FR3039898A1 - METHOD FOR QUANTIFICATION OF TOTAL SILICON FROM VOLATILE ORGANIC VOLATILE COMPOUNDS PRESENT IN A GAS - Google Patents

Abstract

A method for detecting and / or quantifying total silicon resulting from the volatile organic compounds present in a gas, in which: a) a sample of said gas is taken, b) said sample of said gas is brought into contact with at least one solvent possibly polar or apolar, able to extract at least a portion of said volatile organic compounds silicon in said solvent, c) the total amount of silicon from the volatile organic compounds silicon contained in at least one solvent used in step b), d the total amount of silicon resulting from the silicon volatile organic compounds present in said gas is calculated, said process being characterized in that between step b) and step c) at least a portion of the silicon-containing volatile organic compounds are converted in dissolved silica.

Description

Process for the quantification of total silicon from volatile organic silicon compounds present in a gas

TECHNICAL FIELD OF THE INVENTION The invention relates to the field of analytical chemistry and instrumentation, including sampling and analysis. It relates to a detection and / or quantification of the total silicon contained in the silicon volatile organic compounds, including the siloxanes, in a gas, by simple and non-segregative techniques.

STATE OF THE ART The industry of producers, users and caterers of gas and in particular of biogas expresses the need to be able to detect and / or quantify the total silicon contained in the gas. Silicon is found in natural gases or in biogas, especially in the form of volatile organic compounds of silicon, hereinafter referred to as COVSi. In the gases their origin is largely related to the presence of anthropogenic silicon compounds. For example in natural gas, the presence of such compounds is explained by the degradation of silicon compounds (eg polydimethylsiloxanes or PDMS) injected into the wells to increase the recovery rate of crude oil. In biogas, these compounds come from the degradation of silicon compounds widely used as additives in many commonly used products (cosmetics, paints, plastics, lubricants, etc.). Knowledge of the total silicon content in the gas can be used to control the gas treatment in order to optimize the elimination of COVSi. Indeed, it is desirable to minimize their content in gas utilization, treatment and recovery facilities, including energy recovery, because COVSi can form deposits or solid particles (especially silicates or silicates) when they are oxidized (burned). For example, in an energy recovery plant of a gas, the particles formed, very abrasive, are likely to damage certain elements of the facilities (catalyst, burner, turbines, engines in particular). To know the content of a gas in COVSi, one must first have a simple, fast and reliable method to quantify the silicon content; the availability of such a method will then make it possible to implement an optimization of the gas recovery process and / or measures for eliminating COVSi in said gas.

Several analytical techniques make it possible to identify, detect and quantify silicon compounds in a gas. The COVsi whose siloxanes present in a gas are mainly analyzed by gas chromatography coupled to mass spectrometry (GC / MS). The COVSi can also be analyzed and quantified by a technique using non-dispersive infrared radiation, as taught in the patent application WO2015 / 028 720.

These analytical techniques make it possible to individually detect and quantify known silicon compounds in a gas. The amounts of silicon compounds thus determined can be added so as to obtain an allegedly total content of silicon compounds contained in the gas. However, such a method only makes it possible to approach the total amount of silicon originating from the silicon compounds contained in the gas phase in the gas, since it requires the prior identification of known silicon compounds, necessarily in limited numbers, in view of the multitude various and varied silicon compounds contained in the gases. The gases can contain a multitude of silicon compounds, some of which are in the form of traces, such as siloxanes, silanes, silanols, silarenes, or derivatives thereof.

However, compared to the problem raised, the main information required, at least for regular monitoring of a method of use, treatment or recovery of gas, is the amount of deposits or silicon particles that will form when the gas is used, processed or valued. The techniques described above, based on a prior separation of the molecules of COVSi, are too sophisticated and provide too much information, useless to the gas manager. In addition, these methods are complex to implement, since they require the existence or the availability of standards for each of the silicon compounds detected. In fact, these methods make it possible to reach, if necessary, an allegedly total content of silicon compounds contained in the gas, which is necessarily underestimated.

