Method for separating and recovering superabsorbent polymers (SAPs) from used absorbent sanitary products

Abstract

A method for separating a superabsorbent polymer (SAP) fraction from a used absorbent sanitary product, the used absorbent sanitary product further comprising at least one cellulose fraction and one plastic fraction. The method comprises at least the steps of sterilizing the used absorbent sanitary product and treating the used absorbent sanitary product by immersion in a bath containing an aqueous solution containing at least one oxidizing agent. The oxidizing agent is preferably selected from the group consisting of sodium persulfate, potassium peroxodisulfate, ammonium persulfate, potassium peroxymonosulfate, and hydrogen peroxide, preferably hydrogen peroxide. The immersion treatment allows for crosslink cleavage and solubilization of the SAP contained in the used absorbent sanitary product, obtaining a suspension comprising i) a solid fraction and ii) a liquid fraction, the liquid fraction containing linear polyacrylate (LPA) resulting from the crosslink cleavage and solubilization of the SAP.

Description

[Technical Field]

[0001] This disclosure relates to the recycling of used absorbent sanitary products, and in particular to a method for separating used absorbent sanitary products into their various components for continuous reuse. [Background technology]

[0002] Absorbent sanitary products are generally composed of different materials including, for example, plastic films, cellulose fluff, and superabsorbent polymers (SAPs). These sanitary products therefore contain valuable materials, the recovery of which for reuse in the marketplace is clearly a desirable goal.

[0003] Currently known methods for treating absorbent hygiene products to separate the various components may involve, for example, mechanical separation by vibration, enzymatic action on cellulose combined with mechanical separation of SAP deactivated with calcium chloride (CaCl), or extraction in a supercritical phase, in which the cellulose fraction is separated from the superabsorbent polymer (SAP). There are also known methods for separating the plastic fraction (previously deactivated with calcium or Al ions or the like) from the SAP using a combination of enzymatic action and physical separation.

[0004] Problems with known methods for treating used absorbent sanitary products can stem from the difficulty of effectively separating superabsorbent polymers (SAPs) from other components, such as cellulose and plastic fractions. The cellulose and plastics recovered from these used products can in fact contain varying amounts of SAP residues, which can affect the degree of purity of the separated components. Object of the invention

[0005] The objective of the present specification is to provide a method for treating used absorbent sanitary products that makes it possible to achieve an effective separation of superabsorbent polymers (SAPs) from plastic and cellulose fractions while maintaining the quality of the product for convenient reuse or recycling in the market.

[0006] According to this specification, this object is achieved by a method having the characteristics forming the subject matter of the appended claims, which, in relation to the method described, form an integral part of the disclosure provided herein.

[0007] The present specification provides a method for separating a fraction of superabsorbent polymers (SAP) from used absorbent sanitary products, the used absorbent sanitary products further comprising at least one cellulose fraction and one plastic fraction, the method comprising at least the steps of: sterilizing the used absorbent sanitary products to obtain sterilized material; treating the used absorbent sanitary products by immersion in a bath with an aqueous solution comprising at least one oxidizing agent, preferably selected from the group consisting of sodium persulfate, potassium peroxodisulfate, ammonium persulfate, potassium peroxymonosulfate, and hydrogen peroxide, preferably hydrogen peroxide, to cleave crosslinks and solubilize the SAP contained in the used absorbent sanitary products; and obtaining a suspension comprising i) a solid fraction and ii) a liquid fraction, the liquid fraction comprising non-crosslinked linear polyacrylate (LPA) resulting from the crosslink cleavage and solubilization of the SAP.

[0008] The sterilization step is carried out by heating the used absorbent sanitary product at a temperature of 120°C to 140°C and a pressure of 1 bar to 3.6 bar (1000 to 3600 hectopascals). Preferably, the sterilization step may be carried out in an autoclave.

[0009] In one or more embodiments, the aqueous solution may contain only hydrogen peroxide as the oxidizing agent. Furthermore, the immersion treatment step may advantageously be carried out at a temperature of from 65°C to 100°C.

[0010] The methods described herein may further comprise a step for separating the solid phase from the liquid phase.

[0011] In one or more embodiments, the method may further comprise at least one solid phase washing step, which is preferably carried out with water.

[0012] In one or more embodiments, the method may comprise at least one step of purifying the liquid fraction comprising linear polyacrylate (LPA) from any cellulose or plastic residues, preferably by using filtration on a disc filter.

[0013] The optionally purified liquid phase can be used in the crosslinking process of linear polyacrylates (LPA), as described by way of example below, and for the subsequent production of, for example, new SAPs.

[0014] The solid fraction obtained from the described method, which may be subjected to at least one washing step, may contain cellulose and plastics of a high degree of purity, with an SAP content of less than 1 weight percent (wt / wt). The purity and identity of the cellulose obtained from the method were determined and confirmed by Fourier transform infrared spectroscopy (FTIR) analysis combined with ATR attenuated total reflectance for the analysis of cellulose, American Journal of Analytical Chemistry, 2018, Vol. 9, pp. 303-310. The purity and identity of the plastics obtained from the method were determined and confirmed by Fourier transform infrared spectroscopy (FTIR) analysis combined with the methods of UNI EN ISO 6427 / 2013 and ISO 16152 / 2005. [Brief explanation of the drawings]

[0015] The method will now be described in detail with reference to the accompanying drawings, which are provided purely as non-limiting examples. [Figure 1]1 shows a diagram of a known method for treating used absorbent sanitary products. [Figure 2] FIG. 2 is a plan view of an apparatus that can be used, for example, in the method diagrammed in FIG. 1. [Figure 3] 1 shows a diagram of a method according to an embodiment of the present disclosure, wherein the steps for cross-linking and solubilization of SAP are carried out by soaking a sterilized used absorbent sanitary product. [Figure 4] 1 shows a diagram of a method according to an embodiment of the present disclosure, wherein the SAP cross-linking and solubilization steps are carried out by immersion of crushed, sterilized used absorbent sanitary products. [Figure 5] 1 shows a diagram of a method according to an embodiment of the present disclosure, wherein the SAP cross-linking and solubilization steps are carried out by maceration of the separated cellulose and plastic fractions. [Figure 6] A comparison of the IR spectra of LPA obtained in the liquid fraction from the method described (above) and LPA from a database (below, Spectra DataBase: Spectrum ID 8XQMEFCFImm, Copyright® 1980, 1981-2018 Bio-Rad Laboratories, Inc.) is shown. [Figure 7] Figure 1 shows a C-NMR spectrum performed on a sample of the liquid fraction from the described method, performed in deuterium oxide using a Bruker Avance 300 MHz spectrophotometer. The signal at approximately 84 ppm, typical of the C carbon -CH- of crosslinkers (-OCH, -NHCHNH-, etc.) bearing alpha heteroatoms such as oxygen and / or nitrogen, is absent, and is instead attached to the carbonyl group C=O. DETAILED DESCRIPTION OF THE INVENTION

[0016] In the following description, numerous specific details are provided to enable a thorough understanding of the embodiments. The embodiments may be realized without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the embodiments.

[0017] References throughout this disclosure to "one embodiment" or "an embodiment" indicate that a particular aspect, structure, or characteristic described with reference to this embodiment is included in at least one embodiment. Thus, at various points throughout this specification, the appearances of the phrases "in one embodiment" or "in an embodiment" do not necessarily refer all to the same embodiment. Furthermore, particular aspects, structures, or characteristics may be combined in any convenient manner in one or more embodiments. The headings provided in this description are for convenience only and do not interpret the scope or intent of the present embodiments.

[0018] The expression "absorbent hygiene products" generally refers to disposable absorbent products such as, for example, baby diapers, adult incontinence pads, sanitary napkins, bed liners, etc. These absorbent products may contain plastic, superabsorbent polymers, cellulose, or even just plastic and superabsorbent polymers.

