THIS INVENTION relates to recycling or processing of layered packaging material. In particular, the invention relates to a method of recycling or processing layered packaging material, to the use of layered packaging material in the manufacture of value-added products and to an aluminium-containing product or feedstock when produced by said method of recycling or processing layered packaging material.

Recycling or processing of polymer-based multilayer packaging materials, e.g. used multilayer packaging materials, presents an ongoing challenge worldwide. The commonly used multi-layered packaging materials that are often referred to as 'Tetra Pak' after the packaging materials and packaging produced by the company Tetra Pak are the most widely used packaging materials for perishable food products such as juices and dairy products due to their ability to extend shelf life. Conventionally, these packaging materials are produced through the process of lamination of paperboard, low density poly ethylene (LDPE) and thin aluminium foil (Al) in order to form a layered composite material. These packaging materials are typically composed of 75 wt % of paperboard, 20 wt % LDPE and 5 wt % Al foil with each of these layers serving an important role for food preservation. For example, the paperboard aims to improve on the materials strength and the Al foil provides protection from light, odours and microorganisms (among others) whereas the polymeric layer(s) (most often LDPE) aims to protect the food content from getting into direct contact with the aluminium layer as well as acting as a bonding material during the hot sealing process. Due to the complexity of this layered structure, used layered packaging materials often present a recycling challenge. Therefore, their significant accumulation in municipal waste dumps requires dedicated and innovative technologies that will not only make the recycling of these packaging materials economically feasible but also ensure sustainability of the recycling process.

Broadly, the common practices for recycling packaging made from layered packaging material can be classified into two main categories i.e. 1) those relying on hydropulping as the first step to enable the separation of cellulosic fibre from Poly-AI laminate, and 2) those based on recycling the whole packaging material as it is. The second approach of non-separated recycling often involves energy recovery (either through incineration, gasification or pyrolysis) or by reforming/reprocessing the used packaging material to obtain low quality products such as laminated boards or other shaped products through hot-pressing with other binders. On the other hand, the process involving hydropulping typically results in a paper pulp that is processed into different paper-based products and a Poly-AI laminate/composite, which may be in the form of pellets.

The Poly-AI composite resulting from the hydropulping of used layered packaging material is typically composed of 20 wt % Al and 80 wt % polyethylene. Technologies for optimal and high value recycling of the Poly-AI are still under development. In most cases, the Poly-AI composite is mainly used for energy recovery either through direct incineration or through pyrolysis. The solid materials obtained from the energy recovery route are often of low value since they are mostly either AI2O3 or a mixture of Al metal and AI2O3. Alternatively, the Poly-AI composite can also be shaped into other functional materials through hot-pressing or moulding to result in items such as roof-tiles and trays, among others. There are studies that have reported on either an acid or solvent-based delamination approach to recover Al and LDPE powder. Additionally, there are reports on application of a solvent based extraction process for recovering LDPE by dissolving it in an organic solvent at elevated temperatures followed by separation of undissolved materials (Al and/or residual paper or other polymers).

Owing to the fact that existing technologies for recycling Poly-AI composites are either too complicated or often result in low-value products that makes their recycling unattractive, there is a need to develop other approaches or technologies that can contribute in making the recycling of used layered packaging material, such as Tetra Pak-type packaging material, economically more feasible. It would be an added advantage if such a recycling technology can also produce high value-added products.

According to one aspect of the invention, there is provided a method of recycling or processing layered packaging material, the method including B admixing a polymer-metal composite obtained from or forming part of layered packaging material with a reactant selected to react with the metal of the polymer-metal composite at elevated temperatures; and

reacting the polymer-metal composite with the reactant at an elevated reaction temperature to form a metal-containing compound of the metal of the polymer-metal composite and burning or driving off, at said elevated reaction temperature, the polymer of the polymer- metal composite and any other non-metal layer material of the layered packaging material that may be present.

