CHARACTERIZATION OF HETEROGENEOUS CATALYSTS BY ELECTRICAL MEASUREMENTS

Abstract

This invention is directed to a method of monitoring the relative activity of various heterogeneous catalysts by analyzing their bulk electrical properties such as specific conductivity or resistance. The difference between the resistance of fresh and spent catalysts is to be large (as high as four orders of magnitude). These large differences make this invention a very sensitive indicator of changes that may happen at the surface and/or in the bulk of the catalyst. The simplicity of this new invention renders it to be a sensitive potential on-line testing method of catalyst activity.

Description

FIELD OF THE INVENTION

[0001] The present invention is concerned with heterogenous catalysts, methods to determine their activity, and more particularly, to rapid degree of activity detection.

BACKGROUND OF THE INVENTION

[0002] The activity of heterogeneous catalysts has traditionally been assessed by chemical measurements. For instance, the activity of potassium-promoted Fe2O3 catalyst used to convert ethyl benzene to styrene, can be measured by the amount of styrene produced by a unit (weight or volume) amount of catalyst (J. Matsui, T. Sodesawa and F. Nozaki: Applied Catalysis 51, 203 (1989)). The catalyst is considered exhausted when the production of the desired compound falls below a predetermined limit. In industrial practice, the reactor temperature is increased to compensate for the decreased activity of the catalyst, and the reactor is taken off-line when the reactor temperature reaches an upper limit (K. M. Sundaram, H. Sardian, J. M. Ferandez-Baujin and J. M. Hildreth: Hydrocarbon Processing, January 1991, 93). Depending on the particular application, the exhausted catalyst then is discarded or regenerated. The “goodness” of the regeneration is tested in the laboratory using a chemical reaction, or a specific chemical or physical characterization of the active sites on the catalyst. For instance, the activity of the above mentioned potassium-promoted Fe2O3 was correlated with the potassium content, and the effect of carbonation was shown to be minor. In the case of other catalytic processes, studies showed a correlation between the acidic and catalytic properties of many inorganic solids (K. Tanabe: “Solid Acids and Bases”, Academic Press, N.Y. 1970). In one particular and most relevant example, the catalytic activity of binary metal oxides (Al2O3+ZnO) was investigated by acid-base titrations, X-ray and IR spectroscopy, and TGA and DTA measurements (M. A. Mousa, E. M. Diefallah, A. A. Abdel Fattah, Z. A. Omran: J. Mater, Sci. 25, 3067 (1990)). The specific electrical conductivity of the catalyst was measured and correlated with the ZnO content of the catalyst. At lower than 1000° C. calcination temperatures higher ZnO content showed higher conductivity, while at a 1000° C. calcination temperature a minimum conductivity was observed at 50% ZnO content. The conductivity of pure Al2O3 was reported to be σ*=1.0×10−13 (14° C.); 3.3×10−9 (300° C.); and 2.9×10−4 (800° C.) [Ω−1 cm−1] (CRC Handbook of Chemistry and Physics 76th Ed., D. R. Lide Editor-in Chief, CRC Press Inc. N.Y. (1995)).

[0003] The conductivity increase in the lower calcination temperature range was explained by the increase of the Ali3+ ion concentration with increasing ZnO content, which is reported to be the charge carrier in Al2O3. The catalytic activity of the Al2O3 +ZnO catalysts with varying amount of ZnO (0-100 wt %) was investigated using the chemical reaction of hydrogen peroxide decomposition. The catalytic activity of the fresh catalysts was then correlated with the ZnO content. The catalytic activity increased with increasing ZnO content, reaching a maximum value at about 30% ZnO, dropping to a minimum at 50% ZnO and going back to the maximum above 80% ZnO for all three calcination temperatures investigated. Therefore the electrical conductivity of these catalysts was found not to correlate with catalytic activity. The conductivity of the catalyst during and after the reaction, and the conductivity of the exhausted (spent) catalyst was not investigated. Table 1 is illustrative of conductivity data obtained in the prior art.

	TABLE 1
	Calcination temperature [° C.]
	300	600	1000
	ZnO mol %	Conductivity (σ*) [Ω−1cm−1]
	0	1.1 × 10−11	9.2 × 10−9	3.7 × 10−8
	15	1.4 × 10−11	9.4 × 10−9	1.2 × 10−8
	30	4.6 × 10−11	3.4 × 10−8	1.0 × 10−7
	50	1.5 × 10−9	5.1 × 10−8	2.5 × 10−9
	70	1.8 × 10−9	1.4 × 10−6	6.1 × 10−6
	85	1.8 × 10−7	5.0 × 10−4	1.2 × 10−8
	100	1.2 × 10−6	5.5 × 10−4	3.7 × 10−3

[0004] Conductivity measurements are used to monitor ionic chemical reactions (e.g., ionic polymerizations) in solution. However, the measurements are very difficult and the changes are usually very small. Attempts were made to follow the kinetics of ionic polymerizations, but the difficulties mentioned above rendered this method quite impractical. (J. E. Puskas, S. Smith-Kehl and B. Cass: Polymer Preprints 37, 355 (1996); L. Balogh, L. Fabian, I. Majoros and T. Kelen: Polym. Bull. 23, 75 (1990); D. W. Gratton, P. H. Plesch: Electroanal. Chem. 178, 2235 (1977); R. H. Biddulph, P. H. Plesch: Chem. Ind. 1482 (1959)).

