CA1070479A - Process for oxidizing sulfur dioxide - Google Patents
Process for oxidizing sulfur dioxideInfo
- Publication number
- CA1070479A CA1070479A CA234,220A CA234220A CA1070479A CA 1070479 A CA1070479 A CA 1070479A CA 234220 A CA234220 A CA 234220A CA 1070479 A CA1070479 A CA 1070479A
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- Canada
- Prior art keywords
- ppm
- catalyst
- sulfur dioxide
- vanadium
- manganese
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B17/00—Sulfur; Compounds thereof
- C01B17/69—Sulfur trioxide; Sulfuric acid
- C01B17/74—Preparation
- C01B17/76—Preparation by contact processes
- C01B17/775—Liquid phase contacting processes or wet catalysis processes
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- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Inorganic Chemistry (AREA)
- Catalysts (AREA)
- Treating Waste Gases (AREA)
- Exhaust Gas Treatment By Means Of Catalyst (AREA)
Abstract
A B S T R A C T
The invention concerns a novel catalyst for use in the manufacture of sulphuric acid from sulphur dioxide, the catalyst being less readily rendered inactive during the reaction process. The invention also relates to a process for oxidising sulphur dioxide which comprises contacting sulfur dioxide with oxygen in an aqueous solution containing at least 3 ppm each of pentavalent vanadium, divalent manganese and trivalent iron.
The invention concerns a novel catalyst for use in the manufacture of sulphuric acid from sulphur dioxide, the catalyst being less readily rendered inactive during the reaction process. The invention also relates to a process for oxidising sulphur dioxide which comprises contacting sulfur dioxide with oxygen in an aqueous solution containing at least 3 ppm each of pentavalent vanadium, divalent manganese and trivalent iron.
Description
ThiS invention relates to a process for oxidiz-ing and converting sulfur dioxide to sulfuric acid.
~ he process in which a vanadium catalyst is used in the oxidation of sulfur dioxide is being widely practiced in the production of sulfuric acid. However, since the activity of this catalyst is poor at low tem-peratures, elevated temperatures of ca. 450 - 500C.
are required in carrying out the process. In this case the equilibrium conversion of sulfur dioxide is, however, only about 80 - 98%. It has been made known that the reason why only an equilibrium conversion of this order can be attained is due to the face the oxidation reaction of sulfur dioxide is subjected to thermodynamic restrictions at elevated temperatures. Hence, although this vapor phase process using a vanadium catalyst is valuable as a process for producing concentrated sulfuric acid or fuming sulfuric acid using concentrated sulfur B dioxide as the starting material, it has the drawback that an uuroa~ gas in which the concentration of sulfur dioxide amounts ~o a~ much as 1500 - 4000 ppm is discharged.
In contrast, a method of oxidizing sulfur dioxide at a low temperature of ca. 50C. using an active carbon as catalyst has been tried. However, this method was not practical, because a major portion of the Product (sulfuric acid) was firmly a~sorbed by the active carbon.
Mbreover, this impeded the oxidation reaction of the sul-fur dioxide. Hence, the active carbon catalyst could not be used continuously over a prolonged period of time.
~or instance, after using the active carbon for half a day, it had to be washed with a large amount of water for a prolonged period of time before it could be reused.
The aqueous solutions of ferrous sulfate, ferric sulfate and manganese sulfate have also been known from of old to be usable in the oxidation of sulfur dioxide at low temperatures. However, in the case of all of these aqueous solutions of metal salts not only is there -the formation and accumulation of sulfuric acid in the reaction system (catalyst solution), but the oxidation -reaction is also impeded.
Having previously found that an aqueous solution containing both pentavalent vanadium and divalent manganese was superior as a catalyst for the oxidation of sulfur dioxide with air at low tempera~ures, an application for letters patent therefor has been filed by us under Canadian Patent Application No. 194.97~. In accordance with the proce~s of this application, it became possible to carry out the air oxidation reaction of sulfur dioxide even at a low temperature of ca~ 50C. notwithstanding the fact that vanadium was used as one of constituents of the catalyst system. Hence, it was possible to convert all of the sulfur dioxide present dissolved in the catalyst solution without being subaected to the thermodynamic restrictions as to the equilibrium reaction rate. Purther, even though sulfuric acid forms and accumulates in the reaction system (catalyst solution), the effects of such a formation and accumulation of sulfuric acid in impeding the reaction is small. ~here is ~urthermore the advantage that poisoning by ~uch foreign matter as copper and phenol as in the case where manganese sulfate is used alone as the catalyst is not noted.
Thus, this aqueous pentavalent vanadium-divalent manganese type catalyst solution was superior in its catalytic activity as well as resistance to poisoningJ but when this catalyst was repeatedly used over a prolonged period of time, its activity gradually declined. We found that this catalyst deterioration phenomenon was due to the gradual reduction to tetravalent vanadium of the pentavalent vanadium that had been combined with the divalent manganese and that thus the catalytic activity could be maintained by oxidizing the deteriorated catalyst and regenerating the tetravalent vanadium to pentavalent vanadium, and an application for letters patent therefor has been filed under Canadian Patent Application No. 209.157. Thus, it becomes possible to make continuous, repeated use of the pentavalent vanadium- -divslent manganese catalyst by use of a method of regenerating the deteriorated catalyst. However, when considered from the economic standpoint, a process not requiring hardly any regeneration of the catalyst is still to be desired.
We furthered our researches ~ith a view to finding a way by which it would be possible to greatly reduce the deterioration of the catalyst and, as a consequence, found for the first time that it was possible to obtain a catalyst that is far more difficult to deteriorate than the pentavalent vanadium-divalent manganese :107V479 type by combining a small amount of iron with the pentavalent vanadium-divalent manganese type catalyst.
Accordingly, the present invention provides a process for oxidizing sulfur dioxide which comprises contacting sulfur dioxide with oxygen in an aqueous solution containing pen~avalent vanadium , divalent manganese and trivalent iron, in the ranges, calculated as metals of 3-~000 ppm, 3-200 ppm and 3-250 ppm, respectively, oxidation being carried out by blowing S02 and
~ he process in which a vanadium catalyst is used in the oxidation of sulfur dioxide is being widely practiced in the production of sulfuric acid. However, since the activity of this catalyst is poor at low tem-peratures, elevated temperatures of ca. 450 - 500C.
are required in carrying out the process. In this case the equilibrium conversion of sulfur dioxide is, however, only about 80 - 98%. It has been made known that the reason why only an equilibrium conversion of this order can be attained is due to the face the oxidation reaction of sulfur dioxide is subjected to thermodynamic restrictions at elevated temperatures. Hence, although this vapor phase process using a vanadium catalyst is valuable as a process for producing concentrated sulfuric acid or fuming sulfuric acid using concentrated sulfur B dioxide as the starting material, it has the drawback that an uuroa~ gas in which the concentration of sulfur dioxide amounts ~o a~ much as 1500 - 4000 ppm is discharged.
In contrast, a method of oxidizing sulfur dioxide at a low temperature of ca. 50C. using an active carbon as catalyst has been tried. However, this method was not practical, because a major portion of the Product (sulfuric acid) was firmly a~sorbed by the active carbon.
Mbreover, this impeded the oxidation reaction of the sul-fur dioxide. Hence, the active carbon catalyst could not be used continuously over a prolonged period of time.
~or instance, after using the active carbon for half a day, it had to be washed with a large amount of water for a prolonged period of time before it could be reused.
