CA2267295A1 - Method for producing chlorine dioxide using methanol and hydrogen peroxide as reducing agents - Google Patents
Method for producing chlorine dioxide using methanol and hydrogen peroxide as reducing agents Download PDFInfo
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- C01—INORGANIC CHEMISTRY
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- C01B11/00—Oxides or oxyacids of halogens; Salts thereof
- C01B11/02—Oxides of chlorine
- C01B11/022—Chlorine dioxide (ClO2)
- C01B11/023—Preparation from chlorites or chlorates
- C01B11/026—Preparation from chlorites or chlorates from chlorate ions in the presence of a peroxidic compound, e.g. hydrogen peroxide, ozone, peroxysulfates
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Abstract
A method is described for producing chlorine dioxide by reacting alkali metal chlorate with methanol and hydrogen peroxide in an aqueous acidic medium. Combining these reducing agents causes an unexpected enhancement in chlorine dioxide generation.
Description
_ METHOD FOR PRODUCING CHLORINE DIOXIDE USING METHANOL AND
HYDROGEN PEROXIDE AS REDUCING AGENTS
FIELD OF INVENTION
The present invention relates to a method for producing chlorine dioxide.
BACKGROUND OF THE INVENTION
Chlorine dioxide is employed in a wide variety of industrial applications, including bleaching wood pulp for paper making, bleaching textiles, treating water, and abating odors. The use of chlorine dioxide for bleaching wood pulp has increased because chlorine dioxide is more environmentally friendly than chlorine or hypochlorite) which can leave larger quantities of chlorinated organic compounds in bleaching effluent.
In a typical commercial processes for generating chlorine dioxide, sodium chlorate is reacted with a reducing agent in a strongly acidic aqueous medium.
A metal chloride salt, sulfur dioxide, methanol, or hydrogen peroxide is commonly used as the reducing agent. The typical acid used is sulfuric acid or hydrochloric acid, generally to obtain an acidity of between about 3 to 10 N for the reaction mixture.
The reduction of sodium chlorate with sodium chloride can be represented by the following formula:
NaC103 + NaCI + HzS04 --------> C102 + '/a C12 + Na2S04 + H,O (1) A principle disadvantage of this process is the formation of half a mole of chlorine gas for each mole of chlorine dioxide produced. At one time this chlorine gas was used for bleaching pulp. This use, however, is now disfavored because of environmental concerns.
Less chlorine gas is generated if sodium chloride is replaced by sulfur dioxide or methanol in this process. The methanol based process is termed the Solvay process, while the sulfur dioxide process is termed the Mathieson process.
However, the reaction between chlorate and either sulfur dioxide or methanol is very slow, resulting in a low rate of chlorine dioxide generation. The following reactions occur initially, resulting in generation of chloride ion, which acts as a reducing agent:
C103- + 350, + 3H,0 ----- > CI- + 3HZSO4 (2) 2C103- + 3CH30H ---- > 2C1- + 2HCOOH + 4H0 + COZ (3) The chloride ions reduce chlorates present in the reaction mixture according to formula (1) shown above, resulting in the production of chlorine gas. The chlorine gas reacts with the sulfur dioxide or methanol to regenerate chloride ions according to the following formula:
SO~ + Ch + 2H=O ----- > 2HCI + HZS04 (4) CH30H + 3C12 + HBO ----- > 6HC1 + COZ (5) The overall reaction using methanol as reducing agent is as follows:
9NaC103 + 2CH30H- + 6H~S0,, ----- > 9ClOz + (b) 3Na3H(S04)2 + 1/zCO~ + 1.SHCOOH + 7H,0 When using sulfur dioxide or methanol as reducing agent, however, at least a small amount of chlorine gas by-product is produced. Also, when using methanol as reducing agent at high chlorate concentrations and acidity, the chloride formed in reactions 2-5 can be consumed in the subsequent formation of chlorine dioxide faster than it is generated.
When the chloride is exhausted, chlorine dioxide generation ceases and a phenomenon known as "whiteout" results, i.e., the reaction medium becomes clear. To prevent this, it is often necessary to add a small amount of sodium chloride continuously, or to avoid certain high concentrations of chlorate and acid.
Hydrogen peroxide has been used as a reducing agent in chlorine dioxide generation to eliminate production of chlorine. Using hydrogen peroxide also results in a significantly faster chlorine dioxide generation rate than other processes.
The reaction using hydrogen peroxide is represented by the following formula:
2NaC103 + HZOz + HZS04 ------ > 2C10 + Na~S04 + 2H20 + OZ (7) An important disadvantage of this process, however) is that hydrogen peroxide is much more expensive than methanol, sodium chloride, or sulfur dioxide. For this reason, the hydrogen peroxide based process is not used as commonly as the methanol and sulfur dioxide based processes.
There is therefore a need for a method of producing chlorine dioxide that is efficient and economical, which does not generate substantial amounts of chlorine, and which reduces the possibility of a whiteout condition.
SUMMARY OF THE INVENTION
The present invention relates to a method for producing chlorine dioxide by reacting alkali metal chlorate with reducing agents in an aqueous acidic medium, wherein the reducing agents are methanol and hydrogen peroxide. It has been determined that combining hydrogen peroxide and methanol causes an unexpectedly strong enhancement in the rate of chlorine dioxide generation.
HYDROGEN PEROXIDE AS REDUCING AGENTS
FIELD OF INVENTION
The present invention relates to a method for producing chlorine dioxide.
