FR3033645A1 - METHOD FOR IDENTIFYING AND QUANTIFYING THE PROPORTIONS RELATING TO THE VARIOUS CRYSTALLIZED FRACTIONS PRESENT IN A HYDRATE SLAB AND ITS USE FOR REFRIGERANT FLUIDS - Google Patents

Abstract

Process for the identification and quantification of the relative proportions of the different crystallized and liquid fractions present in a hydrate slurry, defined as a solid suspended in a carrier fluid, characterized in that it is carried out by means of a spectrometer of low-field nuclear magnetic resonance and a radio frequency probe for detecting and quantifying protons by direct measurement on said hydrate slurry. The hydrate slurry is for example composed of an alkyl-onium hydrate clathrate. Application to the identification, characterization and quantification of different polymorphs of hydrates formed in diphasic refrigerant fluids, in static or dynamic mode.

Description

The present invention relates to the field of hydrate slurries, or clathrates, and more particularly to a method of quantifying the relative proportions of the different crystallized fractions present in a slurry of hydrate. Clathrates are crystalline solids in which an atom or so-called guest molecule is trapped in a cage formed by a three-dimensional assembly of molecules called hosts. The three-dimensional assembly of the host molecules is via hydrogen bonds. Water-clathrate, ice-like structures known as clathrates hydrates are particularly known. Various guest molecules can be used to form these clathrates hydrates. In general, the guest molecule must, on the one hand, meet dimensional criteria to be able to penetrate the cage structure formed by water (sufficiently small molecule) and stabilize the entire structure (molecule sufficiently large), and secondly, do not present a group capable of forming hydrogen bonds. Examples of guest molecules include gas molecules such as argon, methane, CO2, SO2. Alkyl-onium salts, such as tetra-n-butyl ammonium bromide (TBAB), have also been used to form clathrate hydrates; in this case, these invited molecules are not only inserted into the cages of the three-dimensional structure, but also participate in the structure itself, in particular the anions. These types of clathrates are called semi-clathrates. They can also accommodate smaller gas molecules in cavities not occupied by salt. An example of such a known semi-clathrate structure is shown schematically in FIG. 4 (showing TBA + and B ions (, H20 water molecules and gas molecules).

These materials are particularly good candidates for storage of gases and phase change materials usable for energy storage or cooling applications, in the form of hydrate slurry (s), i.e. in the form of solids suspended in a carrier fluid. This carrier fluid is generally an aqueous solution.

The industrial processing conditions influence the physical properties and in particular the flow properties of these slurries, which depend, among other things, on their solid fraction, that is to say on their content of crystals in suspension in the phase. liquid. In addition, the properties of these hydrate clathrates, particularly thermodynamically, are dependent not only on their chemical nature, but also on their crystal structure. This crystalline structure is in particular a function of temperature and pressure. It is therefore essential, particularly to envisage a use in the field of energy, to quantify, in the hydrate slurry, the proportion of crystals suspended in the liquid phase.

Since the properties of these hydrate slurries can also be influenced by the relative proportions of the various crystallized fractions, it is also necessary to be able to quantify these relative proportions. Some current methods for estimating the solid content of a multiphase material use the Nuclear Magnetic Resonance (NMR) technique.

In particular, US 2009/0256562 discloses a method of detecting precipitates in a hydrocarbon stream. In Example 2 of this document, this method comprises a low-field NMR measurement of a THF: D20 hydrated clathrate allowing, using a CPMG sequence, to determine the T2 relaxation times (around 2-3 ms) of the THF alone and study the formation of these hydrates and their dissociation processes. However, this study only deals with deuterated samples (that is to say, very different from real conditions), focusing only on the variations in the relaxation time corresponding to THF to deduce the degree of formation or dissociation of the hydrate. without quantifying the crystal fraction.

A first object of the invention is therefore to overcome the disadvantages of the prior art by proposing a method for quantifying the fraction of crystals present in the solid / liquid mixture of a hydrate slurry. Another object of the invention is to provide a method which further makes it possible to identify and quantify the relative proportions of the various fractions (water and guest molecule) within the solid fraction present in a hydrate slurry.