[0019] As anticipated in the previous section, methods are currently known for treating used absorbent sanitary products to obtain separation of various components such as, for example, cellulose, plastics, and superabsorbent polymers (SAPs).

[0020] A currently known method for treating and separating the various components of used absorbent sanitary products may comprise the steps shown, for example, in Figure 1 of the present application and described by the same applicant in document WO2018 / 060827. The method may comprise a step SR of sterilizing the used absorbent sanitary products, a step SH of crushing the sterilized product, a step DR of drying the sterilized and crushed product, and a step SEP of separating the sterilized, crushed and dried product into plastic and cellulose.

[0021] Problems with methods for treating used absorbent sanitary products can stem from the difficulty of effectively separating the superabsorbent polymer (SAP) from other components, such as the cellulose and plastic fractions.

[0022] The cellulose and plastics recovered from used hygiene products may in fact contain varying amounts of SAP residues, as explained below.

[0023] Superabsorbent polymers are typically prepared by copolymerization of one or more monomers (acrylic acid, sodium or potassium acrylic acid or methacrylate, and / or acrylamide) that form the basic structure (backbone) of the material, i.e., sodium linear polyacrylate (LPA) (Spectral database: Spectral ID 8XQMEFCFImm, Copyright 1980, 1981-2018 Bio-Rad Laboratories, Inc.).

[0024] The use of bifunctional cross-linkers (e.g., N,N-methylenebisacrylamide (MBA), ethylene glycol dimethacrylate (EGDMA), diallyl phthalate (DP), or triethylene glycol dimethacrylate (TEGDMA)) results in cross-linking of linear polyacrylate (LPA) to an extent that depends on the amount of cross-linker used. This results in the formation of negatively charged carboxylate groups (-COO -) is formed. Due to electrostatic repulsion, the network can expand locally, providing spaces within it that can absorb (and hold) a volume of water or an aqueous solution. Crosslinking also makes the SAP polymer insoluble in aqueous environments.

[0025] The inventors of the present application have identified specific operating conditions for a method comprising treating used absorbent sanitary products by immersion in a bath with an aqueous solution containing an oxidizing agent. The at least one oxidizing agent is preferably selected from the group consisting of sodium persulfate, potassium peroxodisulfate, ammonium persulfate, potassium peroxymonosulfate, and hydrogen peroxide, preferably hydrogen peroxide. The aqueous solution may also contain only hydrogen peroxide as the oxidizing agent.

[0026] This step makes it possible to obtain a suspension comprising i) a solid fraction comprising at least one of a cellulose and a plastic fraction, and ii) a liquid fraction comprising non-crosslinked linear polyacrylate (LPA) resulting from the crosslink cleavage and solubilization of SAP. In particular, the liquid fraction comprises non-crosslinked linear polyacrylate in the form of sodium or potassium non-crosslinked linear polyacrylate (LPA).

[0027] The soaking treatment step is preferred for efficient cross-link cleavage, solubilization, and separation of SAP from the solid fraction, including plastics and cellulose.

[0028] In particular, the treatment step of immersion in a solution containing at least one oxidizing agent determines the destruction of the crosslinks present between the polymers that constitute the SAP, releasing the basic structure or linear polyacrylates (LPAs) (also defined as acrylate polymers in linear form) that pass into the liquid fraction.

[0029] The method described here also makes it possible to i) reduce to a complete inhibition the ability of SAP to swell by absorbing water, and ii) obtain complete solubilization of SAP as a linear polyacrylate (LPA).

[0030] This linear polyacrylate (LPA) can then advantageously be subjected to a crosslinking step to produce, for example, a new SAP.

[0031] As will be apparent from the following description, the step of cross-linking and solubilization of SAP can be carried out by direct immersion of sterilized used absorbent sanitary products (Figure 3). Satisfactory results are also obtained when this step is carried out by immersion of sterilized and crushed products (Figure 4) or when this step is carried out directly by immersion of separated plastic and cellulose fractions (Figure 5).

[0032] The treatment by immersion of the absorbent sanitary products to be treated can be carried out in a bath with an aqueous solution containing at least one oxidizing agent, preferably hydrogen peroxide, in an amount comprised between 5% and 50% (w / w) of this solution.

[0033] The step of treatment by immersion may advantageously be carried out at a temperature of between 65°C and 100°C.

[0034] Furthermore, the product immersed in the bath must be subjected to a 5N / cm 2 ~20N / cm 2 The material may be subjected to compressive forces exerted by pressures in the range of .

[0035] The method has the advantage that it does not comprise a step designed to inactivate the SAP, for example by treating the material with an organic or inorganic acid.

[0036] The method makes it possible to obtain recovered products from post-consumer materials, i.e., cellulose, plastics, linear polyacrylate (LPA), where the quality is maintained for convenient reuse.

[0037] In one or more embodiments, the method may comprise one or more of the steps shown schematically in Figure 1, for example, or rather as described, for example, in document WO 2018 / 060827 by the same applicant and reported below: a sterilization step SR of used absorbent sanitary products, a crushing step SH of the sterilized products, a drying step DR of the sterilized and crushed products, a separation step SEP of plastics and cellulose products. In particular, the method may comprise a collection step ST of used absorbent sanitary products coming from recycling collection in a storage container. Figure 2 shows an apparatus 10, in which the storage container is designated by the reference number 12. A waste collection vehicle unloads the used absorbent sanitary products into an unloading area 14, and a conveyor 16 loads the used absorbent sanitary products into the storage container 12. The collected used absorbent sanitary products have a density of 150 to 300 kg / m 3 It may have a density of the order of 1000 and a moisture content of the order of 65-80%.

[0038] The total moisture content of the material, understood as the percentage of water contained therein, is calculated from the dry weight of the sample (according to the IRSA-CNR1984-notebook 64 and UNI936 UNICHIM10506 / 1996 methods).

[0039] The collection stage ST is followed by a sterilization stage SR, which is carried out, for example, by loading the products into a rotary autoclave 18. In the example shown in Figure 2, the device 10 comprises two autoclaves 18, into which used absorbent sanitary products coming from the storage containers 12 are alternately loaded. A conveyor 28 removes the products from the storage containers 12 and transports them to the autoclaves 18. Two loaders 30 load the products into each autoclave 18. During product loading, the autoclave doors 20 are opened and the cylindrical bodies rotate, gradually moving the products backward. Once loading is finished, the doors 20 are closed and the autoclaves 18 are heated and pressurized by supplying steam directly or indirectly until a temperature of approximately 135°C and an internal pressure of approximately 3.1 bar (3100 hectopascals) is reached. In one or more embodiments, the sterilization step ST may be carried out by heating the used absorbent sanitary products at a temperature of 120° C. to 140° C. and a pressure of 1 to 3.6 bar (1000 to 3600 hectopascals). Alternatively, during the sterilization process, the autoclave may rotate clockwise and counterclockwise around its axis to allow movement of the products contained therein.

[0040] The sterilization stage ST aims to heat the product to a temperature that allows complete sterilization of the bacterial load. The sterilization stage can be carried out for a period of 20 minutes to 2 hours. At the end of the sterilization process, the steam contained in the autoclave 18 is extracted and purified in a scrubber 34. The door 20 is then opened and the body is rotated to discharge the product. In the example of Figure 2, two autoclaves 18 are provided that operate alternately. The first autoclave 18 carries out the sterilization process, while the other autoclave 18 unloads the sterilized material and loads a new batch. In this way, an essentially continuous flow of sterilized material can be obtained downstream of the autoclave 18.

[0041] At the end of the sterilization process, the sterilized material exiting the autoclave is collected in a storage container 32. The sterilized material exiting the autoclave is approximately 300-400 kg / m 3The density may be between 100°C, a temperature between 80 and 100°C, and a total moisture content of the order of 70-85% calculated from the dry weight of the sample (according to the IRSA-CNR1984-notebook64 and UNI936 UNICHIM10506 / 1996 methods).

