Method for quantifying the microplastic content in a biomass sample or a sample derived from biomass

Abstract

The invention relates to a method and system for quantifying the microplastic content in a sample of biomass or a product derived from biomass or an amended surface formation. The method involves heating the sample under an inert atmosphere, with continuous measurement of at least one quantity of hydrocarbon compounds. Gaussian deconvolution is applied, and from the curve representing the evolution of hydrocarbons released by the sample during heating, and a specific area of ​​the Gaussian curve for the type of microplastics present, at least one content of that type of microplastic is determined in the sample. Abstract figure: 2 to be published.

Description

Title of the invention: Method for quantifying the microplastic content in a sample of biomass or derived from biomass technical field

[0001] The present invention relates to the fields of soil science, environmental geosciences, and agronomy and agriculture. More specifically, the present invention relates to the quantification of microplastics contained in or derived from a biomass sample.

[0002] The present invention finds particular application for the evaluation of conformity with current standards relating to spreading products in agriculture.

[0003] In an economic context of increasing food and environmental yields, with the primary objective of reducing the use of industrial nitrogen fertilizers and organic waste, the spreading of organic matter (raw or processed organic matter) on agricultural soils is of major agronomic interest, particularly for assessing soil health. Indeed, the purpose of spreading organic matter on the soil is to promote the return of nutrients and organic matter to the soil, thereby reducing the need for mineral fertilizers and maintaining soil carbon (C) stocks. Organic products thus have a dual agronomic value: 1) fertilizing (providing mineral and / or organic nutrients) and 2) improving (contributing carbon to the soil).These organic amendments, even with equal organic matter content, can behave very differently, especially since today they are very numerous and increasingly varied.

[0004] Bio-based products (crop residues, organic waste of animal, plant, or urban origin) or organic waste products (OWP) from physical and biological treatments (composts, digestates, sludge, etc.) are recognized as a source of microplastics (MP) introduction into the environment following their application to agricultural soils. Microplastics are not currently detected during the production processes of these products. Thus, the application of biomass-derived products leads to soil contamination by these elements, the impact of which on life and the resulting biological functioning of the soil remains poorly understood. However, current and future regulations in France and Europe aim to significantly limit future sources of plastic introduction into the environment.Thus, quantifying microplastics through the addition of bio-based products to the soil is a societal challenge. Previous technique

[0005] The following documents will be cited during the description:

[0006] Paterson, GA, & Heslop, D. (2015). New methods for unmixing sediment grain size data. Geochemistry, Geophysics, Geosystems, 16(12), 4494-4506.

[0007] Sebag, D., Disnar, JR, Guillet, B., Di Giovanni, C., Verrecchia, EP, & Durand, A. (2006). Monitoring organic matter dynamics in soil profiles by 'Rock-Eval pyrolysis': bulk characterization and quantification of degradation. European journal of soil science, 57(3), 344-355.

[0008] Romero-Sarmiento M., Ravelojaona H., Pillot D., Rohais S., Polymer quantification using the Rock-Eval® device for identification of plastics in sédiments, Science of The Total Environment, Volume 807, Part 3, 2022, 151068, ISSN 0048-9697, https: / / doi.org / 10.1016 / j. scitoten v.2021.151068

[0009] Among the methods commonly used to quantify (by number or mass) or even identify isolated microplastics, we know of spectroscopic methods (Infrared or Raman, for example), Differential Scanning Calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared microspectroscopy (pFTIR, for "micro Fourier Transform Interferometer"), and pyrolysis coupled with gas chromatography-mass spectrometry (Py-GC-MS). However, since these methods do not allow for the separation of organic matter from plastic particles, the organic matter must first be removed from the sample to be analyzed, or the microplastics must be highly concentrated beforehand.More specifically, it is generally necessary to remove most of the sample matrix (mineral and organic), preferably by isolating the microplastic particles from the matrix and removing any substances adhering to them. For inhomogeneous solid samples such as soils, isolating microplastics is challenging and becomes even more so as the grain size of the soil matrix and the size of the microplastic particles decrease. Isolation methods (extraction-purification) require numerous extractions using solvents and separation methods (filtration, sieving, density, etc.) before the isolated microplastics can be quantified (by number or mass) or even identified using spectroscopic (IR or Raman, for example), microscopic, and / or thermal methods (DSC, TGA, Py-GC-MS, etc.). Isolation methods are solvent-intensive, laborious, time-consuming, and cumbersome to implement.After this overconcentration, the methods of quantification remain more or less effective and are not harmonized.