Another method for approximating the total amount of silicon from the silicon compounds contained in the gas phase in a fuel gas has been described in patent FR 2 886 409. This document teaches that a large part of the silicon compounds contained in a gas is soluble in certain liquid solvents, so that a simple quantitative analysis of the silicon element contained in the liquid phase, by inductively coupled plasma atomic emission spectrometry, makes it possible to approach the total amount of silicon compounds originally contained in the gaseous phase . However, even if it does not require a separation of the different COVSi, the quantitative analysis of the silicon element by atomic emission spectrometry is a complex method to implement, time-consuming and expensive, which can not be used as a method of analysis. routine online analysis. It requires the return of liquid samples in a specialized laboratory.

In view of the foregoing, an object of the present invention is to overcome, at least partially, the disadvantages of the quantitative determination techniques in volatile organic compounds silicon mentioned above. Thus, the object of the present invention is to provide a method for the quantification of total silicon, which is simple, inexpensive and easy to implement, in particular on a reliable industrial site, which makes it possible to obtain a rapid response. This process must in particular allow gas producers, users or reprocessors to easily measure the amount of volatile organic compounds contained in the gas in the course of production, use or treatment, and this preferably at the production site and with a time of pretty short answer.

The present invention also aims to provide a total silicon quantification device, simple, compact, easy to implement, reliable, can be transportable or used to provide a result directly on the site of production, use, reprocessing or gas distribution.

figures

Figures 1 to 4 illustrate various aspects of embodiments of the invention, without limiting its scope.

Figure 1 schematically illustrates the flow of the process, as explained in great detail in the description.

Figure 2 schematically illustrates a device according to the invention, as explained in great detail in the description.

Figure 3 shows the absorbance as a function of the wavelength of a solution of a so-called "molybdenum blue" complex used for the determination of silicon, for two different samples.

Figure 4 shows the calibration curve of this assay, namely the variation of the absorbance as a function of the silicon concentration.

Object of the invention

The present invention relates to a process for the detection and / or quantification of total silicon resulting from volatile organic compounds present in a gas, such as a biogas of discharge or purification station, a biomethane, a synthesis gas, a process gas or a natural gas, so as to obtain a global quantitative indicator of said volatile organic compounds silicified in said gas. It also relates to a total silicon quantization device and its use for determining or estimating the total amount of silicon contained within said gas. It also relates to an assembly comprising a total silicon quantization device according to the invention, and the reagents necessary for the use of the total silicon quantization device.

A first object of the present invention is a method of detecting and / or quantifying the total silicon resulting from the volatile organic compounds present in a gas, in which: a) a sample of said gas is taken, b) said sample of said gas in contact with at least one possibly polar or apolar solvent, capable of extracting at least a part of said volatile organic compounds silicified in said solvent, c) determining the total amount of silicon derived from the volatile organic compounds containing silicon contained in at least one solvent used in step b), d) calculating the total amount of silicon resulting from the volatile organic compounds present in said gas, said process being characterized in that between step b) and step c) is transformed at least a part of the silicon volatile organic compounds dissolved silica.

According to the invention, a part of the silicon volatile organic compounds are siloxanes.

Advantageously, at least a portion of the silicon volatile organic compounds is converted into dissolved silica by an oxidation process.

In a particular embodiment of the process according to the invention, at least a part of the volatile organic silicon compounds is converted into dissolved silica by an oxidation process selected from advanced oxidation processes (for example with the aid of peroxide hydrogen, or another oxidant, under irradiation in the ultraviolet range or possibly another wavelength range).

In a particular embodiment of the method according to the invention, the determination of the total amount of silicon according to step c) is carried out by a molybdosilicate colorimetric method.

In a particular embodiment of the process according to the invention, the amount of polar silicon volatile organic compounds converted into dissolved silica is at least 50% w, preferably greater than 80% w and even more preferably greater than 99% w.

In a particular embodiment of the process according to the invention, the absorption according to step b) comprises contacting the sample with at least one bath.

In a particular embodiment of the process according to the invention, in step b) the absorption of the volatile organic compounds is carried out using a solvent chosen from water and / or another polar compound. , preferably methanol or ethanol, and / or an apolar compound, preferably cyclohexane.

In a particular embodiment of the process according to the invention, the absorption of the volatile organic compounds siliconized according to step b) is carried out by bubbling the gaseous sample in at least one bath of solvent.