Another aim of the invention is to propose a method for determining the different solid fractions present in a hydrate slurry by means of a non-destructive and non-invasive method, which is applicable when the carrier fluid is water. slight (H20). Another object of the invention is to provide a method for determining the different crystallized fractions present in a hydrate slurry that would be applicable both in static mode and in dynamic mode. These objects are achieved by the process according to the present invention. To this end, the present invention relates to a method for identifying and quantifying the relative proportions of the different crystallized fractions present in a hydrate slurry, defined as a solid suspended in a carrier fluid, produced by means of a spectrometer of low-field nuclear magnetic resonance and a dead time radiofrequency probe, less than 15 ps, for detecting and quantifying protons by direct measurement on said hydrate slurry.

It has been found that a measurement of RNM with a probe whose dead time is less than 15 ps, preferably less than 12 ps, makes it possible to observe short T2 relaxation times, corresponding to the solid phase of the grout hydrate. Such quantification of the crystals was not possible by the method described in US 2009/0256562 in view of the dead time of 60 ps of the probe of the NMR spectrometer 20 implemented. Advantageously, the method according to the invention comprises the following successive steps: introduction of a sample of said hydrate slurry into a low-field NMR spectrometer, within a radio frequency coil detecting the protons and placed in said magnetic field permanent, while regulating the temperature of said sample, - measuring the relaxation of the relaxation signal, - determining the different T2 transverse relaxation times of the protons of the sample and their relative amplitudes, the relative amplitudes of the lower short relaxation times at 1 ms corresponding to the relative proportions of the different crystallized fractions present in the said hydrate slurry and the relative amplitudes of the relaxation times greater than or equal to 1 ms, corresponding to the relative proportions of the molecules of the liquid phase of said slurry; hydrate. Preferably, the determination of the different T2 transverse relaxation times of the protons of the sample and their relative amplitudes is performed: by a nonlinear regression method - and / or by the inverse Laplace transform. to distinguish and quantify the chemical compounds present in the crystallized and liquid phases of the hydrate slurry. The process according to the invention has proved particularly advantageous when the hydrate slurry is an alkyl-onium hydrate clathrate, such as an ammonium or phosphonium quaternary salt hydrate clathrate. Preferably, the hydrate slurry is a tetra-n-butyl ammonium halide hydrate clathrate, such as tetra-n-butyl ammonium bromide hydrates (TBAB), tetra-n-butyl ammonium chloride (TBACI) ) or tetra-n-butylammonium fluoride (TBAF). Alternatively the hydrate slurry may be composed of a tetrahydrofuran hydrate clathrate (THF) suspended in a liquid phase. Advantageously, the applied magnetic field is less than 100 MHz, preferably less than or equal to 30 MHz, more preferably less than or equal to 20 MHz. The method according to the invention is entirely appropriate when the carrier fluid is light water H 2 O. This non-invasive and non-destructive process then makes it possible to determine the different crystallized fractions of a hydrate slurry under the conditions that are as close as possible to the industrial conditions.

