Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2001-12-13
2004-09-07
King, Roy (Department: 1742)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
Reexamination Certificate
active
06787009
ABSTRACT:
The present invention relates to an electrolysis cell consisting of 2 monopolar electrodes and one or more intermediate bipolar electrodes, where
the one monopolar electrode and the parts of the bipolar electrodes charged in the same sense thereto together form the working electrode and the other monopolar electrode and the parts of the bipolar electrodes charged in the same sense thereto together form the counter electrode
the space between counter and working electrode is undivided
the surface of the counter electrode consists of electrochemically active and inactive parts
the sum of the electrochemically active parts of the surface of the counter electrode is smaller by a large amount than that of the electrochemically active parts of the surface of the working electrode.
The invention furthermore relates to processes for the preparation of organic and inorganic compounds using the abovementioned electrolysis cells, in particular the preparation of di(C
1
- to C
6
-alkyl) azodicarboxylates.
Electrolysis cells are employed in modern chemistry in a variety of shapes for a multiplicity of tasks. A general survey on the possibilities of construction of electrolysis cells is found, for example in D. Pletcher, F. Walsh, Industrial Electrochemistry, 2nd Edition, 1990, London 60 ff. The article by D. Degner, Topics in Current Chemistry, 148, 1 ff, 1988 offers a general survey on industrial, electrochemical processes. A frequently used and also industrially employed form of electrolysis cells is the stacked plate cell or capillary gap cell (cf. Ullmann's Encyclopedia of Industrial Chemistry, sixth Edition, 2000 Electronic Release, Chapter 5.4.3.2. “Cell Design”). Frequently, in the arrangement of the capillary gap cell, the electrodes and corresponding separating elements are arranged like a filter press and separated by spacer media such as spacers or diaphragms. A so-called undivided cell usually comprises only one electrolyte phase, a divided cell has two or more phases of this type. As a rule, the phases adjacent to the electrodes are liquid. However, ‘solid electrolytes’ such as ion exchange membranes can also be employed as electrolyte phases. If the electrode here is applied directly to the ion exchange membrane, e.g. in the form of an electrocatalytic and finely porous layer, contacts are additionally necessary which, on the one hand, have to be designed as current collectors, on the other hand as substance transport promoters. The individual electrodes can be connected in parallel (monopolar) or in series (bipolar).
In order to achieve a substance turnover in the electrolyte cells which is as high as possible, according to general teaching the electrolyte should be guided onto the electrodes in such a way that an optimum substance transport is achieved. In the case of liquid electrolytes, it is frequently proposed to allow the electrolyte liquid to flow parallel to the electrodes.
The space-time yield and the selectivity of the electrolysis also depend, besides the flow towards the electrodes, on the electrode materials used. These influence the durability, size and weight of the cell substantially.
In known stacked plate cells, the electrodes are mainly employed as massive plates, e.g. graphite disks.
These are also especially employed in the abovementioned industrial processes, such as in the synthesis of anisaldehyde dimethyl acetal in DE 2 848 397, tolylaldehyde dimethyl acetal in EP 129795 or for the preparation of &agr;-hydroxymethyl ketals as described in EP 0460451.
Electrodes of this type have various disadvantages, which result from the massiveness of the material, e.g. the surface area, which is reduced compared with a porous material, and the decreased substance turnover accompanying it, which makes itself noticeable in lower current yields, higher weight and a greater space requirement. Furthermore, as a result of the bipolar switching of the massive electrodes, the anode corresponds in size to the area of the cathode.
In these cases, so-called three-dimensional electrodes offer a possibility of increasing the substance transport and thus a possibility of increasing the current yield.
Attempts at the optimization of the surface ratios are described, for example, in DE 19533773; a felt anode of large surface area was combined here with a flat cathode. In this case, electrodes differ in their surface area in that in the case of the counter electrode only the surface turned toward the electrolyte acts as an active surface, while the working electrode of the electrolyte can be flowed through. From the surface weights supplied by the manufacturers, surface ratios of working electrode to counter electrode of 1.2 to 2.4 can be calculated for the felts employed.
Montiel et al. (Ind. Eng. Chem. Res. 1998, 37 (11), 4501-11) likewise describe the use of graphite felts in a filter press in order to enlarge the surface area of the working electrode.
Often, however, it can occur that the anode space and cathode space have to be separated; this is preferably the case if chemical side reactions or back reactions are to be excluded or if subsequent substance separations are to be simplified. This can furthermore be the case if a substance is both readily oxidizable and reducible, so that an ‘electron shuttle process’ is present. If no separation of anode and cathode space is performed, the amount of charge used increases and undesired side reactions may occur.
An example of an reaction which, because of side reactions/back reactions, hitherto had to be run in a divided cell is the oxidation described, for example, in FR 02043109 (DT 2016764) of hydrazodicarboxylic acid amides or hydrazodicarboxylic acid esters to the corresponding azo compounds. The separation of the electrolysis circulations is achieved here by a diaphragm or a membrane.
In this case, as a rule, divided cells are used. A plane-parallel electrode arrangement or candle-shaped electrodes are frequently used here. As the separation medium, ion exchange membranes, microporous membranes, diaphragms, filter fabric made of nonelectron-conducting materials, glass frits and also porous ceramics may be employed. The construction of such cells, however, is relatively complicated. Ion exchange membranes, in particular cation exchange membranes, are furthermore used, preferably those which consist of a copolymer of tetrafluoroethylene and a perfluorinated monomer which contains sulfo groups. These conductive membranes are commercially obtainable under the trade names Nafion® (E. T. DuPont de Nemours and Company) and Gore Select® (W. L. Gore & Associates, Inc.).
The use of these membranes often comes up against limiting factors as soon as operations are carried out in organic solvents. The membranes swell and are not suitable for further use in electrolysis.
As an alternative to the divided cells just described, ‘quasi-divided or pseudo-divided cells’ can also be employed here which hitherto were especially used on the laboratory scale. The principle which underlies this type of cell is that the working electrode has a markedly greater surface area than the corresponding counter electrode.
Investigations to this end were carried out, for example, by Hamzah and Kuhn (Chem.-Ing.-Tech. 52, (1980), 762-763). The influence of surface ratios of anode and cathode on the formation of hypochlorite from chloride was determined, the surface ratios being varied from 0.76/1 to 1.8 to 1.
An electrolysis cell was described by E. Steckhan et al. Tetrahedron, 52, 1996, 9743-9754 in which a wire electrode is combined with a flat or three-dimensional electrode which can be flowed through, also in the form of a cylindrical arrangement.
In Electrochimica Acta 27, 1982, 263-268, Birkett et al. describe the use of a monopolar plate and frame cell, which has considerable area differences between anode and cathode. Birkett et al. achieved the area difference by spraying electrodes with lacquer and thus insulating the surface by means of a nonconductive layer. Alternatively to this, the surface area of a massive two-dimensional electrode was ma
Brudermüller Martin
Merk Claudia
Pütter Hermann
BASF - Aktiengesellschaft
King Roy
Oblon, Spviak, McClelland, Maier & Neustadt, P.C.
Wilkins, III Harry D.
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