The present invention refers to a new type of oxygen absorbers, a method for their activation and the use of such absorbers in anaerobic environments.

Oxygen absorbers, also commonly referred to in the technical field with the term "oxygen scavengers", have a variety of applications. Among the most common ones there are food and medicine preservation. At industrial level there is a wide spectrum of other possible applications, spanning from the use within metallic piping in order to prevent corrosion, such as the ones for oil transportation, to the use within solid state or organic electronic systems, in order to prevent oxidation and degradation of the components installed therein. The most important devices of this latter category are OLED screens (Organic Light Emitting Display) and Organic Solar Cells (OSC). Another field of application of particular relevance is given by chemical syntheses or preparations that in intermediate process phases may be subject to the undesired generation of oxygen, which leads to the needing of its removal.

In this technical field, the use of zeolites exchanged with a metallic element is known, as disclosed in patent US 5,798,055, which describes a manufacturing process for zeolites exchanged with various metals brought to the zero valence state by means of a reduction phase in hydrogen.

In this case the oxygen scavenger remains essentially inert to oxygen until it is exposed to a meaningful concentration of humidity, which activates its function of O ₂ scavenger. In particular, US 5,798,055 discloses a preferred mode of use that provides for heating of the scavenger precursor once installed within the device in order to ease the H ₂ O generation in the anaerobic environment and therefore trigger the functionality of the activated scavenger.

This type of solution has two different problems, the first one regarding the necessity of the presence of H ₂ O in the closed environment for an effective O ₂ sorption that is incompatible with many final application. A typical example in this case is provided by the organo-electronic devices, where the presence of H ₂ O is detrimental to the features of the device and therefore cannot be guarantee. The second problem is related to the scavenger preservation, that must be made in an anhydrous environment in order to avoid its premature activation and the consequent loss of capacity.

Both the above described problems are common to several oxygen scavengers described in the prior art. As example, the international patent application published as WO 99/47351 discloses an alternative oxygen scavenging composition based on hydroxosulfϊtometalate on inorganic support. Also in this case it is pointed out that the oxygen scavenging composition must be maintained in the absence of oxygen or moisture during storage.

Similarly, the international patent application published as WO 97/06104 describes the use of metallic mixture, as for example iron and manganese both in their zero valence state and supported on porous means. A reduction step in the production process is required in order to guarantee the absence of water in the purified gas and the oxygen scavenger is used mixed to a drying material.

Object of the present invention is to provide a new and efficient oxygen scavenger precursor composition, which can overcome the problems of the prior art. This oxygen scavenger precursor composition comprise microporous aluminosilicates exchanged with bivalent metallic ions having a silica to alumina molar ratio comprised between 1.5 and 5 characterized in that said bivalent exchanged aluminosilicates are in their hydrated form.

Among the advantages deriving from the use of the scavenger precursor composition of the invention, there is the possibility of storing and shipping them without particularly caring about the exposure to air. These scavengers are inert to air because, being pre-saturated with H ₂ O as a consequence of the production process of the exchanged aluminosilicates. H ₂ O occupies essentially all the sites active for the removal of O ₂ . In other words, H ₂ O molecules occupy a number of active sites that is consequence of the thermodynamical equilibrium with the environmental humidity (generally equivalent to a water content comprise between 3.2 and 28% respect the total weight of the aluminosilicates) resulting in a limitated reactivity of the composition respect oxygen moleules until its activation treatment.

Although they are suitable to carry out the present invention, zeolites having a molar ratio silica to alumina lower than 2 require particular solutions in order to be manufactured. For this reason, in a preferred embodiment, such molar ratio is comprised between 2 and 2.5.

In the present description the definition "aluminosilicates" also encompasses structures that may optionally comprise other metals/substituents such as e.g. germanium as substituent within the reticular structure of some silicon atoms, or gallium as substituent of some aluminum atoms.

Among the aluminosilicates, zeolites known in the field as Faujasite X, Faujasite Y and LTA, also known with the term Linde type A, X, Y are particularly suitable to carry out the invention.

The use of aluminosilicates exchanged with chromium or copper and chromium as catalysts is disclosed in patent US 5,234,876, which teaches the use of aluminosilicates exchanged with trivalent chromium ions having a molar ratio silica to alumina comprised between 3 and 200. Differently from the present invention, US 5,234,876 discloses materials suitable for the manufacturing of honeycomb catalytic systems, that also exhibit different properties, with particular reference to thermal stability at very high temperatures that can reach even 1000 ⁰ C.

Patent US 3,503,901 describes the catalytic use of aluminosilicates exchanged with divalent ions, preferably in association with a noble metal loading (i.e. Palladium). Differently to the present invention, it describes material suitable for manufacturing catalytic systems useful for organic chemistry reactions, with particular reference to hydrocarbon conversion reaction.

The inventors have instead focused their studies on a different application and technical problem, namely the oxygen removal, for which they have found that the use of aluminosilicates having a molar ratio between silica (SiO ₂ ) and alumina

(Al ₂ O ₃ ) comprised between 1.5 and 5 exchanged with bivalent metallic ions is particularly advantageous

The aluminosilicates exchanged with bivalent ions, that are the object of the present invention, are typically used in the form of micrometric powders dispersed in a suitable polymeric matrix. In a preferred embodiment aluminosilicates are used in nanometric form, also in this case dispersed in a suitable polymeric matrix, the single elements of the matrix having a size below 400 nm. The expression "single element" means the single particle of the aluminosilicates.

