Method for quantifying pyrogenic carbon present in a sample of an organo-mineral or mineral matrix comprising coal and / or biochar

Abstract

The present invention relates to a method for quantifying the pyrogenic carbon content of a sample comprising an organo-mineral or mineral matrix and charcoal and / or biochar. The method comprises heating the sample in an inert atmosphere, then heating the residue from the inert heating in an oxidizing atmosphere, and measuring the amount of CO2 released during the oxidizing heating. The measured curve is decomposed into a first component corresponding to the portion of the curve associated with temperatures below a limiting temperature, and a second component corresponding to the portion of the curve associated with temperatures at or above the limiting temperature, the limiting temperature being between 500°C and 550°C, and preferably 530°C. The pyrogenic carbon content is determined from the areas of the first and second components. Figure 2 to be published

Description

Title of the invention: Method for quantifying pyrogenic carbon present in a sample of an organo-mineral or mineral matrix comprising coal and / or biochar. Technical field

[0001] The present invention may relate in particular to the field of soil science, agronomy and the environment, and more generally to any field interested in the quantification of biochar and / or charcoal present in a mineral or organo-mineral matrix.

[0002] The present invention may, for example, relate to the field of production and marketing of biochar, in particular when it is marketed in the form of a mixture with an organo-mineral or mineral matrix, for example for use as an organic amendment (biochar-sediment) or as a building material, like hybrid green concrete (biochar-calcium carbonate) or simply by mixing biochar with concrete (mineral matrix).

[0003] In the environmental field, in order to address environmental challenges and, in particular, to limit global warming to 1.5°C compared to pre-industrial levels, it is necessary to achieve the goal of "Net Zero Emissions" by 2050. To this end, it is necessary not only to drastically reduce our CO2 emissions, but also to develop negative emission technologies. Biochar, a product of biomass pyrolysis, constitutes a negative emission technology since it is a carbon-rich and biologically stable material. Furthermore, in recent decades, pyrogenic organic matter has been recognized as an important component of the highly fertile soils of the Amazon. Indeed, this material can have beneficial effects on soil fertility, particularly in terms of water and nutrient retention and liming.The name given to pyrolyzed organic matter varies depending on its end use. It is called "biochar" when organic matter is pyrolyzed with the aim of amending the soil to improve its properties. In the literature, "black carbon" describes the volatile components resulting from the incomplete combustion of biomass. In some studies, the term "black carbon" is also used to describe a broader range of material, forming a continuum from charcoal to soot. The term "char" (or "charcoal") or sometimes "wood charcoal" is used when organic matter is deliberately pyrolyzed, for example, for use as a biochar. fuel or filter. Note that coal differs from geological coal (or coal of geological origin) in their production methods, as well as their very different chemical and physical properties. Unlike coal produced by the pyrolysis of biomass, geological coal (for example, bituminous coal) is produced by geological processes under high pressure and high temperature, over a much longer timescale (several thousand years). In particular, geological coal does not contain pyrogenic carbon.

[0004] Thus, forms of coal other than geological coal (i.e., charcoal, char, or biochar) can be present in soil due to various circumstances, such as wildfires and intentional soil amendments aimed at improving soil properties. Since coal is rich in biologically stable carbon (i.e., aromatic compounds), its quantification can be achieved through the pyrogenic carbon that constitutes its majority. The benefits of being able to quantify pyrogenic carbon in soil are numerous and depend on the context in which it was introduced. In the case of wildfires, the pyrogenic carbon content serves as a marker of fire frequency.This marker is particularly useful for archaeological studies, since high fire frequencies at a single site can indicate previous human occupation, while lower intensities are more likely to result from naturally occurring fires. In the case of biochar amendments, quantifying pyrogenic carbon in an amended plot allows for monitoring the remaining biochar content in the soil. Indeed, biochar can easily degrade physically. Furthermore, quantifying pyrogenic carbon outside the amended plot allows for monitoring the fate of biochar in the environment, particularly its deposition zones. Previous technique.

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

[0006] Arroyo-Kalin, M. A. (2008). Steps towards an ecology of landscape: A geoar-chaeological approach to the study of anthropogenic dark earths in the central Amazon région, Brazil (Doctoral dissertation, University of Cambridge).

[0007] Aubertin, M. L. (2022). Biochar-compost mixtures: interactions and impact on carbon séquestration and soil fertility (Doctoral dissertation, Sorbonne université).

[0008] Behar, F., Beaumont, V., & Penteado, H. D. B. (2001). Rock-Eval 6 technology: performances and developments. Oil & Gas Science and Technology, 56(2), 111-134.

[0009] Chalk, P., & Smith, C. J. (2022). 13C méthodologies for quantifying biochar stability in soil: A critique. European Journal of Soil Science, 73(3), el3245.

[0010] Cuypers, C., Grotenhuis, T., Nierop, K. G., Franco, E. M., de Jager, A., & Rulkens, W. (2002). Amorphous and condensed organic matter domains: the effect of persulfate oxidation on the composition of soil / sediment organic matter. Chemosphere, 48(9), 919-931.

[0011] Glaser, B., Haumaier, L., Guggenberger, G., & Zech, W. (1998). Black carbon in soils: the use of benzenecarboxylic acids as spécifie markers. Organic geochemistry, 29(4), 811-819.