The layered packaging material is typically used layered packaging material or layered packaging material that is to be reprocessed or reworked. The layered packaging material typically includes at least three layers, including a cellulose-based or wood pulp-based layer, e.g. a paperboard layer, a metal or metal foil layer and a layer or film of a synthetic plastics or polymeric material. Typically, the metal or metal foil layer is of aluminium. The polymer and the aluminium may be in the form of a polymer-aluminium composite. Thus, the reactant may be selected to react with the aluminium, e.g. with the aluminium of a polymer-aluminium composite, to form an aluminium-containing compound.

The synthetic plastics or polymeric material may be one or more of low or high density polyethylene, polypropylene, polyamide, polyethylene terephthalate, polyvinyl chloride and polystyrene. Typically, at least one layer is of polyethylene.

In one embodiment of the invention, the layered packaging material includes at least a paperboard layer, an aluminium foil layer and one or more polyethylene layers or films. Typical examples of such layered packaging material are the multi-layered packaging materials produced by Tetra Pak, part of the Tetra Laval Group headquartered in Switzerland.

The reactant may be a metal salt. The metal of the metal salt may be Na, K, Ca, Mg or other alkali and alkaline-earth metals. Instead, the reactant may be a non-metal material such as one or more ammonium salts, e.g. ammonium sulphates, carbonates or nitrates, and/or one or more metalloid-based materials such as boron-containing oxyanions.

The reactant may be in the form of a hydroxide, a carbonate, a chloride, a nitrate, a phosphate, an oxalate or a sulphate.

In one embodiment of the invention, the reactant is a sodium salt, e.g. NaOH, Na ₂ C03, Na ₂ S0 ₄ , NaCI. The metal-containing compound formed at the elevated reaction temperature may thus be sodium aluminate.

The reaction temperature of the thermo-chemical method of the invention may be in the range of about 200°C to about 800°C, or in the range of about 300°C to about 700°C, or in the range of about 400°C to about 650°C, e.g. about 550°C.

The polymer-metal composite and the reactant may be admixed in a ratio of from about 1:1 to about 8:1, or in the ratio of from about 2:1 to about 6:1, or in the ratio of from about 3:1 to about 5:1, e.g. about 1:1 or about 2:1 or about 3:1 or about 4:1, on a mass basis.

Admixing of the polymer-metal composite and the reactant may be by means of physical agitation. Instead, admixing of the polymer-metal composite and the reactant may be heat-induced.

The method may include hydropulping the layered packaging material to provide the polymer-metal composite, with said polymer-metal composite thus being substantially free of paperboard or other cellulose-based or wood pulp-based layer material.

Instead, the polymer-metal composite may include paperboard or other cellulose- based or wood pulp-based layer material, with the polymer-metal composite thus forming part of used layered packaging material or layered packaging material that is being reprocessed and that was not subjected to hydropulping. Preferably, the polymer-metal composite is in particulate form, e.g. in the form of pellets of the polymer-metal composite or in the form of comminuted or shredded layered packaging material, e.g. comminuted or shredded used layered packaging material. It is however to be appreciated that the method of the invention can be used with whole packaging made from layered packaging material as hereinbefore described.

The method may include withdrawing a gaseous stream driven off at the elevated reaction temperature, said gaseous stream including the polymer of the polymer-metal composite or one or more compounds formed at elevated temperature from the polymer of the polymer-metal composite. The method may include combusting the withdrawn gaseous stream to provide heat for the reaction between the polymer-metal composite and the reactant. Thus, the reaction may be conducted at pyrolytic conditions to subject the polymer of the polymer- metal composite to pyrolysis.

Instead, the reaction may be conducted under combustion or incineration conditions to subject the polymer of the polymer-metal composite and any other non-metal layer of the layered packaging material that may be present, to combustion.

