Device and method for quantifying a total nitrogen content present in a sample of a porous medium and / or derived from biomass

Abstract

The invention relates to a device and a method for quantifying a total nitrogen content in a sample of a porous medium and / or derived from biomass. The sample is heated in an inert atmosphere to between a temperature of between 50 and 300°C and a temperature of between 650 and 1000°C, and contents of NH3, N2O, and N2, as well as first contents of NO and NO2 are determined; the effluents of the first heating step undergo continuous oxidation at at least 900°C, and second contents of NO and NO2 are determined; a residue of the sample is heated in an oxidising atmosphere to between a temperature of between 50 and 300°C and a temperature of at least 850° C, and third contents of NO and NO2 are determined. The total nitrogen content corresponds to the sum of the contents of NH3, N2O, N2, and of the first, second and third contents of NO and NO2.

Description

[0001] DEVICE AND METHOD FOR QUANTIFYING A TOTAL NITROGEN CONTENT PRESENT IN A SAMPLE OF A POROUS MEDIUM AND / OR DERIVED FROM BIOMASS

[0002] Technical field

[0003] The present invention relates to the field of quantification of nitrogen present in a sample of a porous medium and / or derived from biomass.

[0004] Applied to the field of soil science, environmental geosciences or even agriculture, the present invention can in particular allow the quantification of the nitrogen present in a soil sample, a surface formation, or even a fertilizer for a soil.

[0005] Nitrogen is an essential element for plant growth. Nitrogen fertilization is necessary for crop development. Thus, a nitrogen deficiency jeopardizes crop yield and quality. On the other hand, an excess of nitrogen is harmful to the environment, particularly because under certain conditions, nitrogen fertilizers are transformed into nitrous oxide, a powerful greenhouse gas.

[0006] Thus, in addition to carbon content, nitrogen content is an indicator that provides information on the state of a soil, particularly in the context of organic farming which aims to reduce or even eliminate the use of synthetic fertilizers in a context of climate issues. Note that, if the use of synthetic nitrogen fertilizer by fixing atmospheric nitrogen allowed in the 1930s what is called the "green revolution", it is precisely its excessive use that also leads today to a disastrous environmental effect on aquatic environments following the process of eutrophication.

[0007] The term nitrogen refers to two groups: organic nitrogen and inorganic nitrogen. Organic nitrogen is the nitrogen present in all organic compounds (such as amino acids, proteins, nitrogen bound to decaying plant and animal matter, etc.) and inorganic nitrogen is the nitrogen present in inorganic compounds (such as ammonium (NH4) + ), nitrates (NOs-), nitrogen gas (N2) and nitrites (NO2-)).

[0008] In soil, nitrogen is mainly present in organic form (approximately 95% of the total nitrogen in a soil). These forms of nitrogen are not directly assimilated by plants (with the exception of urea, a small molecule). Organic nitrogen is made up of various nitrogen compounds whose mineralization under the effect of microbial activity is very variable and very difficult to predict. In mineral form, nitrogen can be present in nitrates: KNO3 (saltpeter) and NaNCh (Chilean nitrate), ammonium nitrates (fertilizers most used in France), and in urea (nitrogen fertilizers). Mineral nitrogen in soils includes nitrogen dissolved in the soil solution or fixed on the clay-humic complex, the main forms of which are nitrate ions (NO , nitric nitrogen) and ammonium (NH4 +, ammoniacal nitrogen). Plants obtain nitrogen in mineral form. Nitric nitrogen (NO3) is the most available form for plants and ammoniacal nitrogen comes mainly from the hydrolysis of amino acids. Thanks to its positive charge, NH4 + binds to the clay-humic complex of the soil, which limits the risk of deep entrainment (by leaching) but also its instant availability for plants. Microbial activity in soils consumes ammonium and transforms it into nitric nitrogen, this is the process of nitrification. In the event of leaching or denitrification, nitrogen is lost to the ecosystem.

[0009] Nitrogen can be present in several oxidation states ranging from the most reduced volatile gaseous form to the most oxidized: NH3 (ammonia), N2 (dinitrogen), N2O, NO, NO2.

[0010] We then call "total nitrogen" all the forms of nitrogen present in a sample in its organic and / or mineral configuration. The nitrogen stock in the soil changes over time according to three phenomena: mineralization, leaching and the development of the plant cover. Soil fertility (or quality of a soil) is based, among other things, on an elementary analysis of carbon and nitrogen. In addition to the texture and structure of the soil, the pH and the pedoclimatic conditions, this fertility (rate of decomposition of the organic matter in the soil and of mineralization of nitrogen) will depend on the organic content of the soil in C and N (its quality and quantity) and the inputs of organic or mineral fertilizers and amendments.Organic fertilizers are very numerous and increasingly varied, and knowledge of the elementary composition of soils alone (in principle, corresponding to the organic C / organic N ratio, but which is often equated with total C / total N) makes it increasingly difficult to predict their evolution in the soil. This C / N ratio provides information on the degree of evolution of organic matter, the biological activity of the soil and the potential for nitrogen supply by the soil (mineralization). However, total nitrogen does not provide any information on the mineral nitrogen available to the plant.

[0011] Prior art

[0012] The following documents will be cited during the description:

[0013] Jaber AMY, Mehanna NA, Sultan SM; 2009. Determination of ammonium and organic bound nitrogen by inductively coupled plasma emission spectroscopy, Taianta 78 (4-5), pp. 1298-1302, https: / / doi.Org / 10.1016 / j.talanta.2009.01.060. Hsieh, Y. P. (2007). A novel multielemental scanning thermal analysis (MESTA) method for the identification and characterization of solid substances. Journal of AOAC International. 90. 54-9.

[0014] Hsieh YP, Bugna GC, 2008. Analysis of black carbon in sediments and soils using multielement scanning thermal analysis (MESTA), Organic Geochemistry, Vol. 39 (11), pp 1562-1571, ISSN 0146-6380, https: / / doi.Org / 10.1016 / j.orggeochem.2008.07.015.

[0015] Current methods for analyzing soil nitrogen are most often carried out on fresh and dried fine soil (particles smaller than 2 mm). Indeed, without special precautions, the quantity of nitric nitrogen (NO ) and ammoniacal nitrogen (NH4 +) can, through mineralization of organic matter, evolve very quickly (in less than 24 hours). These different methods of measuring nitrogen are either physicochemical or thermal.

[0016] Physicochemical methods generally use standards. For example, total soil nitrogen (in its ammonium, nitrate, nitrite and organic form) can be measured by the so-called "Dumas" method (elemental analysis - NF ISO 13878), which determines the total nitrogen content by dry combustion, more precisely by combustion in the presence of oxygen of the crushed soil in a furnace at 950°C. The so-called "modified Kjeldahl" method (NF ISO 11261) is also known for determining total nitrogen (in its ammonium, nitrate, nitrite and organic form, namely N-tot. = N-org. + N-NH4 + N-NO3), which involves three steps: a) mineralization in the form of ammonium nitrogen by H2SO4 (which transforms the organic matter into NH4 +), b) distillation of the NH3 formed with water vapor and c) titration of the distillate using boric acid. The quantities required for the measurement vary from 0.1 to 10 g of samples. As for mineral nitrogen (N-NH4 and N-NO3), it can be measured in two parts according to the NF ISO 14256 standard which uses colorimetric methods. More precisely, the determination of nitrates, nitrites and ammonium in raw soils is obtained by extraction with a potassium chloride solution followed by spectrophotometric analyses of the different types of nitrogen (reading at 543 nm for nitrites and nitrates and at 660 nm for ammonium). The results of total nitrogen contents and those in its different forms following the Kjeldahl method are indicated respectively in mg / kg on wet soil, mg / kg on dry soil and kg / ha. The calculation of organic nitrogen can also be obtained by the difference between total nitrogen and mineral nitrogen.These measurements obtained according to standardized procedures are generally carried out by accredited design offices or laboratories.