[0012] Llorente, M., Turriôn, M. B., & Glaser, B. (2018). Rapid and economical quantification of black carbon in soils using a modified benzene polycarboxylic acids (BPCA) method. Organic Geochemistry, 115, 197-204.

[0013] Paterson, G. A., & Heslop, D. (2015). New methods for unmixing sédiment grain size data. Geochemistry, Geophysics, Geosystems, 16(12), 4494-4506.

[0014] Poot, A., Quik, J. T., Veld, H., & Koelmans, A. A. (2009). Quantification methods of Black Carbon: Comparison of Rock-Eval analysis with traditional methods. Journal of Chromatography A, 1216(3), 613-622.

[0015] Sebag, D., Disnar, J. R., Guillet, B., Di Giovanni, C., Verrecchia, E. P., & Durand, A. (2006). Monitoring organic matter dynamics in soil profiles by ‘Rock-Eval pyrolysis’: bulk characterization and quantification of dégradation. European journal of soil science, 57(3), 344-355.

[0016] Sebag, D., Garcin, Y., Adatte, T., Deschamps, P., Ménot, G., & Verrecchia, E. P. (2018). Correction for the siderite effect on Rock-Eval parameters: application to the sédiments of Lake Barombi (Southwest Cameroon). Organic Geochemistry, 123, 126-135.

[0017] Simpson, M. J., & Hatcher, P. G. (2004). Overestimates of black carbon in soils and sédiments. Naturwissenschaften, 91(9), 436-440.

[0018] Various techniques are known for quantifying pyrogenic carbon in soil or sedimentary material, based on chemical, magnetic, optical or thermal differences between the soil and the coal or by the presence of molecular markers.

[0019] A commonly used technique is the quantification of benzene polycarboxylic acids (BPCAs) by extraction following the chemical oxidation of aromatic structures, by gas chromatography analysis, as described, for example, in the document (Glaser et al., 1998), or by elemental analysis, as described, for example, in the document (Llorente et al., 2018). However, extraction is time-consuming and can introduce bias into the quantification of BPCAs.

[0020] The use of the natural carbon isotope is a direct, precise, and reproducible method of quantification, making it possible to distinguish the source of a carbon atom from a mixture of two carbon components with significantly different isotopic signatures (δ¹³C), as described, for example, in the document (Aubertin et al., 2022). However, isotopic analysis can only be applied in the case of a a coal-soil mixture, where the two components have significantly different isotopic signatures. Isotopic enrichment methods can also be used to quantify pyrogenic carbon, but this involves incubation (time-consuming) and the results can be biased by the non-uniform distribution of the labeled carbon added in the plant, as described, for example, in the paper (Chalk and Smith, 2022).

[0021] Other methods for quantifying coal are based on observing differences in the color or density of coal particles from a microscopic photograph, as described, for example, in the document (Arroyo-Kalin, 2008). However, these methods are time-consuming (time required for preparing thin sections and for handling the sample), only take into account particles larger than a certain diameter, are not very reproducible because they are operator-dependent, and only provide an approximation of the coal mass, based on a count of a surface area.

[0022] Among thermal methods, the thermochemical oxidation method involves a chemical oxidation pretreatment with an acid to remove inorganic carbon, followed by the separation of pyrogenic and non-pyrogenic carbon by combustion at temperatures around 350 °C for a minimum of 2 hours, and then analysis of the residual carbon by 13C NMR or elemental analysis, as described, for example, in the document (Poot et al. 2009). Besides being time-consuming, this method can also lead to overestimations of pyrogenic carbon due to the formation of pyrogenic carbon during the combustion phase, as described, for example, in the document (Simpson and Hatcher, 2004).Thermogravimetric analysis measures several emission peaks during heating, but it is difficult to differentiate between emission peaks related to pyrogenic carbon and those related to soil components using this method, as described, for example, in the document (Cuypers et al., 2002). One method for quantifying pyrogenic carbon in soil is differential scanning calorimetry (DSC), in which the sample induces changes in heat flux as a function of the temperature gradient. A close correlation can be established between these heat flux variations and the amount of carbon. To quantify pyrogenic carbon, it is sufficient to calculate the difference between the amount of carbon above a threshold temperature, around 400°C, in a sample of the same soil / sediment with and without carbon.However, DSC is an indirect measure of stable carbon in a sample, which can introduce inaccuracies in carbon quantification.

[0023] Thus, despite its obvious interest, the quantification of pyrogenic carbon in soil often remains difficult to achieve, and the various existing techniques have disadvantages due, for example, to their price, analysis time, accuracy, or the fact that they are not always easily reproducible.

[0024] Thermal analysis methods for soil organic matter are also known, 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 sequence of temperatures in an inert atmosphere (pyrolysis phase) and / or to a sequence of temperatures in an oxidizing atmosphere (oxidation phase). These methods were initially developed in the petroleum industry for the purpose of characterizing the organic fraction of sedimentary rocks. For example, the "ROCK-EVAL® BULK ROCK" method, initially developed for conventional source rock samples, is known and allows for the distinction between pyrolyzed organic carbon and refractory organic carbon (Behar et al., 2001). The document (Poot et al.(2009) describes how the amount of refractory carbon measured during such a thermal analysis can be used to approximate the amount of pyrogenic carbon in a soil or sediment sample. Specifically, this document describes how the "ROCK-EVAL® BULK ROCK" method allows for the easy and rapid separation of pyrolyzable carbon (PC) from residual carbon (RC). RC corresponds to refractory organic carbon, derived from organic matter that is thermally resistant to the pyrolysis phase and is oxidized during the oxidation phase. This document thus proposes approximating RC as a measure of pyrogenic carbon, which it calls "black carbon" and defines as a continuum ranging from pyrolyzed biomass charcoal to soot. However, this latter approach remains imprecise, since RC can also be partially produced during the pyrolysis phase.Thus, the pyrogenic carbon analyzed with this method may be slightly overestimated.

