APPARATUS AND METHOD TO MEASURE THE KINETICS PARAMETERS OF A POROUS POWDER CATALYST

Abstract

An apparatus and method are disclosed for measuring the kinetic parameters of a catalyst powder, which include the reaction rate constants, active site concentration and intraparticle diffusivity. The measurement of the active site concentration selectively measures just the active sites and not the entire exposed atom concentration. The apparatus and method use surface concentrations less than 50% and larger than 1% the total active site concentration and a dynamic pulsed flow to avoid including weak adsorption sites not involved in the catalysis. The measurement is more accurate because (1) it uses a reactant gas and non-steady state adsorption at temperatures near to reaction temperatures, and (2) it uses the chemical kinetics expressions to extract the measured active site concentration to perform the measurement so as to count just those sites actually active for that reactant. This is better than the prior art methods that measure an entire surface atom concentration under non-dynamic conditions because the latter is not necessarily the same as the active site concentration in the chemical kinetics expression. The intraparticle diffusivity measured by the apparatus and method is the effective gas diffusivity in a porous powder, and this is useful as a characterization of the tortuosity of the porous powder.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a schematic view of an apparatus (embodiment 1) to measure the active site concentration of a catalyst powder.

FIG. 2 is a sectional view of the gas flow path part of the embodiment 1 apparatus.

FIG. 3 is a sectional view of the gas flow path part of an embodiment 2 apparatus.

FIG. 4 is a sectional view of the gas flow path part of an embodiment 3 apparatus.

FIG. 5A and FIG. 5B are the experimental and simulation response curves, respectively, that measure the oxygen adsorption site concentration of a V—Mo-based catalyst powder.

FIG. 6A is a simulation result of when adsorption is slow and shows that the response curves lack sensitive shape changes with pulse size, and FIG. 6B is a simulation result that shows the response curves have enhanced curve shape changes due to adding a layer of smaller particles downstream of the catalyst packed bed.

Claims

1. A device for the low pressure delivery of feed gas for measuring kinetics parameters comprising: (a) a sample tube which is cylindrical and demountable;(b) a metal block having a smoothed-wall, cylindrical cavity in immediate communication with one end of the sample tube, wherein the cavity has a diameter at least as large as the diameter of the sample tube and the cavity has at least one valved opening on its circumference;(c) valving means for opening the valved opening for injection of feed gas, and;(d) a vacuum chamber and a vacuum pump in communication with the other end of the sample tube.

2. The device of claim 1 wherein any point within the cavity has a line of sight with all of the sample tube.

3. The device of claim 1 wherein the volume of the cavity is at least 0.1 ml.

4. An apparatus for measuring the kinetics parameters of a catalyst powder comprising: (a) a cylindrical, demountable sample tube having a packed bed comprising at least the catalyst powder;(b) a metal block having a smoothed-wall, cylindrical cavity in immediate communication with the upstream end of the sample tube, wherein the cavity has a diameter at least as large as the diameter of the sample tube and the cavity has a plurality of valved openings on its circumference;(c) means for injecting cleaning gas through a first valved opening;(d) means for pulse injecting of feed gas through a second valved opening, wherein the pulsed gas amount is sufficiently small to satisfy the condition for Knudsen flow;(e) a furnace that encloses the packed bed;(f) gas removing means in communication with the downstream end of the sample tube;(g) at least one gas concentration measuring means in communication with the downstream end of the sample tube; and(h) a data acquisition and treatment system in communication with the gas concentration measuring means.

5. The apparatus of claim 4 wherein the gas removing means is a cylindrical vacuum chamber with a vacuum pump with pumping speed at least 1500 liters per second attached at the outlet end, and wherein the gas concentration measuring means is attached inside the vacuum chamber and the vacuum chamber is empty except for the gas concentration measuring means.

6. The apparatus of claim 4 wherein the gas removing means is alternatively an exhaust, a roughing pump, or a cylindrical vacuum chamber and a vacuum pump with pumping speed at least 1500 liters per second attached at the outlet end, and wherein the gas concentration measuring means is attached inside the vacuum chamber and the vacuum chamber is empty except for the gas concentration measuring means.

7. The apparatus of claim 4 wherein the cavity in the metal block has a volume that is at least 0.1 ml.

8. The apparatus of claim 4 wherein the packed bed is at least 7 mm long but sufficiently short so that the bed diffusion time constant is less than the intraparticle diffusion time constant in the catalyst powder.

9. The apparatus of claim 4 wherein the means for pulse injecting is an electronically controlled solenoid valve that injects gas pulses of varied size comprising at least one reactant and an inert gas, wherein the largest and smallest pulses differ by at least ten-fold, and wherein the amount of active sites on the catalyst powder is less than 2×1017 sites.

