out for a time sufficient to remove the surface of the Restore the anode and again allow operation at an effective low voltage. Usually this can be achieved if the aqueous base for about 1 to 60, preferably 5 to 30 minutes through the device.

The temperature at which the electrodes are contacted with the aqueous base can be vary over a wide range extending from the freezing point to the boiling point of the solution. In general, treatment at room temperature is satisfactory. In the case of lead dioxide anodes are however, temperatures of greater than 65.6 ° C. are generally required. The speed at which Material is passed in a circle can also be varied considerably. A linear speed through the cell in the range of 1.52 to 182.9 cm / sec is desirable during operation, with the lower Values in this range are preferred.

The basic washing solution used in the method according to the invention is a solution of a strong base, which has considerable solubility in water. Thus, according to the invention, preferably Alkali metal hydroxides are used, although organic bases such as tetramethylammonium hydroxide are also used can be applied if desired. To avoid unwanted contamination the electrohydrodimerization process with foreign cations is preferably used as Base a base whose cations are already contained in the process system. For example, one uses Process in which a significant amount of potassium phosphates are used as circulating conductive salts a solution of potassium hydroxide can be used as the preferred aqueous base. The base can be in the aqueous washing solution in any concentration necessary for the renewal of the surface of the anode is effective, be included. In general, the concentration of the basic compound is in the solution at 1 to 20, preferably 5 to 15 percent by weight.

It is believed that the benefits of the invention result from the regular removal of itself on the anode forming deposits are brought about. For example, lead is a particularly active material for the electrohydrodimerization process. However, when using lead electrodes in systems, which contain salts, such as phosphates, and other organic reagents, will appear on the anode Deposit is formed which comprises a combination of lead, phosphorus and organic material. if the anode is brought into contact with the aqueous basic rinsing solution, the main amount, if does not remove all of the deposit while in a relatively manageable form. According to the invention, the corrosion of the electrodes, such as the corrosion of the lead anode, is not prevented, however, this corrosion is made easier to handle, so that the entire electrohydraulic humerization · Procedure is only marginally affected.

Since the solid particles of the corrosion products are carried away from the anode in this way and into the iir Circulating aqueous basic solution are introduced, it is generally desirable to have facilities provide with which these particles can be separated in a suitable manner. This can can be done in a simple manner that you yourself

ίο solids accumulating in the solution of the aqueous base The aqueous base is filtered off or periodically a solid slurry is removed from the storage tank withdraws.

After the appropriate solution of the aqueous base for a sufficient time to the surfaces to regenerate the electrode has been circulated, the rinsing operation is interrupted and the Circulation of the emulsion mixture through the cell and across the electrodes resumed.

if so desired, the scavenging gear can be carried out without interrupting the flow of current. In this case, a certain amount of hydrogen is used during of the flushing operation, but this is in comparison to the time-consuming switching off and on again the strong currents can be neglected.

The following example is intended to explain the invention further without, however, restricting it.

3 «Example

Using similar devices and procedural measures as shown schematically in the 1, acrylonitrile was continuously converted into adipic dinitrile over 202.7 hours, whereupon the approach was deliberately interrupted. The aqueous part of the circulated Emulsion consisted of a solution of potassium phosphates with a concentration of potassium ions of

+ o l, 5n that with orthophosphoric acid to a pH from 7.5 to 7.7 was neutralized. In the state of equilibrium, this aqueous stream is in the form of a Emulsion with acrylonitrile and other organic products. The total content of organic Materials based on total emulsion was 4 to 5 percent by weight. There were also in the emulsion about 0.1 weight percent tetrabutylammonium ions are present.

The system was continuous in a similar manner

5 "operated as shown in FIG. 1, but with off the isolation zone 6 neither acrylonitrile nor water or salts were returned to the process. After 24 to 36 hour intervals, the cell voltage increased from the nominal value of 4.2 volts to a value of about 4.7 volts. At that point it was the flow and circulation of the emulsion through the cell was stopped and it became a 10 weight percent aqueous solution of potassium hydroxide for 10 to 15 minutes at room temperature through the

Cell led. After this rinsing time, the cell was freed from the rinsing solution, whereupon the current turned on again and the circulation of the reaction emulsion through the cell at normal Operating temperature from 48.9 to 50.0 Γ resumed.

⁶ were taken.

Further reaction conditions are shown in the following table as well as the results of this approach summarized.

