DE102013015342A1 - Dynamic gravimetric method for determining the amount of gases or vapors dissolved in dense or porous solids. - Google Patents

Abstract

A method of determining the amount of a gas or vapor dissolved or adsorbed in a dense or porous solid by simultaneously measuring the apparent weight of the gas-laden solid contained in a patented working space, the sorption resonator, by means of a balance, and the Frequency of small, adiabatic vibrations of a specimen in the sorptive gas of the sorption resonator (reversal of the Rüchhardt experiment). In addition to the sorbed gas quantity, the volume of the gas-laden, rigid or swelling solid in the sorption resonator can also be determined. These data are needed for the exact design and operation of technical sorption processes. Examples of such processes are adsorptive separation and purification processes for air and industrial gases, adsorption refrigeration and heat pump processes and characterization processes for novel porous materials.

Description

Technical area

• a) Feststoffe zu charakterisieren, d. h. ihre mit der Gaslöslichkeit verbundenen technischen Eigenschaften beurteilen zu können sowie Kenntnisse über ihre möglicherweise vorhandene Porosität bzw. ihr inneres Porensystem zu erlangen und/oder
• b) Basisdaten zur Berechnung und technischen Auslegung adsorptiver Gastrenn- oder Speicherverfahren wie z. B. Luftzerlegungsverfahren, Verfahren zur Rückgewinnung von Lösemitteln oder adsorptive Abluftreinigungsverfahren zur Verfügung zu haben.

The invention consists in a method for measuring the amount of absorbed in any solid or adsorbed on its outer or inner surface gas or gas mixture according to the preamble of the claim. The knowledge of this approximately related to the mass unit of the solid amount of gas is necessary or advantageous to

• (a) to characterize solids, that is, to assess their gas solubility related technical properties and to obtain knowledge of their potential porosity or intrinsic pore system; and / or
• b) Basic data for the calculation and technical design of adsorptive gas separation or storage processes such. As air separation processes, methods for the recovery of solvents or adsorptive air purification method to have available.

Problem / state of the art

All solids absorb gas molecules from their environment. With dense materials one speaks of absorption or solubility of the gas in the solid. In the case of surface-active and / or porous substances such as activated carbons, zeolites, porous polymers, etc., this is referred to as adsorption of the gas [1-4]. The mass of the adsorbed gas is called Adsorbatmasse. The different degrees of binding of different gas molecules to the molecules / atoms of the solid (physisorption, chemisorption) is the basis for numerous technical processes for the decomposition or purification of gases, for the conditioning of the solid, and many others [3, 5-8]. For the technical design of these methods, the amount of gas (adsorptive) is usually required, which dissolves in a predetermined amount of the solid (adsorbent) at a known pressure and temperature of the gas or is adsorbed in it. This so-called. Adsorbatmasse can not yet hypothesis-free with the currently known experimental measurement methods, d. H. can not be determined without additional approximate assumptions [1]. Even a calculation by molecular-statistical methods (Probability Density Functional Theory (PDFT)) is only approximately and not exactly possible today [9].

An exception, however, is the one recently made by the author in the patent Az. 10 2013 012 387.9 reported dynamic-volumetric measurement methods for gas adsorbates [10]. However, the dynamic gravimetric measuring method proposed in the present document has the advantage to be faster and also more accurate compared to that which will be described below.

The methods most commonly used today for scientific and industrial purposes for the determination of adsorbate mass, volumetry or manometry and gravimetry [1], require the use of at least one additional hypothesis in addition to the actual measurement. As such, the so-called helium hypothesis is generally used, which states that helium is not adsorbed by the considered substance at room temperature and low gas pressure, or that the adsorbed helium mass is neglected or can be set equal to zero. A detailed description of these facts is u. a. in [1, 2] and [9].

Presentation of the invention

To determine the mass of gases dissolved in solids, the so-called. Adsorbatmasse, without further additional hypotheses such. As the helium hypothesis, the invention proposes to provide the known gravimetric measuring method [1, 2, 6-8] with a device that allows to investigate small damped oscillating amounts of Sorptivgaskörpers that surrounds the solid-sorbate system and with He is in thermodynamic equilibrium. ( Reversal of the experiments according to Rüchhardt, 1929, and Rinkel, 1929 , [11, 12]). Such a plant is schematically in 1 . 2 shown. It consists of a microbalance - preferably a magnetic levitation balance, Rubotherm GmbH, Bochum ( 1 ) - whose suspended part is in one with measuring or sorptive gas ( 16 ) filled sorption space (volume V _AC ) ( 2 ), which also serves as a sorption resonator, is located.

