US3759804A - Electrochemical oxidation of thallium derivatives - Google Patents

Electrochemical oxidation of thallium derivatives Download PDF

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US3759804A
US3759804A US00115477A US3759804DA US3759804A US 3759804 A US3759804 A US 3759804A US 00115477 A US00115477 A US 00115477A US 3759804D A US3759804D A US 3759804DA US 3759804 A US3759804 A US 3759804A
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anolyte
thallous
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catholyte
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Bris L Le
D Michelet
M Rakoutz
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Rhone Poulenc SA
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G15/00—Compounds of gallium, indium or thallium
    • C01G15/003—Preparation involving a liquid-liquid extraction, an adsorption or an ion-exchange
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals

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  • the present invention relates to an electrochemical process for oxidising thallous ions to thallic ions.
  • metal ions reducible to metals are thallous and/or thallic ions, scarcely anything other than platinised platinum or platinised titanium is suitable for the cathode.
  • platinised platinum or platinised titanium is suitable for the cathode.
  • the more common and generally less expensive metals such as stainless steel or copper cannot be used in this process.
  • the main subject of the present invention is to provide an electrochemical process for oxidising thallous ions which does not have the aforementioned disadvantage and which allows cathodes based on common metals to be employed.
  • the present invention provides a process for the electrochemical oxidation of thallous ions to thalic ions which comprises passing a direct electric current between an anode and a cathode of an electrolysis cell divided into at least two compartments by at least one membrane having anion exchange properties, the anolyte comprising thallous and thallic ions and the catholyte comprising an alkali metal hydroxide, an ammonium hydroxide, an alkali metal salt of a volatile weak acid or an ammonium salt of a volatile weak acid.
  • catholyte denotes the solution in the cathode compartment and the term anolyte denotes the solution in the anode compartment.
  • a cell having two compartments separated by a single anion exchange membrane is used.
  • This first way will be denoted, in the text that follows, by (M and the two compartments will be denoted by (A) for the anode compartment, and (Ct) for the cathode compartment.
  • the nature of the solvent or solvents contained in the catholyte and the anolyte is not critical, it is usually preferred to use water.
  • the amount of thallous and thallic ions present in the anolyte is preferably such that the number of gram atoms of thallium per litre of solution is: between 0.01 and 0.8, particularly between 0.1 to 0.5.
  • an acid for example perchloric acid, sulphuric acid, nitric acid, fiuoroboric acid, alkylsulphuric acids, or saturated aliphatic acids which are soluble in water, such as acetic acid. It is usually preferred, and especially in a sulphuric acid medium, to operate at a pH below 2; with an aliphatic acid it is preferred to operate at a pH less than 5.
  • the catholyte containing an alkali metal or ammonium hydroxide or salt of a volatile weak acid the alkali metal may be lithium, sodium, potassium, rubidium or caesium and the ammonium compound may be quaternary or otherwise.
  • Ammonium derivatives which can be used are compounds comprising the grouping of formula:
  • R represents an organic radical, particularly alkyl, the group (I) preferably containing not more than 16 carbon atoms and preferably being in the form of a salt of a volatile weak acid.
  • Carbonates and bicarbonates are conveniently used as salts of a volatile weak acid.
  • the concentration of alkali metal or ammonium compound in the catholyte is generally between 0.1 and 5 mols/litre and preferably between 0.5 and 2 mols/litre.
  • the anion exchange membranes separating the various compartments can be homogeneous membranes or heterogeneous membranes; the exchange groups can, in particular, be ammonium, phosphonium or sulphonium groups, as well as amine groups when the catholyte contains a salt of a volatile Weak acid.
  • Ion exchange membranes of which the permeation selectivity (measured according to the technique described in French patent specification No. 1,584,187) is greater than 40%, preferably greater than are preferably used.
  • the electric current densities in the process according to the invention are generally between 0.5 and a./ dmfi, preferably between 5 and 25 a./dm.
  • An electrically conducting material which is insoluble in the anolyte under the operating conditions is used as used as the material constituting the anode.
  • Suitable materials include graphite, platinum, lead dioxide, as well as lead and its alloys, particularly with silver, antimony and tin.
  • the cathode may be of steel, particularly stainless steel, iron, copper, chromium, nickel, graphite, mercury or lead or its alloys, particularly with silver, antimony and tin.
  • a simple electrolysis cell or an assembly of cells joined together for example by the filterpress system can be used.
  • the oxidation according to the invention can be carried out continuously or discontinuously.
  • the electrolyser is fed with a solution of TH and simultaneously electrolysed solution is withdrawn.
  • the process of the invention can also be combined in one and the same system with an oxidation process for organic compounds using Tl the thallous-thallic solution continuously circulating alternately, first in the electrolysis cell, and then in the oxidisor for the organic compound.