[0010] Patent application WO 2022 / 243080 A1 and the document (Maria-Fernanda Romero-Sarmiento et al., 2022) are also known, both relating to a thermal analysis for characterizing the plastic content in samples of a porous medium such as sand. More specifically, this method is based on measurements of the quantities of hydrocarbon compounds (HC), carbon monoxide (CO), and / or carbon dioxide (CO2) released over time by a sample subjected to a heating sequence in an inert atmosphere followed by a heating sequence in an oxidizing atmosphere, applied to solid samples. A database of reference samples, previously prepared from different mineral matrices and several types of polymers (e.g., PE, PP, PE100, PA6, PAU, PFA, and PET), distributed in predetermined concentrations, is established beforehand.Parameters derived from the thermal analysis results for the sample under analysis are compared to those from the reference sample database for the identification and differentiation of polymer families. This approach therefore requires that the type(s) of microplastic(s) present in the sample be included in the reference sample database and involves a step to identify these different polymer types. Specifically, the identification of the microplastic type can be performed by identifying the peak temperatures in the measured HC, CO, and / or CO2 curves and by cross-referencing them with the peak temperatures of the corresponding curves measured for the plurality of reference samples. Quantification for each polymer type is then performed by integrating the areas of the identified peaks.However, the quantification procedure described in this document is not suitable when organic matter is present in the sample. Indeed, depending on the organic matter-to-polymer ratio, the polymer-related peaks may not be distinguishable because organic matter can release compounds within the same temperature ranges as polymers. Therefore, implementing this method on a sample containing organic matter requires prior removal of the organic matter, for example, by cleaning with hydrogen peroxide.

[0011] The present invention aims to overcome the drawbacks of the prior art. In particular, the present invention allows, from a thermal analysis comprising a single heating sequence under an inert atmosphere (pyrolysis), a rapid and simple quantification of the maximum microplastic content of a biomass sample or a product derived from biomass or an amended surface formation. The method according to the invention has the advantage of not requiring any prior pretreatment and requires only a sample of a few mg. Given that the introduction of microplastics into soils by means such as the spreading of raw biomass or The transformation can be significant; the method according to the invention, applied upstream of spreading, can contribute to reducing the penetration of plastics and microplastics into the environment. This invention is easy to implement, allowing for regular and rapid inspections of the quality of amendments. Summary of the invention

[0012] The invention relates to a method for quantifying the microplastic content in a sample of biomass or derived from biomass or an amended surface formation. It comprises at least the following steps:

[0013] A) said sample is heated in an inert atmosphere according to a predefined temperature sequence of which an initial temperature (T0) is between 100 and 300°C, and a final temperature (TF) is between 650 and 800°C, said temperature sequence comprising at least a thermal gradient between 1°C / min and 50°C / min, and at least a quantity of hydrocarbon compounds released during said heating in an inert atmosphere is continuously measured;

[0014] B) from a database associating at least one reference temperature for each type of microplastics with a plurality of types of microplastics, and from a curve representing the evolution as a function of temperature of said quantity of hydrocarbon compounds released during said heating in an inert atmosphere of said sample, for at least one of said types of microplastics from said database, a Gaussian deconvolution is applied to said curve so as to determine at least one Gaussian centered on said reference temperature associated with said type of microplastics;

[0015] C) from the curve of the evolution of hydrocarbon released by said sample as a function of the sample during heating of said sample, and of an area of ​​said at least one Gaussian determined for said type of microplastics, at least one content of said type of microplastics present in said sample is determined.

[0016] According to one embodiment, said database is constructed in the following manner:

[0017] I) said plurality of types of microplastics is defined in the form of a list of types of microplastics preferably comprising at least polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS) and polyamide (PA).

[0018] II) For each of the defined types of microplastics, step A) is applied to a plurality of reference samples composed of particles of said type of microplastics and particles of an unconsolidated solid matrix that does not release hydrocarbon compounds or releases hydrocarbon compounds at a temperature below 440°C of said heating in an inert atmosphere, and a curve is obtained representative reference of the evolution as a function of temperature of a quantity of hydrocarbon compounds released during said heating in an inert atmosphere of said reference sample; and

[0019] III) for each of the defined types of microplastics, from said reference curve determined for said type of microplastics, said reference temperature associated with said type of microplastics is determined by determining the temperature of a peak of said reference curve.

[0020] According to one implementation, said temperature sequence under inert atmosphere includes a first isothermal plateau at the initial temperature (T0), followed by a predetermined thermal gradient so as to raise the temperature of the sample up to the final temperature (TF).

[0021] According to one aspect, said temperature sequence includes a second isothermal plateau at the final temperature (TF).

[0022] According to one configuration, said temperature sequence includes at least one isothermal plateau at an intermediate temperature between said initial temperature (T0) and the final temperature (TF).

