US1919721A - Preparation of bromates - Google Patents

Description

, depolarizer.

' No Drawing;

Patented July 25, 1933 CARRO L-A. HOCHWAL'I imn aorrn BQWALIUSZIS, or DAYTONLOHIQ; AssIGnoIts 'ro MORTON SALT COMPANSQOF cr-ncaico; rumorsqagcongronn'rron or IL I OIS 'I REPAR TIQN or BnoMATEs and to' a method of purifying bromjates.

One of the principal objcctsof this inven- 5 tion is toproduce a pure andjcol orless bro"- 1nate,sucl1 as potassium bromate, froman in pureibromate such as is producedby .el'e'ctrolytic methods and using a chromateas I 'A'notherobject of the inyention' is to "pi-0 found most elfective forthis purpo'se is'me'a.

.. duce albromate which is free from chromates, by the use of an adsorbing mater al whlch has special affinity for the chromat e, such as metallic inc or zinc dust.- v

Other obj-ects'and advantages of theinventionjvill' be apparent from the following de scription and appended claims;

mide solutions. It is generally recognized that in order to produce a commercially prac-l v tical yield of bromat e,lthe' use of "a depola1- tassiumfdichromateg. It is found,,hoWeVer,

and yellow discoloration is thereby pro- 5 duced inthe finished crystals of bromate,

1 found practically impossibleto separatethis chromate from the bromate by fractional crystallization or wash ng or repreclpltag 7 ,tion as sufiicient chromate stlll remalns ,to

such' as potassium, bromate. It has been givean objectionable yellovv color to the bromate' crystals.- Ordinary adsorbing agents also have been found comme'rciallyinefl'e'c- -tive.-

- as an adsorbingagent therefor. V The material p 7 Q Various factorsare to be taken into account vide a. simple and practical method for pro- V 'ducing such pure and colorless bromate; Another objectof thisinvention is topro; 7

that. when achroinate is used in the ordinary manner as adepolarizer, part ofthe chromate' 1s carrledover into the solution of bromate,

We have now discovered that such 101-05; mates, containing chromate --as an impurity,

- can be-efiectively decolorized lily-treatment with a materialftound to, have a peculiar at finity for the chromate impurity "whenused 1 Application filedlvlarch13,1932, se ia1j ,'nb."ee0,065,

tallic zinc, which is conveniently and efi'ec-' ti ely used inthe form of zinc dust. r i As an example of thecarrying out of this? invention the following procedure is de-- scribed; i,

mides, such as potassium bromide, to pro duce a bromate such as'1:)otass1um bromate.

, Any suitable type of; cell construction} may be utilized for the electrolysis of broand calculated in the construction of theipar ticular cell used, so as to obtain a current sity of 3 to 9amperes per square decimeter has been found" to produce goodyields of I bromates. Carbon electrodes are foundsatis factory. The particular, cell described is givenmeiely asan example, as it willbe'read ily unde'rstoodthat such a cell may be con- One ofthe rnethods of commercial pro f duction of bromates is by electrolysis of brostructed to sa tisfy widely varying conditions; The essential factors iniany cell areso calcu-w lated and adjusted'as to produce the required bromates." v, A cell designed ;asjfollows was found to produce good :results :7 The cell used has 'a capacity of gallons, The ei'ghtof "100 conditions '1 for electrolytic j production of gallons of 25 per cent potassium bromide b solution is approximately pounds, the Weight of potassium br'oui ide'heing approxl mately'256 pounds. 4 The current required for *conversion of this amount of bromidelto bro;

mate is calculated as 1 57,0 49r ampere hoursi 7 required is'19 6l3hours; the theoifeticalfpro Assuming a current of 800 amperes,the}time duct-ion is 359 .2*pounds oi potassiumfbro mate. Assuming a cell efficiency of 66 'perg cell is 239.2'pounds1 l V H q i. The cell us'ed was' arectangular iron-tank cent, the broinate produced" l '7 lined with'tile, V Anydesired non-corr'osiveor.