[0017] Among the thermal methods, we know the method described in the document (Jaber et al., 2009), which is based on inductively coupled plasma spectrometry ("Inductively Coupled Plasma Emission Spectrometer" in English, also known by the acronym "ICP-AES") integrating an improved plasma flow generation system. This method makes it possible to obtain total nitrogen contents comparable with those obtained by the standard Kjeldahl method, but is much more sensitive. It is also more sensitive than the classic ICP-AES elemental analysis which has the disadvantage of generating a lot of matrix interferences.

[0018] More recent elemental analyzers are also known, for example the 828 and 928 elemental analyzers developed by the LECO company (USA) for the measurement of total nitrogen, coupling dry combustion under O2 with detection of N2 generated using a thermal conductivity detector (TCD) under He or Ar current using a heated catalytic furnace (Cu) for the reduction of nitrogen oxide species (NOx) to N2. Depending on the type of samples (soil, fertilizer, plants), the samples are sieved (0.150 to 0.5 mm) and dried (85 to 105°C) beforehand. The quantity of samples varies from 0.05 to 2g and the method requires ceramic boats. This sensor, by measuring only N2, makes it possible to determine the quantity of total nitrogen present in a sample using a high-temperature catalytic furnace.

[0019] Like all the other elemental analyzers described above, these new analyzers improve the Dumas combustion method for measuring total nitrogen by providing reliability, higher analytical yield and ease of use. The advantage of these analyzes is that they are faster and do not use any solvent or pre-treatment compared to the Kjeldahl method for measuring total nitrogen. However, these methods only measure total nitrogen from one nitrogen form (e.g. N2) while the Kjeldahl method measures up to three nitrogen forms to describe total nitrogen: N-Org., N-NH4 and N-NO3.

[0020] A multi-element thermal scanning method (MESTA) is also known, described in the documents (Hsieh, 2007; Hsieh and Bugna, 2008), which allows the simultaneous determination of the decomposition of carbon, nitrogen, and sulfur compounds as a function of temperature. More precisely, this method is implemented using two furnaces: a furnace for the sample (which can weigh between 0.3 and 10 mg) programmable from room temperature to 800 °C with a gradient of 50 °C / min under a flow of an extra-pure O2 / He mixture (40 / 60%), and a combustion furnace maintained at 1100 °C and constantly purged with 100% ultra-pure C>2. After pyrolysis, the effluents are transported by the carrier gas into the combustion furnace where they are oxidized to CO2, NO2, and SO2.The oxidized materials then pass successively through C (infrared CO2 analyzer), N (nitrogen chemiluminescence detector or "NCD") and S (sulfur chemiluminescence detector, or "SCD") detectors. This method measures the total nitrogen content but from a single nitrogen form (NO2), obtained only after oxidation. However, this method provides information on the quality of total nitrogen as a function of temperature.

[0021] Thus, various methods are used to determine the total nitrogen of samples, for example from soil. For organic nitrogen, it can be obtained solely by the Kjeldahl method or by difference between total and mineral nitrogen. However, most of these methods are cumbersome to implement with complicated procedures, time-consuming and solvent-intensive, and also associated with problems such as limitation to high nitrogen concentrations, matrix interferences (with the exception of ICP AES), and a virtually non-existent dynamic range (continuously measured signal) (except for the thermal MESTA method).

[0022] Summary of the invention

[0023] The present invention makes it possible to overcome these drawbacks. More specifically, the present invention relates to a device and a method for measuring the total nitrogen content present in a sample of a porous medium and / or derived from biomass, by means of heating sequences in an inert atmosphere and in an oxidizing atmosphere, the characteristics of which allow complete thermal cracking of the various nitrogen compounds contained in a sample of a porous medium and / or derived from biomass, and by means of measurements of the various nitrogen compounds contained in the effluents resulting from these heatings.

[0024] The present invention makes it possible to quantify total nitrogen in a single step in a sample, without prior treatment, and on small quantities (from a few mg to a hundred mg at most). The dynamic character (signal measured continuously) provides a second piece of information on the quality of the nitrogenous constituents present in a sample according to their thermal stability (continuous recording of the signal over time and temperature). These parameters make it possible to better identify the different mechanisms (N2 fixation, nitrification, denitrification) involved during the respiration and fermentation processes linked to the carbon cycle. Furthermore, the present invention, due to the detection of several nitrogenous compounds, makes it possible to have in addition information on the type of nitrogenous compounds present in the sample (and not only concerning NO2 or N2 depending on the analysis method used), while associating it with its thermal stability.

[0025] The present invention relates to a device for quantifying a total nitrogen content present in a sample of a porous medium and / or derived from biomass, said device being characterized in that it comprises: o means for heating said sample in an inert atmosphere; o means for heating in an oxidizing atmosphere a residue from said means for heating said sample in an inert atmosphere; o means for oxidizing effluents from the means for heating said sample in an inert atmosphere; o means capable of continuously measuring: a quantity of NH3, a quantity of NO, a quantity of NO2, a quantity of N2O and a quantity of N2 from said means for heating said sample in an inert atmosphere; a quantity of NO and a quantity of NO2 from said means for oxidizing effluents from said means for heating said sample in an inert atmosphere;a quantity of NO and a quantity of NO2 from said means for heating in an oxidizing atmosphere a residue from said means for heating said sample in an inert atmosphere;

[0026] According to one implementation of the invention, said means for heating said sample in an inert atmosphere may comprise a pyrolysis furnace in an inert atmosphere, and said means for heating said residue from said means for heating said sample in an inert atmosphere in an oxidizing atmosphere comprise an oxidation furnace.

[0027] According to one implementation of the invention, said means for heating said sample in an inert atmosphere and said means for heating said residue from said means for heating said sample in an inert atmosphere in an oxidizing atmosphere may comprise a single pyrolysis furnace, capable of operating in an inert atmosphere and in an oxidizing atmosphere.

[0028] According to one implementation of the invention, the device further comprises means for determining a total nitrogen content from continuous measurement of a quantity of NH3, a quantity of NO, a quantity of NO2, a quantity of N2O and a quantity of N2 from the means for heating said sample in an inert atmosphere, a quantity of NO and a quantity of NO2 from the means for oxidizing effluents from the means for heating said sample in an inert atmosphere, and a quantity of NO and a quantity of NO2 from the means for heating a residue from the means for heating said sample in an inert atmosphere in an oxidizing atmosphere. These means for determining a total nitrogen content may comprise computer means, in particular a computer or a server, comprising at least one processor and a computer memory.According to one implementation of the invention, said means for oxidizing said effluents from said means for heating said sample in an inert atmosphere may comprise an oxidation furnace.

[0029] According to an implementation of the invention, said means capable of continuously measuring said quantity of NH3 originating from said means for heating said sample in an inert atmosphere, as well as said means capable of continuously measuring said quantity of NO and / or said quantity of NO2 originating from said means for heating said sample in an inert atmosphere and / or originating from said means for oxidizing effluents originating from said means for heating said sample in an inert atmosphere and / or originating from said means for heating a residue originating from said means for heating said sample in an inert atmosphere in an oxidizing atmosphere may comprise an optical sensor operating in the ultraviolet range, said optical sensor comprising a source of UV radiation for illuminating a measurement zone and a spectrometer for measuring the intensity as a function of the wavelength of the UV radiation having passed through said measurement zone.

