JP4913057B2 - Method for producing chlorine dioxide - Google Patents

Description

【Technical field】
[0001]
The present invention relates to a process for the continuous production of chlorine dioxide under non-crystallizing conditions in at least two reaction vessels.
[Background]
[0002]
Chlorine dioxide used in aqueous solution has considerable commercial benefits not only in pulp bleaching, but also in water purification, fat bleaching, phenol removal from industrial wastes and the like. It is therefore desirable to provide a method by which chlorine dioxide can be produced efficiently.
[0003]
There are a number of different methods for the production of chlorine dioxide. The most extensive method in commercial applications is the continuous reaction of alkali metal chlorates with reducing agents such as hydrogen peroxide, methanol, chloride ions or sulfur dioxide in acidic reaction media to form chlorine dioxide. And recovering this from the reaction medium as a gas. Generally, the acidity is provided primarily by the addition of sulfuric acid, and the sulfate is recovered as a by-product in the form of a solid alkali metal sulfate or dissolved in a spent reaction medium.
[0004]
In one type of process, the reaction medium is maintained in a single reaction vessel under boiling conditions at a pressure below atmospheric pressure, in which case the alkali metal salt of the acid is precipitated and recovered as a salt cake. . Such a method is described in Patent Document 1, Patent Document 2, and Patent Document 3.
[0005]
In another type of process, the reaction medium is maintained under non-crystallizing conditions, generally at substantially atmospheric pressure. In most cases, the spent reaction medium from the first reaction vessel is brought to a second reaction vessel for further reaction to produce chlorine dioxide. Early examples of such methods are those of Mathieson and Solvay that use sulfur dioxide and methanol as reducing agents. Attempts to modernize these methods by at least partially using hydrogen peroxide as the reducing agent are described in, for example, Patent Document 4, Patent Document 5 and Patent Document 6, but to a very limited extent. It is commercialized only in One breakthrough arrived by the method disclosed in US Pat. No. 6,057,836 using hydrogen peroxide as the reducing agent in both the first and second reaction vessels. Such a method is commercialized under the trade name HP-A (registered trademark), is easy to operate, and enables production of chlorine dioxide in a high yield and a high volume by a simple apparatus.
[Patent Document 1]
US Patent No. 5,770,171 [Patent Document 2]
US Patent No. 5,091,166 [Patent Document 3]
US Patent No. 5,091,167 [Patent Document 4]
Japanese Patent Application Publication No. 1988-008203 [Patent Document 5]
Japanese Patent Application Publication No. 1991-115102 [Patent Document 6]
WO 01/077012 [Patent Document 7]
EP 612686 [Disclosure of the Invention]
[0006]
In the non-crystallization method, the spent reaction medium recovered from the final reaction vessel is an acid, an alkali metal salt of the acid, and an unreacted alkali metal chlorate, and therefore the alkali metal chlorate is Lost. In that case it is believed that the above method should be operated with the lowest possible chlorate concentration in the final reaction vessel (usually the second) to minimize losses. I came. On the other hand, it has been found that if the chlorate concentration is too low, the corrosion of process equipment (generally made at least partially from titanium) proceeds. Surprisingly, however, one method using hydrogen peroxide as the reducing agent now has a higher chlorate concentration than previously believed without significantly increasing chlorate loss. It has been found that it can be manipulated.
[0007]
Therefore, the present invention
Supplying an alkali metal chlorate, a 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 mineral acid in the reaction medium to form chlorine dioxide and an alkali metal salt of the mineral acid;
Recovering chlorine dioxide as a gas from the reaction medium in the first reaction vessel;
Recovering a consumed reaction medium comprising a mineral acid, an alkali metal chlorate and an alkali metal salt of the mineral acid from the first reaction vessel and supplying it to the second reaction vessel;
Supplies hydrogen peroxide to said reaction medium of the second reaction vessel, about 9 to about 75 millimeter mol / l of the reaction medium in said vessel, preferably about 14 to about 56 millimeter a step of maintaining the concentration of the alkali metal chlorate of from about 20 to about 47 millimeter mol / l mol / liter, and more preferably,
Reacting alkali metal chlorate, hydrogen peroxide and mineral acid in the reaction medium to form chlorine dioxide and an alkali metal salt of the mineral acid;
Recovering chlorine dioxide as a gas from the reaction medium in the second reaction vessel;
Recovering a consumed reaction medium containing a mineral acid and an alkali metal salt of the mineral acid from the second reaction vessel.
