US3849266A - Process for the electrolysis of alkali chloride solution - Google Patents

Abstract

The anodic overvoltage and the decomposition of the amalgam during the electrolysis of alkaline chloride solutions in electrolytic cells are reduced by adding to the electrolyte small quantities of one or more compounds selected from the group consisting of the ethers of alcohols or phenols with polyoxyethylenes and of the esters of carboxylic acids with polyoxyethylenes.

Description

United States Patent 191 H Corradi et al.

[ Nov. 19, 1974 PROCESS FOR THE ELECTROLYSIS OF ALKALI CHLORIDE SOLUTION Inventors: Bruno Corradi', Corso ltalia;

Vincenzo Petrillo, Cirie; Giordano Cimarosti, Roverbella, all of Italy Montecatini Edison S.p.A., Milan, Italy Filed: Aug. 2, 1973 Appl. No.: 385,042

Related U.S. Application Data Continuation of Ser. No. 130,472, April 1, 1971, abandoned, which is a continuation-in-part of Ser. No. 796,190, Feb. 3, 1969, abandoned.

Assignee:

Foreign Application Priority Data Feb. 6, 1968 Italy 12416/68 U.S. Cl 204/98, 204/99, 204/128 Int. Cl. C01d 1/06, COld 1/08 [58] Field of Search 204/98, 99, 128

[56] References Cited UNITED STATES PATENTS 3,630,863 12/1971 Jeffery et al. 204/98 Primary Examiner-R. L. Andrews Attorney, Agent, or FirmStevens, Davis, Miller &

I Mosher [5 7] ABSTRACT 12Claims, No Drawings PROCESS FOR THE ELECTROLYSIS OF ALKALI v CHLORIDE SOLUTION This is a continuation, of application Ser. No. 130,472, filed Apr. l, 1971 and now abandoned which in turn was a continuation-in-part of application Ser.

No. 796,190, file Feb. 3, 1969, and now abandoned.

This invention relates to a process for the electrolysis of solutions of alkaline chlorides. More particularly, this invention has for its object a process for reducing the anodic overvoltage during the electrolysis of solutions of alkaline chlorides in cells having a mercury cathode and in diaphragm cells and for reducing the decomposition of the amalgam during the electrolysis of said solutions in cells having a mercury cathode.

It is well known that the voltage that must be applied in practice to said cells is definitely in excess of the sum of the electromotive force of the electrolysis reaction and of the voltage drops due to the resistance of the electrolyte, of the electrodes and of the electrical connections. One of the main reasons for this voltage excess lies in the gaseous barrier arising from the formation on the anode surface of relatively large chlorine bubbles which reduce the active surface of the anode itself.

Another drawback in the operation of cells having a mercury cathode arises from the development of hydrogen caused prevailingly by the presence of impurities in the brine, which impurities act on the surface of the amalgam as active centers for the decomposition of the amalgam itself.

This decomposition, although of relatively little extent, causes however a useless consumption of current and leads to a contamination of the chlorine produced in the cell, with consequential complications arising in the liquefaction plant for the produced chlorine.

Furthermore, if the development of hydrogen reaches values exceeding about 7 percent by volume, explosive mixtures may form.

Thus, one object of this invention is that of reducing the anodic overvoltage during the electrolysis of solutions of alkaline chlorides in electrolytic cells having a mercury cathode and in diaphragm cells.

Still another object of this invention is that of reducing the decomposition of the amalgam in electrolytic cells having a mercury cathode.

A further object is that of attaining all the objects specified before also in the electrolysis operations when carried out under high temperatures, that is, at temperatures between 70 and 90C.

All these objects, as well as many others, are attained by the process of this invention, according to which the anodic overvoltage (in cells having a mercury cathode and in diaphragm cells) and the decomposition of the amalgam (in cells having a mercury cathode) during the electrolysis of solutions of alkaline chlorides are reduced by adding to the electrolyte from 2 to 200 ppm of at least one compound selected from a group consisting of alcohol ethers or phenol ethers with polyoxyethylenes and of esters of carboxylic acids with polyoxyethylenes.

In the case of ethers of alcohols with polyoxyethylenes, the alcohols used are generally aliphatic or aromatic alcohols of which the alkyl radical contains from 2 to carbon atoms. The aliphatic chain linked to the alcoholic group may be linear or variously branched. The alcohols may contain one or more additional functional groups, and more particularly: OH, Cl, Br, F, SO H, SO Me wherein Me is an alkali metal, COOR wherein Ris an alkyl radical containing from one to four carbon atoms, and

wherein R and R are hydrogen or alkyl radicals containing from 1 to 12 carbon atoms. Preferably, the alcohols contain from 8 to 20 carbon atoms. Particularly suitable are the aliphatic alcohols containing from 12 to 18 carbon atoms.

