JPS605004A - Manufacture of chlorine dioxide - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a method for producing chlorine dioxide. [Prior Art] A method for producing chlorine dioxide by reducing an aqueous solution of chlorine using methanol has been developed in the United States. Patent no.
It is described in the specification of g i, o, y co, and is known. However, the method is very slow, involves the treatment of a large amount of effluent, and has low efficiency.Recently, our U.S. Pat. It is stated that the problems of the prior art can be overcome by the use of a single vessel generator-evaporator-crystallizer. U.S. Patent No. 9, Og/,! ; the process described in No. 0 operates with high efficiency; no effluent is produced;
It has speed up to the layer where it is.

U.S. Patent No. DA, θg I,! During industrial scale implementation of the process of No. 20, periodic and variable losses of chlorine dioxide production were observed. The phenomenon is considered to arise from the complete depletion of trace chloride ions as a result of unknown changes in the reaction medium under the conditions of the process.

It is well known that all chlorine dioxide generation methods involving reaction gold using chlorate ions proceed according to the following equation: U.S. Pat.
Since the chloride ions used in the method No. 2 are formed during the chlorine dioxide production reaction by the reaction between methanol and the symbiotic acid chlorine, a large amount of chlorine is likely to be produced as a by-product. Therefore, chlorine dioxide contains little or no ions depending on the overall efficiency of the process. Therefore, if for some reason all the chloride ions are consumed by the above reaction f', then The production of chlorine dioxide will be interrupted until chloride ions are produced by reduction of chlorate ions with methanol.

This periodically occurring and variable loss of chlorine dioxide production is referred to by the term "whiteout" in wood cutting tubules.
0ut) J.

According to the present invention, U.S. Patent No. '1. The problem of whiteout in the method of Og/320 is eliminated, while other useful properties of the method, most importantly high efficiency, are achieved by the continuous addition of chloride ions to the reaction medium. Retained. By optionally adding chloride ions to the reaction medium, the presence of chloride ions is ensured at all times, thereby eliminating the possibility of whiteout.

Any beneficial result of continuous addition of chloride ions
It is not O, even if it involves serious disadvantageous consequences. US Patent No. 6Og for the production of chlorine dioxide from chlorate ions
The high efficiency characteristic of the process of No. 5.20 is maintained with an acceptable rate of chlorine dioxide production. The addition of chloride to the reaction medium results in the production of some chlorine along with chlorine dioxide, but the production of chlorine is usually acceptable and often desirable in noglubu mill environments. US Patent No. 1. Og/,! The lowest operable total acid normality disclosed in No. 20 is normal. The reason for this is that it has previously been found that highly efficient production of chlorine dioxide cannot be achieved at a total acid normality lower than the above-mentioned minimum total acid normality. The experiments leading to the above conclusions were carried out on a laboratory scale, and the volume of the reaction medium in this experiment was approximately θ, h~o, gg/hr/m2 (5 surface volumes of the reaction medium). It consisted of a volume yielding a gas phase (water vapor, chlorine dioxide, and chlorine) with an evaporation rate of [IO-co θ1b/hour/square foot (surface area of reaction medium)].

Contrary to the above data, it was surprisingly discovered that under industrial-scale flint conditions, it was possible to produce with high efficiency at a total failure standard of about 7 normal, which is lower than the standard for chlorine dioxide.
1 Therefore, it has now surprisingly been found that the process of the present invention can be carried out at a total normality of at least about 7N. methanol is continuously charged into said reaction zone in an amount sufficient to form chlorine dioxide from said reaction medium; Chlorine is continuously removed from the reaction zone in the form of a gaseous mixture with steam and dissolved in water to form an aqueous chlorine dioxide solution, and acidic sodium sulfate is continuously precipitated from the reaction medium in the zone. A highly efficient continuous process for producing chlorine dioxide by reduction of sodium chloride salt with methanol in said reaction medium, comprising: (a) charging said sulfuric acid into said reaction medium and at least about 7 normal dissolving chlorine in the aqueous chlorine dioxide solution in an amount at least sufficient to maintain normality and (b) prevent periodic irregular losses of chloride ions from outside the reaction zone to the prepacked reaction medium; It is an object of the present invention to provide a highly efficient continuous production method for chlorine dioxide, characterized in that the amount of chlorine that is below a limit is charged so that the amount is present in the gaseous mixture.

