KR20070061894A - Method for producing chlorine dioxide - Google Patents

Abstract

The present invention relates to a process for the continuous production of chlorine dioxide under non-crystallization conditions in at least two reaction vessels comprising the following steps:

Supplying alkali metal chlorate, mineral acid and hydrogen peroxide to a first reaction vessel to form an acidic reaction medium maintained in the first reaction vessel, in the reaction medium Reacting alkali metal chlorate, hydrogen peroxide and inorganic acid to form an alkali metal salt of chlorine dioxide and inorganic acid, recovering chlorine dioxide as a gas from the reaction medium in the first reaction vessel, alkali metal salt of inorganic acid, alkali metal chlorate and inorganic acid Recovering the depleted reaction medium from the first reaction vessel and feeding the second reaction vessel to the second reaction vessel, supplying hydrogen peroxide to the reaction medium in the second reaction vessel, and a concentration of 9 to 75 millimoles / liter of alkali metal chlorate Maintaining the reaction medium in the reaction medium, alkali metal chlorate in the reaction medium, Reacting hydrogen peroxide and inorganic acid to form alkali metal salts of chlorine dioxide and inorganic acid, recovering chlorine dioxide as a gas from the reaction medium in the second reaction vessel, and a depleted reaction medium comprising alkali metal salts of inorganic and inorganic acids. Recovering from the second reaction vessel.

Description

Production method of chlorine dioxide {A PROCESS FOR THE PRODUCTION OF CHLORINE DIOXIDE}

The present invention relates to a process for the continuous production of chlorine dioxide under non-crystallization conditions in at least two reaction vessels.

Chlorine dioxide used in aqueous solutions is of considerable commercial interest primarily for pulp bleaching, as well as removal of phenols from water purification, fat bleaching, industrial waste, and the like. Therefore, it is desirable to provide a method for efficiently producing chlorine dioxide.

Chlorine dioxide production methods vary. Most of the large-scale methods of commercial use are the continuous reaction of alkali metal chlorate with reducing agents such as hydrogen peroxide, methanol, chloride ions or sulfur dioxide in an acidic reaction medium, Forming chlorine dioxide, which is recovered as a gas. Generally, acidity is provided primarily by the addition of sulfuric acid and the sulfate is recovered in the form of a solid alkali metal sulfate or dissolved in a depleted reaction medium.

In one method, the reaction medium is maintained under boiling conditions at subatmospheric pressure in a single reaction vessel, where an alkali metal salt of the acid precipitates and is recovered as a salt cake. do. Such a method is disclosed, for example, in US Pat. Nos. 5,701,71,5091166 and 5,511,671.

In another method, the reaction medium is generally maintained under non-crystallization conditions at substantial atmospheric pressure. In most cases the depleted reaction medium from the first reaction vessel is sent to a second reaction vessel for further reaction to produce chlorine dioxide. An initial example of this method is the Mathieson and Solvay methods, respectively, using sulfur dioxide and methanol as reducing agents. Attempts to modernize the process by using hydrogen peroxide at least in part as reducing agents have been disclosed, for example, in Japanese published applications, Published Nos. 1988-008203, 1991-115102 and WO 01/077012, but commercially Have very limited limits. A new method of using hydrogen peroxide as reducing agent in both the first and second reaction vessels, disclosed in EP 612686, has been proposed. The method has been commercialized under the trade name HP-A ^® , which is easy to implement and allows the large-scale production of chlorine dioxide with high yields in simple equipment.

In the non-crystallization process, the depleted reaction medium recovered from the final reaction vessel contains acid, alkali metal salt of acid and finally unreacted alkali metal chlorate lost. It is therefore believed that the method should be carried out at the lowest possible concentration of chlorate in the final (generally second) reaction vessel in order to minimize losses. On the other hand, it has been found that if the concentration of chlorate is too low, the corrosion of the process equipment (generally at least partly made of titanium) increases. However, it has now been surprisingly found that in processes using hydrogen peroxide as the reducing agent, it is possible to perform at higher concentrations of chlorate than previously thought, without much increase in chlorate loss.