[0023] According to one embodiment, the CO2 and CO levels released are measured during heating, and the said CO2 and CO levels released are taken into account to determine the said microplastic content.

[0024] Advantageously, the quantity of hydrocarbons released is measured by means of a pyrolyzed carbon parameter defined by the formula: PC = [(S1 + S2) xO,8.3+(S3x||) + ((S3CO+^^) x^j)] x^

[0025] With SI, quantity of free hydrocarbon compounds in the sample and mainly thermally desorbed (from T0 to the end of the 1st temperature step); S2, the quantity of HC released by thermal cracking in mg HC.g 1 (T end of the 1st step at temperature TF); S3, the CO2 released by thermal cracking before 400°C in mg CO2.g *, S3CO, the CO released by thermal cracking from T0 to the minimum of CO production observed (between 450° and 600°C); S3'CO in mg CO.g *, the CO released by thermal cracking from the temperature above the S3CO peak to temperature TF.

[0026] According to one embodiment of the invention, a maximum content of type i microplastics in said sample is determined using the following formula: QMPt = SGMPy *100 / x [mg / g]

[0027] Where SGMPy is the surface area of ​​the Gaussian QMP^ determined for the type of microplastics of type i MP^ and 100 / x is a stoichiometric coefficient to allow the conversion of microplastic into microplastic carbon.

[0028] According to one embodiment, the step of determining a maximum content for a plurality of types of microplastic is repeated and a maximum content of microplastic is determined by summing each maximum content of each type of microplastic.

[0029] Furthermore, the invention relates to a system for quantifying the microplastic content in a sample of biomass or derived from biomass or from a surface formation amended for the implementation of the process according to one of the preceding characteristics, comprising a pyrolysis furnace in an inert atmosphere for carrying out said temperature sequence, means for measuring hydrocarbon compounds at the outlet of said pyrolysis furnace, and analytical means for applying said Gaussian deconvolution and for determining said content of said type of microplastics present in said sample. List of figures [Fig AI]

[0030] Fig. 1A schematically illustrates an example of implementation of the temperature sequence under inert atmosphere of the process according to the invention. [Fig IB]

[0031] Fig. 1B schematically illustrates another example of implementation of the temperature sequence under inert atmosphere of the process according to the invention. [Fig 2]

[0032] Figure 2 illustrates, for example, a curve of the evolution over time of the quantity of hydrocarbons released by a sample of biomass of the biowaste type including microplastics. [Fig 3]

[0033] Figure 3 illustrates, for example, a curve of the evolution over time of the quantity of hydrocarbons released by a sample of biomass of the household waste type including microplastics. Description of the implementation methods

[0034] The invention relates to a method for quantifying microplastics contained in a sample of biomass or derived from biomass or from an amended surface formation.

[0035] The term “biomass” means any mass of living or recently living matter (animal, plant, terrestrial, aquatic) existing in equilibrium on a given surface of the Earth. This may include, but is not limited to, plants, wood, agricultural and organic biowaste, algae, frass, etc.

[0036] The term “Organic Residual Products (ORP)” refers to all organic waste and by-products resulting from human activities such as agriculture, farming, The agri-food industry or household waste. These organic products derived from biomass can be transformed by various processes (biological, thermal, etc.) for their valorization. Products derived from biomass and processed include compost, vermicompost, digestate, biochar, etc.

[0037] The term "amended surface formation" refers to any type of soil onto which any type of amending material, primarily organic (dead or living) combined with its nutrient cocktail, can be applied in order to improve the characteristics of the surface soil. An amendment is the addition of carbon-rich material to the soil, altering its chemical, physical, or biological properties. These amendments can increase the surface area in contact with the soil, thereby stimulating its decomposition and improving its properties, particularly for high-performing agriculture. ...

[0038] Microplastics are defined as any particle comprising one or more polymers and being less than 5 mm in size. For example, microplastics according to the invention may comprise particles of different types of polymers such as polyethylene terephthalate (PET), polyethylene (PE), polyamide (PA), perfluoroalkoxy (PFA), and / or polypropylene (PP), among others. Microplastics may be in various forms, such as fibers, films, powder, or pellets. Microplastics according to the invention may, in particular, cover chemical textile microfibers, that is, particles from woven, non-woven, or knitted materials (such as clothing or linen) composed of synthetic fibers (i.e., derived from hydrocarbon products, such as PET, PA, etc.).) and / or artificial fibers (such as viscose) resulting from the chemical transformation (i.e., a transformation changing the nature of the fiber) of a natural material (cellulose, wood, plant, etc.).

[0039] The process according to the invention requires having at least one sample of biomass or a product derived from biomass to be analyzed.