Furthermore, the method according to the invention can be realized in static mode or in dynamic mode, such as in "stop-and-flow" mode. The present invention also relates to a device for implementing the method described above, comprising: a low-field NMR spectrometer equipped with a probe for detecting and quantifying protons, means for regulating the temperature of the the sample; a sample receiving tube for static mode operation or a hydrate slurry circulation loop for dynamic mode operation; means for processing the relaxation signals. Among the advantageous and surprising applications of the process according to the invention, mention may be made of the use to identify, characterize and quantify the various hydrate polymorphs formed in diphasic refrigerant fluids, in static mode or in dynamic mode, or else the use to identify, characterize and quantify the different polymorphs forming the solid phase of a slurry of quaternary salt hydrates. The method and the device according to the invention can find an advantageous use for the control of a refrigeration plant using a two-phase refrigerant fluid comprising a hydrate slurry, or else in the field of gas storage or transport (such as that CO2 or CH4) using slurries of hydrates. The invention will be better understood on reading the following description of nonlimiting exemplary embodiments, with reference to the appended drawings in which: FIG. 1 shows the distribution of T2 relaxation times before crystallization of different solutions composed of TBAB and H20; Figure 2 shows the distribution of T2 relaxation times after crystallization of different solutions composed of TBAB and H20; Figure 3 shows the linear relationship between the intensity of the NMR signals and the inverse of the temperature for different solutions composed of TBAB and H20; FIG. 4 schematizes the structure of a tetra-n-butyl ammonium bromide semi-clathrate (TBAB) containing gas molecules; FIG. 5 is a diagram representing a measurement installation in dynamic mode (stop and flow). EXAMPLE 1 The principle of formation of salt hydrates is based on the cooling of an aqueous solution of quaternary salts (tetra-n-butyl ammonium bromide, TBAB in the example presented here) at a temperature below its melting point. crystallization. Depending on the salt concentration in the initial solution, cooling may lead to the crystallization of part or all of the solution: - To crystallize the entire solution, it is necessary to place at the stoichiometric concentration, that is to say at a concentration of the solution corresponding to the concentration of the hydrate (considered as a defined compound). At this concentration, the formation of hydrates does not lead to an enrichment or a depletion of the salt solution. The whole solution can then crystallize in the form of hydrates, since the two compounds (water and salt) are present in solution in the right proportions until the end of the crystallization process. - On the other hand, if the initial salt concentration of the solution is lower than the stoichiometry, it is lower than the concentration of the hydrates that will be formed by cooling. Crystallization will then lead to a depletion of the liquid phase in salt. Conversely, for a concentration of the solution greater than that of the hydrates, the crystallization will lead to an enrichment of the liquid phase in salt. In the present case, in static mode, different concentrations were studied: a concentration corresponding to stoichiometry (40% TBAB), in order to form only hydrate and no longer have a residual liquid phase; several concentrations below stoichiometry, in order to maintain a residual liquid phase (10, 20 and 32% TBAB). Four solutions of tetra-n-butyl ammonium bromide TBAB (sold by the company Fiers, Kuurne, Belgium) were prepared in distilled H 2 O or in D 2 O (Aldrich Company) at weight concentrations of TBAB of 10, 20, 32 and 40 respectively. %. For each of the percentages, the TBAB: H 2 O solutions (in triplicate) and TBAB: D 2 O (two copies) were introduced into the NMR tubes (10 mm in diameter), weighed and sealed before the 3033645 measurements. NMR. The samples were analyzed at two different temperatures, namely on the one hand at 18 ° C. and, on the other hand, after cooling to either 0.3 ° C. for the 10% and 20% TBAB samples, ie to 3 ° C. 6 ° C for 32% and 40% TBAB samples. Crystallization of the samples was carried out overnight in a cryostat whose temperature was set at 0.3 ° C or 3.6 ° C depending on the concentration of TBAB. The proton NMR measurements of each sample were made using a low-field NMR spectrometer (Minispec BRUKER, Germany) operating at a resonance frequency of 20 MHz, and a radio-frequency time-lag probe. 11 ps. The RNM apparatus was equipped with a temperature control device regulated to ± 0.1 ° C. The measurement parameters were: 90 ° pulse of 2.9 ps, 8 scans at 18 ° C and 32 scans for crystallized samples. The recycle time (RD) was between 1 s and 10 s depending on TBAB concentration and temperature. Two types of pulse sequences were used: a Fast Saturation Recovery (FSR) sequence with 100 points between 5 ms and RD, and a FID-Carr-Purcell-Meiboom-Gill pulse sequence (FID-CPMG). ) with a delay of 0.4 ps between each point in the FID- (Free Induction Decay) signal and an echo time of 0.2 ms in the CPMG signal acquired with a maximum of 22000 echoes.

