WO2015162440A1

WO2015162440A1 - Process for preparing chlorine dioxide

Info

Publication number: WO2015162440A1
Application number: PCT/GB2015/051219
Authority: WO
Inventors: David Selby; Al SAYED
Original assignee: Ximax Oil & Gas Solutions Limited
Priority date: 2014-04-25
Filing date: 2015-04-27
Publication date: 2015-10-29
Also published as: GB2527275A; CA2983875A1; GB201407348D0; GB2527275B

Abstract

The invention provides a process for producing chlorine dioxide by the reaction of two precursor components. The first component contains a solution of a compound containing chlorine in the +1 oxidation state, a source of H+ ions and a source of iodide ions. The second component contains an inorganic base and an inorganic acid salt. The process comprises mixing the two components in a reactor to produce chlorine dioxide. The invention also provides a kit providing the two components for mixing to form a chlorine dioxide containing disinfectant solution.

Description

Process for Preparing Chlorine Dioxide

The present invention relates to a process for generating chlorine dioxide in liquid form. More particularly, the process allows a purer form of chlorine dioxide to be produced than is available from conventional processes. The chlorine dioxide of the present invention has improved stability relative to existing processes for generating it and consequently has a longer shelf life. The invention also relates to a number of uses of the higher quality chlorine dioxide produced by the process.

Chlorine dioxide is a well known and well established disinfectant. It operates as an oxidising biocide in the same way that the disinfectant agents ozone and chlorine do. This means that chlorine dioxide is effective at killing micro-organisms by disrupting the transport of nutrients across the cell wall, not by disrupting metabolic process. Chlorine dioxide is therefore not a metabolic toxin.

Chlorine dioxide is a broad-spectrum disinfectant that is effective against spoors, viruses, fungi and algae. This efficacy operates over a wide pH range and temperature range thereby providing a further advantage over chlorine itself.

Chlorine dioxide is less reactive than ozone and chlorine and consequently is more selective in its action. This means chlorine dioxide can be used effectively at much higher concentrations than would be the case for ozone or chlorine on account of its selectivity. It is used in a variety of processes including a large number of bactericidal applications. It finds particular usage in water treatment and the reduction or elimination of odours. There are a number of problems with traditional chlorine treatment including poor retention times and elevated pH levels in water. It is also difficult to obtain adequate "CT" values that are prescribed by regulatory authorities. The CT is the product of the disinfectant residual concentration and the contact time which is required to achieve 1 ,000 fold reduction of certain pathogens. A further problem of chlorine is that it can engage in unwanted reactions with organic compounds that might be present in the water to form halogenated organic compounds. Such materials are known to be harmful and have greatly extended half lives in the environment leading to potential environmental problems. Chlorine dioxide has a lower CT value than chlorine and thus is a safer, more environmentally friendly alternative for the treatment of water etc.

Chlorine dioxide itself is a gaseous compound which is relatively unstable. It is therefore necessary to produce chlorine dioxide at the intended site of use rather than to produce it in a factory and transport it to its intended site of use. Several well known processes exist for the production of chlorine dioxide, many of which follow the same theme. Generally such methods involve the production of chlorine dioxide by the reaction of a chlorite with dilute hydrochloric acid and the resulting material is then used directly in water treatment etc. In some circumstances, chlorine dioxide can be obtained in stabilised form. In such methods, stabilised chlorine dioxide is provided as a buffered aqueous solution to which acid is then added to activate and make available the chlorine dioxide. Generally, however, chlorine dioxide is obtained in situ. Conventional processes for producing chlorine dioxide may also start with chlorous acid. In one known process, chlorous acid is produced by ion exchange of the H⁺ ion with the Na⁺ ion in sodium chloride. The resulting compound, chlorous acid, is the precursor for the formation of chlorine dioxide which is then produced by a disproportionation reaction of chlorous acid to chlorine dioxide and hydrochloric acid and water. One problem with this process is that it is very time and concentration dependent. It also frequently yields unwanted chlorinated by-products and chlorine itself. This can be a significant problem.

US 4,292,292 discloses a process for preparing chlorine dioxide using a concentrated sodium chlorite solution which is then reacted with concentrated hydrochloric acid in the absence of any dilution water. This reaction is said to produce 4 moles of chlorine dioxide for every 5 moles of sodium chlorite based on the stoichiometric equation for the reaction.

