Catalyst structure and method of Fischer-Tropsch synthesis

Details Catalyst structure and method of Fischer-Tropsch synthesis Catalyst structure and method of Fischer-Tropsch synthesis

1999-08-17

2002-09-17

Richter, Johann (Department: 1621)

Chemistry: fischer-tropsch processes; or purification or recover

Group viii metal containing catalyst utilized for the...

C518S700000, C502S332000, C502S325000

Reexamination Certificate

active

06451864

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 &mgr;m) are used to mitigate the heat and mass transfer limitations. In addition, Fischer-Tropsch reactors are operated at lower conversions per pass 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 Residence Times Effects in Fischer-
Tropsch Experimentation
Con-
CH
4
Residence
ver-
selec-
Ref
(A)
Catalyst
Conditions
time
sion
tivity
1
Co/ZSM-5
240° C., 20-atm,
3.6-sec 
60%
21%
H
2
/CO = 2
2
Co/MnO
220° C., 21-atm,
0.72-sec  
13%
15%
H
2
/CO = 2
3
Co-Ru/TiO
2
200° C.,
 3-sec
61%
 5%
20-atm, H
2
/CO = 2
Co/TiO
2
200° C.,
 8-sec
49%
 7%
20-atm, H
2
/CO = 2
4
Co/TiO
2
200° C.,
 2-sec
9.5% 
~9%
20-atm, H
2
/CO = 2.1
200° C.,
12-sec
72%
~6%
20-atm, H
2
/CO = 2.1
5
Ru/Al
2
O
3
222° C.,
4.5-sec 
20%
?
21-atm, H
2
/CO = 3
222° C.,
7.2-sec 
36%
21-atm, H
2
/CO = 3
222° C.,
8.4-sec 
45%
21-atm, H
2
/CO = 3
222° C.,
9.6-sec 
51%
21-atm, H
2
/CO = 3
222° C.,
12-sec
68%
21-atm, H
2
/CO = 3
222° C.,
14-sec
84%
21-atm, H
2
/CO = 3
6
Ru/Al
2
O
3
250° C.,
7.2-sec 
38%
 5%
22-atm, H
2
/CO = 2
7
Ru/Al
2
O
3
225° C.,
12-sec
66%
13%
21-atm, H
2
/CO = 2
222° C., 12-sec
77%
34%
21-atm, H
2
/CO = 3
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 residence 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 residence time (3 sec or longer). Low H
2
/CO (especially 2-2.5), long residence time, low temperature, and higher pressure favor Fischer-Tropsch synthesis. Selectivity to CH
4
can be significantly increased by increasing H
2
/CO ratio from 2 to 3. Increasing residence 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 residence 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 residence 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 both rely upon the catalyst structure having 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 is placed upon the first pore surface area. Finally, a Fischer-Tropsch catalyst selected from the group consisting of cobalt, ruthenium, iron, rhenium, osmium and combinations thereof is placed upon the second pore surface area.
Further improvement is achieved by using a microchannel reactor wherein the reaction chamber walls define a microchannel with the catalyst structure placed therein through which pass reactants. The walls may separate the reaction chamber from at least one cooling chamber.
The present invention also includes a method of Fischer-Tropsch synthesis having the steps of:
(a) providing a catalyst structure having a first porous structure with a first pore surface area and a first pore size of at least about 0.1 &mgr;m;
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 placed upon the first pore surface area;
a Fischer-Tropsch catalyst selected from the group consisting of cobalt, ruthenium, iron rhenium, osmium and combinations thereof placed upon 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.
It is an object of the present invention to provide a catalyst structure for Fischer-Tropsch synthesis.
It is another object of the present invention to provide a method of Fischer-Tropsch synthesis having shorter residence time.
Advantages of the invention include (i) at residence time shorter than the prior art, higher conversions are achieved with no increase to methane selectivity; and (ii) as residence times increase, conversion increases and methane selectivity decreases (slightly). Surprisingly, the present invention represents an increase in conversion efficiency of at least a factor of 3 on the basis that equivalent conversion with conventional catalyst would require correspondingly greater residence time.
The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements.


REFERENCES:
patent: 4196099 (1980-04-01), Hunter et al.
patent: 4422961 (1983-12-01), Gray
patent: 4738948 (1988-04-01), Iglesia et al.
patent: 4801620 (1989-01-01), Fujitani et al.
patent: 4806427 (1989-02-01), Stein et al.
patent: 4935392 (1990-06-01), Kainer et al.
patent: 4945116 (1990-07-01), Abrevaya
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