WO2008107505A1

WO2008107505A1 - Method and equipment for measuring the high-pressure sorption isotherms of supercritical fluids and gases

Info

Publication number: WO2008107505A1
Application number: PCT/ES2008/000126
Authority: WO
Inventors: Enrique Gadea Ramos; Fabián SUAREZ GARCIA; Diego Cazorla Amoros; María Jorda Beneyto; Angel Linares Solano
Original assignee: Universidad De Alicante
Priority date: 2007-03-07
Filing date: 2008-03-06
Publication date: 2008-09-12
Also published as: ES2356418B2; ES2356418A1

Abstract

The invention relates to a piece of equipment that is used to perform a method for measuring the quantity of a supercritical fluid or gas absorbed by a sample, including a distributor (2) and a cell (4) for the sample, which can be communicated with one another. The inventive method comprises the following steps: the free volume of the sample cell (4) is calibrated by determining a mass balance for a calibration gas in the distributor/cell unit, the effective temperature of the sample cell is calculated by determining a mass balance for the calibration gas in the distributor/cell unit, and the quantity of supercritical fluid or gas sorbed by the sample is calculated by determining a mass balance for the supercritical fluid or gas in the distributor/cell unit, using a real gas equation in each of said steps in order to define the state of the supercritical fluid or gas.

Description

METHOD AND EQUIPMENT FOR THE MEASUREMENT OF SORTION ISOTHERMES TO HIGH PRESSURES OF GASES AND SUPERCRITICAL FLUIDS

The present invention relates to a method and equipment for the measurement of sorption isotherms at high pressures of gases and supercritical fluids, said equipment comprising: a distributor, at least one sample cell, a gas source, a vacuum source , a pressure sensor to measure the pressure of the distributor and the sample cell, and a set of pipes and shut-off valves that join the mentioned parts of the equipment together.

BACKGROUND

The interest in the realization of high pressure sorption isotherms arises not only from a fundamental point of view of the study of the sorption of gases at high pressures (in general in supercritical conditions), but from an applied point of view of the use of porous solids as systems for the capture and storage of gases and vapors at high pressures, as well as in different industrial processes that are carried out at high pressures [PG Menon, "Adsorption at high pressures", Chemical Reviews, 68, 277-293 (1968)]. In recent years, interest in the development of porous adsorbents capable of storing large amounts of gas and / or steam for different applications, such as: methane storage [D. Lozano-Castelló et al., "Advances in the study of methane storage in porous carbonaceous materials", Fuel, 81, 1777-1803 (2002)] or hydrogen [L. Schlapbach et al. "Hydrogen-storage materials for mobile applications", Nature, 414, 353-358 (2001)] in porous solids for later use as fuels in mobile applications. Both to determine the capacity of gas stored in a porous solid (amount of sorbed gas) and to carry out an exhaustive study of the variables that affect the sorption, it is necessary to carry out sorption isotherms under similar conditions (pressure and temperature) at which your application will take place.

The current equipment that allows the realization of isotherms of sorption of gases and vapors at different temperatures and that use a volumetric method for the determination of the quantity absorbed at each pressure, work at pressures below the saturation pressure of the sorbate, at the working temperature. These working pressures are usually of the order of atmospheric pressure. These equipment are described, among others, in the following US patents: US 3,850,040; US 4,566,326; US 4,972,730; US 5,239,482; US 5,360,743; US 5,637,810; US 5,895,841 and US 6,595,036, in Japanese patents: JP 4,230,831 and JP 4,140,643 and in Great Britain patent: GB 2,161, 607.

The basic scheme of the volumetric equipment described in the aforementioned patents are similar to each other: they all consist of a distributor of known volume provided with at least one pressure sensor, to which the inlet lines are joined by a series of shut-off valves of gases, of vacuum and at least one cell that contains the sample to be analyzed, which may or may not be provided with a pressure sensor. The patents referenced above have as a common objective the determination of the amount of gas absorbed by a solid, by a volumetric method, by the use of an analysis gas (usually Nitrogen, Argon and / or CO ₂ ) under subcritical conditions and reaching up to absolute pressures of the order of atmospheric pressure. The volumetric method for determining the amount of gas absorbed by a solid is based on the measurement of the variation of the pressure in a known volume due to the presence of the sample to be analyzed. For which, essentially, a calibrated volume (normally the volume of the distributor) is needed from which to dose a quantity of gas to the sample cell, also of known volume, and a pressure sensor that measures in the range of working pressures .

Most of the equipment defined in the aforementioned patents are designed to perform nitrogen adsorption-desorption isotherms at the temperature of liquid nitrogen (77K), whereby, the pressure sensors, valves, pipes and other components are suitable for working in the range of pressures from the vacuum to the saturation pressure of the liquid nitrogen at its normal boiling temperature, which is of the order of atmospheric, and to measure with sufficient precision the changes in the pressure due to the sorption of the gas by part of the sample, so that the maximum of the range of Measurement of the pressure sensors is of the order of atmospheric pressure. These equipment can be used to measure the sorption capacity of other gases (for example, Argon or CO ₂ ) of a solid, without modifying the design of the equipment. In the working conditions for which these equipments are designed, the ideal gas law for the description of the state of the same can be used, without incurring appreciable errors, this equation being used in the methods described in the patents above. cited. The differences observed in the described patents derive from the attempt to improve the accuracy of the measurements, the cost of the equipment and the analysis and the duration of the analysis.

Thus, the equipment described in US patents: US 3,850,040 and US 5,360,743, and in the Japanese patent: JP 4,140,643, do not have pressure meters in the sample cell (or cells), which entails a reduction in the cost of the equipment . However, in the case of equipment that has more than one sample cell (for example, the equipment described in US Patent 3,850,040) with meters only in the distributor, they make the duration of the analysis much longer.

On the other hand, US patents: US 4,566,326, US 4,972,730, US 5,239,482, US 5,895,841 and US 6,595,036, and the Japanese and Great Britain patent: JP 4,230,831 and GB 2,161, 607, respectively, describe equipment that has both pressure meters in the distributor as in the sample cell (or cells), with which a decrease in the analysis time is achieved, although the cost of the equipment increases. An examination of the equipment described in the aforementioned patents shows that two strategies have been followed to increase the precision of the pressure measurements (especially in the range of very low pressures): on the one hand there is the use of several sensors of absolute pressure that have different measuring ranges and, on the other hand, is the use of differential pressure sensors. Examples of the first option (several absolute pressure sensors of different ranges) are described in US patents: US 4,972,730 and US 5,637,810. In US patent 5,895,841 a device is described that has followed the second strategy to increase the precision in the measurements by using sensors differential pressure in the cell or sample cells. In this case it is necessary to have at least one reference cell.

Regarding the calibration of the volume of the distributor, it is carried out without taking into account that the temperature of the calibration cell may vary throughout this determination or, if this has been taken into account, the calibration cell has been thermostatized to a temperature different from that of the distributor, whereby a temperature gradient is established that prevents the measurement of the actual temperature of the calibration cell, which introduces an error. The error that this configuration produces is explained below in the analysis of the sample cell volume calculation.

