DE2162487A1 - Chlorine prepn - by electrolysis of hydrochloric acid and polyvalent metal chlorides - Google Patents

Abstract

An electrolysis cell, divided into an anolyte and catholyte compartment by a diaphragm, has an anolyte of HCl and a catholyte of a polyvalent metal chloride, and is operated at 1A/sq. in current density. Chlorine is generated in the anolyte compartment, removed with the anolyte stream and sepd., the depleted anolyte being replenished with HCl and recycled. Simultaneously the polyvalent metal chloride is reduced in the catholyte compartment, then contacted externally with an oxidising atmosphere to reoxidise the metal sufficiently to achieve >90% current efficiency. Spec., the anolyte is 3-8 M HCl, the catholyte 0.5-2.0 M copper chloride and the oxidant is air. High purity Cl2 (>99.7% purity) is produced.

Description

Process for the production of chlorine by electrolysis of u hydrogen chloride and polyvalent metal chlorides.

The present invention relates to a dual electrolyte system under Use of an electrolytic diaphragm cell.

A well-known process for the production of chlorine by electrolysis of hydrogen chloride uses a polyvalent metal chloride in the electrolyte solution. For example, U.S. Patent No. 2,468,766 (Low, May 3, 1949) describes an electrolysis process described, with electrolyte-containing hydrogen chloride and a polyvalent metal chloride (e.g. CuCl2) in the space between the anode and cathode of a cell without a diaphragm is introduced; this releases chlorine at the anode. and the polyvalent metal chloride is reduced at the cathode. Then the electrolyte passes through the porous cathode withdrawn and reoxidized the polyvalent metal chloride with air and hydrogen chloride, so that it can be returned to the cycle. Through this procedure is the one usually required for the direct electrolysis of chlorine-hydrogen Cell tension decreased. however, the efficiency of the electricity suffers because of the System inherent flow properties, which are a reverse reaction of the dissolved Allow chlorine and the low-grade state of metal chloride.

In the German patent 1,277,216 there is an electrolysis system described, attempting to use the electrolyte flow pattern of a diaphragm between anode and cathode. While maintaining a pressure difference of zero, the diaphragm reduces the reaction of the dissolved Chlorine (anode side) with the low-value metal chloride (cathode side). Through this Although the efficiency of the current is increased, the method has disadvantages. In this system there is a reoxidation of the polyvalent metal chloride within of the cathode part of the cell. Because reoxidation is the slowest reaction is in the cell, this limits the efficiency of the cell and its size. You also get only when using oxygen as an oxidizing agent Gas better results.

The present invention overcomes the above disadvantages by use a separate, double current flow of electrolytes, which hydrochloric acid and contain a reducible polyvalent metal chloride. The invention used An electrolyte cell has a diaphragm which divides the cell into an anode and Cathode space divides. Anolyte and catholyte are in the anode and cathode compartment, respectively initiated. Preferably the cell is operated so that there is virtually no liquid flow flows through this diaphragm. The current density is up to 1 amp per 6.45 cm2.

The anolyte flows through the anode part where the hydrochloric acid is formed is electrolyzed by gaseous chlorine. The chlorine-containing anolyte is derived from the Cell removed and the gaseous chlorine separated from the remaining anolyte. The anolyte can be replenished with hydrochloric acid by absorbing hydrogen chloride, whereupon it is sent in a cycle through the anode space.

The catholyte flows through the cathode space, where polyvalent metal chloride is reduced to low-power metal chloride, e.g. CuCl2 to Cu2C12. This reduced Catholyte is removed from the cathode chamber. The metal chloride can be used to higher quality State to be reoxidized, whereupon the reoxidized catholyte is circulated through conducts the cathode compartment.

The double-flow method according to the invention provides very pure chlorine at an extremely high efficiency of the current (about 95), which means a minimal reverse reaction between the produced chlorine and the low-value state of the metal chloride in the cell. In addition, the reoxidation of the catholyte takes place outside the Cell instead, which means that more versatile devices and apparatus can be used. In this way the system works more efficiently, ie the rate of reoxidation does not limit the cell response.

Anolyte and catholyte can be hydrochloric acid and any polyvalent metal chloride contain, which is present in at least two oxidation states, e.g. copper chloride, Ferric chloride and chromium chloride. Copper chloride is preferably used. The concentration areas can vary within wide limits and the concentration between catholyte and anolyte can be different; however, there is a particularly preferred concentration range between about 0.5 and z moles of CuCl2 and about 3-8 moles of HO1. When diaphragm and reaction conditions are suitable, the @atholyt can actually consist essentially of polyvalent Metallchlorid.and / or the anolyte consist essentially of hydrochloric acid.