[0025] The present invention makes it possible to overcome these drawbacks. In particular, the present invention makes it possible to rapidly and precisely quantify pyrogenic carbon in a sample of an organo-mineral or mineral matrix such as soil, by means of a thermal analysis, including in particular the analysis of carbon emissions during an oxidation phase of the sample. Summary of the invention

[0026] The present invention relates to a method for quantifying the pyrogenic carbon content present in a sample comprising an organo-mineral or mineral matrix as well as charcoal and / or biochar. The method according to the invention comprises at least the following steps:

[0027] A) said sample is heated in an inert atmosphere according to a first sequence of temperatures, the initial temperature of which (T0) is between 100 and 300°C, and is preferably 200°C, and a final temperature (TF) is between 500 and 800°C, and is preferably 650°C;

[0028] B) a residue of said sample obtained from said heating in an inert atmosphere is heated in an oxidizing atmosphere according to a second sequence of temperatures having an initial temperature (T0') between 100 and 300 °C, and preferably 200°C, and a final temperature (TF') between 700 and 1000°C, and preferably 850°C, and at least a quantity of CO2 (QCO2) released during said second sequence of temperatures is measured;

[0029] C) from a curve representing the evolution as a function of temperature of said quantity of CO2 released during said heating in an oxidizing atmosphere, said curve is decomposed into at least a first and a second component, said first component corresponding to a part of said curve associated with temperatures below a limit temperature, and said second component corresponding to a part of said curve associated with temperatures above or equal to said limit temperature, said limit temperature being between 500°C and 550°C, and preferably 530°C;

[0030] D) From the surfaces of said first and second components, said pyrogenic carbon content X3 present in said sample is determined according to a formula of the type: [00311 v A 3-“Ü77F

[0032] where A] and X2 are carbon contents determined respectively from the surfaces of said first and second components, A is a coefficient representing the proportion of said matrix in said second component relative to said first component, and B is a coefficient representing the proportion of said charcoal and / or said biochar in said first component relative to said second component.

[0033] According to one embodiment of the invention, said first temperature sequence may include an isothermal plateau of predetermined duration at said initial temperature (T0) of said first temperature sequence, followed by a thermal gradient to reach said final temperature (TF) of said first temperature sequence, said predetermined duration of said isothermal plateau of said first temperature sequence being between 1 and 5 minutes, and preferably being 3 minutes, and said thermal gradient of said first temperature sequence being between 1°C / min and 50°C / min, preferably between 15°C / min and 35°C / min, and very preferably being 25°C / min.

[0034] According to one embodiment of the invention, said second temperature sequence may include at least one thermal gradient between 1°C / min and 50°C / min, preferably between 15°C / min and 35°C / min, and very preferably 25°C / min.

[0035] According to one embodiment of the invention, said second temperature sequence may further include an isothermal plateau of predetermined duration at a temperature between 490 and 600°C, preferably between 500 and 550°C, and preferably 520°C, said predetermined duration of said isothermal plateau of said second temperature sequence being between 1 and 5 minutes, and preferably 3 minutes.

[0036] According to one embodiment of the invention, a sample of said organo-mineral or pure mineral matrix may also be made available, and said coefficient A of step D) may be determined beforehand in the following manner: steps A) to C) are applied to said sample of said organo-mineral or pure mineral matrix, and the coefficient A is determined by calculating the ratio between the surface area of ​​a second component and the surface area of ​​a first component determined from said sample of said organo-mineral or pure mineral matrix.

[0037] According to one embodiment of the invention, a sample of said biochar and / or said pure coal may be made available, and said coefficient B of step D) may be determined beforehand in the following manner: steps A) to C) are applied to said sample of said biochar and / or said coal, and the coefficient B is determined by calculating the ratio between the surface area of ​​said first component and the surface area of ​​said second component determined from said sample of biochar and / or pure coal.

[0038] According to one embodiment of the invention, step D) can be applied by means of a coefficient A between a value of 0.08 and a value of 0.76 and preferably 0.09, and / or a coefficient B between a value of 0.90 and a value of 46.60 and preferably 20.73.

[0039] According to one embodiment of the invention, a total mass of pyrogenic carbon Qc, bc_mix present in said sample can be determined according to a formula of the type: Qc, bc_mix = A3 / C * K, where C is a ratio between a carbon content determined from a surface of a second component determined for a sample of biochar and / or pure coal, and a total mass of carbon in said sample of biochar and / or pure coal, and where A is a multiplicative coefficient between 3.5 and 4.0, and preferably 3.7.

[0040] Alternatively, a total mass of pyrogenic carbon Qc, bc_mix present in said sample can be determined according to a formula of the type: Qc, bc_mix = A3 / C * K, where C is a ratio between a value of 0.04 and a value of 0.74 and preferably equal to 0.07, and where K is a multiplicative coefficient between 3.5 and 4.0, and preferably equal to 3.7.