  • the operating conditions are generally controlled so as to maintain an electrolyte temperature which is neither below C. nor above 60 C.
  • the oxidation is preferably carried out at a temperature in the range 1535 C.
  • the liquid (also called electrolyte) used in the compartment of type (B should have the same characteristics as those defined previously for the catholyte; it is preferred in practice that the composition of the electrolyte (B be the same as that of the catholyte, except for the fact that the latter does not contain any thallous ions at all; the concentration of the alkali metal or ammonium derivative in the electrolyte (B can however be different to that of the catholyte.
  • the electrolyte (B is preferably subjected to a separate electrolysis in an auxiliary electrolyser, which allows any traces of thallium which may be present to be deposited in metal form;
  • this auxiliary electrolyser which is of small dimensions in practice, is advantageous provided with an anion exchange membrane separating the catholyte and the anolyte, and the catholyte consists of liquid which comes from (B and the anolyte has a composition similar to that of the catholyte except as regards thallium, which is absent in the anolyte of this auxiliary electrolyser.
  • the liquid (or electrolyte) present in the compartment of type (B is an aqueous solution containing thallous ions, thallic ions being absent or almost absent (preferably less than 0.1% by weight, calculated as T1 metal).
  • This solution can also contain an acid; the proportion of thallous ions and the nature and proportion of acid in this solution are selected in accordance with the same criteria as for the anolyte.
  • the compartments (B are fed with the thallous solution coming from a reactor using thallic ions, and then the thallous solution leaving (B is transferred to the anode compartment (A), where it is subjected to anodic oxidation.
  • the compartments of type (A) and (B are simultaneously fed with a thallous solution such as that coming from a reactor for the oxidation of olefines by thallic ions, the solution present in the compartment (B is withdrawn at a rate sufficient to maintain the proportion of thallic ions Within the limit indicated above, and the said solution which has been withdrawn from the compartment (B is transferred directly to the reactor for utilising the thallic ions; anolyte is withdrawn simultaneously to transfer it also to the reactor for utilising the thallic ions.
  • a thallous solution such as that coming from a reactor for the oxidation of olefines by thallic ions
  • the oxidation process according to the invention allows good electrical yields to be obtained. It also prevents any progressive concentration of non-thallous or non-thallic salts or ions in the anolyte.
  • the (M and (M methods of carrying out the process according to the invention moreover allow the deposit of thallium on the cathode to be removed, this deposit having a tendency to be formed during operations of a very long duration when the permeation selectivity of the membranes is not close to 100%.
  • the (M method allows the life of the membranes to be increased.
  • Thallic ions are useful as catalysts in the oxidation of organic compounds e.g. olefines, as described in US. patent specification No. 3,048,636 and in such processes are reduced to thallous ions.
  • the process of the present invention is useful in converting such thallous ions back to thallic ions.
  • Tl+ is oxidised to Tl+++ in an electrolysis cell having the following characteristics:
  • Catholyte 100 cm. of aqueous 2.5 N sodium hydroxide solution.
  • Anolyte 500 cm. of aqueous solution initially containing one mol/litre of sulphuric acid and 99 millimols/litre of thallous sulphate. Stirring is performed by means of a magnetic stirrer.
  • Anion exchange memberane homogeneous memberane containing quaternary ammonium groups and based on a divinylbenzene-styrene copolymer (exchange capacity: 0.55 milliequivalent/g.; permeation selectivity: 90%).
  • the cathode-membrane distance is 5 mm.
  • the anode-membrane distance is 10 mm.
  • the electric current passed is 5 a.
  • the voltage is 8 v.
  • the temperature is 27 C.
  • the useful surfaces of the anode and cathode are equal to 2 dm.
  • the cathode is of stainless steel.
  • the nature The expansion vessel is fed at a rate of about 25 cmfi/ minute.
  • the membrane has a permeation selectivity of 72%.
  • the anolyte initially contains 0.4 gram ions/litre of thalof the anode is indicated in the table
  • EXAMPLE 9 A circulation of electrolyte is established in each of the I compartments of the electrodialyser; the rate of movel 1S OXIdIScd to Ti in an electroly l Cell having ment over the electrodes is 30 cm./seconds; the electhree compartments, the p ing OH it OIIS being as trolyte circuits pass through a cooler, which allows the 15 follows:
  • the letter M indicates a concentration The i f of lead. contamzmg 10% of antlmony; its of 1 mol/litre; in the case where this letter is preceded usg u sur ace ⁇ area is 1 by a number this latter indicates the concentration ex-
  • the Cathode havmg the same surface area 15 of Stamless pressed in mols/litre.