The reactions that take place in the system according to the invention using an HCl-CuOl2 electrolyte are as follows: Cathode reaction: 2 CuCl2 # Cu2Cl2 + 2 Cl- Anode reaction: 2 HCl # 2H + Cl2 Oxidation reaction: Cu2Cl2 + 1/2 02 + 2H + 2 Cl 2 CuCl2 + H20 These reactions add up to a total reaction of 2 KC1 + 1/2 O2 # C12 + H2O. The figure shows a schematic flow diagram which shows an embodiment of the double-flow electrolysis system according to the invention.

The electrolysis cell 10 consists of the cathode 11 and the anode 12 and the diaphragm 13; it is connected to the power source 14. As an electrode material one uses the substances commonly used in electrolyte cells, such as Carbon or graphite. Synthetic materials can be used as diaphragm materials, which have sufficient resistance and dimensional stability, e.g. polypropylene and copolymers of vinyl chloride and acrylonitrile, as well as polyvinyl chloride.

In the anolyte cycle, the anolyte, which hydrochloric acid and polyvalent Metallonlorid contains, filled in the anode space A of the cell. The hydrochloric acid of the anolyte is electrolyzed and produces chlorine gas. The anolyte becomes out of the cell removed and the chlorine gas separated in a degassing unit 15. The drained one Anolyte runs through the heat exchanger 22 into an absorption tower 16, where it is with gaseous or liquid hydrogen chloride is brought into contact (preferably gaseous).

The hydrogen chloride is absorbed in sufficiently close so that the hydrochloric acid used up during the electrolysis is renewed. The filled one The anolyte then circulates back into the cell through a filter 23.

The chlorine gas obtained in this way can be further processed by passing it through a condenser 17 which is an essential part the hydrogen chloride in the chlorine gas is removed, after which it is dried in the chlorine dryer 18, e.g. using sulfuric acid. The hydrogen chloride-cold condensates can be returned to the anolyte.

During the catholyte cycle, the catholyte is placed in the cathode compartment C, where polyvalent metal chloride is reduced to the lower oxidation state. The reduced catholyte is withdrawn from the cell and passed through the heat exchanger 22 into an oxidation tower where it is oxidized, e.g. by mixing with an oxidizing atmosphere such as oxygen-containing gas or dilute chlorine-containing Gas; this reoxidizes the metal chloride. In the picture is the oxidizer 19 shown as a countercurrent device; however, according to the invention, any tower or use tank unit which has contact with the oxidizing atmosphere the reduced anolyte allowed.

The reoxidized anolyte is then circulated through a filter 23 led into the cathode room.

The gases blown out from the oxidation tower contain some HC1 which can be recovered by passing the gases through a condenser 20 heads. The HCl-containing condensate can be circulated to the oxidation device be directed. In U.S. Patent 2,665,024 (Low et al., January 12, 1954) is a somewhat more complicated recovery system described, which according to the invention can be used but is not necessary.

Anolyte and catholyte can, for example, by means of the pumps 21 or others usual devices are driven in the circuit. The temperature becomes advantageous controls what happens using the ärmeaustawscher 22. In some In some cases it is desirable that the electrolyte streams introduced are filtered, to remove solids. All types of filter devices 23 can be used for this purpose use.

A single cell system is shown in the figure; of course series of cells can be connected in series and used according to the invention will. For example, the cells can be arranged so that one side acts as the cathode for one cell and the other side acts as an anode for a second cell.

The invention is explained in more detail in the following examples, wherein the general procedures and apparatus described below can be used. Unless otherwise specified, the term "electrolyte" refers to the anolyte and the catholyte.

A double flow system similar to the figure is set up.

Catholyte and anolyte circulate separately by means of pumps. The flow rate is set to 0-65Q ml / min. regulated. The flow of anolyte and catholyte becomes two Measured by rotameters. Copper (I) chloride, which was formed at the cathode, is reoxidized with oxygen or air in the oxidizer.

The latter is made of Pyrex glass, which has an active volume of has about 1,080 cm3. The output gas stream flows through a condenser. oxygen or air gets into the oxidizer through a medium-sized sintered glass sheet directed.

The absorption of hydrogen chloride takes place in a glass tube. The connecting lines are either made of polyethylene or pure rubber.

The electrode used for the cell is made from a graphite block came here. The active electrode zone is 96.8 cm2, the electrodes are 0.16 cm away from the diaphragm. All parts except for the electrode part themselves are painted with a vinylidene chloride-vinyl chloride copolymer zeiment to prevent electrolysis on these surfaces. For the inputs and outputs of the electrolyte are nipples for polytetrafluoroethylene or vinylidene chloride-vinyl chloride copolymer used. Two of these electrodes are punched together with one in between Tissue diaphragm clamped so that they form an electrolytic cell. Leaks are diminished by a silicone polymer film along the 2.54 cm frame of the cell, the same area on the diaphragm being painted with plastic cement and the corners of the diaphragm are fused.