[0040] Advantageously, the sample can be sieved using a sieve with orifices having a diameter of 2 mm, dried at a temperature below 40°C, and then ground to obtain fragments with dimensions less than 200 µm. Furthermore, it is not necessary to pretreat the sample (in particular, no decarbonation, purification, or extraction), especially with solvents. The sample can have a mass between 1 and 100 mg, preferably between 1 and 20 mg. Indeed, the process according to the invention, particularly when implemented using the ROCK-EVAL® device (IFP Energies nouvelles, France) described below, does not require a large sample mass due to the sensitivity of the detectors.

[0041] The process according to the invention can advantageously, but not exclusively, be implemented using the ROCK-EVAL® device (IFP Energies nouvelles, France), as described in patents FR 2227797 (US 3953171) and FR 2472754 (US 4352673). Indeed, the ROCK-EVAL® device comprises at least:

[0042] - a pyrolysis oven in an inert atmosphere,

[0043] - means for measuring hydrocarbon compounds (HC), for example under the form of a flame ionization detector (FID).

[0044] For an implementation described later in step 2), the device may further include means for measuring CO and CO2, for example in the form of an IR (Infrared) infrared spectrophotometer.

[0045] The process can alternatively be implemented using any furnace allowing heating in an inert atmosphere, cooperating with one or more devices for measuring hydrocarbon compounds.

[0046] The method according to the invention can also be implemented using analytical means. These analytical means may include computer-based means such as a computer, a processor, or a calculator.

[0047] The method according to the invention comprises at least the following steps:

[0048] 1) Heating sequence under an inert atmosphere (pyrolysis)

[0049] 2) Application of a Gaussian deconvolution to the measured quantity of HC

[0050] 3) Quantification of microplastics present in the sample

[0051] The steps of the process according to the invention are described below.

[0052] 1) Heating sequence under an inert atmosphere (pyrolysis)

[0053] During this step, the sample is heated under an inert atmosphere (such as, for example, under a flow of nitrogen, argon, or helium) according to a temperature sequence in which the initial temperature (hereafter denoted T0) is between 100 and 300°C and preferably 200°C, and the final temperature (hereafter denoted TF) is between 650 and 800°C and preferably 650°C. Furthermore, the temperature sequence according to the invention includes at least one thermal gradient between 1°C / min and 50°C / min, preferably 25°C / min. In addition, according to the invention, at least one quantity of HC released during heating under an inert atmosphere is continuously measured.

[0054] The initial temperature of the process according to the invention allows the most labile organic compounds (having a cracking temperature below 400°C) to be released in a dissociated manner from the more resistant or even refractory organic compounds (having a cracking temperature above 400°C), which are of interest for the process according to the invention as will be described below.

[0055] The final temperature of the process according to the invention is sufficient for the release of highly refractory organic compounds to be complete.

[0056] According to one embodiment of the invention, the temperature sequence under an inert atmosphere may include a first isothermal plateau at the initial temperature T0, optionally followed by a predetermined thermal gradient to raise the sample temperature to the final temperature TF. Figure 1A schematically illustrates the evolution of the temperature T as a function of time t in such a temperature sequence, exhibiting an isothermal plateau at temperature T0, followed by a thermal gradient until reaching temperature TF.

[0057] Alternatively, the temperature sequence under an inert atmosphere may include a second isothermal plateau, optionally in addition to the first isothermal plateau, at the final temperature TF. This allows, if necessary, the cracking of compounds with a cracking temperature close to the final temperature TF of the temperature sequence under an inert atmosphere according to the invention to continue. Figure 1B schematically illustrates the evolution of the temperature T as a function of time t in a temperature sequence, exhibiting two isothermal plateaus, at temperatures T0 and TF as defined above, and linked by a thermal gradient.

[0058] According to one embodiment of the invention, the isothermal plateau(s) of the temperature sequence under an inert atmosphere may have a predetermined non-zero duration (for example, greater than half a minute), preferably between 1 and 5 minutes, and most preferably 3 minutes. Such durations allow the cracking of compounds having a cracking temperature close to the temperature of the isothermal plateau to be considered complete. According to the embodiment of the invention in which the temperature sequence under an inert atmosphere comprises several isothermal plateaus, and in particular two isothermal plateaus at temperatures T0 and TF, the duration of one isothermal plateau may differ from the duration of the other isothermal plateau(s).

[0059] Advantageously, the temperature sequence of the inert atmosphere heating may further include one or more so-called intermediate isothermal plateaus, at temperatures between the initial and final temperatures of the inert atmosphere heating temperature sequence. According to one embodiment of the invention, the inert atmosphere heating temperature sequence may include an intermediate isothermal plateau at a temperature between 455 and 460 °C, preferably 457 °C (to release PET), another between 493 and 499 °C, preferably 499 °C (to release PE), etc.

