CA1089627A - Process for manufacturing chlorine dioxide - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Chlorine dioxide is generated very efficiently and safely by reducing a chlorate in a strong acid in the presence of a catalyst containing thallium ions together with palladium ions or silver ions.

Description

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1. ~ield of the Invention ~ .
~ his invention relates to a process ~or manufacturing chlorine dioxide by reducing a chlorate in a strong acid in the presence o~ a catal~t.

2. ~Descri~tio~ of Prior Art:
Chlorine dio~ide is a commercially important material in such ~ields as pulp bleaching, water treatment and ~at decoloring, and also has recently been used in the fields of denitration o~ i~dustrial waste gases and removal o~ phenols ~rom industrial sewage. ~hus it is highly desirable to have a process by which chlorine dioxide can be manufactured `
economicall~. Further it is desirable to have a safe pxocess in which the generation of chlorine dioxide can be easily controlled withsut any danger of explosion.
One of the mëthods for generating chlorine dioxide is to reduce a chlorate with a reducing agent in a strong acid. ~he reactions which occur are exemplified below, wherein, for the sake o~ illustration, the chlorate used is sodium chlorate and the reducing agent is hydrochloric acid.
NaC103 ~ 2HCl--~ C102 ~ 1kCl2 + NaCl + H20 (1) ~aC103 + 6HCl~-~ 3C12 + ~aCl + 3H20 (2) ~urther, the reactions which occur are exemplified bèlow wherein the chlorate used is sodium chlorate, the ~ F
reducing agent is sodium chloride and the stro~g acid is sulfuric acid.
NaClO + ~aCl ~ X2S04--~ C102 ~ ~C12 2 4 2 NaClO3 ~ 5~aCl + 3H2S04 ~ 3Cl2 ~ 3Na2S~ + 3~2 (4) Chlorine dioxide is formed by reac-tion (13 or (3), but . .
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not formed by reaction (2) or (4) which compete~ with reaction (1) or (3).
Accordi~gl~, reaction (1) or (3) mu~t be accelerated ' , in order to generate chlorine dioxide efficie~tly. A use-ful method to achieve thi3 purpose is to use a catalyst which accelerates reaction (1) or (3) in preference to reaction (2) or (4). ,, Palladium wa& described in Japa~ese Patent Publica-tion No. 2,645/1970 as a catal~st ~or chlorine dioxide produc~io~. Yanadium pentoxide, sil~er io~ manganese ion, dichromate io~ and arsenic ion were de~cribed in U.~. Pa~. '