The aqueous solutions of ferrous sulfate, ferric sulfate and manganese sulfate have also been known from of old to be usable in the oxidation of sulfur dioxide at low temperatures. However, in the case of all of these aqueous solutions of metal salts not only is there -the formation and accumulation of sulfuric acid in the reaction system (catalyst solution), but the oxidation -reaction is also impeded.
Having previously found that an aqueous solution containing both pentavalent vanadium and divalent manganese was superior as a catalyst for the oxidation of sulfur dioxide with air at low tempera~ures, an application for letters patent therefor has been filed by us under Canadian Patent Application No. 194.97~. In accordance with the proce~s of this application, it became possible to carry out the air oxidation reaction of sulfur dioxide even at a low temperature of ca~ 50C. notwithstanding the fact that vanadium was used as one of constituents of the catalyst system. Hence, it was possible to convert all of the sulfur dioxide present dissolved in the catalyst solution without being subaected to the thermodynamic restrictions as to the equilibrium reaction rate. Purther, even though sulfuric acid forms and accumulates in the reaction system (catalyst solution), the effects of such a formation and accumulation of sulfuric acid in impeding the reaction is small. ~here is ~urthermore the advantage that poisoning by ~uch foreign matter as copper and phenol as in the case where manganese sulfate is used alone as the catalyst is not noted.
Thus, this aqueous pentavalent vanadium-divalent manganese type catalyst solution was superior in its catalytic activity as well as resistance to poisoningJ but when this catalyst was repeatedly used over a prolonged period of time, its activity gradually declined. We found that this catalyst deterioration phenomenon was due to the gradual reduction to tetravalent vanadium of the pentavalent vanadium that had been combined with the divalent manganese and that thus the catalytic activity could be maintained by oxidizing the deteriorated catalyst and regenerating the tetravalent vanadium to pentavalent vanadium, and an application for letters patent therefor has been filed under Canadian Patent Application No. 209.157. Thus, it becomes possible to make continuous, repeated use of the pentavalent vanadium- -divslent manganese catalyst by use of a method of regenerating the deteriorated catalyst. However, when considered from the economic standpoint, a process not requiring hardly any regeneration of the catalyst is still to be desired.
We furthered our researches ~ith a view to finding a way by which it would be possible to greatly reduce the deterioration of the catalyst and, as a consequence, found for the first time that it was possible to obtain a catalyst that is far more difficult to deteriorate than the pentavalent vanadium-divalent manganese :107V479 type by combining a small amount of iron with the pentavalent vanadium-divalent manganese type catalyst.
Accordingly, the present invention provides a process for oxidizing sulfur dioxide which comprises contacting sulfur dioxide with oxygen in an aqueous solution containing pen~avalent vanadium , divalent manganese and trivalent iron, in the ranges, calculated as metals of 3-~000 ppm, 3-200 ppm and 3-250 ppm, respectively, oxidation being carried out by blowing S02 and
2 into the aqueous solution or by dissolving the S02 in the aqueous solution and then contacting the so obtained S02- containing liquid with either air or other 2- containing liquid with either air or other 2- containing gases The present invention will be more fully described below.
The iron that has been caused to be copresent with the pentavalent vanadium-divalent manganese system in the aqueous catalyst solution used in the invention process mskes it possible to prolong the catalytic life of the pentavalent vanadium-divalent manganese catalyst without impairment of its activity in the least. ln this case, effects which could not possibly have been foreseen as being the mere additive effects between the pentavalent vanatium-divalent manganese catalyst previously provided by us and the iron catalyst that has been under investigation from the first of this century have been made known for the first time. That is to say, the catalyst used in this invention is valuable as a unique new catalyst which is far superior to the iron catalyst in its catalytic activity while, on the other hand, it excels the pentavalent vanadium-divalent manganese type in its catalytic life.
The practical value of the present invention, which has been per-fected on the basis of this new B
1070475' discovery, resides in the fact that it has made it possible to increase to a marked degree the catalytic life of the pentavalent vanadium-divalent manganese catalyst, whose application for letters patent was previously made by us.
We have already stated that the rate o~
deterioration of the pentavalent vanadium-divalent man~anese catalyst was influenced by the reaction tem-perature (Canadian Patent Application No. 209.157). That is, when the temperature was about 20-35C., the catalytic life was relatively long. Hence, the catalyst could be repeatedly used in oxidizing sulfur dioxide after regenerating the catalyst slightly (Canadian Patent Application No. 209.157). However, at reaction temperatures of above 40C., and especially above 45C., there was a considerable reduction in the catalytic life, with the con~equence that a further increase in the frequency of catalyst regeneration had to be made. In the case of this invention, there is however the advantage that the strong activity characteristic of the pentavalent vanadium-divalent manganese type catalyst can be maintained even at 55 - 65C., not to mention 45C., with no special increase in the frequency of catalyst regeneration.
The catalyst solution containing the three components of pentavalent vanadium, divalent manganese and trivalent iron can be prepared by adding a pentavalent vanadium salt, a divalent manganese salt and trivalent iron salt to an acidic, nuetral or alkaline water. The 11~70479 so obtained catalyst solution usually exhibits a suspended state in an alkaline aqueous solution, and it also ;~
exhibits a partially suspended state even in a neutral or acidic aqueous solution. However, in any case, when it is used for the oxidation reaction of sulfur dioxide, it promptly turns to a practically transparent and homogeneous aqueous solution. Hence, as a practical matter, it is of no hindrance at all in carrying out the reaction.
Usable as the foregoing pentavalent vanadium salts are the oxides, halides, and oxyhalides of vanadium, metavanadates, polyvanadates and vanadium ores as typified by vanadium pentoxide, vanadium pentafluoride, vanadyl trifluoride, vanadyl chloride, -vanadyl tribromide, ammonium metavanadate, vanadinite, ammonium pervanadate and sodium orthovanadate. Further, the low valent vanadium compounds such as the oxides, halides and oxyhalides of tetravalent vanadium as typified by vanadium dioxide, vanadium tetrafluoride, vanadium tetrachloride, vanadium tetrabromide, vanadyl difluoride, vanadyl dibromide, vanadyl sulfate and acid vanadyl sulfate;
the oxides, halides and oxyhalides of trivalent vanadium as typified by the vanadites, oxysulfates, vanadium trioxide, vanadium trifluoride, vanadium trichloride, vanadium tribromide, vanadyl monochloride, vanadyl monobromide and vanadic sulfate; the oxides, halides, sulfates and hydroxides of divalent vanadium as typified by the sulfates, vanadium monoxide, vanadium dichloride, vanadium dibromide, vanadium sulfate and vanadium hydroxide;
10~4'79 and metallic vanadium can also be used after conversion to a pentavalent salt by means of the known oxidizing agents as typified by potassium permanganate, potassium bichromate, ozone and ammonium persulfate, as well as hydrogen peroxide, man~anese dioxide and air.
Usable as the divalent manganese salts are those divalent manganese salts (except manganese iodide), typical examples of which are manganese sulfate, manganese chloride, manganese fluoride, manganese nitrate, manganese lactate, manganese acetate, manganese benzoate, manganese formate, manganese dithionate, manganese dihydro-gen phosphate and manganese hypophosphite. Further, those manganese compounds which form divalent manganese ions as the result of the ~ction of sulfur dioxide or sulfuric acid, such as manganese dioxide, manganese hypo-phosphite, manganese pyrophosphate, managanese monoxide, manganese hydroxide, manganese carbonate, manganese sulfide, manganic phosphate, manganese borate and metallic manganese can also be used with no trouble at all. The high valent manganese salts as typified by potassium permanganate, potassium manganate and manganic sulfate can also be used in this invention, since these salts are converted to divalent manganese salts by sulfur dioxide.