Another object of the present invention is a device for detecting and / or quantifying total silicon resulting from the volatile organic compounds present in a gas to be analyzed, comprising: a) means for sampling a sample of said gas, b) absorption means for the silicon-containing volatile organic compounds by contacting the gaseous sample with at least one solvent; c) means for converting at least a portion of the silicon-containing volatile organic compounds into dissolved silica. d) and means for determining the total amount of silicon from the volatile organic silicon compounds solubilized in step b),

Advantageously, this device further comprises calculating means for determining the total amount of silicon contained in the volatile organic silicon compounds of said gas to be analyzed,

According to a particular embodiment of the invention, the device is configured to detect the presence of COVSi in a gas above a given threshold in total silicon, preferably between 0.1 and 1 mgSi / Nm3.

Another object of the invention is the use of a device for detecting and / or quantifying total silicon to determine the total concentration of silicon compounds in a gas.

Another object of the invention is the use of a total silicon detection and / or quantification device for controlling installations generating, using, treating or upgrading gases.

A last object of the invention is a control method of an industrial plant generating gas and / or consuming gas in which the method according to the invention or the device according to the invention is implemented and in which from a threshold of silicon compounds, preferably between 0.1 and 1 mgSi / Nm3, activates a purification unit and / or the gas is diverted to a consumer facility less sensitive to the harmful effects of said silicon compounds.

detailed description

"Biogas" means any gas produced by the fermentation of vegetable, animal or organic matter contained in waste in the absence of oxygen, ie by "anaerobic digestion" or "anaerobic digestion".

"Silicon compounds" means any compound, entity, or chemical species comprising one or more silicon atoms, which is in the gas phase in the gas in question. Among these silicon compounds are the volatile organic silicon compounds (hereinafter called COVSi), such as siloxanes, silanes, silanols, silarenes, and derivatives thereof, for example halogenated.

These compounds, which may be present in the trace state in the biogas, are for example derived from the anaerobic fermentation of the discharge waste which contains more and more silicones (for example in cosmetic products and in packaging). There is a large number of COVsi and it is still difficult to characterize them accurately and specifically. As an indication, with current techniques, only about ten siloxanes can be isolated and dosed in the landfill biogas, and in gases in general.

By "quantification of the silicon compounds" is meant the determination of the total amount of silicon contained in the silicon compounds, that is to say compounds containing silicon (including volatile organic compounds silicides), present in a gas. As opposed to "quantitative," qualitative qualifies what relates to the separation, identification, characterization or description of said compounds, without involving notions of magnitude (concentration or content). In the present case, the present invention does not seek the qualitative analysis of the silicon compounds present in the gas and soluble in any suitable solvent, nor the individual quantification of each of these compounds, but proposes a quantization method making it possible to obtain a global quantitative indicator (total Si) of said compounds within said gas.

A sequential scheme of the process is presented in FIG. 1 and explained below.

The first step of the process according to the invention therefore consists in taking a sample of the gas (1). This step is carried out by any appropriate sampling means, for example by the opening of a valve in a conduit which carries said gas, for example in a conduit (1 ') of bypass installed for this purpose. At the end of sampling, said valve can be closed. Said bypass duct can lead directly into a gas-liquid exchange space.

In a second step (2), this gaseous sample is brought into contact with a liquid solvent (a), in which the silicon compounds are capable of being absorbed. This step is implemented in a gas-liquid exchange space. As such, any installation that allows the contact of a liquid with a gas may be suitable. This contacting can for example be carried out by bubbling.

This solubilization trapping technique of the silicon compounds makes it possible to avoid losses or the dilution of samples usually encountered when sampling a Tedlar® bag gas or to avoid any problems of adsorption / desorption during the sampling of a gas on an adsorbent cartridge.

According to a variant of the present invention, absorption takes place by contacting the gaseous sample with at least one solvent bath. In this case, the number of baths is determined so as to exhaust said gaseous sample to silicon compounds. According to an advantageous embodiment of the present invention, a process is used in which the absorption of the silicon compounds takes place in a single solvent bath, unsaturated with silicon compounds, said silicon compounds being solubilized in said bath because of circulation of the gas in said bath (this circulation can be carried out for example by bubbling). By "unsaturated" it is meant that the solubility limit of the silicon compounds in the chosen solvent is not reached.