It relates to a process for the continuous production of chlorine dioxide under non-crystallizing conditions in at least two reaction vessels.
[0008]
The reactions performed in each of the above reaction vessels are complex and not all details are fully known. The main products are chlorine dioxide, oxygen and alkali metal salts of the above mineral acids. Under certain circumstances, some of the chlorate is converted to chloride as the final product instead of chlorine dioxide. It has been found that the amount of chloride obtained as the final product can be reduced by increasing the chlorate concentration in the second reaction vessel. Therefore, reducing the amount of chloride in the spent reaction medium recovered from the second reaction vessel compensates for losses due to high chlorate concentration to a considerable extent.
[0009]
Preferably, the dilution gas is sent through each of the reaction vessels, so that stirring is activated and chlorine dioxide is diluted to a safe concentration. It is also possible to introduce some dilution gas above the liquid level in each reaction vessel. Although any available diluent gas such as nitrogen or oxygen can be used, it is usually preferred to use air for cost reasons.
[0010]
Chlorine dioxide and oxygen formed in each reaction vessel are collected as a gas together with any diluted gas sent through each vessel. The gas is preferably brought into the absorbent where it is contacted with water so that chlorine dioxide is dissolved while oxygen and other major parts of the insoluble gas are passed through. The chlorine dioxide water can then be collected in a storage tank and used for any desired purpose, such as pulp bleaching.
[0011]
The spent reaction medium recovered from the second reaction vessel is preferably brought to a stripper to which dilution gas is supplied so that chlorine dioxide and other gaseous species still remaining in the reaction medium are released. The The gas from the stripper can then be brought into the absorber along with the gas from each reaction vessel. Stripped spent reaction media, also referred to as spent acid, can often be used for pH adjustment and / or as a source of sulfur in the pulping process. Also, for example, as described in U.S. Pat. No. 5,487,881 and U.S. Pat. No. 6,322,690, the acidity is increased electrochemically in the cell and, optionally, it is completely or partially with respect to the first reaction vessel. It can also be recycled, where it constitutes at least part of the mineral acid feed.
[0012]
Usually, chlorates of sodium, potassium or mixtures thereof are used, but other alkali metals can be considered. The alkali metal chlorate is usually preferably supplied in the form of an aqueous solution at a high concentration, for example from about 3 mol / liter to saturation. In most cases, it is not necessary to supply any chlorate to the second reaction vessel apart from what is contained in the depleted reaction medium from the first reaction vessel.
[0013]
Alkali metal chlorates usually contain a small amount of chloride as an impurity, but it is preferred if this amount is as small as possible to reduce the formation of chlorine as a by-product. The amount of chloride in the alkali metal chlorate feed is less than about 1 mol%, more preferably less than about 0.5 mol%, most preferably less than about 0.05 mol%, and most preferably about 0.02 mol%. It is preferable that it is less than.
[0014]
The mineral acid is preferably a halogen-free acid such as sulfuric acid or phosphoric acid, of which sulfuric acid is most preferred, for example at a concentration of about 60 to about 98% by weight. A mixture of mineral acids can also be considered. In most cases, it is not necessary to supply any mineral acid to the second reaction vessel apart from what is contained in the depleted reaction medium from the first reaction vessel.