As the trivalent iron salts, usable are such ferric salts as, for example, ferric hydroxide, ferric oxide, ferric sulfate, ferric sulfide, ferric vanadate, ferric bichromate, ferric chromate, ferric benzoate and iron ammonium alum. Again, also usable are the ferrous 10'70'~79 salts that are converted to the ferric salts in the reaction system of the invention as a result of the action of sulfur dioxide, sulfuric acid and oxygen, included being such, for example, as ferrous hydroxide, ferrous nitrate, ferrous oxide, ferrous sulfate, ferrous sulfide, ferrous chloride, ferrous carbonate, ferrous sulfite, ferrous phosphate, ferrous perchlorate, ferrous formate and ferrous ~mmonium sulfate, as well as metallic iron.
~he concentration in which the pentavalent vanadium, divalent manganese and trivalent iron are contained in the aqueous catalyst solution used in this invention can be in the ranges, calculated as metals, of 3-8000 ppm, 3-200 ppm and ~-250 ppm, respectively.
While a catalytic activity can also be noted at lower r t~cse B concentration than ~oos ranges, such lower concentrations are not to be preferred, because the reaction of oxidizing Rulfur dioxide becomes slow. On the other hand, concentrations exceedin~ the ~oregoing ranges may be used, but no advantages are had by raising the concentrations above the ranges indicated above, for there is hardly any difference in the catalytic activity.
When in preparing the catalyst solution a low valent vanadium i.e., 0-4 valent vanadium,is used and this is directly rendered into an aqueous solution (or suspension), such a solution or suspension must be submitted to an oxidizing treatment to convert at least a part of the va~adium to pentavalent vanadium so as to raise the concentration of the pentavalent vanadium ions ~0 ~ ~7~3 to at least ~ ppm. On the other hand, when metallic manganese is used as the manganese, the catalyst solution must be held in an acidic condition and at least part of the metallic manganese must be dissolved so as to raise the concentration of the divalent manganese ions to at least 3 ppm. When a high valent manganese salt having a valence of 4 - 7 is used as the manganese, no preliminary treatments are necessary in such a case, because these high valent manganese salts can be readily con~erted to divalent manganese as a result of the action of sulfur dioxide (or the tetravalent vanadium or divalent iron). When metallic iron is used as the iron, at least part of the metallic iron must be dissolved by maintaining the catalyst solution in an acidic condition, and further it must be converted to trivalent iron by means of air or sulfur dioxide and air or a known oxidizing means as typified by such as manganese having a valence of 4-7, hydrogen peroxide, pentavalent vanadium, etc., so as to raise the concentration of iron ions to above 3 ppm. Even in the case when a ferrous salt is used instead of metallic iron, it is necessary to form trivalent iron ions by submitting the catalyst solution (alkaline, neutral or acidic) to t~e hereinabove-described oxidizing treatment.
The reaction of oxidizing the sulfur dioxide can be carried out at a temperature of O - 100C. in this invention, but the reaction can be carried out especially promptly at a temperature of 20 - 80C. While it is also possible to carry out the reaction at a low 10'70479 temperature of below 20C., in this case the reaction proceeds relatively slowly. While the reaction can be carried out at above 80C., and even above 100C. under superatmospheric pressures, there is no great difference in the reaction speeds as compared with the case where the reaction is carried out at 20 - 80C.
While the oxidation reaction of sulfur dioxide can be carried out by blowing sulfur dioxide and oxygen into the aqueous catalyst solution, as another method it can also be carried out by a procedure consisting of first dissolving the sulfur dioxide in the aqueous cata~yst solution and then contacting the so obtained sulfur dioxide-containing liquid (sulfurous acid solution) with either air or other oxygen-containing gases.
According to the invention process, the sulfuric acid formed in the reaction becomes dissolved as such in the catalyst solution and accumulates therein, but despite this accumulation of sulfuric acid this catalyst solution can be used as such repeatedly in the oxidation of sulfur dioxide. The catalytic life is exceedingly long, and the catalyst ~olution can be repeatedly used over a long period of time. While the cattlytic life will vary depending upon the concentration of the sulfur dioxide and the concentration of the oxygen copresent in the sulfur dioxide-containing gas, as well as the foregoing reaction temperature, in any event the life of our previously proposed pentavalent vanadium-divalent manganese catalyst is greatly prolonged.
However, the catalytic life is, of course, not infinite 10'70479 even in the case of this invention. Hence, in the process of repeatedly using the catalyst solution a part of the deteriorated catalyst solution must be dis-charged externally of the reaction system in concomitance with the decline in reaction performance, and instead a fresh catalyst solution or a regenerated catalyst solution resulting from the separate oxidation treat-ment of a deteriorated catalyst solution must be supplied to the reaction system. For the regeneration of the deteriorated catalyst solution, usable are those known agents that are used for oxidizing tetravalent vanadium, typical being ozone, potassium permanganete, potassium bichromate, cerium sulfate, chlorine and ammonium persulfate. In addition, usable are manganese dioxide, hydrogen peroxide and air as previously proposed by us.
The catalytic activity possessed at the outset can be maintained practically intact by replenishing the catalyst solution with a fresh catalyst solution or a regenerated catalyst in this manner. And as compared with the conventlonal pentavalent vanadium-divalent manganese catalyst, the present invention makes it possible to greatly reduce the amount of the fresh catalyst solution or regenerated catalyst that needs to be replenished.
~he following examples will serve to more fully illustrate the present invention.
~xam~le 1 A specimen gas consisting of 1300 ppm of sulfur dioxide, 6. 5% of oxygen and 93% of nitrogen and of 50C. was fed at a rate of 1980 Nm3/hr to the bottom 1070~73 of a Raschig ring-packed column (absorption column) hav-ing an inside diameter of 88 cm and a height of 6 meters.
At the same time an aqueous solution containing 26 ppm of pentavalent vanadium~ 189 ppm of tetravalent vanadium, 27 ppm of divalent manganese, 27 ppm of trivalent iron and 6 wt.% of sulfuric acid and of 52C. was fed at a rate of 33 m3/hr to the top of the column. The liquid flowing out from the bottom of the absorption column was fed at the rate of 33 m3/hr to the bottom of a 10-tray (sieve) oxidation column having an inside diameter of 44 cm and a height of 6 meters. 99.5/~ of the liquid flowing out from the top of the oxidation column was recycled to the top of the aforesaid absorption column and, at the same time, the unreacted air flow-ing out from the top of the oxidation column was combinedwith the feed gas that was fed to the bottom of the absorptioD column.
1/190 of the liquid flowQng out from the top of the oxidation column was discharged externally of the system and, at the same time, a fresh catalyst solution (200 ppm of pentavalent vamadium, 10 ppm of tet~avalent vanadium, 27 ppm of divalent manganese and 27 ppm of trivalent iron, pH 2, 27C.) was supplied at a rate of 170 liters/hr to the top of the absorption column.
In consequence of thi~ series of operations, the con-centration of the sulfur dioxide of the desulfurized gas discharged from the absorption column was held at 98 to 107 ppm for a period of four months, and the amount of sulfur dioxide in the unreacted air from the top of 47~
the oxidation colwDn was only 4 ppm. It was thus found that 9~/~ of the sulfur dioxide contained in the specimen gas was oxidized.
