CS242432B1 - Chemisorption volumetric or flow chromatographic instrument with optional metal dispersion measurement function - Google Patents

Abstract

The solution concerns the construction of a chemisorption device for measuring the dispersion of metals in mono- and polymetallic catalysts, created from a combination of a volumetric device operating on the monometric principle and a pulse-flow chromatography device, which, using a built-in upstream microdoser and a system of valves, allows the selection of the gas flow either for measurement by the classical volumetric principle, or by flow chromatography mode, or by parallel dosing from the adsorption space through a separable intermediate flow.

Description

(54) Chemisorption bulk or flow chromatography instrument with optional metal dispersion measurement function

The solution concerns the construction of a chemisorption device for measuring the dispersion of metals in mono- and polymetallic catalysts, created from a combination of a volumetric device operating on the monometric principle and a pulse-flow chromatography device, which, using a built-in upstream microdoser and a system of valves, allows the selection of the gas flow either for measurement by the classical volumetric principle, or by flow chromatography mode, or by parallel dosing from the adsorption space through a separable intermediate flow.

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The invention describes a chemisorption device for measuring metal dispersion in polymetallic catalysts, which, using built-in valves, allows the selection of the gas flow, which, depending on the valve settings, can be measured using the classical volumetric principle using classical high-vacuum technology, or in flow chromatography mode with possible pulse dosing at the inlet, or parallel dosing from the adsorption space through a separable intermediate space.

Currently, two basic procedures and types of instruments are used to measure the dispersion of metals on supports; a classic volumetric instrument, where highly accurate adsorption isotherms are measured (in some cases, a weighing instrument as well), but this procedure does not allow for the practical distinction of chemisorption of gases on individual metals, or a simple chromatographic instrument is used, mainly in a pulsed configuration. It is practically impossible to measure the dispersion of metals in polymetallic catalysts by the chemisorption procedure on such types of instruments. In these types of catalysts, ESCA spectroscopy is mainly used to measure the dispersion of metals.

For the measurement of adsorption isotherms, especially of monometallic catalysts, a volumetric apparatus is currently used, shown in Fig. 1, where: 1 - adsorption vessel - microreactor, 2 - furnace with temperature control circuits, 2 - hydrogen flow inlet for catalyst reduction, 4 - separating valve for dosing and measuring parts of the apparatus from the adsorption vessel, 2 - valve for switching the adsorption

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- 2 vacuum pipe containers, 6 - inlet hydrogen isolating valve, 7 - outlet hydrogen isolating valve + vent valve, 8 - freezing container for mercury vapor, % - Mc Leod manometer isolating valve, 10 - compression Mc Leod manometer, 11 - mercury isolating valve between mercury reservoir 12 and Mc Leod manometer 10, 12 - mercury reservoir, 13 - valve for pneumatic control of mercury position in Mc Leod manometer by negative pressure, 14 - valve for pneumatic control of mercury level in Mc Leod manometer by positive pressure, 15 - measuring and dosing space isolating valve, 16 - dispenser isolating valve 17, 17 - dispenser, 18 - pressure reduction space inlet isolating valve 20, 21 - pressure reduction space adjustment valve 20 to high-vacuum pipe 22, 22 - high-vacuum pipe p«0, |iPa, 23 - valve for connecting the storage space to the high-vacuum pipe, 24 - adjustment valve of the mercury U-manometer 25.

- mercury U-manometer, 26 - mercury isolating valve between mercury reservoir 22 and U-manometer 25. 28 - valve for pneumatic control of mercury level in U-manometer by negative pressure, 29 - valve for pneumatic control of mercury level in U-manometer by positive pressure, 30 - gas inlet for filling reservoirs £2, £4, 36 and 38.

- tank isolation valve 32. 32 - oxygen tank, 34 tank isolation valve £4, 34 - hydrogen tank, 35 - tank isolation valve 36. 36 - carbon monoxide tank,

- tank isolation valve £8, 38 - helium tank·

This device allows to measure adsorption isotherms exactly in wide pressure ranges (in a specific configuration from about 0.1 Pa to about 0.1 MPa). Its advantage is high precision and accuracy, but its disadvantage is complexity and relatively low operability for polymetallic catalysts, when it is necessary to comprehensively include thermoreduction and thermodesorption procedures in the measurement; however, these experimental procedures are practically excluded by the volumetric type of device.

