WO2015078830A1

WO2015078830A1 - Aqueous solution suitable for the chemical sterilization of packaging materials, process for its preparation and its use

Info

Publication number: WO2015078830A1
Application number: PCT/EP2014/075459
Authority: WO
Inventors: Paul Deschrijver
Original assignee: Solvay Sa
Priority date: 2013-11-26
Filing date: 2014-11-25
Publication date: 2015-06-04

Abstract

Aqueous solution suitable for the chemical sterilization of packaging materials, process for its preparation and its use Aqueous hydrogen peroxide solution containing 10-50%wt hydrogen peroxide and 10-50 ppm in weight of citric acid with a dry residue at 230°C of at most 10mg/kg.

Description

Aqueous solution suitable for the chemical sterilization of packaging materials, process for its preparation and its use

This application claims priority to European application N° EP 13194351.6 filed on November 26, 2013, the whole content of this application being incorporated herein by reference for all purposes.

The present invention is related to aqueous solutions suitable for the chemical sterilization of packaging materials, especially those containing hydrogen peroxide. It is also related to a process for the preparation of these aqueous solutions and to their use for the chemical sterilization of packaging materials.

It is known to use hydrogen peroxide solutions for the chemical

sterilization of packaging materials. Two such aseptic packaging processes exist. The first is a dip bath packaging process, in which the packaging materials are dipped in the hydrogen peroxide solution. The second is a spray packaging process, in which the packaging materials are purged with a hydrogen peroxide solution. The hydrogen peroxide solutions used in these processes must have a very low dry residue in order to prevent incrustations in the evaporator or spraying section and to avoid thereby frequent cleaning. The dry residues can, amongst others, originate from the stabilizers present in the H2O2 solution. Thus, the spray technology requires a low amount of stabilizer.

To this end, patent application EP 1926502 in the name of the Applicant discloses an aqueous solution suitable for the chemical sterilization of packaging materials, comprising hydrogen peroxide and at least one foodstuff-compatible stabilizer, wherein the said solution but without the foodstuff-compatible stabilizer has a maximum phosphorous content expressed as P0₄ ^3~of 10 mg/kg, and presents a dry residue at 105°C of at most 10 mg/kg. The foodstuff- compatible stabilizer disclosed therein is a phosphonic acid, preferably aminotrismethylene phosphonic acid. It is explained therein that the use of a foodstuff-compatible stabilizer preferably in a sufficiently low amount, combined with a low amount of impurities present in the solution before addition of the foodstuff-compatible stabilizer, allows to yield a low dry residue. Although this solution gives indeed good results in practice, alternative stabilizers have been sought to provide improved performance on high temperature aseptic filling machines.

In recent years, new aseptic packaging machines were developed, among which some spray machines which work at higher temperature namely of about 230°C and higher, versus 100-130°C in the past. Such machines are namely manufactured by the company SIG Combibloc.

US 2009/0263539 discloses a peroxide solution for aseptic packaging processes, namely spraying processes, which solution comprises an enzyme, a carboxylic acid (among which citric acid), a percarboxylic acid, up to 0.5%wt of hydrogen peroxide and a stabilizer which may be citric acid in an amount of at least 0.01% i.e. 100 ppm. This solution is heated only to about 40 to 65°C.

It is also known to use citric acid as buffer/stabilizer/antioxydant in diluted hydrogen peroxide solutions for instance in skin disinfection or hair treatment.

The Applicant has now found that surprisingly, citric acid can be used as stabilizer in spraying machines working with more concentrated hydrogen peroxide solutions at high temperature (typically of about 230°C and higher as explained above) without leaving much residue and that the little amount of residue left can be cleaned with water, preferably hot water or steam, even without dismantling the spraying machines. This finding is surprising because similar volatile carboxylic acids which are also foodstuff-compatible were not effective as stabilizers for hydrogen peroxide solutions, at least not in the low concentration range required to have a low dry residue.

To this end, the present invention concerns an aqueous hydrogen peroxide solution containing 10-50%wt hydrogen peroxide and 10-50 ppm in weight of citric acid. In one embodiment, this solution consists essentially of water, hydrogen peroxide and citric acid, which means that it only contains those constituents and eventually impurities but at a level below the ppm.

The solution according to the invention preferably does not contain any other stabilizer than citric acid and more particularly: does not contain a tin stabilizer. It may however contain an acid, more specifically nitric acid, in an amount of 20 ppm or less. Hence, in another preferred embodiment of the invention, the solution consists essentially of water, hydrogen peroxide, citric acid and a mineral acid, preferably nitric acid. The aqueous solution of the invention generally presents a conductivity of from 20 to 150 μΞ/α , particularly from 50 to 90 μΞ/α , preferably from 50 to 60 μΞ/α . The conductivity is measured according to the method of the standard DIN IEC 60746-1. The conductivity of the aqueous solution can de adjusted by the addition therein of a salt, such as for instance ammonium nitrate.