Some specific examples of suitable alcohols are, for instance, lauryl alcohol, oleyl alcohol, stearyl alcohol and phenylethyl alcohol.

The ethers derived from the condensation of such alcohols with ethylene oxide contain, in general, from 2 to l5O molecules of ethylene oxide for each molecule of alcohol. Preferably they contain from 10 to molecules of ethylene oxide for each alcohol molecule. The degree of ethoxylation that gives the best results depends in part on the nature of the R-radical. Amongst the alcohol ethers with polyoxyethylenes which have yielded the best results may be listed the monolaurylethers of polyethylenglycols containing from 10 to 30 ethoxy groups and the monooleylethers of polyethylenglycols containing from 60 to 120 ethoxy groups.

The ethers of phenols with polyoxyethylenes suited for the purposes of this invention may be represented by the general formula:

o-om-cm)..oir

wherein:

R is an alkyl or aralkyl radical having from 1 to 20 carbon atoms and n is between 2 and 40, inclusive.

The alkyl radical R (or the alkyl part of the radical) may be linear or variously branched.

The radical may contain one or more additional functional groups, in particular those already specified for the alcohol condensates with ethylene oxide.

Preferably, the R radical contains from 8 to 20 carbon atoms. Particularly suitable are the compounds in which R contains from 8 to 13 carbon atoms. If R is an alkyl radical, it may for instance be an octyl, nonyl, dodecyl or tridecyl group.'lf it is an aralkyl radical it may, for instance, be a cumyl or methylcumyl group. The radical may be in an ortho-, paraor metaposition with respect to the polyethoxy chain.

Because of the method of their preparation these compounds are generally mixtures of numerous isomers and homologues, both as far as the alkyl chain is concerned, which may be variously branched, as well as with regard to the position of the R radical with re spect to the ethoxy group.

Although good results are obtained when all the compounds have a degree of ethoxylation between 2 and 40, in general those are preferred which have a degree of ethoxylation between 5 and 30. Here again, the degree of ethoxylation which gives best results depends on the nature of the R radical.

Amongst the compounds having an alkyl R radical which have yielded the best results may be listed the following:

lst. the mixtures of paraand orthoisomers (e.g., with 90 percent of para and 10 percent of ortho) of the ethoxy derivatives of nonyl-phenol, having a degree of ethoxylation between 20 and 30, and

2nd. the ethoxy derivatives of iso-octylphenol, having .a degree of ethoxylation between 9 and 10; such products are well known under the trade name Triton X-lOO.

Amongst the preferred compounds having an aralkyl radical, there may be mentioned the derivatives of para-alpha-cumyl-phenol having the following general formula:

wherein: n is between 5 and 25, inclusive.

The esters of carboxylic acids with polyoxyethylenes suitable for the purposes of thisinvention are compounds having a degree of ethoxylation between 200 and 6000, derived from aliphatic or aromatic acids containing from 6 to 20 carbonatoms. The aliphatic radical of these acids may be linear or variously branched. The acids may contain one or more additional functional groups, and in particular those already specified previously. Preferably the acids are aliphatic acids containing from 12 to 18 carbon atoms. A few specific examples of acids suitable for the purpose are lauric, oleic, stearic and palmitic acids.

In the place of one single compound or of one single mixture of isomers there may be used with just as good results mixtures of compounds such as for instance a mixture of compounds having a differentdegree of ethoxylation derived from the same hydroxy compound or a mixture of compounds derived from different hydroxy compounds. Such mixtures of compounds may, for instance, include mono(para-alphacumylphenyl)ethers of heptaethylenglycol and of eicosane-ethylenglycol, that is, the derivatives of paraalpha-cumylphenol mentioned above where n=7 and n==20, or the mono(para-alpha-cumylphenyl)ether of heptaethylenglycol mixed with the mono-nonylphenyl ethers of eicosane-ethylene-glycol, that is, the derivatives of the nonylphenol mentioned above where n=20.

The quantities of additive may be varied within wide limits. Excellent results are obtained by using quantities between 5 and 20 p.p.m. by weight. The results are, however, just as good when greater quantities are used, for instance, from 20 to 200 ppm, although it is not necessary to make use of these higher quantities. Good results are also obtained with lower quantities, for instance with from 2 to 5 p.p.m.