Control 1 Th~ specimen gas used in Example 1 was fed to an absorption column of the same type as that used in Example 1 aild, at the same time, an aqueous solution containing 27 ppm of pentavalent vanadium, 188 ppm of tetravalent vanadium, 27 ppm of divalent manganese, 2 ppm of trivalent iron and 6 wt.% of sulfuric acid and of 52C. was fed at a rate of 33 m3/hr to the top of the column. Operating as in Example 1, 99.5% of the liquid flowing out from the top of the oxidation column was recycled to the top of the absorption column, while 1/190 thereof was dischar~ed externally of the system. At the same time, a fresh catalyst solution (200 ppm of pentavalent vanadium, 10 ppm of tetravalent vanadium, 27 ppm of divalent manganese and 0.4 ppm of trivalent iron, pH 2, 27C.) was supplied at a rate of 170 liters/hr to the top of the absorption column. In consequence of this series of operations, the concentration of the sulfur dioxide of the desulfurized gas rose to 500 ppm after 90 hours o~ operation. At this point, the concentration of the pentavalent vanadium in the recycle li~uid decreased to 1.0 ppm, and in correspondence therewith the concentration of the tetravalent vanadium increased to 215 ppm. As opposed to the case of Example 1 where the concentration of the pentavalent vanadium was always maintained at 23 - 27 ppm, it is clear that 107047g in this control experiment w~ere the presecribed amount of iron was not added to the catalyst solution there was a deterioration of the catalyst in spite of the replenishment of the recycle catalyst solution with a fresh catalyst, with the consequence that a marked drop in the performance of the desulfurization operation was demonstrated.
In this control experiment it was found that not until the temperature of the recycle liquid was reduced to 26C. or the amount discharged of the recycle catalyst and the amount supplied of the fresh catalyst were increased to 550 liters/hr was it possible to achieve a desulfurization performance of the same order as that of Example l. On the other hand, as seen in Example 1, it is clear that the amount supplied of the fresh catalyst can be greatly reduced at 52C. by using a catalyst solution containing 27 ppm of iron.
Control 2 ~he specimen gas used in Example l was fed to an absorption column of the same type as that used in Example 1 and, at the same time, a 52C. aqueous solu-tion containing 250 ppm of trivalent iron and 6 wt.% of sulfuric acid was fed at a rate of 33 m3~hr to the top of the column. For maintaining the concentration of the sulfuric acid in the recycle liquid at 6 wt.% as in the case of Example l, l/l90 o~ the effluent liquid from the top of the oxidation column was discaharged externa~l~
of the system, while a fresh catalyst solution (250 ppm of trivalent iron, pH 2) was supplied to the 107047~
top of th~ absorption column at a rate of 170 liters/hr.
In this case the concentration of the sulfur dioxide of the desulfurized gas discharged from the top of the absorption colu~n was 2~0 ppm, i.e., a value 17~/o greater than the case of Example 1.
Although the iron concentration of the recycle catalyst solution was raised to 1500 ppm in this control experiment, an improvement in the concentration of the unreacted sulfur dioxide of only as much as 200 - 210 ppm was achieved. This was 100% greater than the case of Example 1.
Thus, as apparent from the foregoing results, even though the treatment of sulfur dioxide is carried out under identical operating conditions as in Example 1, there is demonstrated a great difference in the performance of oxidizing sulfur dioxide when the conventional iron catalyst is used, and thus a performance comparable to that of Example 1 cannot be obtained.
~xamPle 2 A 55C. specimen gas containing 1600 ppm of sulfur dioxide, 5.3% of oxygen and 94% of nitrogen was fed at a rate of 1200 m3/hr to the bottom of a Raschig ring-packed column (absorption column) having an inside diameter of 68 cm and a height of 6 meters. At the same time a 55C. aqueous solution containing 10 ppm of pentavalent vanadium, 195 ppm of tetravalent vanadium, 43 ppm of divalent manganese, 123 ppm of trivalent iron and 4 wt.% of sulfuric acid was fed at a rate of 30 m3/hr to the top of the column. The liquid flowing out from the bottom of the absorption column was conveyed at a rate of 30 m3/hr to a lo-tray (sieve) oxidation column having an inside dimeter of 44 cm and a height of 6 meters and, at the same time, air was fed at a rate of 20 m~hr to the bottom of the oxidation column. 99.3% of the liquid flowing out from the top of the oxidation column was recycled to the top of the aforesaid absorp-tion column, while the unreacted air flowing out from the top of the oxidation column was combined with the feed gas fed to the bottom of the absorption column.
1/150 of the effluent liquid from the top of the oxidation column was discharged externally of the system and, at the same time, a fresh catalyst (195 ppm of penta~alent vanadium, 10 ppm of tetravalent vanadium, 43 ppm of divalent manganese and 123 ppm of trivalent iron, pH 3) was supplied at a rate of 200 liters/hr to the top of the absorption column.
In consequence of this series of operations, the concentration of pentavalent vanadium in the recycle liquid was maintained at 9-11 ppm over a period of three months. On the other hand, the concentration of unreacted sulfur dioxide discharged from the absorption column was 90-98 ppmO
Control 3 Example 2 was repeated but without incorporating the recycle catalyst solution with ironO In this case the concentration of the pentavalent vanadium declined to 0.7 ppm after 100 hours from the initiation of the recycle operation, and the concentration of sulfur dioxide of the desulfurized gas rose to 450 ppm.
It was found that an oxidation reaction performance comparable to that of Example 2 could be achieved by reducing the temperature of the recycle liquid to 25C or by discharging 1/50 of the effluent liquid from the top of the oxidation column externally of the system and supplying a fresh catalyst (195 ppm of pentavalent vanadium, 10 ppm of tetravalent vanadium and 43 ppm of divalent manganese, pH 3) to the absorption column at a rate of 600 liters/hr. However, it is apparent from Example 2 that by uslng a pentavalent vanadium-divalent manganese-trivalent iron type catalyst the amount supplied of the fresh catalyst solution could be greatly reduced at 55C.
Control 4 ~ he specimen gas used in Example 2 was fed to the bottom of an absorption column of the same type as that used in Example 2 and, at the same time, a 55C.
aqueous solution containing 170 ppm of trivalent iron and 4 wt~% of sulfuric acid was fed at a rate of 30 m3/hr to the top of the columnO 1/150 of the liquid flowing out from the top of an oxidation column of the same type as that used in Example 2 was discharged exter-nally of the system while, at the same time, a fresh catalyst solution (170 ppm of trivalent iron, pH 3) was supplied at a rate of 200 liters/hr to the top of the absorption column.
In this series of operations, the concentration ~; of the unreacted sulfur dioxide discharged from the '1071~479 absorption column was 235 ppm, i.e., it was 150 % `
greater than the case of Example 2. Next, the concentra-tion of trivalent iron of the recycle liquid was raised up to 500 ppm, and the operation was carried out in the same manner, but the concentration of the unreacted sulfur dioxide fell to only 150 - 160 ppm, which was still 60/~ greater than in the case of Example 2. Further, even though the concentration of the trivalent iron of the recycle liquid was raised up to 1500 ppm, there was no further improvement. Thus, it was absolutely impos-sible to achieve oxidation results comparable to those of Example 2 with the use of the conventional iron catalyst.
