Method for photocatalytic degradation of plastic materials under visible light
Patent Information
- Application Number
- EP2023789293
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-10-14
- Filing Date
- 2023-10-10
- Publication Date
- 2025-08-20
AI Technical Summary
Current methods for degrading plastic materials are inefficient, particularly in visible light, often require organic solvents or high temperatures, and can lead to the release of nanoparticles into the environment, with limitations in degrading microplastics and producing recoverable carbon products.
A process involving the production of agglomerated and activated titanium oxide (TiO2/MxOy) photocatalysts, which are attached to plastic surfaces through covalent bonds, allowing for photocatalytic degradation in visible light without organic solvents or high temperatures, and enabling the degradation of plastic mixtures and microplastics, while preventing nanoparticle dispersion.
This process enables rapid and efficient degradation of plastic materials, producing recoverable carbon products and avoiding nanoparticle release, with the capability to degrade plastic waste in visible light, including microplastics, and recover valuable organic compounds.
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Abstract
Description
[0001] Photocatalytic degradation process of plastic materials in the visible range
[0002] The invention relates to the photocatalytic degradation of plastic materials.
[0003] State of the art
[0004] Photocatalysis is an oxidation process allowing the production of oxidizing species, in particular radicals, by irradiation at wavelengths corresponding to energies higher than that of the band gap energy of certain semiconductor solids, in the presence of water and oxygen.
[0005] Photocatalysis involves a photocatalyst, i.e. a catalyst activated by light energy with water and oxygen from the air as oxidants. The photocatalyst makes it possible to accelerate a chemical reaction, without ultimately being consumed. It is generally a semiconductor belonging to the oxide (TiOs, ZnO) or sulfide (CdS, ZnS) type chalcogenides, the most widely used photocatalyst to date being titanium dioxide.
[0006] There are eleven crystal structures for titanium dioxide, seven of which are stable at room temperature and pressure. In nature, titanium dioxide occurs mainly in the anatase and rutile forms, and more rarely in the form of brookite or TiC>2( B). Titanium dioxide is synthesized most often in the anatase form, or in the rutile form, and much more rarely in the form of brookite. There are other forms that are more difficult to synthesize, as well as various TiOs-x sub-oxides, or TiOs+x super-oxides.
[0007] The reference photocatalytic material in most laboratory studies is marketed by Evonik-Degussa under the name Aeroxide TiOP25 (formerly Degussa P25). This product consists of a mixture of approximately 80% anatase and 20% rutile for the crystalline phases and a small fraction of TiO in amorphous form. The exact structure of this Aeroxide product is debated, see for example Jiang et al, Anatase and rutile in evonik aeroxide P25: heterojunctioned or individual nanoparticles?, Catalysis today, Vol 300, February 2018, pages 12-17. For a quantitative characterization of this Evonik Aeroxide P25 product, one can refer for example to the document Tobaldi et al, Fully quantitative X-ray characterization of Evonik Aeroxide TiOs P25, Materials Letters, May 2014, Vol 122, 345-347.
[0008] Anatase has a band gap of 3.23 eV. Anatase activity is thus limited to wavelengths below the band gap, i.e. λ<387 nm. Rutile has a band gap of 3.02 eV. Rutile activity is thus limited to wavelengths below the band gap, i.e. λ<41 1 nm. These gap values can be slightly modulated depending on the size of the material, by quantum confinement effect, or by doping with ions or metal nanoparticles.
[0009] In its most common commercial forms, TiOs is therefore mainly activated by ultraviolet rays, with rutile also absorbing a small part of the visible spectrum. The useful wavelength ranges for rutile and anatase correspond to only about 6% of the solar radiation received on Earth, compared to about 50% for the visible range.
[0010] Much work has been done to expand the effectiveness of titanium dioxide in visible light: black titanium dioxide (Ullattil et al, Black TiC nanomaterials: a review of recent advances, Chemical Engineering Journal 343, 2018, pages 708-736; Rajaraman et al, Black TiC: a review of its properties and conflicting trends, Chemical Engineering Journal Vol 389, 2020); doped titanium dioxide (Kumaravel et al, Photocatalytic hydrogen sensitized titanium dioxide, by heterojunction with a semiconductor, or by plasmon effect, or even by contact with a conjugated compound. The invention relates in particular to the degradation of plastic materials by heterogeneous photocatalysis, the photocatalyst being in solid phase and the reactants being in gaseous or aqueous phase.
[0011] By "plastic material" we mean a synthetic material based on the use of macromolecules, and transformable in particular by molding or forming.