As mentioned previously, the volumetric method for determining the amount of gas absorbed by a solid is based on the measurement of the variation of the pressure in a known volume due to the presence of the sample to be analyzed. Therefore, to obtain the amount that a certain solid is capable of retaining of a certain substance, at a certain pressure and temperature by means of the volumetric method it is necessary to know exactly the volume not occupied by the sample in the cell of the sample, which is called cell volume, empty volume, free volume or dead volume. Methods for calculating the cell volume with two different basic philosophies have been described in the literature: those in which values of different parameters are experimentally obtained by initially connecting the empty sample cell (US 5,360,743), and others (GB 2,161 , 607; US 5,895,841; US 3,850,040; US 6,595,036) in which the sample cell containing the sample to be analyzed is connected from the beginning. In both cases, the volume of the cell is calculated by expanding a gas from a known and calibrated volume, usually from the distributor. In the first option (procedure described in US 5,360,743) the volume of the empty cell is calculated. During the analysis (with sample within the cell of the sample) it is necessary to provide the mass of the sample, as well as its real density in order to be able to calculate the volume of the cell not occupied by the sample (free or dead volume) . In the second option (procedure described, for example, in the patents: GB 2,161, 607; US 5,895,841; US 3,850,040; US 6,595,036) the gas that is used for the calculation of the free volume must be a gas that is not adsorbed in the sample under the conditions of pressure and temperature in which the measurement is made for the calculation of the volume. In general, the gas used is Helium and the pressure at which the measurement is made is the lowest possible. The advantages of the first option (calibration of the empty cell) are the saving of gases, since it is not necessary to have a gas that is not adsorbed (He) for calibration, which can be done with the analysis gas. On the contrary, this method requires more time, as well as the need to know the real density of the sample in order to adequately calculate the free volume of the cell.

As described in the cited patents, the form of thermostatization of a fixed part of the sample cell, in which the solid to be analyzed is located, consists in submerging the sample cell in a bath, usually in liquid nitrogen (when the isotherms are carried out at 77 K, as is the most common case) and check that the level is constant, either by controlling the position of the bath or by adding liquid nitrogen as it evaporates. Therefore, a part of the sample cell is at the temperature of the bath (for example at 77 K) and another part is at another temperature, generally at room temperature. It is therefore not possible to directly measure the temperature of the cell, since it establishes a temperature gradient. Due to this, the experimental procedure followed by the patents (GB 2,161, 607; US 5,895,841; US 3,850,040; US 6,595,036) for the calculation of the free volume of sample cell consists of introducing a known amount of gas (generally He) into Ia cell at room temperature (in thermal equilibrium with the environment) and measure the pressure once it stabilizes, then introduce the sample cell in the bath at the study temperature (usually at 77 K) and, measuring the variation of pressure that occurs in the sample cell, thus obtaining a parameter that describes the final state of the gas. The parameter used in these patents to describe this state has been known as cold volume.

The basic reasoning is based on the idea that gases behave like ideal gases and that when the sample cell is immersed in the bathroom, it can be considered that a part of the volume of the sample cell is cooled to the bath temperature and that the other part stays at the initial temperature, keeping the amount of matter constant, so that the relationship between both volumes can be calculated as follows:

PV P V P V

Where Pj and P∑ are the initial and final pressure of the sample cell respectively, Ti and T _∑ are the initial and final temperature of the sample cell, respectively, and x is the ratio between the volume that is supposed to remain at Ia initial temperature when the sample cell is immersed in the bath and the total volume of the sample cell. Reorganizing the equation (1) you get:

PT - PT x = ^ ² ^ ¹ (1)

P ₂ - (T ₂ - T ₁ )

It is easy to demonstrate that when fulfilled (1), the pressure in the sample cell resulting from introducing two quantities of gas is equal to the sum of the pressures that those two quantities of gas would exert in the sample cell individually, which means that the parameter x remains constant throughout the experiment-and, therefore, is a good way to idealize the state of the sample cell. This reasoning is only true when the calibration gas is not absorbed in the sample and also behaves as an ideal gas. However, considering that the gas behaves as real gas, this is no longer true and, therefore, the parameter x is no longer a useful parameter for defining the state of the sample cell. Because the present patent describes a device capable of measuring sorption isotherms in a wide range of pressures and temperatures, in general, under conditions in which gases and supercritical fluids behave like real gases, it is not possible to use this parameter . Once the free volume of the sample cell and the parameter x (equation 1) is known, by measuring the pressure and with the application of a state equation, the amount of substance (moles of gas) in the interior of it. As indicated above, the cited patents describe equipment that is designed to work at pressures normally below atmospheric and under conditions in which the state equation can be used, without incurring appreciable errors. of the ideal gases to describe the balance of matter. Therefore, the amount of gas absorbed by the sample under study is determined as the balance of matter between the amount of gas added or removed from the sample cell and the amount of gas in the cell after the thermodynamic equilibrium is reached.

There are four major problems that are not solved by following the methodologies described in the patents cited above. The first two problems arise when it is intended to calculate the free or dead volume of the cell of the sample under conditions far from ideality. The third and fourth problem refers to the fact that the description of the state of the gases in the working conditions may not be properly carried out by means of the ideal gas law.

The problems are: 1) The variations of the temperature during the analysis, both in the distributor and in the at least one, sample cell and the volume that connects both, decrease the precision of the measurements of the quantity absorbed; 2) When a part of the cell of the sample is found at the analysis temperature and another part at another temperature (in general at room temperature), a temperature gradient is established, so that a temperature that defines cannot be directly measured exactly the state of the gas in the at least one sample cell. In addition, during the conduct of the experimental procedure, according to the temperature and pressure conditions at which the study is carried out, the gas used to calculate the temperature that defines the state of the gas in the at least one sample cell ( Classically, Helium has been used from the expansion of the same from the distributor, it can be retained by the sample, so that the amount of this gas present in the sample cell is greater than the measurement through the reading of his pressure; 3) The gases used throughout the experimental procedure can behave very far from the ideal, being necessary to take into account in the calculations the non-ideality of these; 4) No equation of state for real gases perfectly defines the state of a gas in any condition. DESCRIPTION OF THE INVENTION

If the solutions that can be provided to minimize errors in both the experimental procedure and the calculation method are analyzed in detail, the following conclusions are reached: a- The problem listed as 1) is not important only when the temperature of the sample cell , of the distributor, of the connection valves and their respective connections are identical, and equal to the gas temperature. Therefore, to eliminate this problem, the distributor assembly, the sample cell, the connection valves and the pipes should be thermostatized at the temperature at which it is desired to carry out the study. Although technically this is not a problem for temperatures in a range close to common ambient temperatures, it is technically unfeasible when the study temperature is outside this range. The usual (as shown in the patents described above) and technologically feasible, is to keep only part of the sample cell, which must necessarily include the specific area in which the sample is located, at the study temperature, being the the rest of the assembly at another temperature (usually at room temperature), so that the problem described in point (1) cannot be ignored.