BACKGROUND OF THE INVENTION
Chlorine dioxide is employed in a wide variety of industrial applications, including bleaching wood pulp for paper making, bleaching textiles, treating water, and abating odors. The use of chlorine dioxide for bleaching wood pulp has increased because chlorine dioxide is more environmentally friendly than chlorine or hypochlorite) which can leave larger quantities of chlorinated organic compounds in bleaching effluent.
In a typical commercial processes for generating chlorine dioxide, sodium chlorate is reacted with a reducing agent in a strongly acidic aqueous medium.
A metal chloride salt, sulfur dioxide, methanol, or hydrogen peroxide is commonly used as the reducing agent. The typical acid used is sulfuric acid or hydrochloric acid, generally to obtain an acidity of between about 3 to 10 N for the reaction mixture.
The reduction of sodium chlorate with sodium chloride can be represented by the following formula:
NaC103 + NaCI + HzS04 --------> C102 + '/a C12 + Na2S04 + H,O (1) A principle disadvantage of this process is the formation of half a mole of chlorine gas for each mole of chlorine dioxide produced. At one time this chlorine gas was used for bleaching pulp. This use, however, is now disfavored because of environmental concerns.
Less chlorine gas is generated if sodium chloride is replaced by sulfur dioxide or methanol in this process. The methanol based process is termed the Solvay process, while the sulfur dioxide process is termed the Mathieson process.
However, the reaction between chlorate and either sulfur dioxide or methanol is very slow, resulting in a low rate of chlorine dioxide generation. The following reactions occur initially, resulting in generation of chloride ion, which acts as a reducing agent:
C103- + 350, + 3H,0 ----- > CI- + 3HZSO4 (2) 2C103- + 3CH30H ---- > 2C1- + 2HCOOH + 4H0 + COZ (3) The chloride ions reduce chlorates present in the reaction mixture according to formula (1) shown above, resulting in the production of chlorine gas. The chlorine gas reacts with the sulfur dioxide or methanol to regenerate chloride ions according to the following formula:
SO~ + Ch + 2H=O ----- > 2HCI + HZS04 (4) CH30H + 3C12 + HBO ----- > 6HC1 + COZ (5) The overall reaction using methanol as reducing agent is as follows:
9NaC103 + 2CH30H- + 6H~S0,, ----- > 9ClOz + (b) 3Na3H(S04)2 + 1/zCO~ + 1.SHCOOH + 7H,0 When using sulfur dioxide or methanol as reducing agent, however, at least a small amount of chlorine gas by-product is produced. Also, when using methanol as reducing agent at high chlorate concentrations and acidity, the chloride formed in reactions 2-5 can be consumed in the subsequent formation of chlorine dioxide faster than it is generated.
When the chloride is exhausted, chlorine dioxide generation ceases and a phenomenon known as "whiteout" results, i.e., the reaction medium becomes clear. To prevent this, it is often necessary to add a small amount of sodium chloride continuously, or to avoid certain high concentrations of chlorate and acid.
Hydrogen peroxide has been used as a reducing agent in chlorine dioxide generation to eliminate production of chlorine. Using hydrogen peroxide also results in a significantly faster chlorine dioxide generation rate than other processes.
The reaction using hydrogen peroxide is represented by the following formula:
2NaC103 + HZOz + HZS04 ------ > 2C10 + Na~S04 + 2H20 + OZ (7) An important disadvantage of this process, however) is that hydrogen peroxide is much more expensive than methanol, sodium chloride, or sulfur dioxide. For this reason, the hydrogen peroxide based process is not used as commonly as the methanol and sulfur dioxide based processes.
There is therefore a need for a method of producing chlorine dioxide that is efficient and economical, which does not generate substantial amounts of chlorine, and which reduces the possibility of a whiteout condition.
SUMMARY OF THE INVENTION
The present invention relates to a method for producing chlorine dioxide by reacting alkali metal chlorate with reducing agents in an aqueous acidic medium, wherein the reducing agents are methanol and hydrogen peroxide. It has been determined that combining hydrogen peroxide and methanol causes an unexpectedly strong enhancement in the rate of chlorine dioxide generation.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic representation of a continuous process embodiment of the invention.
Figure 2 is a graph showing chlorine dioxide generation using the process of the invention at atmospheric pressure, 60' C, and 12N HZS04. The points on the graph shown with a " D " indicate chlorine dioxide generation rates for combinations of methanol and hydrogen peroxide reducing agent in the equivalent strength ratios indicated. The dotted line connecting the points for l00 mole % CH30H and 100 mole %
H20, shows the expected chlorine dioxide generation rate for a combination of hydrogen peroxide and methanol reducing agents.
Figure 3 is a graph showing chlorine dioxide generation using the process of the invention at a sub-atmospheric pressure of 300 mm Hg, 60' C, and 10 N
H~S04.
The points on the graph shown with a " Cl " indicate the amount of chlorine dioxide generated for 100 % methanol, combinations of methanol and hydrogen peroxide, and 100 % hydrogen peroxide. The dotted line shows the expected amount of chlorine dioxide generation for a combination of methanol and hydrogen peroxide reducing agents. The point on the graph shown with a "+" indicates the amount of chlorine dioxide generated for a combination of sodium chloride, methanol, and hydrogen peroxide in a l0:80:10 equivalent strength molar ratio.