10. An apparatus for measuring the active site concentration of a catalyst powder comprising: (a) a metal block having a cavity with a plurality of valved openings on the cavity circumference;(b) means for injecting cleaning gas through a first valved opening;(c) means for pulsed injecting of feed gas through a second valved opening, wherein the gas pulse is sufficiently small to satisfy the condition for Knudsen flow;(d) a demountable sample tube having at least the catalyst powder disposed as a packed bed which is attached at the upstream end to the mouth of the cavity, wherein the number of active sites on the catalyst powder is less than 100 times the number of adsorbate fragments in the largest gas pulse that is sufficiently small to satisfy the condition for Knudsen flow;(e) a furnace that encloses the packed bed;(f) gas removing means in communication with the downstream end of the sample tube;(g) at least two gas concentration measuring means in communication with the downstream end of the sample tube; and(h) a data acquisition and treatment system in communication with the gas concentration measuring means.

11. The apparatus of claim 10 wherein the gas removing means is a cylindrical vacuum chamber with a vacuum pump with pumping speed at least 1500 liters per second attached at the outlet end, and wherein the gas concentration measuring means are attached inside the vacuum chamber and the vacuum chamber is empty except for the gas concentration measuring means.

12. The apparatus of claim 10 wherein the gas removing means is alternatively an exhaust, a roughing pump, or a cylindrical vacuum chamber with a vacuum pump with pumping speed at least 1500 liters per second attached at the outlet end, and wherein the gas concentration measuring means are attached inside the vacuum chamber and the vacuum chamber is empty except for the gas concentration measuring means.

13. The apparatus of claim 10 wherein the means for pulsed injecting is an electronically controlled solenoid valve that injects gas pulses of varied size comprising at least one reactant and an inert gas, wherein the largest and smallest pulses differ by at least ten-fold.

14. The apparatus of claim 10 further including an auxiliary packed bed of inert particles comprising a particle size between 1 and 200 micron disposed downstream of the packed bed.

15. The apparatus of claim 10 wherein the packed bed is of sufficient length so that the bed diffusion time constant is larger than the intraparticle diffusion time constant in the catalyst powder, and wherein the packed bed may include a diffusively similar inert powder to get it to the required length.

16. The apparatus of claim 10 wherein the cavity in the metal block is smooth-walled, cylindrical, and in immediate communication with the sample tube.

17. A method for measuring the active site concentration of a catalyst powder, comprising the steps: (a) providing a metal block having a cavity with a plurality of valved openings on the cavity circumference;(b) providing valving means for a first valved opening and preparing a cleaning gas therein;(c) providing pulsed valving means for a second valved opening and preparing a feed gas comprising at least one reactant and an inert gas therein;(d) providing a demountable sample tube, disposing at least the catalyst powder as a packed bed therein, and attaching it at the upstream end to the mouth of the cavity, wherein the number of active sites on the catalyst powder is less than 100 times the number of adsorbate fragments in the largest gas pulse that is sufficiently small to satisfy the condition for Knudsen flow;(e) providing gas removing means that is in communication with the downstream end of the sample tube;(f) providing a furnace that encloses the packed bed;(g) heating and cleaning the catalyst powder by a delivery of cleaning gas using the valving means and removing gas using the gas removing means;(h) stopping the delivery of cleaning gas and desorbing adsorbed gas from the catalyst powder by heating and removing gas using the gas removal means to provide a vacuum in the sample tube;(i) providing for the packed bed to be at an adsorption temperature, using the pulsed valving means to deliver a feed gas pulse into the sample tube, and removing gas using the gas removal means, wherein the feed gas pulse is sufficiently small so that the feed gas flows in Knudsen flow;(j) providing at least two gas concentration measuring means that are in communication with the downstream end of the sample tube, measuring the response curves of the inert gas and at least one reactant as they are removed, and using the area of the inert gas response curve to calculate the injected pulse size; and(k) using a mathematical model and fitting at least the response curve of the reactant to extract the active site concentration on the catalyst powder.

18. The method of claim 17 further including repeating steps 17 (g) to (k) using a different pulse size in step (i), wherein the largest and smallest pulses differ by at least ten-fold.

19. The method of claim 17 wherein the gas removing means in step 17 (e) is a cylindrical vacuum chamber with a vacuum pump with pumping speed at least 1500 liters per second attached at the outlet end, and wherein the gas concentration measuring means are attached inside the vacuum chamber and the vacuum chamber is empty except for the gas concentration measuring means.

20. The method of claim 17 wherein the gas removing means in step 17 (e) is alternatively an exhaust in step 17 (g), a roughing pump in step 17 (h), or a cylindrical vacuum chamber with a vacuum pump with pumping speed at least 1500 liters per second attached at the outlet end in step 17 (i), and wherein the gas concentration measuring means are attached inside the vacuum chamber and the vacuum chamber is empty except for the gas concentration measuring means.

21. The method of claim 17 wherein the cavity in step 17 (a) is at least 0.1 ml in volume and in immediate communication with the sample tube.

22. The method of claim 17 further including disposing an auxiliary packed bed of inert particles comprising a particle size between 1 and 200 micron downstream of the packed bed in step 17 (d).

23. The method of claim 17 wherein the packed bed in step 17 (d) is of sufficient length so that the bed diffusion time constant is larger than the intraparticle diffusion time constant in the catalyst powder, and wherein the packed bed may include a diffusively similar inert powder to get it to the required length.

24. The method of claim 17 further including measuring the response curves of at least one product gas in step 17 (j) and fitting the response curve of the product gas in step 17 (k).