The aqueous solution of the invention preferably presents a dry residue (or NVM or Non Volatile Matter) at 105 °C of at most 20 mg/kg. The aqueous solution of the invention preferably presents a dry residue at 130 °C of at most 15 mg/kg. The aqueous solution of the invention preferably presents a dry residue at 230 °C of at most 10 mg/kg.

The dry residue is measured on the solution by a gravimetric method according to the following procedure:

1. Place a platinum dish in a muffle furnace at 900 °C for 1 h.

2. Cool the dish in a dessicator and then weigh to the nearest 0.0001 g; let this weight be B, g.

3. Weigh to the nearest 0.0001 g a 100 ml beaker and record the weight; add to this beaker :

• 100 g of sample (if the H₂0₂ concentration is 50 % or lower)

• 50 g of sample (if the H₂0₂ concentration is higher than 50 %).

4. Reweigh the beaker to the nearest 0.0001 g. The weight difference of the beaker before and after the sample addition will be W, g.

5. Dilute the sample to approximately 100 ml with demineralised water if using 50 g of sample.

6. Transfer progressively and carefully the sample into a platinum evaporating dish, surrounded by cold water. If the dish is extremely clean (it will be shiny), it would be iced down. Caution must be taken: the decomposition of hydrogen peroxide is accompanied by the production of substantial amount of heat and gas formation; sample must be added carefully, in small portions, with adequate cooling.

7. Evaporate the solution carefully until dry, on the steam bath. Caution must be taken: failure to completely decompose the hydrogen peroxide prior to evaporation could concentrate the sample sufficiently to produce an explosion hazard.

8. Place the dish in an oven at 105°C, 130 or 230°C (depending on the test temperature required)

9. Cool in a dessicator for 30 minutes and weigh the dish to the nearest 0.0001 g. Let this weight be A, g.

10. Calculate the residue at 105 °C using the equation : Residue at 105 °C, g/kg = x 1000

W

Where :

• A (in g) is the weight of the dish containing the evaporation residue

• B (in g) is the weight of the empty dish

· W (in g) is the weight of the sample added to the dish.

The aqueous solution of the invention usually presents a hydrogen peroxide concentration of from 10 to 50 % wt, in particular from 20 to 45 % wt, most preferably from 30 to 40 % wt, typically of about 35 % wt. The hydrogen peroxide concentration is measured according to the ISO standard 7157 (draft version).

The aqueous solution of the invention contains citric acid as a foodstuff- compatible stabilizer and in an amount of between 10 and 50 ppm, preferably between 20 and 40 ppm.

Due to the presence of this stabilizer, the hydrogen peroxide concentration in the aqueous solution of the invention presents a high stability at room temperature i.e. typically at 30°C or lower. It is usually so that the relative percentage of titration loss after 1 year at room temperature is lower than or equal to 1 % of the initial hydrogen peroxide concentration. The stability is measured according to the method of the ISO standard 7161 (draft version).

The aqueous solution of the present invention can be prepared by any adequate method which allows to prepare an aqueous solution of hydrogen peroxide, to purify it to such an extent that it contains no impurities at a level above the ppm, and by adding thereto citric acid as described above.

A possible process for the preparation of a hydrogen peroxide solution consists in the well known auto -oxidation process using anthraquinones.

A possible process for the purification of the so obtained hydrogen peroxide solution consists in treating the hydrogen peroxide solution by reverse osmosis using a membrane. Examples can be found in the patent applications EP 0930269 and WO2005/033005 in the name of the Applicant.

The invention therefore also concerns a process for the preparation of the aqueous solution described above, wherein the hydrogen peroxide solution, before adding thereto citric acid, is purified by reverse osmosis using a membrane.

The aqueous solution of the invention can advantageously be used for the chemical sterilization of packaging materials. The invention is therefore also related to the use of the aqueous solution described above for the chemical sterilization of packaging materials.

One of the advantages of the aqueous solution of the invention resides in the fact that the same solution can be used in spray aseptic packaging processes especially at high temperatures, preferably above 150°C, more preferable above 200°C and typically, between 230 and 290°C.

Therefore, the present invention also concerns the use of the above described H202 solution in spray aseptic packaging processes preferably at a temperature above 150°C, more preferable above 200°C and typically, between 230 and 290°C.

Due to the low stabilizer content, the risk of incrustations and blockages in the heaters of a spray packaging machine is minimized. And should there be such incrustations, it was found that these are easy to clean with water, preferably hot water or steam, even without dismantling the spray machine.

Therefore, the present invention also concerns the use of the above described H202 solution in aseptic packaging processes using a spray machine, wherein said machine is cleaned with water, preferably hot water or steam.

The cleaning water can have a temperature from "ambient" (above 5°C generally for tap water) up to 40°C and even, up to 60°C.

The invention is further described by way of illustration in the following examples.

Example 1: Stabilizing efficiency of citric acid versus other foodstuff- compatible volatile carboxylic acids

Several stabilisers were tested by adding them in different concentrations and/or different combinations to a 35% H202 solution.