[0015]
Except for impurities in the alkali metal chlorate, it is preferred that substantially no chloride is supplied to the process. However, small amounts of chloride may also be present in other feed streams such as mineral acids. Preferably, the total amount of chloride supplied to the process, including impurities in the alkali metal chlorate, is less than about 1 mole percent of the alkali metal chlorate feed, more preferably about 0.5. Less than about mol%, most preferably less than about 0.05 mol%, and most preferably less than about 0.02 mol% of chloride.
[0016]
Hydrogen peroxide is used as the reducing agent in both the first and second reaction vessels and usually has a concentration of preferably about 10 to about 70% by weight, most preferably about 25 to about 60% by weight. Supplied as an aqueous solution. Preferably, the amount of hydrogen peroxide fed is from about 0.5 to about 2 moles per mole of alkali metal chlorate fed, most preferably per mole of alkali metal chlorate fed. About 0.5 to about 1 mole, and most preferably about 0.5 to about 0.6 mole per mole of alkali metal chlorate fed. Preferably, the first reaction vessel is fed from about 50 to about 99.9%, most preferably from about 85 to about 99.5% of the total amount of hydrogen peroxide. Apart from the small amount of chloride present as an impurity in the chlorate, it is preferably a reducing agent to which only hydrogen peroxide is added, such as methanol, formaldehyde, formic acid, sugar alcohol, sulfur dioxide and chloride. It is fully possible to add other reducing agents. If other reducing agents are added, the amount of hydrogen peroxide added may be reduced.
[0017]
Each of the above reactants may be supplied as a separate or premixed feed stream. In particular, it is possible to premix hydrogen peroxide and alkali metal chlorate into a common feed stream, while preferably the mineral acid is fed separately.
[0018]
The temperature of the reaction medium in each of the reaction vessels 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 can be operated at different temperatures. Preferably, the temperature of the reaction medium in the first and second reaction vessels is lower than the boiling point at the pressure being used. Depending on the ambient temperature, the temperature of the feed stream, the rate of dilution gas feed, and other process conditions, it may be necessary to heat or cool each of the above reaction vessels to maintain the desired temperature. Absent.
[0019]
The absolute pressure maintained in each of the reaction vessels is preferably about 50 to about 120 kPa, most preferably about 80 to about 110 kPa, and most preferably about atmospheric pressure. Although not necessarily required, the pressure is substantially the same in the first and second reaction vessels.
[0020]
The acidity of the reaction medium in the first and second vessels is preferably maintained from about 4 to about 14N, most preferably from about 6 to about 12N. In most cases there will be a slight difference in acidity between the first and second reaction vessels, preferably less than about 15%, and most preferably less than about 10%.
[0021]
The concentration of alkali metal chlorate in the reaction medium in the first reaction vessel is preferably from about 0.05 to saturation, more preferably from about 0.075 to about 2.5 moles / liter, most preferably from about 0.1 to Maintained at about 1 mole / liter.
[0022]
In preferred embodiments and comparative examples , 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, about 40 to about temperature of about 80 ° C., and from about 80 to about while being maintained at an absolute pressure of 110 kPa, the reaction medium of the second reaction vessel is preferably an alkali metal chlorate of from about 14 to about 56 millimeter mol / l Maintained at a salt concentration, an acidity of about 6 to about 12 N, a temperature of about 40 to about 80 ° C., and an absolute pressure of about 80 to about 110 kPa.
[0023]
The same type of reaction vessel and other process equipment (eg, Mathison, Solvay and HP-A®) can be used as in other non-crystallization methods. Process equipment such as a reaction vessel in contact with the reaction medium is suitably made or backed by a material that is resistant to chemicals therein. Suitable materials are titanium and other metals or alloys with the ability to form and maintain a protective oxide layer in contact with the reaction medium, although some of the equipment is such as fluoroplastics or other polymer materials It may be made from other resistant materials. Preferably, at least a portion of the instrument, such as the second reaction vessel, that contacts the reaction medium is made of or lined with titanium.