A common problem with all processes for preparing chlorine dioxide is that the product is frequently contaminated with chlorites, chlorates and free chlorine itself. Some of the conventional processes also use hazardous reagents.

It is therefore an aim of the present invention to provide a process which is able to generate very pure chlorine dioxide. It is a further aim of the present invention to produce chlorine dioxide which does not contain significant levels of harmful by-products. A further aim of the invention is to provide a reliable and economical process for generating chlorine dioxide. It is an aim to provide a convenient to use process which avoids the need for solids handling. The present invention thus provides a process which uses its component reagents in liquid form. The invention also aims to avoid the need for complicated generating apparatus. Another aim is to provide a process which uses conventional reagents and ideally reagents which do not present significant risk of harm either to the operator during use. It is a further aim to provide a process which is environmentally friendly in terms of the by-products formed. The present invention also seeks to improve the convenience of chlorine dioxide generation by providing a more stable form of chlorine dioxide which remains active and yet which can be stored in a ready to use concentrate form over an extensive period of time.

The present invention satisfies some or all of the above aims.

According to the present invention, there is provided a process for producing chlorine dioxide by the reaction of two precursor components which on mixing release chlorine dioxide, the first component comprising a solution of a compound containing chlorine in the +1 oxidation state, a source of H⁺ ions and a source of iodide ions; and a second component containing an inorganic base and an inorganic acid salt, wherein the process comprises mixing the two components in a reactor to produce chlorine dioxide.

In an embodiment, the compound containing chlorine in the +1 oxidation state in the first component is sodium, potassium or calcium hypochlorite. Preferably the compound containing chlorine in the +1 oxidation state is sodium hypochlorite on account of its ease of use and availability. A further advantage of sodium hypochlorite is that ultimately it degrades to the relatively harmless compound, sodium chlorite.

In an embodiment, the source of H⁺ ions is an inorganic acid. Preferably, the acid is hydrochloric acid, sulphuric acid or a phosphoric acid. Alternatively, the acid may be selected from chlorous acid, hypochlorous acid, chloric acid or perchloric acid. The acid may be a mixture of more than one of the above acids. Preferably the acid is a monoprotic acid. It is important that the acid and its reaction products are compatible with the end use of the chlorine dioxide. For this reason, hydrochloric acid is preferred. Preferably, the acid is used in concentrated form. The acid is preferably greater than 0.5M, more preferably greater than 1 .0M, and most preferably greater than 3.0M.

In an embodiment, the source of iodine ions is potassium iodide or sodium iodide.

The inorganic base in the first component may be an alkaline metal or alkaline earth hydroxide or carbonate. Preferred alkali metals are sodium and potassium. Preferred alkaline earths are magnesium and calcium. The preferred base is a hydroxide. Preferred hydroxides include sodium hydroxide, potassium hydroxide and calcium hydroxide. Amongst these, sodium hydroxide is preferred since its reaction product (sodium chloride) is compatible with the end use of the chlorine dioxide.

The acid salt is an alkali metal bisulphate or bicarbonate or a hydrogen phosphate salt of an alkali metal or alkaline earth. Preferably the acid salt is sodium hydrogen sulphate or potassium hydrogen sulphate. More preferably, the acid salt is sodium hydrogen sulphate.

The chlorine dioxide produced by the process of the present invention has a number of performance benefits. The reaction generates substantially no free chlorine and no other harmful residual compounds. Either minor or undetectable amounts of chlorites and chlorates are observed as a result of the reaction and, when present, these side products are well below established safety levels. There are therefore no harmful residual compounds in the chlorine dioxide product of the present invention. This is a significant advantage of the invention.

A further advantage of the present invention is that a conventional chlorine dioxide generator is not required.

The chlorine dioxide of the present invention is generated by mixing the first component and the second component in the appropriate ratio. The reactor in which this this generation occurs can be any suitable vessel in which they can be mixed. There is no disclosure of a two-part liquid component system in the prior art. Mixing can be preceded by dilution of the components.

Conventional two component systems which are used in the prior art are normally provided in powder form. One problem with powder systems is that of handling. There are frequently difficulties in handling powders due to inhalation of dust and the risk of explosion. It is also difficult to dispense and measure out the correct quantities of powders. The present invention avoids the problem of powder handling entirely by virtue of using a two component liquid system. The liquid-based process of the present invention does not require the use of a generator. This also is a major advantage.