Also, in the case where a single bath is used, the solvent used to solubilize the silicon compounds present in the gaseous sample may consist of a mixture of solvents.

According to another embodiment of the present invention, the absorption takes place in at least two baths, for example arranged in series. In this case, the liquids constituting each of these baths are identical or different. Preferably in this case, the solvents used in the baths are of different natures, so as to allow the absorption of polar or apolar compounds depending on the polar or apolar nature of the solvents used.

In the case where two baths are used, a method is preferred in which the first bath of solvent is not saturated with silicon compounds capable of being solubilized in said bath because of the circulation of the gas within said bath; and wherein the last bath contains, after step b) of said method, an amount of silicon compounds dissolved in said bath below the detection limits of the measuring apparatus subsequently used for the assay. This is a way to see the depletion of the silicon compounds in said gas. The absence of silicon compounds detected in the second solvent bath makes it possible to confirm the absorption of the silicon compounds in the first solvent bath.

In one embodiment of the invention, the volume of solvent in each bath is between 100 mL and 10 L, preferably between 0.5 and 2 liters. It is, for example, 1 liter. According to a variant of the present invention, the gaseous sample is brought into contact with the solvent by bubbling the gaseous sample into the solvent bath. Advantageously, the sparging time is between 10 minutes and 3 hours, preferably between 15 minutes and 60 minutes. Advantageously, the gas flow rate is between 0.1 to 4 L / min, preferably between 0.5 and 2 L / min.

Furthermore, depending on the COVSi content of the biogas, the flow rate of the gas introduced into the bath (s), the gas sparging time in the bath (s) and the solvent volume of each bath can be adapted to optimize the solubilization and detection of the silicon compounds initially present in the gas to be analyzed.

According to the invention, a sample of said gas is contacted with a suitable solvent. Advantageously, the latter is chosen according to its polarity and therefore its ability to absorb some COVSi. By way of indication, mention may be made, as polar compounds, of water, alcohols, such as methanol and ethanol and, as nonpolar compounds, cyclohexane. In an advantageous embodiment, demineralised water is used.

Additives may be added to the solvents, for example acids or bases, oxidizing or complexing agents. Advantageously, the appropriate solvent consists of a mixture of solvents of different polarities, such as a mixture of deionized water and ethanol in all possible proportions, or any other mixture of polar or apolar solvents in all possible proportions. The use of water as a solvent has many advantages. It is a polar solvent for solubilizing polar COVSi, and it is an economical and readily available solvent, even in the demineralized form which is very highly preferred in the context of the present invention.

The solvent can be advantageously used at a temperature of between 5 ° C and 30 ° C.

The third step of the process (3) consists of converting at least a portion and preferably all of the silicon-containing volatile organic compounds into dissolved silica, i.e. silicic acid or other dissolved form of the silica). This transformation can be carried out by any technique making it possible to obtain dissolved silica from silicon compounds. By "dissolved silica" is meant all dissolved forms of silica, especially silicic acid. Advantageously, oxidation processes are used to convert silicon compounds into dissolved silica. As such, it is possible to use "advanced oxidation processes", and in particular chemical (Η202 / 03), photochemical (H2O2 / UV, O3 / UV), catalytic (H2O2 / Fe2 +), photocatalytic (Fe2 + / H2O2) oxidation. / UV and TiO 2 / UV), sonochemical or electrochemical.

The term "advanced oxidation processes", according to the article "Oxidation and reduction applied to the treatment of water - Ozone - Other oxidants - Advanced oxidation -Reducers" by S. Baig and P. Mouchet, published in 2010 in the Techniques de l'Ingénieur collection (chapter W2702), water treatment processes operating at ambient temperature and pressure and involving the production of a more powerful secondary oxidant from a primary oxidant.

In the context of the present invention, the conversion of the silicon compounds into dissolved silica may advantageously be carried out by a process which combines the action of H 2 O 2 with that of UV radiation. This process is relatively inexpensive. The photochemical activation of the oxygenated water by UV radiation induces a homolytic cleavage of the 0-0 bond allowing the formation of hydroxyl radicals, which are strongly oxidizing. The effectiveness of the H2O2 / UV process is a function, in particular, of the hydrogen peroxide concentration, the temperature and the pH.

