CS207602B2 - Method of making the chlorine dioxide - Google Patents

Description

(54) A method for producing chlorine dioxide

The present invention relates to the production of chlorine dioxide.

U.S. Pat. No. 3,864,456 is known to produce chlorine dioxide and chlorine by reducing sodium chlorate with sodium chloride and / or hydrogen chloride in the presence of sulfuric acid at a low total acidity of about 2 to 4.8 N.

The reactions that take place in the reaction medium in this earlier process are as follows:

NaClO 4 - NaCl + H 2 SO 2 - CIO 2 + + 1/2 Ch + H: O 4 Na 2 SO 2 (1)

NaClO + 5 NaCl + 3 H2SO1 -> 3 Clz 4 - 3 HzO + 3 Na2SO4 (2)

When some or all of the sodium chloride is replaced with hydrogen chloride, the hydrogen chloride then also provides a portion of the acid required in the system, thus reducing the need for sulfuric acid and sodium sulfate production accordingly.

From Canadian patent no. No. 913,328, it is also known to produce chlorine dioxide and chlorine by reducing sodium chlorate by chloride ions in an acidic aqueous medium into which chloride ions are introduced by hydrochloric acid, thereby achieving acidity.

The reactions leading to the reduction of chlorate with hydrochloric acid in this procedure are:

NaClO 4 4- HCl - CIO 2 + V 2 Cl 2 + 4 H 2 O 4 - NaCl (3)

NaC10 ₂ 4- 6 HCl -> 3 Cl2 + 3 H2O 4- 3 NaCl (4)

The processes described in each of the aforementioned earlier patents are carried out in a single-chamber vessel serving as a generator, evaporator and crystallizer to form chlorine dioxide in the reaction vessel. The reaction medium is maintained at the boiling point at the usual absolute pressure in the reaction vessel and at a temperature below the temperature at which substantial decomposition of chlorine dioxide occurs. The reaction vessel is maintained at a pressure below atmospheric pressure to maintain the reaction medium at boiling point and water vaporized from the reaction medium is used as a diluent gas for chlorine dioxide and chlorine. Upon initiation, the salt is formed as a by-product and its concentration rises until the reaction medium is saturated, the salt precipitates from the reaction medium in the reaction vessel, and is removed therefrom after saturation. In the process described in U.S. Pat. No. 3,864,456, the by-product salt is anhydrous neutral sodium sulphate; 913 328 is a byproduct of salts, sodium chloride.

The process is generally carried out under constant conditions, in which the amount of water introduced into the reaction vessel with the reaction vessel is substantially constant. the components are in equilibrium with the amount of water removed from the reaction vessel mainly as a diluent gas for chlorine dioxide and chlorine, so that the level of liquid in the reaction vessel is kept substantially constant.

In the respective reactions in the reaction medium of the two previous processes, the portion of the chlorate reacting according to formulas (2) and (4) above produces only chlorine and is therefore not effective in the process. The "efficiency" of the process by which chlorine dioxide is produced refers to the amount in which sodium chlorate is converted to chlorine dioxide according to the reactions expressed in (1) and (3).

Efficacy can be expressed as a percentage or as a "grammatome percentage of chlorine dioxide" (also referred to as GA% COžž), which is a quantitative expression of the conversion efficiency of sodium chlorate to chlorine dioxide, according to the reactions expressed by (1j and (3j) to the amount of chlorine atoms formed as chlorine dioxide as a percentage of the total number of chlorine atoms, especially in the gas mixture.

G.A.% CIO2

Cl in CIO2 in ClOz + Cl in Cla x 100 (5)

It follows from equation (5) that the maximum grammatoma percentage of chlorine dioxide that can be achieved is 50%, which is equal to 100% efficiency.

In the procedures described in U.S. Pat. No. 3,864,456; 913 328 is less than 100% effective; typically an efficiency equivalent to a GA o / _o CIO2 value of about 30 to about 44% is achieved.

Now, the authors have surprisingly found that the effectiveness of the process described in U.S. Pat. No. 3,864,456 and the efficacy of the process described in Canadian patent no. 913,328 can preferably be increased up to about 100% (equivalent to G.A.% ClO2 to 50 why) by adding a small amount of methanol. Methanol is consumed in the generator and continuous feed must be maintained in a continuous process.

The present invention relates to a process for producing chlorine dioxide by reducing an alkali metal chlorate in an aqueous acidic reaction medium containing chloride ions, the medium being maintained at a temperature below 85 ° C at ambient boiling point, at a pressure below atmospheric pressure and at saturation a byproduct, a chlorate cation salt, wherein the salt separates as a solid phase and is removed from the reaction vessel, characterized in that methanol is added to the reaction medium.

In the present invention, it has been observed that the production efficiency increases as the amount of methanol increases until it reaches an efficiency of approximately 100% (corresponding to 50 gramamatoma% of chlorine dioxide in the gaseous mixture resulting from the reaction medium). for example, the reactor is operated at about 70 ° C, the most efficient reaction being when up to about 0.1 g of methanol is added per g of chlorine dioxide.