In an embodiment, the first component and/or the second component may independently contain one or more additives. Additives that may be included in one or both components include surfactants, corrosion inhibitors and stabilisers. Preferably the or each additive is in the first precursor component. The half life of the chlorine dioxide produced by the present invention is at least 30 days and may be up to 90 days after preparation. Without wishing to be bound by theory the stability of the chlorine dioxide solutions produced by the present invention is thought to be due at least in part to the low impurity levels and the lack of any autocatalytic decomposition. This represents a significant advantage relative to conventional systems where the chlorine dioxide has a limited shelf life and may typically last only 5 to 10 days.

The chlorine dioxide has a number of applications in the treatment of biofilm. Chlorine dioxide releases and clears biofilm. One advantage of the chlorine dioxide of the present invention is that it is able to clear biofilm completely and disinfect and destroy bacteria and other pathogens. After use, the treated water may be discharged into sewers or rivers without risk of hazard to the environment on account of the very low or undetectable levels of impurities and on account of the fact that there are substantially no hazardous components in the treated water which originates from the chlorine dioxide production.

A further advantage of chlorine dioxide produced by the process of the present invention is the fact that higher chlorine dioxide concentrations can be obtained relative to the prior art. Typically, the liquid chlorine dioxide solutions produced in accordance with the present invention have concentrations of around 3,300 ppm as compared with about 2,900 ppm for conventional systems. A benefit of this higher concentration is that a smaller amount of the solution is required to achieve the same effect, e.g. a small amount would treat the same volume of water. The chlorine dioxide of the present invention finds a number of uses in treating water supplies. This is of particular interest in the printing industries, nuclear power generation industry and water treatment industries.

A further application of the chlorine dioxide resides in its utility for improving the shelf life of vegetables such as potatoes, carrots, etc. We have found that root vegetables irrigated with water treated using this reagent enjoy improved shelf life relative to untreated specimens. Similarly, fruit and vegetables which have also been washed with water treated in this manner before packaging also enjoy improved shelf life relative to untreated specimens.

We have also found that livestock that are fed drinking water that has been treated using the process of the present invention are healthier, bigger and enjoy a lower mortality rate. This is particularly noticeable in poultry. It is correct to say that the treated drinking water improves the overall general health of livestock such as cattle, sheep, pigs and poultry.

In use, kits for preparation of a disinfectant solution containing chlorine dioxide prepared according to the present invention may be provided to allow preparation of the disinfecting solution extemporaneously by end users. The simplicity of the process and selection of specific types of precursors make that possible. Such kits may have a container of each component, which are mixed when required either with or without further water. One of the containers may provide a vessel in which to mix the precursors to generate the chlorine dioxide.

It may be supplied as a ready to use kit in which a small volume of one component (an "activator") is added to a larger volume of the second component. Such a ready to use kit may be used to prepare 20L of a 0.35% chlorine dioxide solution (3500ppm) as follows:

1 ) Add 1 L of the first component from its container to a jerry can containing 19L of the second component

2) Gently agitate

3) Replace cap and seal tightly

4) Leave for 30 to 60 minutes

5) Gently agitate again

6) Use disinfectant solution, further diluted or not as required.

A super concentrate kit can also be supplied in which the second component is diluted in water prior to addition of the activator component (first component). Such a concentrate kit may be used to prepare 50L of a 0.35% chlorine dioxide solution (3500ppm) as follows:

1 ) Add 2.5L of the second component to 45L of water in a suitable container

2) Add to that 2.5L of the first component

3) Seal vessel

4) Gently agitate

5) Leave for 60 minutes

6) Gently agitate again

7) Use disinfectant solution, further diluted or not as required.

Clearly kits with different volumes and concentrations of first and second components can be provided to allow production of different amounts and concentrations of disinfectant solution. Examples

The production and efficacy of various embodiments of chlorine dioxide disinfecting solutions according to the present invention is discussed below for ease of reference and understanding.

Example 1 : Determination of bactericidal activity

A stock disinfectant solution was initially prepared by dissolving 50ml of a liquid component B (the second component) into 900ml of standardised hard water and then mixing 50ml of a liquid component A (the first component or "activator") therein. This produced a solution of approximately 0.35% chlorine dioxide (about 3500ppm) which is as described above. Components A and B are stored separately and can be combined in the correct ratio when chlorine dioxide is to be generated.