[0041] Other features and advantages of the process according to the invention will become apparent from the following description of non-limiting examples of embodiments, with reference to the figures attached and described below. List of figures [Fig AI]

[0042] Fig. 1A schematically illustrates the evolution of temperature over time in the temperature sequence of the first step of the process according to the invention. [Fig IB]

[0043] Fig. 1B schematically illustrates the evolution of temperature as a function of time for a variant of the temperature sequence of the first step of the process according to the invention. [Fig 2]

[0044] Figure 2 shows, on an example of application, the CO2 curve measured during step 2) of the process according to the invention, as well as the first and second components resulting from the decomposition according to step 3) of the process according to the invention. [Fig 3]

[0045] Fig. 3 schematically shows the proportion of the organo-mineral or mineral matrix and the proportion of biochar and / or charcoal in the first component resulting from decomposition according to step 3) of the process according to the invention, as well as the proportion of biochar and / or charcoal and the proportion of the organo-mineral or mineral matrix in the second component resulting from decomposition according to step 3) of the process according to the invention. Description of the implementation methods

[0046] The invention relates to a method for quantifying the pyrogenic carbon present in a sample comprising an organo-mineral or mineral matrix as well as charcoal and / or biochar.

[0047] Pyrogenic carbon means the organic fraction that has undergone pyrolysis, that is to say, that has undergone the effect of fire and / or heat (temperature > 200°C) in the absence or in low concentration of oxygen.

[0048] By organo-mineral or mineral matrix, we mean an unconsolidated, porous material, consisting of a mixture of organic and / or mineral particles, of varying size and chemical and / or mineralogical composition.

[0049] By charcoal, we mean the solid residues of a chemical transformation under the effect of a rise in temperature, resulting from pyrolysis or incomplete combustion of plant or animal biomass.

[0050] Biochar means a charcoal produced with the intention of using it as organic amendment, particularly to improve the physico-chemical properties of a soil or its carbon storage.

[0051] The process according to the invention requires having at least one sample comprising an organo-mineral or mineral matrix as well as charcoal and / or biochar.

[0052] According to one embodiment of the invention, the sample comprising an organo-mineral or mineral matrix as well as charcoal and / or biochar may be a soil sample containing charcoal and / or biochar. The term "soil" refers to all the external layers of the Earth's surface formations. A soil sample may be taken manually from a pit or by coring using an auger.

[0053] According to one embodiment of the invention, the sample comprising an organo-mineral or mineral matrix as well as charcoal and / or biochar can be a sample of an amendment comprising an organo-mineral or mineral matrix as well as charcoal and / or biochar.

[0054] According to one embodiment of the invention, the sample comprising an organo-mineral or mineral matrix as well as charcoal and / or biochar can be a soil sample, a sample of natural sediment or sediment polluted by fire residues, or a sample of mineral materials (concrete, excavated soil, sediments) mixed with charcoal / biochar. The soil can be agricultural soil or an anthrosol intentionally enriched with biochar.

[0055] Advantageously, the sample can be sieved using a sieve with orifices of 2 mm diameter, dried at a temperature below 40°C, and then ground to obtain fragments with dimensions of less than 200 pm.

[0056] Preferably, a sample of said organo-mineral or pure mineral matrix, i.e. not comprising biochar or charcoal, may also be made available.

[0057] Advantageously, a sample of the biochar and / or charcoal present in the sample under consideration may also be made available.

[0058] 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:

[0059] - a pyrolysis oven in a non-oxidizing atmosphere,

[0060] - means for transferring pyrolysis residues into an oxidation furnace,

[0061] - an oxidation furnace in an oxidizing atmosphere,

[0062] - means for measuring the quantity of hydrocarbon compounds (HC) released at pyrolysis process,

[0063] - means for measuring carbon monoxide (CO) and carbon dioxide (CO2).

[0064] The process can also be implemented using a single pyrolysis furnace, capable of operating in both a non-oxidizing and an oxidizing atmosphere, cooperating with a device for measuring the quantity of hydrocarbon compounds released during pyrolysis, and a device for measuring carbon monoxide and carbon dioxide.

[0065] The method according to the invention comprises at least the following steps:

[0066] 1) Heating sequence under an inert atmosphere (pyrolysis)

[0067] 2) Heating sequence under an oxidizing atmosphere (oxidation)

[0068] 3) Two-component decomposition

[0069] 4) Determination of the pyrogenic carbon content

[0070] The steps of the process according to the invention are detailed below.

[0071] 1. Heating sequence under an inert atmosphere (pyrolysis)

[0072] During this step, the sample comprising an organo-mineral matrix or mineral as well as biochar and / or coal is heated under an inert atmosphere (such as under a flow of nitrogen or helium) according to a sequence of temperatures in which the initial temperature (denoted T0 hereafter) is between 100 and 300 °C and is preferably 200°C, and the final temperature (denoted TF hereafter) is between 500 and 800°C, and is preferably 650°C.

[0073] Preferably, the temperature sequence under an inert atmosphere may include at least one isothermal plateau at the initial temperature T0, followed by a predetermined thermal gradient to raise the sample temperature to the final temperature TF. Figure 1A schematically illustrates the evolution of 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.

[0074] Advantageously, the temperature sequence under an inert atmosphere in this embodiment may further include a second isothermal plateau at the final temperature TF. In other words, a second isothermal plateau at the final temperature TF follows the phase of the temperature sequence that takes the form of a thermal gradient. This allows 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, if necessary. Figure 1B schematically illustrates the evolution of the temperature T as a function of time t in such a temperature sequence, exhibiting two isothermal plateaus at temperatures T0 and TF as defined above, and linked by a thermal gradient.