The relaxation curves obtained by the CPMG sequence were processed using the Scilab software according to the maximum entropy method (MEM) (described in F. Mariette et al., Continuous Relaxation Time Distribution Decomposition by MEM, Vol. DN Rutledge), Elsevier, Paris, 1996, pp. 218-234) which provides a continuous distribution of relaxation times without assumptions about their number. The Levenberg-Marquardt algorithm (DW Marquardt, Journal of the Society for Industrial and Applied Mathematics 1963, 11, 431-441) was also used to process the FID CPMG data using a multi-term model according to the equation (I) below: B x exp (- T 2j 7-22i 2 t) = EAi X exp 1 = 1 3033645 where T21 and Tz are the relaxation times of amplitude Ai and Bj with n = 2 or n = 3 depending on the concentration of tetra-n-butyl ammonium bromide. The results are presented in FIGS. 1 and 2 and in Table 1. FIGS. 1 and 2 show the distribution of the T2 values of the different TBAB: H20 mixtures respectively before (FIG. 1 at 18 ° C.) and after (FIG. ) crystallization. Note that the lower the TBAB concentration, the higher the T2 values. At 18 ° C the mixtures give T2 relaxation time distributions whose value and proportions of the longest T2 relaxation time decrease as the TBAB concentration increases. The distribution of the relaxation times T2 measured on the crystallized samples (FIG. 2) is narrower than those of the same samples at 18 ° C. (FIG. 1). This observation is consistent with the weakening of the NMR signal due to the crystallization of the samples. It can be seen that the T2 transverse relaxation times have a first series of components (components 1, 2 and 3) at very short times (values much less than 1 ms, or even less than 0.250 ms) which corresponds to the solid fraction of the grout and a second series of components (components 4, 5 and 6) at times much greater than 1 ms, which corresponds to the liquid phase. The 10% and 20% blends crystallize at 0.3 ° C but still contain a significant amount of liquid as confirmed by the high T2 values at 1175 ms and 968 ms (respectively) in Figure 2. The blends containing 32% and 40% TBAB crystallize at 3.6 ° C, but a liquid phase is still present in the sample at 32% as confirmed by the time-centered distribution of about 150 ms and 580 ms on the FIG. 2. Furthermore, the 40% TBAB mixtures, which appeared visually fully crystallized, almost exclusively have short T2 relaxation times (less than 0.215 ms). The results obtained for these different hydrate slurries are reported in Table 1 which shows the relative amplitudes A (1) to A (6), the values of the relaxation times T2 (1) to T2 (6) and the quantity of solid slurries hydrates TBAB: H20.

The relaxation time measurements indicate, for the four mixtures made (10, 20, 32 and 40% TBAB), a first del-2 component around 15 μs. This relaxation time is typical of proton relaxation time involved in a crystal lattice as observed for ice (crystallized water). Its amplitude increases with the concentration of TBAB with values close to the mass concentration of hydrates in TBAB (Table 1). By performing the comparative measurements in D20, it was possible to assign this first component at 15 ps to the crystallized TBAB. A second T2 short relaxation time (second component) between 30 ps and 55 ps is observed, with a lower amplitude for the higher TBAB concentrations.

For the hydrates at 32 and 40% mass concentration TBAB, the rest of the signals of the solid phase is characterized by a 3rd component with a relaxation time respectively of 234 and 214 ps, representing 48.8% and 54%. 5% of the total amplitude of the signals. The other values of T2 vary between 22 and 1174 ms corresponding to mobile protons supposed to be in the liquid phase. The T2 (6) values observed for 10 and 20% mixtures are characteristic of liquid water. In order to assign to each component of T2, NMR relaxation times were measured for TBAB: D20 hydrates made with percentages of 32 and 40% TBAB in D20 instead of H20.

The values of the first and second T2 were in the same range and comparable to those determined in H20. No value of T2 (3) was measured in the 200-260 ms range as opposed to the mixture in H20. Two other longer relaxation times T2 (4) and T2 (5) were observed but with different values and amplitudes compared to the mixture in H2O.

This experiment confirmed that the first two components T2 (1) and T2 (2) with short relaxation times in the microsecond range could be attributed to TBAB in the hydrate crystals, the T2 component (3). absent in D20 corresponding to the hydrates formed with the percentages 32 and 40% of TBAB at 3.6 ° C.