This stock solution was further diluted as follows:

A) 349 parts water to 1 part stock solution (approximately 1 0ppm chlorine dioxide).

B) 6 parts water to 1 part stock solution (approximately 500ppm chlorine dioxide).

C) 3.7 parts water to 1 part stock solution (approximately 750ppm chlorine dioxide).

These ready to use solutions were then subjected to the British Standards Institution (BSI), 2000 BSEN 1 656:2000 test for chemical disinfectants and antiseptics. This is a quantitative suspension test for the evaluation of bactericidal activity of chemical disinfectants and antiseptics used in the veterinary field. In this test the three different concentrations of disinfectant according to the present invention were used to treat water containing four different pathogens, namely, Aeromonas salmonicida, Lactococcus gargieae, Camobacterium piscicola and Yersinia ruckeri at a temperature of 4°C for a 30 minute contact time. The reduction in viability over that period was then measured. The results of this test are outlined in the table below:

Table 1 : Reduction in viability at concentrations of 0.286% (v/v), 1.43%

(v/v) and 2.14% (v/v) at 4°C for 30 min contact time

To achieve a pass in the above test the disinfectant solutions needed to demonstrate a reduction in viability (R) of greater than 1 .0 x 10⁵. As can be seen at dilutions of 6 parts water to 1 part stock solution (which is equivalent to approximately 1 .43% v/v of the original first and second components) or stronger the disinfectant is effective at destroying such waterborne pathogens.

Example 2: Determination of efficacy against fungal spores

Tests were carried out to investigate the efficacy of the present invention against fungal spores. These tests were carried out using cultures of Fusarium oxysporum, Septoria tritici and a Phytophthora species. Suspensions of spores of those organisms were produced having approximately 2.7 x 1 0⁴ spores per ml. 1 ml aliquots of the suspensions were added to disinfectant solutions containing chlorine dioxide prepared according to the present invention using two part precursors to form a stock solution as described above. These were diluted to produce concentrations of 0, 20, 40, 60, 80 and 100ppm of chlorine dioxide. 0.5ml aliquots of the combination of spore suspensions and disinfectant were then removed and plated onto potato dextrose agar plates after 5 and 10 minutes of exposure. These plates were then incubated for 10 days, after which colony counts of Septoria, Fusarium and Phytophthora were carried out. The results of these are shown below:

Table 2A: Fusarium oxysporum

Concentration Mean No. of viable spores after Mean No. of viable spores

(ppm) 5 minute exposure after 10 minute exposure

0 (SDW control) Too many to count Too many to count

20 0 0

40 0 0

60 0 0

80 0 0

100 0 0

Table 2B: Septoria tritici

Concentration Mean No. of viable spores after Mean No. of viable spores

(ppm) 5 minute exposure after 10 minute exposure

0 (SDW control) 61 61

20 0 0

40 0 0

60 0 0

80 0 0

100 0 0.33 Table 2C: Inaeaualis

The results of this show that chlorine dioxide solutions according to the present invention are very effective at killing spores even at very low concentrations.

Example 3: Determination of virucidal activity

In order to assess the virucidal activity of the disinfectant prepared according to the present invention a modified version of British Standards Institute's (BSI), 2000.BS EN14675:2006 {Chemical Disinfectants and Antiseptics - Quantitative Suspension Test for the Evaluation of Virucidal Activity of Chemical Disinfectants and Antiseptics Used in the Veterinary Field) was carried out.

In this test the three disinfectant solutions of differing concentration were used. These were as prepared in Example 1 (ie A, B and C) with concentrations of approximately 1 0ppm, 500ppm and 750ppm chlorine dioxide. In the test these three different concentrations were contacted for a period of 30 minutes at a temperature of 4°C with a water based preparation containing infectious pancreatic necrosis virus. The soiling level of these preparations was adjusted using 10g/I bovine serum albumin and 10g/I yeast extract. After contact between the disinfectants solutions A, B and C and the virus test preparation the reduction in viral count was assessed, summarised in the table below:

Table 3

The results above show that at concentrations achieved by a dilution of

1/7 of a stock solution comprising approximately 0.35% chlorine dioxide the disinfectants according to the present invention achieve sufficient reduction in viral efficacy to pass the test. Higher concentrations also function, and lower concentration ones would likely also work, especially in lower soiling conditions.