If the amount of methanol rises above the required level to achieve 100% efficiency of chlorine dioxide production from the reaction medium, then the relative chlorine dioxide to chlorine ratio is constantly increasing, but the reaction which is then performed is a very inefficient form of the Solvay process.

The Solvay process for producing chlorine dioxide, as described, for example, in U.S. Pat. No. 2,881,052, comprises reacting a chlorate with methanol in the presence of aqueous sulfuric acid. The reaction proceeds according to the following relation:

NaClO 3 + 2 H 2 SO 1 - | - CH 2 OH -> 2 CIO 2. + 2 NaHSO 1 + HCHO + 2 II 2 O

This reaction proceeds relatively slowly and inefficiently, and it takes place on an industrial scale to remain in the process in a number of reactors and produces a large volume of liquid wastes containing sulfuric acid. The conversion efficiency of chlorate to chlorine dioxide is always lower and generally does not exceed 90%. As the amount of methanol increases with the use of authors protected processes, the decrease in potency is likely due to the portion of the chlorate that is reduced to chlorine dioxide by the Solvay-type procedure.

The term "acidity" has a number of possible explanations, but usually means all the acid present, as determined by titration with a sodium hydroxide solution of known concentration to a predetermined pH end titration. The determination of acidity is expressed by the term normality, i.e. the equivalent number of gram ions of hydrogen ions per liter of solution corresponding to the titrated value.

The acidity determined in this way may be referred to as the "total acidity of the acid". Thus, the process described in U.S. Pat. 3,864,456 is carried out at a total acidity of about 2 to 4.8 val / l.

As detailed in our co-pending application no. No. 7188/76, filed in the United Kingdom, in an aqueous system in which polyvalent anions capable of forming other types of anions with hydrogen ions are present, where other types of anions have a low dissociation constant for hydrogen ion binding, the overall acid normality does not represent the concentration of hydrogen ions suitable for reaction. Bound hydrogen ions, although not present in the solution as dissociable or as true hydrogen ions, will be included in the calculation of normality derived from the titration value when determining total acidity.

Therefore, total acidity is not a necessary and real measure of the "true concentration of hydrogen ions", which term is used herein to refer to the concentration of hydrogen ions capable of reacting. The term "actual hydrogen ion concentration" as used herein refers to a value determined by a pH meter calibrated with a 0.1 val / l hydrochloric acid solution, provided that the solution is 100% dissociated at that concentration. This value can be expressed as pH or as a normality, i.e., the number of vals of actual hydrogen ions per liter of solution corresponding to the determined pH.

The distinction between "true hydrogen ion concentration" and "total acid normality" is an important feature of the invention relating to the process of Canadian patent no. When the chlorine dioxide system of Canadian patent no. No. 913,328 contains only chlorate, chloride and hydrogen ions, then the actual concentration of hydrogen ions is substantially the same as the overall acidity of the acids in the reaction medium, and this acidity of about 0.05 to 0.3 val / l is found possible to achieve satisfactory chlorine dioxide production rates.

When polyhydric acid anions are also present in the reaction medium, it is necessary for a satisfactory rate of chlorine dioxide production that the actual concentration of hydrogen ions be in the range of about 0.05 to 0.3 val / l. Therefore, irrespective of the presence or absence of polyvalent acid anions, the actual concentration of hydrogen ions in the reaction medium according to the invention according to the process of Canadian patent no. 913,328 is maintained in the range of about 0.05 to 0.3 val / l.

When the procedure of Canadian patent no. No. 913,328, the sodium chloride deposited in the reaction zone and removed therefrom can be used in the form of a sodium chlorate solution for recirculation to the reaction zone after electrolysis of the aqueous sodium chloride solution.

Sodium chloride may also be used in the form of sodium hydroxide and chlorine obtained in an aqueous solution electrolysis plant. If it is not desired to proceed with any of the electrolytic processes, sodium chloride may be discarded.

The following examples further illustrate the invention.

Example 1

The single-chamber chlorine dioxide generator is operated under the conditions described below and the chlorine dioxide production efficiency and the chlorine dioxide purity are determined. Only the sodium chlorate solution, sodium chloride solution, sulfuric acid and methanol are metered into the reactor. The reaction medium is maintained at a boiling point below atmospheric pressure. Anhydrous sodium sulfate precipitates from the aqueous phase. Reaction conditions and results are. listed in Table I.

TABLE I

Temperature 66 ^Q C Pressure 19,062 kPa Fluid feed rate: methanol (MeOH) 53% 0.73 rpm / min H2SO1 9 M 9.6 ml / min NaClCte 5.4 M 9.6 ml / min NaCl 4.5 M 12.4 ml / min Generator Fluids: HzSOi 3.65 val / l NaCICú 1.62 mol / l NaCl 0.79 mol / l CIO2 production rate 0.24 g / l / min crystals NažSOi gas analysis 64% ClO2 36% Cl2 efficiency related 99% to chlorate Handle required for 1 kg 0.11 kg CH 2 OH produced by CIO2 0.98 kg NaCl

The chlorate efficiency of the chlorine dioxide generator under substantially the same conditions as in Table I, but in the absence of methanol, is about 96%.