The method may include converting the sodium aluminate to aluminium sulphate. Typically, this conversion includes reacting the sodium aluminate with water to form aluminium hydroxide and reacting the aluminium hydroxide with sulphuric acid to form aluminium sulphate. Aluminium sulphate is useful in the treatment of water.

The method may include converting the aluminium sulphate to a metal organic framework (MOF) through the addition of an organic linker. The organic linker may be fumaric acid to produce an Al-fumarate metal organic framework. MOFs are a new class of porous materials that are reported to have many industrial and commercial applications.

The method may include converting the sodium aluminate to a zeolite by reacting the sodium aluminate with a source of silicon in a basic aqueous solution. In one embodiment of the invention, the source of silicon is fly ash. The invention extends to use of layered packaging material that includes aluminium in the manufacture of aluminium sulphate or aluminium hydroxide.

The invention also extends to use of layered packaging material which includes aluminium in the manufacture of a zeolite.

The invention further extends to use of layered packaging material that includes aluminium in the manufacture of an Al-containing metal organic framework.

The layered packaging material may be as hereinbefore described.

The zeolite may be zeolite A.

The invention also extends to an aluminium-containing product or feedstock when produced by a method as hereinbefore described.

The aluminium-containing product or feedstock may be selected from the group consisting of sodium aluminate, aluminium sulphate, aluminium hydroxide, a zeolite and an aluminium-containing metal organic framework.

The invention is now described with reference to the following non-limiting laboratory examples and the accompanying drawings, in which

Figure 1 shows pictures of whole/unprocessed multi-layered packaging material and Poly- Al pellets;

Figure 2 shows pictures of Al containing pharmaceutical multi-layered packaging materials (blisters and strips);

Figure 3 shows comparative XRD patterns of commercial sodium aluminate, whole/unprocessed multi-layered packaging material derived sodium aluminate and Poly-AI derived sodium aluminate obtained using the method of the invention;

Figure 4 shows comparative SEM images of sodium aluminate resulting from whole/unprocessed multi-layered packaging material and Poly-AI pellets using the method of the invention; Figure 5 shows comparative XRD patterns of sodium aluminate obtained from Poly-AI with the use of different sodium salts (NaOH, Na ₂ C0 ₃ , Na ₂ S0 ₄ and NaCI) using the method of the invention;

Figure 6 shows comparative XRD patterns of sodium aluminate obtained from pharmaceutical multi-layered packaging materials (blisters and strips) using the method of the invention;

Figure 7 shows XRD patterns of commercial aluminium sulphate and Poly-AI derived aluminium sulphate obtained using the method of the invention;

Figure 8 shows TGA plots for Poly-AI composite together with Al-hydroxide and Al- sulphate derivatives obtained using the method of the invention;

Figure 9 shows XRD patterns of zeolite A derived from commercial Na-aluminate and from Poly-AI derived Na-aluminate obtained using the method of the invention;

Figure 10 shows SEM images of zeolite A derived from commercial Na-aluminate and from Poly-AI derived Na-aluminate obtained using the method of the invention;

Figure 11 shows XRD patterns of Al-Fum MOF derived from commercial Al-sulphate and from Poly-AI derived Al-sulphate obtained using the method of the invention; and

Figure 12 shows SEM images of Al-Fum MOF derived from commercial Al-sulphate and from Poly-AI derived Al-sulphate obtained using the method of the invention.

Example 1

Method for obtaining aluminium-based hydroxide and sulphate.

