DD144427A1 - DEVICE FOR CARRYING OUT UNDER GAS DEVELOPMENT OF ELECTRO-CHEMICAL PROCESSES - Google Patents

Abstract

The invention has an apparatus for carrying out electro-chemical processes to the content, which minimizes the undesirable influence of gas evolution on the Sellenwiderstand and an adaptation of the flow behavior to the requirements of respective electrode process taking advantage of the promotional Effect of the gases formed allows. This is achieved by that the electrode space in single, by connecting lines Hydrodynamically coupled circulation systems of at least 1 m in height, which consists of vertical electrode channels as well as behind or in the electrode angecrdneten return flow channels formed above and / or above Overflow openings with the interposition of Gasabtrennzonen The different hydrodynamic Coupling allows the well-known fluidic To approximate reactor types and in conjunction with constructive variants for the design of the electrode and Return flow channels various anodic and cathodic processes perform.

Description

21-3 oil « - * -

Vorrichtun g ica to lektrochem the implementing under gas- wicklu ng expiring e he pro ze sse

Field of application of the invention

The invention relates to a novel device for carrying out anodic and / or cathodic processes which proceed under gas evolution, such as e.g. many organic electrosyntheses

 Characteristic of the known technical solutions

The effectiveness of an electrolysis process is determined to a large extent by the applied cell voltage »It is therefore anxious to keep the distance between the electrodes as small as possible. These requirements are met in particular by capillary gap cells with a minimum electrode spacing of about 0.1 mm (F.Beck and H. Guthke, Chemie-Ing.-Techn. Hj \ _, 9 ^ 3 (19-69)) arose when the electrolysis process at the same gases at öen electrodes develop (R _e Dworalc u H.Wendt, chemical engineer. "- techn. MS h7k)" They bother ate laminar flow of electrolyte in the electrolytic cell and in particular increase the electrical conductivity of the electrolyte , resulting% \ x an increase in the cell voltage ira compared to the "gas-free electrolyte.

Furthermore, the gas bubbles block a part of the electrode surface before they are detached. As a result, the current density at the effectively available Elektrodonflache, which leads to an increase in overvoltages leads. After all, bsi the! Mismatch of geometrical dimensions accounts for requirements of evacuation of the developed gases

to wear. In vertical electrolyzers, therefore, the thickness of the electrode space must be chosen to be greater, the greater the evolving amount of gas. This not only results in a further increase in the cell voltage with an increase in the amount of gas developed per charge quantity, the current density and the electrode height, but also a limitation of the cell height and thus the capacity of the electrolyzer achievable per unit area (K.Hertwig, Ch Tenner and R. Thiele, Chem.-Teehn 29 (1977) 513).

In order to eliminate or minimize these negative effects of gas evolution, for example, "efforts are made to separate the stream of the electrode space through which the stream flows from the cross section through which the removal of the gas takes place. For this one uses so-called ⁿ Vorgehängter electrodes ", which are perforated and on the back of which the evacuation of the arising gases takes place { F. Beck, electro-organic chemistry, academy publisher Berlin 197 * 0 · with it one achieves nevertheless low distances anode - cathode and / or electrode Diaphragm and a reduction in the proportion of gas phase in the actual electrolysis space, but not better separation of the gas bubbles from the electrode surface.As a result of uncontrolled backmixing also results in lower flow velocities along the electrode surface and thus unfavorable conditions for power transport

Another possibility is a forced circulation of the electrolyte through the cell with subsequently arranged degassing zone. As a result, the gas loading of the electrolyte in the stationary state can be arbitrarily reduced while increasing the flow velocities along the electrode surface. There are both good conditions for the separation of the gas bubbles from the Elektrodonoberfläche as well as for the mass transfer. However, such a forced circulation requires not only higher expenditure on equipment and an additional energy requirement (N.IbI, E.Adam, Chemie-Ing * Tecfcn «3ί7 (ΐ965) 573)> but also approximates that of a stationary stirred tank

a series of electrochemical processes lower yields.