Example 3 A flue gas containing 1950 ppm of sulfur dioxide, ~/0 of oxygen, 10% of carbon dioxide and 9 wt.% of water was first removed of the dust contained therein as well -as cooled to 50C. at a cooling tower and then fed at ~ rate of 1200 m3/hr to the bottom of a Raschig ring-packed column (absorption column) having an inside diameter of 68 cm and a height of 6 meters A~ the same time, a 46C. aqueous solution of 25 ppm of pentavalent vanadium, 150 ppm of tetravalent vanadium, 15 ppm of divalent manganese, 15 ppm of trivalent iron and 6 wt.%
of sulfuric acid was fed to the top of the column at a rate of 30 m3/hr. ~he absorbed liquid flowing out from the bottom of the absorption column was fed at a rate of 30 m3/hr to the bottom of a 10-try (sieve) oxidation column having an inside diameter of 44 cm and a height of 6 meters while, at the same time, air was fed at a 10~704~7g rate of 24 m3/hr to the bottom of the oxidatior column.
99.5/u of the effluent liquid from the top of the oxidation column was recycled to the top of the aforesaid absorption column and, at the same time, the unreacted air flowing out from the top of the oxidation column was combined with the feed gas that was fed to the bottom of the absorption column. On the other hand, 1/190 of the liquid flowing out from the top of the oxidation column (160 liters/hr) was discharged externally of the system and, at the same time, a catalyst solution (1~5 ppm pentavalent vanadium, 50 ppm tetravalent vanadium, 15 ppm of divalent manganese and 15 ppm of trivalent iron, pH 2) was supplied to the top of the absorption column at a rate of 160 liters~hr. In consequence of this series of operations, the pentavalent vanadium of the recycle liquid was maintained at 22 - 26 ppm for a period of four months, while the concentration of the unreacted sulfur dioxide was likewise held at 150-163 ppm.
Control ~
~xample 3 was repeated but without incorporating iron in the recycle catalyst solution. In this case, there was a gradual decrease of the pentavalent vanadium with a corresponding increase of the tetravalent vanadium.
~hat is, 96 hours after initiation of the recycling operation, the concentration of the pentavalent vanadium declined to 0.9 ppm, while the concentration of the unreacted sulfur dioxide rose to 540 ppm. i.e., a 250 %
increase over that of the case of Example 3. It was possible to obtain oxidation results comparable to those 1070~`79 of Example ~ by reducing the temperature of the r~cycle liquid to 26C. or by increasing the amount discharged of the recycle liquid and the amount supplied of the catalyst solution to 430 liters/hr. However, as is apparent from Example 3, it is clear that the amount of catalyst that needs to be replenished can be greatly reduced at 46C. by the conjoint use of iron.
Control 6 The flue gas used in Example 3 was fed to the bottom of an absorption column of the same type as that used in Example 3 while, at the same time, a 46C.
aqueous solution containing 30 ppm of trivalent iron and 6 wt.% of sulfuric acid was fed at a rate of 30 m3/hr to the top of the column. 1/190 of the liquid flowing out from the top of an oxidation column of the same type as that used in Example 3 was discharged externally of the system and, at the same time, a catalyst solution (~0 ppm of trivalent iron, pH ~) was supplied at a rate of 160 liters/hr to the top of the absorption column.
In this series of operations the concentration of the unreacted sulfur dioxide discharged from the top of the absorption column was 830 - 920 ppm, an amount 5 - 6 times that of the case of Example 3. Although the concentration of the recycle liquid was raised up to 350 ppm, the concentration of the unreacted sulfur dioxide was still 420 - 450 ppm.
In this Control 6 the apparatus used and the various conditions such as the composition of the specimen gas and its flow rate, the flow rate of the recycle liquid and its sulfuric acid concentration, and operating temperatures werè identical to those of Example 3, the only difference being the use of the conventional iron catalyst as the catalyst solution. There was however a marked difference in the desulfurization (oxidation of sulfur dioxide) results. A far superior catalytic activity was noted in the case of Example 3 as compared with the case of Control 6.
The iron that has been caused to be copresent with the pentavalent vanadium-divalent manganese system in the aqueous catalyst solution used in the invention process mskes it possible to prolong the catalytic life of the pentavalent vanadium-divalent manganese catalyst without impairment of its activity in the least. ln this case, effects which could not possibly have been foreseen as being the mere additive effects between the pentavalent vanatium-divalent manganese catalyst previously provided by us and the iron catalyst that has been under investigation from the first of this century have been made known for the first time. That is to say, the catalyst used in this invention is valuable as a unique new catalyst which is far superior to the iron catalyst in its catalytic activity while, on the other hand, it excels the pentavalent vanadium-divalent manganese type in its catalytic life.
The practical value of the present invention, which has been per-fected on the basis of this new B
1070475' discovery, resides in the fact that it has made it possible to increase to a marked degree the catalytic life of the pentavalent vanadium-divalent manganese catalyst, whose application for letters patent was previously made by us.
We have already stated that the rate o~
deterioration of the pentavalent vanadium-divalent man~anese catalyst was influenced by the reaction tem-perature (Canadian Patent Application No. 209.157). That is, when the temperature was about 20-35C., the catalytic life was relatively long. Hence, the catalyst could be repeatedly used in oxidizing sulfur dioxide after regenerating the catalyst slightly (Canadian Patent Application No. 209.157). However, at reaction temperatures of above 40C., and especially above 45C., there was a considerable reduction in the catalytic life, with the con~equence that a further increase in the frequency of catalyst regeneration had to be made. In the case of this invention, there is however the advantage that the strong activity characteristic of the pentavalent vanadium-divalent manganese type catalyst can be maintained even at 55 - 65C., not to mention 45C., with no special increase in the frequency of catalyst regeneration.
The catalyst solution containing the three components of pentavalent vanadium, divalent manganese and trivalent iron can be prepared by adding a pentavalent vanadium salt, a divalent manganese salt and trivalent iron salt to an acidic, nuetral or alkaline water. The 11~70479 so obtained catalyst solution usually exhibits a suspended state in an alkaline aqueous solution, and it also ;~
exhibits a partially suspended state even in a neutral or acidic aqueous solution. However, in any case, when it is used for the oxidation reaction of sulfur dioxide, it promptly turns to a practically transparent and homogeneous aqueous solution. Hence, as a practical matter, it is of no hindrance at all in carrying out the reaction.
Usable as the foregoing pentavalent vanadium salts are the oxides, halides, and oxyhalides of vanadium, metavanadates, polyvanadates and vanadium ores as typified by vanadium pentoxide, vanadium pentafluoride, vanadyl trifluoride, vanadyl chloride, -vanadyl tribromide, ammonium metavanadate, vanadinite, ammonium pervanadate and sodium orthovanadate. Further, the low valent vanadium compounds such as the oxides, halides and oxyhalides of tetravalent vanadium as typified by vanadium dioxide, vanadium tetrafluoride, vanadium tetrachloride, vanadium tetrabromide, vanadyl difluoride, vanadyl dibromide, vanadyl sulfate and acid vanadyl sulfate;
the oxides, halides and oxyhalides of trivalent vanadium as typified by the vanadites, oxysulfates, vanadium trioxide, vanadium trifluoride, vanadium trichloride, vanadium tribromide, vanadyl monochloride, vanadyl monobromide and vanadic sulfate; the oxides, halides, sulfates and hydroxides of divalent vanadium as typified by the sulfates, vanadium monoxide, vanadium dichloride, vanadium dibromide, vanadium sulfate and vanadium hydroxide;
10~4'79 and metallic vanadium can also be used after conversion to a pentavalent salt by means of the known oxidizing agents as typified by potassium permanganate, potassium bichromate, ozone and ammonium persulfate, as well as hydrogen peroxide, man~anese dioxide and air.