So that this problem is not a source of error, the effect that the variations of the temperature will have on the equipment along the medium in which it is located during the duration of the experiment must be minimized, or know exactly how affect. For reasons of accuracy in the measurement, economy and reliability of the method and of the equipment, in addition to being technologically very simple to implement, the design of the equipment described in this patent tries to minimize these effects. For this there are two solutions; The first would be to place the equipment in an isothermal room, which would make the installation and operation cost of the equipment very high; The second is to thermostatize the distributor assembly at a certain temperature, thermostatize the part of the sample cell in which the solid to be analyzed is located, at the test temperature and decrease the volume that connects the distributor assembly with the area thermostated of The sample cell and thermally isolate it from the medium so that the internal temperature profile is not influenced by changes in the ambient temperature. b- As shown above, considering that the gas behaves like real gas, the methodology described in the cited patents cannot be applied (GB 2,161, 607; US 5,895,841; US 3,850,040; US 6,595,036) to define the state of the gas and, therefore, the parameter x (relation between the cell volume and the cold volume) is no longer a useful parameter for defining the state of the sample cell. In addition, if the gas that is being used to perform the cold volume measurement is retained in the sample when the sample cell is introduced into the bath at test temperature (which occurs even with helium at low temperatures and pressures of the order of Ia atmospheric pressure), the method described in the referenced patents cannot be used. It is therefore necessary to define another method to know exactly the amount of gas present in the sample cell, in a given experiment, by reading the pressure thereof. This methodology describes the methodology necessary to solve this problem, as will be shown later. c- It is necessary to use real gas state equations to describe the state of the gases used in this equipment because the working range, both pressure and temperature, is very wide, and the behavior of gases is only It is advisable to approximate it as ideal when they are at very low pressures and / or temperatures well above its critical temperature. d- It is very important to use the appropriate state equation in each case, depending on the gas being used and the specific pressure and temperature conditions, to calculate with the least possible error, which is impossible to avoid completely, matter balances. In the bibliography many state equations are proposed to describe the behavior of real gases, as well as studies on the reliability of some of them in the description of the behavior of a certain gas in a certain range of pressures and temperatures. Due to this inaccuracy, in order to obtain the volume of the distributor, as well as the free volume of the ₁ at least one, sample cell, it is advisable to repeat the method by which these values are obtained under different experimental conditions, averaging the error caused by the use of a certain state equation, as well as the experimental error.

This invention relates to a method and equipment by which is able to perform supercritical gas and fluid isotherms (He, N ₂ , Ar, CO ₂ , H ₂ , CH4, 0 ₃ He ₁ C ₄ H ₁₀ ,. ..). and to know the characteristics of a sample relative to the ability to sip said supercritical gases or fluids under conditions in which they may not be accurately described by means of the ideal gas law. These substances in a gaseous state can be used in the analysis both in subcritical, critical and supercritical conditions. The results are obtained with precision and the analysis can be carried out in a very wide range of pressures and temperatures ranging from vacuum to several thousand pressure atmospheres and from 4.2 K to several hundred Kelvin degrees of temperature, solving the aforementioned problems and Obtaining measurements with precision. According to one aspect of the invention, a volumetric method for measuring the amount of a gas or a supercritical fluid absorbed by a sample comprises the steps of: a) thermostatizing a gas distributor; b) introduce the sample into a cell communicable with said distributor; c) thermostatizing said sample cell at a temperature in which a calibration gas is not significantly absorbed by the sample; d) pressurize the distributor with said calibration gas; e) calibrate the free volume of the sample cell based on solving a material balance for the calibration gas in the distributor-cell assembly, using a real gas equation to define the state of the calibration gas; f) calculate the effective temperature of the sample cell based on solving a balance of matter for the calibration gas in the distributor-cell assembly, using a real gas equation to define the state of the calibration gas; g) produce a vacuum in the distributor-cell assembly; h) pressurize the distributor with the gas or supercritical fluid; i) calculate the amount of gas or supercritical fluid absorbed by the sample based on solving a balance of matter for the gas or supercritical fluid in the distributor-cell assembly, using a real gas equation to define the state of the gas or of the supercritical fluid.

Other particularities of the steps are defined in the claims. In accordance with another aspect of the invention, equipment is provided for carrying out said method. In one embodiment, said equipment comprises: a pressure sensor for the distributor;

- a shut-off valve disposed in the connection line of the sample cell with the distributor;

- a source of gas or supercritical fluid communicable with the distributor through a gas line provided with a shut-off valve; and - a vacuum source communicable with the distributor through a vacuum line provided with a shut-off valve; Y

- a system for the thermostatization of the distributor, the pressure sensor and said shut-off valves connectable to said distributor, which can delimit an isothermal zone containing these elements, while the sample cell is arranged outside said isothermal zone. Other embodiments are defined in the claims. The equipment accurately measures the amount of supercritical gas or fluid absorbed by a solid taking into account that the state of the analysis gas and / or the state of the calibration gas may not be accurately described by the ideal gas law, with The difference and improvement with respect to the equipment described above that the isotherms can be performed in a very wide range of pressures and temperatures.

The at least one pressure gauge used has a measuring range of at least the range of pressures to which the analysis is to be performed, the measurements being obtained in absolute value and with sufficient precision.

The at least ₁ , gas source or supercritical analysis fluid must supply the same at a pressure at least equal to the maximum analysis pressure. When an external source is not available to supply such pressure, The equipment has a compressor capable of compressing the gas or supercritical analysis fluid from the pressure supplied by the source to at least the maximum analysis pressure.

If a system is available to calibrate the volume of the distributor, it is housed in the thermostated area of the distributor, maintaining the assembly formed by the distributor, the calibration cell and the piece of known volume, as well as the pipes and valves that they connect to each other, at the same temperature throughout the calibration, avoiding, in this way, the errors that are made if the calibration cell is not thermostatted at the same temperature as the distributor.

To solve the problem described in the background section, problem (1), the distributor is thermostated at a temperature higher than the ambient temperature (typically 30 to 50 ⁰ C) with a control system capable of maintaining the temperature with a deviation standard less than a preset value. A part of the volume of the at least one sample cell, which necessarily includes the at least one sample to be analyzed, is thermostated at the analysis temperature by means of a system that guarantees that the thermostated volume is kept constant and with a variation in the temperature less than a preset value. The volume that connects the distributor with the thermostated zone of Ia, at least one, sample cell, is made using a conduit that is externally insulated. In this way it is achieved that there are no variations in the temperature of the distributor, of the part of the at least one sample cell that contains the sample and the volume that connects both that influence the accuracy of the analysis. To solve the problem described in the background section, problem (2), it is necessary to define a parameter that we will call Effective Cell Temperature, whose function is to offer a temperature value that describes the state of the gas in the at least one cell of sample in any condition of analysis, even in one that is far from the ideal. The methodology used consists of introducing a known quantity of the calibration gas into the at least one sample cell before it is thermostatized at the analysis temperature. Subsequently, at least one sample cell is thermostatized at the analysis temperature, recording the pressure reached in Ia, at least one, sample cell when no variation in pressure is observed. If there is no sorption of the calibration gas by the at least one, shown in the experimental conditions, the Effective Cell Temperature is that which resolves the balance of matter through the use of the law of real gases. In the event that the thermostatting Ia cell exists gas sorption calibration by Ia ₁ at least one sample in the analysis conditions, it is performed, at least one expansion of a known amount of calibration gas from the distributor. In this situation, the material balances cannot be resolved because the amount of calibration gas absorbed by the at least one sample is unknown. However, if it is assumed that the sorbed quantities can be defined by an equation, such as Henry's law, which is fulfilled in the initial section of any sorption isotherm, it is possible to solve the balance of matter through the use of Ia Law of Real Gases, obtaining the parameter of Effective Cell Temperature. To solve the problem described in the background section, problem (3), the law of real gases is used, instead of the ideal gas law, which is the one used in the aforementioned patents. The use of one law by the other does not imply a modification of the methods presented in the aforementioned patents in a trivial way, since as it has been seen, the calculation of the state of the at least one sample cell (cold volume) It cannot be defined by the method that was being used.