[0075] According to one embodiment of the invention, the initial temperature T0 is preferably 200°C. This temperature is indeed sufficient to release the most labile organic compounds present in most soil, organic amendment or sediment samples.

[0076] According to one embodiment of the invention, the final temperature TF is preferably 650°C, so as to avoid obtaining CO and CO2 curves showing incomplete peaks at the end of pyrolysis measured in particular on natural samples (fresh and dried plant tissues, litter, peat, and plant composts, organo-mineral and mineral soils, surface formations).

[0077] 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).

[0078] According to one embodiment of the invention, the thermal gradient(s) of the temperature sequence under an inert atmosphere can be between 1 and 50°C / min, preferably between 15° and 35°C / min, and preferably 25°C / min. Such values ​​represent a compromise that allows for the thermal cracking of the compounds while limiting the implementation time of the process.

[0079] According to one embodiment of the invention, the quantity of hydrocarbon compounds released during heating under an inert atmosphere, and / or the quantity of CO2 and / or the quantity of CO contained in an effluent resulting from said heating, can be measured continuously (i.e., continuously over time). In other words, during this sequence, the quantity of HC, CO, and CO2 released from the sample by thermal cracking of the organic matter and by the thermal decomposition of the carbonate minerals can be continuously measured. The measurement of the quantity of hydrocarbon compounds can be carried out using a flame ionization detector (FID). The measurement of the quantity of CO and CO2 released can be carried out using an infrared (IR) detector. Alternatively, other means of measuring the quantity of HC, CO, and / or CO2 can be used.According to this implementation, at the end of this step applied to a given sample, one can obtain a first curve representing the quantity of hydrocarbon compounds released over time during the pyrolysis phase, as well as two other curves representing the quantity of CO and CO2 released over time during the pyrolysis phase. Such measurements can help determine standard parameters for this type of thermal analysis, in particular the parameter denoted TOC (for "Total Organic Carbon"), which corresponds to the carbon content of the sample, determined from the amount of hydrocarbons released by the sample and the amounts of CO and CO2 released below threshold temperatures during the pyrolysis and oxidation phases; and the parameter denoted MinC (for "Mineral Carbon"), which corresponds to the mineral carbon content of the sample, determined from the amounts of CO and CO2 released by the sample above threshold temperatures during the pyrolysis and oxidation phases. A description of these general parameters can be found in the document (Behar et al., 2001).

[0080] In general, this particular heating sequence under an inert atmosphere is sufficient to allow the thermal cracking of classes of compounds comprising mineral carbon and organic carbon, in particular:

[0081] - highly thermally labile compounds, which are particularly abundant in fresh biological tissues, which are generally released at temperatures between approximately 80 and 360°C;

[0082] - thermally labile compounds, which are predominant in the gold samples organic materials such as bedding or peat, and which are generally released at temperatures between approximately 360 and 420°C;

[0083] - the heat-resistant compounds, which are predominant in the samples organo-mineral (soils) or mineral (alluvium, colluvium), and which are generally released at temperatures between approximately 420°C and 470°C;

[0084] - thermally refractory compounds, which are generally released at temperatures temperatures between approximately 470 and 520°C;

[0085] - and highly thermally refractory compounds, which are present in larger quantities proportions in decomposition residues or exogenous fractions, such as pyrogenic or petrogenic organic matter, and which are generally released at temperatures between approximately 520 and 650°C.

[0086] According to one embodiment of the invention, the temperature sequence under an inert atmosphere 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 form 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 temperature sequence under an inert atmosphere according to the invention. This preliminary phase can help to initiate the thermal cracking of compounds whose cracking temperature is below the temperature initial temperature of the temperature sequence under inert atmosphere according to the invention, particularly in the case of fresh biological tissues.

[0087] 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.

[0088] 2) Heating sequence under an oxidizing atmosphere (oxidation)

[0089] During this second step, the solid residue of the sample obtained at the end of the heating sequence under an inert atmosphere as described in step 1 above is subjected to oxidation according to a predefined temperature sequence, the initial temperature of which (hereafter denoted T0') is between 100 and 300 °C and is preferably 200 °C, and the final temperature (hereafter denoted TF') is between 700 and 1000 °C, and is preferably 850 °C (so as to deplete the mineral carbon stock).

[0090] According to one embodiment of the invention, the temperature sequence of this heating under an oxidizing atmosphere includes at least one thermal gradient between 1 and 50°C / min, preferably between 15° and 35°C / min, and is preferably 25°C / min. In particular, this second temperature sequence may include such a thermal gradient to link the initial temperature T0' and final temperature TF' of the temperature sequence under an oxidizing atmosphere.

[0091] In general, the preferred temperature range for the initial temperature T0' of the temperature sequence under an oxidizing atmosphere makes it possible to avoid episodes of instantaneous combustion of the sample residue at the beginning of the oxidation cycle.

[0092] According to one embodiment of the invention, the temperature sequence under an oxidizing atmosphere may further include an isothermal plateau at the initial temperature T0' of a predetermined non-zero duration (for example greater than half a minute), and may preferably be between 1 and 5 minutes, most preferably 3 minutes.