[0060] The intermediate isothermal plateau(s) may have a predetermined non-zero duration (for example, greater than half a minute), preferably between 1 and 5 minutes, and most preferably 3 minutes. Such durations are sufficient to allow the peaks associated with the different classes to be separated. of organic compounds. According to this embodiment of the invention, the temperature sequence of heating under an inert atmosphere can comprise a number of thermal gradients NG defined by NG = NII+1 where NII is the number of intermediate isothermal plateaus in the temperature sequence. Thus, the intermediate isothermal plateau(s) are linked together by thermal gradients, and the intermediate isothermal plateau at the lowest (respectively highest) temperature is also linked by a thermal gradient to the initial (respectively final) temperature of the temperature sequence.

[0061] According to one embodiment of the invention, the thermal gradient(s) of the temperature sequence under an inert atmosphere can be between 1°C / min and 50°C / min, preferably between 10°C and 35°C / min, and most preferably 25°C / min. Such values ​​represent a compromise that allows for the thermal cracking of organic compounds while limiting the implementation time of the process.

[0062] According to the invention, a representative quantity of hydrocarbon compounds (HC) contained in an effluent resulting from said heating is continuously measured (i.e., continuously over time). In other words, during this sequence, the representative quantity of HC released by the sample through thermal cracking of organic matter and thermal decomposition of microplastics can be continuously measured. The measurement of the representative quantity of hydrocarbon compounds can be carried out using a flame ionization detector (FID). Note that such sensors measure an HC flux and provide values ​​measured in millivolts (mV).Conventionally, the amount of HC can be determined by calculating the area under the curve measured (possibly between predefined temperatures) by these sensors, and dividing this area by the mass in mg of the sample, possibly using a calibration coefficient (determined relative to a standard sample). Alternatively, other methods of measuring the amount of HC can be used.

[0063] According to one embodiment of the invention, the representative quantity of hydrocarbons released by the sample can be determined by means of a parameter PC (from the English "pyrolyzed carbon"). This parameter can be written in the form: PC = [(S1 + S2) xO.83+ (S3x||) + ((S3CO+^2) x||)] x^

[0064] With SI, the quantity of free HC in the sample and mainly thermally desorbed (from T0 to the end of the first temperature plateau); S2, the quantity of HC released by thermal cracking in mg HC.g (T at the end of the first plateau at temperature TF); S3, the CO2 released by thermal cracking before 400°C in mg CO2.g*, S3CO, the CO released by Thermal cracking of TO at the minimum observed CO production (between 450° and 600°C); S3'CO in mg CO.g*, the CO released by thermal cracking from the temperature above the S3CO peak to the TF temperature. S3 and S3' are obtained under the same conditions as those yielding S2.

[0065] According to one embodiment of the invention, the inert atmosphere temperature sequence according to the invention may be preceded by a heating phase of the pyrolysis furnace, which may be in the form of a thermal gradient, for example, between 1 and 50°C / min, preferably between 20 and 25°C / min, or any other type of heating curve for the pyrolysis furnace. This preliminary heating phase of the pyrolysis furnace allows the pyrolysis furnace to be brought to the initial temperature of the inert atmosphere temperature sequence according to the invention. This preliminary phase can help to initiate the thermal cracking of compounds whose cracking temperature is lower than the initial temperature of the inert atmosphere temperature sequence according to the invention.

[0066] According to one embodiment of the invention, the temperature sequence under an inert atmosphere according to the invention can be followed by a phase of lowering the temperature of the pyrolysis furnace, which can be in the form of a thermal gradient, for example, between -1 and -50°C / min, preferably between -20 and -25°C / min, or any other form of temperature decrease curve for the pyrolysis furnace. This final phase of lowering the temperature of the pyrolysis furnace allows, if necessary, the completion of the thermal cracking of the compounds associated with the final temperature of the temperature sequence under an inert atmosphere according to the invention.

[0067] According to the invention, at the end of this step, a curve is obtained representing the quantity of HC released over time during the pyrolysis phase, hereafter denoted C(t). It is quite obvious to a person skilled in the art to go from a curve representing the quantity of HC released over time to a curve representing the quantity of HC released as a function of temperature C(T), since the temperature sequence (evolution of the temperature as a function of time T(t)) is known.

[0068] 2) Application of a Gaussian deconvolution to the measured quantity of HC

[0069] In this step, using a database associating at least one reference temperature for each type of microplastic with a plurality of microplastic types, and using the curve representing the temperature evolution of the quantity of hydrocarbon compounds measured in the previous step for at least one of the microplastic types in the database, a Gaussian deconvolution is applied to the measured curve so as to determine at least one Gaussian centered on the reference temperature associated with the type of microplastics considered.