The second currently used method for measuring metal dispersion, especially in monometallic catalysts, is the pulse chromatographic method, shown in Fig. 2, where dsjel - carrier gas, 2 - adsorbate, £ - thermal conductivity detector, 4 - dispenser, J? - adsorption

- 3 242 432 vessel - microreactor, 6 - furnace with temperature control circuits, £ isolating valve for setting the adsorption vessel bypass, 8 three-way valve for setting the adsorption vessel bypass.

This method consists in dosing the adsorbate into the carrier gas and thus measuring the total adsorbed amount. The device for this type of measurement can be used for thermoreduction, or thermooxidation and, last but not least, for thermodesorption in the case of mixing a mixed carrier gas. The advantage of this type of device is the simplicity of construction, operability and simplicity of measurement. The disadvantage is the difficult or not completely rigorously defined initial measurement conditions, consisting in the not completely defined surface cleanliness before measurement.

A chemisorption volumetric or flow-through chromatography apparatus with an optional function for measuring the dispersion of metals in mono- and polymetallic catalysts, created by a combination of a volumetric apparatus operating on the manometric principle and a pulsed flow-through chromatography apparatus, is designed according to the invention in such a way that a pre-intermediate feeder 6 is built in front of the adsorption vessel - microreactor 1, while the adsorption vessel - microreactor 1 is placed in parallel between the volumetric part of the manometric type apparatus and the chromatography apparatus equipped with valves 8 to 9 and 12 to 16, by which either the pre-intermediate feeder 6 itself or the pre-intermediate feeder 6 with the adsorption vessel - microreactor 1 can be connected in series either to the chromatographic part of the apparatus, or in parallel to the volumetric part of the apparatus or to a high-vacuum aggregate, a filter element 17 is built into the chromatography circuit for eliminating the water vapor signal by its condensation or adsorption and to the vacuum pipe 22, a filter element 18 to 21 is built in to eliminate the water vapor signal for thermodesorption measurements on vacuum detectors 23 and 24 with analog pressure sensing.

A chemisorption functionally selectable volumetric or flow-through chromatographic device for measuring metal dispersion in polymetallic as well as monometallic catalysts according to the invention is shown in Fig. 3, where 1 is an adsorption vessel - microreactor, 2 - an oven with temperature control circuits, £ - carrier gas of the chromatographic

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- 4 circuits, 4 - carrier gas with adsorbate, - thermal conductivity detector, 6 - dispenser, 2 " intermediate dispensing space, 8 - separating valve of the adsorption part of the apparatus from the volumetric part of the apparatus, £ " carrier gas inlet for equalizing pressure shocks, 10 - carrier gas 11 - separating valve on the high-vacuum pipe 22, 12 separating valve of the carrier gas inlet to the intermediate dispenser, 13 - outlet valve from the intermediate dispenser to the chromatographic circuit, 14 to 15 - separating valves of the adsorption vessel, 16 - valve for adjusting the forward direction of the chromatographic circuit, 17 - condensation vessel cooled to 195 K for filtering water vapor signals, 18 - condensation vessel cooled to 80 K for filtering water vapor signals during thermal desorption of gases into vacuum, 19 to 21 - separating valves, high vacuum for condensation vessel 18, 22 - high vacuum pipe p=0, 1/iPa, 23 - Pirani gauge, 24 - Penning gauge, 25 condensation vessel for mercury vapor, 26 - Pirani gauge, 27 - Mc Leod compression manometer isolating valve, 2 8 - Mc Leod manometer, 29 - mercury isolating valve, 30 - mercury reservoir,

- control valve for pneumatic control of mercury level in McLeod compression manometer by positive pressure, 32 - control valve for control of mercury level by negative pressure, 33 - separation valve of the reduction tank, 34 - tanks, 35 - valve for connecting the tank 34 to the high-vacuum pipe, 36 - separation valve of the dispenser, 37 - dispenser, 38 - inlet separation valve of the dispenser, 39 - valve for connecting the dosing part of the apparatus to the high-vacuum pipe 22, 40 - valve of the first tank 41, 41 first tank, 42 - valve of the second tank 43. 43 - second tank, 44 - valve of the third tank, 45 - third tank, 46 - valve of the fourth tank 42, 47 - fourth tank, 48 - valve of the apparatus filling, 49 - adsorbate inlet, 50 - valve of the U-manometer 51,

- U-manometer, 52 - isolating valve, 53 - mercury reservoir,

- valve for regulating the mercury level in the reservoir of the U-manometer £1 by negative pressure, 55 - valve for regulating the mercury level in the reservoir of the U-manometer 51 by positive pressure.