[0042] The sterilized material is transported from the storage container 32 to a shredder 36 by a conveyor belt 38. The shredder may, for example, comprise two rotors driven by a motor. The rotors are provided with teeth that effect the shredding of the material. The shredding makes it possible to obtain material with a particle size of less than 10 cm, preferably less than 3 cm, more preferably less than 1 cm.

[0043] After crushing, the material is crushed at 400-500 kg / m 3 It may have a density of the order of 0.05, a temperature of about 75-95°C, and a total moisture content of the order of 70-85%, calculated from the dry weight of the sample (according to the methods of IRSA-CNR1984-notebook 64 and UNI936 UNICHIM10506 / 1996).

[0044] The materials subjected to the sterilization and crushing stages are transported by conveyor 44 to dryer 42, where the drying stage DR is carried out. Dryer 42 includes a housing housing two horizontal perforated conveyors, which are alternately driven in opposite directions and vertically overlap each other. Conveyor 44 deposits the material onto the upper conveyor. At the discharge of each horizontal conveyor, the material falls onto the lower conveyor. While the material is transported horizontally, passing continuously from one conveyor to the next, a heated air flow passes through the housing from bottom to top. The air flow passes through the perforated conveyors and the materials placed on them. The air flow is generated by a fan 50 connected to a filter. The air flow is heated in a battery of heat exchangers 54, which are supplied with steam. The air flow leaving heat exchanger 42 is sucked by a second fan and sent to a condensation discharge device 58, a scrubber. At the discharge of dryer 42, the material is deposited onto a conveyor belt 62. The dryer 42 may be equipped with a microwave generator facing the upper conveyor to accelerate heating of the material and increase the drying effect. The material at the entrance of the dryer has a temperature of about 70 to 90°C. The drying air temperature in the dryer 42 is about 140°C.

[0045] The product coming out of the dryer 42 has a temperature of about 50 to 70°C and a drying rate of about 35 to 50 kg / m 3 and a total moisture content of the order of 5-20% calculated from the dry weight of the sample (according to the methods of IRSA-CNR1984-notebook64 and UNI936UNICHIM 10506 / 1996).

[0046] Downstream of the drying stage DR, the sterilized, shredded and dried material is sent to a separation assembly 64 where a step of separating plastics and cellulose is carried out.

[0047] The separation steps may be carried out in at least one centrifuge. The separation assembly 64 may, for example, include at least one first centrifuge including a base and having an inlet for the material to be separated. In the example shown in Figure 2, two centrifuges 66, 67 are provided in cascade.

[0048] The centrifuge 66 may include a separation chamber containing a perforated cylindrical filter mounted on a rotor rotatable about a horizontal axis. The inlet material projects radially outward from the perforated filter. Cellulose, having smaller dimensions than plastics, passes through the filter and is collected at a first outlet, while plastics remain inside the filter and are collected at a second outlet. Preferably, plastics exiting the first centrifuge 66 are sent to a second centrifuge 67 having a filter with smaller holes. At the outlet of the centrifuge 66, the cellulose stream 80 may be sent to a cellulose shredder and cellulose pelletizer 82. Plastics exiting the separator 66 may be sent to a plastic shredder 84 and then to an extruder or densifier 86.

[0049] A method comprising the steps described above may make it possible to obtain cellulose with a purity of 55% to 90% and plastic with a purity of 80% to 97%.

[0050] These values ​​were determined by analysis in Fourier transform infrared spectroscopy (FTIR) combined with ATR attenuated total reflectance for the analysis of cellulose, American Journal of Analytical Chemistry, 2018, Vol. 9, pp. 303-310, and FTIR combined with the methods of UNI EN ISO6427 / 2013 and ISO16152 / 2005 for determining the purity of plastics.

[0051] In particular, the isolated cellulose may contain a certain amount of residual SAP, in weight proportions ranging from 5% to 15%, on average of the order of 11%, according to an evaluation carried out using FTIR infrared spectroscopy analysis.

[0052] The recovered plastic fraction may contain, in addition to traces of cellulose, residual SAP amounts of 3% to 9% by weight, with an average of 5% by weight, according to assessments carried out using FTIR infrared spectroscopy analysis.

[0053] The subject of the method herein, which comprises steps for cross-linking, solubilization, removal and recycling of SAP, makes it possible to obtain plastics and cellulose with a significantly higher degree of purity.

[0054] As shown diagrammatically in Figure 3, the step for cross-linking and solubilizing SAPs can be carried out after the sterilization step by immersing the sterilized hygiene products in a bath with an aqueous solution containing at least one oxidizing agent. This step can be carried out in a thermally insulated (adiabatic) cylindrical reactor immersed in the aqueous solution containing at least one oxidizing agent.

[0055] The aqueous solution may contain at least one oxidizing agent, preferably hydrogen peroxide, in an amount comprised between 10% and 50% (w / w), preferably equal to 15% (w / w).

[0056] In one or more embodiments, the aqueous solution comprises at least one oxidizing agent, preferably hydrogen peroxide, in an amount comprised between 150% and 340% by weight relative to the dry weight of the immersed sterilized sanitary product.

[0057] Furthermore, the ratio between the volume of the aqueous solution containing at least one oxidizing agent and the weight of the sterilized used absorbent sanitary products to be treated with the composition may be between 3 and 12 l / kg (liters per kilogram) (i.e., between 3:1 and 12:1), preferably between 5 and 8 l / kg (i.e., between 5:1 and 8:1). Advantageous results have been observed when the soaking step of the moist, hot material leaving the rotary autoclave 18 is carried out in a bath at room temperature. The soaked material may have a temperature between 80°C and 100°C, a total moisture content of the order of 70-85%, and a size between 3 cm and 80 cm.

[0058] Furthermore, optimal separation results of SAP from retained solid components are obtained when the treated product is kept in constant motion by a mechanical stirring rod with fixed blades at an adjustable speed of 0-120 revolutions per minute (rpm), preferably 60 rpm.

[0059] Furthermore, the inventors have observed that even more advantageous results can be obtained if the sterilized used sanitary products placed in the bath are subjected to a compressive force exerted by, for example, a disk head piston with a hole preferably having a diameter of 1 cm, which exerts pressure operated by a hydraulic pump. The pressure exerted is between 5 and 25 N / cm 2 It could be.

[0060] Generally, the compression applied to the material treated by immersion keeps all of the material's mass permeated, preventing the liquid fraction from separating from the solid fraction. In fact, in the absence of adequate counterpressure, the solid fraction tends to separate from the aqueous solution containing the reactive oxidizing agent. The applied pressure, preferably within the ranges described above, can be maintained constant or varied. For example, it can be increased at the end of the immersion treatment step to facilitate the subsequent step of separating the liquid fraction from the solid fraction.

[0061] By adopting the described operating conditions, the immersion step in the bath can be carried out for a period of less than 90 minutes, preferably between 55 and 80 minutes.

[0062] The advantage of carrying out the SAP soaking and solubilization step directly on the sterilized product, prior to the sterilized product crushing step, lies in the fact that, as explained previously, the product leaving the autoclave has a total moisture content of the order of 70-85% and a temperature of 80°C-100°C. These properties allow: 1. Considering the already high contribution of water present in the material, the volume of water added to constitute the aqueous solution containing at least one oxidizing agent is reduced. 2. Because SAP is extracted as soluble LPA, the loss of SAP in the form of fine particles during the subsequent crushing, drying and mechanical separation steps is minimized. 3. Because SAP is extracted as soluble LPA, cellulose and plastic contamination is minimized. 4. As a result of point 1, the heat hold times of the subsequent drying stage DR are reduced. 5. As a result of point 3, high purity cellulose and plastic fractions are obtained. 6. The reactor is not heated during the entire duration of the solution with the oxidizing agent, since the material itself exchanges heat with the solution and becomes activated accordingly.