Poly-AI pellets obtained from the hydropulping of Tetra Pak (trade name) layered packaging material were thoroughly mixed with NaOH powder in different ratios (i.e. Poly-AI: NaOH ratio was 1:1, 2:1, 3:1, 4:1) and transferred into a crucible that was inserted in a muffle furnace. The mixture was heated up to 550°C and held at the same temperature for 1.5 hours. The XRD pattern for the resulting Na-aluminate powder is shown in Figure 1 and is also compared with those of commercial Na-aluminate powder. The obtained patterns were closely similar but with some peak shifts and splitting which could be due to subtle crystallographic or compositional differences. In order to transform the obtained Poly-AI derived Na-aluminate to Al-based hydroxide and sulphate, water was firstly added to the Na-aluminate in order to recover Al- hydroxide. Sulphuric acid was thereafter stoichiometrically added to the recovered Al-hydroxide to obtained Na-sulphate. Figure 2 shows XRD pattern of the recovered Poly-AI derived aluminium sulphate and also compares it with an XRD pattern for aluminium sulphate obtained commercially.

TGA plots for the Poly-AI composite, derived Al-hydroxide and derived Al-sulphate are shown in Figure 3. The expected ~20 wt % of Al content in the Poly-AI composite is confirmed from the TGA whereas the derived Al-based hydroxide and sulphate are also in agreement with expectations.

Example 2

Synthesis of zeolite A from coal fly ash and Poly-AI derived Na-aluminate

A mass ratio of 1:1.2 (fly ash to NaOH) powder was initially ground together to achieve a homogenous mixture. The resulting fly ash-NaOH powdered mixture was poured into a porcelain crucible and transferred into a muffle furnace and left to fuse for 1.5 hours at 550°C. The fused material was removed and allowed to cool to room temperature. The cooled fused material was ground to achieve a fine powder. In order to obtain single phase zeolite A crystals, a clear extract of the fused fly ash was used. In this case, a mass ratio of 1:5 (fused fly ash to water) was used to achieve a slurry that was later filtered to obtain a clear extract. In a different step, a Na-aluminate solution was prepared by mixing water, Poly-AI derived Na-aluminate powder and Na-hydroxide in a corresponding mass ratio of 20:0.6:1.2. In order to synthesize zeolite A, 50 ml of the fused fly ash extract was mixed with 20 ml Poly-AI derived Na-aluminate solution and transferred to Teflon-lined reactors and hydrothermally treated at 100°C for 2 hours. Thereafter, zeolite crystals were recovered by filtration, washed and dried at 90°C for 12 hours. The same procedure was repeated but with the use of commercially obtained Na- aluminate powder for comparison purposes. Figures 4 and 5 present the comparative XRD patterns and SEM images of zeolite A obtained using Poly-AI derived Na-aluminate and commercial Na-aluminate. The obtained zeolites are almost of the same quality. Example 3

Synthesis of Al-Fum MOF from Poly-AI derived Na-sulphate

3.23 g of fumaric acid and 2.35 g of NaOH were mixed with 48 ml of deionized water and a resulting linker solution (solution A) was heated in an oil bath at 60°C for one hour. Simultaneously, a different solution containing 9.3 g Poly-AI derived aluminium sulphate was dissolved in 40 ml of water and also was heated at 60°C for one hour (solution B). Thereafter, the linker solution (solution A) was slowly added to the aluminate solution whilst stirring and the resulting mixture was further heated for an additional two hours (still at 60°C). Thereafter, a resulting white precipitate was recovered by filtration, thoroughly washed with deionized water and dried for 12 hours at 90°C. The above procedure was also repeated using commercially sourced Al ₂ (SO4) ₃ .18H ₂ 0 for comparison purposes. Figures 6 and 7 present a comparison of XRD patterns and SEM images for the Al-Fumarate MOF synthesized using the Poly-AI derived Al feedstock and commercially sourced Al ₂ (SO4) ₃ .18H ₂ 0. The results show that similar product had been obtained and thus proves that the Poly-AI derived Al sulphate obtained from layered packaging material can be a good feedstock for a MOF.

The thermo-chemical method of the invention provides an attractive approach for generating value-added chemicals or feedstocks from, typically used, layered packaging material that includes a metal layer or foil, such as aluminium. Advantageously, the method of the invention, as illustrated, does not require the use of a solvent or an acid to recover the metal, e.g. aluminium, of the layered packaging material.