  • the degree of convarsion is the fraction (percentage The two membranes separating the three compartments in numbers f ions) f converted into 13+ in the are heterogeneous membranes containing quaternary course f the experiment ammonium groups; the matrix and the ion exchange
  • the electric current yield is the percentage of coulom-bs T6510 f in P P Q y Weight, of 32/63; the which have served to oxidise 11+ to 13+ matrix 1s a vinyl chloride/butyl maleate copolymer TABLE I Catholyte Anolyte Concentration Degree Electric Current of con cuirent Nature of the Concen- Volume, Volume, $12 894. passed Voltage Number of version, yield, Ex. anode Nature tration cm.
  • cm. B04112 initial in a. 1n v. coulombs percent percent 1 750 000 1 0.165 20 4. 30,000 71.5 01.5 2 iiEiL'IIIIIIIIIII $285 750 600 0.5 0.171 20 4.2 31,825 78 96.5 as 1 3- 193 a a s 0 N OH ii i880 600 1 0.165 10 as 30,700 67.5 84.5
  • EXAMPLE 7 and 5 lead back from the expansion vessels 12 and 13 to the anode and cathode compartments.
  • Expansion vessel 12 has inlet and outlet ports 10 and 11 for anolyte.
  • the initial concentration of thallous ions is 0.298 gram ions/litre.
  • the total volume of anolyte in circulation is 600 cmfi.
  • the total volume of catholyte in circulation is 1000 cm
  • the ion exchange membrane which contains quaternary ammonium groups, has a permeation selectivity of 89%
  • a solution containing 0.298 gram ions/litre of Tl+ (in the form of sulphate) and 1 mol/ litre of H 80 is introduced via port 10, at the rate of approximately 26.1 cmfi/minute, to the anolyte; simultaneously the same quantity of electrolysed solution is withdrawn from the anolyte via port 11.
  • thallic ions are obtained with a degree of conversion of 68% and with an electric current yield of 84.5%.
  • the current passed is 27 a.
  • the voltage is 5.1 v.
  • the ion exchange resin is a resin containing quaternary ammonium groups and is based on a styrene-divinylbenzene copolymer.
  • the permeation selectivity of the membrane is 78%, and its substitution resistance is 15 ohms cmF.
  • each compartment is 1 mm., and an interposed polypropylene grill allows the membranes to be kept in place and the outflow of the liquids to be suitably distributed.
  • the electrolytes which pass through the three compartments circulate in co-current, the pressure at the inlet being 2.3 bars absolute and at the outlet being 1.1 bars.
  • the liquid passing through the central compartment and the catholyte are initially an aqueous normal solution of sodium hydroxide.
  • a closed circuit circulation is established in the anolyte and in the catholyte.
  • the anolyte consists initially of an aqueous solution containing 100 g./l. of thallous sulphate and 20% by weight of H 50 it is fed at the: rate of 0.5 litre/hour by a solution having the same composition; the amount of anolyte is kept constant by a feed at a corresponding rate of flow.
  • the current passed is 10 a.
  • the temperature is 30 C.
  • the voltage is 6 v.
  • Electrolysis is carried out for 5 3 hours.
  • the anode is of lead and has a useful surface area of 1
  • the cathode is of stainless steel and has the same surface area.
  • the three membranes are identical to those of Example 9.
  • the thickness of the compartments is 1 mm., these compartments being provided with spacers as in Example 9.
  • the electrolytes passing through the four compartments circulate in co-current, the pressure at the inlet being 2.2 bars absolute, and at the outlet being 1 bar absolute.
  • the catholyte and electrolyte contained in the compartment next to the cathode compartment consist initially of an aqueous normal solution of sodium hydroxide.
  • the catholyte circulates in a closed circuit.
  • the electrolyte contained in compartment (B next to the cathode compartment circulates and is subjected to an auxiliary electrolysis in the same way as the electrolyte of the central compartment (B of Example 9,
  • the anolyte consists initially of an aqueous solution containing 8.7% by weight of sulphuric acid and 7.02% by weight of TH (taken as Tl metal) in the form of Tl SO
  • the electrolyte contained in the compartment (B next to the anode compartment has initially the same composition as the anolyte.
  • a closed circuit circulation is established in the anolyte
  • the compartment (B next to the anode compartment is ,fed continuously at the rate of 0.456 l./hur with a thallous solution having the same composition as that given for the anolyte at the start of the electrolysis; withdrawal of liquid from the same compartment allows the amount of liquid circulating therein to be kept constant, and serves to feed the anolyte.
  • a fraction of the anolyte is withdrawn so as to keep its volume constant.
  • the current passed is a.
  • the temperature is about 27 C.
  • the voltage is 6.4 v.