[0063] The immersion process makes it possible to obtain a suspension comprising i) a mixed solid fraction containing cellulose and plastics, and ii) a liquid fraction containing solubilized SAPs, in particular non-crosslinked linear polyacrylates (LPAs).

[0064] The solid fraction can be separated from the liquid fraction, for example, by further compressing the material. By applying pressure with a hydraulic piston, the solution is allowed to rise above the perforated piston head. The pressure is between 10 and 25 N / cm. 2 An outlet valve allows the collection of the waste solution (liquid fraction), which may be subjected to a purification step, for example by filtration on a disc filter.

[0065] The solid fraction containing the plastic and cellulose fraction purified from SAP can then be subjected to shredding SH, drying DR, and separation SEP as described. The solid fraction containing cellulose and plastic can potentially be subjected to at least one washing step, preferably with water, in the same adiabatic reactor before conveying the material to a shredder to recover additional SAP residues. The solution collected by the outlet valve can be pooled.

[0066] Downstream of the shredding stage SH, which is carried out as described in the previous section, the solid fraction can be dried, preferably in a dryer. The drying air temperature is between 100° C. and 140° C. Downstream of the drying stage, a separation stage SEP of cellulose from plastics can follow, preferably using at least one centrifuge, as described in the previous section.

[0067] The cellulose and plastics thus obtained have a purity of more than 99%. The purity and identity of the solid fractions obtained by the described method were determined and confirmed by analysis in Fourier transform infrared spectroscopy (FTIR) combined with ATR attenuated total reflectance for the analysis of cellulose, American Journal of Analytical Chemistry, 2018, Vol. 9, pp. 303-310, and FTIR combined with the methods of UNI EN ISO 6427 / 2013 and ISO 16152 / 2005 for the analysis of plastics.

[0068] Figure 4 shows a method comprising the steps of sterilization (SR), shredding (SH), drying (DR), and separation (SEP), as described in the previous section. Figure 4 also shows that a step of solubilizing SAP is carried out downstream of the shredding step (SH), i.e., on the sterilized and shredded used absorbent sanitary products. In particular, the treated material has a particle size of 1 cm to 10 cm, a temperature of about 75°C to 95°C, and a total moisture content of 70% to 85%.

[0069] The sterilized and crushed product is immersed in a bath containing an aqueous solution containing an oxidizing agent, preferably in an insulated cylindrical reactor.

[0070] The aqueous solution contains at least one oxidizing agent, preferably hydrogen peroxide, in an amount comprised between 10% and 50% (w / w), preferably equal to 15% (w / w).

[0071] In one or more embodiments, the aqueous solution comprises at least one oxidizing agent, preferably hydrogen peroxide, in an amount comprised between 150% and 340% by weight of the dry weight of the soaked and crushed sterilized sanitary product.

[0072] Furthermore, the ratio between the volume of the aqueous solution containing at least one oxidizing agent and the weight of the sterilized and crushed used absorbent sanitary products to be treated with the composition may be 3 to 12 l / kg (i.e. 3:1 to 12:1), preferably 5 to 8 l / kg (i.e. 5:1 to 8:1).

[0073] Advantageous results have been observed when the steeping step of the moist, hot material conveyed by the conveyor 44 is carried out in a bath at room temperature. The steeped material may have a temperature of 75°C to 95°C and a total moisture content on the order of 70 to 85%.

[0074] Optimal separation results of the SAP from the remaining solid components are obtained when the material is kept constantly moving by a mechanical stirring rod with fixed blades, again at an adjustable speed between 0 and 60 revolutions per minute (rpm), preferably 30 rpm.

[0075] Furthermore, the inventors have observed that even more advantageous results can be obtained if the sterilized used sanitary products placed in the bath are subjected to a compressive force exerted by, for example, a disk head piston with a hole of 1 cm diameter, which exerts pressure operated by a hydraulic pump. The pressure exerted is between 5 and 20 N / cm. 2 It could be.

[0076] Generally, the compression applied to the material treated by immersion keeps all of the mass of the material permeated and prevents the liquid fraction from separating from the solid fraction. In fact, in the absence of adequate counter pressure, the solid fraction tends to separate from the aqueous solution containing the oxidizing agent.

[0077] By adopting the operating conditions described, the immersion step in the bath can be carried out for a period of 30 to 45 minutes, not longer than 60 minutes.

[0078] Furthermore, similar to what was observed in connection with Figure 3, advantageous results were observed when the SAP soaking and solubilization steps proceeded directly on sterilized and crushed products placed in the soak and subjected to compressive forces.

[0079] This advantage stems from the fact that, as previously explained, the crushed product conveyed by the conveyor 44 has a temperature of approximately 75-95% and a total moisture content of the order of 70-85%, calculated from the dry weight of the sample (according to the methods of IRSA-CNR1984-notebook64 and UNI936UNICHIM10506 / 1996). These properties allow: 1. Considering the already high contribution of water present in the material, the volume of water added to constitute the aqueous solution containing at least one oxidizing agent is reduced. 2. Because SAP is extracted as soluble LPA, the loss of SAP in the form of fine granules during the subsequent drying and mechanical separation steps is minimized. 3. Because SAP is extracted as soluble LPA, cellulose and plastic contamination is minimized. 4. As a result of point 1, the heat hold times of the subsequent drying stage DR are reduced. 5. As a result of point 3, high purity cellulose and plastic fractions are obtained. 6. The reactor is not heated during the entire working time of the aqueous solution, since the material itself exchanges heat with the solution and activates accordingly.

[0080] The process of solubilizing SAP, carried out as described, involves forming a suspension containing i) a mixed solid fraction containing plastics and cellulose purified from SAP, and ii) a liquid fraction containing solubilized SAP.

[0081] The mixed solid fraction can be separated from the liquid fraction by further compressing the material. For example, by applying pressure with a hydraulic piston, the solution is allowed to rise above the perforated piston head. The pressure is 10-25 N / cm. 2 The outflow valve allows for the collection of waste solution (liquid fraction).

[0082] The liquid fraction may be subjected to a purification step, for example by filtration on a disc filter.

[0083] The solid fraction separated from the liquid phase may be subjected to subsequent drying DR and separation SEP steps, preferably carried out using at least one centrifuge, as described in the previous section. To recover further SAP residues, the mixed solid fraction containing cellulose and plastics may be subjected to at least one washing step, preferably with water, in the same adiabatic reactor, before conveying the material to the dryer. The fractions collected by the outlet valve may be pooled.

[0084] Downstream of the drying step, which is carried out as described in the previous section, there may be a step of separating the cellulose from the plastics, preferably using at least one centrifuge, as described in the previous section.

[0085] The cellulose and plastics thus obtained have a purity of more than 99%. The purity and identity of the solid fractions obtained by the described method were determined and confirmed by analysis in Fourier transform infrared spectroscopy (FTIR) combined with ATR attenuated total reflectance for the analysis of cellulose, American Journal of Analytical Chemistry, 2018, Vol. 9, pp. 303-310, and FTIR combined with the methods of UNI EN ISO 6427 / 2013 and ISO 16152 / 2005 for the analysis of plastics.

[0086] As shown in Figure 5, a step for cross-link cleavage and solubilization of SAP can be carried out downstream of the separation step SEP of the cellulose fraction from the plastic fraction.