[0070] By Gaussian deconvolution, we mean a decomposition of a curve (in this case the curve representing the evolution as a function of temperature of the quantity of HC released during heating in an inert atmosphere) into elementary components, each corresponding to a Gaussian distribution.

[0071] Thus, this step aims to extract at least one Gaussian curve from the curve representing the temperature evolution of the amount of HC released during heating under an inert atmosphere, said Gaussian curve being centered on the characteristic temperature (the reference temperature) of a microplastic from a pre-established database. Indeed, as shown in application WO 2022 / 243080 A1, the curve representing the temperature evolution of the amount of HC released by a given polymer during heating under an inert atmosphere exhibits a peak at a characteristic temperature. In other words, the characteristic temperatures of the peaks associated with the different polymers are, in a way, "signatures" of these polymers.A Gaussian deconvolution centered on the characteristic temperature of a given polymer allows us to extract a Gaussian curve representative of at least the contribution of the polymer in question to the amount of HC released "around" this characteristic temperature.

[0072] When the sample includes, in addition to microplastics, organic matter in the form of biomass (raw or processed), the Gaussian distribution resulting from the Gaussian deconvolution extraction according to the invention also includes the hydrocarbon compounds released by the organic matter present in the sample. Thus, the quantification as described in step 3) leads to the determination of a maximum microplastic content, and not an exact content. However, in the case of biomass, particularly for non-plant organic biowaste, it is known that the signal of hydrocarbons released by the biomass (original or processed) in the temperature range corresponding to microplastics is minimal, which makes the extraction of the microplastic content by Gaussian deconvolution a realistic possibility.

[0073] According to one embodiment, the determination of the microplastic content can be improved by relying on the CO2 (S3) and CO (S3CO) signal profiles of pyrolysis carried out during step 1 of the process by measurements of CO2 and CO.

[0074] According to one embodiment of the invention, step 1 can be supplemented by an oxidation step as described in particular in patent application WO 2022 / 243080 Al and the document (Maria-Femanda Romero-Sarmiento et al., 2022). For this embodiment of the invention, HI (Hydrogen Index) and OI (Oxygen Index) parameters can be determined. Oxygen Index (which can be translated as oxygen index) based on measurements taken during heating. We can write: r?T _ cl nr _ S3 with S2 the measurement of the — TOC — TOC cumulative signal by the hydrocarbon compound detector (for example in the form of a flame ionization detector (FID) during pyrolysis which is then converted into mg HC / g rock taking into account the mass of sample used, S3 an amount of CO2 measured by means of an IR (Infrared) spectrophotometer during pyrolysis and TOC (for "Total Organic Carbon" in English) the carbon content of the sample, determined from the total amount of HC released by the sample and the amounts of CO and CO2 released during the pyrolysis and oxidation phases.

[0075] According to a non-limiting embodiment of the invention, the residual Gaussian deconvolution method described in the document (Sebag et al., 2006) can be used. More specifically, this method consists of progressively subtracting the Gaussians centered on the principal peaks of the signal.

[0076] According to another embodiment, the Gaussian deconvolution method can be used by means of an End-Member Mixing Analysis described in particular in the document (Paterson and Heslop, 2015), which consists of determining, by means of an algorithm, the Gaussian components which best describe the signal, with a given number of Gaussians.

[0077] Figure 2 illustrates a curve C(t) of the evolution as a function of time t of the quantity of HC QHC released by a biowaste-type biomass sample containing microplastics. The GMP curve corresponds to a Gaussian curve centered on a temperature TMP of 445°C characteristic of a type of microplastic (in this case, a mixture of microplastics isolated from the biowaste-type biomass sample consisting mainly of PE, PP, PET and PS).

[0078] Figure 3 illustrates a curve C(t) of the evolution over time t of the quantity of HC QHC released by a municipal solid waste biomass sample containing microplastics. The GMP curve corresponds to a Gaussian curve centered on a temperature TMP of 447°C characteristic of a type of microplastic (in this case, a mixture of MPs isolated from the municipal solid waste biomass sample consisting mainly of PE, PP, PET, and PS).

[0079] According to one embodiment of the invention, the database can be constructed as follows:

[0080] I) a plurality of types of microplastics are defined in the form of a list of types of microplastics preferably including at least polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), and polyamide (PA).