[0093] According to the invention, at least a certain quantity of CO2 (and optionally a certain quantity of CO) released during this second temperature sequence is continuously measured. According to one embodiment of the invention, this measurement can be performed using an infrared (IR) detector. It should be noted that such a sensor provides measured values ​​in millivolts (mV). Conventionally, a quantity of CO2 is determined. released during this second temperature sequence, hereafter denoted Xtot, by determining an area under the curve measured (possibly between predefined temperatures) by this sensor, according to a formula of the type:

[0094] = (1)

[0095] where Surf C corresponds to the area under the curve (also called a thermogram) representing the amount of CO2 released during this second temperature sequence, mass corresponds to the mass of the sample, and where Xtot is expressed in mg / g of sample. Alternatively, other means of measuring the amount of CO2 may be used.

[0096] Advantageously, the temperature sequence under an oxidizing atmosphere may further include an isothermal plateau of predetermined duration at a temperature between 490 and 600°C, preferably between 500 and 550°C, and preferably at 520°C. This isothermal plateau allows for better separation, in a curve representing the temperature evolution of the amount of CO₂ released during heating under an oxidizing atmosphere, of a component attributed to biochar or charcoal from a component attributed to the mineral or organo-mineral matrix present in the sample under consideration. This notably helps to improve the result of step 3) of the process according to the invention described below. This isothermal plateau may have a non-zero predetermined duration (for example, greater than half a minute), preferably between 1 and 5 minutes, and most preferably 3 minutes.According to this embodiment, the temperature sequence under an oxidizing atmosphere may include two thermal gradients, preferably between 1 and 50°C / min, preferably between 15 and 35°C / min, and most preferably 25°C / min. According to this implementation, the isothermal plateau at a temperature between 490 and 600°C, preferably between 500 and 550°C, and preferably 520°C, may be both preceded and followed by the at least two thermal gradients of this implementation. 3) Two-component decomposition

[0097] During this step, a curve representing the evolution as a function of temperature of said quantity of CO2 released during the second heating sequence is decomposed into at least a first and a second component, the first component corresponding to the part of said curve associated with temperatures below a limit temperature, and said second component corresponding to the part of said curve associated with temperatures above or equal to said limit temperature, said limit temperature being between 500°C and 550°C, and preferably 530°C.

[0098] In other words, during this step, we delimit, on the CO2 curve measured at Step 2), two components as a function of a vertical line passing through the limiting temperature according to the invention. This is illustrated in [Fig. 2], which shows the result of the decomposition of a curve C measuring the quantity of CO2QCO2 released during step 2) of the process according to the invention into two components Cl, C2 as a function of a vertical line D passing through the limiting temperature TL, 520°C for this illustration.

[0099] The limiting temperature according to the invention corresponds to the temperature below which most of the CO2 from the mineral or organo-mineral matrix is ​​emitted and above which most of the CO2 from the biochar or charcoal is emitted. This limiting temperature has been observed in several soil or sediment samples containing biochar or charcoal. This yields a first component representing the proportion of CO2 released primarily by the mineral or organo-mineral matrix composing the sample under consideration, and a second component representing the proportion of CO2 released primarily by the biochar and / or charcoal composing the sample under consideration.

[0100] According to one embodiment of the invention, the limiting temperature according to the invention can be determined by determining the temperature of an inflection point of the curve representing the evolution as a function of temperature of the quantity of CO2 released during the second heating sequence in a part of this curve between 500°C and 550°C.

[0101] 4) Determination of the pyrogenic carbon content

[0102] During this step, starting from the surfaces of the first and second components determined in step 3), the pyrogenic carbon content present in the sample is determined. More specifically, according to the invention, the pyrogenic carbon content present in the sample, hereafter denoted X3, is determined according to a formula of the type:

[0103] y _ *2^1 (2)

[0104] where Xj and X2 are carbon contents determined respectively from the surfaces of said first and second components, A is a coefficient representing the proportion of said matrix in said second component relative to said first component, and B is a coefficient representing the proportion of said charcoal and / or said biochar in said first component relative to said second component.

[0105] According to one embodiment of the invention, 2Q can be determined according to the formula:

[0106] = Surf CA (3)

[0107] and X2 according to the formula •

[0108] X2 = SurfG2(4)

[0109] where Sur f G1 and Sur f G2 are respectively the surfaces of the first and second components determined at the end of step 3 of the process according to the invention.

[0110] Equation (2) arises from the fact that the decomposition according to step 3) is imperfect for separating the contribution of the organo-mineral or mineral matrix from the contribution of the biochar and / or charcoal in a curve measuring the quantity of CO2 released during an oxidation phase. In other words, the first component resulting from the decomposition according to the invention certainly comprises mainly a contribution related to the organo-mineral or mineral matrix (denoted X] „,at hereafter), but also includes a contribution from the biochar and / or charcoal (denoted XUx hereafter). Similarly, the second component resulting from the decomposition according to the invention certainly comprises mainly a contribution from the biochar and / or charcoal (denoted Xy>c hereafter), but also includes a contribution related to the organo-mineral or mineral matrix (denoted XI, bc hereafter). This is illustrated in particular in [Fig.3], which schematically represents the proportion of the organo-mineral or mineral matrix XI,mat and the proportion of biochar and / or coal XI,bc in the first component Cl, as well as the proportion of biochar and / or coal X2,bc and the proportion of the organo-mineral or mineral matrix X2,mat in the second component C2, the components Cl and C2 being delimited by the line D. With these notations, the coefficients A and B according to the invention can be described by the following formulas: . [YES] 4 _ (5) 21 — y