[0030] The invention further relates to a method for quantifying a total nitrogen content present in a sample of a porous medium and / or derived from biomass, characterized in that said method comprises at least the following steps:

[0031] - said sample is heated in an inert atmosphere, between a first temperature of between 50 and 300°C and a second temperature of between 650 and 1000°C, following a first sequence of temperatures, at least a quantity of NH3, a quantity of NO, a quantity of NO2, a quantity of N2O and a quantity of N2 released during said heating in an inert atmosphere are continuously measured and an NH3 content, an N2O content, an N2 content, a first intermediate NO content and a first intermediate NO2 content are deduced therefrom;

[0032] - at least a portion of the effluents from said heating in an inert atmosphere of said sample are continuously oxidized by means of heating in an oxidizing atmosphere at a third temperature at least equal to 900°C, at least a quantity of NO and a quantity of NO2 released during said continuous oxidation of said portion of said effluents from said heating in an inert atmosphere are continuously measured, and a second intermediate NO content and a second intermediate NO2 content are deduced therefrom;

[0033] - a residue of said sample resulting from said heating in an inert atmosphere is heated in an oxidizing atmosphere between a fourth temperature of between 50 and 300°C and a fifth temperature greater than or equal to 850°C, following a second sequence of temperatures, at least one quantity of NO and one quantity of NO2 released during said heating in an oxidizing atmosphere of said residue are continuously measured and a third intermediate NO content and a third intermediate NO2 content are deduced therefrom; and in that at least one total nitrogen content present in said sample is determined from the sum of said NH3, N2O and N2 contents, said first, second and third intermediate NO contents and said first, second and third intermediate NO2 contents.According to an implementation of the invention, said first temperature sequence may comprise a first isothermal stage, of a first predetermined duration, at said first temperature and a second isothermal stage, of a second predetermined duration, at said second temperature, said first and second isothermal stages being connected to each other by a first thermal gradient.

[0034] According to an implementation of the invention, said second temperature sequence may comprise a third isothermal stage, of a third predetermined duration, at said fourth temperature and a fourth isothermal stage, of a fourth predetermined duration, at said fifth temperature, said third and fourth isothermal stages being connected to each other by a second thermal gradient.

[0035] According to one implementation of the invention, said first and / or second and / or third and / or fourth predetermined durations may be between 1 and 10 minutes, and said first and / or second thermal gradients may be between 15°C / min and 40°C / min.

[0036] According to one implementation of the invention, said method can be implemented by means of the device according to any one of the variants described above.

[0037] Other characteristics and advantages of the device and method according to the invention will appear on reading the following description of non-limiting examples of embodiments, with reference to the figures appended and described below.

[0038] List of figures

[0039] Figure 1 illustrates an example of the implementation of the first temperature sequence, implemented for the first step of the method according to the invention.

[0040] Figure 2 illustrates an example of the second temperature sequence, implemented for the third step of the method according to the invention.

[0041] Figure 3 illustrates an example of implementation of the device according to the invention.

[0042] Figure 4 illustrates an alternative implementation of the device according to the invention.

[0043] Figure 5 shows the evolution of the sum of NO and NO2 released as a function of temperature during the application of the first step of the method according to the invention, in the case of a first type of sample.

[0044] Figure 6 shows the evolution of the sum of NO and NO2 released as a function of time during the application of the first step of the method according to the invention as well as the sequence of temperatures used for this step, in the case of a second type of sample.

[0045] Description of embodiments The invention relates to a device and a method for quantifying a total nitrogen content present in a sample of a porous medium and / or derived from biomass.

[0046] Total nitrogen means the content of both organic nitrogen and inorganic nitrogen (or in other words, mineral nitrogen) contained in the sample considered.

[0047] A sample of a porous medium is a sample of any porous material, whether consolidated or unconsolidated. This may include, but is not limited to, a sample of soil, recent marine sediments, fertilizer, or sedimentary rock. It may also include (dried) sludge from a wastewater treatment plant, sediment from dredging a river or port. It may also include wet soils (marshes, mangroves).

[0048] Biomass is any mass of living matter (animal, plant, terrestrial, aquatic) existing in equilibrium on a given surface area of ​​the Earth. This may include, but is not limited to, plants, biowaste, or residual organic residues (which include all waste and organic by-products resulting from human and agricultural activities).

[0049] The sample of porous medium or biomass, previously sieved (particles less than or equal to 2 mm), dried and ground homogeneously (particles less than or equal to 0.25 mm) can have a mass of between 1 and 100 mg. Indeed, the method according to the invention, in particular if it is implemented by means of the device according to the invention, does not require samples of large mass due to the sensitivity of the detectors and the optimization of the circuits used. Furthermore, it is not necessary to pretreat the sample (in particular, no decarbonation, purification or extraction), in particular with solvents.

[0050] In general, the method according to the invention is based on the measurement over time of all the nitrogen compounds contained in effluents released during heating of the sample under an inert atmosphere, including the nitrogen compounds contained in an oxidation of the effluents released during heating of the sample under an inert atmosphere, and on the measurement of all the nitrogen compounds contained in effluents released during heating under an oxidizing atmosphere of a residue of the sample resulting from heating under an inert atmosphere. In general, the nitrogen species produced by thermal cracking of all the nitrogen chemical families contained in a sample of a porous medium and / or derived from biomass are: NH3, NO, NO2, N2O and N2.

[0051] More specifically, the method according to the invention comprises at least the following steps:

[0052] 1. Heating the sample in an inert atmosphere

[0053] 2. Oxidation of part of the effluents from heating in an inert atmosphere 3. Heating in an oxidizing atmosphere of the residue from heating in an inert atmosphere

[0054] 4. Determination of total nitrogen content of the sample

[0055] The device according to the invention comprises means for heating the sample under an inert atmosphere, means for oxidizing the effluents released during heating the sample under an inert atmosphere, means for heating a residue of the sample under an oxidizing atmosphere, as well as means for continuously measuring the quantities of NH3, NO, NO2, N2O and N2 released during heating the sample under an inert atmosphere, means for continuously measuring the quantities of NO and NO2 released during the oxidation of the effluents released during heating the sample under an inert atmosphere, and means for continuously measuring the quantities of NO and NO2 released during heating a residue of the sample under an oxidizing atmosphere. The method according to the invention can advantageously be implemented using the device according to the invention.

[0056] The steps of the method according to the invention are detailed below.

[0057] 1. Heating the sample in an inert atmosphere

[0058] During this step, said sample is heated in an inert atmosphere, between a first temperature (hereinafter referred to as T1) of between 50°C and 300°C and a second temperature (hereinafter referred to as T2) of between 650 and 1000°C, following a first sequence of temperatures, a quantity of NH3, a quantity of NO, a quantity of NO2, a quantity of N2O and a quantity of N2 released during said heating in an inert atmosphere are continuously measured, and an NH3 content, an N2O content, an N2 content, a first intermediate NO content and a first intermediate NO2 content are deduced therefrom.

