DD250026A3 - ANODE FOR ELECTROLYTIC PROCESSES WITH GAS DEVELOPMENT - Google Patents

Abstract

The invention relates to a dimensionally stable anode made of valve metal, which is particularly suitable for the alkali chloride electrolysis. The specific electrical energy consumption can be significantly reduced in such processes, if the previously required electrolyte gap between the electrodes and separation system is as far as possible largely reduced. According to the invention, this is achieved by V-shaped arranged on the anode curved baffles and with the baffles corresponding openings in the anode.

Description

have and in each anode half of each anode segment, which is bounded by two baffles, at least one located on the outer edge of the anode lateral opening whose cross-section is matched to the necessary electrolyte and gas flow rate.

2. anode according to item 1, characterized in that baffles and anode are made in one piece.

3. Anode according to item 1, characterized in that the edges of the baffles are provided in the flow direction with a Anschrägwinkel y between 30 ° and 90 °.

For this 4 pages drawings

Field of application of the invention

The invention relates to an anode of valve metal for electrolytic processes with gas evolution, in particular a so-called dimensionally stable anode for use in the electrolysis of alkali metal chloride solutions and other salt solutions which are decomposed under electrolysis conditions. The invention is particularly useful in the recovery of chlorine by the diaphragm method. It is important that the anode is arranged vertically in the electrolyzer.

Characteristic of the known technical solutions

In electrolytic processes with gas evolution at the electrodes, dimensionally stable anodes are increasingly used. The geometric design of the most lattice-shaped, provided with electrolytically active surface coating anodes should cause as far as possible removal of the resulting gases from the electrode gap to keep the formation of electrically poorly conducting two-phase mixtures as low as possible.

A known anode (DE-AS 2059868) therefore has openings in the form of openings or slots which are distributed over the entire anode surface. To improve the gas discharge downwardly inclined guide or baffles are arranged above the openings and slots. The guide or baffles protrude from the anode plane and may have a curved cross-section.

For effective gas removal, however, a liquid phase flow in the electrolyte gap must be ensured in known structured anodes.

As a result, a relatively high proportion of gas phase occurs, especially in the upper third of the electrolyte gap.

However, the resulting voltage drop increases the electrical energy consumption per unit of quantity of final product produced. It has also been proposed an electrode with V-shaped baffles that ensures a gas discharge without liquid phase circulation in the vertical direction. However, the geometric shape of the baffles is not optimally chosen.

Object of the invention

The aim of the invention is to reduce the specific electrical energy consumption in electrolytic processes.

Explanation of the essence of the invention

The invention has for its object to make the anode so that the achieved by the elimination of the electrolyte gap effect of energy conservation is further enhanced by a suitable choice of the geometric shape of the inclined baffles.

This object is achieved in that the guide plates, which are arranged symmetrically to the vertical anode center line and to this with respect to their longitudinal axes at an angle α between 90 ° and 135 °, preferably about 110 °, V-shaped inclined in the perpendicular to the Anode-level vertical plane has a curvature according to the function

H (bi) = A- (e ^B ">' ^b ' - 1).

Mean

H - vertical coordinate with O <H <HS

HS - height of the baffle projected on the anode plane

b-i - horizontal coordinate with 0 <bi SbFi

b _F | - maximum distance anode surface diaphragm

B _O pt - Constant which is to be determined as a function of the gas phase fraction and current density in such a way that minimal cell voltage results

A - Form factor for adapting the e-function to the true geometric length LE of the baffle The value of the constant A is determined by the adaptation of the arc integral of the function H (bi) to the length LE of the baffle predetermined for manufacturing reasons (to be extracted from the plane in the case of manufacture) (Figure 2):

B _opt has been determined so that for given quantities LE, b _F i and at a given average current density! a minimum cell voltage results or the gas phase content in the electrolyte gap does not exceed a maximum permissible value of 0.7.

In FIG. 1, the determined values for B _opt are shown graphically. They relate to the reaction kinetic data of the electrodes and dimensions of the separation systems which are customary in the chloralkali electrolysis according to the diaphragm or membrane process.

Another essential feature of the invention is that in each anode half of each anode segment, which is bounded by two baffles, at least one located on the outer edge of the anode side opening, whose cross-section is matched to the necessary electrolyte and gas flow rate.

In particular embodiments of the invention baffles and anode are made in one piece and the edges of the baffles provided in the flow direction with a Anschrägwinkel γ between 30 ° and 90 °.

The anode according to the invention allows such an arrangement in the electrolyzer that the ends of the bent baffles touch the surface of the separation system, especially in the case of diaphragm and membrane cells. Contrary to conventional structured anodes, in the case of the electrode according to the invention a liquid phase flow is achieved from the sides through the slots formed by the machining.

Thus, while maintaining an optimal average electrode spacing of the continuous vertical electrolyte gap between the electrode and separation system for the circulation is obsolete, the resulting gas is completely transported behind the anode. This results in a minimum ohmic resistance. The electrode geometry according to the invention ensures a sufficient mechanical strength, which may still be increased by current distribution devices

embodiment

The invention will be explained below with reference to an embodiment. In the accompanying drawing show

1: diagram for determining B _opt ,

2: geometry of a guide plate with position to the separation system,

3: front view of the electrode,

Fig. 4: flow path at the electrode.

According to Fig. 2 are located on a base plate 1 made of pretreated titanium sheet, with the Stromleit- or. Stabilizing rails 2 is connected, 40 baffles 3, the V-shaped (herringbone) are bent out of the plane of the base plate. The height of the vertical baffle pieces is marked b. The counter electrode 5 is separated from the anode by the separation system 4 (diaphragm, membrane and the like)

 The following geometric sizes were realized:

a = 110 ° 'm y = 30 ° (according to FIG. 1) A = 4.86 ΊΟ "" ⁶ B opt = 2,800 m " ¹ LE = 0.025 m b _F1 = 0.003 m b = 0.005 m

At the given guide plate length LE of 25 mm results after processing of the coated baffles a resulting height HS of 21.6 mm. With this electrode, it is possible to achieve ² cell voltage values of 3.06 V (calculated for a representative subcell consisting of one DSA each, modified asbestos diaphragm and steel network cathode of technically relevant dimensions) for a mean current density T of 2500 nm.

Due to the geometry of the anode, the flow pattern shown in Figure 4 is achieved. The gas G developed at the top of the baffles (elements) flows behind the anode to form a two-phase mixture GF with the liquid F flowing in from the sides, at the bottom of the respective overlying baffle.

Claims (1)

An anode for electrolytic processes with gas evolution, which has distributed over the anode surface openings and protruding from the anode plane, downwardly inclined curved'Leitbleche, characterized in that the baffles (3) symmetrical to the vertical anode center line and to this with respect to their longitudinal axes an angle α between 90 ° and 135 °, preferably about 110 °, V-shaped inclined, in the vertical plane perpendicular to the anode plane, a curvature according to the function HKb ₁ ) = A- (e ^B ° "- ^bl - 1)