Structurally, the device according to the invention is therefore arranged from two basic devices, i.e. a classical volumetric device operating on the manometric principle and a pulsed-flow chromatographic device, which form two separate independent

242 432 parts of the device. Both of these parts are connected to an intermediate dispenser by means of valves, ensuring selection and connection to the circuits:

- the volumetric part of the device operating on the manometric principle,

- buffer-flow chromatography apparatus,

- to its own adsorption vessel, which does not have to be connected to the chromatographic circuit (intermediate dispenser) even during chromatographic measurement,

- to a vacuum branch with a built-in indication of the pressure of desorbed gases using an analog signal from vacuum gauges.

The volumetric part of the device is practically identical to a classic volumetric device, equipped with automatic dosing, regulation and measurement of gas (adsorbate) pressure. It consists of gas reservoirs 41, 43, 45, 47, separated by valves 40, 42, 44, 46 with an adsorbate inlet 49 and a U-manometer 51 with accessories 52 to 55. This inlet part is connected to a high-vacuum pipeline by valve 39. The arrangement of the device according to the invention is equipped with automatic pressure regulation conditioned by sensing pressure differences on the U-manometer 51. This part of the device, the volume of which is limited by valves 48 and 38, operates in the pressure range 1 εζ 100 kPa and serves either for direct measurement in this pressure range, or for measuring input defined conditions for pressure reduction on a low-pressure dispenser. The second separate part of the volumetric device (dosing space), which is designed for the pressure range of 0.1 WPa to 1 kPa, has, in addition to the built-in Me Leod compression manometer 28 with accessories 29 to 32 (automatic pneumatic control and measurement), also a dispenser 17 with a volume of V(D(1))| which cascades the gas from the basic dosing part of the device into its own evacuated dispenser with a volume of V(D(3)) and an evacuated expansion space V(D(2)) with a volume of approximately 101, thereby reducing the input pressure to a value

Y(D(1)) p(V(D(3))) * (V(D(1)) + V(D(2)) + V(D(3)j)

The entire procedure is fully automated in the invention used and the actual dosing is carried out using valve 8.

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The chromatographic part of the device, in contrast to the currently used type of device, has a built-in condensation vessel cooled to 195 K for condensation of water vapor at the outlet from the adsorption vessel before entering the second cell. The chromatograph itself - i.e. the carrier gas, the composition of which can be freely adjusted at the inlet part, passes through the thermal conductivity cells 2t, a dispenser 6 with a volume of V(D(4)) into which any concentration of the adsorbate in the carrier gas can be adjusted, ensuring high sensitivity of the device. The chromatographic circuit has built-in valves 16 for bypass, ' i.e. setting the zero line of the device, a valve for the input connection of the chromatographic circuit 12 and a valve u for selective connection of the outlet from the intermediate dispenser 2 ⁰ with a volume of V(D(5)) and a valve 15 for connecting the outlet from the adsorption vessel to the chromatographic circuit. The condensation vessel 17 is of fundamental importance for the operation of the chromatographic part of the instrument, consisting primarily in the elimination of the parasitic signal of water vapor released during thermal desorption and thermal reduction. In addition to this basic function, the condensation vessel 17 can be filled with an adsorbent (molecular sieve or activated carbon) and, by supercooling, completely adsorb the chromatographic signal (adsorbate) of low intensity but large dose on the filling and then analyze the desorbed gas by subsequent thermal desorption.

The basic function of the proposed device according to the invention is then performed by the intermediate dispenser 2 (V(D(5))), with which the appropriate measurement procedure can be selected by selecting the function of the valves on the device. With valve 8 it is connected to the volumetric dispensing and measuring part of the device, with valve 14 to the adsorption part itself (volume V(D(6))), with valve 11 it is connected to a high-vacuum pipeline with a built-in filtration device 18 to 21 for condensation of H^O vapors at 80 K and with a measuring and indicating device 23 to 24 with analog pressure recording in the range of 0.1 to 100 mPa and 0.1 to 10 Pa. The intermediate dispenser 2 is further connected to a pipeline with carrier gas by means of valve 9 for the purpose of replenishing the dispenser 2 θ eliminating pressure surges when the intermediate dispenser is serially connected to the series of the chromatographic circuit. This arrangement according to the invention allows only an intermediate dispenser, or an intermediate dispenser with an adsorption container, to be connected in series to the chromatographic circuit, thereby performing measurements that previously had to be performed only on

- 7,242,432 volumetric or weight types of devices, and use this intermediate dispenser as an absolute one, with chromatographic detection of concentration changes, where this intermediate dispenser has the function of a manometer for the chromatographic part of the apparatus, working on concentration measurement in a chromatographic arrangement.

