MXPA98001874A - Method for producing chloro dioxids - Google Patents

Abstract

The invention relates to a process for the production of chloride dioxide by reducing chlorate ions with hydrogen peroxide as a reducing agent in a tubular reactor, preferably in the presence of a mineral acid, wherein the preferred degree of conversion of chlorate to chloride dioxide in the reactor is above about 75%, preferably about 80 to about 10.

Description

METHOD FOR PROD? XCTR DTOXTDQ CHLORIDE The present invention relates to a method for the production of chloride dioxide by reducing the chlorate ions with hydrogen peroxide as a reducing agent in a tubular reactor.

Chloride dioxide is mainly used in pulp bleaching, but there is a growing interest in using it also in other applications such as water purification, fat bleaching or phenol extraction from industrial waste. Because chloride dioxide can not be stored stably, it must be produced in situ.

The large-scale production of chloride dioxide is generally carried out by the reaction of alkali metal chlorate or doric acid with a reducing agent with chloride ions, methanol or hydrogen peroxide at subatmospheric pressure as it is described, for example, in EP 445493, U.S. Patent 5091166 and U.S. Patent 5091167. These production methods are highly efficient, but are only suitable for large-scale production, for example in pulp mills that consume considerable amounts of chloride dioxide for bleaching »In small-scale applications, for example for water purification, chloride dioxide is generally produced by reaction of sodium chlorite with an acid.

Patent EP 612686 discloses the production of chloride dioxide from an alkali metal chlorate and hydrogen peroxide at substantially pressures U.S. Patent 5376350 discloses a method of producing chloride dioxide from chlorate ions and a reducing agent in a plug flow reactor that is suitable for small scale production. Although the method works well, you still want to improve efficiency more.

It is an object of the invention to provide an improved process suitable for the small scale production of cioride dioxide from a chlorate, metal or chlorido acid and a reducing agent. Particularly, it is an objective to provide a process involving a high proportion of chloride dioxide production and low chemical consumption in a reactor with low space requirements. These objectives can be achieved by a continuous production process of chloride dioxide by reducing chlorate ions with hydrogen peroxide or a reducing agent in a tubular reactor, preferably in the presence of a mineral acid, more preferably sulfuric acid, - wherein the preferable degree of the conversion of chlorate to chloride dioxide in the reactor is about above 75%, preferably about 80 to 100%, more preferably about 95 to 100%.

According to one aspect of the invention, the process comprises the steps of: (a) feeding hydrogen peroxide and a metal chlorate or doric acid or a mixture thereof and optionally a mineral acid at one end of a tubular reactor to form a reaction mixture; (b) reducing the chlorate ions in the reaction mixture in the tubular reactor to form the chloride dioxide, wherein the rate of conversion of chlorate to chloride dioxide in the reactor is from about 75% to 100%, and : (c) recovering the product containing the chloride dioxide at the other end of the tubular reactor.

According to another aspect of the invention, the process comprises the steps of: (a) feeding hydrogen peroxide and a metal chlorate or doric acid or a mixture thereof and optionally a mineral acid at one end of a tubular reactor to form a reaction mixture, wherein the molar ratio H202: CI03 fed to the reactor is from about 0.5: 1 to about 2: 1, preferably about 0.5: 1 to about 1: 1; (b) reducing the chlorate ions in the reaction mixture in the tubular reactor to form the chloride dioxide, and; (c) recovering a product containing chloride dioxide at the other end of the tubular reactor - In step (a) it is particularly preferred to feed the hydrogen peroxide, - a metal chlorate, preferably the alkali metal chlorate such as sodium chlorate and a mineral acid, preferably sulfuric acid. In order to achieve a high degree of chlorate conversion it is usually recommended to feed the hydrogen peroxide in an amount exceeding the stoichiometric amount which is 0.5 mole H202 per mole of CI03. However, it has surprisingly been found that too much hydrogen peroxide has a negative impact on the chlorate conversion.

According to another aspect of the invention, the process comprises the steps of: (a) feeding hydrogen peroxide, a metal chlorate, preferably alkali metal chlorate such as sodium chlorate, and sulfuric acid at one end of the tubular reactor to form a reaction mixture, - wherein the sulfuric acid fed it has a concentration of about 70 to about 96% by weight, preferably about 75 to about 85% by weight and preferably at a temperature of about 0 to about 1%, more preferably about 20 to about 50 ° C ( b) reduce the chlorate ions in the reaction mixture in the tubular reactor to form the cioride dioxide, and (c) recovering a product containing chloride dioxide at the other end of the tubular reactor.