DETAILED DESCRIPTION OF THE INVENTION
We have determined that a synergism between methanol and hydrogen peroxide reducing agents results in the generation of chlorine dioxide at a higher rate than would have been expected. This higher rate allows more chlorine dioxide production from a given generator volume, thereby reducing capital cost. It also allows, for example, a smaller generator to be used to meet a given chlorine dioxide demand. In addition, by varying the ratio of methanol to hydrogen peroxide, one can increase or decrease the chlorine dioxide generation rate. This degree of flexibility in choosing a desired chlorine dioxide generation rate is unique to the present invention.
For example, it has been found) at atmospheric pressure, that by substituting 10 % of the methanol in the methanol type process described above with the same amount, on an equivalent strength basis, of hydrogen peroxide) the generation rate of chlorine dioxide is doubled. The generation rate of chlorine dioxide obtained using hydrogen peroxide is known to be higher than that obtained using methanol. But the increase obtained by substituting only 10 % hydrogen peroxide in the methanol process represents about 40 % of the increase obtained if 100 % hydrogen peroxide is used. Thus the increase in chlorine dioxide generation that is obtained using a methanol/hydrogen peroxide mixture is unexpectedly high.
As noted above, the invention results in surprising benefits at atmospheric pressure. Preferred pressures are between about 400 and 900 mm Hg. It has been determined, however, that the benefits of the invention can also be enjoyed when the process is carried out at sub-atmospheric pressure, a preferred sub-atmospheric pressure being from about 100 mm Hg to 400 mm Hg. At sub-atmospheric pressure, when 10%
of methanol in the methanol-based process was substituted for an equivalent amount of hydrogen peroxide, generation of chlorine dioxide was increased by 20 % . When 30 % of - methanol was substituted for by an equivalent strength of hydrogen peroxide, the generation of chlorine dioxide was increased by 68 % .
The method of the invention is preferably carried out as a continuous process. In one embodiment, depicted in a flow diagram in Figure l, sodium chlorate is reacted with hydrogen peroxide and methanol reducing agents in the presence of concentrated sulfuric acid. The reactants can be introduced together, but preferably are introduced separately into a conventional reaction vessel. The reaction can be carried out at atmospheric pressure, with air, or other inert gas such as nitrogen, circulating through the reaction vessel. The reaction should be maintained substantially in a steady state by continuously feeding the reactants, and by ensuring that they are evenly distributed in the reaction medium. The chlorine dioxide gas that is generated can be collected and absorbed outside of the reaction vessel. Water vapor and other gaseous byproducts should also be continuously removed from the reaction vessel, and vented to a chlorine dioxide absorber. Reaction medium containing alkali metal salt (Na2SOd in Figure 1}, unreacted chlorate, acid and reducing agents should also be continuously removed (e.g., "HzS04 Effluent" in Figure 1 ). Sodium acid sulfate deposited in the reaction at sub-atmospheric conditions can be removed and subjected to a metathesis reaction to form neutral sodium sulfate and acidic aqueous solution.
Preferably, the reaction medium that is withdrawn from a reaction vessel running at atmospheric pressure is cascaded into a second reaction vessel operating at sub-atmospheric pressure, such as a "single vessel process" (SVP''") reactor.
For the preferred reactants, the withdrawn medium from a reaction vessel at atmospheric pressure contains largely sulfuric acid, with lesser amounts of chlorine dioxide, sodium chlorate, sodium sulfate, and hydrogen peroxide. The withdrawn medium, new reducing agents, sodium chlorate, and sulfuric acid are preferably added separately to the second vessel, and the second vessel kept at a sub-atmospheric pressure of between 100 and 400 mm WO 98l13295 PCT/US97J17758 Hg, preferably between 100 and 300 mm Hg. Chlorine dioxide gas is recovered outside of the first and second reaction vessels. In the cascade process run under these conditions, the only by-product generated in the second reactor can be a neutral metal salt, or acidic salt cake, depending on the acidity of the reaction medium.
If desired, catalysts that enhance the generation of chlorine dioxide are added to the reaction as well. Such catalysts include, e. g. , silver nitrate, manganese sulfate, vanadium pentoxide, ruthenium oxide, rhodium oxide, and palladium oxide.
The process is conducted in a temperature range of between about 20~ C
and about 140~ C, preferably between about 35~ C and 80~ C, and most preferably between about 50 ~ C and 75 ~ C.
Suitable acids for use in the reaction include, e.g., sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, and chloric acid. Sulfuric acid is preferred. The acid normality is maintained in the aqueous reaction medium between about 1 N to 15 N, preferably between about 4 N and 12 N. Most preferably, the normality is maintained at between about 7 N and 10 N for atmospheric conditions, and between about 4 N and 5 N or 7 N to 10 N for subatmospheric conditions.
Performance of the process at 7 N to 10 N generates acid salt cake while performance at 4 N to 5 N
generates neutral saltcake.
Alkali metal chlorates that can be used in this process include, e. g. , sodium chlorate and potassium chlorate. Sodium chlorate is preferred. The alkali metal chlorate concentration employed in the reaction is between about 0.01 M and saturation concentration, preferably between about 0.01 M and 4 M. It is most preferably between about 0.05 M and 0.3 M at a pressure between about 400 and 900 mm Hg, and between about 0.3 M and 1.5 M at a pressure between about 100 and 400 mm Hg.
Figure 1 is a schematic representation of a continuous process embodiment of the invention.