Polymers with thermoplastic or thermosetting characteristics or, more generally, polymers and their precursors that do not interfere with the oxygen absorbing function of the dispersed material can be employed as polymeric matrix.

Suitable polymeric materials for carrying out the invention are, as a non- limiting example, vinyl polymers, polyesters, polyethers, polyamides, polymers deriving from condensation of phenolformaldehyde, polysiloxanes, ionic polymers, polyurethanes, epoxy resins, acrylates, styrene block copolymers (SBS or SEBS gums) and natural polymers such as cellulose. Particularly interesting are also polymers chosen from the polyolefm family, also comprising block co-polymers of the same, among which butyl rubber and ethyl-vinyl-acetate copolymers have a particular importance.

In a second aspect thereof, the invention relates to an activation process for oxygen scavenger precursor, which can overcome the problems of the prior art. This activation process consist in a thermal heating of the oxygen scavenger precursor composition comprising hydrated aluminosilicates exchanged with bivalent metallic ions having a silica to alumina molar ratio comprised between 1.5 and 5 and characterized in that the water amount removed by said activation process is comprised between 3 and 25 wt % respect to the aluminosilicate weight.

This mechanism is exploited for a quick and simple activation in situ, because the removal of H ₂ O reinstates the activity of the absorber versus oxygen. In this case it is very important to determine the correct characteristics of the activation process. If a small amount of H ₂ O is removed in fact, the competing mechanism between H ₂ O and oxygen on the active sites leads to a scavenger having a reduced capacity, whereas an activation process that removes an excessive amount of H ₂ O jeopardizes the O ₂ removal ability due to the catalytic action of the water in its absorption mechanism.

In particular, by employing the aluminosilicates object of the present invention, it has been found that an efficient activation process leads to a weight loss comprised between 5 and 20% after they have been saturated with H ₂ O. Obviously, in case of composite systems that comprise the aluminosilicates of the present invention, the estimation of the percentage weight loss shall be made with respect to the whole amount of aluminosilicates.

Such weight loss may be achieved by means of a suitable heating, typically carried out in vacuum or inert gas, for example by heating for a time ranging between 5 and 30 minutes and temperatures between 120 ⁰ C and 300 ⁰ C. Obviously, when low activation temperatures are used the corresponding activation times are longer. Atypical example of suitable activation process leading to a 7% weight loss can be achieved by heating at 200 ⁰ C for 10-15 minutes. In alternative, when heating is carried out in no inert conditions, scavenger properties can be substantially preserved simply limiting the exposure to the environment before its complete cooling.

In a third aspect thereof the invention relates to the use of aluminosilicates exchanged with bivalent metallic ions having a molar ratio between silica and alumina comprised between 1.5 and 5 for the removal of O ₂ from anaerobic environments, characterized in that said aluminosilicates have a water amount comprised between 0.2 and 3 wt% respect the aluminosilicates weight. These aluminosilicates are in fact the activated form of the oxygen precursor composition described above by the previous described aspect of the invention.

In a preferred embodiment the method provides for the use of aluminosilicates exchanged with bivalent ions of chromium, manganese or combinations of bivalent ions of chromium and manganese.

In another preferred embodiment the aluminosilicates are used in the form of powder dispersed in a suitable polymeric matrix, although the aluminosilicates may also possibly be used within suitable permeable containers or in pill form, in which a suitable binder is added to the zeolite in order to grant mechanical integrity.

The method may advantageously be applied in the case of food and medicine packaging, or used for oxygen removal from the internal atmosphere of electronic or organo-electronic devices, such as OLED screens and organic solar cells.

The method can also be advantageously used for the oxygen removal in chemical syntheses or preparations. EXAMPLE 1 :

A batch of oxygen scavenger was prepared by exchanging a Faujasite X with

Cr(II). The ion exchange reaction was performed in degassed, oxygen free water under inert atmosphere (Argon) by using Cr(Cl) ₂ at a concentration of 1 mol/liter for 10 minutes under stirring. The solid was rinsed with degassed deionized water under inert gas atmosphere using schlenk equipment. It was dried at ambient temperature overnight. The Zeolite changed is color from white to light blue.

Chemical analyses performed by means of ICP after dissolution of the exchanged zeolite in acidic media showed a Cr content of 7.5% by weight. The sample was stored in atmospheric air for one week.

500 mg of sample was the heated under dynamic vacuum at 200 ⁰ C for 60 minutes, naturally cooled to room temperature and then exposed to dry air. The sample gained about 3.5 % wt, and turned its color to brown.

Other 100 mg were loaded in a Rubotherm microbalance, heated under dynamic vacuum for 60'. Then cooled to 25°C and exposed to different pressure/temperature conditions.

The capacity observed in the different conditions, in terms of oxygen weight gain with respect to the weight of the non activated material, have been summarized in the Table 1, showing that an effective sorption capacity is measurable also when sample is exposed to low oxygen concentrations.

Table 1