The sorption space ( 2 ) is by a vertical riser ( 3 ), which has a shut-off valve ( 4 ), a storage device ( 5 ) and a cylindrical oscillating body ( 6 ) contains. The adsorption space ( 2 ) also contains temperature sensors ( 8th ) and the pressure ( 9 ) of the sorptive gas ( 16 ) as well as connections to supply lines for filling ( 10 ) or emptying and evacuating ( 11 ). The system is advantageously placed in a thermostatic bath (not shown) to ensure the same and constant thermal conditions throughout her.

The riser ( 3 ) with the oscillating body (cylinder) ( 6 ) is more detailed in 2 shown. It contains, according to Flammersfeld [15], a small opening which is separated from the oscillating body ( 6 ) periodically covered by vibrations, ie closed or released again. The vibrations of the adsorptive gas body and thus of the oscillating body ( 6 ) are caused by the fact that after adjusting the thermodynamic equilibrium between a suspended on the balance and saturated with gas solid (adsorbent material ( 14 ) and adsorbate ( 13 )) a very small gas flow over the gas supply ( 10 ) is still supplied to the system. This minimizes the pressure of the gas. The oscillating body ( 6 ), first the valve ( 18 ) has closed, something rises, thus gives the valve ( 18 ) whereby a small amount of gas escapes, the gas pressure drops slightly and the float moves back or in the following small oscillations (angular frequency ω) performs an equilibrium position. From the measured angular frequency ω and substance data of the sorptive gas, the volume V ^{f of} the gas body can be calculated. This is the key to determining which in the adsorbent ( 14 ) dissolved adsorbate mass ( 13 ) as will be explained below.

experiment

For determination of in a solid state ( 14 ) dissolved or adsorbed gas quantity ( 13 ) is in the pilot plant after 1 . 2 following experiment:
At the beginning, a known mass (m ^s ) of the sorbent solid ( 14 ) in the activated state or with fixed presorption in the bottom of the magnetic levitation ( 1 ) hanging sample basket filled. Thereafter, the adsorption space ( 2 ) and via the evacuation line ( 11 ) and the vacuum pump ( 15 ) evacuated as much as possible.

Thereafter, the sorption space (volume (V _AC )) ( 2 ) via the gas supply line ( 10 ) with sample gas or adsorptive ( 16 ) and this - especially in gas mixtures - to accelerate sorption by means of the circulation pump ( 12 ) in the sorption chamber. If the display of the microbalance ( 1 ) is either constant or at least in "technical equilibrium" [1, p. 24], the valve ( 4 ) in the riser ( 3 ) open. This will cause the vibrating body ( 6 ) from his starting point, where he is on the shelf ( 5 ), raised to a slightly higher position. Now, about the gas supply ( 10 ) supplied an additional, but very small gas stream to the adsorption. As a result, the gas pressure rises minimally, the vibrating body ( 6 ) is raised a little and thereby - as described above - a small opening (gas valve ( 18 )) in the riser ( 3 ) free, so that some gas can flow out and thus the gas pressure drops slightly for a short time again. This process excites the vibrating body ( 6 ) to small damped oscillations (amplitude Δx, angular frequency ω) about a middle position (position coordinate x = 0) in the riser, which stop as long as the gas flow is maintained. The periodic pressure fluctuations (amplitude Ap) in the gas generally result in too small periodic changes (Dm ^{(a) either} in the adsorbent 14 ) Adsorbed amount of gas (mass m ^a ). However, a more detailed analysis of this situation shows that the adsorbate changes (Δm ^a ) are proportional to the square of the pressure changes (Δp) and the oscillation amplitude (Δx): Δm ^α ≈ (Δp) ² ≈ (Δx) ² . (1)

The mass changes (Δm ^a ) can therefore be neglected in the context of a first-order theory (Δx, Δp, ω) as small of the second order. (This does not apply if, in addition to the adsorbate mass (m ^a ), the mass transfer gas-solid is also considered, which can be described, for example, by a diffusion coefficient of the adsorbed gas molecules in the porous solid.)