Figure 2 is a graph showing chlorine dioxide generation using the process of the invention at atmospheric pressure, 60' C, and 12N HZS04. The points on the graph shown with a " D " indicate chlorine dioxide generation rates for combinations of methanol and hydrogen peroxide reducing agent in the equivalent strength ratios indicated. The dotted line connecting the points for l00 mole % CH30H and 100 mole %
H20, shows the expected chlorine dioxide generation rate for a combination of hydrogen peroxide and methanol reducing agents.
Figure 3 is a graph showing chlorine dioxide generation using the process of the invention at a sub-atmospheric pressure of 300 mm Hg, 60' C, and 10 N
H~S04.
The points on the graph shown with a " Cl " indicate the amount of chlorine dioxide generated for 100 % methanol, combinations of methanol and hydrogen peroxide, and 100 % hydrogen peroxide. The dotted line shows the expected amount of chlorine dioxide generation for a combination of methanol and hydrogen peroxide reducing agents. The point on the graph shown with a "+" indicates the amount of chlorine dioxide generated for a combination of sodium chloride, methanol, and hydrogen peroxide in a l0:80:10 equivalent strength molar ratio.
DETAILED DESCRIPTION OF THE INVENTION
We have determined that a synergism between methanol and hydrogen peroxide reducing agents results in the generation of chlorine dioxide at a higher rate than would have been expected. This higher rate allows more chlorine dioxide production from a given generator volume, thereby reducing capital cost. It also allows, for example, a smaller generator to be used to meet a given chlorine dioxide demand. In addition, by varying the ratio of methanol to hydrogen peroxide, one can increase or decrease the chlorine dioxide generation rate. This degree of flexibility in choosing a desired chlorine dioxide generation rate is unique to the present invention.
For example, it has been found) at atmospheric pressure, that by substituting 10 % of the methanol in the methanol type process described above with the same amount, on an equivalent strength basis, of hydrogen peroxide) the generation rate of chlorine dioxide is doubled. The generation rate of chlorine dioxide obtained using hydrogen peroxide is known to be higher than that obtained using methanol. But the increase obtained by substituting only 10 % hydrogen peroxide in the methanol process represents about 40 % of the increase obtained if 100 % hydrogen peroxide is used. Thus the increase in chlorine dioxide generation that is obtained using a methanol/hydrogen peroxide mixture is unexpectedly high.
As noted above, the invention results in surprising benefits at atmospheric pressure. Preferred pressures are between about 400 and 900 mm Hg. It has been determined, however, that the benefits of the invention can also be enjoyed when the process is carried out at sub-atmospheric pressure, a preferred sub-atmospheric pressure being from about 100 mm Hg to 400 mm Hg. At sub-atmospheric pressure, when 10%
of methanol in the methanol-based process was substituted for an equivalent amount of hydrogen peroxide, generation of chlorine dioxide was increased by 20 % . When 30 % of - methanol was substituted for by an equivalent strength of hydrogen peroxide, the generation of chlorine dioxide was increased by 68 % .
The method of the invention is preferably carried out as a continuous process. In one embodiment, depicted in a flow diagram in Figure l, sodium chlorate is reacted with hydrogen peroxide and methanol reducing agents in the presence of concentrated sulfuric acid. The reactants can be introduced together, but preferably are introduced separately into a conventional reaction vessel. The reaction can be carried out at atmospheric pressure, with air, or other inert gas such as nitrogen, circulating through the reaction vessel. The reaction should be maintained substantially in a steady state by continuously feeding the reactants, and by ensuring that they are evenly distributed in the reaction medium. The chlorine dioxide gas that is generated can be collected and absorbed outside of the reaction vessel. Water vapor and other gaseous byproducts should also be continuously removed from the reaction vessel, and vented to a chlorine dioxide absorber. Reaction medium containing alkali metal salt (Na2SOd in Figure 1}, unreacted chlorate, acid and reducing agents should also be continuously removed (e.g., "HzS04 Effluent" in Figure 1 ). Sodium acid sulfate deposited in the reaction at sub-atmospheric conditions can be removed and subjected to a metathesis reaction to form neutral sodium sulfate and acidic aqueous solution.
Preferably, the reaction medium that is withdrawn from a reaction vessel running at atmospheric pressure is cascaded into a second reaction vessel operating at sub-atmospheric pressure, such as a "single vessel process" (SVP''") reactor.
For the preferred reactants, the withdrawn medium from a reaction vessel at atmospheric pressure contains largely sulfuric acid, with lesser amounts of chlorine dioxide, sodium chlorate, sodium sulfate, and hydrogen peroxide. The withdrawn medium, new reducing agents, sodium chlorate, and sulfuric acid are preferably added separately to the second vessel, and the second vessel kept at a sub-atmospheric pressure of between 100 and 400 mm WO 98l13295 PCT/US97J17758 Hg, preferably between 100 and 300 mm Hg. Chlorine dioxide gas is recovered outside of the first and second reaction vessels. In the cascade process run under these conditions, the only by-product generated in the second reactor can be a neutral metal salt, or acidic salt cake, depending on the acidity of the reaction medium.
If desired, catalysts that enhance the generation of chlorine dioxide are added to the reaction as well. Such catalysts include, e. g. , silver nitrate, manganese sulfate, vanadium pentoxide, ruthenium oxide, rhodium oxide, and palladium oxide.
The process is conducted in a temperature range of between about 20~ C
and about 140~ C, preferably between about 35~ C and 80~ C, and most preferably between about 50 ~ C and 75 ~ C.
