GB2103245A

GB2103245A - Process for the electrolytic production of ozone

Info

Publication number: GB2103245A
Application number: GB08122777A
Authority: GB
Inventors: Heinz Peter Fritz; Dietrich Wabner; Jordan Thanos; Peter Faber
Original assignee: Rheinisch Westfaelisches Elektrizitaetswerk AG
Current assignee: RWE AG
Priority date: 1981-07-23
Filing date: 1981-07-23
Publication date: 1983-02-16

Abstract

The process is carried out by using an electrode consisting of a titanium carrier on intermediate layer comprising a titanium (IV) adsorbed layer produced following normal cleaning but before coating with lead peroxide by boiling in a solution of oxalic acid containing additional titanium oxalate complexes, and an anodically deposited lead peroxide coating in which the anodic deposition takes place in an aqueous electrolyte containing a lead (II) salt of the amido-, imido, nitrodo- or fluoroderivatives of sulphuric or phosphoric acid, or in an aqueous electrolyte consisting of one of the aforementioned acids, and by using an electrolyte which consists of an aqueous solution of salts and/or dilute acids in the highest condition of oxidation of their central ions by anions with low specific adsorption on lead peroxide, this being in a pH range of 2 to 8, with current densities up to 500 mA/sq.cm., and at a temperature from room temperature up to 60 DEG C. To increase the yield, materials that supply F-ions can be added to the electrolyte.

Description

SPECIFICATION Process for the production of ozone This invention relates to a process for the production of ozone using at least one working electrode possessing a coating of lead peroxide in an electrolyte, and ozone is liberated on this coating by electrolysis at a specific current density. The electrode consists of a titaniumcarrier and possesses an intermediate layer of titanium (IV) ions below the lead peroxide coating.

The electrolytic production of ozone dates back to Schonbein (1840) using a working electrode consisting of lead, on which the lead peroxide coating is formed. This known process had difficulty in obtaining acceptance as industrial practice because the working electrodes "disintegrated". In fact, during the whole of the electrolysis the lead of the anode is converted into lead peroxide which continuously falls off into the electrolyte, decomposes any ozone which is still in solution, and reduces the yield. Immediate disintegration is also observed with working electrodes which possess a titanium-carrier and a lead peroxide coating on a titanium (IV) intermediate layer, which is an oxide according to the known procedures. Accordingly industrial practice has for a very long time adopted other methods and operates with quite different processes.The following points of detail should also be mentioned: Ozone is increasingly becoming a very important material in ecological chemistry. It is used e.g. on an increasing scale in place of chlorine for the purification of water for drinking and for general use. The bactericidal and fungicidal effect of dissolved ozone is of the same order of magnitude as that of chlorine, but in contrast with the latter no objectionable or even poisonous products are formed. The use of ozone in gaseous form is indicated for purposes of air purification. Ozone is required industrially on a large scale for oxidation reactions and special syntheses. The inevitable production of materials harmful to the environment is thereby reduced or even completely eliminated. By far the larger part of the ozone used is produced by means of static electrical discharges.From this a flow of oxygen is produced with a maximum of 7% ozone by weight, usually less, which is unsatisfactory for many purposes. Of course industrial practice also includes certain variations of electrolysis by which ozone is formed from water. Such may typically be operated under the following conditions: low temperatures down to -400 to -600C) high current densities (up to 81 amps/sq.cm (!)), and the use of precious metal electrodes (preferably platinum) with highly concentrated acids (phosphoric acid (in syrup form), perchloric acid, etc.) This is expensive on account of the precious metal electrodes and the high current density, and is in need of improvement as regards the yield.

The object of the invention is to provide a process for the production of ozone using at least one working electrode in an electrolyte, the electrode consisting of a titanium carrier with a coating of an intermediate layer of titanium (IV) ions and a lead peroxide coating anodically deposited thereon in such a manner that the working electrode or electrodes can operate with a high yield of ozone without deleterious "disintegration".