[0059] In other words, during this step, the sample is pyrolyzed in a reducing medium, according to a sequence of temperatures whose lower and upper limits correspond to the temperatures T1 and T2 according to the invention. The applicant has in fact been able to observe, by means of tests carried out on numerous types of samples of porous media and derived from biomass, that pyrolysis under an inert atmosphere carried out between these two temperatures T1 and T2 makes it possible to release, in the form of effluents, all of the nitrogen compounds that can be pyrolyzed in a reducing medium contained in a sample. Depending on the type of samples considered, the quantities of nitrogen and the thermal stability of the compounds that contain it can be very variable, from thermally unstable (volatile compounds) to very thermally stable.These temperature ranges make it possible to better discriminate between the different thermal stability groups of the nitrogen compounds generated; the signals have better resolution. In addition, these tests have shown that the following nitrogen compounds can be released during this step: NH3, NO, NO2, N2O and N2. According to the invention, the following quantities of nitrogen compounds are continuously measured (i.e., measured over the heating time in an inert atmosphere): a quantity of NH3, a quantity of NO, a quantity of NO2, a quantity of N2O and a quantity of N2. From the quantities of NH3, NO, NO2, N2O and N2 measured, an NH3 content, an N2O content, an N2 content, a first intermediate NO content and a first intermediate NO2 content are deduced. We speak here of “intermediate contents” for the nitrogen compounds NO and NO2 because additional contents are determined at the end of steps 2 and 3 of the process according to the invention.In other words, the total content of NO and NO2 is not determined during this single step, unlike the nitrogen compounds NH3, N2O and N2. It is clear that one or more of the quantities of nitrogen compounds measured may be zero, in particular depending on the nature of the sample considered. Indeed, certain samples of porous media or from biomass may not release NH3 and / or NO and / or NO2, and / or N2O and / or N2 during the first step of the process according to the invention.

[0060] According to one implementation of the invention, the temperature sequence used for implementing this step may comprise a first isothermal stage at temperature T1 (i.e. temperature T1 is maintained for a first predetermined duration) and a second isothermal stage at a temperature T2 (i.e. temperature T2 is maintained for a second predetermined duration), the two isothermal stages being linked together by a thermal gradient (i.e. the first isothermal stage at temperature T1 is followed by a linear increase in temperature until the second isothermal stage at temperature T2 is reached).

[0061] Figure 1 illustrates, in a schematic and non-limiting manner, an example of embodiment of the first temperature sequence, implemented for the first step of the method according to the invention. More precisely, this example of the first temperature sequence comprises a first isothermal stage A at temperature T1, a second isothermal stage C at temperature T2, the two isothermal stages A, C being connected to each other by a thermal gradient B.

[0062] According to an implementation of the invention, the first predetermined duration of the hold at temperature T1 and / or the second predetermined duration of the hold at temperature T2 may be between 1 and 10 min. Such durations make it possible to release all the pyrolyzable nitrogen compounds present in a sample by distinguishing the lightest and thermovaporizable nitrogen compounds (of low molecular weights) during temperature T1 with those obtained by pyrolysis cracking which are increasingly heavy (of medium to heavy molecular weights) with the increase in temperature following the thermal gradient and this until the end of temperature T2. Advantageously, the thermal gradient may be between 15°C / min and 40°C / min.Such a gradient in fact makes it possible to release all of the pyrolyzable nitrogen compounds contained in the sample, and this, in a time of between 15 and 75 minutes depending on the implementation, which is a short duration compared to the methods according to the prior art, in particular compared to chemical methods.

[0063] According to another implementation of the invention, the temperature sequence used for this step may comprise a first temperature stage at temperature T1 (i.e. temperature T1 is maintained for a first predetermined duration, for example lasting between 1 and 10 minutes), a second isothermal stage at a temperature T2 (i.e. temperature T2 is maintained for a second predetermined duration, for example lasting between 1 and 10 minutes), as well as a plurality of intermediate isothermal stages (for example 4 intermediate isothermal stages, for example lasting between 1 and 10 minutes) between the first and second stages, the stages being connected to each other by thermal gradients (for example between 15°C / min and 40°C / min).Such a sequence allows for even more precise separation of the lightest and most thermovaporizable nitrogen compounds from the thresholded nitrogen compounds between different temperature ranges related to different nitrogen chemical classes from the start of thermal cracking to the end of thermal cracking of the last temperature step. The same amount of total nitrogen is obtained with this multi-step sequence while obtaining a better resolution of the different signals providing better information on the different thermal classes of the nitrogen species present in the sample.

[0064] According to one implementation of the invention, the temperature sequence used for this step may comprise a succession of at least six isothermal stages of a predetermined duration comprising a first isothermal stage at temperature T1, here between 80 and 200°C, a first intermediate isothermal stage at a temperature between 340 and 380°C, a second intermediate isothermal stage at a temperature between 400 and 440°C, a third isothermal stage at a temperature between 450 and 490°C, a fourth intermediate isothermal stage at a temperature between 500 and 540°C, and a second isothermal stage at temperature T2, equal to 650°C, the isothermal stages, intermediate or non-intermediate, being connected to each other by a thermal gradient.Advantageously, for this embodiment, it is also possible to continuously measure a quantity of hydrocarbon compounds, a quantity of CO and a quantity of CO2 released during this heating sequence.

[0065] According to one implementation of the invention, the inert gas used for this step may be helium He or argon Ar. It is clear that nitrogen N2 is advantageously avoided for the implementation of this step, so as not to distort the measurements carried out. In other words, during this step, said sample is heated in an inert atmosphere, using an inert gas, excluding nitrogen. According to the invention, a quantity of NH3, a quantity of NO, a quantity of NO2, a quantity of N2O and a quantity of N2 released during the heating time in an inert atmosphere are measured. For each nitrogen compound, a curve can then be established representing the evolution of the quantity of this nitrogen compound as a function of time, relative to the weight of the sample considered.Generally speaking, the applicant observed that the curves representative of the evolution over time of the quantity of each of the nitrogen compounds released during steps 1, 2 or 3 present one to several peaks.

[0066] According to an implementation of the invention, for each nitrogen compound, from the surface (or the area) under the curve representing the evolution over time of the quantity of this nitrogen compound released during a given step (step 1, 2 or 3), it is possible to determine a content of this nitrogen compound released during the step considered. This determination can in particular be carried out using the means for determining a total nitrogen content according to the invention, such as computer means. Subsequently, Nx is denoted by any nitrogen compound chosen from the following list: NH3, NO, NO2, N2O and N2.

[0067] According to an implementation of the invention, whatever the step considered (step 1, 2 or 3), the N content can be determined NX into a nitrogen compound Nx according to a formula of the type: where %wt N NX is the nitrogen content (in mass percentage) of the nitrogen compound Nx, M N is the molar mass of nitrogen (M N =14 g-mol -1 ), M Nx is the molar mass of the nitrogen compound Nx considered (for example M N0 = 30 g-mol -1 ), Surf ace _Nx ecb is the area under the curve representing the evolution over time of the quantity of nitrogen compound Nx released during the step considered (1, 2 or 3), and F calib _Nx is a calibration factor for the nitrogen compound Nx established on a reference sample.

[0068] According to an implementation of the invention, the calibration factor F can be determined calib_Nx associated with the nitrogen compound Nx from at least one reference sample of which the content(s) of nitrogen compound(s) Nx are known, sample which is subjected to the step considered (i.e. step 1, 2 or 3). Then the calibration coefficient is determined from the area under the curve representing the change over time in the quantity of the nitrogen compound(s) Nx released by this reference sample during the step considered according to a formula of the type: where m_ref_Nx is the mass of the reference sample for the nitrogen compound Nx, Surface_Nx ref is the area under the curve representing the change over time in the quantity of the nitrogen compound Nx released by the reference sample during the step considered. According to one implementation, the reference sample may be a sample of a porous medium or biomass of which the nitrogen compound content(s) are known, obtained for example by means of elemental analysis and a modified Kjeldahl method. Alternatively, in the absence of a solid sample, the reference sample may consist solely of one or more nitrogen compounds Nx, for example in the form of a mixture or not of pure gases.