3,5~3,702 for the ~a~e uæage. ~urt~er~ for the,same purpose Japa~ese Pate~t,Publications ~os. ~,~19/1960~ 7~01/~962 , 14,958/1964, 17,047~1966 disclose manganese co~pounds;
silver ion or a co~bination of silver ion and manganese ion;
manganese(II) chelate cn~pounds alone or,combi~ation of manga~ese ¢helate compounds a~d metal,~equestering age~ts;
' lead ion or a combination of lead ion9 ~angaaese ion and 3ilver ion; re~pectivel~. It is well known in the field of this invention that the ratio of the rate of reactio~ ' t1 ) or (3) to that of reaction (2) or (4) decrea~es at lower ~ ' values of the chlorate-to-reducing agent molax ratio and at ,.
lo~er acid concentrations o~ the reaction medium~ ~owever, , , - although the generatio~ of chlorine dioxide under such ~:
co~ditions can be controlled more easily, tho~e catal~t~ ,:
do not have sati~acto~y activities u~der the co~ditions de~cribed abo~e. Even with palladium which shows the :' highest acti~it~ among thema the ratio of the rate of :
reaction (1) to that of rea~tion (2) ~ound under the following ~,,- ,.
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conditions scarcely exceeds a value of 17: an acid concentration ' '. "', - 3 ~ , : :, -~: ,.
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of 0.4 moles per liter of the reaction medium, a chlorate-to-reducing agent molar ratio of 0.27 and a palladium(II) concentration of.O.001 mole per liter of the reaction . medium.
Recently, a process for manu~acturing chlorine dioxide at lower acid concentrations and at remarkably high concentrations of a reducing agent ~e.g., Bri-tish Patent No. 1,347,740) has been developed. Under such reaction conditions even more active catal~sts are re~uired in order to generate chlorine dioxide without loss of efficiencyO ~'' - SUMMARY OF ~HE INV~TION
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- It is an object of this invention~ therefore, to provide an eæcellent catalyst for e~ficiently manufacturing chlorine dioxide, said catal~st having a high catalytic activity even under the easil~ controlla~le conditions of low acid concentrations and low chlorate-to-reducing agent molar ratlos of the reaction medium.
It~is another object of this invention to provide a process for e~ficien-tly manufac-turing chlorine dioxide by using an excellent catalyst which has a high catalytic activity even under the easily controllable conditions of low acld concentrations and low chlorate-to-reducing agent molar ratios o~ the reaction medium. .
Other objects and advantages of the present invention may become apparent to those skilled in the art from the following description and disclosure.
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HE DR~AWING
Figure 1-shows the synergism experimentally found between thallium ions and palladium ions; and -; _ ~. "' ,:
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~ igure 2 shows the s~nergi~m experimentally found between thallium ion~ and silver ions.
D~SCRIPTION 0~ ~HE PREFERRED EMBODIME~T
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~his invention relates to a process for manufactur-ing chlorine dioxide b~ reducing a chlorate in a strong ' ' acid in the presence of a thallium ion catalyst or a mixed oQtal~t consisting o~ said thallium ion catalyst and an ionic catalyst selected ~rom the group consisting of silYer ;
ions~ manganese ions9 dichromate ions, lead ions and pal ladium ions.
~he strong acid u~ed in the process of this invention is selected from the group consisting of sulfuric acid, hydrochloric acid and a mixture thereof. ,~he concentration , , of the sulfuric acid may be from about 0.5 to about 6 moles per liter of the reaction medium. ~he concentration of the h~drochloric acid may be ~rom about 0.01 to about 4 moles per liter of the reaction mediumO But if the conce~tration of ~ulfuric acid is below,O~5 or that of hydroohloric acid ~ ' , below 0.01 mole per liter, the rate o~ chlori~e,dioxide , ~' gener~tion becomes too ~low. On the other hand, if the ~'''~ ' conce~tration of sulfuric acid exceed~ 6 or that of hydro-chloric acid ~ moles per liter, the rate of reactio~ become~
too ~ast to assure safet~
, ~aid chlorate i5 gener,ally selected from the group consisting of sodium chlorate, potassium chlorate, calcium c~lorate and magnesium chlora~e. ~he concentration of the '~ ~;
chlorate ma~ be from 0.0~ to 5 moles per liter of the reactio~ medium. If it i~ below 0.01 mole per liter~ the ¦
rate of chlorine dioxide ge~eratio~ becomes too ~low. 0~ ¦
the other hand, ifit exceed~ 5 mole~ per liter of the "~

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reaction medium~ i~ becomes ~oo f~st to assure safet~ in operation and the loss of the expensive c lorate increase~.
As said reducing agent 9 sulfur diogide 9 methanolg sodium chloride~ calcium chloride~ potassium chlorate or hydrocbloric acid is commonly u~ed.
The concentration of said thallium ion catalyst may be from 0.00001 to 0.1 mole per liter of the reaction mediumO If it i3 below 0.0000~ mole per liter, the rate of chloriue dioxide generatio~ is ~ot accelerated by a measura~le amount. 0~ the other hand-9 when it i9 above 001 mole per liter of the reaction medium, there is no particular adva~tage and the productio~ cost becomes higher.
~he preferred concentration of said thallium ion catal~st is ~rom 0.00005 to 0.05 moles per liter of the reaction medium.
The compounds forming said th~llium ion catal~st in the reaction medium include thallium chloride~ thallium fluoride, thallium bromide, thallium iodide, thallium oxide, thallium hydroxide, thallium sul~ide9 thallium sulfa~e, thallium nitrate, thallium formate, thallium malo~ate a~d the Iike.
If the thallium ion catal~st is used together with any co~ventional catalyst~ catalytic acti~it~ increa~es remarkabl~ uch catal~ts~ ~ilYer ion~, m~ngane~e ions, dichroma~e ions, lead io~3 or palladium io~ are u~ed.
The co~centratio~ of ~ilver ions, mangane~e ions, dichromate io~s, lead ions and palladium ion~ in the reactio~ medium ma~ be from 0.00001 to 0.01 mole per liter, ~rom 0.00001 ~o 1 mole per litsr, from 0.00001 to 0.1 mole pex liter, ~rom 0.00001 to 0~1 mole per liter and from 0.00001 to 0.1 mole .

