Electrolytic hydrodimerization of olefinic compounds

Beginning of the patent period: June 15, 1970,

In the hydrodimerization of olefinic nitriles, esters and / or carboxamides by passing electric current through an aqueous, olefinic nitrile, ester and / or carboxamide-containing catholyte separated from an aqueous, acidic anolyte by a solid, cation-permeable membrane, is The rate of membrane wear is unexpectedly low and the leakage of anolyte and catholyte components through the membrane is inhibited, if the cation-permeable membrane is an electrically conductive polymeric structure which is used by at least two substantially parallel surfaces formed by woven glass cloth embedded in the structure.

It is known that unsaturated compounds such as olefinic nitriles, esters and carboxamides can be hydrodimerized in an electrolytic cell having a cathode compartment and an anode compartment separated by a solid, cation-permeable membrane. Usually, an aqueous solution containing at least one the nitrile, the ester and / or the carboxamides and an electrolytic salt (for example a quaternary ammonium salt or an amine salt) are circulated through the cathode compartment of the cell while an aqueous solution of a strong acid (usually a mineral acid such as sulfuric acid) is circulated through the anode compartment. When passing electric current through the solutions and through the intervening membrane, hydrogen ions from the anolyte pass through the membrane into the cathode compartment and, using these water-containing substances, the nitriles, esters and / or carboxamides are dimerized in an electrolytic reaction at the cathode. General conditions under which electrolysis can be suitably carried out are described in U.S. Pat. Nos. 3,193,476, 3,193,481 and (with particular reference to the electrolytic hydrodimerization of acrylonitrile to adiponitrile) No. 3,193,480. The disclosures of these patents are referenced in connection with the invention.

One of the major problems in carrying out electrohydrodimerization in a technical process has been the development of a cell division membrane which satisfies satisfactorily the required ion exchange function for a reasonably long and predictable life. This problem has been complicated by the unusually high stresses to which the membrane is subjected. For example, the process will usually be at current densities up to one hundred times greater than those used in conventional electrolytic processes such as desalination and for optimum results at a significant pressure differential (0.703 to 1.053 kg / cm²The cell is also normally operated at high anolyte and catholyte flow rates, which can result in vibration of the membrane at elevated temperatures (up to 60 ° C) and at low pj [levels very different on the opposite sides of the cell

No. 287670, driven.

Conventional ion exchange membranes, which are thick enough to withstand the stresses encountered in the process, usually have impractically high resistance to the required current flow. On the other hand, thinner membranes tend to wear rapidly under such conditions, with cracks and cracks, and eventually the membrane becomes permeable, after which the anolyte is contaminated inversely by components of the catholyte or r. The problems caused by such impurities (eg Complication of the purification of the hydrodimerization product, anode corrosion by olefinic compounds from the catholyte, difficulty in controlling potassium concentrations and despj value after leaching of aqueous acid from the anolyte, etc.), become so severe in a short time that they involve costly sanitizing and catholyte clearing and service stoppages require for the purpose of membrane exchange.

Various reinforcing materials for membranes have been tested with the intention of improving the length and consistency of the life of the membrane and the contamination of the membranes

To reduce anolyte and catholyte without significantly affecting the effectiveness of the process. For example, without significant success, membranes containing a nonwoven cloth embedded in a polymeric structure have been tried (described in U.S. Patent No. 3,356,607). Likewise, the use of a variety of thin, non-reinforced membranes did not significantly improve the length and reproducibility of the service life of the membranes.

Due to the lack of a satisfactory substitute for the conventional types of polymeric ion exchange membrane materials, there is a significant demand for a useful type of reinforced membrane and it is an object of the invention to provide an electrohydrodimerization process utilizing such a reinforced membrane.

It would be found that the above-mentioned electrohydrodimerization process can be carried out with a significantly longer and more consistent average service life of the membrane and with a much lower degree of anolyte and catholyte contamination, if the membrane is made of a solid, electrically conductive, cation-permeable polymer comprising at least two reinforced substantially parallel glass fiber fabric, which are embedded in the structure.

The invention will be further explained with reference to the drawings in which Fig. 1 is a perspective view of a rectangular piece of ion exchange membrane in which the polymeric structure has been partially broken away to show the plurality of glass cloth layers embedded therein; electrolytic cell arrangement in which the method according to the invention using a membrane according to FIG. 1 3 is a graph showing the durability of the conventional membranes recommended in the method of the present invention as compared to other conventional membranes recommended for similar uses, in which the water leakage rate of each membrane is shown as a function the time during which it was in Elektrohydrodimerisationsverfahren in use, is applied.