non-contaminating material be used for;

construction of the tank. For example, glass i lined tanks are satisfactory. The ins de d151,

mensions of this cell 5' are: 29 inclies'by 22" inches by 42: inches infheight. The liquor 'levelwhen the; @611 is filled with 100 gallonsof-liquorhasa' height of 3.017-fet. An elec-} trode immersionof} 27 inches was required'in' order to give a current density of 7 amperes per square decimeter. The electrodes are of graphite 2 inches square and 33 inches long. The 12, electrodes used displace about 1 linches of'liquor. i The exactdisplacement is determined with each setfof electrodes'used. These dimensions allow a 10 inch free space onthe bottom ofth'e tank, the liquor level being about4s5 inches below the top of the tank. j v

i The potassium bromide solution (100 gallonsof 25% potassium bromidesolution) containing 0.5 gram of potassium chromate per liter asa depolarizer, is electrolyzed in the described cell. The electrolysis is continued for the calculatedperiod of time required for com plete conversion of potassium bromide to po-l' tassium bromate. V The solution is then pumped intofan adjoining jacket tank. This tank may be constructed or lined with any desired non-corrosible material, for example the tank may be glass lined or enamel lined. In

tank the solution is diluted with a suiiicient volume of water .to completely dissolve all potassium bromate crystals. The diluted solution is'preterably boiled until complete solution has taken place. The solution is then filteied toremove any foreign'matter,

such as graphite particles from the electrodes.

When the mother liquor is used for make-up liquor, it is found that a number of runs may he made withoutfurther addition of potasium chromate. "After 5 or 6 runs, however,

3 an additonal small amount of potassium chromate, such as, fonexample, about; 13

grams .per gallon of electrolyte, isfound to increase theyieldofsbromat The-crystals of potassium bromate which at .thisstage are Y llow in color, are redissolvedin asuitable amount ofwater; for example, for the amount specified, about gallons of water was used. The. solution is. gieat'etl and then treated with a material which d rbs chromium such as mistallizinc or zinodust. When zinc dust is used, the .pro-

portion of approximately 2 grams of zinc I vdust .per 100 grams of potassium bromate a-rysta'ls h as been found to be eiit'ective." Mater-ially smaller proportions of ,zinc' 'appan 5 ently. do not-produce complete decolorization of the bromate crystals. --;The zinc dust shmilldibeadded to h .P assium bromate. ifdlliifl l'a y and Wi h: continuous -a it tron in order toget good contact.

"In this-treatment it 'is believed that two Y reactions go on simultaneously; in the first reaction the zinc. dust appears. to adsorb the chromate ions 1n somewhatthesame manner as activated charcoal adsorbs organic material. In the second reaction the Zinc appears to react with free potassium hydroxide which is'present in the solution, probably forming a potassium zincate, which apparently in turn hydrolyzes to form zinc hydroxide. The Zinc hydroxide then precipitates from the solution. The zinc hydroxide together with unchanged .Zinc dust, which carry along the chromate, are then filtered oif. The filtrate is evaporated until potassium bromate crystals begin to form and the solution is then cooled until the potassium.

bromate has been crystallized out. I The motherliquor is'decanted ofl and may be pumped back into the original mother liquor and used as make-up liquor for another electrolysis. tained in the form of pure white crystals.

When potassium bromate crystals produced from an electrolysis subsequent to the first electrolysis ina series of runs, are treated according to this method, it is found that the alkalinity of the bromate solution is increased, anddecolorization is in some cases not complete. 'However, in such cases, the alkalinity of the solutioninay -be adjusted by the addition of a small proportion of hy-' drobromic acid to the bromate solution.

"Complete decolorization upon treatment with zinc may thus be obtained. For exam- The potassiumbromate is now ob ple, about 05% by weight of hydrobromic coloriz ed when the pH value of the solution is approximately 8.00. However, determinatlons of pH values on bromate solutions have been found somewhat unreliable. The proportionjolf hydrobromicacid (if any) re quired for any run may be determined by taking test samples of the bromate solution before the treatment with metallic zinc. Suchftest samples are treated with zincv and the potassium bromate crystallized accord-.

necessary to produce white crystals of potassium bromate, and the proportion of hydrofor zinc and potassium bromide are negative.

A saturated solution of these potassium bromate crystals in Water is a water-white liquor, with no trace of insoluble material.