The disadvantage of the additional expenses for the forced circulation can be avoided if the buoyancy of the developing gases in the sense of mammoth purapen principle is used for circulation. It has proved to be particularly advantageous if the Elektrolyseräurae divided into parallel flow channels v / ground, which are connected at the top and bottom by transverse channels with a return flow channel and at the upper end of a degassing zone © is arranged (eg, DD 995 ^ S) _e This backpack channel can be located both inside and outside the cell. In both cases, there are relatively long Verbindungskr.näle and large circulating liquid quantities in technical electrolysers there «The then present, sometimes confusing hydrodynamic conditions lead to additional pressure losses and thus to a reduction of usable for the circulation portion of the buoyancy of the gas-liquid mixture logo CNRS logo INIST If the return flow channel is arranged parallel to the flow channels within the cell, then part of the total area usable as the electrode surface is required, which has a diminishing effect on the achievable space-time yield.

It has also been proposed to arrange the Ruckströmkanal for circulation within or behind the electrodes, but is not supported by backmixing within the ElektrodenraxjTiies diö maximum possible circulating amount between return flow and Elektrodenr'aura. In DD 115 582 ribbed, but before the diaphragm continuous, gap-shaped electrolyte channels of 1.5 to 2mra width forming electrodes are used, which can be connected to an arranged behind, the entire width of the electrode occupying return flow. In the case of examples with and without a backflow channel (2.68 to 2.76 V), the specified low voltage difference is the electric characteristic in this case. Trolyte cycle via the return flow channel almost ineffective »

In addition, the circulation can be used by the promoting effect of the gases formed only in those processes in which the present complete RüClevermischung does not lead to yield reductions »

Object of the invention

The aim of the invention is a novel apparatus for carrying out catodic and / or anodic processes taking place under gas evolution, with eletrontrolgators having a low internal idenity, favorable mass transfer conditions and as compact a construction as possible, in which the unwanted influence of the gas blast minimizes and Strößiungsverhalten of the electrolyte is well adapted to the requirements of the electrode process to be performed, and a low specific electrical energy consumption and high space-time yields can be achieved.

Explanation of the invention of the invention

It is an object of the invention to construct circulation systems with a high circulation rate of the electrolyte by constructional measures, which are hydrodynamically coupled in different ways according to the requirements of the electrolysis process. A device for carrying out cathodic and / or anodic processes taking place under gas evolution proposed electrodes in which at one or both electrodes of the Elektrodenraua into individual, hydrodynamically coupled by connecting lines Uralaufsysterne of at least 1 ib height, which consists of vertical Elektrodenixkanälen 2 to 20 mm wide and 0.5 to 5 mm thickness and arranged behind or in the electrode, 1 to 10 mm thick return flow channels are formed, which are connected via bottom and top arranged overflow openings with the interposition of Gasabtrennzonen.

The geometric shape of the electrode channels can be rectangular or also have any other cross-sectional shapes. Preferably, such profilings are used, ie, a large xiirksanie electrode surface as uniform as possible

Stromdichteverteilung'ergeben. This is the case, for example, with trapezoidal or semicircular cross sections of the Elelctroden channels and the narrowest possible intermediate bridges. The cross-section of the Ruck tricikariä Ie must have at least twice the cross-section of the electrode channels. "At gap widths between 0.5 and 5 mra, the voltage drop j <b> after the gas evolution velocity, the material properties of the electrolyte and the electrode height will go through a pronounced minimum.

The stationary two-phase gap flow and the high rotational speeds) in which the stationary gas phase fraction in the electrolyte is low and the mass transfer to and from the electrode is favored, are fully formed only at electrode heights of at least 1 m. Particularly advantageous flow conditions result at heights of the channels at or above 2 ta. This makes it possible at the same time to accommodate large power capacities per base unit. "

Under these conditions according to the invention, it is possible to achieve high circulating speeds with minimal spacing of electrode diaphragms in divided cells or anode in undivided cells, whereby the stationary gas phase content in the electrolyte is kept low and the mass transfer to and from the electrode is favored.