The arrangement of the combined device according to the invention preserves all the functional advantages of the volumetric type of adsorption device, i.e. high sensitivity and accuracy of measurement, and of the simultaneously used chromatographic type of device, i.e. speed and operability of measurement, and at the same time eliminates the basic disadvantages of the individual types of devices, i.e. limited use of the volumetric device and difficultly defined initial conditions reducing the accuracy of measurement in the chromatographic type of device. In addition, by incorporating separation valves and an intermediate dispenser, it works on a qualitatively higher function allowing in situ combination of individual physical and physicochemical measurement procedures, which allow measuring the dispersion of metals in polymetallic catalysts procedures: thermoreduction, thermodesorption, chemisorption of selected gases, defined chemisorption of oxygen at low pressures and subsequent thermoreduction of the chemisorption bond of oxygen on various metal components of the catalyst, including the balance of dissolved hydrogen in metals. The device according to the invention thus meets the requirements not only of a highly sensitive analytical device, but also of a device for sensitive study of catalyst start-up conditions, deactivation and activation.

The function of the device is illustrated by the following example:

Example

An example of using a chemisorption functionally selectable volume or flow chromatography device to measure metal dispersion in polymetallic catalysts is the evaluation of platinum and rhenium dispersion in a bimetallic Pt-Re-AlgO-j catalyst.

Table 1 lists the basic functions of the device in matrix notation.

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Table 1

Matrix notation of physical function selection by valve setting selection valve setting

f ce Phys. FCE 3 4 6 7 8 9 10 ii : 12 13 14 15 16 I evacuation of the model - - thermodes. into vacuum - 1 0 0 0 1 0 0 1 0 1 II classical measurementads about isotherm 1 1 0 0 0 0 0 1 0 1 III thermoreduction thermooxidation 0 1 0 0 0 0 1 0 1 1 0 IV measurement of ads. isotherm chromatographically cyclically switched face II and function III In pulse chrom. - - - 1 0 0 0 0 1 0 1 1 0

A sample of the dried catalyst after co-impregnation of AlgO^ with chloroplatinic acid + rhenic acid is placed in the microreactor 1 and in the chromatographic mode, function III is set, the carrier gas concentration Η ₂ ~Αγ with a concentration x(H ₂ ) ^B of 0.33 is set in the pipe J, the heating in the furnace is turned on and the limiting temperature of 773 K and the temperature increase rate of 5 K/min are set. The condensation vessel 17 is undercooled to 195 K and the changes in hydrogen concentration are registered on the recorder. The results of the thermoreduction measurement of the Pt-Re-AlgO^ system with hydrogen with a hydrogen concentration x(Hg) = 0.33 depending on the Re concentration are shown in Fig. 4, where

- Pt-AlgO (0.35% Pt)

- Pt-Re-Al ₂ O ₃ (0.35%

- Pt-Re-Al ₂ 0 ₃ (0.35%

- Pt-Re-Al ₂ O ₃ (0.35%

- Pt-Re-Al ₂ O ₃ (0.35%

- Re-Al ₂ O ₃ (0.35% T(red) = 773°K

Fri, 0.15 % Re) Fri, 0.25 % Re) Fri, 0.35 % Re) Fri, 0.70 % Re) Re)

- Pt-Re-Al ₂ O ₃ (0.35% Pt, 0.05% Re)

- 9 ~

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Then, the sample is degassed for a selected time (2 to 4 h) at p = 0.1 yuPa with the function I set.

In the third stage, the microreactor 1 with the sample is cooled to 298 K by removing the furnace 2 and using the classical function II, oxygen is dosed onto the sample at low pressure and the ads. isotherm is measured using the classical volumetric procedure. After closing the valves J3 and filling with Ar 10%, the apparatus is switched to function V and hydrogen, or an Ar-H ₂ mixture of defined concentration, is dosed in pulses. These cycles are repeated 2 to 3 times. The measurement results are shown in Fig. 5, where the Pt dispersion is practically zero due to the Pt being covered by a rhenium film.