Suitable acids for use in the reaction include, e.g., sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, and chloric acid. Sulfuric acid is preferred. The acid normality is maintained in the aqueous reaction medium between about 1 N to 15 N, preferably between about 4 N and 12 N. Most preferably, the normality is maintained at between about 7 N and 10 N for atmospheric conditions, and between about 4 N and 5 N or 7 N to 10 N for subatmospheric conditions.
Performance of the process at 7 N to 10 N generates acid salt cake while performance at 4 N to 5 N
generates neutral saltcake.
Alkali metal chlorates that can be used in this process include, e. g. , sodium chlorate and potassium chlorate. Sodium chlorate is preferred. The alkali metal chlorate concentration employed in the reaction is between about 0.01 M and saturation concentration, preferably between about 0.01 M and 4 M. It is most preferably between about 0.05 M and 0.3 M at a pressure between about 400 and 900 mm Hg, and between about 0.3 M and 1.5 M at a pressure between about 100 and 400 mm Hg.
WO 98l13295 PCT/US97/17758 The optimum percentage of hydrogen peroxide with respect to the total amount of reducing agent used in the process, on an equivalent strength basis, depends on the chemical costs, chlorine dioxide demand, and byproduct demands. It can vary from 1 % to 99 % , but for a typical paper mill is preferably less than 50 % , more preferably less than 30 % , and most preferably between about 5 and 10 % . The amount of total reducing agent consumed in the reaction is preferably from about 100 % to 120 % of the stoichiometrically calculated amount.
If desired, the method of the invention can be practiced by adding hydrogen peroxide to an existing chlorine dioxide generator that uses a methanol reducing agent. The method can also be practiced by adding methanol to an existing generator that uses a hydrogen peroxide reducing agent. Alternately, hydrogen peroxide can be added to an existing generator that uses methanol reducing agent, or a combination of hydrogen peroxide and methanol can be added to an existing generator that uses sulfur dioxide reducing agent.
The invention is illustrated by the following examples, which are intended to merely exemplify the invention, not to limit its scope.
EXAMPLE 1: PARTIAL SUBSTITUTION OF METHANOL REDUCING AGENT
WITH HYDROGEN PEROXIDE AT ATMOSPHERIC PRESSURE
Sodium chlorate (27 grams/liter) and sulfuric acid {588 grams/liter) were added to a laboratory reaction vessel equipped with a nitrogen sparger to obtain a 600 ml reaction mixture having a chlorate concentration of 0.25M and an acid normality of 12 N.
The reactor was operated at atmospheric pressure and 60~ C.
If desired, the method of the invention can be practiced by adding hydrogen peroxide to an existing chlorine dioxide generator that uses a methanol reducing agent. The method can also be practiced by adding methanol to an existing generator that uses a hydrogen peroxide reducing agent. Alternately, hydrogen peroxide can be added to an existing generator that uses methanol reducing agent, or a combination of hydrogen peroxide and methanol can be added to an existing generator that uses sulfur dioxide reducing agent.
The invention is illustrated by the following examples, which are intended to merely exemplify the invention, not to limit its scope.
EXAMPLE 1: PARTIAL SUBSTITUTION OF METHANOL REDUCING AGENT
WITH HYDROGEN PEROXIDE AT ATMOSPHERIC PRESSURE
Sodium chlorate (27 grams/liter) and sulfuric acid {588 grams/liter) were added to a laboratory reaction vessel equipped with a nitrogen sparger to obtain a 600 ml reaction mixture having a chlorate concentration of 0.25M and an acid normality of 12 N.
The reactor was operated at atmospheric pressure and 60~ C.
WO 98/13295 PCT/U597i17758 Methanol, methanol and hydrogen peroxide mixtures, or hydrogen peroxide, were added to the reactor based on the stoichiometric amount that was equivalent to 0.15 moles sodium chloride. As shown in reaction formula { 1 ) above, only one mole of salt is added for every mole of chlorate in the process for producing chlorine dioxide.
The amount of methanol that was equivalent to 0.15 moles of salt was calculated by the following equation:
0.15 x 32/4.5 = 1.07 gram.
The "32" in this equation is the molecular weight of methanol. The "4.5" is derived from the reaction stoichiometry for producing chlorine dioxide with methanol shown in equation (6) above, in which one mole of methanol produces 4.5 moles of chlorine dioxide.
The amount of hydrogen peroxide that was equivalent to 0.15 moles of salt was determined by the following equation:
0.15 x 34/2 = 2.55 grams The "34" in this equation is the molecular weight of hydrogen peroxide. The "2" is derived from the reaction stoichiometry for producing chlorine dioxide with hydrogen peroxide shown in equation (7) above, in which one mole of hydrogen peroxide produces 2 moles of chlorine dioxide.
Figure 2 shows the amount of chlorine dioxide (in grams) generated over 1.5 minutes when methanol was used alone, methanol was mixed with hydrogen peroxide in a 9:1 equivalent strength ratio, methanol was mixed with hydrogen peroxide in a 7:3 equivalent strength ratio, and hydrogen peroxide was used alone. The rate of chlorine dioxide generation in this system was calculated by the following formula:
The amount of methanol that was equivalent to 0.15 moles of salt was calculated by the following equation:
0.15 x 32/4.5 = 1.07 gram.
The "32" in this equation is the molecular weight of methanol. The "4.5" is derived from the reaction stoichiometry for producing chlorine dioxide with methanol shown in equation (6) above, in which one mole of methanol produces 4.5 moles of chlorine dioxide.