The additives may be used with excellent results at any temperature between room temperature and C.

The feature of being able to use the additives at high temperatures (e.g., 7090C) represents a considerable advantage because said high temperatures correspond to high current densities and therefore to a greater potentiality of the cells.

The process of this invention may be applied with excellent results to all types of mercury cathode cells, that is, both to the horizontal cathode types and to the vertical cathode types and to all types of diaphragm cells as well as to all the types of anodes, that is both to the graphite anodes and to the metal anodes, for instance titanium anodes.

When the present process is applied to diaphragm cells, one does not see, obviously, the particular advantage due to the reduction of the decomposition of the amalgam.

The additives have proved to be equally efficacious throughout the range of current densities that are used in the electrolytic cells, that is in the range from about 20 to about amp/dm when working with graphite anodes and from about 20 to about 200 amp/dm when working with metal anodes. The current density is not a critical feature of the process of the invention but depends solely upon the characteristics of the cells employed.

The additive, which at room temperature may be solid or liquid, may be added as such to the brine before the introduction thereof into the cell or as solution in water or in the brine.

The solutions used for the purposes of the present invention have in general a concentration between 0.1 to 10 percent by weight. During the admixture of the additive to the brine, one must ensure an effective mixing in order to bring about a homogeneous distribution of the additive in the brine.

The following detailed working examples are given for the purpose of still better illustrating the inventive idea:

EXAMPLE 1 The tests were carried out in small experimental cells having Plexiglass walls, into which were placed in a horizontal position one or two graphite anodes at an adjustable distance from the level of the mercury that flowed on the bottom of the cell.

The anodic surface amounts to about 2.0 dm The concentration in NaCl of the brine fed into the cell amounts to 310 gr/lt (grams per liter): its pH is between 3 and 4. Its NaCl concentration at the outletequals 260-270 gr/lt. Its content in impurities is the following:

Turbidity (expressed as SiO,) 10 ppm (parts per million) CaO 0.0l-0.04 gr/lt MgO 0.005 gr/lt Fe 0.00l grllt Other metal cations 0.0l ppm Sulphate anions, expressed as S0, 2-5 grllt A current density of 70 amp/dm was applied. The temperature of the brine at the outlet of the cell was 76C.

The tests were carried out with different infraelectrodic distances, with the following additives:

l. mono(para-alpha-cumylphenyl) ether of heptaethyleneglycol (PCP-7);

For comparative purposes, each test was also repeated without the additives.

30 minutes after the starting of the cells, their voltage was measured and the concentration of the hydrogen in the electrolysis gas, which contains about 99.0 percent of chlorine by volume, was checked.

These measures were repeated every 15 minutes ,throughout the test, which lasted 3 hours. The conditions, as recorded below in Table l, were maintained practically constant throughout the test average temperature of the brine cell: 85C,

current density: 70 amp/dm The brine used was identical with that used in Example 1 its concentration in NaCl at the outlet of the cell being 270 gr/lt.

The experiments were carried out with the following additives:

1 mono-para-alpha-cumylphenyl) thyleneglycol (PCP-7);

2. nonylphenylethers of 30-ethyleneglycol (NF-30),

the mixture containing about 90 percent of paraisomers and percent of ortho isomers;

3. iso-octylphenylether of 9- and IO-ethylenegly'col (IOF-9 and lOF-IO), this product being known under the trade name: Triton X-lOO.

Tests nos. 1, 2 and 4 were carried out with anodes having been in operation for several months; in the case at the outlet of the ether of heptaeobserved a better distribution and uniformity in the development of gaseous bubbles on the anodes and inside th sqluti t.-. .1

The development of hydrogen was reduced, on the average, by about percent.

It may be noted that the conditions which obtain in .ths sualL inet msn ieellsss. stfqflrrsflssaiafa TABLE 1 Percentages by volume of Additive Concentration lnfraelectrode Tension in volts in the electi olysis gas in distance without with without with ppm in mm additive additive additive additive PCF-7 10 2.5 4.36 4.12 0.8 0.7 PCF-7 10 4.0 4.55 4.32 0.7 0.6 PCP- 10 2.5 4.35 4.15 0.7 0.6 NF-26 10 2.0 4.56 4.36 0.7 0.6 AL-20 10 2.0 4.32 4.15 0.7 0.6 AO-lOO 2.0 4.35 4.15 0.6 0.5

of test no. 2, the cell was very dirty. Test no. 3 was carried out with new anodes.