The vibrations of the vibrating body ( 6 ) are basically damped because of the friction of the body against the pipe wall and because of the internal friction in the oscillating gas body. The damping coefficient ( 1 ) of the damped oscillation can be measured by an empty measurement, ie a measurement of the oscillation frequency (ω ₀ ) of the oscillating body at the same pressure (p) and temperature (T) of the gas in the empty, ie gas-filled, sorption space ( 2 ). From the measurements of both angular frequencies (ω, ω ₀ ), the inverse of the experiment of Rüchhardt [11, 15], the volume (V ^f ) of the sorptive gas in the adsorber space provided with sorbent material ( 2 ) (Void volume V _AC ) can be calculated according to the relationship

In this formula, V _{AC is} the volume of the empty adsorption space ( 2 ), m the mass and F = πr ² the cross - sectional area of the cylindrical oscillating body with radius (r), and κ the adiabatic exponent of the Sorptivgases. Dividing the volume (V _AC ) of the sorption chamber ( 2 ) into the volume of sorbent gas Vf / AC and a volume V ^{as of} the sorbate-filled solid sorbent, V _AC = V f / AC + V ^as , (3) thus V ^as according to Eq. (2, 3) are calculated as

This size is of particular physical and technical interest in sorbent-swelling sorbents, such as porous polymers or organometallic materials (MOFs).

The microbalance ( 1 ) now supplies the mass of the adsorbate (m ^a ) reduced by a buoyancy term, ie the size, by means of a few calibration measurements on the empty or evacuated system [1] Ω = m ^a - ρV ^as . (5)

Here, ρ ^f = ρ ^f (p, T) means the density of the sorptive gas [14]. With V ^as according to equation (4), therefore, according to (5), the mass sorbed in the sorbent of the mass (m ^s ) is obtained

So this mass can with the in 1 . 2 apparatus by measuring the apparent weight of the gas-loaded sorbent sample (Ω) using the microbalance ( 1 ) and 2 vibration tests with a vibrating body, which is excited to Flammersfeld by a very small flow of measuring gas to vibrate, and the angular frequencies of the oscillations (ω, ω ₀ ) provides, can be determined experimentally without further hypotheses. The experiment described above can in principle be carried out at all pressures (p) and temperatures (T), if suitable riser pipes ( 3 ) with matching oscillating bodies ( 6 ) and gas valves ( 18 ) be available.

literature

• [1] KELLER JU, STAUDT R. Gas Adsorption Equilibria, Experimental Methods and Adsorption Isotherms, Springer NY etc. 2005 ,
• [2] ROUQUEROL F, ROUQUEROL J, SING KSW, Adsorption by Powders & Porous Solids, Academic Press, San Diego, etc., 1999 ,
• [3] BATHEN D. Breitbach M., adsorption technique, VDI book, Springer, Berlin etc., 2001 ,
• [4] STEELEN W., The interaction of gases with solid surface, Pegamon press, New York, 1974 ,
• [5] DABROWSKI A., Editor, Adsorption and its Application in Industry and Environmental Protection, Vols. 1-2, Elsevier, The Netherlands, 1998 ,
• [6] BASMADJIAN D., The Little Adsorption Book, CRC Press, Boca Raton, 1996 ,
• [7] YANG RT, Gas Separation by Adsorption Processes, Imperial College Press, Singapore, 1998 ,
• [8th] YANG RT, Adsorbents, Fundamentals and Application, Wiley-Interscience, Hoboken, New Jersey, 2003 ,
• [9] ROUQUEROL J. et al. The Characterization of Macroporous Solids: An Overview of the Methodology, article in: Microporous to Mesoporous Materials, Vol. 154 (2012), p. 2-6 ,
• [10] KELLER JU Dynamic volumetric method for determining the amount of gases or vapors dissolved in dense or porous solids. Patent Az. 10 2013 012 387.9 dated 26-07-2013, German Patent and Trademark Office Munich, 2013.
• [11] ZEMANSKY MW, Heat and Thermodynamics, An Intermediate Textbook, p. 128-130, Mc Graw Hill, 5th. Edition NY etc., 1968 ,
• [12] KELLER JU Thermodynamics of irreversible processes, Part 1, Thermostatic and fundamental concepts, p. 319, 358-359, W. de Gruyter, Berlin-New York, 1977 ,
• [13] National Institute of Standards and Technology (MIST), USA, 2011, Thermophysical Properties of Fluid Systems, webbook.nist.gov./chemistry/fluid, (www) ,
• [14] DECHEMA Chemical Databases, DETHERM, http://i-systems.dechema.de/
• [15] FLAMMERSFELD A. Zeitschrift fur Naturforschung, Vol. 27a (1972), p. 3 ,

LIST OF REFERENCE NUMBERS

1

Mikrowaage/Magnetschwebewaage

2

Sorptionsraum oder Gasresonator Volumen V_AC

3

Steigrohr für Gas im Adsorptionsraum

4

Absperrventil im Steigrohr

5

Ablage für Schwingkörper (6)

6

Schwingkörper im Steigrohr (3)