[0081] II) for each of the defined types of microplastics, step 1) described above is applied to a plurality of reference samples, each composed of particles of the type of microplastics and particles of an unconsolidated solid matrix that does not release or releases little hydrocarbon compounds or does not release hydrocarbon compounds at a temperature above 440°C when heated in an inert atmosphere according to the invention (indeed, the most commonly used polymers release HC compounds above 440°C; an unconsolidated solid matrix that does not release hydrocarbon compounds at a temperature above 440°C avoids generating interference in the HC measurement curve), and a reference curve is obtained that represents the evolution as a function of temperature of the quantity of hydrocarbon compounds released during heating in an inert atmosphere according to the invention of the reference sample;

[0082] III) for each of the types of microplastics defined, from the reference curve determined for the type of microplastics considered (pure or in mixture), the reference temperature associated with the type of microplastics considered is determined by determining the temperature of the peak of the reference curve considered, and the database is completed by associating the reference temperature thus determined with the type of microplastics.

[0083] According to an alternative or cumulative embodiment, the database may include the following reference temperatures: a reference temperature between 455 and 459°C, preferably 457°C, for a PET-type microplastic; a reference temperature between 493 and 499°C, preferably 496°C, for a PE-type microplastic; a reference temperature between 470 and 476°C, preferably 473°C, for a PP-type microplastic; a reference temperature between 457 and 461°C, preferably 459°C, for a PE 100 (high-density polyethylene) microplastic; a reference temperature between 442 and 452°C, preferably 447°C, for a PA11 (polyamide 11) microplastic; a reference temperature between 583 and 587°C and preferably 585°C for a PFA (polyfluoroalkyl) type microplastic.

[0084] Additionally or cumulatively, the database may include mixtures of the microplastics mentioned above. Temperatures may vary depending on the mixture.

[0085] It can also be noted that the indicated temperatures may vary depending on the operation of the aging, doping, etc. of the microplastic.

[0086] 3) Determination of a maximum microplastic content of the sample

[0087] During this step, from the surface of at least one Gaussian determined in the previous step for one of the types of microplastics, at least a maximum content of at least the type of microplastics present in said sample is determined.

[0088] According to one embodiment of the invention, from a determined Gaussian QMP as described in the previous step for the type of microplastic M.Pr, a maximum content of the type of microplastic MP^ in the sample can be determined according to a formula of the type:

[0089] QMP. = SGMPy *100 / x [mg / g] (1)

[0090] Where SGMP is the area of ​​the Gaussian QMP determined for the type of microplastics MP^ and 100 / x is a stoichiometric coefficient to allow the conversion of MP to carbon from MP (x representing the average %C of the MP in the sample). By way of non-limiting examples, for PE, x can be 87 ± 4%, for PP, x can be 90 ± 1%.

[0091] According to one embodiment of the invention, the quantification below can be repeated for each type of microplastic in the database. In other words, equation (1) below is applied for i ranging from 1 to N. A maximum microplastic content QMP can then be determined as follows:

[0092] qMp = QMPi <2)

[0093] Furthermore, the invention relates to a system for quantifying the microplastic content in a sample of biomass or a sample derived from biomass or an amended surface formation for carrying out the process according to any of the variants or any combination thereof described above, comprising a pyrolysis furnace in an inert atmosphere for performing said temperature sequence, means for measuring hydrocarbon compounds at the outlet of said pyrolysis furnace, and analytical means for applying said Gaussian deconvolution and for determining said content of said type of microplastics present in said sample. In other words, the analytical means are capable of carrying out the steps of the process according to the invention, in particular steps 2 and 3. The analytical means may include computing means such as a computer, a processor, or a calculator. Examples

[0094] The characteristics and advantages of the process according to the invention will become clearer upon reading the application examples below.

[0095] The process according to the invention has been applied to samples corresponding to composts from industrial platforms and resulting from the transformation of waste from different origins (biowaste, green waste, and residual household waste).

[0096] The aforementioned figures 2 and 3 were obtained for two of these samples. The application of the process according to an embodiment of the invention to the samples led to a maximum mass percentage of microplastics of 3.1 + / - 0.2% by mass (i.e. 31 + / - 2 kg of microplastics / tonne of sample) and 2.1 + / - 0.4% by mass (i.e. 2.1 + / - 4 kg of microplastics / tonne of sample), respectively.

[0097] Quantification of coarse microplastics corresponding to sizes between 2 and 5 mm present in these composts by an extraction process according to the prior art made it possible to reliably quantify the coarse microplastics of these samples and to confirm these results on microplastics (<200 mm) which are of the same order of magnitude.

[0098] Thus, the present invention makes it possible, from a quantity of hydrocarbon compounds released during a heating sequence in an inert atmosphere, to determine a maximum quantity of microplastics present in a sample of biomass or amended surface formation in a simple and rapid manner. These results are obtained from a single heating sequence (in this case, under an inert atmosphere) and do not require pretreatment of the sample to be analyzed, which facilitates the implementation of the process according to the invention. Estimating a maximum quantity of microplastics provides information that allows a decision to be made whether or not to utilize a given biomass, for example, for spreading, and thus to limit the penetration of microplastics into the environment.