[0005] Conductivity measurements in the solid phase are relatively easy and are used to characterize materials containing ionic species. For instance, the electrical conductivity of pure and doped Fe2O3, and the effect of gamma-irradiation on the electrical conductivity was studied (M. A. Mousa, E. A. Gomaa, A. A. El-Khouly and A. A. M. Aly: Mater. Chem. Phys. 11, 433 (1984)). Doping either increased or decreased the electrical conductivity of pure Fe2O3 (σ*=1.5×10−6 [Ω−1 cm−1]), depending on the type and amount of doping elements. Gamma-irradiation increased the conductivity of pure Fe2O3, which in turn decreased upon annealing. Higher doses caused higher conductivity increases, which was explained by increasing charge carrier (Fe2+) concentrations. The above mentioned paper investigated these oxides in terms of semiconducting properties. Inorganic oxides such as Fe2O3 and Al2O3 alone or as carriers are often used as heterogeneous catalysts.

[0006] There remains a real need to develop methods which can monitor the relative activity or degree of activity of a catalyst and which are feasible on a large scale and are cost-effective. The present invention addresses the problems of the prior art by employing novel methods to detect subtle changes on the surface and/or in the bulk of heterogeneous catalysts.

SUMMARY OF THE INVENTION

[0007] The present invention is directed to a method of monitoring the relative activity of the catalyst at various stages in a heterogeneous catalytic process by measuring an electrical property of the catalyst which relates to conductivity of the catalyst, and correlating level of conductivity with level of catalyst exhaustion or optimum regeneration.

[0008] According to another aspect of the invention, the method is used as an on-line indicator of catalyst activity in industrial catalytic processes.

[0009] In a preferred embodiment, several electrodes are placed within a packed bed to be used as an indicator of progressive catalyst exhaustion throughout the bed. The difference between the conductivity of a single bead and that of a packed bed of the same beads may be used as a measure of the void.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The invention is described in more detail herein with reference to the accompanying drawings, in which:

[0011] FIG. 1 is a graphical representation of the different classes of heterogeneous catalysts.

[0012] FIG. 2 is a schematic diagram illustrating a method of measuring the resistance of a single bead.

[0013] FIG. 3 is a schematic diagram illustrating a method of measuring resistance in a packed catalyst bed.

[0014] FIG. 4 is a schematic illustrating voltage drop measurement.

[0015] FIGS. 5A and 5B illustrate a comparison of the conductivities of fresh and used catalysts.

[0016] FIGS. 6A and 6B illustrate a comparison of the conductivies of fresh, regenerated and used hydrotreating catalyst.

[0017] FIG. 7 is a representative DME kinetic plot.

[0018] FIGS. 8A and 8B are graphical representations of a comparison of the conductivity of unused vs exhausted aluminum oxide catalyst 1.

[0019] FIG. 9 is a comparison of the conductivities of unused and exhausted Aluminum oxide catalyst 2 as measured on a single bead.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The present invention is concerned with easy monitoring methods to follow and interpret chemical and/or physical reactions on the surface and/or in the bulk of heterogeneous catalysts.

[0021] Heterogeneous catalysts are extensively used in industry. They are classified traditionally as a) conductors, b) semiconductors, and c) insulators, but a large number of catalyst are mixtures of a, b and/or c. The difference between insulators, semiconductors and conductors is due to the ability of their electrons to move and transfer the electric current. Basically, electrons around the atom nuclei are at different energy levels. The highest energy level corresponds to the outermost or valence electrons. This upper occupied band is called the valence band. In an insulator, the valence band is full and the energy gap between the top of the valence band and the next allowed band is so large (a few eVs, e.g. 6 eVs for diamond) that even large amounts of energy can not move the valence electrons to the conduction band. The conduction band is the energy level at which the electrons can conduct electric currents. In a conductor, the uppermost occupied level is very close to the conduction band. Therefore, an applied voltage can easily drive the electrons to a conduction band. In a semiconductor, the energy gap between the uppermost occupied level and the conduction band is small (less than 1 eV) and the electrons in the valence band, which is full, can go to the conduction band with a small amount of energy, such as heat or light. FIG. 1 shows graphically the different classes. There are intrinsic semiconductors, such as pure germanium, which show this behavior. By adding small amount of impurities called dopants to a semiconductor material, different semiconductors can be made. If the impurities supply extra electrons, the semiconductor is called a donor or n-type and if they can accept electrons from the valence band, a p-type semiconductor is produced. The addition of both types of impurities results in a mixed-type semiconductor.