To solve the problem described in the background section, problem (4), for the calculation of the free cell volume, the known method of expanding the calibration gas from the distributor to the at least one sample cell is used. of different initial pressures in the distributor and averaging the values of free cell volume obtained, using, in this calculation the equation of state of the real gases. In the same way the method used for calibrating the volume of the distributor is repeated and the values obtained are averaged.

BRIEF DESCRIPTION OF THE FIGURES

The following components always appear in the numbered figures in the same way: 1 and 14.- Absolute pressure sensor 2.- Distributor

3, 5, 7, 8, 10, 15 and 17.- Shut-off valves 4.- Sample cell 6, 9, 11 and 16.- Restriction 12.- Temperature sensor 13.- Thermostated zone 18.- Cell calibrated 19.- Part of known volume 20.- Compression system

FIGURE 1: Schematic view of the equipment comprising: a distributor (2); a pressure sensor (1) in the distributor; at least one sample cell (4), which is connected by conduits to the distributor through a shut-off valve (3); a gas inlet with the restriction (11) and connected through the shut-off valve (10); a vacuum line with restriction (9) connected through the shut-off valve (8) and a vacuum line without restriction connected through the cut-off valve (7); a temperature sensor (12) in the distributor; and a thermostatted zone (13) comprising the distributor (2). FIGURE 2: Schematic view of the equipment described in Figure 1 which also has a pressure sensor (14) in Ia, at least one, sample cell 4. FIGURE 3: Schematic view of the equipment described in Figure 2 to which I have added a supercritical gas or fluid inlet attached to the distributor 2 through a shut-off valve (15) and a restriction (16). FIGURE 4: Schematic view of the equipment described in Figure 2 to which a calibration cell (18) has been added, in the thermostated area of the equipment (13), connected to the distributor (2) through a shut-off valve ( 17) and a piece of known volume (19). FIGURE 5: Schematic view of the equipment described in Figure 2 to which a gas compression system (20) has been added.

FIGURE 6: Graph of the sorption isotherm of excess nitrogen up to 200 bar of an active carbon. FIGURE 7: Graph of the sorption isotherm of excess hydrogen up to 200 bar of an active carbon.

FIGURE 8: Flowchart describing the working method of the equipment presented in Figure 1. FIGURE 9: Flowchart describing the working method of the equipment presented in Figure 2.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

This invention describes a method and equipment by which is able to perform supercritical gas and fluid isotherms (He, N ₂ , Ar, CO ₂ , H ₂ , CH ₄ , C ₃ H ₈ , C ₄ Hi ₀ ,. ..). and to know the characteristics of a sample relative to the ability to sip said supercritical gases or fluids under conditions in which they may not be accurately described by means of the ideal gas law. These substances in a gaseous state can be used in the analysis both in subcritical, critical and supercritical conditions. The results are obtained with precision and the analysis can be carried out in a very wide range of pressures and temperatures ranging from vacuum to several thousand atmospheres of pressure and from cryogenic temperatures to several hundred degrees. Two basic configurations of the equipment that present different working algorithms are described, on the one hand that in which only one pressure sensor is available, located in the distributor area (2) (configuration shown in Figure 1) and, by on the other hand, the one in which pressure sensors are available both in the distributor (2) and in the at least one, sample cell (4) (configuration shown in Figure 2). The first configuration is optimized when the equipment has a single sample cell, while the second is the result of optimizing the precision and duration of the analysis in a device that has more than one sample cell. In addition, variations of the two basic configurations are described, with more or less benefits that are not fundamental to implement the working method but which can provide the system with additional recommended functionalities. Although the equipment described here is automated, neither the processor nor the controllers or signal conditioners used for read the temperature and pressure measurements, as well as to send the control signals to the valves, pumps, resistors and in general any of the systems involved, in addition to performing the calculations necessary to implement the working algorithm. The terms controller and processor can be exchanged here and refer to electronic mechanisms capable of carrying out operations on electrical signals. The term "stable" here referred to the measurement of a sensor refers to the fact that the variation in the signal of the sensor meets certain pre-established requirements.

a) Preferred description of the invention with the configuration with a single pressure sensor in the distributor

Figure 8 shows the algorithm of operation of the equipment whose configuration is shown in Figure 1 and which only has a pressure sensor located in the distributor (2). Because in this configuration a pressure sensor is not available in the at least one sample cell (4), the measurements of the pressure in this cell must be made with the pressure sensor (1) located in the distributor (2), having to keep the valve (3) open. Looking at figure 1 and the flow chart of figure 8, the operation of the system begins by thermostating the distributor (2) at a pre-established temperature, indicated by the table (30) of figure 8, followed by the distributor calibration (2) , if necessary, indicated by the table (31) of figure 8. In this configuration the volume of the distributor (V _D ) is previously known. Before starting the analysis, the sample or samples to be analyzed are introduced into the at least one sample cell (4), indicated by the table (32) of Figure 8. It is emptied to a pre-established level and for a pre-established time. in Ia, at least one, sample cell (4), acting on the valves (3) and (8) and / or (7) and, if deemed necessary, it is possible to heat to a temperature greater than that of the analysis Ia At least one sample cell (4) to remove possible sipped species from its surface. Once this process is finished, at least one sample cell (4) is allowed to reach room temperature. Once the sample or samples to be analyzed have been prepared and, with the entire system at a pre-established vacuum level, the volume of Ia is calculated, at minus one, sample cell (4) and its effective temperature, indicated by the table (33) in figure 8.

First, the part of the at least one sample cell (4) containing the sample at a temperature at which the calibration gas used is not significantly retained by the sample is thermostatized. Although the gas used to perform this measurement can be any gas that meets the aforementioned condition, the use of helium is recommended. Next, the volume of the at least one sample cell (4) is calculated. The distributor (2) is pressurized with a certain amount of calibration gas, acting on the corresponding valves, and when the pressure measured by the sensor (1) is stable, its measurement and the temperature of the measured assembly (13) are recorded. by the sensor (12) (P ₁ and Ti, respectively); the valve (3) is then opened and the sensor measurement (1) is recorded when it is stable (P2); the valve (3) is closed and the sensor measurement (1) is recorded when it is stable and the temperature of the assembly (13) measured by the sensor (12) (P ₃ and T ₃ , respectively). Vacuum is made in the distributor (2) acting on the valves (5) and (8) and / or (7) of the vacuum line up to a certain vacuum level and this procedure is repeated for each of the sample cells (4) available to the team and containing sample to analyze.