Thus, the amount of crystallized water and TBAB crystallized in TBAB: H20 hydrates, referred to as SC solid content (in%), can be calculated according to the following equation (II): SC = 5 in which 1 and Ihq are NMR signal intensities of the solid and liquid components expressed in volts. A theoretical quantity of SCtheo crystals can also be calculated with the following formula (III): SCtheo = 10 The total intensity It can be obtained at each temperature by applying the Curie law which gives a linear relationship between the intensity It / m (V / g) TBAB mixtures: H20 (of total mass m) and the inverse of temperature (in degree K). This linear relationship has been validated on each mixture (see Figure 2). Calculation of SC by Equation (III) confirmed that the 10-20% blends were bi-phasic and contained a large amount of liquid phase. The higher TBAB concentration, the greater the SC value. Since the density of the NMR signals is proportional to the total amount of protons, the mass intensity of TBAB and H2O in the hydrates can be determined using the intensity of the proton density corrected T2 components of each molecule. But the proton density of water and TBAB is the same (equal to 0.111). Thus, the mass intensities can be calculated without regard to the nature of the molecule. The calculated values indicate that the hydrates at 10 and 20% are composed of two relaxation components in a 26/74 ratio whereas the hydrates at 32 and 40% have three components with an average proportion of 36/5/59. . These proportions indicate the presence of two different types of hydrates formed in TBAB: H20 solutions. Indeed, different crystalline structures, called polymorphs, called type A and type B, have been proposed by different authors, based on the X-ray diffraction of individual crystals. They are differentiated by their number of hydration. From the OYAMA (Fluid Phase Equilibria, 2005, 234, 131-135) phase diagrams, the hydration numbers of the TBAB hydrates were determined for type A for 26, and for type B for 38, corresponding to ratios of TBAB: H20 10 weightings of 40/60 and 32/68 respectively. These differences can thus be detected by NMR. In the present application, the two NMR methods tested made it possible to demonstrate: i) that the first three components of T2 at a short relaxation time can be attributed to the solid phase of the hydrate slurries ii) that the total intensity The signal lt can be deduced by extrapolation, at low temperature, of the Curie law and only the larger components (T2 much greater than 1 ms) are attributed to the liquid phase. The comparison between these NMR estimates and the solid content determined using the segment law confirms this total correspondence between these three methods. For mixtures containing 10 and 20% TBAB, only two components of T2 were measured at 14 ms and 48 ms. Calculations of their mass intensity showed that the first component at 14 ms accounted for about 26% of the solid fraction and 74% for the second component. According to the NMR results obtained for the 10% and 20% hydrate slurries, the TBAB: H20 ratio was closer to the 32/68 ratio and therefore should correspond to type B crystals as expected (compared to the phases). For the 32 and 40% mixtures, three T2 components with short relaxation times accounted for 36/5/59 relative proportions. Assignment of the third component T2 (3) to the solid fraction was confirmed by analysis of TBAB: D20 hydrates for which no third component was detected. This allocation was confirmed by calculating the mass intensities in the TBAB: H20 samples because the third component totaled 59% of the solid fraction in agreement with the water content of the type A crystals. The T2 relaxation time (3 ) around 230 ms was therefore attributed to the water in the hydrate crystals but as an amorphous state. The first T2 (1) relaxation time measured for the 32 and 40% samples respectively represented 35 and 37% of the solid fraction representing the TBAB crystals. The T2 component (2) (at 30 and 50 ms) which represents 3 to 7% of the total solid fraction was also present, and at a high intensity in hydrates TI3AB: D20. As a result, this T2 (2) component has also been attributed to TBAB in the crystals.

The results of the study of Example 1 show that low-field NMR is able not only to estimate a solid content in TBAB: H20 slurries, but also to distinguish and quantify TBAB as well as water in crystals and differentiate between type A and type B crystals.