Claims

Demands

1. A method for quantifying the microplastic content in a sample of biomass or derived from biomass or an amended surface formation, characterized in that it comprises at least the following steps: A) said sample is heated in an inert atmosphere according to a predefined temperature sequence of which an initial temperature (TO) is between 100 and 300°C, and a final temperature (TF) is between 650 and 800°C, said temperature sequence comprising at least a thermal gradient between 1°C / min and 50°C / min, and at least a quantity of hydrocarbon compounds released during said heating in an inert atmosphere is continuously measured;B) From a database associating at least one reference temperature for each type of microplastic with a plurality of microplastic types, and from a curve representing the evolution as a function of temperature of said quantity of hydrocarbon compounds released during said heating in an inert atmosphere of said sample, for at least one of said microplastic types in said database, a Gaussian deconvolution is applied to said curve so as to determine at least one Gaussian curve centered on said reference temperature associated with said microplastic type; C) From the curve of the evolution of hydrocarbon released by said sample as a function of the sample during heating of said sample, and from an area of ​​said at least one Gaussian curve determined for said microplastic type, at least one content of said microplastic type present in said sample is determined.

2. A method according to claim 1, wherein said database is constructed as follows: I) said plurality of microplastic types is defined in the form of a list of microplastic types preferably comprising at least polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), and polyamide (PA). II) for each of the defined microplastic types, step A) is applied to a plurality of reference samples composed of particles of said type of microplastics and particles of an unconsolidated solid matrix not releasing hydrocarbon compounds or releasing hydrocarbon compounds at a temperature below 440°C of said heating in an inert atmosphere, and a reference curve is obtained representing the evolution as a function of temperature of a quantity of hydrocarbon compounds released during said heating in an inert atmosphere of said reference sample; and III) for each of the types of microplastics defined, from said reference curve determined for said type of microplastics, said reference temperature associated with said type of microplastics is determined by determining the temperature of a peak of said reference curve.

3. A method according to any one of the preceding claims, wherein said temperature sequence under inert atmosphere comprises a first isothermal plateau at the initial temperature (TO), followed by a predetermined thermal gradient so as to raise the temperature of the sample up to the final temperature (TF).

4. Method according to claim 3, wherein said temperature sequence includes a second isothermal plateau at the final temperature (TF).

5. A method according to any one of the preceding claims, wherein said temperature sequence includes at least one isothermal plateau at an intermediate temperature between said initial temperature (TO) and the final temperature (TF).

6. A method according to any one of the preceding claims, wherein the CO2 and CO levels released are measured during heating, and said CO2 and CO levels released are taken into account to determine said microplastic content.

7. A method according to any one of claims 3 to 6, wherein said quantity of released hydrocarbons is measured by means of a pyrolyzed carbon parameter defined by the formula: PC = [(S1+S2) x 0.83+(S3x) + ((S3CO+) x ij)] x jL Where SI is the quantity of free hydrocarbon compounds in the sample, primarily thermally desorbed (from T0 to the end of the first temperature step); S2 is the quantity of hydrocarbon compounds released by thermal cracking in mg HC.g (T from the end of the first step to the temperature TF); S3, the CO2 released by thermal cracking before 400°C in mg CO2.g', S3CO, the CO released by thermal cracking from T0 to the minimum of observed CO production (between 450° and 600°C); S3'CO in mg CO.g*, the CO released by thermal cracking from the temperature above the S3CO peak to the temperature TF.

8. A method according to any one of the preceding claims, wherein a maximum content of type i microplastic in said sample is determined by means of the following formula: QMP. = SGMP, *100 / x [mg / g] Where SGMP is the area of ​​the Gaussian QMP^ determined for the type i microplastic MP and 100 / x is a stoichiometric coefficient to enable the conversion of microplastic into microplastic carbon.

9. A method according to any one of the preceding claims, wherein the step of determining a maximum content for a plurality of types of microplastic is repeated and a maximum microplastic content is determined by summing each maximum content of each type of microplastic.

10. System for quantifying the microplastic content in a sample of biomass or derived from biomass or from an amended surface formation for carrying out the process according to any one of the preceding claims, comprising a pyrolysis furnace in an inert atmosphere for carrying out said temperature sequence, means for measuring hydrocarbon compounds at the outlet of said pyrolysis furnace, and analytical means for applying said Gaussian deconvolution and for determining said content of said type of microplastics present in said sample.

Images