[0112] and

[0113] B = (6)

[0114] According to a first embodiment of the invention, coefficient A and / or coefficient B can be determined from a sample of the pure organo-mineral or mineral matrix and a sample of pure biochar and / or charcoal, respectively, representative of the organo-mineral or mineral matrix and the biochar and / or charcoal present in the sample under consideration, to which steps 1), 2), and 3) described above are applied. Coefficient A can then be determined by the ratio between the surface area of ​​the second component and the surface area of ​​the first component determined from the sample of pure organo-mineral or mineral matrix. Coefficient B can be determined by the ratio between the surface area of ​​the first component and the surface area of ​​the second component determined from the sample of pure biochar and / or charcoal.

[0115] According to a second embodiment of the invention, and in particular if samples of the pure organo-mineral or mineral matrix and / or of pure biochar and / or charcoal, representative of the organo-mineral or mineral matrix and of the biochar and / or charcoal If the values ​​present in the sample under consideration are not available, equation (2) above can be implemented using a coefficient A between a value of 0.08 and a value of 0.76 and preferably 0.09, and / or a coefficient B between a value of 0.90 and a value of 46.60 and preferably 20.73. These ranges and preferred values ​​of coefficients A and B were determined from a plurality of samples of organo-mineral or pure mineral matrix and a plurality of samples of pure biochar and / or coal, of different types, to which the method described above was applied.Specifically, samples of organo-mineral or pure mineral matrix of soil and sediment type were used, obtained from various climatic conditions and with varying total organic carbon contents, and samples of pure biochar and / or charcoal from various plant biomass and from various pyrolysis temperatures, ranging from 450 °C to 650 °C. The preferred value of coefficients A and B corresponds to the median of the values ​​thus determined for the plurality of samples.

[0116] Thus, at the end of this step, we obtain the content of pyrogenic carbon present in the sample considered, comprising both a mineral or organo-mineral matrix and charcoal and / or biochar.

[0117] According to one embodiment of the invention, the total mass of pyrogenic carbon present in the sample considered, hereinafter denoted Qc, bc_mix, can be determined according to a formula of the type:

[0118] Qc, bc_mix = X3 / C *X(7)

[0119] Where

[0120] - C is the ratio between the carbon content determined from the surface of the The second component, determined in the case of a sample of pure biochar and / or charcoal, denoted X2, is the total mass of carbon in the sample of pure biochar and / or charcoal; in other words, the ratio C can be written

[0121] C = X2, bc / (TOC, bc * Qty, bc) (8)

[0122] where TOC,bc and Qty,bc correspond respectively to the total organic carbon and the total mass of a pure biochar / charcoal sample. According to one embodiment of the invention, and in particular if a pure biochar and / or charcoal sample representative of the biochar and / or charcoal present in the sample under consideration is not available, equation (2) above can be implemented using a ratio C between a value of 0.04 and a value of 0.74, and preferably 0.07. This range and this preferred value were determined from a plurality of pure biochar and / or charcoal samples of different types. The preferred value corresponds to the median of the values ​​thus determined for the plurality of samples.

[0123] - K is a multiplicative coefficient. According to one embodiment of the invention, the co efficient K can be between 3.5 and 4.0, and preferentially is 3.7. Such values ​​were determined from a plurality of samples of pure biochar and / or charcoal, of different types. Examples

[0124] The characteristics and advantages of the method according to the invention will become clearer upon reading the application example below.

[0125] The present invention is applied for the purpose of determining the mass of pyrogenic carbon present in a sample corresponding to a soil-biochar mixture,

[0126] A plurality of samples are generated, for different mass ratios of biochar to soil, by a homogeneous mixture of agricultural soil and industrial biochar made from herbaceous plants. The total organic carbon (TOC) of the biochar and the soil amounts to 82.60% and 5.55%, respectively. Each sample thus formed is dried at a temperature of 40°C or lower until its weight stabilizes, and then ground to a particle size below 200 µm.

[0127] Each sample is subjected to heating under an inert atmosphere according to the invention, and then its residue is subjected to heating under an oxidizing atmosphere according to the invention. Figure 2 shows, in the case of a sample containing 1% biochar by mass, the curve C of the quantity of CO2 QCO2 measured during step 2) of the process according to the invention, as well as the result of step 3) of the process according to the invention, in the form of two components Cl, C2 delimited by the vertical line D passing through the limiting temperature TL equal to 520°C.

[0128] Table 1 shows the mass of pyrogenic carbon (given in mg of carbon, mgC) present in the samples considered, determined at the end of step 4 of the process according to the invention applied according to the first variant described above (determination of the coefficients A and B of equation (2) from samples of pure soil and biochar; column Qc,bc_mix_V1) and according to the second variant described above (determination of the coefficients A and B of equation (2) from their preferred values ​​defined above; column Qc,bc_mix_V2), as well as the actual mass of pyrogenic carbon present in the samples considered (column Qc,bc_mix_REAL), as a function of their mass ratio between biochar and soil (column Ratio). It can be observed that the mass of pyrogenic carbon determined by the present invention, applied according to its first or second variant, is very close to the actual values ​​(average error of 1.36% and maximum of 26%).37% for the first variant; average error of -18.43% and maximum of -46.80% for the second variant).