~96Z~7 per liter, respectivel~.
~he compounds of the silver ion catalyst include bro,~e er acetate, silver axsenite, silver ~æc~ ilver carbonate, silver chloride, silver chxomate, silver dichromate, silver fluoride, silver nitrate, silver nitrite, silver oxide, silver perchlorate, silver phosphate, silver ~ulfide, silver sulfate, silver sulfiteg silver thiosulfate, silver chlorate9 silver thiocyanate and the like.
'~he compounds forming the palladium ion catalyst in the reaction medium include palladiuffi fluoride, palladium chloride, palladium bromide, palladium oxide, p~lladium sulfide, palladium nitrate, palladium nitrite~ palladium sulfate9 palladium thiocyanate, palladium ammonium chloride, palladium sodium chloride, palladium potassium chloride and the like ~he compounds forming the manganese ions catalyst in the reaction medium include manganese acetate~ manganese ammonium sulfate, manganese phosphate, manganese bromide, manganese carbonate, manganese chlsride, m~nganese dioxide~
manganese hypophosphite, manganese nitrate~ manganese ~ormate, mang~nese pyrophosphate, manganese sulfate, m~ng~nese sulfite and the like.
The compounds ~orming the dichromate ions in reaction medium i~clude zinc dichromate, ammonium dichromate, potas sium dichromate, silver dichromate, sodium dichromate, -~barium dichromate7 lithium dichromate and the like.
~he compounds of the lead ion catal~st include lead acètate, lead ar~enite, lead bromide, lead carbona~e, lead ~;~
chloride, lead fluoride, lead formate, lead h~pophosphite, lead mol~bdate, lead nitrate, lead phosphate, lead phosphite, . . : ..................... . ............... . . . .
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lead sulfate, lead sulfide, lead thiocyanate, lead vanadate and the like.
~ he thallium ion catalyst of the present invention accelexates the rate of reaction (1), but doe~ not accelerate that of reaction (2). ~ccordingly, the catalyst increases the conversion from the chlorate to chlorine dioxide.
Furthermore, if the thallium ion catalyst is used together with the ions selected from the group consisting of silver ions, manganese ions~ dichromate ions1 lead ions and palladium ions, catalytic activity increases remarkably. -~or example, the ratio of the rate of reaction (1) to that of reactio~ (2) in hydrochloric acid was fou~d to be 30 in the presence of palladium ions only, whereas a value of as :~
high as 60 was obtained with a mixed catalyst consisting ;
1~ of thallium ions and palladium ionsO
Advantages obtained with the present invention are as ~ollows: The rate of reaction (1~ is remarkably accele-rated by add1ng the thallium ion catalyst or the mixed oatal~st consisting of said thallium ion catalyst and con-ve~tional catalyst to the reaction medium even at low acidconcentrations or low chlorate-to-reducing agent molar ratio~
Accordingly, the volume of the reaction vessel re~uired for generating chlorine dioxide at a given rate can be reduced remarkably from those most frequently used in the prior art.
~he concentrations of the chlorabe and the strong acid in the reaction medium can be reduced by adding thereto the thallium ion catalyst or the mixed catalyst consisting of said thallium ion catalyst and a conven~ional catalyst. As a result, the generation of chlorine dioxide is controlled ~-more easily and becomes more efficient~ ~urthermore, ;. ' ~ "'.
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~' ' ,, ;'' ' ', ,. ", . " ~,' ' ' '. ' ' ' 1 , ~96Z7 ab~o~al ganeration or 0xplos~0n of chlorine dioxide ca~
be avoided, since lower reaction temperatures ca~ be u~ed.
The ~ollowing e~amples are given to further illustrate this invention, but it should be understood that the invention i~ b~ no means limited thereto. On the contrary, the~ are given only to clarif~ some o~ the essential working modes of the present invention.