It has been found that if the sulfuric acid feed has a concentration within the specified range, no heating or external cooling is needed since the energy of the dilution is sufficient to operate the reactor diabetically. It was also found that the specified temperature field facilitates the stable operation of the process.

According to yet another aspect of the invention, the process comprises the steps of: (a) feeding hydrogen peroxide, a metal chlorate, preferably an alkali metal chlorate such as sodium chlorate and sulfuric acid at one end of the tubular reactor to form a reaction mixture; (b) reducing the chlorate ions in the reaction mixture in the tubular reactor to form the chloride dioxide, and; (c) recovering a product containing chloride dioxide at the other end of the tubular reactor, wherein from about 2 to about 10 K. of H2SO4, preferably from about 3 to about 5 Kg. H2SO4 is fed per kg of CI02 produced.

Surprisingly it was found that it is possible to operate at a degree of conversion of chlorate above about 75% despite the comparatively low amount of sulfuric acid fed.

According to a particularly preferred embodiment, the invention is interested in a process for the production of chloride dioxide by means of the reduction of chlorate ions with hydrogen peroxide as a reducing agent in a tubular reactor comprising the steps of: (a) feeding the hydrogen peroxide, a metal chlorate, preferably an alkali metal chlorate such as sodium chlorate and sulfuric acid at one end of the tubular reactor to form a reaction mixture, wherein the molar ratio H202: CI03 fed to the reactor is from about 0.5: 1 to about 2: 1, preferably from about 0-5: 1 to about 1: 1, and wherein the sulfuric acid feed has a concentration from about 70 to about 96 % by weight, preferably from about 75 to about 85% by weight and preferably at a temperature from about 0 to about 100 ° C, more preferably from about 20n to about 50 ° C. (b) reducing the chlorate ions in the reaction mixture in the tubular reactor to form the cioride dioxide, and; (c) recovering a product containing chloride dioxide at the other end of the tubular reactor, wherein from about 2 to about 10 Kg- of H2SO4, preferably from about 3 to about 5 Kg. H2SO4 is fed per Kg of CI02 produced .

It is evident that it is possible to combine the characteristics of all the aspects and modalities described above. Other features that are particularly preferred in all aspects and embodiments of the invention will now be described - The recovered product contains chloride dioxide, oxygen and optionally a metal salt of the mineral acid.

It usually also contains unreacted chemicals such as mineral acid and small amounts of chlorate ions. However, it was found possible to avoid any chloride formation.

It is preferred to operate without circulating unreacted chemicals such as chlorate or sulfuric acid of the product back to the reactor. In many applications, the complete mixture of the product can be used without separation, for example in the purification of water. Another option is to separate the gaseous product, ie, chloride dioxide and oxygen, and to use the liquid containing chlorate as an agent in another chloride dioxide generator, for example, in the processes described above, mentioned in Patent EP 445493, United States Patent 5091166 and United States Patent 5Q9L167.

Although the ideal tubular reactor is normally operated with a plug flow without any backward setting, it was found that the process of the invention is highly effective even if operated without a substantial concentration of gradients in the reactor.

The reaction mixture in the bulk of the reactor preferably contains from 0 to about 2, more preferably from 0 to about 0.1 moles per liter of chlorate ions and from about 3 to about 10, most preferably from about 54 to about 6. moles per liter of sulfuric acid. It is preferred to keep the concentration of chlorate and sulfate below saturation to avoid crystallization of the metal salts thereof.

All chemical feeds, ie, hydrogen peroxide, metal chlorate or doric acid and mineral acid are preferably supplied as aqueous solutions. It was found that too much water in the system increases energy consumption and decreases chemical efficiency, while too little water results in loss of stability. Therefore, the feed solution of the hydrogen peroxide has been preferably concentrated from about 30 to about 70% by weight, more preferably from about 40 to about 60% by weight. The solution of the chlorate feed, preferably an alkali metal chlorate such as sodium chlorate, suitably has a concentration of about 0.5 moles per liter of saturation, preferably from about 3 to about 6 moles per liter, more preferably about 4.5. up to about 5.5 moles per liter. The mineral acid feed, preferably the sulfuric acid, preferably has a concentration of about 50 to about 96% by weight, more preferably about 75 to about 85% by weight. It is preferred not to add any substantial amount of chloride ions to the reactor, except that the chloride is always present as an impurity in the chlorate feed. Preferably, conventional alkali metal chlorates are used without adding extra chloride, which typically contains less than about 0.5, often less than about 0.05, preferably less than about 0.02, more preferably less than about 0.01% by weight of metal chloride alkali calculated as NaCl in NaCl03.