As shown in Figure 1, the membrane -3- consists of a solid, substantially uniform thickness, ion exchange polymeric material which has been partially broken away to reveal the upper layer -4- and the upper layer -5- of woven glass cloth. The polymeric material may be of any composition which permits a suitable rate of permeation of the cations (e.g., hydrogen ions) from the anolyte to the catholyte of the electrohydrodimerization cell. Various polymeric materials having the desired general properties and methods for their preparation are described in U.S. Pat. No. 2,731,411. A composition preferably for use as a membrane structure in the method according to the invention can be prepared by reacting a mixture of compounds containing at least about 20 mol% and preferably about 30 to about 80 mol% of one or more polyvinylaromatic compounds (for example divinylbenzenes, divinylnaphthalenes, divinyldiphenyls, alkyl-substituted derivatives thereof, etc.) and at least 80 mol% of other monovinyl compounds, which copolymerize with the polyvinyl aromatic compounds (for example, styrene, vinylnaphthalenes, alkyl-substituted derivatives thereof, etc.) while preventing the mixture in a suitable inert solvent (for example, an aromatic hydrocarbon such as diethylbenzene) under conditions which preferably prevent evaporation of the solvent. polymerized. The polymerization can with the aid of any of the known aids, such as Pressure, heat (for example 3

No. 28,76570, 50 to 100 ° C) and / or a catalytic accelerator, such as benzoyl peroxide, and is continued until an insoluble, infusible gel is formed throughout the solution. The resulting gel structure is then sulfonated in the solvated state, preferably to the extent that not more than about 4 equivalents of sulfonic acid groups are formed for each mole of polyvinyl aromatic compound in polymer and not less than about 1 equivalent of sulfonic acid groups per 10 moles of vinyl aromatic compound in polymer ,

In the production of a membrane of the type shown in Fig. 1, the above-described preparation of the polymeric structure in an appropriate manner then takes place after the glass cloth surfaces -4 and 5- were arranged in the appropriate position in the mixture consisting of polymerizable compounds and solvents. The fabric surfaces -4 and 5- have the visibly open structures (preferably, but not necessarily, 50 to 75% of the total fabric area) characteristic of woven fabrics, and are woven from glass fibers, which are preferably staple fibers, but may alternatively be made from staple fibers continuous threads can be made. Fabric weave and fabric weight can vary widely, for example

Fiber weave 21 X 14 and the weight 169, 5 to 509 g / m², The choice of the respective glass fiber depends on the desired properties of the membrane. The fiber orientation in the fabric surface may be parallel or oblique and, if greater stiffness is desired, the threads of adjacent fabric surfaces may be quilted together prior to polymerisation of the fabric.

According to a particularly preferred method for the preparation of the membrane is a woven

Glass cloth, 9 ounces, 21 x 14, to give better adhesion between glass and polymer with a size (for example the mixture of methacrylic acid and chromium chloride known as Volan) and then coated in surfaces of suitable dimensions for the intended purpose (e.g. , 5 x 101.6 cm for a Elektrohydrodimerisationszelle preferred size) cut. At least two of these sheets of sized glass cloth are placed horizontally on top of a glass plate in a polymerization kettle, whose horizontal dimensions are slightly larger than those of the cloth surfaces, after which the threads of adjacent cloth surfaces can be sewn or quilted. Then a second glass plate is placed on the glass cloths and the stack consisting of glass plates and glass cloths is covered with a mixture containing approximately equal amounts of polymerizable compounds and solvents and a catalytically effective amount of a polymerization catalyst of the type described above. The mixture is heated to a suitable polymerization temperature (preferably 80 to 90 ° C) and held at this temperature for several hours, after which the resulting, unbroken, gelatinous structure with the glass sheet surfaces embedded therein is removed from the glass plates. The polymerization solvent may then be removed by washing, although it is generally convenient to use it directly

5 by replacing a suitable sulfonating solvent (for example, a hydrocarbon such as heptane) by leaching the polymerized gel in such a solvent.