[0022] With recent developments, a fourth catalyst class of transition or rare earth metal complexes (e.g. metallocenes) has to be considered. Catalysts, especially metals of transition metal complexes are often used on a carrier. The carrier can be inactive or can participate in the catalytic process. This latter is called a promoter. Examples of the various types are given in Table 2.

TABLE 2
EXAMPLES OF CATALYSTS
METALS	USE	REFERENCE
Ag	Dehydrogenation of methanol	A. Aicher, H. Haas, H. Diem, C.
		Dudeck, F. Brunnmuller and G.
		Lehmann, UK Patent, 1,526,245
		(1978); German Patent, 2,444,586
		(1976).
Fe—Co Alloys	Dehydrogenation of	Materials Science and Engineering,
	cyclohexane	A204, 186-192, 1995, Elsevier
		Science S. A., Lausanne, Switzerland.
Ir	Reforming catalyst	Farrauto R. J., and Bartholomew C.
		H., Fundamentals of Industrial
		Catalytic Processes, Blackie
		Academic & Professional, 557,
		(1997).
Pt	Ammonia oxidation	Farrauto R. J., and Bartholomew C.
		H., Fundamentals of Industrial
		Catalytic Processes, Blackie
		Academic & Professional, 480,
		(1997).
Pt—Ir (bimetallic)	Dehydrogenation of	Moser, W. R., Knapton, J. A.,
	methylcyclohexane to toluene	Koslowski, C. C., Rozak, J. R., and
		Vezis, R. H. (1994). Catal. Today,
		21, 157.
Pt—Sn (bimetallic)	Dehydrogenation of	Moser, W. R., Knapton, J. A.,
	methylcyclohexane to toluene	Koslowski, C. C., Rozak, J. R., and
		Vezis, R. H. (1994). Catal. Today,
		21, 157.
Re, Ru	Organic acids to alcohols	Farrauto R. J., and Bartholomew C.
		H., Fundamentals of Industrial
		Catalytic Processes, Blackie
		Academic & Professional, 413,
		(1997).
Rh	Nitriles to secondary amines	Farrauto R. J., and Bartholomew C.
		H., Fundamentals of Industrial
		Catalytic Processes, Blackie
		Academic & Professional, 414,
		(1997).
Ni	Hydrogenation of alkenes	Farrauto R. J., and Bartholomew C.
		H., Fundamentals of Industrial
		Catalytic Processes, Blackie
		Academic & Professional, 417,
		(1997).
Cu	Hydrogenation of	Farrauto R. J., and Bartholomew C.
	nitrobenzene	H., Fundamentals of Industrial
		Catalytic Processes, Blackie
		Academic & Professional 417,(1997)
Al	Dehydration of alcohols	Farrauto R. J., and Bartholomew C.
		H., Fundamentals of Industrial
		Catalytic Processes, Blackie
		Academic & Professional, 417,
		(1997).
Pt, W	Decomposition of N2O, NH3	Lecture notes, University of Western
	Oxidation of SO2	Ontario
Pd, Pt	Oxidation of H2	Lecture notes, University of Western
		Ontario
Co	Steam reforming	Twigg, Martyn V, Catalyst
		Handbook, 2nd Ed., 244 (1996).
INSULATORS	USE	REFERENCE
MO2C	Dehydrogenation of hydrocarbons	Bevan, D. J. M., and Kordis, J.
		(1964). J. Inorg. Nucl. Chem., 26,
		1509.
Glass	Oxidation of NO	Lecture notes, University of
		Western Ontario
Boric Acid	Oxidation of n-paraffin	Thomas C. L., Catalytic
		Processes and Proven Catalysts,
		Academic Press, 196, (1970).
MgO	Benzoic acid to phenol	Thomas C. L., Catalytic
		Processes and Proven Catalysts,
		Academic Press, 195, (1970).
γ-Al2O3	Dehydration of alcohols to	Thomas C. L., Catalytic
	Olefinic hydrocarbons	Processes and Proven Catalysts,
		Academic Press, 36, (1970).
SiO2—Al2O3	Alcohols to amines	Thomas C. L., Catalytic
		Processes and Proven Catalysts,
		Academic Press, 228, (1970).
SiO2—MgO	Hydrocracking	Thomas C. L., Catalytic
		Processes and Proven Catalysts,
		Academic Press, 176, (1970).
BaO	Dehydrochlorination	Thomas C. L., Catalytic
		Processes and Proven Catalysts,
		Academic Press, 234, (1970).
SEMICONDUCTORS	USE	REFERENCE
V2O5	Oxidation of SO2	Farrauto R. J., and Bartholomew
		C. H., Fundamentals of
		Industrial Catalytic Processes,
		Blackie Academic &
		Professional, 475-477, (1997).
NiS—WS3	Hydrogenation of Butene	Lecture notes, University of
		Western Ontario.
Si, Ge		Lecture notes, University of
(doped with B or Ga)		Western Ontario.
TRANSITION
METAL
COMPLEXES	USE	REFERENCE
RhCl (PPh3)3	Alkene hydrogenation	Farrauto R. J., and
Wilkinson catalyst		Bartholomew C. H.,
		Fundamentals of Idustrial
		Catalytic Processes, Blackie
		Academic & Professional,
		675, (1997).
Metallocenes	Polymerization	Brintzinger et. al., Angew.
	(Polyethylene,	Chem, Int. Ed. 34, 1143-1170,
	Polypropylene,	(1995).
	Polybutadiene etc.)
HRh(CO)(P(C6H5)3)3	Oxo Process	Farrauto R. J., and
		Bartholomew C. H.,
		Fundamentals of Industrial
		Catalytic Processes, Blackie
		Academic & Professional,
		679, (1997).