[0024]
The invention is further illustrated by the following examples and comparative examples .
[Examples and Comparative Examples ]
[0025]
Chlorine dioxide was continuously produced in a generator equipped with a first reaction vessel (main reactor) and a second reaction vessel (auxiliary reactor). To the first reaction vessel, sodium chlorate, sulfuric acid and hydrogen peroxide (containing about 0.01 wt% sodium chloride as impurities) were supplied. Overflow of reaction medium from the first reaction vessel was brought to the second reaction vessel, which was also fed with hydrogen peroxide. The reaction medium overflow from the second reaction vessel was recovered as waste acid after passing through the stripper. Air was sent through the reaction medium in both reaction vessels to dilute the chlorine dioxide recovered from the vessels. Both reaction vessels were maintained at atmospheric pressure and a temperature of 57 ° C. Data was collected several times under steady state conditions. The results are shown in the table below.
[0026]
[Table 1]
[0027]
A decrease in the sodium chlorate concentration in the second reaction vessel seems to lead to an increase in the 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 unconverted chlorate due to the increased concentration of unconverted chlorate in the second reaction vessel is at least partially compensated by reducing the loss due to chloride formation. Even though the total loss can be even greater in certain cases, it is still within an acceptable level given the benefit of low process equipment corrosion.

Claims (9)

Supplying an alkali metal chlorate, a 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 mineral acid in the reaction medium to form chlorine dioxide and an alkali metal salt of the mineral acid;
Recovering chlorine dioxide as a gas from the reaction medium in the first reaction vessel;
Recovering a consumed reaction medium comprising a mineral acid, an alkali metal chlorate and an alkali metal salt of the mineral acid from the first reaction vessel and supplying it to the second reaction vessel;
Supplying hydrogen peroxide to the reaction medium in the second reaction vessel and maintaining the reaction medium in the vessel at a concentration of 9 to 75 mmol / liter of alkali metal chlorate;
Reacting alkali metal chlorate, hydrogen peroxide and mineral acid in the reaction medium to form chlorine dioxide and an alkali metal salt of the mineral acid;
Recovering chlorine dioxide as a gas from the reaction medium in the second reaction vessel;
From the second reaction vessel, and recovering the depleted already reaction medium containing an alkali metal salt of a mineral acid and mineral acids,
A process for continuously producing chlorine dioxide under non-crystallizing conditions in at least two reaction vessels ,
The method wherein at least a portion of the equipment in contact with the reaction medium is made of or lined with titanium .   The method of claim 1, wherein the concentration of alkali metal chlorate in the second reaction vessel is maintained at 14-56 mmol / liter.   The method of claim 2, wherein the concentration of alkali metal chlorate in the second reaction vessel is maintained at 20-47 mmol / liter.   The method according to any one of claims 1 to 3, wherein a dilution gas is supplied through each reaction vessel.   The method according to any one of claims 1 to 4, wherein the amount of chloride in the alkali metal chlorate supplied to the method is less than 1 mol%.   The process according to any one of claims 1 to 5, wherein the temperature of the reaction medium in the first and second reaction vessels is lower than the boiling point at the pressure used.   The method according to any one of claims 1 to 6, wherein the acidity of the reaction medium in the first and second vessels is maintained between 4 and 14N.   The method according to any one of claims 1 to 7, wherein the mineral acid is sulfuric acid.   The reaction medium in the first reaction vessel is maintained at an alkali metal chlorate concentration of 0.05 to 2.5 mol / liter, an acidity of 6 to 12 N, a temperature of 40 to 80 ° C., and an absolute pressure of 80 to 110 kPa. Meanwhile, the reaction medium in the second reaction vessel is maintained at an alkali metal chlorate concentration of 14 to 56 mmol / liter, an acidity of 6 to 12 N, a temperature of 40 to 80 ° C., and an absolute pressure of 80 to 110 kPa. 9. The method according to any one of claims 1 to 8, wherein: