Patent Description:
Hydrogen peroxide (H<NUM>O<NUM>) is the dominant chemical used for sterilization of material surfaces. Aseptic packaging of dairies and beverages and sterilization of medical devices are some examples of such applications. In the so-called Vapor Hydrogen Peroxide (VHP) aseptic decontamination process, the beverage containers, closures, and aseptic filling equipment are treated with a hydrogen peroxide vapour. The hydrogen peroxide solutions used for evaporation in this process must produce a very low dry residue in order to prevent incrustations in the evaporator or spraying equipment to avoid production downtime caused by frequent cleaning or damage of the equipment. The dry residues can originate primarily from the added stabilizers and to a lesser extent from the impurities present in the H<NUM>O<NUM> solutions. On the other hand, hydrogen peroxide must be stable during production, transportation, storage and handling. In some cases, it should be possible to store H<NUM>O<NUM> solution up to one year without any significant decomposition thereof. Such a high stability is usually achieved by addition of suitable stabilizers. These stabilizers are commonly non-volatile chemicals, which contribute to residue formation on vaporization. Much effort has been made to reduce the residue levels caused by the presence of stabilizers.

<CIT> discloses an aqueous hydrogen peroxide solution suitable for chemical sterilization of packaging materials comprising at least one stabilizer, wherein the said solution but without the stabilizer has a maximum phosphate content of <NUM>/kg and a dry residue at <NUM> of at most <NUM>/kg. Such a H<NUM>O<NUM> solution feedstock was prepared by the anthraquinone process followed by a reverse osmosis purification using the membrane SWC3 at <NUM> bar. It is emphasized in this patent application that it is necessary to stabilize the thus obtained purified hydrogen peroxide solution with <NUM> / kg H<NUM>O<NUM> solution of aminotrismethylene phosphonic acid prior to its use in spray aseptic packaging machines.

Similarly, <CIT> discloses aqueous solutions suitable for the chemical sterilization of packaging materials containing <NUM>-<NUM> wt% of hydrogen peroxide with a dry residue at <NUM> of at most <NUM>/kg (<NUM>-<NUM>/kg at <NUM>) containing <NUM>-<NUM> ppm of citric acid as a stabilizer. The stabilized solution of H<NUM>O<NUM> according to <CIT> was shown to be stable for <NUM> months at <NUM>.

<CIT> discloses <NUM>-<NUM> wt% hydrogen peroxide solutions suitable for vapour packaging sterilization, which contain no more than <NUM> ppb Fe, at least <NUM> ppb Al and no more than <NUM> ppm of a stabilizer comprising orthophosphoric acid. Stability tests performed at room temperature showed that a non-stabilized H<NUM>O<NUM> solution containing no stabilizers and having an evaporation residue of < <NUM> ppm (comparative example <NUM>) was much less stable than the inventive solutions containing orthophosphoric acid as a stabilizer and evaporation residues of <NUM>-<NUM> ppm.

<CIT> describes a sterilization process using a hydrogen peroxide vapour made from an aqueous hydrogen peroxide solution having a dry residue of <NUM> ppm.

It is well known from the prior art that minimizing dry residue of hydrogen peroxide solutions will improve the performance for vapour packaging sterilization. However, all relevant documents of the prior art explicitly teach to add various stabilizers in order to achieve appropriate stability of such H<NUM>O<NUM> solutions, which inevitably increases the dry residue level of such stabilized solutions.

The inventors of the present patent application have surprisingly found that hydrogen peroxide solutions having dry residues at <NUM> of at most <NUM> ppm and typically containing no stabilizers, contrary to the teachings from the prior art, may be both stable and well suitable for using in vapour sterilization methods, if the content of some impurities, particularly transition metal ions, does not exceed a particular low level.

The object of the present invention is a process for sterilization or disinfection treatment, comprising the following steps:.