The amount of hydrogen peroxide that was equivalent to 0.15 moles of salt was determined by the following equation:
0.15 x 34/2 = 2.55 grams The "34" in this equation is the molecular weight of hydrogen peroxide. The "2" is derived from the reaction stoichiometry for producing chlorine dioxide with hydrogen peroxide shown in equation (7) above, in which one mole of hydrogen peroxide produces 2 moles of chlorine dioxide.
Figure 2 shows the amount of chlorine dioxide (in grams) generated over 1.5 minutes when methanol was used alone, methanol was mixed with hydrogen peroxide in a 9:1 equivalent strength ratio, methanol was mixed with hydrogen peroxide in a 7:3 equivalent strength ratio, and hydrogen peroxide was used alone. The rate of chlorine dioxide generation in this system was calculated by the following formula:
ClOz generation = (grams of C102/67.5 grams/mole)/(0.6 liter x 1.5 min) The amount of chorine expected to have been generated is shown by the dotted line.
This substitution of 10 % of methanol reducing agent with hydrogen peroxide resulted in a chlorine dioxide generation rate of 6.6 x 10-2 moles/(liter-minute), which was surprisingly greater than the rate obtained using methanol alone of 3.1 x 10-Z
moles/(liter-minute). Use of 100% hydrogen peroxide resulted in a generation rate of 12.2 X 10-Z moles/(liter-minute). Thus, substitution of IO% methanol increases the generation rate by about 39 % of the total increase in the chlorine dioxide generation rate achieved using 100% hydrogen peroxide.
The increase in chlorine dioxide generation that was obtained using a 7:3 equivalent strength ratio {i. e. , 30 % hydrogen peroxide) was 9.3 x 10-Z
moles/(liter-minute). This amounted to about 68 % of the increase in chlorine dioxide generation rate that was produced using 100% hydrogen peroxide.
Thus, by substituting a relatively small amount of hydrogen peroxide for methanol reducing agent, a surprisingly large increase in the chlorine dioxide generation rate was obtained.
EXAMPLE 2: PARTIAL SUBSTITUTION OF METHANOL WITH HYDROGEN
PEROXIDE AT SUB-ATMOSPHERIC PRESSURE
The experiment described in Example 1 was carried out as described therein, except that the process was carried out at a sub-atmospheric pressure of 300 mm Hg and 490 grams/liter of sulfuric acid was used to obtain a reaction mixture having an acid normality of 10 N. The results of this experiment are shown in Figure 3.
At a 9:1 equivalent strength ratio of methanol:hydrogen peroxide, (i.e., a % equivalent strength of hydrogen peroxide) a chlorine dioxide rate of 7. b x 10'2 moles/(liter-minute) was obtained. This rate was surprisingly higher than the rate obtained using only methanol (6.8 x 10'z moles/(liter-minute)), and represented about 20%
of the increase in the rate that was obtained when 100 % hydrogen peroxide was used {11.2 x 10-2 moles/(liter-minute)).
At a 7:3 equivalent strength ratio of methanol:hydrogen peroxide, (i.e., 30% equivalent strength hydrogen peroxide), a chlorine dioxide generation rate of 9.8 x 10-Z moles/(liter-minute) was obtained, which was significantly higher than that obtained using only methanol (6.8 x 10-Z moles/(liter-minute)). This amounted to about 68 % of the increase in the chlorine dioxide generation rate that was obtained using 100 %
hydrogen peroxide.
Thus, substitution of 10% or 30% of methanol with hydrogen peroxide resulted in a surprising increase in chlorine dioxide generation.
As shown in Figure 3, use of a combination of sodium chloride:methanol:hydrogen peroxide in a 10:80:10 equivalent strength ratio also resulted in a high chlorine dioxide generation rate. The use of chloride ion in combination with methanol and hydrogen peroxide reducing agents is a separately patentable invention that is the subject of copending application serial no. 08/720,087, entitled "Method for Producing Chlorine Dioxide using Methanol, Chloride, and Hydrogen Peroxide as Reducing Agents", filed on the same date as the present application.
This substitution of 10 % of methanol reducing agent with hydrogen peroxide resulted in a chlorine dioxide generation rate of 6.6 x 10-2 moles/(liter-minute), which was surprisingly greater than the rate obtained using methanol alone of 3.1 x 10-Z
moles/(liter-minute). Use of 100% hydrogen peroxide resulted in a generation rate of 12.2 X 10-Z moles/(liter-minute). Thus, substitution of IO% methanol increases the generation rate by about 39 % of the total increase in the chlorine dioxide generation rate achieved using 100% hydrogen peroxide.
The increase in chlorine dioxide generation that was obtained using a 7:3 equivalent strength ratio {i. e. , 30 % hydrogen peroxide) was 9.3 x 10-Z
moles/(liter-minute). This amounted to about 68 % of the increase in chlorine dioxide generation rate that was produced using 100% hydrogen peroxide.
Thus, by substituting a relatively small amount of hydrogen peroxide for methanol reducing agent, a surprisingly large increase in the chlorine dioxide generation rate was obtained.
EXAMPLE 2: PARTIAL SUBSTITUTION OF METHANOL WITH HYDROGEN
PEROXIDE AT SUB-ATMOSPHERIC PRESSURE
The experiment described in Example 1 was carried out as described therein, except that the process was carried out at a sub-atmospheric pressure of 300 mm Hg and 490 grams/liter of sulfuric acid was used to obtain a reaction mixture having an acid normality of 10 N. The results of this experiment are shown in Figure 3.