Thus, advantageously, hydrogen peroxide (b) is added, with stirring, to the bath (s) containing the silicon compounds. For example, it is possible to use a concentration of hydrogen peroxide in the baths of between 0.02 and 0.2 mol / l, which in many cases allows complete oxidation. At a hydrogen peroxide concentration of less than 0.02 mol / L, the amount of hydroxyl radicals formed is sometimes insufficient to convert all of the silicon compounds initially present in dissolved silica.

After homogenization, the bath is subjected to UV irradiation, for example using a 55 W UV lamp, in static mode for 45 minutes. The silicon organic compounds solubilized in the aqueous solution are thus converted into dissolved silica.

According to a variant of the present invention, the solution contained in the bath can be circulated in the UV reactor. As an indication, the irradiation time may be between 10 minutes and 3 hours, preferably between 15 minutes and 30 minutes. As an indication, the flow rate of the solution contained in the bath may be between 1 and 10 L / h, preferably between 2 and 5 L / h.

In an advantageous embodiment of the process according to the invention, the conditions, and in particular the irradiation time and the flow rate, are adjusted so as not to exceed a total silicon content in the bath of 5 mgSi / l, and preferably so as not to exceed 1.3 mgSi / l so that the quantification method of the dissolved silica is optimal, ie the relationship between the absorbance of the reaction medium and the amount of silica present in said medium is linear; for reasonable sparging and oxidation times In general, in the process according to the invention the formation of colloidal silica which would distort the value obtained for the total silicon content contained in the gas should be avoided.

The fourth step of the process (4) consists in complexing the previously dissolved silica formed by the use of reagents (c) explained in more detail below, in order to allow its quantification by colorimetric assay. To do this, the reaction medium is first acidified by addition of a strong acid, such as hydrochloric acid (for example with a concentration of 6M). A solution of ammonium molybdate (for example at a concentration of 100 g / l) is then added to the reaction medium containing dissolved silica. It is known that silica reacts with oxides, especially with molybdate. The reaction of the dissolved silica with molybdate leads to the production of a yellow silicomolybdic complex; this compound has a limited stability over time. The yellow silicomolybdic complex thus formed can be detected by measurement of light absorption at silica concentrations of the order of a few mg / l. Other solutions of molybdenum oxyanions can be used to form a silicomolybdic complex, but ammonium molybdate is preferred which is effective and cheap.

A developer, such as oxalic acid (for example in a concentration of 75 g / L), may be added to the reaction medium to develop and intensify the color of the silicomolybdic complex; this avoids interference from glassware, water used, tannins, the presence of iron, sulfites or phosphates present in the aqueous sample to be analyzed. Indeed, in the presence of ammonium molybdate, the phosphates present in the sample to be analyzed are converted into dodecamolybdophosphates, which themselves are decomposed under the action of oxalic acid: this avoids interference during the subsequent dosing.

The reaction medium is left stirring for 10 minutes to 20 minutes (and advantageously for 15 minutes) so that the molybdate can react with the silica in solution to form the dodecamolybdosilicate, a yellow silicomolybdic complex. Within 10 minutes, the reaction between the molybdate and the dissolved silica is not complete, and it is preferred not to leave the reaction medium for more than 20 minutes with stirring because the silicomolybdic complex is not very stable.

The silicomolybdic complex can be detected, and its concentration can be determined by measuring the optical absorption of the reaction medium, and more specifically by the optical absorption of the silicimolybdic complex. However, because of the low solution stability of the silicomolybdic complex and especially because of the relatively high detection limit of the silicimolybdic complex of the order of a few mg / l, the inventors prefer that the concentration of dissolved silica present in the sample is determined by another method.