Aqueous hydrogen peroxide solution employed in the inventive process can be obtained by a well-known anthraquinone process (AO process), which generates hydrogen peroxide by hydrogenating a working solution of an alkylanthraquinone or an alkyltetrahydroanthraquinone in a water immiscible solvent and oxidizing the hydrogenated solution with molecular oxygen (O<NUM>), usually with air. The hydrogen peroxide is then extracted with water from the oxidized working solution in an extraction column and the working solution is reused for generating hydrogen peroxide. Furthermore, the aqueous hydrogen peroxide solution can be concentrated in a distillation. An overview of the anthraquinone process is given in <NPL>, and in particular in Fig. <NUM> on page <NUM>. A possible process for the purification of the H<NUM>O<NUM> solution, e.g. that obtained by the above-described AO process, may include at least one further distillation, treatment with ion-exchange resin and/or reverse osmosis using a membrane. Examples of purification processes based on reversed osmosis can be found in the patent applications <CIT> and <CIT>. The exact purification procedure for obtaining the purified hydrogen peroxide solution to be employed in the inventive process should be selected based on the nature and concentrations of the impurities present in the used unpurified H<NUM>O<NUM> solution. The main criterium of selecting the suitable production and purification method for a hydrogen peroxide solution is that it will provide an H<NUM>O<NUM> solution having a dry residue at <NUM> of at most <NUM> ppm and a total content of Fe, Cr, Mn and Ni in the solution of at most <NUM> ppb, without containing any added stabilizer. The total content of Fe, Cr, Mn and Ni in the solution of at most <NUM> ppm belongs to the content of all mentioned metal species together. The metal analysis was performed by ICP-MS, which can detect any form of these metals in solution, therefore the metals do not have to be in elemental form, and metals in different forms will not affect the quantitative analysis results. However, preferably the metals are present as cations in hydrogen peroxide solution and can be detected accordingly.

The dry residue of the hydrogen peroxide solution determined at <NUM>, also referred to as "dry residue at <NUM>" in the present patent application, can be measured by the gravimetric method according to the following procedure, which is common in the field and is also similar to the procedure described in <CIT>:.

The aqueous hydrogen peroxide solution employed in step a) of the process according to the invention has a dry residue determined at <NUM>, e.g. according to the method describe above, of at most <NUM> ppm, preferably at most <NUM> ppm. Most preferably, the dry residue at <NUM> is below the level detectable by this method, i.e. essentially no dry residue exceeding the error of the method can be determined by this method.

The non-volatile impurities in the employed hydrogen peroxide solution are usually in a lower ppb range. Some organic impurities may be present in the H<NUM>O<NUM> solution in a lower ppm range, but they are usually either volatile or degradable during the evaporation, and therefore leave little residue after the hydrogen peroxide is vaporized.

Importantly, to achieve such a low dry residue levels, very low total amounts of H<NUM>O<NUM> stabilizers, especially of non-volatile H<NUM>O<NUM> stabilizers, e.g. at most about <NUM> ppm, preferably at most about <NUM> ppm, more preferably at most about <NUM> ppm, more preferably at most about <NUM> ppm, more preferably no such H<NUM>O<NUM> stabilizers at all, should be present or be added to the solution.

The term "non-volatile" refers in the context of the present invention to the components, which cannot be vaporized at <NUM>, i.e. remain at least partly in the dry residue obtained after drying of the residue at <NUM> as described above.

The hydrogen peroxide solution used in the inventive process preferably contains no H<NUM>O<NUM> stabilizers at all, neither the volatile, nor the non-volatile ones. Unnecessary stabilizer chemicals may be harmful, increasing the residue level and accelerating corrosion.

The term "H<NUM>O<NUM> stabilizer" refers to any additive added to slow down the H<NUM>O<NUM> decomposition. Such H<NUM>O<NUM> stabilizers of various types are well known from the prior art.

Metal ions, particularly transition metal ions can initiate hydrogen peroxide decomposition. Activity of the different metal ions varies significantly; some metal impurities may act synergistically. Since the most equipment for producing of hydrogen peroxide solution is made of stainless steel, the primary metal impurities to initiate peroxide decomposition are believed to be the components of the stainless steel such as iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn) and copper (Cu).