30 minutes after starting to feed the cells with the brine containing the additive, the voltage of each cell and the concentration in hydrogen of the electrolysis gas were measured, the electrolysis gas containing about 96% by volume of C1 The measurements were repeated every 15 minutes ,for a total duration of 8 hours. The resulting values are recorded below in Table 2 and remained practically constant throughout the respective tests.

TABLE 2 Percentages by volume of Number Additive Concentration Tension in volts H in the electrolysis gas of in without with without with Test ppm additive additive additive additive l PCP-7 20 4.58 4.42 1.0 0.6 2 PCP-7 10 4.70 4.40 0.9 0.8 3 NF-3O 10 4.65 4.40 1.1 0.9

lOF-lO) .as the decomposition of the amalgam is concerned, the

conditions actually existing in the larger industrial cells in which, on the contrary, there is found a much stronger decrease in the development of hydrogen. This is shown in the following example: 1

EXAMPLE 2 These experiments were conducted on an industrial scale in commercial De Nora cells having the following operational characteristics:

distamaabe n pu assua e;.absattttn..-

g The cells that operated with additive were maini. the ethers of alcohols with polyoxyethylenes tained in a condition of greater cleanliness. which R a. are derived from alcohols selected between all- EXAMPLE 3 phatic and aromatic ones and having from 8 to 20 carbon atoms, and

The tests of this example were carried out in pilot scale De Nora cells fitted out with dimentionally stable anodes manufactured by-Permelec. These anodes are made of titanium coated with metallic oxides such as ruthenium, iridium, tantalum and titanium oxides (for 10 a description of said kind of anodes, see, for instance,

b. contain from 2 to 150 molecules of ethylene oxide for each molecule of alcohol, ii. the ethers of phenols with polyoxyethylenes having the following formula:

'Dutch Patent Application No. 68/ 17957). The exact R composition of the coating is not specified by the manufacturer.

The whole anodic surface amounted to about 54.0 dm o-orr,-orr, norr The operational characteristics were: distance between anodes and cathode: about 3 mm;

. wherein average temperature of the brine at the cell outlet: 0 a. R is a radical selected between alkyl and aralkyl 85C; and has from 1 to carbon atoms, and current density: 125 (test 1) and 150 (test ,2) b. n is between 2 and 40, inclusive,

amp/dm iii. the esters of carboxylic acids with polyoxyethy- The brine used was identical with that used in Examlenes ple 1, its concentration in NaCl at the outlet of the cell which being 290 gr/lt. a. are derived from acids selected between ali- The experiments were carried out with nonylphenphatic and aromatic ones and having from 6 to ylethers of -ethyleneglycol (NF-30), the mixture 20 carbon atoms, and containing about 90 percent of para-isomers and 10 b. contain from 200 to 6000 ethylene oxide molepercent of ortho-isomers. 30 cules for each molecule of acid.

Thirty minutes after starting to feed the cells with 2. The process of claim 1, wherein the ethers of alcobrine containing the additives, the voltage of the cell hols with polyoxyethylenes contain from 10 to 120 and the concentration in hydrogen of the electrolysis molecules of ethylene oxide for each molecule of alcogas were measured, the electrolysis gas containing hol.

about 97 percent by volume of Cl 3. The process of claim 2, wherein the ethers of alco- The measurements were repeated every 2 hours for hols with polyoxyethylenes are derived from alcohols a total period of 8 days. having from 12 to 18 carbon atoms.

The resulting values are recorded in Table 3. They 4. The process of claim 3, wherein the alcohol is seremained practically constant throughout the respeclected from the group consisting of lauryl alcohol, oleyl tiyelests V w n alcohol, stearyl alcohol and phenylethyl alcohol.

TABLE 3 Percentages by volume of Number Additive Concentration Current Tension in volts H in the electrolysis gas of v in Density without with without with Test ppm amp/dm additive additive additive additive l NF-30 10 125 3.90 3.74 0.9 0.6 2 NF-30 I0 150 4.03 3.85 0.9 0.6

From an examination of Table 3, it can be seen that 5. The process of claim 1, wherein the R radicalof also in this case there was a considerable drop (0.16 the ethers of phenols with polyoxyethylenes contains 0.18 volt) in anodic potential. It can also be seen that from 8 to 20 carbon atoms and n is between 5 and 30,

the effectiveness of the additives is not lowered by an inclusive. increase in the current density as a higher drop (0.l8 6. The process of claim 5, wherein R contains from volt) has been reached with the higher density (150 8 to 13 carbon atoms.