[0012] Three main families of plastic materials are marketed: thermoplastics (in particular polyethylenes PE, polypropylenes PP, polystyrenes PS, polyvinyl chlorides PVC, polyamides PA, polyethylene terephthalates PET, polymethyl methacrylate PMMA, polycarbonates PC, polytetrafluoroethylene PTFE), thermosets (for example polyurethane), elastomers.
[0013] Plastic materials are present in many sectors of activity, particularly in packaging, construction, automotive, agriculture, and textiles. Depending on the uses, plastic materials contain functional additives, for example plasticizers, flame retardants, and stabilizers. Plastic materials often contain fillers and pigments.
[0014] Environmental contamination by polymer materials is one of the most serious problems facing the world today.
[0015] According to a literature review presented by Ariza-Tarazona et al. (Microplastic pollution reduction by a carbon and nitrogen-doped T1O2: Effect of pH and temperature in the photocatalytic degradation process, Journal of Hazardous Materials 395 (2020) 122632), for the period from the 1950s to 2018, 6.3 billion tons of plastic waste were generated worldwide, with approximately 79% of this plastic waste ending up in the environment. The amount of plastics produced worldwide since the 1950s is expected to exceed the threshold of 12 billion tons by 2050. Plastic waste is particularly present in the form of microplastics (MPs) and nanoplastics (NPs).
[0016] Microplastics are polymeric waste materials in the form of debris between 1 micron and 5 mm in size (Frias et al, Microplastics: finding a consensus on the definition, Marine Pollution Bulletin, 2019). Microplastics originate from the fragmentation of plastic waste or from the release of manufactured micrometric plastic products. A classification of plastic waste according to their size and a classification of microplastics according to their morphology are presented by Crawford et al, (Microplastic identification techniques. Microplastic Pollutants, 2017, 219-267).
[0017] By "nanoplastics", some authors refer to elements whose size is between 1 nm and 100 nm, other authors use this expression to refer to particles whose size is between 1 nm and 1000 nm (Hughes et al, Human and ecological health effects of nanoplastics: May not be a tiny problem, Current Opinion in Toxicology, volume 28, 2021).
[0018] Microplastics are ingested by marine organisms and enter the food chain (Danopoulos et al, Microplastic Contamination of Seafood Intended for Human Consumption: A Systematic Review and Meta-Analysis, Environmental Health Perspectives, 2020). The effects of microplastics and nanoplastics on human health are the subject of studies (Kumar et al, Micro(nano)plastics pollution and human health: How plastics can induce carcinogenesis to humans?, Chemosphere, volume 298, 2022; Hang et al, The ecotoxicological effects of microplastics on aquatic food web, from primary producer to human: A review, Ecotoxicology and Environmental Safety, volume 173, 2019).
[0019] As pointed out by Zhang et al, ( Current technologies for plastic waste treatment: A review, Journal of Cleaner Production 2021 , 282), a large number of techniques have been proposed in the prior art for the treatment of plastic waste, in particular reuse, incineration, landfilling, pyrolysis, and different degradations (photodegradation, thermodegradation, biodegradation by invertebrates or microorganisms). Another presentation of these known plastic waste treatment techniques is proposed by Ali et al, Degradatation of conventional plastic wastes in the environment: a review on current status of knowledge and future perspectives of disposal, Science of The Total Environment, Volume 771, 2021.
[0020] Most of these techniques have drawbacks. The return of certain plastic waste to product status in circular economy sectors, according to the SSD procedure (exit from waste status) or reuse cannot be implemented for all plastic waste. Pyrolysis allows fuel to be produced by distillation, but generates residues. Incineration generates energy, but produces waste (refiom, bottom ash) and fumes. Landfilling can allow energy recovery from biogas, but requires collection and treatment of leachates, for the protection of groundwater. The biodegradation of plastic materials by microorganisms or invertebrates is very slow (Shahnawaz et al, Bioremediation Technology for Plastic Waste, 2019).For example, document CN 1 1 0507945 (Xiangrong, 2019) describes the use of Galleria mellonella for the degradation of plastics, with treatment lasting 400 days. Zhu et al (Journal of Cleaner Production, volume 310, 2021) mentions a degradation of 35% of a polyurethane and 13% of a polystyrene, by Galleria mellonella larvae, after seven days.
[0021] Photodegradation appears to be the most promising answer to the treatment of plastic waste, especially when the energy source is sunlight.
[0022] It has been proposed to promote this photodegradation by using photodegradable plastics, see for example document WO201 0 / 075609 (Goody Environment, 201 0). The manufacture of this type of plastic is however expensive, due to the use of additives to promote degradation. Controlling the irradiation time is also difficult (Daglen et al. Photodegradable plastics: end-of-life design principles, Green Chemistry Letters and Reviews. 3(2), 2010). Document EP231 2959B1 (Rhodia, 2017) describes a photodegradable plastic material having a cellulose ester content, and containing dispersed titanium dioxide, in particular anatase, the plastic material being used for the manufacture of cigarette filters.