The total content of Fe, Cr, Mn and Ni in the hydrogen peroxide solution employed in the inventive process is at most <NUM> ppb, preferably at most <NUM> ppb, more preferably at most <NUM> ppb, as determined by Inductively Coupled Plasma - Mass Spectrometry (ICP-MS) analysis. The ICP-MS method is known to those skilled in the art to provide reliable analysis results for determining of very low metal concentrations in the solution.

The Cu content in the employed hydrogen peroxide solution is preferably at most <NUM> ppb, more preferably at most <NUM> ppb, more preferably at most <NUM> ppb, as determined by ICP-MS analysis.

The Cr content in the employed hydrogen peroxide solution is preferably at most <NUM> ppb, more preferably at most <NUM> ppb, more preferably at most <NUM> ppb, as determined by ICP-MS analysis.

The Fe content in the employed hydrogen peroxide solution is preferably at most <NUM> ppb, more preferably at most <NUM> ppb, more preferably at most <NUM> ppb, as determined by ICP-MS analysis.

The Mn content in the employed hydrogen peroxide solution is preferably at most <NUM> ppb, more preferably at most <NUM> ppb, more preferably at most <NUM> ppb, as determined by ICP-MS analysis.

The Ni content in the employed hydrogen peroxide solution is preferably at most <NUM> ppb, more preferably at most <NUM> ppb, more preferably at most <NUM> ppb, as determined by ICP-MS analysis.

The total content of all metals in the employed hydrogen peroxide solution is preferably at most <NUM> ppb, more preferably at most <NUM> ppb, more preferably at most <NUM> ppb, as determined by ICP-MS analysis.

The ppm and ppb values are calculated defined as weight data.

The usual construction materials for the equipment suitable for storage and use of the hydrogen peroxide solution before and during the inventive process include specific polymers and metals. For long-term storage of H<NUM>O<NUM> solutions used in the inventive process, polymers such as high-density polyethylene (HDPE) and polytetrafluoroethylene (PTFE) are most suitable. Aluminum, preferably of types <NUM>, <NUM>, <NUM> and stainless steel, preferably of types <NUM>, <NUM>, <NUM> and <NUM> can be used for pieces of equipment that will have a short contact time with the peroxide, such as pumps, valves, or small buffer containers. Glass can be used as a suitable construction material in certain cases, e.g. for lab experiments or stability tests.

The hydrogen peroxide solution used in the inventive process preferably has an active oxygen loss of no more than <NUM> wt-%, preferably of no more than <NUM> wt-%, as determined after heating the solution for <NUM> hours at <NUM> in a glass vessel.

The hydrogen peroxide solution employed in the process of the invention is preferably suitable for storing for at least four days, more preferably for at least <NUM> days, more preferably for at least <NUM> days in an appropriate stainless steel (e.g. of types <NUM>, <NUM>, <NUM> and/or <NUM>) or aluminum (e.g. aluminium of types <NUM>, <NUM>, and/or <NUM>) container at <NUM>- <NUM> temperature, preferably under room temperature of <NUM>-<NUM>, most preferably under room temperature of <NUM> with a peroxide concentration drop of less than <NUM> wt%.

Hydrogen peroxide concentration drop can be determined according to the ISO <NUM> by a titration method.

The hydrogen peroxide solution used in the inventive process preferably contains <NUM>% to <NUM>%, more preferably <NUM>% to <NUM>%, more preferably <NUM>% to <NUM>%, by weight of hydrogen peroxide. The hydrogen peroxide content can be measured according to the ISO <NUM> by a titration method.

The acidity of the solution (as H<NUM>SO<NUM> equivalent) in the invention usually does not exceed <NUM> ppm, preferably not more than <NUM> ppm.

The used hydrogen peroxide solution can have a pH of <NUM>-<NUM>, preferably <NUM>-<NUM>.

The aqueous H<NUM>O<NUM> solution employed in the inventive process preferably presents a conductivity of from <NUM> to <NUM>/cm, more preferably from <NUM> to <NUM>/cm, more preferably from <NUM> to <NUM>/cm. The conductivity can be measured according to the method of the standard DIN IEC <NUM>- <NUM>. The conductivity of the employed hydrogen peroxide solution is low and can be adjusted by adding nitric acid when higher conductivity is needed. The conductivity of the hydrogen peroxide solutions can be roughly increased by <NUM>/cm per ppm nitric acid addition.