A copper plate, to which the copper lines are soldered, is screwed onto the outside of each graphite plate using two short brass screws. The entire device is placed in a temperature-controlled heating chamber.

The concentration of hydrochloric acid is determined by titration with 1N sodium hydroxide solution determined using methyl red as an indicator.

The copper (IfI) concentration in the catholyte is determined by the iodometric Standard method measured, The copper (I) concentration is measured in the following way certainly. A sample is quickly added to a ferric ammonium sulfate solution in sulfuric acid. The amount of iron (II) formed is determined with 0.1N-sulfate solution using of berroin as an indicator to iron (III) oxidized-.

Chlorine is dissolved in 600 ml of a potassium iodide solution (400 g / liter) in sulfuric acid absorbed, diluted to 1000 ml, whereupon aliquots with O, lN sodium thiosulphate titrated.

Gas analyzes are made with the Orsat method, The efficiency of the current is determined by looking at the actual amount of Comparing chlorine with the theoretically producible amount.

Table e conditions.

Composition of the electrolyte: 1.505 mol CuCl2, 5.8 mol HCl Electrolyte flow: 610 ml / min.

Diaphragm: copolymer made of vinyl chloride and acrylonitrile resistor between anode and cathode connections: 33 milliohms (70 ° C).

Example current density volts temp. Current efficiency no. (Amps / cm) (C) 1 0.052 0.960 71 94.36 2 0.078 1.110 71 95.95 3 0.104 1.270 71 96.93 4 0.130 1.440 71n 97.77 5 0.156 1.680 71 97.64 6 0.052 0.92 80 95.33 7 0.078 1.055 80 95.97 8 0.104 1.20 80 95.13 9 0.130 1.35 80 97.52 10 0.156 1.51 80 97.90 Table I. shows the current efficiencies of the system according to the invention at different current densities and corresponding voltages at two temperatures. As can be seen, become extreme high current efficiencies (95 ß and more) achieved in almost all cases, even with very low current densities; The cell voltages are correspondingly low (less than 1 volt).

Table II Conditions: Composition of the electrolyte: 1.46 Mol CuOl2, 5.03 Mol HCl Electrolyte flow: see table Diaphragm: Polypropylene Resistance: 17 milliohms (temp. 70-70.5 ° C).

Example current density volts electrolyte flow current effect no. (Amps / cni2) Speed, @ degrees (ß) (ml / min.) 11 0.078 0.890 610 95.97 12, 0.078 0.895 5i0 95.97 13 0.078 0.895 400 95.97 14 0.078 0.900 300 95.32 15 0.078 0.910 213 95.75 16 0.156 1.055 610 97.69 17 0.156 1.07 510 97.69 18 0.156 1.10 400 97.69 19 0.156 1.17 300 97.47 20 0.052 0.825 510 92.75 21 0.078 0.890 510 95.32 22 0.104 0.945 510 96.13 23 0.130 0.995 510 97.13 24 0.156 1.060 510 97.68 Table 7 shows two Aspects of the inventive system.

On the one hand, high current efficiencies can be achieved within a wide range Range of electrolyte flow levels can be achieved (Examples 11-15 and 16-19). These examples show little or no decrease in the current efficiency level, when the flow rate decreases. On the other hand, the current efficiency level can be increased by increasing the current density (Examples 20-24).

Table III Conditions Composition of the electrolyte: 1.40 Mol CuC12, 6.0 mol HC1 electrolyte flow: 510 ml / min.

Diaphragm: Polypropylene Resistance: 17 Milliohm (Temp .: 70-70.5 ° C).

Example no. Current density Volts O2 flow in amount of current (Amps / cm2) der Oxida- Cu + action pre- im reox. degree (%) direction catholy- (ml / min.) th (g / l) 25 0.078 0.90 660 0 90.39 26 0.104 0.96 660 0 94.20 27 0.130 1.04 660 0 94.43 28 0.156 1.12 660 0 95.65 29 0.078 0.92 35 1.3 88.26 30 0.104 0.995 45 1.3 91.62 31 0.130 1.055 80 1.4 93.26 32 0.156 1.14 93 1.4 92.64 33 0.078 0.92 25 2.9 79.2 34 0.104 0.99 21 3.8 82.6 35 0.130 1.055 65 2.7 89.53 36 0.078 1.14 90 2.5 92.6 Table III shows another feature of the system according to the invention - namely the ability even with incomplete reoxidation of the polyvalent metal chloride chlorine in relative produce high yield. Examples 26-28 are similar to those shown above, with a substantial excess of oxidizing gas over that for conversion practically all of the Cu2Cl2 in CuCl2 is available. Even if, however the flow of the oxidizing gas in the oxidizer is reduced, so that a significant amount of Cu + in the circulating driven Catholyte remains, the system according to the invention still shows high levels of current efficiency, especially at high current densities (Examples 33-36).