According to this other method, the silicimolybdic complex is converted into a more easily quantifiable complex by optical absorption measurement. To do this, the silicimolybdic complex, previously obtained, is reduced by amino-phenolsulfonic acid (for example at a concentration of 2.5 g / l) in the presence of Na 2 SO 3 (for example at 50 g / l) and NaHSO 3. (For example at 150 g / L) in a blue complex called "molybdenum blue" of formula [Μο154θ462Η14 · 70Η2θ] 14 ~ whose color is due to the change in the degree of oxidation of molybdenum, ie Mo (V ) in Mo (VI). In order that the silicimolybdic complex present in the reaction medium can be reduced to a molybdenum blue complex by aminonaphtholesulphonic acid, the reaction medium is left stirring for 5 minutes.

The reduction of the silicomolybdic complex to a molybdenum blue complex allows a more sensitive detection of the silica concentration of the test sample, i.e. with a lower detection limit. Thus, a dissolved silica concentration of the order of a few pg / l can be determined. The absorbance of the sample at 810 nm, corresponding to the absorption peak of the molybdenum blue complex, is then measured and correlated with the amount of silicon initially present in the aqueous sample to be analyzed. A calibration curve is previously carried out so as to quickly determine the silicon concentration (in the form of dissolved silica) contained in the sample to be analyzed. The calibration curve obtained is linear for concentrations of between 0 and 5 mg of silicon per liter. For silicon concentrations greater than 5 mg of silicon per liter, the sample is diluted before analysis and / or (preferably) the sparging time is reduced. The limit of quantification was evaluated at 0.006 mg of silicon per liter, the limit of detection is evaluated at 0.002 mg of silicon per liter. The data thus obtained are then recorded (5).

In an advantageous embodiment of the invention and in order not to reach the silicon quantification limits present in solution, the gas sparging time in the solvent bath is reduced when the silicon concentration approaches the upper limit indicated in FIG. -above.

This method of detection by spectrophotometry is a robust analytical technique, inexpensive and easy to use in an industrial site of production, use, treatment and recovery of gas.

The present invention also relates to a device hereinafter referred to as a "quantization kit" for the total silicon contained in the silicon compounds contained in a gas, making it possible to obtain a global quantitative indicator (total Si) of said compounds within said gas, said kit being shown in FIG. 2 and characterized in that it comprises: (i) a device for sampling the gas from a pipe (1), this device possibly consisting of a pump and a flow meter, preferably a totalizer, and a flow control valve (manual or automatic), which allows said gas to be bubbled into at least one vial (2) (typically between 100 mL to 1 L) containing the solvent (or mixture of solvents (a)) capable of absorbing the COVSi after bubbling, the solution is transferred to the following device; the vial containing a vent (2 ') through which gas bubbled into the solvent can escape; (ii) a device making it possible to transform the COVSi into dissolved silica, which may for example comprise a device allowing the metered addition of reagents (b) as well as a reactor equipped with a UV lamp (3) and a control system; agitation; (iii) a device intended and capable of implementing the colorimetric method (4) which makes it possible to determine the concentration of the dissolved silica sample, said device being particularly suitable for carrying out the sampling operations of a given sample volume, metered additions and successive and minute mixtures of the reagents (c), and the measurement of the optical absorbance of the sample, for example by means of an optical fiber or a measuring cell (4 '); (iv) means for calculating the concentration of the dissolved silica sample and the gas content in mgSi per unit volume of gas (eg Nm3) from the measured absorbance; (v) a device for acquiring measured data, calculation operations based on such data and automated control of required operations; (vi) means for displaying certain physical parameters considered important for the operation of the kit and the results of any calculations made by the PLC.

The first three devices are capable of allowing the necessary emptying and rinsing operations between several samples, in particular by the use of rinsing solution (d).

Devices containing solvents and reagents are designed to be easily replaced or filled by a qualified operator.

Fluid transfer operations in liquid form can for example be performed using peristaltic pumps. All the elements or devices constituting the kit are physically connected by pipes, which may be made of polymeric materials or metal (steel for example). The entire kit and / or some of its constituent elements may optionally be temperature-controlled, with set-point temperatures preferably between 10 ° C. and 40 ° C., and even more preferably between 20 ° C. and 30 ° C. From the solution having undergone the advanced oxidation process, the determination of the dissolved silica concentration can be carried out several times for each sample, in order to obtain duplicate or triplicate results.

