Chemistry of inorganic compounds – Sulfur or compound thereof – Oxygen containing
Reexamination Certificate
2000-10-12
2002-12-31
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Sulfur or compound thereof
Oxygen containing
C423S532000, C423S533000, C423S534000, C423S535000, C423S538000
Reexamination Certificate
active
06500402
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a catalyst for reacting SO
2
with molecular oxygen to form SO
3
, and also to a process of producing sulfuric acid from SO
3
and water, where the SO
3
is produced catalytically by reacting SO
2
with molecular oxygen.
BACKGROUND OF THE INVENTION
The production of sulfuric acid from SO
2
, which first of all is catalytically oxidized to form SO
3
, is described in detail in Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, vol. A25, pages 644 to 664. The known catalysts for the oxidation of SO
2,
which contain for instance V
2
O
5
as active component, preferably operate at a temperature in the range from 380 to 620° C. Higher temperatures will damage the catalyst. This leads to the fact that the gas supplied to the catalysis should have an SO
2
content of not more than about 12 vol-%, so that the exothermicity of the oxidation reaction can easily be controlled. The DE-C-27 10 350 describes a catalyst for the conversion of SO
2
into SO
3
, which operates at a temperature in the range from 600 to 800° C. The catalyst has a silicon oxide carrier with a tridymite structure and an active component containing iron, copper and an alkali metal.
OBJECT OF THE INVENTION
It is the object underlying the invention to create a catalyst suitable for continuous operation, whose activity and stability are also ensured at temperatures of 700° C. and above. Furthermore, the catalyst should form the basis for a process of producing sulfuric acid, where gases with a high concentration of SO
2
are used.
SUMMARY OF THE INVENTION
In accordance with the invention, the catalyst comprises a porous carrier and an active component connected with the carrier, where the active component consists of 10 to 80 wt-% iron, the carrier has a BET surface of 100 to 2000 m
2
/g and an SiO
2
content of at least 90 wt-%, and the weight ratio carrier:active component lies in the range from 1:1 to 100:1. As carrier materials there may be used silicates, in particular zeolites (e.g. zeolites of the beta type), mesoporous silica gels (e.g. zeolites of the beta type), mesoporous silica gels (e.g. synthesized in accordance with U.S. Pat. No. 3,556,725 or MCM-41 of Mobil Oil as pure SiO
2
material), also those mesoporous silica gels with up to 10 wt-% foreign elements (e.g. boron), diatomaceous earth, amorphous SiO
2
or mesoporous alumosilicate (e.g. aluminum-containing MCM-41 of Mobile Oil). Advantageous carriers comprise for instance 90 to 100 wt-% of a zeolite or mesoporous SIO
2
. Details concerning the mesoporous SiO
2
can also be found in WO-A-91/11390 and in “Microporous Materials” 10 (1997), pages 283-286.
The iron-containing active component of the catalyst may in particular consist of at least 80 wt-% iron oxides. The active component may in addition contain sodium, potassium and/or cesium. The content of these alkali metals may be up to 10 wt-%, based on the total weight of the catalyst.
The active component of the catalyst may furthermore include vanadium and/or sulfur compounds (e.g. pyrosulfate). In the active component, the weight ratio V:Fe may lie in the range from 1:1 to 1.3:1. For the sulfate content in the catalyst, 1 to 7 wt-% are recommended, based on the total weight of the catalyst. When the active component of the catalyst also contains copper, the Cu content will be up to 1 wt-% of the Fe content.
In the laboratory, the following catalysts were prepared:
First Catalyst
As starting material, there was used a mesoporous SiO
2
with an ordered pore structure, with amorphous walls and a pore system with a regular hexagonal array with pore sizes between 2 and 8 nm (synthesized in accordance with WO-A-91/11390). It has a good thermal stability up to 1000° C. and a BET surface of about 1000 m
2
/g. To 10 g of an aqueous 25% C
16
H
33
N(CH
3
)
3
Cl solution a mixture of 1.8 g soda waterglass (composition: 27.5 wt-% SiO
2
, 8.3 wt-% Na
2
O, plus water), 1.3 g SiO
2
and 10 g water was added within 15 minutes. After stirring for 30 minutes, the suspension was heated for 48 hours in a screwed polypropylene vessel to a temperature of 90° C. Then, it was filtrated, washed and dried for 8 hours at 90° C. The dried mixture was heated to 550° C. with a heating rate of 1° C. per minute and maintained at this temperature for 5 hours. 1 g of this product was thoroughly mixed with 3.5 ml of a 0.95 mol Fe(NO
3
) solution and subsequently dried for 2.5 hours a 90° C. The product was stirred for one hour in 25 g distilled water, filtrated, dried at 90° C. and then thermally treated as follows: heating to 400° C. with a rise of 5° C. per minute, maintaining at 400° C. for 3 hours, then heating to 700° C. with a rise of 5° C. per minute, and subsequently maintaining at this temperature for 3 hours. The product had a BET surface of 478 m
2
/g, the weight ratio Si:Fe was 5:1.
