Chemistry: fischer-tropsch processes; or purification or recover – Group viii metal containing catalyst utilized for the...
Reexamination Certificate
2002-10-28
2004-06-15
Parsa, J. (Department: 1621)
Chemistry: fischer-tropsch processes; or purification or recover
Group viii metal containing catalyst utilized for the...
C518S700000
Reexamination Certificate
active
06750258
ABSTRACT:
FIELD OF THE INVENTION
The present invention is a catalyst structure and method of making, and a method of Fischer-Tropsch synthesis.
BACKGROUND OF THE INVENTION
Fischer-Tropsch synthesis is carbon monoxide hydrogenation that is usually performed on a product stream from another reaction including but not limited to steam reforming (product stream H
2
/CO~3), partial oxidation (product stream H
2
/CO~2), autothermal reforming (product stream H
2
/CO~2.5), CO
2
reforming (H
2
/CO~1) coal gassification (product stream H
2
/CO~1) and combinations thereof.
Fundamentally, Fischer-Tropsch synthesis has fast surface reaction kinetics. However, the overall reaction rate is severely limited by heat and mass transfer with conventional catalysts or catalyst structures. The limited heat transfer together with the fast surface reaction kinetics may result in hot spots in a catalyst bed. Hot spots favor methanation. In commercial processes, fixed bed reactors with small internal diameters or slurry type and fluidized type reactors with small catalyst particles (>50 microns, &mgr;m) are used to mitigate the heat and mass transfer limitations. In addition, one of the important reasons that Fischer-Tropsch reactors are operated at lower conversions per pass is to minimize temperature excursion in the catalyst bed. Because of the necessary operational parameters to avoid methanation, conventional reactors are not improved even with more active Fischer-Tropsch synthesis catalysts. Detailed operation is summarized in Table 1 and FIG.
1
.
TABLE 1
Comparison of Contact Times Effects in Fischer-
Tropsch Experimentation
Contact
CH
4
Ref
(A)
Catalyst
Conditions
time
Conversion
selectivity
1
Co/ZSM-5
240° C., 20-atm, H
2
/CO = 2
3.6-sec
60%
21%
2
Co/MnO
220° C., 21-atm, H
2
/CO = 2
0.72-sec
13%
15%
3
Co—Ru/
200° C., 20-atm, H
2
/CO = 2
3-sec
61%
5%
TiO
2
Co/TiO
2
″
8-sec
49%
7%
4
Co/TiO
2
200° C., 20-atm, H
2
/CO = 2.1
2-sec
9.5%
~9%
12-sec
72%
~6%
5
Ru/Al
2
O
3
222° C., 21-atm, H
2
/CO = 3
4.5-sec
20%
?
″
7.2-sec
36%
″
8.4-sec
45%
″
9.6-sec
51%
″
12-sec
68%
″
14-sec
84%
6
Ru/Al
2
O
3
250° C., 22-atm, H
2
/CO = 2
7.2-sec
38%
5%
7
Ru/Al
2
O
3
225° C., 21-atm, H
2
/CO = 2
12-sec
66%
13%
222° C., 21-atm, H
2
/CO = 3
12-sec
77%
34%
For references that contained results for multiple experimental conditions, the run which best matched our conversion, selectivity and/or conditions was chosen for comparison of contact time.
(A)