[0129] These results were obtained in less than 90 minutes for each sample, duration which essentially corresponds to the heating time in an inert atmosphere and the heating time in an oxidizing atmosphere for each sample.

[0130] Thus, the present invention makes it possible to quantify quickly and precisely the pyrogenic carbon in a sample of an organo-mineral or mineral matrix further comprising biochar or charcoal, by means of a simple thermal analysis to implement.

[0131] [Tables 1] Ratio Qc ,bc_mix_RE AL (mgC) Qc,bc_mix_V 1 (mgC) Qc,bc_mix_V2 (mgC) 0.05 4.5 5.7 2.4 0.11 9.0 9.4 9.7 0.21 17.3 17.3 17.7 0.51 43.2 39.3 40.2 0.56 47.3 42.3 38.8 1.02 84.9 78.9 76.0 1.11 93.0 97.8 100.1

Claims

1. Claims Method for quantifying the pyrogenic carbon content present in a sample comprising an organo-mineral or mineral matrix as well as coal and / or biochar, characterized in that: A) said sample is heated in an inert atmosphere according to a first sequence of temperatures of which an initial temperature (T0) is between 100 and 300°C, and is preferably 200°C, and a final temperature (TF) is between 500 and 800°C, and is preferably 650°C; B) a residue of said sample from said heating in an inert atmosphere is heated in an oxidizing atmosphere according to a second sequence of temperatures of which an initial temperature (T0') is between 100 and 300°C, and is preferably 200°C, and a final temperature (TF') is between 700 and 1000°C, and is preferably 850°C, and at least a quantity of CO2 (QCO2) released during said second sequence of temperatures is measured; C) from a curve representative of the evolution as a function of the temperature of said quantity of CO2 released during said heating in an oxidizing atmosphere, said curve is broken down into at least a first and a second component, said first component corresponding to a part of said curve associated with temperatures lower than a limit temperature, and said second component corresponding to a part of said curve associated with temperatures greater than or equal to said limit temperature, said limit temperature being between 500°C and 550°C, and preferably being 530°C; D) From the surfaces of said first and second components, said pyrogenic carbon content X3 present in said sample is determined according to a formula of the type: v X2-AX, -3“ 1+AB where A] and X2 are carbon contents determined respectively from the surfaces of said first and second components, A is a coefficient representing the proportion of said matrix in said second component relative to said first component, and B is a coefficient representing the proportion of said coal and / or said biochar in said first component relative to said second component.

2. The method of claim 1, wherein said first temperature sequence comprises an isothermal plateau of a predetermined duration at said initial temperature (TO) of said first temperature sequence, followed by a thermal gradient to reach said final temperature (TF) of said first temperature sequence, said predetermined duration of said isothermal plateau of said first temperature sequence being between 1 and 5 minutes, and preferably being 3 minutes, and said thermal gradient of said first temperature sequence being between 1°C / min and 50°C / min, preferably between 15°C / min and 35°C / min, and very preferably being 25°C / min.

3. Method according to one of the preceding claims, in which said second temperature sequence comprises at least one thermal gradient between 1°C / min and 50°C / min, preferably between 15°C / min and 35°C / min, and very preferably 25°C / min.

4. Method according to one of the preceding claims, in which said second temperature sequence further comprises an isothermal stage of a predetermined duration at a temperature between 490 and 600°C, preferably between 500 and 550°C, and preferably 520°C, said predetermined duration of said isothermal stage of said second temperature sequence being between 1 and 5 minutes, and preferably 3 minutes.

5. Method according to one of the preceding claims, in which a sample of said pure organo-mineral or mineral matrix is ​​also available, and in which said coefficient A of step D) is previously determined in the following manner: steps A) to C) are applied to said sample of said pure organo-mineral or mineral matrix, and coefficient A is determined by calculating the ratio between the surface area of ​​a second component and the surface area of ​​a first component determined from said sample of said pure organo-mineral or mineral matrix.

6. Method according to one of the preceding claims, in which a sample of said biochar and / or said pure coal is also available, and in which said coefficient B of step D) is previously determined in the following manner: steps A) to C) are applied to said sample of said biochar and / or said coal, and coefficient B is determined by calculating the ratio between the surface area of ​​said first component and the surface area of ​​said second component determined at from said sample of biochar and / or pure charcoal.

7. Method according to one of the preceding claims, in which step D) is applied by means of a coefficient A between a value of 0.08 and a value of 0.76 and preferably having a value of 0.09, and / or a coefficient B between a value of 0.90 and a value of 46.60 and preferably having a value of 20.

73.

8. Method according to one of the preceding claims, in which a total mass of pyrogenic carbon Qc, bc_mix present in said sample is determined according to a formula of the type: Qc, bc_mix — X3 / C * K, where C is a ratio between a carbon content determined from a surface area of ​​a second component determined for a sample of biochar and / or pure coal, and a total mass of carbon in said sample of biochar and / or pure coal, and where K is a multiplicative coefficient between 3.5 and 4.0, and preferably having a value of 3.

7.

9. Method according to one of claims 1 to 7, in which a total mass of pyrogenic carbon Qc, bc_mix present in said sample is determined according to a formula of the type: Qc, bc_mix = X3 / C * K, where C is a ratio between a value of 0.04 and a value of 0.74 and preferably being 0.07, and where K is a multiplicative coefficient between 3.5 and 4.0, and preferably being 3.7.

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