The operating parameters of the chlorine dioxide generation process can be varied over a wide range. The concentrations of the reactants are usually controlled by the flow rates of the aqueous sodium chlorate solution, sulfuric acid, and methanol into the reaction zone, which is typically in the form of a single-chamber, single-vessel generator-evaporator-crystallizer. As mentioned above, the total normality of sulfuric acid in the reaction medium is maintained at at least about 7N and can be varied up to about 1N, and the conversion efficiency of chlorate ions to chlorine dioxide increases as the total normality decreases. It is therefore preferable to use a sulfuric acid total normality within the range of about 10 normal to about io normal. The sulfuric acid is usually charged to the reaction medium in the form of concentrated sulfuric acid (93%).

Production of chlorine dioxide on an industrial scale with high efficiency is described in our US Patent No. 1I,01? F) different from the teaching of βλθ?
This can be done with a zero loss standard, which is lower than the standard. At the same time that increased efficiency was observed at lower acidity, a significant increase in the concentration of sodium chloride present in the reaction medium was also observed, typically to about 0.2 molar. The aforementioned differences in behavior cannot be satisfactorily explained, but may arise from the large volume of reaction medium available for the reaction under plant conditions, which results in a longer effective residence time in the reaction medium. It is believed that more efficient use of methanol leads to reduced evaporation losses.

Large-scale operations also provide the ability to produce chlorine dioxide very effectively with lower total failure normalities of about 2. ／＝'
I, j kg / hour / force (surface area of the reaction medium [sO ~
5001 b/hour/sq ft (surface area of reaction medium)
An increased gaseous mixture evaporation rate in the range of .

The evaporation rate is determined by the liquid volume in the reaction zone and the liquid recycling rate.

In a modified operation of the present invention, the industrial scale chlorine dioxide production described above can be carried out at total normality lower than 9N, which can be reduced to about 7N, while adding chloride ions to the reaction medium. Continuous addition is discontinued.

The concentration of sodium chlorate in the reaction medium in the process of the invention is usually about θ, 2 mol to mol S mol, preferably about 0.9
mole - changes to about 81 moles.

Sodium chlorate is usually charged to the reaction medium in the form of an aqueous sodium chlorate solution with a concentration of about 5 molar to about 7 molar.

As mentioned above, under normal operating conditions, chloride ions are present in the reaction medium as a result of the reduction of chlorine in the reaction medium by methanol. Even when the salt, sodium chloride, is continuously charged to the medium according to the invention, the concentration of chloride ions present in the reaction medium is not significantly higher than in the absence of the added sodium chloride. The reason for this is that the added chloride ions are converted to chlorine in the reaction zone.

Normally, the concentration of qkJ chloride ions in the reaction medium ranges from about 9 normal to about 2 mol with total normality in the specified range.
It changes to about 0.3 mole, but on the other hand? At lower normality than normal, the chloride ion concentration in the reaction medium is usually about o,i
mol to about 0.3 mol.

The chloride ion when added to the reaction medium is generally in the form of an aqueous sodium chloride solution and usually has a concentration of about S molar. Sodium chloride may be added as part of the sodium chlorate solution; hydrochloric acid or hydrogen chloride may also be used to provide chloride ions in the reaction medium.

Methanol is added to the reaction medium in the form of 100% methanol or methanol containing 1 weight or more of methanol *dissolved).
Although at least about aV wt. It can vary from 0°C to about 7S°C. Higher temperatures usually result in faster reaction rates 9 and also increase the rate of chlorine dioxide production; however, at excessively high temperatures, decomposition of chlorine dioxide occurs, reducing the yield of chlorine dioxide.

The chlorine dioxide present in the gaseous mixture stream produced from the reaction medium in the chlorine dioxide generator is purchased by bleaching, condensing, and then making an aqueous solution of chlorine dioxide by contacting with a water stream of sufficient volume to dissolve all the chlorine dioxide. is formed. In this one-step condensation and dissolution process, the first condensation step is approximately
This can be carried out by cooling to a temperature of ~60°C, preferably from about 7υ to about 60°C, while the subsequent melting step is carried out by cooling the cooled gas stream from the condensation step to about 60°C. Here ℃
, preferably at a temperature of about 3υ to about 7 to 7.Depending on the flow rate of the water involved in the production of chlorine dioxide, the temperature of the condensed water and the dissolved water, about 6~0g/l, preferably about 10~/s,
A chlorine dioxide solution with a chlorine dioxide concentration in the range of 171/13 is formed.