In the fourth stage, function III is set - the selected temperature of 723 K is set on the microreactor and a He-Og mixture with a concentration of 0^ x(0 ₂ ) = 0.33 is selected for the chromatographic circuit and after two hours the system is flushed with pure Ar (at the same time, oxygen concentration changes are measured).

In the fifth stage, the functions of stages II and III are repeated without change, where the results are shown in Fig. 5, which shows the relative dispersion of platinum in the Pt-Re-AlgO^ catalyst for 0.35% Pt and variable Re content:

1- - direct reduction of impregnated AlgO.^

- reduction for reoxidation.

In the sixth measurement stage, which can be included between stages III and IV in special cases, after the end of the oxygen adsorptive isotherm measurement, function III is set, carrier gas 2 is set to a concentration of x(H ₂ ) - 0.03 to 0.05 in the Ar-Hg mixture and the thermoreduction of the ReO chemisorption bond is performed. The results are shown on samples with pre-chemisorbed oxygen at 298°K and p(Og) = kPa after gradual dosing

- Pt-Re-Al ₂ 0 ₃ (0.35

- Pt-Re-AlgOj. (0.35

- Pt-Re-Al ₂ 0 ₃ (0.35

- Pt-Re-Al ₂ O ₃ (0.35

- Pt-Re-A1 ₂ Q ₃ (0.35

- Pt- -A1 ₂ O ₃ (0.35

- Re-Al ₂ O ₃ (0.35

- relative dispersion

on fig. . 6, where % Fri, 0.70 % Re) % Fri, 0.35 % Re) % Fri, 0.25 % Re) % Fri, 0.15 % Re) % Fri, 0.05 % Re) % Fri) % Re)

Re

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The use of the device is not limited to the documented type of catalyst, but has a much broader application, which includes practically all types of industrial catalysts (metal).

The device according to the invention, designed in this way, allows studying the conditions of catalyst start-up in defined atmospheres, namely the desorption of substances from the catalyst surface and the concentration changes of the carrier gas during reduction (carrier gas Hg - Ar or NgJ, oxidation (carrier gas Og - He), dissolution of hydrogen in metals, purification of catalysts in high vacuum, measurement of chemisorption of gases of choice (Hg, Og, CO, NO, CgH^ etc.) by a classical volumetric method or by a chromatographic method, thermal desorption of chemisorbed gases into high vacuum or with chromatographic detection (carrier gas He or Ar) and especially thermal reduction of chemisorbed oxygen in the Hg - Ar system with an Hg concentration of 3 to 5% by volume.

In contrast to the frontal or pulse chromatographic procedure used so far, the device according to the invention allows in situ combining the function of sensitive and fine dosing of gases by the volumetric principle with measurement of the adsorbate pressure under equilibrium conditions by using washing of the microdoser, including its pumping (by vacuum) for subsequent doses.

The main advantage of this designed device is its universality and high sensitivity, where reduction and reoxidation processes can be monitored in situ and thus, in industrial research, effects that have so far been addressed in basic research mainly using ESCA spectroscopy can be observed.

Claims (1)

SUBJECT OF THE INVENTION 242 432 Chemisorption volumetric or flow chromatographic instrument with optional function for measuring the dispersion of metals in mono- and polymetallic catalysts, formed by a combination of a volumetric instrument operating on a manometric principle and a pulse-flow chromatographic instrument, characterized in that an overpriced intermediate dispenser is installed (6), wherein the adsorption vessel-microreactor (1) is arranged in parallel between the volumetric portion of the manometric type apparatus and the chromatographic apparatus equipped with valves (8 to 9 and 12 to 16) through which the pre-dispenser (6) itself or the pre-dispenser (6) with adsorption vessel - microreactor (1) in series either to the chromatographic part of the instrument, or parallel to the volume part of the instrument or to the high-vacuum aggregate, a filter element (17) for elim by filtering the water vapor signal by condensation or adsorption, and a filter element (18-21) is incorporated in the vacuum line (22) to eliminate the water vapor signal for thermodesorption measurements on vacuum detectors (23 and 24) with analog pressure sensing.