[0023] It has been proposed to integrate nanoscale photocatalysts into polymer materials. A state-of-the-art review is presented by Nabi et al. Application of titanium dioxide for the photocatalytic degradation of macro and micro plastics: A review, Journal of Environmental Chemical Engineering, 9, 2021.
[0024] The paper Coburn et al. (Industrial scalable additives for enhanced decomposition of plastic waste through photocatalysis, Academic Journal of Polymer Science, 2020) describes the integration of ZnO, WO3 and FesOs and TiOs (anatase) oxides, in the form of nanoparticles, into four types of polymer films: polyethylene terephthalate (PET), high-density polyethylene (HDPE), low-density polyethylene (LDPE) and polystyrene (PS), these films then being placed in salt water, and photodegraded by ultraviolet light.
[0025] Bandara et al. (Is nano ZrO2a better photocatalyst than nano TiO2for degradation of plastics, RSC advances, 2017, vol. 7, 83) describes the photocatalysis of polyethylene (PE) and polypropylene (PP) using nanoparticles of zirconium oxide ZrOs or titanium oxide TiOs (anatase), suspended in tetrahydrofuran, with treatment times ranging from 20 hours to 100 hours. Both materials were synthesized using high-temperature treatment, 450°C for TiOs and 700°C for ZrOs. After 20 hours of irradiation under a solar simulator (solar simulator 1 h = 10 h of sunshine), the reactivity of ZrOs nanoparticles, compared to TiOs nanoparticles, was respectively 7% and 20% higher for PE and PP.
[0026] The use of nanoscale titanium oxide for the degradation of plastic materials is also proposed in the following documents: Lee et al., Water 2020, 12, 3551 (treatment of polyamide 66 microfibers), Wang et al., Sol. Energy Mater. Sol. Cells 143, 2015 (treatment of high-density polyethylene), Ali et al., Environ. Nanotechnol. Monit. Manag. 5, 44-53 (treatment of low-density polyethylene films with TiOs nanotubes).
[0027] Photodegradation of plastic materials using doped titanium oxide has been proposed in the following papers: Nguyen et al, e-Polymers 2018 (benzophenone), Shang et al, Environ. Soi. Technol. 2003, 37, 4494-4499 (copper phthalocyanine), Li et al, Polym. Plast. Technol. Eng. 49, 400-406 (polypyrrole).
[0028] The use of dopants has disadvantages. Some dopants, for example benzophenone (CAS 1 19-61-9) are harmful to human health.
[0029] The modification of TiOs by doping adds an additional preparation step to the photocatalytic process, as well as a stability problem with respect to the composite material obtained.
[0030] The use of photocatalysts in nanometric form leads to risks of dissemination of nanoparticles into the environment.
[0031] Given the potential health risks that titanium dioxide in its nanometric form could present, it has been proposed to fix titanium dioxide on a support.
[0032] However, one of the major drawbacks of fixing titanium dioxide on a support is the strong reduction in photocatalytic activity, compared to dispersed TiOs.
[0033] Invention
[0034] The invention aims to overcome the drawbacks of known methods for degrading plastic materials. A first object of the invention is to provide a method for the photocatalytic degradation of plastic materials allowing rapid degradation and production of recoverable carbon products.
[0035] A second object of the invention is to provide a method for the photocatalytic degradation of plastic materials allowing degradation in visible light, without the use of organic solvents or high-temperature treatment.
[0036] Another object of the invention is to provide a method meeting at least one of the above objects, and allowing the degradation of mixtures of plastic materials.
[0037] Another object of the invention is to provide a method meeting at least one of the above objects, and allowing the degradation of plastic materials without prior treatment of these materials, only grinding being possibly carried out.
[0038] Another object of the invention is to provide a method meeting at least one of the above objects, and allowing the degradation of microplastics.
[0039] Another object of the invention is to provide a method meeting at least one of the above objects, and allowing the total degradation of plastic waste by photodegradation, and the recovery and use of the degradation products.
[0040] Another object of the invention is to provide a method meeting at least one of the above objects, and allowing the degradation of plastic materials, without risk of releasing nanoparticles into the environment.
[0041] Another object of the invention is to provide a method meeting at least one of the above objects, the method being integrated in-situ, all the steps of the method being able to be carried out on a single site.