13 T (° C) TBAB Component 1 Component 2 Component 3 Component 4 Component 5 Component 6 Total (%) Solid (%) A (1) T2 (1) A (2) T2 (2) A (3) T2 (3) A (4) T2 (4) A (5) T2 (5) A (6) T2 (6) (%) (ms) (%) (ms) (%) (ms) (%) (ms) / o) (ms) (/ o) (ms) 6.8 0.0140 20.5 0.0483 5.2 237 67.5 1174 27.3 0.3 10 (0.6) (0.0004) (0.2) (0.0017) (0.4) (4) (0.4) (23) (0.8) 16.2 0.0140 45.6 0.0485 4.2 115 10.5 579 23.7 1131 61.7 0.3 20 (0.8) (0.0000) (0.2) (0.0035) (1.6) (0) (4.2) (20) (6) , (4) (43) (0.6) 27.6 0.0160 2.8 0.0302 48.8 0.234 5.9 151 14.9 581 78.9 3.6 32 (0.4) (0, 0006) (4.0) (0.0427) (4.2) (0.030) (2.2) (87) (2.3) (91) (1.3) 36.5 0.0149 6.7 0.0547 54.5 0.214 2.3 22 97.7 3.6 40 (0.4) (0.0006) (0.3) (0.0019) (0.9) (0.005) (0.1 ) (0) (0,1) TABLE 1 (The values in italics in parentheses correspond to the standard deviations of the different measurements made) 3033645 14 Temperature Concentration Fraction of crystals by NMR Theoretical fraction of crystals measured in mass ° C TBAB 0.3 10 25% 25% 0.3 20 61% 59% 3.6 32 80% 73% 3.6 40 97% 100% TABLE 2: Fraction of crystals as a function of the mass concentrations of TBAB, calculated by NMR and by the law of the segments (theoretical solid rate). The amplitude ratio between the first three components of T2 thus corresponds to a value close to the stoichiometry of 28 or 36 water molecules per molecule of theoretical TBAB given by the literature (Oyama et al., Fluid Phase Equilibria 2005, 234, 131-135). Thus, these results show that NMR not only makes it possible to distinguish the signal from hydrates from that of uncrystallized water and TBAB, but also that it makes it possible to measure characteristic relaxation times of hydrates A and B. It is therefore It is possible to quantify not only the total solid content of the hydrate slurry, but also to quantify the relative proportions of the crystals A and B in this solid fraction, on the basis of the intensity of the T2 characteristic of these crystals. Given the measured T2 values, the calculation of the solid rate is based on the amplitude of the 1st, 2nd and 3rd components. Relaxation times beyond 50 ms correspond to the liquid phases. The results obtained in static mode demonstrate the remarkable sensitivity of NMR measurements to identify, characterize and quantify quaternary salt hydrates. No other technique has yet been able to allow the experimental quantification of the two types of hydrates A and B formed in the TBAB: H20 mixtures.

EXAMPLE 2 Tetrahydrofuran Hydrate Clathrate THF: H 2 O Measurements of the T2 relaxation time of a THF: H 2 O mixture (16% THF by weight, ie a THF / H 2 O molar ratio = 1/19) were carried out at 1 ° C. ° C. The fit of the data, performed according to the following algorithm (IV), gives the results shown in Table 3: t2 3 (IV) t Kt) Ai X eXp () + / Ai X eXp) T2 2 (1) j = 2 T2 (j) A (1) T2 (1) A (2) T2 (2) A (3) T2 (3) 10.9 0.195 86.0 0.2520 3.1 248 10 TABLE 3 Legend: A relative amplitudes (in%), T2 transverse relaxation time (in milliseconds) of hydrate THF: H20 at 1 ° C standard errors less than 0.3 ° A.

These results indicate the presence of two relaxation times which are characteristic of an amorphous solid phase and a third relaxation time corresponding to a small proportion (3.1%) of a liquid phase. The proton density of THF is very close to that of water (0.109 / 0.110).

Thus in the THF: H 2 O mixture containing 16% THF, the THF NMR signal intensity should be 15.95% of the total signal for 84.05% water-attributable signal.

This is indeed what the results of the NMR measurements confirm: these NMR signal intensity ratios confirm that the T2 (1) relaxation time at 0.11995 ms represents the relaxation of the THF in the hydrate, that T2 (2) at 0.252 ms characterizes the water in the hydrate while a proportion of 3.1% of THF has not crystallized and is found in the liquid phase (T2 (3) at 248 ms). These data are in agreement with the results obtained in Example 1 for TBAB: H20 hydrates at 32% and 40%, characterized by a water relaxation time in the hydrates around 214-234 ps (T2 (3)). ) in Table 1) and shows that the process is extrapolable to other hydrates.

EXAMPLE 3 Measurement in Dynamics A dynamic measurement installation 1 is shown in FIG. 5. It comprises a low-field NMR spectrometer 2 traversed by a glass tube 4 connected to a dynamic loop 3 in which circulates the grout. 'hydrate. This dynamic loop is divided into two branches 4 and 5 arranged in parallel, the branch 4 constituting the tube passing through the magnet of the NMR spectrometer and the branch 5 being a bypass which makes it possible, by actuating the valves 6, to carry out the measurements. in stopand-flow. A cooling circuit 7 connected to a cryostat 8 makes it possible to cool the samples and to regulate the temperature of the sample to be measured.