The quantization kit according to the invention can be designed to be portable (i.e. it can be transported in the field by an operator for each measurement operation), or it can be designed in such a way that it can be be permanently installed (fixed) on an industrial site.

Here we describe embodiments of each of these two kits. Regarding the so-called "portable" version, several operating parameters can be set manually by the operator (flow and bubbling time, number of replicates). The "portable" version of the kit does not necessarily contain a controller. In addition, certain fluid transfer operations can in this case be performed manually by a skilled operator. Similarly, for the "portable" version, the colorimetric measuring device may be external to the kit.

Concerning the so-called "fixed" version of the kit, it is designed to allow fully automated measurement operations, with tools for remote monitoring and communication with the general PLC controlling all the processes of the chain to which the kit is connected.

The storage capacities of the different reagents vary according to the two versions of the kit.

The duration of an analysis comprising bubbling, advanced oxidation and colorimetric method may vary according to, in particular, the bubbling time (itself a function of the assumed content of the silicon gas), that of the UV irradiation, and the number of replicates desired. for measurement by colorimetry. By way of example, for a silicon gas content of between 0.1 and 100 mg / Nm3 and a single measurement, the result is obtained in 80 minutes. It is conceivable that the measurement frequency is less than 30 minutes since bubbling and advanced oxidation can take place in two separate devices: the next sample can take place during the oxidation of the previous one.

The device may be used to monitor compliance with a standard or specification for the total silicon content of a gas. It can also be used for the purpose of controlling the treatment of a gas treatment. For example, in the case of an activated carbon filter treatment, the total silicon content measured at the outlet can serve as an indicator of saturation of the filter and indicate the necessity of renewal.

Advantageously, the method and kit for detecting and / or quantifying total silicon makes it possible to detect the presence of COVSi in a gas, in particular a quantity of COVSi of the order of 0.1 mgSi / Nm3 corresponding to the maximum concentration of COVSi tolerated in a biomethane that can be injected into the distribution network, and a quantity of COVSi of the order of 1 mgSi / Nm3 corresponding to the specification of the engine manufacturers beyond which the biogas upgrading equipment is likely to be degraded. The invention is illustrated below by examples which, however, do not limit the invention; these examples highlight certain advantages and features of the present invention.

Examples 1) Polar and / or polar COVSi trapping step

A biogas flow at 1 L / min was bubbled in 1.2 L of water for 20 minutes. The volatile organic silicon compounds initially contained in the biogas were absorbed into the solution by bubbling the biogas. 2) Transformation of the COVSi into Silicon Compounds 5 mL of a solution of hydrogen peroxide at 30% by volume was introduced into the aqueous solution (1.2 L of water) having solubilized the volatile organic silicon compounds initially contained in the biogas .

This solution was then irradiated under UV with a UV lamp with a nominal power of 55 W, in static mode for 45 minutes. The organic silicon compounds solubilized in the aqueous solution were thus converted into dissolved silica. 3) Determination of silicon by a colorimetric method with molybdenum blue a. Complexing step of the dissolved silica 50 ml of the previous aqueous solution containing dissolved silica were taken. 1 mL of a 50% HCl solution was added with stirring, followed by 2 mL of a solution of (ΝΗ4) 6Μθ4θ24, 4H20 at 0.08 mol / L, and finally 2 mL of a solution of oxalic acid at 0.6 mol / l. The reaction medium was left stirring for 15 minutes so that the ammonium molybdate could react with the silica in solution to form dodecamolybdosilicate, a yellow silicomolybdic complex. b. Stage of reduction of the silicomolybdic complex

A reducing solution with amino-naphthol sulfonic acid was developed by mixing a first and a second aqueous solution: said first aqueous solution was made by dissolving 500 mg of amino-2-naphthol-4-sulfonic acid and 1 g of Na 2 SO 3 in 50 ml of water, said second solution was made by dissolving 30 g of NaHSO 3 in 150 ml of water. These two solutions were mixed with stirring to be homogeneous, and the mixture was then filtered: thus was obtained the reducing solution.