FIGS. 1 and 2 show the schematic structure of such a circulation system in a single half-cell. FIG. 1 shows a longitudinal section through a single circulation system, FIG. 2 shows a cross-section in height of the center line. Therein, 1 represents the electrode carrier, in which the jerk streams 2 and the degassing zone 3 are incorporated. The separated gases leave the cell through the nozzle k. On the electrode support, the electrode 5 is located above and below the overflow openings 6 to the return flow channels. The electrolysis electrode channels 7 are bounded laterally by the sealing beams 8 or the spacer strips 10 on which the diaphragm 9 rests. 2, the position of the individual Ströjnungskanäle is visible to each other through the

Spacer strips 10 or · are separated from one another by ribs on the electrode carrier · The stub 11 is used to supply the electrolly. The discharge takes place at the upper end of the electrolyzer on the side opposite the inlet stub (not shown in the figure).

Di © can trötnkanälen inventive arrangement of parallel arranged electrolysis and jerk preferably in devices according to Fig. H and implement 5 which are constructed according to the filter press principle using plate-shaped electrodes "This allows combine simultaneously a plurality of individual elements to a compact electrolytic cell. However, the device according to the invention is by no means limited to filter press cells alone. For the structural design of the electrolysis and Rückströmkanäle a half-cell, the following possibilities arise, which are shown sehematiseh in Figure 3 (a-1): in which mean:

1 electrode carrier

2 spacer strips for backpack transmission channels

3 electrode

k Spacer strips for electrolysis channels 5 Diaphragm Design variants for the return flow channels:

Return flow channels integrated into $ <ε> η electrode body (FIG. 3, ac)

" Ruckströmkanäle incorporated in the electrode carrier made of electrically conductive or insulating material. (Fig. 3, d ~ f)

- Return flow channels integrated in the electrode carrier made of conductive or insulated material (Fig. 3 »g-i)

- Backflow channels, formed by spacer strips of non-conductive, flexible material between electrode carrier and electrode (Fig. 3 »Ö-l)

Constructive Varianton for the Slektrodenkanäleί

- Electrode channels, formed by spacer strips of flexible ^, non-conductive material between electrode and diaphragm (Fig. 3 »a, d _t g, j)

U Λ \ i

- Electrode channels, incorporated into the electrode (Fig. 3 b, ©, h, It)

- Electrode channels, formed by ribbed diaphragms (Fig. 3, o, f, i, 1)

The electrodes may consist of both compact materials and, in Forra, composite electrodes, e.g. from a valve metal with fully or partially activated surface can be used.

Both microporous flexible materials, for example PVC or ion-exchange membranes, for example of sulfonated polytetrafluoroethylene, can be used as diaphragms.

According to a further feature of the present invention, the hydrodynamic coupling of the individual circulation systems and thus the flow behavior is adapted to the electrodetection process by a corresponding arrangement of the connection channels according to one of the following variants:

- The electrolyte is supplied to the top and bottom by common connecting lines to «and discharged, so that all circulating systems are flowed through in parallel.

The electrolyte flows through all the circulation systems in succession via connection channels arranged alternately at the top and bottom between each two adjacent circulation systems.

- The electrolyte flows through each electrode channel successively by connecting the return channel of the preceding channel to the electrode channel of each subsequent cell line terminal.

- The circulation systems are summarized in groups of the electrolyte flows through successively, while they are flowed through in parallel within the groups.

In this case, the overflow openings or connecting lines between the circulation systems in the plane of the Rüclcströmkanäle, the electrodes or the Slektrodenkanäle or in multiple levels can be arranged.

The various types of flow electrochemical reactors that can be realized in conjunction with the illustrated

constructive variants, and the selection of suitable electrodes, materials, allow a wide range of applications of the present invention.

Example embodiments

By way of example, embodiments of the present invention will be described

Example 1

By indicated in Fig. 1 gas bubble development in the electrolyte flow channel and the consequent buoyancy of the electrolyte circulation is effected via the Überströmö'ffnungen and the RuckströmkanäIe. In a divided cell, such a half-cell shown in FIGS. 1 and 2 can be combined with another, constructed according to the invention or any other counter-electrode to form a complete electrolysis cell. In the case of undivided inlay, the counterelectrode is used instead of the diaphragm. When dimensioning the electrode and return flow channels according to the present invention, mean gas phase fractions of 0.1 to 0.2 and flow rates, based on the pure liquid phase, of 0.1 to 0, * lm / s achieved. It forms a two-phase Spaltströtsung with preferably small gas bubbles, which quickly detach from the electrode surface. Depending on the gap thickness, the voltage drop passes through a pronounced minimum, which adjusts depending on the gas evolution rate, the material properties of the electrolyte and the electrode height at gap thicknesses between 0.5 and 5 years »

Example 2

All individual circulation systeiae are connected above and below by common bus to each other, as shown schematically in Fig. K, Dsr circulation of the electrolyte in any one of the five parallel-connected circulating systems is illustrated by arrows "The meaning of the numerals is the same as in the description of Fig. 1 and 2 indicated »The electrolyte leaves the cell ara port 12,

_ Q <_ έ «9 B '% J?