The volume of the at least one sample cell (4) can be calculated by the following equations, which are derived from the real gas equation;

PV n _x = ^J ^ - (2)

¹ Z _x RT _x 'where, neither are the moles of gas initially present in the distributor (2), V ₀ is the volume of the distributor (2), Zi is the compressibility factor of the gas to Pi and Ti, which can be calculated through a real gas state equation;

where, n ₂ are the moles of gas present in the distributor assembly (2) and sample cell (4) once the valve (3) has been opened, Vc is the volume of the at least one sample cell (4), Tx is the temperature at which the distributor assembly (2) is located and the sample cell (4), which is being calibrated, and which cannot be measured experimentally, Z ₂ is the gas compressibility factor at P2 and T _x , which can be calculated through a real gas state equation;

P v Z ₂ RT _x where, n ₄ are the moles of gas present in the distributor (2) when the valve (3) is open, Z ₂ is the compressibility factor of the gas at P ₂ and Tx, which can be calculated through a real gas state equation;

P V n, = - ^ - (5)

where, n ₃ are the moles of gas present in the distributor (2) after having put this into communication with the at least one, sample cell (4) and closed the valve (3) and Z ₃ is the factor of gas compressibility at P ₃ and T ₃ , which can be calculated through a real gas state equation; Taking into account that n ₃ = n ₄ , the value of T _x can be obtained by means of the following expression:

T _x = T ₃ ^ - (6)

* 3 ^Z 2

Because Z ₂ is a function of T _x , this is calculated by solving the previous equation by an iterative method. Taking into account that:

«1 =« 2 ( ⁷ ) Substituting (2), (3) and (6) into (7) and reorganizing, you get:

Obtaining the volume of Ia, at least one, sample cell (4). In order to eliminate the possible experimental errors that could have been committed as well as those derived from the non-accuracy of the state equation used in the calculations, it is convenient to repeat this measurement several times, starting from any initial pressure in the at least one cell of sample (4) and choosing an average of these volumes calculated as definitive value.

Next, the effective temperature of the assembly formed by the distributor (2) and Ia, at least one, sample cell (4), which we will now call "assembly", is calculated. A certain gas pressure is introduced in the distributor (2) and in the sample cell (4), acting on the valve (10) of the calibration gas line and opening the valve (3), the measurement of the sensor (1) when it is stable (Psi) - Then the part of the cell containing the sample is thermostatized at the analysis temperature and the sensor measurement (1) is recorded when it is stable (Ps2) -

The moles of calibration gas present in the assembly initially (nsi) can be calculated by:

"^" Z ₁ IiT ₁ ⁽⁹⁾ where, T _x is the temperature obtained by equation (6) and Zi is the compressibility factor of the calibration gas calculated with an equation of real gas state at P _S i and T _x .

The moles of calibration gas that are not absorbed after bringing at least one sample cell (4) to the analysis temperature (ns2) are calculated by:

n _S2 = ^Ps ^ ^{Vc + V} ^ (10)

⁵² Z ₂ RT _E where, T _E is the Effective Temperature of the set and Z ₂ is the compressibility factor of the calibration gas calculated with a real gas state equation at Ps ₂ and T _E. The moles of sorbed calibration gas can be obtained by n _adsl = n _sι - n _S2 (11) where, n _ad if it is the amount of calibration gas retained by the sample. The valve (3) is closed and the distributor (2) is pressurized at a certain pressure with the calibration gas acting on the valve (10) and the sensor measurement (1) is recorded when it is stable (P _m i) and The measurement of the sensor (12) (T _m i), the moles of calibration gas in the distributor (2) (n _m1 ) are obtained by PV ».. = - ^ - ⁽¹²⁾ where, Z ₃ is the compressibility factor of the gas at P _m i and T _m1 , which can be calculated through a real gas state equation. Now, the valve (3) is opened and the sensor measurement (1) is recorded when it is stable (Ps ₃ ). The moles of free calibration gas in the set (ns ₃ ):

The amount of calibration gas retained by the sample in this new stage

(n _a ds2) can be expressed as: yn _ad s ₂ ^{= n} s _{2 v} l _v + n _ml - n _S3 (14)

"c +" D To obtain the effective temperature (T _E ) of the set it is necessary to solve equations 9-14. Because this system of equations is undetermined, the assumption is introduced that the sorption of the gas calibrated by the sample at the analysis temperature is governed by an equation that describes an isotherm of sorption, as for example, by the law of Henry (that is: the amount of sorbed gas is proportional to the pressure), achieving that these equations can be solved.

Introduced the assumption is true if the PS2 and PS ₃ pressures are within Ia of Ia sorption isotherm calibrated gas whereto the law met Henry. In the case of using another equation to relate the amount of sorbe calibrated gas according to the pressure, it will be necessary to verify that the measurements made in this step effectively comply with the assumption made. Taking this into account, you can write: n _ads = K - P (15) where, n _ad s is the amount of calibration gas retained by the sample, P is the pressure in the at least one sample cell (4 ) and K is a constant. This equation is derived

n _adsX = K - P _S2 (16)

Substituting (10) in (11) you get

substituting (10), (12) and (13) in (14) you get: pypyp (Y ₊ γ \

_ ^r S2 ^v C. ^r mV D ^r S3 VC ^ ^and D / C \ Q) a ^ds2 Z ₂ RT _E Z ₃ RT _1n Z ₄ RT _E

the system of equations formed by (16), (17), (18) and (19) form a given system of equations, whose solution is

_P ^r PS2 V ^r D rS3 (V _Y D ₊ ⁺ r ^V C / A ^j ₇ __J y _] _

T _ε V ^ ^Z 2 ' ^Z - "4 J ^Z ' = 0 (20)

Because Z ₂ and Z ₄ are a function of TE, it is necessary to use an iterative method to obtain the effective set temperature (TE) that is recorded and accessible by the processor for when necessary. This process is carried out in all the sample cells (4) available to the system and that contain sample to be analyzed.

Next, the assembly is emptied as shown in the table (34) of figure 8, for which the valves (3), (5) and (7) and / or (8) are operated until reaching a certain vacuum, closing all these valves. It is checked if the end condition has been reached (table (35) of figure 8), in the event that such condition has not been reached, the distributor (2), represented in table (36) of figure 8, is pressurized, with a certain gas pressure analysis, acting on the valve (10) (figure 1). A source of analysis gas with a pressure greater than the maximum required for the analysis must be available. The measurement of the sensor (1) is recorded when it is stable and of the sensor (12). Next, the valve (3) is opened (frame (37) of figure 8). The cell goes to the "not free" state (table (38) of figure 8), the device waits for that the pre-established condition of sorption balance is fulfilled (table (39) of figure 8). When the sample cell (4) in the "non-free" state fulfills the pre-established condition of sorption equilibrium, the measurement of the sensor (1) (table (40) in Figure 8) is recorded and goes to the "free" state ( table (41) of figure 8). With the recorded values, the amount absorbed is calculated by solving the corresponding material balances using a real gas state equation in this sample cell (4).