[0069] Thus, at the end of this step, we obtain an NH3 content, an N2O content, an N2 content, a first intermediate NO content and a first intermediate NO2 content.

[0070] 2. Oxidation of part of the effluents from heating in an inert atmosphere

[0071] During this step, it is a matter of continuously oxidizing at least a portion of the effluents (fluids) resulting from the heating in an inert atmosphere of the sample considered, by means of heating in an oxidizing atmosphere at a temperature at least equal to 900°C (which is subsequently noted T3), of continuously measuring a quantity of NO and a quantity of NO2 released during this continuous oxidation of the portion of the effluents resulting from said heating in an inert atmosphere, and of deducing therefrom a second intermediate content of NO and a second intermediate content of NO2. According to an implementation of the invention, the oxidation may be a catalytic oxidation.

[0072] In other words, during this step, at least part of the effluents resulting from pyrolysis in an inert atmosphere are subjected to oxidation. The objective of this step is to quantify the nitrogen compounds contained in the heaviest effluents generated during the pyrolysis phase in a reducing medium, by means of high-temperature oxidation (T3 greater than or equal to 900°C). The applicant has observed, by means of tests carried out on numerous different types of samples, that only the nitrogen compounds NO and NO2 can be released during this step. Thus, according to the invention, a quantity of NO and a quantity of NO2 released during this oxidation of the effluents resulting from pyrolysis are continuously measured. For each nitrogen compound released during this step, a curve can then be established representing the evolution of the quantity of the nitrogen compound considered, relative to the weight of the sample considered, as a function of time.Finally, from the quantities of NO and NO2 measured during this step, a second intermediate NO content and a second intermediate NO2 content are deduced. This determination can in particular be carried out using the means for determining a total nitrogen content according to the invention, such as computer means. We speak here of “intermediate contents” because additional contents are determined at the end of steps 1 and 3 of the method according to the invention. It is clear that the quantity of NO and / or the quantity of NO2 measured during this step may be zero, depending on the nature of the sample considered. Indeed, certain samples of porous media or from biomass may not release NO and / or NO2 during the second step of the method according to the invention.

[0073] According to one implementation of the invention, for each of the nitrogen compounds NO and NO2 released during step 2, from the area under the curve representing the change over time in the quantity of the nitrogen compound released during step 2, the intermediate content of this nitrogen compound released during this step can be determined by means of the general formula of equation (1) described in step 1.

[0074] According to one implementation of the invention, this step can be carried out by means of an oxidation furnace heated to a minimum of 900°C, and swept by a gas mixture comprising between 30 and 100% of O2 and up to 70% of an inert gas (for example He or Ar) at a flow rate for example of between 50 and 400 ml / min. According to one implementation of the invention, this step can be carried out by means of a catalytic oxidation furnace.

[0075] According to one implementation of the invention, the heating in an oxidizing atmosphere of at least part of the effluents resulting from the heating in an inert atmosphere of the sample considered can be carried out by means of a heating sequence having a single isothermal stage at the third temperature T3 worth at least 900°C (temperature T3), of a duration at least equal to the duration of step 1.

[0076] Thus, at the end of this step, we obtain a second intermediate content of NO and a second intermediate content of NO2.

[0077] 3. Heating in an oxidizing atmosphere of the residue resulting from heating in an inert atmosphere

[0078] During this step, a residue (solid) of the sample resulting from heating in an inert atmosphere is heated in an oxidizing atmosphere between a fourth temperature (hereinafter referred to as T4) of between 50°C and 300°C and a fifth temperature (hereinafter referred to as T5) greater than or equal to 850°C, following a second sequence of temperatures, then a quantity of NO and a quantity of NO2 released during said heating in an oxidizing atmosphere of said residue are continuously measured, and a third intermediate NO content and a third intermediate NO2 content are deduced therefrom.

[0079] Thus, during this step, the residue (solid) from step 1 is subjected to oxidation according to a sequence of temperatures whose lower and upper limits correspond to temperatures T4 and T5 according to the invention. The purpose of this step is to release, in the form of oxidized gases, all of the non-pyrolyzable nitrogen compounds (under the conditions of step 1) contained in the sample. The applicant has observed, by means of tests carried out on numerous different types of samples, that only the following nitrogen compounds can be released during heating of the pyrolysis residue in an oxidizing atmosphere: NO and NO2. According to the invention, the quantities of NO and NO2 released are then measured continuously (i.e., the residue is heated in an oxidizing atmosphere) during the time of heating.Then, from the quantities of NO and NO2 measured during this step, a third intermediate NO content and a third intermediate NO2 content are deduced. We speak here of "intermediate contents" because additional contents are determined at the end of steps 1 and 2 of the method according to the invention as described above. It is clear that the quantity of NO and / or the quantity of NO2 measured during this step may be zero, depending on the nature of the sample considered and / or the characteristics of the temperature sequence of step 1. Indeed, certain samples of porous media or derived from biomass may not release NO and / or NO2 during the third step of the method according to the invention. Furthermore, the quantity of NO and / or the quantity of NO2 measured may also be zero when the temperature T2 of the first step of the method according to the invention is very high (for example 1000°C).Indeed, in this case, all the pyrolyzable nitrogen compounds may already have been released during the first step of the process according to the invention.

[0080] According to one implementation of the invention, the temperature sequence used for this step may comprise a first isothermal stage at temperature T4 (i.e., temperature T4 is maintained for a fourth predetermined duration) and a second isothermal stage at a temperature T5 (i.e., temperature T5 is maintained for a fifth predetermined duration), the two isothermal stages being connected to each other by at least one thermal gradient (i.e., the isothermal stage at temperature T4 is followed by a linear increase in temperature until the isothermal stage at temperature T5 is reached). According to one implementation of the invention, the fourth predetermined duration of the stage at temperature T4 and / or the fifth predetermined duration of the stage at temperature T5 may be between 1 and 10 min.Such durations allow for often incomplete combustion (NO and NO2) of the organic nitrogen compounds still present in the pyrolysis residue depending on their combustion kinetics. Advantageously, the thermal gradient can be between 15°C / min and 40°C / min. Such a gradient in fact allows for the release of all the non-pyrolyzable nitrogen compounds (under the conditions of step 1) contained in the sample residue, and this, in a limited time (between 20 and 30 minutes depending on the conditions used, which is a short time compared to the methods according to the prior art). This rapid increase in temperature makes it possible to accelerate the combustion kinetics of very refractory effluents.

[0081] Figure 2 illustrates, in a schematic and non-limiting manner, an example of the second temperature sequence, implemented for the third step of the method according to the invention. More precisely, this example of the second temperature sequence comprises a first isothermal stage D at temperature T4, a second isothermal stage F at temperature T5, the two isothermal stages D, F being connected to each other by a thermal gradient E.

[0082] According to the invention, a quantity of NO and a quantity of NO2 released during the heating time of the sample residue in an oxidizing atmosphere are measured. For each nitrogen compound released during this step, a curve can then be established representing the evolution of the quantity of this nitrogen compound as a function of time, relative to the weight of the sample considered.