2 ml of this reducing solution with stirring was then added to the 55 ml of the solution containing the yellow silicomolybdic complex (obtained in step 3a above). The reaction medium was then left stirring for 5 minutes, so that the dodecamolybdosilicates present in the reaction medium can be reduced to a blue molybdenum complex. vs. Quantification of the silicon contained in the bath to be analyzed The absorbance of the sample at 810 nm was then measured and correlated with the amount of silicon initially present in the aqueous sample to be analyzed.

Figure 3 shows the variation of absorbance measured as a function of wavelength for two samples. The peak of absorbance of the reduced complex was observed at 810 nm. According to the calibration curves made (see FIG. 4), the measured absorbance of 0.144 corresponds to a silicon concentration of 0.19 mg / l in the initial bubbling solution.

The content in the biogas was then evaluated by taking into account the flow of biogas during the trapping step. This measure in solution after UV / H 2 O 2 treatment corresponds to a content of polar COVSi in the biogas of approximately 11 mg Si / Nm 3.

This concentration was confirmed by measurements performed by ICP (11.4 mgSi / Nm3).

Claims (15)

A method for detecting and / or quantifying the total silicon resulting from the volatile organic compounds present in a gas, in which: a) a sample of said gas is taken, b) said sample of said gas is brought into contact with at least one optionally polar or apolar solvent, capable of extracting at least a portion of said volatile organic compounds in said silicon, c) determining the total amount of silicon from the volatile organic compounds contained in at least one solvent used in step b) d) calculating the total amount of silicon derived from the volatile organic compounds present in said gas, said process being characterized in that between step b) and step c) at least a portion of the organic compounds are converted into siliceous volatiles in dissolved silica. 2. Method according to claim 1, characterized in that at least a portion of the volatile organic compounds silicones are siloxanes. 3. Method according to claim 1, characterized in that at least a portion of the volatile organic compounds silicon is converted into dissolved silica by an oxidation process. 4. Method according to claim 3, characterized in that at least a portion of the silicon volatile organic compounds is converted into dissolved silica by an oxidation process selected from advanced oxidation processes, preferably with the aid of hydrogen peroxide, or other oxidant, under irradiation in the ultraviolet or other wavelength range. 5. Method according to any one of the preceding claims, characterized in that the determination of the total amount of silicon according to step c) is performed by a molybdosilicate colorimetric method. 6. Process according to any one of the preceding claims, characterized in that the amount of polar volatile organic compounds converted into dissolved silica is at least 50% w, preferably greater than 80% w and even more preferably greater than 99% w. % w. 7. Process according to any of the preceding claims, characterized in that the absorption according to step b) comprises contacting the sample with at least one bath. 8. Process according to any one of the preceding claims, characterized in that in step b) the absorption of the volatile organic compounds is carried out using a solvent chosen from water and / or another polar compound, preferably methanol or ethanol, and / or an apolar compound, preferably cyclohexane. 9. Process according to any one of the preceding claims, characterized in that the absorption of the volatile organic compounds silicified according to step b) is carried out by bubbling the gaseous sample in at least one bath of solvent. 10. Apparatus for detecting and / or quantifying total silicon resulting from the volatile organic compounds present in a gas to be analyzed, comprising: a) means for sampling a sample of said gas, b) means for absorbing organic compounds silicic volatiles by contacting the gaseous sample with at least one solvent; c) means for converting at least a portion of the silicon volatile organic compounds into dissolved silica. d) and means for determining the total amount of silicon from the volatile organic silicon compounds solubilized in step b), 11. Device according to claim 10, further comprising calculating means for determining the total amount of silicon contained in the silicon volatile organic compounds of said gas to be analyzed, 12. Device according to one of claims 10 or 11, characterized in that it is configured to detect the presence of COVSi in a gas above a given threshold in total silicon, preferably between 0.1 and 1 mgSi / Nm3. 13. Use of a total silicon quantization device according to one of claims 10 to 12 for determining the total concentration of silicon compounds in a gas. 14. Use of the device according to one of claims 10 to 12 for controlling facilities generating, using, treating or upgrading gases. 15. Process for controlling an industrial plant generating gas and / or consuming gas in which the method according to one of Claims 1 to 9 or the device according to one of Claims 10 to 12 and in which from a threshold of silicon compounds, preferably between 0.1 and 1 mgSi / Nm3, activates a purification unit.