If sodium chloride is continuously charged to the reaction medium in the practice of the invention, chlorine is formed together with chlorine dioxide.
Ru. This chlorine is dissolved in VC in a chlorine dioxide solution with n1 of about 0.
/ ~2. Ol/13% preferably about θ, t-
o, present in an amount of s9/Ij.

In order to avoid the need for a cumulative dissolution device, chlorine must be produced with the chlorine dioxide in amounts that would raise the solubility limit of chlorine in the chlorine dioxide solution.

Ru. The acid content of this acidic sodium sulfate is determined by our US Patent No. 3-5. The acidic sodium sulfate can be recovered from the reaction medium by converting it to neutral sodium sulfate by treatment with water and methanol as described in No. 31, and the recovered sulfuric acid is recycled to the reaction zone. be done.

Alternatively, the acidic sodium sulfate may be added to the reaction medium of other chlorine dioxide production processes in which sodium chlorate and sodium chloride and/or hydrogen chloride are reacted in an acidic aqueous medium at a total normality of less than about a, g specification. , in which case the nucleic acid sodium sulfate is described in our U.S. Patent No. 3. Rizaq
, IOT, to provide all or a portion of the acid requirements of the process.

Sodium acid sulfate is usually removed from the reaction medium as a slurry, the sodium acid sulfate is separated from the reaction medium, the reaction medium is usually fresh, and the chlorine dioxide is diluted using steam generated by boiling of the reaction medium. , this steam is produced at low operating pressures typically around 1001
Combined with the use of 1Hy, chlorine dioxide is maintained below explosive concentrations. An aqueous solution of chlorine dioxide is formed by dissolving the chlorine dioxide in water, and then most of the steam is condensed.At the bottom of the absorption tower, under the aforementioned low pressure, the concentration of chlorine dioxide is maintained at a safe level. Ru.

But the method is about '! It is possible to operate at subatmospheric pressures or higher pressures by mixing in sufficient purge air to maintain a chlorine dioxide partial pressure below OrgrttHg. The actual operating pressure depends to a large extent on the temperature of the reaction medium, but is preferably between about 6θ and θθIIHy, preferably about ? θ~72011H! It can be varied over a wide range of 9. The ability to vary the operating pressure by controlling the amount of purge air is intended for chlorine dioxide production plants designed to use higher subatmospheric pressures to process large amounts of chlorine produced with e.g. chlorine dioxide. This is advantageous if the plant is used for the reduction of sodium chlorate with alcohol to form chlorine dioxide.

〔Example〕

The present invention will be explained below with reference to Examples.

EXAMPLE 1 Experiments were carried out using a chlorine dioxide production apparatus with a production capacity of F)/s per day, in which an acidic sodium chlorate solution was reduced with methanol, while the reaction medium was boiled under reduced pressure conditions. Sodium chlorate' is formed from sodium chlorate crystals as an aqueous solution of 1 min (2,2σ) sufficient to maintain the chlorate ion concentration in the reaction medium at /M
8 GPM) into the reaction medium continuously. Sulfuric acid again? J%HtSo, the acidity of the reaction medium is approximately 2 ~
711/91-<2.
The reaction medium was continuously charged at a flow rate of 0σ8 GPM). 31/min CO as methanol t-5O wt% aqueous solution
, IUBCkPM) into the reaction medium continuously. The average temperature of the generator liquid was approximately 0.degree. C. and the sodium sesquisulfate crystals were removed from the generator.

The generator is operated under substantially steady state conditions for producing chlorine dioxide, i.e. first without intentionally added sodium chloride and then with a 5M sodium chloride solution f
/, 9117% CO,SIJSGPM).

The steam was condensed by cooling the exhaust gas from the generator to 30°C and the cooled gas was dissolved in water in an absorption tower using 70°C water.

The chemical efficiency of the conversion of chlorate ion to chlorine dioxide was determined in each case.