The present invention therefore relates to a process for the continuous production of chlorine dioxide under non-crystallization conditions in at least two reaction vessels, the process comprising the following steps:

Supplying alkali metal chlorate, mineral acid and hydrogen peroxide to the first reaction vessel to form an acidic reaction medium maintained in the first reaction vessel,

Reacting alkali metal chlorate, hydrogen peroxide and inorganic acid in the reaction medium to form alkali metal salts of chlorine dioxide and inorganic acid,

Recovering chlorine dioxide as a gas from the reaction medium in the first reaction vessel,

Recovering from the first reaction vessel a depleted reaction medium comprising an inorganic acid, an alkali metal chlorate and an alkali metal salt of an inorganic acid, and feeding it to a second reaction vessel,

Hydrogen peroxide is supplied to the reaction medium in the second reaction vessel and the reaction medium is supplied at a concentration of 9 to 75 mmol / liter, preferably 14 to 56 mmol / liter, most preferably 20 to 47 mmol / liter alkali metal chlorate. Maintaining step,

Reacting alkali metal chlorate, hydrogen peroxide and inorganic acid in the reaction medium to form alkali metal salts of chlorine dioxide and inorganic acid,

Recovering chlorine dioxide as a gas from the reaction medium in the second reaction vessel, and

Recovering from the second reaction vessel a depleted reaction medium comprising an inorganic acid and an alkali metal salt of an inorganic acid.

The reaction taking place in the reaction vessel is complex and not fully known in detail. Main products are alkali metal salts of chlorine dioxide, oxygen and inorganic acids. Under certain circumstances, some of the chlorate is converted to chloride instead of chlorine dioxide as the final product. It is known that the amount of chloride obtained as the final product decreases by increasing the concentration of chlorate in the second reaction vessel. Thus, due to the high concentration of chlorate, a small amount of chloride in the depleted reaction medium withdrawn from the second reaction vessel makes up the loss to a great extent.

Preferably an inert gas is blown into the reaction vessel to increase agitation and dilute chlorine dioxide to a safe concentration. It is also possible to inject some inert gas above the liquid level in the reaction vessel. All available inert gases such as nitrogen or oxygen can be used, but the use of air is generally preferred due to cost.

Chlorine dioxide and oxygen formed in the reaction vessel are recovered as a gas together with the inert gas blown into the vessel. The gas is preferably sent to an absorber where it is contacted with water to dissolve chlorine dioxide while most of the oxygen and the remaining insoluble gas pass through. Chlorine dioxide water can then be collected in storage tanks and used for desired purposes such as pulp bleaching.

The depleted reaction medium recovered from the second reaction vessel is preferably sent to a stripper which is supplied with an inert gas to exhale chlorine dioxide and the remaining gases still remain in the reaction medium. The gas from the stripper can then be sent to the absorber with the gas from the reaction vessel. Stripped depleted reaction medium, called waste acid, can in many cases be used for pH adjustment and / or as a source of sulfur in the pulping process. It is also possible to electrochemically increase its acidity in cells as described, for example, in U.S. Pat.Nos. 5,788,788 and 6322690, optionally recycling it completely or partially to the first reaction vessel. It is possible to make up at least part of the inorganic acid feed.

In general sodium chloride, potassium or chlorate salts of these mixtures are used, but other alkali metals may also be discussed. Alkali metal chlorate is generally supplied in the form of a high concentration of aqueous solution, preferably for example from about 3 mol / liter to saturated. In most cases no chlorate needs to be fed to the second reaction vessel other than that contained in the depleted reaction medium from the first reaction vessel.

Alkali metal chlorates generally contain small amounts of chloride as impurities, but are preferred when the amount is small enough to reduce the formation of chlorine as a byproduct. It is preferred that the amount of chloride in the alkali metal chlorate feed is about 1 mol%, more preferably about 0.5 mol%, most preferably 0.05 mol%, particularly most preferably less than 0.02 mol%.

The inorganic acid is preferably a halogen-free acid such as sulfuric acid or phosphoric acid, where sulfuric acid at a concentration of, for example, about 60 to about 98% by weight is most preferred. Mixtures of inorganic acids can also be discussed. In most cases, no inorganic acid needs to be supplied to the second reaction vessel other than that contained in the depleted reaction medium from the first reaction vessel.

It is preferred that chlorides other than impurities in the alkali metal chlorate are not substantially fed to the process. However, small amounts of chloride may be present in another feed stream, such as an inorganic acid. Preferably the total amount of chloride fed to the process, including impurities in the alkali metal chlorate, is about 1 mol%, more preferably about 0.5 mol%, most preferably about 0.05 mol%, in particular of the alkali metal chlorate feed Most preferably less than 0.02 mol% chloride.