[0083] According to an implementation of the invention, for each nitrogen compound, from the surface of the peak (or the area under the curve) of the curve representative of the quantity of a nitrogen compound released during step 1, it is possible to determine the content of a nitrogen compound Nx released during this step by means of the general formula of equation (1) described in step 1. This determination can in particular be carried out by means of the means for determining a total nitrogen content according to the invention, such as computer means.

[0084] According to one implementation of the invention, the temperature T4 may be between 150 and 300°C and the temperature T5 may be between 850 and 1200°C. Advantageously, it is also possible to continuously measure a quantity of CO and a quantity of CO2 released during this heating sequence.

[0085] Thus, at the end of this step, we obtain a third intermediate content of NO and a third intermediate content of NO2.

[0086] 4. Determination of the total nitrogen content of the sample

[0087] During this step, it is a question of determining at least one total nitrogen content present in said sample from the NH3, N2O and N2 contents determined in step 1, the first, second and third NO contents determined respectively in steps 1, 2 and 3, and the first, second and third NO2 contents determined respectively in steps 1, 2 and 3.

[0088] In other words, during this step, the total nitrogen content is determined by the sum of all the contents determined during steps 1, 2 and 3. This is in fact the total nitrogen content because all the nitrogen compounds that have been identified as released during steps 1, 2 and 3 are taken into account after several tests carried out on numerous types of samples of porous media and from biomass. As a reminder, steps 1 and 2 measure the pyrolyzable nitrogen content while step 3 measures the non-pyrolyzable nitrogen under the conditions of step 1. This determination can in particular be carried out using the means for determining a total nitrogen content according to the invention, such as computer means.

[0089] According to an advantageous implementation of the method according to the invention, and if a quantity of hydrocarbon compounds, a quantity of CO and a quantity of CO2 released during the first step implemented as described above have also been continuously measured, and a quantity of CO and a quantity of CO2 released during the third step implemented as described above, it is also possible to characterize and quantify the carbon present in the sample considered, for example by applying the method described in patent application WO2022 / 200091.

[0090] The invention further relates to a device for quantifying a total nitrogen content present in a sample of a porous medium and / or derived from biomass comprising: o means for heating said sample in an inert atmosphere; o means for heating at least a portion of effluents from said means for heating said sample in an inert atmosphere in an oxidizing atmosphere; o means for heating in an oxidizing atmosphere a residue from said means for heating said sample in an inert atmosphere; o means capable of continuous measurement of:

[0091] - a quantity of NH3, a quantity of NO, a quantity of NO2, a quantity of N2O and a quantity of N2 from the means for heating the sample in an inert atmosphere;

[0092] - a quantity of NO and a quantity of NO2 from the means of oxidation of effluents from the means for heating the sample in an inert atmosphere;

[0093] - a quantity of NO and a quantity of NO2 from the means for heating in an oxidizing atmosphere a residue from the means for heating the sample in an inert atmosphere.

[0094] According to a first design of the device according to the invention, the means for heating a sample of the medium in an inert atmosphere may comprise a pyrolysis furnace, the means for heating a residue from the means for heating the sample in an inert atmosphere in an oxidizing atmosphere may comprise a first oxidation furnace and the means for heating at least part of the effluents from the means for heating the sample in an inert atmosphere in an oxidizing atmosphere may comprise a second oxidation furnace, which may be catalytic. Thus, in this design, the device comprises three separate furnaces. The pyrolysis furnace may be a furnace swept by a flow of inert gas, such as helium He or argon Ar, at a flow rate of between 50 and 300 ml / min. It is clear that nitrogen N2 may be advantageously avoided, so as not to distort the measurements taken.The first oxidation furnace may be swept by a gas mixture comprising between 20 and 90% of C>2 and up to 80% of an inert gas (for example He or Ar, the inert gas preferably not corresponding to N2), at a flow rate for example between 50 and 200 ml / min. The second oxidation furnace may be swept by pure oxygen to allow heating in a super-oxidizing atmosphere at a temperature at least equal to 900°C with a flow rate between 50 and 400 ml / min. In this design, the device may comprise means for circulating the effluents released by the pyrolysis furnace towards the measuring means capable of continuously measuring at least one quantity of NH3, NO, NO2, N2O and N2 in the form of conduits in which an inert carrier gas circulates, such as helium He or argon Ar, the inert gas preferably not corresponding to N2.In this design, the device may further comprise means for circulating the effluents from the first oxidation furnace to the measuring means capable of continuously measuring at least one quantity of NO and NO2 in the form of pipes in which circulates a gas mixture comprising between 20 and 90% of O2, preferably 20% of O2, and between 10 and 80% of an inert gas, preferably 80% of inert gas (for example He or Ar, the inert gas preferably not corresponding to N2). In this design, the device may further comprise means for circulating the effluents from the second oxidation furnace to the measuring means capable of continuously measuring at least one quantity of NO and NO2 in the form of pipes in which circulates a pure gas O2.

[0095] According to one implementation of the invention, at least one of the furnaces of the device according to the invention can be made of stainless steel, alumina, porcelain. Such materials are capable of withstanding the high temperatures used in the method according to the invention.

[0096] According to one implementation of the invention, the device may further comprise a nacelle intended to receive the sample of porous medium and / or derived from biomass. The nacelle may be, for example, made of stainless steel, alumina or porcelain, and may be introduced into the pyrolysis furnace and / or the oxidation furnace by means, for example, of a piston.

[0097] In an alternative design of the device according to the invention, the means for heating a sample of a porous medium and / or derived from biomass in an inert atmosphere and the means for heating a residue from the means for heating the sample in an inert atmosphere in an oxidizing atmosphere may comprise a single pyrolysis furnace, which may operate either in an inert atmosphere or in an oxidizing atmosphere, and the means for heating at least part of the effluents from the means for heating the sample in an inert atmosphere in an oxidizing atmosphere in an oxidizing atmosphere may comprise an oxidation furnace (separate from the pyrolysis furnace which may operate either in an inert atmosphere or in an oxidizing atmosphere). In this configuration, the oxidation furnace, which may be catalytic, separate from the pyrolysis furnace, allows the effluents from the heating in an inert atmosphere to be oxidized continuously, i.e. as they are released by the heating in an inert atmosphere.

[0098] According to a preferred implementation of the invention, the measuring means capable of continuously measuring a quantity of NO (respectively a quantity of NO2) N2 from the means for heating the sample in an inert atmosphere, the measuring means capable of continuously measuring a quantity of NO (respectively a quantity of NO2) from the means for oxidizing effluents from the means for heating the sample in an inert atmosphere, and the measuring means capable of continuously measuring a quantity of NO (respectively a quantity of NO2) from the means for heating a residue from the means for heating the sample in an inert atmosphere in an oxidizing atmosphere may correspond to a single detector, capable of at least detecting and measuring NO (respectively NO2). This makes it possible not to multiply the number of detectors since the NO and NO2 detectors can then be used for implementing the three steps of the method according to the invention.

[0099] According to a preferred implementation of the invention which can be combined with the previous one, the measuring means capable of continuously measuring at least: a quantity of NH3, a quantity of NO, a quantity of NO2, a quantity of N2O and a quantity of N2 from the means for heating the sample in an inert atmosphere; a quantity of NO and a quantity of NO2 from the means for oxidizing effluents from the means for heating the sample in an inert atmosphere; a quantity of NO and a quantity of NO2 from the means for heating a residue from the means for heating the sample in an inert atmosphere in an oxidizing atmosphere; correspond to a single detector, capable of continuously measuring the following nitrogen compounds: NH3, NO, NO2, N2O and N2.