Chemical efficiencies of approximately 0% were observed both in experiments without consciously added sodium chloride and in experiments with consciously added sodium chloride. The chlorine dioxide solution obtained during the period of deliberate addition of sodium chloride is approximately 7θ
g/l of chlorine dioxide and about 0.7 to θ, trl/l of chlorine, while the chlorine dioxide solution obtained during the initial operating period without agglomerated sodium addition is about i.

11/l of chlorine dioxide and about θ, S~0. b g/l chlorine content. Furthermore, during the production of chlorine dioxide, an increase in the production rate was observed during the period of intentional addition of IJ (chloride) to the reaction medium.

EXAMPLE An acidic solution of sodium cochlorate is reduced using methanol, while the reaction medium is boiled under reduced pressure conditions.
An experiment was conducted using a chlorine dioxide generator with a production capacity of lI tons.◇As a 5M aqueous solution of sodium chlorate made from sodium chlorate crystals, the chlorate ion concentration in the reaction medium f! Enough trap 35j/min(?,
It was continuously charged into the reaction medium at a flow rate of σSGPM). Sulfuric acid was also continuously charged to the reaction medium as 3H,So at a flow rate sufficient to maintain the desired acidity of the reaction medium. methanol as a SO heavy aqueous solution,
The reaction medium was continuously charged at a flow rate of y 17 min (0, lσEl() PM ). The average temperature of the generator liquid is approximately go
°C, the sodium sesquisulfate crystals were removed from the generator.

The generator was operated under substantially steady state conditions to produce chlorine dioxide at various normalities.

The steam was condensed by cooling the entire exhaust gas from the generator to 30°C, and the cooled gas was dissolved in water in an absorption tower using water at 10°C. The chemical efficiency of the conversion of chlorate ion to chlorine dioxide was determined in each case.

Defeat standard level (N) 7.2~g, Ri de~IO'7. g
~g0g Experimental time (hours) /2 /2 g, s Chemical efficiency (%il, 9g)? ? >99 7th above
From the table, does high chemical efficiency operation have a normality? It is also observed when the temperature is maintained below the specified level.

SUMMARY OF THE INVENTION The present invention relates to improvements in the operation of a high efficiency chlorine dioxide production process without adversely affecting chemical efficiency. Modifications within the scope of the invention are possible.

Claims (1)

[Claims] / Aqueous sodium chlorate solution and sulfuric acid are charged into a boiling aqueous acidic reaction medium in a reaction zone maintained under reduced pressure in amounts sufficient to form chlorine dioxide from said reaction medium; is continuously removed from said reaction zone in the form of a gaseous mixture with steam and dissolved in water to form an aqueous chlorine dioxide solution, and acidic sodium sulfate is continuously precipitated from said reaction medium in said zone. In the highly efficient continuous production method of chlorine dioxide by reduction of sodium chlorate with methanol in the reaction medium, comprising: (a)
The sulfuric acid is charged into the reaction medium at least about 7
Maintaining the specified total normality and (Li) Periodic and variable losses of chloride ions from outside the reaction zone to the reaction medium. A highly efficient continuous production method for chlorine dioxide characterized by binding the book so that the amount of chloride ions present in the chlorine dioxide is maintained at 9 to 1 by the charged sulfuric acid, and the chloride ions are kept in an aqueous solution. The chloride ion concentration in the reaction medium is maintained at about 0.00 by continuously feeding it into the reaction medium as
2. The method according to claim 1, wherein the amount is 2 to about 0.3 mol. 3 Maintain a lower normality than the normality using charged sulfuric acid, and continuously supply chloride ions as an aqueous solution to the reaction medium to reduce the concentration of chloride ions in the reaction medium. 2. The method according to claim 1, wherein the amount is from about o.i mol to about 0.3 mol. The manufacturing method according to claim 2 or 3, wherein the weak chloride ion aqueous solution is a sodium chloride aqueous solution having a concentration of S mol. ! The production method according to claim 5, in which the charged sulfuric acid maintains a total acid normality lower than the normality, and chloride ions are not charged. Area of medium 1
Manufacturing method 02 according to claim 5, in which the gaseous mixture is boiled at an evaporation rate of m2.
Air is introduced into the reaction zone under reduced pressure of I00 mmHg, maintaining the boiling point of the reaction medium, and the partial pressure of chlorine dioxide in the gas mixture is adjusted to ? The manufacturing method according to any one of claims 1 to 6, wherein the temperature is maintained at OmmHg or less.