[0087] In this case, the method comprises a step SR of sterilizing the used absorbent sanitary products, a step DR of drying the sterilized material, a step SH of optionally crushing the sterilized material, a step SEP of separating the cellulose and plastic fractions from the sterilized and dried material, a step of treating the cellulose and / or plastic fractions by immersion in a bath with an aqueous solution comprising at least one oxidizing agent, preferably selected from the group consisting of sodium persulfate, potassium peroxodisulfate, ammonium persulfate, potassium peroxymonosulfate and hydrogen peroxide, to break crosslinks and solubilize the SAP contained in said cellulose and plastic fractions, and a step of obtaining a suspension comprising i) a solid phase comprising the cellulose and / or plastic fraction and ii) a liquid fraction comprising linear polyacrylate (LPA).

[0088] In particular, the cellulose fraction and / or plastic fraction to be separated at room temperature are each immersed in respective, preferably separate reactors, preferably heatable, insulated cylindrical reactors in a bath with an aqueous solution comprising at least one oxidizing agent.

[0089] The ratio between the volume of the aqueous solution containing at least one oxidizing agent, preferably hydrogen peroxide, and the weight of each cellulose and plastic fraction to be treated with the composition is 10-30 l / kg (i.e. 10:1-30:1), preferably 17-25 l / kg (i.e. 17:1-25:1).

[0090] When treating by immersion of the cellulose fraction, the ratio is preferably 10 to 30 l / kg, more preferably 14 to 25 l / kg. When treating by immersion of the plastic fraction, the ratio is preferably 10 to 25 l / kg, more preferably 12 to 22 l / kg.

[0091] In one or more embodiments, the aqueous solution contains hydrogen peroxide in an amount ranging from 150% to 300% by weight based on the dry weight of the cellulose fraction or the immersion-treated plastic fraction.

[0092] In one or more embodiments, the treatment of the cellulose fraction by immersion may be carried out in an aqueous solution containing at least one oxidizing agent, preferably hydrogen peroxide, in an amount comprised between 10% and 50% (w / w), more preferably equal to 15% (w / w).

[0093] Optimal results have been observed when the immersion treatment of the plastic fraction is carried out in an aqueous solution containing hydrogen peroxide in an amount ranging from 5% to 50% (wt / wt), preferably equal to 10% (wt / wt).

[0094] In one or more embodiments, the soaking treatment step is carried out at a temperature between 65° C. and 100° C. Preferably, the soaking treatment step for the cellulose fraction is carried out at a temperature of 85° C., and the soaking treatment step for the plastic fraction is preferably carried out at a temperature of 75° C. The tanks can be heated by carrying out a heat exchanger, by circulating a heat transfer fluid in a coil, or by ohmic heating carried out by electrical resistance.

[0095] In one or more embodiments, the step of treating the cellulose fraction by soaking may be carried out for a period ranging from 20 minutes to 60 minutes, preferably for a period of 35 minutes.

[0096] In one or more embodiments, the step of treating the plastic fraction by immersion may be carried out for a period ranging from 15 minutes to 40 minutes, preferably for a period of 20 minutes.

[0097] The efficiency of the SAP dissociation process depends on the time of action of the oxidizing composition: after initial thermal activation, it proceeds rapidly until the maximum action is exhausted within the indicated time, after which a time-independent plateau is reached.

[0098] The inventors have also observed that optimal results are obtained when the cellulose fraction and / or the plastic fraction are subjected to compressive forces during the immersion treatment step.

[0099] Compression can be carried out, for example, by a piston with a perforated disk head (the diameter of the holes is preferably 1 cm) operated by a hydraulic pump, resulting in a pressure of 5 to 20 N / cm for cellulose. 2 , 5 to 20 N / cm for plastic fraction 2 , preferably 5 to 15 N / cm 2 Apply pressure of .

[0100] In general, the compression applied to the material treated by immersion (Figures 3-5) allows a number of advantages to be obtained. Compression prevents the liquid fraction from separating from the solid fraction. In fact, in the absence of an adequate counterpressure, the solid fraction tends to separate from the aqueous solution containing the oxidizing agent. Due to the convection currents generated at high temperatures, the evolution of oxygen and water vapor, and the different densities of the solid components, the latter are pushed upward and lie above the liquid mass.

[0101] The compression applied to the solid fraction (both cellulose and plastics (mixed solid fraction) or cellulose and plastics separately) also allows for: The material to be treated is not too dense and compressible, which allows maintaining an optimal ratio between the volume of the aqueous solution containing at least one oxidizing agent and the weight of the solid fraction, thereby allowing a volume of aqueous solution to be used to keep the material to be treated in a permeated state. The materials to be treated (both cellulose and plastics, or cellulose and plastics separately) remain saturated with an aqueous solution containing at least one oxidizing agent throughout the duration of the soaking phase. Furthermore, at the end of the soaking period, it is possible to further increase the pressure, thereby compressing the solid fraction at the bottom of the reactor and allowing optimal separation of the liquid fraction, which is pushed upwards through the holes contained in the head of the piston. Facilitates optional washing cycles of the cellulose and plastic fractions when separated from the liquid fraction containing linear polyacrylates (LPA). downstream of said cycle, containing wastewater with a volume not more than twice the initial volume of the oxidizing solution used.

[0102] The immersion treatment step may be carried out by stirring using a mechanical stirring rod with fixed blades at an adjustable speed of 0 to 60 revolutions per minute (rpm), preferably 30 rpm.

[0103] The methods described herein may further comprise the step of separating the solid phase from the liquid phase, which may be performed by opening a side outlet valve or by suction.

[0104] In one or more embodiments, the method may also comprise at least one washing step of the solid phase, preferably carried out with water, to recover additional residues derived from the SAP. The solid phase (cellulose / plastic) may be subjected to drying, for example, in a dryer, as described in the previous section.

[0105] The liquid phase separated from the solid fraction downstream of the plastic fraction immersion treatment stage may contain a total solid residue of 1.0 to 15.5 g / L, with an average of 2.7 to 3.6 g / L.

[0106] The liquid phase separated from the solid fraction downstream of the steeping treatment stage of the cellulose fraction may contain a total solids residue of 6.1 g / L to 11.3 g / L.

[0107] The liquid phase separated from the solid fraction downstream of the steeping treatment stage of the mixed fraction exiting the shredder may contain a total solids residue of 7 g / L to 13 g / L.

[0108] The liquid phase separated from the solid fraction downstream of the steeping treatment stage of the mixed fraction exiting the autoclave may contain a total solids residue of 8 g / L to 12 g / L.

[0109] The liquid phase recovered following the solubilization of SAP downstream of the drying and separation step can be used to crosslink linear polyacrylates (LPA) to obtain superabsorbent polymers based on polysaccharides (polysaccharide-based SAPs), for example, by two modalities: i) by adding a crosslinker and an activator; and ii) by adding a monomer, a crosslinker, and an activator (US Pat. No. 4,295,987, "Cross-linked absorbent sodium polyacrylate"; US Pat. No. RE.32,649E, "Hydrogel-forming polymer compositions for use in absorbent structures").

[0110] According to modality i), after removing dissolved oxygen with nitrogen bubbling, the crosslinker N,N'-methylenebis(acrylamide) (MBA) is added to the reactor containing the liquid phase in an amount equal to 0.01-0.5% (wt / vol), preferably 0.15 (wt / vol, g / ml). Subsequently, an activator, or rather ammonium peroxodisulfate or potassium peroxodisulfate (APS or KPS), is added in an amount of 0.1-0.8% (wt / vol). By carrying out the reaction at 75 °C, precipitation of the crosslinked polymer is observed within 1 hour.

[0111] According to the procedure described in point ii), after removing dissolved oxygen with nitrogen bubbling, a monomer (acrylamide (AM), acrylic acid (AA), or methacrylic acid (MA) or its sodium or potassium salt) is added to the reactor containing the liquid fraction in an amount ranging from 1% to 7% (weight / volume), preferably equal to 4.7%. Furthermore, an activator, or rather, ammonium peroxodisulfate or potassium peroxodisulfate (APS or KPS), is added in an amount of 0.1 to 0.8% (weight / volume). After 1 hour, the pH is adjusted to an alkaline value using 10% NaOH, and then a crosslinker (MBA) is added in an amount of 0.01 to 0.5%, preferably 0.15% (weight / volume; g / ml). By carrying out the reaction at 80 °C, precipitation of the crosslinked polymer is observed after at least 1 hour.