[0042] For these purposes, there is provided, according to a first aspect, a method for producing agglomerated and activated TiOs or TiOs / MxOy to degrade a plastic material or a mixture of plastic materials, the method comprising the following sub-steps: preparation and heating of an aqueous solution at neutral pH or at a given acidic pH, for example by addition of hydrochloric acid, without surfactant, addition to the acidic or neutral aqueous solution of a titanium oxide precursor, or of a mixture of a titanium oxide precursor TiOs and at least one other precursor of another oxide M x O y , composed of more than 80 mol% TiOs and less than 20 mol% of another metallic or semi-metallic oxide M x O y, and stirring the acidic or neutral aqueous reaction medium, immersing a plastic material or a mixture of plastic materials, previously ground, in the acidic or neutral aqueous reaction medium, heating the acidic or neutral aqueous reaction medium, at a temperature between 30°C and 90°C, to condense the precursors of the acidic or neutral aqueous reaction medium on the surface of the plastic materials, the precursors attaching by covalent bonds to this surface, and forming TiO2 / M x O y agglomerated and activated, photocatalytic degradation, at neutral or slightly acidic pH, of the plastic material or mixture of plastic materials, so as to obtain TiC>2 / M x O y agglomerated and activated without the plastic material, capable of allowing the degradation of one or more other plastic materials.
[0043] In some implementations, a filtration step is performed between the heating step and the photocatalytic degradation step, in order to remove by-products formed during the crystallization of TiOs or TiOs / M x O y , this step allowing to improve the kinetics of photocatalytic degradation of plastic materials.
[0044] The previously ground plastic material or mixture of plastic materials allows the titanium oxide precursors (or the mixture of the titanium oxide precursor and at least one other precursor of the other metallic or semi-metallic oxide) to crystallize on the surface of the plastic materials, the TiC>2 / M x O yobtained being attached (grafted) to the surface of plastic materials, by covalent bonds. In certain implementations, the pH is chosen between 0 and 1, so as to obtain the TiOs of the TiOs / MxOy agglomerated and activated on the plastic(s), in rutile crystalline form.
[0045] In other implementations, the pH is chosen between 5 and 7, so as to obtain the TiOs of the TiOs / MxOy agglomerated and activated on the plastic(s), in brookite crystalline form.
[0046] In certain implementations, the method comprises a step of adding a titanium precursor carried out with the addition of a metal oxide WO3, the pH of the reaction medium being between 0 and 7, so as to obtain the TiOs of the TiOs / WOs agglomerated and activated on the plastic(s), in anatase crystalline form.
[0047] Advantageously, the titanium precursor is chosen from the group comprising titanium isopropoxide, sodium titanate Na2Ti3O7 or a derivative.
[0048] Advantageously, the metallic or semi-metallic oxide is chosen from the group comprising SiOs, ZrOs, AI2O3, Fe2O3, CeC>2, MgO, CuO, NiO, CU2O, SnO2, RUO2, Bi20s, WO3, V2O5, Ag3PO4.
[0049] A second aspect is proposed, a TiO2 / M x O y agglomerated and activated, to degrade a plastic material or a mixture of plastic materials, obtained by the process presented above.
[0050] Advantageously, a material for photocatalysis based on TiO2 or TiO2 / M is proposed. x O y , resulting from the process presented above, this material is agglomerated and activated to degrade a plastic material or a mixture of plastic materials, from visible and / or UV light, in an acidic or neutral aqueous reaction medium at a temperature less than or equal to 90°C, composed of more than 80% by moles of TiC>2 and less than 20% by moles of another metallic or semi-metallic oxide Mx Oy, and in which the TiO2 or TiC>2 / M x O y agglomerate is activated after photocatalytic degradation of a first plastic material or a mixture of plastic materials, according to the process presented above.
[0051] In some implementations, TiOs or TiOs / M x O y , agglomerate has agglomerates of 300 nm up to 5 microns, advantageously 300 nm up to 1 micron,
[0052] Advantageously, the material for photocatalysis based on TiOs or TiOs / M x Agglomerated Oy shows traces of the first plastic material or mixture of plastic materials, visible by spectroscopy.
[0053] In some implementations, the material for photocatalysis based on TiOs or TiOs / M x O y agglomerated is only agglomerated TiOs, with traces of the first plastic material or mixture of plastic materials visible by spectroscopy.
[0054] In some implementations, the material for photocatalysis based on TiOs or TiOs / M x O y agglomerate is only TiC>2 / M x O y agglomerated, with traces of the first plastic material or mixture of plastic materials visible by spectroscopy.
[0055] Advantageously, for the material for photocatalysis based on TiOs or TiOs / M x O y agglomerated, TiOs or TiO2 / M x O y agglomerated and activated is obtained without calcination.
[0056] In some implementations, in the material for photocatalysis based on TiO2 or TiO2 / M x O y agglomerated, TiO2 of TiO2 alone agglomerated or TiO2 / M x Agglomerated Oy has a rutile crystalline form.