Second Catalyst
3 g commercial SiO
2
(BASF D11-10) were added to a solution of 0.18 g NH
4
VO
3
in 20 ml water. Then, 0.62 g FE(NO
3
)
3
9H
2
O, dissolved in 1 g water, were added dropwise by stirring quickly. The product was filtrated, washed, dried, heated to 800° C. and maintained at 800° C. for 24 hours. The weight ratio Si:Fe:V is 33:1:1.3. In the same way, iron vanadate can be applied onto carriers with a large surface.
Third Catalyst
Here, a zeolite-like iron silicate (structural type beta-zeolite) is used as carrier material; the iron silicate has a three-dimensional system of micropores and has a large BET surface of 600 m
2
/g. A first aqueous solution was prepared as follows: 78.5 g 40% tetraethylammonium hydroxide and 10.7 g 40% hydrogen fluoride were added to 260.4 g tetraethyl orthosilicate in a polypropylene vessel. 70% of this solution were separate, and to the remaining 30% of the first solution 3.6 g FeCl
3
, dissolved in 9 g water, were added by stirring. Finally, there were added 22.2 g NH
4
F to the previously separated solution. The preparation was heated for 24 hours at 70° C. in the open vessel, and the dry gel was subsequently dissolved in 10 g water. Upon inoculation with nuclei (beta-zeolite, 5 wt-%) the product crystallized in the course of 15 days in the polytetrafluoro-ethylene vessel at 170° C. The product was heated to 200° C. of 2° per minute, maintained at this temperature for 3 hours, then heated to 550° C. of 5° C. per minute, and maintained at this temperature for 10 hours. The elemental analysis of the product revealed an atomic composition of H:Si:Fe:O:F= 104:60:4.3:178:0.4.
Samples of the three catalysts described above were tested in the laboratory, so as to determine their activity with respect to the oxidation of SO
2
to form SO
3
. Of each catalyst, 0.5 ml of a fraction with particle sizes between 500 to 1000 &mgr;m were maintained in the nitrogen stream for three hours at 324° C. for activation purposes. For measuring the activity, 24.7 ml/min of a gas consisting of 20 vol-% SO
2
, 22 vol-% 0
2
, and 58 vol-% N
2
were passed over the activated catalyst samples, where a dwell time of 1.2 s in the catalyst bed was obtained. The activity (percentage of the converted SO
2
) in dependence on the temperature is indicated in the following Table.
Temperature
1st catalyst
2nd catalyst
3rd catalyst
500° C.
46%
18%
44%
550° C.
58%
29%
62%
600° C.
72%
43%
77%
650° C.
65%
55%
65%
700° C.
51%
51%
51%
The catalysts in accordance with the invention are particularly suited as precontact, so as to partly convert a gas with a high content of SO
2
into SO
3
and produce sulfuric acid, before the residual gas with a reduced content of SO
2
can be passed for instance into a conventional production of sulfuric acid. The gas containing SO
2
and O
2
with an SO
2
content of 13 to 50 vol-% and an oxygen content corresponding to O
2
/SO
2
volume ratio of at least 1:2 is supplied to a precontact stage, in the precontact stage the gas and the oxygen are passed through at least one bed (precontact bed) of a granular catalyst (precontact), where the precontact has the features described above, and the maximum temperature at the precontact is mainta
Anastasijevic Nikola
Hollnagel Achim
Schmidt Georg
Schüth Franz-Ferdinand
Werner Dietrich
Dubno Herbert
Metallgesellschaft Aktiengesellschaft
Myers Jonathan
Silverman Stanley S.
Vanoy Timothy C
LandOfFree
Catalyst for oxidizing SO2 to SO3 and utilization of the... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Catalyst for oxidizing SO2 to SO3 and utilization of the..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Catalyst for oxidizing SO2 to SO3 and utilization of the... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2976008