This process is repeated in all the sample cells (4) that contain the sample to be analyzed until the end condition (table (35) of Figure 8) is reached in all of them.

The end condition represented in the table (35) of Figure 8 can be defined by the user as appropriate, although it is usually defined as a certain maximum equilibrium pressure in each of the sample cells (4). When the end condition is fulfilled in all the sample cells (4) that contain the sample to be analyzed, the analysis ends (Table (42) of Figure 8).

The system shown in Figure 1 is optimized for a device that has a single sample cell (4), the analysis execution time being much more extended when there is more than one sample cell (4) compared to the equipment schematized in Figure 2, which has a pressure sensor (14) in Ia, at least one, sample cell (4).

b) Preferred description of the invention with the configuration with pressure sensor in the distributor and in the at least one sample cell. Figure 2 shows a configuration of the equipment with the minimum components that differs from that shown in Figure 1 in that it has a pressure sensor (14) in Ia, at least one, sample cell (4). The operation algorithm of the equipment represented in Figure 2 is shown in Figure 9. Looking at Figure 2 and in the flow chart of Figure 9, the operation of the system begins, as for the equipment presented in Figure 1 , thermostatizing the distributor (2) at a preset temperature, indicated by the table (50) in figure 9, followed by the distributor calibration (2), if necessary, indicated by the table (51) of figure 9. In this configuration the volume of the distributor (V ₀ ) is previously known.

The sample or samples to be analyzed are introduced in Ia, at least one, sample cell (4), (table (52) of Figure 9) and are prepared acting in an identical manner to that described above for the system of Figure 1.

Next, the volume of the at least one sample cell (4) and its effective temperature is calculated, indicated by the table (53) of figure 9. A part of the at least one cell of the thermostat is thermostatized. sample (4) containing the sample at a temperature at which the calibration gas used is not adsorbed significantly by the sample. Although the gas used to perform this measurement can be any gas that meets the aforementioned condition, the use of helium is recommended

Next, the valves that were open are closed, the valve (3) of one of the at least one of the sample cells (4) is opened and it is pressurized with calibration gas to a preset pressure acting on the valve (10 ). The measurement of the sensor (1) (P _A ) is recorded when it is stable. Then the valve (3) is closed and the measurement of the sensor (1) (P _B ) is recorded when it is stable and the measurement of the sensor (12) (TB) and the measurement of the sensor (14) (Pc) when it is stable .

where, n _A are the moles of gas present in the distributor set (2) and sample cell (4), Vc is the volume of the at least one sample cell (4), Tx is the temperature at which there is the distributor set (2) and the sample cell (4), which cannot be measured experimentally, Zi is the compressibility factor of the gas at PA and T _x , which can be calculated through a state equation of real gas and R is the universal gas constant;

where, n _B are the moles of gas present in the distributor 2 when the valve (3) is closed, Z ₂ is the compressibility factor of the gas at PB and T _B , which can be calculated through a state equation of real gas; PV n _c = ^cVc (23)

where, nc are the moles of gas present in the sample cell (4) after closing the valve (3), T _am b is the temperature at which the sample cell (4) is located, which cannot be measured experimentally and Z ₃ is the compressibility factor of the gas at P _c and T _at m _b , which can be calculated through a real gas state equation; Taking into account that:

n _A ^V ° = n _B (24)

V _D + V _C ^B

The value of T _amb can be obtained by means of the following expression:

T _amb = T _B ^~ r (26)

Because Z ₃ is a function of T _{amb, the} previous equation is solved by an iterative method.

Next, the volume of the at least one sample cell (4) at T _a m _b> is calculated to which it is known that the solid is not able to retain the calibration gas. The distributor (2) is pressurized with a certain amount of calibration gas, acting on the valve (10), and when the pressure measured by the sensor (1) is stable, its measurement and the temperature of the assembly (13) are recorded. ) measured by the sensor (12) (Pi and T ₁ , respectively); the measurement of the sensor (14) is recorded when it is stable (P ₂ ); then the valve (3) is opened and after a predetermined time it is closed again; when, both the pressure measured by the sensor (1), and the pressure measured by the sensor (14) are stable, the measurement of the sensor (1) and the temperature of the assembly (13) measured by the sensor (12) are recorded. (P ₃ and T ₃ , respectively), as well as the measurement of the sensor (14) (P4) of the at least one sample cell (4). This procedure is repeated for each of the sample cells (4) available to the team and containing sample to be analyzed. The volume of the at least one sample cell (4) can be calculated by the following equations, which are derived from the real gas equation;

PV n _x = - ^^ - (27)

where, neither are the moles of gas initially present in the distributor (2), V ₀ is the volume of the distributor (2), Zi is the compressibility factor of the gas at Pi and T ₁ , which can be calculated through a real gas state equation; pvn ₂ = ^{2 C} (28)

Z ₂ RT _amb where, n2 are the moles of gas initially present in Ia, at least one, sample cell (4), V _c is the volume of the ₁ at least one, sample cell (4), Z ₂ is the compressibility factor of the gas at P ₂ and T _amb , which can be calculated through a real gas state equation and R is the universal gas constant;

PVU ₁ = - ^ - (29)

³ Z, RT, where, n ₃ are the moles of gas present in the distributor (2) after having put this into communication with the at least one sample cell (4) and Z ₃ is the compressibility factor of the gas at P ₃ and T ₃ , which can be calculated through a real gas state equation; pv

At ₄ = ^ ^C (30)

⁴ Z ₄ RT _amb where, n ₄ are the moles of gas present in the at least one sample cell (4) after having put this in communication with the distributor (2) and Z ₄ is the compressibility factor of the gas at P ₄ and T _a m _b , which can be calculated through a real gas state equation. By means of a material balance, you get: n _x + n ₂ = « ₃ + n ₄ (31) Substituting (27), (28), (29) and (30) into (31) and reorganizing, you get:

Obtaining the volume of Ia, at least one, sample cell (4). To eliminate the possible experimental errors that could have been committed, as well as those derived from the non-accuracy of the state equation used in the calculations, it is convenient to repeat this measurement several times, starting from any initial pressure in the at least one cell of sample (4) and choosing an average of these volumes calculated as definitive value. Next, the effective temperature of the at least one sample cell (4) is calculated for which a certain calibration gas pressure is introduced into it, acting on the valve (10) and opening the valve (3) , which closes when said pressure is reached and the measurement of the sensor (14) is recorded when it is stable (Peí) - Then the part of the cell containing the sample of the at least one sample cell is thermostatized. 4) at the analysis temperature and the sensor measurement (14) is recorded when it is stable (Pc ₂ ) -

The moles of calibration gas initially present in Ia, at least one, sample cell (4) (nc-i) can be calculated by: _W P Vc_ ₍₃₃₎ z _λ RT _amb where, Z ^ is the compressibility factor of the calibration gas calculated with a real gas state equation at Pa and T _amb .