Hydrogen peroxide is used as reducing agent in both the first and second reaction vessels and is generally supplied as an aqueous solution, preferably at a concentration of about 10 to about 70 wt%, most preferably about 25 to about 60 wt%. Preferably the amount of hydrogen peroxide supplied is from about 0.5 to about 2 moles, most preferably from about 0.5 to about 1 mole, particularly most preferably from about 0.5 to about 0.6 moles per mole of alkali metal chlorate fed. Preferably about 50 to about 99.9%, most preferably about 85 to about 99.5% of the total amount of hydrogen peroxide is fed to the first reaction vessel. Although it is completely possible to add another reducing agent such as methanol, formaldehyde, formic acid, sugar alcohol, sulfur dioxide and chloride, hydrogen peroxide is preferably the only one except for a small amount of chloride present as impurities in chlorate Reducing agent to be added. If another reducing agent is added, the amount of hydrogen peroxide added may decrease.

The reactants may be fed as separated or pre-mixed feed streams. It is particularly possible to pre-mix hydrogen peroxide and alkali metal chlorate into a common feed stream, while inorganic acids are preferably fed separately.

The temperature of the reaction medium in the reaction vessel is preferably maintained at about 30 to about 100 ° C, most preferably about 40 to about 80 ° C. The temperature may be substantially the same in the first and second reaction vessels, but it is also possible to carry out at different temperatures. Preferably the temperature of the reaction medium in the first and second reaction vessels is below the boiling point under prevailing pressure. Depending on the ambient temperature, the temperature of the feed stream, the inert gas blowing rate, and other process conditions, it may be necessary to heat or cool the reaction vessel to maintain the required temperature.

The absolute pressure maintained in the reaction vessel is preferably about 50 to 120 kPa, most preferably about 80 to about 110 kPa, particularly most preferably about atmospheric pressure. The pressure is not necessary but is generally substantially the same in the first and second reaction vessels.

The acidity of the reaction medium in the first and second vessels is preferably about 4 to about 14 N, most preferably about 6 to about 12 N. In most cases there is only a small difference in acidity between the first and second reaction vessels, preferably less than about 15%, most preferably less than about 10%.

The concentration of alkali metal chlorate in the reaction medium in the first reaction vessel is preferably maintained at about 0.05 to saturation, more preferably about 0.075 to about 2.5 moles / liter, most preferably about 0.1 to about 1 moles / liter. .

In a preferred embodiment the reaction medium in the first reaction vessel preferably has an alkali metal chlorate concentration of about 0.05 to about 2.5 moles / liter, an acidity of about 6 to about 12 N, a temperature of about 40 to about 80 ° C. and about 80 to While maintained at an absolute pressure of about 10 kPa, the reaction medium in the second reaction vessel preferably has an alkali metal chlorate concentration of about 14 to about 56 moles / liter, an acidity of about 6 to about 12 N, about 40 to about 80 It is maintained at a temperature of ℃ and an absolute pressure of about 80 to about 10 kPa.

Other process equipment (eg Mathieson, Solvay and HP-A ^® ) can be used, such as in the same type of reaction vessel and another non-crystallization method. Process equipment in contact with the reaction medium, including the reaction vessel, should suitably be made or lined with materials resistant to the chemicals therein. Although part of the equipment may be made of another resistive material such as fluoro plastics or another polymeric material, the preferred material is capable of forming and maintaining a protective oxide film in contact with titanium or the reaction medium. Another metal or alloy that is capable. At least part of the equipment, including the second reaction vessel, preferably in contact with the reaction medium should be made of or lined with titanium.

The present invention is further illustrated by way of the following examples:

EXAMPLE: Chlorine dioxide was produced continuously in a generator comprising a first reaction vessel (first reactor) and a second reaction vessel (second reactor). Sodium chlorate (containing about 0.01% by weight sodium chloride as impurities), sulfuric acid and hydrogen peroxide were fed to the first reaction vessel. The reaction medium effluent from the first reaction vessel was sent to a second reaction vessel, to which hydrogen peroxide was also fed. The reaction medium effluent from the second reaction vessel was recovered to waste acid after passing through a stripper. Air was blown into the reaction medium in both reaction vessels to dilute the chlorine dioxide gas recovered from the reaction vessel. Both reaction vessels were maintained at atmospheric pressure and 57 ° C. temperature. Data was collected in several experiments under steady state conditions. The results are shown in the table below.

It is seen that a decrease in sodium chlorate concentration in the second reaction vessel causes an increase in sodium chloride concentration. Since this increase is the result of the conversion of chlorate to chloride as the final product, this also represents a loss through waste acid. Thus, the loss of chlorate not converted by increasing the chlorate concentration in the second reaction vessel is at least partly compensated for by less loss due to chloride production. Despite the high overall losses in some cases, it is still within acceptable levels, given the advantages of less corrosion in process equipment.