[0023] We have surprisingly found that the electrical conductivity of selected catalysts changes dramatically due to exhaustion and goes back nearly to the original value upon regeneration. The data presented herein and detailed in the examples below demonstrate that coking on the surface of catalysts is not the exclusive cause of the measured conductivity changes, and that the novel method of the present invention is sensitive enough to detect subtle changes on the surface and/or in the bulk of activated charcoal. The electrical property which is measured and which relates to electrical conductivity of commercial catalysts may be measured by the following preferred two methods. One method measures the resistance of a single bead as shown in FIG. 2.

[0024] A representative method for measuring a resistance of a single bead is shown in FIG. 2. The device 10 comprises a base 12 of suitable rigid material such as “Plexiglas” mounted on the base is a support 14 for fixing the position of a conductive rod 16 which may be of stainless steel. A second standard 18 is mounted on the base 12 and supports a conductive rod 20 which is spring loaded by way of compression spring 22. The sample to be tested, which is normally in particle form, is shown at 24 and is captured between the end portions 26 and 28 of the respective rods 16 and 20. The conductivity of the catalyst particle is measured by way of a conductivity measurement device 26. The device 26 has its two terminals 28 and 30 connected to the conductive rods 16 and 20. The conductivity measurement device include a visual display 28 to provide the operator with a readout on the conductivity.

[0025] The device of FIG. 3 is provided for measuring the conductivity of a bulk sample of catalyst. A support 32 is provided for a container 34 which contains the bulk catalyst 36. The container has a lid 38 with a cylindrical land 40. The land supports and has extending there through electrodes 42 and 44. The electrodes extend down into the bed of catalyst 36. The terminals 46 and 48 are connected to a suitable conductivity measuring device.

[0026] As shown in FIG. 4, a device 50 is schematically shown for measuring voltage drop. This device is compared to a standard system for measuring resistivity. Voltage meters 52 and 54 are provided for measuring the voltage drop across a catalyst particle or catalyst bed 56. The voltage meter has the electrodes 58 and 60 which may be connected to the electrical wires 28 and 30 of FIG. 2 for measuring voltage drop or electrodes 46 and 48 of FIG. 3. Voltage meter 52 measures the voltage drop across a resistor 62 having a known resistance value. Power for the circuitry is delivered via AC lines 64 which is then stabilized to a voltage of 120 volts and 60 hertz by way of stabilizer 66. A comparison of the voltage drop across the known resistance 62 and the catalyst particle 56 provides a measurement for the voltage drop across the catalyst.

[0027] The following abbreviations will be used to describe the various methods:

[0028] RS=direct resistance measurement, single bead

[0029] RP=direct resistance measurement, packed bed

[0030] VS=voltage drop measurement, single bead

[0031] VP=voltage drop measurement, packed bed

[0032] In the case of voltage drop measurements, the resistance is obtained from calibration curves constructed by using known resistors as Rx, to account for the internal impedance of the electrometer (Keithley Model 600 B).

[0033] The direct resistance measurement and the voltage drop measurement yield identical values within experimental error as expected. The resistance in a packed bed is a combination of the resistance of the catalyst beads and the voids (in this case air). The specific conductivity σ*[Scm−1 or Ω−1 cm−1] is calculated from equation 1:

R =(σ*)−1 L/A  [I]

[0034] where R is the resistance and L and A are the length and the cross section of the resistor in cm and cm2, respectively. In case of a single bead average bead dimensions are used; in case of the packed bed L is the distance of the parallel plates (L=1.2 cm) and A is the surface of the electrodes immersed in the bed (A=4 cm2). The change in conductivity from fresh to used catalysts is very large (100% to several order of magnitude). The conductivity of regenerated catalyst samples are nearly identical to that of the fresh samples.