[0112] The method may also comprise at least one purification step of the liquid fraction carried out by filtration, preferably carried out using a disc filter.

[0113] The purified liquid fraction containing linear polyacrylate (LPA) can be used for cross-linking of LPA and for the production of new SAPs.

[0114] For example, the purified liquid fraction can be subjected to a subsequent crosslinking step by exchange of calcium ions or other divalent or trivalent metals (Me), typically LPA, using a monovalent alkali metal, preferably sodium or potassium. The crosslinking step, carried out as described in U.S. Pat. No. 5,558,745, allows for the production of an insoluble compound (metal polyacrylate (PA-Me)) that can be separated by filtration. Calcium salts (or salts of other divalent or trivalent metals) allow for crosslinking, as multidentate metals bond two or more carboxylate groups to themselves, linking linear chains with crosslinks. Salts that can be used include chlorides, sulfates, nitrates, calcium carbonate, magnesium, zinc, and aluminum, preferably calcium chloride, and even more preferably calcium nitrate, the latter being more soluble and inert. Calcium salts can be used in an amount (wt / v) ranging from 1% to 5%, preferably equal to 3% (wt / v). Once the precipitate of metal-bound polyacrylate is obtained, the solvent can be evaporated to obtain a transparent solid material.

[0115] The liquid fraction, preferably purified by filtration, can also be subjected to a crosslinking step of the linear acrylate polymer by adding a crosslinker and a radical activator, as described, for example, in U.S. Pat. No. 4,295,987. Briefly, after removing dissolved oxygen by nitrogen bubbling and maintaining an inert atmosphere, the crosslinker N,N'-methylenebis(acrylamide) (MBA) is added to the purified liquid phase contained in a reactor or tank. The amount of MBA ranges from 0.02 to 0.25% (g / L), preferably equal to 0.12% (g / ml). Subsequently, an activating compound, such as ammonium peroxodisulfate or potassium peroxodisulfate (APS or KPS), is added at room temperature in an amount of 0.1% to 0.8% (wt / vol). The reaction, carried out at 60°C for a period of 2 hours, is accompanied by the precipitation of the crosslinked polymer.

[0116] The liquid fraction, preferably purified by filtration, can also be subjected to crosslinking by adding a monomer in addition to the crosslinker and activator. The monomer (acrylamide (AM), or acrylic acid (AA) or methacrylic acid (MA), or its sodium or potassium salt) is added in an amount ranging from 0.5% (wt / vol) to 7% (wt / vol), preferably 4% (wt / vol). The activator compound, or rather ammonium peroxodisulfate or potassium peroxodisulfate (APS or KPS), is then added in an amount ranging from 0.1 to 0.8% (wt / vol). After a period of 1 hour, the pH is brought to an alkaline value by adding 10% NaOH, and the reactor temperature is raised to 60°C for at least 3 hours. Finally, under the same conditions as described above, the crosslinker (MBA) is added in an amount ranging from 0.04% to 0.15% (preferably 0.08% mol / mol) relative to the monomer, and the activator compound is added.

[0117] As demonstrated in the examples below, the described method allows for the whitening of cellulose without damaging the polysaccharide backbone, while at the same time allowing for the cross-link cleavage and solubilization of SAP to obtain linear polyacrylate (LPA).

[0118] The cellulose obtained by the described method has a SAP content lower than 1% (w / w) and a purity higher than 99%. The purity and integrity of the cellulose obtained from the described method was determined and confirmed by analysis in Fourier transform infrared spectroscopy (FTIR) combined with ATR attenuated total reflectance (ATR), American Journal of Analytical Chemistry, 2018, Vol. 9, pp. 303-310.

[0119] Furthermore, the method makes it possible to maintain the polyolefins that constitute the plastic fraction and at the same time obtain cross-linking and solubilization of the SAP.

[0120] The plastics obtained by the described method have a SAP content below 1% (w / w) and a purity greater than 95%. The purity and integrity of the plastic-containing fractions obtained from the described method were determined and confirmed by analysis in Fourier transform infrared spectroscopy (FTIR) combined with the methods of UNI EN ISO 6427 / 2013 and ISO 16152 / 2005. example

[0121] 1. Step flow for solubilizing SAP for mixed cellulose and plastic fractions (Figure 3)

[0122] The used absorbent sanitary materials were sterilized in an autoclave at 135°C for 20 minutes at a pressure of 2.1 bar (2100 hectopascals).

[0123] At the end of the sterilization process, as explained in the previous section, the sterilized material exiting the autoclave is collected in a storage container 32. The collector may also have a reactor function. Cellulose + plastic (particle size 10cm to 35cm including SAP)

[0124] A mixed fraction consisting of cellulose, plastics, and SAP with a combined moisture content of 82% and a temperature of approximately 96°C is processed in a 1500-liter cylindrical stainless steel adiabatic reactor. The reactor has a rod with fixed blades for mechanical agitation. 81 liters of a commercial 30% (v / v) aqueous hydrogen peroxide solution with a density of 1.11 kg / L (300% on a dry basis) is fed into the low-temperature reactor along with another 60 L of water (the final oxide concentration is approximately 15% by weight of the total water). A total of 50 kg of mixed material with a moisture content of 82% by weight and a temperature of approximately 96°C is transferred into the reactor, and a disk-head piston with a 1 cm diameter hole, operated by a hydraulic pump, closes the head of the cylindrical reactor and applies a force of 8 N / cm to the material. 2The piston stroke is stopped when the level sensor indicates the liquid level is above the surface of the disc. The blade rod agitation is run for 80 minutes. After this period, the material is subjected to a pressure of 25 N / cm 2 By applying a pressure of 1000 kJ / min, the material is completely compressed and the solution is allowed to rise above the perforated piston head. An outlet valve allows the collection of waste solution. Two subsequent cycles using 50 L, which can be carried out with water only, allow any traces of residual LPA to be recovered from the first stage of the process. A solid mass with a residual moisture content of 36% by weight remains in the reactor. A 1 L fraction of the aqueous extract recovered downstream of the washing step is dried in an oven at 120 °C. A layered material suitable for film analysis by infrared spectroscopy (FTIR combined with ATR) is recovered. The sample is placed in direct contact with a transmission quartz crystal for ATR, revealing the presence of an IR spectrum compatible with LPA. The dried compound dissolved in deuterium oxide is also analyzed by carbon nuclear magnetic resonance spectroscopy ( 13 Analysis by C-NMR revealed the absence of a signal at approximately 84 ppm, which is characteristic of intramolecular cross-linking of SAP (Liu, ZS, Rempel, GL, Preparation of SAP by cross-linking acrylic acid and acrylic amide copolymers, Appl Polym Sci 64: 1345-1353, 1997).

[0125] The wet solid fraction is collected from the bottom of the reactor. To check for any SAP residues, an approximately 100 g aliquot is dried at 120°C to a constant weight (to allow for a degree of purity), reduced to particles at least smaller than 3 cm, and subjected to separation by density fractionation carried out in water (e.g., as described in U.S. Patent No. 2015 / 0238974 A1, Liquid Density Separation System). The less dense plastic fraction floats in the device, while the cellulose fraction sinks to the bottom. In this way, the two fractions are taken separately to assess the degree of residual SAP contamination. Analysis is performed by FTIR infrared spectroscopy combined with ATR. Both components do not have more than 1% SAP contamination.

[0126] Therefore, almost all of the SAP derivatives pass into the recovered water after at least two wash cycles.