At a 9:1 equivalent strength ratio of methanol:hydrogen peroxide, (i.e., a % equivalent strength of hydrogen peroxide) a chlorine dioxide rate of 7. b x 10'2 moles/(liter-minute) was obtained. This rate was surprisingly higher than the rate obtained using only methanol (6.8 x 10'z moles/(liter-minute)), and represented about 20%
of the increase in the rate that was obtained when 100 % hydrogen peroxide was used {11.2 x 10-2 moles/(liter-minute)).
At a 7:3 equivalent strength ratio of methanol:hydrogen peroxide, (i.e., 30% equivalent strength hydrogen peroxide), a chlorine dioxide generation rate of 9.8 x 10-Z moles/(liter-minute) was obtained, which was significantly higher than that obtained using only methanol (6.8 x 10-Z moles/(liter-minute)). This amounted to about 68 % of the increase in the chlorine dioxide generation rate that was obtained using 100 %
hydrogen peroxide.
Thus, substitution of 10% or 30% of methanol with hydrogen peroxide resulted in a surprising increase in chlorine dioxide generation.
As shown in Figure 3, use of a combination of sodium chloride:methanol:hydrogen peroxide in a 10:80:10 equivalent strength ratio also resulted in a high chlorine dioxide generation rate. The use of chloride ion in combination with methanol and hydrogen peroxide reducing agents is a separately patentable invention that is the subject of copending application serial no. 08/720,087, entitled "Method for Producing Chlorine Dioxide using Methanol, Chloride, and Hydrogen Peroxide as Reducing Agents", filed on the same date as the present application.
Claims (44)
1. In a method for producing chlorine dioxide wherein an alkali metal chlorate is reacted with a reducing agent in an aqueous acidic medium, the improvement comprising reacting said alkali metal chlorate with a combination of methanol and hydrogen peroxide reducing agents.
2. A method for producing chlorine dioxide comprising reacting alkali metal chlorate with reducing agents and an acid, wherein said reducing agents comprise methanol and hydrogen peroxide, said hydrogen peroxide comprising less than 50%, on an equivalent strength basis, of said reducing agents.
3. The method of claim 2 wherein said acid is selected from the group consisting of sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, and chloric acid.
4. The method of claim 3 wherein said acid is sulfuric acid.
5. The method of claim 2 wherein said alkali metal chlorate is sodium chlorate.
6. The method of claim 2 wherein said reaction is carried out at a temperature of between about 20°C and about 140°C.
7. The method of claim 2 wherein said reaction is carried out at a temperature of between about 35~C and about 80~C.
8. The method of claim 2 wherein said reaction is carried out at a temperature of between about 50~C and about 75~C.
9. The method of claim 2 wherein said reaction is carried out a pressure of between about 400 and 900 mm Hg.
10. The method of claim 2 wherein said reaction is carried out at about atmospheric pressure.
11. The method of claim 2 wherein said reaction is carried out a pressure of between about 100 mm Hg and 400 mm Hg.
12. The method of claim 2 wherein the acid normality of said reaction medium is between about 4 N and 12 N.
13. The method of claim 12 wherein the acid normality of said reaction is between about 7 N and 10 N.
14. The method of claim 2 wherein a catalytic species for enhancing generation of chlorine dioxide is added to said reaction.
15. The method of claim 14 wherein said catalytic species is selected from the group consisting of silver nitrate, manganese sulfate, vanadium pentoxide, ruthenium oxide, rhodium oxide, and palladium oxide.
16. The method of claim 2 wherein said step of reacting is carried out at a pressure between about 400 and 900 mm Hg and said alkali metal chlorate is reacted at a concentration of between about 0.05 M and 0.3 M.
17. The method of claim 2 wherein said step of reacting is carried out at a pressure of between about 100 and 400 mm Hg and said alkali metal chlorate is reacted at a concentration of between about 0.3 M and 1.5 M.
18. The method of claim 2 wherein said hydrogen peroxide comprises less than 30%, on an equivalent strength basis, of said reducing agents.
19. The method of claim 2 wherein said hydrogen peroxide comprises between and 10%, on an equivalent strength basis, of said reducing agents.
20. The method of claim 2 comprising a continuous process.
21. A method for producing chlorine dioxide comprising reacting alkali metal chlorate with reducing agents in an aqueous acidic solution, said reducing agents comprising methanol and hydrogen peroxide, said hydrogen peroxide comprising less than 50%, on an equivalent strength basis, of said reducing agents, wherein said method is conducted at:
a. a temperature of between about 35~ C and about 80~ C;
b. an acid normality of between about 4 N and 12 N;
c. a pressure of between about 400 and 900 mm Hg; and d. an alkali metal chlorate concentration of between about 0.01 mole/liter and 4 moles/liter.
a. a temperature of between about 35~ C and about 80~ C;
b. an acid normality of between about 4 N and 12 N;
c. a pressure of between about 400 and 900 mm Hg; and d. an alkali metal chlorate concentration of between about 0.01 mole/liter and 4 moles/liter.
22. The method of claim 21 wherein said acid is selected from the group consisting of sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, and chloric acid.