7

Auftriebskörper an der Mikrowaage im Sorptivgas

8

Temperaturmessfühler, Thermometer

9

Drucksensoren, Manometer

10

Gasversorgungsleitung

11

Evakuierungsleitung

12

Umwälzpumpe

13

Adsorbiertes Gas oder Adsorbat

14

Poröser Festkörper oder Adsorbens

15

Vakuumpumpe

16

Messgas oder Adsorptiv

17

Magnetkupplung

18

Ventil im Steigrohr

19

Behältnis zur Aufnahme von Adsorbensmaterial

Fig. 1, Fig. 2

1

Microbalance / magnetic suspension balance

2

Sorption space or gas resonator volume V _AC

3

Riser for gas in the adsorption space

4

Shut-off valve in the riser

5

Tray for vibrating body ( 6 )

6

Oscillating body in the riser ( 3 )

7

Float on the microbalance in the sorptive gas

8th

Temperature sensor, thermometer

9

Pressure sensors, pressure gauges

10

Gas supply line

11

evacuating line

12

circulating pump

13

Adsorbed gas or adsorbate

14

Porous solid or adsorbent

15

vacuum pump

16

Sample gas or adsorptive

17

magnetic coupling

18

Valve in the riser

19

Container for receiving adsorbent material

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102013012387 [0003]

Cited non-patent literature

• Reversal of the experiments according to Rüchhardt, 1929, and Rinkel, 1929 [0005]

Claims (5)

Method of gases or vapors adsorbed in solids, ie either dissolved or absorbed, or deposited or adsorbed on external or internal surfaces of the solid by a combined dynamic gravimetric measurement in a patented instrument called an oscillation gravimeter 1 consisting of - a microbalance ( 1 ), preferably a magnetic levitation balance with magnetic coupling ( 17 ), - a sorption space or gas resonator ( 2 ), - a container, ie vessel or wire basket ( 19 ) for absorbing sorbent material, - a riser ( 3 ) for the adsorptive gas ( 16 ), which a shut-off valve ( 4 ), a vibrating body (cylinder) ( 6 ), a clipboard ( 5 ) for the oscillating body and above the valve ( 4 ) according to a proposal from Flammersfeld another gas valve ( 18 ), which can be opened or closed by vertical movements of the oscillating body, - sorbing solid or adsorbent ( 14 ) in the sorption space ( 2 ), - piping and valves ( 10 . 11 ) for filling and emptying the sorption space ( 2 ) with sorptive gas ( 16 ), - a vacuum pump ( 15 ) and a circulation pump ( 12 ) for gas circulation, - sensors and measuring instruments for measuring pressure ( 9 ) and temperature ( 8th ) of the sorptive gas, and in which for measuring the amount of adsorbed gas (adsorbate, mass (m ^a )) after filling the sorbent solid (adsorbent, mass (m ^s )) in the container ( 19 ) - the sorption space ( 2 ) via the vacuum pump ( 15 ) first evacuated, then - via the gas supply ( 10 ) filled with sorptive gas and this by means of the circulation pump ( 12 ) in the sorption space ( 2 ) is circulated after adjusting an equilibrium state, the pressure (p) and the temperature (T) of the gas and the microbalance ( 1 ) the apparent weight (Ω) of the adsorbate ( 13 ) of the sorbent sample ( 14 ), and then after opening the valve ( 4 ) and by supplying a very small gas flow from the gas supply system ( 10 ) the vibrating body ( 6 ) to stimulate small, damped oscillations whose amplitude can be adjusted by suitable arrangement of the gas valve ( 18 ) in the riser ( 3 ) can be limited, cf. 2 so that the frequency (ω) of these oscillations can be accurately measured, for example, via a laser-based optical system (photocells) - in order to obtain from the measured data of gas pressure (p), apparent sample weight (Ω), oscillation frequency (ω), a calibration frequency (ω ₀ ) and the adiabatic exponent of the sorptive gas (κ) and other system data to calculate the mass of the adsorbate (m ^a ) according to equation (6). Measuring method according to claim 1, characterized in that the sorbent solid may be either a powder, a pellet bed, a piece sample or a liquid or plastic gel. Measuring method according to claim 1, characterized in that the sorbent solid may be either rigid or swelling or shrinking material in a sorption process. Measuring method according to claim 1, characterized in that the measurement takes place in the pressure range 0 <p <1000 bar and in the temperature range 20 K <T <773 K. Measuring method according to claim 1, characterized in that a thermostat is used in the measurement (not shown in FIG 1 ) in which a thermal fluid is used, which either an inert gas (N ₂ , Ar, He) air, water with or with freeze-preventing additives such as methanol, ethanol, etc., or a thermostatic oil with a high, that is above 200 ° C boiling point or but also liquid nitrogen or another cold brine to achieve low temperatures can be less than 0 ° C.

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