References
1. Bessell, S., Appl. Catal. A: Gen. 96, 253 (1993).
2. Hutchings, G. J., Topics Catal. 2, 163 (1995).
3. Iglesia, E., S. L. Soled and R. A. Fiato (Exxon Res. and Eng. Co.), U.S. Pat. No. 4,738,948, Apr. 19, 1988.
4. Iglesia, E., S. C. Reyes, R. J. Madon and S. L. Soled, Adv. Catal. 39, 221 (1993).
5. Karn, F. S., J. F. Shultz and R. B. Anderson, Ind Eng. Chem. Prod. Res. Dev. 4(4), 265 (1965).
6. King, F., E. Shutt and A. I. Thomson, Platinum Metals Rev. 29 (44), 146 (1985).
7. Shultz, J. F., F. S. Karn and R. B. Anderson, Rep. Invest. - U.S. Bur. Mines 6974, 20 (1967).
Literature data (Table 1 and
FIG. 1
) were obtained at lower H
2
/CO ratio (2:1) and longer contact time (3 sec or longer) in a fixed bed type reactor. Low H
2
/CO (especially 2-2.5), long contact time, low temperature, and higher pressure favor Fischer-Tropsch synthesis. Selectivity to CH
4
is significantly increased by increasing H
2
/CO ratio from 2 to 3. Increasing contact time also has a dramatic favorable effect on the catalyst performance. Although reference 3 in Table 1 shows satisfactory results, the experiment was conducted under the conditions where Fischer-Tropsch synthesis is favored (at least 3 sec residence time, and H
2
/CO=2). In addition, the experiment of reference 3 was done using a powdered catalyst on an experimental scale that would be impractical commercially because of the pressure drop penalty imposed by powdered catalyst. Operating at higher temperature will enhance the conversion, however at the much higher expense of selectivity to CH
4
. It is also noteworthy that contact time in commercial Fischer-Tropsch units is at least 10 sec.
Hence, there is a need for a catalyst structure and method of Fischer-Tropsch synthesis that can achieve the same or higher conversion at shorter contact time, and/or at higher H
2
/CO.
SUMMARY OF THE INVENTION
The present invention includes a catalyst structure and method of making the catalyst structure for Fischer-Tropsch synthesis that have a first porous structure with a first pore surface area and a first pore size of at least about 0.1 &mgr;m, preferably from about 10 &mgr;m to about 300 &mgr;m. A porous interfacial layer with a second pore surface area and a second pore size less than the first pore size disposed on the first pore surface area. A Fischer-Tropsch catalyst selected from the group consisting of cobalt, ruthenium, iron, nickel, rhenium, osmium and combinations thereof is placed upon the second pore surface area.
The present invention also provides a method of making a Fischer-Tropsch catalyst having the steps of: providing a catalyst structure comprising a porous support with a first pore surface area and a first pore size of at least about 0.1 &mgr;m; optionally depositing a buffer layer on the porous support; depositing a porous interfacial layer with a second pore surface area and a second pore size less than said first pore size, upon the buffer layer (if present); and depositing a Fischer-Tropsch catalyst upon the second pore surface area.
The present invention further includes a method of Fischer-Tropsch synthesis having the steps of:
providing a catalyst structure having a first porous support with a first pore surface area and a first pore size of at least about 0.1 &mgr;m;
a buffer layer disposed on the porous support;
a porous interfacial layer with a second pore surface area and a second pore size less than the first pore size, the porous interfacial layer disposed on the buffer layer (if present) or on the first pore surface area; and
a Fischer-Tropsch catalyst disposed on the second pore surface area; and
(b) passing a feed stream having a mixture of hydrogen gas and carbon monoxide gas through the catalyst structure and heating the catalyst structure to at least 200° C. at an operating pressure, the feed stream having a residence time within the catalyst structure less than 5 seconds, thereby obtaining a product stream of at least 25% conversion of carbon monoxide, and at most 25% selectivity toward methane.
The present invention also includes various supported Fischer-Tropsh catalysts that are characterized by their properties. For example, a catalyst is provided that, if exposed to a feed stream consisting of a 3 to 1 ratio of hydrogen gas to carbon monoxide, at 250° C. and a residence time of 12.5 seconds, exhibits a selectivity to methane that is greater at 24 atmospheres (contact time of 1 second) than it is at 6 atmospheres pressure (contact time of 4 seconds), even though the conversion is higher at lower pressure.
Catalytic activity is an intrinsic property of a catalyst. In the present invention, this property is defined by various testing conditions. For example, a preferred catalyst has a Fischer-Tropsch catalytic metal supported on a porous support; where the catalyst possesses catalytic activity such that, if the catalyst is placed in a tube inside an isothermal furnace and exposed to a feed stream consisting of a 3 to 1 ratio of hydrogen gas to carbon monoxide, at 250° C., at 6 atm, at a contact time less than 5 seconds and the product stream is collected and cooled to room temperature, the selectivity to methane is less than 25%, and the carbon monoxide conversion is greater than 25%. To check whether a catalyst meets a claimed activity property requires only a test at the specified conditions.
The
Baker Eddie G.
Gao Yufei
Tonkovich Anna Lee Y.
Vanderwiel David P.
Wang Yong
Battelle (Memorial Institute)
Harrington Todd J.
Rosenberg Frank
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