[0035] The change may be due to the appearance of conductive species such as ions and/or carbon. Upon regeneration, the carbon is burned, while the ionic species may be reduced to less ionic or neutral metallic species, ready to catalyze the specific reactions again. Conductivity measurements do not differentiate between conductive species, but from the practical point of view it is enough to pinpoint a change signaling catalyst exhaustion. This change is specific to the catalyst, reaction conditions and parameters such as flow pattern of fluidization regimes. This method applies to any type of heterogeneous catalyst where an electrical surface property of the catalyst can be measured. Exemplary types of catalysts include zeolytes, silicalites, precious metal catalysts such as platinum or palladium, activated carbon, transition metal catalysts, and the like. In order to establish the correlation of measured conductivity to catalyst activity, one generally measures conductivity of fresh catalyst and compares the conductivity measurements obtained as the catalyst is gradually used and exhausted.

[0036] As mentioned above, this measurement conceivably can be used to measure voidage in a fixed bed. In a fixed bed, one can a) measure the resistivity of a single particle, b) measure the resistivity in a packed bed, and c) correlate the difference with voidage.

[0037] This measurement can also be used to predict the movement of a reaction (adsorption) front in a fixed bed. A number of electrodes are placed along the bed and the change in resistivity is monitored to predict the reaction front.

[0038] The catalyst specific surface can be predicted by measuring the change in resistivity of a single bead or measuring the change in the active surface area (e.g. analysis of reaction products) and correlating the two measurements.

[0039] To check the type of adsorption (mono-layer or multi-layer) the change in resistivity is monitored and the stepwise change in resistivity is correlated to the number of adsorbed layer.

[0040] This system can also be used to control catalytic fixed bed reactors. To do this, the change in resistivity during the reaction is measured and the process is calibrated for the given reaction. Deviation from the expected values will be due to the side reaction, poisoning etc.

EXAMPLES

[0041] Since the direct resistance and voltage drop measurements provide similar results, the results obtained by these two methods are presented only in Example 1. The catalysts used in industrial units are usually subjected to uneven temperature distribution, deposition of side products, occurrence of side reactions etc. Therefore individual catalyst particles might show relatively large variations in their properties. Thus, the relatively high standard deviation found in certain samples with single bead measurements might be construed as an indicator of uneven process conditions within a catalyst bed. In case of packed bed measurements, the standard deviation is small as the errors arising from the individual measurements are averaged out. These examples are described solely for purposes of illustration and are not intended to limit the scope of the invention.

Example 1

[0042] A commercial catalyst used for the dehydrogenation of ethyl benzene to produce styrene was investigated. These examples are labeled as “New 3, New 045 and Old 045”. These types of catalysts are iron oxide based, containing K2Fe22O34, with about 50% Fe content. The spent catalyst contains Fe2O3 and K2CO3 (50% Fe and 8-10% K). The conductivity of the fresh catalyst was RS=2.44×10−7 and VS=2.42×10−7 [ω−1 cm−1] (all the conductivity values specified in the Examples are average values of ten measurements) measured on a single cylindrical bead (L=0.56 cm; A=0.056 cm2). This compares well with values published in the literature for iron oxides (M. A. Mousa, E. A. Gomaa, A. A. El-Khouly and A. A. M. Aly: Mater. Chem. Phys. 11, 433 (1984)). The conductivity of the spent catalyst dropped to RS=4.66×10−4 and VS=4.98×10−4 [Ω−1 cm−1] which is a three orders of magnitude change. The data are summarized in the Tables 3A and 3B, and the comparison is shown graphically in FIG. 5.

TABLE 3A
Conductivity Data of Potassium-promoted Iron-oxide Catalyst
Direct Resistance Measurement - Single bead - RS
	New 3,	New 045,	Old 045,
Test #	(Ω-cm)−1 × 10−7	(Ω-cm)−1 × 10−7	(Ω-cm)−1 × 10−4
1	3.33	2.45	4.65
2	2.46	2.95	4.86
3	1.84	2.32	5.42
4	2.38	2.21	5.99
5	2.77	2.94	4.70
6	2.84	2.36	4.65
7	2.45	2.34	3.96
8	2.02	2.05	4.95
9	1.95	2.55	3.77
10	2.37	2.04	3.66
STDEV	0.45	0.32	0.73
Average	2.44	2.42	4.66
TABLE 3B
Voltage Drop Measurement, Single bead - VS
	New 3,	New 045,	Old 045,
Test #	(Ω-cm)−1 × 10−7	(Ω-cm)−1 10−7	(Ω-cm)−1 × 10−4
1	2.71	2.25	5.63
2	2.42	2.71	5.49
3	3.06	2.86	4.58
4	2.83	2.65	4.60
5	2.25	3.19	4.39
6	2.33	2.32	4.22
7	2.20	3.14	4.81
8	2.08	2.49	5.38
9	2.56	2.84	5.22
10	2.54	3.00	5.45
STDEV	0.30	0.32	0.52
Average	2.50	2.75	4.98