Tests for "all metals except potassium are negative. Where potassium bromate of a particularly high degree of purity is rewhetherfthe addition ofhyd'robromic acid is quired, recrystallization of the bromate crys tion is not limited to these precise features,-

and that changes may 'be made therein-withoutdepartingfrom the scope of the inven- What is cla'imed'is:

tionwhichis definedin theappended claims;

1. In theipro'cess of making-a colorless alkali bromate from an alkali bromate containing a chroinate, the step of removing the chromate by treating. the alk tion with metallicfzinc, 7' f 2. In the process of making acolorless 7 alkali "bromate from' a discolored alkali bromate containing a chromate, the steps of. adding" hydrobromic acid j to' the alkali bromate solution, and then removing the tion with metalliczinc chromate by treatingthe: alkali bromatesolu- In the manufacturelof alkali bromates by the electrolysis of bromideswherein an alkali bromide solution containing a 'chro mate asa dep'olarizer is electr'olyz edto producealkali bromate crystals*containing chro I mate as an vimpurity, and impure br'omate 'to obtain an alkali bromate free'from chro crystals are separated from the solution, the

steps which comprise forming a solution'ot the impure alkali,bromatecrystals,adding ymetallic lzincto the solution to adsorb the chromate impurities and separating the zinc i with the chromate from the bromate solution mate, Q v i 4. In the manufacture of bromate by elec taining 'chromate as an impurity,-the steps which comprise forming a-solution of the im- V to adsorb the chromatic iIIlPIIIIt-lGS,

V to obtain a bromate free from chrom'a'teQ ,1 y I i I 5. In the manufacture of alkali'brom ates by electrolysis of bromides-wherein a solution of an alkali bromide containing achromate as a depolarizer is electrolyzed'to'producealkali bromate containing chromate as an impurity, the step which comprises treating the alkali hromate in solution form with metallic zinc ali bromate solumates bythe electrolysis of bromides-whereinproduce potassium bromate crystals containa potassium 'gbromide solutioncontaining-a- 1 I chromate as adepolarizer ls'electrolyzed to g ing chromate; as an impurity, and impure potassium bromate' crystals are separated from the solution, the steps Which comprise forming asolut on of the lmpure potass um bromate crystals, adding metallic zinc to the solutionitofadsorb the chromate impurities I and separating the zinc with the chromate potas from the bromate solution to obtain a sium bromate free from chromate.

7. In the manufacture of alkali bro'mates by electrolysis of bromides wherein an alkali bromide solution containing a chromate as a impurity, the steps which comprise forming a solution of the impure alkali bromate con f tamlng a'chromate as an impur ty, adding hydrobromic acid, treating. the alkali brosolution. a r V V r 8. Inthe manufacture of'br'omates by the electrolysis of bromides wherein a bromide solution containing a chromate as a depolariz er is electrolyze'd to produce br'omate crystals containing chromate as an lmpurlty and the impure bromate is separated from the depolarizer is electrolyzed toproduce'alkali bromate crystals containing chromate'as an solution, the steps which comprise'forming a 7 solution of the impure bromate-crystals, adding hydrobromic acid, treating the bromate V solution With metallic Zinc to adsorb the V chromate impurities, and separating the zinc j trolysis of bromides Whereina bromide 'solu; tion containing a chromate as adepolarizeris .electrolyzed to produce bromate crystals con with the chromate from the bromate solution.

9. Infthe manufacture of alkali bromates by the electrolysis'of bromides wherein an alkali bromide solution containing a chro- .mate as a depolarizer is electrolyzedto-propure bro'mate'cr'ystals, adding metalliczinc to!" r the solution to adsorbthe chromate impuri ties and separating zinc with the chromate from the bromater solution,

duce alkali bromate crystalsicontaining chro mate as an impurity and the mpure bromate alkali'bromate crystals, adding hydrobromicy acid, adding metallic zinc to the solution to adsorb. the chromate impurities, separating thezinc with the chromate from the alkali bromate-solution, and evaporating the bromate solution to obtain White alkali bromate crystals; f v a CAR-ROLLA; HOCHWALT JOHN B. WALIUSZIS.