  • a process for the electrochemical oxidation of thallic ions which comprises passing a direct electric current between an anode and a cathode of an electrolysis cell divided into at least two compartments by at least one membrane having anion exchange properties, the anolyte comprising thallous and thallic ions and the catholyte comprising a compound M+A- where M+ represents an alkali metal or ammonium ion and A- represents a hydroxide, carbonate or hydrogen carbonate ion.
  • liquid contained in the compartment next to the anode compartment is an aqueous solution containing thallous ions.
  • a process according to claim 1 wherein the electrolyte temperature is 0 C. to 60 C.
  • alkali metal is lithium, sodium, potassium, rubidium or caesium and the ammonium ion is of formula NH R where x and y are independently 0 or a positive integer, the sum x+y being equal to 4, and R represents an alkyl radical the group R containing up to 16 carbon atoms.

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Abstract

A VOLATILE WEAK ACID, STAINLESS STEEL, LEAD OR COPPER ELECTRODES CAN BE SATISFACTORILY.

THALLOUS IONS ARE OXIDISED ELECTROCHEMICALLY TO THALLIC IONS IN A CELL DIVDED INTO AT LEAST TWO COMPARTMENTS BY AN ANION EXCHANGE MEMBRANE DIVIDER, THE ANOLYTE COMTAINING THALLOUS AND THALLIC IONS AND THE CTHOLYTE CONTAINING AN ALKALI METAL OR AMMONIUM HYDROXIDE OR SALT OF

Description

ELECTROCHEMICAL OXIDATION OF THALLIUM DERIVATIVES Filed Feb. 16, 1971 I I HHI' mm:
INVENTORS LOUIS LE BRIS, DANIEL MICHELET, MICHEL RAKOUTZ Attorneys United States Patent (ifice Patented Sept. 18, 1973 Int. Cl. C01g 15/02); C23b 5/30, 5/46 US. Cl. 204-93 16 Claims ABSTRACT OF THE DISCLOSURE Thallous ions are oxidised electrochemically to thallic ions in a cell divided into at least two compartments by an anion exchange membrane divider, the anolyte containing thallous and thallic ions and the catholyte containing an alkali metal or ammonium hydroxide or salt of a volatile weak acid. Stainless steel, lead or copper electrodes can be used satisfactorily.
The present invention relates to an electrochemical process for oxidising thallous ions to thallic ions.
It has been known for a long time that thallous ions may be oxidised electrochemically to thallic ions, see G. Grube et al., Zeitsch. fiir Elektrochem. 26, 291-7 (1920). The Grube et al. process used an electrolysis cell divided into two compartments by means of a diaphragm. However, the diaphragms employed at that time were not selective with regard to the ions, and as a result, a substantial migration of thallic ions towards the cathode compartment was produced, which resulted in a poor electric current yield. A11 electrochemical process for oxidising thallous ions similar to that of Grube et a1 has been described in U.S. patent specification No. 3,479,262.
Another process for the electrochemical oxidation of a solution of thallous or cerous ions is described in US. patent specification No. 3,486,992, which involves passing the solution of ions to be oxidised first into the cathode compartment and then into the anode compartment of an electrolytic cell, the cathode consisting of a material of which the hydrogen overvoltage is sufiiciently low to prevent the reduction of the metal ions to the zero valency state (metal state).
When the metal ions reducible to metals are thallous and/or thallic ions, scarcely anything other than platinised platinum or platinised titanium is suitable for the cathode. The more common and generally less expensive metals such as stainless steel or copper cannot be used in this process.
The main subject of the present invention is to provide an electrochemical process for oxidising thallous ions which does not have the aforementioned disadvantage and which allows cathodes based on common metals to be employed.
The present invention provides a process for the electrochemical oxidation of thallous ions to thalic ions which comprises passing a direct electric current between an anode and a cathode of an electrolysis cell divided into at least two compartments by at least one membrane having anion exchange properties, the anolyte comprising thallous and thallic ions and the catholyte comprising an alkali metal hydroxide, an ammonium hydroxide, an alkali metal salt of a volatile weak acid or an ammonium salt of a volatile weak acid.
In the present specification, the term catholyte denotes the solution in the cathode compartment and the term anolyte denotes the solution in the anode compartment.
According to a first way of carrying out the invention, a cell having two compartments separated by a single anion exchange membrane is used. This first way will be denoted, in the text that follows, by (M and the two compartments will be denoted by (A) for the anode compartment, and (Ct) for the cathode compartment.
According to a second way of carrying out the invention, denoted in the text which follows by (M at cell having three compartments separated from one another by two anion exchange membranes is used; the three compartments will be respectively denoted, going from the anode to the cathode, by (A), B and (Ct).
According to a third way of carrying out the invention, denoted in the test that follows by (M a cell having four compartments separated from one another by three anion exchange membranes is used; the four compartments will be respectively denoted, going from the anode to the cathode, by (A), (B (B and (Ct).