One hundred and fifty ml of a~ aqueous solution .; .
~0 containi~g NaCl and ~aC103 were charged in a ~our-necked ~lask and the solution was kept at 70~C. One hundred and - fifty ml of a~other aqueous solution containing HCl, NaCl and thallium chloride were heated up to 70C and wa~ added to the ~ir~t solution. ~hus, chlorine dioxide was generated.
~5 ~he compositio~ of the reaction medium was 0.4 mol/~ HCl, 100 g/~ NaC103, 200 g/~ NaCl and 0.01 mol/~ thallium ions.
The reaction medium was agitated b~ introdu~ing air thereto a~ about 500 ml/min and then the reactio~ medium and the gas phase were ~nalyzed eve~ ~ minutes.
The rate at which NaC103 was consumed b~ reactio~
(1), R1, was 0.72 m mol/~-min and that by reaction (2), R2, wa~ 0.12 m mol/~min whiie the concentration of HCl decreased to 0.~ mol/~. Accordingl~9 the ratio of R1 to R2 was 6Ø
~ . ': . ~he experiment of Example 1 was repeated but without thallium ions.
~he rate at ~hich NaC1~3 was consumed by reaction (1), R1, wa~ 0.24 m mol/~omin and that b~ reaction (2~, R27 was 0.13 m mol/~-mîn while the concentration of HCl decreased to 0.3 mol/~. Accordingl~, the ratio o~ R1 to R2 was 1.8.

89~2 Exam~les 2 - 5 and Reference ExamDle 2 The experimen~ of Example 1 was repeated except that a mixed catalyst co~sisting o~ thallium ions and palladium lons or a palla~lum ion catal~st was used.
~he re~ults obtained are given i~ Table 1 below.
Table 1 .
Concentration of Rate at which ~aClO~ was Example c ~ ~ _ consumed Reference ~hal- Pal~ r(eaction By reaction R /R
Example lium ladium ( ) 1 2 ~.
ions ions ~1 R2 ~

Example 2 0.009 0.001 3.80.11 35 :
Example 3 0OOo7 0~003 6.60.12 55 Example 4 0.005 0.005 7020.12 60 . . ......... ....... . . . . .. .. .. . . . .
Example 5 O r OO3 0 ~ 007 6.80~13 52 ReferelCe2 0.0 0.01 3A9 _,, '.
~ he relation between the ratio of the rate at which ~aC103 was consumed b~ reactio~ (1) to that by reac~ion (2) and the concentration o~ the mixèd catal~st consisting of thallium ions and palladium ions in the reaction medium in ~xamples 1 - 5 a~d ~efere~ce ~xample 2 described hereinbefore ~;
are illustrated in ~igure 10 ' ~igure 1 obviousl~ show~ a catal~tic s~nergism betwee~
bhallium ions and palladium ions.
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q~he ex~?eriment of :Example 1 was repeated except that the :nature a~d the co~cerltra~ion of the cataly~t were .
ch~nged., ~ i ,: ,, 1 il .. .
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~he results obtained axe given in ~able 2 below. -~

~able 2 ~_ ~ , Conce~tration of mixed Rate at which NaClO was ~==~ . . .
~xamAdditional By reaction By reaction ~ ~h lli tal t (1) (2) R1fR2 ion Concen- R~ R~
--(mol/R) ions tration (m mol/~-min)(m mol/R'min) 60.001 Mn2~ o.oo5 6.0 0.12 50 70.001 Cr207~ 0.01 2.7 0.11 25 80.001 Pb2+ 0.01 2.9 0.11 27 If manganese ions, dichromate ions and lead ions alone ' were used at a concentration in the reaction medium of as -high as in Examples 6 - 8, the ratios of R1 to R2 were 24 6, and 5, respectivel~. Accordingly~ catal~tic s~nergism ~as obviously proved betwee~ thallium ion and other catal~sts. l-1 :' One hu~dred and ~ift~ ml of an aqueous solution containing ~aCl and ~aC103 wexe charged in a four~ecked flask a~d the solutio~ was kept at 70~C. One hundred and ~ift~ ml o~ another a~ueous solution containing H~SO~ ~ j NaCl, thallium nitxate and silver nitrate hea~ed up to 70 C
were added to the fir~t solution. ~hu~ chlorine dioxide .
was generated. ~he composition of the reaction medium was 2 mol/~ H2S04~ 100 g/,e ~aClO3, 50 g/R ~aCl, 0.0008 mol/,e ~15 thalli~im ions aIld 0.0002 3ilver io~ he reaction medium wa~ agitated by introducing ai:r thereto at about 1.5 R/min a~d then t:he reaction medium and ~he ga~ phase were analy~ed ~ .
e~ery 5 minutesO . I .

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~he ra~e at which NaClO3 was consumed b~ reaction : .
~3)~ was 27.0 m mol/~ min and that by reaction (4), R2, was 0.27 m mol/~-min while the concentration of E2~04 decreaæed to 1~75 mol/~. ~ccordingly, the ratio of R3 I:
~o. R4 was 100.