The stability of the preparations (lh, 96 °C) was measured and compared to the stability of an existing spray grade (also a 35% H202 solution).

For this test, a sample of at least 25 ml is heated at 96 °C for one hour; the volume of oxygen evolved is collected in a gas burette. The volume of oxygen is measured and the stability is calculated as follows:

First, the volume of oxygen liberated per minute by 25 ml of the sample at 96°C, or ml02, is calculated.

Then, the "absolute" stability is obtained by expressing the stability in g of H202 decomposed after 1 hour for 1 kg of 100 % hydrogen peroxide

(gH2O2/h.kgH202). This absolute stability is hence calculated according to the following equation: Absolute stability (gH2O2/h.kgH202) =

ml02 * 273/T * P/1013*60/(25*d)*(2*34)/22.4* 1000/C =

mo 102* 1963 *P/(T*d*C)

where :

T = room temperature, in K

P = room pressure, in hPa

d = density of the hydrogen peroxide solution, in kg/1

C = concentration of the hydrogen peroxide, in g/kg

The compositions tested and the results obtained are summarized in Table 1 below:

Example 2: Dry residue (NVM or non volatile matter)

Table 2 below shows the NVM values measured according to the method disclosed above, on the compositions indicated

Product / Stabiliser NVM mg/kg

105°C 130 °C 230 °C

Commercial Spray grade 5.2 4.4 3.2

H202 35% + Citric Acid 20 12.2 4.5 1.6 mg/Kg

H202 35% + Citric Acid 30 17.2 6.8 2.0 mg/Kg

H202 35% + Citric Acid 50 42.1 14.8 7.2 mg/Kg

Example 3: Long term storage stability

The shelf life at 25 and 30°C was determined in laboratory conditions for Citric acid 20 and 30 ppm and compared to a commercial spray grade.

The different stabilisers were tested by adding the correct quantity to a 35%) Η₂0₂ solution in passivated glass bottles with a vented cap. The solutions obtained were stored in climatized room at 25 °C and 30°C during at least 12 months and measured for their H₂0₂ content in regular intervals (once a month). The results are shown in Figures 1 and 2 attached.

Example 4: Testing on aseptic filling machines

Solution used: 35% aqueous H202 solution with 20mg/kg Citric Acid and 8 mg/Kg Nitric Acid

A. Tests were made with a CFA 606 FP filling machine SIG Combibloc. For each test 1 ,000 liters of peroxide were evaporated. This equals a net production time of 257 hours, which is approx. twice the actual prescribed interval between two cleanings of the peroxide heaters. In these tests, approx. 3.9 liters peroxide per hour were evaporated at a temperature of 250 to 290°C. The amount of residue formed was about the same or even less than with the standard commercial spray grade and although it looked dark and compact, it was easy to clean.

B. Tests were made with a CFA 712-32 filling machine from SIG Combibloc at a temperature of about 270°C. There was little dry residue so that the machine could run during 1 month in normal industrial conditions without having to be cleaned and said residue was easy to clean.

Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

Claims

C L A I M S

1 - Aqueous hydrogen peroxide solution containing 10-50%wt hydrogen peroxide and 10-50 ppm in weight of citric acid, characterized in that it presents a dry residue at 230 °C of at most 10 mg/kg. 2 - Aqueous solution according to claim 1, characterized in that it consists essentially of water, hydrogen peroxide and citric acid.

3 - Aqueous solution according to claim 1, characterized in that it presents a conductivity of from 20 to 150 μΞ/α .

4 - Aqueous solution according to claim 3, characterized in that it contains nitric acid in an amount of 20 ppm or less.

5 - Aqueous solution according to claims 3 or 4, characterized in that it consists essentially of water, hydrogen peroxide, citric acid and nitric acid.

6 - Aqueous solution according to any one of claims 1 to 5, characterized in that it presents a maximum acidity of 5 mmol/kg. 7 - Aqueous solution according to any one of claims 1 to 6, characterized in that it presents a dry residue at 105 °C of at most 20 mg/kg.

8 - Aqueous solution according to any one of claims 1 to 7, characterized in that it presents a dry residue at 130 °C of at most 15 mg/kg.

9 - Aqueous solution according to any one of claims 1 to 8, characterized in that it presents a hydrogen peroxide concentration of from 20 to 45 % wt.

10 - Aqueous solution according to any one of claims 1 to 9,

characterized in that the relative percentage of titration loss after 1 year at room temperature is lower than or equal to 1 % of the initial hydrogen peroxide concentration. 11 - Process for the preparation of the aqueous solution of any one of claims 1 to 10, wherein the hydrogen peroxide solution, before adding thereto the citric acid, is purified by reverse osmosis using a membrane. 12 - Use of the aqueous solution of any one of claims 1 to 10 for the chemical sterilization of packaging materials.

13 - Use according to claim 12, wherein the solution is used in a spray aseptic packaging process at a temperature of 150°C or higher. 14 - Use according to claim 13, wherein said process uses a machine which is cleaned with water, preferably hot water or steam.