[0100] Figure 3 illustrates in a schematic and non-limiting manner, an exemplary implementation of the device according to the invention, comprising three separate furnaces and a single detector capable of measuring a quantity of each of the different nitrogen compounds released by a sample. More specifically, the device according to this exemplary embodiment of the device according to the invention comprises a pyrolysis furnace 1 for heating a sample in an inert atmosphere, a first oxidation furnace 2 for heating a residue of the sample resulting from the heating in an inert atmosphere in an oxidizing atmosphere (the means of transfer from the pyrolysis furnace to the oxidation furnace are not shown), and a second oxidation furnace 3 for heating the effluents resulting from the heating of the sample in an inert atmosphere in an oxidizing atmosphere.In this design, a pipe 4 connects the pyrolysis furnace 1 to the second oxidation furnace 3, to allow the transfer of a portion of the effluents from heating in an inert atmosphere to the high-temperature oxidation furnace. The pyrolysis furnace 1, the first oxidation furnace 2 and the second oxidation furnace 3 are connected by pipes 5 to a detector 10 capable of measuring a quantity of each of the different nitrogen compounds that can be released by a sample.

[0101] According to one implementation, the measuring means capable of continuously measuring at least one quantity of NH3 originating from the means for heating the sample in an inert atmosphere, as well as the measuring means capable of continuously measuring a quantity of NO and a quantity of NO2 originating from the means for heating the sample in an inert atmosphere and / or originating from the means for heating the sample in an inert atmosphere and / or originating from the means for heating a residue originating from the means for heating the sample in an inert atmosphere in an oxidizing atmosphere, can be produced by means of an optical sensor operating in the ultraviolet (UV) range.According to one implementation of the invention, the optical sensor may comprise a source of UV radiation for illuminating a measurement zone (intended to receive effluents from any of the steps of the method according to the invention), and a spectrometer for measuring the intensity as a function of the wavelength of the UV radiation having passed through the measurement zone. Those skilled in the art have perfect knowledge of methods for determining the quantity of different chemical species from measurements carried out with such an optical sensor. For example, reference may be made to the method described in patent application WO 2019 / 020326 A1, which relates to a method for measuring the concentration of different chemical species contained in exhaust gases.According to an implementation of the invention, from the measurement of the intensity as a function of the wavelength of the UV radiation having passed through the measurement zone and an intensity as a function of the reference wavelength, it is possible to determine an absorbance as a function of the wavelength of the effluents contained in the measurement zone. Then, it is possible to determine the concentration of each nitrogen compound present in the effluents considered, from the absorbance of the effluents thus calculated, and also from predetermined absorbance characteristics and information relating to the temperature (known in our method since the temperature of the furnaces is known at all times) and the pressure (known in our method and equal to atmospheric pressure) of each of the chemical species that it is desired to quantify.

[0102] According to an implementation of the invention that can be combined with the previous one, the measuring means capable of continuously measuring a quantity of N2 can correspond to a micro-chromatograph (or micro GC). A micro-chromatograph consists of an injector, a molecular sieve and a micro-TCD detector (thermal conductivity detector). In this implementation, it is possible, by means of an internal sampling pump, to take a volume of gas from the flow coming from the line of the device according to the invention to send it to the micro-GC.

[0103] According to an implementation of the invention which can be combined with the previous one, the measuring means capable of continuous measurement of a quantity of NH3 can correspond to an electrochemical detector. The principle of an electrochemical detector is based on an oxidation-reduction reaction.

[0104] According to an implementation of the invention that can be combined with the previous one, the measuring means capable of continuously measuring a quantity of NO can correspond to an infrared (IR) detector or a chemiluminescence analyzer (CLD). The principle of CLD is based on the production of light following a chemical reaction, such as for example a redox reaction between a reduced species and an oxidant, for example such as oxygen. Here, the chemiluminescence comes from the photons (light) emitted during the reaction between nitrogen monoxide (NO) and ozone (03) which are detected by a photomultiplier tube. Generally, an IR detector comprises a spectroscopic sensor reacting to infrared radiation. Advantageously, the infrared detector can use a narrowband spectral region corresponding to that of NO gas.

[0105] According to an implementation of the invention which can be combined with the previous one, the measuring means capable of continuously measuring a quantity of NO2 can correspond to an infrared detector. Advantageously, the infrared detector can use a narrow band spectral region corresponding to that of the NO2 gas.

[0106] According to an implementation of the invention which can be combined with the previous one, the measuring means capable of continuous measurement of a quantity of N2O can correspond to an infrared detector. Advantageously, the infrared detector can use a narrow band spectral region corresponding to that of the N2O gas.

[0107] According to an implementation in which the device comprises at least two distinct nitrogen compound detectors, these detectors can be arranged in series, that is to say that the gas flow passes through the detectors one after the other, each being capable of detecting a specific nitrogen compound.

[0108] Advantageously, the device according to the invention may further comprise a flame ionization type detector (FID) for continuous measurement of a quantity of hydrocarbon compounds and / or an infrared type detector (IR) for continuous measurement of a quantity of CO and CO2. Figure 4 illustrates in a schematic and non-limiting manner, an alternative implementation of the device according to the invention, in all respects identical to the device of Figure 3 (thus the elements in common will not be described again) except for the fact that it comprises a detector specific to each of the different nitrogen compounds released by a sample, instead of a single detector. More precisely, the device according to this alternative comprises five detectors 11, 12, 13, 14, 15 arranged in series, each of the detectors being able to specifically measure a quantity of one of the following nitrogen compounds: NH3, NO, NO2, N2O and N2.The order in which the detectors 11, 12, 13, 14, 15 are arranged has no impact. The pyrolysis furnace 1, the first oxidation furnace 2 and the second oxidation furnace 3 are connected by pipes 5 to the first specific detector 11 of the series of detectors 11, 12, 13, 14, 15, and the detectors 11, 12, 13, 14, 15 are connected two by two by pipes 6 which have the same technical characteristics as the pipes 5.

[0109] Thus, the device and the method according to the invention make it possible to quantify the total nitrogen present in a sample of a porous medium and / or derived from biomass in a single step, without prior treatment, and on small quantities (from a few mg to a maximum of a hundred mg). The dynamic nature (signal measured continuously) provides a second piece of information on the quality of the nitrogenous constituents present in a sample as a function of their thermal stability (continuous recording of the signal over time and temperature). These parameters make it possible to better identify the different mechanisms (N2 fixation, nitrification, denitrification) involved during the respiration and fermentation processes linked to the carbon cycle.Furthermore, the present invention, due to the detection of each nitrogen compound (by a single detector or several detectors), makes it possible to have additional information on the type of nitrogen compounds present in the sample (and not only concerning NO2 or N2 depending on the analysis method used), while associating it with its thermal stability.

[0110] Examples

[0111] The characteristics and advantages of the device and method according to the invention will appear more clearly on reading the application example below.

[0112] Samples containing varying amounts of nitrogen (0.2 to 35% by mass) were analyzed by the method according to the invention, using the device according to the invention. The results of the quantification of total nitrogen are comparable to the total nitrogen values ​​measured by a reference analysis such as elemental analysis according to the Dumas method.

[0113] The results of the implementation of the method according to the invention are presented more particularly below, using the device according to the invention, for a first example corresponding to a sample of a mineral fertilizer (KNO3) and for a second example corresponding to digested biowaste (digestate).