The nature of the solvent or solvents contained in the catholyte and the anolyte is not critical, it is usually preferred to use water.
The amount of thallous and thallic ions present in the anolyte is preferably such that the number of gram atoms of thallium per litre of solution is: between 0.01 and 0.8, particularly between 0.1 to 0.5.
In order to improve the solubility of the thallic derivatives, it is often advantageous to add an acid to the anolyte, for example perchloric acid, sulphuric acid, nitric acid, fiuoroboric acid, alkylsulphuric acids, or saturated aliphatic acids which are soluble in water, such as acetic acid. It is usually preferred, and especially in a sulphuric acid medium, to operate at a pH below 2; with an aliphatic acid it is preferred to operate at a pH less than 5.
In the process according to the invention the catholyte containing an alkali metal or ammonium hydroxide or salt of a volatile weak acid; the alkali metal may be lithium, sodium, potassium, rubidium or caesium and the ammonium compound may be quaternary or otherwise.
Ammonium derivatives which can be used are compounds comprising the grouping of formula:
NH R
in which x and y are positive integers or are zero, the sum x-l-y is equal to 4, and R represents an organic radical, particularly alkyl, the group (I) preferably containing not more than 16 carbon atoms and preferably being in the form of a salt of a volatile weak acid. Carbonates and bicarbonates are conveniently used as salts of a volatile weak acid.
The concentration of alkali metal or ammonium compound in the catholyte is generally between 0.1 and 5 mols/litre and preferably between 0.5 and 2 mols/litre.
The anion exchange membranes separating the various compartments can be homogeneous membranes or heterogeneous membranes; the exchange groups can, in particular, be ammonium, phosphonium or sulphonium groups, as well as amine groups when the catholyte contains a salt of a volatile Weak acid. Ion exchange membranes of which the permeation selectivity (measured according to the technique described in French patent specification No. 1,584,187) is greater than 40%, preferably greater than are preferably used.
The electric current densities in the process according to the invention are generally between 0.5 and a./ dmfi, preferably between 5 and 25 a./dm.
An electrically conducting material which is insoluble in the anolyte under the operating conditions is used as used as the material constituting the anode. Suitable materials include graphite, platinum, lead dioxide, as well as lead and its alloys, particularly with silver, antimony and tin.
The cathode, may be of steel, particularly stainless steel, iron, copper, chromium, nickel, graphite, mercury or lead or its alloys, particularly with silver, antimony and tin.
In order to carry out the electrochemical oxidation according to the invention, a simple electrolysis cell or an assembly of cells joined together for example by the filterpress system, can be used.
The oxidation according to the invention can be carried out continuously or discontinuously. To operate continuously, the electrolyser is fed with a solution of TH and simultaneously electrolysed solution is withdrawn. The process of the invention can also be combined in one and the same system with an oxidation process for organic compounds using Tl the thallous-thallic solution continuously circulating alternately, first in the electrolysis cell, and then in the oxidisor for the organic compound.
In all cases it is advantageous to establish a closed circuit circulation of electrolyte in each of the compartments of the electrolyser; in particular, this allows:
(a) The concentration of these electrolytes to be rendered uniform.
(b) These electrolytes to be cooled (the electrolysis gives rise to heating).
(c) The catholyte to be decanted externally if necessary, in the case where small quantities of thallium in suspension are formed.
The operating conditions are generally controlled so as to maintain an electrolyte temperature which is neither below C. nor above 60 C. The oxidation is preferably carried out at a temperature in the range 1535 C.
In the course of the oxidation there is a migration of hydroxyl ions from the catholyte towards the anolyte. These hydroxyl ions combine with protons to form water; as a result there is a slight increase in volume of anolyte and a reduction in its concentration, which can be easily corrected, particularly in the case of operations carried out over a long period of time or continuously, by a simple partial distillation of the anolyte.
When a salt of a volatile acid is used in the catholyte, there may occur liberation of a gas in the anolyte (CO in the case of a catholyte containing carbonates). In order to stabilise the basicity of the catholyte, it is advantageous to collect this gas which is liberated and to recycle it to the catholyte.
The various technical details which have been described above are valid for the three ways (M (M and (M In the following discussion, other technical details will be given, which relate more particularly to the (M or (M methods. The second, and if appropriate the third, ion exchange membrane, should have the same characteristics as those indicated previously for the membranes used in the (M process.