Usable as the divalent manganese salts are those divalent manganese salts (except manganese iodide), typical examples of which are manganese sulfate, manganese chloride, manganese fluoride, manganese nitrate, manganese lactate, manganese acetate, manganese benzoate, manganese formate, manganese dithionate, manganese dihydro-gen phosphate and manganese hypophosphite. Further, those manganese compounds which form divalent manganese ions as the result of the ~ction of sulfur dioxide or sulfuric acid, such as manganese dioxide, manganese hypo-phosphite, manganese pyrophosphate, managanese monoxide, manganese hydroxide, manganese carbonate, manganese sulfide, manganic phosphate, manganese borate and metallic manganese can also be used with no trouble at all. The high valent manganese salts as typified by potassium permanganate, potassium manganate and manganic sulfate can also be used in this invention, since these salts are converted to divalent manganese salts by sulfur dioxide.
As the trivalent iron salts, usable are such ferric salts as, for example, ferric hydroxide, ferric oxide, ferric sulfate, ferric sulfide, ferric vanadate, ferric bichromate, ferric chromate, ferric benzoate and iron ammonium alum. Again, also usable are the ferrous 10'70'~79 salts that are converted to the ferric salts in the reaction system of the invention as a result of the action of sulfur dioxide, sulfuric acid and oxygen, included being such, for example, as ferrous hydroxide, ferrous nitrate, ferrous oxide, ferrous sulfate, ferrous sulfide, ferrous chloride, ferrous carbonate, ferrous sulfite, ferrous phosphate, ferrous perchlorate, ferrous formate and ferrous ~mmonium sulfate, as well as metallic iron.
~he concentration in which the pentavalent vanadium, divalent manganese and trivalent iron are contained in the aqueous catalyst solution used in this invention can be in the ranges, calculated as metals, of 3-8000 ppm, 3-200 ppm and ~-250 ppm, respectively.
While a catalytic activity can also be noted at lower r t~cse B concentration than ~oos ranges, such lower concentrations are not to be preferred, because the reaction of oxidizing Rulfur dioxide becomes slow. On the other hand, concentrations exceedin~ the ~oregoing ranges may be used, but no advantages are had by raising the concentrations above the ranges indicated above, for there is hardly any difference in the catalytic activity.
When in preparing the catalyst solution a low valent vanadium i.e., 0-4 valent vanadium,is used and this is directly rendered into an aqueous solution (or suspension), such a solution or suspension must be submitted to an oxidizing treatment to convert at least a part of the va~adium to pentavalent vanadium so as to raise the concentration of the pentavalent vanadium ions ~0 ~ ~7~3 to at least ~ ppm. On the other hand, when metallic manganese is used as the manganese, the catalyst solution must be held in an acidic condition and at least part of the metallic manganese must be dissolved so as to raise the concentration of the divalent manganese ions to at least 3 ppm. When a high valent manganese salt having a valence of 4 - 7 is used as the manganese, no preliminary treatments are necessary in such a case, because these high valent manganese salts can be readily con~erted to divalent manganese as a result of the action of sulfur dioxide (or the tetravalent vanadium or divalent iron). When metallic iron is used as the iron, at least part of the metallic iron must be dissolved by maintaining the catalyst solution in an acidic condition, and further it must be converted to trivalent iron by means of air or sulfur dioxide and air or a known oxidizing means as typified by such as manganese having a valence of 4-7, hydrogen peroxide, pentavalent vanadium, etc., so as to raise the concentration of iron ions to above 3 ppm. Even in the case when a ferrous salt is used instead of metallic iron, it is necessary to form trivalent iron ions by submitting the catalyst solution (alkaline, neutral or acidic) to t~e hereinabove-described oxidizing treatment.
The reaction of oxidizing the sulfur dioxide can be carried out at a temperature of O - 100C. in this invention, but the reaction can be carried out especially promptly at a temperature of 20 - 80C. While it is also possible to carry out the reaction at a low 10'70479 temperature of below 20C., in this case the reaction proceeds relatively slowly. While the reaction can be carried out at above 80C., and even above 100C. under superatmospheric pressures, there is no great difference in the reaction speeds as compared with the case where the reaction is carried out at 20 - 80C.
While the oxidation reaction of sulfur dioxide can be carried out by blowing sulfur dioxide and oxygen into the aqueous catalyst solution, as another method it can also be carried out by a procedure consisting of first dissolving the sulfur dioxide in the aqueous cata~yst solution and then contacting the so obtained sulfur dioxide-containing liquid (sulfurous acid solution) with either air or other oxygen-containing gases.
According to the invention process, the sulfuric acid formed in the reaction becomes dissolved as such in the catalyst solution and accumulates therein, but despite this accumulation of sulfuric acid this catalyst solution can be used as such repeatedly in the oxidation of sulfur dioxide. The catalytic life is exceedingly long, and the catalyst ~olution can be repeatedly used over a long period of time. While the cattlytic life will vary depending upon the concentration of the sulfur dioxide and the concentration of the oxygen copresent in the sulfur dioxide-containing gas, as well as the foregoing reaction temperature, in any event the life of our previously proposed pentavalent vanadium-divalent manganese catalyst is greatly prolonged.
However, the catalytic life is, of course, not infinite 10'70479 even in the case of this invention. Hence, in the process of repeatedly using the catalyst solution a part of the deteriorated catalyst solution must be dis-charged externally of the reaction system in concomitance with the decline in reaction performance, and instead a fresh catalyst solution or a regenerated catalyst solution resulting from the separate oxidation treat-ment of a deteriorated catalyst solution must be supplied to the reaction system. For the regeneration of the deteriorated catalyst solution, usable are those known agents that are used for oxidizing tetravalent vanadium, typical being ozone, potassium permanganete, potassium bichromate, cerium sulfate, chlorine and ammonium persulfate. In addition, usable are manganese dioxide, hydrogen peroxide and air as previously proposed by us.
The catalytic activity possessed at the outset can be maintained practically intact by replenishing the catalyst solution with a fresh catalyst solution or a regenerated catalyst in this manner. And as compared with the conventlonal pentavalent vanadium-divalent manganese catalyst, the present invention makes it possible to greatly reduce the amount of the fresh catalyst solution or regenerated catalyst that needs to be replenished.
~he following examples will serve to more fully illustrate the present invention.
~xam~le 1 A specimen gas consisting of 1300 ppm of sulfur dioxide, 6. 5% of oxygen and 93% of nitrogen and of 50C. was fed at a rate of 1980 Nm3/hr to the bottom 1070~73 of a Raschig ring-packed column (absorption column) hav-ing an inside diameter of 88 cm and a height of 6 meters.
At the same time an aqueous solution containing 26 ppm of pentavalent vanadium~ 189 ppm of tetravalent vanadium, 27 ppm of divalent manganese, 27 ppm of trivalent iron and 6 wt.% of sulfuric acid and of 52C. was fed at a rate of 33 m3/hr to the top of the column. The liquid flowing out from the bottom of the absorption column was fed at the rate of 33 m3/hr to the bottom of a 10-tray (sieve) oxidation column having an inside diameter of 44 cm and a height of 6 meters. 99.5/~ of the liquid flowing out from the top of the oxidation column was recycled to the top of the aforesaid absorption column and, at the same time, the unreacted air flow-ing out from the top of the oxidation column was combinedwith the feed gas that was fed to the bottom of the absorptioD column.