It was found that chemical efficiency is improved by high operating pressure, although too high a pressure would result in high partial pressure of chloride dioxide. The appropriate pressure in the reactor is from about 125 to about 900 mm Hg (about 16.7 to about 120 kPa), preferably from about 350 to about 760 mm Hg (about 46.7 to about 101 kPa), more preferably from about 500 to about 650 mm Hg (about 66.7 to about 86.7 kPa), The partial pressure of the cioride dioxide is furthermore increases by the oxygen and / or vapor formed in the reactor. Although not normally necessary, it is also possible to supply an extra-inert gas such as air. The temperature of preference is maintained from about 30 ° C to the boiling point of the reaction mixture, more preferably at about boiling point.

It was found that the degree of reactivation of the reactors affects the efficiency and it is preferred that the chlorate feed disperse substantially uniformly in the mineral acid at the reactor inlet to avoid any gradient of substantial radial concentration above the cross section of the reactor. reactor. It is also preferred that the chlorate feed be mixed with the hydrogen peroxide before dispersing in the mineral acid. In order to minimize the gradients of the radial concentration it was found favorable to use a tubular reactor with an internal diameter of about 25 to about 250 mm, preferably from approximately 70 to approximately 130 mm.

Surprisingly it was found possible to achieve a high production rate of chloride dioxide, preferably from about 0.2 to about 7 Kg / hr, more preferably from about 0.45 to about 4.5 Kg / hr, and to a high degree of conversion of chlorate into a comparatively short tubular reactor preferably having a length of about 50 to about 500 mm, more preferably about 100 to about 300 mm. It was also found favorable to use a tubular reactor having a length ratio in the inner diameter of from about 12: 1 to about 1: 1, more preferably from about 3: 1 to about 1.5: 1. Suitably adequate residence time in the reactor is from about 1 to about 100 minutes, preferably from about 4 to about 40 minutes.

A small-scale production plant usually consists of only one tubular reactor, but it is possible to distribute several, for example, up to about 10 tubular reactors in parallel, for example as a tube bundle.

The invention will now be further described in connection with the following examples, however the suals are not intended to be construed as limiting the scope of the invention.

Example 1: A process according to the invention was carried out by means of continuous feeding to a tubular reactor having an internal diameter of 100 mm and a length of 300 m with 45 ml / min. of 5 M aqueous partner chlorate, 46 ml / min. of 78% by weight of sulfuric acid and 10 ml / min of 50% by weight of hydrogen peroxide. The reactor was operated at a pressure of 630 mm Hg and a temperature of 50 ° C. The experiments carried out in different molar proportions of H202 to NaCl03 showed that the degree of convention of chlorate was significantly affected as it appears in the table below: Mole ratio Kg H2O2 Proportion of degree dß H2O2 NaCIOs per Kg CIO2 prod. CIO2 (kgh; CI03 conversion <% > 0. 75 0.38 0.91 98 0.76 0.38 0.91 99 0.78 0.38 0.91 100 0.82 0.39 0.86 97 1.19 0.95 0.91 63 2.40 1.70 0.86 70 Example 2: A process was carried out in two different tubular reactors having a length of 300 mm. The internal diameters of the reactors were 100 and 150 mm, respectively. The reactors - were continuously fed with a 5 M aqueous sodium chloride, 78% by weight of sulfuric acid and 50% by weight of hydrogen peroxide. The reactors were operated at a pressure of 630 mm Hg and a temperature of 60 ° C. It was found that the size of the reactor affected the degree of conversion of chlorate as shown in the following table: Diameter of Kg H2Q2 Proportion of reactor grade < nm) by Kg CIO2 prod. CIO2 (kg / h) CIO3 conversion (% > 150 5.97 0.91 83 150 7.14 3.75 100 5.36 2.70 93 100 4.60 0.87 97 Example 3: A process was carried out by continuous feeding with a tubular reactor having an internal diameter of 100 mm and a length of 300 mm with a 5 M aqueous sodium chlorate, 78% by weight of sulfuric acid and 50% by weight. Weight of hydrogen peroxide. The reactor was operated at a pressure of 630 mm Hg and at a temperature of 60 ° C. The amount of the sulfuric acid feed was varied to achieve different compositions of the reaction mixture in the reactor. The results are shown in the following table: [?? 2S04] [NaCJGa] Na ClOs H2SO4 H2O2 Provided Grade of (M) () (mi / min) (ml / min) (mi / min) produced. CIO2 conver CIO3 4. 59 0.040 22.7 20.4 5.1 0.45 100 4. 77 0.000 22.7 20.4 5.1 0.45 98 . 20 0.003 22.7 20.4 5.1 0.45 100 . 59 0.140 113.7 130.7 25.5 2.27 94 . 37 0.120 113.7 130.0 25.5 2.27 94 5.25 0.045 113.7 130.0 25.5 2.18 97 6. 30 0.065 113.7 130.0 25. 2.18 96