~he experiment o~ Example 9 was repeated except I .
that the concentration of the mixed catalgst consisting ,~`
o~ thallium ions and silver ions was varied.
The results obtained are given in Table 3 below.

able ~ ,.

Concentration of Rate at which ~a~lO was Example c ~ l/~) consumed 3 _ or ~hallium ~ilver By reac)lon By reaction Re~erenCe ions ions R3 (24 R /R
(m mol/R~min)(m mol/R min) -- - ---- --- - . ~ , Example 9. O.0008 0.0002 27 .27 100 Example10 0.001 0.0 3.3 0.27 12 .
Example11 0.0006 0.0004 27 0.28 96 ~ ~
~Xample12 0.0004 ODOOO6 17 0.27 63 .
Example13 000002 0.0008 14 0.28 50 ~xample 3 ' 0.001 11 0.28 39 Re~erence E~ample 4 ~ 0.0 1.6 0.27 5-9 ..
The relation between the ratio of the rate at which NaC103 was consumed by reaction (3) to that by reaction (4) and the concentration of the ~ixed`catalys-t consisting of ::
thaDium ions and silver ions in the reaction medium in ~xamples 9 - 1~ ana Reference Examples 3 - 4 described here-inbefore are illustrated in ~igure 2. - : :

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1~8~ 7 1 Figure 2 shows obviously the catalytic synergism between thallium ions and silver ions.
Example 14 . _ Two and one-half liters of an aqueous solution con-taining 100 g/Q sodium chlorate, 240 g/~ sodium chloride, 0.177 g/Q
palladium chloride and 2.40 g/Q thallium chloride was filled in a reaction vessel and water was withdrawn therefrom at a rate of approximately 3 g/min under a reduced pressure of 195 mmHg at a temperature of 70C. Concentrated hydrochloric acid and a 700 g/Q sodium chlorate solution were continuously fed to the reaction vessel to maintain the volume and composition of the reaction medium substantially constant. Samples were taken every 30 minutes to analyze the gaseous mixture and the reaction medium.
The mean composition of the reaction medium was found to be 0.2 mol/Q in hydrochloric acid~ 100 g/Q sodium chlorate and 278 g/Q -sodium chloride.
The ratio of the rate at which NaC103 was consumed by reaction (1~, Rl, to that by reaction ~2), R2, was 49.
The results reported in ~'ig. 1 establish that the best results are obtained when the thallium ions are in a concentration between 0.003 and 0.007 mol/Q and the palladium ions are in a concentration between 0.007 and 0.003 mol/Q. This is a preferred ratio of thallium ions to palladium ions of from 3:7 to 7:3.
The data reported in Fig. 2 establishes that the best results are obtained when the thallium ions are in a concentration between 0.0004 and 0.0008 mol/Q and the silver ions are in a concentration between 0.0002 and 0.0006. This is a ratio of thallium ions to ;~
silver ions of from 4:6 to 8:2.
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Claims (4)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for manufacturing chlorine dioxide by reducing a chlorate with chloride ions in a strong acid selected from the group consisting of sulfuric acid present in a concentration of from about 0.5 to about 6 moles per liter of reaction medium, hydrochloric acid in a concentration of from about 0.01 to about 4 moles per liter of reaction medium, and a mixture thereof, in the presence of a mixed catalyst consisting of (i) a thallium ion catalyst present in a concentration of from 0.00001 to 0.1 moles per liter of reaction medium, and (ii) an ionic catalyst selected from the group consisting of silver ions and palladium ions, when said ionic catalyst is silver, the ratio of said thallium ions to silver ions is from 4:6 to 8:2, and when said ionic catalyst is palladium, the ratio of thallium ions to palladium ions is from 3:7 to 7:3.

2. The process of claim 1, wherein said chlorate is selected from the group consisting of sodium chlorate, potassium chlorate, calcium chlorate and magnesium chlorate, the con-centration of said chlorate being from 0.01 to 5 moles per liter of the reaction medium.

3. The process of claim 1, wherein said ionic catalyst is silver ions, said silver ions being present in a concentration of from about 0.00001 to 0.01 mole per liter of the reaction medium.

4. The process of claim 1, wherein said ionic catalyst is palladium ions, said palladium ions being present in a con-centration of from 0.00001 to 0.1 mole per liter of the reaction medium.