1/190 of the liquid flowQng out from the top of the oxidation column was discharged externally of the system and, at the same time, a fresh catalyst solution (200 ppm of pentavalent vamadium, 10 ppm of tet~avalent vanadium, 27 ppm of divalent manganese and 27 ppm of trivalent iron, pH 2, 27C.) was supplied at a rate of 170 liters/hr to the top of the absorption column.
In consequence of thi~ series of operations, the con-centration of the sulfur dioxide of the desulfurized gas discharged from the absorption column was held at 98 to 107 ppm for a period of four months, and the amount of sulfur dioxide in the unreacted air from the top of 47~
the oxidation colwDn was only 4 ppm. It was thus found that 9~/~ of the sulfur dioxide contained in the specimen gas was oxidized.
Control 1 Th~ specimen gas used in Example 1 was fed to an absorption column of the same type as that used in Example 1 aild, at the same time, an aqueous solution containing 27 ppm of pentavalent vanadium, 188 ppm of tetravalent vanadium, 27 ppm of divalent manganese, 2 ppm of trivalent iron and 6 wt.% of sulfuric acid and of 52C. was fed at a rate of 33 m3/hr to the top of the column. Operating as in Example 1, 99.5% of the liquid flowing out from the top of the oxidation column was recycled to the top of the absorption column, while 1/190 thereof was dischar~ed externally of the system. At the same time, a fresh catalyst solution (200 ppm of pentavalent vanadium, 10 ppm of tetravalent vanadium, 27 ppm of divalent manganese and 0.4 ppm of trivalent iron, pH 2, 27C.) was supplied at a rate of 170 liters/hr to the top of the absorption column. In consequence of this series of operations, the concentration of the sulfur dioxide of the desulfurized gas rose to 500 ppm after 90 hours o~ operation. At this point, the concentration of the pentavalent vanadium in the recycle li~uid decreased to 1.0 ppm, and in correspondence therewith the concentration of the tetravalent vanadium increased to 215 ppm. As opposed to the case of Example 1 where the concentration of the pentavalent vanadium was always maintained at 23 - 27 ppm, it is clear that 107047g in this control experiment w~ere the presecribed amount of iron was not added to the catalyst solution there was a deterioration of the catalyst in spite of the replenishment of the recycle catalyst solution with a fresh catalyst, with the consequence that a marked drop in the performance of the desulfurization operation was demonstrated.
In this control experiment it was found that not until the temperature of the recycle liquid was reduced to 26C. or the amount discharged of the recycle catalyst and the amount supplied of the fresh catalyst were increased to 550 liters/hr was it possible to achieve a desulfurization performance of the same order as that of Example l. On the other hand, as seen in Example 1, it is clear that the amount supplied of the fresh catalyst can be greatly reduced at 52C. by using a catalyst solution containing 27 ppm of iron.
Control 2 ~he specimen gas used in Example l was fed to an absorption column of the same type as that used in Example 1 and, at the same time, a 52C. aqueous solu-tion containing 250 ppm of trivalent iron and 6 wt.% of sulfuric acid was fed at a rate of 33 m3~hr to the top of the column. For maintaining the concentration of the sulfuric acid in the recycle liquid at 6 wt.% as in the case of Example l, l/l90 o~ the effluent liquid from the top of the oxidation column was discaharged externa~l~
of the system, while a fresh catalyst solution (250 ppm of trivalent iron, pH 2) was supplied to the 107047~
top of th~ absorption column at a rate of 170 liters/hr.
In this case the concentration of the sulfur dioxide of the desulfurized gas discharged from the top of the absorption colu~n was 2~0 ppm, i.e., a value 17~/o greater than the case of Example 1.
Although the iron concentration of the recycle catalyst solution was raised to 1500 ppm in this control experiment, an improvement in the concentration of the unreacted sulfur dioxide of only as much as 200 - 210 ppm was achieved. This was 100% greater than the case of Example 1.
Thus, as apparent from the foregoing results, even though the treatment of sulfur dioxide is carried out under identical operating conditions as in Example 1, there is demonstrated a great difference in the performance of oxidizing sulfur dioxide when the conventional iron catalyst is used, and thus a performance comparable to that of Example 1 cannot be obtained.
~xamPle 2 A 55C. specimen gas containing 1600 ppm of sulfur dioxide, 5.3% of oxygen and 94% of nitrogen was fed at a rate of 1200 m3/hr to the bottom of a Raschig ring-packed column (absorption column) having an inside diameter of 68 cm and a height of 6 meters. At the same time a 55C. aqueous solution containing 10 ppm of pentavalent vanadium, 195 ppm of tetravalent vanadium, 43 ppm of divalent manganese, 123 ppm of trivalent iron and 4 wt.% of sulfuric acid was fed at a rate of 30 m3/hr to the top of the column. The liquid flowing out from the bottom of the absorption column was conveyed at a rate of 30 m3/hr to a lo-tray (sieve) oxidation column having an inside dimeter of 44 cm and a height of 6 meters and, at the same time, air was fed at a rate of 20 m~hr to the bottom of the oxidation column. 99.3% of the liquid flowing out from the top of the oxidation column was recycled to the top of the aforesaid absorp-tion column, while the unreacted air flowing out from the top of the oxidation column was combined with the feed gas fed to the bottom of the absorption column.
1/150 of the effluent liquid from the top of the oxidation column was discharged externally of the system and, at the same time, a fresh catalyst (195 ppm of penta~alent vanadium, 10 ppm of tetravalent vanadium, 43 ppm of divalent manganese and 123 ppm of trivalent iron, pH 3) was supplied at a rate of 200 liters/hr to the top of the absorption column.
In consequence of this series of operations, the concentration of pentavalent vanadium in the recycle liquid was maintained at 9-11 ppm over a period of three months. On the other hand, the concentration of unreacted sulfur dioxide discharged from the absorption column was 90-98 ppmO
Control 3 Example 2 was repeated but without incorporating the recycle catalyst solution with ironO In this case the concentration of the pentavalent vanadium declined to 0.7 ppm after 100 hours from the initiation of the recycle operation, and the concentration of sulfur dioxide of the desulfurized gas rose to 450 ppm.
It was found that an oxidation reaction performance comparable to that of Example 2 could be achieved by reducing the temperature of the recycle liquid to 25C or by discharging 1/50 of the effluent liquid from the top of the oxidation column externally of the system and supplying a fresh catalyst (195 ppm of pentavalent vanadium, 10 ppm of tetravalent vanadium and 43 ppm of divalent manganese, pH 3) to the absorption column at a rate of 600 liters/hr. However, it is apparent from Example 2 that by uslng a pentavalent vanadium-divalent manganese-trivalent iron type catalyst the amount supplied of the fresh catalyst solution could be greatly reduced at 55C.
Control 4 ~ he specimen gas used in Example 2 was fed to the bottom of an absorption column of the same type as that used in Example 2 and, at the same time, a 55C.
aqueous solution containing 170 ppm of trivalent iron and 4 wt~% of sulfuric acid was fed at a rate of 30 m3/hr to the top of the columnO 1/150 of the liquid flowing out from the top of an oxidation column of the same type as that used in Example 2 was discharged exter-nally of the system while, at the same time, a fresh catalyst solution (170 ppm of trivalent iron, pH 3) was supplied at a rate of 200 liters/hr to the top of the absorption column.