According to the present invention there is provided a process for the production of ozone using at least one working electrode in an electrolyte, the electrode consisting of a titanium carrier with a coating of an intermediate layer of titanium (IV) ions and a lead peroxide coating anodically deposited thereon, wherein a working electrode is used in which the titanium carrier possesses as intermediate layer a titanium (IV) absorbed layer, which is produced following the normal cleaning but before the coating with lead peroxide by boiling in a solution of oxalic acid containing additional titanium oxalate complexes, and in which the anodic deposition of the lead peroxide coating takes place in an aqueous electrolyte containing a lead (II) salt of the amido-, imido-, nitrodo- or fluoroderivates of sulphuric or phosphoric acids, or on an aqueous electrolyte consisting of one of the aforementioned acids, and wherein an electrolyte is used which consists of an aqueous solution of salts and/or dilute acids in the highest condition of oxidation of their central ions by anions with low specific absorption of lead peroxide (e.g. with HP042-, CIOJ), in the pH range of 2 to 8, the operation taking place at current densities up to 500 mA/sq.cm. and at a temperature of from room temperature up to 600C. Such an electrolyte functions to a considerable extent as a buffer solution. In order to increase the yield, materials that supply F-ions can be added to the electrolyte.

Surprisingly the process according to the invention can be operated at very low current densities namely at densities of 60 to 200 mA, and this at room temperature or the temperature of tap water.

Surprisingly the invention has proved that a very much simpler means of conducting the process results in better practical and realistic yields of ozone. The invention differs from the conditions hitherto regarded as essential.

Electrolysis takes place at about room temperature or the temperature of tap-water (as most +60"C), and with low current densities (up to 500 mA/sq.cm.) with dilute aqueous electrolytes. The results in continuous operation are better than the ozone yields of the static electrical charge (1 (1013% 03 by weight in the 02 - flow compared with typically 57% 9s by weight in the O2 of the commercial ozonisers with static discharge). Compared with the above-mentioned precious metal electrodes the electrodes used are extremely cheap and easily manufactured, but notably they also have very much longer life than the lead peroxide anodes anodically produced in situ from lead.Compared with the anodes used by Schonbein and others the anodes used in the process of the invention do not shed any powdery particles even after operation for long periods.

The electrolytes that can be used are very much less dangerous than.the highly reactive, possibly oxidizing, concentrated acids of the electrolytic process previously practised and are also not corrosive in practice. Accordingly no heavy demands are made on the materials of an equipment to carry out the process according to the invention; glass, ceramics, plastics or a series of metals (apart from precious metals those with passivating properties or provided with a passive coating) can be used without difficulty. The low current densities simplify the construction of the equipment and reduce the cost of production, as also does the fact that no low temperatures have to be maintained by heavy consumption of energy, but, as mentioned, it is possible to work at room temperature or at the temperature of normal tap-water.

Example of performance Working electrode: Titanium with PbO2 coating.

Electrolyte: 0.12 gjlitre KF, 90 g./litre K2 HPO 30 g./litre KH2PO in water.

Current density: 100 to 200 mA/sq. cm.

Temperature: 200 to 250C.

Claims

1. A process for the production of ozone using at least one working electrode in an electrolyte, the electrode consisting of a titanium carrier with a coating of an intermediate layer of titanium (IV) ions and a lead peroxide coating anodically deposited thereon, wherein a working electrode is used in which the titanium carrier possesses as intermediate layer a titanium (IV) absorbed layer, which is produced following the normal cleaning but before the coating with lead peroxide by boiling in a solution of oxalic acid containing additional titanium oxalate complexes, and in which the anodic deposition of the lead peroxide coating takes place in an aqueous electrolyte containing a lead (II) salt of the amido-, imido-, nitrido- or fiuornderivates of sulphuric or phosphoric acid, or in an aqueous electrolyte consisting of one of the aforementioned acids, and wherein the electrolyte is used which consists of an aqueous solution of salts and/or dilute acids in the highest condition of oxidation of their central ions by anions with low specific absorption on lead peroxide, in the pH range of 2 to 8, the operation taking place at current densities up to 500 mA/sq. cm., and at a temperature of from room temperature up to 600 C.

2. A process according to Claim 1, wherein materials that supply F-ions are added to the electrolyte.

3. A process for the production of ozone substantially as hereinbefore described.