[0057] In other implementations, for the material for photocatalysis based on TiO2 or TiO2 / M x O yagglomerated, TiO2 of TiO2 alone agglomerated or TiO2 / M x Agglomerated Oy has a brookite crystalline form.
[0058] According to a third aspect, there is provided a method of degrading a second plastic material or a mixture of plastic materials, using a material for photocatalysis based on TiO2 or TiO2 / M x O yagglomerated and activated, and having already degraded a first plastic material or a mixture of plastic materials, the degradation method comprising in a first cycle: a step 1) of suspension by stirring of the agglomerated and activated TiOs or TiOs / MxOy, having degraded a first plastic material or mixture of plastic materials, advantageously at a pH between 5 and 7; a step 2) of adding to the solution, one or more second plastic materials previously ground; a step 3) of heating the solution, advantageously between 70°C and 90°C, to graft the agglomerated and activated TiOs or TiOs / MxOy in suspension by stirring, onto the second plastic material or mixture of plastic materials; a step 4) of photocatalytic degradation of the second plastic material or mixture of plastic materials grafted with the agglomerated and activated TiOs or TiOs / MxOy, at least in the visible range, forming decomposition products.
[0059] Advantageously, the degradation process comprises one or more repetitions of steps 2) to 4), each repetition of these steps 2) to 4) corresponding to a cycle, using the same agglomerated and activated TiOs / MxOy.
[0060] Advantageously, the photocatalytic degradation step is carried out in natural light or under visible radiation.
[0061] In some implementations, the photocatalytic degradation step is carried out by contact with oxygen in the air, at atmospheric pressure.
[0062] In some implementations, the decomposition products are of the carboxylic acid or alcohol type.
[0063] Advantageously, the decomposition products are selected from the following list: acetone, acetic acid, formic acid, isopropanol, methanol, methyl formate, methyl acetate, glycerol, glyoxal, ethanol. Advantageously, the decomposition products include biogases such as hydrogen, methane, CO, and / or CO2.
[0064] In some implementations, suspension is carried out, during step 4), using a peristaltic pump or a flow of compressed air.
[0065] In some implementations, step 4) of degradation of the plastic material or plastic materials grafted with the agglomerated and activated TiOs or TiOs / MxOy in suspension by stirring is carried out in the solution.
[0066] In some implementations, the acidic or neutral aqueous solution in which the plastic material or mixture of plastic materials is degraded is only water, such as tap water.
[0067] In some implementations, in step 1) a mixture of crystalline forms of agglomerated TiOs alone or agglomerated TiOs / MxOy is added which includes the rutile form and the brookite crystalline form.
[0068] In certain implementations, the method comprises a step 3) of heating the solution, between 30°C and 90°C, advantageously at 90°C, and a step 4) of degradation of the second plastic material or of the mixture of plastic materials grafted with the agglomerated and activated TiOs or TiOs / MxOy, at a temperature between 30°C and 90°C.
[0069] Other objects and advantages of the invention will appear in the light of the description of embodiments, given below with reference to the appended drawings in which:
[0070] - Figure 1 is a diagram showing the production of agglomerated and activated titanium oxide TiOs, and the process of degradation of plastic materials with this titanium oxide;
[0071] - Figure 2 shows infrared spectra, for wavelengths (wavenumber) between 500 and 4000 cm' 1 , for a mixture of plastic materials comprising polystyrene PS, polyethylene PE and polybutylene PBE, at a concentration of 5g / L, in the initial state (solid curve) and after photocatalysis treatment for 20 hours (dashed curve), the photocatalysis being carried out with light in the visible range, the titanium oxide used being in rutile form;
[0072] - Figure 3 shows infrared spectra, for wavelengths between 500 and 4000 cm' 1, for a mixture of plastic materials comprising polystyrene PS, polyethylene PE and polybutylene PBE, at a concentration of 5g / L, in the initial state (solid curve) and after photocatalysis treatment for 20 hours (dashed curve), with light in the visible range, the titanium oxide used being in brookite form;
[0073] - Figure 4 shows infrared spectra, for wavelengths between 1000 and 1600 cm' 1 approximately, for polyvinyl chloride, at a concentration of 1.6g / L, in the initial state (solid curve) and after photocatalysis treatment for 2 hours (dashed curve), with light in the visible range, the titanium oxide used being in rutile form;
[0074] - Figure 5 is a partial view of an NMR spectrum 1H showing the degradation products of PVC by a titanium oxide, according to a process as represented in figure 1, the photodegradation being carried out in the visible, the titanium oxide being in brookite form.
[0075] First, a process for producing an agglomerated and activated TiOs / MxOy material for degrading plastic materials is described.
[0076] The method comprises preparing and heating an aqueous solution at neutral pH, or at acidic pH, for example by adding hydrochloric acid without surfactant.