Preferably, the performed sterilization and/or disinfection treatment of an object is performed for a few seconds, more preferably <NUM>-<NUM> seconds, most preferred <NUM>-<NUM> seconds.

The inventive process can advantageously be used for different types of sterilization and disinfection treatments, particularly for the chemical sterilization of packaging materials by hydrogen peroxide vapor in aseptic packaging processes.

The object to be sterilized can preferably be selected from the group consisting of packaging materials such as beverage and dairy containers, cartons, bottles, caps and other closures, as well as vessels, aseptic and other cold-fill shelf-stable filling equipment and machinery, ambulance or rooms, and medical devices. The inventive method is not limited to sterilization. The objects such as fruits and vegetables can also be disinfected with the vaporized hydrogen peroxide by the inventive process.

In the inventive process, the hydrogen peroxide vapor can be produced by evaporation or vaporization of the hydrogen peroxide solution. Evaporation or vaporization of the H<NUM>O<NUM> solution can be achieved e.g. under normal (<NUM> atm), reduced (< <NUM> atm) or increased (> <NUM> atm) pressure optionally followed by spraying thereof onto the object to be sterilized. H<NUM>O<NUM> solution can be heated, e.g. to at least <NUM> prior to or during the evaporation. Evaporation or vaporization of the hydrogen peroxide solution can also be affected by passing a stream of a carrier gas, e.g. air or nitrogen through the evaporator or vaporizer.

The particular advantage of the employed H<NUM>O<NUM> solution for the inventive process resides in the combination of (<NUM>) the high stability of the hydrogen peroxide solution and (<NUM>) very low dry residue of this H<NUM>O<NUM> solution.

As a result, the process of the invention can be carried out for at least <NUM> hours, preferably for at least <NUM> hours, more preferably for at least <NUM> hours without the need to clean the residue after obtaining the hydrogen peroxide vapour in step a) of the process. In most cases, no cleaning at all will be required for a usual operation time of the continuously used evaporation equipment before the usual maintenance service, e.g. once in a year thereof. The residue referees to any non-volatile impurities left in the heaters. It can coat on the heating surfaces, decrease the heat transfer rate, corrode the surface and contaminate customer's products. So the residue must be removed periodically. Chemical and mechanical cleanings are usually performed. The cleaning can cause a major production down time, and damage the expensive heating parts.

Samples #<NUM>-#<NUM> of <NUM>% wt% unstabilized hydrogen peroxide solutions with low metal contents were prepared by the known from the prior art purification methods of hydrogen peroxide solution prepared from the anthraquinone process, such as by ion-exchange resin treatment, distillation and/or reversed osmosis.

The decomposition rate of <NUM>% wt% unstabilized hydrogen peroxide solutions in HDPE bottles with a vented cap at room temperature (<NUM>) was measured by determining the assay drop and the H<NUM>O<NUM> loss. The assay drop was the differential decrease of hydrogen peroxide concentration after <NUM> days. the H<NUM>O<NUM> loss was the decrease of hydrogen peroxide in <NUM>% basis from <NUM> of the test solution after <NUM> days. The dependence of the hydrogen peroxide decomposition rate on impurity concentrations can be seen from the comparison of the test results in Tables 1a and 1b.

Samples #<NUM>-#<NUM> of <NUM>% wt% unstabilized hydrogen peroxide solutions with higher metal contents were prepared by the known from the prior art purification methods of hydrogen peroxide solution prepared from the anthraquinone process by ion-exchange resin treatment, distillation and/or reversed osmosis.

The decomposition rate of the <NUM>% wt% unstabilized hydrogen peroxide solutions in HDPE bottles with a vented cap at room temperature (<NUM>) was measured by determining the assay drop and the H<NUM>O<NUM> loss after <NUM> days of storage. The results are summarized in Table 1b.