p l 7. The process of claim 6, wherein R is selected from The development of hydrogen was reduced on the the group consisting of octyl, nonyl, dodecyl, tridecyl, average, by about 3 3 percent. cumy] and methylcumyL What claimed 8. The process of claim 1, wherein the carboxylic 1. In a process for the electrolysis of alkaline chloride b solutions in mercury cathode cells and diaphragm cells, gf fi ahphanc aclds havmg from 12 to 18 car on the improvement comprising reducing the anodic overvoltage in both kinds of cells and the decomposition of The Process of lem 1 8,Wherel n the acid 15 selecteg the amalgam in mercury cathode cells during the elecfl p conslstmg of laune, Olele, Steam trolysis by adding to the electrolyte from 2 to 200 ppm Palmmc acldof at least one compound selected from the group con- 10. The process of claim 1, wherein the aliphatic or sisting of, aromatic alcohol and acid moieties contain one or m or e aiafiofia l O H; Cl, Br, F, SO H, SO Me groupsin which Me is an alkali radical con- Q M e CQQIia Q g H taining from one to four carbon atoms, and

R1 I I R1 r N/ N groups in which Me is an alkaline metal, R is an alkyl groups in which R, and R are hydrogen or alkyl radiradical containing from 1 to 4 carbon atoms, and R gals tai i from 1 to 12 carbon atoms. and 2 are hydrogen alkyl Tadlcals comammg from 12. The process of claim 1, wherein from 5 to 20 ppm 1 to 12 carbon atoms. b ht f 10 d 11. The process of claim 1, wherein the R radical y 0 a a ls emp ye

Claims (12)

1. IN A PROCESS FOR THE ELECTROLYSIS OF ALKALINE CHLORIDE SOLUTIONS IN MERCURY CATHODE CELLS AND DIAPHRAGM CELLS, THE IMPROVEMENT COMPRISING REDUCING THE ANODIC OVERVOLTAGE IN BOTH KINDS OF CELLS AND THE DECOMPOSITON OF THE AMALGAM IN MERCURY CATHODE CELL DURING THE ELECTROLYSIS BY ADDING TO THE ELECTROLYTE FROM 2 TO 200 PPM OF AT LEAST ONE COMPOUND SELECTED FROM THE GROUP CONSISTING OF, I. THE ETHERS OF ALCOHOLS WITH POLYOXYETHYLENES WHICH A. ARE DERIVED FROM ALCOHOLS SELECTED BETWEEN ALIPHATIC AND AROMATIC ONES AND HAVING FROM 8 TO 20 CARBON ATOMS, AND B. CONTAIN FROM 2 TO 150 MOLECULES OF ETHYLENE OXIDE FOR EACH MOLECULE OF ALCOHOL, II. THE ETHERS OF PHENOLS WITH POLYOXYETHYLENES. HAVING THE FOLLOWING FORMULA:

2. The process of claim 1, wherein the ethers of alcohols with polyoxyethylenes contain from 10 to 120 molecules of ethylene oxide for each molecule of alcohol.

3. The process of claim 2, wherein the ethers of alcohols with polyoxyethylenes are derived from alcohols having from 12 to 18 carbon atoms.

4. The process of claim 3, wherein the alcohol is selected from the group consisting of lauryl alcohol, oleyl alcohol, stearyl alcohol and phenylethyl alcohol.

5. The process of claim 1, wherein the R radical of the ethers of phenols with polyoxyethylenes contains from 8 to 20 carbon atoms and n is between 5 and 30, inclusive.

6. The process of claim 5, wherein R contains from 8 to 13 carbon atoms.

7. The process of claim 6, wherein R is selected from the group consisting of octyl, nonyl, dodecyl, tridecyl, cumyl and methylcumyl.

8. The process of claim 1, wherein the carboxylic acids are aliphatic acids having from 12 to 18 carbon atoms.

9. The process of claim 8, wherein the acid is selected from the groups consisting of lauric, oleic, stearic and palmitic acid.

10. The process of claim 1, wherein the aliphatic or aromatic alcohol and acid moieties contain one or more additional -OH, -Cl, -Br, -F, -SO4H, -SO4Me, -COOR and

11. The process of claim 1, wherein the R radical contains one or more -OH, -Cl, -F, -Br, -SO4H, -SO4Me groups in which Me is an alkali radical containing from one to four carbon atoms, and

12. The process of claim 1, wherein from 5 to 20 ppm by weight of additive is employed.