The gel is then selectively cation permeable by treating it with a suitable sulfonating agent such as sulfuric acid containing dissolved sulfur trioxide, for example at 50 to 60 ° C until the sulfonation of the aromatic nuclei in gel 40 has occurred to the extent described above The sulfonating agent and solvent are then preferably washed out of the gel by immersing it in water, whereby drying and possible jumping of the gel prior to installation in the cell is prevented. The removal of the solvent from the gel leaves a microporous structure in which the proportion of pore space determines the water transfer properties of the membrane during use in the cell 45. When the polymerization step is carried out with a mixture containing a solvent content in the aforementioned range, the resulting membrane normally has a porosity which permits the transfer of from about 20 to about 80 (generally 30 to 55) ml of water per Faraday through the membrane through current, as at a current density of 0.5 A per cm² in a cell with aqueous 0.5 M sulfuric acid was measured in both the Anolyt- and in the Katholyt50 compartment. For carrying out the process of the invention, a membrane reinforced by two or three sheets of glass preferably to be sufficiently stiff has a thickness of at least about 0.1 cm, but is usually not more than about 0.25 cm, thus undesirable brittleness , which occurs in membranes with too high a content of polymer is prevented.

Fig. 2 shows schematically a system in which a membrane of the type shown in Fig. 1 in the electrohydrodimerization of one or more olefinic nitriles, esters and / or Carb4

No. 287670 oxamide can be used. The system according to FIG. 2 has an anode wing -6- and a

Cathode wings -7- which are assembled and clamped under suitable pressure to one

Prevent liquid passage. The anode blade -6- has a plate-like anode -8- which is mounted on its right side, whereas on the left side of the cathode blade -7- is mounted in the same way a plate-like cathode -9-. The anode -8 and the cathode -9- may be made of any suitable electrode material, such as metals, such as lead or lead alloys. The ion exchange membrane-10 is tightly clamped between the edge parts of the anode wing -6 and cathode wing -7- and thus separates the space between the wings -6 and 7- in an anode compartment -11- and a cathode compartment -12-.

During operation, an aqueous anolyte containing an acid, such as sulfuric acid, is pumped through the anolyte pump -13- from a buffertank -14- into the anode compartment -11-, through which it contacts the anode -8 and membrane upwardly -10- flows and then flows back into the tank -14-. An aqueous catholyte containing olefinic nitrile, olefinic ester and / or olefinic carboxamide, and preferably an electrolytic salt (for example, a quaternary ammonium salt or an amine salt such as tetraalkylammonium alkyl sulfate or sulfonate) is likewise removed from the buffer tank -16- into the catholyte compartment by a catholyte pump. 12- pumped, through which it flows upwards through the space between the cathode and membrane -10- and then flows back into the tank -16-. When passing an electric current between the anode -8- and the cathode -9- via the anolyte, the membrane -10- and the catholyte, hydrogen ions pass from the anolyte through the membrane -10- in the catholyte, in which they are at the electrolytic Participate in the dimerization of the olefinic compound at the cathode -9-.

In technical operation, the cell is run continuously, the dimerization product being continuously withdrawn from the tank, oxygen and other gases being allowed to escape from the tank, and fresh acid and fresh olefinic feed being continuously fed to the tank. 16- be supplied. In such a technical operation, the risk of destruction of the membrane -10- (mainly on the cathode side) is particularly pronounced and therefore the need for a consistently durable membrane is particularly important, it has been shown that the resistance of a through a variety of fabrics woven glass cloth ver30 strengthened membrane is unexpectedly large. For example, under normal operating conditions, the life of such a membrane was usually two or more times greater than the average life of membranes with only one sheet of glass cloth equally embedded in a fabric of the same polymeric material. The invention will be further illustrated by the following examples without being limited thereto. Unless otherwise indicated, all 35 values ​​given in connection with the water transfer rate and the water leaching rate of the membranes in the examples refer to 100 cm² Membrane surface.

Example 1: Acrylonitrile was electrohydrodimerized continuously in a series of cells of a conversion plant to adiponitrile as described above, using in each cell an aqueous sulfuric acid as the anolyte, tetraethylammonium ethyl sulfate as the electrolytic salt in the catholyte, and an ion exchange membrane consisting of a solid structure of sulfonated divinylbenzene-styrene copolymer (0.106 cm thick) reinforced with two substantially parallel surfaces of woven glass cloth, 255 g, thread count 21 x 14, which had been embedded in the polymeric structure in the course of the above-described preparation of the membrane. The glass cloths were made to the staple fibers with parallel fiber orientation and the membranes had a porosity which allowed the passage of 32 ml of water from the anolyte to the catholyte per Faraday of electrical current sent through the membrane, such as at a current density of 0.5 A / cm²Membrane surface was measured in a cell with aqueous 0.5 M sulfuric acid in both the anolyte and in the catholyte compartment. The wear of the membrane was measured by measuring the rate of water permeability through each membrane at a hydrostatic pressure differential of 50 to 0.281 kg / cm² measured at the anolyte in the cell. After using the membrane for 2200 hours, the water permeation rate was about 0.2 ml / h / 100 cm² Membrane surface.