Example 4

In order to assess the stability and shelf life of a chlorine dioxide disinfectant solution prepared according to the present invention a solution was made up by mixing appropriate quantities of the first component and second component and water in order to achieve a chlorine dioxide level of approximately 0.43%. The solution was then stored at room temperature and the chlorine dioxide level thereof was then periodically tested. The results are summarised in the table below:

Table 4

Time Chlorine dioxide level (%)

1 hour 0.43%

3 hours 0.42%

24 hours 0.38%

ays .

As can be seen from the table above, the disinfectant solution produced is stable enough that the chlorine dioxide levels do not decrease below efficacious levels after 30 days of storage. It is believed that storage for considerably longer may also be possible.

Claims

1 . A process for producing chlorine dioxide by the reaction of two precursor components which on mixing release chlorine dioxide, the first component comprising a solution of a compound containing chlorine in the +1 oxidation state, a source of H+ ions and a source of iodide ions; and a second component containing an inorganic base and an inorganic acid salt, wherein the process comprises mixing the two components in a reactor to produce chlorine dioxide.

2. A process as claimed in claim 1 , wherein the compound containing chlorine in the +1 oxidation state in the first component is selected from sodium hypochlorite, potassium hypochlorite or calcium hypochlorite.

3. A process as claimed in claim 1 or claim 2, wherein the source of H+ ions is an inorganic acid.

4. A process as claimed in claim 3, wherein the inorganic acid is hydrochloric acid, sulphuric acid, a phosphoric acid, chlorous acid, hypochlorous acid, chloric acid or perchloric acid.

5. A process as claimed in claim 3 or claim 4, wherein the acid may be a mixture of more than one acid.

6. A process as claimed in claim 3, wherein the acid is a monoprotic acid, preferably hydrochloric acid.

7. A process as claimed in any of claims 3 to 6, wherein the acid is provided for mixing in a concentrated form.

8. A process as claimed in claim 7, wherein, in order of increasing preference, the concentration of the acid before mixing is greater than 0.5M, greater than 1 .0M, or greater than 3.0M.

9. A process as claimed in any of the preceding claims, wherein the source of iodide ions is potassium iodide or sodium iodide.

10. A process as claimed in any of the preceding claims, wherein the inorganic base is a hydroxide or carbonate of an alkaline metal or alkaline earth metal.

1 1 . A process as claimed in claim 1 0, wherein the alkali metal is selected from sodium and potassium and the alkaline earth metal is selected from magnesium and calcium.

12. A process as claimed in claim 10, wherein the base is a hydroxide.

13. A process as claimed in any of claims 1 0 to 1 2, wherein the base is selected from sodium hydroxide, potassium hydroxide and calcium hydroxide.

14. A process as claimed in any of the preceding claims, wherein the inorganic acid salt is an alkali metal bisulphate or bicarbonate or a hydrogen phosphate salt of an alkali metal or alkaline earth metal.

15. A process as claimed in claim 14, wherein the inorganic acid salt is sodium hydrogen sulphate or potassium hydrogen sulphate.

16. A process as claimed in any of the preceding claims, which includes the step of mixing the first component and the second component in an appropriate ratio.

17. A process as claimed in any of the preceding claims, wherein one or both components may be diluted prior to mixing of the components.

18. A process as claimed in any of the preceding claims, wherein the first component and/or the second component may independently contain one or more further additive.

19. A process as claimed in claim 18, wherein the one or more further additive may be selected from surfactants, corrosion inhibitors and stabilisers.

20. A process as claimed in any of the preceding claims, which produces a liquid chlorine dioxide solution.

21 . A kit for extemporaneous preparation of a chlorine dioxide containing disinfectant solution prepared according to the process of any of the preceding claims.

22. A kit for extemporaneous preparation of a chlorine dioxide containing disinfectant solution, the kit including a container of a first component comprising a solution of a compound containing chlorine in the +1 oxidation state, a source of H+ ions and a source of iodide ions; and a container of a second component which comprises an inorganic base and an inorganic acid salt, such that the first and second component may be mixed when required to form the disinfectant solution.

23. A kit as claimed in claim 22, wherein one of the containers provides a reactor in which to mix the components and generate the chlorine dioxide containing disinfectant solution.