Thus, the results from Table I above show an increase in chlorine dioxide production efficiency at low total acidity below about 4.8 N in the presence of a small amount of methanol.

Example 2

The single-chamber chlorine dioxide generator is operated with the addition of a solution of sodium chlorate, hydrochloric acid and methanol as the sole batches, maintaining the reaction medium at a boiling point below atmospheric pressure. Sodium chloride precipitates from the reaction medium. The production efficiency of chlorine dioxide is determined.

The reaction conditions and results are shown in Table II.

TABLE II

Temperature 70 'U Pressure 25,327 kPa Fluid feed rate: MeOH 50% 0.75 ml / min HCl 37% 4.1 ml / min NaCIOj 5.4 M 8.7 ml / min Generator Fluids: HCl 0.2 val / l NaGlOj 4.51 mol / l NaCl 2.14 mol / l Crystals NaCl CIO2 production rate 0 3 g / l / min Gas analysis 65.5% CIO2 Efficiency related 34.5% Clz 95.2% to chlorate Handle required for 1 kg 0.11 kg CH 2 OH

produced ClCU

The efficiency of the chlorine dioxide generator under substantially the same conditions as given in Table II, but in the absence of methanol, is about 93.4%.

Thus, the results from Table II above show that the production efficiency of chlorine dioxide and a low total acidity reaction medium where the reaction medium contains sodium chlorate and hydrochloric acid and precipitates sodium chloride can be increased by using a small amount of methanol.

Example 3.

The chlorine dioxide generator of the type described in Example 1 is operated intentionally under inefficient conditions (high molar ratio of chloride ions to chlorate ions in the generator fluid) and then in the presence of an additional amount of methanol. The results obtained are reproduced in Table III,

TABLE III

Try

Temperature (average)

Pressure (average)

Duration of the experiment

The ratio of chloride to chlorate in the Acidita generator

GA% ClOr in the absence of methanol GA% ClO 2 in the presence of methanol Total NaClO 3 feed (2.85 mol / l) (liters) Total IUSO ¹ feed (77 ^L wt%) (ml) * * Total MeOH feed (50% v / v). ) (ml)

Note:

* In Experiment A, 150 ml of sulfuric acid was used to adjust the pH of the original reaction mixture to 3.4 val / l before chlorine dioxide production began, whereas in Experiment B, 500 ml of sulfuric acid was used to adjust the pH of the original reaction mixture to 3.9 val / l.

The results from Table III above show that even the normally very low efficiency of the chlorine dioxide generator system can be increased to very high values when the amount of methanol is used.

Example 1 a d 4

The chlorine dioxide generator of the type described above in connection with Example 2 is operated under intentionally unfavorable efficiency conditions, i.e. at a high molar ratio of chloride ions to chlorate ions. The results are shown in Table IV.

A B

70 ° C 68 ° C 20,662 kPa 20,395 kPa 248 min 244 min 0.91 1.0 3.4 val / l 3.9 val / l 35.6 35.0 49.6 49.8 2.92 2.73 565 990 620 420 TABLE IV Temperature (average) 71 DEG Pressure (average) 23,461 kPa Duration of the experiment 131 min The ratio of chloride to chlorine 1.19 reionate ions Acidity (total normality) 0.37 val / l acids] Efficiency in absentia 87% of methanol Efficiency in the present 99.5 «/ o of methanol Total NaClOs charge 2.80 (6.27 M) (liters) HC1 total batch 2.51 (12 val / 1) (liters) MeOH total batch 1.62 (50% vol.) (Liters)

The results from Table IV above show that a highly inefficient chlorine dioxide recovery process can become highly effective when methanol is used.

The present invention therefore represents a significant improvement in earlier chlorine dioxide production systems. Modifications are also possible within the scope of this invention.

Claims (4)

SUBJECT CLAIMS 1. A process for producing chlorine dioxide by reducing an alkali metal hypochlorite in an aqueous acidic reaction medium containing chloride ions, said medium being maintained at a temperature below 85 ° C at an ambient boiling point at atmospheric pressure and saturated with a by-product; a salt of the starting hypochlorite cation, wherein the salt separates as a solid phase and is removed from the reaction vessel, characterized in that methanol is added to the reaction medium. 2. The process of claim 1, wherein sodium chlorate, chloride and sulfuric acid are added to the reaction medium, and anhydrous neutral sodium sulfate is precipitated, wherein the reaction medium has a total acidity of 2 to 4.8 val / l, characterized in that: methanol is metered into the reaction medium. 3. The process of claim 1, wherein sodium chlorate, hydrochloric acid and sodium chloride are added to the reaction medium, wherein methanol is metered into the reaction mixture at an actual hydrogen ion concentration of 0.05 to 0.3 val / liter. 1. 4. A process according to any one of claims 1 to 3, wherein up to 0.1 grams of methanol per gram of chlorine dioxide produced is used.