The circulation of the hydrate slurry in the loop 3 is ensured by means of a pump 9. The refrigeration and air-conditioning sectors are very interested in the development of refrigerant fluids whose role is to convey the cold since the refrigerating machine to the user stations. The biphasic refrigerant fluids (FFD) consisting of hydrates suspended in a carrier liquid (hydrate slurries) are good refrigerants from an energy point of view but also from a practical point of view since they make it possible to consider a significant reduction in the size of the installation and the diameter of the pipes. Knowledge of the flow conditions of gas hydrate slurries is required, not only to better understand their transport to the cold location of demand, but also to improve the efficiency of heat exchanges in connection with their properties to store and restore energy. For this we must take into account the two-phase nature of these grouts. The method according to the present invention based on a low-field NMR measurement has the advantage of a non-invasive analysis and to quantify the crystal content of hydrate slurries, and their nature, in real time.

Claims (14)

REVENDICATIONS1. A process for identifying and quantifying the relative proportions of the different crystallized fractions present in a hydrate slurry, defined as a solid suspended in a carrier fluid, produced by means of a low field nuclear magnetic resonance spectrometer and a dead time radiofrequency probe less than 15 ps, for detecting and quantifying protons by direct measurement on said hydrate slurry. 2. Method according to claim 1, characterized in that it comprises the following successive steps: - introduction of a sample of said hydrate slurry in a low-field NMR apparatus, within a radio frequency coil detecting the protons and placed in said permanent magnetic field, while regulating the temperature of said sample, - measuring the decay of the relaxation signal, - determining the different T2 transverse relaxation times of the protons of the sample and their relative amplitudes, the amplitudes relative short relaxation times less than 1 ms, corresponding to the relative proportions of different crystallized fractions present in said hydrate slurry and the relative amplitudes of the relaxation times greater than or equal to 1 ms, corresponding to the relative proportions of the molecules in phase liquid of said hydrate slurry. 3. Method according to claim 1 or 2, characterized in that the determination of the different T2 transverse relaxation times of the protons of the sample and their relative amplitudes is performed: by a nonlinear regression method 25 and / or by the inverse Laplace transform. to distinguish and quantify the chemical compounds present in the crystallized and liquid phases of the hydrate slurry. 3033645 19 4. Process according to any one of the preceding claims, characterized in that the hydrate slurry is an alkyl-onium hydrate clathrate, such as an ammonium or phosphonium quaternary salt hydrate clathrate. 5. Process according to any one of the preceding claims, characterized in that the hydrate slurry is a tetra-n-butyl ammonium halide hydrate clathrate, such as tetra-n-butyl bromide hydrate clathrates. ammonium (TBAB), tetra-n-butyl ammonium chloride (TBACI) or tetra-butyl ammonium fluoride (TBAF). 6. Process according to any one of claims 1 to 3, characterized in that the hydrate slurry is a tetrahydrofuran hydrate clathrate (TH F). 7. Method according to any one of the preceding claims, characterized in that the applied magnetic field is less than 100 MHz, preferably less than or equal to 30 MHz, more preferably less than or equal to 20 MHz. 8. Process according to any one of the preceding claims, characterized in that the carrier fluid is H20 light water. 9. Method according to any one of the preceding claims, characterized in that it is performed in static mode or in dynamic mode, such as "stopand-flow" mode. 10. Device for implementing the method according to any one of the preceding claims, characterized in that it comprises: - a low-field NMR spectrometer (2) equipped with a radio frequency probe for detecting and quantifying the protons; means for regulating the temperature of the sample; a sample receiving tube for static mode operation or a loop for circulating the hydrate slurry for mode operation; dynamic, means for processing the relaxation signals. 3033645 20 11. Use of the method according to any one of claims 1 to 9, for identifying, characterizing and quantifying the different polymorphs of hydrates formed in two-phase refrigerant fluids, in static mode or in dynamic mode. 12. Use of the method according to any one of claims 3 or 4, for identifying, characterizing and quantifying the different polymorphs forming the solid phase of a slurry of quaternary salt hydrates. 13. Use according to one of claims 11 or 12 for the control of refrigeration system using a two-phase refrigerant fluid comprising a hydrate slurry. 10 14. Use according to one of claims 11 or 12 in the field of storage or transport of gas using slurries hydrates.