The liquid (also called electrolyte) used in the compartment of type (B should have the same characteristics as those defined previously for the catholyte; it is preferred in practice that the composition of the electrolyte (B be the same as that of the catholyte, except for the fact that the latter does not contain any thallous ions at all; the concentration of the alkali metal or ammonium derivative in the electrolyte (B can however be different to that of the catholyte. Moreover, the electrolyte (B is preferably subjected to a separate electrolysis in an auxiliary electrolyser, which allows any traces of thallium which may be present to be deposited in metal form; this auxiliary electrolyser, which is of small dimensions in practice, is advantageous provided with an anion exchange membrane separating the catholyte and the anolyte, and the catholyte consists of liquid which comes from (B and the anolyte has a composition similar to that of the catholyte except as regards thallium, which is absent in the anolyte of this auxiliary electrolyser.
The liquid (or electrolyte) present in the compartment of type (B is an aqueous solution containing thallous ions, thallic ions being absent or almost absent (preferably less than 0.1% by weight, calculated as T1 metal). This solution can also contain an acid; the proportion of thallous ions and the nature and proportion of acid in this solution are selected in accordance with the same criteria as for the anolyte.
According to a first method for carrying out the (M process, the compartments (B are fed with the thallous solution coming from a reactor using thallic ions, and then the thallous solution leaving (B is transferred to the anode compartment (A), where it is subjected to anodic oxidation.
According to a second method of carrying out the (M process, the compartments of type (A) and (B are simultaneously fed with a thallous solution such as that coming from a reactor for the oxidation of olefines by thallic ions, the solution present in the compartment (B is withdrawn at a rate sufficient to maintain the proportion of thallic ions Within the limit indicated above, and the said solution which has been withdrawn from the compartment (B is transferred directly to the reactor for utilising the thallic ions; anolyte is withdrawn simultaneously to transfer it also to the reactor for utilising the thallic ions.
In addition to the advantages already stated, the oxidation process according to the invention allows good electrical yields to be obtained. It also prevents any progressive concentration of non-thallous or non-thallic salts or ions in the anolyte. The (M and (M methods of carrying out the process according to the invention moreover allow the deposit of thallium on the cathode to be removed, this deposit having a tendency to be formed during operations of a very long duration when the permeation selectivity of the membranes is not close to 100%. Finally, the (M method allows the life of the membranes to be increased.
Thallic ions are useful as catalysts in the oxidation of organic compounds e.g. olefines, as described in US. patent specification No. 3,048,636 and in such processes are reduced to thallous ions. The process of the present invention is useful in converting such thallous ions back to thallic ions.
The following examples are given to illustrate the invention:
EXAMPLE 1 Tl+ is oxidised to Tl+++ in an electrolysis cell having the following characteristics:
Anodez, lead, arranged horizontally, surface area 0.33
Cathode, copper, surface area 0.35 dm.
Catholyte, 100 cm. of aqueous 2.5 N sodium hydroxide solution.
Anolyte, 500 cm. of aqueous solution initially containing one mol/litre of sulphuric acid and 99 millimols/litre of thallous sulphate. Stirring is performed by means of a magnetic stirrer.
Anion exchange memberane, homogeneous memberane containing quaternary ammonium groups and based on a divinylbenzene-styrene copolymer (exchange capacity: 0.55 milliequivalent/g.; permeation selectivity: 90%).
The cathode-membrane distance is 5 mm.
The anode-membrane distance is 10 mm.
The electric current passed is 5 a., the voltage is 8 v., and the temperature is 27 C.
After 15,000 coulombs have passed, of the thalous ions have been converted into thallic ions; the electric current yield is 95.4%.
EXAMPLES 2 TO 6 A series of experiments involving the oxidation of Tl+ to T1 is carried out.
The particular conditions relating to each example and the results obtained are given in Table I. l
The general conditions which are common to the various examples are as follows:
The useful surfaces of the anode and cathode are equal to 2 dm. The cathode is of stainless steel. The nature The expansion vessel is fed at a rate of about 25 cmfi/ minute.
The membrane has a permeation selectivity of 72%.
The anolyte initially contains 0.4 gram ions/litre of thalof the anode is indicated in the table The membrane 5 lous and thallic ions in a numerical proportion of /90.
is one having quaternary ammonium groups and a permeation selectivity above After the passage of 1,350,000 coulombs, the degree of The electrodes are separated from the membrane by a converslon 865%: and the yleld 15 955%- polypropylene fabric which is 2 mm. thick and has 10 large meshes. EXAMPLE 9 A circulation of electrolyte is established in each of the I compartments of the electrodialyser; the rate of movel 1S OXIdIScd to Ti in an electroly l Cell having ment over the electrodes is 30 cm./seconds; the electhree compartments, the p ing OH it OIIS being as trolyte circuits pass through a cooler, which allows the 15 follows:
temperature to be kept at 27 C.