23. The method of claim 22 wherein said acid is sulfuric acid.
24. The method of claim 21 wherein said alkali metal chlorate is sodium chlorate.
25. The method of claim 21 wherein said reaction is carried out at a temperature of between about 50~ C and about 75~ C.
26. The method of claim 21 wherein said reaction is carried out at about atmospheric pressure.
27. The method of claim 21 wherein the acid normality of said reaction is between about 7 N and 10 N.
28. The method of claim 21 wherein said hydrogen peroxide comprises less than 30%, on an equivalent strength basis, of said reducing agents.
29. The method of claim 21 wherein said hydrogen peroxide comprises between 5 and 10 %, on an equivalent strength basis, of said reducing agents.
30. The method of claim 21 wherein a catalytic species for enhancing generation of chlorine dioxide is added to said reaction.
31. The method of claim 21 comprising a continuous process.
32. A method for producing chlorine dioxide comprising continuously feeding alkali metal chlorate, reducing agents, and acid into a reaction chamber, while removing chlorine gas, water vapor, other gaseous byproducts, alkali metal salt, unreacted chlorate and acid and methanol and hydrogen peroxide, wherein:
a. said reducing agents comprise methanol and hydrogen peroxide, and said hydrogen peroxide comprises less than 50%, on an equivalent strength basis, of said reducing agents;
b. said process is conducted at a temperature of between about 35° C
and about 80°;
c. said process is conducted at an acid normality of between 4 N and 12 N;
d. said alkali metal chlorate is present in said reaction medium in a concentration of between about 0.01 mole/liter and 4 moles/liter.
a. said reducing agents comprise methanol and hydrogen peroxide, and said hydrogen peroxide comprises less than 50%, on an equivalent strength basis, of said reducing agents;
b. said process is conducted at a temperature of between about 35° C
and about 80°;
c. said process is conducted at an acid normality of between 4 N and 12 N;
d. said alkali metal chlorate is present in said reaction medium in a concentration of between about 0.01 mole/liter and 4 moles/liter.
33. The method of claim 32 wherein said acid is selected from the group consisting of sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, and chloric acid.
34. The method of claim 33 wherein said acid is sulfuric acid.
35. The method of claim 32 wherein said alkali metal chlorate is sodium chlorate.
36. The method of claim 32 wherein said reaction is carried out at a temperature of between about 50~ C and about 75~ C.
37. The method of claim 32 wherein said reaction is carried out a pressure of between about 400 and 900 mm Hg.
38. The method of claim 32 wherein said reaction is carried out at about atmospheric pressure.
39. The method of claim 32 wherein said reaction is carried out a pressure of between about 100 mm Hg and 400 mm Hg.
40. The method of claim 32 wherein the acid normality of said reaction is between about 7 N and 10 N.
41. The method of claim 32 wherein said hydrogen peroxide comprises less than 30 %, on an equivalent strength basis, of said reducing agents.
42. The method of claim 32 wherein said hydrogen peroxide comprises between 5 and 10 %, on an equivalent strength basis, of said reducing agents.
43. The method of claim 32 wherein a catalytic species for enhancing generation of chlorine dioxide is added to said reaction.
44. The method of claim 43 wherein said catalytic species is selected from the group consisting of silver nitrate, manganese sulfate, vanadium pentoxide, ruthenium oxide, rhodium oxide, and palladium oxide.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US72008896A | 1996-09-27 | 1996-09-27 | |
| US08/720,088 | 1996-09-27 | ||
| PCT/US1997/017758 WO1998013295A1 (en) | 1996-09-27 | 1997-09-29 | Method for producing chlorine dioxide using methanol and hydrogen peroxide as reducing agents |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2267295A1 true CA2267295A1 (en) | 1998-04-02 |
Family
ID=24892590
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002267295A Abandoned CA2267295A1 (en) | 1996-09-27 | 1997-09-29 | Method for producing chlorine dioxide using methanol and hydrogen peroxide as reducing agents |
Country Status (3)
| Country | Link |
|---|---|
| AU (1) | AU4742497A (en) |
| CA (1) | CA2267295A1 (en) |
| WO (1) | WO1998013295A1 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FI115903B (en) * | 2002-12-05 | 2005-08-15 | Kemira Oyj | Process for the preparation of chlorine dioxide |
| EP1720797B1 (en) * | 2004-02-23 | 2015-06-10 | Akzo Nobel N.V. | Process for production of chlorine dioxide |
| CN110382409A (en) * | 2018-08-30 | 2019-10-25 | 广西博世科环保科技股份有限公司 | A kind of methanol combines the method that reduction prepares chlorine dioxide with high purity with hydrogen peroxide |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE500043C2 (en) * | 1990-08-31 | 1994-03-28 | Eka Nobel Ab | Process for continuous production of chlorine dioxide |
| SE500042C2 (en) * | 1990-08-31 | 1994-03-28 | Eka Nobel Ab | Process for continuous production of chlorine dioxide |
| US5273733A (en) * | 1992-04-14 | 1993-12-28 | Eka Nobel Inc. | Process for the production of chlorine dioxide |
| US5380517B1 (en) * | 1993-02-26 | 1999-01-19 | Eka Nobel Inc | Process for continuously producing chlorine dioxide |
-
1997
- 1997-09-29 AU AU47424/97A patent/AU4742497A/en not_active Abandoned
- 1997-09-29 WO PCT/US1997/017758 patent/WO1998013295A1/en active Application Filing
- 1997-09-29 CA CA002267295A patent/CA2267295A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| AU4742497A (en) | 1998-04-17 |
| WO1998013295A1 (en) | 1998-04-02 |
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