Tabel

Duration of the approach 202.7 hours

Electrodes 99.9% lead

Size 10.16 x 91.4 x 0.317 cm

Distance 0.317 cm

Voltage of the cell

4.7 volts before flushing

after flushing 4.2 volts

Amperage 200 A, 21.53 A / cm ²

Emulsion temperature 48.9 to 50.0'C

(Cell)

Temperature of the separation column. 10.0 to 12.8 ° C

Acrylonitrile feed rate. .0,500 kg / h

Emulsion flow rate

to the cell 17.69 kg / min

to the separating column 24.95 kg / h

speed

through the gap 91.4 cm / sec

Acrylonitrile conversion
per run

through the cell about 2%

total 77.9%

Material balance 98.3%

Yield of adiponitrile. 89.5 kg / 100 kg

converted acrylonitrile

Efficiency looks !. Adiponitrile

chemically 87.7% (related

on acrylonitrile)

electrical 86.5%

Required DC energy (average) 2.53 kWh / kg

Adipic acid dinitrile

Lead loss 0.0067 kg / kg

Adipic acid dinitrile product stream

Adipic acid dinitrile 0.664 weight percent fraction

Acrylonitrile 0.210 weight percent fraction

In the following table is the composition of a typical organic process effluent, the after the last 24 hour period has been obtained:

Weight percent

Water 4.23

Acrylonitrile 19.88

Propiononitrile 2.41

Succinic nitrile 0.69

Tetrabutylammonium ions 0.69

Adipic acid dinitrile 67.78

Bis (2-cyanoethyl) ether 0.17

Hydrotrimer of acrylonitrile I 3.69

ίο hydrotrimers of acrylonitrile II 0.28

Methyl glutaric acid nitrile 0.24

unknown materials 0.04

The results of this approach, carried out over a relatively long period of time, show that the Cell and electrode rinsing method according to the invention long lasting, smooth operating times at relatively constant and low voltage, with no polarizations and other operational interruptions occur and with a high degree of efficiency with regard to the desired products results.

In similar comparative approaches that were carried out without the rinsing treatment according to the invention, it was found that the cell voltage increased slowly, so that after a few days of operation it was necessary to maintain it the voltage required for the desired current density is the capacity of the energy supply and the cell polarized. Here, a periodic dismantling of the cell was necessary in order to remove the anode and physically clean it to restore an effective conductive surface. According to the method of the invention, this requirement is relatively frequent disassembly no longer given to the cell.

In addition to the approaches of the electrohydrodimerization process, where lead anodes were used, equally successful approaches have been used under similar conditions carried out by cells that had a lead cathode and a lead dioxide anode. At intervals from 22 to 58 hours the cell was at a temperature of 82.2 C with a 10 weight percent Potassium hydroxide solution rinsed. The periodic rinsing prevented one polarization and one Maintain a relatively low average cell voltage.

1 sheet of drawings

Claims (1)

to achieve ongoing, continuous and economic comparison, as the pro- S vd ih B ^ * r i_, - ,, ",.". "crhwierie to achieve, since the pro- Claim: AAS Ovation of the organic Process for the production of adipic acid charge material «^ {Ι ^^ ΑΑ “Itril by electrolysis of a compound ₅ Jm yielded sc ^ ^ '~ ^ß J _{if z B dl} f _e Acrylonitrile stream. that by a not-edged ^pro ^ ^ra _R S _t f; £ ° ^ / wipe two lead electric Electrolysis cell, which has a cathode and an anode suitable R ^ ^1IO " ^S ™ * JJ * _ird , _{are the} conditions has, flows, thereby ^{gekennze.ch- de η <m ™ on} sand lun ^ n and selectivities net, that one periodically the supply of the high Umwanaiu g; Acry.nitri.current to the cell interrupts a _lo j ^^ SffiÄ ^ Ä Rinsing flow, which consists of a basic aqueous lo- in the area of the α ιεικαιu considerable corrosion sing that the basic compound in a Concentration ₌ - -jch to a ^ «^^ SSn tration in the range from 1 to 20 percent by weight and deposition ^ b '«" "« aui contains, persists, for a period of about 5 to Furthermore, the cortex is on the anode m t 30 minutes in contact with the cathode and the ₁₅ losses associated with it because « Pass the anode through the cell, and then the E.ektro- ^ «^» J ^ SeTC ^ trrX lyse w, eder takes up. causes ^ j ^^ _{the products of} corrosion and or tend to oxidize to a certain extent , “To increase the internal resistance of the cells. as a result of which unnecessarily high cell voltages are required