[0114] First example

[0115] The application of the method according to the invention for the first example reveals that only the nitrogen compound NO is released in the case of a nitrogen mineral of the KNO3 type. In other words, no quantities of N2, NO2, N2O and NH3 were measured during the method according to the invention. As an example, Figure 5 shows curves representing the evolution of the sum of NO and NO2 released (through the intensity I of the measured signal) as a function of the temperature T (the temperature being related to time via the temperature sequence) during the first step for KNO3 samples having different masses: 4.55 mg (curve KNO3-4.55 mg), 2.61 mg (curve KNO3-2.61 mg), and 1.42 mg (curve KNO3-1.42 mg).The first step of the method according to the invention was applied with a temperature sequence comprising a first isothermal plateau at 250°C maintained for 10 min, followed by a thermal gradient of 25°C / min, until reaching a temperature of 100°C, maintained for 3 minutes. It can be observed that the curves have similar geometries, but not the same intensity as a function of mass. Thus, the response of the NO signal is linear with the mass of the sample to be analyzed. Table 1 presents the quantities of total nitrogen NT (in mass %) obtained for the different masses of the sample, as well as the quantities of N2, NO2, N2O and NH3 (zero quantities), and a total nitrogen value determined by an independent elemental analysis NAE. It can be observed that the mass % of total nitrogen, determined by applying the method according to the invention, is similar to that determined by elemental analysis to within 20%.

[0116] [Table 1]

[0117] Second example The application of the method according to the invention to the second example shows that the following nitrogen compounds are released in the case of a digestate sample: NO, NO2, NH3 and N2. Figure 6 shows curves representing the evolution of the quantity (through the intensity

[0118] 1 of the measured signal) of cumulative NO and NO2 (because the measured NO2 signal was negligible; NO+NO2 curve), NH3 (NH3 curve) and N2 (N2 curve) released as a function of time t during the first step of the process according to the invention, as well as the temperature sequence used for this step (evolution of temperature T as a function of time t). We can observe that the different nitrogen compounds are not released at the same temperatures: in particular, NO and NO2 are released at the lowest temperatures while N2 is released at the highest temperatures. Part of the NO / NO2 signal also seems to be correlated with that of NH3, indicating that these two gases come from the cracking of the same chemical family. More than 90% of the NT content of the digestate comes from the N2 signal. The table

[0119] 2 shows the quantities (in mass %) of total nitrogen NT, N2, NO2, N2O and NH3 obtained by the method according to the invention, as well as the total nitrogen determined by an independent elemental analysis NAE. It can be observed that the quantification obtained by the method according to the invention is in good agreement with that of the elemental analysis.

[0120] [Table 2]

Claims

Claims 1. Device for quantifying a total nitrogen content present in a sample of a porous medium and / or derived from biomass, said device being characterized in that it comprises: o means for heating said sample in an inert atmosphere (1); o means for heating a residue from said means for heating said sample in an inert atmosphere (2); o means for oxidizing (3) effluents from the means for heating said sample in an inert atmosphere; o means capable of continuous measurement (10, 11, 12, 13, 14, 15) of: a quantity of NH3, a quantity of NO, a quantity of NO2, a quantity of N2O and a quantity of N2 from said means for heating said sample in an inert atmosphere (1); a quantity of NO and a quantity of NO2 from said oxidation means (3) of effluents from said means for heating said sample in an inert atmosphere (1);a quantity of NO and a quantity of NO2 from said means for heating in an oxidizing atmosphere (2) a residue from said means for heating in an inert atmosphere (1) said sample.; 2. Device according to claim 1, in which said means for heating said sample in an inert atmosphere (1) comprise a pyrolysis furnace in an inert atmosphere, and said means for heating said residue from said means for heating said sample in an inert atmosphere (2) comprise an oxidation furnace.

3. Device according to claim 1, in which said means for heating said sample in an inert atmosphere (1) and the means for heating said residue from said means for heating said sample in an inert atmosphere (2) in an oxidizing atmosphere comprise a single pyrolysis furnace, capable of operating in an inert atmosphere and in an oxidizing atmosphere.

4. Device according to one of the preceding claims, in which said means (3) for oxidizing said effluents from said means for heating said sample in an inert atmosphere comprise an oxidation furnace.

5. Device according to one of the preceding claims, in which said means capable of continuous measurement of said quantity of NH3 coming from said means for heating in inert atmosphere (1) said sample, as well as said means capable of continuous measurement of said quantity of NO and / or said quantity of NO2 from said means for heating in an inert atmosphere (1) said sample and / or from said means for oxidizing effluents from said means for heating in an inert atmosphere (1) said sample and / or from said means for heating in an oxidizing atmosphere (2) a residue from said means for heating in an inert atmosphere (1) said sample comprise an optical sensor operating in the ultraviolet range, said optical sensor comprising a source of UV radiation for illuminating a measurement zone and a spectrometer for measuring the intensity as a function of the wavelength of the UV radiation having passed through said measurement zone.

6. Method for quantifying a total nitrogen content present in a sample of a porous medium and / or derived from biomass, characterized in that said method comprises at least the following steps: - said sample is heated in an inert atmosphere, between a first temperature (T1) of between 50 and 300°C and a second temperature (T2) of between 650 and 1000°C, following a first sequence of temperatures, at least a quantity of NH3, a quantity of NO, a quantity of NO2, a quantity of N2O and a quantity of N2 released during said heating in an inert atmosphere are continuously measured and an NH3 content, an N2O content, an N2 content, a first intermediate NO content and a first intermediate NO2 content are deduced therefrom; - at least a portion of the effluents from said heating in an inert atmosphere of said sample are continuously oxidized by means of heating in an oxidizing atmosphere at a third temperature at least equal to 900°C, at least a quantity of NO and a quantity of NO2 released during said continuous oxidation of said portion of said effluents from said heating in an inert atmosphere are continuously measured, and a second intermediate NO content and a second intermediate NO2 content are deduced therefrom; - a residue of said sample resulting from said heating in an inert atmosphere is heated in an oxidizing atmosphere between a fourth temperature (T4) of between 50 and 300°C and a fifth temperature (T5) greater than or equal to 850°C, following a second sequence of temperatures, at least one quantity of NO and one quantity of NO2 released during said heating in an oxidizing atmosphere of said residue are continuously measured and a third intermediate NO content and a third intermediate NO2 content are deduced therefrom; and in that at least one total nitrogen content present in said sample is determined from the sum of said NH3, N2O, N2 contents, said first, second and third intermediate NO contents and said first, second and third intermediate NO2 contents.

7. Method according to claim 6, wherein said first temperature sequence comprises a first isothermal stage (A), of a first predetermined duration, at said first temperature (T1) and a second isothermal stage (C), of a second predetermined duration, at said second temperature (T2), said first and second isothermal stages being connected to each other by a first thermal gradient (B).

8. Method according to one of claims 6 to 7, in which said second temperature sequence comprises a third isothermal stage (D), of a third predetermined duration, at said fourth temperature (T4) and a fourth isothermal stage (F), of a fourth predetermined duration, at said fifth temperature (T5), said third and fourth isothermal stages being connected to each other by a second thermal gradient (E).

9. Method according to one of claims 6 to 8, in which said first and / or second and / or third and / or fourth predetermined durations are between 1 and 10 minutes, and said first and / or second thermal gradients are between 15°C / min and 40°C / min.

10. Method according to one of claims 6 to 9, wherein said method is implemented by means of the device according to any one of claims 1 to 5.

Images