Example 2: When Example 1 was repeated except that the membranes were 0.14 cm thick and had a porosity permitting water passage of 42 ml of water per Faraday current, no leakage of water could be measured after 1500 hours of use of the membranes become.

Example 3: Repeating the procedure of Example 1 except that the

No. 28 7670

Membranes were 0.14 cm thick and had a porosity which the passage of 56 ml of water per

Faraday's current allowed, after a duration of use of 1400 h of the membranes, the water leakage rate was 0.2 ml / h.

Example 4; Using the procedure of Example 1 except that the membrane contained three pieces of the same woven glass cloth and had a thickness of 0.22 cm, and had a porosity which allowed the passage of 44 ml of water per Faraday stream after 1500 h of use of the membranes no leakage of

Water are measured.

Comparative Example A.

The procedure used in Example 1 was repeated except that two back-to-back membranes were used, each containing a patch of woven glass cloth and having a porosity permitting passage of 49 ml of water per Faraday stream in place the membrane was used with two glass cloth surfaces. The leakage rate of water was about 0.2 ml / h after 80 h, 1.8 ml / h after 575 h, 2 ml / h after 1030 h and 4 ml / h after

1600 h Useful life of the membranes.

Comparative Example B.

Repeating the procedure used in Example 1 except that each of the membranes contained only one sheet of woven glass cloth and had a thickness of 0.063 cm and a porosity permitting the passage of 29 ml of water / Faraday current, the average was Leakage rate of water about 2.7 ml / h after 350 h, 3 ml / h after 540 h and 5.2 ml / h after 824 h of use of the membranes.

Comparative Example C.

Repeating the procedure used in Example 1, except that each of the membranes contained only one sheet of woven glass cloth and had a thickness of 0.06 cm and had a porosity permitting the passage of 50 ml of water / Faraday current The average rate of leakage of water was about 1.8 ml / h after 820 h and 7.25 ml / h after 960 h of use of the membranes.

Comparative Example D.

Repeating the procedure used in Example 1, except that each of the 30 membranes contained only a patch of woven glass cloth and had a porosity permitting the passage of 63 ml of water / Faraday current, the transmittance rate of

Water about 2.5 ml / h after 550 h and 4.25 ml / h after 639 h of use of the membranes.

Comparative Example E.

Repeating the procedure used in Example 1 except that the membrane contained only a sheet of 567 g of woven glass cloth and had a thickness of 0.101 cm and a porosity permitting the passage of 50 ml of water / Faraday's current tore Membrane after 168 h of use.

Comparative Example F.

Repeating the procedure used in Example 1 except that each of the 40 membranes contained a sheet of woven teflon cloth sandwiched between two sheets of nonwoven polypropylene cloth and had a porosity permitting the passage of 38 ml of water / Faraday stream, the water leakage rate was about 1.9 ml / h after 525 h, 2.1 ml / h after 700 h, 2.8 ml / h after 1280 h and 4 ml / h after 1780 h of use of the membrane.

Comparative Example G,

Repeating the procedure of Example F except that the teflon blanket was replaced by a woven glass cloth patch and the membrane had a porosity permitting passage of 44 ml of water / Faraday current, the average water leakage rate was about zero , 4 ml / h after 525 h, 0.6 ml / h after 700 h, 1.2 ml / h after 1280 h,

2.8 ml / h after 2000 h and 3.7 ml / h after 2050 h of use of the membrane.

Comparative Example H.

Using the procedure employed in Example G except that the membranes had a porosity permitting 49 ml of water / Faraday flow, the average water leaching rate was approximately 1.0 ml / h after 700 h, 1, 6 ml / h after 860 h, 3.1 ml / h after 1020 h, 7.3 ml / h after 1240 h Use of the membrane.

The results of Examples 1 to 4 and Comparative Examples A to H are shown graphically in FIG. 3

No. 287670, which shows that the membranes containing at least two sheets of woven glass cloth lasted significantly longer in the process of the invention than ion exchange membranes with other reinforcements for use in similar processes. In particular, FIG. 3, that the leakage rate of the other membranes (for example, those with only a sheet of glass or Teflon fabric, with or without additional reinforcement by non-woven fabrics) during operation of the cell at a rate of at least seven times the Durchleckgeschwindigkeit of membranes, such as used in the process according to the invention increase.

Although the invention has been described with reference to particular embodiments, it will be obvious that many modifications and variations are possible without thereby exceeding the scope of the invention.