Claims (1)

1. • D? PTVINDICATIONS 1. A process for continuously increasing the chloride dioxide by reducing the chlorate ions with hydrogen peroxide or a reducing agent in a tubular reactor is characterized in that it comprises the steps of (a) feed the hydrogen peroxide and a metal chlorate or Doric acid or a mixture of the glycosides on ii n rjo 1 n ^ "vt- Tarnn 3 ríal roarfr -,? - phnl ar? I? -ai form a reaction mixture, (b) reducing the chlorate ions in the reaction mixture in the tubular reactor to form chloride dioxide, and (c) recovering a product containing dioxide '• ji iUI? cu CJ. uui? I =? JL d u ueJ. ica ^ t? i? _ UJJ J_CIJ_. ¿. a pxεo as claimed in claim 1, wherein the degree of conversion of chlorate to chloride dioxide in the reactor is approximately 75% to 100%. 3. Claims 1-2, wherein the H2O2 molar ratio: CIOs fed into the tubular reactor is from about 0.5: 1 to about 2: 1. 4. A process as claimed in claim 3, wherein the CIG¿ molar ratio fed into the tubular reactor is from about 0.5: 1 to about 1: 1. 5. A process as claimed in any of claims 1-4, wherein step (a) includes ia CL_- -.??i- ?? The x ±? U cl a uiiucí ai. 6 * An as claimed in the quai-knives of claims 1-5, wherein step (a) also includes the sulfuric acid feed having a concentration of about 70 to about 96% by weight of the tubular reactor. 7. A process as claimed in claim 6, wherein the sulfuric acid feed has a temperature uc a and ±. uAiinaaamtipte ^ U naS ta api u? ± iftaClauíep ut; jul . 8. A process as claimed in any of Claims 6-7, wherein from about 2 to about 10 Kg H2SO4 is fed per Kg of produced CIO2. 3 > . A process as claimed in claim 8, wherein from about 3 to about 5 K ^ H2SO4 is fed per Kg of produced CIO2. or. A process as claimed in any of claims 1-9, wherein substantially no chlorate or unreacted mineral acid of the product in step (c) is recirculated back to the reactor. 11 TTn nrri asn rrrnin = 30 re "1 'tf" í pH p ra rial ppi pr? rp l ac: claims 1-10, wherein the inner diameter of the tubular reactor is from about 25 to about J? m. 12. A process as claimed in any of claims 1-11, wherein the tubular reactor has a ratio of the internal diameter length to approximately 19 • 1 hac-Ha anroyirnaHamoril-o 1 • 1 13. A process as claimed in any of the reactions 1-12 where the pressure in the reactor is not present. hao a a rnyí mpHs YiD? fO Q00 H eadly 16.7 to approximately 120 kPa) 14. An ore as claimed in any one of claims 1-13, wherein the reaction mixture in the bulk of the reactor contains from about 0 to about 2 GIO-TS per liter of chlorate ions and of pnrnYi marfa? | Q? ' (-a "^ ha« + - to anrriYirnaHampril-Q 10 mnl o? nnr 1 i rn of sulfuric acid. IJ. a proLtíao como s > tí rei in ica _¡n ucti uiti t _? < =: Reactions 1-15 wherein the reaction mixture in the bulk of the reactor contains from about 0 to about 0.1 moles per liter of chlorate ions. 16. A method as claimed in any of claims 1-15, wherein there is no substantial concentration gradient in the mixture of 17, A process as claimed in any of claims 1-16, wherein no substantial amount of chloride ions are added to the reactor.