The present invention relates to a process for the continuous production of chlorine dioxide under non-crystallization conditions in at least two reaction vessels comprising the following steps:

Supplying alkali metal chlorate, mineral acid and hydrogen peroxide to a first reaction vessel to form an acidic reaction medium maintained in the first reaction vessel, in the reaction medium Reacting alkali metal chlorate, hydrogen peroxide and inorganic acid to form an alkali metal salt of chlorine dioxide and inorganic acid, recovering chlorine dioxide as a gas from the reaction medium in the first reaction vessel, alkali metal salt of inorganic acid, alkali metal chlorate and inorganic acid Recovering the depleted reaction medium from the first reaction vessel and feeding the second reaction vessel to the second reaction vessel, supplying hydrogen peroxide to the reaction medium in the second reaction vessel, and a concentration of 9 to 75 millimoles / liter of alkali metal chlorate Maintaining the reaction medium in the reaction medium, alkali metal chlorate in the reaction medium, Reacting hydrogen peroxide and inorganic acid to form alkali metal salts of chlorine dioxide and inorganic acid, recovering chlorine dioxide as a gas from the reaction medium in the second reaction vessel, and a depleted reaction comprising alkali metal salts of inorganic and inorganic acids. Recovering the medium from the second reaction vessel.

Claims (10)

A process for the continuous production of chlorine dioxide under non-crystallization conditions in at least two reaction vessels comprising the following steps: Supplying an alkali metal chlorate, an inorganic acid and hydrogen peroxide to the first reaction vessel to form an acidic reaction medium maintained in the first reaction vessel, Reacting alkali metal chlorate, hydrogen peroxide and inorganic acid in the reaction medium to form alkali metal salts of chlorine dioxide and inorganic acid, Recovering chlorine dioxide as a gas from the reaction medium in the first reaction vessel, Recovering from the first reaction vessel a depleted reaction medium comprising an inorganic acid, an alkali metal chlorate and an alkali metal salt of an inorganic acid, and feeding it to a second reaction vessel, Supplying hydrogen peroxide to the reaction medium in the second reaction vessel and maintaining the reaction medium at a concentration of 9 to 75 mmol / liter of alkali metal chlorate, Reacting alkali metal chlorate, hydrogen peroxide and inorganic acid in the reaction medium to form alkali metal salts of chlorine dioxide and inorganic acid, Recovering chlorine dioxide as a gas from the reaction medium in the second reaction vessel, and Recovering from the second reaction vessel a depleted reaction medium comprising an inorganic acid and an alkali metal salt of an inorganic acid. The method of claim 1, wherein the concentration of alkali metal chlorate in the second reaction vessel is 14 to 56 mmol / liter. 3. A process for the production of chlorine dioxide according to claim 2, wherein the concentration of alkali metal chlorate in said second reaction vessel is 20 to 47 mmol / liter. 4. A process for the production of chlorine dioxide according to any one of claims 1 to 3, wherein an inert gas is blown into the reaction vessel. The process for producing chlorine dioxide according to any one of claims 1 to 4, wherein the total amount of chloride fed to the process is less than 1 mol% of the alkali metal chlorate feed. 6. The process according to claim 1, wherein the temperature of the reaction medium in the first and second reaction vessels is below the boiling point at prevailing pressure. 7. 7. Process according to any one of the preceding claims, characterized in that the acidity of the reaction medium in the first and second reaction vessels is maintained between 4 and 14 N. 8. A process for the continuous production of chlorine dioxide according to any one of claims 1 to 7, wherein said inorganic acid is sulfuric acid. The reaction medium of claim 1, wherein the reaction medium in the first reaction vessel is 0.05 to 2.5 mol / liter of alkali metal chlorate, an acidity of 6 to 12 N, a temperature of 40 to 80 ° C., 80 It is maintained at an absolute pressure of from 110 kPa, while the reaction medium in the second reaction vessel is 14 to 56 mmol / liter of alkali metal chlorate, an acidity of 6 to 12 N, a temperature of 40 to 80 ° C., a temperature of 80 to 110 A process for the continuous production of chlorine dioxide, characterized in that it is maintained at an absolute pressure of kPa. 10. The method of any one of the preceding claims, wherein at least a portion of the equipment in contact with the reaction medium is made of titanium or lined with titanium.