Example 2

[0043] A commercial hydrotreating catalyst was investigated. These type of catalysts are alumina based, containing Ni—Mo or Co—Mo and used to remove sulfur and nitrogen from crude oil distillates such as gasoline or gas oil. The conductivity of the fresh catalyst was RS=2.01×10−7 and VS=2.12×10−7 [Ω−1 cm−1] on a single bead (L=0.57 cm; A=0.01 cm2), and RP=1.43×10−11 and VP=1.28×10−11 [Ω−1 cm−1] in a packed bed. The conductivity of the used catalyst (samples taken from the top and the bottom of a commercial reactor) was measured to be several order of magnitudes higher than that of the fresh catalyst−RS=5.34×10−3, VS=5.11×10−3; RP=2.54×10−6 and VP=2.51×10−6 [Ω−1 cm−1]. The conductivity of the regenerated catalyst, on the other hand, was practically equal to the fresh catalyst−RS=2.22×10−7; VS=2.41×10−7; RP=1.75×10−11; and VP=1.30×10−11 [Ω−1 cm−1]. The data are summarized in Tables 4A amd 4B, and the comparison is shown graphically in FIG. 6. The huge differences between the conductivity of unused and spent catalyst demonstrate the utility of the method for indicating catalyst exhaustion.

TABLE 4A
Voltage Drop Measurement, Single bead - VS
	Fresh,	Regenerated	Used top 20%
	(Ω-cm)−1 ×	(Ω-cm)−1 ×	(Ω-cm)−1 ×	Used bottom 80%
Test #	10−7	10−7	10−3	(Ω-cm)−1 × 10−3
v1	2.21	2.83	6.21	4.40
2	2.39	2.38	6.00	4.86
3	2.43	2.51	6.86	4.08
4	2.20	2.43	5.53	3.97
5	1.93	1.90	4.47	3.81
6	2.00	2.08	4.86	4.95
7	2.23	2.39	3.85	5.15
8	1.91	2.65	4.05	4.82
9	2.04	2.50	5.48	5.44
10	1.84	2.41	3.78	4.46
STDEV	0.20	0.26	1.07	0.54
Average	2.12	2.41	5.11	4.59

[0044]

TABLE 4B
Voltage drop Measurement - Packed bed - VP
	Fresh,	Regenerated	Used top 20%	Used bottom 80%
	(Ω-cm)−1 ×	(Ω-cm)−1 ×	(Ω-cm)−1 ×	(Ω-cm)−1 ×
Test #	10−11	10−11	10−6	10−6
1	1.15	1.31	2.35	2.15
2	1.46	1.20	2.21	2.55
3	1.49	1.09	2.66	2.61
4	1.46	1.08	2.58	2.54
5	1.25	1.26	2.82	2.36
6	1.09	1.26	2.31	2.09
7	0.99	1.35	2.90	2.78
8	1.27	1.42	2.72	2.68
9	1.31	1.53	2.46	2.33
10	1.30	1.52	2.08	2.41
STDEV	0.17	0.16	0.27	0.22
Average	1.28	1.30	2.51	2.45

Example 3

[0045] A commercial Al2O3 Aluminum oxide catalyst “1” was investigated. This catalyst was found to catalyze the hydrolysis of methyl chloride, forming metbanol (CH3OH MeOH) and/or dimethyl ether (CH3—O—CH3, DME) according to the following reactions: 1

[0046] These reactions proceed at high temperature. The formation of these compounds can be followed by gas chromatography. Table 5 shows data at various temperatures.

TABLE 6A
Alumina Catalyst 1
Voltage Drop Measurement, Single bead - VS
	Unused	Exhausted
Test #	(Ω-cm)−1 × 1011	(Ω-cm)−1 × 109
1	1.25	3.47
2	5.56	9.62
3	10.00	7.58
4	0.81	20.83
5	1.04	9.62
6	0.27	5.56
7	1.47	4.90
8	2.19	6.94
9	2.12	3.42
10	4.39	52.08
STDEV	2.99	14.82
Average	1.07	8.09

[0047] A representative DME kinetic plot is shown in FIG. 7. Decreasing DME formation with time demonstrates the disappearance of catalytic sites.