[0127] Chemical analysis confirms that the two cellulose and plastic fractions also comply with the provisions of the Regulation on the Termination of the Requirements for Waste from Absorbent Products for Human Use, No. 62 of May 15, 2019, pursuant to Article 184, paragraph 2 of Decree No. 152 of April 3, 2006.

[0128] 2. Step flow for solubilizing SAP for mixed cellulose and plastic fractions (Figure 4)

[0129] The used absorbent sanitary materials were sterilized in an autoclave at 135°C for 20 minutes at a pressure of 2.1 bar (2100 hectopascals).

[0130] The sterilized material was crushed in a shredder to obtain material of a size less than 10 cm.

[0131] At the end of the milling process, the sterilized and milled material is transferred from conveyor 44 to a reactor before the dryer. Cellulose + plastic (particle size 3cm to 10cm including SAP)

[0132] A mixed fraction consisting of cellulose, plastics, and SAP with a combined moisture content of 77% and a temperature of approximately 75°C is processed in a 1500-liter cylindrical stainless steel adiabatic reactor. The reactor has a rod with fixed blades for mechanical agitation. 104 liters of a commercial 30% (v / v) aqueous hydrogen peroxide solution with a density of 1.11 kg / L (301% on a dry basis) is fed into the reactor along with another 90 L of water (the final oxide concentration is approximately 15% by weight of the total water). A total of 50 kg of mixed material with a moisture content of 77% by weight and a temperature of approximately 75°C is transferred into the reactor, and a disk-head piston with a 1 cm diameter hole, operated by a hydraulic pump, closes the head of the cylindrical reactor and applies a pressure of 6 N / cm to the material. 2 The piston stroke is stopped when the level sensor indicates the liquid level is above the surface of the disc. The blade rod stirring is turned on and additional heating is performed up to 75°C and maintained for 40 minutes. After this period, the material is subjected to a pressure of 22 N / cm 2 By applying a pressure of 1000 kJ / min, the material is completely compressed and the solution is allowed to rise above the perforated piston head. An outlet valve allows the collection of waste solution. Two subsequent cycles, each using 50 L, which can be carried out at low temperature with only water, allow any traces of residual LPA to be recovered from the first stage of the process. A solid mass with a residual moisture content of 33% by weight remains in the reactor. A 1 L fraction of the aqueous extract recovered downstream of the washing step is dried in an oven at 120 °C. A layered material suitable for film analysis by infrared spectroscopy (FTIR combined with ATR) is recovered. The sample is placed in direct contact with a transmission quartz crystal for ATR, revealing the presence of an IR spectrum compatible with LPA. The dried compound dissolved in heavy water can also be analyzed by carbon nuclear magnetic resonance spectroscopy ( 13Analysis by C-NMR revealed the absence of a signal at approximately 84 ppm, which is characteristic of intramolecular cross-linking of SAP (Liu, ZS, Rempel, GL, Preparation of SAP by cross-linking acrylic acid and acrylic amide copolymers, Appl Polym Sci 64: 1345-1353, 1997).

[0133] The wet solid fraction was collected from the bottom of the reactor. To check for any SAP residues, an approximately 100 g aliquot was dried at 120 °C to a constant weight (to allow for a degree of purity to be expressed) and subjected to separation by density fractionation carried out in water (e.g., as described in U.S. Patent No. 2015 / 0238974 A1, Liquid Density Separation System). The less dense plastic fraction floats in the device, while the cellulose fraction sinks to the bottom. In this way, the two fractions are taken separately to assess the degree of residual SAP contamination. Analysis is performed by FTIR infrared spectroscopy combined with ATR. The solid sample is placed in direct contact with a transmission quartz crystal for the ATR, allowing for the recording of typical IR spectra of the cellulose and plastic fractions. Both components have no more than 1% SAP contamination.

[0134] Therefore, almost all of the SAP derivatives pass into the recovered water after at least two wash cycles.

[0135] Chemical analysis confirms that the two cellulose and plastic fractions also comply with the provisions of the Regulation on the Termination of the Requirements for Waste from Absorbent Products for Human Use, No. 62 of May 15, 2019, pursuant to Article 184, paragraph 2 of Decree No. 152 of April 3, 2006.

[0136] 3. Step flow for solubilizing SAP for cellulose and plastic fractions (Figure 5)

[0137] The used absorbent sanitary materials were sterilized in an autoclave at 135°C for 20 minutes at a pressure of 2.1 bar (2100 hectopascals).

[0138] The sterilized material was crushed in a shredder to obtain material less than 3 cm in size.

[0139] The material subjected to sterilization and crushing was subjected to drying carried out in a dryer in which the dry air had a temperature of about 140°C.

[0140] Downstream of the drying stage, the material was separated into a cellulose fraction and a plastic fraction by using a centrifuge that utilizes two fractions of different densities, as described in the previous section. Cellulose (particles smaller than 3cm including SAP)

[0141] The cellulose fraction was processed in a 1500-liter cylindrical stainless steel adiabatic reactor, which was thermostable by heat exchange, circulation of a heat-transfer fluid in a coil, or ohmic heating achieved by electrical resistance. The reactor used had a rod with fixed blades for mechanical stirring. A total of 419 liters of a commercial 30% (v / v) aqueous hydrogen peroxide solution with a density of 1.11 kg / L (300% dry weight) was fed into the reactor along with another 550 L of water (a final oxide concentration of approximately 15% by weight compared to water) and heated to a temperature of 70°C. A total of 50 kg of cellulose with a moisture content of 7% and a temperature of approximately 20°C was transferred to the reactor and placed in a tank to obtain a suspension. A disk-head piston with a 1-cm diameter hole, operated by a hydraulic pump, closed the head of the cylindrical reactor and applied a force of 6 N / cm to the material. 2 The piston stroke was stopped when the level sensor indicated the liquid level was above the surface of the disc. The blade rod agitation was turned on and additional heating was obtained until a temperature of 85°C was reached in the bath and maintained at this temperature for 35 minutes. After this period, a pressure of 20 N / cm was applied to the material. 2By applying pressure of 0.05 mm, the material is fully compressed, allowing the solution to rise above the perforated piston head. An outlet valve allows for the collection of the waste solution (liquid fraction). Two washing cycles of 75 L each, performed at low temperature using only water, allow any traces of residual LPA to be recovered from the first stage of the process. 1 L aliquots of the liquid fraction recovered downstream of the washing stage were dried in an oven at 120 °C. Layered material suitable for film analysis by infrared spectroscopy (FTIR combined with ATR) is recovered. The sample is placed in direct contact with a transmission quartz crystal for ATR, revealing the presence of an IR spectrum compatible with LPA (Figure 6).

[0142] The dry compound dissolved in heavy water was also analyzed by carbon nuclear magnetic resonance spectroscopy ( 13 Analysis by C-NMR revealed the absence of a signal at approximately 84 ppm, which is characteristic of intramolecular crosslinking of SAP (Liu, ZS, Rempel, GL, Preparation of SAP by crosslinking acrylic acid and acrylic amide copolymers, Appl Polym Sci 64: 1345-1353, 1997) (Figure 7).

[0143] The cellulose fraction, separated from the liquid fraction and subjected to two washes with water, contains an amount of SAP less than 1% (analysis carried out in FTIR spectrophotometry combined with ATR). The solid sample is placed in direct contact with a transmission quartz crystal for ATR, allowing the recording of a typical IR spectrum of cellulose.

[0144] Therefore, almost all of the SAP passes into the liquid fraction separated from the suspension after at least two washing steps of the solid fraction.