[0077] The method then comprises a step of adding to the acidic or neutral aqueous solution, a titanium oxide precursor (or a mixture of a titanium oxide precursor TiOs and at least one other precursor of another oxide M x O y , composed of more than 80 mol% TiOs and less than 20 mol% of another metallic or semi-metallic oxide M x O y), with stirring of the acidic or neutral aqueous reaction medium.
[0078] The method then comprises a step of immersing a plastic material or a mixture of plastic materials, previously ground, in the acidic or neutral aqueous reaction medium to condense the precursors of the acidic or neutral aqueous reaction medium on the surface of the plastic materials, TiC>2 / M x O y agglomerated and activated obtained by attaching (grafting) by covalent bonds on this surface.
[0079] The grinding of the plastic material or the mixture of plastic materials is advantageously carried out so as to obtain a maximum grain size of a few millimeters.
[0080] The process then comprises heating the acidic or neutral aqueous reaction medium, advantageously to a temperature between 30°C and 90°C.
[0081] The previously ground plastic material or mixture of plastic materials allows the TiC>2 / M material to crystallize x O y from titanium oxide precursors (or the mixture of titanium oxide precursor and at least one other precursor of the other metallic or semi-metallic oxide) on the surface of plastic materials, the material TiC>2 / M x O y agglomerated and activated being attached (grafted) to the surface of plastic materials by covalent bonds.
[0082] Advantageously, a filtration step is carried out in order to eliminate the by-products formed during crystallization, this step making it possible to improve the kinetics of photocatalytic degradation of plastic materials.
[0083] The process then includes a step of photocatalytic degradation, in a slightly acidic or neutral pH medium, of the plastic material or the mixture of plastic materials grafted onto the TiC>2 / Mx O y agglomerated and activated. This degradation of plastic materials is now described using agglomerated and activated TiOs / MxOy.
[0084] The process takes place in a suitable reactor in acidified or non-acidified aqueous solution. The pH range is between 0 and 7. Tap water can be used, as can rainwater.
[0085] The titanium precursor (for example 97% titanium isopropoxide) or a mixture of titanium precursor and another oxide (for example aluminum, iron, or tungsten oxide) is then incorporated at a temperature of 50°C and with vigorous stirring (600 rpm).
[0086] When the precipitate which forms instantly has completely dissolved, 300mg to 1300mg of plastic material (or mixture of plastic materials), previously ground, are then added.
[0087] Plastic materials include polystyrene, polyethylene, polyvinyl chloride, polypropylene, polyurethane, polymethyl methacrylate, and polyperfluorinated polystyrene.
[0088] Stirring then becomes moderate when a new precipitate appears (approximately 300 rpm). The temperature is maintained at 50°C for at least 5 hours (ideally 24 hours), then increased to 90°C for 19 hours (ideally 24 hours).
[0089] The composite materials obtained are micrometric or millimetric in size.
[0090] The reaction medium is then placed in a new enclosure and then advantageously irradiated by visible radiation, to degrade the plastic material(s).
[0091] In some embodiments, a filtration step is performed prior to photocatalytic degradation of the plastic materials to remove by-products formed during TiOs / MxOy crystallization, this step improving the photocatalytic degradation kinetics of the plastic materials.
[0092] The particles in solution are advantageously suspended, for example by passing compressed air or by a fluidic pump for better contact with light.
[0093] Once the plastic material (or mixture of plastic materials) has been degraded, the agglomerated and activated TiOs / MxOy is directed to the synthesis reactor, to replenish 300mg to 1300mg of plastic material for the recycling cycle.
[0094] In the synthesis reactor, the reaction medium, neutral or weakly acidic (range 5-7), is suspended by stirring and heated to 90°C for up to 24 hours.
[0095] The TiOs / MxOy / plastic material (or TiOs / MxOy / mixture of plastic materials) reintroduced into the photocatalysis chamber, is suspended by stirring in solution and then irradiated. Once the new plastic material (or new mixture of plastic materials) has degraded, a new cycle of recycling and then degradation can be carried out, and so on.
[0096] The invention has many advantages.
[0097] The obtained agglomerated and activated TiOs / MxOy has a long lifespan, and allows a multitude of recycling and degradation.
[0098] TiOs / MxOy / plastic material (or TiOs / MxOy / plastic material mixture) composite materials are also active in open air, without the presence of water. Thus, after synthesis or recycling cycles, the composite materials can be filtered, dried, and the powder can be advantageously irradiated by visible radiation in open air.
[0099] The process allows the degradation of plastic materials that are not recyclable or are not very recyclable or reusable to date (PVC, low density PE, PMMA, PU, PS, perfluorinated polymers such as polytetrafluoroethylene PTFE), as well as mixtures of these polymers.