In this series of operations, the concentration ~; of the unreacted sulfur dioxide discharged from the '1071~479 absorption column was 235 ppm, i.e., it was 150 % `
greater than the case of Example 2. Next, the concentra-tion of trivalent iron of the recycle liquid was raised up to 500 ppm, and the operation was carried out in the same manner, but the concentration of the unreacted sulfur dioxide fell to only 150 - 160 ppm, which was still 60/~ greater than in the case of Example 2. Further, even though the concentration of the trivalent iron of the recycle liquid was raised up to 1500 ppm, there was no further improvement. Thus, it was absolutely impos-sible to achieve oxidation results comparable to those of Example 2 with the use of the conventional iron catalyst.
Example 3 A flue gas containing 1950 ppm of sulfur dioxide, ~/0 of oxygen, 10% of carbon dioxide and 9 wt.% of water was first removed of the dust contained therein as well -as cooled to 50C. at a cooling tower and then fed at ~ rate of 1200 m3/hr to the bottom of a Raschig ring-packed column (absorption column) having an inside diameter of 68 cm and a height of 6 meters A~ the same time, a 46C. aqueous solution of 25 ppm of pentavalent vanadium, 150 ppm of tetravalent vanadium, 15 ppm of divalent manganese, 15 ppm of trivalent iron and 6 wt.%
of sulfuric acid was fed to the top of the column at a rate of 30 m3/hr. ~he absorbed liquid flowing out from the bottom of the absorption column was fed at a rate of 30 m3/hr to the bottom of a 10-try (sieve) oxidation column having an inside diameter of 44 cm and a height of 6 meters while, at the same time, air was fed at a 10~704~7g rate of 24 m3/hr to the bottom of the oxidatior column.
99.5/u of the effluent liquid from the top of the oxidation column was recycled to the top of the aforesaid absorption column and, at the same time, the unreacted air flowing out from the top of the oxidation column was combined with the feed gas that was fed to the bottom of the absorption column. On the other hand, 1/190 of the liquid flowing out from the top of the oxidation column (160 liters/hr) was discharged externally of the system and, at the same time, a catalyst solution (1~5 ppm pentavalent vanadium, 50 ppm tetravalent vanadium, 15 ppm of divalent manganese and 15 ppm of trivalent iron, pH 2) was supplied to the top of the absorption column at a rate of 160 liters~hr. In consequence of this series of operations, the pentavalent vanadium of the recycle liquid was maintained at 22 - 26 ppm for a period of four months, while the concentration of the unreacted sulfur dioxide was likewise held at 150-163 ppm.
Control ~
~xample 3 was repeated but without incorporating iron in the recycle catalyst solution. In this case, there was a gradual decrease of the pentavalent vanadium with a corresponding increase of the tetravalent vanadium.
~hat is, 96 hours after initiation of the recycling operation, the concentration of the pentavalent vanadium declined to 0.9 ppm, while the concentration of the unreacted sulfur dioxide rose to 540 ppm. i.e., a 250 %
increase over that of the case of Example 3. It was possible to obtain oxidation results comparable to those 1070~`79 of Example ~ by reducing the temperature of the r~cycle liquid to 26C. or by increasing the amount discharged of the recycle liquid and the amount supplied of the catalyst solution to 430 liters/hr. However, as is apparent from Example 3, it is clear that the amount of catalyst that needs to be replenished can be greatly reduced at 46C. by the conjoint use of iron.
Control 6 The flue gas used in Example 3 was fed to the bottom of an absorption column of the same type as that used in Example 3 while, at the same time, a 46C.
aqueous solution containing 30 ppm of trivalent iron and 6 wt.% of sulfuric acid was fed at a rate of 30 m3/hr to the top of the column. 1/190 of the liquid flowing out from the top of an oxidation column of the same type as that used in Example 3 was discharged externally of the system and, at the same time, a catalyst solution (~0 ppm of trivalent iron, pH ~) was supplied at a rate of 160 liters/hr to the top of the absorption column.
In this series of operations the concentration of the unreacted sulfur dioxide discharged from the top of the absorption column was 830 - 920 ppm, an amount 5 - 6 times that of the case of Example 3. Although the concentration of the recycle liquid was raised up to 350 ppm, the concentration of the unreacted sulfur dioxide was still 420 - 450 ppm.
In this Control 6 the apparatus used and the various conditions such as the composition of the specimen gas and its flow rate, the flow rate of the recycle liquid and its sulfuric acid concentration, and operating temperatures werè identical to those of Example 3, the only difference being the use of the conventional iron catalyst as the catalyst solution. There was however a marked difference in the desulfurization (oxidation of sulfur dioxide) results. A far superior catalytic activity was noted in the case of Example 3 as compared with the case of Control 6.
Claims (3)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for oxidizing sulfur dioxide which comprises contacting sulfur dioxide with oxygen in an aqueous solution containing pentavalent vanadium, divalent manganese and trivalent iron, in the ranges, calculated as metals of 3-8000 ppm, 3-200 ppm and 3-250 ppm, respectively, oxidation being carried out by blowing SO2 and O2 into the aqueous solution or by dissolving the SO2 in the aqueous solution and then contacting the so-obtained SO2- containing liquid with either air or other O2- containing gases.
2. The process of claim 1 which comprises carrying out the contact of sulfur dioxide with oxygen at a temperature in the range of 0 - 100°C.
3. The process of claim 2 wherein said temperature is 20 - 80°C.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP49097487A JPS5125496A (en) | 1974-08-27 | 1974-08-27 | Nisankaiono sankahoho |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1070479A true CA1070479A (en) | 1980-01-29 |
Family
ID=14193620
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA234,220A Expired CA1070479A (en) | 1974-08-27 | 1975-08-26 | Process for oxidizing sulfur dioxide |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5125496A (en) |
| CA (1) | CA1070479A (en) |
| FR (1) | FR2283093A1 (en) |
| GB (1) | GB1511865A (en) |
| NL (1) | NL7510132A (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5367687A (en) * | 1976-11-29 | 1978-06-16 | Mitsubishi Gas Chem Co Inc | Washing method for exhaust gas |
| JPS58220864A (en) * | 1982-06-16 | 1983-12-22 | 帝人株式会社 | Prevention of friction scum of synthetic fiber |
| CN115041195B (en) * | 2022-07-27 | 2023-11-14 | 广西民族大学 | Composite catalyst for flue gas treatment and preparation method and application thereof |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AT334252B (en) * | 1971-06-21 | 1976-01-10 | Swarovski & Co | DEVICE FOR CALLING MOTION IMAGES AND METHOD OF MANUFACTURING |
| DE2141502B2 (en) * | 1971-08-19 | 1974-07-04 | Carl Schenck Maschinenfabrik Gmbh, 6100 Darmstadt | Essentially rigid recirculating body bearings |
-
1974
- 1974-08-27 JP JP49097487A patent/JPS5125496A/en active Granted
-
1975
- 1975-08-26 GB GB3518975A patent/GB1511865A/en not_active Expired
- 1975-08-26 CA CA234,220A patent/CA1070479A/en not_active Expired
- 1975-08-27 NL NL7510132A patent/NL7510132A/en not_active Application Discontinuation
- 1975-08-27 FR FR7526403A patent/FR2283093A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| NL7510132A (en) | 1976-03-02 |
| FR2283093B1 (en) | 1978-04-07 |
| DE2538197B2 (en) | 1977-06-16 |
| GB1511865A (en) | 1978-05-24 |
| JPS5628845B2 (en) | 1981-07-04 |
| JPS5125496A (en) | 1976-03-02 |
| DE2538197A1 (en) | 1976-03-11 |
| FR2283093A1 (en) | 1976-03-26 |
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