[0048] When no more DME is formed, the catalyst is exhausted. We have found a correlation between the conductivity and the activity of this catalyst when used in an industrial unit.

[0049] Using samples from an industrial reactor, the conductivity of the unused catalyst was RS=2.45×10−9 and VS=2.91×10−11 on a single bead. The conductivity of the exhausted catalyst was measured to be more than two orders of magnitude higher than that of the unused catalyst RS=11.7×10−9, VS=12.4×10−9. The data are summarized in Tables 6A and 6B and the comparison is shown in FIG. 8A.

[0050] The same Al2O3 catalyst was also investigated using a packed bed configuration. The average conductivity of the unused catalyst was VP=1.98×10−13 [Ω−1 cm−1] versus 2.80×10−11 [Ω−1 cm−1] for the exhausted catalyst. The data are summarized in Table 6 and the comparison is shown graphically in FIG. 8B.

[0051] Large standard deviation obtained on single catalyst beads turned out to be very small in packed bed measurements. This is most probably due to local conditions and precipitation of side products on catalyst beads.

TABLE 6A
Alumina Catalyst 1
Voltage Drop Measurement, Single bead - VS
	Unused	Exhausted
Test #	(Ω-cm)−1 × 1011	(Ω-cm)−1 × 109
1	1.25	3.47
2	5.56	9.62
3	10.00	7.58
4	0.81	20.83
5	1.04	9.62
6	0.27	5.56
7	1.47	4.90
8	2.19	6.94
9	2.12	3.42
10	4.39	52.08
STDEV	2.99	14.82
Average	1.07	8.09

[0052]

TABLE 6B
Alumina catalyst 1
Voltage drop measurement-Packed bed-VP
	Unused	Exhausted
Test #	(Ω-cm)−1 × 10−13	(Ω-cm)−1 × 10−11
1	1.91	2.69
2	1.91	2.45
3	1.66	2.63
4	1.78	2.69
5	1.66	2.63
6	1.91	2.63
7	1.91	2.63
8	1.78	2.34
9	1.78	2.51
10	1.91	2.45
STDEV	0.10	0.12
Average	1.98	2.80

EXAMPLE 4

[0053] Another commercial Al2O3 (Aluminum oxide catalyst 2) catalyst that catalyzes the hydrolysis of methyl chloride, (forming MeOH and/or DME) was also investigated.

[0054] The conductivity of the unused catalyst was RS=9.54×10−9 and VS=9.37×10−9 [Ω−1 cm−1] on a single bead. The conductivity of the exhausted catalyst was measured to be two order of magnitudes higher than that of the unused catalyst−RS=7.67×10−7; VS=7.64×10−3 [Ω−1 cm−1]. The data are summarized in Table 7 and the comparison is shown in FIG. 9.

TABLE 7
Alumina Catalyst 2
Voltage Drop Measurement, Single bead - VS
	Unused	Exhausted
Test #	(Ω-cm)−1 × 108	(Ω-cm)−1 × 107
1	9.37	7.26
2	9.10	7.93
3	9.86	6.72
4	8.88	8.00
5	9.41	7.65
6	9.28	7.86
7	9.56	7.62
8	9.33	7.80
9	9.55	7.57
10	9.24	7.63
STDEV	0.269	0.375
Average	9.37	7.64

[0055] The huge difference between the conductivity of unused and exhausted catalyst demonstrate the utility of the method for indicating catalyst exhaustion.

[0056] Although preferred embodiments of the invention have been described herein in detail, be understood by those skilled in the art that variations may be made thereto without departing from the spirit of the invention or scope of the appended claims.

Claims

1. A method for evaluating the catalytic activity of a heterogeneous particulate catalyst, the method comprising monitoring electrical conductivity of said particulate catalyst.

2. A method of claim 1, wherein said step of monitoring conductivity of said particulate catalyst comprises measuring an electrical property of said particulate catalyst which relates to conductivity.

3. A method of claim 2, wherein said measured electrical property is resistivity and correlating measured resistivity with catalyst activity.

4. A method of claim 2, wherein said measured electrical property is capacitance and correlating capacitance with catalyst activity.

5. A method of claim 1 wherein said electrical conductivity of said particulate catalyst is monitored over time to determine a change in electrical conductivity of said catalyst, correlating a change in conductivity with a decrease in catalytic activity and correlating an opposite change in conductivity with an increase in catalytic activity.

6. A method of claim 5 wherein said electrical conductivity increases with decreasing catalytic activity and decreases with increasing catalytic activity.

7. A method of claim 6 wherein a determined extent of increase in conductivity correlates with said catalyst being spent.

8. A method of claim 6 wherein a determined extent of decrease in conductivity correlates with said catalyst being regenerated.