The connection channels are arranged in the planes of the return flow channels and the electrode. There is almost complete backmixing within the cell (flow analogous to the stationary stirred tank). In the case of very wide cells, if the electrolyte is supplied on the one side at the bottom and exits on the diagonally opposite side, it can also come to overlay with a directed flow and thus a concentration gradient from the inlet to the exit point. This can be prevented by adequate dimensioning of the transverse channels or by arranging a common return flow channel for all electrolysis channels flowed through in parallel.

Example · ^

The individual circulating systems are flowed through alone or in groups successively by the electrolyte, while within the circulating systems approximately complete backmixing prevails (Ströraungsforra analogous to a stirred tank cascade). Thus, the possibility is given, any number of reaction stages successively turn su, without the maximum possible, caused by the evolution of gas fluid circulation needs to be limited within the individual circulation systems. In Fig. 5, such an arrangement, with an otherwise analogous structure as in Fig. H, shown.

The electrolyte is swished to the electrode channels 7 "the overflow openings 6 and the return flow channels. 2 circulated, as illustrated by arrows. Due to the large circulation speed in comparison with the dosing speed, almost complete backmixing is again achieved within the individual circulation systems. This circulating liquid flow is superimposed by the metered amount a much smaller, directed volume flow, the benefit over the entry (hidden in the picture) in the first Uralaufsystent and by the alternately arranged top and bottom, jo two circulation systems connecting Übgrströmöfftmngen 6 to the outlet nozzle 12th The separated gases are passed through the above the Fiüssigkeitsspiegels degassing zone 3 through the

, - ίο - ^ VS

Neck h dissipated. The meaning of the remaining digits is the same as in Fig. 1 _? 2 and k.

The overflow openings to the adjacent Uralaufsystemen are to be dimensioned in this variant so that backmixing between them is largely suppressed. The Umströraöffnungen arranged in Fig. 5, for example, in the plane of the electrode can also be arranged in the planes of the electrode channels or the »return flow channels. It is also possible to separate the overflow openings within a circulation system from the connecting channel between the individual circulating systems (different levels, different heights in the electrolyzer). In this case, a continuous channel connecting all circulation systems can also be arranged, if the backmixing is largely prevented by a dilution which is correctly adapted to the volume flow. A connection channel arranged at the bottom has the advantage that the cell can be completely emptied via the inlet connection. «

Finally, in the case of larger electrolyzers, it may be advantageous to connect circulating systems grouped in groups according to the equation given in FIG. 5, while the hydrodynamic coupling according to example 2 takes place within a group.

example H

A flow rate approached to the ideal flow tube is achieved when the individual Ural flow systems are successively flowed through at high electrolyte velocities without the possibility of backmix mixing between them. For this purpose, each return flow channel is connected to the electrode channel of the adjacent row , as shown schematically in FIGS. 6 to 8. Pig. 6 shows the plan view of a half cell (without diaphragm) with partially interrupted planes of the electrode channels or electrodes, FIG. 7 shows one. Sectional view at the level of the upper overflow openings and Fig. 8 is a sectional view Iu Höbe the center line. Boron at 11 incoming electrolyte passes through the first © the overflow

into the first slektrodenkanal 7 and over the upper Überströ'm opening in the Ruckströmkanal, which is connected to the lower overflow opening to the adjacent Elektrodenieana1 »The electrolyte thus successively passes through all electrode channels and leaves the cell through the outlet nozzle 12. All Rückströmicanäle are above the liquid level through the Gasabtrennzone 3 connected »The separated gases exit through the neck k · The remaining numbers have the same meaning as in Fig. 1, 2, h and 5

In this variant, the number of electrode channels to be connected in series or the metered quantity can only be freely selected within a certain range. The metered amount is limited by the Volunienstrom, which can be transported due to the promotional effect of the developed amount of gas maximum. Otherwise, a Wiveaudifferenz between inlet and outlet side builds up, which would lead to a liquid transfer through the Gasabtrennzone _e By combination with Example 2, ie by connecting several parallel connected segments in series, this principle can be largely adapted to the respective electrode process.