In the Table I the letter M indicates a concentration The i f of lead. contamzmg 10% of antlmony; its of 1 mol/litre; in the case where this letter is preceded usg u sur ace {area is 1 by a number this latter indicates the concentration ex- The Cathode havmg the same surface area 15 of Stamless pressed in mols/litre. Steel The degree of convarsion is the fraction (percentage The two membranes separating the three compartments in numbers f ions) f converted into 13+ in the are heterogeneous membranes containing quaternary course f the experiment ammonium groups; the matrix and the ion exchange The electric current yield is the percentage of coulom-bs T6510 f in P P Q y Weight, of 32/63; the which have served to oxidise 11+ to 13+ matrix 1s a vinyl chloride/butyl maleate copolymer TABLE I Catholyte Anolyte Concentration Degree Electric Current of con cuirent Nature of the Concen- Volume, Volume, $12 894. passed Voltage Number of version, yield, Ex. anode Nature tration cm. cm. B04112 initial in a. 1n v. coulombs percent percent 1 750 000 1 0.165 20 4. 30,000 71.5 01.5 2 iiEiL'IIIIIIIIIII $285 750 600 0.5 0.171 20 4.2 31,825 78 96.5 as 1 3- 193 a a s 0 N OH ii i880 600 1 0.165 10 as 30,700 67.5 84.5
1 Concentration in mols/litre.
EXAMPLE 7 and 5 lead back from the expansion vessels 12 and 13 to the anode and cathode compartments. Expansion vessel 12 has inlet and outlet ports 10 and 11 for anolyte.
The electrolysis conditions are similar to those of Example 2, with the following modifications:
The initial concentration of thallous ions (in the form of sulphate) is 0.298 gram ions/litre.
The total volume of anolyte in circulation is 600 cmfi.
The total volume of catholyte in circulation is 1000 cm The ion exchange membrane, which contains quaternary ammonium groups, has a permeation selectivity of 89% After the passage of 27,500 coulombs, a solution containing 0.298 gram ions/litre of Tl+ (in the form of sulphate) and 1 mol/ litre of H 80 is introduced via port 10, at the rate of approximately 26.1 cmfi/minute, to the anolyte; simultaneously the same quantity of electrolysed solution is withdrawn from the anolyte via port 11.
After the passage of a total of 432,500 coulombs, thallic ions are obtained with a degree of conversion of 68% and with an electric current yield of 84.5%.
EXAMPLE 8 Example 7 is repeated, with the following modifications:
The current passed is 27 a. The voltage is 5.1 v.
(96/4); the ion exchange resin is a resin containing quaternary ammonium groups and is based on a styrene-divinylbenzene copolymer. The permeation selectivity of the membrane is 78%, and its substitution resistance is 15 ohms cmF.
The thickness of each compartment is 1 mm., and an interposed polypropylene grill allows the membranes to be kept in place and the outflow of the liquids to be suitably distributed.
The electrolytes which pass through the three compartments circulate in co-current, the pressure at the inlet being 2.3 bars absolute and at the outlet being 1.1 bars.
The electrolyte of the central compartment (B passes,
in close circuit and in succession, through the compartment (B and then through the cathode compartment of an auxiliary electrolytic cell having a copper cathode of 5 cm. which functions under a current of 0.5 a.
The liquid passing through the central compartment and the catholyte are initially an aqueous normal solution of sodium hydroxide.
A closed circuit circulation is established in the anolyte and in the catholyte.
The anolyte consists initially of an aqueous solution containing 100 g./l. of thallous sulphate and 20% by weight of H 50 it is fed at the: rate of 0.5 litre/hour by a solution having the same composition; the amount of anolyte is kept constant by a feed at a corresponding rate of flow.
The current passed is 10 a.
The temperature is 30 C.
The voltage is 6 v.
Electrolysis is carried out for 5 3 hours.
1924.6 g. of Tl+++ (expressed in T1 metal) are obtained, with an electric current yield of Moreover, it is found that there is no deposit of metallic thallium on the cathode of the main electrolyser, and the membranes are not deformed.
7 EXAMPLE 1o Tl+ is oxidised to Tl+++ in an electrolysis cell having four compartments, the operating conditions being as follows:
The anode is of lead and has a useful surface area of 1 The cathode is of stainless steel and has the same surface area.
The three membranes are identical to those of Example 9.
The thickness of the compartments is 1 mm., these compartments being provided with spacers as in Example 9.
The electrolytes passing through the four compartments circulate in co-current, the pressure at the inlet being 2.2 bars absolute, and at the outlet being 1 bar absolute.
The catholyte and electrolyte contained in the compartment next to the cathode compartment consist initially of an aqueous normal solution of sodium hydroxide.
The catholyte circulates in a closed circuit.
The electrolyte contained in compartment (B next to the cathode compartment circulates and is subjected to an auxiliary electrolysis in the same way as the electrolyte of the central compartment (B of Example 9,
The anolyte consists initially of an aqueous solution containing 8.7% by weight of sulphuric acid and 7.02% by weight of TH (taken as Tl metal) in the form of Tl SO The electrolyte contained in the compartment (B next to the anode compartment has initially the same composition as the anolyte.