[0100] The process allows the recovery of degradation products, in particular organic products (methanol, acetone, isopropanol, acetic acid, gas).
[0101] The process allows the elimination of microplastics, for example in seas or oceans.
[0102] The process advantageously allows photodegradation using energy-efficient LED light sources or sunlight.
[0103] The process avoids the risk of dispersion of nanoparticles into the environment, as the particles of titanium oxide or a mixture of titanium oxide and another agglomerated and activated oxide are recycled in a closed environment.
[0104] Advantageously, once bound to the surface of a plastic material or a mixture of plastic materials, the particles of agglomerated and activated TiOs / MxOy are of micrometric size, and retain a size greater than the nanometric threshold dangerous for the environment (Decree No. 2012-232 of February 17, 2012 relating to the annual declaration of substances in nanoparticle state, taken in application of Article L. 523-4 of the Environmental Code), even after degradation of the plastic material which served as their support.
[0105] The resulting photoactive composite materials are at least on the micrometric scale.
[0106] The process allows the production of alcohols, carboxylic acids, ketones and biogas. The process allows the elimination of a plastic material (or mixtures of plastic materials) in very short times, in the order of 2 to 24 hours of irradiation.
[0107] The process uses titanium oxide in a pure rutile phase or a pure brookite phase.
Claims
Claims . Process for producing TiOs or TiOs / MxOy, agglomerated and activated to degrade a plastic material or a mixture of plastic materials, comprising the following sub-steps: preparation and heating of an aqueous solution at neutral pH or at a given acidic pH, and without surfactant, addition to the acidic or neutral aqueous solution of a titanium oxide precursor, or of a mixture of a titanium oxide precursor TiOs and at least one other precursor of another oxide M x O y , composed of more than 80 mol% TiOs and less than 20 mol% of another metallic or semi-metallic oxide M x O y, and stirring the acidic or neutral aqueous reaction medium, immersing a plastic material, or a mixture of plastic materials, previously ground, in the acidic or neutral aqueous reaction medium, heating the acidic or neutral aqueous reaction medium, at a temperature between 30°C and 90°C, to condense the precursors of the acidic or neutral aqueous reaction medium on the surface of the plastic material(s), the precursors attaching by covalent bonds to this surface and forming the TiOs / M x O y agglomerated and activated, photocatalytic degradation, at neutral or acid pH, of the plastic material or mixture of plastic materials so as to obtain TiOs / M xAgglomerated and activated Oy, without the plastic material, and capable of allowing the degradation of one or more other plastic materials. . Production method according to claim 1, characterized in that a filtration step is carried out between the heating step and the photocatalytic degradation step, in order to eliminate the by-products formed during the crystallization of TiOs or TiOs / MxOy, this step making it possible to improve the kinetics of photocatalytic degradation of the plastic materials. . Production method according to one of claims 1 to 2, characterized in that the pH is chosen between 0 and 1, so as to obtain the TiOs of the TiOs / MxOy agglomerated and activated on the plastic material(s), with a rutile crystalline form. . Method according to one of claims 1 to 2, characterized in that the pH is chosen between 5 and 7, so as to obtain the TiOs of the TiOs / MxOy agglomerated and activated on the plastic material(s) in brookite form. . Method according to one of claims 1 to 2, characterized in that the step of adding a titanium precursor is carried out with the addition of a metal oxide WO3, the pH of the reaction medium being between 0 and 7, so as to obtain the TiOs of the TiOs / WOs agglomerated and activated on the plastic material(s), with an anatase crystalline form. . Process according to any one of claims 1 to 5, characterized in that the titanium precursor is chosen from the group comprising titanium isopropoxide, sodium titanate Na2Ti3O7 or a derivative.Method according to any one of claims 1 to 6, characterized in that the metallic or semi-metallic oxide is chosen from the group comprising SiOs, ZrOs, AI2O3, Fe2O3, CeC>2, MgO, CuO, NiO, CU2O, SnO2, RUO2, Bi20s, WO3, V2O5, Ag3PO4- . Material for photocatalysis based on TiC>2 or TiC>2 / M. x O y , resulting from the process according to one of claims 1 to 7, this material is agglomerated and activated to degrade a plastic material or a mixture of plastic materials, from visible and / or UV light, in an acidic or neutral aqueous reaction medium at a temperature less than or equal to 90°C, composed of more than 80% by mole of TiO2 and less than 20% by mole of another metallic or semi-metallic oxide M x O y , and in which the TiC>2 or TiC>2 / M x O yagglomerate is activated after photocatalytic degradation of a first plastic material or a mixture of plastic materials, according to the method defined according to one of claims 1 to 7. . Material for photocatalysis according to claim 8, characterized in that the TiOs or TiOs / M x O y , agglomerate has agglomerates from 300 nm up to 5 microns, advantageously 300 nm up to 1 micron.