9. A method of claim 2 wherein said electrical property is measured on a single catalyst particle.

10. A method of claim 2, wherein said electrical property is measured “in situ” of a catalytic reactor.

11. A method of claim 2 wherein said electrical property is measured “in situ” of a catalyst regenerator.

12. A method of claim 10 wherein said electrical property is measured between two spaced apart electrodes positioned in a bed of said particulate catalyst.

13. A method of claim 12 wherein said bed is static or fluidized.

14. A method of claim 11 wherein said electrical property is measured between two spaced apart electrodes positioned in a bed of said particulate catalyst.

15. A method of claim 14 wherein said bed is static or fluidized.

16. A method of claim 1 wherein said particulate catalyst is selected from the group consisting of electrically conductive catalytic material, electrically insulative catalytic material and electrically semi-conductive catalytic material.

17. A method of claim 16 wherein said electrically conductive catalytic material is selected from the group consisting of Group VIII, Group Ib, Group IVa, Group VIIb, Group IIIa, or Group VIb metals or combinations thereof.

18. A method of claim 16 wherein said electrically insulative catalytic material is selected from the group consisting of metal oxides and siliceous oxides.

19. A method of claim 16 wherein said electrically semi-conductive catalytic material is selected from the group consisting of n-type, p-type and inherent semiconductors.

20. A method of claim 17 wherein said catalyst is selected from the group consisting of Ag, Fe—Co alloys, Ir, Pt, Pt—Ir, Pt—Sn, Re, Ru, Rh, Ni, Cu, Al, Pt, W, Pd and Co.

21. A method of claim 18 wherein said catalyst is selected from the group consisting of Mo2C, SiO2, BH3O3, MgO, γ-Al2O3, SiO2—Al2O3, SiO2—MgO and BaO.

22. A method of claim 19 wherein said catalyst is selected from the group consisting of V2O5 NiS—WS3 Si, Ge, hCl(PPh3)3, mettallocenes and HRh(CO)(P(C6H5)3)3.

23. A method of claim 20 wherein said selected catalyst is provided on a carrier.

24. A method of claim 23 wherein said carrier is a metal oxide.

25. A method of claim 24 wherein said carrier is an oxide of aluminum.

26. A method of claim 18 wherein said selected catalyst is a potassium promoted oxide of iron.

27. A method of claim 16 wherein said selected catalyst is activated carbon.

28. A method of claim 23 wherein said selected catalyst is a hydrotreating catalyst on a carrier.

29. A method of claim 28 wherein said carrier is an oxide of aluminum.

30. A method of claim 27 wherein said catalyst is nickel-molybdenum or cobalt-molybdenum.

31. A method of claim 20 wherein said catalyst is Ni, Cu, Pt or Pd.

32. A method of claim 21 wherein said catalyst is silicon dioxide based.

33. An apparatus for assessing electrical conductivity of a particulate catalyst to determine catalyst activity, said apparatus comprising: i) means for monitoring electrical conductivity of said particulate catalyst; and ii) means for correlating monitored conductivity with catalyst activity.

34. An apparatus of claim 33 wherein said monitoring means comprises spaced apart electrodes in contact with particulate catalyst.

35. An apparatus of claim 34 wherein means retains a catalytic particle between said electrodes.

36. An apparatus of claim 35 wherein said retaining means biases said electrodes against a catalytic particle.

37. An apparatus of claim 34 wherein said spaced apart electrodes are adapted to be placed in a bed of particulate catalyst to measure conductivity thereof.

38. An apparatus of claim 33 wherein said correlating means includes a programmable means for generating catalyst activity information based on monitored value for conductivity.

39. An apparatus of claim 38 wherein said monitoring means determines at any point in time a value for electrical conductivity and said activity information generating means providing a corresponding value for catalyst activity.

40. An apparatus of claim 38 wherein said monitoring means monitors electrical conductivity over time to determine a change in electrical conductivity of said catalyst, said activity information generating means correlating an increase in conductivity with a decrease in catalytic activity and correlating a decrease in conductivity with an increase in catalytic activity.

41. An apparatus of claim 40 wherein said activity information generating means is programmed to correlate a determined extent of increase in conductivity with a catalyst being spent.

42. A catalytic reactor having an apparatus of claim 33 for monitoring catalytic activity in said reactor.

43. A catalyst regenerator having an apparatus of claim 33 for monitoring catalytic activity during a catalyst regeneration cycle.

44. A processor for correlating catalyst activity with measured surface electrical conductivity of particulate catalyst comprising: i) means for receiving a signal representative of surface electrical conductivity, and ii) programmable means for generating catalyst activity information based on monitored value for conductivity.

45. A processor of claim 44 wherein said programmable means is programmed with a custom program for correlating conductivity with catalyst activity.