An example of the chlorine gas analysis in any of the above Example is given below: Cl2 - 99.69 So CO2 - 0.24 O2 - 0.01 N2 - 0.06 So the system according to the invention ur recovery of very pure chlorine by Electrolysis of hydrogen chloride and a polyvalent metal chloride at very high Current efficiencies within a wide range of electrolyte concentrations, Current densities and flow rates can be used.

3 e i s p i e 1 e 37-41 A larger diaphragm cell with an active Electrode area of 413 cm2 is introduced into the system according to the invention. the Construction of the cell is similar to that used in the previous examples became. As the oxidized gas in the oxidation tower, air becomes a flow rate of about 42.5 liters / min. used.

Table IV Composition of the electrolyte: 1.50 moles CuCl2, 5.5 Mol HCl electrolyte flow: see table Diaphragm: Polypropylene Resistance: not measured (temp. 70 ° C).

Example current density volts electrolyte flow current no. (Amps / cm) Speed . Efficiency (ml / min.) Grad. (%) 37 0.078 0.94 85 91.4 38 0.078 0.92 185 92.0 39 0.078 0.89 400 92.0 40 * 0.078 1.0 760 95.5 41 * 0.078 1.0 -190 93 . 2 Active electrode area 362 cm distance diaphragm / electrode 0.32 cm.

Table IV shows the high power efficiencies achieved by the system according to the invention using air as the owidierendes gas within a wide range of electrolyte flow rates can be achieved. the Examples 40 and 41 are from a continuous mini-plant.

B e i e 1 e 42-43 If desired, the inventive System with different HCl concentrations in the anolyte and catholyte work, whereby the same excellent current efficiencies are achieved (cf. following examples in which the cell according to Examples 40-41 was used).

Table V Composition of the electrolyte: 1.50 mol CuCl2, 5.5 mol HCl electrolyte flow: 180 ml / min.

Diaphragm: Polypropylene Resistance: not measured (temp. 72-75 ° C).

Example current density volts HCl-Konc. Electricity effect no. (Amps / cm2) (Mol / liter) degree (%) anolyte catholyte 42 0.078 1.02 6.0 3.8 92.1 43 0.078 1.00 7.5 4.2 91.5

Claims (2)

P a t e n t a n s p r ü c h e 1. Continuous process for production of chlorine, characterized in that (a) separate anolyte and catholyte streams through the anode or. Cathode chamber of an electrolysis cell conducts which by means of a diaphragm is divided, with anolyte and catholyte aqueous hydrochloric acid and contain a polyvalent metal chloride, so that chlorine gas is produced at the anode and at the cathode the polyvalent metal chloride of a superior state is reduced to a lower order state, this cell having a current density of up to 1 ampere / 6.45 cm2 is operated, (b) the anolyte stream containing chlorine gas removed from the anode space and the reduced catholyte flow from the cathode space, (c) separating the chlorine gas from the anolyte stream, (d) the anolyte stream with hydrogen chloride added to replace the hydrogen chloride consumed in the electrolysis, and returns the filled anolyte stream in the circuit to the anode compartment of the cell, (e) introducing an oxidizing atmosphere into the reduced catholyte stream to remove the reoxidize polyvalent metal chloride, and the reoxidized catholyte stream in the circuit in the cathode area of the cell. 2. Device for the production of chlorine by electrolysis, consisting of: (a) at least one electrolytic cell containing an anode, a cathode and in between a diaphragm, which divides the cells into anode and cathode space, and connections to an energy source, (b) devices connected to the cell for introducing the anolyte and catholyte into the anode and cathode compartment of the Cell where anolyte and catholyte use aqueous hydrochloric acid and a polyvalent metal chloride included so%? Chlorine gas is produced at the anode and polyvalent gas at the cathode Metal chloride reduced from the superior state to a inferior state will, (c) removal devices associated with the cell the anolyte and catholyte from the cell, (d) devices for removing the Chlorine gas from the anolyte, which is connected to the devices for removing the anolyte are connected, (e) devices which are connected to the chlorine gas removal Serving devices are connected to additional hydrogen chloride in the anolyte to absorb, so that these are circulated in the anode space of the real one can be, and (f) devices c-n, which are used with the catholyte removal Devices are connected to oxidize the reduced catholyte, i.e. the polyvalent metal chloride and reoxidize it in circulation in the cathode room to redirect. L e r s e i t e