28, SU IS / 8-oiM;

Claims (2)

Eyewear claim 1 «Device for carrying out gas evolution cathodic and / or anodic processes, marked by the fact that at one or both electrodes of the electrode space in individual, hydrodynamically coupled by connecting lines Uralauf systems of at least 1 m in height is uplifted, which from vertical electrode channels of 2 to 20 mm width and 0.5 to 5 mm thickness and behind or in the electrode arranged 1 to 10 mm thick return flow channels are formed, which are connected via bottom and / or top arranged overflow openings with the interposition of a Gasabtrennzone · 2 _e device according to item 1, characterized Geke nzzeichnet that the cross section of the Elektrodenkanälo is preferably rectangular, trapezoidal or semi-circular and the intermediate webs are kept narrow · H ₆ device according to the points 1 and % dadurc h indicates that the height of the circulation system is around or above Z m · ^ Device according to the points 1 to 3 draws characterized in that the return flow channels have at least twice the cross section of the electrode channels. Device according to the points 1. characterized by the fact that electrolysis cells constructed according to the principle of pressure-pressing are preferably used with plate-shaped electrodes. Device according to the points 1 to <characterized gek enn characterized in that the © return flow channels are integrated into the electrode body. Device according to points 1 to H characterized in that the return flow channels are incorporated in the electrode support of electrically conductive or insulating material. Device according to the points 1 to t & characterized in that the Rüekströmlchanäle are formed by spacer strips of non-conductive, flexible material. Device according to points 1 to B characterized in that the electrode channels are formed by spacer strips of flexible, non-conductive material between the electrode and diaphragm or electrodes and counter electrode. Devices according to points 1 to f | , characterized gekenn ze ichnet that the electrode channels are incorporated into the electrode. Device according to the points 1 · to ά dad urch characterized in that the Elaktrodenkanäle have been formed by using ribbed diaphragms. Device according to items 1 to 41, characterized gekonn te I net, that plate-shaped fixed electrodes are used made of compact material. Device according to the points 1 to 4 $ S skilfully characterized in that composite electrodes are used from a valve metal with fully or partially activated surface. Device according to Ptmkten I.bis 4 #, dadu rch gek ennzeichnet that in divided cells diaphragms of microporous flexible materials, eg «made of polyvinyl chloride, are used. Device according to the points 1.bis t% , dadur ch indicates that in split cells ion exchange membranes, eg made of polytetrafluoroethylene, are used. Device according to the points 1 · to 4t§, thereby ^ jekejina_ej_chn_ejb, that the hydrodynamic © coupling of the individual Umlaufsystetae by oban and below in the electrolysis cell arranged common connecting lines takes place in such a way that they are durchheflossen by the supplied electrolyte in parallel. Device according to points 1 to * IS, eichne gekennz characterized t that the hydrodynamic coupling of adjacent Uralaufsysteme is carried out by alternately up and down disposed in the electrolytic cell connecting lines in such a way that they flow through "ground sequentially" on the supplied electrolyte. Device according to the points 1, to τ? > characterized in that the hydrodynamic coupling of the individual Uni run systems erfogt by connecting dos Rückströmkanals the previous with the electrode channel of the subsequent Zollenelernents and the electrolyte flows through all © electrode channels successively. Device according to point 1 to 4%, characterized marked et et, that the overflow openings or »connecting lines between the Uralaufsystemen in the plane of the Rückströiakanäle, the electrodes or the electrode channels or are arranged in multiple levels * Device according to point 1. to Ίϋί ', dadu rch geken nze_ichn © _t that the circulation systems are summarized in groups and the electrolyte flows through succession -werden, while the circulation systems are flowed through within a group in parallel. Device 1 to Jl-O "dad urch marked ζeichnejfc that a common Ruckströmkanal is arranged to point in parallel flow-through electrode channels.