The moles of calibration gas that are not absorbed after bringing the at least one sample cell (4) to the analysis temperature (n _C 2) are calculated by:

where, T _E is the Effective Temperature of the at least one of the sample cell (4) and Z ₂ is the compressibility factor of the calibrated gas calculated with a real gas state equation at Pc2 and T _E. The moles of calibration gas absorbed in the at least one sample cell (4) can be obtained by

« _O ώl =« Cl - «C2 (35) where, n _ads i is the amount of calibration gas retained by the sample. The distributor (2) is then pressurized at a certain pressure with the calibration gas acting on the valve (10) and the sensor measurement (1) is recorded when it is stable (P _m i) and the sensor measurement (12 ) (T _m i), the moles of calibration gas in the distributor (2) (n _m i) are obtained by

PV n = ^{mλ D} (36)

^Z 3 ^KI m \ where, Z ₃ is the compressibility factor of the gas at P _m i and T _m i, which can be calculated through a real gas state equation. Now, the valve (3) is opened and closed after a certain time. The measurement of the sensor (1) is recorded when it is stable (P _m2 ) and the measurement of the sensor (12) (T _m2 ) as well as the measurement of the sensor (14) when it is stable (Pc ₃ ) - The moles of gas calibrated in the distributor (n _m2 ) and in Ia, at least one, sample cell (4) (nc ₃ ) are obtained by the following equations:

"„ 2 = ——- (37)

Z ₄ RT _n m2

P V

»C3 = ^~~ (38)

"Z ₅ RT _E

The amount of calibration gas retained by the sample in this new stage (n _ad s2) can be expressed as: nads2 = ⁿ C2 + "mi ~" m2 ~ »C3 (39)

To obtain the effective temperature (TE) of Ia, at least one, sample cell (4), it is necessary to solve equations 33-39. Because this system of equations is undetermined, as for the equipment represented in Figure 1, the same assumption is introduced (the sorption of the gas calibrated by the sample at the analysis temperature is governed by an equation that describes a isotherm of sorption, as for example, by Henry's law) and following an analogous reasoning it is obtained that:

«„ *, = K - P ₀₂ (40) n _ads2 = K - (P _Ci - P _C2 ) (41) substituting (34) in (35) you get

« _Flώl =« α - ^ # - (42) substituting (34), (36), (37) and (38) in (39) you get:

_ ^I P C2V ^r C, ^Á P mVV D _ ^λ P m2V ^v D _ * P C3V ^r C (42λ to ^dsl Z ₂ RT _E Z ₃ RT _ml Z ₄ RT _m2 Z ₅ RT _E

the system of equations formed by (40), (41), (42) and (43) form a given system of equations, whose solution is

Because Z ₅ and Z ₂ are a function of T _E , it is necessary to use an iterative method to obtain the Effective Temperature of the at least one sample cell (4) (TE) that is registered and accessible by the processor to when necessary. This process is carried out in all the sample cells (4) available to the system and that contain sample to be analyzed.

Next, a vacuum is carried out both in the at least one sample cell (4) and in the distributor (2), as shown in the table (54) of Figure 9, for which the valves are operated. (3), (5) and (7) and / or (8) until a certain vacuum is reached, closing all these valves. As shown in table (55) of figure 9, the system checks if there is any free cell, that is, if there is any sample cell (4) that is not waiting for the sorption balance and in case there is none He waits until someone is released. If there are free cells, it is checked if the end condition has been reached (table (56) of figure 9), in the case that such condition has not been reached, the distributor (2), represented in the table (57) is pressurized ) of Figure 9, with a certain gas pressure analysis, acting on the valve (10). It must have an analysis gas source with pressure greater than Ia maximum required for analysis. The measurement of the sensor (1) is recorded when it is stable and of the sensor (12). Then the valve (3) is opened and closed after a certain time (table (58) of figure 9). The cell goes to the "non-free" state (table (59) of figure 9), at this point the equipment is, on the one hand, waiting for the pre-established condition of sorption balance to be fulfilled (table (60) of figure 9) and, on the other hand, repeat the process shown in the tables (56) to (59) of figure 9 in the other sample cells (4) with the state of "free" until the end condition (table ( 56) of Figure 9). When the sample cell (4) in the "non-free" state fulfills the pre-established condition of sorption equilibrium, the measurement of the sensor (14) (table (61) of Figure 9) is recorded and goes to the "free" state ( table (62) of figure 9). With the recorded values, the amount absorbed is calculated by solving the corresponding material balances using a real gas state equation in this sample cell (4) The end condition represented in table (56) of Figure 9 can be defined by the user as appropriate, although it is usually defined as a certain maximum equilibrium pressure in each of the sample cells (4). When the end condition is met in all the sample cells (4) that contain the sample to be analyzed, the analysis ends (Table (63) of Figure 9).

c) Preferred description of the invention with the configuration with pressure sensor in the distributor and in Ia, at least one, sample cell and, at least another, gas inlet. In Figure 3 a configuration of the equipment equal to that represented in Figure 2 is shown, to which an additional gas inlet composed of the shut-off valve (15) and the restriction (16) that enables the input has been added from another gas to the distributor (2). With this configuration, the equipment is prepared to work with an analysis gas and a calibration gas, which may be different. For this, any of the gas inlet lines must be joined to any of the gas sources. The working method of the equipment presented in Figure 3 is identical to that described in section b) with the only difference that to perform the pressurization of the Distributor (2) with calibration gas will act on the corresponding shut-off valve (10 or 15) of the line connected to the source of calibration gas and similarly when it is required to pressurize the distributor (2) with analysis gas. Although to this configuration represented in Figure 3 only one additional gas inlet line has been added with respect to the equipment represented in Figure 2, there is no limitation for the number of inlet gas lines to be installed.

All these arguments have been shown on the equipment represented in Figure 2, although they are naturally applicable to the system represented in Figure 1.

d) Preferred description of the invention with the configuration with pressure sensor in the distributor and in the at least one, sample cell and a distributor volume calibration system.

Figure 4 shows a device with the same configuration as that shown in Figure 2 to which a system has been added for in situ calibration of the volume of the distributor (2) consisting of a calibration cell (18) attached to the distributor through a shut-off valve (17) and a piece of known volume (19). This calibration system is located in the thermostatted zone (13) of the distributor (2).

Having this system of calibration in the equipment allows to be able to measure in situ the volume of the distributor (2) with precision and to be able to perform periodic calibrations of the volume of the distributor (2) as well as after any repair or modification made on the equipment that may have been imply a change in the volume of the distributor (2).