0. Material for photocatalysis based on TiOs or TiOs / M x O y Agglomerate according to claim 8 or 9, wherein the material for photocatalysis has traces of the first plastic material or the mixture of plastic materials, visible by spectroscopy.
1. Material for photocatalysis based on TiOs or TiOs / M x O yagglomerate according to any one of claims 8 to 10, wherein the material is only agglomerated TiOs, with traces of the first plastic material or mixture of plastic materials visible by spectroscopy.
2. Material for photocatalysis based on TiOs or TiOs / M x O y agglomerate according to any one of claims 8 to 11, wherein the material is only TiC>2 / M x O y agglomerated, with traces of the first plastic material or mixture of plastic materials visible by spectroscopy.
3. Material for photocatalysis based on TiOs or TiOs / M x O y agglomerate according to any one of claims 8 to 12, in which the TiOs or TiC>2 / M x O y agglomerated and activated is obtained without calcination.
4. Material for photocatalysis based on TiC>2 or TiC>2 / M x O yagglomerate according to any one of claims 8 to 13, in which the TiO2 of the agglomerated TiC>2 alone or of the TiC>2 / M x O y agglomerate has a rutile crystalline form.
5. Material for photocatalysis based on TiC>2 or TiC>2 / M x O y agglomerate according to any one of claims 8 to 14, in which the TiO2 of the agglomerated TiC>2 alone or of the TiC>2 / M x O y agglomerate has a brookite crystalline form.
6. A method of degrading a second plastic material or a mixture of plastic materials, using a material for the photocatalysis based on TiOs or TiOs / MxOy, agglomerated and activated according to one of claims 8 to 15, having already degraded a first plastic material or mixture of plastic materials, the degradation method comprising in a first cycle: a step 1) suspension by stirring of the agglomerated and activated TiOs or TiOs / MxOy having degraded a first plastic or mixture of plastic materials, advantageously at a pH between 5 and 7; a step 2) of adding to the solution, one or more second plastic materials previously ground; a step 3) of heating the solution, advantageously between 70°C and 90°C, to graft the agglomerated and activated TiOs or TiOs / MxOy in suspension by stirring, onto the second plastic material or mixture of plastic materials; a step 4) of photocatalytic degradation of the second plastic material or of the mixture of plastic materials grafted with the agglomerated and activated TiOs or TiOs / MxOy, at least in the visible range,forming decomposition products.
7. Method according to claim 1 6, characterized in that the method comprises one or more repetitions of steps 2) to 4), each repetition of these steps 2) to 4) corresponding to a cycle, using the same agglomerated and activated TiOs or TiOs / MxOy.
8. Degradation method according to claim 1 6 or 17, characterized in that the photocatalytic degradation step is carried out in natural light or under visible radiation.
9. Degradation method according to any one of claims 16 to 18, characterized in that the photocatalytic degradation step is carried out by contact with atmospheric oxygen, at atmospheric pressure.
0. Degradation method according to any one of claims 16 to 19, characterized in that the decomposition products are of the carboxylic acid or alcohol type., 1. Degradation method according to any one of claims 16 to 20, characterized in that the decomposition products are chosen from the following list: acetone, acetic acid, formic acid, isopropanol, methanol, methyl formate, methyl acetate, glycerol, glyoxal, ethanol.
2. Degradation method according to any one of claims 16 to 21, characterized in that the decomposition products comprise biogases such as hydrogen, methane, CO, and / or CO2.
3. Degradation method according to any one of claims 16 to 22, characterized in that suspension is carried out during step 4), using a peristaltic pump or a flow of compressed air.
4. Degradation method according to any one of claims 16 to 23, characterized in that step 4) of degradation of the plastic material or plastic materials grafted with the TiOs or TiOs / MxOy agglomerated in suspension by stirring is carried out in the solution. 5.Degradation method according to any one of claims 16 to 24, characterized in that the acidic or neutral aqueous solution in which the plastic or the mixture of plastic materials is degraded is only water, such as tap water.
6. Degradation method according to any one of claims 16 to 25, characterized in that in step 1) a mixture of crystalline forms of agglomerated TiOs alone or agglomerated TiOs / MxOy is added which comprises the rutile crystalline form and the brookite crystalline form.
7. Degradation method according to any one of claims 16 to 26, comprising: a step 3) of heating the solution, between 30°C and 90°C, advantageously at 90°C; a step 4) of degrading the second plastic material or plastic materials grafted with the TiOs or TiOs / M. x O y agglomerated and activated, at a temperature between 30°C and 90°C.