A closed circuit circulation is established in the anolyte,
and in the compartment (B The compartment (B next to the anode compartment is ,fed continuously at the rate of 0.456 l./hur with a thallous solution having the same composition as that given for the anolyte at the start of the electrolysis; withdrawal of liquid from the same compartment allows the amount of liquid circulating therein to be kept constant, and serves to feed the anolyte.
A fraction of the anolyte is withdrawn so as to keep its volume constant.
The current passed is a.
The temperature is about 27 C.
The voltage is 6.4 v.
After the passage of 1,431,000 coulombs, 1312 g. of T1+++ calculated as T1 metal) are obtained, with an electric current yield of 86.6%.
It is found that there is no deposit of thallium on the cathode of the main electrolyser, and the mechanical and electrochemical properties of the membranes have not altered.
We claim:
1. A process for the electrochemical oxidation of thallic ions which comprises passing a direct electric current between an anode and a cathode of an electrolysis cell divided into at least two compartments by at least one membrane having anion exchange properties, the anolyte comprising thallous and thallic ions and the catholyte comprising a compound M+A- where M+ represents an alkali metal or ammonium ion and A- represents a hydroxide, carbonate or hydrogen carbonate ion.
2. A process according to claim 1, wherein a liquid circulation is established in each of the compartments.
3. A process according to claim 1, wherein the electrolysis cell is divided into two compartments by means of one anion exchange membrane.
4. A process according to claim 1, wherein the electrolysis cell is divided into three compartments by means of two anion exchange membranes.
5. A process according to claim 1, wherein the electrolysis cell is divided into four compartments by means of three anion exchange membranes.
6. A process according to claim 4, wherein the composition of the liquid contained in the compartment next to the cathode compartment is essentially the same as that of the catholyte.
7. A process according to claim 6, wherein the liquid in the compartment next to the cathode compartment is subjected to electrolysis in an auxiliary electrolyser to convert any thallium present into the metallic form.
8. A process according to claim 5, wherein the composition of the liquid contained in the compartment next to the cathode compartment is essentially the same as that of the catholyte.
9. A process according to claim 8, wherein the liquid in the compartment next to the cathode compartment is subjected to electrolysis in an auxiliary electrolyser to convert any thallium present into the metallic form.
10. A process according to claim 5, wherein the liquid contained in the compartment next to the anode compartment is an aqueous solution containing thallous ions.
11. A process according to claim 1 wherein the cathode is stainless and the anode is lead, lead oxide or a lead/ silver or lead/antimony alloy, the anolyte contains sulphuric acid and the catholyte comprises an aqueous solution of sodium hydroxide or sodium hydrogen carbonate.
12. A process according to claim 11 wherein the cell has from 2 to 4 compartments separated from one another by from 1 to 3 membranes respectively, having quaternary ammonium groups, electrolyte is circulated in each compartment, the temperature of the electrolyte is maintained at about 30 C. and the current density is about 5-25 amperes/sq. decimetre.
13. A process according to claim 1 wherein the concentration of the salt in the catholyte is 0.1-5.0 moles/ litre.
14. A process according to claim 1 wherein the current density is 0.5- amp./dm.
15. A process according to claim 1 wherein the electrolyte temperature is 0 C. to 60 C.
16. A process according to claim 1 wherein the alkali metal is lithium, sodium, potassium, rubidium or caesium and the ammonium ion is of formula NH R where x and y are independently 0 or a positive integer, the sum x+y being equal to 4, and R represents an alkyl radical the group R containing up to 16 carbon atoms.
References Cited UNITED STATES PATENTS 3,479,262 11/1969 MacLeau et a1. 204-80 3,616,276 10/1971 Schneder et al. 204-86 X 3,057,794 10/ 1962 Carlin 204-252 3,113,911 12/1963 Jones 20494 3,486,992 12/ 1969 Frye 204--86 FOREIGN PATENTS 73,069 8/1943 Bohemia and Moravia FREDERICK C. EDMUNDSON, Primary Examiner US. Cl. X.R. 20486, 91, R
V UNITED STATES ATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 r r 804 Dated September 18 1-973 I Inventor(s) LOUIS LE BRIS t al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
m In the heading:
Please correct the claim for Convention priority v .as follows; I t
-'--Claims priority, applications F rance' t February 17, 1970, No. 70,05623 and v 'December 31, 1970, No. 7o,47s48-- I y I Signed arid sealed this 30th day of July 1974.
v L) v r Attest:
MeCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents USCOMM'DC 60316-969 FORM Po-wsq no-s9).
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