The location of the distributor volume calibration system (2) within the thermostated zone (13) is essential to increase the precision in the measure because this determination is made at a homogeneous, constant and known temperature, avoiding errors in the measurement of the pressure and the determination of the compressibility factor of the calibration gas. Looking at the configuration represented in Figure 4, the procedure for calibrating the distributor (2) is performed as follows. It becomes empty in the distributor (2) and in the calibration cell (18) opening the valves (17) and (8) and / or (7) of the vacuum line to a certain vacuum level. The valves (17), (7) and (8) are closed and the distributor (2) is pressurized to a certain pressure, measured with the sensor (1), acting on the shut-off valve of a gas inlet line. When the measurement of the pressure sensor (1) is stable, the measurement of this sensor and the temperature of the assembly (13) are recorded by the sensor (12). The valve (17) is then opened and when the measurement of the sensor (1) is stable, its measurement and the temperature of the assembly (13) are recorded by the sensor (12). Next, the piece of known volume (19) is introduced into the calibration cell (18) and the same process is repeated. With these recorded measurements and using an appropriate real gas state equation, a balance of trivial matter is resolved and the volume of the distributor (2) is obtained. This calibration process of the distributor (2) can be repeated as many times as is considered, and the volume value of the distributor (2) obtained can be averaged, minimizing the possible experimental errors that could have been committed as well as those derived from the non-accuracy of the equation of state used in the calculations. The volume value of the distributor (2) (V _D ) obtained is recorded in such a way that it is accessible to the processor when necessary. The work method of the equipment represented in Figure 4 is identical to that described in section b) with the only difference that the volume of the distributor (2) is not assumed previously known, but is measured in situ. All these arguments have been shown on the equipment represented in Figure 2, although they are naturally applicable to the system represented in Figure 1.

e) Preferred description of the invention with the configuration with pressure sensor in the distributor and in the at least one, sample cell and a gas compression system. Figure 5 shows a device with the same configuration as that shown in Figure 2 to which a gas compression system (20) has been added. Having a gas compression system (20) allows the analysis to be carried out when an analysis gas source is not available at a pressure higher than the maximum required for the analysis. Normally gas sources are usually commercial pressure gas bottles, the maximum pressure of which is around 200 atmospheres. This limits the maximum working pressure to less than 200 atmospheres and forces the gas bottle to change without consuming an important part of its capacity, since as soon as there is a small gas consumption, the pressure of this gas decreases below 200 atmospheres, making the process more expensive and reducing flexibility to the team's work. The working method of the equipment presented in Figure 5 is identical to that described in section b) with the only difference that to perform the pressurization of the distributor (2), the compression system (20) will be operated when a higher pressure is required to Ia supplied by the gas source. This compression system can be installed on any gas inlet line.

All these arguments have been shown on the equipment represented in Figure 2, although they are naturally applicable to the system represented in Figure 1

f) Preferred description of the invention with the configuration with pressure sensor in the distributor and in at least one, sample cell and / or, at least another, gas inlet and / or a distributor volume calibration system and / or a gas compression system.

The equipment described in Figures 3 to 5 provide additional functionality to that represented in Figure 2 for the realization of the gas sorption or supercritical fluid isotherms that follow the same work methodology described in section b). Any equipment that is a combination of these functionalities, as well as any other functionality that is not essential for the working method is also possible and would be included within the object of this patent.

All these arguments have been shown on the equipment represented in Figure 2, although they are naturally applicable to the system represented in Figure 1. Figures 6 and 7 show, by way of example, the sorption isotherms of excess nitrogen (figure 6) and hydrogen (figure 7) at 298 K and up to 200 bar of final pressure in an activated carbon using equipment such as the one indicated in this section and following the procedure indicated in figure 9. The present patent wants to protect two basic configurations of the equipment, on the one hand that in which only one pressure sensor is available, located in the area of the distributor and, on the other, the one in which pressure sensors are available both in the distributor and in Ia, at least one, sample cell (figures 1 and 2, respectively). Variations of the basic configurations have also been shown.

Although the invention has been illustrated and described here based on specific configurations and procedures, in no way has the attempt been made to delimit the invention to the details shown, since small variations in both the configuration of the equipment and the procedures, for example, by means of which the free volume and the effective temperature of the at least one sample cell are obtained, as well as that of the calculation of the sorbed quantity, can also be valid without modifying the spirit of the invention.

Claims

1. Volumetric method for measuring the amount of a gas or a supercritical fluid absorbed at high pressures by a sample, comprising the steps of: a) thermostatizing a gas distributor (2); b) insert the sample into a cell (4) communicable with said distributor

(2); c) thermostatizing said sample cell (4) at a temperature in which a calibration gas is not significantly absorbed by the sample; d) pressurize the distributor (2) with said calibration gas; e) calibrate the free volume of the sample cell (4) based on solving a balance of matter for the calibration gas in the distributor-cell assembly, using a real gas equation to define the state of the calibration gas; f) calculate the effective temperature of the sample cell (4) based on solving a balance of matter for the calibration gas in the distributor-cell assembly, using a real gas equation to define the state of the calibration gas and having consider your possible sorption; g) produce a vacuum in the distributor-cell assembly; h) pressurize the distributor (2) with the gas or supercritical fluid; i) calculate the amount of gas or supercritical fluid absorbed by the sample based on solving a balance of matter for the gas or supercritical fluid in the distributor-cell assembly, using a real gas equation to define the state of the gas or of the supercritical fluid.

2. Method according to claim 1, wherein, in step (c), a part of the volume of the sample cell (4), comprising said sample, is thermostated at a temperature different from that of the rest of the cell .

3. Method according to claim 1 or 2, wherein, when there is sorption of the calibration gas, in step (f) an additional equation defining said sorption is used.

Method according to any one of the preceding claims, in which a calibration cell (18) with a piece of known volume (19) is used to calibrate the volume of the distributor (2), based on solving a balance of matter.

5. Method according to any of the preceding claims, wherein before stage (f) the distributor (2) is pressurized with the calibration gas and the sample cell (4) is thermostated at an analysis temperature.

Method according to any one of the preceding claims, in which several sample cells (4) are used.

Method according to any one of the preceding claims, in which several different real gas equations are used to define the state of the gases or the supercritical fluid in at least one of the stages.

8. Equipment for carrying out a method according to any of the preceding claims.

9. Equipment according to claim 8, comprising:

- a pressure sensor (1) for the distributor (2);

- a shut-off valve (3) disposed in the connection line of the sample cell (4) with the distributor (2);

- a source of gas or supercritical fluid communicable with the distributor (2) through a gas line provided with a shut-off valve (10);

- a vacuum source communicable with the distributor (2) through a vacuum line provided with a shut-off valve (8); Y

- a system for the thermostatization of the distributor (2), the pressure sensor (1) and said shut-off valves connectable to said distributor, which delimits the thermostatted zone (13) that contains these elements.

10. Equipment according to claim 9, comprising an additional vacuum line provided with a shut-off valve (7) disposed within the thermostated zone (13).

11. Equipment according to any of claims 8 to 10, wherein the sample cell (4) is provided with a pressure sensor (14) disposed within the thermostatted zone (13).

12. Equipment according to any of claims 8 to 11, comprising at least one additional source of gas or supercritical fluid communicable with the distributor (2) through a gas line provided with a shut-off valve (15) disposed within The thermostatted zone (13).

13. Equipment according to any of claims 8 to 12, comprising a calibration cell (18) for a piece of known volume (19) communicable with the distributor (2) through a shut-off valve (17), so that both the calibration cell (18) and its shut-off valve (17) are disposed within the thermostatted zone (13).

14. Equipment according to any of claims 8 to 13, comprising a gas compression system (20) for pressurizing the gases or supercritical fluid.

15. Equipment according to any of claims 8 to 14, comprising several sample cells (4) connectable to the distributor (2) through corresponding shut-off valves (3) disposed within the thermostated zone (13).