It can be seen from the results that increase in the metal impurity level of the unstabilized H<NUM>O<NUM> solutions from the samples in Table 1a to those of Table 1b led to a significant increase in the decomposition rate of the latter samples.

The starting hydrogen peroxide solution for sample #<NUM> was stored in HDPE bottles with a vented cap under three different temperatures: <NUM>, <NUM> and <NUM>, respectively. The decomposition rates of these unstabilized hydrogen peroxide solutions (samples #<NUM>-<NUM>) at the specified temperatures were measured in HDPE bottles with a vented cap, for each tested sample twice, by determining the assay drop and the H<NUM>O<NUM> loss after <NUM>st <NUM> and <NUM>nd <NUM> days of storage, respectively.

The results are shown in Table <NUM>. It was observed that there was no problem to store this unstabilized hydrogen peroxide solution under slightly elevated temperature. The hydrogen peroxide concentration after <NUM> days remained almost unchanged after the storage at <NUM> (positive values of the assay drop), and actually increased under elevated temperatures, due to the evaporation of the solution. H<NUM>O<NUM> loss even after <NUM> days of storage at <NUM> was still below <NUM>% (<NUM> per <NUM>) of the solution. The decomposition rates of the peroxide in the second <NUM> days test was similar to the first <NUM> days test.

The starting hydrogen peroxide solution for sample #<NUM> was exposed to SS (stainless steel) coupons in glass Kjeldahl flasks. Both glassware and coupons were passivated by following industry's standards. <NUM> solution was in contact with each coupon (<NUM>" x <NUM>" x <NUM>") at <NUM> initially and the samples were analysed twice: after a <NUM>-days period and then after a <NUM>-days period (total of <NUM> days). Then the samples (#22a and 22b) were moved into an incubator at <NUM>, and kept in it for another <NUM>-days period before a third analysis for the samples.

Additionally, a stabilized hydrogen peroxide solution sample #<NUM> was prepared by adding 1ppm of amino tris(methylenephosphonic acid) (ATMP), a common H<NUM>O<NUM> stabilizer, to the same starting solution as for sample #<NUM> and tested under the same conditions as the unstabilized samples #22a/#22b. Blank samples (the same peroxide solutions to samples #21a/#21b and #22a/#22b but without SS coupons) were also run in parallel as a reference.

The decomposition rates of the unstabilized samples #22a/#22b and the stabilized samples #21a/#21b at the specified temperatures and times are summarized in Table <NUM>.

Stainless steel is the primary construction material for aseptic filling machines. The accumulative contact time of the hydrogen solution with stainless steel in these machines can be up to four days under ambient conditions and even longer.

When both solutions were in contact with stainless steel coupons, the peroxide solution with <NUM> ppm ATMP was slightly more stable for the first <NUM> days under room temperature (<NUM>-<NUM>). However, after the samples were moved into an incubator and stored for another <NUM> days at <NUM>, the hydrogen peroxide containing <NUM> ppm ATMP surprisingly started to decompose even faster than the sample without ATMP. The ATMP in the peroxide might promote more metal leaching than stabilizing the metals.

Unstabilized <NUM>% wt% hydrogen peroxide solution (<NUM>) from the starting solution of sample #<NUM> was slowly evaporated in a Pt crucible according to steps <NUM>-<NUM> of the method described in the description above. Almost no residue could be visually observed in the crucible, as shown in <FIG>. The residue value was too low to be quantitatively determined (below <NUM> ppm).

The residue test described in example <NUM> was repeated using <NUM> of a commercially available stabilized premium hydrogen peroxide solution for vapor applications. A significant amount of a residue was formed from the hydrogen peroxide as can be seen in <FIG>.

Claim 1:
A process for a sterilization or disinfection treatment, comprising the following steps:
a) obtaining a hydrogen peroxide vapour from an aqueous hydrogen peroxide solution containing no stabilizer and having a dry residue determined at <NUM> of at most <NUM> ppm and a total content of Fe, Cr, Mn and Ni in the solution of at most <NUM> ppb as determined by ICP-MS analysis;
b) sterilization or disinfection treatment of an object to be sterilized or disinfected with a hydrogen peroxide vapour obtained in step a).