[0145] Chemical analysis confirms that the cellulose fraction also complies with the provisions of the Regulation on the Termination of the Requirements for Waste from Absorbent Products for Humans, DECREE, No. 62, of May 15, 2019, pursuant to article 184, paragraph 2, of Decree No. 152, of April 3, 2006. Plastics (particles smaller than 3cm, including SAP)

[0146] The plastic fraction was placed in a 1500-liter cylindrical stainless steel adiabatic reactor, which was thermally stable by heat exchange, through the circulation of a heat-transfer fluid in a coil, or through ohmic heating achieved by electrical resistance. The reactor used had a rod with fixed blades for mechanical stirring. A total of 442 liters of a commercial 30% (v / v) aqueous hydrogen peroxide solution with a density of 1.11 kg / L (300% dry weight) was fed into the reactor along with another 550 L of water (a final oxide concentration of approximately 15% by weight compared to water) and heated to a temperature of 70°C. A total of 50 kg of plastic, containing 2% moisture and at a temperature of approximately 20°C, was transferred to the reactor and placed in a bath. A disk-head piston with a 1-cm diameter hole, operated by a hydraulic pump, closed the head of the cylindrical reactor and applied a pressure of 6 N / cm. 2 The piston stroke is stopped when the level sensor indicates the liquid level is above the surface of the disc. The blade rod stirring is turned on and additional heating is performed up to 75°C and maintained for 20 minutes. After this period, the material is subjected to a pressure of 16 N / cm 2 By applying a pressure of 0.05 L, the material is fully compressed, allowing the solution to rise above the head of the perforated piston. An outlet valve allows for the collection of waste solution. One subsequent cycle, using 75 L each, which can be run at low temperature using only water, allows any traces of residual LPA to be recovered from the first stage of the process.

[0147] Before treatment by immersion, the separated plastic fraction has a purity percentage of 85%, assessed by FTIR spectrophotometry combined with a method for extracting the polyolefin fraction soluble in hot xylene (method ASTM D5492 - ISO 16152:2005, Plastics, Determination of xylene soluble substances in polypropylene; UNIEN ISO 6427:2013, Plastics, Determination of substances extractable by organic solvents).

[0148] The aqueous fraction collected downstream of the wash was dried and analyzed by infrared spectroscopy (FTIR combined with ATR) revealing the presence of an IR spectrum compatible with LPA; 13 Analysis using C-NMR revealed the absence of a signal at approximately 84 ppm, which is characteristic of intramolecular cross-linking of SAP.

[0149] The plastic fraction, separated from the liquid fraction and washed with water, contains less than 1% SAP. The solid sample is placed in direct contact with the transmission crystal for the ATR, allowing the recording of a typical IR spectrum of the plastic components, essentially based on polypropylene and polyethylene. Thus, almost all of the SAP is separated from the solid fraction into the liquid fraction.

[0150] FTIR spectrophotometric analysis combined with ATR reveals the presence of cellulose components as minor residual contaminants in the plastic fraction. Known methods, such as extraction in supercritical phases or by enzymatic hydrolysis or physical separation, are capable of removing even minor contamination caused by cellulose residues from the plastic fraction.

[0151] Chemical analysis confirms that the plastic fraction also complies with the provisions of the Regulation on the Termination of the Requirements for Waste from Absorbent Products for Humans, DECREE, No. 62, of May 15, 2019, pursuant to article 184, paragraph 2, of Decree No. 152, of April 3, 2006.

[0152] Of course, without violating the principles of the present invention, the details of construction and the present embodiment may be widely varied without thereby departing from the scope of the present invention as defined by the following claims.

Claims

1. 1. A method for separating a superabsorbent polymer (SAP) fraction from a used absorbent sanitary product, said used absorbent sanitary product further comprising at least one cellulose fraction and one plastic fraction, said method comprising at least Sterilizing (SR) said used absorbent sanitary product; treating the used absorbent sanitary product by immersion in a bath with an aqueous solution containing at least one oxidizing agent to break crosslinks contained in the used absorbent sanitary product and solubilize the SAP, wherein the step of breaking the crosslinks and solubilizing the SAP is carried out after the sterilizing step (SR) by immersing the sterilized used absorbent sanitary product in a bath with the aqueous solution to form a suspension; Obtaining the suspension comprising i) a solid fraction and ii) a liquid fraction, wherein the solid fraction comprises the cellulose fraction and the plastic fraction, and the liquid fraction comprises linear polyacrylate (LPA) resulting from the cleavage of the crosslinks and solubilization of the SAP; A method for providing the above.

2. 2. The method according to claim 1, wherein the sterilizing step (SR) is carried out by heating the used absorbent sanitary product at a temperature between 120°C and 140°C and at a pressure comprised between 1 bar and 3.6 bar (1000 hPa and 3600 hPa).

3. 3. The method of claim 1, wherein the at least one oxidizing agent is selected from the group consisting of sodium persulfate, potassium peroxodisulfate, ammonium persulfate, potassium peroxymonosulfate, and hydrogen peroxide.

4. 4. The method according to any one of claims 1 to 3, wherein the method also comprises a step of crushing (SH) the sterilized used absorbent sanitary products to obtain sterilized and crushed absorbent sanitary products having a particle size of less than 10 cm.

5. 5. The method of claim 4, wherein the method also comprises drying (DR) the shredded used absorbent sanitary products to obtain shredded and dried used absorbent sanitary products.

6. 6. The method of claim 5, wherein the method also comprises a step (SEP) of separating the plastic fraction and / or the cellulose fraction from the shredded and dried used absorbent sanitary products.

7. 6. The method according to claim 4 or 5, wherein the step of breaking the crosslinks and solubilizing the SAP is carried out after the crushing step (SH) by immersing the sterilized and crushed used absorbent sanitary product in a bath with the aqueous solution to form the suspension, and the solid fraction comprises the cellulose fraction and the plastic fraction.

8. 7. The method according to claim 6, wherein the step of breaking the crosslinks and solubilizing the SAP is carried out by immersing the plastic fraction and / or the cellulose fraction separated from the shredded and dried used absorbent sanitary products in a bath of the respective aqueous solution.

9. 8. The method according to claim 7, wherein the ratio between the volume of the aqueous solution comprising at least one oxidizing agent and the weight of the sterilized used absorbent sanitary product is comprised between 3 l / kg and 12 l / kg.

10. 9. The method according to claim 8, wherein the ratio between the volume of the aqueous solution containing at least one oxidizing agent and the weight of the cellulose fraction or the plastic fraction is comprised between 10 l / kg and 30 l / kg.

11. 8. The method according to claim 7, wherein the step of treating the sterilized used absorbent sanitary products by immersion is carried out in a bath having an aqueous solution containing at least one oxidizing agent in an amount comprised between 10% and 50% (w / w).

12. said step of treating said cellulose fraction is carried out by immersion in a bath having an aqueous solution containing at least one oxidizing agent in an amount comprised between 10% and 50% (w / w); and / or 9. The method according to claim 8, wherein said step of treating said plastic fraction is carried out by immersion in a bath having an aqueous solution containing at least one oxidizing agent in an amount comprised between 5% and 50% (w / w).

13. 13. The method according to any one of claims 1 to 12, wherein said step of treating by immersion is carried out at a temperature comprised between 65°C and 100°C.

14. During the step of treating by immersion, the sterilized used absorbent sanitary product, and The cellulose and / or plastic fraction separated from the dried used absorbent sanitary product and immersed in the respective bath of the aqueous solution is subjected to a water-absorbent force of 5 N / cm ２ ~20N / cm ２ is subjected to a compressive force under pressure of 9. The method according to claim 7 or 8.

15. 15. The method of any one of claims 1 to 14, wherein the method also comprises separating the solid fraction from the liquid fraction contained in the suspension.

16. 16. The method of claim 15, wherein the method also comprises purifying the liquid fraction comprising linear polyacrylate (LPA).

17. 17. The method according to any one of claims 1 to 16, wherein the method comprises obtaining a linear polyacrylate (LPA) separated from a used absorbent sanitary product.

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